Gray's Anatomy of the human body [30 ed.]

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Gift of Michigan Bell

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Anatomy off the Human Body

Henry Gray appears in the foreground, third from the left. (Reproduced by permission of the Governors of St. George’s Hospital.)

by Henry Gray, f.rs. Late Fellow of the Royal College of Surgeons; Lecturer on Anatomy at St. George’s Hospital Medical School, London

Thirtieth American Edition EDITED BY

Carmine D. Clemente, a.b„ m.s., PhD. Professor of Anatomy and Director of the Brain Research Institute University of California at Los Angeles School of Medicine AND *

Professor of Surgery (Anatomy), Charles R. Drew Postgraduate Medical School, Los Angeles, California

PHILADELPHIA

LEA & FEBIGER 1985

Lea & Febiger

600 Washington Square Philadelphia, Pa. 19106-4198 U.S.A. (215) 922-1330

gray’s anatomy

Translations: 29th Edition— Japanese Edition by Hirokawa Publishing Co., Tokyo, Japan—1981 Portuguese Edition by Editora Guanabara Koogan, Rio de Janeiro, Brazil—1977 Spanish Edition by Salvat Editores, S.A., Barcelona, Spain—1976

Library of Congress Cataloging in Publication Data Gray, Henry, 1825-1861. Anatomy of the human body. Includes bibliographies and index. I. Anatomy, Human. I. Clemente, Carmine D. II. Title. [DNLM: 1. Anatomy. QS 4 G779anJ QM23.2.G73 1984 611 84-5741 ISBN 0-8121-0644-X Copyright © 1985 by Lea & Febiger. Copyright under the International Copyright Union. All Rights Reserved. This book is protected by copyright. No part of it may be reproduced in any manner or by any means without written permission of the Publisher. PRINTED IN THE UNITED STATES OF AMERICA

Print Number:

5

4

3

2

1

DEDICATION My work on this 30th Edition of Gray’s Anatomy is gratefully dedicated to my father and mother,

Ermanno Clemente and Caroline Clemente, who with great wisdom, taught me in my youth the everlasting value of education, and to

Dr. William Frederick Windle, my teacher, who taught me to understand a way of life so effectively stated in the following passage from Robert Frost: . . . My object in living is to unite My avocation and my vocation, As my two eyes make one in sight. Only when love and need are one, And the work is play for mortal stakes, Is the deed ever truly done, For Heaven and the future’s sakes.

C.D.C.

American Editions of Gray’s Anatomy DATE

EDITION

EDITOR

June 1859

First American Edition

Dr. R. J. Dunglison

February 1862

Second American Edition

Dr. R. J. Dunglison

May 1870

New Third American from Fifth English Edition

Dr. R. J. Dunglison

July 1878

New American from the Eighth English Edition

Dr. R. J. Dunglison

August 1883

New American from the Tenth English Edition

Dr. R. J. Dunglison

September 1887

New American from the Eleventh English Edition

Dr. W. W. Keen

September 1893

New American from the Thirteenth English Edition

Dr. W. W. Keen

September 1896

Fourteenth Edition

Drs. Gallaudet, Brockway and McMurrich

October 1901

Fifteenth Edition

Drs. Gallaudet, Brockway and McMurrich

October 1905

Sixteenth Edition

Dr. J. C. DaCosta

September 1908

Seventeenth Edition

Drs. DaCosta and Spitzka

October 1910

Eighteenth Edition

Dr. E. A. Spitzka

July 1913

Nineteenth Edition

Dr. E. A. Spitzka

October 1913

New American from Eighteenth English Edition

Dr. R. Howden

September 1918

Twentieth Edition

Dr. W. H. Lewis

August 1924

Twenty-first Edition

Dr. W. H. Lewis

August 1930

Twenty-second Edition

Dr. W. H. Lewis

July 1936

Twenty-third Edition

Dr. W. H. Lewis

May 1942

Twenty-fourth Edition

Dr. W. H. Lewis

August 1948

Twenty-fifth Edition

Dr. C. M. Goss

July 1954

Twenty-sixth Edition

Dr. C. M. Goss

August 1959

Twenty-seventh Edition

Dr. C. M. Goss

August 1966

Twenty-eighth Edition

Dr. C. M. Goss

January 1973

Twenty-ninth Edition

Dr. C. M. Goss

October 1984

Thirtieth Edition

Dr. C. D. Clemente

Henry Gray F.R.S., F.R.C.S.

The originator of this now famous book, which has reached its one hundred and twenty-fifth year of continuous publication in America, was born in Windsor, England, in 1825. A letter written to Lea & Febiger, by Henry Gray’s great nephew, F. Lawrence Gray, has supplied this date as well as some interesting biographical information. Henry’s father, William Gray, was born in 1787. He is reported to have been an only child. Whether for protection or from spe¬ cial interest, he was placed in the royal household where he was brought up. In 1811, before the Regency, and while he was in his twenties, he was Deputy Treasurer to the Household of the Prince of Wales. On the accession of George IV as Regent in 1820, William Gray became the King’s private messenger and continued in this capacity, with William IV, until his death at the age of forty-seven. He married Ann Walker in 1817 and during George IV’s reign lived at Wind¬ sor Castle in accommodations provided for him and his wife. When William IV acceded to the throne in 1830, the Grays moved to London in order to be near Buckingham Pal¬ ace, and either immediately or soon after that No. 8 Wilton Street became the family residence. Henry Gray had two brothers and one sister. His younger brother, Robert, trained to become a naval surgeon. He died at sea in his twenty-second year. Henry’s sister, younger than he, apparently never was mar¬ ried. His older brother, Thomas William, adopted the legal profession, and was Attor¬

ney to the Queen’s Bench in 1841, and, in 1846, Solicitor of the High Court of Chan¬ cery. He had a large family—seven sons and three daughters. His third son, Charles, the nephew whom Henry treated for smallpox in 1861, lived to the ripe age of fifty-three. His fifth son, Frederick, moved to South Af¬ rica, married in 1881 and had six children, one of whom was the F. Lawrence Gray mentioned above. After his father’s death in 1834, Henry Gray continued living at 8 Wilton Street with his mother, brothers and sister. This is undoubtedly the address from which he later carried on his short practice and the place where he wrote his famous book. He and his brothers were educated at one of the large London schools, possibly Westminster, Charterhouse, or St. Paul’s. He was engaged to be married at the time of his death. Henry Gray’s signature appears on the pupil’s book at St. George’s Hospital, Lon¬ don, as a “perpetual student” entering on the 6th of May, 1845. Four years later, in 1849, his name appears in the Proceedings of the Royal Society with the M.R.C.S. after it, the approximate equivalent of our M.D. While still a student in 1848, he won the triennial prize of the Royal College of Surgeons for an essay entitled “The Origin, Connections and Distribution of the Nerves to the Human Eye and Its Appendages, Illustrated by Compara¬ tive Dissections of the Eye in Other Verte¬ brate Animals.” He was appointed for the customary year as house surgeon to St. George’s Hospital in 1850. Successively thereafter he held the posts of demonstrator of anatomy, curator of the museum, and lec¬ turer on anatomy at St. George’s Hospital. In 1861 he was surgeon to St. James Infirmary and was a candidate for the post of assistant surgeon to St. George’s Hospital and would certainly have been elected had he not died from confluent smallpox which he con¬ tracted from his nephew, Charles, whom he was treating. He was buried at Highgate Cemetery in June 1861. Sir Benjamin Brodie, president of the Royal Society, wrote, “I am much grieved about poor Gray. His death, just as he was on the point of obtaining the reward of his labors, is a sad event indeed . . . Gray is a great loss to the hospital and school. Who is there to take his place?” During his lifetime Henry Gray received outstanding recognition for his original in¬ vestigations. That they have received so litVII

viii

HENRY GRAY

tie mention since his death is as surprising as the lack of information about his life. The study of the eye which won him the Royal College of Surgeons prize was expanded into an embryological work, “On the devel¬ opment of the retina and optic nerve, and of the membranous labyrinth and auditory nerve,” published in the Philosophical Transactions of the Royal Society in 1850. It contains the earliest description of the histo¬ genesis of the retina. Two years later the Transactions contained another article, “On the development of the ductless glands in the chick.” This must have stimulated Gray’s interest in the spleen, which he classed as a ductless gland, because he obtained an allot¬ ment of funds for further study from the annual grant placed at the disposal of the Royal Society by Parliament for the promo¬ tion of science. The result was a monograph of 380 pages, “On the Structure and Use of the Spleen,” which won him the triennial Astley Cooper Prize of £300 (about $1,500.00) in 1853. It was published by J. W. Parker and Son in 1854, but appears now to be rare. Numerous “first observations” recorded in this book have escaped notice by all subse¬ quent authors writing about the spleen. Gray described, among other things, the origin of the spleen from the dorsal mesogastrium ten years before Muller, who is usually given credit for the discovery As a result of his ability and accomplish¬ ment, Henry Gray was made a Fellow of the Royal Society at the very young age of twenty-five. Besides anatomy, his interests also included pathologic and clinical inves¬ tigation. In 1853 he had a paper in the Medico-Chirurgical Proceedings entitled, “An Account of a Dissection of an Ovarian Cyst Which Contained Brain,” and in 1856 a more extensive treatise entitled, “On Myeloid and Myelo-Cystic Tumours of Bone; Their Struc¬ ture. Pathology, and Mode of Diagnosis.” His crowning achievement, however, and the one which is the source of his lasting fame is the publication, Anatomy, Descrip¬ tive and Surgical, now widely known as Gray’s Anatomy.

125 Years of Gray's Anatomy The first edition of Gray’s Anatomy was published in London by J. W. Parker and Son in 1858 and in June of 1859 in Philadelphia

by Blanchard and Lea, who purchased the American rights for the book. The American edition was identical with the English, ex¬ cept that many typographic errors had been corrected, the index considerably improved, and the binding made more rugged. It con¬ tained xxxii + 754 pages and 363 figures. The drawings were the work of Dr. H. Van Dyke Carter, of whom Gray writes in his preface, “The Author gratefully acknowl¬ edges the great services he has derived, in the execution of this work, from the assis¬ tance of his friend, Dr. H. V. Carter, late Demonstrator of Anatomy at St. George’s Hospital. All the drawings, from which the engravings were made, were executed by him. In the majority of cases, they have been copied from, or corrected by, recent dissec¬ tions, made jointly by the Author and Dr. Carter.” Blanchard and Lea obtained the services of Dr. R. J. Dunglison to edit the first and the next four American editions. Dunglison cor¬ rected the typographic and other small er¬ rors and improved the index but made few alterations or additions in the text. Almost no adaptation was required because medical education in this country and in England were still much alike. Henry Gray had just finished preparing the second edition before his untimely death. This was published in 1860 in Eng¬ land and in 1862 in this country under the editorship of Dunglison. The next edition published in America was a “New American from the 5th English Edition.” This appeared in 1870 and was bound in either cloth or sheep. Another pause, and there appeared the “New American from the 8th English” in 1878, and “The New American from the 10th English” in 1883. Dunglison was again the editor, but a new editor, W. W. Keen, revised extensively the section of topographic anat¬ omy at the end of the book. The following edition, a “New American from the Eleventh English,” published in 1887, was edited and thoroughly revised by W. W. Keen. Color was used for the first time in the chapters on blood vessels and nerves. The “New Ameri¬ can from the Thirteenth English” appeared in 1893, apparently edited by Keen and others. In 1896 the reference to the English edition was dropped and we have the fourteenth edition with the editors Bern B. Gallaudet, F. J. Brockway, and J. P. McMurrich. J. C.

HENRY GRAY

DaCosta, editor of the sixteenth edition in 1905, expanded the book, introducing much new material. E. A. Spitzka assisted DaCosta with the seventeenth edition in 1908 and edited the next two alone in 1910 and 1913. The publishers also tried a “New American from the Eighteenth English Edition” in 1913, but its sale was much smaller than that of the American edition of that year. In 1918, W. H. Lewis began his editorship, giving the book a scholarly treatment, reducing its length, improving the sections on embryol¬ ogy, and generally giving a more straightfor¬ ward treatment of the various chapters. For his last edition, the twenty-fourth, published in 1942, he had the assistance of six associate editors. Beginning with the twentieth edition in 1918, new editions appeared at regular inter¬ vals of six years; their dates and the names of the editors are listed on page vi. Dr. Charles Mayo Goss became responsible for the twenty-fifth through the twenty-ninth American Editions, these being spaced at five- to seven-year intervals. The twenty-

IX

seventh Edition was published in 1959 in order to have its publication fall on the 100th year. Since the beginning of this century, the American and English editions have tended to drift apart. Even from an early date, new American editions were less frequent than the English, and if the American editions had been numbered independently from the beginning, the present edition would be the twenty-fifth, whereas the current English edition is the thirty-sixth. Somewhat more of the imprint of Henry Gray has been pre¬ served in this American edition, in the illus¬ trations especially, as it still has nearly 200 drawings based on the original illustrations by Carter. This treatise, offered initially by a young English anatomist and surgeon, is the oldest continuously revised textbook still currently in use by the medical professions. After one hundred and twenty-five years, this enduring recognition is a tribute that, perhaps, even Henry Gray may not have conceived would happen.

When I was asked to consider the prepara¬ tion of this 30th American Edition of Gray’s Anatomy, I spent an afternoon with Dr. Charles Mayo Goss at his home near Wash¬ ington, D.C. Dr. Goss, who was affectionately known as “Chiz” by his many friends, had edited the five previous editions and had for the preceding three decades masterfully suc¬ ceeded in retaining both the effectiveness and popularity of the book to students and practitioners of the medical, dental and other allied health professions. Dr. Goss warmly encouraged me to assume the re¬ sponsibility for this 30th edition and recom¬ mended that I attempt to retain the classical tradition and style of the book, even if I planned, as he thought was necessary, a major revision of the text and figures. Chiz’s twinkling smile should have alerted me to the enormous task that I was considering. Sadly, Dr. Goss’s death in 1981 came about two years after I commenced serious work on this project, and I never had a further opportunity to benefit from his wisdom. Eleven years have elapsed since the 29th American Edition appeared in 1973. Recog¬ nizing the special regard held for this book by generations of American anatomists, I felt that it was of special importance for me to understand the views held by many of my esteemed colleagues in the United States and Canada about the current usefulness of the book and how it might be altered or im¬ proved. Many informal discussions almost invariably pointed to the lasting value of having available for student and profes¬

sional use a comprehensive anatomic trea¬ tise that is organized by systems. Many valu¬ able suggestions from these conversations have been incorporated in this edition and my appreciation is extended to my many friends for their interest and their patience with my many questions. Nearly two thirds of the chapters in this edition have been thoroughly revised and the remainder have been edited. The chapter on Developmental and Gross Anatomy of the Central Nervous System has virtually been rewritten as have extensive sections in at least ten other chapters. Many hundreds of new paragraphs and pages have replaced those of the 29th edition and, thus, numerous subjects have received some expanded at¬ tention and updating. To list them all here would not be appropriate, but a few of these are: certain aspects of the new cellular biol¬ ogy and embryology; the physical features and properties of bone and its formation; the development, classification and movement of joints; the form, attachment and actions of muscles, as well as the structure of skeletal and cardiac muscle; the vascular supply to the central nervous system; and the develop¬ ment of veins and lymphatics. Certainly, due to time limitations, many subjects did not get the attention they deserved, and thus, much still needs to be done in subsequent editions. Because the value of this book is essentially its information on the gross anatomy of the human body, it was not the intention of the editor to offer the reader comprehensive treatments in the fields of embryology, mi¬ croscopic anatomy, physiology, and neuro¬ science. Excellent texts written by scholars expert in these subjects already exist, and to recount detailed features of their disciplines here is unnecessary and would have been presumptuous. I have attempted to retain the classical style of the text, long considered one of the most elegant examples of descriptive scien¬ tific literature. In the extensively revised chapters, however, few paragraphs remain totally intact. I have tried to match the new with the old, to simplify some of the more complex sentence structure in order to clar¬ ify meaning, and to maintain a uniformity of prose. I hope that at least to some extent this effort has been successful. A nearly complete change has been intro¬ duced in the headings within the chapters, yet the chapter subjects remain the same. XI

xii

PREFACE

Using color print for various headings and subheadings will make it easier to find perti¬ nent information on structures that in the past had to be identified by bold print within the paragraphs. In this respect, the student who must study and the practitioner who more quickly seeks information may both find the format of this edition beneficial. Additionally, the entire text has been reset and hundreds of more modern references and others that have proved valuable over time have been added to the reference lists at the end of each chapter. Many citations, in addition to those used in the text, have been made available for readers who require more knowledge than this book attempts to offer. A significant number of new figures, never before published, have been introduced into this edition, along with numerous others borrowed from various sources. Many of the latter have come from original journal arti¬ cles. The labels on most of the figures have been replaced with type that is easier to read. Certain older, less effective figures have either been eliminated or replaced by drawings that illustrate more clearly the subject matter. I believe the publishers should be commended for having done an excellent job in abiding by the principle to modernize the information and format and yet retain the classical look of this oldest (now 125 years), continuously used textbook in biomedical science. Grateful acknowledgment must go to the many friends and colleagues who have con¬ tributed to this new edition, and my heartfelt appreciation is extended to so many authors and publishers who have allowed the repro¬ duction of figures from their works or copy¬ righted properties. Especially mentioned, however, should be Professors Helmut Ferner and Jochen Staubesand, editors of Benninghoff and Goerttler’s Lehrbuch der Anatomie des Menschen, published by Urban and Schwarzenberg in Munich, from which a considerable number of figures

were taken. Along the way, I have benefited greatly from the advice, suggestions, or con¬ tributions on one subject or another from Professors Leslie B. Arey, Malcolm B. Car¬ penter, James D. Collins, Jack Davies, George E. Erikson, Fakhry G. Girgis, W. Henry Hollinshead, Lawrence Kruger, Lee V. Leak, Raymond J. Last, David S. Max¬ well, Keith L. Moore, Charles R. Noback, Keith R. Porter, Nabil N. Rizk, Charles H. Sawyer, William F. Windle, Luciano Zamboni, and the late Elizabeth C. Crosby and Jan Langman. Many others, as well, have contributed greatly to the work of this revision. Among those who deserve special mention and much praise are Jill Penkhus, who created much of the new artwork for this edition; Dr. Charles F. Bridgman, who allowed the use of several of his drawings made of brain dis¬ sections prepared by the late Professor A. T. Rasmussen; Thomas Colaiezzi, at Lea & Febiger, who handled production; Howard N. King, who designed this new edition; Anne Cope who prepared the index; Dr. Caroline Belz Caloyeras, whose dedicated assistance with typing and editing was absolutely es¬ sential for this book to have appeared; and Dorothy Di Rienzi and, earlier, Mary Mansor of Lea & Febiger, who copy-edited all of the chapters. My appreciation also is extended to John F. Spahr and George Mundorff of Lea & Febiger who suggested that I under¬ take the work on this edition and then pa¬ tiently waited for its completion. Most importantly, I wish to offer my grati¬ tude to Julie, my wife, who through the years has made her special contributions to what¬ ever work I have undertaken. Her hearten¬ ing and unfailing encouragement to me and her belief in the fundamental objectives of education have been my inspiration and have lightened the thousands of hours spent on this book. Carmine

D.

Clemente

Los Angeles, California

Bones of the Shoulder Girdle and Upper Limb Bones of the Lower Limb Sesamoid Bones Comparison of the Bones of the Hand and Foot Histologic Structure of Connective Tissues Connective Tissue Types

1. Introduction 2 4 4 5

2. Cytology and Embryology The Cell Cell Division The Spermatozoon The Ovum The Development of the Embryo Early Growth of the Embryo Fetal Membranes and Placenta The Placenta The Growth of the Embryo and Fetus

7 11 21 23 34 36 51 58 61

3. Surface and Topographical Anatomy The The The The The The The The

Head Neck Back Thorax Abdomen Perineum Upper Limb Lower Limb

69 73 79 80 85 96 98 107

4. Osteology Ossification and Skeletal Development Ossification Skeletal Development Axial Skeleton The Vertebral Column The Thorax The Skull The Appendicular Skeleton

305 306 308

5. The Joints

Contents Terms of Position and Direction Terms for Movements at Joints Nomenclature Approaches to the Study of Anatomy

226 261 304

114 114 119 126 127 147 158 225

Development of the Joints Classification of Joints Fibrous Joints Cartilaginous Joints Synovial Joints Movements at Joints Structures of Synovial Joints Articulations of the Axial Skeleton Articulation of the Mandible Articulation of the Vertebral Column with the Cranium Articulations of the Atlas with the Axis Articulations of the Vertebral Column Costovertebral Joints Sternocostal, Interchondral, and Costochondral Joints Articulations of the Sternum Lumbosacral, Sacrococcygeal, and Intercoccygeal Joints Articulations of the Pelvis Articulations of the Upper Extremity Shoulder Girdle Shoulder Joint Elbow Joint Radioulnar Joints Radiocarpal or Wrist Joint Intercarpal Joints Carpometacarpal Joints Intermetacarpal Joints Metacarpophalangeal Joints Interphalangeal Joints Articulations of the Lower Limb Hip Joint Knee Joint Tibiofibular Joints Talocrural or Ankle Joint Intertarsal Joints Tarsometatarsal Joints Intermetatarsal Joints Metatarsophalangeal Joints Interphalangeal Joints Arches of the Foot

329 330 330 333 333 335 336 338 338 341 345 346 351 354 357 358 360 366 366 370 375 380 382 384 386 388 388 389 390 390 397 408 409 413 419 421 422 422 422

6. Muscles and Fasciae Development of Muscles Fasciae

429 431

xiii

xiv

CONTENTS

Form and Attachments of Muscles Actions of Muscles Muscles and Fasciae of the Head Facial Muscles Muscles of Mastication Anterolateral Muscles and the Fasciae of the Neck Superficial Cervical Fasciae Deep Cervical Fasciae Superficial Cervical Muscle Lateral Cervical Muscles Suprahyoid Muscles Infrahyoid Muscles Anterior Vertebral Muscles Lateral Vertebral Muscles Fasciae and Muscles of the Trunk Deep Muscles of the Back Suboccipital Muscles Muscles of the Thorax Fasciae and Muscles of the Abdomen Muscles and Fasciae of the Pelvis Muscles and Fasciae of the Perineum Muscles and Fasciae of the Upper Limb Muscles Connecting the Upper Limb to the Vertebral Column Muscles Connecting the Upper Limb to the Thoracic Wall Muscles of the Shoulder Muscles of the Arm Muscles of the Forearm Fasciae, Retinacula, Tendon Sheaths and Compartments of the Wrist and Hand Muscles of the Hand Fasciae and Muscles of the Lower Limb Muscles and Fasciae of the Iliac Region Fasciae and Muscles of the Thigh Muscles and Fasciae of the Leg Muscles and Fasciae of the Foot Structure of Skeletal Muscle

434 436 437 438 447 452 453 453 456 456 457 459 461 463 463 464 473 475 483 498 501 512 512 516 521 525 529

541 550 556 556 558 573 584 590

7. The Heart Development of the Heart Peculiarities in the Vascular System of the Fetus Fetal Circulation Changes in the Vascular System at Birth The Pericardium General Features of the Heart External Features of the Heart Chambers of the Heart Right Atrium Right Ventricle Left Atrium Left Ventricle Structure of the Cardiac Wall Conduction System of the Heart Histology and Ultrastructure of Cardiac Muscle

606 618 619 621 621 623 625 627 627 631 634 634 636 637 640

8. The Arteries Development of the Arteries Pulmonary Arterial Vessels Pulmonary Trunk The Aorta Ascending Aorta Arch of the Aorta Brachiocephalic Trunk Arteries of the Head and Neck Common Carotid Artery Arteries of the Upper Limb The Axilla Arteries of the Thorax and Abdomen Thoracic Aorta Abdominal Aorta Arteries of the Pelvis, Perineum, and Gluteal Region Common Iliac Arteries Arteries of the Lower Limb

650 657 657 662 662 664 665 666 666 709 710 728 728 731 748 748 760

9. The Veins Development of the Veins Parietal Veins Visceral Veins The Pulmonary Veins Right Superior Pulmonary Vein Right Inferior Pulmonary Vein Left Superior Pulmonary Vein Left Inferior Pulmonary Vein The Systemic Veins Veins of the Heart Coronary Sinus Anterior Cardiac Veins Smallest Cardiac Veins Superior Vena Cava and its Tributaries Superior Vena Cava Veins of the Head and Neck Veins of the Upper Limb Veins of the Thorax Inferior Vena Cava and its Tributaries Inferior Vena Cava Veins of the Abdomen Veins of the Pelvis and Perineum Veins of the Lower Limb Histology of the Blood Vessels Arteries Veins

788 788 792 794 795 796 796 796 797 798 798 799 799 799 799 801 820 826 832 832 834 839 845 850 850 855

10. The Lymphatic System Development of Lymphatic System Distribution of Lymphatic Vessels Microscopic Structure of Lymphatic Vessels and Lymph Nodes Structure of Lymphatic Vessels Structure of Lymph Nodes Large Lymphatic Vessels Thoracic Duct Right Lymphatic Duct

867 868 871 871 873 876 876 879

CONTENTS

Lymphatic Vessels and Nodes of the Head and Neck Lymphatic Vessels of the Head Lymph Nodes of the Head Lymphatic Vessels of the Neck Lymph Nodes of the Neck Lymphatic Vessels and Nodes of the Upper Limb Lymphatic Vessels of the Upper Limb Lymph Nodes of the Upper Limb Lymphatic Vessels and Nodes of the Thorax Lymphatic Vessels of the Thorax Lymph Nodes of the Thorax Lymphatic Vessels and Nodes of the Abdomen and Pelvis Lymphatic Vessels of the Abdomen and Pelvis Lymph Nodes of the Abdomen and Pelvis Lymphatic Vessels and Nodes of the Lower Limb Lymphatic Vessels of the Lower Limb Lymph Nodes of the Lower Limb The Spleen Development of the Spleen Relationships of the Adult Spleen Microscopic Structure of the Spleen The Thymus Development of the Thymus Relationships of the Thymus Microscopic Structure of the Thymus

879 880 883 884 886 887 887 888 890 890 893 896 896 906 913 913 915 917 917 918 919 924 924 925 925

Accessory Nerve Hypoglossal Nerve The Spinal Nerves Dorsal Primary Divisions of the Spinal Nerves Ventral Primary Divisions of the Spinal Nerves Visceral Nervous System Visceral Afferent Fibers Autonomic or Visceral Efferent System

XV

1189 1190 1191 1193 1195 1245 1245 1247

13. Organs of the Special Senses Organ of Smell Organ of Taste Organ of Sight: The Eye Bulb of the Eye Refracting Media Accessory Organs of the Eye Organ of Hearing and Equilibration: The Ear Development External Ear Middle Ear or Tympanum Internal Ear or Labyrinth

1283 1283 1285 1290 1302 1303 1312 1312 1315 1319 1328

14. The Integument Development Structure Appendages of the Skin

1345 1345 1350

11. Development and Gross Anatomy of the Central Nervous System 15. The Respiratory System Development of the Nervous System Gross Anatomy of the Central Nervous System Spinal Cord Medulla Oblongata The Pons The Cerebellum The Midbrain The Diencephalon The Telencephalon

933 957 959 976 981 988 998 1016 1035

12. The Peripheral Nervous System Cranial Nerves Olfactory Nerve Optic Nerve Oculomotor Nerve Trochlear Nerve Trigeminal Nerve Abducent Nerve Facial Nerve Vestibulocochlear Nerve Glossopharyngeal Nerve Vagus Nerve

1149 1150 1151 1155 1158 1158 1170 1170 1177 1178 1181

Development Upper Respiratory Tract Nose Larynx Trachea and Bronchi Pleura Mediastinum Lungs (Pulmones) Surfaces Borders Fissures and Lobes Root Further Subdivision of the Lung Blood Vessels of the Lungs Structure

1357 1358 1358 1365 1377 1380 1383 1385 1385 1386 1386 1387 1388 1389 1395

16. The Digestive System Development of the Digestive System Mouth and Associated Structures Pharynx and Postpharyngeal Alimentary Tube Rectum and Anal Canal

1402 1403 1404 1409

XVI

CONTENTS

The Mouth Vestibule Mouth Cavity Proper Lips Cheeks Gums Palate The Teeth General Characteristics Permanent Teeth Deciduous Teeth Structure of the Teeth Development of the Teeth Eruption of the Teeth The Tongue Borders and Surfaces Papillae Muscles Structure of the Tongue Salivary Glands Parotid Gland Submandibular Gland Sublingual Gland Structure of the Salivary Glands Accessory Glands The Fauces Palatoglossal Arch Palatopharyngeal Arch Palatine Tonsil Muscles of the Palate Structure of the Soft Palate The Pharynx Nasal Part of Pharynx Oral Part of Pharynx Laryngeal Part of Pharynx Muscles of the Pharynx Structure of the Pharynx The Esophagus Structure of the Esophagus The Abdomen Boundaries Apertures Regions Disposition of the Abdominal Viscera The Peritoneum Parietal Peritoneum Visceral Peritoneum Peritoneal Rescesses or Fossae The Stomach Shape and Position Openings Curvatures Surfaces Component Parts Interior of the Stomach Structure of the Stomach Small Intestine Duodenum Jejunum and Ileum Structure of the Small Intestine

1410 1410 1410 1411 1412 1412 1412 1413 1413 1415 1417 1417 1420 1424 1425 1425 1427 1428 1431 1432 1432 1434 1435 1435 1436 1436 1437 1437 1437 1439 1441 1441 1442 1442 1442 1442 1445 1446 1446 1448 1448 1449 1449 1449 1450 1453 1457 1460 1463 1463 1464 1464 1465 1465 1465 1466 1469 1470 1472 1473

Large Intestine Cecum Colon Rectum Anal Canal Structure of the Large Intestine The Liver Surfaces and Borders Fissues and Fossae Lobes Internal Lobes and Segments Ligaments Fixation of the Liver Structure of the Liver Excretory Apparatus of the Liver The Pancreas Development Head Neck Body Tail Pancreatic Duct Structure of the Pancreas

1478 1479 1482 1483 1485 1485 1489 1491 1493 1493 1494 1496 1497 1497 1500 1502 1502 1503 1504 1504 1505 1505 1506

17. The Urogenital System Development of Urinary Organs Pronephros and Mesonephric Duct Mesonephros Metanephros and Permanent Kidney Urinary Bladder Development of Generative Organs Genital Glands Testis Male Mesonephric Duct Descent of the Testes Prostate Ovary Female Mesonephros and Mesonephric Duct Paramesonephric Ducts Descent of the Ovaries External Organs of Generation Urethra Urinary Organs Kidneys Ureters Urinary Bladder Male Urethra Female Urethra Male Genital Organs Testes and Their Coverings Ductus Deferens Seminal Vesicles Ejaculatory Duct The Penis Prostate Bulbouretheral Glands Female Genital Organs Ovaries

1515 1515 1515 1516 1517 1518 1518 1518 1519 1519 1521 1521 1522 1522 1523 1524 1524 1525 1525 1537 1539 1545 1548 1548 1548 1557 1558 1559 1559 1564 1566 1566 1567

CONTENTS

Uterine Tube The Uterus The Vagina External Genital Organs Mammary Gland

1570 1571 1578 1579 1581

18. The Endocrine Glands Thyroid Gland Development Anatomy Structure Parathyroid Glands Development Anatomy Structure

1596 1596 1596 1598 1599 1599 1599 1600

XVII

Hyphophysis Cerebri or Pituitary Gland Development Anatomy Lobes Suprarenal or Adrenal Gland Development Anatomy Accessory Glands Structure Paraganglia, Glomera, and “Glands” or “Bodies” Paraganglia Aortic Bodies or Lumbar Paraganglia Glomus Coccygeum

1600 1600 1601 1601 1604 1604 1604 1605 1606

Index

1617

1607 1607 1607 1608

.

Introduction

In ancient Greece, at the time of Hippocra¬ tes (460 B.c.), the word anatomy, Avaro/ny, meant a dissection, from to/jo7, a cutting, and the prefix diva, meaning up. Today anatomy is still closely associated in our minds with the dis¬ section of a human cadaver, but the term was extended very early to include the whole field of knowledge dealing with the structure of living things. The history of anatomy is one of the most exciting sagas in the ascent of human civili¬ zation. Since the subject deals with the structure of the body, it has lured some of the greatest minds not only to contemplate the nature of man, but to discover first hand by the method of dissection how the human being is put together. However, religious and other social pressures and taboos over the centuries made dissection of the human ca¬ daver frequently a dangerous and secret ac¬ tivity. The study of the structure of the human body was the first of the medical sci¬ ences, and from it have derived all the rest. Even before human dissection was practiced by Herophilos and Erasistratos (300-250 B.c.), Aristotle (384-323 B.c.) dissected ani¬ mals, wrote a treatise on their anatomy, and laid the groundwork for a scientific study of their form and structure. Today it is considered that the greatest contributor to the subject matter of human anatomy was a young Flemish physician from Brussels who worked in Padua, Italy

Fig. 1-1. Andreas Vesalius (1514-1564). This figure was copied from the second edition of Vesalius’ De Humani Corporis Fabrica, published in 1555. Having also ap¬ peared in the first edition (1543), it illustrates Vesalius during his late twenties and is still the only authenti¬ cated portrait of him known to exist.

during the height of the Renaissance. In 1542, at the age of 28, Andreas Vesalius, breaking boldly from the millennia and the prevailing traditions of Galen, published his great treatise De Humani Corporis Fabrica (Fig. 1-1). His work was so impressive and accurate that his books became the principal texts used by students of medicine for the next 200 years. Vesalius had substituted ob¬ servation by dissection for authoritarianism, thereby grounding his findings on a scientific basis. Anatomy has therefore become the branch of knowledge concerned with struc¬ ture or morphology. Our fund of anatomical information has been increased greatly dur¬ ing the last three or four centuries by the study of minute structure with the micro¬ scope, by following the development of the embryo, and by the addition of new and re¬ fined technical methods. The whole field of anatomy has become very large, and as a re¬ sult a number of subdivisions of the subject

1

2

INTRODUCTION

have been recognized and named, usually to correspond with a specialized interest or avenue of approach. Gross anatomy is the study of morphol¬ ogy, by means of dissection, with the un¬ aided eye or with low magnification such as that provided by a hand lens. The study of the structure of organs is organology. The study of the tissues is histology. Microscopic anatomy is the study of struc¬ ture with the aid of a microscope, and since it deals largely with the tissues, it is often called histology. Microscopic anatomy has another branch, the study of the cell, or cy¬ tology. An enormous increase in research into the finer structure of the cell has taken place in recent years, due to the adaptation of the electron microscope to the observa¬ tion of ultrathin sections of the tissues. Embryology or developmental anatomy deals with the growth and differentiation of the organism from the single-celled ovum to birth. These processes of development and maturation are also called ontogeny. It is impossible to understand clearly all the structures found in the adult body without some knowledge of embryology. Since human embryos, particularly the younger stages, are difficult to obtain for study, a large part of our knowledge has been gained from animals, that is, from comparative embryology. The second chapter in this book is devoted to a brief summary of human embryology. The development of each system is outlined in the appropriate chapters and sections. Comparative anatomy refers to the study of the structure of all living creatures, in contradistinction to human anatomy which refers only to man. A comparison of all the known animal forms, both living and fossil, indicates that they can be arranged in a scale which begins with the simplest forms and progresses through various gradations of complexity and specialization to the most highly evolved forms. The unfolding of a particular race or species is called phylogeny. Many of the earlier stages of develop¬ ment in man and other higher animals re¬ semble the adult stages of animals lower in the scale; hence it has been said that ontog¬ eny repeats phylogeny. The study of com¬ parative anatomy has contributed vitally to the understanding of human anatomy and physiology.

Terms of Position and Direction (Fig. 1-2) the anatomical position. The traditional anatomical position, which has been arbi¬ trarily accepted, places the body in the erect posture with the feet together, the arms hanging at the sides, and the thumbs point¬ ing away from the body. This position is used in giving topographic relationships, especially those which are medial and lat¬ eral in reference to the limbs. The muscle actions and motions at the joints are also given with reference to this position unless it is stated otherwise. It is particularly impor¬ tant that the anatomical position be remem¬ bered in descriptions using anterior and pos¬ terior, or the more general and ambiguous terms such as up, down, over, under, below, and above. The median plane is a vertical plane that divides the body into right and left halves; it passes approximately through the sagittal suture of the skull, and therefore any plane parallel to it is called a sagittal plane. Fron¬ tal planes are also vertical, but they course at right angles to the sagittal planes. Since one frontal plane passes approximately through the coronal suture of the skull, they are also called coronal planes. Transverse or horizontal planes cut across the body at right angles to both sagittal and frontal planes. Ventral and dorsal refer to the front and back of the body, and are synonymous with anterior and posterior. The use of these terms in courses of comparative anatomy may lead to some confusion for the student of human anatomy, since man’s posture is erect. In the hands, palmar or volar is substi¬ tuted for ventral or anterior. The sole of the foot is called plantar, while dorsal is re¬ tained for the top or opposite surface of both the hand and foot. Cranial and caudal indicate the head and tail respectively, and are synonymous with superior and inferior when human subjects are in the anatomical position. In compara¬ tive anatomy the latter terms might be con¬ fused with dorsal and ventral when referring to four-footed beasts. Median refers to structures along the mid¬ line or median sagittal plane of the trunk or limb.

TERMS OF POSITION AND DIRECTION

Medial

Dorsal

CORONAL PLANE (FRONTAL)

Fig. 1-2.

Diagrams illustrating the planes of the body and the terms of position and direction.

3

4

INTRODUCTION

Medial and lateral refer to structures nearer or farther away from the median plane. It should be noted that the Latin word “medius” means middle, not medial. The Latin word for medial is “medialis.” Superficial and deep indicate the relative depth from the surface, and are preferable to over and under, and above or below, since the latter may be confused with superior and inferior. Proximal and distal indicate a direction toward or away from the attached end of a limb, the origin of a structure, or the center of the body. Proximal refers to a structure closer to the center of the body, while distal refers to a structure farther from the body center. External and internal are most commonly used for describing the body wall, or the walls of cavities and hollow viscera. At times these terms may be synonymous with superficial and deep, or even with lateral and medial.

Terms for Movements at Joints (Fig. 1-2) Flexion is that action which approximates two parts of the body connected at a joint. Flexion of the forearm at the elbow joint approximates the forearm to the arm; flexion of the calf at the knee joint approximates the calf to the posterior thigh. Extension is the act of straightening a limb, thereby dimin¬ ishing the angle formed by flexion. Thus, straightening the flexed forearm at the elbow joint is an example of extension. Flexion and extension are, therefore, antagonistic ac¬ tions. Abduction is the movement of a limb or other structure away from the middle line. Elevating an upper limb from the ana¬ tomical position at the side of the trunk to any point more lateral is an example of ab¬ duction. The opposite action, i.e., returning the abducted limb toward the midline is called adduction. The movements of flexion, extension, abduction, and adduction may be sequentially performed in a manner by which the end of a limb describes a circle or a cone; this is called circumduction. Pronation is that movement of the forearm by which the palm of the hand is rotated to a backward position when the upper extrem¬ ity hangs by the side of the body in the ana¬ tomical position. The pronated hand will

rest palm down on the surface of the table. Supination is the opposite, i.e., the rotation of the hand so that the palm faces forward in the anatomical position. The supinated hand rests with its palmar surface upward on a table surface. Rotation is a revolving or turning movement of a limb or other struc¬ ture, such as the back or head, around its long axis. Both medial and lateral rotation are commonly observed at the shoulder and hip joints. Protraction is the forward move¬ ment of a body part such as the jaw or shoulder. Retraction is the opposite, i.e., the backward movement of these structures. Eversion is the outward rotation of the sole (plantar surface) of the foot so that it faces laterally. Oppositely, inversion is the inward rotation of the sole of the foot resulting in the plantar surface facing medially.

Nomenclature Although the majority of the common anatomical names are derived from those used by the ancient Greeks, considerable disagreement and confusion have arisen because of conflicting loyalties to teachers, schools, or national traditions. Shortly be¬ fore the end of the 19th century, however, the need for a comprehensive system of nomenclature was realized, and a commis¬ sion of eminent authorities from various countries was organized for this purpose. The system devised by this commission was adopted by the German Anatomical Society in 1895 at its meeting in Basel, Switzerland, and it has since been called the Basle Nomina Anatomica or the BNA (His, 1895). The BNA gives the names in Latin, and many nations, including the United States, and Great Britain, adopted it, translating the terms into their own language whenever desirable. The French anatomists, however, did not entertain this nomenclature with much enthusiasm, preferring their own quite ancient tradition. The British anatomists gradually found certain inaccuracies and inconsistencies with their time-honored tra¬ dition which favored human anatomy re¬ lated to the arbitrary “anatomical position.” They broke away from the BNA and adopted their own revision in 1933 which they called the Birmingham Revision or BR. Even the German anatomists became restless under the restrictions of the BNA adoption of the

APPROACHES TO THE STUDY OF ANATOMY

“anatomical position” and preferred an at¬ tempt to establish a scientific language ap¬ plicable to the comparative anatomy of ver¬ tebrates as well as to human anatomy. In 1937 the Anatomische Gesellschaft met in Jena and adopted a revision that is known as the Jena Nomina Anatomica or INA. The anatomists of the United States remained faithful to the BNA. At the Fifth International Congress of Anatomists held at Oxford in 1950 a com¬ mittee was appointed to attempt a new revi¬ sion of anatomical names. This International Nomenclature Committee met at Paris in July 1955, and approved the Paris Nomina Anatomica or PNA. This book utilizes the terms designated in the PNA except in a few instances where it has been abandoned deliberately in the in¬ terests of clarity. Since Latin is less familiar to students today than in the past, names are usually given in English with the official Latin name at times italicized in parentheses. Other recognized names are also added in parentheses. Anatomical eponyms, that is, designations by the names of persons, are popular among clinicians and specialists. Many eponyms have been added to the other names in pa¬ rentheses in order to expose the student to terms commonly used in clinical medicine.

Approaches to the Study of Anatomy Human anatomy may be presented from at least three points of view: (1) descriptive or systemic anatomy, (2) regional or topo¬ graphical anatomy, and (3) applied or practi¬ cal anatomy. This book is primarily con¬ cerned with systemic anatomy, but regional and applied anatomy are introduced when their use facilitates communication. systemic anatomy. The body is com¬ posed of a number of systems whose parts are related by physiological as well as ana¬ tomical considerations. Each system is com¬ posed of several organs or tissues whose combined functions serve the body uniquely. Thus, although the anatomy of the oral cavity is remarkably different from that of the stomach or duodenum, these organs are presented in the same section because they all contribute to the functions of the digestive system. Although the study of

5

anatomy is concerned primarily with mor¬ phology, the knowledge of structure be¬ comes more understandable and of practical value if the close association between struc¬ ture and function is continually considered. The systems of the body are as follows: The skeletal system, the study of which is called osteology, consists of bones and carti¬ lage. Its function is to support and protect the soft parts of the body. The system of joints or articulations (arthrology) allows for the movement of bones while they are held together by strong fibrous bands, the ligaments. The muscular system (myology) forms the fleshy parts of the body and is responsible for the purposeful movements of the bones at the joints. The vascular system (angiology) includes the circulatory system consisting of the heart and blood vessels and the lymphatic system which transports the lymph and tissue fluids. The nervous system (neurology) includes the central nervous system, composed of the brain and spinal cord, the peripheral nerv¬ ous system, consisting of nerves and ganglia, and the sense organs, such as the eye and ear. The nervous system controls and coor¬ dinates all the other organs and structures, and relates the individual to his environ¬ ment. The integumentary system forms a protec¬ tive covering over the entire body and is composed of the skin, hair and nails. The alimentary system is composed of the food passages and the associated organs and glands of digestion. The respiratory system supplies the body with oxygen and eliminates the carbon di¬ oxide which results from the metabolic processes in the cells. It is composed of the air passages and lungs. The urogenital system includes the kid¬ neys and urinary passages and the reproduc¬ tive organs in both sexes. The endocrine system includes the thy¬ roid, suprarenal, pituitary, and other duct¬ less glands which control certain bodily functions by secreting hormones into the blood stream. Splanchnology is the term that applies to the study of all the internal organs, espe¬ cially those in the thorax and abdomen. An account of the anatomy of any system would be incomplete without consideration of the microscopic anatomy and embryology

6

INTRODUCTION

of the organs in that system. Sections dealing with these fields are appropriately located in the text. TOPOGRAPHICAL

OR

REGIONAL

ANATOMY.

Regional anatomy deals with the structural relationships within the various parts of the body, e.g., the pectoral region or axilla. Stu¬ dents in the laboratory usually approach the subject of anatomy regionally because they dissect by regions rather than by systems. Although the acquisition and organization of anatomical knowledge are easier for begin¬ ners if followed by systems, students in the medical fields must continually be on the alert to learn the relationship of the various parts to each other and to the surface of the body, because the final purpose of their study is to visualize these relationships in living subjects. The recent introduction of new radiologic scanning techniques in the clinics has reemphasized the importance of

human dissection and of learning anatomical relationships. In addition to the dissection of the body, the study of topographical anat¬ omy is carried out by the study of surface anatomy, cross sectional anatomy, and radi¬ ographic or x-ray anatomy. Applied anatomy has a number of subdi¬ visions, and is concerned with the practical application of anatomical knowledge in some clinical field or specialty. Surgical anatomy, pathological anatomy, and radio¬ logical anatomy are probably the largest fields. Physical anthropology is closely related to human anatomy because it relies heavily on anatomical studies and measurements of man and other primates. It is more broadly a subdivision of human biology with particu¬ lar emphasis on racial development, evolu¬ tion, genetics, and paleontology.

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.) Barclay, f. 1803. A New Anatomical Nomenclature Re¬ lated to the Terms which are Expressive of Position and Aspect in the Animal System. Ross and Black¬ wood, Edinburgh, 182 pp. Donath, T. 1969. Anatomical Dictionary with Nomen¬ clature and Explanatory Notes. English Translation edited by G. N. C. Crawford. Pergamon Press, Ox¬ ford, 634 pp. His, W. 1895. Die anatomische Nomenclature. Nomina Anatomica. Verzeichniss der von der anatomischen Gesellschaft auf ihrer IX. Versammlung in Basel angenommenen Namen. Archiv fuer Anatomie und Physiologie, anatomische Abteilung, Supplementband. 1895. Viet & Comp., Leipzig, 180 pp. Knese, K. H. 1957. Nomina Anatomica, 5th edition. Georg Thieme Verlag, Stuttgart, 155 pp. Lassek, A. M. 1958. Human Dissection, Its Drama and Struggle. Charles C Thomas, Springfield, Ill., 310 pp. Nomina Anatomica. 1965. Third edition with index. Revised by the International Anatomical Nomen¬ clature Committee and adopted at the Eighth Inter¬ national Congress of Anatomists. Wiesbaden. Ex-

cerpta Medical Foundation, Amsterdam, 164 pp. Nomina Embryologica. 1970. Compiled by the Embryol¬ ogy Subcommittee of the I.A.N.C. and adopted at the Ninth International Congress of Anatomists, Leningrad 1970. 70 pp. Nomina Histologica. 1970. Compiled by the Histology Subcommittee of the I.A.N.C. and adopted at the Ninth International Congress of Anatomists, Lenin¬ grad 1970, 111 pp. O’Malley, C. D. 1964. Andreas Vesalius of Brussels 1514-1564. University of California Press, Berkeley, 480 pp. Rufus of Ephesus. Second Century. On Names of the Parts of the Human Body. In: Oeuvres de Rufus d’Ephese by Daremberg and Ruelle, 1879. Paris, pp. 133-185. Triepel, H. 1957. Die Anatomischen Namen. Ihre Ableitung und Aussprache. 25th edition by Robert Herrlinger. J. F. Bergmann, Mvinchen, 82 pp. Skinner, H. A. 1963. The Origin of Medical Terms. 2nd ed. The Williams & Wilkins Company, Baltimore, 437 pp.

Cytology ani Embryology

The Cell The human body is composed of struc¬ tural units of protoplasm, called cells, which together with the intercellular material— especially plentiful in the bones, cartilages, tendons, and ligaments—form the tissues and organs. The individual cells are micro¬ scopic in size and occur in many gradations of shape and composition corresponding to their diversified functions (Figs. 2-1; 2-4). Every human being begins life as a single cell, the fertilized ovum. By the process of cell division there soon results a great in¬ crease in the number of cells. Additionally, by the processes of differentiation and me¬ tabolism, the tissues assume their varied functional states. All cells are composed of two parts: the outer soft, jelly-like cytoplasm surrounded by a limiting plasma membrane, and an inner nucleus composed of nucleo¬ plasm which is surrounded by a nuclear envelope. During the interval between peri¬ odic divisions of the cell, the nucleus is in a

resting stage; during periods of division, the nucleus undergoes a series of changes called mitosis. The cytoplasm of a cell appears homoge¬ nous when seen with the light microscope, but in reality is very complex in structure. Within it are embedded many intracellular bodies and organelles (Fig. 2-1). Although most of these structures are recognizable with the light microscope, their finer details have only been seen through the higher magnifications of the electron microscope. Today it is appreciated that most cytoplas¬ mic organelles are composed of delicate lipid-protein membranes. The outer surface of the cell, the cell membrane (plasma mem¬ brane or plasmalemma), is frequently stud¬ ded with microvilli or cilia or other surface specializations. Generally considered to be composed of two layers of protein between which rests a molecular layer of lipid, the cell membrane, or unit membrane, as it is now frequently called, appears trilaminar in structure. Functionally, the membrane is a very important structure because it controls the exchange of materials between the cell and its environment by osmosis, phagocyto¬ sis, pinocytosis, secretion, and other phe¬ nomena. A specialized region of cytoplasm called the central body or centrosome with its tubular centrioles, not always visible with the light microscope, usually lies at one side of the nucleus near the central part of the cell. It serves as a dynamic center with other intracellular structures such as the Golgi complex arranged around it, and it is espe¬ cially important during cell division, as de¬ scribed on page 12. The mitochondria, visi¬ ble in living cells seen with the phase contrast microscope, appear in the form of threads, rodlets, and granules. They are likely to be destroyed by the action of lipid solvents during the preparation of routinely preserved and stained microscope slides. Their internal organization has been re¬ vealed by the electron microscope (Figs. 2-1; 2-2). It has been demonstrated that mito¬ chondria are composed of two membranes. One, a continuous outer limiting membrane, surrounds a second inner membrane whose surface area is enlarged by a series of folds called cristae (Palade, 1952, 1953). By their isolation with differential centrifugation, mitochondria have been shown to contain important enzymes necessary for the meta¬ bolic processes of oxidative phosphoryla7

8

CYTOLOGY AND EMBRYOLOGY

THE CELL

tion. The Golgi apparatus (also called Golgi bodies or complex; Fig. 2-1) can be demon¬ strated in nearly all cells by special methods of preparation, but is seldom identifiable in living cells. With the electron microscope it has been shown to include large and small vacuoles, granules, and membranes associ¬ ated with vesicles or clefts (Dalton and Felix, 1954). The Golgi apparatus appears to be importantly related to secretory functions in many cell types. Protein synthesized in the endoplasmic reticulum appears to move into the Golgi apparatus where it is “packaged” with a membrane and then discharged as a vesicle. The Golgi apparatus also seems to play a role in the secretion of mucus, hor¬ mones, lysosomes, and various intracellular granules. Electron micrographic studies have also shown that within the cell’s cytoplasm can be found irregular networks of branch¬ ing tubules with membranous walls which have been called the endoplasmic reticulum (Figs. 2-1; 2-4). Two types of endoplasmic reticulum have been identified, a rough or granular type and a smooth or agranular type. The rough endoplasmic reticulum con¬ tains particles called ribosomes, which are composed of basophilic ribonucleic acid (RNA) and protein, and either adhere to the membrane of the endoplasmic reticulum or lie free between the membranes. These structures appear to be importantly involved in protein synthesis. At times a number of these ribosomes are seen together in groups or clusters and, as such, are called polyribo¬ somes. These granules, about 150 angstrom units (A) in diameter (see white arrows, Fig. 2-1) may also be scattered throughout the cell (Palade, 1955). The agranular (smooth) endoplasmic reticulum does not contain basophilic ribosomes attached to its mem¬ branes and, therefore, usually is acidophilic in its staining property. It is found in large amounts in muscle cells as the sarcoplasmic

9

Longitudinal section of a mitochondrion from a secretory cell of the pancreas. 64,000 X • Arrows indi¬ cate where the inner of the two limiting membranes is continuous with the membrane forming the cristae. (From Porter and Bonneville, Fine Structure of Cells and Tissues, Lea & Febiger, 1973.) Cr—Cristae X—Sites where mitochondrion may be growing or enlarging *—Dense granules Arrows—Inner limiting membrane-cristae sites of continuity Fig. 2-2.

Fig. 2-1. Electron micrograph showing a plasma cell and illustrating a number of cellular organelles. 29,000 x • (From Porter and Bonneville, Fine Structure of Cells and Tissues, Lea & Febiger, 1973.) Co—Collagen N—Nucleus Ch—Chromatin NF—Nerve fiber Cp—Capillary NuE—Nuclear envelope ER—Endoplasmic reticulum P—Pore G—Golgi apparatus White arrows—Free ribosomes M—Mitochondrium

1 0

CYTOLOGY AND EMBRYOLOGY NUCLEAR PORE

Nucleoplasm Chromatin Fibrous lamina Perinuclear cisterna

Cytoplasm

B

Nucleoplasm Chromatin

Nuclear Pores

Fibrous lamina

Perinuclear Cisterna

Cytoplasm

Pores in the nuclear envelope of cells. A, Diagrammatic representation of a nuclear pore in the envelope (“membrane”) which surrounds the nucleus. Observe that the pore is traversed by a thin septum and by the fibrous lamina of filamentous material. B, An electron micrograph of the nuclear envelope showing at least two such pores. (From Fawcett, Amer. J. Anat., 1966.) Fig. 2-3

reticulum and in the cells of certain glands. Its function appears to be related to choles¬ terol and its derivative steroids as well as to certain cellular ionic mechanisms. Another cytoplasmic organelle is the lysosome. These electron dense bodies are also surrounded by membranes, and they contain certain hydrolytic enzymes that are capable of breaking down and “digesting” proteins and carbohydrates. Lysosomes also release their enzymes when a cell dies, and autolysis of the cell results. Other cellular organelles include microtubules, fibrils, and fibrillar material. The cytoplasm of the cell also con¬ tains many cytoplasmic inclusions, among which are granules of metabolic products such as glycogen, secretion granules, vacu¬

oles, lipid inclusions, and inert or ingested material. The nucleus of a cell in the intermitotic or resting stage is a spherical or elongated body surrounded by a thin nuclear envelope (membrane), which is interrupted by open¬ ings called nuclear pores (Fig. 2-3, A and B). It appears that through these pores certain substances may be interchanged between the nucleoplasm and the cytoplasm. The nucleoplasm contains several semisolid, basophilic staining bodies called nucleoli, which are variable in size in different cells. The nucleus also contains the genetic sub¬ stance. desoxyribonucleic acid (DNA), which in combination with the histone pro¬ teins forms a threadlike material called

THE CELL

1 1

Microvilli Mitochondrion

Golgi membranes

RNA granules

Endoplasmic reticulum

Golgi vacuoles

Plasma membrane

Centrioles Mitochondrion

Nucleus Nuclear envelope

Secretory granules

Endoplasmic reticulum Nucleolus

Schematic representation of a cell as seen with the light microscope and enlargements showing the fine structure of some of the cell constituents as revealed by electron microscopy. The endoplasmic reticulum is shown in three dimensions, other structures are in section. (From Copenhaver, Bailey’s Textbook of Histology, Williams & Wilkins Co., 1964.)

Fig. 2-4.

chromatin. These strands may be brought out by staining the nuclei with various dyes, the one most commonly used being hema¬ toxylin. The chromatin material is invisible in living resting nuclei except possibly with phase microscopy, but during cell division it is aggregated first into threads and then into refractive bodies called chromosomes. The process is called mitosis from the Greek word mitos (yiros) meaning thread. The chro¬

mosomes of the germ cells carry the factors for the genetic or hereditary constitution of the individual.

CELL DIVISION

Although the division of a cell by mitosis is a continuous process, it is the custom to identify four different stages: prophase, met-

1 2

CYTOLOGY AND EMBRYOLOGY

aphase, anaphase, and telophase (Fig. 2-5). In preparation for the prophase, the centrosome divides into two parts which become oriented at opposite poles of the nucleus. During the prophase, the chromatin, which has been scattered throughout the nucleus, condenses into chromomeres which are scattered along a thread or chromonema. The threads are individual entities com¬ posed especially of desoxyribonucleic acid (DNA); they become condensed into more compact bodies, the chromosomes. During the metaphase the chromosomes become oriented in a plane, the equatorial plate, lo¬ cated midway between the two centrosomes, with a clear area, the spindle, leading toward each centrosome. At this time each chromo¬ some has doubled. The two parts are named chromatids and are attached to each other at a particular site, the centromere. In late met¬ aphase and early anaphase, each centromere divides. During anaphase the two chroma¬ tids of each chromosome separate, pulled apart by a spindle fiber leading to one or the other of the two centrosomes. The two sets of chromatids, now called daughter chromo¬ somes, are grouped around the two centro¬ somes, which move to opposite ends of the cell. In telophase the chromosomes form a compact mass, lose their individuality, and disperse into the chromatin of the intermitotic nucleus. The division of living cells cannot be ob¬ served in the intact body, even with high magnifications of the microscope. Harrison (1910), however, discovered that embryonic cells can survive and will divide on glass slides if they are placed in an appropriate medium with aseptic precautions. Since then many observations have been made using this method, known as tissue culture, on a wide range of different animal forms, in¬ cluding tissues from human fetuses, normal adults, and tumors. The following descrip¬ tion (by W. H. Lewis) of cell division is based on observations of connective tissue cells or fibroblasts in cultures of tissues from chick embryos; descriptions of the process in other cells, such as those in the whitefish blastula, are virtually the same (Fig. 2-6, A to E). MITOSIS IN TISSUE CULTURE. An hour Or two before division begins, the centrosome material separates into two parts and is placed at opposite poles of the nucleus. Dur¬ ing prophase (Figs. 2-5; 2-6, B), the chromatin is formed into threads and then into chro¬

mosomes. The cell retracts its processes and tends to become spherical, with the nucleus centrally placed and mitochrondria or other intracellular bodies arranged around it. Near the end of prophase, which takes about an hour, the nuclear membrane disappears and the chromosomes are released and move into the equatorial plane. During metaphase (Figs. 2-5; 2-6, C), which lasts about six minutes, the chromosomes oscillate back and forth in short paths in the equatorial region, as if they were pulled first toward one pole and then toward the other by strings or fibers. Although these fibers are not visible in living fibroblasts, they are visi¬ ble in many cell types, especially after fixa¬ tion. Together with the chromosomes these fibers make up the mitotic spindle. Each chromosome splits longitudinally into two equal and similar daughter chromosomes. During anaphase (Figs. 2-5; 2-6, D and E), which lasts about three minutes, one set of daughter chromosomes moves to each pole of the spindle, or is pulled there by contraction of the spindle fibers, and is clumped into a compact mass. As the chro¬ mosomes approach the poles, the cell be¬ comes elongated and a groove encircles it at the equator. During telophase (Figs. 2-5; 2-6, F), which lasts about three minutes, the groove sinks farther into the cell, gradually pinching it into two daughter cells, which remain con¬ nected for a short time by a stalk. Each daughter cell receives approximately onehalf the mitochondria, but the division of fat droplets and other intracellular bodies ap¬ pears more haphazard. The chromosomes lose their identity in the compact mass of the daughter nuclei. The daughter nuclei slowly increase in size, as clear areas split the com¬ pact mass into granules, and a nuclear enve¬ lope forms. As the clear areas increase, the chromosomal granules become invisible except for those that become the nucleoli. It takes several hours for the nucleus to attain the final resting or intermitotic condition. amitosis. Direct division of the cell, or amitosis, has been described but probably does not occur under normal conditions. Degenerating cells may show nuclear frag¬ mentation without division of the cytoplasm or the centrosome. Binucleate cells are not uncommon, espe¬ cially in certain organs, and are formed ei¬ ther by mitotic division of the nucleus with-

THE CELL

Interphase

Late prophase

Anaphase

Late telophase

Early prophase

Mid prophase

Early metaphase

Late metaphase

13

Early telophase

Daughter cells

Diagrammatic representation of various stages in mitosis. (From Winchester, Genetics, A Survey of the Principles of Heredity, Houghton Mifflin, 1972.)

Fig. 2-5.

14

CYTOLOGY AND EMBRYOLOGY

THE CELL

out cleavage of the cytoplasm, or by some process not clearly understood such as frag¬ mentation. Chromosomes In the last three decades, dramatic ad¬ vances in electron microscopy, biochemical genetics, and cytogenetics have enhanced our understanding of the mechanisms in¬ volved in cell division and of the fundamen¬ tal biochemistry of genetic material. Con¬ cepts have emerged as to the nature of the control exerted by the nucleus over the ac¬ tivities of the cytoplasmic organelles. Addi¬ tionally, this knowledge has even extended into an appreciation of how and where these processes can go wrong, thereby elucidating better than ever before the mechanics of genetic mutation and the hereditary nature of certain diseases. The interdisciplinary fields of cellular and molecular biology are oriented toward closing the gap between the structure observed by the anatomist using the electron microscope and the molecular chains so beautifully unravelled and recon¬ structed by the biological and physical chemists. Chromosomes are the unique biological structures responsible for the continuity of an animal species through its generations. Further, through their genetic material, chromosomes dictate the proper functional activities of every living animal cell. In each animal species there is a characteristic num¬ ber of chromosomes. In mail there are 23 pairs or 46 chromosomes. This number, i.e., 46 chromosomes, is known as the diploid number. In the nucleus of the human sperm or ovum the chromosome number is exactly half, or 23, and this is known as the haploid number. When the male gamete fertilizes the female gamete, the diploid number of 46 is

15

attained. Thus, each pair of chromosomes consists of a maternal and a paternal chro¬ mosome. The random distribution of mater¬ nal and paternal chromosomes is such that in the germ cells, during maturation, over 16,000,000 possible combinations can result in the daughter cells. Of the 23 pairs in man, 22 are called autosomes and the remaining pair are the sex chromosomes which can be identified under the microscope by their size and shape. The sex pair in all the cells of a male organism consists of a large X and a small Y chromosome (Fig. 2-8). The sex pair of a female contains two X but no Y chro¬ mosomes (Fig. 2-7). structure of chromosomes. At metaphase just prior to cell division, each chro¬ mosome can be observed to consist of two identical strands of chromatin called chro¬ matids. The chromatids are connected at a constriction in the chromosome called the centromere or kinetochore, and each will become a separate chromosome when the centromere divides. The location of the cen¬ tromere allows for a descriptive morpho¬ logic classification of chromosomes (Fig. 2-9). When the centromere is located in the mid¬ dle of the chromosome, the chromosome is referred to as metacentric. As such its arms are of equal length. A chromosome in which the centromere is situated somewhere be¬ tween its midpoint and one of its ends is called a submetacentric chromosome. In such chromosomes one arm is somewhat longer than the other. When the centromere is located very close to the end of a chromo¬ some, the term acrocentric is used in its de¬ scription, and it follows that such a chromo¬ some has one very short arm and one that is considerably longer. The short arm of a chromosome is called “p,” for “petite,” while the long arm is designated by the letter “q” (Fraser and Nora, 1975).

Stages of mitosis in whitefish blastula. A, Interphase: This is a “resting” stage daring which the chromatin material appears dispersed, although it is thought that the chromosomes continue to maintain their individual integrity. B, Prophase: Chromatin commences to aggregate into discrete threads. Asters develop around the divided centriole at each end of the cell, and the nuclear envelope disintegrates. C, Metaphase: The chromosomes move into a horizontal equatorial plane. Each chromosome is attached to a spindle fiber at its centromere and begins to split into two chromatids. D, Anaphase: Each pair of chromatids abruptly becomes pulled apart to form daughter chromosomes which move toward the poles of the spindle. E, Late Anaphase: The spindle continues to lengthen and a constriction of the cell body begins to pinch the cytoplasm into two cells. F, Telophase: Separation is virtually complete. The daughter cells, however, are still connected by a fine cytoplasmic stalk which eventually is broken. (From Genes in Action, The Upjohn Co., 1967.)

Fig. 2-6.

1 6

CYTOLOGY AND EMBRYOLOGY

%

a

~

V*

u

t%

s

♦

*

*

,

x

•

&

/

\

•'*

Sacrotuberous ligament Femur

Fig. 3-20. Thoracic and abdominal viscera shown in their normal relationship to the skeleton, from the left side. (Eycleshymer and Jones, 1925.)

vertical, reaches the transpyloric line, and ends at the duodenojejunal flexure, about 2.5 cm to the left of the midline. Jejunum and Ileum. The coils of small intestine, comprising the jejunum and ileum, occupy most of the abdomen. Usually the greater part of the jejunum is situated on the left side of the abdomen, while the coils of the ileum are located on the right side and

partially within the pelvis. The small intes¬ tine terminates at the ileocolic junction, which is slightly below and medial to the intersection of the right lateral and transtubercular lines (Fig. 3-21). Cecum and Vermiform Appendix. The cecum is in the right iliac and hypogastric regions. Its position varies with its degree of distention, but a line drawn from the right

THE ABDOMEN

91

Fig. 3-21.

Surface lines on the anterior aspect of the thorax and abdomen. Observe the arbitrary subdivision of the abdomen into nine zones by two transverse planes (transpyloric and transtubercular) and two vertical planes (right and left lateral lines).

anterior superior iliac spine to the upper margin of the symphysis pubis will mark approximately the middle of its lower bor¬ der. The position of the base of the appendix is indicated by a point on the lateral line, level with the anterior superior iliac spine (Fig. 3-22). Ascending Colon (Figs. 3-17; 3-19; 3-22; 326). The ascending colon, in contact with the posterior wall of the abdomen, passes upward from the right iliac region through the right lumbar region, lateral to the right lateral line. It bends abruptly at the right colic flexure, which is situated at the inter¬

section of the subcostal and right lateral lines. The right costal margin, the right lobe of the liver, and the gallbladder overlie the right colic flexure. Transverse Colon (Figs. 3-17; 3-20; 3-22; 3-23). The transverse colon is the most mo¬ bile part of the large intestine and it crosses the abdomen in the epigastric region. Its lower border is located on a level slightly above the umbilicus, while its upper border lies just below the greater curvature of the stomach (Fig. 3-17). Descending Colon (Figs. 3-19; 3-20; 3-26). Under cover of the left costal margin and in

92

SURFACE AND TOPOGRAPHICAL ANATOMY

- Transpyloric plane

Orifice of vermiform process

Transtubercular plane

Sigmoid colon Rectum

Fig. 3-22.

Anterior aspect of abdomen showing the surface projections for the liver, stomach, and large intestine.

relationship to the spleen, the transverse colon turns sharply downward and becomes the descending colon at the left colic flexure. This flexure is situated approximately at the intersection of the left lateral and trans¬ pyloric lines. The descending colon courses interiorly through the left lumbar region, lat¬ eral to the left lateral line, as far as the iliac crest. Sigmoid Colon (Figs. 3-17; 3-20). The iliac and pelvic portions of the large intestine form the sigmoid colon. The iliac portion is contained in the left iliac fossa, and contin¬ ues as the pelvic colon at the left lateral line. The sigmoid colon is freely moveable since it has a mesentery, and it becomes the rec¬ tum anterior to the sacrum in the midline (Figs. 3-19; 3-20; 3-23; 3-27). Liver (Fig. 3-17; 3-22). The liver is located in the right hypochondrium, extending across the midline toward the left into the upper part of the epigastric region. Although the liver moves up and down with respira¬ tion, the upper limit of its right lobe, in the midline, is at the level of the junction be¬ tween the body of the sternum and the xiph¬

oid process. On the right side the superior border of the liver carries upward as far as the fifth costal cartilage in the midclavicular line. On the left side the liver extends across the midline as far as 7 or 8 cm. Its upper mar¬ gin is somewhat lower than on the right, reaching the sixth costal cartilage. The infe¬ rior extent of the liver can be indicated by a line drawn 1 cm below the lower margin of the thorax on the right side as far as the ninth costal cartilage, then obliquely up¬ ward to the eighth left costal cartilage, cross¬ ing the midline just above the transpyloric plane. Finally, with a slight left convexity, the inferior border reaches the end of the line, indicating the upper limit at about the fifth left interspace. Gallbladder. The gallbladder is attached to the inferior (visceral) surface of the liver (Figs. 3-17; 3-23). Its fundus is directed interi¬ orly and projects just beyond the lower bor¬ der of the right lobe of the liver at the ninth right costal cartilage close to the lateral mar¬ gin of the rectus abdominis. Pancreas (Fig. 3-24). The pancreas lies in front of the second lumbar vertebra. Its head

THE ABDOMEN

93

Fig 3-23. Thoracic and abdominal viscera shown in their normal relationship to the skeleton from the right side. (Eycleshymer and Jones, 1925.)

occupies the curve of the duodenum and is therefore indicated by the same lines as that viscus; its neck corresponds to the pylorus. Its body extends along the transpyloric line, the bulk of it lying above this line; the toil is in the left hypochondriac region, extending slightly to the left of the lateral line and above the transpyloric line.

Spleen (Figs. 3-15; 3-17; 3-19; 3-20; 3-25). The long axis of the spleen corresponds to that of the tenth rib on the left side. It is situ¬ ated between the upper border of the ninth and the lower border of the eleventh ribs. It is separated from the ribs by the diaphragm. Its medial end is about 4 cm to the left of the midline of the back. Its lateral extent is the

94

SURFACE AND TOPOGRAPHICAL ANATOMY

Fig. 3-24. Front of abdomen, showing surface projections for duodenum, pancreas, and kidneys. AA', Plane through the xiphisternal junction. BB', Plane midway between AA' and transpyloric plane. CC', Plane midway between transpyloric and transtubercular planes. The vertical lines are the left and right lateral lines between which is the midline.

left midaxillary line at the ninth intercostal space. Lying obliquely in the left hypochondrium, the superior border of the spleen at times can extend more medially into the epigas¬ trium. The inferior pole of the spleen is gen¬ erally described as extending to the level of the first lumbar vertebra in the cadaver; however, in the erect, living person, it usu¬ ally extends significantly lower, to the third lumbar vertebra.

Fig. 3-25. Back of lumbar region, showing surface projections for kidneys, ureters, and spleen. The lower portions of the lung and pleura are shown on the right side.

Kidneys (Figs. 3-19; 3-20; 3-23; 3-24 to 327). The kidneys are located in the poste¬ rior abdomen on each side of the spinal col¬ umn. The right kidney usually lies about 1 cm lower than the left because of the pres¬ ence of the liver on the right side, but for practical purposes similar surface markings may be taken for each. Projected anteriorly, the upper pole of each kidney lies along a line midway be¬ tween the plane of the xiphisternal junction and the transpyloric plane. The upper pole of each kidney is found about 5 cm from the midline (see Plane BB' in Fig. 3-24). The lower poles are situated along a plane mid¬ way between the transpyloric and intertubercular planes, 7 cm from the midline (see Plane CC' in Fig. 3-24). The hilum of each kidney lies along the transpyloric plane, 5 cm from the midline. Around these three points a bean-shaped figure 4 to 5 cm broad is drawn, two thirds of which lies medial to the lateral line. To indicate the position of the kidney from the back, a parallelogram may be used. Two vertical lines are drawn, the first 2.5 cm, the second 9.5 cm from the midline; the parallelogram is completed by two horizontal lines drawn at the level of the tip of the spinous process of the eleventh thoracic and the lower border of the spinous process of the third lumbar vertebra. The hilum is 5 cm from the midline at the level

THE ABDOMEN

of the spinous process of the first lumbar ver¬ tebra. Ureters. The ureters are flattened tubes, 28 to 34 cm in length, which extend verti¬ cally, one on each side, from the kidneys to the bladder (Figs. 3-26; 3-27). Projected on the anterior aspect of the abdomen, the line of the ureter courses from the hilum of the kidney to the pubic tubercle. Their vertical course can be visualized posteriorly extend¬ ing from the hilum of the kidney and passing practically across the posterior superior iliac spine (Fig. 3-26). Vessels (Fig. 3-28). The course of the infe¬ rior epigastric artery can be approximated to the umbilicus. This line also indicates the lateral boundary of Hesselbach’s triangle, the other boundaries of this triangle being the lateral border of the rectus abdominis muscle and the medial half of the inguinal

95

ligament. This triangle is of importance in the classification of inguinal hernias. There are two types of inguinal hernias, indirect (lateral, oblique, or congenital) and direct (medial or acquired). An indirect inguinal hernia is generally congenital, and the herni¬ ation commences lateral to the inferior epi¬ gastric artery. The path of the herniation fol¬ lows the course of the spermatic cord or round ligament of the uterus through the inguinal canal, and hence it does not pene¬ trate through Hesselbach's triangle. A direct inguinal hernia is usually due to some un¬ derlying weakness or defect in the lower anterior abdominal wall. The herniation occurs medial to the inferior epigastric ar¬ tery and, therefore, commences through Hesselbach’s triangle. The abdominal aorta begins in the midline about 4 cm above the transpyloric line and

Fig. 3-26. Projection showing the average position of certain abdominal and pelvic viscera in the female. Anterior view. (Eycleshymer and Jones, 1925.)

96

SURFACE AND TOPOGRAPHICAL ANATOMY

twelfth ends about midway between the umbilicus and the upper border of the sym¬ physis pubis. The first lumbar nerve courses parallel to the thoracic nerves. Its iliohypo¬ gastric branch becomes cutaneous above the subcutaneous inguinal ring, while its ilio¬ inguinal branch becomes cutaneous by pen¬ etrating through the ring.

The Perineum

Fig. 3-27. Projection showing the average position of the female pelvic organs. Lateral view. (Eycleshymer and Jones, 1925.)

extends to a point 2 cm below and to the left of the umbilicus (AA', Fig. 3-28). The point of bifurcation of the abdominal aorta corre¬ sponds to the level of the fourth lumbar ver¬ tebra. A line drawn from that site to a point midway indicates the course of the common iliac artery and one of its branches, the ex¬ ternal iliac. Of the larger branches of the abdominal aorta, the celiac artery is 4 cm above the transpyloric line. The superior mesenteric artery is 2 cm above and the renal arteries are 2 cm below the same line. The inferior mesenteric artery is 4 cm above the bifurca¬ tion of the abdominal aorta (Fig. 3-28). Nerves. The skin of the anterior abdomi¬ nal wall is innervated by anterior and lateral cutaneous branches of spinal nerves T7 through Ll. These course around the trunk in a manner that could be represented by lines continuing those of the bony ribs. The termination of the seventh thoracic nerve is at the level of the xiphoid process; the tenth reaches the vicinity of the umbilicus; the

A line drawn transversely between the ischial tuberosities divides the perineum into a posterior or rectal triangle and an an¬ terior or urogenital triangle (see Fig. 6-38). This line passes through the central tendi¬ nous point of the perineum, which is situ¬ ated in the female about 2.5 cm anterior to the center of the anal aperture, or, in the male, midway between the anus and the re¬ flection of the skin onto the scrotum. rectal examination (Fig. 3-29). A finger inserted through the anal orifice is com¬ pressed by the external anal sphincter, passes into the region of the internal anal sphincter, and more deeply encounters the resistance of the puborectalis; beyond this it may reach the lowest of the transverse rectal folds. Anteriorly, the urethral bulb and the membranous urethra are first identified, and then about 4 cm deep to the anal orifice in the male the prostate is felt. Beyond the prostate, the seminal vesicles, if enlarged, and the fundus of the bladder, when dis¬ tended, are palpable. On either side of the anus is the ischiorectal fossa. Posterior to the anus can be felt the anococcygeal body, the pelvic surfaces of the coccyx and lower end of the sacrum, and the sacrospinous lig¬ aments. Additionally, rectal examination in the female allows the posterior wall and fornix of the vagina, and the cervix and body of the uterus to be felt in front, while somewhat laterally the ovaries can just be reached. SUPERFICIAL MALE UROGENITAL ORGANS. The penis and the testes within their scrotal sac constitute the male superficial urogenital organs. The penis consists of two corpora cavernosa penis, which can be followed backward to their crura attached to the sides of the pubic arch, and the corpus spongio¬ sum penis, the middle portion, which is tra-

THE PERINEUM

... . ... , Junction of muscular fibers and

Linea semilunaris

97

Linpa alha

cd dlud

Fig. 3-28. The front of the abdomen showing the surface projection of the arteries and the inguinal canal. The line AA' is drawn at the level of the highest points of the iliac crests. Observe that the region bounded by the inguinal ligament, the linea semilunaris (lateral border of the rectus abdominis muscle), and the inferior epigastric artery is the triangle of Hesselbach.

versed by the urethra. The distal portion of the corpus spongiosum penis is the glans penis, which is covered by the prepuce. The external urethral orifice can be examined at the tip of the glans penis, and the course of the urethra can be traced along the under¬ surface of the penis to the bulb, which is sit¬ uated immediately in front of the central point of the perineum. The testis can be pal¬ pated through the wall of the scrotum on ei¬ ther side. It lies toward the back of the scro¬ tum, and along its posterior border the epididymis can be felt. Passing upward along the medial side of the epididymis is the spermatic cord, which is palpable as far as the superficial inguinal ring. SUPERFICIAL FEMALE UROGENITAL ORGANS (Figs. 3-26; 3-27). The female urogenital structures that are observable superficially include the labia majora, the labia minora, and the clitoris. The labia majora are two prominent and rounded folds of skin cover¬ ing fatty and areolar tissue which extend from a site anterior to the anus to the mons

pubis, a soft mound of tissue in front of the symphysis pubis. Between the labia majora are two smaller and more narrow longitudi¬ nal folds, the labia minora. In the pudendal cleft between the labia minora are the open¬ ings of the vagina and urethra. In the virgin the vaginal opening is partly closed by a thin fold of mucous membrane, the hymen. After coitus the remains of the hymen are repre¬ sented by small rounded elevations called the carunculae hymenales. Between the hymen and the frenulum of the labia minora is the fossa navicularis, while in the grooves between the hymen and the labia minora, the small openings of the greater vestibular (Bartholin’s) glands can be seen. These glands, when enlarged, can therefore be felt on either side of the posterior part of the vaginal orifice. The clitoris, composed of erectile tissue, is situated in the midline an¬ terior to the urethral orifice. It is palpable at the anterior ends of the labia minora and is an organ homologous to the male penis. vaginal examination (Fig. 3-30). With the

98

SURFACE AND TOPOGRAPHICAL ANATOMY

Rectum Bladder

Seminal vesicle Ejaculatory duct

Prostate gland

Internal anal sphincter

Urethra External anal sphincter

Fig. 3-29.

The digital rectal examination. With the gloved index finger the anal canal in both sexes can be examined for tumors or other pelvic problems for a distance of about three inches. In the male the prostate gland and seminal vesicle can be palpated anteriorly. In the female the posterior wall of the vagina and the uterine cervix may be explored and by moving the finger laterally, the uterine tubes and ovaries may be felt.

examining finger inserted into the vagina the following structures can be palpated through its posterior wall from below up¬ ward: the anal canal, the rectum, and the rectouterine excavation. Projecting into the roof of the vagina is the vaginal portion of the uterine cervix with its external uterine orifice. In front of and behind the cervix the anterior and posterior vaginal fornices can be examined. With a finger still in the vagina and with the other hand exerting pressure on the abdominal wall, the entire cervix and body of the uterus as well as the uterine tubes and ovaries can be palpated. If a spec¬ ulum is introduced into the vagina, its walls, the vaginal portion of the cervix, and the external uterine orifice can all be visually examined.

The external urethral orifice lies in front of the vaginal opening, and the angular gap in which the orifice is situated between the two converging labia minora is termed the vestibule. The urethral canal in the female is easily dilatable and can be explored with the finger. About 2.5 cm in front of the external orifice of the urethra are the glans and pre¬ puce of the clitoris, and still farther forward is the mons pubis.

The Upper Limb bones. The clavicle can be felt through¬ out its entire length (Figs. 3-17; 3-18). It is a curved bone and its extremities are enlarged both medially, where it articulates with the

THE UPPER LIMB

99

Uterus Cervix

Rectum

Rectouterine pouch Posterior fornix of vagina Anal canal

Fig. 3-30.

The digital vaginal examination. Digital palpation of the vaginal walls also allows for direct examination of the uterine cervix, as well as palpation of the uterus, bladder, and urethra anteriorly and the uterine tubes and ovaries laterally.

sternum, and laterally, where it articulates with the acromion of the scapula. The clavi¬ cle is fractured more frequently than any other bone in the body. The only parts of the scapula (Figs. 3-19; 3-31) that are truly subcutaneous are the spine and acromion, but the coracoid proc¬ ess, the vertebral border, the inferior angle, and to a lesser extent the axillary border can also be readily palpated. The acromion and spine are recognizable surface landmarks throughout their entire extent, forming with the clavicle the arch of the shoulder. The acromion forms the point of the shoulder; it joins the clavicle at an acute angle—the acromial angle—slightly medial to, and be¬ hind the tip of the acromion. The scapular spine can be felt as a distinct ridge, marked on the surface as an oblique depression which becomes less distinct and ends in a slight dimple a little lateral to the spinous processes of the vertebrae (Figs. 3-11, 3-31). The spine of the scapula helps to define the

muscle-filled infraspinatus and supraspinatus fossae. Below the spine the contour of the infraspinatus muscle can readily be in¬ spected, whereas above the spine the supraspinatus muscle is covered smoothly by the trapezius (Fig. 3-31). The coracoid process is situated about 2 cm below the junction of the middle and lateral thirds of the clavicle. It is covered by the anterior border of the deltoid, and thus lies a little lateral to the infraclavicular fossa or depression which marks an interval bounded by the pectoralis major, the deltoid, and the clavicle called the deltopectoral triangle. Through this triangle the superficially coursing cephalic vein pen¬ etrates the deep fascia to enter the axillary vein just below the level of the clavicle. The humerus (Figs. 3-32, 3-33, 3-34) is al¬ most entirely surrounded by muscles, and the only parts that are strictly subcutaneous are small portions of the medial and lateral epicondyles. Additionally, however, the tu¬ bercles and a part of the head of the hu-

1 00

SURFACE AND TOPOGRAPHICAL ANATOMY

Pectoralis major Cephalic vein

Musculocutaneous nerve

Medial

Lateral

Median nerve Medial antebrachial cutaneous nerve Brachial artery Basilic vein Medial brachial cutaneous nerve Ulnar nerve A. profunda brachii Radial nerve

Triceps brachii (medial head)

Fig. 3-31. Cross-section, viewed from above, through the right arm at a level immediately below the proximal one-third of the humerus.

Cephalic vein Medial

Lateral Musculocutaneous nerve

Median nerve Brachial artery Basilic vein Medial antebrachial cutaneous nerve Superior ulnar collateral artery

Radial nerve Arteria profunda brachii

Ulnar nerve

Nerve to anconeus

Medial collateral branch of arteria profunda brachii

Fig. 3-32. humerus.

Cross section, viewed from above, through the right arm, a little below the middle of the shaft of the

THE UPPER LIMB

101

Extensor digitorum Lateral

Ext. carpi ulnaris Ext. carpi radialis

brachi Vertebra prominens

Trapezius

Acromion

Spine of scapula

Inferior angle of scapula —

Erector spinae

Fig. 3-33.

Posterior view of the back and upper extremities demonstrating surface muscle contours.

merits can be felt under the skin and muscles by which they are covered. The greater tu¬ bercle forms the most prominent bony point of the shoulder, extending even beyond the acromion. This tubercle, covered by the del¬ toid muscle, forms the roundness of the lat¬ eral aspect of the shoulder. On the distal end of the humerus the medial and lateral epicondyles can be palpated on either side of the elbow joint. Of these, the medial epicondyle is the more prominent, but the medial supracondylar ridge passing upward from it is much less marked than the lateral, and as a rule is not palpable. The most prominent part of the ulna, the olecranon, can easily be identified behind the elbow joint. The prominent dorsal bor¬ der of the ulna can be felt along its whole length in the forearm (Figs. 3-35; 3-36), and

the styloid process forms a prominent tuber¬ cle at the distal end of the ulna. It is continu¬ ous above with the dorsal border and ends below in a blunt apex at the level of the wrist joint. Below the lateral epicondyle of the hu¬ merus a portion of the head of the radius is palpable. When the forearm is extended, a depression can be observed in the postero¬ lateral aspect of the elbow joint. Rotation of the head of the radius can be palpated in this depression while the subject pronates and supinates the forearm. The upper half of the body of the radius is obscured by muscles (Figs. 3-35; 3-36); the lower half, though not subcutaneous, can be traced downward to the lateral aspect of the wrist joint. Here, a conical projection of bone, the styloid proc¬ ess of the radius, can be observed to project

1 02

SURFACE AND TOPOGRAPHICAL ANATOMY

Musculocutaneous nerve Radial nerve Cephalic vein

Median nerve

Brachial artery

Dorsal antebrachial cutaneous nerve

Medial antebrachial cutaneous nerve Basilic vein

A. profunda brachii

Inferior ulnar collateral artery Superior ulnar collateral artery

Radial collateral branch of arteria profunda brachii

Ulnar nerve

Lateral

Medial

Fig. 3-34. humerus.

Cross section, viewed from above, through the right arm 2 cm. proximal to the medial epicondyle of the

5 to 6 mm distal to the styloid process of the ulna. The radius and ulna articulate distally with the carpal bones at the wrist joint. On the front of the wrist are two subcutaneous eminences: one, on the radial side, the larger and flatter, is produced by the adjacent tu¬

bercle of the scaphoid bone and ridge of the trapezoid bone; the other, on the ulnar side, is formed by the pisiform bone. The rest of the palmar surface of the carpal bones is covered by tendons and the transverse car¬ pal ligament, and is entirely concealed. An exception is the hamulus (or hook) of the ha-

Median nerve

Fig. 3-35.

Cross section, viewed from above, through the right forearm at the level of the radial (bicipital) tuberosity.

THE UPPER LIMB Medial antebrachial cutaneous nerve (anterior branch) Ulnar artery

1 03

Median nerve Palmaris longus Radial artery Superficial branch of radial nerve

Ulnar nerve

Lateral antebrachial cutaneous nerve Brachioradialis Extensor carpi radialis longus Pronator teres

Medial antebrachial cutaneous nerve (ulnar branch)

Medial

Lateral

Anterior interosseous vessels and nerve Extensor pollicis longus Dorsal antebrachial cutaneous nerve Dorsal interosseous artery and deep branch of radial nerve Fig. 3-36.

Cross section, viewed from above, through the middle of the right forearm.

mate bone on the ulnar side of the wrist, which, however, is also somewhat difficult to define. On the dorsal surface of the carpus only the triquetral bone can be clearly rec¬ ognized by palpation. Distal to the wrist the dorsal surfaces of the metacarpal bones, covered by the exten¬ sor tendons, are visible only in very thin hands. The dorsal surface of the fifth meta¬ carpal bone is, however, subcutaneous throughout almost its entire length. The heads of the metacarpal bones are their dis¬ tal extremities, and they can be plainly seen and felt, rounded in contour and standing out under the skin when the fist is clenched, forming the prominences of the knuckles. The head of the third metacarpal is the most prominent. The enlarged ends of the phalanges can be easily felt. When the digits are bent the proximal ends of the phalanges form promi¬ nences. In the joints between the first and second phalanges, these prominences are slightly hollow, but they are flattened and square-shaped between the second and third. articulations. The sternoclavicular joint is subcutaneous, and its position can be identified by the enlarged sternal extremity of the clavicle, lateral to the cord-like sternal head of the sternocleidomastoid. Upon re¬ laxing this muscle, a depression between the end of the clavicle and the sternum can be felt, defining the position of the joint. The sternoclavicular joint is the only articulation between the upper extremity and the trunk.

Posterior to this joint on the right side is found the pleural covering of the right lung along with the right brachiocephalic artery and vein. On the left side, in addition to the pleura, the left brachiocephalic vein, the left common carotid artery, and the thoracic duct underlie this joint. The position of the acromioclavicular joint can generally be ascertained by deter¬ mining the slightly enlarged acromial end of the clavicle, which usually projects some¬ what above the level of the acromion, thereby overriding it. Sometimes this en¬ largement is considerable, forming a rounded eminence. The shoulder joint is deeply seated and cannot be palpated. It should be appreci¬ ated, however, that the glenoid cavity of the scapula, into which the spherical head of the humerus fits, is exceedingly shallow. This, along with the looseness of the articular cap¬ sule, allows for the elegant freedom of movement at that joint. At the same time, however, the shoulder joint is weakly con¬ structed. Although it receives some protec¬ tion from tendons, muscles, and the coracoid and acromial processes and their associated ligaments, dislocations occur more fre¬ quently at this joint than at any other. These usually are directed initially inferiorly to assume a subglenoid position, but then sec¬ ondarily the head of the humerus may be directed anteriorly, beneath the coracoid process of the clavicle, or posteriorly, be¬ neath the acromion or spine of the scapula.

1 04

SURFACE AND TOPOGRAPHICAL ANATOMY

The elbow joint consists of two articula¬ tions: the humeroulnar, in which the troch¬ lea of the humerus fits into the trochlear notch of the ulna, and the humeroradial, in which the capitulum of the humerus articu¬ lates with the head of the radius. Behind the curved trochlear notch of the ulna is the thick and prominent olecranon. When the forearm is flexed, the olecranon becomes the pointed bony eminence of the elbow. When the forearm is extended, the olecranon fits snugly between the epicondyles of the hu¬ merus, forming a continuous line between forearm and arm. If the forearm is slightly flexed, a curved crease or fold with its con¬ vexity downward is seen in front of the elbow, extending from one epicondyle to the other; the elbow joint is slightly distal to the center of the fold. The position of the humeroradial joint can be ascertained by feeling for a slight groove or depression be¬ tween the head of the radius and the capitulum of the humerus, at the back of the elbow joint. In addition to their articulation with the humerus, the radius and ulna articulate with each other proximally, below the elbow joint, along their shafts by way of the inter¬ osseous membrane, and distally, just above the carpal bones. The position of the proxi¬ mal radioulnar joint is marked on the sur¬ face at the back of the elbow by a slight de¬ pression, which indicates the position of the head of the radius. The site of the distal radi¬ oulnar joint can be defined by feeling for the slight groove at the back of the wrist be¬ tween the prominent head of the ulna and the lower end of the radius, when the fore¬ arm is pronated. Of the three transverse skin furrows on the front of the wrist, the middle corre¬ sponds fairly accurately with the wrist joints, while the most distal indicates the position of the midcarpal articulation. The metacarpophalangeal and interphalangeal joints are readily available for sur¬ face examination. The former are situated just distal to the prominences of the knuck¬ les; the latter are sufficiently indicated by the furrows on the palmar and the wrinkles on the dorsal surfaces of the fingers. muscles. The large muscles that arise on the trunk and insert on the shoulder girdle form the superficial layers of muscle of the thorax, both on the chest and on the back. The pectoralis major (Figs. 3-18; 3-37), latis-

simus dorsi (Fig. 3-31), and trapezius (Figs. 3-11: 3-13; 3-31) muscles are easily visible in most subjects. The serratus anterior (Figs. 3-13; 3-37) is mostly concealed by the scap¬ ula, but its serrations, interdigitating with the external oblique on the anterolateral aspect of the chest, are usually visible in muscular or thin subjects (Fig. 3-37). The pectoralis minor is completely hidden by the pectoralis major. The deltoid (Figs. 3-11; 3-13; 3-31) and the teres major (Fig. 3-37) are prominent on the shoulder. The biceps (Fig. 3-37), coracobrachialis, and brachialis are easily distinguish¬ able on the anterior, and the triceps (Fig. 3-37) on the posterior aspect of the arm. The muscles of the forearm form two groups: a medial group, consisting of the flexors and the pronators arising from the medial epi¬ condyle, and a lateral group, comprised of the extensors and supinators arising from the lateral epicondyle. Many tendons of the individual forearm muscles can be identified at the wrist (Fig. 3-37). The antecubital fossa, in front of the elbow joint, is triangular in shape. Its bound¬ aries are a lateral group forearm muscle, the brachioradialis, a medial group muscle, the pronator teres, and a line joining the medial and lateral epicondyles above. The brachial and supinator muscles form the floor of the fossa, and within it the brachial artery and median nerve may be palpated. Through the fossa courses the median cubital vein, mak¬ ing it readily accessible clinically for intra¬ venous injections or blood withdrawal. The synovial tendon sheaths of the palm and dorsum of the hand cannot be identified except as they follow the various tendons across the wrist and distally in the fingers. arteries. Above the middle of the clavi¬ cle the pulsation of the subclavian artery can be detected by pressing downward, backward, and medialward against the first rib. The pulsation of the axillary artery as it crosses the second rib can be felt below the middle of the clavicle just medial to the cor¬ acoid process. The course of the artery can be followed along the lateral wall of the ax¬ illa to the medial border of the cora¬ cobrachial muscle. The brachial artery can be recognized along practically its entire extent, coursing down the medial margin of the biceps. The radial artery becomes super¬ ficial over the lower end of the radius, be¬ tween the styloid process and flexor carpi

THE UPPER LIMB

105

Flexor digitorum Palmaris longus

Biceps Sternocleidomastoid m.

Teres major Triceps, medial head Triceps, lateral head

Subscapularis

Pectoralis major Serratus anterior

External oblique m.

Fig. 3-37.

Anterior view of head and chest and the upper extremities demonstrating surface muscular contours.

radialis. It is used clinically for observations of the pulse (Figs. 3-38; 3-40). The ulnar ar¬ tery also becomes more superficial in its course down the medial aspect of the distal forearm, and at the wrist, the ulnar nerve lies just medial to the artery. Both the ulnar and the radial arteries enter the hand (Fig. 3-40). In the hand the superficial palmar arch (Fig. 3-40), derived mainly from the ulnar artery, can be indicated by a line starting from the radial side of the pisiform bone and curving distalward and lateralward as far as the base of the thumb, with its convexity toward the fingers. The summit of the arch is usually on a level with the ulnar border of the outstretched thumb. The deep palmar arch (Fig. 3-40), derived mainly from the ra¬ dial artery, is practically transverse, and is situated deeper in the hand and somewhat more distal to the superficial palmar arch. veins. The superficial veins of the upper limb are easily rendered visible by com¬ pressing the proximal trunks. The basilic vein forms from the venous network on the ulnar side of the dorsal hand and then passes up the medial aspect of the forearm and arm

to join the more deeply coursing brachial vein to form the axillary vein. The cephalic vein (Fig. 3-13) commences on the radial as¬ pect of the dorsal hand, courses up the lat¬ eral aspect of the forearm and arm, and passes in the groove between the deltoid and pectoralis major muscles to enter the axil¬ lary vein. In front of the elbow, the median cubital vein communicates between the ce¬ phalic and basilic veins. nerves (Figs. 3-38; 3-39). The uppermost trunks of the brachial plexus are palpable for a short distance above the clavicle as they emerge from under the lateral border of the sternocleidomastoid; the larger nerves derived from the plexus can be rolled under the finger against the lateral axillary wall, but cannot be identified with certainty at this site. The axillary nerve (Fig. 3-39) emerges from the posterior cord of the brachial plexus. It then courses around the shaft of the humerus under cover of the deltoid muscle. The musculocutaneous nerve (Fig. 3-32) lies deep within the musculature of the

1 06

SURFACE AND TOPOGRAPHICAL ANATOMY

Fig. 3-38.

Anterior aspect of right upper extremity, showing surface projection of bones, arteries, and nerves.

Fig. 3-39.

Posterior aspect of right upper extremity showing surface projection of bones and nerves.

Fig. 3-40. Palm of left hand, showing position of skin creases and bones, and surface projection for the palmar arterial arches.

flexor compartment in the arm, but becomes superficial about 7.5 cm above the cubital fossa, lateral to the tendon of the biceps brachii. The line of the median nerve (Figs. 3-32; 3-33; 3-38) in the arm is practically the same as that for the brachial artery and may even be injured when pressure is applied to the artery. Anterior to the elbow, the nerve lies medial to the artery in the center of the cubi¬ tal fossa. Descending the forearm under cover of the anterior forearm muscles, it reaches the wrist lateral to the palmaris longus, and enters the palm of the hand by passing deep to the flexor retinaculum within the carpal tunnel. The ulnar nerve (Figs. 3-34 to 3-36; 3-38) also follows the course of the brachial artery in the upper arm, then diverges and de¬ scends in the groove behind the medial epicondyle over the elbow, where it lies just beneath the skin. In the upper forearm it descends along the ulnar side under the flexor carpi ulnaris, while more distally in the forearm it courses with the ulnar artery, with which it enters the ulnar aspect of the palm of the hand superficial to the flexor ret¬ inaculum. The radial nerve (Figs. 3-32; 3-33; 3-34; 3-35; 3-38; 3-39) derives from the posterior cord of the brachial plexus and achieves the posterior compartment of the arm by cours-

THE LOWER LIMB

ing deeply between the medial and long heads of the triceps brachii. Here it is ac¬ companied by the profunda brachii artery along the spiral groove of the humerus. Be¬ cause of this relationship with the bone, it is liable to injury in fractures of the humerus or may be severely compressed by pressure. Supplying the extensor compartment mus¬ cles in the forearm, the radial nerve eventu¬ ally achieves the dorsum of the hand, which it helps to innervate with sensory fibers.

The Lower Limb bones. The pelvis or hip bones are largely covered with muscle, so that only at a few sites do they lie immediately beneath the skin surface. The highest part of the pel¬ vis on each side is the thick iliac crest. This can be easily palpated, except in very obese individuals, and can be traced anteriorly to the anterior superior iliac spine, and posteri¬ orly to the posterior superior iliac spine. The latter bony spine is indicated by a slight de¬ pression. On the outer lip of the crest, about 5 cm behind the anterior superior spine, is the prominent iliac tubercle. In thin subjects the pubic tubercle, located near the superior lateral border of the symphysis pubis, is very apparent, but in the obese it is obscured by the pubic fat. It can, however, be detected by following the tendon of origin of the adduc¬ tor longus superiorly. Additionally, the in¬ guinal ligament can be followed from the anterior superior iliac spine to the pubic tu¬ bercle. Another part of the bony pelvis that is accessible to touch is the ischial tuberos¬ ity, situated beneath the gluteus maximus. When the hip is flexed, this tuberosity can easily be felt, since it is then not covered by muscle. The femur (Figs. 3-41 to 3-43) is enveloped by muscles, so that the only palpable parts are the lateral surface of the greater trochan¬ ter and the lower expanded end of the bone. The greater trochanter can be felt on the upper lateral aspect of the thigh. It is gener¬ ally indicated by a depression, owing to the thickness of the gluteus medius and gluteus minimus which project above it. The greater trochanter becomes a more prominent pro¬ tuberance if the thigh is flexed and crossed over the opposite one. At the lower end of the femur the lateral condyle is more easily felt than the medial. Both epicondyles can

107

be readily identified, and at the summit of the medial epicondyle the sharp adductor tubercle can be recognized without diffi¬ culty. The anterior surface of the patella is sub¬ cutaneous (Fig. 3-44). This sesamoid bone lies within the tendon of the quadriceps femoris muscle, and when the muscle is re¬ laxed, the patella can be moved from side to side. Upon flexion of the leg the patella re¬ cedes between the condyles of the femur, but upon extension it lies anterior to the condyles. By its position, the patella helps to protect the knee joint from injury, strength¬ ening the structure of the quadriceps tendon as well. A considerable portion of the tibia or shin bone is subcutaneous (Figs. 3-46; 3-47). At the upper end the tibial condyles can be felt just below the knee joint. In front of the upper

f Iliac crest

Ant. sup. iliac spine

Inguinal ligament

Femoral triangle Sartorius

Adductors

Rectus femoris

Vastus lateralis Vastus medialis

Patella Patellar tendon Tibial tu berosity

Lateral malleolus

Fig. 3-41. Anterior view of lower limbs and abdomen demonstrating surface muscular contours.

1 08

SURFACE AND TOPOGRAPHICAL ANATOMY

Profunda femoris vessels

Branches of femoral nerve Great saphenous vein

Femoral artery

Femoral vein

Medial

Lateral

Obturator nerve

Sciatic nerve

Semimembranosus

Fig. 3-42.

Cross section through the right thigh, viewed from above, at the level of the apex of the femoral triangle.

end of the bone, between the condyles, is an oval eminence, the tibial tuberosity, which is continuous below with the anterior crest of the bone. At the lower end of the bone, the medial malleolus (Fig. 3-44) forms a broad prominence, situated at a higher level and somewhat farther forward than the lateral malleolus of the fibula (Fig. 3-44). The only subcutaneous parts of the fibula are the head, the lower part of the body, and the lat¬ eral malleolus. The lateral malleolus is a narrow elongated prominence, from which the lower third or half of the lateral surface of the body of the bone can be traced up¬ ward (Fig. 3-44). It is difficult to distinguish the individual tarsal bones on the dorsum of the foot by palpation alone. An exception is the head of the talus, which forms a rounded projection in front of the ankle joint when the foot is forcibly extended. The whole dorsal surface of the foot has a smooth convex outline, the

summit of which is the ridge formed by the head of the talus, the navicular, the interme¬ diate cuneiform, and the second metatarsal bone. On the medial side of the foot the me¬ dial process of the tuberosity of the calca¬ neus and the ridge separating the posterior from the medial surface of the bone are dis¬ tinguishable; in front of this, and below the medial malleolus, is the sustentaculum tali. The tuberosity of the navicular is palpable about 2.5 to 3 cm in front of the medial mal¬ leolus. Farther forward, the ridge formed by the base of the short and thick first metatarsal bone can be felt. The head of the first meta¬ tarsal is large, and its prominence on the plantar aspect of the foot is called the ball of the large toe. Beneath the base of the first phalanx is the medial sesamoid bone. On the lateral side of the foot, in the region of the heel, the most posterior bony point is the lat¬ eral process of the tuberosity of the calca-

Nerve to vastus medialis Saphenous nerve Femoral artery in the adductor canal Arteria profunda femoris

Great saphenous vein

Biceps femoris (short head) Femoral vein Sciatic nerve

Medial

Lateral

Posterior femoral cutaneous nerve

Fig. 3-43. Cross section, viewed from above, through the middle of the right thigh. Observe the sciatic nerve coursing along the posterior surface of the adductor magnus muscle. Tendon of quadriceps femoris Suprapatellar bursa

Lateral

Medial

Descending genicular artery Popliteal artery Adductor magnus

Popliteal vein Common peroneal nerve

Saphenous nerve

Tibial nerve

Great saphenous vein Gracilis

Small saphenous vein Posterior femoral cutaneous nerve

Semitendinosus

Fig. 3-44. Cross section, viewed from above, through the right thigh 4 cm proximal to the adductor tubercle of the femur. Note that the neurovascular structures have entered the proximal part of the popliteal fossa.

109

1 1 0

SURFACE AND TOPOGRAPHICAL ANATOMY

Gluteus maxirmus Greater trochanter

Tensor fasciae latae Rectus femoris

Iliotibial tract of fascia lata Hamstrings Vastus medialis Vastus lateralis Biceps femoris Popliteal fossa

Patella

Tibial tuberosity

Right side of lower limbs to show surface contours of muscles and bones.

Fig. 3-45.

neus. In front of this the greater part of the lateral surface of the calcaneus is subcutane¬ ous. Farther forward the base, body, and head of the fifth metatarsal bone are promi¬ nent. The dorsal surfaces of the metatarsal bones are easily defined; the plantar surfaces are obscured by muscles. The phalanges in their whole extent are readily palpable. articulations. The hip joint is deeply seated and cannot be palpated. The interval between the tibia and femur can always be felt; if the knee joint is extended this interval lies at a higher level than the apex of the patella, but if the leg is slightly flexed it lies directly behind the apex. The ankle joint can be felt on either side of the extensor tendons, and during plantar flexion of the foot, the superior articular sur¬

face of the talus is palpable below the ante¬ rior border of the lower end of the tibia. muscles (Figs. 3-41 to 3-45). The promi¬ nent muscles on the anterior aspect of the thigh are the quadriceps femoris and the sartorius, while laterally the tensor fasciae latae attaches to a broad tendon, the iliotib¬ ial band, which extends downward to the knee joint. At the medial side of the thigh are the adductors, and on the posterior thigh are the three hamstrings, medially the semi¬ membranosus and semitendinosus and lat¬ erally the biceps femoris. Above the thigh, the prominence of the buttock is caused mostly by the gluteus maximus. Below the knee joint, the contour of the calf on the back of the leg is due to the gas¬ trocnemius and soleus muscles, which term¬ inate at the heel in the tendon of Achilles or tendo calcaneus (Figs. 3-46 to 3-48). Lateral to the anterior border of the tibia (or shin bone), the tibialis anterior and the peroneus longus and brevis can usually be recognized (Figs. 3-46, 3-47). The femoral triangle (Fig. 3-44) is bounded above by the inguinal ligament, laterally by the medial border of the sartorius muscle, and medially by the medial border of the adductor longus. A large superficial vein of the lower limb, the great saphenous vein, penetrates this triangle by way of the hiatus saphenus to join the femoral vein. The cen¬ ter of this hiatus is about 4 cm below and lateral to the pubic tubercle; its vertical di¬ ameter measures about 4 cm and its trans¬ verse about 1.5 cm. Medial to the femoral vein is the femoral ring. This ring is about 1.25 cm lateral to the pubic tubercle, and it is the oval-shaped cranial aperture of the fem¬ oral canal through which femoral hernias may occur. This type of hernia is about three times more frequent in females than in males. Midway down the medial aspect of the thigh is located the adductor canal. This canal begins at the apex of the femoral tri¬ angle and lies deep to the vertical part of the sartorius muscle; for this reason, it is also sometimes called the subsartorial canal. Through the adductor canal passes the fem¬ oral artery in order to achieve the back of the knee in the popliteal fossa (Fig. 3-42). This important fossa is bounded above by the medial and lateral hamstrings, and below by the medial and lateral heads of the

THE LOWER LIMB

1 1 1

Anterior tibial artery

Popliteus

Superficial peroneal nerve

Great saphenous vein

Saphenous nerve Medial

Lateral Deep peroneal nerve

Flexor digitorum longus

Tibial nerve Posterior tibial artery Plantaris

Peroneal anastomotic nerve

Small saphenous vein Medial sural cutaneous nerve Fig. 3-46. Cross section, viewed from above, through the right leg, 9 cm. distal to the knee joint. Observe the relationship of the tibial nerve with the posterior tibial artery and the deep peroneal nerve with the anterior tibial artery. Note also the superficial peroneal nerve in the lateral compartment.

Deep peroneal nerve

Anterior tibial artery

Tibialis anterior

Extensor digitorum longus Extensor hallucis longus

Superficial peroneal nerve Saphenous nerve

Peroneus tertius

•

Perforating branch of peroneal artery

Great saphenous vein Medial

Peroneal artery Tibialis posterior Lateral Flexor digitorum longus

Peroneus longus

Posterior tibial artery

Tibial nerve

Plantaris

Sural nerve Small saphenous vein Soleus Tendo calcaneus

Fig. 3-47.

Cross section, viewed from above, through the right leg, 6 cm. proximal to the tip of the medial malleolus.

1 12

SURFACE AND TOPOGRAPHICAL ANATOMY

Gastrocnemius

Soleus

Tibialis anterior

Peronei Extensor digitorum

Tendon of Achilles —•sj l' Peronei —sme?

Medial malleolus

Fig. 3-48.

Right side of leg to show surface contours of muscles and bones.

gastrocnemius muscle. In this fossa the pop¬ liteal artery and sciatic nerve are covered only by subcutaneous tissue and fat, and through it the small saphenous vein joins the popliteal vein. arteries. The femoral artery enters the anterior thigh midway between the anterior superior iliac spine and the pubic tubercle, just below the inguinal ligament. Its pulsa¬ tions can be felt at this point, but they be¬ come increasingly difficult to detect as the artery courses inferiorly toward and into the adductor canal. When the leg is flexed at the knee joint, the pulsation of the popliteal ar¬ tery, which is the continuation of the femo¬ ral artery, can easily be detected in the pop¬ liteal fossa behind the joint. On the lower part of the front of the tibia, the anterior tibial artery becomes superficial (P’ig. 3-47) and can be traced over the ankle

joint into the dorsal foot as the dorsalis pedis artery. This latter vessel can be fol¬ lowed to the proximal end of the first intermetatarsal space. On the back of the leg, the pulsation of the posterior tibial artery be¬ comes detectable near the lower end of the tibia, and is easily felt behind the medial malleolus. veins. By compressing the proximal trunks, the venous arch on the dorsum of the foot, together with the great and small sa¬ phenous veins leading from it, is rendered visible. nerves. The only nerve of the lower limb that can be located by palpation is the com¬ mon peroneal as it winds around the lateral side of the neck of the fibula. Because of its subcutaneous location and its position adja¬ cent to bone, this nerve is quite vulnerable to injury at this site.

REFERENCES

1 13

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.) Anson, B. J. 1966. Morris’ Human Anatomy. A Complete Systemic Treatise. 12th ed. McGraw-Hill Book Co., New York, 1623 pp. Bargmann, W., H. Leonhardt, and G. Tondury. 1968. Lehrbuch und Atlas der Anatomie des Menschen (von) Ftauber (und) Kopsch. 20th ed. Georg Thieme Verlag, Stuttgart, 3 vols. Basmajian, J. V. 1975. Grant’s Method of Anatomy. 9th ed. The Williams and Wilkins Co., Baltimore, 654 pp. Bassett, D. L. 1952-63. A Stereoscopic Atlas of Human Anatomy. Sawyer’s Inc., Portland, and The C. V. Mosby Co., St. Louis, 23 vols. Clemente, C. D. 1981. Anatomy, An Atlas of the Human Body, 2nd ed., Urban & Schwarzenberg, Baltimore, 387 pp. Crouch,J. E. 1978. Functional Human Anatomy. 3rd ed. Lea & Febiger, Philadelphia, 663 pp. Eycleshymer, A. C., and T. Jones. 1925. Hand-Atlas of Clinical Anatomy. 2nd ed. Lea & Febiger, Philadel¬ phia, 425 pp. Ferner, H., and J. Staubesand. 1975. Benninghoff und Goerttler’s Lehrbuch der Anatomie des Menschen. 11th ed. Urban and Schwarzenberg, Munich, 3 vols. Figge, F. H. J., and W. J. Hild. 1974. Sobotta’s Atlas of Human Anatomy. 9th English ed. Urban and Schwarzenberg, Munich, 3 vols. Gardner, E. D., D. J. Gray, and R. O'Rahilly. 1975. Anat¬ omy, A Regional Study of Human Structure. 4th ed. W. B. Saunders Co., Philadelphia, 821 pp. Grant, J. C. B. 1972. Atlas of Anatomy. 6th ed. The Williams and Wilkins Co., Baltimore, no pagina¬ tion, 655 figures. Hamilton, W. J., G. Simon, and S. G. Hamilton. 1971. Surface and Radiological Anatomy. 5th ed. The Williams and Wilkins Co., Baltimore, 397 pp. Healey, Jr., J. E., and W. D. Seybold. 1969. A Synopsis of Clinical Anatomy. W. B. Saunders Co., Philadel¬ phia, 324 pp. Hollinshead, W. H. 1971. Anatomy for Surgeons. 2nd ed. Harper and Row, Hagerstown, Md., 3 vols. Kaplan, E. B. 1965. Functional and Surgical Anatomy of the Hand. 2nd ed. J. B. Lippincott, Philadelphia, 488 pp. Kiss, F.. and J. Szentagothai. 1964. Atlas of Human Anatomy. 17th ed. Macmillan Publishing Co., Inc., New York, 3 vols.

Lachman, E. 1971. Case Studies in Anatomy. 2nd ed. Oxford University Press, London, 342 pp. Last, R. J. 1972. Anatomy, Regional and Applied. 5th ed. Churchill-Livingstone, Edinburgh, 925 pp. Lockhart, R. D., G. F. Hamilton, and F. W. Fyfe. 1969. Anatomy of the Human Body. 3rd ed. J. B. Lippin¬ cott, Philadelphia, 705 pp. Lopez-Altunez, L. 1971. Atlas of Human Anatomy. Translated by H. Monsen, W. B. Saunders Co., Phil¬ adelphia, 366 pp. Pernkopf, E. 1963. Atlas of Topographical and Applied Human Anatomy. Edited by H. Ferner. Translated by H. Monsen, W. B. Saunders Co., Philadelphia, 2 vols. Pansky, B., and E. L. House. 1975. Review of Gross Anatomy. 3rd ed. Macmillan Publishing Co., Inc., New York, 508 pp. Rasch, P. J., and R. K. Burke. 1978. Kinesiology and Applied Anatomy: The Science of Human Move¬ ment. 6th ed. Lea & Febiger, Philadelphia, 496 pp. Rehman, I., and N. Hiatt. 1965. Descriptive Atlas of Surgical Anatomy. McGraw-Hill, New York, 180 pp. Romanes, G. J. 1972. Cunningham’s Textbook of Anat¬ omy. 11th ed. Oxford University Press, London, 996 pp. Rouviere, H. 1962. Anatomie Humaine, Descriptive et Topographique. 9th ed. Rev. by G. Cordier and A. Delmas, Masson, Paris, 3 vols. Snell, R. S. 1973. Clinical Anatomy for Medical Stu¬ dents. Little, Brown and Co., Boston, 909 pp. Thorek, P. 1962. Anatomy in Surgery. 2nd ed. J. B. Lip¬ pincott, Philadelphia, 904 pp. Tondury, G. 1970. Angewandte und Topographische Anatomie. 4th ed. Georg Thieme Verlag, Stuttgart, 636 pp. Warfel, J. H. 1973. The Head, Neck and Trunk. 4th ed. Lea & Febiger, Philadelphia, 128 pp. Warfel, J. H. 1974. The Extremities. 4th ed. Lea & Febi¬ ger, Philadelphia, 124 pp. Wolf-Heidegger, G. 1972. Atlas of Systemic Human Anatomy. Hafner, New York, 3 vols. in one, 635 pp. Woodburne, R. T. 1973. Essentials of Human Anatomy. 5th ed. Oxford University Press, New York, 629 pp.

The patellae are included in this enumera¬ tion, but the smaller sesamoid bones are not; also, the sternum is considered as one bone. Bones can be classified into four general types according to their shape and form. Long bones, such as the humerus and femur, are found in the limbs (Fig. 4-1), whereas short bones, such as those in the hand and foot, are more compact and subjected to more limited movement. Other bones, illus¬ trated by the parietal bones of the skull or the scapulae (Fig. 4-1), are flat bones, while irregular bones form the vertebral column (Fig. 4-1), as well as other structures.

Ossification and Skeletal Development

The study of bones is called osteology. Bones provide a framework for the body, and when assembled in their proper posi¬ tion, they form the skeleton (Fig. 4-1). In the living body, bones are frequently held in position by strong fibrous bands, the liga¬ ments, which form articulations or joints. Attached to bones across the joints are most of the muscles of the body, and muscular contraction results in the movement of bones and their associated body parts. In addition to providing internal support for the body, the skeleton protects the vital or¬ gans of the head and chest by forming the cranial and thoracic cavities. Because of its large mineral content, bone is a hard un¬ yielding tissue and is ideally suited for the mechanical functions of support, protection, and movement. In life it is also a dynamic substance and is importantly involved with other tissues and organs in the metabolism of calcium. The interior of bones contains the bone marrow, which consists of the blood-forming, hemopoietic tissue. In the skeleton of the adult there are 206 distinct bones, as follows: Axial Skeleton

Appendicular Skeleton

Vertebral column .... 26 Skull.28 Hyoid bone. 1 Ribs and sternum ... 25 Upper extremities ... 64 Lower extremities ... 62

80

126 Total.206

The skeleton, like some other structures, is derived from mesoderm, which migrates from the primitive streak during the forma¬ tion of the three primary germ layers. Its cells multiply, undergo certain changes, move into appropriate regions, and form cel¬ lular aggregates or sheets which can be rec¬ ognized as the membranous skeleton. The cells of these primordia, except in certain parts of the cranium, soon elaborate an in¬ tercellular substance that converts the tissue into cartilage. After the cartilaginous skele¬ ton is well established, centers of ossifica¬ tion appear which gradually spread to form the bony skeleton. In some of the cranial bones ossification centers arise in the mem¬ branous skeleton without the intervention of cartilage. OSSIFICATION The term ossification refers to the forma¬ tion of bone. In the development of certain bones, such as those forming the roof and sides of the skull, bone formation occurs di¬ rectly within clusters of primitive mesen¬ chyme cells surrounded by a more definitive connective tissue membrane. In other bones, such as those in the limbs, the formation of bone occurs within rods of pre-existing car¬ tilage. Hence, two forms of ossification are described: intramembranous and endochon¬ dral. The latter type is sometimes called intracartilaginous. INTRAMEMBRANOUS OSSIFICATION. In the case of bones that are developed in mem¬ brane, no cartilaginous mold precedes the

OSSIFICATION AND SKELETAL DEVELOPMENT

Fig. 4-1.

Jones.)

1 1 5

The skeleton as projected on the surface of the body. Ventral and dorsal views. (From Eycleshymer and

1 1 6

OSTEOLOGY

appearance of bony tissue. The connective tissue membrane, which surrounds the cen¬ ters of ossification, persists and ultimately forms the periosteum; it is composed of fi¬ bers and granular cells in a matrix. The pe¬ ripheral portion is more fibrous, while in the interior the primitive mesenchymal cells dif¬ ferentiate into osteoblasts; the whole tissue is richly supplied with blood vessels. At the outset of the process of bone formation, a lit¬ tle network of eosinophilic extracellular spicules is noticed forming between the branching vascular elements. At their growth points, these rays consist of a network of fine clear fibers and osteoblast cells with an intervening ground substance. The fibers are termed osteogenic fibers, and are made up of fine collagen fibrils differing little from those of other connective tissue. The membrane soon assumes a dark and granular appear¬ ance from the deposition of calcium-con¬ taining crystals (hydroxyapatite) in the fi¬ bers and in the intervening matrix. As the bony trabeculae enlarge, some of the osteo¬ blasts become surrounded by the newly de¬ posited calcified material. With the deposi¬ tion of mineral salts, the newly formed osteoid tissue again assumes a more trans¬ parent appearance, and the fibrils are no longer so distinctly seen. The involved oste¬ oblasts form the corpuscles of the future bone, the spaces in which they are enclosed constituting the lacunae. As the osteogenic fibers grow toward the periphery, they con¬ tinue to ossify and give rise to fresh bone spicules. Thus a network of woven bone is formed, the meshes of which contain blood vessels and a delicate connective tissue crowded with osteoblasts. The bony trabec¬ ulae thicken by the addition of fresh layers of bone formed by the osteoblasts on their surface. Subsequently, successive layers of bony tissue are deposited under the perios¬ teum and around the larger vascular chan¬ nels, which become the Haversian canals as the bone increases in thickness. The entrap¬ ped osteoblasts of developing bone become the osteocytes of mature bone, and these cells may well be importantly involved in the release of calcium from bone to blood. ENDOCHONDRAL OSSIFICATION. Ossification in long bones of the extremities, in por¬ tions of the basal bones of the skull, and in the vertebrae, the sternum, the ribs, and the pelvis occurs in masses of pre-existing de¬ veloped hyaline cartilage, which present a

model form of the fully ossified bone. In a long bone, which may be taken as an exam¬ ple (Fig. 4-2), the process commences in the center of the diaphysis, or shaft, and pro¬ ceeds toward the extremities, called the epiphyses, which for some time remain car¬ tilaginous. Subsequently a similar ossifica¬ tion process commences in one or more sites of the epiphyses and gradually extends through them. The epiphyses do not, how¬ ever, become joined to the shaft of the bone by bony tissue until growth has ceased; be¬ tween the diaphysis and either epiphysis a layer of cartilaginous tissue termed the epi¬ physeal cartilage persists for a definite pe¬ riod. The first stage in the ossification of carti¬ lage takes place at the center of ossification,

Fig. 4-2.

Photograph of the upper half of the tibia of young girl, showing the proximal bony epiphysis, the cartilaginous epiphyseal plate, and the shaft or diaphy¬ sis. (From Bloom and Fawcett, A Textbook of Histology, W. B. Saunders Co., 1975.)

OSSIFICATION AND SKELETAL DEVELOPMENT

where cartilage cells enlarge and arrange themselves in rows (Fig. 4-3). The matrix in which they are embedded increases in quan¬ tity, so that the cells become separated from each other. Deposits of calcium-containing crystals now accumulate in this matrix, be¬ tween the rows of cells, so that the cartilage cells become separated from each other by longitudinal columns of calcified matrix which appear granular and opaque. At some sites the matrix between two cartilage cells of the same row also becomes calcified, and transverse bars of calcified substance stretch across from one calcified column to another. Thus, there are longitudinal groups of carti¬ lage cells enclosed in oblong cavities, the walls of which consist of calcified matrix and effectively cut off all nutrition from the cells. In consequence, the cells atrophy, leaving spaces called the primary areolae. At the same time that this process occurs in the center of the solid bar of cartilage, cer¬ tain changes are taking place on its surface. This is covered by a highly vascular mem¬ brane, the perichondrium, entirely similar to the embryonic connective tissue already described as constituting the basis of mem¬ brane bone. On its inner surface, that is, on the surface in contact with the cartilage, are gathered rows of osteoblasts. These cells form a thin layer of bony tissue, called a per¬ iosteal bone collar, between the perichond¬ rium and the cartilage by the intramembranous mode of ossification already described. There are, then, in this first ossification stage of cartilaginous bone, two processes going on simultaneously: in the center of the carti¬ lage, the formation of a number of oblong spaces, surrounded by calcified matrix and containing the withered cartilage cells, and on the surface of the cartilage, the formation of a layer of true membranous bone. The second stage of intracartilaginous os¬ sification (Fig. 4-3) occurs when blood ves¬ sels perforate the periosteal bone collar to invade the deeper osteogenic regions of the cartilage. Additionally, osteoclasts, or bone destroyers, make their appearance. These giant cells seem associated with the absorp¬ tion of osteogenic matrix, possibly by their secretion of hydrolytic enzymes. Osteoclasts can be observed occupying minute cham¬ bers called Howship’s lacunae, which, by erosion, they may have created themselves on the bone surface. There is evidence that osteoclasts are derived from the fusion of

1 1 7

Epiphyseal ca rtilage Perichondrium

Blood vessel

Embryonic marrow' space

Entrance site of blood vessel

Subperiosteal bone

Primitive marrow cavity

Fig. 4-3. Osteogenesis. Subperiosteal stage of ossifica¬ tion in an embryonic long bone. 20 X. (Redrawn from Sobotta.)

mononuclear osteogenic cells, yet some may come from mononuclear cells in the blood such as monocytes. Regardless of their ori¬ gin, as they come into contact with the calci¬ fied walls of the primary areolae, osteoclasts

1 1 8

OSTEOLOGY

cause a fusion of the original cavities, which creates larger spaces termed the secondary areolae or medullary spaces. These second¬ ary spaces become filled with embryonic marrow, osteoblasts, and vessels, derived from the osteogenic layer of the periosteum (Fig. 4-4). Traced thus far has been the formation of enlarged medullary spaces, the perforated walls of which are still formed by calcified cartilage matrix, containing an embryonic marrow derived from the osteogenic layer of periosteum, and consisting of blood vessels

and osteoblasts. At this time the walls of these secondary areolae are of only incon¬ siderable thickness, but they become thick¬ ened by the deposition of layers of true bone on their surface. This process takes place in the following manner: some osteoblasts in the embryonic marrow, after undergoing rapid division, arrange themselves in an epi¬ thelioid manner on the surface of the wall of the space. This layer of osteoblasts forms a bony stratum, and thus the wall of the space becomes gradually covered with a layer of true osseous substance in which some of the

Hyalin cartilage

Rows of cartilage cells

Hyalin matrix

Calcified matrix

Enlarged cartilage cell and lacuna Osteoclast in Howship's lacuna

Osteoblast

Primitive marrow Osteoblast Periosteum Endochondral bone

Calcified cartilage Subperiosteal bone

Endochondral bone formation proceeding from the center of the shaft of a long bone toward one of the two extremities. 40 X. (Redrawn from Sobotta.)

Fig. 4-4.

OSSIFICATION AND SKELETAL DEVELOPMENT

bone-forming cells are included as bone cor¬ puscles. The next step in the process consists in the removal of these primary bone spic¬ ules by the osteoclasts. One of these giant cells may he found lying in a Howship’s la¬ cuna at the free end of each spicule. The removal of the primary spicules goes on pari passu with the formation of permanent bone by the periosteum, and in this way the med¬ ullary cavity of the body of the bone is formed. Commencing in the center of the diaphysis of the cartilaginous bony model, this se¬ ries of changes gradually proceeds toward the extremities of the bone, so that in a spec¬ imen of ossifying bone all the aforemen¬ tioned changes may be seen at different sites, from true bone at the center of the shaft to hyaline cartilage at the extremities. While the ossification of the cartilaginous body is extending toward the articular ends, the cartilage immediately in advance of the osseous tissue continues to grow until the length of the adult bone is reached. During the period of growth the articular end, or epiphysis, remains for some time en¬ tirely cartilaginous, then a bony center ap¬ pears within it, initiating at this site, as well, the process of intracartilaginous ossification. This is a secondary center of ossification. The epiphysis remains distinct from the os¬ sified diaphysis by a narrow cartilaginous zone called the epiphyseal plate. This, too, ultimately ossifies, and the histologic dis¬ tinction between diaphysis and epiphysis is obliterated, the bone assuming its completed form and shape. Similar events also occur in bony processes that ossify separately, such as the trochanters of the femur. The bones continue to grow until the body has acquired its full stature, increasing in length by ossifi¬ cation toward the epiphyses and in circum¬ ference by the deposition of new bone from the deeper inner layer of the periosteum. At the same time bone resorption takes place from within, thereby enlarging the medul¬ lary marrow cavities. A review of the stages in the development of a typical long bone is presented in the diagrams of Figure 4-5. Permanent bone, when first formed by the periosteum, is spongy or cancellous in struc¬ ture. Later, as osteoblasts contained in its spaces become arranged in the concentric layers characteristic of the Haversian sys¬ tems, the bone assumes the more solid struc¬ ture of compact bone.

1 19

The number of ossification centers varies in different bones. In most of the short bones, ossification commences at a single central site, and proceeds toward the sur¬ faces. In long bones there is a central point of ossification for the shaft or diaphysis, and one or more for each extremity, or epiphy¬ sis. That for the diaphysis is the first to ap¬ pear. The times of union of the epiphyses with the diaphysis vary inversely with the dates at which their ossifications began (with the exception of the fibula). This proc¬ ess also influences the direction of growth of the nutrient arteries of the bones. Thus, the nutrient arteries of the bones of the arm and forearm are directed toward the elbow, since the epiphyses at this joint become united to the diaphyses before those at the opposite extremities at the shoulder and wrist. In the lower limb, on the other hand, the nutrient arteries are directed away from the knee: that is, upward in the femur and downward in the tibia and fibula. In these bones it is observed that the upper epiphysis of the femur, and the lower epiphyses of the tibia and fibula unite first with the diaphyses. Where there is only one epiphysis, the nutri¬ ent artery is directed toward the opposite end of the bone; for example, toward the acromial end of the clavicle, toward the dis¬ tal ends of the metacarpal bone of the thumb and the metatarsal bone of the great toe, and toward the proximal ends of the other meta¬ carpal and metatarsal bones.

SKELETAL DEVELOPMENT

The central axis of the embryo around which the vertebrae de¬ velop is the notochord. This rod of cells lies in the median line between the neural tube and the primitive gut, extending from the level of the midbrain to the end of the tail. The somites in the paraxial mesoderm on either side of the neural tube give rise to three primordia, the sclerotome, myotome, and dermotome. The cells of the sclerotome eventually form the vertebrae, as well as other structures. During the fourth embryonic week these cells multiply rapidly and mi¬ grate toward the notochord, forming a mes¬ enchymal layer on either side. The segmen¬ tal primordia of the individual vertebrae are still recognizable, but soon each sclerotome differentiates into a densely arranged cauvertebral column.

F

Fig. 4-5. Diagram of the development of a typical long bone as shown in longitudinal sections (A to /) and in cross sections A', B\ C', and D' through the centers of A, B, C, and D. Pale blue, cartilage; purple, calcified cartilage; black, bone; red, arteries. A, Cartilage model. B, Periosteal bone collar appears before any calcification of cartilage. C, Cartilage begins to calcify. D, Vascular mesenchyme enters the calcified cartilage matrix and divides it into two zones of ossification, E. F, Blood vessels and mesenchyme enter upper epiphyseal cartilage and the epiphyseal ossification center develops in it, G. A similar ossification center develops in the lower epiphyseal cartilage, H. As the bone ceases to grow in length, the lower epiphyseal plate disappears first, I, and then the upper epiphyseal plate, J. The bone marrow cavity then becomes continuous throughout the length of the bone, and the blood vessels of the diaphysis, metaphyses, and epiphyses intercommunicate. (From Bloom and Fawcett, A Textbook of Histology, W. B. Saunders Co., 1975).

OSSIFICATION AND SKELETAL DEVELOPMENT

1 21

Myotome Intervertebral disc

Cranial portion of sclerotome Notochord Caudal portion of sclerotome Intermyotomic septum Costal process

A

B

Fig. 4-6. Diagrams showing the manner in which each vertebral centrum is developed from portions of two adjacent somites or body segments. A, The segmental structure of the sclerotome differentiates into a more dense caudal portion and a more loosely arranged cranial portion around the notochord. B, The lateral and somewhat cranial migration of some of the densely arranged cells forms a costal process laterally and the primordium of the intervertebral disc cranially as seen in C. C, Note the disc formed by densely arranged cells and the centrum of the vertebrae formed by parts of two adjacent sclerotomes.

dal portion and loosely arranged cranial portion (Fig. 4-6,A). The ventral portion of the densely arranged cells then migrates lat¬ erally and cranially (Fig. 4-6,B). Upon reach¬ ing the level of the center of their original somite, these cells spread back to the mid¬ line around the notochord. The dense por¬ tion becomes the future intervertebral disc, and the loosely arranged portion and the adjacent dense portion left in close juxtapo¬ sition combine to become the future verte¬ bral body or centrum (Fig. 4-6,C). Similarly, the dorsal portion of the sclerotome around the neural tube forms the future vertebral arch from its loosely arranged cells, and liga¬ ments from its dense portion. Since the primordia of each vertebra come from two

sclerotomes, they are intersegmental in ori¬ gin, in contrast to the intervertebral discs, which are segmentally derived. The most ventral extension of the sclerotome forms the future costal process from its looser por¬ tion and ligaments from the dense portion (Figs. 4-6,B and C; 4-7,A). This mesenchymal stage is succeeded by that of the cartilaginous vertebral column (Fig. 4-7). In the sixth week two cartilaginous centers make their appearance, one on each side of the notochord; these extend around the notochord and form the body of the car¬ tilaginous vertebra. A second pair of carti¬ laginous foci appear more dorsally in the mesenchyme surrounding the neural tube to form the cartilaginous vertebral arch, and a

primary ossification centers

Fig. 4-7. Diagrams illustrating the stages of vertebral development. A, Precartilaginous (mesenchymal) vertebra at five weeks. B, Chondrification centers in a mesenchymal vertebra at six weeks. C, Primary ossification centers in a cartilaginous vertebra at seven weeks. (From Moore, K. L., The Developing Human, W. B. Saunders Co., 1973.)

122

OSTEOLOGY

separate cartilaginous center appears for each costal process. Somewhat after the sec¬ ond month the cartilaginous arch has fused with the body, and in the fourth month the two halves of the arch are joined on the dor¬ sal aspect of the neural tube. The spinous process develops from the junction of the two halves of the neural or vertebral arch. The transverse process grows out from the vertebral arch dorsal to the costal process. In the more cranial cervical vertebrae a band of mesodermal tissue connects verte¬ bral ends of the costal processes, spanning the ventral aspects of the centra and the in¬ tervertebral discs. This is termed the hypochordal bar or arch; in all except the first vertebra, it is transitory and disappears by fusing with the discs. In the atlas, however, the entire bar persists and undergoes chondrification; it develops into the ventral arch of the atlas, while the cartilage repre¬ senting the body of that bone forms the dens or odontoid process, which then fuses with the body of the second cervical vertebra, the axis. The portions of the notochord that are sur¬ rounded by the bodies of the vertebrae atro¬ phy, and ultimately disappear, while those that lie in the centers of the intervertebral discs undergo enlargement, and persist throughout life as part of the central nucleus pulposus of the discs. the ribs. The ribs are formed from the ventral or costal processes of the primitive vertebrae which extend between the muscle plates (Fig. 4-6,B and C). In the thoracic re¬ gion of the vertebral column the costal proc¬ esses grow lateralward to form a series of precartilaginous arches, the primitive costal

arches. As already described, the transverse process grows out dorsal to the vertebral end of each arch. Initially the transverse process is connected to the costal process by contin¬ uous mesoderm, but the interconnecting mesoderm cells become differentiated later to form the costotransverse ligament. Be¬ tween the costal process and the lateral tip of the transverse process, the costotransverse joint is formed by absorption. The costal process becomes separated from the verte¬ bral centrum by the development of the costocentral joint. In the cervical vertebrae (Fig. 4-8) the transverse process forms the posterior boundary of the foramen transversarium, while the costal process, corre¬ sponding to the head and neck of a thoracic rib, fuses with the body of the vertebra and forms the anterolateral boundary of the fo¬ ramen. The distal portions of the primitive costal arches remain undeveloped. Occa¬ sionally the arch of the seventh cervical ver¬ tebra undergoes greater development, form¬ ing an accessory cervical rib complete with costovertebral joints. A cervical rib (which may even be bilateral) may compress the trunks of the brachial plexus and the subcla¬ vian vessels, resulting in symptoms in the upper extremity. In the lumbar region (Fig. 4-8) the distal portions of the primitive costal arches fail to develop, while the proximal portions fuse with the true transverse proc¬ esses to form the “transverse processes” of descriptive anatomy. Occasionally movable ribs may develop in connection with the first lumbar vertebra. In the sacral region costal processes are developed only in connection with the upper three or four vertebrae; the processes of adjacent sacral segments fuse

Fig. 4-8. Diagrams showing the portions of the adult vertebrae derived respectively from the bodies (yellow), verte¬ bral arches (red), and costal processes (blue) of the embryonic vertebrae.

OSSIFICATION AND SKELETAL DEVELOPMENT

with one another to form the lateral masses of the sacrum. The coccygeal vertebrae are devoid of costal processes. the sternum. The sternum arises from a pair of mesenchymal bands in the ventrolat¬ eral body wall. Although the sternum devel¬ ops separately from the ribs, on each side the ventral ends of the upper six or seven ribs become joined to these longitudinal bars of mesenchyme, which by this time are called sternal plates. These plates become cartilag¬ inous and migrate ventrally toward the mid¬ line. The sternal plates of the two sides then fuse in a craniocaudal direction in the mid¬ line to form the manubrium and body of the sternum. The xiphoid process is formed by a caudal extension of the sternal plates. the skull. The bones of the skull, like those elsewhere in the body, are derived from mesenchyme. The cranial vault grows around the developing brain and is therefore referred to as the neurocranium. Addition¬ ally, other bones in the head are derived from the branchial arches and the term viscerocranium is applied to these. The mesenchymal membranes that form the neurocranium in some regions become transformed into bone by endochondral os¬ sification and in other sites by way of intramembranous ossification. Thus, reference is frequently made to the cartilaginous neuro¬ cranium or chondrocranium, which includes the bones at the base of the skull, and the membranous neurocranium, which includes certain flat bones of the skull. The first observable indications of the developing skull are found in the basal oc¬ cipital and basal sphenoid regions and around the auditory vesicles. Condensation of the primordial mesodermal cells from which the skull will be formed gradually extends from these basal areas completely around the brain until the latter becomes enclosed by a membranous cranium, also called the blastemal skull or desmocranium. The membranous cranium is incomplete in the regions where large nerves and vessels pass into or out of the cranium. Cartilaginous Neurocranium. Before the membranous cranium is even complete, chondrification begins to show in the basilar part of the developing occipital bone (basioccipital). It should be appreciated that chondrification centers develop in relation to the notochord, which extends into the developing cranium from spinal levels (Fig.

123

Fig. 4-9. Sagittal section through the cephalic end of the developing skeleton showing that the notochord ex¬ tends cranially as high as the basisphenoid. Note that above the atlas the rostral and caudal parts of the noto¬ chord become surrounded by the parachordal cartilage, while its middle portion lies between the parachordal cartilage and the wall of the pharynx. (From Gaupp.)

4-9). Two centers appear, one on each side of the notochord near its entrance into the con¬ densed mesoderm of the occipital blastema. Chondrification gradually spreads from these centers—medially around the noto¬ chord (parachordal cartilages), laterally about the roots of the hypoglossal nerve, and cranialward to unite with the spreading car¬ tilaginous center of the developing basal sphenoid bone (hypophyseal cartilages). This process forms an elongated basal plate of cartilage extending from the foramen magnum caudally to the cranial end of the sphenoid. It continues into the blastema of the ethmoid region, which later also be¬ comes chondrified (trabeculae cranii). Other smaller cartilages lateral to the hypophyseal cartilages unite with the main continuous cartilaginous mass. The ala orbitalis (orbitosphenoid) forms the lesser wing of the sphe¬ noid bone, and the ala temporalis (alisphenoid) forms the greater wing of the sphenoid bone (Fig. 4-10). When the auditory capsules begin to chondrify, they are quite widely separated from the basal plate. By the time the embryo is 20 mm in length the cochlear portion of the auditory or otic cap¬ sule (periotic capsule) is fused to the wid¬ ened basal plate, and the jugular foramen has become separated from the foramen lacerum (Fig. 4-11). From the lateral region

1 24

OSTEOLOGY

trabeculae cranii

Fig. 4-10. Diagram showing the different components that play a role in the formation of the base of the skull or chondrocranium. (From Langman, Williams and Wil¬ kins, 1975.)

of the occipital cartilage a broad thin plate of cartilage (tectum posterius or nuchal plate) extends around the caudal region of the brain in a complete ring (Fig. 4-12), form¬ ing the primitive foramen magnum. The

complete chondrocranium or cartilaginous neurocranium is shown in Figure 4-12. Although the chondrocranium forms only a small part of the future ossified skull, it does give rise to most of the base of the skull. Ossification centers then develop in the car¬ tilage and give rise to all of the occipital bone (except the upper part of its squama), to the petrous and mastoid portions of the temporal bone, to the sphenoid bone (except its medial pterygoid plates and part of the temporal wings), and to the ethmoid bone. Membranous Neurocranium. The mem¬ branous neurocranium consists of those bones of the cranial vault and face which ossify directly in the mesoderm of the mem¬ branous cranium. They comprise the upper part of the squama of the occipital bone (in¬ terparietal), the squamae and tympanic parts of the temporal bones, the parietal bones, the frontal and vomer bones, the medial pterygoid plates of the sphenoid bone, and the bones of the face. Some membranous bones remain as distinct bones throughout life, e.g., parietal and frontal, while others join with bones of the chondrocranium, e.g., the squama of the occipital, squamae of temporals, and medial pterygoid plates.

Crista galli

Nasal capsule Mesethmoid

Optic foramen

Jacobson's cartilage Orbital wing Basal part orbital wing Sella turcica — Alar process -Temporal wing Cochlear part otic capsule

Aqueduct vestibuli Fossa subarcuata

Internal acoustic meatus Basioccipital Canalicular part otic / Endolymphatic sulcus

Mastoid foramen

- Anterior root

Transverse sulcus

Medial root •'// --j— Posterior root

Jugular foramen

Occipital neural arch

jL Jfc——d. Occipital fissure —d— Occipital neural arch

Alar lamina

Squama occipital cartilage Neural arch

Hypoglossal canal

Anterior atlas

Occipital condyle Lateral mass basioccipital

Fig. 4-11.

Cartilaginous skull of 21-mm human embryo. Age of embryo is estimated to be six weeks.

OSSIFICATION AND SKELETAL DEVELOPMENT

1 25

Fig. 4-12. Model of the chondrocranium of a human embryo 8 cm long. Its age might be estimated to be 11 weeks. The developing intramembranous bones are not shown. (From Gaupp.)

Cartilaginous Viscerocranium (Figs. 4-13; 4-14). Each developing branchial arch has a mesodermal core of mesenchyme covered by an ectodermal exterior and an ectoder¬ mal interior. In addition to musculature and blood vessels, the branchial mesoderm de¬ velops a skeletal primordium which subse¬ quently chondrifies (Fig. 4-13,A). The dorsal end of the cartilage of the first branchial arch (Meckel’s cartilage) forms the malleus and also probably the incus of the middle ear, while its intermediate portion forms the anterior malleolar and sphenomandibular ligaments (Fig. 4-13,B). The ventral portion of Meckel’s cartilage largely regresses and becomes surrounded by the mesenchyme of the mandible, which then develops by intra¬ membranous ossification. The cartilage of the second branchial arch is called Reichert’s

cartilage. Its dorsal end, directed toward the developing ear, separates to form the stapes of the middle ear. Continuing ventrally it gives rise to the styloid process of the tempo¬ ral bone (Fig. 4-14), the stylomandibular liga¬ ment, and the lesser horn (and probably the upper part of the body) of the hyoid bone (Fig. 4-13,B). The cartilage of the third bran¬ chial arch gives rise to the greater horn and the lower part of the body of the hyoid bone. The cartilages of the fourth, fifth, and sixth branchial arches do not ossify but develop as the laryngeal cartilages (Fig. 4-13,B). Membranous Viscerocranium. The re¬ maining skeletal derivatives of the branchial arches develop by intramembranous ossifi¬ cation. From the maxillary process of the first branchial arch, intramembranous ossifi¬ cation of mesenchyme results in the forma-

126

OSTEOLOGY

Site of developing inner ear

Meckel's cartilage

Malleus

Anterior ligament of malleus

Reichert's cartilage

Incus Stapes

Spine of sphenoid

Styloid process

Sphenomandibular ligament

Stylohyoid ligament Greater cornu

Former site of Meckel's cartilage

Thyroid cartilage Cricoid cartilage

A.

Body of hyoid bone

First arch cartilage

Second arch

Y//M cartilage

sss

Third arch cartilage

Fourth and sixth arch cartilages

Fig. 4-13.

The developing branchial arch cartilage. A, Schematic lateral view of the head and neck region of a four-week embryo, illustrating the location of the branchial arch cartilages. B, Similar view of a 24-week fetus illustrating the derivations of the branchial arch cartilages. (From Moore, K. L., The Developing Human, W. B. Saun¬ ders Co., 1973.)

tion of the premaxilla, maxilla, and the squama and zygomatic process of the tem¬ poral bone. From the mandibular process of the first branchial arch, the mandible devel¬ ops around the ventral portion of Meckel’s cartilage by intramembranous ossification as described (Fig. 4-14). The other branchial arches do not develop bone by intramem¬ branous ossification.

Optic foramen

Axial Skeleton The axial skeleton consists of the verte¬ bral column, its cranial extension, the skull, and the thoracic cage, comprised of the ster¬ num and ribs, to which the vertebral column is articulated. In contrast, the term appen¬ dicular skeleton relates to the bones of the extremities. This central osseous axis of the

Small wing of sphenoid Great wing of sphenoid

Nasal capsule Sept nasi Maxilla

Vomer

Palatine bone Mandible Styloid process Meckel's cart. Cricoid cart. Thyroid cart.

Handle of malleus

Cochlear window

Canal for hypoglossal nerve

Fig. 4-14. Model of the chondrocranium of a human embryo, 8 cm in length. Viewed from the left side, this is the same model illustrated in Fig. 4-12. Note that certain of the membranous bones of the right side are shown in yellow. (From Gaupp.)

AXIAL SKELETON

1st cervical or All

body, although flexible in its structure, af¬ fords stability and support to the viscera of the head, trunk, and abdomen and allows for the effective locomotor functions of the ap¬ pended extremities.

2nd cervical or Axis

VERTEBRAL COLUMN The vertebral column or backbone (columna vertebralis; spinal column) (Fig. 4-15) is formed by a series of bones called vertebrae. The 33 vertebrae are grouped under the names cervical, thoracic, lumbar, sacral, and coccygeal, according to the re¬ gions they occupy. There are seven in the cervical region, twelve in the thoracic, five in the lumbar, five in the sacral, and four in the coccygeal. The cervical, thoracic, and lumbar verte¬ brae remain distinct throughout life, and are known as true or movable vertebrae. Those of the sacral and coccygeal regions are termed false or fixed vertebrae, because they unite or fuse with one another to form two adult bones: five form the sacrum, and four form the terminal bone or coccyx. Between any two adjacent moveable vertebrae (ex¬ cept between the first and second cervical vertebrae) rests a tough, but elastic, fibrocar¬ tilaginous intervertebral disc.These interver¬ tebral cushions contribute to the stability of the spinal column because they are strongly bound to the vertebrae, yet they allow con¬ siderable movement between the adjoining bones. Furthermore, they allow the spinal column to absorb significant shocks such as those received in jumping from heights or from certain types of exercises and condi¬ tioning procedures. A typical vertebra consists of two essen¬ tial parts: a ventral segment, the body, and a dorsal part, the vertebral arch (arcus vertebralis; neural arch), which encloses the vertebral foramen. Since the bodies of the vertebrae are articulated by the interverte¬ bral discs, they form a strong pillar for the support of the head and trunk, and the verte¬ bral foramina form a longitudinal tube, the vertebral canal, which encloses the spinal cord.

Spinous process

7 1st thoracic

2 3

Transverse process 5 6

7

8 9

10 Intervertebral disc

12

1st lumbar

Intervertebral foramen 4

Sacrum

Coccyx

Vertebral Column as a Whole The average length of the vertebral col¬ umn in the male is about 71 cm. Of this length the cervical part measures 12.5 cm,

127

Fig. 4-15.

Lateral view of the vertebral column. Ob¬ serve the cervical, thoracic, lumbar, and pelvic curva¬ tures.

1 28

OSTEOLOGY

the thoracic about 28 cm, the lumbar 18 cm, and the sacrum and coccyx 12.5 cm. The female column averages about 61 cm in length. curvatures. A lateral view (Fig. 4-15) of the vertebral column presents several curves, which correspond with the different regions of the column and are called cervi¬ cal, thoracic, lumbar, or pelvic. The cervi¬ cal curve, convex ventrally, from the apex of the odontoid process of the axis to the mid¬ dle of the second thoracic vertebra, is the least marked of all the curves. The thoracic curve, concave ventrally, begins at the mid¬ dle of the second and ends at the middle of the twelfth thoracic vertebra. Its most prom¬ inent point dorsally corresponds to the spi¬ nous process of the seventh thoracic verte¬ bra. The lumbar curve is more marked in the female than in the male; it begins at the mid¬ dle of the last thoracic vertebra and ends at I he sacrovertebral angle. It is convex ven¬ trally, the convexity of the more caudal three vertebrae being much greater than that of lh(! more cranial two. The pelvic curve begins at the sacrovertebral articulation, and ends at the point of the coccyx; its concavity is directed caudally and ventrally. The tho¬ racic and pelvic curves are termed primary curves, because they alone are present dur¬ ing fetal life. The cervical and lumbar are compensatory or secondary curves, and are developed after birth, the former when the? child is able to hold up its head (at three or four months) and to sit upright (at nine months), the latter when the child begins to walk (at twelve; to eighteen months). The vertebral column also has a slight lateral cur¬ vature, the convexity of which is directed toward the right side in right-handed people and toward the left side in individuals who are left-handed. Because of the correlated handedness of the lateral curva¬ ture. tt is thought by some to be produced by longcontinued muscular action. Others, however, be¬ lieve this curvature to be produced by the aortic arch and upper part of the descending thoracic aorta, a view that is supported by the fact that in cases where the viscera are transposed and the aorta is on the right sido, the convexity of the curve is directed to the left side. surfaces. I/antra! Surface. Consistent with tin increasing weight-bearing function from above downward, the width of the bodies of the vertebrae increases from the second cervical to the first thoracic, dimin¬ ishes slightly in the next three, then again

progressively increases from the fifth tho¬ racic vertebra as far as the sacrovertebral angle. From this point there is a rapid dimi¬ nution to the apex of the coccyx. Dorsal Surface. The median line of the dorsal surface of the vertebral column is occupied by the spinous processes. In the cervical region (with the exception of the second and seventh vertebrae), these are short and nearly horizontal, with bifid ex¬ tremities. In the upper part of the thoracic region they are directed obliquely down¬ ward; in the mid-thoracic region they are almost vertical; and in the lower thoracic and lumbar regions they are nearly horizon¬ tal. The spinous processes are separated by considerable intervals in the lumbar region and by narrower intervals in the neck, but are closely approximated in the middle of the thoracic region. Occasionally one of these processes deviates a little from the median line, a fact to be remembered in practice, as irregularities of this sort are at¬ tendant also in fractures or dislocations of the vertebral column. Important clinical landmarks are the protruding spinous proc¬ esses of the seventh cervical vertebra, which is called the vertebra prominens, and that of the first thoracic vertebra, which is virtually as prominent. With the upper extremity in the anatomical position, the inferior angle of the scapula lies at the level of the seventh thoracic spinous process, while the superior border of the iliac crest lies at the plane of the spinous process of the fourth lumbar vertebra. Lateral to the spinous processes on both sides are longitudinal vertebral grooves con¬ taining the deep back muscles. In the cervi¬ cal and lumbar regions these grooves are shallow and they are formed by the laminae of the dorsal arches. In the thoracic region the grooves are deep and broad, and they are formed not only by the laminae but by the transverse processes as well. Lateral to the laminae are the superior and inferior articu¬ lar processes, and still more laterally the transverse processes. In the thoracic region, the transverse processes are on a plane con¬ siderably dorsal to that of the transverse processes in the cervical and lumbar regions. In the cervical region, the transverse proc¬ esses are placed ventral to the articular proc¬ esses, lateral to the pedicles, and between the intervertebral foramina. In the thoracic region they are dorsal to the pedicles, inter¬ vertebral foramina, and articular processes.

AXIAL SKELETON

In the lumbar region they are ventral to the articular processes, but dorsal to the inter¬ vertebral foramina. Lateral Surfaces (Fig. 4-15). The lateral surfaces are separated from the dorsal sur¬ face by the articular processes in the cervi¬ cal and lumbar regions, and by the trans¬ verse processes in the thoracic region. The ventrolateral aspect of the vertebral column is formed by the sides of the bodies of the vertebrae, marked in the thoracic region by the facets for articulation with the heads of the ribs. More dorsally the intervertebral foramina are formed by the juxtaposition of the vertebral notches. These foramina are oval in shape, smallest in the cervical and cranial part of the thoracic regions, and gradually increase in size to the last lumbar vertebra. They transmit the spinal nerves and vessels and are situated between the transverse processes in the cervical region, and ventral to them in the thoracic and lum¬ bar regions. vertebral canal. The vertebral canal, which contains the spinal cord, follows the different curves of the column; it is large and triangular in those parts of the column that enjoy the greatest freedom of movement, such as the cervical and lumbar regions; it is small and rounded in the thoracic region, where motion is more limited. General Characteristics of a Vertebra

With the exception of the first and second cervical, the true or movable vertebrae have in common certain characteristics that may be studied in a typical vertebra from the

middle of the thoracic region (Fig. 4-16). Characteristically a mid-thoracic vertebra consists of a body or centrum on its anterior aspect and a vertebral arch on its posterior aspect surrounding the vertebral foramen, within which lies the spinal cord. The verte¬ bral arch is formed by two pedicles, which attach to the vertebral body, and a roof, formed by two laminae between which pro¬ jects the spinous process dorsally. Addition¬ ally, two superior and two inferior interver¬ tebral articular processes stud the pedicles and, dorsolaterally, project the transverse processes which, in the thoracic region, af¬ ford attachments on each side for the ribs, as do the costal fovea on the vertebral body. The body (corpus vertebra; centrum) is the largest part of a vertebra, and is nearly cylin¬ drical in shape. On its cranial and caudal surfaces attach the intervertebral discs. These surfaces are rough in the central areas, but a smooth and slightly elevated rim forms their circumference. The surface com¬ pact bone ventrally presents a few small apertures for the passage of nutrient blood vessels. The dorsal surface, which faces the vertebral canal, has one or more large, irreg¬ ular apertures (foramen vasculare) for the passage of the basivertebral veins (Fig. 4-17). The vertebral arch (arcus vertebralis), which lies posterior to the vertebral body, consists of a pair of pedicles and a pair of laminae which together support seven proc¬ esses: four articular, two transverse, and one spinous. The pedicles (pediculi arci vertebrae) are two short, thick processes that project dor¬ sally, one on either side, from the cranial

Superior costal fovea Pedicle or root of vertebral arch

Transverse process

Vertebral foramen

Transverse costal fovea

Lamina

Superior articular process

Spinous process Fig. 4-16.

129

A typical thoracic vertebra, cranial aspect.

1 30

OSTEOLOGY

Foramen vasculare

Spinous process Spongy inner bone

Compact surface bone

Pedicle

Fig. 4-17.

Sagittal section of a lumbar vertebra showing the foramen vasculare for the passage of the basivertebral

vein.

part of the vertebral body at the junction of its dorsal and lateral surfaces (Fig. 4-16). The pedicles are interposed between the trans¬ verse processes and the body. They are con¬ stricted in the middle, forming the concave superior and inferior vertebral notches which, when combined in two articulated adjacent vertebrae, form the intervertebral foramina. The laminae (laminae arci vertebrae) are two broad plates directed dorsally and me¬ dially from the pedicles (Fig. 4-16). They fuse at the midline to complete the dorsal part of the arch surrounding the vertebral foramen and they provide a base for the spinous process. Their superior borders and the cau¬ dal parts of their ventral surfaces are rough for the attachment of the ligamenta flava. processes. The transverse processes (processus transversi) project laterally on each side from the point where the laminae join the pedicles and between the superior and inferior articular processes (Fig. 4-16). They serve for the attachment of muscles and ligaments. The spinous process (processus spinosus) is directed dorsally from the junction of the laminae, and serves for the attachment of muscles and ligaments (Fig. 4-16). The articular processes (processus articulares), two superior and two inferior, spring from the vertebral arch at the junc¬ tions of the pedicles and laminae. The supe¬ rior processes project cranially, but their ar¬ ticular surfaces are directed dorsally. The inferior processes are projected caudally and their articular surfaces face ventrally. The articular surfaces are coated with hya¬ line cartilage and, meeting with those of ad¬ joining vertebrae, form synovial joints.

structure of a vertebra (Fig. 4-1 7). The body is composed of cancellous or spongy bone, covered by a thin coating of compact bone, whereas the arches and processes have a thick covering of com¬ pact bone. The interior of the body is traversed by one or two large canals for the basivertebral veins, which converge toward a single large, irregular ap¬ erture (foramen vasculare) at the dorsal part of the body. The thin bony lamellae of the cancellous tis¬ sue are more pronounced in lines perpendicular to the upper and lower surfaces and develop in re¬ sponse to greater pressure from this direction. The dorsal vertebral arch and the processes projecting from it have thick coverings of compact tissue.

Cervical Vertebrae

The cervical vertebrae (vertebrae cervicales; Figs. 4-12; 4-13) are the smallest of the true vertebrae, and can readily be distin¬ guished from those of the thoracic or lumbar regions by the presence of a foramen in each transverse process. The first, second, and seventh present exceptional features and will be described separately; the following characteristics are common to the remaining four. The body is small, oval, and broader trans¬ versely than dorsoventrally. The ventral and dorsal surfaces are flat and of equal height; the ventral surface is positioned at a slightly lower level than the dorsal and its inferior border is prolonged downward, overlap¬ ping the subjacent vertebra in the articulated column (Fig. 4-15). The cranial surface of the cervical vertebral body (Fig. 4-18) is concave transversely, and presents a projecting lip on each lateral aspect; the caudal surface is convex from side to side, and presents shal¬ low concavities laterally which receive the corresponding projecting lips of the subja-

AXIAL SKELETON

131

Anterior tubercle of transverse process Foramen transversarium

Transverse process

Posterior tubercle of transverse process

Superior articular process Inferior articular process

process

Fig. 4-18.

A typical cervical vertebra, cranial view.

cent vertebra. The interlocking nature of the adjacent cervical vertebrae increases the sta¬ bility of the intervertebral joints. The pedi¬ cles are attached to the body midway be¬ tween its cranial and caudal surfaces, so that the superior vertebral notch is as deep as the inferior, yet at the same time it is narrower. The laminae are narrow and long, and the superior border is thinner than the inferior. The vertebral foramen is large and triangu¬ lar in shape, rather than round. The spinous process is short and bifid, the two projec¬ tions often being of unequal size (Fig. 4-18). The superior and inferior articular proc¬ esses are fused to form an articular pillar (Fig. 4-19), which is situated on the lateral aspect of the junction of the pedicle and lamina. The articular facets are flat and oval: the superior are directed dorsally, cranially, and slightly medially, while the inferior face ventrally, caudally, and slightly laterally. The transverse processes (Fig. 4-18) are each pierced by a foramen transversarium, which, in the first six vertebrae, transmits the vertebral artery and vein, accompanied by a plexus of sympathetic nerves. Each transverse process consists of a ventral and a

dorsal part. The portion ventral to the fora¬ men is the homologue of the rib, and is therefore named the costal process or costal element (see Fig. 4-8). It arises from the side of the vertebral body and ends as the ante¬ rior tubercle. The dorsal part may be consid¬ ered the “true” transverse process, homolo¬ gous to that seen in a thoracic vertebra. It springs from the vertebral arch dorsal to the foramen and is directed ventrally and later¬ ally, ending in a flattened vertical promi¬ nence, the posterior tubercle. The bar of bone joining the two portions of the trans¬ verse process lateral to the foramen exhibits a deep sulcus on its cranial surface for the passage of the corresponding spinal nerve (Fig. 4-19). The costal element of a cervical vertebra includes not only the portion that springs from the side of the vertebral body, but also the anterior and posterior tubercles and the bar of bone that connects them (Fig. 4-8). The first cervical vertebra (Fig. 4-20) is named the atlas after a Titan in Greek my¬ thology because it supports the globe of the head. Its chief peculiarity is that it has no vertebral body, and this is because during

Superior articular surface Articular pillar

Body Anterior tubercle of transverse process

Spinous process Sulcus for nerve

Fig. 4-19.

Posterior tubercle of transverse process

Side view of a typical cervical vertebra.

1 32 Outline of section of dens

Anterior tubercle

Anter. Arch

Outline of section of trans3 atlantal ligament

Transverse process

Tubercles for transverse ligament

Groove for vertebral artery and first cervical nerve

^tcr^xiW''

Posterior tubercle

Fig. 4-20.

First cervical vertebra, or atlas.

development its centrum fused with that of the second vertebra to form an osseous pivot, the dens (odontoid process) of the axis, which projects superiorly through the atlas and around which the atlas turns. The dens is held in place by the transverse atlantal ligament (see Fig. 4-20). Its other peculiarities are that it has no spinous proc¬ ess, is ring-like, and consists of an anterior and a posterior arch and two lateral masses. The anterior arch forms about one-fifth of the ring; the center of its ventral surface presents the anterior tubercle for attachment of the anterior longitudinal ligament and the longus colli muscles. The dorsal or internal surface of the anterior arch is marked by a smooth, oval or circular facet (fovea dentis) for articulation with the dens of the axis. The cranial border gives attachment to the anterior atlanto-occipital membrane which stretches to the occipital bone; along the caudal border of the arch attaches the ante¬ rior atlantoaxial ligament which connects it with the axis. The posterior arch forms about two-fifths of the circumference of the ring (Fig. 4-20); it ends dorsally in the posterior tubercle, which is the rudiment of a spinous process and gives origin to the two recti capitis posteriores minores. The diminutive size of the spinous process obviates interference with the movements between the atlas and the skull. The cranial surface of the dorsal part of the arch presents a rounded edge for the attachment of the posterior atlantooccipital membrane. Posterior to each lat¬ eral mass, the cranial surface of the posterior arch is marked by a groove (sulcus arteriae vertehralis), which is sometimes converted into a foramen by a delicate bony spicule

growing from the posterior end of the supe¬ rior articular process. It serves for the trans¬ mission of the vertebral artery, which, after ascending through the foramen in the trans¬ verse process, winds around the lateral mass in a dorsal and medial direction. Within the groove is also found the suboccipital (first spinal) nerve. Along the caudal surface of the posterior arch, dorsal to the articular fac¬ ets, are two shallow grooves, the inferior vertebral notches, which contribute to the formation of the intervertebral foramina through which pass the second cervical pair of spinal nerves. The inferior border gives attachment to the posterior atlantoaxial liga¬ ment. The lateral masses are the most bulky and solid parts of the atlas and support the weight of the head. Each has a superior and an inferior articular facet. The superior fac¬ ets are large, oval, and concave, and con¬ verge ventrally. They face cranialward, medialward, and dorsalward, each forming a cup for the corresponding condyle of the occipital bone. At times the superior facets are partially subdivided by indentations that encroach upon their margins. Just inferior to the medial margin of each superior facet is a small tubercle for the attachment of the transverse atlantal ligament, which stretches across the ring of the atlas and divides the vertebral foramen into two unequal parts (Fig. 4-20). The ventral or smaller part re¬ ceives the dens of the axis, the dorsal trans¬ mits the spinal cord and its membranes. This part of the vertebral canal is of considerable size, much greater than is required for the accommodation of the spinal cord, and hence lateral displacement of the atlas may occur as a result of trauma without compres-

133

AXIAL SKELETON

sion of the cord. The inferior articular facets are circular in form, flattened or slightly convex, and directed caudalward and medialward. They articulate with the axis. The transverse processes of the atlas project laterally from the lateral masses, and serve for the attachment of muscles that assist in rotating the head. They are long, their ante¬ rior and posterior tubercles are fused into a single mass, and the foramen transversarium is slanted dorsalward (Fig. 4-20). The second cervical vertebra (Figs. 4-21; 4-22) is named the axis or epistropheus be¬ cause it forms the pivot upon which the first vertebra, carrying the head, rotates. The axis is the strongest and thickest of the cervical vertebrae. Its most distinctive characteristic is the cranial extension of the body into a strong, tooth-like bony process, the dens (odontoid process). The ventral surface of the body is marked by a median ridge for the attachment of the longus colli muscle and is prolonged inferiorly into a lip, which over¬ laps the third vertebra when articulated. The dens (Figs. 4-21; 4-22), which meas¬ ures 12 to 15 mm in length, exhibits a slight constriction or neck where it joins the body. Within a shallow groove on the dorsal sur¬ face of the neck, which frequently extends onto its lateral surfaces, rests the transverse atlantal ligament. On its ventral surface is an oval or nearly circular facet for articulation with the facet on the anterior arch of the

Dens For alar ligaments For trans. ligament of atlas Superior articular surface

Foramen transversarium

Pedicle Inferior articular process Lamina

Spinous process

Fig. 4-21.

Second cervical vertebra or axis, cranial

aspect.

atlas. The apex of the dens is pointed and gives attachment to the apical dental liga¬ ment. Near its junction with the vertebral body, the sides of the dens have rough im¬ pressions for the attachment of the alar liga¬ ments, which connect it to the occipital bone. The internal structure of the dens is more compact than that of the body. The pedicles are broad and strong, espe¬ cially ventrally, where they coalesce with the sides of the vertebral body and the root

Articular facet for anterior arch of atlas

Dens

Superior articular surface Spinous process

Body Transverse process

Fig. 4-22.

Second cervical vertebra, axis or epistropheus, from the side.

1 34

OSTEOLOGY

of the dens. They are covered cranially by the superior articular surfaces. The laminae are thick and strong, and the vertebral fora¬ men is large, but smaller than that of the atlas. The small transverse processes end in a single tubercle, perforated by the foramen transversarium, which is oriented in an ob¬ liquely lateral direction. The superior artic¬ ular surfaces, which are oval, slightly con¬ vex, and directed cranially and laterally, are supported by the body, pedicles, and trans¬ verse processes. They articulate with the in¬ ferior articular facets of the atlas. The infe¬ rior articular surfaces are directed interiorly and ventrally in a manner similar to that of the other cervical vertebrae (Fig. 4-22). The superior vertebral notches are shallow and lie dorsal to the superior articular processes; the inferior lie ventral to the inferior articu¬ lar processes, as in the other cervical verte¬ brae. The spinous process is large, strong, deeply channeled on its caudal surface, and presents a bifid, tuberculated extremity. The seventh cervical vertebra (Fig. 4-23) is distinguished by its characteristic long and prominent spinous process. This spine, along with that of the first thoracic vertebra, protrudes dorsally beyond the upper six cer¬ vical spines in the articulated skeleton, and since it is the most cranial spinous process that is palpable, it is a useful landmark in

Body

Fig. 4-23. above.

Seventh cervical vertebra, viewed from

identifying and counting the other spines. The seventh cervical vertebra is named, therefore, the vertebra prominens. Its spi¬ nous process is thick, resembling that of a thoracic vertebra; it is nearly horizontal in direction, not bifurcated, and terminates in a tubercle to which the caudal end of the ligamentum nuchae is attached. The transverse processes are of considerable size, their dor¬ sal components are large and prominent, their ventral, small and faintly marked. The ventral component is derived from the costal element or process (see Fig. 4-8) and may develop into an anomalous cervical rib. The foramen transversarium may be as large as that in the other cervical vertebrae, but more usually it is smaller on one or both sides; at times it is double and occasionally it is ab¬ sent. On the left side it may give passage to the vertebral artery. More frequently, how¬ ever, the vertebral vein traverses it on both sides. The usual arrangement is for both ar¬ tery and vein to pass ventral to the trans¬ verse process of the seventh cervical verte¬ bra and not through its foramen. Thoracic Vertebrae

The thoracic vertebrae (vertebrae thoracicae; Fig. 4-24) are intermediate in size be¬ tween the cervical and lumbar, providing a gradual transition from the small cervical cranially to the large lumbar vertebrae caudally. This enlargement of successively more caudal vertebrae may be correlated with the increased weight-bearing require¬ ments of these lower spinal column bones. The thoracic vertebrae are distinguished by the presence of costal facets on the sides of their bodies for articulation with the heads of the ribs, and other articular facets on the transverse processes of the upper ten tho¬ racic vertebrae for articulation with the tu¬ bercles of the ribs. The bodies of vertebrae in the mid-tho¬ racic region are heart-shaped, and as broad anteroposteriorly as the transverse diameter. They are flat and slightly thicker dorsally. In fact the ventral length of a thoracic vertebral body measures as much as 2 mm less than its dorsal length, accounting for the thoracic curve of the spinal column (see Fig. 4-15). On the lateral aspect of each thoracic vertebral body are found two costal demifacets, one superior near the root of the pedicle, the

AXIAL SKELETON

Superior articular process

135

Demifacet for head of rib

Facet for articular part of tubercle of rib

Demifacet for head of rib Inferior vertebral notch Inferior articular process

Fig. 4-24.

A typical thoracic vertebra, right lateral view.

other inferior, ventral to the inferior verte¬ bral notch. In life these articular surfaces are covered with cartilage, and when the verte¬ brae are articulated in sequence, each two adjacent demifacets form oval surfaces for the reception of the heads of the ribs. The pedicles (Fig. 4-24) are directed dorsally and slightly cranialward from the transverse processes, and the inferior verte¬ bral notches are large and extend more deeply than in any other region of the verte¬ bral column. The laminae are broad, thick, and imbricated—that is to-say, they overlap those of subjacent vertebrae like tiles on a roof. The vertebral foramen is small and cir¬ cular, and accommodates the narrowed tho¬ racic spinal cord. The spinous processes are long, triangular in coronal section, directed obliquely caudalward, and end in tuberculated extremities. The fifth to the eighth thoracic spines are more oblique and over¬ lapping than those of the upper and lower thoracic vertebrae. The superior articular processes (Fig. 4-24) are thin plates of bone that project su¬ periorly from the junctions of the pedicles and laminae. Their articular facets are prac¬ tically flat, being directed dorsally and a lit¬ tle laterally. The inferior articular processes are fused to a considerable extent with the laminae, and project but slightly beyond the inferior borders of the laminae. Their facets are directed ventrally and a little medially

and interiorly to receive the superior articu¬ lar processes of subjacent vertebrae. The transverse processes arise on each side from the dorsal vertebral arch at the junction of the lamina and the pedicle. These processes are long, thick, and strong and are directed obliquely dorsally and laterally. Each trans¬ verse process ends in a clubbed extremity, on the ventral aspect of which is a small, concave surface for articulation with the tubercle of a rib (Fig. 4-24). The first, ninth, tenth, eleventh, and twelfth thoracic vertebrae present certain peculiarities, and will be considered sepa¬ rately (Fig. 4-25). The first thoracic vertebra has an entire articular facet for the head of the first rib and a demifacet for the cranial half of the head of the second rib, on each side of the vertebral body. Its centrum is broad trans¬ versely like that of a cervical vertebra, which emphasizes the transitional structure of the first thoracic vertebra. The superior articular surfaces are directed cranially and dorsally; the spinous process is thick, long, and almost horizontal. The transverse proc¬ esses are also long, and each contains an ar¬ ticular facet for the tubercles of the first ribs. The superior vertebral notches are deeper than those of the other thoracic vertebrae. The ninth thoracic vertebra, although otherwise the same as other thoracic verte¬ brae, may have no demifacets caudally on its

136

OSTEOLOGY

An entire facet above A demifacet below

A demifacet above

One entire facet

One entire facet No facet on transverse process

Transverse process

One entire facet No facet on transverse process

Inferior articular process turned laterally as in lumbar

Fig. 4-25.

Nontypical thoracic vertebrae.

vertebral body (Fig. 4-25). In some instances, however, two demifacets have been found on each side of the vertebral centrum; when this occurs the tenth vertebral body has demifacets only on its cranial portion. The tenth thoracic vertebra has (except as just mentioned) a single entire articular facet on each side, which also extends partly onto the lateral surface of the pedicle (Fig. 4-25). The eleventh thoracic vertebra has a body that approaches the form and size of the lumbar vertebrae. The articular facets for the heads of the ribs are large and placed chiefly on the pedicles. The pedicles on the

eleventh and twelfth thoracic vertebrae are the thickest and strongest of any in the tho¬ racic portion of the spinal column. The spi¬ nous process is short, and nearly horizontal in direction. The transverse processes are very short, tuberculated at their extremities, but have no costal articular facets, since the eleventh pair of ribs articulates only on the lateral aspect of the pedicles. The twelfth thoracic vertebra (Fig. 4-25) has a number of characteristics in common with the eleventh. It may, however, be dis¬ tinguished from it because (1) its inferior ar¬ ticular surfaces are convex and directed lat-

AXIAL SKELETON

erally, like those of the lumbar vertebrae, (2) in general form of the body, laminae, and spinous process, it resembles the lumbar vertebrae, and (3) each transverse process is subdivided into three elevations, the supe¬ rior, inferior, and lateral tubercles. The su¬ perior and inferior tubercles correspond to the mammillary and accessory processes of the lumbar vertebrae. Less marked but simi¬ lar elevations are identifiable on the trans¬ verse processes of the tenth and eleventh thoracic vertebrae. Lumbar Vertebrae

The lumbar vertebrae (vertebrae lumbales; Figs. 4-26; 4-27) are the largest of the true or moveable vertebrae, a feature that allows them to be distinguished from other verte¬ brae. Additionally, lumbar vertebrae have no articular facets on the sides of their centra as are found in thoracic vertebrae, and they have no foramina in their transverse proc¬ esses as are found in cervical vertebrae. The foramen vasculare for the basivertebral vein is larger than in the other vertebrae. The body of a lumbar vertebra is large, wider transversely than dorsoventrally, and a little thicker ventrally than dorsally (Fig. 4-26). It is flat or slightly concave superiorly and inferiorly. The sides of the centrum are concave, so that a finger can easily encircle the circumference of the vertebral body within its grooved concavity. Strong but short pedicles unite on the cranial part of the body, leaving deep inferior vertebral notches (Fig. 4-26). The laminae are broad, short, and strong. The vertebral foramen is

Fig. 4-26.

137

triangular, larger than in the thoracic, but smaller than in the cervical region. The spi¬ nous process is thick, broad, and somewhat quadrilateral in shape and ends in a rough, uneven border, which is thickest caudally where it is occasionally notched. The supe¬ rior and inferior articular processes are well defined, projecting from the junctions of pedicles and laminae (Fig. 4-27). The facets on the superior processes are concave and face dorsally and medially; those on the in¬ ferior are convex, and are directed ventrally and laterally. The superior facets are wider apart than the inferior; in the articulated col¬ umn the inferior articular processes are embraced by the superior processes of the subjacent vertebra. The transverse proc¬ esses are long, slender, and horizontal in the cranial three lumbar vertebrae, but incline a little dorsally in the caudal two. In the upper three vertebrae the transverse processes arise from the junctions of the pedicles and laminae, but in the lower two they are set farther ventrally and spring from the pedi¬ cles and dorsal parts of the bodies. Situated ventral to the articular processes instead of dorsal as in the thoracic vertebrae, the trans¬ verse processes can be considered homolo¬ gous with the ribs. Two additional tubercles found on lumbar vertebrae bear description. On the posterior borders of the large superior articular proc¬ ess are rounded enlargements called the mammillary processes, and arising from the dorsal part of the bases of the transverse processes are small rough elevations called the accessory processes (Fig. 4-27). The fifth lumbar vertebra (Fig. 4-28) is

A lumbar vertebra, lateral view.

138

OSTEOLOGY

Spinous process Inferior articular process

Transverse process

process Accessory process

Superior articular process

Pedicle

Body

Fig. 4-27.

A lumbar vertebra, craniodorsal aspect viewed from left.

massive in its structure and its body is much deeper ventrally than dorsally, which ac¬ cords with the prominent sacrovertebrcil angle formed at the lumbosacral articula¬ tion. The spinous process is smaller than that of other lumbar vertebrae, but the trans¬ verse processes are bulky, short, and thick

and arise from the body as well as from the pedicles. The inferior articular processes, which attach to the sacrum, are more widely separated in the fifth lumbar vertebra than in other lumbar vertebrae; the distance ap¬ proaches or even exceeds that which sepa¬ rates the superior articular processes.

Spinous process Lamina Superior articular facet Inferior articular process Superior articular process Transverse process

Vertebral foramen

Pedicle

Body

Fig. 4-28.

Fifth lumbar vertebra, cranial aspect.

AXIAL SKELETON

variations. The last lumbar vertebra is subject to certain defects described as bifid and separate neural arches, the latter occurring three times as fre¬ quently as the former. Both defects result from an incomplete union of the bony vertebra and cause weakness in the spinal column: the bifid arch by impairing ligamentous attachments, the separate ^rch through loss of bony anchorage of the column to its base.

Sacral and Coccygeal Vertebrae

At an early period of life the sacral and coccygeal vertebrae consist of nine separate segments which, in the adult, are united to form two bones, five entering into the forma¬ tion of the sacrum, four into that of the coccyx. THE SACRUM (os sacrum) The sacrum is a large, triangular bone, which is situated in the lower part of the ver¬ tebral column and forms the dorsal bony wall of the true pelvis (see Fig. 4-191). The broad, superior end of the bone, considered its base, articulates with the last lumbar ver¬ tebra, while its more narrow apex articu¬

Fig. 4-29.

139

lates interiorly with the coccyx. Inserted like a wedge between the two hip bones, its base projects ventrally and forms the prominent sacrovertebral angle when articulated with the last lumbar vertebra. Its central part is projected dorsally (see Fig. 4-190). It encases the sacral canal within which course the sac¬ ral nerves. The pelvic surface (facies pelvina; Fig. 4-29) is concave, giving increased capacity to the pelvic cavity. Its median part is crossed by four transverse ridges, the positions of which correspond to the original planes of separation between the five segments of the fetal bone (see Fig. 4-44). The four ridges rep¬ resent the intervertebral discs of the im¬ mature sacrum which then ossified and fused. Intervening between the ridges are the bodies of the sacral vertebrae. The body of the first segment is large, and in form re¬ sembles that of a lumbar vertebra. Succeed¬ ing ones diminish in size, are flat and curve with the form of the whole sacrum. Four pairs of rounded pelvic sacral foramina are located at the ends of the transverse ridges. These foramina communicate with the sac¬ ral canal by means of intervertebral foram-

Sacrum, pelvic surface.

1 40

OSTEOLOGY

ina. Through them course the ventral divi¬ sions of the first four sacral nerves along with the lateral sacral arteries and veins. Lateral to the pelvic sacral foramina are the lateral parts of the sacrum, which consist of five separate segments at an early period of life, but blend with the bodies and with each other during maturation. Four broad, shallow grooves which lodge the ventral di¬ visions of the sacral nerves extend laterally from the foramina. These are separated by prominent ridges of bone which give origin to the piriformis muscle. Inserting onto the lateral aspect of the most inferior sacral seg¬ ment is the coccygeus muscle. The dorsal surface (facies dorsalis) (Fig. 4-30) is convex and narrower than the pelvic surface. In its midline is located the median sacral crest. On this elevated ridge are mounted three or four tubercles, the rudi¬ mentary spinous processes of the upper three or four sacral segments (Fig. 4-31). On both sides of the median sacral crest, shal¬

low sacral grooves are formed by the united laminae of the corresponding vertebrae, and give origin to the multifidus. Overlying the multifidus and taking origin in a U-shaped manner around the multifidus is the erector spinae muscle. Some aponeurotic fibers of origin for the latissimus dorsi muscle also arise from the median sacral crest. The lami¬ nae of the fifth sacral vertebra fail to meet in the midline dorsally, leaving an enlarged aperture into the sacral canal, the sacral hia¬ tus (Fig. 4-31). On the lateral aspect of the sacral groove is a linear series of tubercles produced by the fusion of the articular proc¬ esses, which together form the indistinct in¬ termediate crests (Fig. 4-30). The articular processes of the first sacral vertebra are large and oval in shape. Their facets are con¬ cave, face dorsomedially, and articulate with the facets on the inferior processes of the fifth lumbar vertebra. The tubercles that represent the inferior articular processes of the fifth sacral vertebra are prolonged down-

Articular processes for fifth lumbar vertebra

Multifidus

Sacral tuberosity

Erector spinae

Gluteus maximus

Posterior sacral foramina Inferior lateral angle Sacral hiatus

Sacral cornu Apex articulates with coccyx

Fig. 4-30. The sacrum, dorsal aspect. Observe that the origin of the multifidus muscle is surrounded by the U-shaped origin of the erector spinae (sacrospinalis) muscle.

AXIAL SKELETON

141

Articular process Median sacral crest Body

Promontory

Cornu of sacrum Cornu of coccyx

Fig. 4-31.

Lateral aspect of sacrum and coccyx.

ward as rounded processes named the sacral cornua, which are connected to the cornua of the coccyx (Fig. 4-30). Lateral to the inter¬ mediate crest are the four posterior sacral foramina (Fig. 4-30). Smaller in size and less regular in form than the ventral foramina, they transmit the dorsal divisions of the sac¬ ral nerves. Lateral to the dorsal foramina, a series of tubercles represents the transverse processes of the sacral vertebrae and forms the lateral crests of the sacrum (Fig. 4-31). The tubercles of the first and second sacral segments receive the attachment of the hori¬ zontal parts of the posterior sacroiliac liga¬ ments; those of the third vertebra give at¬ tachment to the oblique fasciculi of the dorsal sacroiliac ligaments; and those of the fourth and fifth to the sacrotuberous liga¬ ments. The lateral surface (Fig. 4-31) of the sac¬

rum is broad and irregular cranially, narrow caudally, and formed by the union of ele¬ ments comparable to the costal and trans¬ verse processes seen in other vertebrae (Fig. 4-32). The upper half of this surface presents a large ear-shaped articular facet, the auricu¬ lar surface, which is covered with cartilage in the fresh state for articulation with the ilium. Dorsal to it is a rough surface, the sac¬ ral tuberosity (Fig. 4-31), on which are three deep and uneven impressions for the attach¬ ment of the posterior sacroiliac ligament. The caudal half of the lateral surface is thin and ends in a projection called the inferior lateral angle (Fig. 4-30); medial to this angle is a notch that is converted by the transverse process of the first coccygeal segment into a foramen for transmission of the ventral divi¬ sion of the fifth sacral nerve. The thin caudal half of the lateral surface gives attachment

1 42

OSTEOLOGY

Sacral canal Spinous process Articular process

Fig. 4-32.

Base of sacrum. This superior end of the sacrum articulates with the fifth lumbar vertebra.

to the sacrotuberous and sacrospinous liga¬ ments, to some fibers of the gluteus maximus muscle, and to the coccygeus muscle. The base of the sacrum (basis ossis sacri; Fig. 4-32), which is its cranial surface, is broad and expanded laterally. In its center is the upper surface of the body of the first sac¬ ral vertebra. The ventral border of the body projects into the pelvis as the promontory. The articulation between the body of the first sacral segment and the body of the fifth lumbar vertebra is interposed by an inter¬ vertebral disc. The orifice of the sacral canal lies dorsal to this articulation. As is seen throughout the vertebral column, the sacral canal is completed dorsally by the laminae and spinous process. The superior articular processes on either side are directed dorsomedially, as are the superior articular proc¬ esses of a lumbar vertebra. They are at¬ tached to the body of the first sacral vertebra and to the wings, or alae, by short thick pedi¬ cles. On the cranial surfaces of each pedicle is a vertebral notch that forms the caudal part of the intervertebral foramen between the last lumbar and the first sacral vertebrae. On either side of the body, a large triangular surface called the ala supports the psoas major muscle and the lumbosacral nerve trunk, and receives the attachment of a few fibers of the iliacus muscle. The dorsal quar¬ ter of the ala represents the transverse proc¬ ess, and its ventral three-quarters the costal process of the first sacral segment (Fig. 4-32). The apex (apex ossis sacri) is the caudal extremity of the sacrum and presents an oval facet for articulation with the coccyx. The sacral canal (canaiis sacralis; Figs.

4-26; 4-27), the vertebral canal in the sacrum, is incomplete inferiorly due to the nondevel¬ opment of the laminae and spinous proc¬ esses of the last one or two segments. The resultant widened aperture into the caudal end of the sacral canal, the sacral hiatus (Fig. 4-30), is used by anesthesiologists for the in¬ sertion of a flexible needle to produce cau¬ dal analgesia. The canal lodges the sacral nerves of the lower spinal cord’s cauda equina, and its walls are perforated by the dorsal and ventral sacral foramina through which these nerves pass. structure. The sacrum consists of cancellous bone enveloped by a thin layer of compact bone. In a sagittal section through the center of the sacrum (Fig. 4-33), the bodies appear united at their circum¬ ferences by bone, but in the center are wide intervals which, in the intact body, are filled by the interverte¬ bral discs. This union may be more completely ossi¬ fied between the caudal segments than between the cranial segments in some sacra. articulations. The sacrum articulates with four bones: the last lumbar vertebra cranially, the coccyx caudally, and the hip bone on each side. DIFFERENCES IN THE SACRUM OF THE MALE AND

The wider female pelvic cavity is par¬ tially explained by the fact that the female sacrum is shorter and wider than the male. The cranial half of the sacrum is nearly straight while the caudal half presents a curvature. In women the caudal half forms a greater angle with the cranial half. The fe¬ male sacrum being more oblique and dorsally di¬ rected renders the sacrovertebral angle more promi¬ nent. In the male the curvature of the sacrum is more evenly distributed over the whole length of the bone. variation. The sacrum may consist of the rem¬ nants of six segments, in which case a part of the the female.

AXIAL SKELETON Superior articular process

Sacral canal

Intervertebral foramina

Fig. 4-33.

often exists as a separate bone. The lowest three segments diminish in size, and are usu¬ ally fused with one another. Of these, the last segment is a mere module of bone. The pelvic surface is marked with three transverse grooves, which indicate the junc¬ tions of the different segments. It gives at¬ tachment to the ventral sacrococcygeal liga¬ ment, and to its lateral margins are inserted muscle fibers of the coccygeus and levator ani muscles. Additionally, it is in contact with a part of the rectum. The dorsal surface has a row of tubercles on both sides; these are the rudimentary articular processes. The large first pair of tubercles is called the coc¬ cygeal cornua; it articulates with the cornua of the sacrum, and on each side completes the intervertebral foramen for the transmis¬ sion of the dorsal division of the fifth sacral nerve. On the lateral borders of the coccyx a se¬ ries of small eminences represents the trans¬ verse processes. The uppermost pair is the largest, and on each side the transverse proc-

Median sagittal section of the sacrum.

last lumbar or first coccygeal vertebra is included (sacralization). More occasionally the number is re¬ duced to four. The bodies of .the first and second may fail to unite. Sometimes the uppermost trans¬ verse tubercles are not joined to the rest of the ala on one or both sides, or the sacral canal may be open throughout a considerable part of its length in con¬ sequence of the imperfect development of the lami¬ nae and spinous processes. The sacrum also varies considerably with respect to its degree of curvature.

THE COCCYX (os coccygis) Usually formed of four rudimentary verte¬ brae, the coccyx (Figs. 4-34; 4-35) may consist of three or as many as five segments. This small triangular bone articulates superiorly with the apex of the sacrum, and its inferior tip is the lowest part of the spinal column. Rudimentary bodies and articular and trans¬ verse processes can be identified in the first three segments, but coccygeal vertebrae are destitute of pedicles, laminae, and spinous processes. The first segment is the largest, and, resembling the last sacral vertebra, it

1 43

externus

Fig. 4-35.

Coccyx, dorsal surface.

1 44

OSTEOLOGY

ess often joins the thin lateral edge of the sacrum, thus completing the foramen for the transmission of the ventral division of the fifth sacral nerve. The narrow borders of the coccyx receive the attachments of the sacrotuberous and sacrospinous ligaments later¬ ally, the coccygeus muscle and the ilio¬ coccygeal portion of the levator ani muscle ventrally, and the origin of the gluteus maximus muscle dorsally. The oval facet on the surface of the base articulates with the sac¬ rum. The rounded apex may be bifid, or de¬ flected to one side, and has the tendon of the sphincter ani externus attached to it.

Variations and Anomalies of the Vertebral Column number OF vertebrae. Variation in the total number of vertebrae cranial to the coccyx is less common than variations in the normal number within the different regions. The number of seg¬ ments in the coccyx is the most variable, the sacral next, then the thorax, and finally variation in the number of cervical vertebrae the least common. The number of vertebrae in one region may be increased at the expense of the number in a neighboring re¬ gion however. Variations in the lumbosacral and cervicothoracic region are rather frequent and usually can be traced to anomalies in the development of the costal processes (Fig. 4-8). The costal proc¬ esses of the twelfth thoracic vertebra may be want¬ ing, in which case there will be eleven thoracic and six lumbar vertebrae. Conversely, the costal element of the first lumbar may develop into a rib, resulting in thirteen thoracic and four lumbar vertebrae. The costal element of the last lumbar may unite with the first sacral, a condition known as sacralization of the lumbar vertebra, resulting in four lumbar and six sac¬ ral segments. True sacralization does not take place, however, unless the fifth lumbar enters into the ar¬ ticulation with the ilium. Again, the first sacral seg¬ ment may fail to unite with the other sacrals, result¬ ing in six lumbar and four sacral segments. There may be a secondary sacral promontory. cervical rib. Occasionally a cervical rib condi¬ tion develops in which the costal element of the sev¬ enth cervical is elongated into a separate rib-like structure. In rare instances, such a rib may be long enough to articulate with the sternum. This anomaly may cause interference with blood flow in the sub¬ clavian artery or paralysis in the upper extremity due to pressure on the brachial plexus. asymmetry. One side of a vertebra may develop defectively to a greater or lesser degree. When this occurs on one side of the centrum or body, the re¬ sulting condition is called congenital scoliosis or lat¬ eral curvature. In other situations an overgrowth or failure of the costal process may occur on one side.

especially in the lumbosacral region, or there may exist one-sided defects in the pedicles and laminae. spina bifida. At times laminae fail to unite and form a spinous process. Not uncommonly it involves only one or two vertebrae and causes few symp¬ toms (spina bifida occulta). Depending on the size of the defect, there may be a small fat pad or lipoma in its place, but larger defects may contain a menin¬ gocele or a myelomeningocele produced by fluid and the protrusion of tissues from the spinal canal. The most common site of spina bifida is the lumbar re¬ gion, less common is the cervical region. In some instances the absence of spinous processes may ex¬ tend distally through the entire sacrum, leaving the sacral canal exposed. Other parts of the neural arch may have similar defects. The union of the pedicles with the body may fail on one or both sides; the resulting weakness of the arch may cause displace¬ ment of one vertebra over the other, the condition named spondylolisthesis.

Ossification of the Vertebral Column Each cartilaginous vertebra is ossified from three primary centers (Fig. 4-36), two for the vertebral arch and one for the body. Ossification of the verte¬ bral arches begins in the upper cervical vertebrae during the seventh or eighth week of fetal life, and gradually extends to more caudal vertebrae. The ossific granules first appear at the sites from which the transverse processes eventually project. Ossifica¬ tion spreads dorsally to the spinous process, ven¬ trally into the pedicles, and laterally into the trans¬ verse and articular processes. Ossification of the vertebral bodies begins about the eighth week in the lower thoracic region, and subsequently extends cranially and caudally along the column. The initial ossification center for the body does not give rise to the entire centrum of the adult vertebra, since the dorsolateral portions are ossified by extensions from the vertebral arch. During the first few years of life the body of a vertebra, therefore, shows two lines of union of the neural arch with the centrum. These sites of junction are called neurocentral synchrondroses (Fig. 4-37). In the thoracic region, the facets for the heads of the ribs lie dorsal to the neurocentral synchondroses and are ossified from the centers for the vertebral arch. At birth the vertebra consists of three parts, the body and the two halves of the vertebral arch joined by cartilage. During the first year the halves of the arch unite dorsally, union taking place first in the lumbar region and then extending cranially through the thoracic and cervical regions. About the third year the bodies of the upper cervical vertebrae are joined to the arches on each side, but this union in the caudal lumbar vertebrae is not completed until the sixth year. During the years before puberty these primary ossification centers gradually increase in size, while the cranial and caudal surfaces of the bodies and the ends of the transverse and spinous

AXIAL SKELETON

THREE PRIMARY CENTERS

145

THREE OSSIFICATION CENTERS 1 for anterior arch (end of 1st year) 1 for each lateral mass (7th week) Cartilage

1 for each side of vertebral arch (7th week)

Fig. 4-39. vertebra).

Ossification centers in the atlas (first cervical

Fig. 4-36.

FIVE SECONDARY CENTERS

Fig. 4-37.

1 for upper surface 1 of body I S(1 6th year) 1 for under surface 1 of body 1

Fig. 4-38.

Figs. 4-36 to 4-38. Ossification of a vertebra. Fig. 4-36. The three primary ossification centers are indicated. Fig. 4-37. Three secondary centers, to which are added two other secondary centers on the upper and lower surfaces of the vertebral body (Fig. 4-38).

processes remain cartilaginous. About the sixteenth year (Fig. 4-37), five secondary centers appear, one for the tip of each transverse process, one for the extremity of the spinous process, one for the cranial and one for the caudal surface of the body (Fig. 4-38). The secondary centers fuse with the rest of the bone about the age of twenty-five. The mode of ossification just described occurs in vertebrae of the spinal column from the third through the sixth cervical and the twelve thoracic segments. Exceptions to this ossification pattern, however, occur in the first, second, and seventh cer¬ vical vertebrae, and in the lumbar, sacral, and coc¬ cygeal vertebrae. atlas. The atlas is usually ossified from three centers (Fig. 4-39). Two of these usually appear in the lateral masses during the seventh week of fetal life. At birth, the dorsal portions of bone are sepa¬ rated from one another by a narrow interval filled

with cartilage. Between the third and fourth years the posterior arch becomes united either directly or through the development of a separate ossification center in the cartilage. The anterior arch consists of cartilage at birth; a separate center appears toward the end of the first year after birth and eventually joins the lateral masses between the sixth and eighth years. The lines of this union extend across the ven¬ tral portions of the superior articular facets (Fig. 439). Occasionally there is no separate center for the ventral arch, or it may ossify from two centers, one on each side of the midline. axis or epistropheus. The axis ossifies from five primary and two secondary centers (Fig. 4-40). The body and arch are ossified in the same manner as in the other vertebrae, i.e., one primary center for the body, and two for the vertebral arch. The centers for the arch appear about the seventh or eighth week of fetal life, that for the body about the fourth or fifth month. The dens (being the representation of the body of the atlas) commences ossification during the sixth fetal month from two laterally placed primary centers in its base. These two centers join before birth and form a conical mass of bone which has a cleft superiorly. The interval between the sides of the cleft is filled by a wedge-shaped piece of cartilage, thereby forming the summit of the process. This car¬ tilaginous apex of the dens has a separate secondary ossification center which appears during the second year and joins the main part of the process about the twelfth year. The base of the dens is separated from the vertebral body by a cartilaginous disc, which gradually becomes ossified at its circumference, but remains cartilaginous in its center until advanced age. In this cartilage, rudiments of the caudal epi¬ physeal lamella of the atlas and the cranial epiphys¬ eal lamella of the axis may sometimes be found. Additionally, there is a secondary center for a thin epiphyseal plate on the caudal surface of the body of the bone which ossifies at about the seventeenth year. seventh cervical vertebra. In addition to the ossification centers described for typical cervical and thoracic vertebrae, the ventral or costal part of the transverse processes of the seventh cervical vertebra is sometimes ossified from separate centers which appear about the sixth month of fetal life. These gen¬ erally join the body and dorsal part of the transverse process between the fifth and sixth years. They may continue to grow laterally as cervical ribs.

1 46

OSTEOLOGY

SEVEN OSSIFICATION CENTERS 1 for apex of dens (2nd year) 2 for base of dens (6th month) AT BIRTH

2 for vertebral arch (7th week) 1 for body (4th month) 1 for epiphyseal plate (1 7th year) Fig. 4-40.

Ossification centers in the axis (second cervi¬ cal vertebra).

lumbar vertebrae. Each lumbar vertebra (Fig. 4-41) has two additional ossification centers for the mammillary processes, as well as those described for typical cervical and thoracic vertebrae. Similar to those in the transverse and spinous processes, the mammillary processes ossify at about the seven¬ teenth year. The transverse process of the first lum¬ bar is sometimes developed separately, and may remain permanently apart from the rest of the bone, thus forming a rare peculiarity, a lumbar rib. THE sacrum (Figs, 4-42 to 4-45). The body of each sacral vertebra is ossified from a primary center and two epiphyseal plates, while each vertebral arch becomes ossified from two centers. Cranial and lat¬ eral to the pelvic foramina, six or more additional ossification centers develop, two (one on each side) for each of the upper three or four sacral vertebrae. These represent the costal elements of the sacral segments (Figs. 4-42; 4-43). On the cranial and caudal surfaces of each sacral vertebral body, ossifi¬ cation centers for the epiphyseal plates develop (Fig. 4-44). Further, on each lateral surface two epiphys¬ eal plates are formed (Figs. 4-44; 4-45): one for the auricular surface, and another for the remaining lower part of the thin lateral edge of the bone. About the eighth or ninth week of fetal life, ossifi¬ cation of the central part of the body of the first sac¬ ral vertebra commences; similarly, ossification rap¬ idly follows in the second and third. Ossification does not commence in the bodies of the last two sacral segments until the fifth to eighth month of fetal life. Between the sixth and eighth months ossi¬ fication of the vertebral arches odcurs, and at about the same time the costal centers make their appear¬ ance laterally. The vertebral arches join with the

Fig. 4-42. The sacrum at birth shows ossification not only in the five centra, but also in the costal elements on each side of the upper three or four sacral vertebrae (marked by asterisks).

Fig. 4-43. By 4% years, the ossified lateral sacral proc¬ esses have joined the centra, but the lateral epiphyseal plates and those between the bodies are still cartilagi¬ nous.

Fig. 4-44. By the twenty-fifth year, ossification centers have appeared not only in the intervertebral epiphyseal plates, but in those bordering the lateral margins of the sacrum (marked by asterisks).

Center for neural arch

Center for neural arch

Mammillary process (17th year)

Transverse process (1 7th year)

Spinous process (17th year)

Fig. 4-41. Ossification centers in lumbar vertebrae in¬ clude an additional two secondary centers for the mammillary processes.

Costal element

Costal element

Lateral epiphysis

boclY

Lateral epiphysis

Fig. 4-45. Base of the sacrum in a child of four to five years (viewed from above).

AXIAL SKELETON

bodies in the more caudal vertebrae as early as the second year, whereas this does not occur in the more cranial until the fifth or sixth year. About the sixteenth year the epiphyseal plates for the superior and inferior surfaces of the bodies are formed; and between the eighteenth and twentieth years, those for the lateral surfaces make their appearance. Dur¬ ing early life the bodies of the sacral vertebrae are separated from each other by intervertebral discs, but by about the eighteenth year the last two seg¬ ments become united by bone, and the process of bony union gradually extends cranially. Between the twenty-fifth and thirtieth years of life all the sacral segments are united intervertebrally. the coccyx. The coccyx is ossified from four pri¬ mary centers, one for each segment. These centers make their appearance soon after birth in the first segment and between the fifth and tenth years in the second segment. Ossification of the third segment commences before puberty (between the tenth and fifteenth years), and after puberty in the fourth seg¬ ment (between the fourteenth and twentieth years). As age advances, the segments unite intervertebrally. The union between the first and second segments is frequently delayed until after the age of twenty-five or thirty. At a late period of life, especially in women, the coccyx often fuses with the sacrum.

THE THORAX The skeleton of the thorax or chest (Figs. 4-46 to 4-48) forms an osseocartilaginous cage which protects the principal organs of respiration and circulation. It extends interi¬ orly over the upper part of the abdomen, thereby covering portions of certain abdom¬ inal organs. It is conical in shape, so that its superior or cervical inlet is of lesser diame¬ ter than its inferior abdominal end. In transverse section it appears kidney-shaped because of the projection of the vertebral bodies into the cavity. The thoracic cage is formed by the ribs with their costal carti¬ lages attached anteriorly to the sternum (Fig. 4-46) and posteriorly to the thoracic verte¬ brae of the spinal column (Fig. 4-48). boundaries. The dorsal surface is formed by the twelve thoracic vertebrae and the dorsal parts of the twelve ribs. The ven¬ tral surface is formed by the sternum and costal cartilages. The lateral surfaces are formed by the ribs, separated from each other by the eleven intercostal spaces within which are located the intercostal muscles and membranes. The superior opening of the thoracic cage is broader from side to side than dorsoven-

147

trally. It is formed by the first thoracic verte¬ bra, the cranial margin of the sternum, and the first rib on each side. Its dorsoventral diameter is about 5 cm, and its transverse diameter about 10 cm. The plane of the aper¬ ture slopes caudally from the spinal column toward the sternum, since the upper border of the sternum lies 3 to 5 cm below the upper border of the body of the first thoracic verte¬ bra. Thus, the thoracic inlet faces ventralward as well as cranialward (Figs. 4-46; 4-48). The inferior opening or thoracic outlet is formed dorsally by the twelfth thoracic ver¬ tebra, laterally by the eleventh and twelfth ribs, and ventrally by the cartilages of the tenth, ninth, eighth, and seventh ribs, which slope on each side to form the infrasternal angle at the xiphoid process. This caudal opening, also wider transversely than dorsoventrally, inclines obliquely caudalward and dorsalward. It is closed by the dia¬ phragm, which forms both the floor of the thorax and the roof of the abdomen. The thorax of the female differs from that of the male as follows: (1) its capacity is less; (2) the ster¬ num is shorter; (3) the cranial margin of the sternum is on a level with the caudal part of the body of the third thoracic vertebra, whereas in the male it is on a level with the caudal part of the body of the second; and (4) the upper ribs are more movable, permitting a greater expansion of the cranial part of the thorax.

The Sternum

The sternum (Figs. 4-49 to 4-53) is an elon¬ gated, flat bone, which forms the middle portion of the ventral wall of the thorax. Its cranial end supports the clavicles, and its lateral margins articulate with the cartilages of the first seven pairs of ribs. The adult ster¬ num consists of three parts, the manubrium, the body, and the xiphoid process. In early life, the sternum consists of six segments. The first and sixth remain as separate parts, the manubrium and xiphoid process respec¬ tively, while the intermediate four segments or sternebrae fuse to become the sternal body. The sternum is broad superiorly where the first ribs attach and in the region of the body where the fourth and fifth ribs attach. It narrows at the junction of the ma¬ nubrium with the body, where the second ribs articulate, and once again at its inferior extremity (Fig. 4-49). In its natural position, the sternum is directed inferiorly, the caudal

1 48

OSTEOLOGY

First thoracic vertebra

Manubrium (of sternum)

Body (of sternum)

Xiphoid process (of sternum)

9th rib

Fig 4-46. The ventral aspect of the thoracic cage. Observe that all 12 pairs of ribs articulate with their respective thoracic vertebrae: however, only the first seven pairs attach directly to the sternum. The eighth and ninth ribs attach to the cartilage of the seventh rib on each side, while the tenth, eleventh and twelfth pairs have no anterior articula¬ tion. (From Spalteholz.)

end of the bone being inclined somewhat anteriorly and away from the vertebral col¬ umn. Its average length in the adult is about 17 cm. being rather longer in males than in females. Projected posteriorly onto the ver¬ tebral column, the manubrium lies at the level of the third and fourth thoracic verte¬ brae. Its articulation with the sternal body is level with the intervertebral disc between the fourth and fifth vertebrae. The body of the sternum lies anterior to the fifth to tenth thoracic vertebrae. A line from the xiphoid process projects back to the eleventh tho¬ racic vertebra. The manubrium (manubrium sterni) is quadrangular in shape, broad and thick

cranially. but more narrow caudally at its junction with the body. Its ventral surface is smooth, and on each side affords attachment to the pectoralis major and sternocleidomastoideus muscles (Fig. 4-49). The ridges limiting the attach¬ ments of these muscles are at times quite dis¬ tinct. Its dorsal surface, concave and smooth, affords attachment on each side to the sternohvoid and sternothvroid muscles (Fig. 4-50). ‘ The cranial border of the manubrium is thick and presents at its center the jugular (suprasternal) notch, on each side of which, at the clavicular notch, is an oval articular surface for the sternal end of the clavicle.

AXIAL SKELETON

149

First thoracic vertebra

9th thoracic vertebra

9th rib

Fig. 4-47.

The dorsal aspect of the thoracic cage. Note that each rib articulates with its respective thoracic vertebra, and upon encircling the trunk in an inferolateral direction, articulates anteriorly at a site lower than its vertebral commencement. Thus, any respective intercostal space lies higher dorsally than ventrally. (From Spalteholz.)

The caudal border, oval and rough, is sur¬ faced by a thin layer of cartilage for articula¬ tion with the body. The upper aspect of the lateral borders is marked by a depression for the first costal cartilage. Found caudally is a small facet that forms part of the notch for the reception of the costal cartilage of the second rib. The body (corpus sterni) of the sternum is considerably longer, narrower, and thinner than the manubrium. Its ventral surface is nearly flat and is marked by three transverse ridges which cross the bone opposite the third, fourth, and fifth costal articular de¬ pressions. These ridges define the sites of ossification of the original four sternebrae.

This anterior surface affords attachment on each side to the sternal origin of the pectoralis major, the line of origin of this muscle continuing down from the manubrium. At the junction of the third and fourth sterne¬ brae of the body, a sternal foramen of vary¬ ing size and form is occasionally seen. The slightly concave dorsal or internal surface is also marked by three transverse lines, less distinct, however, than the ventral; from its caudal part, the transversus thoracis muscle takes origin on each side (Fig. 4-50). The cranial border of the sternal body is oval and articulates with the manubrium, the junction of the two forming the sternal angle (angle of Louis). The caudal border is

1 50

OSTEOLOGY

First thoracic vertebra

Facet for clavicle Angle of ribs Sternum

Body of ribs

Twelfth thoracic vertebra

Costal cartilages

9th rib

First lumbar vertebra

Fig. 4-48. The thoracic cage viewed from the right side. Observe that the lateral wall of the thorax is supported by the bodies of the ribs. Note that the ribs initially course in an inferolateral direction from the vertebral column and then inferomedially to achieve the costal cartilages and the sternum. (From Spalteholz.)

narrow, and articulates with the xiphoid process. Each lateral border (Fig. 4-51), at its cranial end. has a small facet which, with a similar facet on the manubrium, forms a cavity for the cartilage of the second rib. Caudal to this are found four angular de¬ pressions which receive the cartilages of the third, fourth, fifth, and sixth ribs. At its cau¬ dal end the sternal body has a small facet, which combines with a corresponding one on the xiphoid process to form a notch for the cartilage of the seventh rib. These articu¬ lar depressions are separated by a series of curved interarticular intervals, which di¬ minish in length caudally, and correspond to the ventral extremities of the intercostal spaces. Most of the costal cartilages extend¬

ing from the true ribs articulate with the sternum at the lines of junction of its primi¬ tive component sternebrae segments. This is frequently seen even more clearly in many lower animals, in which the sternebrae re¬ main distinct longer than in man. The xiphoid process (processus xiphoideus) is the smallest of the three parts of the ster¬ num. It is thin and elongated, cartilaginous in youth, but more or less ossified proximally in the adult. Its ventral surface affords attachment on each side to the ventral costoxiphoid ligament and to a small part of the rectus abdominis muscle. Onto the dor¬ sal surface are attached the dorsal costoxi¬ phoid ligament and some of the fibers of the diaphragm and the transversus thoracis

AXIAL SKELETON

1 51

Sternocleidomastoid Trapezius Clavicular notch Deltoid Sternal angle

Pectoralis minor Biceps brachii and Coracobrachialis

Vertebrosternal or true ribs

Subclavius — Triceps brachii Subscapularis

Costal cartilages

Vertebrocostal ribs (false)

}

Vertebral ribs (false and floating)

angle

Fig. 4-49. The anterior surface of the sternum and ribs. Observe the costal cartilages and their manner of articulation with the sternum. Suprasternally note the jugular notch on the superior border of the manubrium, lateral to which articulate the clavicles. The infrasternal angle is formed by the midline articulation of the costal margins of the two sides. Muscle origins are in red, insertions in blue.

muscles. The lateral borders give attachment to some fibers of the aponeuroses of the ab¬ dominal muscles. The xiphoid process articulates with the sternal body, and at each superior angle presents a facet for part of the cartilage of the seventh rib. The pointed caudal extrem¬ ity gives attachment to the linea alba. The xiphoid process varies much in form; it may be broad and thin, pointed, bifid, perforated, curved, or deflected considerably to one side or the other.

structure. The sternum is composed of highly vascular cancellous bone, covered by a thin, com¬ pact layer which is thickest in the manubrium be¬ tween the articular facets for the clavicles. When necessary, the sternum is utilized by hematologists for sternal puncture, in which a needle of large bore is thrust through the thin subcutaneous cortical bone and a specimen of red marrow aspirated.

ossification. The sternum early appears as two cartilaginous bars, situated one on each side of the median plane. Each of these two sternal plates is connected with the cartilages of the upper nine ribs of its own side. The two bars then fuse along the midline to form the cartilaginous sternum, which is subsequently ossified from six centers: one for the manubrium, four for the body, and one for the xiph¬ oid process (Fig. 4-52). The ossification centers ap¬ pear in the intervals between the articular depres¬ sions for the costal cartilages, in the following order: in the manubrium and first piece of the body during the sixth prenatal month; in the second and third sternebrae of the body during the seventh month of fetal life; in the fourth sternebrae of the body during the first year after birth; and in the xiphoid process between the fifth and eighteenth years. As a rule, ossification commences in the more superior parts of the segments and proceeds caudalward. Occa¬ sionally two additional small episternal centers may develop on each side of the jugular notch. These are probably vestiges of the episternal bone of the monotremes and lizards.

1 52

OSTEOLOGY

Sternohyoid For 1st costal cartilage

however, the bony tissue is usually superficial, and the central portion of the intervening cartilage re¬ mains unossified. articulations. The sternum articulates on each side with the clavicle and first seven costal carti¬ lages.

2nd

The Ribs

Xiphoid process

The ribs (costae) are flattened, narrowed, elastic arches of bone, which form a large part of the thoracic skeleton. There are usu¬ ally twelve pairs. The first seven pairs, called true or vertebrosternal ribs, are connected dorsally with the vertebral column, and ventrally by means of costal cartilages, with the sternum (Figs. 4-46 to 4-49). The remaining five pairs are false ribs and consist of two types: the eighth, ninth, and tenth have their cartilages attached to the cartilage of the rib above (vertebrochondral), while the elev¬ enth and twelfth are free at their ventral ex¬ tremities and termed floating or vertebral ribs, since they do not attach to the sternum.

Fig. 4-50. Dorsal surface of the sternum. Observe the transverse lines of union between the segments of the sternal body. Note also the attachments of the sternohy¬ oid and sternothyroid muscles on the manubrium and the diaphragm and transverse thoracis muscles inferiorly.

If /gSR t illllJL

Articular surface for clavicle Depression for 1 st costal cartilage

Multiple ossification centers within the sternal segments are frequently encountered, the number and position of which vary. Thus, manubrium may develop from two, three, or even six centers. When two are present, they are generally situated one su¬ perior to the other, the cranial being the larger. The second piece seldom has more than one center, while the third, fourth, and fifth pieces are often formed from two laterally placed centers, the irregu¬ lar union of which explains the rare occurrence of a sternal foramen. The imperfect union of the longitu¬ dinally oriented cartilaginous bars may result in a vertical fissure constituting the malformation known as fissura sterni. This condition is seen more fre¬ quently lower in the sternum, but may occur even in the manubrium. If extensive, pulsations of the heart may be readily observed through the skin of the an¬ terior chest wall. Union of the four segments of the sternal body commences at puberty and proceeds cranially from the lower segments (Fig. 4-53). By the age of twenty-five the segments of the sternal body are all united. The xiphoid process may become ossified to the sternal body before the age of thirty, but this occurs more frequently after forty; at times the xiphisternal junction remains ununited in old age. In advanced life the manubrium may occasionally be joined to the body by bone. When this happens.

Manubrium Sternal angle Demifacets for 2nd costal cartilage

Facet for 3rd costal cartilage Body

Facet for 4th costal cartilage

Facet for 5th costal cartilage Facet for 6th costal cartilage Facet for 7th costal cartilage Xiphoid process

Fig. 4-51. Lateral border of the sternum. Observe that the facets for the second costal cartilages lie laterally at the junction of the manubrium and sternal body, while the facets for the seventh cartilages lie laterally at the xiphisternal junction.

AXIAL SKELETON

Fig. 4-52. Ossification centers for the sternum and their times of appearance. Multiple centers are frequently seen in certain of the segments.

The ribs vary somewhat in their shape and direction, the upper ones being less oblique, and curving at a more acute angle than the lower. The obliquity reaches its maximum at the ninth rib, and gradually decreases again from that rib to the twelfth. The ribs are ar¬ ranged in a serial manner below one an¬ other, each being separated from the next by intercostal spaces. The length of each space around the thorax corresponds to that of the adjacent ribs and their cartilages. The breadth of the intercostal spaces is greater ventrally than dorsally and greater between the more superior ribs than between the lower ones. The ribs increase in length from the first to the seventh, then diminish to the twelfth. CHARACTERISTICS OF THE RIBS (FigS. 4-54; 4-55). A rib from the middle of the series may be used to study the common character¬ istics of these bones. Each rib has two ex¬ tremities, a dorsal or vertebral, and a ventral or sternal. The intervening portion is called the body or shaft.

Fig. 4-53. Times when ossified union occurs between the six segments of the sternum.

1 53

The dorsal or vertebral extremity presents for examination a head, neck, and tubercle. The head is marked by two articular facets which are separated by a horizontal interarticular crest (Fig. 4-55). The more inferior of the two facets is usually the larger and articulates onto the centrum of the segmentally corresponding vertebra. The cranial facet is smaller and articulates with the next superior vertebral body. The crest is at¬ tached to the intervertebral disc by the interarticular ligament. The neck (Fig. 4-55) is the flattened portion of the rib which extends lateralward from the head. It is about 2.5 cm long, and is placed ventral to the transverse process of the more caudal of the two vertebrae with which the rib head articulates. Its ventral surface is flat and smooth; its dorsal surface is roughened for the attachment of the costo¬ transverse ligament (of the neck of the rib) and perforated by numerous foramina. Of its two borders the cranial is roughest and pre¬ sents a sharp crest (crista colli costae) for the attachment of the anterior costotransverse ligament. The caudal border is rounded and is continuous laterally with the ridge of the costal groove. The tubercle is an eminence on the posterior surface of the rib at the junction of the neck and body, and consists of an articular and a nonarticular portion (Fig. 4-55). The articular portion, the more caudal and medial of the two, presents a small, oval facet for articulation with the end of the transverse process of the numeri¬ cally corresponding vertebra (the more cau¬ dal of the two vertebrae to which the head is connected). The nonarticular portion is a rough elevation, and affords attachment to the lateral costotransverse ligament (liga¬ ment of the tubercle of the rib). The tubercle is much more prominent in the upper than in the lower ribs. The body or shaft of a rib is thin and flat and presents an external and an internal sur¬ face along with two borders, a superior and an inferior. About six centimeters beyond the tubercle, the external surface is marked by a prominent line which gives attachment to a tendon of the iliocostalis muscle. At this site the shaft of the rib turns ventrally at a point, the angle. The rib is bent in two direc¬ tions, and at the same time twisted on its long axis. If placed upon its inferior border, the portion dorsal to the angle is bent medialward and at the same time tilted

1 54

OSTEOLOGY

Nonarticular part of tubercle Articular part of tubercle

Costal groove

Body

cranialward. Because the rib is twisted, the external surface dorsal to the angle looks caudalward, while ventral to the angle, the external surface faces slightly cranialward. The distance between the angle and the tu¬ bercle becomes progressively greater from the second to the tenth ribs. The external surface between the angle and the tubercle is rounded, rough, and irregular, and serves for the attachment of the longissimus tho¬ racis muscle. The internal surface of the rib shaft is concave and smooth, except for a bony ridge which commences at the head of the rib and is strongly marked as far as the angle, but gradually flattens at the junction of the ventral and middle thirds of the bone. Between this ridge and the inferior border lies the costal groove which contains the in¬ tercostal vessels and nerve. Dorsally, the costal groove lies along the rib’s inferior bor¬ der, but beyond the angle, where the groove is deepest and broadest, it courses along the internal surface. The superior edge of the groove is rounded and serves for the attach¬ ment of the internal intercostal muscle; the inferior edge corresponds to the margin of the rib, and gives attachment to the external intercostal muscle (Fig. 4-54). Within the groove are found orifices of numerous small foramina for nutrient vessels. The superior border is thick and rounded, and is marked by an external and an internal lip, which are more distinct dorsally and also serve for the attachment of the external and internal in¬ tercostal muscles. The ventral or sternal extremity of a rib is flat, and presents a porous, oval depression into which the costal cartilage is received. PECULIAR RIBS

Fig. 4-54. The inferior aspect of a typical central rib from the left side. Note that the principal parts of the bone include the head, neck, tubercle (which possesses an articular eminence and a nonarticular eminence), and the curved body or shaft. The costal groove lodges the intercostal vessels and nerve.

The first, second, tenth, eleventh, and twelfth ribs present certain variations from the common characteristics described above, and require special consideration. The first rib (Fig. 4-56) is the most curved

AXIAL SKELETON

1 55

Superior articular facet Interarticular crest Inferior articular facet Articular part of tubercle Nonarticular part of tubercle

Body

Costal groove

Fig. 4-55. A typical central rib from the left side viewed from behind. Observe that the vertebral extremity at the head end of the rib contains a large inferior facet for the numerically corresponding vertebra and a smaller facet for the adjacent vertebra above. Between them is the interarticular crest which attaches to the intervertebral disc.

and usually the shortest of all the ribs. It is broad and flat, its surfaces face cranially and caudally, and its borders internally and ex¬ ternally. The rounded head is small, and possesses only a single articular facet by which it articulates with the body of the first thoracic vertebra. The neck is narrow and also rounded, while the tubercle, thick and prominent, is placed on the outer border. There is no angle, but at the tubercle the rib is slightly bent, presenting a cranial convex¬ ity. The superior surface of the body is

marked by two shallow grooves, separated from each other by a slight ridge prolonged internally as the scalene tubercle, onto which attaches the scalenus anterior muscle. The ventral groove transmits the subclavian vein; the dorsal groove, the subclavian ar¬ tery and the inferior trunk of the brachial plexus (Fig. 4-56). Beyond the dorsal groove is a rough area for the insertion of the scalenus medius. The caudal surface is smooth, and has no costal groove. The outer border is convex, thick, and rounded, and at

Fig. 4-56.

The right first rib viewed from above. Observe the large tubercle below the rib head and the scalene tubercle accentuating the shaft.

Fig. 4-57. The right second rib viewed from above. Note the small tubercle, the slight angle nearby, and the tuberosity for serratus anterior.

156

OSTEOLOGY

its dorsal part gives origin to the first digitation of the serratus anterior. The inner border is concave, thin, sharp, and marked near its center by the scalene tubercle al¬ ready described. The anterior (sternal) ex¬ tremity is larger and thicker than that of any other rib and gives origin to the subclavius muscle. The second rib (Fig. 4-57) is considerably longer than the first, but has a similar curva¬ ture. The nonarticular portion of the tuber¬ cle is small and the angle, situated close to the tubercle, is slight. The body shaft of the rib is not twisted, so that both ends touch any plane surface upon which it may be laid. The shaft is not flattened horizontally like that of the first rib, but proceeding ventrally from the tubercle, there is a cranial convexity, which is smaller than that seen in the first rib. Near the middle of its outer sur¬ face is the roughened tuberosity of the sec¬ ond rib, on which arises part of the first and the whole of the second digitation of the ser¬ ratus anterior. Extending dorsally from the tuberosity is the insertion of the scalenus posterior. The internal surface is smooth and concave, and on its posterior part there is a short costal groove. The tenth rib (Fig. 4-58) usually has only a single articular facet on its head for articula¬ tion with the body of the tenth thoracic ver¬ tebra. The eleventh and twelfth ribs (Figs. 4-59; 4-60) each have a large single articular facet

on the rib head for articulation with the cen¬ trum of their respective vertebra. These two ribs have no necks or tubercles, and are nar¬ row or pointed at their anterior ends. The eleventh has a slight angle and a shallow costal groove, but the twelfth has neither. It is much shorter than the eleventh, and at times even shorter than the first. Its head is inclined slightly upward. COSTAL CARTILAGES

The costal cartilages (cartilagines costales; Figs. 4-46; 4-49) are bars of hyaline cartilage which prolong the ribs ventrally, and which render the chest wall a more elastic nature in order to accommodate, among other things, the movements of respiration. The first seven pairs are connected with the sternum; the next three each articulate with the lower border of the cartilage of the preceding rib; the last two have pointed anterior extremi¬ ties which end in the musculature of the abdominal wall. They increase in length from the first to the seventh, then gradually decrease to the twelfth. Their breadth di¬ minishes from the first to the last, as do the intercostal spaces between them. The first two are the same breadth throughout their extent, while the third, fourth, and fifth are broader at their lateral attachments to the ribs than at their sternal ends. The sixth, sev¬ enth, and eighth are enlarged where their margins are in contact. The cartilages also

Single articular facet—

Single articular facet —

Single articular facet

Figs 4-58 to 4-60. Peculiar or atypical ribs. Each has but a single facet on its rib head. The eleventh and twelfth have no neck or tubercle, and the twelfth has no angle or costal groove.

AXIAL SKELETON

vary in their orientation; the first three are horizontal, the others angular. Each costal cartilage presents two surfaces, two borders, and two extremities. The ventral surface of the first cartilage gives attachment to the costoclavicular liga¬ ment and the subclavius muscle. The sternal ends of the first six or seven cartilages give origin to the pectoralis major (Fig. 4-49). The lower costal cartilages are covered by, and give partial attachment to, some of the flat muscles of the abdomen. The dorsal surface of the first cartilage gives attachment to the sternothyroid muscle, those of the third to the sixth inclusive to the transversus tho¬ racis, and the last six or seven to the trans¬ versus abdominis and diaphragm. The superior borders are concave while the inferior borders are convex. They afford attachment to the internal intercostal mus¬ cles along with the external intercostal membranes. Generally, the upper aspect of the fifth and sixth cartilages also give origin to some fibers of the pectoralis major. The inferior borders of the sixth, seventh, eighth, and ninth cartilages present heel-like pro¬ jections at their points of greatest convexity. These projections bear smooth oblong facets which articulate with facets on slight projec¬ tions from the superior borders of the sev¬ enth, eighth, ninth, and tenth cartilages, re¬ spectively. extremities. The lateral end of each car¬ tilage is continuous with the osseous tissue of its corresponding rib. -The medial end of the first is continuous with the sternum, while the rounded medial ends of the six succeeding ones are received into shallow concavities on the lateral margins of the ster¬ num (Fig. 4-51). The medial ends of the eighth, ninth, and tenth costal cartilages are more pointed, and each is connected with the cartilage immediately above. Those of the eleventh and twelfth are pointed and free. In old age the costal cartilages are prone to lose some of their elasticity and undergo superficial ossification. structure. The ribs consist of highly vascular cancellous bone enclosed in a thin layer of compact bone.

ossification. Cartilaginous models of the ribs are seen in the eight-week-old fetus. At about this time a primary ossification center develops near the angle of the rib shaft. Generally this is seen first in

157

the sixth and seventh ribs. Three additional epiphys¬ eal centers, one for the head and one each for the articular and nonarticular parts of the tubercle, de¬ velop postnatally. The epiphyses for the head and tubercle make their appearance between the six¬ teenth and twentieth years, and are united to the body about the twenty-fifth year. The first rib has only three ossification centers, a primary center for the shaft and one secondary center for the rib head and only one for the tubercle. The eleventh and twelfth ribs each have only two centers, those for the tubercles being wanting. variations and clinical interest. Cervical ribs derived from the costal process of the seventh

cervical vertebra (Fig. 4-8) are not infrequent (about 1 %) and are important clinically because they may give rise to neural and vascular symptoms. The cer¬ vical rib may be a mere epiphysis articulating only with the transverse process of the vertebra, but more commonly it consists of a defined head, neck, and tubercle, with or without a body. It extends laterally into the posterior triangle of the neck where it may terminate freely or join the first thoracic rib, the first costal cartilage, or even the sternum. It may vary much in shape, size, direction, and mobility. If a cer¬ vical rib reaches far enough ventrally, the roots or trunks of the brachial plexus and the subclavian ar¬ tery and vein cross over it and are apt to be com¬ pressed. Pressure on the artery may obstruct the cir¬ culation while pressure on the nerves, especially the lower trunk of the brachial plexus (eighth cervical and first thoracic), may cause paralysis, pain, and paresthesia. The thorax is frequently altered in shape by cer¬ tain diseases. Rickets causes the ends of the ribs to become enlarged where they join the costal carti¬ lages, giving rise to the so-called "rachitic rosary,” which in mild cases is only found on the internal surface of the thorax. Lateral to these bead-like en¬ largements, the softened ribs are depressed, leaving a groove along each side of the sternum, which in turn is forced outward by the bending of the ribs, thereby increasing the dorsoventral diameter of the chest. The ribs so affected are the second to the eighth. Those below are prevented from being de¬ pressed by the underlying abdominal organs. Since liver and spleen enlargement frequently occurs in rickets, the abdomen becomes distended and the lower ribs may be pushed anteriorly, causing a transverse groove just above the costal arch. This deformity or forward projection of the sternum, often asymmetrical, is known as pigeon breast, and may be taken as evidence of active or old rickets except in cases of primary spinal curvature. An opposite condition known as funnel breast occurs in some rachitic children or adults, and also in others who give no further evidence of having had rickets. The lower part of the sternum is deeply de¬ pressed backward, producing an oval hollow in the lower sternal and upper epigastric regions. This does

1 58

OSTEOLOGY

not appear to produce disturbances in vital func¬ tions. The flattened phthisical chest, sometimes seen in pulmonary tuberculosis, is long and narrow, pre¬ senting a great obliquity of the ribs and projection of the scapulae. Contrastingly, the barrel chest of pul¬ monary emphysema is enlarged in all its diameters, and presents on section an almost circular outline. In severe cases of scoliosis, or lateral curvature of the vertebral column, the thorax becomes much dis¬ torted. Due to rotation of the vertebral bodies, the ribs opposite the convexity of the dorsal curve be¬ come extremely convex behind. This distortion re¬ sults in a bulging of the ribs posteriorly and a flatten¬ ing anteriorly, so that the two ends of the same rib are almost parallel. Coincidentally, the ribs on the opposite side, i.e., on the concavity of the curve, are sunken and depressed behind, and bulging and con¬ vex in front.

THE SKULL

The skull, or bony framework of the head, presents by far the most complex skeletal anatomy of the body. Lodging and protecting the vitally required brain with its equally important vasculature, the human head, as in other vertebrates, contains organs housing the special senses of sight, hearing, balance, taste, and smell, as well as structures in the mouth and nasal cavity related to the spe¬ cialized life-maintaining mechanisms of feeding, respiration, and communication. The fact that food is ingested into the oral cavity, and that this entrance to the digestive tract is located conveniently close to visual, auditory, and olfactory receptors, and to the brain itself, is probably more than coinci¬ dental. The bones of the head may be divided into two types: (1) those of the cranium, which enclose the brain and consist of eight bones, and (2) those of the skeleton of the face, numbering fourteen bones. For the most part the bones are either flat or irregular and, except for the mandible, are joined to each other by immovable articulations called su¬ tures. Prior to describing the characteristics of each separate bone, important features of the anatomy of the skull as a whole will be outlined. The exterior of the skull may be viewed from above (norma verticalis); from the side (norma lateralis); toward the face (norma frontalis); from the back (norma occipitalis); and from below (norma basalis).

Exterior of the Skull

NORMA VERTICALIS

The skull cap or calvaria, viewed from above, varies greatly in different skulls. In some skulls its shape is more or less oval, in others more nearly circular. It is traversed by three sutures: (1) the coronal suture, nearly transverse in direction, between the frontal and parietal bones; (2) the sagittal suture, placed in the midline, between the two parietal bones, and (3) the upper part of the lambdoidal suture, separating the parietals and the occipital. The point of junction of the sagittal and coronal sutures is named the bregma, and the junction of the sagittal and lambdoid sutures is called the lambda. In the adult skull, these two sites indicate the positions of the anterior and posterior fontanelles, or the so-called soft spots in the skull of an infant. On each side of the sagittal suture are the parietal emi¬ nences where the smooth, rounded surface of the parietal bones is maximally convex. Lateral to the sagittal suture and anterior to the lambda may be found, on one or both sides, the parietal foramen, through which courses a small emissary vein. A craniometric term, obelion, is applied to that point on the sagittal suture at the level of the pari¬ etal foramina, while the vertex, near the middle of the sagittal suture, is the topmost point of the skull. Anteriorly, the frontal eminences form the two prominences of the forehead. Below these is a smooth promi¬ nence above the root of the nose, the glabella, on each side of which are the two super¬ ciliary arches. Immediately above the gla¬ bella, in a small percentage of skulls, a frontal suture persists and extends along the midline to the bregma. NORMA LATERALIS (Fig. 4-61)

Both cranial and facial bones of the skull can be inspected from the lateral aspect. Vis¬ ible are the frontal, parietal, occipital, tem¬ poral, and zygomatic bones, as well as the great wing of the sphenoid, the orbital lam¬ ina of the ethmoid, and the lacrimal, nasal, and maxillary bones. The mandible also can be seen, but its description here is omitted. The following sutures can be observed from a lateral view: temporozygomatic, frontozy-

AXIAL SKELETON

Fig. 4-61.

1 59

Side view of the skull. (Norma lateralis.)

gomatic, squamosal, zygomaticomaxillary, and surrounding the great wing of the sphe¬ noid—the sphenofrontal, sphenoparietal, and sphenosquamosal sutures. Addition¬ ally, several sutures on the medial aspect of the orbit between the lacrimal, ethmoid, maxillary, and frontal bones can be seen, as well as those sutures that extend laterally from above. Near the posterior base of the skull is the occipitomastoid suture joining the occipital and temporal bones. The sphenoparietal suture varies in length in dif¬ ferent skulls, and is absent when the frontal bone articulates with the temporal squama. The point corresponding with the posterior end of the sphenoparietal suture is named the pterion. It is situated about 4 cm above the zygomatic arch and about 3 cm posterior to the frontozygomatic suture. The pterion overlies the anterior division of the middle meningeal artery. The squamosal suture arches posteriorly from the pterion and lies between the tem¬

poral squama and the inferior border of the parietal. This suture is continuous posteri¬ orly with the short, nearly horizontal parie¬ tomastoid suture, which unites the mastoid process of the temporal with the parietal bone at its mastoid angle. Extending across the cranium are the cor¬ onal and lambdoidal sutures, of which the latter is continuous with the occipitomastoid suture. The mastoid foramen, which trans¬ mits an emissary vein, lies in or near the oc¬ cipitomastoid suture. The meeting point of the parietomastoid, occipitomastoid, and lambdoidal sutures is known as the asterion. Arching across the side of the cranium are the temporal lines (Fig. 4-61), which mark the superior limit of the temporal fossa. The temporal fossa (fossa temporalis) is a region on the lateral aspect of the skull occu¬ pied by the temporalis muscle which arises from the cranium as far superiorly as the temporal lines (Fig. 4-61). Extending from the zygomatic process of the frontal bone

1 60

OSTEOLOGY

anteriorly, these two lines cross the frontal and parietal bones. Behind, they then curve anteriorly to become continuous with the supramastoid crest and the posterior root of the zygomatic arch. The craniometric term stephanion refers to the point where the su¬ perior temporal line cuts the coronal suture. The inferior temporal line lies somewhat below the superior. The temporal fossa is bounded anteriorly by the frontal and zygo¬ matic bones. Inferiorly, it is separated from the infratemporal fossa by the infratemporal crest on the great wing of the sphenoid (Fig. 4-62), and by a ridge, continuous with this crest, which is carried posteriorly across the temporal squama to the anterior root of the zygomatic process. Laterally the temporal fossa is limited by the zygomatic arch. The fossa communicates with the orbital cavity through the inferior orbital fissure and, in¬ feriorly, the temporal fossa is directly con¬ tinuous with the infratemporal fossa. The floor of the fossa is deeply concave anteri¬ orly and convex behind, and is formed by the zygomatic, frontal, parietal, sphenoid, and temporal bones. The temporal fossa contains the temporalis muscle and its ves¬

sels and nerves, together with the zygo¬ maticotemporal nerve. The muscle descends to its insertion on the coronoid process of the mandible medial to the zygomatic arch. The zygomatic arch is formed by the zygo¬ matic process of the temporal bone and the temporal process of the zygomatic bone, the two being united by an oblique suture. The arch can easily be felt, extending anteriorly from the external auditory meatus. At its junctions with the squamous part of the tem¬ poral bone, the zygomatic process broadens into two bony ridges or roots. An anterior root is directed medially to the mandibular fossa, where it expands to form the articular tubercle. The posterior root expands posteri¬ orly above the external acoustic meatus and is continuous with the supramastoid crest. The superior border of the zygomatic arch gives attachment to the temporal fascia, while the inferior border and medial surface give origin to the masseter muscle. Between the posterior root of the zygo¬ matic arch and the mastoid process is the el¬ liptical orifice of the external acoustic mea¬ tus (Fig. 4-62). The opening is principally bounded by the tympanic part of the tempo-

External acoustic meatus Tympanic part of temporal Styloid process inferior orbital fissure Infratemporal crest Pterygomaxillary fissure

Mandibular fossa Zygomatic process (cut) Lateral pterygoid plate

Pterygoid hamulus Fig. 4-62.

Left infratemporal fossa as observed from the left lateral aspect with the zygoma cut.

AXIAL SKELETON

ral bone, although its superior margin is formed by the squamous part of the tempo¬ ral bone. The cartilaginous segment of the external auditory canal is fixed to this roughened outer bony margin. The small tri¬ angular area between the posterior root of the zygomatic arch and the posterosuperior part of the orifice is termed the suprameatal triangle, on the anterior border of which is sometimes seen a small spinous process, the suprameatal spine. Deep to this triangular area lies the mastoid antrum of the middle ear. Between the tympanic part of the tem¬ poral bone and the articular tubercle lies the mandibular fossa, which is divided into two parts by the petrotympanic fissure. The an¬ terior and larger part of the fossa receives the condyle of the mandible, while the pos¬ terior part is nonarticular and sometimes lodges a portion of the parotid gland. The delicate and pointed styloid process extends downward and forward for a distance of 2.5 to 3.0 cm from the undersurface of the tem¬ poral bone inferior to the external acoustic meatus. It gives attachment to the stylo¬ glossus, stylohyoid, and stylopharyngeus muscles and to the stylohyoid and styloman¬ dibular ligaments. Posterior to the external acoustic meatus is the mastoid process, to the outer surface of which are inserted the sternocleidomastoideus, splenius capitis, and longissimus capitis. The posterior belly of the digastric muscle arises from the mas¬ toid notch, which grooves the medial aspect of the process. The infratemporal fossa (fossa infratemporalis; Fig. 4-62) is an irregularly shaped cavity situated below and medial to the zy¬ gomatic arch. It is bounded in front by the infratemporal surface of the maxilla; behind by the articular tubercle of the temporal bone and the spine of the sphenoid bone; above by the great wing of the sphenoid and by the undersurface of the temporal squama; below by the alveolar border of the maxilla; medially by the lateral pterygoid plate of the sphenoid; and laterally by the zygomatic arch. It contains part of the temporalis and the medial and lateral pterygoid muscles, the maxillary vessels, the mandibular and max¬ illary nerves, and the pterygoid plexus of veins. The foramen ovale and foramen spinosum open into it from above, while the alveolar canals open on its anterior wall. At its superior and medial part are two fissures which meet at right angles, the horizontal

1 61

limb being named the inferior orbital fis¬ sure, and the vertical limb the pterygomaxillary fissure. The inferior orbital fissure (fissura orbitalis inferior) opens into the posterolat¬ eral part of the orbit (Figs. 4-61, 4-62). It is bounded above by the inferior border of the orbital surface of the great wing of the sphe¬ noid; below by the lateral border of the or¬ bital surface of the maxilla and the orbital process of the palatine bone; laterally by a small part of the zygomatic bone; and medi¬ ally it joins the ptergyomaxillary fissure at right angles. Through the inferior orbital fis¬ sure, the orbit communicates with the tem¬ poral, infratemporal, and pterygopalatine fossae. It transmits the maxillary nerve, its zygomatic branch, ascending branches from the pterygopalatine ganglion, the infraor¬ bital vessels, and the clinically important vein that connects the inferior ophthalmic vein with the pterygoid venous plexus. The pterygomaxillary fissure is oriented vertically and descends at right angles from the medial end of the inferior orbital fissure (Fig. 4-61). It is a triangular interval, formed by the divergence of the maxilla from the pterygoid process of the sphenoid. It con¬ nects the infratemporal fossa with the ptery¬ gopalatine fossa, and transmits the terminal part of the maxillary artery and veins. The pterygopalatine fossa (fossa pterygopalatina; Fig. 4-63) is a small cone-shaped or pyramidal region at the junction of the infe¬ rior orbital and pterygomaxillary fissures. It lies just beneath the apex of the orbit and is bounded above by the inferior surface of the body of the sphenoid bone and the orbital process of the palatine bone; in front by the infratemporal surface of the maxilla; behind by the base of the pterygoid process and the lower part of the anterior surface of the sphenoid bone; and medially by the perpen¬ dicular plate of the palatine bone. This fossa communicates with the orbit through the in¬ ferior orbital fissure, with the nasal cavity by the sphenopalatine foramen, and with the infratemporal fossa by way of the pterygo¬ maxillary fissure. Additionally, the pterygo¬ palatine fossa communicates with the cra¬ nial cavity by way of the pterygoid canal, which extends to the foramen lacerum, and with the roof of the oral cavity through the pterygopalatine canal. Of these five commu¬ nicating foramina, the inferior orbital fis¬ sure opens anteriorly into the fossa while the

162

OSTEOLOGY

Frontal bone Great wing of sphenoidal bone Superior orbital fissure Small wing of sphenoidal bone

Zygomatic bone Foramen rotundum Inferior orbital fissure

Sphenoidal air sinus

Maxillary air sinus

Bristle in pterygoid canal

Bristle in infraorbital canal

Pterygopalatine fossa Maxillary air sinus

Fig. 4-63.

Bristle in pterygopalatine canal

The pterygopalatine fossa and the lateral wall of the right orbit.

foramen rotundum and pterygoid canal are posterior. On the medial wall is the spheno¬ palatine foramen and below is found the pterygopalatine canal. The fossa contains the maxillary nerve, the pterygopalatine ganglion, and the terminal part of the maxil¬ lary artery. NORMA FRONTALIS (Fig. 4-64)

The facial aspect of the skull is outlined by the frontal bone superiorly, below which are the nasal bones, maxilla, and body of the mandible medially, and the zygomatic bones and rami of the mandible laterally. The fron¬ tal eminences stand out more or less promi¬ nently above the superciliary arches, which merge into one another at the glabella. Below the glabella is the frontonasal suture, the midpoint of which is termed the nasion. Lateral to the frontonasal suture and at the medial margin of the orbit, the frontal bone articulates with the frontal process of the maxilla and with the lacrimal. Below the superciliary arches, the superior part of the orbital margin is thin and prominent in its lateral two-thirds, but rounded and more massive in its medial third. At the junction of these two portions is the supraorbital fo¬ ramen or notch for the supraorbital nerve and vessels. The supraorbital margin ends laterally in the zygomatic process of the frontal bone (Fig. 4-65), which articulates with the zygomatic bone. Below the fronto¬

nasal suture is the bridge of the nose, formed by the two nasal bones supported posteri¬ orly in the midline by the perpendicular plate of the ethmoid, and laterally by the frontal processes of the maxillae, which form the lower and medial part of the mar¬ gin of each orbit. The bony anterior nasal aperture is bounded by the sharp margins of the nasal and maxillary bones. The lateral and alar cartilages of the nose are attached to the lateral nasal margins, while the infe¬ rior margins are thicker and end in the ante¬ rior nasal spine medially. The bony septum that separates the nasal cavity in the midline shows a large triangular deficiency in the bone anteriorly. This is filled by septal carti¬ lage in the intact body. On the lateral wall of each nasal cavity the anterior part of the in¬ ferior nasal concha is visible. Below and on each side of the pear-shaped aperture of the nose are the maxillae, which articulate in the midline and form much of the anterior bony substructure of the face. The anterior surface of the maxilla is perfo¬ rated near the inferior margin of the orbit by the infraorbital foramen for the passage of the infraorbital nerve and vessels. Interiorly, the alveolar process of each maxilla con¬ tains the osseous sockets for the upper teeth. The vertical ridges formed by the roots of the teeth are clearly visible, and that of the canine tooth, the canine eminence, is the most prominent. The zygomatic bone forms the promi-

AXIAL SKELETON

163

Frontal eminence

Glabella Superciliary arch

WkijF

Supraorbital foramen

Superior orbital fissure Sr-Lamina orbitalis of ethmoid —Lacrimal Inferior orbital fissure Zygomaticofacial foramen nfraorbital foramen Nasal cavity Inferior nasal concha

Mental foramen

Fiq. 4-64.

The skull from the front. (Norma frontalis.)

nence of the cheek, the inferior and lateral portion of the orbital cavity, and the anterior part of the zygomatic arch. On the face it articulates medially with the maxilla, supe¬ riorly with the zygomatic process of the frontal bone, and laterally with the zygo¬ matic process of the temporal bone. The zy¬ gomatic bone is perforated by the zygo¬ maticofacial foramen for the passage of the zygomaticofacial nerve. The maxillae rest on the mandible, or lower jaw, which extends from a character¬ istically human bony landmark, the chin or mental protuberance on the mandibular body, to the mandibular fossae laterally, where the mandibular rami articulate with the temporal bones. Lateral to the mental protuberance are the mental tubercles. The superior or alveolar border contains the

sockets for the lower teeth. Below the incisor teeth is the incisive fossa, and inferior to the second premolar tooth is the mental fora¬ men, which transmits the mental nerve and vessels. An oblique line courses posteriorly from the mental tubercle and becomes con¬ tinuous with the anterior border of the ramus. The posterior border of the ramus is directed downward and forward from the condyle to the angle. The latter frequently is more or less everted. THE ORBITS (orbitae; Fig. 4-65) The orbits are conical cavities which con¬ tain the eyeballs and their associated struc¬ tures and are so placed that their medial walls are approximately parallel with each other and with the midline, but their lateral

164 Small wng cA

J bone

Supraorbital foramen

Superior orbital fissure

Orbital plate of frontal bone Great wing of sphenoid bone

Optic foramen Zygomatic process of frontal bone J

Lamina papyracea of ethmoid bone

Orbital tubercle of r/gc#natc bone

i Lacrimal bone Nasal bone Orbital surface of

zygomatic bone

Frontal process of maxilla Zygomaticofacial foramen

Lacrimal fossa

Inferior orbital fissure

\

Infraorbital groove

C Orbital process of palatine bone

Orbital surface of maxilla Infraorbital foramen Fig 4-65 The anterior aspect of the right orbital cavity. Note the superior orbital fissure, inferior orbital fissure, and optic foramen within the orbital cavity, and the supraorbital, infraorbital, and zygomaticofacial foramina opening onto the surface.

walls are widely divergent. Thus, the longi¬ tudinal axes of the two orbits diverge widely anteriorly, but if prolonged posteriorly, they would cross dorsal to the body of the sphe¬ noid bone near the center of the base of the skull. It is customary' to describe the orbits in terms of a roof, a floor, a medial wall, a lat¬ eral wall, a base, and an apex. The roof of the orbit (see Fig. 4-191), which separates the orbital contents from the overlying frontal lobes of the brain, is formed by the thin orbital plate of the frontal bone and the lesser wing of the sphenoid bone. The orbital surface of this plate presents medi¬ ally the trochlear fovea for the attachment of the cartilaginous pulley of the obliquus su¬ perior oculi laterally. Anterolaterally is lo¬ cated the deep lacrimal fossa for the orbital part of the lacrimal gland. The posterior end of the orbital roof is marked by the spheno¬ frontal suture. The floor of the orbit (Fig. 4-66) is formed chiefly by the orbital surface of the maxilla.

but also by the orbital process of the zygo¬ matic bone, and to a small extent by the or¬ bital process of the palatine. Near the orbital margin medially is the lacrimal sulcus for the nasolacrimal canal, and just lateral to this a small depression for the origin of the obliquus inferior oculi. Located laterally is the maxillozygomatic suture, and at its pos¬ terior part is the suture between the maxilla and the orbital process of the palatine (palatomaxillary suture). Near the middle of the floor is the infraorbital groove, which leads anteriorly into the infraorbital canal and transmits the infraorbital nerve and ves¬ sels to the anterior aspect of the face. The medial wall (Fig. 4-67) is delicate and oriented nearly vertically. It is formed by the frontal process of the maxilla, the lacrimal bone, the lamina orbitalis of the ethmoid, and a small part of the body of the sphenoid. Anteriorly, the lacrimal fossa is a hollow region between the lacrimal bone and the frontal process of the maxilla. It lodges the

AXIAL SKELETON

165

Nasal bone

Lacrimal sulcus Maxilla Zygomatic bone Frontal sinus Infraorbital groove

Ethmoidal air cells Inferior orbital fissure Palatine bone Zygoma Sphenoid bone

Foramen rotundum Sphenoidal sinus Foramen ovale

Foramen lacerum

Foramen spinosum

Temporal bone

Fig. 4-66. Horizontal section through the right orbit demonstrating the bony floor of the orbital cavity from above. Observe the infraorbital groove and the longitudinally oriented suture between the maxilla and the zygomatic bone.

lacrimal sac and is limited behind by the posterior lacrimal crest, from which the lac¬ rimal part of the orbicularis oculi arises. The medial wall contains three vertical sutures: the Iacrimomaxillary, lacrimoethmoidal, and sphenoethmoidal. At the junction of the medial wall and the roof are the frontomaxillary, frontolacrimal, frontoethmoidal, and sphenofrontal sutures. The point of junction of the anterior border of the lacri¬ mal with the frontal is named the dacryon. In the frontoethmoidal suture are the ante¬ rior and posterior ethmoidal foramina, the former transmitting the anterior ethmoidal vessels and nerve, and the latter the poste¬ rior ethmoidal vessels and nerve. The nerves are branches of the nasociliary while the vessels are branches of the ophthalmic. The lateral wall of the orbit (Fig. 4-63) is directed forward and medially and is formed by the orbital process of the zygo¬ matic bone and the orbital surface of the great wing of the sphenoid. These two bones

articulate at the sphenozygomatic suture, which terminates at the anterior end of the inferior orbital fissure. Between the roof and the lateral wall, near the apex of the orbit, is the superior orbital fissure. Communicating with the cranial cavity, this fissure transmits the oculomotor, trochlear, ophthalmic divi¬ sion of the trigeminal, and abducent nerves to the orbit. Also entering the orbit through the superior orbital fissure are sympathetic nerve filaments from the cavernous plexus as well as the orbital branches of the middle meningeal artery. Leaving through the fis¬ sure for the cranial cavity are the superior ophthalmic vein and the recurrent branch from the lacrimal artery to the dura mater. The lateral wall and the orbital floor are sep¬ arated posteriorly by the inferior orbital fis¬ sure. The base of the orbit is its anterior end; it is formed by the orbital margin, and has al¬ ready been described. The apex is situated at the back of the orbit and corresponds to

166

OSTEOLOGY

Frontal bone Orbital plate of frontal bone Anterior ethmoidal foramen Orbital lamina of ethmoid bone Posterior ethmoid foramen Optic foramen Orbital process of palatine bone Nasal bone

Sella turcica Foramen rotundum

Dacryon Lacrimal bone Posterior lacrimal crest

Probe in pterygoid canal

Lacrimal fossa

Sphenopalatine foramen Uncinate process of ethmoid bone Openings of maxillary air sinus

Pterygopalatine canal Inferior nasal concha Palatine bone Lateral pterygoid lamina

Maxillary sinus Pyramidal process of palatine bone Maxilla

Fig. 4-67. Medial wall of left orbit. In this dissection the lateral wall of the left orbit has been removed in order to expose the medial wall, and the left maxillary sinus has been opened from the lateral aspect. Note that the medial wall of the orbit is formed by the maxilla, lacrimal, ethmoid, and, most posteriorly, the sphenoid bone. The ethmoid bone is shown in red, the palatine bone in blue.

the optic foramen, a short, cylindrical canal, which transmits the optic nerve and oph¬ thalmic artery. Ten openings communicate with each orbit: the optic foramen, superior and infe¬ rior orbital fissures, supraorbital foramen, infraorbital canal, anterior and posterior ethmoidal foramina, zygomaticofacial and zygomaticotemporal foramina, and the canal for the nasolacrimal duct.

NORMA OCCIPITALIS

When viewed from behind the cranium presents a circular, dome-like shape, except at its base, which is flattened. In the midline is observed the posterior continuation of the sagittal suture, which extends between the parietal bones to the deeply serrated lambdoidal suture. The latter lies between the parietal bones and the occipital and contin¬

ues laterally into the parietomastoid and oc¬ cipitomastoid sutures. Frequently, one or more sutural bones, such as an interparietal (inca) bone, may be interposed between the parietal and occipital bones. Near the mid¬ dle of the occipital squama is the external occipital protuberance, and extending later¬ ally from it on each side is the superior nu¬ chal line. Also seen is the more faintly marked highest nuchal line, which extends laterally about 1 cm above the superior. If the skull is slightly elevated, the inferior nuchal line comes into view coursing later¬ ally below the superior line. The inion is a craniometric term applying to the midline point on the external occipital protuberance. Descending from the inion to the foramen magnum is a bony ridge, the external occipi¬ tal crest, which affords attachment to the ligamentum nuchae. Laterally and somewhat anteriorly on each side can be seen the mas¬ toid process of the temporal bone, and near

AXIAL SKELETON

the occipitomastoid suture is the mastoid foramen through which passes the mastoid emissary vein. NORMA BASALIS (Figs. 4-68; 4-69)

With the mandible removed, the inferior surface of the base of the skull is formed by the palatine processes of the maxillae, the horizontal plates of the palatine bones, the vomer, the pterygoid processes, the inferior surfaces of the great wings, the spinous proc¬ esses and part of the body of the sphenoid, the inferior surfaces of the squamae and pet¬ rous portions of the temporals, and the infe¬ rior surface of the occipital bone. The anterior part of the normal basalis projects downward beyond the level of the rest of the basal surface and is formed prin¬ cipally by the hard palate. The bony palate is bounded anteriorly and laterally by the alveolar arch containing the sixteen teeth of the maxillae. Just behind the incisor teeth is found the incisive fossa. Within the fossa are two lateral incisive foramina (foramina of Stenson) which continue as the incisive canals and transmit the terminal branches of the greater palatine vessels and the nasopal¬ atine nerves from the nasal cavity. Occasion¬ ally two other median incisive foramina (fo¬ ramina of Scarpa) are found. When present they transmit the nasopalatine nerves. The vault of the hard palate is marked by depres¬ sions for the palatine glands. It is traversed by a cruciate suture formed by the junction of the two palatine processes of the maxillae and the two horizontal plates of the palatine bones of which it is composed. At either posterior angle of the hard palate is the greater palatine foramen, for the transmis¬ sion of the greater palatine vessels and nerve, which descend in the greater palatine canal from the pterygopalatine fossa. Poste¬ rior to the foramen is the pyramidal process of the palatine bone, perforated by one or more lesser palatine foramina through which course the lesser palatine vessels and nerve to the soft palate. At this site also is observed a transverse ridge for the attach¬ ment of the tendinous expansion of the ten¬ sor veli palatini muscle. Projecting back¬ ward from the center of the posterior border of the hard palate is the posterior nasal spine, on which attaches the musculus uvulae. The middle part of the norma basalis

167

commences just behind the hard palate and extends to the level of the anterior border of the foramen magnum. Just behind the hard palate are the choanae or posterior openings into the nasal cavities. They are separated by the vomer, and each is bounded above by the body of the sphenoid, below by the hori¬ zontal part of the palatine bone, and later¬ ally by the medial pterygoid plate of the sphenoid. At the superior border of the vomer, the expanded alae of this bone re¬ ceive between them the rostrum of the sphe¬ noid. The medial pterygoid plate is long and narrow; on the lateral side of its base is the scaphoid fossa, for the origin of the tensor veli palatini muscle, and at its lower extrem¬ ity the pterygoid hamulus, around which the tendon of this muscle turns. The lateral pter¬ ygoid plate is broad; its lateral surface forms the medial boundary of the infratemporal fossa, and affords attachment to the pterygoideus lateralis muscle. Posterior to the vomer is the basilar por¬ tion of the occipital bone, presenting near its center the pharyngeal tubercle for the at¬ tachment of the fibrous raphe of the phar¬ ynx, with depressions on each side for the insertions of the rectus capitis anterior and longus capitis. At the base of the lateral pter¬ ygoid plate is the foramen ovale, through which passes the mandibular nerve and the accessory meningeal artery. Lateral to this is the prominent sphenoidal spine, which gives attachment to the sphenomandibular ligament and the tensor veli palatini. Poste¬ rior and somewhat lateral to the foramen ovale is the foramen spinosum, which trans¬ mits the middle meningeal vessels and a small meningeal branch of the mandibular nerve. Lateral to the sphenoidal spine is the mandibular fossa, which is divided into two parts by the petrotympanic fissure. The anterior portion—concave, smooth, and bounded in front by the articular tubercle— articulates with the condyle of the mandible; the posterior portion is rough and bounded behind by the tympanic part of the temporal bone. Observable in a dried skull at the base of the medial pterygoid plate is an aperture, ir¬ regular in shape and variable in size, named the foramen lacerum. It is not a complete foramen in the intact body, because its infe¬ rior part is covered over by a fibrocartilagi¬ nous plate, across the superior (inner or cer¬ ebral) surface of which passes the internal

1 68

OSTEOLOGY

carotid artery. The foramen lacerum is bounded in front by the great wing of the sphenoid, behind by the apex of the petrous portion of the temporal bone, and medially by the body of the sphenoid and the basilar portion of the occipital bone. The inferior surface of the petrous temporal bone is pierced by the round opening of the carotid canal. The internal carotid artery, coursing within the canal, immediately takes a rightangle turn to reach the side of the foramen lacerum. At the upper end of the foramen lacerum the internal carotid artery enters the cranial cavity, taking an S-shaped course to achieve the undersurface of the brain. Lateral to the foramen lacerum is a groove, the sulcus tubae auditivae, between the pet¬ rous part of the temporal and the great wing of the sphenoid. This sulcus lodges the carti¬ laginous part of the auditory tube which is continuous with the bony part within the temporal bone. At the bottom of this sulcus is a narrow cleft, the petrosphenoidal fis¬ sure. Near the apex of the petrous portion of the temporal bone, the quadrilateral rough surface affords attachment to the levator veli palatini, lateral to which is the orifice or en¬ trance of the carotid canal. The posterior part of the norma basalis is formed principally by the occipital bone; however, laterally are the roughened, bony mastoid processes of the temporal bones. On the medial side of each mastoid process is the mastoid notch for the posterior belly of the digastricus, and medial to the notch is the occipital groove for the occipital artery. Medial and slightly anterior to the mastoid processes and emerging from between the laminae of the vaginal process of the tym¬ panic part of the temporal bone is the styloid process, at the base of which is the stylo¬ mastoid foramen. Through this foramen the facial nerve exits in its course toward the side of the face, and the stylomastoid artery enters to supply the tympanic cavity of the middle ear. Medial to the styloid process and posterior to the carotid canal is the jugular foramen, a large aperture, formed between the jugular fossa of the petrous portion of the temporal bone anteriorly, and the occipi¬ tal bone posteriorly. It is generally larger on the right than on the left side, and may be subdivided into three compartments. The anterior compartment transmits the inferior petrosal sinus; the intermediate, the glosso¬ pharyngeal, vagus, and accessory nerves; the

4 68. The external surface of the left half of the base of the skull. (Norma basalis.)

Fig

posterior, the sigmoid sinus which leads to the internal jugular vein, and some menin¬ geal branches from the occipital and ascend¬ ing pharyngeal arteries. Extending anteri¬ orly from the jugular foramen to the foramen lacerum is the petro-occipital fis¬ sure, occupied in the intact body by a plate of cartilage. Posterior to the basilar portion of the oc¬ cipital bone is the foramen magnum, bounded laterally by the occipital condyles, on the medial surfaces of which attach the alar ligaments. These condyles are oval in

AXIAL SKELETON

169

j.— Incisors

Median incisive foramina

Lateral incisive foramina Molars

Palatine process of maxilla

Grooves for anterior palatine nerve and greater palatine vessels ' Horizontal part of palatine bone Inferior orbital fissure

Greater and lesser palatine foramina Tensor veli palatini Musculus uvulae Pterygoid hamulus Constrictor pharyngis superior

Great wing of sphenoidal bone Lateral pterygoid lamina Foramen ovale Articular tubercle Spina sphenoidalis

Posterior border of vomer Ala of vomer Medial pterygoid lamina Tensor veli palatini Tensor tympani

Foramen spinosum Foramen lacerum

Pharyngeal tubercle

Mandibular fossa Tensor veli palatini Levator veli palatini Styloid process Porus acusticus externus

Carotid canal Basilar part of occipital bone

Occipital condyle

Stylomastoid foramen

Foramen magnum Condyloid fossa

Mastoid foramen Groove for occipital artery

Occipital bone

External occipital protuberance Occipital bone

Fig. 4-69.

Key to Figure 4-68.

shape and project inferiorly to articulate with the superior articular surfaces overly¬ ing the lateral masses of the atlas. Lateral to each condyle is the jugular process, to which attaches the rectus capitis lateralis muscle and the lateral atlanto-occipital ligament, which strengthens the atlanto-occipital ar¬ ticular capsules laterally. The foramen mag¬ num transmits the medulla oblongata and its membranes, the accessory nerves, the verte¬ bral arteries, the anterior and posterior spi¬ nal arteries, and the ligaments connecting the occipital bone with the axis. The mid¬

points on the anterior and posterior margins of the foramen are respectively termed the basion and the opisthion. The hypoglossal canal courses forward and laterally from a foramen on the inner aspect of the occipital bone within the cra¬ nium just above the foramen magnum to an opening that perforates the occipital bone externally at the lateral part of the base of the condyle. It transmits the hypoglossal nerve and a branch of the posterior menin¬ geal artery. Posterior to each condyle is the condyloid fossa, perforated on one or both

170

OSTEOLOGY

sides by the condyloid canal, for the trans¬ mission of a vein from the sigmoid sinus to the vertebral veins in the upper cervical re¬ gion. Posterior to the foramen magnum is the external occipital crest, ending superiorly at the external occipital protuberance. On ei¬ ther side are the superior and inferior nu¬ chal lines which, along with the surfaces of bone between them, are rough for the at¬ tachment of a number of muscles (see Figs. 4-69; 4-85).

Interior of the Skull The cranial cavity is formed by the fron¬ tal, ethmoid, sphenoid, temporal, parietal, and occipital bones. The internal surface of the floor of the cranial cavity, i.e., the base of the skull, is quite irregular in shape, but the inner surfaces of the bones forming the walls and roof of the cranial vault are smoother and encase the rounded hemi¬ spheres of the cerebrum and cerebellum. The capacity of the normal cranial cavity varies between 1300 and 1500 cc, and the weight of the brain in grams is approxi¬ mately the same as the figure for cranial ca¬ pacity expressed in cubic centimeters. The cranial cavity is lined by two fibrous layers or membranes: the periosteal layer, or endocranium, which is closely adherent to the bone, and the dura mater, which is looser and completely covers the brain in a sac-like fashion. The interior of the skull will be de¬ scribed in two sections: the inner surface of the skullcap or calvaria and the internal sur¬ face of the base of the skull.

INNER SURFACE OF THE SKULLCAP

Formed principally by the frontal and pa¬ rietal bones, the skullcap, or calvaria, also includes the upper parts of the squamae of the temporal and occipital bones laterally and posteriorly. Its inner surface is marked by depressions for the convolutions of the cerebrum, and by numerous furrows for the branches of the meningeal vessels. Along the midline is a longitudinal groove, narrow where it commences at the frontal crest, but broader posteriorly. It lodges the superior sagittal sinus, and its margins afford attach¬ ment to the falx cerebri. On each side of this groove are several granular foveolae or pits for the arachnoid granulations, and posteri¬ orly, the openings of the parietal foramina

when these are present. The coronal and lambdoidal sutures can be seen crossing the inner surface of the calvaria transversely while the sagittal suture lies in the median plane between the parietal bones.

INTERNAL OR SUPERIOR SURFACE OF THE BASE OF THE SKULL (Fig. 4-70)

The superior surface of the base of the skull forms the floor of the cranial cavity and is divided into three fossae, called the ante¬ rior, middle, and posterior cranial fossae. anterior cranial fossa (fossa crcinii oin¬ terior). The floor of the anterior cranial fossa, on which rest the frontal lobes of the brain, is formed by the orbital plates of the frontal, and cribriform plate of the ethmoid, and the small wings and anterior part of the body of the sphenoid. It is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the chiasmatic groove. It is traversed by the frontoethmoidal, sphenoethmoidal, and sphenofrontal sutures. Its lateral portions or orbital plates are convex and form the bony roof of the orbital cavities. The middle por¬ tion, formed primarily by the ethmoid bone, overlies the nasal cavities. In the midline most anteriorly is the frontal crest (of the frontal bone) on which attaches the falx cer¬ ebri. Just behind this crest is the foramen cecum, which usually transmits a small vein from the nasal cavity to the superior sagittal sinus. The upward continuation of the per¬ pendicular plate of the ethmoid bone forms a midline bony crest, the crista galli, to which also attaches the falx cerebri. On both sides of the crista galli, the olfactory grooves of the cribriform plate support the olfactory bulbs. These grooves are perforated by fo¬ ramina for the transmission of the olfactory nerves and, more rostrally, by a slit for the nasociliary nerve (Fig. 4-70). In the lateral wall of the olfactory groove are the internal openings of the anterior and posterior eth¬ moidal foramina. The anterior transmits the anterior ethmoidal vessels and the nasociliary nerve; the posterior ethmoidal foramen opens more caudally under cover of the pro¬ jecting lamina of the sphenoid, and trans¬ mits the posterior ethmoidal vessels and nerve. Behind the ethmoid bone are the eth¬ moidal spine of the sphenoid and the ante¬ rior margin of the chiasmatic groove. This groove courses laterally on each side to the

AXIAL SKELETON

1 71

Groove for super, sagittal sinus Grooves for anter. meningeal vessels Foramen cecum Crista galli Slit for nasociliary nerve Groove for nasociliary nerve Anterior ethmoidal foramen Orifices for olfactory nerves Posterior ethmoidal foramen Ethmoidal spine

Olfactory grooves

Optic foramen Chiasmatic groove Tuberculum sellae Anterior clinoid process Medial clinoid process Posterior clinoid process Groove for abducent nerve Foramen lacerum Orifice of carotid canal Depression for trigeminal ganglion

Internal acoustic meatus Slit for dura mater Groove for superior petrosal sinus Jugular foramen Flypoglossal canal Aquaeductus vestibuli Condyloid foramen Foramen magnum Mastoid foramen Posterior meningeal grooves

Fig. 4-70.

Interior of base of the skull, showing the cranial fossae.

upper margin of the optic foramen. Through each optic foramen courses an optic nerve and ophthalmic artery. middle cranial fossa (fossa cranii me¬ dia). The lateral parts of the middle cra¬ nial fossa are of considerable depth, and they support the temporal lobes of the brain.

More medially rests the hypothalamus and midbrain. On each side the middle fossa is bounded anteriorly by the posterior margins of the small wings of the sphenoid, the ante¬ rior clinoid processes, and the ridge forming the anterior margin of the chiasmatic groove; posteriorly, by the superior angles of the pet-

172

OSTEOLOGY

rous portion of the temporals and the dor¬ sum sellae; laterally by the temporal squamae, sphenoidal angles of the parietals, and great wings of the sphenoid. The middle fossa on each side is traversed by the squamosal, sphenoparietal, sphenosquamosal and sphenopetrosal sutures. In the anterior part of the median region are the chiasmatic groove and tuberculum sellae. On each side the chiasmatic groove ends at the optic foramen, posterior to which extends the anterior clinoid process that gives attachment to the tentorium cerebelli. Behind the tuberculum sellae, the hypophy¬ seal fossa forms a deep depression in the sella turcica and lodges the hypophysis. A tubercle, the medial clinoid process, may be present on each side of the anterior wall of the sella turcica. The sella turcica is bounded posteriorly by a quadrilateral plate of bone, the dorsum sellae, the free angles of which are surmounted by the posterior clinoid processes. These afford attachment to the tentorium cerebelli, and below each is a notch for the abducent nerve. On each side of the sella turcica is the carotid groove, which is broad, shallow, and curved. The groove lodges the internal carotid artery and extends from the foramen lacerum to the medial side of the anterior clinoid process, where it is sometimes converted into a caroticoclinoid foramen by the union of the anterior with the medial clinoid process. The carotid groove also contains the cavern¬ ous sinus and may be bounded posterolaterally by the lingula of the sphenoid. The bony lateral surface of the middle cra¬ nial fossa is traversed by furrows for the an¬ terior and posterior branches of the middle meningeal vessels. Commencing near the fo¬ ramen spinosum, the anterior furrow runs to the sphenoidal angle of the parietal, where it is sometimes converted into a bony canal; the posterior runs lateralward across the temporal squama, passing onto the parietal bone near the middle of its inferior border. The following apertures are also to be seen. Rostrally, the superior orbital fissure is bounded above by the small wing, below by the great wing, and medially by the body of the sphenoid; it is usually completed later¬ ally by the orbital plate of the frontal bone. The fissure transmits: (1) to the orbital cav¬ ity— the oculomotor, the trochlear, the oph¬ thalmic division of the trigeminal, and the abducent nerves, sympathetic nerve fibers

from the cavernous plexus, and the orbital branch of the middle meningeal artery; and (2) to the cranial cavity from the orbit—the ophthalmic veins and a recurrent branch of the lacrimal artery to the dura mater. Poste¬ rior to the medial end of the superior orbital fissure is the foramen rotundum through which passes the maxillary nerve. Posterolaterally is the larger foramen ovale through which courses the mandibular nerve, the accessory meningeal artery, and the lesser petrosal nerve. The foramen of Vesalius, often absent, opens at the lateral aspect of the scaphoid fossa inferiorly, and transmits a small vein. Lateral and posterior to the fo¬ ramen ovale is the foramen spinosum, which transmits the middle meningeal ves¬ sels and a recurrent branch of the mandibu¬ lar nerve which supplies the dura mater. Medial to the foramen ovale the foramen lacerum may be seen in a dried skull, but in the fresh state the inferior part of this aper¬ ture is occupied by a layer of fibrocartilage. The internal carotid artery, surrounded by a plexus of sympathetic nerves, passes across the superior part of the foramen but does not traverse its whole extent. The small nerve of the pterygoid canal and a small meningeal branch from the ascending pharyngeal ar¬ tery alone pierce the layer of fibrocartilage and are thus the only structures to pass through the foramen lacerum. On the ante¬ rior surface of the petrous portion of the temporal bone is seen the arcuate eminence formed by the projection of the anterior semicircular canal. Also on this anterior sur¬ face of the petrous temporal bone is found a groove called the hiatus for the greater pe¬ trosal nerve. This nerve, coming from the geniculate ganglion of the facial nerve, courses along the groove and then traverses the foramen lacerum to join the deep petro¬ sal nerve. A bit more lateral is another somewhat smaller hiatus for the lesser pe¬ trosal nerve, which is bound for the otic gan¬ glion and leaves the cranial cavity through the foramen ovale or its own foramen. Be¬ hind the foramen lacerum can be seen the depression for the trigeminal ganglion. posterior cranial fossa (fossa crcinii pos¬ terior). The posterior cranial fossa is the largest and deepest of the three. Within it lies the pons and medulla oblongata medi¬ ally, over which expands the lobes of the cerebellum. The bony floor of this fossa is formed by the dorsum sellae and clivus of

AXIAL SKELETON

the sphenoid, the occipital bone, the petrous and mastoid portions of the temporals, and the mastoid angles of the parietal bones. It is crossed by the occipitomastoid, parieto¬ mastoid, and spheno-occipital sutures. The posterior fossa is separated from the middle fossa in and near the midline by the dorsum sellae of the sphenoid and on each side by the grooved superior margin of the petrous portion of the temporal bone. This margin gives attachment to the tentorium cerebelli, and lodges in its groove the superior petrosal sinus. In the center of the posterior fossa is the foramen magnum, and on each of its lat¬ eral sides is the hypoglossal canal, through which courses the hypoglossal nerve and a meningeal branch from the ascending pha¬ ryngeal artery. Anterior to the foramen mag¬ num, the basilar portion of the occipital and the posterior part of the body of the sphe¬ noid form a grooved surface which supports the medulla oblongata and pons. In the young skull these bones are joined by a syn¬ chondrosis. This grooved basilar region is separated from the petrous temporal by the petro-occipital fissure, which is occupied in life by a thin plate of cartilage. The fissure is continuous with the jugular foramen, and its margins are grooved for the inferior petrosal sinus. The jugular foramen is situated between the lateral part of the occipital and the pet¬ rous part of the temporal. The anterior por¬ tion of this foramen transmits the inferior petrosal sinus; the posterior portion, the sig¬ moid sinus and some meningeal branches from the occipital and ascending pharyn¬ geal arteries; and the intermediate portion, the glossopharyngeal, vagus, and accessory nerves. Superior to the jugular foramen is the internal acoustic meatus, for the facial and vestibulocochlear nerves and internal auditory artery. A narrow fissure is located behind and lateral to the meatus, which con¬ tains the external opening of the aqueduct of the vestibule (aqueductus vestihuli). In the aqueduct is located the endolymphatic duct. Behind the foramen magnum are the inferior occipital fossae, which support the hemi¬ spheres of the cerebellum. These are sepa¬ rated from one another by the internal occipital crest, which serves for the attachment of the falx cerebelli and lodges the occipital sinus. The posterior cranial fos¬ sae are bounded posterolaterally by Sshaped grooves for the sigmoid sinuses

173

which lead to the jugular foramen. Posteri¬ orly these grooves are continuous with those of the transverse sinuses. These grooves ac¬ centuate the inner surface of the occipital bone, the mastoid angle of the parietal, the mastoid portion of the temporal, and the jug¬ ular process of the occipital, and end at the jugular foramen on each side. Where this sinus grooves the mastoid portion of the temporal, the orifice of the mastoid foramen may be seen, and just prior to its termina¬ tion, the condyloid canal opens into it. Both of these orifices transmit emissary veins, but neither opening is constant. nasal cavity (cQvum nasi; Figs. 4-64; 4-71 to 4-73). The nasal cavities are two irregu¬ larly shaped spaces which extend from the base of the cranium to the roof of the mouth. They are separated from each other in the midline by a thin vertical septum. They open on the face through a single pearshaped anterior nasal aperture, since the anterior cartilaginous part of the septum is lacking in a dried skull. Posteriorly, two openings, the choanae, communicate with the nasal part of the pharynx. The nasal cav¬ ities are much narrower superiorly than in¬ teriorly, and they communicate with the frontal, maxillary, ethmoidal, and sphenoi¬ dal sinuses. Each cavity is bounded by a roof, a floor, a medial wall, and a lateral wall. The roof (Figs. 4-71; 4-72) is horizontal centrally, but slopes downward in front and behind. Its middle is 2 to 3 mm wide and is formed by the cribriform plate of the eth¬ moid bone, through which pass nearly 20 foramina for the filaments of the olfactory nerves. Anteriorly, the roof is formed by the nasal bone and the spine of the frontal, and posteriorly, by the body of the sphenoid, the ala of the vomer, and the sphenoidal process of the palatine bone. On the superior and posterior part of the roof is the opening of the sphenoidal sinus. The bony floor (Fig. 4-22) is smooth and is formed by the palatine process of the max¬ illa and the horizontal part of the palatine bone. These represent the bones of the hard palate, which separate the nasal cavity from the oral cavity. Near the anterior end is the opening of the incisive canal, through which pass the nasopalatine nerves and branches of the greater palatine arteries. The medial wall (septum nasi; Fig. 4-71) is the osseous nasal septum which separates

1 74

OSTEOLOGY

Frontal sinus

Nasal spine Nasal

Frontal of max Inf. nasal concha

Pterygoid hamulus Palatine bone Fig. 4-71.

Sagittal section of skull showing the osseous nasal septum formed principally by the perpendicular plate of the ethmoid bone and the vomer anteriorly. Behind and above the septum are seen the bones forming the inner surface of the cranial cavity.

Nasal bone

Probe passed through nasolacrimal canal

Nasal spine of frontal bone

Bristle passed through infundibulum

Cribriform plate of ethmoid Sphenoid

iiiperior)^ T concha »*

concha

■max.sti

Frontal proc. of maxilla Lacrimal Ethmoid Uncinate proc. of ethmoid Inferior nasal concha Palatine Superior meatus Middle meatus Inferior meatus

Anterior nasal spine Palatine proc. of maxilla Horizontal part of palatine Posterior nasal spine Incisive canal

Fig. 4-72.

Roof, floor, and lateral wall of left nasal cavity.

AXIAL SKELETON

Ostium of anterior ethmoid air cells Superior concha Middle ethmoid air cells

175

Frontal sinus Arrow from frontonasal duct into infundibulum

Posterior ethmoid air cells Superior meatus Arrow through ostium of sphenoidal sinus

Cut edge of middle concha

Hiatus semilunaris Bulla ethmoidalis

Sphenoethmoidal recess Uncinate process of ethmoid bone

Sphenoidal sinus

Inferior concha Inferior meatus _Nasal septum, cut edge

Inferior meatus

Fig. 4-73.

Lateral wall of the nasal cavity after the removal of the middle concha to expose the structures and orifices of the middle meatus. Arrows indicate openings from the frontal and sphenoid sinuses.

the two nasal cavities. It extends from the roof to the floor and is frequently deflected to one side or the other, more often to the left than to the right. Although cartilaginous in front, the septum is formed primarily by the perpendicular plate of the ethmoid bone and the vomer. Posteriorly, these bones articu¬ late with the sphenoid, while anteriorly the crest of the nasal bones and the spine of the frontal also contribute to the septum. The lateral wall (Figs. 4-72; 4-73) appears irregular, but in fact is a rather flat surface upon which are projected three curved lami¬ nae or conchae. This wall is formed, anteri¬ orly, by the frontal process of the maxilla and by the lacrimal bone; in the middle, by the ethmoid, maxilla, and inferior nasal con¬ cha; posteriorly, by the vertical plate of the palatine bone, and the medial pterygoid plate of the sphenoid. On this wall are three curved anteroposterior passages, termed the superior, middle, and inferior meatuses of the nose (Fig. 4-72). The superior meatus is the shortest of the three and occupies the middle third of the lateral wall between the superior and middle nasal conchae. The pos¬ terior ethmoidal cells open into the superior

meatus, while the sphenopalatine foramen, an opening in the perpendicular plate of the palatine bone which serves as a means of communication between the pterygopala¬ tine fossa and the nasal cavity, lies just be¬ hind the meatus. The orifice of the sphenoi¬ dal sinus drains into the sphenoethmoidal recess, which lies in the most superior and posterior part of the nasal cavity, formed by the angle of junction of the sphenoid and ethmoid bones. The middle meatus is situ¬ ated between the middle and inferior con¬ chae (Fig. 4-72), and it courses anteroposteriorly above the superior border of the inferior concha along its entire extent. The lateral wall of this meatus can be satisfacto¬ rily studied only after the removal of the middle concha (Fig. 4-73). A curved fissure, the hiatus semilunaris, lies along this meatus between the uncinate process of the ethmoid bone and the bulla ethmoidalis. The middle ethmoidal cells are contained within the bulla and open on or near it. The middle me¬ atus communicates through the hiatus semi¬ lunaris with a curved passage termed the infundibulum, into which the anterior ethmoidal cells open. The frontonasal duct

1 76

OSTEOLOGY

leading from the frontal sinus opens into the anterior end of the infundibulum or directly into the anterior part of the middle meatus. Below the bulla ethmoidalis and hidden by the uncinate process of the ethmoid is the opening of the maxillary sinus, and an ac¬ cessory opening frequently is present above the posterior part of the inferior nasal con¬ cha. The inferior meatus is the space be¬ tween the inferior concha and the floor of the nasal cavity. It extends almost the entire length of the lateral wall of the nasal cavity, and presents anteriorly the inferior orifice of the nasolacrimal canal. Observe the loca¬ tions of the frontal maxillary and sphenoid sinuses in Figure 4-74. The anterior nasal aperture (Fig. 4-64) is a pear-shaped opening, the long axis of which is vertical. It is bounded superiorly by the inferior borders of the nasal bones; laterally by the thin, sharp margins which separate the anterior from the nasal surfaces of the maxillae; and inferiorly by the same borders,

where they curve medialward to join at the anterior nasal spine. Attached to the borders of the bony anterior nasal aperture are the external cartilages of the nose. These pro¬ vide the principal surface features and shape of the external nose and open by way of two elliptical orifices, the nares. The two posterior nasal apertures, or choanae, are bounded superiorly by the body of the sphenoid and ala of the vomer; inferiorly, by the posterior border of the hor¬ izontal part of the palatine bone, which ac¬ tually forms the posterior part of the hard palate; and laterally, by the medial ptery¬ goid plate. The choanae are separated from each other in the midline by the posterior border of the vomer.

Differences in the Skull Due to Age At birth the skull is large in proportion to the other parts of the skeleton, but the facial portion of the cranium in the newborn is small, and equals only

Fig. 4-74 Lateral view roentgenogram of the adult skull. Crosses are placed in the frontal, maxillary, and sphenoidal sinuses. The hypophyseal fossa can be identified directly behind the sphenoid sinus. The dense white region below and behind the fossa is due to the petrous part of the temporal bone. (Courtesy of Doctors Moreland and Arndt.)

AXIAL SKELETON

about one-eighth of the bulk of the skull compared to one-half in the adult. The smallness of the face at birth is due to the rudimentary condition of the max¬ illae and mandible, the noneruption of the teeth, and the small size of the maxillary air sinuses and nasal cavities. At birth the nasal cavities lie almost entirely between the orbits, and the lower border of the ante¬ rior nasal aperture is only a little below the level of the orbital floor. In contrast, the cranial cavity is large to accommodate the large neonatal brain. The frontal and parietal eminences are prominent, and the skull is maximally wide at the level of the parietal tubers (Fig. 4-75). On the other hand, the glabella, superciliary arches, and mastoid processes are not even developed at birth. Ossification of the skull bones is not completed, and many, e.g., the occipi¬ tal, temporals, sphenoid, frontal, and mandible, consist of more than one piece. Unossified membra¬ nous intervals, termed fontanelles, are seen at the angles of the parietal bones. There are six fonta¬ nelles in number: two, an anterior and a posterior, are situated in the midline; two others are found on each side, an anterolateral (sphenoidal) and a poster¬ olateral (mastoid). The anterior or bregmatic fontanelle (fonticulus anterior; Fig. 4-75) is the largest, and is located at the junction of the sagittal, coronal, and frontal su¬ tures. It is diamond-shaped and measures about 4 cm in its anteroposterior and 2.5 cm in its trans¬ verse diameter. The posterior fontanelle is triangu¬ lar in form and is situated at the junction of the sagit¬

177

tal and lambdoidal sutures. The sphenoidal and mastoid fontanelles (Fig. 4-76) are small, irregular in shape, and correspond respectively to the sphe¬ noidal and mastoid angles of the parietal bones. The posterior and lateral fontanelles become closed within a month or two after birth, but the anterior does not completely close until about the middle of the second year. Postnatal growth of the face and enlargement of the jaws are temporally correlated with the eruption of the deciduous teeth. These changes are still more marked after the second dentition. The skull grows rapidly from birth to the seventh year, by which time the foramen magnum and petrous parts of the tem¬ poral bones have reached their full size and the or¬ bital cavities are only a little smaller than those of the adult. Growth of the skull is slow from the seventh year until the approach of puberty, when a second period of rapid skull enlargement occurs. This re¬ sults in an increase of skull size in all directions, but it is especially marked in the frontal and facial re¬ gions, where it is associated with the development of the air sinuses. The time of closure of the individual cranial su¬ tures varies between individuals, but generally be¬ gins between the twentieth and thirtieth years. Usu¬ ally the process commences in the sagittal and sphenofrontal sutures, but closure progresses very slowly and may not be complete in all the sutures until old age. The most striking feature of the old skull is the diminution in the size of the maxillae and

Anterior fontanelle

Frontal tuber (eminence) Frontal suture Coronal suture

Sagittal suture Parietal tuber (eminence)

Lambdoidal suture Posterior fontanelle Fig. 4-75.

Skull at birth, showing frontal and occipital fontanelles. Observe that the greatest width of the skull at this stage is at the level of the parietal tubers.

1 78

OSTEOLOGY

Anterior fontanelle

Coronal suture

Lambdoidal suture

Mastoid fontanelle Sphenoid fontanelle

Fig. 4-76. skull at birth, showing sphenoidal and mastoid fontanelles. Observe the small facial bones and the great difference in size between the facial and cranial vault bones in the neonatal skull.

mandible after the loss of the teeth and the absorp¬ tion of the alveolar processes. This is associated with a marked reduction in the vertical (occlusal) meas¬ urement of the face and with an alteration in the condylar angles of the mandible (Fig. 4-83).

Sex Differences in the Skull Until the age of puberty there is little difference between the skull of the two sexes. The skull of an adult female is, as a rule, lighter and smaller, and its cranial capacity about 10% less than that of the male. Its walls are thinner and its muscular ridges less strongly marked. The glabella, superciliary arches, and mastoid processes are less prominent in females, and the corresponding air sinuses are smaller or may be rudimentary. The upper margin of the orbit is sharp, the forehead vertical, the frontal and parietal eminences prominent, and the vault somewhat flattened. The contour of the face is more rounded, the facial bones are smoother, and the maxillae and mandible and their contained teeth smaller. More of the morphological characteristics seen during the pre-puberty years are retained in the skull of the adult female than in that of the adult male. A well-marked male or female skull can easily be recognized as such, but in some cases the respec¬ tive characteristics are so indistinct that the determi¬ nation of the sex may be difficult or impossible.

Fractures of the Skull Consistent with the primary function of the skull, which is protection of the brain, is the fact that those portions of the skull that are most exposed to exter¬ nal violence are thicker than those that are shielded

from injury by overlying muscles. The skull-cap is thick and dense, whereas the temporal squamae, protected by the temporal muscles, and the inferior occipital fossae, shielded by the muscles at the back of the neck, are thin and fragile. The calvaria aver¬ age about 5 to 6 mm in thickness, while the tempo¬ ral squama is only 1 to 2 mm thick. The thickness of the skull at the glabella is slightly over 1 cm and at the external occipital protuberance between 1.5 and 2.0 cm. The skull is further protected by its elastic¬ ity, its rounded shape, and the fact that its structure contains a number of secondary elastic arches, each made up of a single bone. The manner in which vibrations are transmitted through the bones of the skull is of importance as a protective mechanism, especially as far as the skull base is concerned. The vibrations resulting from a blow on the head are transmitted in a uniform man¬ ner in all directions to the top and sides of the skull, but at the base, due to the varying thickness and density of the bones, this is not so. In this latter region there are special buttresses that serve to carry the vibrations in certain definite directions. The later¬ ally projecting ridge that is formed by the lesser and greater wings of the sphenoid bone and separates the anterior from the middle cranial fossae and, more posteriorly, the ridge that separates the middle from the posterior fossa form such buttresses. If any violence is applied to the cranial vault, the vibrations would be carried along these buttresses to the sella turcica, where they meet and form a center of resist¬ ance. Additionally, the subarachnoid cavity is some¬ what dilated at this site and forms a cushion of fluid, helping to dissipate the vibrations. In like manner, when violence is applied to the base of the skull, as in falls when a person lands on his feet, the vibra¬ tions are carried backward through the occipital

AXIAL SKELETON

crest, and forward through the basilar part of the occipital bone and body of the sphenoid up to the vault of the skull. The calvaria and sides of the cranial cavity are formed by an inner layer of compact bone between which is the spongy diploic layer containing the vas¬ cular channels. Fractures involving the outer com¬ pact layer are relatively easy to identify; however, a blow on the head may be transmitted at times to the inner compact layer, resulting in a fracture of this layer with bony spicules and splinters without evi¬ dence of fracture to the outer compact layer. Basal skull fractures of the anterior cranial fossa may involve the delicate cribriform plate of the eth¬ moid bone and/or the very thin orbital plate of the frontal bone. Such injury can cause lacerations of the dura mater with subsequent discharge of cere¬ brospinal fluid through the nose (cerebrospinal rhinorrhea) and injury to the olfactory nerves result¬ ing in the loss of the sense of smell. Fractures of the orbital plate may result in hemorrhage into the or¬ bital cavity, evidenced by subconjunctival discolora¬ tion and protrusion of the eyeball (exophthalmos). Fractures of the bones of the middle cranial fossa are the most common basal skull fractures, probably because this region is weakened by the many foram¬ ina and canals. The petrous portion of the temporal bone is further weakened by containing the cavities of the inner ear. Fractures of the sphenoid bone fre¬ quently injure the meningeal vessels and may injure the internal carotid artery as well as the cavernous sinus. Injury might also be expected to the third, fourth, and sixth cranial nerves. Fractures in the middle fossa frequently involve the tegmen tympani (roof of the tympanic cavity). In these situations, if the tympanic membrane is ruptured, blood and cere¬ brospinal fluid can escape through the external auditory meatus. Fractures of the petrous portion of the temporal bone may injure the facial and vestibu¬ locochlear nerves. Fractures of the posterior cranial fossa may be exceedingly dangerous because cerebrospinal fluid and blood cannot escape, and even a seemingly small fracture might be fatal because of the pressure that develops on the vital centers in the brain stem. Fractures of the body of the sphenoid bone may para¬ lyze the sixth cranial nerve, whereas fractures of the occipital bone may injure the hypoglossal nerve.

Malformations of the Skull One of the most common developmental malfor¬ mations of the facial bones is cleft palate. The cleft may involve only the uvula or it may extend anteri¬ orly through the soft palate and involve part or even all of the hard palate. In the latter instance, the cleft would extend as far forward as the incisive foramen. In the severest forms, the cleft extends through the alveolar process and continues between the premax¬ illary bone and the rest of the maxilla, that is be¬ tween the lateral incisor and canine teeth. In some

179

instances, the cleft courses between the central and lateral incisor teeth, lending some support to the be¬ lief that the premaxillary bone develops from two centers and not one. The cleft may affect one or both sides. If it is bilateral, the central part is frequently displaced forward and remains united to the septum of the nose, the deficiency in the bony palate being complicated with a cleft lip.

Individual Bones of the Skull THE MANDIBLE

The mandible (Figs. 4-77; 4-78) is the larg¬ est and strongest of the facial bones and ex¬ tends from the chin in the midline to the two mandibular fossae laterally. It contains the lower teeth and consists of a horizontal por¬ tion, the body, and two perpendicular por¬ tions, the rami, which join the body nearly at right angles. body of the mandible. The body (corpus mandibulcie) is curved somewhat like a horseshoe, and has two surfaces and two borders. The external surface of the body (Figs. 4-64; 4-77) is marked in the median line by a faint ridge, indicating the symphysis menti or line of fusion of the two separate halves of the mandible as seen in the fetus. This ridge divides interiorly to enclose a triangu¬ lar eminence, the mental protuberance, the base of which is depressed in the center but raised on each side to form the mental tuber¬ cle. On either side of the symphysis is a de¬ pression, the incisive fossa, which gives ori¬ gin to the mentalis and a small portion of the orbicularis oris. Inferior to the second premolar tooth on each side is the mental fora¬ men, for the passage of the mental vessels and nerve. Coursing posteriorly and upward from each mental tubercle is a faint ridge, the oblique line, which becomes continuous with the anterior border of the ramus. At its anterior end attaches the depressor labii inferioris and depressor anguli oris muscles. The platysma inserts near the inferior bor¬ der (Fig. 4-77). The internal surface of the body (Fig. 4-78) is concave and anteriorly presents two small bony projections on each side. Near the infe¬ rior part of the symphysis on each side is a laterally placed spine, termed the mental spine, which gives origin to the genioglossus. Immediately below these is a second pair of spines, or more frequently a median ridge or

1 80

OSTEOLOGY

Coronoid process

Head \ Condylar process

Temporalis

nmm { w IMA'SS ETER

Groove for facial artery

Fig. 4-77.

The left half of the mandible. Lateral aspect.

Fig. 4-78,

The left half of the mandible. Medial aspect.

AXIAL SKELETON

impression, for the origin of the geniohyoid muscles. On each side of the midline near the inferior margin of the symphysis is an oval depression for the attachment of the anterior belly of the digastric muscle. Ex¬ tending posteriorly from the mental spine on each side of the symphysis is the mylohyoid line, which gives origin to the mylohyoid muscle. The posterior part of this line, near the alveolar margin, behind the third molar tooth, gives attachment to a small part of the superior pharyngeal constrictor, and to the pterygomandibular raphe. Superior to the anterior part of this line is the smooth, trian¬ gular sublingual fossa within which the sub¬ lingual gland rests, and inferior to the poste¬ rior part is the oval submandibular fossa which supports the submandibular gland. The superior border or alveolar part of the mandibular body is hollowed into sockets for the reception of the sixteen teeth. The sockets, or alveoli, arranged sequentially in a curved bar of bone, the alveolar arch, vary in depth and size according to the teeth they contain. The sockets are separated by bony partitions, the interalveolar septa. The buc¬ cinator is attached to the outer lip of the su¬ perior border as far forward as the first molar tooth. The inferior border is called the base of the mandible, and it is rounded, thicker an¬ teriorly than behind, and at the point where it joins the lower border of the ramus there may be a shallow groove for the facial ar¬ tery. The base of the mandible ends posteri¬ orly at the mandibular angle, diagonal to the socket of the third molar tooth. From this point the ramus ascends in a nearly vertical manner. ramus of the mandible. The ramus (ra¬ mus mandibulae) is quadrilateral in shape and has two surfaces, four borders, and two processes. The lateral surface of the ramus (Fig. 4-77) is flat and marked by oblique ridges in its lower portion where the masseter muscle inserts. The medial surface (Fig. 4-72) pre¬ sents near its middle the oblique mandibular foramen for the entrance of the inferior alve¬ olar vessels and nerve into the mandibular canal. The margin of the mandibular fora¬ men presents a prominent ridge, surmounted by a sharp spine anteriorly, the lingula mandibulae, to which attaches the sphenomandibular ligament. The mylohyoid groove

181

runs obliquely downward and forward from the foramen and lodges the mylohyoid ves¬ sels and nerve. Posterior to this groove is a roughened surface extending to the mandib¬ ular angle for the insertion of the medial pterygoid muscle. From the mandibular fo¬ ramen and within the substance of the ramus, the mandibular canal courses ob¬ liquely downward and forward. After reaching the mandibular body, the canal continues horizontally forward, and is placed under the alveoli, communicating with them by small openings. At the level of the second premolar tooth, the canal splits, forming the mental canal, which courses upward and laterally to reach the mental foramen, and the incisive canal, which con¬ tinues toward the symphysis, giving off two small channels to the incisor teeth. In the posterior two-thirds of the bone the mandib¬ ular canal is situated near the internal sur¬ face of the mandible, whereas in the anterior third the canal is nearer its external surface. Through the canal courses the inferior alve¬ olar vessels and nerve, from which branches are distributed to the lower teeth. The inferior border of the ramus is thick and straight and joins the posterior border at the angle of the mandible. The mandibular angle, which measures about 120 degrees, may be either a bit inverted or everted and serves for attachment on its outer aspect of the masseter and on its inner aspect of the medial pterygoid muscle. Between these two muscles, the stylomandibular ligament at¬ taches to the angle. The posterior border is thick, smooth, and rounded. It extends from the condylar process above to the mandibu¬ lar angle below and is covered by the pa¬ rotid gland. The anterior border is continu¬ ous above with the coronoid process and below with the oblique line. The superior border is thin, and is surmounted by the cor¬ onoid process anteriorly and the condylar process posteriorly, separated by the man¬ dibular notch. The coronoid process (processus coronoideus; Fig. 4-77) is a thin, triangular emi¬ nence, and it varies in shape and size. Its anterior border is convex and is continuous with the anterior border of the ramus; its posterior border is concave and forms the; anterior boundary of the mandibular incisure (notch). Along its entire medial surface in¬ serts the temporalis muscle, the insertion

1 82

OSTEOLOGY

extending along the entire rim of the process and over onto the lateral surface. The medial surface is also marked by a bony ridge, which begins near the apex of the process and runs downward and forward to the inner side of the last molar tooth. The condylar process (processus condylaris) is thicker than the coronoid, and con¬ sists of two portions: the articular portion, called the head (condyle), and the con¬ stricted portion that supports it, the neck. The head presents an oval surface covered with fibrocartilage for articulation with the temporal bone at the mandibular fossa. In¬ terposed between the two articular surfaces is the articular disc of the temporomandibu¬ lar joint. In a living subject the head can be manipulated about 1 cm anterior to the tra¬ gus. With the jaw closed it lies totally within the mandibular fossa. When the jaw opens, the head and disc glide forward within the joint capsule, leaving a small depression in front of the tragus. At the lateral extremity of the head is a small tubercle for the attach¬ ment of the lateral (temporomandibular) lig¬ ament. The neck is flattened and strength¬ ened by ridges that descend from the anterior and lateral parts of the head. Its pos¬ terior surface is convex; its anterior presents a depression, the pterygoid fovea, for the insertion of the lateral pterygoid muscle. On the medial surface of the neck just posterior to the insertion of the lateral pterygoid is a blunt crest called the dental trajectory or the mandibular crest. The mandibular incisure or notch, sepa¬ rating the two processes, is a deep semilunar depression, and is crossed by the masseteric vessels and nerve.

lage (Figs. 4-79 to 4-82). Each half of the mandible is formed from a single center, which appears near the mental foramen at about the sixth week of fetal life. By the tenth week the portion of Meckel's carti¬ lage that lies adjacent to the incisor teeth is sur¬ rounded and invaded by the membranous bone. Somewhat later, accessory cartilaginous nuclei make their appearance—as a wedge-shaped nu¬ cleus in the condylar process which extends down¬ ward through the ramus (Fig. 4-82), as a small strip along the anterior border of the coronoid process (Fig. 4-82), and as smaller cartilaginous nuclei in the front part of both alveolar walls and along the front of the lower border of the bone (Fig. 4-83). These accessory nuclei possess no separate ossific centers, but are invaded by the surrounding membranous bone and undergo absorption. The inner alveolar border, usually described as arising from a separate ossific center (splenial center), is formed in the human mandible by an ingrowth from the main mass of the bone. At birth the bone consists of two parts, united anteriorly by the fibrous symphysis menti which ossifies during the first year. articulations. The mandible articulates with the two temporal bones. CHANGES PRODUCED by age. At birth (Fig. 4-83, A) the body of the bone is a mere shell, containing the sockets of the two incisors, the canine, and the two deciduous molar teeth, imperfectly partitioned from one another. The mandibular canal is large and runs near the lower border of the bone, and the mental foramen opens beneath the socket of the first

ossification. The mandible is ossified in the fibrous membrane covering the outer surface of the right and left Meckel's cartilages. These are the cartilaginous bars of the first branchial arch (man¬ dibular arch). Their proximal or cranial ends are connected with the ear capsules, and their distal ex¬ tremities are joined at the symphysis menti by meso¬ dermal tissue. From the proximal end of each carti¬ lage, the malleus and incus, two of the bones of the middle ear, are developed. The next succeeding por¬ tion, as far as the lingula, is replaced by fibrous tis¬ sue, which persists to form the sphenomandlbular ligament. Between the lingula and the canine tooth the cartilage disappears; the remaining portion adja¬ cent to the incisor teeth becomes ossified and incor¬ porated into this part of the mandible. Ossification takes place in the membrane covering the outer surface of the ventral end of Meckel's carti¬

Fig. 4-79. Mandible of human embryo 24 mm long. Outer aspect. Cartilage is in blue, bone in yellow. (From model by Low.)

Lingual nerve Inf. alveolar n.

Stapes Facial nerve Mylohyoid nerve Chorda tympani

Fig. 4-80.

Reichert's cartilage

Mandible of human embryo 24 mm long. Inner aspect. Cartilage is in blue, bone in yellow. (From model by Low.)

AXIAL SKELETON

deciduous molar tooth. The mandibular angle is ob¬ tuse (175 degrees), and the condylar process is nearly in line with the body. The coronoid process is comparatively large and projects above the level of the head of the mandible. After birth (Fig. 4-83, B) the two segments of the bone become joined from below upward at the sym¬ physis in the first year (Fig. 4-83, A), but a trace of separation may be visible in the beginning of the second year near the alveolar margin. The entire length of the mandibular body becomes elongated, but more especially posterior to the mental foramen, which provides space for the three additional teeth developed in this part. The depth of the body in¬ creases due to enlargement of the alveolar part. This allows room for the roots of the teeth, and results in the thickening of the portion below the oblique line, which enables the jaw to withstand the powerful action of the masticatory muscles. The alveolar por¬ tion, however, becomes the deeper of the two parts, and consequently the largest portion of the mandib¬ ular body lies above the oblique line. The mandibu¬ lar canal, after second dentition (Fig. 4-83, C), is situated just above the level of the mylohyoid line and the mental foramen occupies the more adult position. The mandibular angle diminishes due to the separation of the jaws by the teeth, and by the fourth year it is 140 degrees.

183

In the adult (Fig. 4-83, D) the alveolar portion and the portion below the oblique line are usually of equal depth. The mental foramen opens midway between the upper and lower borders of the bone, and the mandibular canal runs nearly parallel with the mylohyoid line. The ramus is almost vertical in direction, and the mandibular angle measures about 1 20 degrees. In old age (Fig. 4-83, E) the mandible becomes greatly reduced in size because the alveolar process is absorbed after the loss of the teeth, leaving the chief bulk of the bone below the oblique line. The mandibular canal with the mental foramen opening from it becomes positioned close to the alveolar bor¬ der. The angle widens once more, measuring about 140 degrees, and the neck of the condylar process becomes oriented slightly backward.

HYOID BONE

The hyoid bone (os hyoideum; Fig. 4-84), named from its resemblance to the Greek letter U, is suspended from the tips of the styloid processes of the temporal bones by the stylohyoid ligaments. It is located in the anterior part of the neck between the chin and the larynx, and is composed of five por-

Mandibular nerve

Anterior process of malleus Fig. 4-81. Mandible of human embryo 95 mm long. Outer aspect. Nuclei of accessory cartilages stippled. Cartilage is in blue, bone in yellow. (From model by Low.)

Auriculotemporal nerve Lingual nerve Meckel's cartilage

Inf. alveolar

Ant. process of malleus Chorda tympani Symphysis

Mylohyoid nerve

Mandible of human embryo 95 mm long showing symphysis. Inner aspect. Nuclei of accessory cartilages stippled. Cartilage is in blue, bone in yellow. (From model by Low.) Fig. 4-82.

1 84

OSTEOLOGY

Fig. 4-83.

The mandible at different periods of life. Left lateral aspect.

tions: a body, two greater cornua, and two lesser cornua. The body (corpus ossis hyoidei) or central part is quadrilateral in shape and placed transversely across the midline of the neck. Its ventral surface (Fig. 4-84) is convex and is directed forward and somewhat cranially. Its upper half is crossed by a well-marked transverse ridge, and in many cases a verti¬ cal median ridge divides it into two lateral

halves. The geniohyoid muscle is inserted into the greater part of the ventral surface, both above and below the transverse ridge. A portion of the origin of the hyoglossus muscle encroaches upon the lateral margin of the geniohyoid attachment. Below the transverse ridge are inserted the mylohyoid, sternohyoid, and omohyoid muscles. The dorsal surface is smooth and concave, and is directed somewhat caudally, being sepa-

AXIAL SKELETON Greater cornu

Constrictor pharyngis medius Hyoglossus Lesser cornu Chondroglossus Genioglossus

!iI

Digastricus & stylohyoideus Thyrohyoideus Body

Omohyoideus

« • , • . ' Geniohyoideus Fig. 4-84.

Sternohyoideus '

Mylohyoideus

185

small, conical eminences, each attached by its base to the angle of junction between the body and the greater horn (Fig. 4-84). The lesser horn is connected to the body of the hyoid by fibrous tissue, and occasionally to the greater horn by a distinct synovial joint, which may either persist throughout life, or become ankylosed. The lesser horn is situated in line with the transverse ridge on the body and appears to be in morphological continuation to it. The stylohyoid ligament is attached to the apex of the lesser horn and the chondroglossus arises from the medial side of its base.

Hyoid bone. Anterior surface viewed from

above.

rated from the epiglottis by the thyrohyoid membrane, an intervening bursa, and a quantity of loose areolar tissue. The superior border is rounded and gives attachment to the thyrohyoid membrane and some apo¬ neurotic fibers of the genioglossus. The infe¬ rior border receives the insertion of the ster¬ nohyoid muscle medially, the omohyoid laterally, and occasionally the medial por¬ tion of the thyrohyoid. It also gives attach¬ ment to the levator glandulae thyroideae, when this muscle is present. In early life the lateral borders of the body are connected by cartilage to the greater cornua, but after mid¬ dle life this union is osseous. The two greater cornua (cornua mcijora) project dorsally from the lateral border of the body (Fig. 4-84). Each cornu, or horn, is flattened and becomes more slender posteri¬ orly, ending in a tubercle to which is fixed the lateral thyrohyoid ligament. The greater cornua can be palpated above the lateral aspects of the thyroid cartilage and their cra¬ nial surfaces are rough near the lateral bor¬ ders for muscular attachments. The most extensive attachments are the origins of the hyoglossus and constrictor pharyngis me¬ dius which stretch along the whole length of the horn. The digastric and stylohyoid mus¬ cles have small insertions near the junction of the horn with the body. The digastric is attached by a small connective tissue loop through which its tendon courses. The thy¬ rohyoid membrane is attached along the medial border of each horn and the thyrohy¬ oid muscle is attached anteriorly along the lateral border. The two lesser horns (cornua minora) are

DEVELOPMENT AND OSSIFICATION The greater horns and much of the body of the hyoid are derived embryologically from the third visceral arch cartilage. A portion of the body, the lesser horns, and the stylohyoid ligaments to which they are attached are derived from the second or hyoid arch. The hyoid is ossified from six centers: two for the body, and one for each horn. Ossification commences in the greater horns toward the end of fetal life, in the body shortly afterward, and in the lesser cornua during the first or second year after birth.

OCCIPITAL BONE

The occipital bone (os occipitale), which forms most of the posterior aspect of the skull as well as part of its base, is trapezoid in shape and internally concave in a cup-like manner (Figs. 4-85; 4-86). It is pierced by a large oval aperture, the foramen magnum, through which the cranial cavity communi¬ cates with the vertebral canal. The curved, expanded plate posterior to the foramen magnum is named the squama; the thick, somewhat quadrilateral portion anterior to the foramen is called the basilar part, and on each side of the foramen is the lateral por¬ tion. the squama. The squama (squama occip¬ italis), situated above and bordering the posterior part of the foramen magnum, is curved and rounded from above downward and from side to side. The external surface is convex and, midway between the summit of the bone and the foramen magnum, presents a bony prominence, the external occipital protuberance (Fig. 4-85). Extending lateralward from this on each side are two curved lines, one a little above the other. The more superior, often faintly marked, is named the

186

OSTEOLOGY

Planum occipitale Highest nuchal line

'%ttocc£ protuiera nee '

Lambdoid suture

L

.? S

f Se«'Sp(Aj

7

Foramen magnum

C^T,^'S

\

V. "W X

Occipital belly i occipitofrontalis

I Occipiitomasl V.• •

•

•

•

• • • • •

•

•

• -

•

•

•

*

•

• •

• • • • • •

• • • • •

• •

•

•

•

•

•

•

•

•

•

•

• •

4

•

• • • • •

•

•

•

•

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Fig. 6-93. Diagrammatic representation of the structure of striated muscle showing the overlapping arrays of the thinner, actin- and thicker myosin-containing filaments. Lower diagrams show cross-sectional patterns of the fila¬ ments through the A and H bands. (From H. E. Huxley, 1969. Science, 164: 1356. Copyright 1969 by the American Association for the Advancement of Science.)

STRUCTURE OF SKELETAL MUSCLE

597

Fig. 6-94. Electron micrograph of frog sartorius myofibrils showing A bands cut in cross section. Note that the thick myosin filaments within the myofibril are each surrounded by six thin actin filaments. 150,000 X. (Modified from H. E. Huxley, 1968.)

I

A

I

Fig. 6-95. This diagram shows the changes that occur in a sarcomere with muscle contraction. During contraction (low part), the thin actin filaments slide toward the center of the A band. This diminishes the width of the I bands and the H band seen in relaxed muscle (upper part). (From Windle, Textbook of Histology, 4th Ed., McGraw-Hill, 1969. Used with permission of McGraw-Hill Book Company.)

598

MUSCLES AND FASCIAE

cidate how the contraction of myofibrils is initiated by arriving nerve impulses to the surface membrane or sarcolemma of the muscle cell. Myofibrils are encased longitu¬ dinally by a parallel array of interconnected membranous tubules and cisternae that composes the sarcoplasmic reticulum (Figs. 6-96; 6-97). Extending along both the A band and the I band, the sarcoplasmic retic¬ ulum fuses to form a cisterna at the H zone. Near both ends of the sarcomere at the Z lines, the tubules expand and coalesce to form terminal cisternae. Each terminal cis¬ terna interfaces another, located on the op¬ posite side of the Z line. At this site (in am¬ phibian muscle) or at the junction of the A band and I bands (in mammalian muscle), the terminal cisternae of the sarcoplasmic reticulum become associated with a trans¬ verse tubular system that courses along the Z line called the T system. The T tubule and the two terminal cisternae are collectively referred to as the triad (Figs. 6-96; 6-97). It has been shown that the T tubule, which passes all the way through the muscle fiber from one side of the sarcolemma to the

other, opens extracellularly. It is in contact with the exterior of the cell and contains extracellular fluid (Fig. 6-98). With the T tubules in continuity with the extracellular space and the sarcoplasmic re¬ ticulum intimately associated with the intra¬ cellular contractile components of the mus¬ cle fiber, a morphological system exists that can communicate surface events oc¬ curring on the sarcolemma to the contractile substructure in the interior of the myofibril. It has been proposed that the contractile wave of depolarization initiated at the myo¬ neural junction spreads not only along the skeletal muscle surface, but also through the T tubule system. In some manner, this exci¬ tation is transmitted across the common membranous wall shared by the T tubule and the terminal cisternae of the sarcoplas¬ mic reticulum, which contains calcium ions. The release of calcium within the sar¬ coplasmic reticulum probably initiates contraction, after which calcium becomes bound once again, perhaps by a relaxation factor, leading to relaxation of the myofi¬ brils.

Fig. 6-96. This drawing depicts the relationship between the myofibrils (four are shown) of a muscle fiber, the associated sarcoplasmic reticulum (SR), and the T system (TS). The sarcoplasmic reticulum expands into terminal cisterns (SR') at the I bands, and forms at the Z lines a triad (see three arrows) with the T tubule. (From Porter and Bonneville, Fine Structure of Cells and Tissues, 4th Ed., Lea & Febiger, 1973.)

STRUCTURE OF SKELETAL MUSCLE

599

Fig. 6-97. Electron micrograph of the sarcoplasmic reticulum and T tubules of a goldfish skeletal muscle myofibril (78,300 x)- T: T tubules; Z: Z lines. Note the fenestrations (f) or pores in the sarcoplasmic reticulum at the H zone of the sarcomere. (From Uehara, Campbell, and Burnstock, Muscle and Its Innervation, Edward Arnold Publishers, Ltd., 1976.)

600

MUSCLES AND FASCIAE

Fig. 6-98. Transverse section of a skeletal muscle fiber cutting across the Z line (Z) and showing the T tubules (T). The arrow indicates that the T tubule is in direct continuity with the external environment. Where the section cuts at the level of the 1 band, the terminal sacs of the sarcoplasmic reticulum (SR) can be seen. 38,500 X- (From FranziniArmstrong and Porter, ). Cell Biol., 1964.)

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.)

General References Bourne, G. H. (ed.). 1973. The Structure and Function of Muscle. 2nd ed. Academic Press, New York, 4 vols. Close, R. I. 1972. Dynamic properties of mammalian skeletal muscles. Physiol. Rev., 52:129-197. Eycleshymer, A. C., and D. M. Shoemaker. 1911. A Cross-Section Anatomy. Appleton-Century-Crofts, New York, 373 pp. Ferner, H., and J. Staubesand. 1975. Benninghoff und Goerttler’s Lehrbuch der Anatomie des Menschen. 11th ed. Urban and Schwarzenburg, Munich, 3 vols. Healey, J. E., and W. D. Seybold. 1969. A Synopsis of Clinical Anatomy. W. B. Saunders, Philadelphia, 324 pp. Hollinshead, W. H. 1968. Anatomy for Surgeons. 2nd ed. Hoeber-Harper, New York, 3 vols. Huxley, A. F. 1974. Muscular contraction. J. Physiol. (Lond.), 243:1-43. Last, R. J. 1978. Anatomy. Regional and Applied. 6th ed. Churchill Livingstone, New York, 598 pp.

MacConaill, M. A., and J. V. Basmajian. 1969. Muscles and Movements. Williams and Wilkins, Baltimore, 325 pp. Rasch, P. )., and R. K. Burke. 1963. Kinesiology and Ap¬ plied Anatomy. 2nd ed. Lea & Febiger, Philadelphia, 503 pp. Rauber-Kopsch, Fr. 1955. Lehrbuch und Atlas der Anat¬ omie des Menschen. 19th ed. Georg Thieme Verlag, Stuttgart, 2 vols.

Muscle Development Arey, L. B. 1938. The history of the first somite in human embryos. Carneg. Instn., Contr. Embryol., 27:235270. Beckham, C., R. Dimond, and T. K. Greenlee, Jr. 1977. The role of movement in the development of a digi¬ tal flexor tendon. Amer. J. Anat., 150:443-460. Bintliff, S., and B. E. Walker. 1960. Radioautographic study of skeletal muscle regeneration. Amer. J. Anat., 106:233-245.

REFERENCES

Butler, N., and A. E. Claireaux. 1963. Congenital dia¬ phragmatic hernia as a cause of perinatal mortality. Lancet, 1:659-663. Chaplin, D. M., and T. K. Greenlee. 1975. The develop¬ ment of human digital tendons. J. Anat. (Lond.), 120:253-274. Gamble, J. F., and G. Allsopp. 1978. Electron microscopic observations of human fetal striated muscle. J. Anat. (Lond.), 126:567-590. Gasser, R. F. 1967. The development of the facial muscles in man. Amer. ). Anat., 120:357-376. Godman, J. C. 1957. On the regeneration and redifferen¬ tiation of mammalian striated muscles. J. Morph., 100:27-81. Goldspink, G. 1970. The proliferation of myofibrils dur¬ ing muscle fiber growth. J. Cell Sci., 6:593-603. Gray, S. W„ and J. E. Skandalakis. 1972. Embryology for Surgeons. W. B. Saunders Co., Philadelphia, 918 pp. Hitchcock, S. E. 1970. The appearance of a functional contractile apparatus in developing muscle. Devel. Biol., 23:399-423. Hitchcock, S. E. 1971. Detection of actin filaments in homogenates of developing muscle using heavy meromyosin. Devel. Biol., 25:492-501. McKenzie, J. 1962. The development of the sternomastoid and trapezius muscles. Carneg. Instn., Contr. Embryol., 37:123-129. Maier, A., and E. Eldred. 1974. Postnatal growth of extraand intrafusal fibers in the soleus and medial gastro¬ cnemius of the cat. Amer. J. Anat., 141:161-178. Ontell, M., and R. F. Dunn. 1978. Neonatal muscle growth: a quantitative study. Amer. J. Anat., 152:539-556. Speidel, C. C. 1938. Growth, injury and repair of striated muscle. Amer. J. Anat., 62:179-235. Spyropoulos, M. N. 1977. The morphogenetic relation¬ ship of the temporal muscle to the coronoid process in human embryos. Amer. J. Anat., 150:395-410. Straus, W. L., and M. E. Rawles. 1953. An experimental study of the origin of the trunk musculature and ribs in the chick. Amer. J. Anat., 92:471-509. Swinyard, C. A. (Ed.). 1969. Limb Development and De¬ formity. Charles C Thomas, Springfield, Ill., 672 pp. Tomanek, R. J., and A. Colling-Salton. 1977. Cytological differentiation of human fetal skeletal muscle. Amer. J. Anat., 149:227-246. Walker, S. M., and M. B. Edge. 1971. The sarcoplasmic reticulum and development of Z lines in skeletal muscle fibers of fetal and postnatal rats. Anat. Rec., 169:661-678. Wells, L. J. 1948. Observations on the development of the diaphragm in the human embryo. Anat. Rec., 100:778. Wells, L. ). 1954. Development of the human diaphragm and pleural sacs. Carneg. Instn., Contr. Embryol., 35:107-134.

Histology and Electron Microscopy Bloom, W., and D. W. Fawcett. 1975. A Textbook of His¬ tology. 10th ed. W. B. Saunders Co., Philadelphia, 1033 pp. Chiakulas, J. J., and J. E. Pauly. 1965. A study of postnatal growth of skeletal muscle in the rat. Anat. Rec., 152:55-61. Comer, R. D. 1956. An experimental study of the “laws” of muscle and tendon growth. Anat. Rec., 125:665682.

601

Constantin, L. L., C. Franzini-Armstrong, and R. (. Podolsky. 1965. Localization of calcium accumulat¬ ing structures in striated muscle. Science, 147:158160. Copenhaver, W. M., D. E. Kelly, and R. L. Wood. 1978. Bailey’s Textbook of Histology. 17th ed. Williams and Wilkins, Baltimore, 800 pp. Di Fiore, M. S. 1974. Atlas of Human Histology. 4th ed. Lea & Febiger, Philadelphia, 252 pp. Eaton, B. L., and F. A. Pepe. 1974. Myosin filaments showing a 430 A axial repeat periodicity. J. Molec. Biol., 82:421-423. Ebashi, S. 1972. Calcium ions and muscle contraction. Nature, 240:217-218. Eisenberg, B. R., A. M. Kuda, and J. B. Peter. 1974. Stereological analysis of mammalian skeletal mus¬ cle. I. Soleus muscle of the adult guinea pig. J. Cell Biol., 60:732-754. Farrell, P. R., and M. R. Fedde. 1969. Uniformity of struc¬ tural characteristics throughout the length of skele¬ tal muscle fibers. Anat. Rec., 164:219-229. Fawcett, D. W. 1960. The sarcoplasmic reticulum of skel¬ etal and cardiac muscle. Circulation, 24:336-348. Franzini-Armstrong, C. 1970. Studies of the triad. I. Structure of the junction in frog twitch fibers. J. Cell Biol., 47:488-499. Franzini-Armstrong, C. 1971. Studies of the triad. II. Penetration of tracers into the junctional gap. J. Cell Biol., 49:196-203. Franzini-Armstrong, C., and K. R. Porter. 1964. Sarcolemmal invaginations constituting the T system in fish muscle fibers. J. Cell Biol., 22:675-696. Gauthier, G. F. 1970. The ultrastructure of three fiber types in mammalian skeletal muscle fibers. In The Physiology and Biochemistry of Muscle as a Food. Edited by E. J. Briskey, R. G. Cassens, and B. B. Marsh. The University of Wisconsin Press, Madi¬ son. Gay, A. J., Jr., and T. E. Hunt. 1954. Reuniting of skeletal muscle fibers after transection. Anat. Rec., 120:853872. Goss, C. M. 1944. The attachment of skeletal muscle fi¬ bers. Amer. j. Anat., 74:259-290. Ham, A. W. 1974. Histology. 7th ed. J. B. Lippincott, Phil¬ adelphia, 1006 pp. Hanson, J., and }. Lowy. 1963. The structure of F-actin and of actin filaments isolated from muscle. J. Molec. Biol., 6:46-60. Hanson, J., and J, Lowy. 1964. The structure of actin fila¬ ments and the origin of the axial periodicity in the I-substance of vertebrate striated muscle. Proc. Roy. Soc. Lond., B 160:449-458. Hay, E. D. 1963. The fine structure of differentiating mus¬ cle in salamander tail. Zeitschr. f. Zellforsch., 59: 6-34. Hess, A. 1970. Vertebrate slow muscle fibers. Physiol. Rev., 50:40-62. Huxley, A. F., and R. Niedergerke. 1954. Structural changes in muscle during contraction. Nature, 173:971-993. Huxley, A. F., and R. E. Taylor. 1958. Local activation of striated muscle. J. Physiol. (Lond.), 144:426-441. Huxley, H. E. 1957. The double array of filaments in cross-striated muscle. I. Biophys. Biochem. Cytol., 3:431-648. Huxley, H. E. 1963. Electron microscopic studies on the structure of natural and synthetic protein filaments from striated muscle. J. Molec. Biol., 7:281-308.

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Blood Vessels and Nerves of Muscles Barrnett. R. J. 1966. Ultrastructural histochemistry of normal neuromuscular junctions. Ann. N. Y. Acad. Sci., 135:27-34. Bowden, R. E. M., and J. R. Napier. 1961. The assessment of hand function after peripheral nerve injuries. J. Bone Jt. Surg., 43-B:481-492. Brockis, J. G. 1953. The blood supply of the flexor and extensor tendons of the fingers in man. J. Bone Jt. Surg., 35-B.T31-138. Bruns, R. R., and G. E. Palade. 1968. Studies on blood capillaries. I. General organization of blood capil¬ laries in muscle. J. Cell Biol., 37:244-276. Duchen, L. W. 1971. An electron microscopic comparison of motor end-plates of slow and fast skeletal muscle fibers of the mouse. J. Neurol. Sci., 14:37-46. Edwards, D. A. W. 1946. The blood supply and lymphatic drainage of tendons. J. Anat. (Lond.), 80:147-152. Grant, R. T., and H. P. Wright. 1970. Anatomical basis for non-nutritive circulation in skeletal muscle exem¬ plified by blood vessels of rat biceps femoris tendon. J. Anat. (Lond.), 106:125-134. Harness, D., and E. Sekeles. 1971. The double anasto¬ motic innervation of thenar muscles. J. Anat. (Lond.), 109:461-466. Harness, D., E. Sekeles, and J. Chaco. 1974. The double motor innervation of the opponens pollicis muscle: An electromyographic study. J. Anat. (Lond.), 117:329-332. Harrison, V. F., and O. A. Mortensen. 1962. Identification and voluntary control of single motor unit activity in the tibialis anterior muscle. Anat. Rec., 144:109116. Hollinshead, W. H., and J. E. Markee. 1946. The multiple innervation of limb muscles in man. J. Bone Jt. Surg.. 28:721-731. Ip, M. C., and K. S. F. Chang. 1968. A study on the radial supply of the human brachialis muscle. Anat. Rec., 162:363-371. McKinney, Jr., R. V., B. Singh, and P. D. Brewer. 1977. Fenestrations in regenerating skeletal muscle capil¬ laries. Amer. J. Anat., 150:213-218. Markee, J. E., W. B. Stanton, and R. N. Wrenn. 1952. The intramuscular distribution of the nerves to the mus¬ cles of the inferior extremity. Anat. Rec., 112:457. Marlow, C. D., R. K. Winkelmann, and J. A. Gibilisco. 1965. General sensory innervation of the human tongue. Anat. Rec., 152:503-511. Morrison, A. B. 1954. The levatores costarum and their nerve supply. J. Anat. (Lond.), 88:19-24. Rakhawy, M. T., S. H. Shehata, and Z. H. Badawy. 1976. The points of nerve entry and the intramuscular nerve branchings in the human muscles of mastica¬ tion. Acta Anat., 94:609-616. Robbins, H. 1963. Anatomical study of the median nerve in the carpal tunnel and etiologies of the carpaltunnel syndrome. J. Bone Jt. Surg., 45-A.953-965. Stillwell. D. L. 1957. The innervation of tendons and apo¬ neuroses. Amer. J. Anat., 100:289-317. Sunderland, S. 1945. The innervation of the flexor digitorum profundus and lumbrical muscles. Anat. Rec., 93:317-321. Sunderland. S. 1946. The innervation of the first dorsal interosseous muscle of the hand. Anat. Rec., 95:7-10. Telford, I. R. 1941. Loss of nerve endings in degenerated skeletal muscles of young vitamin E deficient rats.

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The heart is the central organ of the blood circulatory system. By its rhythmic contrac¬ tion, this dynamic muscular structure pumps the blood through a system of arteries to all parts of the body. Blood flows in a continu¬ ous circulation, delivering oxygen and nutri¬ ents to all organs, including the heart itself. This is accomplished through an enormous ramification of the arteries into minute ves¬ sels called arterioles, which in turn form a network of capillaries that are microscopic in size and have very thin walls. Allowing an exchange of substances with the tissues, the capillaries collect as venules, which then drain into larger veins that progressively increase in diameter and eventually return blood to the heart. The human heart is a four-chambered organ consisting of two ventricles and two atria. The powerful pumping portions of the heart are the right and left ventricles, which are separated by the muscular interventricu¬ lar septum. The ventricles have thick walls and are made to function efficiently by being quickly and forcibly filled with blood by contraction of the right and left atria. As blood is returned to the heart through the superior and inferior venae cavae, it enters the right atrium and is then forced into the right ventricle. From here it is pumped through the pulmonary arteries and into the

606

capillaries of the lungs, where it is refreshed as carbon dioxide is removed and oxygen absorbed. Blood is returned by the pulmo¬ nary veins to the left atrium, which forces it into the left ventricle. The left ventricle pro¬ pels oxygenated blood through the aorta and systemic arteries to the capillaries, and then back to the heart again through the venous system. The right side of the heart, the pul¬ monary arteries, the capillary system in the lungs, and the pulmonary veins constitute the lesser or pulmonary circulation. The left side of the heart, the aorta, the ramifying ar¬ teries to all the organs (except the lungs), and the returning veins (except the pulmo¬ nary veins) constitute the systemic circula¬ tion (Fig. 7-1). Although the systemic circulation to and from most organs characteristically involves only one set of capillaries within the various tissues, an exception is found in the vessels of the abdominal organs. The blood supplied to the spleen, pancreas, stomach, and intes¬ tines by the systemic arteries collects into the large portal vein, which enters the liver and ramifies within it. As the blood passes through the capillary-like hepatic sinusoids, it exchanges nutrient materials with the liver cells, and is then collected into the he¬ patic veins (Fig. 7-1). These drain into the large inferior vena cava, which is transport¬ ing systemic venous blood, just before that vessel opens into the right atrium. This di¬ version of blood by the way of the por¬ tal vein from certain abdominal organs, through the liver and back into the inferior vena cava, constitutes the portal circulation. The field of study of the vascular system is called angiology. It includes the study of blood vessels as well as vessels constituting the lymphatic system. Although the lym¬ phatic system drains into the veins, making the two systems interdependent, there are sufficient differences morphologically and functionally to make their separate treat¬ ment advisable. For convenience of descrip¬ tion, the field of angiology will be treated under four headings: the heart, the arteries, the veins, and the lymphatic system. These constitute the next four chapters.

Development of the Heart The first primordium of the vascular system can be recognized soon after the initial appearance FORMATION OF THE HEART TUBE.

DEVELOPMENT OF THE HEART

607

Pulmonary circulation

Junction of thoracic duct and subclavian vein

To head and upper limb

From head and upper limb Pulmonary artery -Aorta Hepatic vein Thoracic duct---

-Liver

-Portal vein Lymphatic trunks--

-Lymphatic vessels

-Systemic circulation

Fig. 7-1.

Schematic diagram of the blood vascular and lymphatic systems. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, 10th Ed., Vol 2, Urban & Schwarzenberg, 1975.)

of the coelom or body cavity within the embryo. This occurs on about the nineteenth or twentieth prenatal day, at a time when the mesoderm has been formed by the primitive streak, but before it has been organized into the primitive segments or somites. This first coelom is a U-shaped cavity encircling the cephalic end of the neural folds (Fig. 7-2). It is the primordium of the pericardial cavity. Its outer layer, the so¬ matic mesoderm, will become the parietal pericardium; its inner layer, the splanchnic mesoderm, will develop into the myocar¬ dium and epicardium. Scattered cells of

Fig. 7-2. Human embryo with first somite forming, 1.5 mm in length. Dorsal view with amnion removed and ectoderm and mesoderm cut away to show pericardial cavity. (Redrawn from Davis, 1927.)

mesodermal origin, called mesenchyme, mi¬ grate between the compact laminae of the splanchnic mesoderm and the entoderm. This mesenchyme proliferates rapidly and forms strands and sheets, which are the pri¬ mordium of the endocardium. The earliest stages of development of the human heart are imperfectly known because of the scarcity of available human embryos of this age. It is helpful, however, that the early development of the heart in lower mammalian embryos, such as the rat, is sufficiently similar to that seen in man to per¬ mit the use of timed specimens in these animals (Figs. 7-3 to 7-6) to elucidate the period between the human first somite stage (Fig. 7-2) and that of the human eight-somite stage (Fig. 7-7). It is convenient to use the number of somites as an index of the early stages of development because they can be counted accurately and they retain a relatively stable growth relationship to the rest of the embryo.

By the time the embryo has acquired its first three somites or primitive body seg¬ ments and before the neural folds have closed to form the neural tube, the endocar¬ dial mesenchyme has spread in a thin sheet across the midline in the cranial portion of the embryo (Fig. 7-3). It also extends down¬ ward on each side of the still shallow foregut invagination, and a lumen has begun to form

608

the heart

Ectoderm Forebrain Splanchnic mesoderm

Endocardium Foregut portal . Aortic arch A-V junction Aorta Vitelline vein Entoderm

A

B

Fig. 7-3. Rat embryo with 3 somites. A, Ventral view with entoderm removed. Lumen of heart and vessels is incom¬ plete. B, Median sagittal section of same embryo. Drawings of wax reconstruction made at 400 x magnification (From Goss, 1952.)

in these lateral extensions. The splanchnic mesoderm becomes thickened where it is in contact with the endocardium and is thus identifiable as the primordium of the myo¬ cardium. The myocardial layer is also deeply grooved along the lateral endocardial tubes. Thus, the two lateral endocardial tubes with their partial cloak of myocardium constitute the primitive lateral hearts, where the first contractions occur. The site of the future atrioventricular junction is marked by a constriction of the lumen of the lateral tube slightly caudal to the level of the foregut portal. The median sheet of mesenchyme is quickly differentiated into endocardium by having the lumen extend into it from

the lateral tubes. At the same time, the sheet appears to pull in its outlying parts, resulting in a sac rather than a tube, which, with its adjacent myocardial mesoderm, constitutes the primitive ventricle. As the endocardial sac expands, it sinks deep into a pocket in the mesoderm. The pericardial cavity enlarges to accommodate this growth and in a four-somite embryo the entire car¬ diac complex bulges ventrally at the foregut portal (Fig. 7-4). Until this time the myocardium has been entirely dorsal to the endocardium. The rapid expansion of the pericardial cavity in a ventral direction allows the myocardium to protrude ventrally over the endocardial sac, until, in a five-somite

Forebrain Pericardium Myocardium Endocardium Foregut A-V junction Aortic arch Entoderm Aorta Vitelline vein A

B

Rat embryo with 4 somites. A, Ventral view with entoderm removed. Compare endocardium with that in Figure 7-3. B, Median sagittal section of same embryo. (From Goss, 1952.) Fig. 7-4.

DEVELOPMENT OF THE HEART

609

ForebrainCarotid EctodermPericardium Myocardium Ventricular endocardium Atrium Foregut

Vitelline vein Aorta Entoderm B

A

Fig. 7-5. Rat embryo with 5 somites. A, Ventral view with entoderm removed. Ventral part of pericardium cut away to show myocardium. Dotted line indicates extent of endocardium inside ventricle. B, Median sagittal section of same embryo. Compare with Figures 7-3 and 7-4. (From Goss, 1952.)

tic of early mammalian embryos. When the embryo has acquired seven somites, the myocardium completely surrounds the en¬ docardium. The middle portion of the tubu¬ lar ventricle becomes free and only the ends are attached: the arterial end by its continu¬ ity with the aortic sac and first aortic arches, and the venous end by the atria and vitelline veins (Figs. 7-7; 7-9,A and B). DEVELOPMENT OF THE CARDIAC LOOP. The length of the tubular heart increases much more rapidly than the longitudinal extent of the pericardium. The heart tube therefore continues to bend, this time in a loop with convexity to the right, called the bulboventricular loop (Figs. 7-7; 7-9,C). The re¬ sulting groove on the left side is called the bulboventricular sulcus and establishes a

embryo, the heart lies in a plane at right angles to the axis of the embryo with the arterial end more dorsally placed and the venous end more ventrally placed (Fig. 7-5). By a continued rapid growth, the venricular myocardium extends over the entire ventral surface of the endocardium (Fig. 7-6). In a six-somite embryo, it encloses the endo¬ cardium except for a narrow interval along the midline dorsally. This change allows the heart to assume a more tubular shape with cranial and caudal extremities. The opening of the aortic sac is always dorsal rather than cranial to the heart and the whole tube main¬ tains a curvature with ventral convexity. The result is the marked' ventral protrusion of the cardiac complex which is characteris¬

Forebrain Carotid Ectoderm Pharynx Aortic arch Pericardium - Myocardium Ventr. endocardium Atrium Aorta Vitelline vein Entoderm (cut edge) A

B

Rat embryo with 6 somites. A, Ventral view with entoderm removed. Ventral part of pericardium and myocardium also removed to show endocardium. B, Median sagittal section of same embryo. (From Goss, 1952.) Fig. 7-6.

610

THE HEART

subdivision of the tube into the bulbus cordis (or conus) and the primitive ventricle (Figs. 7-8; 7-9,D). The ventricular portion in¬ creases rapidly in all diameters, protruding ventrally and causing another bend at the atrioventricular junction. The opening of the atrium narrows to form the atrioventricular canal, which enters the ventricle dorsally and from the left. The pericardial cavity expands over the two lateral portions of the atrium, which are then brought closer to¬ gether, and a constriction is formed between the veins and the atrium (Fig. 7-8). The proximal portions of the veins be¬ come part of a common chamber and are called the right and left horns of the sinus venosus. The umbilical and common cardi¬ nal veins (from the embryo proper) have joined the vitelline veins on each side just

before they enter the sinus horns (Fig. 7-9,D). The continued bending of the bulboventricular loop eventually folds the bulbus cordis against the atrium on the dorsal and cranial aspect of the heart (Fig. 7-10). The bulbus cordis, which later becomes the conus arteri¬ osus and truncus arteriosus, has remained a relatively narrow tube, and as it presses against the median region of the atrium, the lateral portions bulge out on each side. The resulting two expansions of the atrium are the primitive right and left atria (Fig. 7-10). They represent the first division of the heart into its permanent right and left sides. The tissue between the pericardial cavity and the foregut portal becomes thickened into a mass called the septum transversum (Figs. 7-8; 7-10). As the liver cords grow into the septum there is a reorganization of the

Forebrain

Aortic arch 1

Pericardium Bulbus cordis Bulboventricular loop Atrioventricular sulcus Right atrium

Pharyngeal membrane

Bulbus aortae Bulboventricular sulcus Ventricle Atrioventricular canal Left atrium Foregut portal

Fig. 7-7

Human embryo with 8 somites, 2 mm in length. Ventral view of plaster model of heart and pericardial region. Pericardial wall and myocardium removed to expose endocardium. (Redrawn from Davis, 1927.)

Aortic arch 1

Bulbus cordis

Pharynx

Pericardium Ventricle

Bulboventricular sulcus Atrium Septum transversum Foregut portal

Sinus venosus

Vitelline vein

Fig. 7 8

Human embryo with 11 to 12 somites, 3.09 mm in length. Ventral view of plaster model of heart and pericardial region. Pericardial wall and myocardium removed to expose endocardium. (Redrawn from Davis, 1927.)

DEVELOPMENT OF THE HEART

Arterial end of heart 1st aortic arch artery 1st branchial arch mesoderm Splanchnic mesoderm Fusing heart tubes

Unfused heart tubes Septum transversum Venous end of heart

1st aortic arch artery

Bulbus cordis

Ventricle

Atrium

Truncus arteriosus Bulbus cordis Ventricle Atrium

Sinus venosus Septum transversum

24 ±1 day

1 st & I 2nd J

Aortic arch arteries

Truncus arteriosus Bulbus cordis Ventricle Atrium Sinus venosus Common cardinal vein Umbilical vein Vitelline vein

Fig. 7-9. Four sketches of the ventral view of the devel¬ oping heart during the fourth week, showing fusion of the heart tubes and bending of the single heart tube. (From Moore, K. L., The Developing Human, 2nd Ed., W. B. Saunders Co., 1971.)

61 1

veins. The right vein gradually takes over the drainage of blood from the vitelline, umbilical, and posterior cardinal circula¬ tions of both sides and is thus the precursor of the inferior vena cava. The resultant en¬ largement of the right horn of the sinus ve¬ nosus shifts the sinoatrial opening to the right. The right anterior cardinal vein also becomes dominant and shifts the opening somewhat cranialward. partitioning of the atria. In the narrow part of the atrium between the two expan¬ sions to the right and left of the conus arteri¬ osus, a thin crescent-shaped fold of tissue grows from the dorsocranial wall of the atrium toward the atrioventricular opening. This is known as septum I or the septum primum (Figs. 7-11,A and B; 7-12). As the sep¬ tum primum progresses toward the ventri¬ cles, two mesenchyme covered endocardial swellings appear in the wall of the atrioven¬ tricular canal. These endocardial cushions (Fig. 7-11,C and D: AV canal cushions) soon join across the opening, making a division into a right and left atrioventricular opening. The narrowing open space between the ad¬ vancing septum primum and the endocar¬ dial cushions is the ostium I or ostium primum (Fig. 7-11,B and C). Before the sep¬ tum primum completely closes the opening between the two atria, which would shut off all flow of blood between them, the sub¬ stance of the septum primum, near its at¬ tachment to the cranial part of the atrial wall, becomes perforated and forms ostium II or the ostium secundum (Fig. 7-11,C and D). In the right atrium, a new partition now grows down from the cranial and ventral part of the atrial wall on the right side of septum primum, thus covering the new open¬ ing in the first septum. This second crescen¬ tic membrane is called the septum II or sep¬ tum secundum (Figs. 7-11,D to F; 7-13 to 7-15). Its growth ceases before it is complete, leaving an opening called the foramen ovale (Fig. 7-11,E and F). Its crescentic border per¬ sists as the limbus fossae ovalis, which can still be seen in the adult right atrium. After septum primum has joined with the endo¬ cardial cushions, its remaining part becomes thinner and persists as a flap over the fora¬ men ovale below the crescentic edge of sep¬ tum secundum. At this stage it acts as the valve of the foramen ovale (Fig. 7-11,F). After birth, when the foramen ovale is no

612

THE HEART

Aortic arch 1 Ibus cordis Ventricle Left atrium

Right atrium

Sinus venosus

Septum transversum Vitelline vein portal

Fig. 7-10. Human embryo with 20 somites, 3.01 mm in length. Dorsal view of plaster model of heart. (Redrawn from Davis, 1927.)

longer functional, this flap becomes adher¬ ent to the limbus and seals the opening. Dur¬ ing this development the pulmonary veins evaginate from the dorsal wall of the left atrium, but they are of insignificant size be¬ cause the lungs are still not functioning as aerating organs. The left heart, therefore, receives the bulk of its blood through the foramen ovale rather than from these veins. CHANGES IN THE SINUS VENOSUS. While the interatrial septa are forming, the slit-like opening of the sinus venosus into the right atrium is guarded by two valves, the right and left venous valves (Figs. 7-12 to 7-15). Above the opening, the two venous valves unite as a single fold, the septum spurium, which is a prominent feature at this stage, but is of no significance for the eventual par¬ titioning of the heart (Figs. 7-11; 7-13 to 7-15). As the right atrium increases in size it ab¬ sorbs the sinus venosus into its walls (Fig. 7-16,C and D). The upper part of the sinus then becomes the opening for the superior vena cava. The inferior part becomes di¬ vided by the further growth of the right ve¬ nous valve into two openings, the inferior vena cava and the coronary sinus (Fig. 7-16) The left venous valve disappears except for the lower part, which is absorbed into the septum secundum. The upper part of the right venous valve and the septum spurium almost disappear, but are retained in the adult heart as the crista terminalis (Fig. 7-11, E and F). The lower part of the right valve persists and is divided into two parts by the growth of a transverse fold, the sinus sep¬ tum (Fig. 7-15). These become the valve of

the inferior vena cava and the valve of the coronary sinus. Of the horns of the sinus venosus, the right becomes much more prominent because it furnishes the inferior and superior venae cavae. The left horn re¬ mains small, receiving only the left common cardinal vein. The left anterior cardinal dwindles into the oblique vein (Fig. 7-16,F) and the vestigial fold of Marshall.1 The left common cardinal also loses its connection with the body wall and becomes the coro¬ nary sinus, draining blood only from the substance of the heart (Fig. 7-16). DIVISION OF THE VENTRICLES AND PARTITION¬

The primi¬ tive ventricle becomes divided by the growth of the interventricular septum (Fig. 7-11,A to D). This muscular ridge develops from the most prominent part of the ventric¬ ular wall, and its position on the surface of the heart is indicated by a furrow. The dor¬ sal part of the septum grows more rapidly than the ventral and fuses with the dorsal part of the fused endocardial cushions. The opening between the two ventricles remains for some time, but at about the end of the seventh week, it ultimately is closed by the fusion of the membranous part of the inter¬ ventricular septum, derived from the right side of the united endocardial cushions, and the bulbar ridges, which appear in the bulbus cordis prior to the partitioning of the truncus arteriosus (Figs. 7-11,D to F; 7-17). ING of the truncus arteriosus.

'John Marshall (1818-1891): An English anatomist and surgeon (London).

DEVELOPMENT OF THE HEART

61 3

Septum spurium

Interatrial septum primum

Atriovent. canal

Intervent, septum

A 4-5 mm.

B 6-7 mm

Septum II

Septum I Septum II (caudal limb) A-v. canal cushion Intervent, foramen (closes at 15-17 mm.)

C 8-9 mm

Crista terminalis

Ostium II in septum I

Foramen ovale

Atriovent valves

Atriovent bundle

Papillary muscle

E 25-30 mm. Fig. 7-11.

F 100 mm. TO BIRTH

Frontal sections of human embryonic heart giving a sequential picture of its progressive partitioning at six different stages of development. Stippled areas indicate endocardial cushion tissue, and the diagonal hatching is the myocardium. In F, the asterisk identifies the membranous part of the interventricular septum. (From Patten, B. M„ Human Embryology, 3rd Ed. McGraw-Hill, 1968.)

614

THE HEART

valve Pericardium Pericardium

m I

Right horn of sinus venosus Vena cava opening Sinus venosus Right venous valve

Bulbar ridges Endocardial cushion Fig. 7-12.

Model of heart of 6.5-mm human embryo, interior of lower half seen from above. (From Tandler, 1912.)

Fig. 7-13.

Model of heart of 9-mm human embryo, ventral view of interior of atria. (From Tandler, 1912.)

Closely related to the separation of the ventricles and the closure of the interven¬ tricular foramen is the partitioning of the truncus arteriosus into the pulmonary artery and aorta. The conus arteriosus (bulbus cordis) was at first separated from the ventri¬ cle by a deep fold, the bulboventricular sul¬ cus. This fold gradually recedes, until the conus and ventricle open freely into each • other. This has the effect of allowing the truncus aortae to open directly into the ven¬ tricle, and it comes to lie in line with the path of the growing interventricular septum. The portion of the ventricular wall that had been the conus remains to the right of the interventricular septum and becomes a part of the adult right ventricle. The truncus arteriosus or primitive as¬ cending aorta has at this time developed both its fourth and its sixth, or pulmonary, pairs of arches. The partitioning of the

truncus into the aorta and pulmonary trunk begins by the growth of two thickenings, called truncal ridges, on the interior of the truncus arteriosus at its more cephalic end in the region of the fourth pair of arches. The growth of these ridges toward the bulbus cordis (or conus arteriosus), where they have been called bulbar ridges, is such that they follow a spiral course (Fig. 7-18). As it ex¬ tends away from the heart, the right ridge passes ventrally and then to the left, while the ridge on the left side of the truncus below passes dorsally and to the right as it extends farther from the heart. Their growth inward toward the lumen of the truncus fi¬ nally results in their fusion, thereby forming a spirally oriented aorticopulmonary sep¬ tum (Fig. 7-18). The truncus arteriosus then becomes divided into the pulmonary trunk and the aorta, but because the aorticopul¬ monary septum takes the form of a spiral,

DEVELOPMENT OF THE HEART

615

Septum II Septum spurium Left venous valve Foramen ovale Right venous valve Tricuspid valve Inferior vena cava Fig. 7-14.

Interior of the right atrium in the heart of a 25-mm human embryo. (From Licata, 1954.)

Septum II Septum spurium

Left venous valve Foramen ovale Right pulmonary vein Septum I

Right venous valve (cut) Coronary sinus opening

Inferior vena cava Sinus septum (cut)

Interior of the right atrium in the same heart as Figure 7-14 with the right venous valve removed. (From Licata, 1954.)

Fig. 7-15.

the two vessels become twisted around each other. Adjacent to the heart, the pulmonary trunk comes to lie anterior and to the right of the aorta, while more distally the pulmonary trunk lies to the left and behind the aorta (Fig. 7-18). The right ventricle becomes con¬ nected with the pulmonary arches that go to the lungs, while the left ventricle becomes connected with the fourth arch which forms the aorta. While the aorticopulmonary septum is partitioning the truncus arteriosus, three small local swellings of endocardial tissue develop in both the aorta and pulmonary trunk at the level of transition between the truncus arteriosus and its ventricular exten¬ sion, the conus arteriosus. These special swellings become the semilunar valves. Two of the valve cusps in each vessel are formed from tissue of the ridges that partition the truncus, and they retain this association of position throughout the subsequent rotation and twisting of the vessels (Fig. 7-19,A and B). The third cusp in each vessel is located opposite the points of fusion of the aortico¬ pulmonary septum and develops independ¬ ently from dorsal and ventral intercalated swellings (Fig. 7-19,C to E).

The first con¬ tractions of the heart have not been ob¬ served in human embryos, but it can be as¬ sumed that they follow the same sequence as in other mammals. In a rat embryo with three somites (Fig. 7-3), two lateral heart tubes are recognizable. On the ventricular side of a slight constriction that marks the future atrioventricular junction, a small group of cells in the splanchnic mesoderm begins contracting with a regular rhythm. In a rat embryo, the left lateral heart initiates the contraction at a rate of 20 to 30 per min¬ ute. A few hours later, the right heart com¬ mences with a slower rate and a regular rhythm independent of the left side. As the contraction involves the median portion of the ventricle, the rate increases gradually, the left side acting as pacemaker. By the time the rate has reached 90 per minute, a small part of the atrium adjacent to the atrioven¬ tricular junction has begun contraction and acts as the pacemaker, but with a distinct interval between the atrial and ventricular contraction (Goss, 1940, 1942). It is reasona¬ ble to conclude from these studies on subhu¬ man mammals that the developing human heart begins contracting at the end of the beginning of contraction.

616

the heart

Aortic arch I

Aortic arch Truncus arteriosus

Dorsal mesocardium (cut)

Atrium

Common cardinal v.

Sinus venosus

Umbilical vein

Pulmonary a from arch VI

Rt. com. card, v (sup. vena cava)

com. 1 vein

Pul trunk

Left com. card, v

Pulmonary veins Sinus venosus

Left — auricular app.

vena cava vena cava New tributaries to left common cardinal vein Interventricular sulcus Right ventricle Rt. pul.

Superior vena cava

Left superior pulmonary vein Sulcus terminalis Left. inf. pul. vein Sinus venorum Oblique vein (Marshall) of left atrium Great cardiac v.

Coronary sinus (proximal part of left com. card, v.)

Left ventricle

Peric. refl.

Small cardiac vein

Inferior vena cava

Middle cardiac vein

Fig 7 16. Six stages in the development of the heart seen from the dorsal aspect and showing the changing relations of the sinus venosus and the great veins entering the heart. A, 2% weeks, 8 to 10 somites; B, 3 weeks, 12 to 14 somites; C, 3y2 weeks, 17 to 19 somites; D, 5 weeks, 6 to 8 mm; E, 8 weeks, about 25 mm; F, 11 weeks, about 60 mm. (From Patten B. M., Human Embryology, McGraw-Hill, 1968.)

DEVELOPMENT OF THE HEART

Right truncobulbar ridge

61 7

Aorta Left truncobulbar ridge Aorticopulmonary septum

Right atrium Left atrioventricular orifice

Proliferation of post, atrio¬ ventricular endocardial cushion

Right atrioventricular orifice

Muscular part of interventricular septum

Aorticopulmonary

Membranous part of interventricular septum

Right atrioventricular orifice

Muscular part of interventricular septum

Fig. 7-17. Schematic drawings showing the way in which the truncobulbar ridges, combined with the proliferation of the posterior atrioventricular cushion, close the interventricular foramen and form the membranous portion of the interventricular septum. A, 6 weeks, 12 mm; B, beginning of 7th week, 14.5 mm; C, end of 7th week, 20 mm. (From Langman, J., Medical Embryology, 3rd Ed. Williams and Wilkins, 1975.)

Aorta Pulmonary artery Right atrium

Aortico¬ pulmonary septum

Aorta

Pulmonary artery

Aorta

Pulmonary artery

Membranous interven¬ tricular septum Right atrioven¬ tricular orifice

Pulmonary artery

®

Aorta

Pulmonary artery

Muscular interven¬ tricular septum

©

Left atrioventricular orifice

A, Diagram to show the spiral shape of the aorticopulmonary septum. B, Position of aorta and pulmonary artery at 25-mm stage (8th week). Note that the aorta and pulmonary artery twist around each other. (From Langman, J., Medical Embryology, 3rd Ed. Williams and Wilkins, 1975.) Fig. 7-18.

618

THE HEART

Dorsal intercalated valve swelling Fusing truncus ridges Ventral intercalated valve swelling A

ridge

C

Aorta Truncus septum Pulmonary artery

D

Fig. 7-19. Schematic diagrams of the partitioning of the truncus arteriosus and the origin of the aortic and pulmonary semilunar valves. (From Kramer, 1942.)

third prenatal week or the beginning of the fourth week, i.e., on the twenty-first or twenty-second day. beginning of circulation. The primitive heart, as it enlarges and differentiates, con¬ tinues to contract after the three-somite stage, but in embryonic rats it is ineffective for circulation until the embryo has eight or nine somites (Fig. 7-7). By that time the atrium is well established, the ventricle is an effective muscular pump, the cells in the blood islands of the yolk sac have acquired hemoglobin, and a continuous lumen has been established through the aortae, the umbilical and omphalomesenteric arteries, the yolk sac, and the placental capillaries, and back through the corresponding veins to the heart (Goss, 1942). The development of the arteries and veins is described at the beginning of the corre¬ sponding chapters.

Peculiarities in the Vascular System of the Fetus fetal heart. The chief peculiarities of the fetal heart are the direct communication be¬ tween the atria and the foramen ovale, and the large size of the valve of the inferior vena cava. Among other peculiarities the following may be noted: (1) In early fetal life

the heart lies immediately below the man¬ dibular arch and is relatively large in size. As development proceeds, it is gradually drawn within the thorax, but at first it lies in the midline; toward the end of pregnancy it gradually becomes oriented obliquely to¬ ward the left. (2) For a time the atrial portion exceeds the ventricular in size, and the walls of the ventricles are of equal thickness; to¬ ward the end of fetal life the ventricular por¬ tion becomes the larger and the wall of the left ventricle exceeds that of the right in thickness. (3) The size of the fetal heart is large in relation to the size of the rest of the body, the proportion at the second fetal month being 1 to 50, and at birth, 1 to 120, while in the adult the average is about 1 to 160. The foramen ovale, situated at the lower part of the atrial septum, forms a free com¬ munication between the atria until the end of fetal life. A septum (septum secundum) grows down from the upper wall of the atrium to the right of septum primum, in which the foramen ovale is situated. Shortly after birth, the two septa fuse, and the fora¬ men ovale is obliterated. The valve of the inferior vena cava serves to direct the blood from that vessel through the foramen ovale into the left atrium. fetal arterial system. The principal peculiarities of the arterial system of the fetus are the communication between the

PECULIARITIES IN THE VASCULAR SYSTEM OF THE FETUS

pulmonary artery and the aorta by means of the ductus arteriosus, and the continuation of the internal iliac arteries as the umbilical arteries to the placenta. The ductus arteriosus is a short tube, about 1.25 cm in length at birth, and 4.4 mm in diameter. In the early condition it forms the continuation of the pulmonary artery and opens into the aorta just beyond the ori¬ gin of the left subclavian artery (Fig. 7-20). Most of the blood that leaves the right ven¬ tricle is conducted by way of the ductus ar¬ teriosus into the aorta. When the branches of the pulmonary artery become larger than the ductus arteriosus, the latter is chiefly con¬ nected to the left pulmonary artery. The internal iliac arteries course along the sides of the bladder and then turn upward on the inner aspect of the anterior abdomi¬ nal wall to reach the umbilicus. At the umbili¬ cus they pass out of the abdomen and are continued as the umbilical arteries in the umbilical cord to the placenta (Fig. 7-20). They convey blood from the fetal arterial system to the placenta. FETAL VENOUS system. The peculiarities in the venous system of the fetus are the communications established between the placenta and the liver and portal vein, through the umbilical vein, and between the umbilical vein and the inferior vena cava through the ductus venosus Fig. 7-20). FETAL CIRCULATION

In early fetuses blood is returned from the placenta to the umbilical orifice by a single umbilical vein, which then divides into right and left umbilical veins. The right umbilical vein becomes atrophic early and then com¬ pletely disappears, leaving the left umbilical vein, which remains functional until birth (Fig. 7-20). This vein enters the abdomen at the umbilicus and passes upward along the free margin of the falciform ligament of the liver to the caudal surface of that organ, where it gives off several branches, a large one to the left lobe and others to the quadrate lobe and caudate lobe. At the porta hepatis it divides into two branches, of which the larger is joined by the portal vein and enters the right lobe of the liver and the smaller is continued cranially as the ductus venosus to join the inferior vena cava (Fig. 7-20). The blood that traverses the umbilical vein, therefore, passes to the inferior vena

61 9

cava in three different ways: (1) a considera¬ ble quantity circulates through the liver with the portal venous blood before entering the inferior vena cava by the hepatic veins; (2) some blood enters the liver directly, and is carried to the inferior vena cava by the hepatic veins; and (3) the remainder passes directly into the inferior vena cava through the ductus venosus. In the inferior vena cava, the blood car¬ ried by the ductus venosus and hepatic veins becomes mixed with that returning from the lower extremities and abdominal wall. Entering the right atrium, and guided by the valve of the inferior vena cava, it passes through the foramen ovale into the left atrium, where it mixes with a small quantity of blood returned from the lungs by the pulmonary veins. From the left atrium it passes into the left ventricle and then into the aorta, through which it is distributed almost entirely to the heart, head, and upper extremities; a small quantity is probably also carried into the descending aorta. From the head and upper limbs the blood is re¬ turned by the superior vena cava to the right atrium, where it mixes with a small portion of the blood from the inferior vena cava. From the right atrium it passes into the right ventricle, and thence into the pulmonary artery. Because the lungs of the fetus are inactive, only a small quantity of the blood in the pulmonary artery is distributed to them by the right and left pulmonary ar¬ teries. The blood that does go to the lungs is returned by the pulmonary veins to the left atrium. By far the larger quantity of blood in the pulmonary artery passes through the ductus arteriosus into the aorta, where it mixes with a small quantity of the blood transmitted by the left ventricle into the aorta. By means of this vessel, it is in part distributed to the lower limbs and the vis¬ cera of the abdomen and pelvis, but the greater amount is conveyed by the umbilical arteries to the placenta (Fig. 7-20). From the preceding account of the circula¬ tion of the blood in the fetus, which has been based on solid research evidence, the fol¬ lowing facts can be documented: (1) The pla¬ centa serves the purposes of nutrition and excretion, receiving impure blood that is low in oxygen from the fetus and returning it oxygenated and charged with additional nutritive material. (2) About half of the blood of the umbilical vein traverses the

620

THE HEART

Right common carotid a

Left common carotid a.

-Subclavian a

-Aorta

Superior vena cava

Ductus arteriosus

Pulmonary trunk Foramen ovale

Left atrium

Right atrium LEFT LUNG RIGHT LUNG Left ventricle Right ventricle

— Ductus venosus

-Aorta

Inferior vena cava

Umbilical vein-

-Portal vein

Umbilicus Common iliac a Umbilical cord

External iliac a

Internal iliac a

Fig 7-20. A simplified schema of the fetal circulation. Colors indicate degree of oxygen saturation of the blood Brightest red is highest oxygen saturation, while deepest blue is the lowest oxygen saturation.

THE PERICARDIUM

liver before entering the inferior vena cava; this accounts for the large size of the liver, especially at an early period of fetal life. The remainder of the blood in the umbilical vein bypasses the liver and enters the inferior vena cava through the ductus venosus. (3) The right atrium receives blood from two sources, the inferior vena cava and the supe¬ rior vena cava. At an early period of fetal life, it is quite probable that these two streams remain nearly distinct. Most of the blood flowing in the inferior vena cava is guided by the valve of this vessel directly through the foramen ovale and into the left atrium, but a small amount does seem to mix with blood returning to the right atrium from the head and upper limbs by way of the superior vena cava. It is from these latter sources that blood enters the right ventricle and exits from the pulmonary artery. Be¬ cause the pressure in the right atrium ex¬ ceeds that in the left atrium (which receives only a small amount of blood from the lungs by means of the pulmonary veins), the valve of the foramen ovale (septum primum) opens to the left, allowing blood from the inferior vena cava to flow from the right atrium to the left atrium. (4) The highly oxygenated (about 80% 02 saturated) blood carried from the placenta to the fetus by the umbilical vein, mixed with the blood from the portal vein and inferior vena cava, passes almost directly to the arch of the aorta, and is distributed by the branches of that vessel to the head for the developing brain and to the upper limbs. (5) The blood contained in the descending aorta, derived chiefly from that which has already circu¬ lated through the head and upper limbs, to¬ gether with a small quantity from the left ventricle, is distributed to the abdomen and lower limbs.

CHANGES IN THE VASCULAR SYSTEM AT BIRTH

When breathing commences in the new¬ born child, an increased amount of blood from the pulmonary artery passes through the lungs, and the placental circulation is eliminated by ligation of the umbilical cord. The foramen ovale gradually decreases in size during the first month, but a small open¬ ing frequently persists until the latter part of

621

the first year. The valve of the foramen ovale adheres to the margin of the foramen for the greater part of its circumference, and thereby the septum primum begins to fuse with septum secundum. A slit-like opening, however, may persist between the two atria. Unless this opening is large, it is of no func¬ tional significance. The ductus arteriosus begins to contract immediately after respiration is established, and its lumen gradually becomes obliter¬ ated. It ultimately becomes an impervious cord, the ligamentum arteriosum, which connects the left pulmonary artery to the arch of the aorta (Figs. 7-21; 7-26). The portions of the internal iliac arteries that extend from the sides of the bladder to the umbilicus become obliterated between the second and fifth days after birth, and persist as fibrous cords covered with perito¬ neum, the medial umbilical ligaments. These form ridges on the inner surface of the ante¬ rior abdominal wall. The umbilical vein and ductus venosus no longer receive blood after the umbilical cord has been severed. The umbilical vein be¬ comes the ligamentum teres, while the duc¬ tus venosus becomes the ligamentum veno¬ sus of the liver. The hepatic half of the ductus venosus may remain open, receive tributaries from the liver, and thus function as a hepatic vein in the adult.

The Pericardium Except for its continuity with the roots of the great vessels, the heart is unattached to other organs in the thoracic cavity. It is maintained in its proper position by these vessels and by an enclosing fibroserous sac, the pericardium, which allows the living heart an appropriate freedom of movement required for its contraction cycles (Figs. 7-21; 7-24). The pericardium consists of two quite different components, the membranous se¬ rous pericardium and the thicker fibrous pericardium. serous pericardium. The serous pericar¬ dium is composed of a single layer of mesothelial cells. It lines the inner surface of the fibrous pericardium and is continuous at the roots of the great vessels with the epicardium that forms the outermost layer of the heart wall itself. Its characteristics are such that it provides the interfacing pericar-

622

THE HEART

Brachiocephalic vein Internal thoracic vein Inf. thyroid vein Vagus nerve

Brachiocephalic vein -Vagus nerve Pericardiacophrenic a.

Pericardiacophrenic vein

Phrenic nerve Aortic arch

Superficial cardiac Sup. vena cava Recurrent laryngeal n. Pericardium

Lig. arteriosum Right and left pulmonary aa. Pleura

Transverse sinus Right superior pulmonary vein

Left superior pulmonary vein

Right inferior

Oblique sinus

pulmonary vein

Left inferior pulmonary vein

Inf. vena cava

Diaphragm

Pericardium

Phrenic nerve

^ ^ Anterior view of the dorsal aspect of the pericardial sac with the heart removed. Observe especially the oblique and transverse pericardial sinuses and the eight cut blood vessels that enter or leave the heart. Pulmonary veins and aorta colored red to indicate oxygenated blood; superior and inferior vena cavae and pulmonary artery colored blue to indicate blood with low oxygen levels. (After Sobotta.)

dial sac and heart with smooth and glisten¬ ing surfaces that are completely free and movable. The serous layer of the heart itself may be considered the visceral pericardium. It covers the atria and ventricles and extends beyond them along the great vessels for 2 or 3 cm (Fig. 7-21). The serous layer lining the . fibrous sac may be considered the parietal pericardium. Along the roots of the great vessels this continuous serous membrane folds upon itself, and the point at which the visceral layer becomes the parietal layer is called the reflection of the pericardium. pericardial cavity. Under normal condi¬ tions the two serous membranes are closely apposed, being separated only by enough serous or watery fluid to moisten their sur¬ faces. This allows the heart to move easily during its contraction in systole and its re¬

laxation in diastole. Because the two sur¬ faces are not fused, there is a potential space between them called the pericardial cavity, not unlike the pleural cavity. After injury or due to disease, fluid may exude into the cav¬ ity, causing a wide separation between the epicardium and the fibroserous pericardium. The extension of the epicardium on the great vessels is in the form of two tubular prolongations. One encloses the aorta and pulmonary trunk and is called the arterial mesocardium. The other encloses the supe¬ rior and inferior venae cavae and the four pidmonary veins and is called the venous mesocardium. The reflection of the venous mesocardium forms a U-shaped cul-de-sac in the dorsal wall of the pericardial cavity called the oblique pericardial sinus (Fig. 721). Between the arterial mesocardium and

GENERAL FEATURES OF THE HEART

the venous mesocardium is a serous-lined passage named the transverse pericardial sinus (Fig. 7-21). fibrous pericardium. The fibrous peri¬ cardium forms a cone-shaped sac, the neck of which is closed by its attachment to the great vessels just beyond the reflection of the serous pericardium (Fig. 7-21). It is a tough, dense membrane, much thicker than the pa¬ rietal pleura. Its outer surface is adherent in varying degrees to all the structures sur¬ rounding it. It is attached anteriorly to the manubrium of the sternum by a fibrous con¬ densation, the superior pericardiosternal ligament, and to the xiphoid process by the inferior pericardiosternal ligament. The fibrous tissue intervening posteriorly be¬ tween the pericardial sac and the vertebral column is the pericardiovertebral ligament. The sac is securely attached inferiorly to the central tendon and muscular part of the left side of the dome of the diaphragm. A thick¬ ening of this fibrous attachment in the region of the inferior vena cava has been called the pericardiophrenic ligament. LIGAMENT OF THE LEFT VENA CAVA. This small fibrous strand is covered by a trian¬ gular fold of serous pericardium, and it stretches from the left pulmonary artery to the atrial wall or the subjacent pulmonary vein. It is formed by the remnant of the left common cardinal vein (or left duct of Cuvier) which becomes obliterated during fetal life. If well developed, it may remain as a fibrous band stretching from the highest left intercostal vein to a small vein draining into the coronary sinus, the oblique vein of the left atrium (vein of Marshall). RELATIONS

OF

THE

PERICARDIAL SURFACES.

Laterally, the surfaces of the pericardial sac are apposed to the mediastinal parietal pleura. The pericardium and the mediastinal pleura are adherent but not fused, and the phrenic nerve with its accompanying blood vessels is held between them as it de¬ scends in the thorax. Because of the rounded contour of the heart, the pleural cavity partly encircles the pericardial sac, extend¬ ing anteriorly between it and the chest wall except for a small triangular area on the left side (Figs. 3-14; 3-17). This area corresponds to the caudal portion of the body of the ster¬ num and the medial ends of the left fourth and fifth costal cartilages. As mentioned above, in percussion of the chest for physi¬ cal diagnosis, the triangle is called the area

623

of superficial cardiac dullness because no lung is present to give it resonance. This site is also important clinically as the area through which a needle can be introduced into the pericardial cavity for removal of excess fluid, without traversing the pleural cavity or lungs. More superiorly, the anterior surface may be in contact with the thymus in children. Posteriorly, the pericardial sac is in relation to the bronchi, esophagus, and de¬ scending thoracic aorta. Inferiorly, the peri¬ cardium is attached to the dome of the dia¬ phragm.

General Features of the Heart The heart is a hollow muscular organ shaped like a blunt cone and comparable in size to a human fist. It rests on the diaphragm between the lower part of the two lungs (Figs. 7-22; 7-23). It is enclosed in a fibroserous sac, the pericardium, and occupies a topographi¬ cal compartment of the thorax called the middle mediastinum (Fig. 7-24). Its position relative to the chest wall is described in Chapter 3 and shown diagrammatically in Figure 7-22, and the position and extent of the cardiac shadow in a roentgenogram are shown in Figure 7-23. The heart is partially covered anteriorly by the mediastinal bor¬ ders of the lungs, although a triangular re¬ gion, which can be outlined by percussion, is not covered with lung tissue and is called the area of superficial cardiac dullness. The heart lies deep to the sternum and adjoining parts of the third to sixth costal cartilages. Its apex is directed downward, anteriorly, and to the left. Projecting farther into the left half of the thorax than the right, two-thirds of the heart lies to the left and one-third lies to the right of the median plane (Fig. 7-24). size. The average adult heart measures about 12 cm in length, 8 to 9 cm transversely at the broadest part, and 6 cm anteroposteriorly in thickness. Its weight, in the male, var¬ ies from 280 to 340 grams; in the female, from 230 to 280 grams. The heart frequently con¬ tinues to increase in weight and size until an advanced period of life. This increase is more marked in men than in women, and in many instances is pathological. heart wall. The wall of the heart is com¬ posed of three layers: the outermost is the

624

THE HEART

Common carotid artery

Thyroid gland

Internal jugular vein

n and v.

Right brachiocephalic

Superior vena cava

Pulmonary artery

Fig. 7-22. The heart and cardiac valves projected on the anterior chest wall, showing their relation to the ribs, sternum, and diaphragm. P = pulmonary valve; A = aortic valve; T = tricuspid valve; M = mitral valve. (From Eycleshymer and Jones.)

epicardium, deep to this is the myocardium, and the innermost is the endocardium. The surface layer, or epicardium, is a se¬ rous membrane that is continuous with the inner lining of the fibrous pericardium and reflects over the heart wall at the roots of the great vessels, and can, therefore, be consid¬ ered the visceral pericardium. It consists of a single sheet of squamous mesothelial cells resting on a lamina propria of delicate con¬ nective tissue. Between the epicardium and the myocardium is a layer of heavier fibroelastic connective tissue, which is inter¬ spersed with fatty tissue that fills in the crev¬ ices and sulci to give the heart a smooth, rounded contour. The larger blood vessels and the nerves are also found in this connec¬ tive tissue. The dark reddish color of the myocardium is visible through the epicar¬

dium except where fat has accumulated. The amount of fat varies greatly, but is sel¬ dom absent except in emaciated individuals. It may almost completely obscure the myo¬ cardium in the very obese. The myocardium is composed of layers and bundles of cardiac muscle with a mini¬ mum of other tissue except for the blood vessels. Its detailed structure is described in a later section. The endocardium is the inner lining of the heart. Its surface layer is composed of squa¬ mous endothelial cells, and it is continuous with the endothelial lining of the contiguous blood vessels. The connective tissue be¬ tween this endothelial lining and the myo¬ cardium is quite thin and transparent over the muscular walls of the ventricles, but is thickened in the atria and at the attachments

EXTERNAL FEATURES OF THE HEART

Anterior view of the thorax of an adult showing the contours of the heart and great vessels. 1, Arch of aorta. 2, Left atrium. 3, Left ventricle. 4, Apex. 5, Diaphragm. 6, Vascular shadow in lung. (Courtesy of Dr. James Collins, Department of Radiology, UCLA School of Medicine, Los Angeles.)

Fig. 7-23.

of the valves. It contains small blood vessels, parts of the specialized conduction system, and a few bundles of smooth muscle.

External Features of the Heart The heart consists of four chambers: two large ventricles with thick muscular walls making up the bulk of the organ, and two smaller atria with thin muscular walls. The atria are directed toward the base of the heart, while the ventricles are oriented to¬ ward the apex. The septum that separates the ventricles also extends between the atria, subdividing the whole heart into what frequently are called left and right halves or sides of the heart. As they lie in the body, however, the right side is mostly ventral or anterior and the left side largely dorsal or posterior. surface sulci. The atria are separated from the ventricles on the surface of the heart by the coronary sulcus (Figs. 7-25; 7-26). This groove encircles the heart and is occu¬

625

pied by the coronary vessels that supply the heart. The sulcus is deficient anteriorly be¬ cause the root of the pulmonary trunk arises from the right ventricle at this site. The in¬ teratrial groove, which separates the two atria, is scarcely marked on the posterior surface, while anteriorly it is hidden by the pulmonary trunk and the aorta. The line of separation between the two ventricles is marked by the anterior interventricular sul¬ cus on the sternocostal surface and by the posterior interventricular sulcus on the dia¬ phragmatic surface. Within these two sulci course the anterior and posterior interven¬ tricular branches of the coronary arteries and their accompanying veins (Figs. 7-25; 7-26). The two grooves become continuous just to the right of the apex at a notch termed the apical incisure of the heart. the apex. The apex of the heart points forward, to the left, and downward. Al¬ though its position changes continually dur¬ ing life, the tip remains close to the follow¬ ing point under usual circumstances: deep to the left fifth intercostal space, 8 or 9 cm from the midsternal line. This is about 4 cm below and 2 cm medial to the left nipple in the male. Because the site of the nipple can vary somewhat in females, this latter means of approximating the position of the apex may be less useful. The apex is overlapped by an extension of the pleura and lungs as well as by the structures of the anterior thoracic wall. the base. Although the base of the heart is somewhat more difficult to visualize than the apex, it can be conceived as the base of a blunt cone oriented in a direction opposite the apex. It faces backward, to the right, and upward. It is nearly quadrilateral in shape and is formed mainly by the left atrium, part of the right atrium, and the proximal parts of the great vessels (Fig. 7-27). The base of the heart extends superiorly as far as the bifur¬ cation of the pulmonary trunk, while irtferiorly it is bounded by the posterior part of the coronary sulcus containing the coronary sinus. To the right it is limited by the sulcus terminalis of the right atrium and to the left by the oblique vein of the left atrium. The descending thoracic aorta, the esophagus, and the thoracic duct intervene between the base of the heart and the bodies of the fifth to eighth thoracic vertebrae. At the base of the heart, the four pulmonary veins, two on

626

THE HEART

Internal thoracic vein Brachiocephalic vein Vagus nerve

Brachiocephalic vein

Inferior thyroid vein —■-Vagus nerve Pericardiacophrenic v.

Pericardiacophrenic artery Phrenic nerve

Superficial cardiac plexus Superior vena cava Aortic arch

Recurrent nerve Lig. arteriosum Pulmonary trunk

Pericardium Left atrium Right atrium Right coronary artery

Circumflex branch, left coronary a. Great cardiac v.

Pleura Anterior interventricular branch, left coronary artery Pericardium

Interventricular sulcus Right ventricle

Left ventricle

Phrenic nerve

Fig. 7-24. The anterior or sternocostal surface of the heart and great vessels after removal of the anterior part of the pericardium.

each side, open into the left atrium, while the superior vena cava opens into the upper part and the inferior vena cava into the lower part of the right atrium. surfaces and margins. The heart pre¬ sents several surfaces and margins (or bor¬ ders) which upon clinical examination can be useful in describing surface relationships and possible pathological distortion of its normal shape and contours. The sternocostal surface is formed by the right atrium, and especially its auricular appendage, and the right ventricle, to the left of which is a small part of the left ventricle (Fig. 7-25). The right upper aspect of this sur¬ face is crossed obliquely by the coronary sulcus, while the anterior interventricular sulcus passes from above downward and forms a line of separation between the right and left ventricles. The diaphragmatic surface is formed prin¬

cipally by the left ventricle, but also to some extent by the right ventricle (Fig. 7-26). It rests chiefly upon the central tendon of the diaphragm, and it is crossed obliquely by the posterior interventricular sulcus. Superiorly, it is separated from the base of the heart by the coronary sulcus. Right Margin. The right margin of the heart is longer than the left, and it describes an arc from the superior vena cava to the apex. Its upper part defines the margin of the right atrium, while the lower part of the right margin outlines the border of the right ven¬ tricle. Because the right ventricle lies nearly horizontally on the diaphragm, so does the lower part of the right margin. Coursing along the line of attachment of the dia¬ phragm to the anterior chest wall, the ven¬ tricular part of the right margin tends to be thin and sharp. It extends from the sternal end of the sixth right costal cartilage to the

CHAMBERS OF THE HEART

627

Left common carotid artery Brachiocephalic trunk Left subclavian artery

Superior vena cava Ligamentum arteriosum Left pulmonary artery Ascending aorta Pulmonary trunk Parietal pericardium Left auricle Left coronary artery Left coronary artery, circumflex branch

Right auricle

Ri ght coronary artery Conus arteriosus Anterior cardiac arteries and veins

Left coronary art., ant. interventricular branch

Coronary sulcus

Great cardiac vein

Right ventricle

Left ventricle Small cardiac vein Right coronary artery, marginal branch

Interventricular sulcus

Apex

Fig. 7-25.

The sternocostal surface of the heart viewed from the anterior aspect. (Modified after Sobotta.)

cardiac apex and is sometimes called the acute margin, or even the inferior border, of the heart. The atrial part of the right margin is almost vertical and is situated behind the third, fourth, and fifth costal cartilages, 1.25 cm to the right of the margin of the sternum. Left Margin. The left margin is shorter and more rounded, and is formed mainly by the left ventricle and to a small extent by the left atrium. It extends obliquely downward to the apex from a point 2.5 cm from the ster¬ nal margin in the second left interspace, de¬ scribing a curve that is convex laterally to the left.

Chambers of the Heart The interior of the human heart consists of four chambers, two atria superiorly, and two ventricles interiorly. A continuous septum, passing from the apex to the base, separates

the atria (interatrial septum) and the ventri¬ cles (interventricular septum). On each side of the heart the passage between the atrium and the ventricle is guarded by valves (right and left atrioventricular valves). Other valves (the aortic valve and the pulmonary valve) are interposed between the ventricles and the principal arteries leaving the heart. The interior of each of the four chambers presents specialized structures that contrib¬ ute to its function.

RIGHT ATRIUM

The right atrium (Fig. 7-28) is a somewhat cuboid chamber that has a capacity of about 57 ml. It appears larger than the left, and its wall, which is about 2 mm in thickness, is thinner than that of the left atrium. It con¬ sists of two parts: a principal cavity, situated posteriorly, called the sinus venarum, and a more anterior, smaller, conical pouch called the right auricle (Fig. 7-28).

628

THE HEART

Left subclavian artery

Left common carotid artery

Aortic arch Brachiocephalic trunk

Ligamentum arteriosum Superior vena cava Left pulmonary artery

Pulmonary trunk

- Right pulmonary artery

Left pulmonary veins

Transverse pericardial sinus

Left auricle Right pulmonary veins Great cardiac v*:~ Circumflex branch, left coronary artery

Oblique pericardial sinus Left atrium Parietal pericardium

Coronary sinus

Right atrium

Coronary sulcus Left ventricle

Posterior ventricular vessels

Middle cardiac vein Apex

Inferior vena cava Right coronary artery Posterior interventricular branch, right coronary artery Right ventricle

Fig. 7-26. The diaphragmatic surface and the base of the heart viewed from the dorsal aspect. The visceral pericar¬ dium still overlies the heart, but observe the cut edges of its reflection as the parietal pericardium over the large vessels. (After Sobotta.)

The sinus venarum is the part of the right atrium located between the superior and inferior venae cavae and the atrioventricular opening (Fig. 7-28). Its wall merges with these two large veins, and its interior surface is quite smooth except for certain rudimentary structures to be de¬ scribed. right auricle. The right auricle is a small, conical, muscular pouch which is an extension of the right atrium (Fig. 7-28). It is directed upward and to the left between the superior vena cava and the right ventricle, overlapping the right side of the root of the aorta. The junction of the right auricle with the sinus venarum is marked on the exterior of the atrium by a groove, the sulcus terminalis (Fig. 7-27), which corresponds to a ridge on the atrial inner surface, the crista terminalis. The internal surface of the auric¬ ula has its muscular bundles raised into sinus venarum.

distinctive parallel ridges resembling the teeth of a comb and named, therefore, the musculi pectinati. In addition to the crista terminalis and the musculi pectinati, the interior of the right atrium presents for examination a number of openings, valves, and other specialized structures. OPENING OF THE SUPERIOR VENA CAVA. The superior vena cava opens into the upper pos¬ terior part of the sinus venarum (Fig. 7-28). Its orifice is oriented downward and for¬ ward so that blood entering the atrium through it is directed toward the atrioven¬ tricular opening. The superior vena cava re¬ turns blood from the cranial half of the body, and there is no valve at its opening in the right atrium. OPENING OF THE INFERIOR VENA CAVA. The inferior vena cava opens into the most cau¬ dal part of the sinus venarum near the inter-

CHAMBERS OF THE HEART

629

Aorta

Superior vena cava

Left pulmonary artery

Right auricle Right pulmonary artery

Left auricle

Sulcus terminalis Left pulmonary veins

Right pulmonary veins Left ventricle

Inferior vena cava

Fig. 7-27. The base of the heart viewed from the dorsal and superior aspect. Pulmonary artery shown in blue because of low blood oxygenation level; pulmonary veins shown in red because of high blood oxygenation level.

Superior vena cava Left pulmonary artery

Right pulmonary artery Pulmonary trunk Aorta Left Right auricle Opening of sup. vena cava

Anterior

Semilunar cusps of pulmonary valve

Right Conus arteriosus

Limbus fossae ovalis

Right coronary artery

Fossa ovalis Sinus venarum Valve of coronary sinus Opening of inf. vena cava Valve of inf. vena cava Cusps of I Septal — right | Posterior A-V valve I Anterior

Interventricular septum

Septomarginal trabecula (moderator band)

Inferior vena cava

Anterior papillary muscle Trabeculae carneae Right ventricle

Fig. 7-28. Interior of the right atrium and right ventricle after the removal of the sternocostal wall of the heart. Pulmonary trunk and pulmonary arteries shown in blue to indicate the low level of oxygenation of the blood in these vessels.

630

THE HEART

atrial septum. Returning blood from the lower half of the body, its orifice is larger than that of the superior vena cava. This opening is directed upward and backward toward the fossa ovalis, and the rudimentary valve of the inferior vena cava extends a short distance superiorly from the opening on the interatrial septum. VALVE OF THE INFERIOR VENA CAVA. This valve (sometimes called the Eustachian valve1) is a single crescentic fold attached along the anterior and left margin of the ori¬ fice of the inferior vena cava. Its concave free margin ends in two cornua, of which the left is continuous with the anterior margin of the limbus fossae ovalis and the right spreads out on the atrial wall. The valve con¬ sists of a fold of the membranous lining of the atrium containing a few muscular fibers. In the fetus the valve is more prominent and tends to direct blood from the inferior cava to the left atrium through the foramen ovale, which is open prenatally. In the adult the valve is usually rudimentary and has little if any functional significance. It may be thin and fenestrated, very small, or even entirely absent. OPENING OF THE CORONARY SINUS. The coronary sinus opens into the right atrium between the orifice of the inferior vena cava and the atrioventricular opening. It returns most of the blood from the substance of the heart itself and the opening is protected by a thin valve. VALVE OF THE CORONARY SINUS. This Valve is a single semicircular fold of the lining membrane of the right atrium, and it is at¬ tached to the right and inferior lips of the orifice of the coronary sinus. It may have a cribriform structure and contain many per¬ forations or it may be doubled. The valve is seldom effective for more than partial clo¬ sure of the orifice during contraction of the atrium. FORAMINA VENARUM MINIMARUM. These are openings of small veins, the venae cordae minimi (or thebesian veins), which drain blood from the heart muscle directly into the atrial cavity. A few larger orifices can usually be seen in the septal wall, in¬ cluding those of the anterior cardiac veins. These openings were used by early scientists

to explain the passage of blood from one side of the heart to the other before William Harvey2 discovered the circulation of blood in 1610 a.d. Another orifice in the right atrium is the right atrioventricular opening, a large oval aperture of communication between the atrium and the right ventricle. It is described with the right ventricle. interatrial septum. The interatrial sep¬ tum forms the dorsal wall of the right atrium. It contains rudimentary structures which were of significance in the fetus. The fossa ovalis (Fig. 7-28) is an oval depression in the lower part of the septal wall and cor¬ responds to the foramen ovale of the fetal heart. It lies within a triangular area bounded by the openings of the two venae cavae and the coronary sinus. Its floor is formed by the remnant of the septum primum that initially separated the atria in the fetus. The limbus fossae ovalis is the prominent oval margin of the foramen ovale and repre¬ sents the free border of the septum secun¬ dum. The latter fetal structure forms just to the right of the septum primum in the fetus, and from it is derived most of the muscular part of the interatrial septum in the adult— that is, all except the floor of the fossa ovalis, which persists from the septum primum. The limbus is distinct cranially and at the sides, but it is deficient caudally. Frequently the cranial part of the two fetal septi do not fuse, leaving a slit-like opening in the adult interatrial septum through which a probe may be passed into the left atrium. This is spoken of as probe patency of the foramen and is found in 20 to 25% of all hearts. Larger openings are not uncommon, but these inter¬ atrial defects are seldom of functional signif¬ icance. The intervenous tubercle (of Lower3) is a small raised area in the septal wall of the right atrium between the fossa ovalis and the orifice of the superior vena cava. It is more distinct in the hearts of certain quadrupeds than in man, and in fetal life it may serve to direct blood from the superior cava into the atrioventricular opening.

-William Harvey (1578-1657): An English physician, physiologist, and embryologist. 'Bartolommeo Eustachio (1520-1574): An Italian anato¬ mist (Rome).

'Richard Lower (1631-1691): An English physician and physiologist.

CHAMBERS OF THE HEART

RIGHT VENTRICLE

The right ventricle occupies a large trian¬ gular part of the anterior or sternocostal sur¬ face of the heart and extends from the right atrium almost to the apex (Fig. 7-28). Its right boundary on the surface is the coronary sul¬ cus, while its left is the anterior longitudinal sulcus. Superiorly, the part of the right ven¬ tricle called the conus arteriosus joins the pulmonary trunk. Inferiorly its wall forms the acute margin of the heart and extends for some distance around the diaphragmatic surface. The wall of the right ventricle is thickest near the base of the heart and grad¬ ually becomes thinner toward the apex. The right ventricular wall is about one-third the thickness of that forming the left ventricle,

Aorta

631

but their capacities are the same, about 85 ml (Latimer, 1953). The interior of the right ventricle presents a number of openings and specialized parts (Figs. 7-29; 7-30) that require further descrip¬ tion. RIGHT ATRIOVENTRICULAR ORIFICE. This opening or ostium is a large oval aperture through which the right atrium communi¬ cates with the right ventricle (Figs. 7-28; 729). It measures about 4 cm in diameter and is large enough to admit the tips of four fin¬ gers. It is surrounded by a strong fibrous ring that is covered by the endocardial lining of the heart, and it is guarded by the right atrio¬ ventricular or tricuspid valve. RIGHT ATRIOVENTRICULAR VALVE. The right atrioventricular or tricuspid valve encircles

Lig. arteriosum

Pulmonary trunk

Right auricle Left cusp Anterior cusp Right cusp Conus arteriosus

Pulmonary valve

Left auricle

Supraventricular crest

C.ufPs [ Septal of,h°

Anterior

A-V vale l Pos,erior

Rt. ventricle

Anterior papillary muscle Anterior^ Cusps of the 1 left A-V PosteriorJ valve

Posterior papillary muscle Left ventricle

Fig. 7-29.

The interior of the right and left ventricles to show the atrioventricular and pulmonary valves.

632

THE HEART

leh'10' 1 .

CUSPS of the

I nnlmnnarv v; pulmonary valve

Left I Cusps of Right 1 the Posterior J aortic valve

Cusps of the left A-V valve (bicuspid)

' Anterior . Posterior Septal Anterior Posterior

Cusps of the right A-V valve (tricuspid)

Middle cardiac vein

Fig. 7-30. The atrioventricular, pulmonary, and aortic valves of the heart viewed from above after removal of the atria as well as the pulmonary trunk and aorta.

the right atrioventricular orifice and is notched into three roughly triangular leaflets or cusps. These are attached to the right ven¬ tricular wall, and when the valve opens, the cusps project into the ventricle. The three cusps are named anterior, posterior, and septal, and they are of unequal size (Figs. 7-28 to 7-30). The anterior (or infundibular) cusp is the largest (Figs. 7-28; 7-29) and is interposed between the atrioventricular orifice and the anterior wall of the right ventricle, to which it is attached in the region of the conus arte¬ riosus (or infundibulum). The posterior (or marginal) cusp, which is the smallest, ex¬ tends from the atrioventricular orifice to the ventricular wall adjoining the sternocos¬ tal and diaphragmatic surfaces, sometimes called the acute margin of the heart (Fig. 7-29). The septal (or medial) cusp extends between the interventricular orifice and the right side of the interventricular septal wall. Small intercalated leaflets may occur be¬ tween the three larger ones (Fig. 7-29). Each cusp is composed of strong fibrous tissue that is thick in the central part, but thin and translucent near the margin. The bases of the cusps are attached to the fibrous ring surrounding the atrioventricular orifice, while their apices project into the ventricu¬

lar cavity. The atrial surface of the leaflets is smooth, but the ventricular surface is more irregular and the free border of each cusp presents a ragged edge for the attachment of delicate tendinous cords called the chordae tendineae. In addition to their attachment to the cusps, the chordae tendineae are secured to papillary muscles in the ventricle. This makes the valve as a whole competent enough to withstand the back pressure of the blood during ventricular systole, thereby preventing the regurgitation of blood into the atrium. chordae tendineae. These strong fibrous cords are delicate but inelastic. They are at¬ tached to the ventricular end of the valve cusps at their apices and margins, and then are anchored to the muscular ventricular wall. They number about twenty and are of different length and thickness. The majority are attached to projections of the trabeculae carneae called papillary muscles (Figs. 7-28; 7-29). trabeculae carneae. The trabeculae car¬ neae are irregular bundles and bands of muscle that project from the entire inner surface of the ventricle except at the conus arteriosus, where the surface is smooth (Fig. 7-28). They are of three types: some are at¬ tached along their entire length to form

CHAMBERS OF THE HEART

ridges on the inner ventricular wall; others are fixed at their two extremities to the heart wall and extend across the lumen for short distances; and still others form the more spe¬ cialized structures called papillary muscles, which project from the heart wall at one end and attach to the chordae tendineae at the other (Fig. 7-28). Although the inner surface of the conus arteriosus is quite smooth, its limit is marked by a ridge of muscular tissue, the supraventricular crest, which extends across the dorsal ventricular wall toward the pulmonary trunk from the attachment of the ventral cusp at the atrioventricular ring (Fig. 7-29). The septomarginal trabecula is a stout bundle of heart muscle in the central or api¬ cal part of the right ventricle. It crosses the ventricular lumen from the base of the ante¬ rior papillary muscle to the interventricular septum (Fig. 7-28). It is of variable size and constancy in the human heart, but is more prominent in some larger mammals where it is supposed to resist overdistention of the ventricle. For this reason it is also called the moderator band. When present, it usually contains the right limb of the atrioventricu¬ lar conduction bundle (Truex and Copenhaver, 1947). papillary muscles. The papillary mus¬ cles are conical projections of ventricular muscle, the apices of which afford attach¬ ment to the chordae tendineae. Although their size and number are somewhat variable, the two principal ones are-named the ante¬ rior and posterior papillary muscles. The anterior papillary muscle is the larger of the two prominent papillary muscles, pro¬ truding partly from the anterior and partly from the septal wall of the right ventricle (Fig. 7-28). Its chordae tendineae are at¬ tached to the anterior and posterior cusps of the tricuspid valve, and frequently a portion of this muscle constitutes the moderator band. The posterior papillary muscle usually consists of two or three parts which arise from the posterior ventricular wall and to which are attached the chordae tendineae of the posterior and septal cusps. Another small papillary muscle arises near the septal end of the supraventricular crest. It is called the papillary muscle of the conus arteriosus, and it is attached to the anterior and septal cusps. Other small septal papillary muscles spring directly from the interventricular sep¬

633

tum and attach to individual chordae tendi¬ neae. ORIFICE OF THE PULMONARY TRUNK. At the summit of the conus arteriosus is a circular opening leading to the pulmonary trunk (Figs. 7-28; 7-29). It is close to the interven¬ tricular septum, above and to the left of the atrioventricular aperture, and is guarded by the pulmonary valve. pulmonary valve. This valve consists of three semilunar cusps (or valvula) formed by duplications of the endocardial lining which are reinforced by fibrous tissue (Figs. 7-28 to 7-30). They are attached by their curved margins to the wall of the pulmonary trunk at its site of junction with the conus arteriosus. The free borders of the cusps are directed upward toward the lumen of the pulmonary trunk. Behind each cusp, that is, between the cusp and the wall of the pulmo¬ nary trunk, is a pocket called the pulmonary sinus (sinus of Valsalva1). The point at which the attachments of two adjacent cusps come together is called a commissure. Each cusp is marked by a small thickened fibrocartilaginous nodule (corpus of Arantius2) at the center of the free margin. From the nodule tendinous fibers radiate through the cusps to the commissure of attachment. These strengthen both the free and attached margins of the cusp. Two thin crescentic arcs, free of fibers, are placed one on each side of the nodule immediately adjoining the free margin. These are called the lunules. The line of contact between the cusps, when the valve is closed, is not at the free margin, but by the nodule and lunulae. The three semilunar cusps forming the pulmonary valve are named the right (right anterior), left (posterior), and anterior (left anterior. Two methods are used to name the semilunar cusps of the pulmonary valve. One is based on their position in the adult body. The other, and currently recommended terminology in the Nomina Anatomica, is based on the position of the cusps in the fetus prior to rotation of the pulmonary artery and the aorta. In this book, the latter terminology has been presented as preferred and is printed in bold type above, while the former terminology is shown in pa¬ rentheses.

'Antonio M. Valsalva (1666-1723): An Italian anatomist. 2Giulio C. Arantius (1530-1589): An Italian physician and anatomist.

634

THE HEART

LEFT ATRIUM

The left atrium is rather smaller than the right and the wall is thicker, measuring about 3 mm. It forms a large part of the base and dorsal part of the heart (Figs. 7-26; 7-27). Its separation from the right atrium is not identifiable on the posterior heart surface except when the organ is distended, but the aorta and pulmonary trunk lie between the two atria on the anterior surface. The left atrium consists of two parts, a principal cav¬ ity and the left auricle. principal cavity. The principal cavity of the left atrium contains the openings of the four pulmonary veins, two on each side of the chamber, and they are not guarded by valves. Frequently the two left veins have a common opening. Additionally, the princi¬ pal cavity opens into the left ventricle by means of the left atrioventricular orifice, which is a little smaller than the right and is guarded by the left atrioventricular or mitral valve. The surface of the principal cavity is smooth. The interatrial septum contains a depression that is bounded below by a cres¬ centic ridge. This is the edge of the valve of the foramen ovale, the remnant of the sep¬ tum primum which became fused over the opening of the foramen ovale at birth. left auricle. The left auricle is some¬ what constricted at its junction with the principal cavity. It is longer, narrower, and more curved than the right auricle, and its margins are more deeply indented. It curves anteriorly around the base of the pulmonary trunk, only its tip being visible on the sterno¬ costal aspect of the heart (Fig. 7-25). At this site it also overlies the commencement of the left coronary artery. The inner surface of the auricle is marked by muscular ridges, simi¬ lar to those in the right auricle, called musculi pectinati.

LEFT VENTRICLE

The left ventricle occupies a small part of the sternocostal and about half of the dia¬ phragmatic surface of the heart (Figs. 7-25; 7-26). It forms part of the left margin of the heart and its tip forms the apex. The left ventricle is longer and more conical in shape than the right, and its walls are about three times as thick. In a cross section its cavity is

oval or circular in outline. The interior pre¬ sents two openings: the atrioventricular ori¬ fice guarded by the mitral valve and the aortic aperture guarded by the aortic valve. LEFT ATRIOVENTRICULAR ORIFICE. The left atrioventricular orifice is located below and somewhat posterior to the aortic opening. It is smaller than the corresponding orifice in the right heart and its breadth allows only two fingers to pass. It is surrounded by a dense fibrous ring that supports the left atri¬ oventricular valve, which is also called the mitral or bicuspid valve. LEFT ATRIOVENTRICULAR VALVE. The left atrioventricular or mitral valve is attached to the fibrous ring surrounding the circum¬ ference of the left atrioventricular orifice. It is bicuspid, and its two cusps, which are of unequal size, extend down into the left ven¬ tricle in a manner similar to those of the valve on the opposite side (Fig. 7-29). The cusps are named anterior and posterior ac¬ cording to their position in the ventricle. The larger anterior cusp is placed ventrally and to the right, adjacent to the aortic opening. The smaller or posterior cusp is located behind and to the left of the aortic aperture. Two smaller cusps are sometimes found at the angles of junction between the main cusps. The chordae tendineae are thicker and stronger, but less numerous than those in the right ventricle (Fig. 7-29). trabeculae carneae. There are three types of trabeculae carneae, similar to those described for the right ventricle, but they are more numerous and more densely packed, especially at the apex and on the dorsal wall. papillary muscles. There are two princi¬ pal papillary muscles in the left ventricle. One is attached to the anterior or sternocos¬ tal wall and is therefore called the anterior papillary muscle. The other, attached to the posterior or diaphragmatic wall, is the poste¬ rior papillary muscle. Both are of large size and end in rounded extremities to which the chordae tendineae are attached. Each papil¬ lary muscle has chordae tendineae which go to both cusps of the valve. aortic orifice. The aortic opening is a circular aperture located anterior and to the right of the atrioventricular orifice, from which it is separated by the anterior cusp of the mitral valve. The aortic orifice is guarded by the aortic valve, which consists of three semilunar cusps. It is slightly over 2.5 cm

CHAMBERS OF THE HEART

(one inch) in diameter, and the portion of the ventricle immediately adjacent to the orifice is termed the aortic vestibule, which consists largely of fibrous tissue rather than cardiac muscle. aortic valve. The aortic valve is com¬ posed of three semilunar cusps, similar to those of the pulmonary valve but larger, thicker, and stronger (Fig. 7-31). The cusps surround the aortic orifice and they contain lunules that are more distinct and nodules that are thicker and more prominent than those of the pulmonary valve. Between the cusps and the aortic wall there are dilated pockets called the aortic sinuses (of Valsalva), which are larger than those of the pulmo¬ nary trunk, and from the aortic wall bound¬ ing two of these sinuses the coronary ar¬ teries take origin. The cusps of the aortic valve are named posterior (right posterior), right (anterior), and left (left posterior), based on the embryological development of the aortic septum by division of the truncus arteriosus into the aorta and pulmonary trunk. (In parentheses are the names of the cusps according to their position in the adult heart, but this is no longer recommended by the Nomina Anatomica.) The preferred terminology (in

635

bold face above) is consistent with that used for the pulmonary valve and has the added correlation that behind the left and right cusps, the coronary arteries arise from the aorta. The posterior cusp, therefore, would be the non-coronary cusp. interventricular septum. The left ven¬ tricle is separated from the right ventricle by the interventricular septum. This septum is directed obliquely backward and to the right, and it also has a curvature with con¬ vexity to the right, thus completing the oval of the thick left ventricle and encroaching on the cavity of the right ventricle. Its mar¬ gins correspond to the anterior and posterior interventricular sulci. The greater part of it is thick and muscular and is called the mus¬ cular part of the interventricular septum. The upper portion of the interventricular septum, which separates the aortic vestibule from the lower part of the right atrium and the upper part of the right ventricle, is thinner and fibrous and is called the mem¬ branous part of the interventricular sep¬ tum. This is the last part of the septum to close in embryological development (Fig. 7-17) and is the usual site of the defect in a condition known as patent interventricu¬ lar septum.

Pulmonary trunk

Right coronary artery Aortic sinus — Right coronary artery

Left coronary artery Lunule Left cusp, aortic valve Left coronary artery Great cardiac vein

Right cusp, aortic valve

Nodule Ventricular wal Posterior cusp, aortic valve Anterior cusp of mitral valve

Fig. 7-31. The aortic entrance from the left ventricle has been opened to show the three semilunar cusps of the aortic valve. Within the ventricle a part of the left atrioventricular (mitral) valve is also exposed.

636

THE HEART

Structure of the Cardiac Wall The wall of the heart consists principally of cardiac muscle and a fibrous skeleton, the latter serving, in part, for the attachment of some cardiac muscle fibers and the heart valves. The heart wall is covered by mesothelial linings, both externally by the epicardium and internally by the endocardium. FIBROUS CARDIAC SKELETON. The fibrOUS skeleton of the heart consists of fibrous or fibrocartilaginous tissue which surrounds the atrioventricular, aortic, and pulmonary apertures with fibrous rings. This more re¬ sistant tissue merges with the membranous part of the interventricular septum and serves for the attachment of valves and heart muscle fibers. In the heart of certain large animals, such as the ox, this fibrous tissue may contain cartilage and even bone. Be¬ tween the right margin of the left atrioven¬ tricular ring, and the aortic ring and right atrioventricular ring, the dense tissue forms a triangular mass, the right fibrous trigone (Fig. 7-32). This mass also forms the basal thickening of the membranous septum. A fibrous band from the right trigone and right atrioventricular ring to the posterior side of the conus arteriosus and anterior aspect of the aortic ring is called the tendon of the conus. A similar but smaller mass of fibrous tissue, the left fibrous trigone, lies between the aortic and left atrioventricular rings. The atrioventricular rings and the trigones sepa¬ rate the muscular walls of the atria from those of the ventricles. The bundles of mus¬

cular fibers of both chambers, however, use the fibrous tissue for their attachment. heart musculature. The muscular struc¬ ture of the heart consists of bands of fibers that present an exceedingly intricate inter¬ lacement. Distinct bundles of muscle fibers form the walls of the atria and the ventricles, but those bundles forming the atrial cham¬ bers are functionally separated from those forming the ventricles by the fibrous rings. An additional special bundle of muscle fi¬ bers, the atrioventricular bundle (of His1), which forms the conducting system of the heart, does constitute a functional connec¬ tion between the atrial and ventricular chambers and will be discussed separately. The musculature of the atria can be dissected into the two layers, superficial and deep. The more superficial bundles extend across both atria, encir¬ cling them in single or double loops. The deeper bundles are more generally confined to each atrium, although some fibers pass through the interatrial septum to encircle the other atrium as well. The atrial bundles are attached to the fibrous trigones and the atrioventricular rings, and they extend for short distances to encircle the roots of the venae cavae on the right side and the pulmonary veins on the left. The musculature of the ventricles consists of bundles that probably all arise from the fibrotendinous structures at the base of the heart, converge in spiral courses toward the apex for varying distances, and then turn spirally upward to be inserted on the oppo¬ site side of these same fibrotendinous structures. The superficial bundles spiral to their vortex at or near the apex of the left ventricle before they turn 'Wilhelm His, Jr. (1863-1934): A German anatomist (Leipzig and Berlin).

Pulmonary valve Tendon of the conus ■ Left fibrous trigone —

Right fibrous trigone

Fig. 7-32.

The fibrous skeleton of the heart. The atria have been removed and the heart is viewed toward the ventricles. (Redrawn from Tandler, 1912.)

CONDUCTION SYSTEM OF THE HEART

upward, while the deeper bundles turn upward at varying distances without reaching the apex. The superficial bulbospiral bundle arises from the conus arteriosus, left side of the aortic septum, aortic ring, and left atrioventricular ring, and passes toward the apex of the heart. At their origin the fi¬ bers form a broad thin sheet that becomes thick and narrow at the apex where the bundle twists on itself. It then continues upward and posteriorly in a spiral manner on the inner surface of the left ventricle, spreading out into a thin sheet that is inserted on the opposite side of the fibrotendinous structures from which it arose. These fibers nearly make a double circle that is open at the top, somewhat like a figure 8, around the heart. As the fibers pass toward the apex they lie superficial to the deep bulbospiral bun¬ dle, and as they pass upward from the apex they partly blend and partly pass on the inner side of the deep bundle in directions nearly at right angles to the descending superficial fibers. The superficial sinuspiral bundle arises as a thin layer from the posterior aspect of the right and left atrioventricular rings. The fibers pass more horizon¬ tally around the heart to the apex than do those of the superficial bulbospiral bundle. They encircle the right ventricle and converge as they approach the apex, passing upward into the papillary muscles on the inner wall of the ventricles. They become at¬ tached to the fibrous rings either by way of the chor¬ dae tendineae or directly by the fibers themselves. The deep bulbospiral bundle arises immediately beneath the superficial bulbospiral bundle from the left side of the aortic and left atrioventricular rings. The fibers pass downward to the right and enter the septum through the posterior longitudinal sulcus. They then encircle the left ventricle without reaching the apex. Turning upon themselves on the apical side of the ring, they blend with the fibers of the superficial bundle as they pass Spirally upward to be inserted on the right side of the fibrous aortic and left atrioventricular rings. These fibers also seem to form an open figure 8, with both loops of about the same size. The deep sinuspiral bundle is more especially con¬ cerned with the right ventricle, although its fibers communicate freely with the papillary muscles of both ventricles. Its fibers arise from the posterior part of the left atrioventricular ring and pass diago¬ nally into the deeper layer of the wall of the right ventricle, where they turn upward to the conus arte¬ riosus and membranous part of the interventricular septum. The interventricular bundles are represented in part by the longitudinal bundle of the right ventricle, which passes through the interventricular septum and must be cut in order to unroll the heart, and in part by the interpapillary bands. The circular bands of the conus simply extend from one side of the ten¬ don of the conus arteriosus around the root of the pulmonary trunk and conus to the opposite side of the tendon.

637

Conduction System of the Heart The conduction system of the heart con¬ sists of the sinuatrial node, the atrioventricu¬ lar node, the atrioventricular bundle, and the terminal conducting fibers or Purkinje1 fibers. Although these structures differ from each other in certain details, they are all composed of specially differentiated cardiac muscle fibers that have the capacity to con¬ duct electrical impulses and thus are more highly developed than fibers in the rest of the heart. The musculature of both the ven¬ tricles and the atria has an intrinsic capabil¬ ity to contract spontaneously, independent of any nervous influence. The conduction system, however, initiates and superimposes a rhythmicity to this contraction, which has a rapid rate and is transmitted to all parts of the heart. The rate of the cardiac rhythm is regulated by the autonomic nerves which are under the control of the central nervous system. sinuatrial node. The sinuatrial node (S-A node) is a small mass of specialized heart muscle situated in the crista terminalis at the junction of the superior vena cava and right atrium. It receives its name from the fact that this region develops from the mar¬ gin of the sinus venosus in the embryo. The sinuatrial node consists of very narrow fusi¬ form muscle fibers, which are assembled in a crescent-shaped region less than a centime¬ ter in length and slightly more than a milli¬ meter in breadth. The node is difficult to identify from surrounding muscle tissue at dissection, but may be located by tracing the course of the small sinunodal artery, which usually branches from the right coronary artery and supplies the region. The contrac¬ tion of the heart is initiated by the node, and it is therefore called the pacemaker of the heart. No specialized bundle for the conduc¬ tion of the impulses from this node to the ventricle has, as yet, been identified morpho¬ logically. The fibers of the node merge with the surrounding atrial muscle fibers, and these alone appear to be responsible for transmitting the contractile wave across the atria and the impulses to the atrioventricular node. Johannes E. Purkinje (1787-1069): A German and then Czechoslovakian anatomist (Breslau and Prague).

638

THE HEART

The atrioventricular node (A-V node) is slightly smaller than the sinuatrial node and lies near the ori¬ fice of the coronary sinus in the septal wall of the right atrium (Fig. 7-33). Its muscle fi¬ bers, not being encapsulated by connective tissue, can seldom be recognized except that they are continuous with those of the atrio¬ ventricular bundle below and the atrial mus¬ culature above. The node is supplied by au¬ tonomic nerve fibers and usually receives its blood supply from the posterior interven¬ tricular artery. atrioventricular bundle. The atrioventricular bundle (A-V bundle) begins at the atrioventricular node and follows along the membranous part of the interventricular septum toward the left atrioventricular opening, a distance of about one centimeter. Toward the middle of the septum, the A-V bundle splits into right and left crura, which straddle the summit of the muscular part of the interventricular septum. The right crus of the A-V bundle continues under the en¬ docardium toward the apex, spreading to all parts of the right ventricle (Fig. 7-33). It atrioventricular

node.

Superior vena cava

Right pulmonary artery

breaks up into small bundles of fibers called the terminal conducting Purkinje fi¬ bers, which become continuous with the cardiac muscle fibers of the right ventricle. A large fascicle of terminal fibers enters the septomarginal (or moderator) band, if this is present, to reach the opposite wall of the ventricle and the anterior papillary muscle. The left crus of the A-V bundle penetrates the fibrous septum and comes to lie just under the endocardium of the left ventricle (Fig. 7-34). At first it is a flattened band which soon fans out on the septal wall more quickly than the right crus and breaks up into bundles of the terminal conducting Pur¬ kinje fibers, which are distributed through¬ out the left ventricle. The two crura are surrounded by more or less distinct connective tissue sheaths and may be visible, therefore, on gross examina¬ tion of the heart. They are more easily seen in a fresh specimen than in a preserved one, and the left branch frequently shows more clearly than the right. The bundle and branches may be demonstrated by injecting India ink into the connective tissue sheath of

Left pulmonary artery Pulmonary trunk

Aorta Right auricle

Fossa ovalis Bifurcation of A-V bundle

Left cusp ) Pulmonary Anterior cusp > va|ve Right cusp J Conus arteriosus Right crus, A-V bundle Region of A-V node

Right j Septal A*V valve I Posterior (tricuspid) I Anterior cusp Right ventricle

Inferior vena cava

Septomarginal (moderator) band Anterior papillary muscle Trabeculae carneae

Fig. 7 33.

The conduction system of the heart. The interior of the right side of the heart has been opened to show (in yellow) the right crus of the atrioventricular bundle (of His).

CONDUCTION SYSTEM OF THE HEART

639

Aorta Left pulmonary veins Pulmonary trunk Right pulmonary veins

Cusps of the aortic valve Left crus of A-V bundle

Left atrium Membranous part, interventricular septum Left atrioventricular (mitral) valve

Left ventricle Anterior papillary muscle

Right ventricle

Posterior papillary muscle

Fig. 7-34. The left crus of the atrioventricular bundle exposed after opening the left ventricle. The aorta has been opened to reveal the cusps of the aortic valve and the membranous part of the interventricular septum.

a fresh specimen, a procedure that is partic¬ ularly effective with a sheep or ox heart. The terminal conducting Purkinje fibers are different histologically from the nodal fibers, merging with the nodal tissue at one end of the A-V bundle and with the regular heart muscle at the other. The individual fibers can only be identified with the aid of a microscope. Coursing initially in small bun¬ dles under the endocardium, they then penetrate and ramify as individual fibers throughout the ventricular musculature. CARDIAC CYCLE

The complete cardiac cycle commences at the end of one heart contraction and extends to the end of the next contraction. It therefore includes first a pe¬ riod of cardiac relaxation called diastole, which is then followed by the contraction phase called sys¬ tole. Because each cardiac muscle fiber possesses the ability to contract rhythmically, it remains the important function of the conducting system of the heart to initiate the contraction wave, which has its initial site of generation at the sinuatrial node. After spreading across the atria, the contraction wave al¬ lows the muscle fibers of both atria to contract as a unit. Then, after the electrical impulse reaches the

atrioventricular node, the conduction system of the heart transmits it through both ventricles, causing the cardiac muscle fibers forming the walls of these chambers to contract efficiently and in unison. It is the changes in pressure within the chambers, caused by the contraction and relaxation of the car¬ diac muscle, that open and close the atrioventricular valves as well as the pulmonary and aortic valves. Closure of the valves accounts for the audible heart sounds that can be heard over the anterior chest wall. The graphic representation of the electrical action currents in the heart that can be recorded from the body surface is the commonly used electrocardio¬ gram (Fig. 7-35). Each cardiac cycle, when visual¬ ized on the electrocardiogram, is seen to consist of P, QRS, and T waves. The P wave is generated by the spread of depolarization from the sinuatrial node across the two atria. Atrial contraction soon occurs, causing blood to flow through the open atrioventric¬ ular valves. Approximately 0.16 seconds after the onset of the P wave, the electrocardiogram displays the QRS wave complex. This signals that the depo¬ larization wave is spreading across the two ventri¬ cles, causing them to contract and thereby to elevate intraventricular pressure. The first heart sound is caused by the simultaneous closure of the two atrio¬ ventricular valves as ventricular pressure exceeds atrial pressure. Closure of the atrioventricular valves and continued ventricular contraction force the

640

THE HEART

Fig. 7-35. Events in the cardiac cycle shown in a dia¬ grammatic manner. The upper three traces show aortic, atrial, and left ventricular pressure in millimeters of mercury. The bottom trace is the corresponding electro¬ cardiogram showing the P, QRS, and T waves. This dia¬ gram carries the cardiac cycle through two systoles, in¬ terrupted by a diastole. (Modified from Guyton, 1974.)

valves of the pulmonary artery and aorta to open and blood to flow into these vessels. Slighty before the end of ventricular contraction, the electrocardio¬ gram displays the T wave, which represents the ini¬ tiation of the phase of ventricular relaxation. As a result of blood leaving the ventricles and with the completion of ventricular contraction, the pulmo¬ nary and aortic valves close, causing the shorter but sharper second heart sound. With continuing di¬ minished ventricular pressure, the atrioventricular valves open and the cycle is repeated.

Histology and Ultrastructure of Cardiac Muscle The myocardium is composed of muscle fibers that show many similarities to the fi¬ bers of striated muscle (Fig. 7-36). Cardiac muscle fibers consist of myofibrils that are separated by sarcoplasm, and they also show A, I, Z, H, and M transverse striations. For many years it was thought that cardiac muscle was not composed of individual muscle cells, but that the cardiac fibers were joined in such a way as to form a syncytium. ' Ultrastructural studies have shown this not to be true. It is now recognized that the inter¬ calated discs that cross cardiac muscle fibers in a transverse manner represent sites where individual muscle fibers are joined in an end-to-end arrangement of interdigitating membranes and show specialized surface membrane complexes (Fig. 7-38). Cardiac muscle fibers are oriented in par¬ allel columns similar to skeletal muscle; however, unlike skeletal muscle, cardiac fi¬ bers tend to bifurcate and anastomose (Fig. 7-36). Another difference between skeletal

and cardiac muscle is the fact that the elon¬ gated nuclei of heart muscle fibers lie deep within the substance of the muscle cells rather than directly beneath the sarcolemma of the fiber as is seen in skeletal muscle (Fig. 7-37). Between adjacent cardiac fibers is found loose connective tissue containing nerve fibers and an abundance of capillaries and lymphatics. The myofibrillar substruc¬ ture of cardiac fibers consists of both myosin and actin myofilaments, accounting for the similarity of the transverse striations to those observed in skeletal muscle. Cardiac muscle fibers show a great abun¬ dance of large mitochondria, presumably because of the high metabolic and energy requirements of the tissue (Fig. 7-38). The sarcoplasm is also rich in glycogen and lip¬ ids, helping to serve the energy resources of the muscle fibers. Invaginations of the sarco¬ lemma of heart muscle fibers give rise to a T system which, similar to skeletal muscle, allows the internal structure of cardiac fi¬ bers to be more closely related to the extra¬ cellular space. In heart muscle, however, the transverse tubules are found at the Z line rather than at the A-I junctions and they are somewhat wider in diameter than those of skeletal muscle. The sarcoplasmic reticulum is neither as elaborate nor as abundant as that in skeletal muscle (Fig. 7-39). Although the sarcoplasmic reticulum network extends over the surface of the myocardial sarco¬ mere, terminal cisterns similar to those of skeletal muscle are not seen. In their place are small cisternal expansions that are more irregularly placed and come into indi¬ vidual contact with the T tubular mem¬ brane to form a dyad coupling, in contrast to the triad configuration seen in skeletal muscle. Intercalated discs have long been recog¬ nized as a characteristic microscopic feature of cardiac muscle fibers. They are easily identified by the light microscope in ordi¬ nary hematoxylin and eosin sections, and their visibility may even be enhanced by special stains. Electron micrographs have revealed that the darkly stained intercalated discs observed with the light microscope are junctional intercellular complexes between adjacent cardiac muscle fibers (Fig. 7-40). At the intercalated disc, apposed surfaces of the cardiac fibers are covered by their own cell membranes, which are joined together by specialized complexes that maintain inter¬ cellular cohesion. The transverse parts of

HISTOLOGY AND ULTRASTRUCTURE OF CARDIAC MUSCLE

intercalated discs are arranged in a stepwise fashion, crossing the fibers at right angles, while the lateral parts of the discs are longi¬ tudinally oriented and seen to course paral¬ lel to the myofibrils. conduction system. The sinuatrial node consists of slender fusiform cells largely filled with sarcoplasm but containing a few striated fibrillae. The cells are smaller than the surrounding atrial muscular fibers and they are intermeshed in connective tissue and arranged, more or less, in a parallel manner and in relation to the nodal artery. At the periphery of the node the fusiform nodal fibers merge with the atrial muscula¬ ture. Closely associated with the sinuatrial node are a number of parasympathetic gan¬ glia associated with the vagus nerve, but there are also postganglionic sympathetic fibers nearby. The atrioventricular node is a small mass of slender specialized cells found in the lower part of the interatrial septum. Its fibers are branched and irregularly ar¬ ranged, and they merge with the atrial mus¬ culature on the one hand and continue into the atrioventricular bundle on the other. In the atrioventricular bundle and its first two branches, the specialized fibers remain slen¬ der, but in the more peripheral branches of the A-V bundle the fibers assume the histo-

641

Fig. 7-36. Longitudinal section of human cardiac mus¬ cle fibers showing their branching manner. 400 X magni¬ fication. (From Rauber-Kopsch, 1955.)

Nucleus of heart muscle

Fig. 7-37. Cross section of human cardiac muscle showing the nuclei located deeply within the interior of the fibers rather than immediately beneath the sarcolemma as is seen in skeletal muscle. (From Rauber-Kopsch, 1955.)

642

THE HEART

Electron micrograph of cardiac fibers in longitudinal section. The cells are joined end-to-end by a typical steplike intercalated disc (InD). Mitochondria (Mt) divide the contractile substance, and lipid droplets are found between the ends of the mitochondria. (From Fawcett, D. W., The Cell, An Atlas of Fine Structure, W. B. Saunders Co., 1966.) Fig. 7-38.

HISTOLOGY AND ULTRASTRUCTURE OF CARDIAC MUSCLE

643

Fig. 7-39.

The sarcoplasmic reticulum (SR) consisting of a simple network of anastomosing tubules. The section passes tangential to the inner surface of a mass of myofilaments (M), and the sarcoplasmic reticulum continues across the Z line (Z arrow) without terminal cisternae (From Fawcett and McNutt, J. Cell Biol., 42:1-45, 1969.)

logical characteristics of the Purkinje fibers. These latter fibers are larger in diameter than ordinary cardiac muscle. They contain relatively few peripherally placed myofibrillae, have abundant sarcoplasm, and the cen¬ trally placed nuclei are larger and more ve¬ sicular than those of the usual cardiac muscle. As the ramifications of the bundles spread into the ventricular wall, the individ¬

Fig. 7-40.

ual Purkinje fibers become continuous with fibers of the main cardiac musculature. vessels aimd nerves. The arteries supplying the heart are the right and left coronary arteries, and the veins are mostly tributaries of the coronary sinus. The lymphatics consist of deep and superficial plex¬ uses, which form right and left trunks and end in the tracheobronchial nodes. Detailed descriptions of the blood vessels and lymphatics of the heart can be

Electron micrograph of restricted region of the transverse portion of an intercalated disc. The cell surfaces at the disc are approximately 200 to 300 A apart. Actin filaments are seen to enter accumulations of dense material in the sarcoplasm subjacent to the cell membrane. Other actin filaments near the disc are seen coursing transverse to the prevailing direction of the myofilaments (at arrows). 70,000 X (From Fawcett and McNutt, J. Cell Biol., 42:1-45, 1969.)

644

THE HEART

found in the chapters dealing with these systems. The nerves that supply the heart are cardiac branches of the vagus nerve and sympathetic trunks. These nerves join to form the cardiac plex¬ uses and their ramifications, the coronary plexuses, which accompany the coronary arteries. The sympa¬ thetic fibers are postganglionics from the cervical and upper thoracic ganglia. The vagus fibers are preganglionics, whose ganglion cells form clusters in the connective tissue of the epicardium of the atria and the interatrial septum. The autonomic in¬ nervation of the heart is described in more detail in the chapter on the nervous system.

CONGENITAL MALFORMATIONS OF THE HEART Developmental abnormalities may result from the suppression or overgrowth in varying degrees of the individual parts of the heart. The more prevalent abnormalities, however, are the result of partial fail¬ ure in the partitioning of the heart. Interatrial de¬ fects that allow the passage of a probe through the foramen ovale are quite common (20%), but are of no functional significance. Larger defects of the sep¬ tum are less common and may involve the atrial or ventricular septa or both. Abnormality in the growth of the septum and the endocardial cushions respon¬ sible for separating the truncus arteriosus into the aorta and pulmonary trunk results in what are called transposition complexes. Transposition refers to a shifting of the arterial trunks from their proper ori¬

gins. The abnormalities are designated according to the degree of displacement as (a) overriding, (b) par¬ tial transposition, and (c) complete transposition. In overriding, one of the arterial trunks straddles the ventricular septum in which there is a defect. In par¬ tial transposition, both arterial trunks arise from the same ventricle. In complete transposition, the aorta arises from the right ventricle and the pulmonary trunk from the left ventricle. When abnormalities occur, they are often seen in groups or complexes. One of the better known complexes, called the tetral¬ ogy of Fallot,1 has a combination of the following four abnormalities: (1) overriding of the aorta, (2) a defect in the ventricular septum, (3) pulmonary ste¬ nosis, and (4) hypertrophied right ventricle. The Eisenmenger complex2 is similar to the tetralogy, having (1) an overriding aorta, (2) septal defect, (3) hypoplasia of the aorta, and (4) right ventricular hypertrophy. These and many other congenital mal¬ formations of the heart interfere with the pumping of the proper amount of blood into the pulmonary cir¬ culation. In consequence, the blood sent into the systemic arteries is poorly oxygenated, the predomi¬ nance of venous blood causes cyanosis, and the in¬ dividual is popularly known as a "blue baby." De¬ tailed descriptions of cardiac anomalies have been published by Gould (1953), Lev (1953), and Gray and Skandalakis (1972). Etienne Louis Arthur Fallot (1850-1911): A French phy¬ sician (Marseilles). 2 Victor Eisenmenger (1864-1932): A German physician.

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.)

Embryology of the Heart, Changes at Birth and Anomalies Anderson, R. C. 1954. Causative factors underlying con¬ genital heart malformations. Pediatrics, 14:143-152. Barnard, C. N., and V. Shire. 1968. Surgery of the Com¬ mon Congenital Cardiac Malformations. Staples Press, London, 179 pp. Bedford, D. E. 1960. The anatomical types of atrial septal defect. Amer. ). Cardiol., 6:568-574. Blalock, A., and H. B. Taussig. 1945. The surgical treat¬ ment of malformations of the heart in which there is pulmonary stenosis or pulmonary atresia. J.A.M.A., 128:189-202. Campbell, M. 1970. Natural history of atrial septal de¬ fect. Brit. Heart J., 32:820-826. Christie, G. A. 1963. The development of the limbus fos¬ sae ovalis in the human heart; a new septum. J. Anat. (Lond.), 97:45-54. Cobb, W. M. 1944. Apical pericardial adhesion resem¬ bling the reptilian gubernaculum cordis. Anat. Rec., 89:87-91. Cooper, M. H., and R. O’Rahilly. 1971. The human heart at seven postovulatory weeks. Acta Anat., 79:280299.

Copenhaver, W. M. 1945. Heteroplastic transplantation of the sinus venosus between two species of Amblystoma. J. Exp. Zool., 100:203-216. Davis, C. L. 1927. Development of the human heart from its first appearance to the stage found in embryos of twenty paired somites. Carneg. Instn., Contr. Embryol., 19:245-284. Duckworth, ). W. A. 1967. Embryology of congenital heart disease. In Heart Disease in Infancy and Childhood. 2nd ed., Edited by J. D. Kieth, R. D. Rowe, and P. Vlad. Macmillan Co., New York, 1967, pp. 136-158. Everett, N. B., and R. J. Johnson. 1951. A physiological and anatomical study of the closure of the ductus arteriosus in the dog. Anat. Rec., 110:103-111. Fales, D. E. 1946. A study of double hearts produced ex¬ perimentally in embryos of Amblystoma punctatum. J. Exp. Zool., 101:281-298. Fox, M. H., and C. M. Goss. 1958. Experimentally pro¬ duced malformations of the heart and great vessels in rat fetuses. Transposition complexes and aortic arch abnormalities. Amer. J. Anat., 102:65-92. Goss, C. M. 1935. Double hearts produced experimen¬ tally in rat embryos. J. Exp. Zool., 72:33-49. Goss, C. M. 1940. First contractions of the heart without cytological differentiation. Anat. Rec., 76:19-27.

REFERENCES

Goss, C. M. 1942. The physiology of the embryonic mam¬ malian heart before circulation. Amer. J. Physiol., 137.T46-172. Goss, C. M. 1952. Development of the median coordi¬ nated ventricle from the lateral hearts in rat em¬ bryos with three to six somites. Anat. Rec., 112:761796. Gould, S. E. 1953. Pathology of the Heart. Charles C Thomas, Springfield, Ill., 1023 p. Gray, S. W., and J. E. Skandalakis. 1972. Embryology for Surgeons. W. B. Saunders Co., Philadelphia, 918 pp. de Haan, R. L. 1965. Morphogenesis of the vertebrate heart. In Organogenesis. Edited by R. L. de Haan and H. Ursprung. Holt, Rhinehart and Winston, New York, pp. 377-420. Hay, D. A. and F. N. Low. 1972. The fusion of dorsal and ventral endocardial cushions in the embryonic chick heart: a study in fine structure. Amer. J. Anat., 133:1-23. Hoffman, J. I. E., and A. M. Randolf. 1965. The natural history of ventricular septal defects in infancy. Amer. J. Cardiol., 16:634-653. Keen, E. N. 1955. The postnatal development of the human cardiac ventricles. ]. Anat., 89:484-502. Kerr, A., Jr. and C. M. Goss. 1956. Retention of embryonic relationship of aortic and pulmonary valve cusps and a suggested nomenclature. Anat. Rec., 125:777782. Kramer, T. C. 1942. The partitioning of the truncus and conus and the formation of the membranous portion of the interventricular septum in the human heart. Amer. J. Anat., 71:343-370. Langman, J. 1975. Medical Embryology. 3rd ed. Williams and Wilkins, Baltimore, 421 pp. Lev, M. 1953. Autopsy Diagnosis of Congenitally Mal¬ formed Hearts. Charles C Thomas, Springfield, Ill., 194 pp. Licata, R. H. 1954. The human embryonic heart in the ninth week. Amer. J. Anat., 94:73-126. Maron, B. J., and G. M. Hutchins. 1972. Truncus arterio¬ sus malformation in a human embryo. Amer. J. Anat., 134:167-173. Mayer, F. E., A. S. Nadas, and P. A Ongley. 1957. Ebstein’s anomaly: Presentation of ten cases. Circu¬ lation, 16:1057-1069. Mitchell, S. C., H. W. Berendes, and W. M. Clark, Jr. 1967. The normal closure of the ventricular septum. Amer. Heart J., 73:334-338. Mitchell, S. C., S. B. Korones, and H. W. Berendes. 1971. Congenital heart disease in 56,109 births; incidence and natural history. Circulation, 43:323-332. Moore, K. L. 1973. The Developing Human. W. B. Saun¬ ders Co., Philadelphia, 347 pp. Moss, A. J., and F. H. Adams. 1977. Heart Disease in Infants, Children and Adolescents. Williams and Wilkins, Baltimore, 2nd ed., 757 pp. O’Rahilly, R. 1971. The timing and sequence of events in human cardiogenesis. Acta Anat., 79:70-75. Orts-Llorca, F. 1970. Curvature of the heart: its first ap¬ pearance and determination. Acta Anat., 77:454-468. Patten, B. M. 1931. The closure of the foramen ovale. Amer. J. Anat., 48:19-44. Patten, B. M. 1968. Human Embryology. McGraw-Hill Co., New York, 3rd ed., 651 pp. Reemtsma, K., and W. M. Copenhaver. 1958. Anatomic studies of the cardiac conduction system in congeni¬ tal malformations of the heart. Circulation, 17:271276.

645

Shaner, R. F. 1949. Malformation of the atrioventricular endocardial cushions of the embryo pig and its rela¬ tion to defects of the conus and truncus arteriosus. Amer. J. Anat., 84:431-455. Shaner, R. F. 1963. Abnormal pulmonary and aortic sem¬ ilunar valves in embryos. Anat. Rec., 147:5-13. Smith, R. B. 1970. The development of the intrinsic inner¬ vation of the human heart between 10 and 70 mm stages. J. Anat. (Lond.), 107:271-279. Stalsberg, H., and R. L. de Haan. 1969. The precardiac areas and the formation of the tubular heart in the chick embryo. Devel. Biol., 19:128-159. Tandler, J. 1912. The development of the heart. In Man¬ ual of Human Embryology. Edited by F. Keibel and F. P. Mall. J. B. Lippincott, Philadelphia. 2:534-570. Taussig, H. B. 1963. Cardiac abnormalities. In Birth De¬ fects. Edited by M. Fishbein. J. B. Lippincott, Phila¬ delphia, pp. 268-276. Troyer, J. R. 1961. A multiple anomaly of the human heart and great veins. Anat. Rec., 139:509-513. Vernall, D. G. 1962. The human embryonic heart in the seventh week. Amer. J. Anat., 111:17-24. de Vries, P. A., and J. B. de C. M. Saunders. 1962. Devel¬ opment of the ventricles and spiral outflow tract in the human heart. Carneg. Instn., Contr. Embryol., 37:87-114. Yoshihara, H., and H. Maisel. 1973. An acardiac human fetus. Anat. Rec., 177:209-218.

Histology and Electron Microscopy Bacon, R. L. 1948. Changes with age in the reticular fibers of the myocardium of the mouse. Amer. J. Anat., 82:469-496. Copenhaver, W. M., and R. C. Truex. 1952. Histology of the atrial portion of the cardiac conduction system in man and other mammals. Anat. Rec., 114:601-625. Ellison, J. P. and R. G. Hibbs. 1973. The atrioventricular valves of the guinea pig. I. A light microscopic study. Amer. J. Anat., 138:331-345. Fawcett, D. W. and N. S. Me Nutt. 1969. The ultrastruc¬ ture of the cat myocardium. I. Ventricular papillary muscle. J. Cell Biol., 42.T-45. Forssmann, W. G., and L. Girardier. 1970. A study of the T system in rat heart. J. Cell Biol., 44:1-19. Goss, C. M. 1931. “Slow-motion” cinematographs of the contraction of single cardiac muscle cells. Proc. Soc. Exp. Biol. (N.Y.), 29:292-293. Goss, C. M. 1933. Further observations on the differentia¬ tion of cardiac muscle in tissue cultures. Arch. f. exp. Zellforsch., 14:175-201. Hibbs, R. G., and J. P. Ellison. 1973. The atrioventricular valves of the guinea pig. II. An ultrastructural study. Amer. J. Anat., 138:347-369. Jamieson, J. D., and G. E. Palade. 1964. Specific granules in atrial muscle cells. J. Cell Biol., 23:151-172. Leak, L. V., and J. F. Burke. 1964. The ultrastructure of human embryonic myocardium. Anat. Rec., 149:623-650. Manasek, F. J. 1970. Histogenesis of the embryonic myo¬ cardium. Amer. J. Cardiol., 25:149-168. Me Nutt, N. S., and D. W. Fawcett. 1969. The ultrastruc¬ ture of the cat myocardium. II. Atrial muscle. J. Cell Biol., 42:46-67. Muir, A. R. 1957. An electron microscope study of the embryology of the intercalated disc in the heart of the rabbit. J. Biophys. Biochem. Cytol., 3:193-202.

646

THE HEART

Muir, A. R. 1965. Further observations of the cellular structure of the cardiac muscle. J. Anat. (Lond.), 99:27-46. Nelson, D. A., and E. S. Benson. 1963. On the structural continuities of the transverse tubular system of ral> bit and human myocardial cells. J. Cell Biol., 16:297-313. Peine, C. J., and F. N. Low. 1975. Scanning electron mi¬ croscopy of cardiac endothelium of the dog. Amer. J. Anat., 142:137-157. Rostgaard, J., and O. Behnke. 1965. Fine structural locali¬ zation of adenine nucleoside phosphatase activity in the sarcoplasmic reticulum and T system of the rat myocardium. J. Ultrastruct. Res., 12:579-591. Sachs, H. G., J. A. Colgan, and M. L. Lazarus. 1977. Ultrastructure of the aging myocardium: a morphometric approach. Amer. J. Anat., 150:63-71. Sinclair, J. G. 1957. Synchronous mitosis on a cardiac infarct. Tex. Rep. Biol. Med., 15:347-352. Sjostrand, F. S., E. Andersson-Cedergren, and M. Dewey. 1958. The ultrastructure of the intercalated discs of frog, mouse and guinea pig cardiac muscle. J. Ultra¬ struct. Res., 1:271-287. Sommer, J. R., and E. A. Johnson. 1968. Cardiac muscle. A comparative study of Purkinje fibers and ventric¬ ular fibers. J. Cell Biol., 36:497-526. Song, S. H. 1977. Endocardial surface structures of the feline heart observed with a scanning electron mi¬ croscope. Acta Anat., 99:67-75. Truex, R. C. 1972. Myocardial cell diameters in primate hearts. Amer. J. Anat., 135:269-280. Truex, R. C., and W. M. Copenhaver. 1947. Histology of the moderator band in man and other mammals with special reference to the conduction system. Amer. J. Anat., 80:173-202. Van Winkle, W. B. 1977. The fenestrated collar of mam¬ malian cardiac sarcoplasmic reticulum: a freezefracture study. Amer. J. Anat., 149:277-282.

Conduction System of the Heart Anderson, R. H„ and R. A. Latham. 1971. The cellular architecture of the human atrioventricular node, with a note on its morphology in the presence of a left superior vena cava. J. Anat. (Lond.), 109:443-456. Baerg, R. D„ and D. L. Bassett. 1963. Permanent gross demonstration of the conduction tissue in the dog heart with palladium iodide. Anat. Rec., 146:313317. Davies, F., and E. T. B. Francis. 1946. The conducting system of the vertebrate heart. Biol. Rev., 21:173188. Davies, F., and E. T. B. Francis. 1952. The conduction of the impulse for cardiac contraction. J. Anat. (Lond.), 86:130-143. Davies, F., E. T. B. Francis, and T. S. King. 1952. Neuro¬ logical studies of the cardiac ventricles of mammals. J. Anat. (Lond.), 86:139-143. Erickson, E. E., and M. Lev. 1952. Aging changes in the human atrioventricular node, bundle, and bundle branches. J. Geront., 7:1-12. Field, E. J. 1951. The development of the conducting sys¬ tem in the heart of the sheep. Brit. Heart J., 13:129147. James, T. N. 1961. Anatomy of the human sinus node. Anat. Rec., 141:109-139.

James, T. N. 1961. Morphology of the human atrioven¬ tricular node, with remarks pertinent to its electro¬ physiology. Amer. Heart J., 62:756-771. Kugler, J. H., and J. B. Parkin. 1956. Continuity of Pur¬ kinje fibres with cardiac muscle. Anat. Rec., 126:335-341. Muir, A. R. 1954. The development of the ventricular part of the conducting tissue in the heart of the sheep. J. Anat. (Lond.), 88:381-391. Muir, A. R. 1957. Observations on the fine structure of the Purkinje fibers in the ventricles of the sheep's heart. J. Anat. (Lond.), 91:251-258. Rhodin, J. A., P. del Missier, and L. C. Reid. 1961. The structure of the specialized impulse-conducting sys¬ tem of the steer heart. Circulation, 24:348-367. Rybicka, K. 1977. Sarcoplasmic reticulum in the con¬ ducting fibers of the dog heart. Anat. Rec., 189:237262. Stotler, W. A., and R. A. Me Mahon. 1947. The innerva¬ tion and structure of the conductive system of the human heart. J. Comp. Neurol., 87:57-84. Thaemert, J. C. 1970. Atrioventricular node innervation in ultrastructural three dimensions. Amer. |. Anat., 128:239-263. Thaemert, J. C. 1973. Fine structure of the atrioventricu¬ lar node as viewed in serial sections. Amer. J. Anat., 136:43-65. Titus, J. L., G. W. Daugherty, and J. Edwards. 1963. Anat¬ omy of the normal human atrioventricular conduc¬ tion system. Amer. J. Anat., 113:407-415. Truex, R. C., and M. Q. Smythe. 1967. Reconstruction of the human atrioventricular node. Anat. Rec., 158:11-20. Truex, R. C., M. Q. Smythe, and M. J. Taylor. 1967. Re¬ construction of the human sinoatrial node. Anat. Rec., 159:371-378. Walls, E. W. 1945. Dissection of the atrioventricular node and bundle in the human heart. J. Anat. (Lond.), 79:45-47. Walls, E. W. 1947. The development of the specialized conducting tissue of the human heart. J. Anat. (Lond.), 81:93-110. Wenink, A. C. G. 1976. Development of the human car¬ diac conducting system. J. Anat. (Lond.), 121:617632. White, P. D. 1957. The evolution of our knowledge about the heart and its diseases since 1628. Circulation, 15:915-923.' Widran, J., and M. Lev. 1951. The dissection of the atrio¬ ventricular node, bundle and bundle branches in the human heart. Circulation, 4:863-867.

Gross Anatomy, Blood and Nerve Supply Armour, J. A. and W. C. Randall. 1975. Functional anat¬ omy of canine cardiac nerves. Acta Anat., 91:510528. Blalock, A. 1947. The technique of creation of artificial ductus arteriosus in the treatment of pulmonic ste¬ nosis. J. Thorac. Surg., 16:244-257. Brooks, C. Me C. and H. Lu. 1972. The Sinoatrial Pace¬ maker of the Heart. Charles C Thomas, Springfield, Ill., 179 pp. Ellison, J. P. 1974. The adrenergic cardiac nerves of the cat. Amer. J. Anat., 139:209-225.

REFERENCES

Ellison, J. P., and T. H. Williams. 1969. Sympathetic nerve pathways to the human heart, and their varia¬ tions. Amer. J, Anat., 124:149-162. Gardner, E., and R. O'Rahilly. 1976. The nerve supply and conducting system of the human heart at the end of the embryonic period proper. J. Anat. (Lond.), 121:571-588. Gray, H., and E. Mahan. 1943. Prediction of heart weight in man. Amer. J. Phys. Anthrop., 1:271-287. Gross, L. 1921. 7’he Blood Supply to the Heart. P. B. Hoeber, New York, 171 pp. Gross, L., and M. A. Kugel. 1933. The arterial blood vas¬ cular distribution to the left and right ventricles of the human heart. Amer. Heart J., 9.T65-177. Gross, R. E. 1947. Complete division for the patent duc¬ tus arteriosus. J. Thorac. Surg., 16’:314-327. Guyton, A. C. 1976. Heart muscle; the heart as a pump. Chapter 13 in Textbook of Medical Physiology. 5th ed. W. B. Saunders, Philadelphia, pp. 160-175. Hoar, R. M., and J. L. Hall. 1970. The early pattern of cardiac innervation in the fetal guinea pig. Amer. ). Anal., 128:499-507. James, T. N. 1960. The arteries of the free ventricular walls in man. Anat. Rec., 136:371-384. James, 7’. N., and G. E. Burch. 1958. The atrial coronary arteries in man. Circulation, 17:90-98. James, T. N., and G. E. Burch. 1958. Blood supply of the human interventricular septum. Circulation, 17:391-396. James, T. N., and G. E. Burch. 1958. Topography of the human coronary arteries in relation to cardiac sur¬ gery. J. Thorac. Surg., 36:656-664. Jonsson, L., G. Johansson, N. Lannek, and P. Lindberg. 1974. Intramural blood supply of porcine heart. A postmortem angiographic study. Anat. Rec., 178:647-656. Kirk, G. R., D. M. Smith, D. P. Hutcheson, and R. Kirby. 1975. Postnatal growth of the dog heart. J. Anat. (Lond.), 119:461-470. Langer, G. A., and A. J. Brady. 1974. The Mammalian Myocardium. John Wiley, New York, 310 pp. Latimer, H. B. 1953. The weight and thickness of the ven¬ tricular walls in the human heart. Anat. Rec., 117:713-724.

647

Leak, L. V., A. Schannahan, A. Scully, and W. M. Daggett. 1978. Lymphatic vessels of the mammalian heart. Anat. Rec., 191:183-202. Mikhail, Y. 1970. Intrinsic nerve supply of the ventricles of the heart. Acta Anat., 76:289-298. Mikhail, Y„ and 1. Kamel. 1972. Nerve endings in the atrial muscle of the heart. Acta Anat., 82:138-144. Mitchell, G. A. G. 1956. Cardiovascular Innervation. Liv¬ ingstone, Edinburgh, 356 pp. Papez, J. W. 1920. Heart musculature of the atria. Amer. J. Anat., 27:255-286. Randall, W. C., J. A. Armour, D. C. Randall, and A. A. Smith. 1971. Functional anatomy of the cardiac nerves in the baboon. Anat. Rec., 170:183-198. Rauber-Kopsch, Fr. 1955. Lehrbuch und Atlas der Anato¬ mic des Menschen. 19th ed. George Thieme Verlag, Stuttgart, 2 vols. Smith, R. B. 1971. Innervation of the parietal pericar¬ dium in the human infant, various mammals and birds. J. Anat. (Lond.), 108:109-114. Smith, R. B. 1971. Intrinsic innervation of the atrioven¬ tricular and semilunar valves in various mammals. J. Anat. (Lond.), 108:115-122. Smith, R. B. 1971. The occurrence and location of intrin¬ sic cardiac ganglia and nerve plexuses in the human neonate. Anat. Rec., 169:33-40. Tandler, J. 1913. Anatomie des Herzens. In von Bardeleben's Handhuch der Anatomie des Men¬ schen. Gustav Fischer, Jena, 292 pp. TTiomas, C. E. 1957. The muscular architecture of the ventricles of hog and dog hearts. Amer. J. Anat., 101:17-58. Tomanek, R. J. 1970. Effects of age and exercise on the extent of the myocardial capillary bed. Anat. Rec., 167:55-62. Truex, R. C., and A. W. Angulo. 1952. Comparative study of the arterial and venous systems of the ventricular myocardium with special reference to the coronary sinus. Anat. Rec., 113:467-491. Walmsley, R. 1958. The orientation of the heart and the appearance of its chambers in the adult cadaver. Brit. Heart J., 20:441-458. Woolard, H. H. 1926. The innervation of the heart. J. Anat. (Lond.), 60:345-373.

The Arteries

After reaching the ventricles of the heart, blood is then propelled to all parts of the body through the arteries. Two large arteries leave the heart: the pulmonary trunk and the aorta. The pulmonary trunk divides into a right and left pulmonary artery, each of which courses transversely in the thorax to its corresponding lung. These vessels subdi¬ vide profusely within the lung tissue to form a capillary bed, which exchanges carbon dioxide in the blood for oxygen in the alve¬ oli. The pulmonary arteries, along with the pulmonary veins which return oxygenated blood to the left atrium, constitute the pul¬ monary circulation. The aorta and its many branches also ramify into capillary beds within all the body organs. These arteries and the veins returning blood to the heart form the systemic circulation. The continu¬ ous ramification of the systemic arteries re¬ sults in the distribution of capillaries to all the tissues except the nails, epidermis, cor¬ nea, mucous membranes, and most cartilage. These latter avascular structures receive their nourishment through the processes of diffusion. Arteries may show various patterns in their mode of branching. A short trunk may subdivide into several branches at the same point, such as occurs to the celiac and thyro¬ cervical trunks. Several branches may be

648

given off in succession and the main trunk continue, as in the arteries of the limbs. The division may be dichotomous as at the bifur¬ cation of the abdominal aorta into the com¬ mon iliac arteries. Although the branches of an artery are smaller than their trunk, the combined cross-sectional area of the two resulting arteries is generally greater than that of the parent trunk before the division. The combined cross-sectional area of all the arterial branches, therefore, greatly exceeds that of the aorta. It has been estimated that the total cross-sectional area of all the capil¬ laries in the body is nearly 1,000 times that of the aorta, from which they derive their arte¬ rial blood. Throughout the body generally the larger arterial branches pursue a fairly straight course, but at certain sites they are tortuous. The facial artery and the arteries supplying the lips, for example, are extremely tortuous, being accommodated to the movements of the parts. The uterine arteries also are coiled and tortuous, allowing them to accommo¬ date the increase in size that the uterus undergoes during pregnancy. The larger ar¬ teries usually are deeply placed and occupy other more protected locations such as along the flexor surface of the limbs where they are less exposed to injury. anastomosis of arteries. Arterial branches do not always terminate in capil¬ laries. In many parts of the body they open into branches of other arteries of similar size, forming what are called anastomoses. Anastomosis may take place between larger arteries forming vascular arches such as those in the palm of the hand or the arcades of the intestines. At the base of the brain, the two vertebral arteries join to form the basi¬ lar artery, while branches from the two in¬ ternal carotid arteries and the basilar artery freely join to form the vital cerebral arterial circle of Willis.1 More frequently, however, anastomoses form between smaller arteries of one millimeter or less in diameter. In the limbs, anastomoses are quite numerous around the joints, the branches of an artery above the joint uniting with branches of the vessels below. Definite patterns of anasto¬ mosis between neighboring arteries occur throughout the body, but in any single body all the different anastomoses that are de1 Thomas Willis (London).

(1621-1675):

An

English

physician

DEVELOPMENT OF THE ARTERIES

649

Angular a. Facial a. -Ant. interosseous a. Lingual a. Subclavian a

Radial a. UInar a.

Ant. tibial a■■-■l-li-i Post, tibial a.-

Peroneal a."

Dorsalis pedis a

Fig. 8-1. A schematic representation of the arterial system in the adult male. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, 10th Ed., Vol. 2, Urban & Schwarzenberg, 1975.)

scribed will not be equally well developed nor will they be easily demonstrable at dis¬ section. collateral circulation. When the sup¬ ply of blood to the distal part of an artery that has been occluded is effected through anastomosis of its branches, the resulting

vascular paths constitute a collateral circu¬ lation. It is frequently necessary for a sur¬ geon to tie off or ligate an artery in order to prevent excessive bleeding. The anastomo¬ ses with branches of adjacent arteries may be more numerous in one part of the artery than in another, and the surgeon will en-

650

THE ARTERIES

deavor to place his ligature where advantage can be taken of the most numerous or effec¬ tive anastomoses. Collateral circulation may occur through anastomoses with branches of the proximal part of the same artery or with branches of a large neighboring artery. In some regions, the collateral circulation is free, as it would be if either the radial or ulnar artery of the forearm were ligated. At other sites the collateral circulation might be carried by small arteries only. If the vessels in a part of the body have sustained trauma, and the region can be placed at rest, a small flow of blood through small anastomosing channels will keep the tissues alive until the anastomoses expand. The arteries retain their power of growth throughout life, and over time a small anastomosing artery may enlarge into a main trunk, completely restor¬ ing the circulation to the initially injured region. Arteries in certain parts of the body lack anastomoses and are therefore called end arteries. When vessels such as these are blocked by thrombosis or embolism, the tis¬ sues of the region are left without blood sup¬ ply and become necrotic, resulting in a con¬ dition called an infarct. A prime example of an end artery is the central artery of the ret¬ ina, occlusion of which results in permanent blindness. The collateral circulation of ves¬ sels in other organs may exist only at the capillary level, and if a sudden blockage of a main artery occurs, degeneration of tissue results before revascularization is effective. Notwithstanding the free anastomosing of vessels on the surface of the brain, ineffec¬ tive collateral circulation exists in the sub¬ stance of the brain. Blockage of a vessel within the brain, therefore, causes the clini¬ cal features of stroke. Similar microcirculatory conditions are found in other organs such as the lungs, kidneys, and spleen and at the transitional metaphyseal interface be¬ tween the diaphysis and epiphysis of a long bone. The capillaries of the heart do anasto¬ mose, but this condition becomes more pro¬ nounced as individuals age. These anasto¬ moses may not be capable of maintaining life if a major occlusion occurs in the heart of a young person, whereas a comparable occlusion in a much older person may be survived because of the years that the heart has had to develop anastomoses and collat¬ eral circulation.

Development of the Arteries Blood vessels commence development within the mesoderm of the yolk sac and body stalk by the formation of blood islands as early as the third week (about 16 days). Shortly thereafter, spaces appear within the islands, and the angioblasts become ar¬ ranged in cords and form the endothelial lin¬ ings of the earliest vessels. These vascular channels then continue to enlarge by endo¬ thelial outgrowth and fuse with other nearby developing channels. The primordium of the aorta appears to¬ ward the end of the third week at about the same time as the heart (see Fig. 7-3). Two strands of cells arch dorsally from the endo¬ cardial mesenchyme, pass on each side of the foregut invagination, and turn caudally along the neural groove. The strands beside the foregut are the primordia of the first aortic arches and their continuations are the dorsal aortae. The latter acquire isolated stretches of lumen at the same time as the lateral hearts, i.e., in embryos with three somites. The arches become patent some time later, at seven or eight somites, just be¬ fore circulation begins. The umbilical ar¬ teries also probably arise independently from mesenchyme. After these main chan¬ nels have become connected and the circula¬ tion is established, however, no further growth appears to be by local differentiation from the mesenchyme. The circulation becomes functional when the first blood cells are washed out of the blood islands of the yolk sac at about the stage of nine somites, early in the fourth week. At this time the heart is contracting vigorously, capillaries have connected the aortae with the blood islands which, in turn, drain into the vitelline veins, and the blood cells have elaborated hemoglobin. The um¬ bilical arteries and veins also have become connected, and oxygenation of the blood takes place in the primitive placenta. From this time forward, the circulatory system develops by budding from existing trunks, the formation of new capillary networks, and the selection of parts of the network as arteries and veins. As the bulk of an embry¬ onic part increases in size, the capillaries are lengthened. Soon the hemodynamic forces

DEVELOPMENT OF THE ARTERIES

result in the selection of certain channels as arterioles and arteries and others as venules and veins. Later the pattern of the arteries and veins changes continually according to the growth requirements of the embryo. Not only do some vessels grow larger, but wellestablished vessels may be superseded by others more favorably placed and, in conse¬ quence, either regress or disappear. As the endocardial tubes fuse, beyond the pericar¬ dial cavity the ventral parts of the two aortae join to form the aortic sac, aortic arches. The first aortic arch func¬ tions until the neural tube is closed and the pharynx begins to differentiate into pouches (Figs. 8-2; 8-3). As the second pharyngeal pouch forms, a sprout from the aortic sac joins the dorsal aorta passing between the first and second pouches. The first aortic arch diminishes as this second arch devel¬ ops (Figs. 8-4; 8-5). The third, fourth, and sixth arches are formed in a similar manner and disappear or become modified into vari¬ ous adult structures. The fifth arch is never more than a questionable rudiment in the human embryo.

651

By the time the embryo is 4 mm in length (toward the latter part of the fourth week), the first arch has about disappeared; the sec¬ ond arch has formed, reached its maximum development, and diminished in size; and the third arch is well developed (Figs. 8-4; 8-5). Sprouts may be present for the fourth and pulmonary (sixth) arches. In a 5-mm embryo (beginning of the fifth week), the third and fourth arches have reached a max¬ imum and the dorsal and ventral sprouts of the pulmonary or sixth arches are nearly joined (Figs. 8-6; 8-7). The pulmonary arches are usually complete in a 6-mm embryo (middle of the fifth week). The right one soon begins to regress and by the end of the fifth week has disappeared in 12- to 13-mm embryos. The third arches also have become incomplete by this time (Figs. 8-8; 8-9; 8-10). Although the aortic arches do not persist as such, remnants of them remain as impor¬ tant parts of the arterial system (Fig. 8-11). The first arch, even at the earliest stages, has an extension into the region of the forebrain, the primordium of the internal carotid artery (Figs. 8-5; 8-7). The first arch disappears and

Primitive internal carotid artery Left 1st aortic arch

1st pharyngeal pouch

Precursor of left 2nd aortic arch Aortic sac Precursor of right 2nd aortic arch Left 1st aortic arch Aortic sac Precursor of left 2nd aortic arch Arterial trunk Left paired aorta

Left paired aorta

Right paired aorta Endothelium of ventricular cavity

Origin of ventral branch Endothelium of atrial cavity Myotome

Transverse anastomosis Aorta

Figs. 8-2 and 8-3. Ventral and lateral views of the cranial portion of the arterial system at about the end of the third week in a human embryo of 3 mm. The first aortic arch is at its maximum development and the dorsal and ventral outgrowths, which are to aid in the formation of the second arch, are just appearing. (From Congdon, 1922.)

652

THE ARTERIES

itive internal carotid arteries Left primitive internal carotid artery

Left earlier mandibular artery R & L 2ncl aortic arch

Left earlier mandibular artery

& L 3rd aortic arch udiment of L 4th aortic arch

pouch

4th aortic arch ^ of left pulmonary arch

Left 2nd aortic -arch

. \

Left 3rd aortic arch

Precursor of right pulmonary arch

Rudiment of lef^4,h aortic arch Caudal pharyngeal complex Precursor of left monary arch paired aorta Segmental artery

First segmental artery Left paired aorta Right paired aorta

Aorta

Lung

Aorta Endothelium of ventricular cavity Endothelium of atrial cavity

Figs. 8-4 and 8-5. Ventral and lateral views of an embryo, 4 mm in length, near the end of the fourth week. The first arch has receded, the second is much reduced, and the third well developed. Dorsal and ventral outgrowths for the fourth and probably the pulmonary arch (sixth) are present. (From Congdon, 1922.)

R prim. int. car. art.

1st pharyngeal pouch

m. int. carotid art.

L 3rd aortic arch L 4th aortic arch Rudiment of L pulm. arch

R later hyoid art.

L paired aorta

L later artery L/ L later /mandibular artery

Arterial trunk R 4th aortic arch R pulm. arch

WW

pr

R paired dor. aorta

Y_ Arterial trunk

/IB / /*

Primitive pulmon. arc / J Cephalic pulmon. tributary/ ~

L 4th aortic arch

Rudiment of L pulm. arch L primitive pulmonary art

R primitive pulmon. art.

Aortic sac

Cephalic pulmon. tributary

Pulmonary vein Lung Segmental artery

L paired dorsal aorta Aorta Pulmonary vein

Segmental art.

Transverse anastomosis

Figs. 8-6 and 8-7. Ventral and lateral views of a 5-mm embryo during the early part of the fifth week. The third and fourth arches are in a condition of maximum development. The dorsal and ventral sprouts for the pulmonary arches have nearly met, and the primitive pulmonary arches are already of considerable length. (From Congdon, 1922.)

DEVELOPMENT OF THE ARTERIES

653

Left later hyoid art. 1st pharyngeal pouch Left primitive internal carotid artery Left 3rd aortic arch 4th aortic arch I pharyngeal complex pulmonary arch R & L 3rd aortic arches Ventral pharyngeal art R & L 4th Aortic aortic arches

Aortic sac

Segmental artery

Left pulmonary trunk

h

Aortic trunk

Pulmonary trunk Right pulmonary arch Left primitive pulmonary artery R paired aorta

Left paired aorta

Left paired aorta

Right primitive pulmonary artery

Lung

Aorta

Aorta

Figs. 8-8 and 8-9. Ventral and lateral views of an 11-mm embryo estimated to be between 33 and 35 days old (about 5 weeks). The pulmonary arches are complete and the right is already regressing. The third arch is bent cranially at its dorsal end. (From Congdon, 1922.)

Component of left external carotid artery Rudiment of left common carotid artery

internal carotid artery Remnant of segment of left paired aorta between the 3rd & 4th aortic arches Ductus arteriosus Left paired aorta of L vertebral art. derived from segmental arteries Segment of L vertebral derived from subclavian artery Rudiment of L subclavian art.

Retrocostal anastomosis Left primitive pulmonary artery Rudiment of brachial artery Right primitive pulmonary artery

Segmental artery

Rudiment of left lung — Aorta

Lateral view of a 14-mm embryo estimated to be between five and six weeks old. The last indications of the aortic arch system are just disappearing. (From Congdon, 1922.) Fig. 8-10.

654

THE ARTERIES

□

3rd aortic arch artery

4th aortic arch artery

□

6th aortic arch artery

left dorsal aorta

left dorsal aorta internal carotid artery

external carotid artery

aortic sac aortic arch arteries truncus arteriosus (partly divided into aortic and pulmonary channels)

ductus arteriosus

left dorsal aorta

aortic sac

pulmonary arteries

right subclavian artery

7th intersegmental artery

left subclavian artery

internal carotid arteries

external carotid arteries

left common carotid artery

brachiocephalic artery left subclavian artery

subclavian arteries

ligamentum arteriosum left pulmonary artery

ductus arteriosus

ascending aorta

descending aorta

pulmonary trunk

1

truncus arteriosus

□ aortic sac

dorsal aortae

Fig. 8-11. Schematic drawings illustrating the changing nature of the truncus arteriosus, aortic sac, aortic arch arteries, and the dorsal aorta. The vessels that are not shaded or colored are not derived from these structures. A. The first two pairs of aortic arch arteries have largely disappeared. B. The carotid and subclavian vessels are forming. The parts of the dorsal aortae and aortic arches that normally disappear are indicated with broken lines. C. The arterial arrangement after the second prenatal month. D. Sketch of the arterial vessels of a 6-month-old infant. (From Moore, K. L„ The Developing Human, W. B. Saunders Co., 1973.)

DEVELOPMENT OF THE ARTERIES

the primitive carotid becomes a cranial con¬ tinuation of the dorsal aorta. The second arch (or hyoid arch artery) also disappears early, but its dorsal end gives rise to the stapedial artery, which atrophies in man but persists in some mammals. Passing through the ring of the stapes, the stapedial artery divides into supraorbital, infraorbital, and mandibular branches, which follow the three divisions of the trigeminal nerve. The infraorbital and mandibular arise from a common stem, the terminal part of which anastomoses with the external carotid. On the obliteration of the stapedial artery, this anastomosis enlarges and forms the maxil¬ lary artery. The common stem of the infraor¬ bital and mandibular branches passes be¬ tween the two roots of the auriculotemporal nerve and becomes the middle meningeal artery. The original supraorbital branch of the stapedial artery remains as the small orbital branches of the middle meningeal. The third (or carotid) arch forms the com¬ mon carotid artery and the first part of the internal carotid artery. The proximal seg¬ ment of this arch is connected with the aortic sac and persists as the common ca¬ rotid. The remainder of the internal carotid forms from the cranial extension of the dor¬ sal aorta (Fig. 8-11, A and B). The manner of formation of the external carotid artery is not well understood, but portions of it may be contributed by each of the first three arches. The arch itself persists, keeping its connection with the cranial extension of the dorsal aorta, but losing its connection caudally toward the fourth arch (Fig. 8-11, B). The left fourth arch persists and provides the basis for the adult arch of the aorta, which extends between the aortic sac and the ductus arteriosus. The right fourth arch persists as the proximal part of the right sub¬ clavian artery. Both fifth arch vessels are at best rudimentary and disappear early. The sixth arches are frequently referred to as the pulmonary arches. The proximal or ventral part of the right sixth arch persists as the right pulmonary artery, while the distal or dorsal part of it degenerates and disappears. The proximal part of the left sixth arch be¬ comes absorbed into the pulmonary trunk, forming the region of its bifurcation. The distal segment of the left sixth arch persists as the ductus arteriosus until after birth, at which time it contracts and gradually be¬

655

comes fibrosed into the ligamentum arteriosum (Fig. 8-11, C and D). dorsal aortae. The two dorsal aortae remain separate for a short time, but toward the end of the third week, at about the 3-mm stage, they fuse to form a single trunk caudal to the eighth or ninth somites. The segment of the aorta between the third and fourth arches disappears on both sides. The left dorsal aorta becomes the descending aorta, continuing caudally from the left fourth arch. The right dorsal aorta retains its conti¬ nuity with the left fourth arch, and the part that extends as far as the seventh intersegmental artery becomes the right subclavian artery (Fig. 8-11, B to D). The part of the right dorsal aorta between the seventh intersegmental artery and its original site of junction with the left dorsal aorta disappears (Fig. 8-11, B). A slight constriction called the aortic isthmus is frequently seen in that part of the aorta between the origin of the left subclavian and the attachment of the ductus arteriosus. A more serious congenital nar¬ rowing of the aorta at this site results in the malformation called coarctation of the aorta. Changes in the location of the heart during development produce certain changes in the aortic arches. The heart originally lies ven¬ tral to the most cranial part of the pharynx. It later recedes into the thorax, drawing the aortic arches with it. On the right side the fourth arch recedes to the root of the neck; on the left it is withdrawn into the thorax. The recurrent laryngeal branches of the vagus nerve originally pass caudal to the sixth or pulmonary arches. When the heart descends into the thorax, the nerves are pulled down by these arches. On the right side, however, the sixth arch disappears, al¬ lowing the nerve to slip up to the next arch (i.e., the fourth, because the fifth arch also disappears), and it thus loops around the adult right subclavian artery. On the left side the sixth arch becomes the ductus arterio¬ sus, which in the adult is represented by the ligamentum arteriosum. This explains why the left recurrent laryngeal nerve loops around the ligamentum arteriosum at the part of the aorta to which the ligamentum is attached. SUBCLAVIAN AND VERTEBRAL ARTERIES. Seg¬ mental arteries arise from the primitive dor¬ sal aortae and anastomose between succes-

656

the arteries

sive segments (Figs. 8-7; 8-9). The seventh segmental artery is of special interest be¬ cause it forms the lower end of the vertebral artery and, when the forelimb bud appears, sends a branch to it which becomes the sub¬ clavian artery. From the paired seventh seg¬ mental arteries the entire left subclavian and the greater part of the right subclavian are formed. The second pair of segmental ar¬ teries accompanies the hypoglossal nerves to the brain and is named the hypoglossal ar¬ teries. Each sends forward a branch which forms the cerebral part of the vertebral ar¬ tery and anastomoses with the posterior branch of the internal carotid. The two vertebrals unite on the ventral surface of the hindbrain to form the basilar artery. Later the hypoglossal artery atrophies and the ver¬

Fig 8 1 2

tebral is connected with the first segmental artery. The cervical part of the vertebral is developed from a longitudinal anastomosis between the first seven segmental arteries, so that the seventh of these ultimately becomes the source of the artery. As a result of the growth of the upper limb, the subclavian ar¬ tery increases greatly in size, and the verte¬ bral then appears to spring from it. Several segmental arteries contribute branches to the upper limb bud and form in it a free capillary anastomosis. Of the seg¬ mental branches, only one, that derived from the seventh segmental artery, persists to form the subclavian artery. The subcla¬ vian artery is prolonged into the upper limb during its development and becomes its arte¬ rial stem. Although this axis artery (Fig. 8-12)

Diagram illustrating the embryonic pattern and subsequent development of the arteries to the upper limb. Names in parentheses refer to the adult structures.

PULMONARY ARTERIAL VESSELS

is a continuous vessel, its parts are named topographically subclavian, axillary, and brachial as far as the forearm. The direct continuation of the axis artery in the fore¬ arm is the anterior interosseous artery. A branch that accompanies the median nerve, called the median artery, soon increases in size and forms the main vessel of the fore¬ arm, while the anterior interosseous dimin¬ ishes. Later the radial and ulnar arteries are developed as branches of the brachial part of the stem and, coincidentally with their enlargement, the median artery recedes. Occasionally the median artery persists as a vessel of some considerable size and accom¬ panies the median nerve into the palm of the hand. descending aorta. The segmental ar¬ teries caudal to the seventh develop around the body wall, retaining their segmental character and becoming the intercostal and lumbar arteries. In the early embryo, paired ventral branches of the aorta grow out on the yolk sac as the vitelline arteries. At its caudal end, the ventral branches accompa¬ nying the allantois become the umbilical ar¬ teries. As the gut develops, a number of ven¬ tral visceral branches grow into it. At first these are paired, but with the formation of a mesentery the pairs fuse into single stems. These ventral branches are irregularly spaced, and by a process of shifting along a rich anastomosis, the three main trunks, the celiac, the superior, and the inferior mesen¬ teric, are finally selected. Lateral branches of the aorta grow into the mesonephros. The long course of the testicular and ovarian ar¬ teries is the result of the caudal migration of the gonads after their arteries had become established. Later similar lateral branches grow into the suprarenal glands and the kid¬ neys. In this manner the suprarenal and renal arteries develop. The primary arterial trunk or axis artery of the embryonic lower limb arises from the dorsal root of the umbilical artery and courses along the posterior surface of the thigh, knee and leg (Fig. 8-13). The femoral artery springs from the external iliac and forms a new channel along the anterior as¬ pect of the thigh to its communication with the axis artery above the knee. As this chan¬ nel increases in size, that part of the axis ar¬ tery (called the ischiadic artery) proximal to the communication disappears, except its upper end, which persists as the inferior glu¬

657

teal artery. Two other segments of the axial artery persist: one forms the proximal part of the popliteal artery, and the other forms a part of the peroneal artery (Fig. 8-13).

Pulmonary Arterial Vessels The pulmonary arterial vessels convey deoxygenated blood, i.e., venous blood, from the right ventricle of the heart to the lungs. Consistent with the relatively thin wall of the right ventricle in comparison to that of the left ventricle, the pulmonary arterial ves¬ sels also have walls only one-third the thick¬ ness of vessels of comparable size in the sys¬ temic arterial circulation. This is explained by the differences in blood pressure within the pulmonary and systemic arterial vessels. In a young adult, the systolic pressure in the systemic arteries is about 120 mm Hg, whereas in the pulmonary arterial vessels the systolic pressure averages between 20 and 25 mm Hg. The pulmonary arterial vessels decrease in diameter as they divide. The large pulmo¬ nary trunk, which originates in the right ven¬ tricle, divides into two pulmonary arteries, one directed to each lung. These vessels di¬ vide and then subdivide in association with the bronchi, eventually to send arteries to all of the bronchopulmonary segments that form the different lobes of each lung.

PULMONARY TRUNK The pulmonary trunk (see Figs. 7-24: 7-25; 8-14) arises from the conus arteriosus of the right ventricle at the pulmonary orifice. Being short (5 cm in length) and 3 cm wide in diameter, and ascending obliquely back¬ ward, it passes at first in front of and then to the left of the ascending aorta. In the rounded concavity of the aortic arch at about the level of the fibrocartilage between the fifth and sixth thoracic vertebrae, the pulmonary trunk divides into right and left pulmonary arteries which are of nearly equal size. relations. The entire pulmonary trunk is con¬ tained within the pericardium. It is enclosed with the ascending aorta in a single tube of the visceral layer of the serous pericardium, which is continued up-

658

THE ARTERIES

- Aorta - Right common iliac artery - Internal iliac artery External iliac artery Interior epigastric artery-

'Superior gluteal artery •Inferior gluteal artery • Internal pudendal artery

Deep femoral artery ■

Femoral artery-

Saphenous branch-

■ Axis artery (Ischiadic a.)

Superior communicating branch

Axis artery.

Popliteal artery

Crural perforating branch , Medial communicating branch Anterior tibial recurrent artery Posterior tibial artery Axis artery -

Anterior tibial artery-

Superficial posterior tibial artery Inferior communicating branch Posterior superficial peroneal artery Peroneal artery

Tarsal perforating branchy Dorsalis pedis artery^

Lateral calcaneal branch Medial calcaneal branch Lateral plantar artery Medial plantar artery

Fig. 8-13.

A diagram illustrating the general development of the arteries of the lower limb. The letter P indicates the position of the popliteus; T, that of the tibialis posterior; H, that of the flexor hallucis longus. (From Senior, 1919.)

ward upon them from the base of the heart. The fibrous layer of the pericardium is gradually lost upon the external coats of the two pulmonary ar¬ teries. Anteriorly, the pulmonary trunk is separated from the sternal end of the second left intercostal space by the pleura and left lung, in addition to the pericardium. Initially, the pulmonary artery lies ven¬ tral to the ascending aorta, and a bit more superi¬ orly, it lies anterior to the left atrium, at a plane be¬ hind the ascending aorta. On each side of its origin is the auricle of the corresponding atrium and a cor¬ onary artery. In the first part of its course, the left coronary artery passes behind the pulmonary trunk.

The superficial part of the cardiac plexus lies above its bifurcation, between it and the arch of the aorta. right pulmonary artery. The right pul¬ monary artery (Fig. 8-14) is longer and slightly larger than the left. Originating at the bifurcation of the pulmonary trunk, it curves around the ascending aorta and pro¬ ceeds horizontally to the right. In its course toward the lung, the right pulmonary artery lies behind the aorta and superior vena cava and in front of the right bronchus. At the

PULMONARY ARTERIAL VESSELS

root of the lung it divides into one large branch, the anterior trunk, which is the prin¬ cipal but not the only artery to the superior lobe of the right lung, and a somewhat larger interlobar branch (Fig. 8-15). The principal vessel to the superior lobe of the right lung crosses in front of the superior lobe bron¬ chus, which in consequence is frequently called the eparterial bronchus. The interlo¬ bar trunk, after sending one or more other branches to the superior lobe, furnishes the middle and inferior lobe arteries. The anterior trunk divides into apical, posterior, and anterior segmental arteries, which supply the respective bronchopul¬ monary segments of the upper lobe. Both the

659

anterior and posterior segmental arteries split into ascending and descending branches (Fig. 8-15). The interlobar trunk lies near the bottom of the horizontal fissure that separates the superior and middle lobes. It represents the continuation of the pulmonary artery as far as the origin of the middle lobe artery, and it supplies one or two important ascending branches to the posterior segment of the su¬ perior lobe. These latter vessels arise from the interlobar trunk more deeply in the hori¬ zontal fissure and beyond the site where the anterior trunk branches to ascend to the upper lobe. The middle lobe artery is shown (Fig. 8-15)

660

the arteries

Apical segmental Apical segmental

Anterior segmental Anterior trunk

Post, segmental

Post, segmental ascend Ant. segmental

Superior segmental Interlobar trunk Mid. lobe artery

Interlobar trunk Lingular

Medial basal Anterior basal Anterior basal Medial basal Lateral basal

Lateral basal Posterior basal

Posterior basal

Right Lung

Left Lung

8-15. Diagram showing relation of the branches of the pulmonary artery to the bronchi. (Redrawn after Boyden, Segmental Anatomy of the Lungs, 1955.)

Fig.

as a single artery dividing into a medial and a lateral segmental artery, but it is quite common for the two segmental arteries to arise separately. The lateral segmental artery divides into a posterior and an anterior branch, which supply the lateral broncho¬ pulmonary segment of the middle lobe. The medial segmental artery, which supplies the medial bronchopulmonary segment of the middle lobe, divides into a superior and an inferior branch. The interlobar artery continues into the inferior lobe of the right lung. Its initial branch to the inferior lobe is the superior segmental artery, which supplies the supe¬ rior bronchopulmonary segment of that lobe. This vessel divides into a lateral branch and a superomedial branch. The interlobar artery terminates as the basal segmental artery, which supplies the four basal segments of the lower lobe. It branches into the medial basal, lateral basal, anterior basal, and posterior basal segmental arteries, each of which courses to its respective bronchopulmonary segment. The individual segmental arteries of these four basal segments are quite variable in

their origin and in the number and size of accessory branches. LEFT pulmonary artery. The left pulmo¬ nary artery is shorter and somewhat smaller than the right. It courses horizontally to the left from the bifurcation of the pulmonary trunk, crossing in front of the descending aorta to lie anterior to the left primary bron¬ chus at the hilum of the left lung (Fig. 8-15). In the fetus, the left pulmonary artery is larger and more important than the right because from it branches the ductus arterio¬ sus. In the adult, the ductus has regressed to become a short fibrous cord, the ligamentum arteriosum, connecting the left pulmonary artery with the arch of the aorta just distal to the reflection of the pericardium (Figs. 8-14; 8-16). To the left of the ligamentum arteri¬ osum is found the left recurrent nerve, and to the right of the ligamentum is located the superficial part of the cardiac autonomic plexus. Inferiorly the left pulmonary artery is joined to the superior left pulmonary vein by the ligament of the left vena cava. Although the left pulmonary artery has many similarities with the right, it differs in both general and specific details of branch-

PULMONARY ARTERIAL VESSELS

661

Left common rotid artery Brachiocephalic trunk

Left subclavian artery

Left pulmonary veins Left auricle —Left coronary artery — Great cardiac vein

Anterior cardiac veins

Anterior interventricular artery

Marginal branch, right coronary artery Right hepatic vein Left hepatic veins

Fig. 8-16.

The ascending aorta and the coronary blood vessels on the sternocostal aspect of the heart. The pulmonary trunk and pulmonary valve have been removed. (Redrawn from Rauber-Kopsch.)

ing. It tends to have more separate branches than the right. Within the oblique fissure, the left pulmonary artery gives off a series of vessels (from four to eight in number) to the upper lobe and does not have a common ves¬ sel comparable to the anterior trunk of the right pulmonary artery. Thus, there is no eparterial bronchus at the right hilum. The apical and posterior bronchopulmon¬ ary segments of the superior lobe, which some authors consider to be a single apicoposterior segment, are supplied by separate apical and posterior arteries. The apical seg¬ mental artery arises from the anterior sur¬ face of the left pulmonary artery as the latter arches over the bronchus, and from there the apical segmental artery runs along the bron¬ chus. Rather than a single vessel, there may be two or more branches, one of which may combine with branches to the posterior or anterior segments. The posterior segmental artery arises distal to the apical vessel and continues along the bronchus to the poste¬ rior segment. The anterior segmental artery

may be single or multiple, arising from the superior part of the arched portion of the main artery. Frequently, this segmental ar¬ tery may have both ascending and descend¬ ing branches. The remainder of the left pulmonary ar¬ tery is named the interlobar portion, and it, in fact, supplies the two lingular broncho¬ pulmonary segments of the superior lobe and all five of the segments of the inferior lobe. The lingular artery arises from the ante¬ rior or medial part of the interlobar artery, usually as a single branch. It quickly divides into superior and inferior lingular segmen¬ tal arteries, which course to the two lingular segments of the superior lobe. At times these vessels may arise directly from the interlo¬ bar portion as separate arteries. The superior segmental artery of the left inferior lobe arises unexpectedly from the interlobar artery between the origin of the apical and posterior arteries (or apicoposterior artery) of the superior lobe and that

662

THE ARTERIES

of the lingular artery. It divides into three branches, which may combine with or sup¬ ply branches to other inferior lobe segments. The remainder of the interlobar artery continues as the basal artery. From this ves¬ sel branch the medial basal, lateral basal, anterior basal, and posterior basal segmen¬ tal arteries in a pattern somewhat similar to those of the inferior lobe of the right lung. Each of these basal segmental arteries sup¬ plies its bronchopulmonary segment.

The Aorta The aorta is the main trunk of the systemic arteries which convey oxygenated blood to the tissues of the body. At its commence¬ ment from the aortic opening of the left ven¬ tricle, it is about 3 cm in diameter. It ascends toward the neck for about 5 cm, then arches posteriorly and to the left over the root of the left lung. It descends within the thorax on the left side of the vertebral column and, gradually inclining toward the midline, passes through the aortic hiatus of the dia¬ phragm into the abdominal cavity. Opposite the caudal border of the fourth lumbar ver¬ tebra and considerably diminished in size (about 1.75 cm in diameter), it bifurcates into the two common iliac arteries. The parts of the aorta are the ascending aorta, the arch of the aorta, and the descending aorta. The de¬ scending aorta is further divided into tho¬ racic and abdominal portions of the aorta.

ASCENDING AORTA The ascending aorta (Fig. 8-15) is about 5 cm in length. It is contained within fibrous pericardium and covered by the visceral pericardium, which encloses it in a common sheath with the pulmonary trunk. It com¬ mences at the aortic opening found at the base of the left ventricle on a level with the lower border of the third costal cartilage posterior to the left half of the sternum. The ascending aorta initially curves obliquely to the right, being oriented along the axis of the heart. It ascends as high as the upper border of the second right costal cartilage, lying about 6 cm deep to the inner surface of the sternum. At its origin, opposite the cusps of the aortic valve, are three small dilatations called the aortic sinuses. At the continuation

of the ascending aorta into the aortic arch, the caliber of the vessel is increased by a bulging of its right wall, called the bulb of the aorta. relations. The commencement of the ascend¬ ing aorta is surrounded by the pulmonary artery and the right auricle, except anteriorly at the origin of the coronary artery (Fig. 8-14). More superiorly, its an¬ terior aspect is separated from the sternum by the pericardium, the right pleura, the anterior border of the right lung, some loose areolar tissue, and the remains of the thymus. Posteriorly it rests upon the left atrium and right pulmonary artery, behind which is the right principal bronchus. On the right side, the ascending aorta is related to the superior vena cava, which lies partly behind the aorta, and the right atrium. On the left side are the left atrium and the pulmonary trunk.

The two arteries derived from the ascend¬ ing aorta are the vital right and left coronary arteries, which supply the musculature and other structures of the heart. right coronary artery. The right coronary artery (Figs. 7-25; 7-26; 8-14; 8-16 to 8-18) arises from the aorta behind the right (ante¬ rior) aortic sinus (of Valsalva). It passes to the right and toward the apex, between the conus arteriosus and right auricle, into the coronary sulcus. It follows the sulcus first to the right around the right margin of the heart and then to the left on the diaphragmatic surface. It ends in two or three branches beyond the interventricular sulcus. In its course it supplies small branches to the right atrium, to the right ventricle by way of its marginal branch, and to both ventricles on their diaphragmatic surface by means of the posterior interventricular branch. The atrial branches of the right coronary artery are directed superiorly to the muscu¬ lature of the right atrium. One of these, the sinoatrial nodal artery, passes between the right atrium and the superior vena cava to supply the sinoatrial node. The marginal branch is quite large and arises from the main artery at the right mar¬ gin of the heart, and courses along the sur¬ face of the right ventricle, along the acute margin, to the apex. It terminates beyond the apex on the posterior surface of the right ventricle. Thus, the marginal branch sup¬ plies both the anterior and posterior surfaces of the right ventricle. The posterior interventricular branch of the right coronary artery courses down the

THE AORTA

Left subclavian artery Left carotid artery Ligamentum arteriosum

663

Brachiocephalic trunk Superior vena cava Right pulmonary artery

Left pulmonary artery

Right pulmonary veins

Left pulmonary veins

Sulcus terminalis

Fossa ovalis Oblique vein of left atrium

Limbus Inferior vena cava Small cardiac vein

Great cardiac vein Left posterior artery and vein

Circumflex artery

Posterior interventricular artery

Posterior vein — of left ventricle

Left coronary artery

Fig. 8-17.

The coronary blood vessels of the diaphragmatic aspect of the heart. (Redrawn from Rauber-Kopsch.'

posterior interventricular sulcus two-thirds of the way to the apex, supplying branches to both ventricles as it descends. It anasto¬ moses with the anterior interventricular branch of the left coronary artery near the apex. LEFT coronary artery. The left coronary artery (see Figs. 7-25; 7-26; 8-14; 8-16 to 8-18) arises from the aorta behind the left (left posterior) aortic sinus (of Valsalva). After a short course under cover of the left auricle, it bifurcates into the anterior interventricu¬ lar branch and the circumflex branch. In those instances in which the right coronary artery does not supply the sinoatrial node, a small sinoatrial nodal branch may be given off by the left coronary artery near its origin. The anterior interventricular branch of the left coronary artery passes to the left be¬ tween the pulmonary trunk and the left auri¬ cle to the anterior interventricular sulcus, which it follows to the apex, supplying branches to both ventricles. It anastomoses

with the posterior interventricular branch of the right coronary artery. The circumflex branch of the left coronary artery follows the left part of the coronary sulcus, running first to the left and then, around the left margin, it courses backward to the diaphragmatic surface of the heart and to the right, reaching nearly as far as the posterior interventricular sulcus. It supplies branches to the left atrium and ventricle. It anastomoses with the right coronary artery. variations. The left coronary artery or its de¬ scending branch supplying the left ventricle may arise from the left pulmonary artery. This anomaly can be diagnosed clinically and usually leads to death in infancy. Rarely both coronaries arise from the pulmonary artery. Single coronary arteries have been described. The left coronary may be a branch of the right or both arteries may arise in the same aortic sinus. There may be three coronary arteries, the accessory vessel giving off some of the branches usually derived from the normal coronary arteries.

664

the arteries

Sinuatrial Superior vena cava

Pulmonary vein

Left atrium Aorta Right coronary artery

Coronary sinus-Small cardiac vein—

Left coronary artery Great cardiac vein Circumflex branch, left coronary artery Ant. interventricular branch, left coronary artery; Great cardiac vein

Posterior interventricularbranch, right coronary a.

Middle cardiac vein

8-18. The coronary arteries (in red) and the cardiac veins (in black). The more intensely colored vessels are shown on the sternocostal surface of the heart, while those on the diaphragmatic surface are shown in lighter shades.

Fig

Three patterns of distribution of the coronary arteries have been described. In half the hearts, the right coronary predominates; in a third, the two ves¬ sels are equally balanced; and in the rest, the left coronary predominates. The sinuatrial node is sup¬ plied by a branch of the right coronary in 70%, by the left in 25%, by both in 7%. The atrioventricular node is supplied by the right in 92%. The right atrio¬ ventricular bundle branch generally is supplied by the anterior interventricular branch of the left coro¬ nary; the left bundle branch comes from septal branches of the left coronary artery and small ves¬ sels from the right coronary artery (Gregg, 1950).

ARCH OF THE AORTA The arch of the aorta (Figs. 8-14; 8-16) be¬ gins at the level of the upper border of the right second sternocostal articulation and runs at first upward, backward, and to the left, anterior to the trachea. It is then di¬ rected posteriorly on the left side of the tra¬ chea and finally curves downward to the left side of the body of the fourth thoracic verte¬ bra, at the caudal border of which it be¬ comes the descending aorta. It ihus forms two curvatures: one with its convexity orien¬ ted superiorly, the other with its convexity directed anteriorly and to the left. The upper border of the aortic arch reaches superiorly

to about the middle of the manubrium, and the entire arch, which measures about 4.5 cm in length, is contained within the lower half of the superior mediastinum. relations. Anteriorly, the arch of the aorta is covered by the pleura, the anterior margins of the lungs, and by the remains of the thymus. As the vessel courses posteriorly, its left side is in contact with the left lung and left mediastinal pleura. Addi¬ tionally, to the left of the aortic arch are four nerves coursing downward in the thorax. In order, i.e., from front to back, these are the left phrenic, the inferior cervical cardiac branch of the left vagus, the supe¬ rior cervical cardiac branch of the left sympathetic, and the trunk of the left vagus nerve. As the left vagus nerve crosses the arch, it gives off its recur¬ rent branch, which hooks around the vessel and then passes superiorly on its right side. The left su¬ perior intercostal vein runs obliquely on the left side of the arch, between the phrenic and vagus nerves. On the right side of the aortic arch are the deep car¬ diac plexus, the right recurrent nerve, the esopha¬ gus, and the thoracic duct. The trachea lies posterior to and to the right of the vessel. Superiorly are the brachiocephalic, left common carotid, and left sub¬ clavian arteries, all of which arise from the convexity of the arch and are crossed close to their origins by the left brachiocephalic vein. Interiorly are the bifur¬ cation of the pulmonary trunk, the left principal bronchus, the ligamentum arteriosum, the superfi¬ cial cardiac plexus, and the left recurrent nerve. As

THE AORTA

stated above, the ligamentum arteriosum connects the pulmonary artery near its commencement to the aortic arch. Between the origin of the left subclavian artery and the attachment of the ductus arteriosus, the lumen of the aorta in the fetus is considerably nar¬ rowed, forming what is termed the aortic isthmus, while immediately beyond the ductus arteriosus the vessel presents a fusiform dilation which has been called the aortic spindle. The point of junction of the two parts is marked in the concavity of the arch by an indentation or angle. This situation persists to some extent in the adult, in whom the average diam¬ eter of the spindle exceeds that of the isthmus by about 3 mm. VARIATIONS IN THE COURSE OF THE ARCH OF THE

The height to which the aorta ascends in the thorax is usually about 2.5 cm below the cranial bor¬ der of the sternum. This may vary, however, and the summit of the aorta may not ascend as high as this site, or it may rise as high as the upper border of the sternum. Sometimes the aorta arches over the root of the right lung (right aortic arch) instead of the left, passing along the right side of the vertebral column, a condition that is normal in birds. In such cases, the thoracic and abdominal viscera are usually trans¬ posed. Less frequently the aorta, after arching over the root of the right lung, passes dorsal to the esoph¬ agus to reach its usual position on the left side of the vertebral column. This variation is not accompanied by transposition of the viscera. As in some quadru¬ peds, the aorta occasionally divides into an ascend¬ ing and a descending trunk. In these instances the ascending trunk is directed vertically upward and subdivides into three branches, which supply the head and upper limbs. Sometimes the aorta subdi¬ vides near its origin into two branches, which soon reunite. When this variation occurs, the esophagus and trachea are found to pas's through the interval between the two branches. This is the normal condi¬ tion of the vessel in the reptilian class of vertebrates. aorta.

BRANCHES FROM THE ARCH

OF THE

AORTA.

Arising from the aortic arch are vessels that principally supply the neck, head, upper ex¬ tremity, and, to some extent, the upper tho¬ racic wall. In 83 to 94% of cadavers, there are three branches derived from the arch of the aorta: the brachiocephalic trunk, the left common carotid artery, and the left subcla¬ vian artery (Fig. 8-14). The latter two vessels will be discussed with the vasculature of the head, neck, and upper extremity. The brach¬ iocephalic trunk will be described following a discussion of the possible variations in the branching pattern of these great vessels. VARIATIONS IN THE BRANCHING PATTERN OF THE arch of the aorta. The branches may arise from the commencement of the arch or upper part of the

665

ascending aorta, instead of from the highest part of the arch. The distance between the branches at their origins may be increased or diminished, the most frequent change in this respect being the approxi¬ mation of the left common carotid artery toward the brachiocephalic trunk. The number of the primary branches may be re¬ duced to one, or more frequently two (7%), the left common carotid artery arising from the brachioce¬ phalic trunk. More rarely, the common carotid and subclavian arteries of the left side arise from a left brachiocephalic artery. The number of branches from the aortic arch may be increased to four when the right common carotid and subclavian arteries arise directly from the aorta, the brachiocephalic trunk being absent. In most instances the right sub¬ clavian has been found to be the first branch and to arise from the left end of the arch, but in a few speci¬ mens it is the second or third branch from the arch. Another variation in which there are four primary branches from the aortic arch is that in which the left vertebral artery arises from the arch between the left common carotid and subclavian arteries. Finally the number of trunks from the arch may be increased to five or six, in which cases the external and internal carotid arteries arise separately from the arch, the common carotid being absent on one or both sides. In a few instances both vertebral arteries have been found to arise from the aortic arch. When the aorta arches to the right side, the three branches have a reverse arrangement, with a brachi¬ ocephalic trunk coursing to the left and the right common carotid and subclavian arteries arising sep¬ arately. In other instances, when the aorta takes its usual course to the left, the two carotids may arise as a common trunk, with the subclavian arteries origi¬ nating separately from the arch and the right subcla¬ vian generally arising from the left end of the arch. In some instances, other arteries branch from the arch of the aorta. Of these the most common are one or both of the bronchial arteries and the thyroid ima artery. Although rarely seen, it has been re¬ ported that the internal thoracic and inferior thyroid arteries may arise from the aortic arch.

BRACHIOCEPHALIC TRUNK The brachiocephalic trunk (formerly called the innominate artery) is the largest of the three branches arising from the arch of the aorta, and it measures 4 to 5 cm in length (Fig. 8-14). It arises near the commencement of the arch of the aorta, on a plane anterior to the origin of the left carotid. At its origin the brachiocephalic trunk is positioned be¬ hind the manubrium sterni at about the level of the upper border of the right second cos¬ tal cartilage. The vessel courses superiorly, somewhat posteriorly, and obliquely to the

666

the arteries

right to the level of the upper border of the right sternoclavicular articulation, where it divides into the right common carotid and right subclavian arteries. relation.,. Anteriorly, the brachiocephalic trunk is separated from the manubrium sterni by the sternohyoid and sternothyroid muscles, the remains of the thymus, the left brachiocephalic and right in¬ ferior thyroid veins which cross its root, and some¬ times the cardiac branches of the right vagus. Poste¬ riorly lies the trachea, which the brachiocephalic trunk crosses obliquely. On the right side are the right brachiocephalic vein, the superior vena cava, the right phrenic nerve, and the pleura. On the left side are found the remains of the thymus, the origin of the left common carotid artery, the inferior thy¬ roid veins, and more superiorly, the trachea.

The brachiocephalic trunk usually does not give off branches, but occasionally (in about 10% of cases) a small vessel, the thy¬ roid ima artery, arises from it. At times a thy¬ mic artery or bronchial artery may arise from the brachiocephalic trunk. thyroid IMA artery. The thyroid ima ar¬ tery, when present, ascends anterior to the trachea to the inferior part of the thyroid gland, which it supplies. It varies greatly in size and appears to compensate for a defi¬ ciency or absence of one of the other thyroid arteries. It occasionally arises from the aorta on the right common carotid, subclavian, or internal thoracic arteries. variations. The brachiocephalic trunk some¬ times divides above the level of the sternoclavicular joint, less frequently below it. It may be absent, in which case the right subclavian and the right com¬ mon carotid then arise directly from the aorta. When the aortic arch is on the right side, the brachioce¬ phalic trunk is directed toward the left.

Arteries of the Head and Neck The principal arteries supplying the struc¬ tures of the head and neck are the two com¬ mon carotids. These vessels, one on each side, ascend in the neck, and at the level of the upper border of the thyroid cartilage (of the larynx) each divides into two branches. 1 hese branches are the external carotid ar¬ tery, which supplies the exterior of the head, the face, and the greater part of the neck, and the internal carotid artery, which supplies to

a great extent the structures within the cra¬ nial and orbital cavities. The vertebral ar¬ teries, which branch from the subclavian arteries, also ascend in the neck and assist in supplying the brain. These will be described with the subclavian artery.

COMMON CAROTID ARTERY The common carotid arteries differ in length and in their mode of origin. The right common carotid artery begins at the bifurca¬ tion of the brachiocephalic trunk behind the right sternoclavicular joint and is confined to the neck. The left common carotid artery branches from the highest part of the arch of the aorta immediately to the left and slightly behind the brachiocephalic trunk. It there¬ fore consists of a thoracic and a cervical por¬ tion. The thoracic portion of the left common carotid artery is 2.5 to 3.5 cm in length and ascends from the arch of the aorta through the superior mediastinum to the level of the left sternoclavicular joint, where it becomes the cervical portion. relations. Anteriorly, the thoracic portion of the left common carotid artery is separated from the manubrium sterni by the sternohyoid and sterno¬ thyroid muscles, the anterior portions of the left pleura and lung, the left brachiocephalic vein, and the remains of the thymus. Posteriorly, the vessel is related to the trachea, esophagus, left recurrent la¬ ryngeal nerve, and thoracic duct. To its right side are the brachiocephalic trunk, the trachea, the inferior thyroid veins, and the remains of the thymus. To its left side are the left vagus and phrenic nerves, left pleura, and lung. The left subclavian artery is poste¬ rior and slightly lateral to the left common carotid artery in the thorax.

The cervical portions of the two common carotid arteries resemble each other so closely that one description will apply to both. Each vessel passes obliquely from be¬ hind the sternoclavicular articulation, to the level of the upper border of the thyroid car¬ tilage, where it divides into the external and internal carotid arteries (Figs. 8-19; 8-20; 8-24). In the lower part of the neck the two com¬ mon carotid arteries are separated by a nar¬ row interval which contains the trachea. More superiorly in the neck, however, the thyroid gland, the larynx, and the pharynx

ARTERIES OF THE HEAD AND NECK

667

Fig. 8-19. The triangles of the neck. The sternocleidomastoid muscle separates the anterior from the posterior triangle. Observe the course of the carotid arteries in the neck.

project anteriorly between the two vessels. The common carotid artery is contained in the carotid sheath, which is derived from the deep cervical fascia. The sheath also en¬ closes the internal jugular vein and vagus nerve, the vein lying lateral to the artery, and the nerve between the artery and vein on a plane posterior to both vessels. When the sheath is opened, each of the structures is seen to have a separate fibrous investment. relations. In the lower cervical region, the com¬ mon carotid artery lies quite deep, being covered by the integument, superficial fascia and platysma mus¬ cle, deep cervical fascia, and the sternocleido¬ mastoid, sternohyoid, sternothyroid, and omohyoid muscles. Above the superior belly of the omohyoid muscle, the common carotid artery is more superfi¬ cial, being covered only by the integument, the su¬

perficial fascia and platysma, deep cervical fascia, and the medial margin of the sternocleidomastoid muscle (Fig. 8-1 9). When this muscle is drawn back¬ ward, the artery is seen in a triangular space, the carotid triangle, bounded posteriorly by the sterno¬ cleidomastoid, superiorly by the stylohyoid and pos¬ terior belly of the digastric, and interiorly by the su¬ perior belly of the omohyoid muscle (Fig. 8-1 9). This part of the artery is crossed obliquely, from its me¬ dial to its lateral side, by the sternocleidomastoid branch of the superior thyroid artery; it is also crossed by the superior and middle thyroid veins which flow into the internal jugular. Usually superfi¬ cial to the carotid sheath; but occasionally contained within it are the superior and inferior roots of the ansa cervicalis, which descend in the neck and form an interconnecting nerve loop from which the strap muscles of the neck are innervated (Fig. 8-20). The superior thyroid vein crosses the common ca¬ rotid artery near its termination, and the middle thy-

668

THE ARTERIES

Posterior auricular artery Occipital artery

Superficial temporal artery

Transverse facial artery Maxillary artery

Stylopharyngeus muscle Internal jugular vein External carotid artery Sternocleidomastoid muscle Hypoglossal nerve Ascending pharyngeal artery Internal carotid artery Superior root of ansa cervicalis Ascending cervical branch of inferior thyroid artery Anterior scalene muscle Trapezius muscle Phrenic nerve

Facial nerve Submental artery Facial artery Mylohyoid muscle Digastric muscle (ant.) Hyoglossus muscle Stylohyoid muscle Lingual artery Infrahyoid branch Superior thyroid artery Sternohyoid muscle Vagus nerve Common carotid artery Cricothyroid branch

Brachial plexus

Sternothyroid muscle Thyroid gland Inferior thyroid artery Omohyoid muscle

Transverse cervical artery Suprascapular artery Subclavian art. (3rd part)

Vertebral artery Thyrocervical trunk Subclavian artery (1st part) Subclavian vein

Clavicle Sternocleidomastoid muscle

Superficial dissection of the right side of the neck showing the carotid and subclavian arteries and their branches. Note that the submandibular and parotid glands have been removed, as well as much of the sterno¬ cleidomastoid muscle and internal jugular veins in order to reveal the underlying arteries and nerves.

Fig 8 20.

roid vein crosses the artery a little below the level of the cricoid cartilage. The anterior jugular vein crosses the artery just above the clavicle, but is sepa¬ rated from it by the sternohyoid and sternothyroid muscles. Posteriorly, the artery is separated from the transverse processes of the fourth, fifth, and sixth cervical vertebrae by the longus colli and longus capitis muscles, the sympathetic trunk being inter¬ posed between the common carotid and the mus¬ cles. The inferior thyroid artery crosses behind the lower part of the common carotid artery. Medially, the common carotid artery courses in relation to the esophagus, trachea, thyroid gland (which overlaps it), larynx, and pharynx, the inferior thyroid artery and recurrent laryngeal nerve being interposed. Lat¬ eral to the artery are the internal jugular vein and vagus nerve. In the lower neck the right recurrent laryngeal nerve crosses obliquely dorsal to the artery. The right internal jugular vein diverges from the artery in the lower neck, but the left vein approaches and often overlaps it.

carotid body. The carotid body lies deep to the bifurcation of the common carotid ar¬ tery or somewhat between the two branches. It is a small, flattened, oval structure, 2 to 5 mm in diameter, with a characteristic structure composed of epithelioid cells, which are in close relation to capillary sinu¬ soids, and an abundance of nerve fibers. Sur¬ rounding the carotid body is a delicate fi¬ brous capsule. It is part of the visceral afferent system of the body, containing chemoreceptor endings that respond to low levels of oxygen in the blood or high levels of carbon dioxide and lowered pH of the blood. It is supplied by nerve fibers from both the glossopharyngeal and vagus nerves. carotid sinus. The carotid sinus is a slight dilatation in the wall of the terminal portion of the common carotid artery and of the internal carotid artery at its origin. The

ARTERIES OF THE HEAD AND NECK

dilatation extends for about 1 cm in length and may be limited to the wall of the inter¬ nal carotid artery only. The carotid sinus is an important organ for the regulation of sys¬ temic blood pressure. Special receptorlike nerve endings capable of responding to al¬ terations in blood pressure are found in the arterial wall. The nerve fibers, which consti¬ tute the carotid branch of the glossopharyn¬ geal nerve, transmit these impulses to the medulla oblongata of the brain stem. Cardio¬ vascular reflex changes result from this homeostatic mechanism designed to return blood pressure to its more normal level by altering the rate of the heart beat.

variations. The right common carotid artery arises above the level of the superior border of the sternoclavicular joint in about 1 2% of cadavers. This vessel may arise as a separate branch from the arch of the aorta, or in conjunction with the left common carotid. The left common carotid artery varies more frequently in its origin than the right. In the majority of abnormal specimens, it arises with the brachiocephalic trunk; if the latter vessel is absent, the two common carotids may arise as a single trunk. The site of division of the common carotid artery into its external and internal branches may vary. More frequently this occurs higher than nor¬ mal (at about the level of the hyoid bone). More rarely division occurs more caudally, opposite the middle of the larynx or at the lower border of the cricoid cartilage. Very rarely, the common carotid ascends in the neck without dividing, and thus either the external or the internal carotid is absent. In a few instances the common carotid has been found to be absent, the external and internal carotids arising di¬ rectly from the arch of the aorta. The common carotid artery usually does not give off any branches before its bifurcation, but occasion¬ ally it does give origin to the superior thyroid or its laryngeal branch, the ascending pharyngeal, the in¬ ferior thyroid, or, more rarely, the vertebral artery. collateral circulation. After ligature of one common carotid, collateral circulation can become perfectly established, owing to the free communica¬ tion that exists between the carotid arteries of the two sides, both within the cranium and in the face and neck. Also there is enlargement of the branches of the subclavian artery on the side on which the common carotid artery has been tied. The chief com¬ munications outside the skull take place between the superior and inferior thyroid arteries, and between the deep cervical branch of the costocervical trunk and the descending branch of the occipital artery. Within the cranium, the vertebral artery supplies blood to the branches of the ligated internal carotid artery.

669

External Carotid Artery The external carotid artery (Fig. 8-20) be¬ gins opposite the upper border of the thyroid cartilage, and passing upward, it curves somewhat anteriorly and then inclines pos¬ teriorly to the space behind the neck of the mandible, where, in the substance of the parotid gland, it divides into the superficial temporal and maxillary arteries. It rapidly diminishes in size in its course up the neck, owing to the number and large size of its branches. In the child, it is somewhat smaller than the internal carotid, but in the adult, the two vessels are of nearly equal size. At its origin, the external carotid is more superficial and nearer the midline than the internal carotid, and is contained within the carotid triangle.

Within the carotid triangle, the ex¬ lies deep to the skin, superfi¬ cial fascia, platysma, deep fascia, and anterior mar¬ gin of the sternocleidomastoid muscle. It is crossed by the hypoglossal nerve and its vena comitans and by the lingual, facial, and superior thyroid veins. Just above the carotid triangle it lies deep to the posterior belly of the digastric and stylohyoid mus¬ cles. More superiorly, it penetrates into the sub¬ stance of the parotid gland, where it lies deep to the facial nerve and the junction of the superficial tem¬ poral and maxillary veins. Medial (or deep) to the artery are found initially the hyoid bone, the wall of the pharynx, and the superior laryngeal nerve. More superiorly it is separated from the internal carotid artery by the styloglossus and stylopharyngeus mus¬ cles, the glossopharyngeal nerve, the pharyngeal branch of the vagus nerve, and part of the parotid gland. relations.

ternal carotid artery

Branches of the External Carotid Artery

Eight branches arise from the external carotid artery, usually in the following order: Superior thyroid Ascending pharyngeal Lingual Facial Occipital Posterior auricular Superficial temporal Maxillary

670

THE ARTERIES

SUPERIOR THYROID ARTERY

The superior thyroid artery (Figs. 8-20; 8-21; 8-24) arises from the anterior aspect of the external carotid artery just caudal to the level of the greater horn of the hyoid bone and ends in the thyroid gland. In 16% of ca¬ davers the superior thyroid artery arises from the common carotid artery. From its origin deep to the anterior border of the sternocleidomastoid muscle, it initially courses upward and forward for a short dis¬ tance in the carotid triangle, where it is cov¬ ered by the skin, platysma, and fascia. The superior thyroid artery then arches down¬ ward deep to the omohyoid, sternohyoid, and sternothyroid muscles. To its medial side are the inferior pharyngeal constrictor muscle and the external branch of the supe¬ rior laryngeal nerve.

Branches of the Superior Thyroid Artery

The superior thyroid artery distributes small vessels to adjacent muscles, and usu¬ ally two main branches to the thyroid gland. One of these, the anterior branch, is larger and supplies principally the ventral surface of the gland. At the isthmus of the thyroid gland, the anterior branch anastomoses with the corresponding artery of the opposite side. Also coursing to the thyroid gland is the posterior branch, which descends on the dorsal surface of the gland and anastomoses with the inferior thyroid artery. In addition to the glandular branches and small muscular twigs, the branches of the superior thyroid are: Infrahyoid Sternocleidomastoid Superior laryngeal Cricothyroid infrahyoid branch. The infrahyoid branch of the superior thyroid artery is small and runs along the lower border of the hyoid bone (Fig. 8-20). It lies on the thyrohy¬ oid membrane, deep to the thyrohyoid mus¬ cle, and anastomoses with the suprahyoid branch of the lingual artery and with the infrahyoid branch of the opposite side. STERNOCLEIDOMASTOID BRANCH. The Sternocleidomastoid branch of the superior thy¬ roid artery courses downward and laterally across the carotid sheath and supplies the

middle part of the sternocleidomastoid mus¬ cle and neighboring muscles and integument (Fig. 8-24). It frequently arises as a separate branch from the external carotid artery. superior laryngeal artery. The supe¬ rior laryngeal artery, larger than either of the preceding, passes medially and accompanies the internal laryngeal branch of the superior laryngeal nerve, deep to the thyrohyoid mus¬ cle (Fig. 8-21). It pierces the thyrohyoid mem¬ brane and supplies the muscles, mucous membrane, and glands of the larynx, anasto¬ mosing the inferior laryngeal branch of the inferior thyroid artery with the superior laryngeal artery from the opposite side. It sometimes (13%) arises separately from the external carotid. cricothyroid branch. The cricothyroid branch of the superior laryngeal artery is small and runs transversely across the crico¬ thyroid membrane, anastomosing with the artery of the opposite side (Figs. 8-20; 8-24).

ASCENOING PHARYNGEAL ARTERY

The ascending pharyngeal artery (Figs. 8-20; 8-23; 8-24) is the smallest branch of the external carotid artery. Being a long, slender vessel, it is deeply placed in the neck, dorsal to the other branches of the external carotid and to the stylopharyngeus. It arises from the posterior part of the external carotid ar¬ tery, near the origin of that vessel, and as¬ cends vertically to the inferior surface of the base of the skull, between the internal ca¬ rotid and the side of the pharynx, anterior to the longus capitis muscle. In 14% of cadavers it arises from the occipital artery, and occa¬ sionally it may arise from the internal ca¬ rotid artery.

Branches of the Ascending Pharyngeal Artery

The branches of this vessel are small and somewhat variable. In its ascent, it helps to supply the pharynx, the soft palate, the rec¬ tus capitis and longus capitis muscles, the superior cervical ganglion, the medial wall of the tympanic cavity, and the dura mater covering the brain. It anastomoses with the ascending palatine branch of the facial ar¬ tery. Its branches are: Pharyngeal Palatine

ARTERIES OF THE HEAD AND NECK

Prevertebral Inferior tympanic Meningeal pharyngeal branches. Three or four pharyngeal branches arise from the ascend¬ ing pharyngeal artery. These supply the su¬ perior and middle constrictor muscles, as well as the mucous membrane lining the pharynx. One branch supplies the stylopharyngeus muscles. These branches anasto¬ mose with vessels from the superior thyroid artery. palatine branch. The palatine branch (which is considered by some authors as one of the pharyngeal branches) may take the place of the ascending palatine branch of the facial artery, when that vessel is small. It passes beyond the upper border of the supe¬ rior constrictor muscle and sends ramifica¬ tions to the soft palate and tonsil, supplying also a branch to the auditory tube. prevertebral branches. These are nu¬ merous small vessels that supply the longus capitis and longus colli muscles, the sympa¬ thetic trunk, the hypoglossal and vagus nerves, and a number of the deep cervical lymph nodes. These small arteries anasto¬ mose with the ascending cervical branch of the inferior thyroid artery. inferior tympanic artery. The inferior tympanic artery is a small vessel that passes, with the tympanic branch of the glossopha¬ ryngeal nerve, through a minute foramen, the tympanic canaliculus, in the petrous por¬ tion of the temporal bone. Entering the mid¬ dle ear, it supplies the medial wall of the tympanic cavity and anastomoses with the other tympanic arteries. meningeal branches. Several small me¬ ningeal vessels branch from the ascending pharyngeal artery to supply the dura mater. One, the posterior meningeal artery, enters the cranium through the jugular foramen; a second passes through the foramen lacerum; and occasionally a third passes through the canal for the hypoglossal nerve.

LINGUAL ARTERY

The lingual artery (Figs. 8-20; 8-24) arises from the external carotid between the supe¬ rior thyroid and facial arteries, opposite the tip of the greater horn of the hyoid bone. Supplying structures in the floor of the oral

671

cavity, it is the principal artery to the tongue. Initially it courses obliquely upward and medially above the greater horn of the hyoid bone. It then curves downward and anteri¬ orly to form a loop, which is crossed by the hypoglossal nerve. Coursing deep to the pos¬ terior belly of the digastric and stylohyoid muscles, the lingual artery then runs hori¬ zontally under cover of (i.e., medial to) the hyoglossus muscle to ascend perpendicu¬ larly to the tongue. The artery then turns anteriorly as the deep lingual artery and courses along the inferior surface of the tongue as far as the tip. Frequently, the lingual and facial arteries arise as a common vessel, the linguofacial trunk, from the external carotid artery. The trunk courses a short distance superomedially before dividing into the lingual and fa¬ cial arteries. The first (or oblique) part of the lin¬ lies superficially and is contained within the carotid triangle. It rests on the middle pharyn¬ geal constrictor muscle and is covered by the skin, platysma, and fascia of the neck. Its second (or curved) part also rests on the middle pharyngeal constrictor, being covered at first by the tendon of the digastric muscle and by the stylohyoid muscle, and more anteriorly by the hyoglossus. Its third (or horizontal) part lies between the hyoglossus and genioglossus. The fourth (or terminal) part of the vessel, called the deep lingual artery (ranine artery), runs along the inferior surface of the tongue to its tip. At this site it is quite superficial, being covered only by the mucous membrane. Deep to the artery are the inferior longitudinal muscle of the tongue and, on its medial side, the genioglossus muscle. The hy¬ poglossal nerve crosses the first part of the lingual artery, but is separated from the second part by the hyoglossus muscle. relations.

gual artery

Branches of the Lingual Artery

Four named branches of the lingual artery are usually identified. They are: Suprahyoid Dorsal lingual Sublingual Deep lingual The suprahyoid branch of the lingual artery is quite small and courses along the superior border of the hyoid bone, supplying some of the muscles attached to it (Fig. 8-21). The vessel anastosuprahyoid

branch.

672

the arteries

moses with the infrahyoid branch of the superior thyroid artery and with the supra¬ hyoid branch of the opposite side. dorsal lingual branches. There are usu¬ ally two or three small dorsal lingual branches of the lingual artery, and they arise medial to and under cover of the hyoglossus muscle (Fig. 8-24). They ascend to the poste¬ rior part of the dorsum of the tongue and supply the mucous membrane of this region, the palatoglossal arch, the tonsil, soft palate, and epiglottis. There is some anastomosis with tonsillar arteries and with vessels of the opposite side. sublingual artery. The sublingual ar¬ tery arises at the anterior margin of the hyoglossus muscle and courses anteriorly between the genioglossus and mylohyoid muscles to achieve the sublingual gland. It supplies the gland and gives branches to the

mylohyoid and neighboring muscles and to the mucous membrane of the mouth and gums. Small vessels supply the sides of the tongue, and the artery to the frenulum of the tongue is usually derived from the sublin¬ gual artery. One branch, running medial to the alveolar process of the mandible in the substance of the gum, anastomoses with a similar artery from the other side; another pierces the mylohyoid muscle and anasto¬ moses with the submental branch of the fa¬ cial artery. deep lingual artery. The deep lingual artery (also known as the ranine artery) is the terminal portion of the lingual artery; it pursues a tortuous course, running along the inferior lingual surface, between the inferior longitudinal muscle of the tongue and the mucous membrane (Fig. 8-24). Lying on the lateral side of the genioglossus muscle, it is

frontal Drancn, perficial temporal artery Superficial temporal artery Zygomatico orbital artery

Parietal branch superficial temporal artery-

Occipital branch, post auricular a.

Transverse facial artery

Dorsal nasal branch, ophthalmic artery

Levator labii superioris muscle Posterior auricular artery Angular artery Occipital artery

— Zygomaticus major muscle

Ascending palatine artery ___ Depressor anguli oris muscle Facial artery

• Submental artery Lingual artery ' Suprahyoid artery Superior laryngeal artery Superior thyroid artery

The arteries of the face and scalp viewed from the right side. Both the submandibular and parotid glands have been removed to reveal the course of the external carotid artery behind the ramus of the mandible. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, 1975.) Fig. 8-21

ARTERIES OF THE HEAD AND NECK

accompanied by the lingual vein and the ter¬ minal part of the lingual nerve. It anastomo¬ ses with the artery of the opposite side at the tip of the tongue. FACIAL ARTERY

The facial artery (Figs. 8-20; 8-21; 8-23) arises in the carotid triangle a little superior to the lingual artery and, sheltered by the ramus of the mandible, passes obliquely deep to the posterior belly of the digastric and the stylohyoid muscles. It then arches anteriorly to enter a groove on the posterior surface of the submandibular gland where it joins the facial vein. Becoming quite superfi¬ cial, the facial artery winds around the infe¬ rior border of the mandible at the anterior edge of the masseter muscle to enter the face. It crosses the cheek lateral to the angle of the mouth and, as the angular artery, as¬ cends along the side of the nose, to end at the medial palpebral commissure of the eye. At this site it anastomoses with the dorsal nasal branch of the ophthalmic artery. The facial artery, both in the neck and on the face, is remarkably tortuous. In the neck, this may assist the vessel to accommodate itself to movements of the pharynx in deglutition, and in the face, to movements of the mandi¬ ble, lips, and cheeks. relations. In the neck, the origin of the facial artery is quite superficial, being covered by the in¬ tegument, platysma, and fascia. It then passes deep to the posterior belly of the digastric and the stylohy¬ oid muscle, part of the submandibular gland, and frequently the hypoglossal nerve. It lies on the me¬ dial and superior pharyngeal constrictor muscles, the latter separating the vessel at the summit of its arch from the tonsil. On the face, where the facial artery passes over the body of the mandible, it is also superficial, lying immediately beneath the pla¬ tysma. In its course over the face, it is covered by the integument, the fat of the cheek, and near the angle of mouth, by the platysma, risorius, and zygomaticus major muscles. It rests on the buccinator and levator anguli oris, and passes either superficial or deep to the levator labii superioris. The anterior facial vein lies lateral to the artery and takes a more direct course across the face. Branches of the facial nerve cross the artery.

Branches of the Facial Artery

The branches of the facial artery may be divided into two sets; those given off in the neck, cervical, and those on the face, facial.

673

Cervical Branches Ascending palatine Tonsillar Glandular Submental Facial Branches Inferior labial Superior labial Lateral nasal Angular Additionally, muscular branches are given off both in the neck and in the face. ascending palatine artery. The ascend¬ ing palatine artery (Figs. 8-21; 8-23) arises close to the origin of the facial artery and passes upward between the styloglossus and stylopharyngeus muscles to the side of the pharynx, along which it continues between the superior pharyngeal constrictor and the medial pterygoid muscles toward the base of the skull. It divides near the levator veli palatini muscle into two branches. One branch follows the course of this muscle, and, winding over the upper border of the superior pharyngeal constrictor, supplies the soft palate and the palatine glands, anasto¬ mosing with its fellow of the opposite side and with the greater palatine branch of the maxillary artery. The other branch pierces the superior pharyngeal constrictor muscle and supplies the palatine tonsil and auditory tube, anastomosing with the tonsillar branch of the facial artery and the ascending pha¬ ryngeal branch of the external carotid ar¬ tery. tonsillar branch. The tonsillar branch of the facial artery (Fig. 8-24) ascends be¬ tween the medial pterygoid and styloglossus muscles. On the side of the pharynx, at the level of the palatine tonsil, it perforates the superior pharyngeal constrictor to ramify in the substance of the palatine tonsil and root of the tongue. Penetrating the lower pole of the tonsillar bed, this vessel is usually the primary arterial supply to the tonsil. glandular branches. As the facial artery courses near the submandibular gland, three or four large branches are distributed to the submandibular gland, some being pro¬ longed to the neighboring muscles, lymph nodes, and integument. Generally, a small branch supplies the submandibular duct (of Wharton1). ‘Thomas Wharton (1610-1673): An English anatomist (London).

674

THE ARTERIES

The submental artery, being the largest of the cervical branches, comes off the facial artery just as that vessel emerges from beneath the submandibular gland (Figs. 8-20; 8-21). It runs anteriorly upon the mylohyoid muscle just below the body of the mandible and deep to the ante¬ rior belly of the digastric. It supplies the sur¬ rounding muscles and anastomoses with the sublingual branch of the lingual artery and with the mylohyoid branch of the inferior alveolar artery. At the symphysis menti, the submental artery turns upward over the bor¬ der of the mandible and divides into a super¬ ficial and a deep branch. The superficial branch passes between the skin and the le¬ vator labii inferioris muscle, and anastomo¬ ses with the inferior labial artery. The deep branch runs between this same muscle and the bone, supplies the lip, and anastomoses with the inferior labial and mental arteries. inferior labial artery. The inferior la¬ bial artery arises near the angle of the mouth (Figs. 8-22; 8-23). It passes anteriorly beneath the depressor anguli oris and, penetrating the orbicularis oris, runs a tortuous course along the edge of the lower lip, between this muscle and the mucous membrane. It sup¬ plies the labial glands, the mucous mem¬ brane, and the muscles of the lower lip. The inferior labial artery anastomoses with the same vessel of the opposite side and with the mental branch of the inferior alveolar artery. superior labial artery. The superior labial artery is larger and more tortuous than the inferior (Figs. 8-22; 8-23). It follows a comparable course along the edge of the upper lip, passing deep to the zygomaticus major muscle to lie between the mucous membrane and the orbicularis oris. It sup¬ submental artery.

plies the upper lip and anastomoses with the artery of the opposite side. Additionally, the superior labial artery sends at least two branches that ascend to the nose. These are the septal branch, which ramifies on the nasal septum as far as the point of the nose, and the alar branch, which supplies the ala of the nose. lateral nasal branch. The lateral nasal branch of the facial artery is derived from the larger trunk as that vessel ascends along¬ side the nose. It supplies the ala and dorsum of the nose, anastomosing with its fellow from the other side, with the septal and alar branches of the superior labial artery, with the dorsal nasal branch of the ophthalmic artery, and with the infraorbital branch of the maxillary artery. angular artery. The angular artery (Figs. 8-21; 8-23) is actually the terminal part of the facial. It ascends in the groove lateral to the nose to the medial angle of the orbit, embed¬ ded in the fibers of the levator labii superioris alaeque nasi and is accompanied by the an¬ gular vein. The branches of the angular ar¬ tery anastomose with the infraorbital artery, and after supplying the lacrimal sac and or¬ bicularis oculi muscle, it ends by anastomos¬ ing with the dorsal nasal branch of the oph¬ thalmic artery. muscular branches. Unnamed separate muscular arteries frequently branch directly from the main trunk of the facial artery. From the cervical part of the vessel a branch generally ascends to the medial pterygoid muscle in the face and another supplies the stylohyoid muscle. Muscular branches aris¬ ing from the artery on the face supply the masseter and buccinator muscles as well as the muscles of expression.

Superior labial nerves (maxillary) Labial glands Superior labial artery

Inferior labial artery

Inferior labial nerves (mandibular)

The labial arteries, the glands of the lips, and the nerves of the right side seen from the inner surface of the oral cavity after removal of the mucous membrane. (From Poirier and Charpy.)

Fig. 8-22.

ARTERIES OF THE HEAD AND NECK

The anastomoses of the facial artery are quite numerous, not only across the midline with branches of the same vessel of the opposite side, but in the neck, with the sublingual branch of the lingual, with the ascending pharyngeal, and by its ascending palatine and tonsillar branches with the greater pala¬ tine branch of the maxillary. On the face, branches of the facial artery anastomose with the mental branch of the inferior alveo¬ lar artery as it emerges from the mental fora¬ men, with the transverse facial branch of the superficial temporal artery, with the infraor¬ bital branch of the maxillary artery, and with the dorsal nasal branch of the ophthal¬ mic artery. ANASTOMOSES OF THE FACIAL ARTERY.

variations. The facial and lingual arteries fre¬ quently arise as a common vessel, the linguofacial trunk, which quickly divides into separate facial and lingual branches. The facial artery may vary in size and in the extent to which it supplies the face. It occasionally ends by forming the submental artery at the level of the chin, and not infrequently extends only as high as the angle of the mouth or nose. The deficiency is then compensated for by an enlarge¬ ment of the neighboring arteries.

OCCIPITAL ARTERY

The occipital artery arises from the poste¬ rior part of the external carotid artery, oppo¬ site the origin of the facial artery near the lower margin of the posterior belly of the digastric muscle (Figs. 8-20; 8-21; 8-23). It is generally a vessel of considerable size and ends in the posterior part of the scalp. At its origin, the occipi¬ is covered by the posterior belly of the digastric and the stylohyoid muscles. It is crossed by the hypoglossal nerve as that nerve winds around the vessel in its course toward the tongue. The ves¬ sel crosses the internal carotid artery, the internal jugular vein, and the vagus and accessory nerves. The artery next ascends to the interval between the transverse process of the atlas and the mastoid proc¬ ess of the temporal bone, passing backward and upward along the occipital groove of the latter bone. In its course, the occipital artery is covered by the sternocleidomastoid, splenius capitis, and longissimus capitis muscles, and the posterior belly of the digastric muscle, and rests sequentially on the rec¬ tus capitis lateralis, the obliquus capitis superior, and the semispinalis capitis muscles. Posteriorly at the base of the skull, the artery changes its course and runs vertically upward, piercing the fascia con¬ necting the cranial attachments of the trapezius and COURSE and relations.

tal artery

675

sternocleidomastoid muscles. The occipital artery then ascends in a tortuous course within the superfi¬ cial fascia of the scalp, where it divides into numer¬ ous branches. These branches reach as high as the vertex of the skull, anastomosing with the posterior auricular and superficial temporal arteries. The ter¬ minal portion of the occipital artery is accompanied by the greater occipital nerve.

Branches of the Occipital Artery

Arising from the occipital artery are the following branches: Muscular Sternocleidomastoid Auricular Mastoid Meningeal Descending Terminal (Occipital) muscular branches. Unnamed muscular branches of the occipital artery supply the digastric, stylohyoid, splenius, and longissimus capitis muscles. sternocleidomastoid artery. The ster¬ nocleidomastoid artery generally arises from the occipital artery close to its origin, but sometimes springs directly from the ex¬ ternal carotid (Fig. 8-23). It passes downward and backward over the hypoglossal nerve and enters the substance of the muscle, in company with the accessory nerve. This ar¬ tery anastomoses with the sternocleido¬ mastoid branch of the superior thyroid ar¬ tery. Frequently two sternocleidomastoid vessels arise from the occipital artery. auricular branch. The auricular branch of the occipital artery ascends over the mas¬ toid process of the temporal bone to supply the back of the cartilaginous concha of the external ear. It sometimes replaces the pos¬ terior auricular artery. mastoid branch. The mastoid branch arises either from the occipital artery or from its auricular branch. It is a small vessel that enters the skull through the mastoid fo¬ ramen and supplies the diploe, the dura mater, and the mastoid air cells. It anastomo¬ ses with the middle meningeal artery. meningeal branches. One or more long, slender meningeal branches arise from the occipital artery and ascend, with the internal jugular vein, to enter the cranial cavity through the jugular foramen and condyloid

676

THE ARTERIES

canal. They supply the dura mater lining the posterior fossa of the skull. descending branch. The descending branch is the largest of the vessels arising from the occipital artery (Fig. 8-24). It courses downward in the posterior neck and divides into a superficial and a deep branch. The superficial branch lies deep to the splenius, giving off branches which pierce that muscle to supply the trapezius and anastomose with the superficial branch of the transverse cervical. The deep branch de¬ scends between the semispinales capitis and cervicis and anastomoses with the vertebral artery and with the deep cervical artery, a branch of the costocervical trunk. The anas¬ tomoses among these vessels assist in estab¬ lishing a collateral circulation after ligation of the common carotid or subclavian artery. TERMINAL (OR OCCIPITAL) BRANCHES. The terminal (or occipital) branches of the occip¬ ital artery are distributed to the scalp on the back of the head. They are very tortuous and lie between the skin and the occipital belly of the occipitofrontalis muscle. Anastomos¬ ing with similar vessels from the opposite side and with the posterior auricular and superficial temporal arteries, these terminal branches of the occipital artery supply the occipital belly of the occipitofrontalis mus¬ cle, the skin, and the pericranium. One of the terminal branches may give off a meningeal twig, which passes through the parietal fora¬ men to help supply the dura mater. POSTERIOR AURICULAR ARTERY

The posterior auricular artery is small and arises from the external carotid just above the posterior belly of the digastric and stylo¬ hyoid muscles opposite the apex of the sty¬ loid process (Figs. 8-20; 8-21; 8-23). The ves¬ sel ascends on the styloid process of the temporal bone under cover of the parotid gland to the groove between the cartilage of the external ear and the mastoid process, where it divides into its auricular and occip¬ ital branches.

Branches of the Posterior Auricular Artery

In addition to several small branches that the posterior auricular artery supplies to the digastric, stylohyoid, and sternocleidomas¬

toid muscles and to the parotid gland, this vessel gives off three branches: Stylomastoid Auricular Occipital stylomastoid artery. The stylomastoid artery enters the stylomastoid foramen and supplies the mucous membrane of the tym¬ panic cavity, the mastoid antrum and mas¬ toid cells, and the semicircular canals (Fig. 8-23). In young subjects, a branch from this vessel, the posterior tympanic artery (along with the anterior tympanic artery from the maxillary), forms a vascular ring that sur¬ rounds the inner surface of the tympanic membrane and sends delicate vessels to ramify on that membrane. The stylomastoid artery anastomoses with the petrosal branch of the middle meningeal artery by a twig, which enters the hiatus of the facial canal. auricular branch. The auricular branch of the posterior auricular artery ascends behind the ear, deep to the auricularis poste¬ rior, and is distributed to the back of the au¬ ricle, upon which it ramifies minutely. Some branches curve around the margin of the cartilage, while others perforate it to supply the anterior surface. The auricular branch of the posterior auricular artery anastomoses with the parietal and anterior auricular branches of the superficial temporal artery. occipital branch. The occipital branch passes posteriorly over the sternocleido¬ mastoid muscle to the scalp above and be¬ hind the ear. It supplies the occipital belly of the occipitofrontalis muscle and the other layers of the scalp in this region, and it anas¬ tomoses with the occipital artery (Figs. 8-21; 8-23).

SUPERFICIAL TEMPORAL ARTERY

The superficial temporal artery is the smaller of the two terminal branches of the external carotid and appears to be the con¬ tinuation of that vessel (Figs. 8-20: 8-21; 8-23). It begins in the substance of the parotid gland posterior to the neck of the mandible and crosses over the posterior root of the zygomatic process of the temporal bone. About 5 cm above this process, the superfi¬ cial temporal artery divides into its frontal and parietal branches.

ARTERIES OF THE HEAD AND NECK

relations. As it crosses the zygomatic process, the superficial temporal artery is covered by the auricularis anterior muscle and by a dense fascia. Within the substance of the parotid gland, the artery is crossed by the temporal and zygomatic branches of the facial nerve and one or two veins. In its course along the side of the head, it is accompanied by the auriculotemporal nerve, which lies immediately pos¬ terior to it. Just above the zygomatic process and in front of the auricle, the superficial temporal artery is quite superficial, being covered only by skin and fas¬ cia, and can easily be felt pulsating. This artery is often used for determining the pulse, particularly by anesthesiologists.

Branches of the Superficial Temporal Artery

Besides some twigs to the parotid gland, the temporomandibular joint, and the masseter muscle, the superficial temporal artery gives rise to the following branches: Transverse facial Middle temporal Zygomatico-orbital Anterior auricular Frontal Parietal The trans¬ verse facial artery is the largest branch of the superficial temporal artery and is given off even before the superficial temporal artery emerges from the substance of the parotid gland (Figs. 8-20; 8-21). Initially the trans¬ verse facial artery is deeply placed in the parotid gland, and coursing anteriorly, the vessel then passes transversely across the side of the face, between the parotid duct and the inferior border of the zygomatic arch. It divides into numerous branches, which supply the parotid gland and duct, the masseter muscle, and the skin. Branches of the transverse facial artery anastomose with the facial, masseteric, buccal, and infraor¬ bital arteries. This vessel rests on the mas¬ seter muscle and is accompanied by one or two branches of the facial nerve. MIDDLE TEMPORAL ARTERY. The middle temporal artery arises immediately above the zygomatic arch and, perforating the tem¬ poral fascia, lies against the squama of the temporal bone, where it sends branches to the temporalis muscle (Fig. 8-23). This vessel anastomoses with the deep temporal branches of the maxillary artery. transverse

facial

artery.

ZYGOMATICO-ORBITAL

ARTERY.

The

677 ZygO-

matico-orbital artery courses between the two layers of temporal fascia along the superior border of the zygomatic arch to the lateral angle of the orbit (Fig. 8-21). This ves¬ sel supplies the orbicularis oculi muscle and anastomoses with the lacrimal and palpebral branches of the ophthalmic artery. It may arise from the middle temporal artery in¬ stead of branching directly from the superfi¬ cial temporal artery. ANTERIOR AURICULAR BRANCHES. Three Or four anterior auricular branches are distrib¬ uted to the anterior portion of the auricle, the tragus, the lobule, and part of the exter¬ nal acoustic meatus. They anastomose with the posterior auricular artery. frontal branch. The frontal branch of the superficial temporal artery takes a tortu¬ ous course anteriorly and upward toward the forehead, supplying the muscles, integu¬ ment, and pericranium in this region (Figs. 8-21; 8-23). It anastomoses with the supraor¬ bital and supratrochlear branches of the ophthalmic artery. parietal branch. The parietal branch is larger than the frontal, curves upward and backward on the side of the head, and lies between the skin and the temporal fascia (Figs. 8-21; 8-23). It anastomoses anteriorly with the frontal branch of the superficial temporal artery, posteriorly with the poste¬ rior auricular and occipital branches of the external carotid, and across the vertex of the skull with the parietal branch of the other side. MAXILLARY ARTERY

The maxillary artery is the larger of the two terminal branches of the external ca¬ rotid (Figs. 8-20; 8-23). It arises behind the neck of the mandible and is at first embed¬ ded in the substance of the parotid gland. It passes anteriorly between the ramus of the mandible and the sphenomandibular liga¬ ment, and then courses to the pterygopala¬ tine fossa, either superficial or deep to the lateral pterygoid muscle. It supplies the deep structures of the face and may be divided into mandibular, pterygoid, and pterygopal¬ atine portions. The first or mandibular portion lies be¬ tween the neck of the mandible and the sphenomandibular ligament, courses hori-

678

the arteries

zontally forward, nearly parallel to but a lit¬ tle below the auriculotemporal nerve. It is embedded in the parotid gland and crosses the inferior alveolar nerve while running along the inferior border of the lateral ptery¬ goid muscle. The second or pterygoid portion arches forward and upward under cover of the ramus of the mandible and the insertion of the temporalis muscle. It lies either superfi¬ cial or deep to the lower head of the lateral pterygoid muscle. When it lies superficial to the latter muscle, the vessel is located be¬ tween the lateral pterygoid and temporalis muscles. When the vessel lies more deeply, it is located between the lateral pterygoid muscle and branches of the mandibular nerve, lying close to the lateral pterygoid plate. In this latter situation, the artery then penetrates the muscle to gain entrance to the pterygopalatine fossa. This portion supplies the muscles of mastication and the bucci¬ nator. The third or pterygopalatine portion is a short segment of the maxillary artery, lying in the pterygopalatine fossa. It gives off sev¬ eral important branches and makes its way toward the sphenopalatine foramen, passing beside the pterygopalatine ganglion and ter¬ minating as the sphenopalatine artery. The course of the third part of the maxillary ar¬ tery is the same in both superficially and deeply running vessels. It sends branches to the orbit and anterior face, the paranasal sinuses, nasal cavity and nasopharynx, and the upper teeth and palate. The origin of branches of the first two parts of the maxillary artery differs some¬ what, depending on whether the vessel courses superficial or deep to the lateral pterygoid muscle. Branches of the First (or Mandibular) Portion of the Maxillary Artery

The descriptions of the following branches pertain to those instances in which the maxillary artery takes a more superficial course in the deep face: Deep auricular Anterior tympanic Inferior alveolar Middle meningeal Accessory meningeal

The deep auricular is a small vessel that ascends in the sub¬ stance of the parotid gland, deep to the tem¬ poromandibular articulation (Fig. 8-23). It pierces the cartilaginous or bony wall of the external acoustic meatus and supplies its cuticular lining and the outer surface of the tympanic membrane. It gives a branch to the temporomandibular joint as it courses be¬ hind the articular capsule. anterior tympanic artery. The anterior tympanic artery is small and often arises in common with the deep auricular artery (Fig. 8-23). It passes behind the temporoman¬ dibular articulation and enters the tympanic cavity through the petrotympanic fissure. Within the middle ear it ramifies upon the inner surface of the tympanic membrane, forming a vascular circle around the mem¬ brane with the stylomastoid branch of the posterior auricular artery. The anterior tym¬ panic artery also anastomoses with the ar¬ tery of the pterygoid canal and with the caroticotympanic branch from the internal carotid artery. inferior alveolar artery. The inferior alveolar artery arises from the maxillary ar¬ tery as that vessel courses between the neck of the mandible and the sphenomandibular ligament. It then descends with the inferior alveolar nerve to the mandibular foramen on the medial surface of the ramus of the mandible (Fig. 8-23). The artery then enters the mandibular canal with the nerve and courses through the canal to the first premolar tooth, where it divides into the mental and incisor branches. Along its course, the inferior alveolar artery also gives off mylo¬ hyoid and dental branches and a small lin¬ gual branch. The mylohyoid artery arises from the infe¬ rior alveolar artery just before the latter ves¬ sel enters the mandibular foramen. It runs in the mylohyoid groove on the medial surface of the mandibular ramus, along with the mylohyoid nerve, to the inferior surface of the mylohyoid muscle, which it supplies. The incisor branch, which is one of the terminal branches of the inferior alveolar artery, continues in the mandibular canal to the midline anteriorly, where it gives branches to the incisor teeth and anastomo¬ ses with a similar vessel from the opposite side. The mental branch, which is the other ter¬ minal branch of the inferior alveolar artery, DEEP auricular artery.

ARTERIES OF THE HEAD AND NECK

Middle Parietal branch. superficial temporal a. meningeal a.

Deep temporal aa

Frontal branch, superficial temporal a.

679

Infraorbital a.

_Supraorbital a. Supratrochlear a.

Medial palpebral a. Dorsal nasal a.

Middle temporal a. Superficial temporal a. Ant. tympanic a Deep auricular a -

Infraorbital a.

Occipital branch post, auricular a Maxillary a. Stylomastoid a.

Anterior superior alveolar a.

Angular a. Post, auricular a. -

Buccal a

Ascend, pharyngeal a.~ Inf. alveolar a.

Superior labial a.

Occipital a Ascend, palatine a. Sternocleidomastoid' branch, occipital a.

Inferior labial a. Flypoglossal nerve Facial a. Lingual a.

Mental a. Facial a.

Fig. 8-23. The right maxillary artery exposed in the infratemporal and pterygopalatine regions by the removal of the parotid gland, ramus of mandible, zygomatic arch, and muscles of mastication. Note the facial, occipital, ascending pharyngeal, posterior auricular, and superficial temporal branches of the right external carotid artery. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, 1975.)

emerges with the mental nerve from the mental foramen to supply the chin (Fig. 823). It anastomoses with the submental and inferior labial branches of the facial artery. The dental branches of the inferior alveo¬ lar artery correspond in number to the roots of the lower teeth. They enter the minute apertures at the extremities of the roots and supply the pulp of the teeth. The lingual branch, which is small, arises from the inferior alveolar artery near its ori¬ gin and descends with the lingual nerve to supply the mucous membrane of the mouth. MIDDLE MENINGEAL ARTERY. The middle meningeal artery is the largest of the arteries that supply the dura mater (Fig. 8-23). It as¬ cends between the sphenomandibular liga¬ ment and the lateral pterygoid muscle and between the two roots of the auriculotempo¬ ral nerve to the foramen spinosum of the sphenoid bone, through which it enters the cranial cavity accompanied by two small veins and some sympathetic nerve fibers.

Finally, in a groove on the great wing of the sphenoid bone that extends to the squamous part of the temporal bone, the middle men¬ ingeal artery divides into frontal (or ante¬ rior) and parietal (or posterior) branches. The frontal (or anterior) branch is the larger of the two principal terminal branches. It crosses the great wing of the sphenoid to reach the groove, or canal, in the sphenoidal angle of the parietal bone. It then divides into branches that spread out be¬ tween the dura mater and internal surface of the cranium, some passing upward as far as the vertex, and others backward to the oc¬ cipital region. The parietal (or posterior) branch curves backward on the squamous part of the tem¬ poral bone, and reaching the parietal bone some distance anterior to its mastoid angle, it divides into branches that supply the pos¬ terior part of the dura mater and cranium. The branches of the middle meningeal ar¬ tery are distributed partly to the dura mater,

680

the arteries

but chiefly to the bones. They anastomose with the arteries of the opposite side and with the anterior meningeal (from the ante¬ rior ethmoid) and posterior meningeal (from the vertebral) arteries. The middle meningeal artery, as it enters the cranium, gives off several other branches. A number of small ganglionic ves¬ sels supply the trigeminal ganglion, the roots of the trigeminal nerve, and the dura mater nearby. A petrosal branch, which enters the hiatus for the greater petrosal nerve, sup¬ plies the facial nerve and anastomoses with the stylomastoid branch of the posterior au¬ ricular artery. A superior tympanic artery runs in the canal for the tensor tympani and supplies this muscle and the lining mem¬ brane of the canal. An anastomotic branch with the lacrimal artery passes through the superior orbital fissure or through separate canals in the great wing of the sphenoid bone to achieve the orbit. It anastomoses with the recurrent meningeal branch of the lacrimal artery. Occasionally, the lacrimal artery may arise from the middle meningeal artery. Temporal branches pass through small foramina in the great wing of the sphe¬ noid and anastomose in the temporal fossa with the deep temporal arteries. accessory meningeal artery. The acces¬ sory meningeal artery may arise directly from the maxillary artery or, by means of a common vessel, with the middle meningeal artery. It enters the cranial cavity by passing upward along the course of the mandibular division of the trigeminal nerve through the foramen ovale. The accessory meningeal artery supplies muscles in its upward course in the deep face and, within the cranial cav¬ ity, supplies the trigeminal ganglion and dura mater.

Branches of the Second (or Pterygoid) Portion of the Maxillary Artery

The descriptions of the following branches pertain to those instances in which the max¬ illary artery takes a more superficial course in the deep face. The branches of this second portion supply muscles. Deep temporal Pterygoid

Masseteric Buccal deep temporal branches. There are gen¬ erally two deep temporal branches, an ante¬ rior and a posterior (Fig. 8-23). These ascend between the temporalis muscle and the pericranium, supplying that muscle and anastomosing with the middle temporal ar¬ tery. The anterior deep temporal artery com¬ municates with the lacrimal artery by means of small branches which perforate the zygo¬ matic bone and great wing of the sphenoid. Certainly, the two temporal branches anas¬ tomose with each other. pterygoid branches. The pterygoid branches vary in number and origin, and they supply the two pterygoid muscles. masseteric artery. The masseteric ar¬ tery arises from the maxillary between the neck of the mandible and the sphenomandibular ligament. It is a small vessel and passes laterally through the mandibular notch with the masseteric nerve to the deep surface of the masseter muscle. It supplies that muscle and anastomoses with the masseteric branches of the facial artery and with the transverse facial artery. buccal artery. The buccal artery is a small vessel that courses, along with the buccal nerve, forward and downward be¬ tween the medial pterygoid muscle and the insertion of the temporalis muscle to the ex¬ ternal surface of the buccinator, which it supplies (Fig. 8-23). It anastomoses with branches of the facial, transverse facial, and infraorbital arteries.

variations. The foregoing descriptions of the first and second parts of the maxillary artery apply to those specimens in which the maxillary artery courses superficial to the lateral pterygoid muscle. In about one-third of all cadavers, however, the vessel passes deep to the lateral pterygoid, which results in some variation in the origin of branches from the first two parts. In the latter situation, the deep auric¬ ular and anterior tympanic branches are unchanged. The masseteric and posterior deep temporal arteries come from a common trunk with the inferior alveolar artery from the first portion. The middle and acces¬ sory meningeal arteries arise from the second por¬ tion close to the foramen spinosum. The pterygoid, buccal, and anterior deep temporal branches also arise from the second portion, either separately or from a common trunk, deep to the lateral pterygoid muscle.

ARTERIES OF THE HEAD AND NECK

Branches of the Third (or Pterygopalatine) Portion of the Maxillary Artery

The branches of the third part of the max¬ illary artery arise within the pterygopalatine fossa, and accompanied by branches of the maxillary division of the trigeminal nerve, they pass through foramina or bony canals. These branches are: Posterior superior alveolar Infraorbital Descending palatine Artery of the pterygoid canal Pharyngeal Sphenopalatine POSTERIOR

SUPERIOR

ALVEOLAR

ARTERY.

This vessel arises from the maxillary artery, frequently in conjunction with the infraor¬ bital artery, just as the trunk of the maxillary is passing into the pterygopalatine fossa. Descending upon the tuberosity of the max¬ illa, the posterior superior alveolar artery divides into numerous branches, some of which supply the lining of the maxillary sinus while others enter the alveolar canals to suppy the molar and premolar teeth. Still other branches continue anteriorly on the alveolar process to supply the gums. The vascular branches are accompanied in their course by branches of the posterior superior alveolar nerve, which are derived from the maxillary division of the trigeminal. infraorbital artery. The infraorbital artery arises as a branch frxim the maxillary artery as the latter vessel enters the pterygo¬ palatine fossa, and frequently in conjunction with the posterior superior alveolar artery (Fig. 8-23). It runs along the infraorbital groove and canal with the infraorbital nerve and emerges on the face through the infraor¬ bital foramen. In its course, the infraorbital artery gives off orbital, anterior superior al¬ veolar, and facial branches. The orbital branches arise in the infraor¬ bital canal and they assist in the supply of the lacrimal gland and of the inferior rectus and inferior oblique muscles. The anterior superior alveolar branches of the infraorbital artery, with branches of the middle and anterior superior alveolar nerves, descend through the grooves in the anterior wall of the maxilla (Fig. 8-23). Together the vessels and nerves enter the anterior alveolar canals to supply dental

681

branches to the upper incisor and canine teeth. Some branches also supply the mu¬ cous membrane of the maxillary sinus. The facial branches of the infraorbital ar¬ tery arise after the vessel emerges from the infraorbital foramen. On the anterior face some branches course upward to the medial angle of the orbit, supplying the lacrimal sac and anastomosing with the angular branch of the facial artery. Branches also descend toward the nose and anastomose with the dorsal nasal branch of the ophthalmic ar¬ tery. Other branches descend between the levator labii superioris and the levator labii superioris alaeque nasi muscles and anasto¬ mose with the transverse facial and buccal arteries. descending palatine artery. The de¬ scending palatine artery arises from the maxillary artery in the pterygopalatine fossa and descends in the greater palatine canal with the greater palatine nerve, which is de¬ rived from the maxillary nerve and pterygo¬ palatine ganglion. After emerging from the greater palatine foramen at the palate, the descending palatine artery becomes the greater palatine artery, having already given off several small lesser palatine branches. The greater palatine artery courses anteri¬ orly from the greater palatine foramen to the incisive canal in a groove called the greater palatine sulcus near the alveolar border on the oral surface of the hard palate. Branches of the vessel are distributed to the gums, pal¬ atine glands, and mucous membrane of the roof of the mouth. A terminal branch anasto¬ moses with the nasopalatine branch of the sphenopalatine artery in the incisive canal. The lesser palatine arteries arise from the descending palatine artery and course through the lesser palatine canals to emerge at the lesser palatine foramina. They then course medially, laterally, and posteriorly to supply the oral surface of the soft palate and the palatine tonsil. These vessels anastomose with the ascending palatine branch of the facial artery. artery of the pterygoid canal. This ar¬ tery arises from the maxillary artery in the pterygopalatine fossa and enters the ptery¬ goid canal (Vidian1 canal) with the corre1Vidus Vidius (Latinized name of Guido Guidi, 15001569): An Italian physician and anatomist (Pisa).

682 sponding nerve. It is a long, slender branch that is distributed to the upper part of the pharynx and anastomoses with the ascend¬ ing pharyngeal and sphenopalatine arteries. The artery of the pterygoid canal also sup¬ plies the auditory tube and sphenoidal sinus and sends into the tympanic cavity a small branch that anastomoses with the other tympanic arteries. pharyngeal branch. The pharyngeal branch of the maxillary artery is quite small. It runs posteriorly in the palatovaginal canal with a nerve, the pharyngeal branch of the pterygopalatine ganglion, and is distributed to the auditory tube, the upper part of the pharynx, and the sphenoidal sinus. sphenopalatine artery. The sphenopala¬ tine artery is actually the terminal or contin¬ uation branch of the maxillary artery. It en¬ ters the nasal cavity through the spheno¬ palatine foramen at the posterior end of the superior meatus, close to the pterygopala¬ tine ganglion, and is accompanied by late¬ ral nasal, septal, and nasopalatine nerve branches from the maxillary nerve and pter¬ ygopalatine ganglion. Shortly after travers¬ ing the foramen, the sphenopalatine artery divides into posterior lateral nasal and pos¬ terior septal arteries. The posterior lateral nasal branches run anteriorly, ramifying over the nasal conchae and meatuses that form the lateral wall of the nasal cavity. They also assist in the sup¬ ply of the mucosa that lines the frontal, max¬ illary, ethmoidal, and sphenoidal sinuses. The posterior septal branches arise from the sphenopalatine artery and, arching over the roof of the nasal cavity along the inferior surface of the sphenoid bone, anastomose with branches of the anterior and posterior ethmoidal arteries in the mucosa of the nasal septum. Other vessels ramify anteriorly and inferiorly on the septum. One branch, the nasopalatine artery, courses in a groove on the vomer with the nasopalatine nerve to the incisive canal, where it anastomoses with the greater palatine artery. Internal Carotid Artery

The internal carotid artery ascends in the neck, enters the base of the skull, opens into the cranial cavity, and supplies much of the cerebral hemisphere, the pituitary gland, the eyeball and other orbital structures, the an¬ terior aspect of the forehead, and the exter¬

nal nose. It consists of cervical, petrous, cav¬ ernous, and cerebral portions. The cervical portion of the internal carotid artery begins at the bifurcation of the common carotid opposite the upper border of the thyroid car¬ tilage, and runs perpendicularly upward, anterior to the transverse processes of the first three cervical vertebrae, to reach the inferior surface of the petrous portion of the temporal bone (Fig. 8-24). The vessel then enters the carotid canal, becoming the pet¬ rous portion. It makes an abrupt turn for¬ ward and medially to the foramen lacerum. At the end of the carotid canal, the internal carotid artery curves upward, above the car¬ tilage occupying the foramen lacerum, to enter the middle cranial fossa between the lingula and petrosal process of the sphenoid bone. The cavernous portion of the internal carotid artery is the first part of its course within the cranial cavity, where it is sus¬ pended between the layers of the dura mater that form the cavernous sinus (Fig. 8-25). Ascending toward the posterior clinoid process, the artery curves forward on the lat¬ eral aspect of the body of the sphenoid bone in the carotid sulcus. At the medial aspect of the anterior clinoid process, the vessel then perforates the part of the dura mater that forms the roof of the cavernous sinus. Thus, the cavernous portion of the internal carotid artery makes a double curvature like the let¬ ter S before piercing the dura to achieve the substance of the brain (Fig. 8-31). The cere¬ bral portion of the artery then passes be¬ tween the optic and oculomotor nerves and approaches the anterior perforated sub¬ stance at the medial end of the lateral cere¬ bral sulcus, where it gives off its intracere¬ bral branches. cervical portion. The cervical portion of the internal carotid artery is comparatively superficial at its origin at the bifurcation of the common carotid artery (Fig. 8-24). Here the vessel is contained in the carotid triangle, and lies posterior and lateral to the external carotid artery, overlapped by the sterno¬ cleidomastoid muscle and covered by the deep fas¬ cia, platysma, and integument. It then passes deep to the parotid gland, being crossed by the hypoglos¬ sal nerve, the posterior belly of the digastric muscle, the stylohyoid muscle, and the occipital and poste¬ rior auricular branches of the external carotid artery. More superiorly, the internal carotid artery is sepa¬ rated from the external carotid by the styloglossus and stylopharyngeus muscles, the tip of the styloid process and the stylohyoid ligament, the glossopha-

ARTERIES OF THE HEAD AND NECK

Cavernous part of internal carotid artery

Buccinator muscle

Petrous part of internal carotid artery Cervical part of internal carotid artery Basilar artery Ascend, pharyngeal artery Styloglossus muscle Tonsillar branch of facial artery Stylopharyngeus muscle

Superior pharyngeal constrictor muscle Ascend, palatine a. Deep lingual a. ^Genioglossus muscle ^Sublingual gland Facial artery Dorsal lingual a. _Lingual artery Flyoglossus muscle External carotid a.

OcciDg^l artery Internal carotid artery Descending branch of occipital artery Vertebral artery

683

"• FHyoid bone Superior thyroid a. Sternocleidomastoid branch of superior thyroid artery \ Thyroid cartilage Cricothyroid branch

Deep cervical artery

Cricoid cartilage Common carotid artery Trachea

Costocervicat trun k Subclavian artery Supreme intercostal artery First rib Second rib

Fig. 8-24. This dissection of the deep neck shows the internal carotid and vertebral arteries. Also note the courses and branches of the superior thyroid and lingual arteries.

ryngeal nerve, and the pharyngeal branch of the vagus. Posteriorly, it is in relation with the longus capitis muscle, the superior cervical ganglion of the sympathetic trunk with its internal carotid branch to the carotid plexus that surrounds the artery, and the superior laryngeal branch of the vagus nerve. Later¬ ally, the internal carotid artery is related to the inter¬ nal jugular vein and vagus nerve, the nerve lying on a plane posterior to the artery. Medially, the vessel is related to the wall of the pharynx, the superior laryn¬ geal nerve, and the ascending pharyngeal artery. At the base of the skull, the glossopharyngeal, vagus, accessory, and hypoglossal nerves lie between the artery and the internal jugular vein. petrous portion. When the internal carotid ar¬ tery enters the carotid canal in the petrous portion of the temporal bone, it first ascends a short distance, then curves forward and medially, and again as¬ cends as it leaves the canal to enter the cavity of the skull between the lingula and petrosal process of the sphenoid (Fig. 8-24). The artery lies at first anterior to the cochlea and tympanic cavity. It is separated from the tympanic cavity by a thin, bony lamella, which is cribriform in the young subject and often partly absorbed in old age. More anteriorly, it is sep¬ arated from the trigeminal ganglion by a thin plate of bone that forms the floor of the fossa for the gan¬ glion and the roof of the horizontal portion of the canal. Frequently this bony plate is more or less defi¬ cient; in these instances the ganglion is separated from the artery by fibrous membrane. The artery is

surrounded by a plexus of small veins that helps to drain the tympanic cavity and flows into the cavern¬ ous sinus and internal jugular vein, and by filaments of the carotid plexus of nerves, derived from the in¬ ternal carotid branch of the superior cervical gan¬ glion of the sympathetic trunk. cavernous portion. In this part of its course, the internal carotid artery is situated between the layers of the dura mater forming the cavernous sinus, but it is covered by the lining membrane of the sinus (Figs. 8-25; 8-31). Initially, it ascends to¬ ward the posterior clinoid process, then passes for¬ ward by the side of the body of the sphenoid bone, and again curves upward on the medial aspect of the anterior clinoid process, perforating the dura mater that forms the roof of the sinus. This portion of the artery is surrounded by a plexus of sympathetic nerves, and directly on its lateral aspect courses the abducent nerve. cerebral portion. Flaving perforated the dura mater on the medial side of the anterior clinoid proc¬ ess, the internal carotid artery passes between the optic and oculomotor nerves toward the anterior perforated substance at the medial extremity of the lateral cerebral sulcus, where it divides into its cere¬ bral branches (Figs. 8-28 to 8-32). variations. The length of the internal carotid varies according to the length of the neck and ac¬ cording to the point of bifurcation of the common carotid. It arises sometimes from the arch of the aorta. The course of the artery may be tortuous in-

684

THE ARTERIES

Optic nerve

Ophthalmic artery

Internal carotid artery (cerebral portion)

Anterior clinoid process Ophthalmic vein

Posterior clinoid process Internal carotid artery (cavernous portion)

Abducens nerve

Floor of the middle cranial fossa 0’S

Cavernous sinus Maxillary nerve

Internal orifice of carotid canal

Fig. 8-25. Diagram of the cavernous portion of the internal carotid artery. (From Taveras and Wood, Diagnostic Neuroradiology, 1964.)

stead of straight. A few instances have been re¬ ported in which this vessel was completely absent. In one such case, the common carotid artery as¬ cended in the neck and gave off the usual branches of the external carotid, but the cranial portion of the internal carotid was replaced by two branches of the maxillary artery, which entered the skull through the foramen rotundum and foramen ovale and joined to form a single vessel.

Branches of the Internal Carotid Artery

The cervical portion of the internal ca¬ rotid gives off no branches. Those from the other portions are: Petrous Portion Caroticotympanic Pterygoid Cavernous Portion Cavernous

Hypophyseal • Ganglionic Anterior meningeal Cerebral Portion Ophthalmic Anterior cerebral Middle cerebral Posterior communicating Anterior choroidal CAROTICOTYMPANIC ARTERY

The caroticotympanic branch of the inter¬ nal carotid artery is a small vessel that enters the tympanic cavity through a minute fora¬ men on the posterior wall of the carotid canal. On the surface of the promontory it anastomoses with the anterior tympanic branch of the maxillary and with the stylo¬ mastoid branch of the posterior auricular artery.

ARTERIES OF THE HEAD AND NECK

PTERYGOID BRANCH The pterygoid branch of the internal carotid artery is a small inconstant vessel that passes into the pter¬ ygoid canal. It anastomoses with the pterygoid branch of the maxillary artery; this latter branch en¬ ters the opposite end of the canal from the pterygo¬ palatine fossa.

CAVERNOUS BRANCHES The cavernous branches of the internal carotid ar¬ tery are small vessels that supply the walls of the cavernous and inferior petrosal sinuses. Some of these arteries anastomose with branches of the mid¬ dle meningeal artery.

HYPOPHYSIAL ARTERIES

The superior and inferior hypophysial ar¬ teries branch from each internal carotid ar¬ tery to supply the hypophysis (pituitary gland). Although these are small vessels, they are important because they supply a vital endocrine organ. GANGLIONIC BRANCHES Several small ganglionic branches come off the internal carotid artery to supply the trigeminal gan¬ glion.

ANTERIOR MENINGEAL BRANCH The anterior meningeal branch of the internal ca¬ rotid artery is a small vessel that passes over the lesser wing of the sphenoid bone to supply the dura mater of the anterior cranial fossa. It anastomoses with the meningeal branch from the posterior eth¬ moidal artery. OPHTHALMIC ARTERY

The ophthalmic artery arises from the in¬ ternal carotid, just as that vessel emerges from the dura mater that forms the cavern¬ ous sinus, on the medial aspect of the ante¬ rior clinoid process (Fig. 8-26). It enters the orbital cavity through the optic canal, infe¬ rior and lateral to the optic nerve. Deep to the superior rectus muscle, the ophthalmic artery passes obliquely over the optic nerve from lateral to medial to reach the medial wall of the orbit. The vessel then continues forward along the lower border of the supe¬ rior oblique muscle to the medial end of the upper palpebral region where it divides into

685

two terminal branches, the supratrochlear and dorsal nasal arteries. As the ophthalmic artery crosses the optic nerve, it is accompa¬ nied by the nasociliary nerve and is sepa¬ rated from the frontal branch of the ophthal¬ mic nerve by the superior rectus and levator palpebrae superioris muscles. The ophthal¬ mic artery crosses deep to the optic nerve, rather than above, in about 15% of cases. Branches of the Ophthalmic Artery

The branches of the ophthalmic artery may be divided into an orbital group, dis¬ tributed to orbital structures including the extraocular muscles and regions surround¬ ing the orbit, and an ocular group, which supplies the eyeball (Fig. 8-26). Orbital Group Lacrimal Supraorbital Posterior ethmoidal Anterior ethmoidal Medial palpebral Supratrochlear Dorsal nasal Muscular Ocular Group Central artery of the retina Short posterior ciliary Long posterior ciliary Anterior ciliary lacrimal artery. The lacrimal artery arises from the ophthalmic artery soon after the latter vessel has entered the orbit. Some¬ times it arises before the ophthalmic artery enters the orbit. The lacrimal artery is usu¬ ally the first and often the largest branch derived from the ophthalmic (Fig. 8-26). It accompanies the lacrimal nerve along the superior border of the lateral rectus muscle and supplies the lacrimal gland. Its terminal branches, emerging from the gland, are dis¬ tributed to the eyelids and conjunctiva. Of those supplying the eyelids, the two lateral palpebral arteries are of considerable size. They run medially in the upper and lower lids, respectively, and anastomose with the medial palpebral arteries to form an arterial arch. The lacrimal artery gives off one or two zygomatic branches. One of these passes through the zygomaticotemporal foramen to reach the temporal fossa and anastomoses

686

the arteries

with the deep temporal branch of the maxil¬ lary artery. Another zygomatic branch ap¬ pears on the cheek through the zygomatico¬ facial foramen and anastomoses with the transverse facial and zygomatico-orbital branches of the superficial temporal artery (Fig. 8-27). A recurrent meningeal branch of the lacrimal artery passes backward through the lateral part of the superior orbital fissure to the dura mater where it anastomoses with a branch of the middle meningeal artery. The lacrimal artery is sometimes derived from one of the anterior branches of the middle meningeal artery. supraorbital artery. The supraorbital artery branches from the ophthalmic, the latter vessel crossing over the optic nerve (Fig. 8-26). Initially, it ascends in the orbit along the medial borders of the superior rec¬ tus and levator palpebrae superiors muscles to meet the supraorbital nerve. Accompany¬ ing the nerve between the periosteum and the levator palpebrae superioris, the artery courses forward in the orbit to the supraor¬ bital foramen. Passing through the foramen, the supraorbital artery divides into a super¬

ficial and a deep branch, which supply the integument, the muscles, and the pericranium of the forehead, anastomosing with the supra¬ trochlear branch of the ophthalmic, the fron¬ tal branch of the superficial temporal (Fig. 8-27), the angular branch of the facial artery, and the artery of the opposite side. Within the orbit, the supraorbital artery supplies the superior rectus and the levator palpebrae superioris muscles and sends a branch across the pulley of the superior oblique muscle to help supply the region at the upper medial angle of the orbit. As the su¬ praorbital artery courses through the supra¬ orbital notch, a small branch passes through a foramen to supply the diploe of the frontal bone and the lining of the frontal sinus. POSTERIOR ETHMOIDAL ARTERY. The poste¬ rior ethmoidal artery branches from the ophthalmic artery after the latter vessel has crossed to the medial side of the orbit (Fig. 8-26). It passes through the posterior ethmoi¬ dal canal and supplies the posterior ethmoi¬ dal air cells. Entering the cranium through a slitlike transverse aperture between the sphenoid bone and cribriform plate, it gives Superior oblique muscle

> *r.» • • Superior rectus muscle

Levator palpebrae 'superioris muscle

Meningeal branch of anterior ethmoidal . artery Lacrimal gland Supraorbital artery

Anterior ethmoidal artery vr-

Lat. rectus muscle

► Long posterior ciliary artery

-Lacrimal artery Optic nerve

Posterior ethmoidal artery

Long posterior ciliary artery

Ophthalmic artery Optic nerve Internal carotid artery Fig. 8 26 The ophthalmic artery and some of its branches. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, 1975.)

ARTERIES OF THE HEAD AND NECK

off a meningeal branch to the dura mater. Also, nasal branches descend into the nasal cavity through apertures in the cribriform plate. These anastomose with small vessels that come from the sphenopalatine branch of the maxillary artery. anterior ethmoidal artery. The anterior ethmoidal branch of the ophthalmic artery accompanies the nasociliary nerve through the anterior ethmoidal canal. It supplies the anterior and middle ethmoidal cells and the frontal sinus and, entering the cranium, gives off a meningeal branch to the dura mater. The nasal branches descend into the nasal cavity through a slit lateral to the crista galli and, running along the groove on the inner surface of the nasal bone, supply branches to the lateral wall and septum of the nose. A terminal branch appears on the dorsum of the nose between the nasal bone and the lateral (upper) nasal cartilage. MEDIAL PALPEBRAL ARTERIES. The medial palpebral arteries, two in number, superior and inferior, arise from the ophthalmic ar¬ tery deep to the pulley of the superior oblique muscle. They descend from the orbit, one above the medial palpebral liga¬ ment and one below the ligament. These ves¬

687

sels then encircle the eyelids near their free margins to form a superior and an inferior arch between the orbicularis oculi muscle and the tarsi. The superior palpebral arch anastomoses, at the lateral angle of the orbit, with the zygomatico-orbital branch of the superficial temporal artery, and with the superior of the two lateral palpebral branches from the lacrimal artery (Fig. 8-27). The inferior palpebral arch anastomoses, at the lateral angle of the orbit, with the infe¬ rior of the two lateral palpebral branches from the lacrimal artery and with the super¬ ficial temporal artery, and, at the medial part of the lid, with a twig from the angular branch of the facial artery. From this last anastomosis, a branch passes to the naso¬ lacrimal duct, ramifying in its mucous mem¬ brane as far as the inferior meatus of the nasal cavity. SUPRATROCHLEAR

ARTERY.

The

SUpra-

trochlear artery is one of the terminal branches of the ophthalmic artery. It leaves the orbit at its medial angle with the supra¬ trochlear nerve and, ascending on the fore¬ head, helps to supply the integument, mus¬ cles, and pericranium in the region (Fig. 8-27). It anastomoses with the supraorbital

Blood vessels of the eyelids, anterior view. 1, Branch of dorsal nasal artery that anastomoses with the angular artery. 2, Angular vein. 3, Angular branch of facial artery. 4, Facial vein. 5, Zygomatico-orbital branch of superficial temporal artery. 6, Middle temporal vein receiving orbital vein. 7, Frontal branch of superficial temporal artery. 8, Anastomosis of superior lateral palpebral branch of lacrimal artery with the anterior branch of superficial temporal artery. 9, Lacrimal artery giving rise to the superior and inferior lateral palpebral arteries. 10, Superior palpebral arch. 11, Superior palpebral artery. 12, Inferior palpebral artery. 13, Infraorbital artery. 14, Supraorbital artery and vein. 15, Supratrochlear artery. Fig. 8-27.

688

the arteries

artery and with the artery of the opposite side. dorsal nasal artery. The dorsal nasal artery is the other terminal branch of the ophthalmic, and it emerges from the orbit above the medial palpebral ligament (Fig. 8-27). After giving a twig to the superior part of the lacrimal sac, it divides into two branches. One of these crosses the root of the nose and anastomoses with the angular branch of the facial artery; the other runs along the dorsum of the nose, supplies its outer surface, and anastomoses with the lat¬ eral nasal branch of the facial artery and with the artery of the opposite side. MUSCULAR BRANCHES. TWO groups of muScular branches are derived from the main trunk of the ophthalmic artery. The superior muscular branches supply the levator palpebrae superioris, superior rectus, and superior oblique muscles. The inferior mus¬ cular group passes forward between the optic nerve and the inferior rectus muscle and is distributed to the lateral, medial, and inferior rectus muscles as well as to the infe¬ rior oblique muscle. The anterior ciliary ar¬ teries are derived from the inferior muscular vessels, and additional muscular branches are given off from the lacrimal and supraor¬ bital arteries. CENTRAL ARTERY OF THE RETINA. This ves¬ sel is the first and one of the smallest arteries that branch from the ophthalmic. It also is the most important because it supplies the retina and because, beyond the optic disc, it is an end artery and does not anastomose with any other vessel. If its function is com¬ promised, permanent retinal damage results. The central artery of the retina branches from the ophthalmic artery within the orbit, but close to the optic foramen. It pierces the dural sheath and courses for a short distance in the sheath with the optic nerve. At about 1.25 cm behind the eyeball it pierces the sub¬ stance of the optic nerve obliquely and runs forward in the center of the nerve to the ret¬ ina. Its mode of distribution in the retina will be described with the anatomy of the eye. The central retinal artery may be a branch of the lacrimal artery. The ciliary arteries are divisible into three groups: the short and long posterior, and the anterior. SHORT POSTERIOR CILIARY ARTERIES.

There

are usually more than six but fewer than ten short posterior ciliary arteries. They arise

from the ophthalmic artery or its branches and, surrounding the optic nerve, run to the posterior part of the eyeball. A number of the vessels may branch at this point before piercing the sclera around the entrance of the nerve in order to supply the choroid layer of the eyeball and the ciliary processes. LONG POSTERIOR CILIARY ARTERIES. Usu¬ ally two (but sometimes three) long posterior ciliary arteries arise from the ophthalmic artery on either side of the optic nerve (Fig. 8-26). Coursing forward with the optic nerve and the short posterior ciliary arteries, they pierce the posterior part of the sclera a short distance from the optic nerve and run along either side of the eyeball, between the sclera and choroid, to the ciliary muscle. Reaching the junction of the ciliary body and iris, each vessel divides into an upper and a lower branch. These branches form a vascular cir¬ cle, the circulus arteriosus major, around the circumference of the iris. This circle sends numerous converging branches in the sub¬ stance of the iris to its pupillary margin, where a second arterial circle, the circulus arteriosus minor, is formed. anterior ciliary arteries. The anterior ciliary arteries are derived from muscular branches of the ophthalmic artery. These vessels course to the front of the eyeball along the tendons of the recti muscles, form a vascular zone beneath the conjunctiva, and then pierce the sclera a short distance from the sclerocorneal junction. They end by anastomosing with the circulus arteriosus major around the attached margin of the iris. ANTERIOR CEREBRAL ARTERY

The anterior cerebral artery is one of the terminal branches of the internal carotid ar¬ tery. It commences at the medial extremity of the lateral cerebral sulcus (Figs. 8-28; 8-29; 8-31). It passes anteriorly and medially across the anterior perforated substance, above the optic nerve, to the beginning of the longitudinal cerebral fissure. Here it comes into close relationship with the ante¬ rior cerebral artery of the opposite side, to which it is connected by a short trunk, the anterior communicating artery. From this point the two anterior cerebral arteries run side by side in the longitudinal cerebral fis¬ sure, curve around the genu of the corpus callosum and, turning backward, continue along the upper surface of the corpus callo-

ARTERIES OF THE HEAD AND NECK

689

Olfactory bulb

Olfactory tract

Anterior cerebral artery Anterior communicating artery

Optic chiasma

Internal carotid artery

..--Hypophysis

Posterior communicating a

...Medial cerebral artery

Posterior cerebral artery —

Oculomotor nerve

Superior cerebellar a.

_Trochlear nerve

Basilar a. Trigeminal nerve

-Pons

Anterior inferior cerebellar a.

"■■Facial nerve Nervus "intermedius

Labyrinthine a. —

"Vestibulocochlear nerve -..Glossopharyngeal nerve

Vertebral artery —~

''Vagus nerve Anterior spinal artery"""

Hypoglossal nerve ''-Accessory nerve

Posterior inferior cerebellar artery

'

Cerebellar S hemisphere ''Vermis of the cerebellum Occipital pole 'w

Fig. 8-28. The arteries at the base of the brain. The temporal pole of the left cerebral hemisphere (reader’s right) has been removed to reveal the course taken by the middle cerebral artery to the lateral sulcus of the cerebral cortex. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, 1975.)

Anterior parietal Posterior parietal

Ascending frontal branch

Orbitofrontal branch

Temporal branch Fig. 8-29.

Parieto-occipital branch and Parietotemporal branch

Branches of the middle cerebral artery to the lateral surface of the cerebral hemisphere.

690 Pericallosal branch (continuation of ant. cerebral)

Paracentral branch of callosomarginal artery ■

'— Anterior parietal Post, parietal

Ant. cerebral

Callosomarginal branch (Ant. cerebral) Parieto-occipital branch (Post cerebral)

Frontopolar branch (Ant. cerebral)

Occipital branch (Post, cerebral)

Orbital branch Anterior cerebral artery Temporal branches (Post, cerebral) Temporal branch (Middle cerebral) Fig. 8-30.

Posterior cerebral artery

Medial surface of cerebral hemisphere, showing areas supplied by the three cerebral arteries.

sum to its posterior part. Here they end by anastomosing with the posterior cerebral arteries. Branches of the Anterior Cerebral Artery

In addition to the anterior communicating artery, each anterior cerebral artery gives off central branches and, within the longi¬ tudinal cerebral fissure, several cortical branches. These latter vessels can best be seen coursing over the anterior medial sur¬ face of the cerebral hemisphere when the brain is sagittally sectioned through the mid¬ line. The branches of the anterior cerebral artery are: Anterior Communicating Anteromedial branches Central Branches Recurrent (Medial striate) Cortical Branches Orbital Frontal Parietal ANTERIOR COMMUNICATING ARTERY. This artery connects the two anterior cerebral arteries across the commencement of the longitudinal fissure (Figs. 8-28; 8-32). Usually forming the anterior anastomosis of the arte¬ rial circle of Willis, the vessel varies in its configuration and may be completely absent, doubled, or even tripled. Its length averages about 4 mm, but varies greatly and it may be slender or wide. It gives off some anteromed¬ ial branches that course toward the optic chiasma.

The first, or proximal, part of the anterior cerebral artery gives off several small vessels, which pierce the ante¬ rior perforated substance and the lamina terminalis, to supply the rostrum of the corpus callosum and the septum pellucidum. Addi¬ tionally, a larger vessel, the recurrent artery (of Heubner1), also called the medial striate artery, arises just beyond the anterior com¬ municating artery. Phylogenetically, it is one of the oldest of the cerebral arteries. It takes a rather long recurrent course laterally and backward over the anterior perforated sub¬ stance and pierces the brain. Ascending in the anterior limb of the internal capsule, the recurrent artery supplies the lower anterior portion of the basal ganglia, including the lower part of the head of the caudate nu¬ cleus, the lower part of the frontal pole of the putamen, the frontal pole of the globus pallidus, and the anterior limb of the inter¬ nal capsule up to the dorsal limit of the glo¬ bus pallidus. cortical branches. Cortical branches of the anterior cerebral artery arise from that vessel as it courses backward over the corpus callosum (Fig. 8-29). They ramify over the anterior medial surface of the cere¬ bral hemisphere and are named according to their distribution. Two or three orbital branches are distributed to the orbital sur¬ face of the frontal lobe, where they supply the olfactory lobe, gyrus rectus, and medial orbital gyrus. There are at least two large frontal central branches.

'Johann O. Heubner (1843-1926): A German pediatric neurologist (Berlin).

ARTERIES OF THE HEAD AND NECK

branches, the frontopolar and callosomarginal arteries. The frontopolar artery usually arises from the anterior cerebral just below the genu of the corpus callosum, and it supplies the medial aspect of the superior frontal gyrus, extending branches over the edge of the hemisphere to the lateral aspect of the superior and middle frontal gyri. The callosomarginal artery usually branches just anterior to the genu of the corpus callo¬ sum (Fig. 8-30). It supplies the corpus callo¬ sum, the cingulate gyrus, part of the medial surface of the superior frontal gyrus, and the precentral and postcentral gyri. The anterior cerebral artery continues posteriorly in the cingulate sulcus as far as the parieto-occipital sulcus. Beyond the ori¬ gin of the callosomarginal artery, the ante¬ rior cerebral is often called the pericallosal artery (Fig. 8-30). From this are derived the anterior and posterior parietal branches, which supply the medial surface of the precuneate gyrus and adjacent areas (Fig. 8-30). MIDDLE CEREBRAL ARTERY

The middle cerebral artery is the largest branch of the internal carotid and one of its terminal branches (Figs. 8-28; 8-30; 8-31). Ini¬ tially coursing laterally to enter the lateral sulcus (or Sylvian1 fissure), it then runs backward and upward on the surface of the insula, where it divides into a number of branches that are distributed to the lateral surface of the cerebral hemisphere. Branches of the Middle Cerebral Artery

Similar to the anterior cerebral, the mid¬ dle cerebral artery gives off both central and cortical branches. The central branches are distributed to deep structures, while the cor¬ tical branches ramify more superficially in the sulci of the dorsal and lateral aspects of the cerebral cortex. The branches of the middle cerebral artery are subdivided as fol¬ lows: Central Branches Striate (Lateral striate) Cortical Branches Orbital

691

Frontal Parietal Temporal The central branches of the middle cerebral artery arise soon after that vessel enters the lateral sulcus. Usually more than 10 but less than 15 delicate striate (lenticulostriate) arteries pierce the floor of the lateral sulcus to achieve subcortical structures. These vessels supply the corpus striatum, including the upper part of the head and entire body of the caudate nucleus, and much of the lentiform nucleus. Of the latter structure, the striate arteries supply the internal capsule above the level of the globus pallidus and they even extend into the thalamus. One of the larger striate ar¬ teries, which courses between the lentiform nucleus and external capsule and passes through the internal capsule to terminate in the caudate nucleus, is especially prone to hemorrhage. It has been called “the artery of cerebral hemorrhage” by Charcot,2 and is the vessel frequently involved in cerebral stroke. cortical branches. Cortical branches of the anterior cerebral artery arise as the vessel courses posterosuperiorly in the lateral gyrus (Figs. 8-30; 8-31). The orbital branches, which include the orbitofrontal artery, supply the inferior frontal gyrus (Broca’s3 convolution) and the lateral part of the orbital surface of the frontal lobe. The ascending frontal branches supply the pre¬ central gyrus, the middle frontal gyrus, and part of the inferior frontal gyrus. The ante¬ rior and posterior parietal branches ascend to the postcentral gyrus, the lower part of the superior parietal lobule, and the inferior parietal lobule. Parietotemporal and pari¬ eto-occipital branches supply the supramar¬ ginal and angular gyri, extending to the pari¬ eto-occipital sulcus (Fig. 8-29). The anterior, middle, and posterior temporal branches of the middle cerebral artery are distributed to the lateral surface of the temporal lobe, and they supply the superior, middle, and infe¬ rior temporal gyri from the temporal pole anteriorly up to the occipital gyri posteriorly (Fig. 8-29). central branches.

2Jean M. Charcot (1825-1893): A French neurologist 1Franciscis Sylvius (Latin form of Frangois Dubois or de la Boe, 1614-1672): A Dutch physician and anatomist (Leyden).

(Paris). 3 Pierre P. Broca (1824-1880): A French surgeon and neurologist (Paris).

692

THE ARTERIES

Angiogram of normal left internal carotid artery showing its intracerebral branches, lateral view. 1, Ante¬ rior cerebral artery. 2, Middle cerebral artery. 3, Ophthalmic artery. 4, Posterior cerebral artery. 5, Posterior communi¬ cating artery. 6, 7, and 8, Petrous, cavernous and cerebral portions of internal carotid artery. (From Taveras and Wood, Diagnostic Neuroradiology, 1964.)

Fig. 8-31

POSTERIOR COMMUNICATING ARTERY

The posterior communicating artery arises from the posterior aspect of the internal ca¬ rotid artery just before that vessel terminates into the anterior and middle cerebral ar¬ teries (Figs. 8-28; 8-32). It occasionally arises from the middle cerebral artery. Coursing backward over the optic tract and the oculo¬ motor nerve, the posterior communicating artery anastomoses with the posterior cere¬ bral artery, a branch of the basilar. It varies in size, being sometimes small and occasion¬ ally so large that the posterior cerebral may be considered as arising from the internal carotid rather than from the basilar. It is fre¬ quently larger on one side than on the other and the vessel may even be doubled. Central branches of the posterior communicating artery immediately enter the base of the cer¬

ebrum by piercing the posterior perforated substance, lateral and posterior to the infun¬ dibulum. These supply the anterior onethird of the posterior limb of the internal capsule, the medial thalamus, and the tissue adjacent to the third ventricle.

ANTERIOR CHOROIDAL ARTERY

The anterior choroidal artery arises from the posterior aspect of the internal carotid artery, near the origin of the posterior com¬ municating artery. It is a relatively slender vessel that passes backward along the course of the optic tract and around the cerebral peduncles as far as the lateral geniculate body of the thalamus. It then courses be¬ neath the uncinate gyrus, enters the choroid fissure to achieve the inferior horn of the lat-

ARTERIES OF THE HEAD AND NECK

693

Anterior communicating a. Anterior cerebral a. Internal carotid a. (cerebral portion)

Middle cerebral a. Internal carotid a. (cavernous portion) Posterior communicating a

Posterior cerebral a

Pontine branches

Internal carotid a. (Petrous portion)

Superior cerebellar a.

Basilar artery Labyrinthine artery

Anterior inferior cerebellar a.

Vertebral artery

Anterior spinal a.

Fig. 8-32.

Diagram of the principal vessels that contribute to and branch from the arterial circulation at the base of

the brain.

eral ventricle, and ramifies in the choroid plexus. Along its course, branches are sup¬ plied to the optic tract, the cerebral pedun¬ cles, the lateral geniculate body, the optic radiation, the tail of the caudate nucleus, the posterior limb of the internal capsule, the globus pallidus, the hippocampus and fibria, and the choroid plexus.

ARTERIAL CIRCLE (OF WILLIS)

Because the mode of distribution of the vessels of the brain has an important bearing on a considerable number of the central nervous system lesions, it is important to consider a little more in detail the manner in which the vessels are distributed. All the arterial blood to the brain is de¬ rived from the internal carotid and vertebral arteries, which at the base of the brain form

a remarkable anastomosis known as the ar¬ terial circle of Willis (Figs. 8-28; 8-32). It is formed anteriorly by the anterior cerebral arteries, branches of the internal carotid that are interconnected by the anterior commu¬ nicating artery, and posteriorly by the two posterior cerebral arteries, which are branches of the basilar artery and are con¬ nected on either side with the internal ca¬ rotid artery by the posterior communicating artery (Figs. 8-36; 8-37). The arterial circle underlies the hypothalamus, and the struc¬ tures it encircles include the lamina terminalis, the optic chiasma, the infundibulum, the tuber cinereum, the mammillary bodies, and the posterior perforated substance. The three trunks that supply the cerebral hemi¬ sphere on each side all stem from the arterial circle. From its anterior part issue the two anterior cerebral arteries, from its anterolat-

694

1H-

AR ERIE S

eral parts stem the middle cerebral arteries, and from its posterior part arise posterior cerebral arteries. Each of these principal ar¬ teries contributes vessels that form a contin¬ uous complex network of capillaries, which is of different density in various parts of the central nervous system in relation to the varying requirements of the different re¬ gions. Thus, in comparison to white matter, the gray matter of the brain has a much higher oxygen consumption and, as ex¬ pected, has a much denser capillary bed. The cortical branches of the cerebral ar¬ teries that supply the surface of the brain anastomose quite freely, but significantly large arterial anastomoses of central branches are rare. There is no unequivocal evidence for the existence of arteriovenous anastomoses either in the pia or deep within the brain substance. True end arteries are arteries that have no connections with neighboring vessels. These are quite rare, but perhaps the best example is the central artery of the retina, which, when occluded, results in central retinal degeneration and a permanent loss of sight. Deeply coursing central vessels in the brain only anastomose with surrounding vessels at five capillary levels. Because of the high vulnerability of brain tissue to a lack of oxygen, a sudden occlusion of a main arterial trunk will result in an ischemic region consistent with the zone supplied by the occluded vessel. The inefficiency of the capillary anastomoses among centrally coursing arteries in the brain and their lack of practical benefit make them functional end arteries. Subclavian Artery

The subclavian artery supplies major ves¬ sels and branches to the brain, neck, anterior thoracic wall, and shoulder. The main trunk continues through the axilla as the axillary artery and achieves the arm, where it is called the brachial artery. The subclavian artery arises differently on the two sides. On the right side it stems from the brachioce¬ phalic trunk, deep to the right sternoclavicu¬ lar articulation (Figs. 8-20; 8-24; 8-33; 8-34). On the left side it arises from the arch of the aorta. The first part of the two vessels differs in length, course, direction, and relation¬ ships to neighboring structures. To facilitate their description, each subclavian artery is divided into three parts. The first portion ex¬

tends from the origin of the vessel to the medial border of the scalenus anterior mus¬ cle; the second portion lies deep to this mus¬ cle; and the third portion extends from the lateral margin of the muscle to the outer bor¬ der of the first rib where it becomes the axil¬ lary artery. The first portion of each vessel requires separate description; the second and third parts of the two subclavian ar¬ teries are practically the same. variations. The subclavian arteries vary in their origin, their course, and the height to which they rise in the neck. The right subclavian artery may arise from the brachiocephalic trunk, in some instances above and in others below the sternoclavicular joint. The artery may arise as a separate trunk from the arch of the aorta, and may be either the first, second, third, or even the last branch derived from the arch. Gener¬ ally, however, it is the first or last. When it is the first branch, the right subclavian occupies the ordinary position of the brachiocephalic trunk. When it is the second or third branch, the artery achieves its usual position by passing behind the right common ca¬ rotid artery. When the right subclavian arises as the last branch, it stems from the left extremity of the arch and passes obliquely toward the right side, usu¬ ally dorsal to the trachea, esophagus, and right com¬ mon carotid (sometimes between the esophagus and trachea) to the upper border of the first rib, from which it follows its usual course. In rare instances, the right subclavian artery arises from the thoracic aorta, as far down as the fourth thoracic vertebra. It may occasionally perforate the scalenus anterior, and more rarely, it passes anterior to that muscle. Sometimes the subclavian vein passes with the ar¬ tery behind the scalenus anterior. The artery may ascend as high as 4 cm above the clavicle, or may only ascend to the upper border of that bone; usu¬ ally the right subclavian ascends higher than'the left. The left subclavian artery is occasionally joined at its origin with the left common carotid. It is more deeply placed than the right subclavian in the first part of its course and usually does not reach quite as high a level in the neck.

FIRST PART OF THE RIGHT SUBCLAVIAN ARTERY

The first part of the right subclavian artery arises from the brachiocephalic trunk, deep to the cranial part of the right sternoclavicu¬ lar articulation, and passes upward and lat¬ erally to the medial margin of the scalenus anterior (Figs. 8-20; 8-24). It arches a little above the clavicle, but the height to which it rises varies in different individuals.

ARTERIES OF THE HEAD AND NECK

relations. The first part of the right subclavian artery is covered anteriorly by the skin, superficial fascia, platysma, deep fascia, the clavicular origin of the sternocleidomastoid, as well as the sternohyoid, the sternothyroid, and another layer of the deep fas¬ cia. It is crossed by the internal jugular and vertebral veins, by the right vagus nerve and the sympathetic and vagal cardiac branches, and by the subclavian loop of the sympathetic trunk, called the ansa subclavia, which forms a ring around the vessel. The anterior jugular vein is directed laterally, anterior to the artery, but is separated from it by the sternohy¬ oid and sternothyroid muscles. Posteriorly and inferiorly, the artery is in contact with the pleura, which separates it from the apex of the lung. Posteriorly is found the sympathetic trunk, the longus colli mus¬ cle, and the first thoracic vertebra. The right recur¬ rent laryngeal nerve winds around the proximal part of the vessel.

FIRST PART OF THE LEFT SUBCLAVIAN ARTERY

The first part of the left subclavian artery arises from the arch of the aorta behind the left common carotid artery at the level of the

695

fourth thoracic vertebra (Figs. 8-33; 8-34). It ascends in the superior mediastinum to the root of the neck and then arches laterally to the medial border of the scalenus anterior muscle. relations. The first part of the left subclavian artery is related anteriorly to the vagus, cardiac, and phrenic nerves which course parallel to it in the tho¬ rax. In addition, the left common carotid artery, left internal jugular and vertebral veins, and the com¬ mencement of the left brachiocephalic vein lie in front of the thoracic part of the subclavian artery; all these are covered by the sternothyroid, sternohyoid, and sternocleidomastoid muscles. Posteriorly, it is related to the esophagus, thoracic duct, left recur¬ rent laryngeal nerve, inferior cervical ganglion of the sympathetic trunk, and longus colli muscle. More superiorly, however, the esophagus and thoracic duct lie to its right side, the latter ultimately arching over the vessel to join the angle of union between the subclavian and internal jugular veins. Medial to the left subclavian artery are the trachea, esopha¬ gus, thoracic duct, and left recurrent laryngeal nerve, while lateral to it are found the left mediasti¬ nal pleura and lung.

Inferior thyroid / .Ascending cervical

scapular I thoracic si branch

Deltoid Thyro¬ cervical trunk

Pectoralis minor

Thoraco¬ acromial

Musculocutaneous n. O

—>

< Pectoral branches

2 _t

< or O

IO

ui

Ulnar nerve Med. ant. cut. nerve Circumflex scapular Subscapular Thoraco¬ dorsal

O-

Fig. 8-33.

The subclavian and axillary arteries with their branches. (Redrawn after Rauber-Kopsch.)

696

the arteries

SECOND PART OF THE SUBCLAVIAN ARTERY

The second part of the subclavian artery lies behind the scalenus anterior muscle (Figs. 8-20; 8-33). It is very short, measuring only about 2 cm in length, and forms the highest part of the arch achieved by the ves¬ sel in the root of the neck. relations. The second part of the subclavian artery is covered anteriorly by the skin, superficial fascia, platysma, deep cervical fascia, sternocleido¬ mastoid, and scalenus anterior. On the right side of the neck the phrenic nerve is separated from the second part of the artery by the scalenus anterior, while on the left side the nerve crosses the first part of the artery close to the medial edge of the muscle. Posterior to the vessel are the suprapleural mem¬ brane, the pleura, and the scalenus medius muscle; superiorly, are found the upper two trunks of the brachial plexus; and inferiorly, the pleura and lung. The subclavian vein lies anterior and inferior to the artery, separated from it by the scalenus anterior muscle.

THIRD PART OF THE SUBCLAVIAN ARTERY

The third part of the subclavian artery continues its course inferolaterally from the lateral margin of the scalenus anterior to the outer border of the first rib, where it be¬ comes the axillary artery (Figs. 8-20; 8-33). This, the most superficial portion of the ves¬ sel, crosses the supraclavicular or subcla¬ vian triangle (Fig. 8-19). The posterior border of the sternocleidomastoid muscle corre¬ sponds closely to the lateral border of the scalenus anterior. Thus, the third part of the subclavian artery is the most accessible for surgical procedures, since it can be achieved immediately lateral to the lower part of the posterior border of the sternocleidomastoid muscle. relations. The third part of the subclavian ar¬ tery is covered anteriorly by the skin, the superficial fascia, the platysma, the supraclavicular nerves, and the deep cervical fascia. The external jugular vein crosses its medial part and receives the suprascapu¬ lar, transverse cervical, and anterior jugular veins, which frequently form a plexus in front of the artery. The nerve to the subclavius muscle descends be¬ tween the artery and veins. The terminal part of the artery lies behind the clavicle and subclavius muscle and is crossed by the suprascapular vessels. The

subclavian vein is anterior and slightly inferior to the artery. Posteriorly, the third part of the subclavian artery lies on the inferior trunk of the brachial plexus, which intervenes between the vessel and the scalenus medius muscle. The upper two trunks of the brachial plexus and the inferior belly of the omohyoid muscle are superior and lateral to the ar¬ tery. Inferiorly, it rests on the upper surface of the first rib. collateral circulation. After ligature of the third part of the subclavian artery, collateral circula¬ tion is established mainly by anastomoses between the suprascapular, the descending ramus of the transverse cervical artery, and the subscapular ar¬ tery. An anastomosis also exists between branches of the internal thoracic, lateral thoracic, and sub¬ scapular arteries.

Branches of the Subclavian Artery

The branches of the subclavian artery and the vessels derived from these branches help to supply the brain, the neck, the thoracic wall, and the shoulder region. They include: Vertebral Basilar Thyrocervical trunk Internal thoracic Costocervical trunk Descending scapular On the left side, all the branches except the descending scapular artery arise from the first part of the subclavian artery. On the right side, the costocervical trunk more fre¬ quently stems from the second part of the subclavian artery. On both sides, the verte¬ bral artery, thyrocervical trunk, and internal thoracic artery arise close together at the medial border of the scalenus anterior. In most instances, there is a free interval of 1.25 to 2.5 cm between the commencement of the artery and the origin of the nearest branch. There is quite a variation in the origin of the vessels, which course laterally at the base of the posterior triangle of the neck, but usually one branch stems directly from the third part of the subclavian artery, which passes laterally behind the brachial plexus. VERTEBRAL ARTERY

The vertebral artery is the first and usually the largest branch of the subclavian, arising quite deep in the neck from the upper and posterior surface of the vessel (Figs. 8-20;

ARTERIES OF THE HEAD AND NECK

8-28; 8-32 to 8-36). It angles backward to the transverse process of the sixth cervical ver¬ tebra and runs superiorly through its fora¬ men and the foramina in the transverse processes of the other upper five cervical vertebrae to the inferior surface of the skull. After penetrating the foramen in the atlas it

697

bends abruptly medialward around the lat¬ eral surface of the superior articular process to lie in a groove on the cranial surface of the posterior arch of the atlas. It passes under an arch in the posterior atlanto-occipital mem¬ brane (Figs. 5-11; 5-14), makes an abrupt bend to enter the cranial cavity through the

Splenium of corpus callosum Right posterior cerebral artery

Massa intermedia of thalamus Cerebral peduncle Post. communicating artery

— Superior cerebellar artery

Basilar artery Ant. inf. cerebellar artery Left vertebral artery

Posterior inferior cerebellar artery

Occipital artery

External carotid artery

- ■*

Internal carotid artery-

Common carotid artery

Thyrocervical trunk Costocervical trunk Subclavian artery

Transverse cervical artery

Suprascapular artery

Internal thoracic artery

Cervical and intracranial course of the left vertebral artery and its branches. (From Krayenbiihl and Yasargil, Cerebral Angiography, 1968.)

Fig. 8-34.

698

ARTERIES

foramen magnum, and, after a short course, joins the other vertebral to form the basilar artery. relations. The vertebral artery may be divided into four parts. The first part courses upward and posteriorly in the neck between the longus colli and the scalenus anterior muscles. Anteriorly it is related to the internal jugular and vertebral veins, and it is crossed by the inferior thyroid artery. The left verte¬ bral artery is crossed also by the thoracic duct. Pos¬ terior to the first part of the vertebral artery are the transverse process of the seventh cervical vertebra, the sympathetic trunk, and the cervicothoracic (stel¬ late) ganglion. The second part of the vertebral ar¬ tery ascends in the neck through the foramina in the transverse processes of the first six cervical verte¬ brae; it is surrounded by branches from the cervico¬ thoracic sympathetic ganglion and by a plexus of veins that unite to form the vertebral vein at the cau¬ dal part of the neck. It is situated anterior to the ventral rami of the upper cervical nerves and pur¬ sues an almost vertical course as far as the foramen in the transverse process of the axis. After coursing through this foramen, it runs lateralward to the fora¬ men in the transverse process of the atlas. The third part of the vertebral artery issues from the latter foramen on the medial aspect of the rectus capitis lateralis muscle and curves behind the lateral mass of the atlas, the anterior ramus of the first cervical nerve being on its medial side. It then lies in the groove on the superior surface of the posterior arch of the atlas and enters the vertebral canal by passing under the arched margin of the posterior atlantooccipital membrane. This part of the artery is cov¬ ered by the semispinalis capitis muscle and is con¬ tained in the suboccipital triangle, a region bounded by the rectus capitis posterior major, the obliquus superior, and the obliquus inferior (Fig. 6-22). The first cervical or suboccipital nerve lies between the artery and the posterior arch of the atlas. The fourth part of the vertebral artery pierces the dura mater and inclines medially to the anterior aspect of the medulla oblongata. It is placed be¬ tween the hypoglossal nerve and the anterior root of the first cervical nerve and beneath the first digitation of the ligamentum denticulatum. At the inferior bor¬ der of the pons, it unites with the vessel of the oppo¬ site side to form the basilar artery.

Branches of the Vertebral Artery

The branches of the vertebral artery may be divided into two sets: those given off in the neck and those within the cranium. Cervical Branches Spinal Muscular

Cranial Branches Meningeal Posterior spinal Anterior spinal Posterior inferior cerebellar Medullary spinal branches. Spinal branches of the vertebral artery enter the vertebral canal through the intervertebral foramina, and each divides into two branches. Of these, one passes along the roots of the nerves to supply the spinal cord and its membranes, anastomosing with the other arteries of the spinal cord. The other divides into an as¬ cending and a descending branch, which unite with similar branches from arteries of adjacent segments above and below, so that two lateral anastomotic chains are formed on the dorsal surfaces of the bodies of the vertebrae, near the attachment of the pedi¬ cles. From these anastomotic chains some branches are supplied to the periosteum and the bodies of the vertebrae, while others form communications with similar branches from the opposite side. Arising from these communications are small twigs that join similar branches, both above and below, to form a central anastomotic chain on the dor¬ sal surface of the bodies of the vertebrae. muscular branches. Muscular branches are given off the vertebral artery to the deep muscles of the neck as that vessel curves around the lateral mass of the atlas (Fig. 835). They anastomose with the occipital ar¬ tery and with the ascending and deep cervi¬ cal arteries. meningeal branch. One or two small meningeal branches arise from the vertebral artery at the level of the foramen magnum. They ramify between the bone and dura mater in the cerebellar fossa, and they sup¬ ply the falx cerebelli. posterior spinal artery. The posterior spinal artery may originate from the intra¬ cranial portion of the vertebral artery at the side of the medulla oblongata, or from the posterior inferior cerebellar artery. Passing dorsally, it descends on the medulla beyond the spinomedullary junction, lying ventral to the dorsal roots of the spinal nerves. As the vessel descends on the posterolateral aspect of the spinal cord, it becomes reinforced by a succession of spinal branches and is thereby continued to the end of the spinal

ARTERIES OF THE HEAD AND NECK

cord and the cauda equina. Branches from the posterior spinal arteries form a free anas¬ tomosis around the dorsal roots of the spinal nerves, communicating by means of tortu¬ ous transverse branches with vessels of the opposite side. Close to its origin each poste¬ rior spinal artery gives off an ascending branch that ramifies in the lateral wall of the fourth ventricle. anterior spinal artery. The anterior spi¬ nal artery is a vessel formed by the junction of two branches, one from each vertebral artery (Figs. 8-28; 8-32; 8-35; 8-36). The branches arise near the point at which the two vertebral arteries join to form the basi-

lar artery. Each branch descends ventral to the medulla and generally unites within about 2 cm from its origin at about the level of the foramen magnum. The single trunk thus formed descends in the anterior median fissure of the spinal cord, and it is reinforced by a succession of small branches that enter the vertebral canal through the interverte¬ bral foramina. These branches are derived from the vertebral and the ascending cervi¬ cal branch of the inferior thyroid artery in the neck, the intercostal arteries in the tho¬ rax, and the lumbar, iliolumbar, and lateral sacral arteries of the posterior abdominal and pelvic wall. These vessels anastomose by means of ascending and descending branches to form a single anterior median artery, which extends as far as the lower part of the spinal cord and is continued as a slender twig on the filum terminate. Cours¬ ing within the pia mater, the anterior spinal artery helps to supply that membrane and the substance of the spinal cord, and it also sends off branches at its caudal part to be distributed to the cauda equina. POSTERIOR

Fig. 8-35. Angiogram of the vertebral artery showing the anterior spinal artery descending in the spinal cord (open arrows) and anastomotic radicular branches (solid arrows) which enter the cord with the cervical roots of the spinal nerves. (From Newton and Mani, Radiology of the Skull and Brain, 1974.)

699

INFERIOR

CEREBELLAR

ARTERY.

The posterior inferior cerebellar artery is the largest branch of the vertebral artery (Figs. 8-28; 8-32; 8-33; 8-36). Although this artery varies greatly in its course and distribution, it most often arises from the vertebral ap¬ proximately 1.5 cm before the vertebrals unite to form the basilar, but occasionally it is absent. It courses at first laterally and then posteriorly around the lower end of the olive of the medulla oblongata. Passing between the rootlets of the glossopharyngeal and vagus nerves, over the inferior peduncle to the inferior surface of the cerebellum, the artery divides into two branches. The medial branch is continued posteriorly to the notch between the two hemispheres of the cerebel¬ lum, while the lateral branch supplies the inferior surface of the cerebellum as far as its lateral border. Here it anastomoses with the anterior inferior cerebellar and the supe¬ rior cerebellar branches of the basilar artery. Branches from the posterior inferior cerebel¬ lar artery also supply penetrating branches to the medulla as well as to the choroid plexus of the fourth ventricle. medullary branches. Several small medullary vessels branching from the verte¬ bral artery are distributed to the medulla oblongata.

700

the arteries

BASILAR ARTERY

The basilar artery is formed by the junc¬ tion of the two vertebral arteries (Figs. 8-28; 8-32; 8-34; 8-36). As a single vascular trunk, it courses superiorly in a shallow median groove on the anterior surface of the pons. It extends from the pontomedullary sulcus, which demarcates the rostral medulla and caudal pons, to the level of the emerging oculomotor nerves from the caudal mid¬ brain. The basilar artery is often tortuous and may be slightly curved in its rostral course along the brain stem. Its length varies from 2.5 to 4.0 cm, and after passing between the two oculomotor nerves, the artery termi¬ nates by dividing into the two posterior cere¬ bral arteries.

Branches of the Basilar Artery

In its course the basilar artery gives off the following branches on both sides:

Superior cerebellar Posterior cerebral pontine branches. The pontine branches of the basilar artery consist of a number of small vessels that supply the pons and mid¬ brain (Fig. 8-32). Median vessels arise at right angles from the posterior aspect of the basi¬ lar and enter the pons along its anterior me¬ dian groove. Transverse branches arise from the posterolateral and lateral aspects of the basilar, and in their circumferential course around the brain stem, they send penetrating vessels into the pons. labyrinthine artery. Also known as the internal auditory artery, the labyrinthine artery is a long slender branch that arises near the middle of the basilar artery (Figs. 8-28; 8-32). It accompanies the facial and ves¬ tibulocochlear nerves through the internal acoustic meatus and is distributed to the in¬ ternal ear. It often arises from the anterior inferior cerebellar artery. ANTERIOR

Pontine Labyrinthine Anterior inferior cerebellar

CEREBELLAR

ARTERY.

The anterior inferior cerebellar artery gener¬ ally arises from the lower third of the basilar artery (Figs. 8-28; 8-34; 8-36). Its course is Mammillary body

Posterior communicating artery

INFERIOR

Cerebral peduncle Oculomotor nerve

Posterior cerebral artery

Superior cerebellar artery

Basilar artery Pons VI nerve Anterior inferior cerebellar artery

Middle cerebellar peduncle (cut)

IX nerve X nerve XI nerve

Pyramid of medulla

XII nerve

Olive

Posterior inferior cerebellar artery

Anterior spinal artery

Posterior spinal artery

Cl nerve root ft

Vertebral artery

Fig. 8-36. The ventral surface of the medulla and pons showing the vertebral and basilar arteries and their branches. (From Taveras and Wood, Diagnostic Neuroradiology, 1964.)

ARTERIES OF THE HEAD AND NECK

somewhat variable, but initially it usually courses laterally and posteriorly and lies in contact with either the dorsal (33%) or ven¬ tral (67%) aspect of the abducens nerve. Con¬ tinuing its downward course, the vessel fre¬ quently lies ventral to the roots of the facial and vestibulocochlear nerves. Often it forms a loop in relation to these nerves at the level of the internal acoustic meatus. The main trunk of the anterior inferior cerebellar ar¬ tery sends small branches into the lateral aspect of the pons. At the cerebellopontine angle, the artery divides into lateral and me¬ dial branches, which are distributed to the anterolateral and anteromedial parts of the inferior surface of the cerebellum. The ante¬ rior inferior cerebellar artery anastomoses with the posterior inferior cerebellar branch of the vertebral artery. superior cerebellar artery. The supe¬ rior cerebellar artery arises a few millime¬ ters proximal to the termination of the basi¬ lar artery (Figs. 8-28; 8-34; 8-36). It passes lateralward immediately caudal to the ocu¬ lomotor nerve, which separates it from the posterior cerebral artery. It then winds around the cerebral peduncle, close to the trochlear nerve. Arriving at the superior sur¬ face of the cerebellum, which it supplies, it divides into branches that ramify in the pia mater and anastomose with those of the infe¬ rior cerebellar arteries. Several branches go to the midbrain, the pineal body, the ante¬ rior medullary velum, and the tela choroidea of the third ventricle. POSTERIOR CEREBRAL ARTERY. Embryologically, the posterior cerebral artery develops as a branch of the internal carotid artery and, in some instances, remains a branch of the internal carotid in the adult. In most in¬ stances, however, the posterior cerebral ar¬ teries are the terminal branches of the basi¬ lar artery, and they maintain their attach¬ ment to the internal carotid on each side by way of the posterior communicating artery, forming the posterior part of the arte¬ rial circle of Willis. The posterior cerebral artery is larger than the superior cerebellar artery, and it is separated from that vessel near its origin by the oculomotor nerve (Figs. 8-28; 8-32; 8-36). Passing laterally, parallel to the superior cerebellar artery and receiving the posterior communicating artery from the internal carotid, it winds around the cere¬ bral peduncle and reaches the tentorial sur¬ face of the occipital lobe of the cerebrum,

701

where it breaks up into branches for the sup¬ ply of the temporal and occipital lobes. The posterior cerebral artery gives off central, posterior choroidal, and cortical branches. central branches. The central branches of the posterior cerebral artery can be di¬ vided into mesencephalic and thalamic branches. The mesencephalic branches arise from the posterior surface of each posterior cerebral artery and enter the posterior perfo¬ rated substance to supply the interpeduncu¬ lar region of the midbrain as well as the cer¬ ebral peduncles themselves. Such important structures as the oculomotor nuclei, mesen¬ cephalic reticular formation, substantia nigra, and the corticospinal paths at the midbrain level are supplied by these vessels. Additionally, circumflex mesencephalic branches pass around the midbrain to sup¬ ply perforating arteries to the peduncles and to the substantia nigra, as well as longer branches to dorsal tegmental structures. Anterior and posterior thalamic branches arise from the posterior cerebral artery to perforate and supply both hypothalamic and thalamic centers (Fig. 8-37). The anterior thalamic branches supply the more caudal parts of the hypothalamus, including the mammillary bodies, as well as the optic tract. Certain of these vessels ascend through the hypothalamus to achieve the thalamus and thereby supply its anterior and ventromedial nuclei. Some posterior thalamic branches ascend through the posterior perforated sub¬ stance to supply the more posterior thalamic nuclei, while posterior thalamogeniculate vessels course more superiorly to supply the geniculate bodies (Newton and Potts, 1974). POSTERIOR CHOROIDAL BRANCHES. Two Or more posterior choroidal branches arise from the posterior cerebral artery. The (pos¬ terior) medial choroidal artery branches near the origin of the posterior cerebral and courses dorsally and medially around the midbrain, supplying the corpora quadrigemina and the pineal gland (Figs. 8-37; 8-38). It then courses forward to supply the roof of the third ventricle, ramifies within the choroid plexus of that ventricle, and sends penetrating branches to the dorsal medial nucleus of the thalamus and fre¬ quently to the pulvinar. The (posterior) lat¬ eral choroidal artery may arise singly or as multiple vessels from the posterior cerebral, but it may also arise from the parieto-occipital branch of the posterior cerebral artery

702

TH

ARTERIES

Fig. 8-37 The branches of the posterior cerebral artery as viewed on the medial aspect of the right cerebral hemi¬ sphere. (From Krayenbiihl and Yasargil, Cerebral Angiography, 1968.)

(Figs. 8-37; 8-38). One branch of the lateral choroidal artery courses laterally and enters the choroid fissure to supply the choroid plexus of the temporal horn. Another branch courses back behind the pulvinar to supply the choroid plexus of the lateral ventricle. Branches perforate into the thalamus to sup¬ ply the dorsomedial nucleus, the pulvinar, and the lateral geniculate bodies. Branches of the posterior medial and lateral choroidal arteries anastomose with each other (New¬ ton and Potts, 1974). cortical branches. Generally there are

Medial branch, sup. cerebellar artery

Lateral branch, sup. cerebellar artery

four cortical branches of the posterior cere¬ bral artery that supply the medial surface of the temporal and occipital lobes. They are the anterior temporal, posterior temporal, parieto-occipital, and occipital (calcarine) branches (Figs. 8-30; 8-31; 8-37). The anterior temporal branch extends laterally and ante¬ riorly beneath the temporal lobe to supply the uncus and parahippocampal gyrus, where it anastomoses with the anterior tem¬ poral branch of the middle cerebral artery. The posterior temporal branch courses back along the parahippocampal gyrus to supply

Posterior cerebral artery (branches to cortex) Lateral posterior choroidal branch

Medial posterior choridal branch

Superior cerebellar artery

Ant. inferior cerebellar artery

Vertebral artery

Middle temporal branch (divides into ant and post, temporal branches)

Fig 8 38 The course and branches of the posterior cerebral artery after it arises from the basilar artery. (From Wilson, The Anatomic Foundation of Neuroradiology of the Brain, 1972.)

ARTERIES OF THE HEAD AND NECK

the medial and lateral occipitotemporal gyri. The parieto-occipital branch usually di¬ vides into a number of smaller vessels that course superiorly and posteriorly on the medial surface of the cerebral hemi¬ sphere to supply the precuneate and cuneate gyri. The occipital (calcarine) branch sup¬ plies the primary visual cortex by following the calcarine sulcus as far as the occipital pole. It supplies the lingual and cuneate gyri and frequently the occipital and parieto¬ occipital branches overlap somewhat in their distribution to the visual cortical re¬ ceiving area.

THYROCERVICAL TRUNK

The thyrocervical trunk is a short thick vessel that arises from the first portion of the subclavian artery, close to the medial border of the scalenus anterior muscle (Figs. 8-20; 8-33; 8-34; 8-39; 8-40). Almost immediately it divides into the following three arteries: Inferior thyroid Suprascapular Transverse cervical Inferior Thyroid Artery

The inferior thyroid artery courses cranially anterior to the vertebral artery and longus colli muscle. It then loops medially dorsal to the carotid sheath and its contents, as well as to the sympathetic trunk; the mid¬ dle cervical ganglion often rests on the ves¬ sel (Figs. 8-20; 8-33; 8-39; 8-40). Reaching the lower border of the thyroid gland, the inferior thyroid artery divides into two branches, which supply the inferior parts of the gland and anastomose with the superior thyroid artery and with the inferior thyroid artery of the opposite side. The recurrent laryngeal nerve courses superiorly in the neck, generally dorsal but occasionally ven¬ tral to the artery. Branches of the Inferior Thyroid Artery

In addition to the terminal branches that supply the thyroid gland, the inferior thy¬ roid artery gives off the following branches: Inferior laryngeal Tracheal Esophageal Ascending cervical Muscular

703

inferior laryngeal artery. The inferior laryngeal artery ascends upon the trachea to the dorsal part of the larynx under cover of the inferior pharyngeal constrictor muscle and in company with the recurrent laryngeal nerve. It supplies the muscles and mucous membrane of this region of the larynx, anas¬ tomosing with the branch from the opposite side and with the superior laryngeal branch of the superior thyroid artery. tracheal branches. Tracheal branches of the inferior thyroid artery are distributed to the trachea and anastomose inferiorly with the bronchial arteries and superiorly with tracheal branches from the superior thyroid artery. esophageal branches. The esophageal branches of the inferior thyroid artery sup¬ ply the esophagus and anastomose with esophageal branches that arise directly from the aorta. ascending cervical artery. The ascend¬ ing cervical artery arises from the inferior thyroid as that vessel passes dorsal to the carotid sheath (Figs. 8-20; 8-33; 8-39; 8-40). It may arise directly from the thyrocervical trunk. It ascends in the neck on the anterior tubercles of the transverse processes of the cervical vertebrae in the interval between the scalenus anterior and longus capitis muscles. Lying parallel and medial to the phrenic nerve, the ascending cervical artery supplies some deep muscles of the neck with twigs that anastomose with branches of the vertebral artery. In addition, it sends one or two spinal branches into the vertebral canal through the intervertebral foramina to be distributed to the spinal cord and its mem¬ branes, and to the bodies of the vertebrae in the same way as spinal branches are distrib¬ uted from the vertebral artery. It anastomo¬ ses with the ascending pharyngeal and oc¬ cipital arteries, with branches of the external carotid artery, and with the verte¬ bral artery. muscular branches. Muscular branches of the inferior thyroid artery supply the infrahyoid, the longus colli, the scalenus an¬ terior, and the inferior pharyngeal constric¬ tor muscles.

Suprascapular Artery

The suprascapular artery passes initially downward and laterally across the scalenus anterior and the phrenic nerve, being cov-

704

THE ARTERIES

Deep cervical Transverse cervical Superficial branch of transverse cervical

Vertebral Ascending cervical

Deep branch of transverse cervical Inferior thyroid Thyrocervical trunk Suprascapular Internal thoracic Supreme intercostal Pericardiacophrenic

The subclavian artery and its branches showing the so-called Type I pattern in which the transverse cervical artery branches from the thyrocervical trunk, crosses the lower neck, and divides into a superficial branch. which ascends in the neck, and a deep branch, which descends to the medial scapular region.

Fig. 8-39.

ered by the sternocleidomastoid muscle (Figs. 8-20; 8-33; 8-34; 8-39; 8-40). It then crosses in front of the subclavian artery and the brachial plexus, and running deep to and parallel with the clavicle and subclavius muscle and deep to the inferior belly of the omohyoid muscle, it reaches the superior border of the scapula. It passes over the su¬ perior transverse scapular ligament by which it is separated from the suprascapular nerve to enter the supraspinous fossa. Within the fossa it lies directly on the bone and sends branches to the overlying supraspinatus muscle, which it supplies. It then winds laterally around the neck of the scap¬ ula, descending through the great scapular notch under cover of the inferior transverse scapular ligament to reach the infraspinous fossa. Here it supplies the infraspinatus mus¬ cle and anastomoses with the scapular cir¬ cumflex branch of the subscapular artery and the deep branch of the transverse cervi¬

cal (descending scapular) artery. Besides distributing branches to the sternocleido¬ mastoid. subclavius, and neighboring mus¬ cles, the suprascapular artery gives off a su¬ prasternal branch, which crosses over the sternal end of the clavicle to the skin of the chest, and an acromial branch, which pierces the trapezius to supply the skin over the acromion, anastomosing with the acro¬ mial branch of the thoracoacromial artery. As the artery passes over the superior trans¬ verse scapular ligament, it sends a branch into the subscapular fossa, where it ramifies beneath the subscapularis muscle and anas¬ tomoses with the subscapular artery and deep branch of the transverse cervical (de¬ scending scapular) artery. It also sends artic¬ ular branches to the acromioclavicular and shoulder joint and nutrient branches to the clavicle and scapula. In about 25% of cadav¬ ers studied, the suprascapular artery arises from the third part of the subclavian artery.

ARTERIES OF THE HEAD AND NECK

705

Descending scapular Ascending branch of descending scapular Descending branch of descending scapular

Vertebral Ascending cervical Inferior thyroid Superficial cervical Suprascapular Thyrocervical trunk Internal thoracic Supreme intercostal Pericardiacophenic

Fig. 8-40. The subclavian artery and its branches showing the so-called Type II pattern in which the superficial cervical artery is derived from the thyrocervical trunk and the descending scapular artery arises from the third part of the subclavian. These vessels are distributed to the same regions as the superficial and deep branches of the transverse cervical artery of the Type I pattern.

Transverse Cervical Artery

The transverse cervical artery, in more than half the specimens studied, arises as a single vessel and eventually divides into two main branches, a superficial and a deep branch (Fig. 8-39). In these instances, the transverse cervical artery stems from the thyrocervical trunk, but it may occasionally arise as a single vessel directly from the third part of the subclavian artery rather than from the thyrocervical trunk. When the transverse cervical artery does arise from the thyrocervical trunk, it passes laterally across the posterior cervical triangle in a position somewhat above and behind the suprascapular artery. Medially, it crosses superficial to the scalenus anterior and phrenic nerve and lies deep to the sterno¬ cleidomastoid muscle. Laterally, it crosses the trunks of the brachial plexus and is cov¬

ered only by the platysma, the investing layer of deep fascia, and the inferior belly of the omohyoid. As the artery approaches the anterior margin of the trapezius, it divides into a superficial branch and a deep branch. In another large percentage of cadavers studied, there is no transverse cervical ar¬ tery as such, branching either from the thyrocervical trunk or from the third part of the subclavian artery (Fig. 8-40). In these in¬ stances, the regions supplied by the superfi¬ cial and deep branches of the transverse cer¬ vical artery become supplied by other arteries. Thus, the superficial branch of the transverse cervical artery becomes replaced by the superficial cervical artery, and the deep branch of the transverse cervical ar¬ tery becomes replaced by the descending scapular artery (also known as the dorsal scapular artery, a term no longer found in the Nomina Anatomica).

706

ARTf

Mi

s

Because these two different vascular pat¬ terns are about equally represented in the specimens studied, the descriptions of the superficial and deep branches of the trans¬ verse cervical artery will be followed by descriptions of the superficial cervical artery and the descending scapular artery. SUPERFICIAL BRANCH OF TRANSVERSE CERVI¬ CAL artery. The superficial branch of the transverse cervical artery is the principal blood supply to the trapezius muscle (Fig. 8-39). Lying along the deep surface of this muscle, the artery divides into an ascending and a descending branch. The ascending branch courses superiorly along the anterior border of the trapezius, distributing branches to it and to neighboring muscles and anastomosing with the superficial part of the descending branch of the occipital ar¬ tery. The descending branch accompanies the accessory nerve along the deep surface of the trapezius, supplying the muscle. DEEP BRANCH OF TRANSVERSE CERVICAL AR¬

The deep branch of the transverse cervical artery supplies vessels to the levator scapulae and neighboring deep cervical muscles (Fig. 8-39). Passing deep to the leva¬ tor scapulae muscle, it reaches the superior angle of the scapula and passes down along the vertebral border to the inferior angle, lying deep to the rhomboid muscles and ac¬ companying the dorsal scapular nerve. It supplies muscular branches to the rhom¬ boid, serratus posterior superior, subscapularis, supraspinatus, and infraspinatus mus¬ cles and to other neighboring muscles. These branches anastomose with the suprascapu¬ lar, subscapular, and circumflex scapular arteries. superficial cervical artery. The super¬ ficial cervical artery is seen in cadavers that do not have a transverse cervical artery, and it corresponds to the superficial branch of the transverse cervical (Fig. 8-40). It arises from the thyrocervical trunk, as would the transverse cervical artery, but no vessel comparable to the deep branch of the trans¬ verse cervical artery stems from the superfi¬ cial cervical artery. It passes laterally across the posterior triangle of the neck, deep to the sternocleidomastoid muscle and superficial to the scalenus anterior muscle and phrenic nerve. It then courses cranially across the trunks of the brachial plexus to the anterior border of the trapezius muscle, where its as¬ cending branch supplies the upper part of TERY.

the trapezius and neighboring muscles, anastomosing with the superficial descend¬ ing branch of the occipital artery, and its de¬ scending branch lies against the deep sur¬ face of the trapezius, supplying it with branches and accompanying the accessory nerve. descending scapular artery. The de¬ scending scapular artery (sometimes still carelessly called the dorsal scapular artery) is observed in specimens in which there is no transverse cervical artery. Its distribution corresponds to that of the deep branch of the transverse cervical artery (Fig. 8-40). When present, the descending scapular artery has an independent origin from the third part of the subclavian artery instead of from the thyrocervical trunk. Occasionally it may arise from the second part of the subclavian artery. It passes upward for a short distance, then loops around the brachial plexus, fre¬ quently passing between the anterior and posterior divisions of the upper trunk. The vessel then courses downward toward the scapula and, at the border of the levator scapulae, divides into an ascending and a descending branch. The ascending branch supplies the levator scapulae and neighbor¬ ing deep cervical muscles. The descending branch, usually double, passes deep to the levator scapulae to the superior angle of the scapula, and then descends anterior to the rhomboid muscles along the medial border of the bone as far as its inferior angle. When there are two descending branches, the more medial is accompanied by the dorsal scapu¬ lar nerve, while the larger, more lateral ves¬ sel lies on the costal surface of the serratus anterior muscle. The descending branch(es) supplies the rhomboid, latissimus dorsi, and trapezius muscles and anastomoses with the suprascapular and subscapular arteries, and with the posterior branches of some of the intercostal arteries.

INTERNAL THORACIC ARTERY

The internal thoracic artery arises from the first portion of the subclavian artery about 2 cm above the clavicle, opposite the thyrocervical trunk and close to the medial border of the scalenus anterior muscle (Fig. 8-41). It descends behind the cartilages of the upper six ribs at a distance of about 1.25 cm from the margin of the sternum. At the level

ARTERIES OF THE HEAD AND NECK

of the sixth intercostal space, the internal thoracic artery terminates by dividing into the musculophrenic and superior epigastric arteries. relations. As it descends toward the sternum, the internal thoracic artery lies deep to the sternal end of the clavicle, the subclavian and internal jugu¬ lar veins, and the first costal cartilage. As it enters the thorax, it passes close to the lateral aspect of the brachiocephalic vein, and the phrenic nerve crosses it obliquely from its lateral to its medial aspect. Below the first costal cartilage, it descends almost vertically to its point of bifurcation. It is covered an¬ teriorly by the cartilages of the first six ribs, by the intervening internal intercostal muscles, and by ex¬ ternal intercostal membranes. The vessel is crossed by the terminal portions of the first six intercostal nerves. Between the artery and the pleura is a deep fascial plane as far as the third costal cartilage, and below this level the transversus thoracis muscle sep¬ arates the vessel from the pleura. It is accompanied by a chain of lymph nodes and by a pair of veins that unite to form a single vessel, which ascends medial to the artery and ends in the corresponding brachio¬ cephalic vein.

Branches of the Internal Thoracic Artery

Among other structures, the branches of the internal thoracic artery help to supply the pericardium, pleura, thymus, and bron¬ chi, as well as the transverse thoracis, inter¬ costal, and pectoralis major muscles, the rec¬ tus abdominis and other anterior abdominal muscles, the diaphragm, and even the mam¬ mary gland in the female. Its branches are: Pericardiacophrenic Mediastinal Thymic Bronchial Sternal Anterior intercostal Perforating Lateral costal branch Musculophrenic Superior epigastric pericardiacophrenic artery. The peri¬ cardiacophrenic artery is a long, slender, and somewhat tortuous vessel that arises from the internal thoracic artery just after the latter vessel has entered the thorax (Figs. 7-24; 8-39; 8-40). Accompanying the phrenic nerve to the diaphragm, which it helps to supply, the pericardiacophrenic artery courses between the pleura and pericar¬

707

dium, and it sends branches to both these structures. It anastomoses with the musculo¬ phrenic and the superior and inferior phrenic arteries (Fig. 7-24). mediastinal branches. The mediastinal branches of the internal thoracic artery are small vessels, distributed to the areolar tis¬ sue and lymph nodes in the anterior medias¬ tinum, and they also supply the upper part of the sternocostal surface of the pericar¬ dium. thymic branches. In the adult, the thy¬ mic branches are small and supply the re¬ mains of the thymus. In the infant and child, however, they are more significant vessels. bronchial branches. The bronchial branches from the internal thoracic artery, when present, are distributed to the bronchi and lower part of the trachea. sternal branches. Sternal branches of the internal thoracic artery are distributed to the transversus thoracis muscle and to the posterior surface of the sternum. The mediastinal, pericardial, bronchial, and sternal branches, together with some twigs from the pericardiacophrenic, anasto¬ mose with branches from the posterior, in¬ tercostal, and bronchial arteries from the thoracic aorta to form a subpleural mediasti¬ nal plexus. anterior intercostal arteries. The an¬ terior intercostal branches of the internal thoracic artery supply the first five or six in¬ tercostal spaces, the remaining more caudal spaces being supplied by the musculo¬ phrenic branch. In each space, two small ar¬ teries pass laterally from the internal tho¬ racic, one each at the upper and lower margins of the intercostal space (Fig. 8-41). They supply the intercostal muscles and fi¬ nally anastomose with the external intercos¬ tal arteries from the aorta. At first the ante¬ rior intercostal arteries lie between the pleura and the internal intercostal muscles, and then more laterally between the inner¬ most and internal intercostal muscles. Some branches perforate through the external in¬ tercostal muscles to supply the pectoral muscles and the mammary gland. perforating branches. The perforating branches from the internal thoracic artery pierce the anterior thoracic wall in the first five or six intercostal spaces close to the ster¬ num (Fig. 8-41). These vessels course with the anterior cutaneous branches of the inter¬ costal nerves and penetrate the intercostal

708

the arteries

Scalenus anterior muscle Thyrocervical trunk Common carotid artery Subclavian artery Brachiocephalic trunk Internal thoracic artery Anterior intercostal arteries

Perforating branches

Superior epigastric artery

Musculophrenic artery

Sheath of rectus abdominis muscle (post layer)

Transversus abdominis muscle

Inferior epigastric artery

External iliac artery

Fig. 8-41. The left internal thoracic artery and its branches. Observe the anastomosis between the superior and inferior epigastric arteries.

muscles and pectoral fascia to achieve the deep surface of the pectoralis major muscle. They curve laterally as they become more superficial and supply the pectoralis major muscle and the skin. The arteries of the sec¬ ond, third, and fourth spaces give mammary branches to the breast in the female and be¬ come greatly enlarged during lactation. lateral costal branch. Although fre¬ quently absent or very small, the lateral cos¬ tal branch arises at times from the internal thoracic artery near the first rib. When pres¬ ent (about 25% of cadavers), it descends lat¬ eral to the costal cartilages and behind the ribs and anastomoses with the upper ante¬ rior intercostal arteries.

MUSCULOPHRENIC ARTERY. The muSCulophrenic artery is one of the two terminal branches of the internal thoracic artery, and it is directed obliquely downward and later¬ ally, behind the cartilages of the eighth, ninth, and tenth ribs (Fig. 8-41). It perforates the diaphragm near the eighth or ninth cos¬ tal cartilage, and ends, considerably reduced in size, opposite the last intercostal space. It gives off two anterior intercostal branches to the seventh, eighth, and ninth intercostal spaces. These diminish in size as the inter¬ costal spaces decrease in length and are dis¬ tributed in a manner precisely similar to the anterior intercostals that branch directly from the internal thoracic. Some other

ARTERIES OF THE UPPER LIMB

branches of the musculophrenic artery course to the lower part of the pericardium, some course dorsally to the diaphragm, and still others course down to the abdominal muscles. superior epigastric artery. The supe¬ rior epigastric artery is a terminal branch of the internal thoracic artery, and it continues in the original direction of the parent vessel (Fig. 8-41). It descends through the interval between the costal and sternal attachments of the diaphragm and enters the sheath of the rectus abdominis muscle. At first the superior epigastric muscle lies behind the rectus muscle, but then perforates and sup¬ plies the muscle and thereby anastomoses with the inferior epigastric artery from the external iliac. Branches eventually perforate the anterior layer of the rectus sheath and supply other anterior abdominal wall mus¬ cles and the overlying skin. A small branch passes in front of the xiphoid process and anastomoses with the artery of the opposite side. The superior epigastric artery also gives some twigs to the diaphragm, while from the artery on the right side, small branches extend into the falciform ligament of the liver and anastomose with the hepatic artery. COSTOCERVICAL TRUNK

On the left side the costocervical trunk arises from the first part of the subclavian artery, medial to the scalenus anterior mus¬ cle. On the right side, however, it arises from the dorsal aspect of the second part of the subclavian artery, deep to the serratus ante¬ rior muscle. It courses upward and then arches backward above the cupula of the cervical pleura (Figs. 8-24; 8-34). Passing downward in front of the neck of the first rib, it divides into the supreme (highest) in¬ tercostal and deep cervical arteries. supreme intercostal artery. The su¬ preme or highest intercostal artery descends under the pleura anterior to the necks of the first and second ribs and anastomoses with the most superior of the intercostal arteries derived from the aorta, the one that courses in the third intercostal space (Figs. 8-24; 8-39, 8-40). As the supreme intercostal artery crosses the neck of the first rib, it lies medial to the ventral ramus of the first thoracic nerve and lateral to the cervicothoracic gan¬ glion of the sympathetic trunk. The first pos¬

709

terior intercostal artery branches from the supreme intercostal artery within the first intercostal space, and its distribution is the same as that of the lower posterior intercos¬ tal arteries that arise from the aorta. The supreme intercostal artery then descends, usually to become the second posterior in¬ tercostal artery, being joined by a branch from the highest of the aortic posterior inter¬ costal arteries (the third). This pattern is more common on the right side, but at times the second posterior intercostal artery is de¬ rived from the aorta. DEEP cervical artery. The deep cervical artery arises in most cases from the costo¬ cervical trunk and is analogous to the dorsal branch of an aortic posterior intercostal ar¬ tery (Figs. 8-24; 8-39; 8-40). Occasionally it springs as a separate branch from the sub¬ clavian artery. Passing dorsally above the eighth cervical nerve and between the trans¬ verse process of the seventh cervical verte¬ bra and the neck of the first rib, it ascends along the dorsum of the neck, between the semispinales capitis and cervicis muscles, as high as the axis. It supplies these and adja¬ cent muscles and anastomoses with the deep division of the descending branch of the oc¬ cipital artery and with branches of the verte¬ bral. It gives off a spinal twig, which enters the vertebral canal through the interverte¬ bral foramen between the seventh cervical and first thoracic vertebrae. DESCENDING SCAPULAR ARTERY

In about half the cadavers studied, a de¬ scending scapular artery branches from the third part of the subclavian artery (Fig. 8-40). When this vessel is found, its distribution is usually similar to that of the deep branch of the transverse cervical artery. The vascular pattern in this region and the course of the descending scapular artery are described with the transverse cervical artery.

Arteries of the Upper Limb The axis artery, which supplies the upper limb, continues from its origin to the elbow as a single trunk, but different portions of it are named according to the regions through which they pass. The part of the axis artery that extends from its origin to the outer bor-

710

THE ARTERIES

der of the first rib is termed the subclavian artery. Beyond this point and as far as the distal border of the axilla, formed by the lower margin of the teres major, it is named the axillary artery. From the axilla to a point just beyond the elbow joint in the proximal forearm, the vessel is called the brachial artery; the brachial artery ends by dividing into two branches, the radial and ulnar arteries.

THE AXILLA

The axilla is a cone-shaped or pyramidal region located between the upper lateral part of the chest wall and the medial aspect of the arm. Its anatomy has great relevance because through the axilla course the neuro¬ vascular structures that supply the upper extremity and because its anterior surface is relatively unprotected and vulnerable to in¬ jury. Furthermore, the axilla receives many of the lymphatic channels that drain the an¬ terior thoracic wall, making it a region of strategic importance to disease processes that occur in the mammary gland of fe¬ males. BOUNDARIES OF THE AXILLA. The apex of the axilla is directed superiorly toward the root of the neck and corresponds to the in¬ terval between the outer border of the first rib, the superior border of the scapula, and the posterior surface of the clavicle. Through the apex pass the axillary vessels and accompanying nerves, which descend behind the clavicle from the neck. The base of the axilla is directed downward and later¬ ally and is formed by the skin and fascia of the armpit. It is narrow at the arm, but broader at the chest. The thick axillary fas¬ cia, which helps to form the base, extends between the lower border of the pectoralis major muscle anteriorly and the lower bor¬ der of the latissimus dorsi muscle posteri¬ orly. The anterior wall of the axilla is formed by the pectoralis major and minor muscles, the former covering the whole of this wall and the latter only its central part. The space between the upper border of the pectoralis minor and the clavicle is occupied by the clavipectoral fascia. The posterior wall, which extends somewhat more caudally than the anterior wall, is formed by the subscapularis muscle above and the teres major and latissimus dorsi muscles below. The medial wall is formed by the first four

ribs with their corresponding intercostal muscles and part of the serratus anterior. The narrowed lateral wall of the axilla, where the anterior and posterior walls con¬ verge, is bounded by the intertubercular sul¬ cus (bicipital groove) of the humerus, the coracobrachialis, and the biceps brachii. contents of the axilla. Within the axilla are found the axillary vessels, the infraclavicular part of the brachial plexus and its branches, the lateral cutaneous branches of the intercostal nerves, and a large number of lymph nodes, together with a quantity of fat and loose areolar tissue. The axillary artery and vein, with the brachial plexus of nerves, extend obliquely through the axilla from its apex to its base and are placed much nearer the anterior wall than the posterior wall. The axillary vein lies superficial to and on the thoracic aspect of the artery and partially conceals it. In the anterior part of the axilla and in contact with the pectoral muscles are the thoracic branches of the axillary artery. Coursing downward along the lateral aspect of the chest wall, and frequently along the lateral margin of the pectoralis minor artery, extends the lateral thoracic artery. The sub¬ scapular vessels and nerves and the thoraco¬ dorsal nerve course along the posterior wall of the axilla, in contact with the subscapu¬ laris muscle. The scapular circumflex artery, which is a branch of the subscapular artery, winds around the lateral border of the sub¬ scapularis muscle to the dorsal aspect of the shoulder. Near the neck of the humerus, the posterior humeral circumflex vessels and the axillary nerve also curve dorsally to the shoulder. The upper medial aspect of the axilla has no large vessels, but does contain lymphatics and a few small branches from the supreme thoracic artery. There are in this region, however, the important long tho¬ racic nerve, descending on the surface of the serratus anterior to which it is distributed, and the intercostobrachial nerve, which perforates the upper anterior aspect of the medial wall and passes across the axilla to the medial aspect of the arm. The position and arrangement of the lymph nodes are described in the chapter on lymphatics. Axillary Artery The axillary artery is the continuation of the subclavian, and it commences at the outer border of the first rib and ends at the

ARTERIES OF THE UPPER LIMB

distal border of the tendon of the teres major muscle, where it is called the brachial artery (Figs. 8-42; 8-43). Its direction varies with the position of the limb: thus, the vessel is nearly straight when the arm is directed at right angles to the trunk, but concave superiorly when the arm is elevated, and convex supe¬ riorly when the arm lies by the side. At its origin the artery is quite deeply situated, but near its termination becomes superficial, being covered only by the skin and fascia. Because the pectoralis minor crosses the ax¬ illary artery anteriorly, for descriptive pur¬ poses it is convenient to divide the vessel into three portions: the first part lies proxi¬ mal, the second part deep, and the third part distal to the pectoralis minor. Its branches are subject to considerable variation. RELATIONS

OF THE

FIRST

PART OF

THE

AXILLARY

The first part of the axillary artery is cov¬ ered anteriorly by the skin, the superficial fascia, the clavicular portion of the pectoralis major, and the clavipectoral fascia. The artery is crossed by the lat¬ eral pectoral nerve and the thoracoacromial and ce¬ phalic veins. Posterior to the first part of the axillary artery are the first intercostal space, the correspond¬ ing external intercostal muscle, the first and second digitations of the serratus anterior, the long thoracic and medial pectoral nerves, and the medial cord of the brachial plexus. Laterally, the vessel is in relation to the lateral and posterior cords of the brachial plexus, from which it is separated by a little areolar tissue. Medially, the axillary vein closely overlaps the artery. The first part of the axillary artery is enclosed, together with the axillary vein and brachial plexus, in the fibrous axillary sheath, which is continuous above with the prevertebral layer of the deep cervi¬ cal fascia. artery.

71 1

tegument and fascia. Posteriorly are found the sub¬ scapularis muscle and the tendons of the latissimus dorsi and teres major. On its lateral aspect is the coracobrachialis muscle and on its medial or tho¬ racic aspect the axillary vein. The nerves of the brachial plexus bear the following relations to the third part of the artery: on the lateral aspect are the lateral root and trunk of the median nerve, and the musculocutaneous nerve for a short distance. On the medial aspect (between the axillary vein and ar¬ tery) are found the ulnar nerve and (to the medial aspect of the vein) the medial brachial cutaneous nerve. Anteriorly are the medial root of the median nerve and the medial antebrachial cutaneous nerve, and posteriorly the radial and axillary nerves, the lat¬ ter extending only as far as the distal border of the subscapularis muscle. COLLATERAL CIRCULATION AFTER LIGATURE OF THE

If the axillary artery is tied proxi¬ mal to the origin of the thoracoacromial artery, the collateral circulation achieved is the same as that which results from ligature of the third part of the subclavian. If the ligature is made more distally be¬ tween the thoracoacromial and the subscapular, the latter vessel, by its free anastomosis with the supra¬ scapular and transverse cervical branches of the subclavian, becomes the chief agent in carrying on the circulation. If the lateral thoracic artery is distal to the ligature, it materially contributes to the circu¬ lation by its anastomoses with the intercostal and internal thoracic arteries. A ligature made distal to the origin of the subscapular artery is probably also distal to the origins of the two humeral circumflex arteries, in which case the chief vessels providing blood to more distal structures in the arm are the subscapular and the two humeral circumflex arteries anastomosing with branches of the deep brachial artery. axillary artery.

Branches of the Axillary Artery

RELATIONS OF THE SECOND PART OF THE AXILLARY

The second part of the axillary artery is covered anteriorly by the skin, the superficial and deep fasciae, the pectoralis major muscle, and, immediately anterior to the artery, the pectoralis minor muscle. Dorsal to the second part of the artery are the posterior cord of the brachial plexus and some areolar tissue, both of which intervene be¬ tween the vessel and the subscapularis muscle. Me¬ dially, the axillary vein is separated from the artery by the medial cord of the brachial plexus and the medial pectoral nerve. Laterally is found the lateral cord of the brachial plexus. The cords of the brachial plexus thus surround the artery on three sides and separate it from direct contact with the vein and ad¬ jacent muscles.

artery.

RELATIONS OF THE THIRD

First Part: Supreme thoracic Second Part: Thoracoacromial Lateral thoracic Third Part: Subscapular Posterior humeral circumflex Anterior humeral circumflex

PART OF THE AXILLARY

The third part of the axillary artery extends from the lateral border of the pectoralis minor to the distal border of the tendon of the teres major. Its proximal portion is covered anteriorly by the pecto¬ ralis major muscle, its distal portion by only the in¬

artery.

Although quite variable in their pattern, usually one branch is derived from the first part of the axillary artery, two from the sec¬ ond, and three from the third. They are:

SUPREME THORACIC ARTERY

The supreme thoracic artery is a small vessel which usually arises from the axillary artery just below the clavicle, but it may

712

THE ARTERIES

branch from the thoracoacromial artery or may be absent. It passes medially, generally behind the axillary vein, to the side of the chest in the first intercostal space (Figs. 8-42; 8-43). Coursing between the pectoralis minor and major, the supreme thoracic artery sup¬ plies branches to these muscles, and to the wall of the thorax, anastomosing with the internal thoracic and upper one or two inter¬ costal arteries.

THORACOACROMIAL ARTERY

The thoracoacromial artery is a short trunk that arises anteriorly from the axillary artery, its origin being generally overlapped by the upper (or medial) edge of the pectora¬ lis minor (Figs. 8-35; 8-42; 8-43). At the border of this muscle, the vessel pierces the clavipectoral fascia and divides into four branches: pectoral, acromial, clavicular, and deltoid. pectoral branches. The pectoral branches of the thoracoacromial artery de¬ scend between the two pectoral muscles and are distributed to them and to the breast, anastomosing with the intercostal branches

of the internal thoracic and with the lateral thoracic artery (Fig. 8-33). acromial branch. The acromial branch courses laterally, superficial to the coracoid process and deep to the deltoid muscle to which it gives branches (Figs. 8-33; 8-44). It then pierces that muscle and ends on the acromion in an arterial network, called the acromial rete, formed by branches from the suprascapular, the deltoid branch of the tho¬ racoacromial artery, and the posterior hu¬ meral circumflex artery. clavicular branch. The clavicular branch of the thoracoacromial artery courses upward and medially beneath the clavicle to the sternoclavicular joint. It sup¬ plies this articulation and the subclavius muscle and anastomoses with the supra¬ scapular artery. deltoid branch. The deltoid branch fre¬ quently arises with the acromial branch and crosses laterally, superficial to the pectoralis minor (Fig. 8-33). It courses in the deltopectoral groove with the cephalic vein, passing between the pectoralis major and deltoid, and supplying branches to both mus¬ cles.

Anterior humeral circumflex

Fig. 8-42. The axillary artery and its branches. This vascular pattern shows all six branches of the artery derived from the main stem.

ARTERIES OF THE UPPER LIMB

713

LATERAL THORACIC ARTERY

SUBSCAPULAR ARTERY

The lateral thoracic artery (Figs. 8-42; 8-43) follows the lateral or lower border of the pectoralis minor to the side of the chest. It supplies the serratus anterior and both pec¬ toral muscles and sends branches across the axilla to the axillary lymph nodes and subscapularis muscle. The lateral thoracic ar¬ tery anastomoses with the internal thoracic, subscapular, and intercostal arteries, and with the pectoral branches of the thoracoa¬ cromial. The lateral thoracic artery is often (60%) a branch either of the thoracoacromial artery or of the subscapular artery. It comes directly from the axillary only in about 30% of cases. lateral mammary branches. In the fe¬ male, the lateral mammary branches (some¬ times called the external mammary branches) can be of considerable size. They turn around the free lateral margin of the pectoralis major and supply the breast.

The subscapular artery is usually the larg¬ est branch of the axillary artery and it arises at the distal border of the subscapularis muscle. Lying on the anterior surface of the subscapularis muscle, it descends under cover of the latissimus dorsi. After a short course of about 4 cm, the subscapular artery divides into the circumflex scapular and tho¬ racodorsal arteries (Figs. 8-30; 8-42; 8-43). CIRCUMFLEX SCAPULAR ARTERY. The circumflex scapular artery is generally larger than the thoracodorsal artery. It curves around the lateral border of the scapula, tra¬ versing the triangular space bordered below by the teres major, above by the subscapu¬ laris, and laterally by the long head of the triceps. The vessel then enters the infraspinous fossa between the teres minor and the scapula, remaining close to the bone (Fig. 8-44). It supplies branches to the infraspina¬ tus and anastomoses with the suprascapular

Thoracoacromial

Supreme thoracic

Lateral thoracic Lateral thoracic branch of subscapular

Fig. 8-43. The axillary artery and its branches. Note that in this vascular pattern, the lateral thoracic artery is derived from the thoracoacromial artery rather than directly from the axillary, and a lateral thoracic branch also comes from the subscapular artery. This pattern is seen in about 33% of cases.

714

HE ARTERIES

artery and the deep branch of the transverse cervical artery (which in some cadavers is the descending branch of the descending scapular artery). In the triangular space, the circumflex scapular artery gives a branch to the subscapularis muscle. Another large branch continues along the lateral border of the scapula between the teres major and minor, supplying these muscles as well as the long head of the triceps and the deltoid. Finally, it anastomoses with the deep branch of the transverse cervical artery (or descend¬ ing branch of the descending scapular) at the inferior angle of the scapula. thoracodorsal artery. The thoracodorsal artery (Figs. 8-33; 8-43) is the continuation inferiorly of the subscapular artery through the axilla along the anterior border of the latissimus dorsi muscle. The vessel courses with the thoracodorsal nerve; it gives branches to the subscapularis and is the principal supply to the latissimus. It anasto¬ moses with the circumflex scapular artery and the deep branch of the transverse cervi¬ cal artery (or descending branch of the de¬ scending scapular artery). One or two siza¬ ble branches cross the axilla to supply the serratus anterior and intercostal muscles, anastomosing with the intercostal, lateral thoracic, and thoracoacromial arteries. When the lateral thoracic artery is small or

lacking, a branch of the thoracodorsal may take its place. POSTERIOR HUMERAL CIRCUMFLEX ARTERY

The posterior humeral circumflex artery arises from the axillary artery at the distal border of the subscapularis muscle (Figs. 8-42 to 8-44). It curves dorsally with the axil¬ lary nerve through the quadrangular space bounded by the subscapularis and teres minor muscles above, the teres major below, the long head of the triceps brachii medially, and the surgical neck of the humerus later¬ ally (Fig. 8-44). The artery winds around the neck of the humerus and is distributed to the deltoid muscle and the shoulder joint, anas¬ tomosing with the anterior humeral circum¬ flex and deep brachial arteries. ANTERIOR HUMERAL CIRCUMFLEX ARTERY

The anterior humeral circumflex artery is considerably smaller than the posterior humeral circumflex, and it arises from the lateral aspect of the axillary artery near the lower border of the subscapularis muscle and opposite the posterior humeral circum¬ flex artery (Figs. 8-42 to 8-44). It may arise in

Deep br. of trans. cervical (or desc br of desc. scapular) Suprascapular

Acromial branch of thoracoacromial Anterior humeral circumflex

Termination of subscapular Fig

3 44

The anastomoses on the posterior aspect of the shoulder.

ARTERIES OF THE UPPER LIMB

common with the posterior humeral circum¬ flex or be represented by three or four very small branches. The vessel runs horizontally beneath the coracobrachialis muscle and short head of the biceps brachii, anterior to the neck of the humerus. As it reaches the intertubercular sulcus, it gives off a branch that ascends in the sulcus to supply the head of the humerus and the shoulder joint. The main stem of the artery then continues later¬ ally, deep to the long head of the biceps bra¬

Fig.

8-45.

715

chii and the deltoid, to anastomose with the posterior humeral circumflex artery. Brachial Artery

The brachial artery is the continuation of the axillary artery and originates at the lower margin of the tendon of the teres major muscle. It passes down the arm and ends about 1 cm distal to the bend of the elbow, where it divides into the radial and ulnar arteries (Figs. 8-45; 8-46). At first the

The major arteries of the upper extremity. The branching pattern shown in this diagram is the one most

commonly observed.

716

THE ARTERIES

brachial artery lies medial to the humerus, but as it descends, it gradually curves to the front of the arm, and at the antecubital fossa anterior to the elbow joint, it lies midway between its two epicondyles. relations. The brachial artery is superficial throughout its entire course, being covered anteri¬ orly by the skin and the superficial and deep fasciae. The bicipital aponeurosis, which extends from the biceps brachii muscle, lies anterior to the artery in front of the elbow, separating it from the median cubital vein. The median nerve crosses the brachial artery from lateral to medial, opposite the insertion of the coracobrachialis muscle (Fig. 8-46). Posteri¬ orly, the brachial artery is separated from the long head of the triceps brachii by the radial nerve and the deep brachial artery. It then lies successively on the medial head of the triceps brachii, on the inser¬ tion of the coracobrachialis, and finally on the brachialis muscle. Laterally, the brachial artery is in rela¬ tion more proximally in the arm with the median nerve and the coracobrachialis muscle and more dis¬ tal ly with the biceps brachii, the two muscles over¬ lapping the artery to a considerable extent. Medially, the proximal half of the brachial artery is in relation with the medial antebrachial cutaneous and ulnar nerves, while medial to the distal half of the artery is found the median nerve. The basilic vein also lies to its medial side, but is separated from it in the distal part of the arm by the deep fascia. The artery is ac¬ companied by two venae comitantes, which lie in close contact to it and are interconnected at intervals by short transverse branches.

cubital fossa. On the anterior aspect of the bend at the elbow, the brachial artery sinks deeply into a triangular interval, the cubital fossa. The base of the triangle is di¬ rected proximally and is represented by a line connecting the two epicondyles of the humerus. The sides of the triangle are formed by the medial edge of the brachioradialis muscle and the lateral margin of the pronator teres. The apex of the triangle is directed inferiorly at the point where the two muscles meet. The floor of the cubital fossa is formed by the brachialis and supina¬ tor muscles. This fossa contains the tendon of the biceps brachii muscle, the brachial artery with its accompanying veins, the stems of the radial and ulnar arteries, and a part of the median nerve. The brachial artery occupies the middle of the cubital fossa and divides opposite the neck of the radius into the radial and ulnar arteries. It is covered anteriorly by the skin, superficial fascia, and median cubital vein,

the last being separated from the artery by the bicipital aponeurosis. Posteriorly, it is the brachialis muscle that separates the ar¬ tery from the elbow joint. The median nerve lies close to the medial aspect of the artery in the upper part of the fossa, but is sepa¬ rated from it more distally by the ulnar head of the pronator teres. The tendon of the bi¬ ceps brachii lies to the lateral aspect of the artery. The radial nerve normally lies just outside the fossa, between the supinator and the brachioradialis muscles, but may be exposed by entering through the fossa and deflecting the brachioradialis laterally. VARIATIONS OF THE BRACHIAL ARTERY. The brach¬ ial artery, accompanied by the median nerve, may leave the medial border of the biceps brachii and descend toward the medial epicondyle of the hu¬ merus. In such cases it usually passes behind a su¬ pracondylar process of the humerus, from which a fibrous arch is thrown over the vessel. It then runs beneath or through the substance of the pronator teres to the bend of the elbow. This variation bears considerable analogy with the normal condition of the artery in some of the carnivores. A frequent variation is the presence of a superfi¬ cial brachial artery, which may continue into the forearm to form a superficial antebrachial artery or may rejoin the brachial distally. Frequently the brachial artery divides at a higher level than usual, and the three vessels concerned in this high division are the radial, ulnar, and common interosseous ar¬ teries. Most frequently, the radial artery branches high in the arm, while the other limb of the bifurca¬ tion consists of the ulnar and common interosseous arteries. In some instances, the ulnar arises above the ordinary level, and the radial and common inter¬ osseous form the other limb of the division. Occa¬ sionally the common interosseous arises at a higher level (see Fig. 8-1 2). Sometimes long, slender vessels called vasa aberrantia connect the brachial or axillary artery with one of the arteries of the forearm, or with branches from them. Such vessels usually join the radial artery. collateral circulation. After the application of a ligature to the brachial artery in the upper third of the arm, blood can circulate through branches from the anterior and posterior humeral circumflex and subscapular arteries, which anastomose with ascending branches from the deep brachial artery. If the main stem of the brachial artery is tied below the origin of the deep brachial artery and the superior ulnar collateral, circulation is maintained by branches of these two vessels, which anastomose with the inferior ulnar collateral, the radial and ulnar recurrent arteries, and the posterior interosseous ar¬ tery.

ARTERIES OF THE UPPER LIMB

71 7

Deltoid m.

Pectoralis major m. Latissimus dorsi m. Teres major m. Medial antebrachial cutaneous nerve Coracobrachialis m. Basilic vein Ulnar nerve Deep brachial artery Median nerve Radial nerve Triceps brachii m. (long head)

Biceps brachii m. Muscular branches

Superior ulnar collateral artery

Triceps brachii m. (medial head)

Brachial artery

Ulnar nerve

Inferior ulnar collateral artery

Bicipital aponeurosis

Pronator teres m Brachioradialis m.

Fig.

8-46.

The right brachial artery and some of its branches.

clinical note. To control excessive bleeding, the brachial artery should be compressed laterally against the humerus in the upper third of the arm, laterally and backward in the middle third, and di¬ rectly backward in the lower third as the vessel courses anterior to the humerus in this region.

Branches of the Brachial Artery

around the elbow joint. The branches of the brachial artery are: Deep brachial Principal nutrient artery of humerus Superior ulnar collateral Inferior ulnar collateral Muscular DEEP BRACHIAL ARTERY

As it descends in the arm, the brachial ar¬ tery and its branches supply the humerus, muscles, and other tissues of the region, as well as participate in the anastomosis

The deep brachial artery (profound bra¬ chii) is the largest branch of the brachial ar¬ tery. It arises from the medial and posterior

718

mi

ARTERIES

part of the main stem, just distal to the lower border of the teres major muscle (Figs. 8-45; 8-46). Initially, the deep brachial artery passes backward into the arm between the long and lateral heads of the triceps brachii. It then accompanies the radial nerve in the spiral groove between the lateral and medial heads of the triceps, on the posterior aspect of the humerus. The vessel terminates by dividing into the radial collateral and mid¬ dle collateral arteries. The deep brachial ar¬ tery has four named branches in addition to muscular vessels: Deltoid (ascending) Radial collateral Middle collateral Nutrient The deltoid branch of the deep brachial artery ascends between the long and lateral heads of the tri¬ ceps brachii muscle. It anastomoses with a descending branch of the posterior humeral circumflex artery and helps to supply the brachialis and deltoid muscles. radial collateral artery. The radial col¬ lateral artery, which is frequently described as the terminal portion of the deep brachial deltoid (ascending) branch.

artery, continues into the forearm with the radial nerve. It lies deep to the lateral head of the triceps until it reaches the lateral su¬ pracondylar ridge of the humerus. At this site, it pierces the lateral intermuscular sep¬ tum, descends between the brachioradialis and the brachialis muscles to the palmar aspect of the lateral epicondyle, and ends by anastomosing with the radial recurrent ar¬ tery. Just before the radial collateral artery pierces the intermuscular septum, it gives off a branch that descends to the posterior as¬ pect of the lateral epicondyle and there joins the anastomosis around the elbow. MIDDLE COLLATERAL ARTERY. The middle collateral artery is usually larger than the radial collateral branch (Fig. 8-47). It enters the substance of the long and medial heads of the triceps and descends along the poste¬ rior aspect of the humerus to the elbow, where it anastomoses with the interosseous recurrent and joins into the anastomosis around the elbow. nutrient branch. A nutrient branch, which usually is accessory to the principal nutrient artery from the brachial, enters a nutrient canal of the humerus posterior to the deltoid tuberosity. It may be absent.

Deep brachial

Sup ulnar collateral

Brachial

Radial collateral branch of deep brachial Inf. ulnar collateral

Middle collateral branch of deep brachial

Anterior ulnar recurrent Radial recurrent Posterior ulnar recurrent

Interosseous recurrent

Interosseous Posterior interosseous

Radial

Ulnar Anterior interosseous

Fig

8 47.

Diagram of the anastomosis around the elbow joint.

ARTERIES OF THE UPPER LIMB

PRINCIPAL NUTRIENT ARTERY OF HUMERUS

The main or principal nutrient artery of the humerus arises from the brachial about at the middle of the arm and enters a nutri¬ ent canal near the insertion of the coracobrachialis muscle.

SUPERIOR ULNAR COLLATERAL ARTERY

The superior ulnar collateral artery is a long and slender vessel that arises from the brachial a little below the middle of the arm (Figs. 8-45 to 8-47). It frequently springs from the proximal part of the deep brachial ar¬ tery. It pierces the medial intermuscular sep¬ tum and descends, with the ulnar nerve, on the surface of the medial head of the triceps brachii to the space between the medial epicondyle and olecranon. The vessel ends deep to the flexor carpi ulnaris by anasto¬ mosing with the posterior ulnar recurrent and inferior ulnar collateral arteries. It sometimes sends a branch anterior to the medial epicondyle, to anastomose with the anterior ulnar recurrent artery.

ANASTOMOSIS

AROUND

THE

ELBOW

719

JOINT.

The vessels contributing to this anastomosis may be conveniently divided into those an¬ terior to and those posterior to the medial and lateral epicondyles of the humerus (Fig. 8-47). The branches anastomosing anterior to the medial epicondyle are the anterior branch of the inferior ulnar collateral, the anterior ulnar recurrent, and the anterior branch of the superior ulnar collateral. Those posterior to the medial epicondyle are the inferior ulnar collateral, the posterior ulnar recurrent, and the posterior branch of the superior ulnar collateral. The branches anastomosing anterior to the lateral epicon¬ dyle are the radial recurrent and the radial collateral branch of the deep brachial artery. Those situated posterior to the lateral epi¬ condyle are the inferior ulnar collateral, the interosseous recurrent, and the middle col¬ lateral branch of the deep brachial artery. There is also a transverse arch of anastomo¬ sis, which crosses the posterior aspect of the arm just proximal to the olecranon, formed by the interosseous recurrent joining with the inferior ulnar collateral and posterior ulnar recurrent (Fig. 8-47). Ulnar Artery

INFERIOR ULNAR COLLATERAL ARTERY

The inferior ulnar collateral artery arises about 5 cm above the elbow (Figs. 8-45 to 8-47). Initially, it passes medially upon the brachialis, and piercing the medial inter¬ muscular septum, it then winds around the dorsum of the humerus between the triceps brachii and the bone. By its junction with the middle collateral branch of the deep brachial artery, it forms an arch just above the olecranon fossa. As the vessel lies on the brachialis, it gives off branches that ascend to anastomose with the superior ulnar collat¬ eral, and others that descend in front of the medial epicondyle to anastomose with the anterior ulnar recurrent. Behind the medial epicondyle a branch anastomoses with the superior ulnar collateral and posterior ulnar recurrent arteries.

MUSCULAR BRANCHES

The brachial artery gives off three or four muscular branches which are distributed to the coracobrachialis, biceps brachii, and brachialis muscles.

The ulnar artery is the larger of the two terminal branches of the brachial and, like the radial artery, it begins about 1 cm distal to the bend of the elbow (Figs. 8-48; 8-50 to 8-52). Passing obliquely downward and medially, it reaches the ulnar side of the forearm at a point about midway between the elbow and the wrist. It then runs along the ulnar border to the wrist, crosses the flexor retinaculum on the radial side of the ulnar nerve and pisiform bone, and, immedi¬ ately beyond this bone, becomes the superfi¬ cial palmar arch. In the proxi¬ the ulnar artery is deeply seated, being covered by the pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis muscles. It lies upon the brachialis and flexor digitorum profundus muscles (Fig. 8-51). For about 2.5 cm from its commencement at the elbow, the ulnar artery courses lateral to the median nerve, and then the median nerve crosses anterior to the artery but is separated from it by the ulnar half of the pronator teres muscle. In the distal half of the fore¬ arm, the ulnar artery lies upon the flexor digitorum profundus, being covered by the skin and the super¬ ficial and deep fasciae, and being placed between RELATIONS OF THE ULNAR ARTERY.

mal half of the forearm,

720

THE ARTERIES

the flexor carpi ulnaris and flexor digitorum superficialis (Figs. 8-48; 8-51). The artery is accompanied by two venae comitantes, and it is overlapped in its middle third by the flexor carpi ulnaris. The ulnar nerve lies on the medial side of the distal two-thirds of the artery, and the palmar cutaneous branch of

the ulnar nerve descends on the distal part of the vessel to the palm of the hand. At the wrist the ulnar artery lies on the flexor retinaculum and is covered by skin, the fasciae, and the palmaris brevis (Figs. 8-48, 8-50 to 8-52). On its medial side is the pisiform bone and, slightly dor¬ sal to the artery, the ulnar nerve. variations. The ulnar artery varies in its origin in somewhat less than 10% of cases. It may arise about 5 to 7 cm below the elbow, but more fre¬ quently higher. Variations in the position of this ves¬ sel are more common than in the radial. When its origin from the brachial is normal, the course of the vessel is rarely changed. When it arises higher up, its course is almost invariably superficial to the flexor muscles in the forearm, lying commonly beneath the deep fascia, more rarely between the fascia and skin. In a few instances, its position has been re¬ ported to be subcutaneous in the upper part of the forearm and beneath the deep fascia in the lower part.

Branches of the Ulnar Artery

The branches of the ulnar artery may be arranged into three groups, like those of the radial artery. In the forearm: Anterior ulnar recurrent Posterior ulnar recurrent Common interosseous Anterior interosseous Posterior interosseous Muscular At the wrist: Palmar carpal Dorsal carpal In the hand: Deep palmar Superficial palmar arch Common palmar digital ANTERIOR ULNAR RECURRENT

The anterior ulnar recurrent artery arises immediately below the elbow joint from the medial aspect of the ulnar artery (Fig. 8-51). It courses upward between the brachialis muscle and the pronator teres, supplying these muscles and, in front of the medial epicondyle, anastomoses with the inferior ulnar collateral artery. POSTERIOR ULNAR RECURRENT

Fiq. 8-48. The ulnar and radial arteries and the superfi¬ cial palmar arch.

The posterior ulnar recurrent artery is much larger and arises somewhat more distally than the anterior ulnar recurrent, but

ARTERIES OF THE UPPER LIMB

also from the medial side of the ulnar artery (Figs. 8-49; 8-51). It passes medially and backward between the flexor digitorum superficialis and flexor digitorum profundus, and then it ascends behind the medial epicondyle of the humerus. Between this proc¬ ess and the olecranon it lies beneath the flexor carpi ulnaris and ascends, together with the ulnar nerve, between the two heads of that muscle. The posterior ulnar recurrent artery, which supplies the neighboring mus¬ cles and the elbow joint, anastomoses with the superior and inferior ulnar collateral and the interosseous recurrent arteries. COMMON INTEROSSEOUS ARTERY

The common interosseous artery is a short, thick vessel, only one centimeter long, which arises from the lateral and posterior aspect of the ulnar artery, immediately distal to the tuberosity of the radius (Fig. 8-51). The vessel passes dorsal to the upper border of the interosseous membrane, where it divides into two branches, the anterior and posterior interosseous arteries. anterior interosseous artery. The an¬ terior interosseous artery passes down the forearm on the anterior surface of the inter¬ osseous membrane (Figs. 8-49; 8-51). It is ac¬ companied by the palmar interosseous branch of the median nerve and is overlap¬ ped by the contiguous margins of the flexor digitorum profundus and flexor pollicis longus, giving off muscular branches and nutrient arteries to the radius and ulna. At the proximal border of the pronator quadratus it gives off a small branch that descends dorsal to the pronator to reach the palmar carpal network (Fig. 8-51), and then the an¬ terior interosseous artery pierces the interos¬ seous membrane to enter the posterior compartment of the forearm, where it anastomoses with the dorsal interosseous artery (Fig. 8-49). On the posterior aspect of the interosseous membrane in the lower forearm, the anterior interosseous artery descends in company with the terminal por¬ tion of the posterior interosseous nerve (from the deep branch of the radial nerve) to the dorsum of the wrist to join the dorsal carpal network. The median artery is a long, slender branch that arises from the proximal part of the anterior interosseous artery. It passes forward to the median nerve, which it ac¬ companies and supplies in its course down

721

the forearm. This artery is sometimes much enlarged, and when so, it courses with the median nerve into the palm of the hand and enters into the formation of the superficial palmar arch. POSTERIOR INTEROSSEOUS ARTERY. The posterior interosseous artery, smaller than the anterior, arises from the common inter¬ osseous artery and passes dorsally either over or between the oblique cord and the proximal border of the interosseous mem¬ brane (Figs. 8-49; 8-51). It appears between the contiguous borders of the supinator and the abductor pollicis longus and descends in the posterior compartment of the forearm between the superficial and deep layers of muscles, sending branches to both groups. Coursing along the surface of the abductor pollicis longus and the extensor pollicis brevis, it is accompanied by the posterior interosseous nerve, which is derived from the deep branch of the radial nerve. In the distal forearm, it anastomoses with terminal branches of the anterior interosseous artery and with the dorsal carpal network. The interosseous recurrent artery branches from the posterior interosseous artery near its origin, or at times it may arise directly from the common interosseous ar¬ tery (Fig. 8-49). It ascends on or through the fibers of the supinator to the interval be¬ tween the lateral epicondyle and olecranon, but deep to the anconeus muscle. Here it anastomoses with the middle collateral branch of the deep brachial artery, the pos¬ terior ulnar recurrent artery, and the inferior ulnar collateral artery.

MUSCULAR BRANCHES Many muscular branches arise from the ulnar ar¬ tery in the forearm (Fig. 8-51). These supply the superficial and deep flexors of the fingers and mus¬ cles on the ulnar aspect of the forearm, including the flexors carpi radialis and ulnaris, as well as the pro¬ nator teres.

PALMAR CARPAL BRANCH

The palmar carpal branch is a small vessel that arises from the ulnar artery opposite the carpal bones. It crosses the palmar aspect of the wrist joint, deep to the tendons of the flexor digitorum profundus (Fig. 8-51), and anastomoses with the corresponding palmar carpal branch of the radial artery.

722

THE ARTERIES

Deep brachial artery

Inferior ulnar collateral a

Posterior ulnar recurrent artery

Interosseous recurrent a

Anconeus muscle Supinator muscle Posterior interosseous a

Posterior interosseous artery

Extensor pollicis longus muscle

Extensor indicis muscle Termination of anterior interosseous artery Dorsal carpal branch (of ulnar artery) Extensor carpi ulnaris tendon Extensor indicis tendon

Dorsal metacarpal arteries

Fig. 8-49.

Abductor pollicis longus muscle

Extensor pollicis brevis muscle Extensor pollicis longus tendon Radial artery First dorsal metacarpal a First dorsal interosseous muscle

Arteries on the posterior aspect of the forearm, wrist, and hand.

DORSAL CARPAL BRANCH

The dorsal carpal branch of the ulnar ar¬ tery arises immediately above the pisiform bone and winds dorsally beneath the tendon of the flexor carpi ulnaris (Fig. 8-49). It then passes across the dorsal surface of the wrist beneath the extensor tendons, to anastomose with the corresponding dorsal carpal branch of the radial artery. Just beyond its origin, it gives off a small branch that courses along

the ulnar aspect of the fifth metacarpal bone, supplying the ulnar aspect of the dorsal sur¬ face of the little finger. DEEP PALMAR BRANCH

The deep palmar branch arises from the ulnar artery at the level of the flexor retinac¬ ulum (Figs. 8-48; 8-50 to 8-52). It courses me¬ dially between the abductor digiti minimi and flexor digiti minimi brevis and through

ARTERIES OF THE UPPER LIMB

723

Proper palmar digital arteries

Radial index artery

Common palmar digital arteries

Proper palmar digital arteries ot the thumb

Lumbrical muscles

Superficial palmar arch Synovial sheath for flexor tendons

Adductor pollicis muscle

Opponens digiti minimi muscle

Flexor pollicis brevis muscle

Flexor digiti minimi muscle

Abductor pollicis brevis muscle

Abductor digiti minimi muscle Flexor retinaculum

Deep palmar branch of ulnar artery

Superficial palmar branch of radial artery

Ulnar artery Median nerve Radial artery

The superficial palmar arch and the common and proper digital arteries of the right hand. Note that the ulnar artery is the principal contributor to the superficial palmar arch.

Fig. 8-50.

the origin of the opponens digiti minimi, all of which are muscles of the hypothenar emi¬ nence. The vessel then curves laterally into the palm, accompanied by the deep branch of the radial nerve, to anastomose with the radial artery and complete the deep palmar arch. SUPERFICIAL PALMAR ARCH

The superficial palmar arch is formed pri¬ marily by the deep palmar branch of the ulnar artery and is usually completed by a

branch that comes from the radial artery (Figs. 8-48; 8-50). Most frequently this is the superficial palmar branch of the radial, but it may be the radial index artery or the princeps pollicis artery. More rarely, the median artery, which is a branch of the ante¬ rior interosseous artery, descends to help form the arch. The superficial palmar arch curves across the palm with its convexity oriented distally. It is covered by the skin, the palmaris brevis, and the palmar aponeu¬ rosis, and it lies upon the flexor retinaculum, the flexor digiti minimi brevis and opponens

724

THE ARTERIES

digiti minimi, the tendons of the flexor digitorum superficialis, the lumbrical muscles, and branches of the median and ulnar nerves. The superficial palmar arch gives rise to three common palmar digital arteries. COMMON PALMAR DIGITAL ARTERIES. Three common palmar digital arteries arise from the convexity of the superficial palmar arch and proceed distally on the second, third, and fourth lumbrical muscles (Figs. 8-48; 8-50 to 8-52). Each is joined by the corre¬ sponding palmar metacarpal artery from the deep palmar arch, and then divides into a pair of proper palmar digital arteries (Figs. 8-50 to 8-52). These latter vessels course along the contiguous sides of the index, mid¬ dle, ring, and little fingers dorsal to the cor¬ responding digital nerves. They anastomose freely in the subcutaneous tissue of the fin¬ ger tips and by smaller branches near the interphalangeal joints. Each gives off two dorsal branches, which anastomose with the dorsal digital arteries, and supply the soft parts on the dorsum of the middle and distal phalanges, including the matrix of the fin¬ gernail. The proper palmar digital artery for the ulnar aspect of the little finger springs from the ulnar artery under cover of the palmaris brevis.

Radial Artery

Due to its direction, the radial artery ap¬ pears to be the direct continuation of the brachial trunk, but it is smaller in caliber than the ulnar artery, which is the other ter¬ minal branch of the brachial artery (Figs. 8-45; 8-48; 8-51). It originates at the bifurca¬ tion of the brachial artery opposite the neck of the radius, about 1 cm below the bend of the elbow, and passes along the radial aspect of the forearm to the wrist. It then winds around the lateral aspect of the carpus to the dorsum of the wrist, deep to the tendons of the abductor pollicis longus and the exten¬ sors pollicis longus and brevis, reaching the proximal end of a space between the meta¬ carpal bones of the thumb and index finger. Finally it passes between the two heads of the first dorsal interosseous muscle into the palm of the hand, joining the deep palmar branch of the ulnar artery to form the deep palmar arch. Hence, the radial artery has three parts, one part in the forearm, another at the wrist, and a third part in the hand.

relations of the radial artery. The radial ar¬ tery in the forearm extends from the neck of the radius to the anterior aspect of its styloid process, being placed to the medial aspect of the radial shaft proximally and anterior to the bone distally (Figs. 8-48; 8-51). The upper part of the artery is overlap¬ ped by the fleshy belly of the brachioradialis muscle, while the rest of the artery is superficial, being cov¬ ered only by skin and the superficial and deep fas¬ ciae. In its course through the forearm, the radial artery lies first upon the biceps tendon, and then successively on the supinator muscle, the pronator teres muscle, the radial origin of the flexor digitorum superficialis muscle, the flexor pollicis longus mus¬ cle, the pronator quadratus muscle, and the distal end of the radius. In the proximal third of its course, it lies between the brachioradialis and the pronator teres muscles; in the distal third of its course it lies between the brachioradialis and flexor carpi radialis muscles. The superficial branch of the radial nerve is close to the lateral aspect of the artery in the middle third of its course, and some filaments of the lateral antebrachial cutaneous nerve run along the lower part of the artery as it winds around the wrist. The vessel is accompanied by a pair of venae comitantes throughout its whole course. Distally the radial ar¬ tery lies on the lower anterior aspect of the radius and, being very superficial, is an ideal site for taking the pulse. At the wrist, the radial artery reaches the dorsum of the carpus by passing between the radial collat¬ eral ligament of the wrist and the tendons of the abductor pollicis longus and extensor pollicis brevis muscles (Fig. 8-49). It then descends on the scaph¬ oid and trapezium, and before disappearing between the heads of the first dorsal interosseous muscle, it is crossed by the tendon of the extensor pollicis longus. In the interval between the two extensors of the thumb, sometimes called the "anatomical snuff box," the radial artery is crossed by the dorsal digital nerves as they pass to the thumb and index finger; these nerves are derived from the superficial branch of the radial nerve. In the hand, the radial artery passes through the proximal end of the first interosseous space, be¬ tween the heads of the first dorsal interosseous mus¬ cle (Figs. 8-50; 8-52). It then crosses the palm transversely between the oblique and transverse heads of the adductor pollicis muscle. The vessel then pierces the transverse head and reaches the base of the metacarpal bone of the little finger, where it anastomoses with the deep palmar branch from the ulnar artery, completing the deep palmar arch (Figs. 8-51; 8-52). variations. The origin of the radial artery is higher than usual in about 1 2% of cases. In the fore¬ arm it deviates less frequently from its normal posi¬ tion than does the ulnar artery. It has been observed lying on the deep fascia of the forearm, instead of beneath it. It has also been seen on the surface of the brachioradialis instead of deep to its medial bor-

ARTERIES OF THE UPPER LIMB

725

Biceps brachii m. Inferior ulnar collateral a.

Brachial artery

Ulnar nerve Median nerve

Deep branch of radial nerve Radial recurrent artery Radial nerve Flexor digitorum superficialis m. Posterior interosseous artery

Common tendon of superficial flexor muscles Anterior ulnar recurrent artery

Posterior ulnar recurrent artery Common interosseous artery Ulnar artery

Pronator teres m Anterior interosseous artery Radial artery Flexor pollicis longus muscle

Flexor digitorum profundus muscle Ulnar nerve Muscular branches of ulnar artery

Palmar carpal branch (of ant. interosseous a.) Palmar carpal branch (of radial artery) Superficial palmar branch of radial Deep palmar arch Princeps _ pollicis artery

Pronator quadratus muscle Palmar carpal branch (of ulnar artery) Deep palmar branch of ulnar artery Abductor digiti quinti muscle Flexor digiti quinti brevis muscle Palmar metacarpal arteries Common palmar digital arteries

Radial index artery

Proper palmar digital arteries

Fig. 8-51.

The radial and ulnar arteries in the deep forearm and the deep palmar arch in the hand.

der. in its course around the wrist, the radial artery has been seen lying on the extensor tendons of the thumb instead of beneath them. The presence of a large median artery may replace the radial in the formation of the palmar arches.

Branches of the Radial Artery

The branches of the radial artery may be divided into three groups, which correspond

to the three regions in which the vessel is situated. In the forearm: Radial recurrent Muscular Palmar carpal Superficial palmar At the wrist: Dorsal carpal

726

THE ARTERIES

Proper palmar digital arteries

Common palmar digital arteries

Proper palmar digital arteries of the thumb

Adductor pollicis m. Palmar metacarpal arteries Palmar interosseous mm Deep palmar arch

— Princeps pollicis a

Opponens digiti minimi m

Adductor pollicis m

Flexor digiti minimi brevis muscle

Flexor pollicis brevis m Opponens pollicis m.

Deep palmar branch of ulnar artery

Flexor retinaculum — Palmar carpal network

Ulnar artery Pronator quadratus muscle

Abductor pollicis brevis muscle Superficial palmar branch of radial artery Palmar carpal branch of radial artery Radial artery

Fig. 8-52.

The deep palmar arch and princeps pollicis artery. Note that the radial artery is the principal contributor to this arch, but that it anastomoses with the deep palmar branch of the ulnar artery.

First dorsal metacarpal In the hand: Princeps pollicis Radial index Deep palmar arch Palmar metacarpal Perforating Recurrent RADIAL RECURRENT ARTERY

The radial recurrent artery arises immedi¬ ately below the elbow (Figs. 8-48; 8-51). It ascends between the branches of the radial nerve, lying on the supinator muscle and then between the brachioradialis and brach-

ialis muscles. The vessel supplies these mus¬ cles and the elbow joint and anastomoses with the radial collateral branch of the deep brachial artery. MUSCULAR BRANCHES

The radial artery sends muscular branches to the brachioradialis and pronator teres muscles, as well as to other muscles on the radial aspect of the forearm.

PALMAR CARPAL BRANCH

The palmar carpal branch of the radial artery (Figs. 8-51; 8-52) is a small vessel that arises near the distal border of the pronator

ARTERIES OF THE UPPER LIMB

quadratus and, running across the palmar aspect of the wrist, anastomoses with the palmar carpal branch of the ulnar artery. This anastomosis is joined by a branch from the anterior interosseous artery proximally and by recurrent branches from the deep palmar arch distally, thus forming a palmar carpal network, which supplies the articula¬ tions of the wrist and the carpal bones (Fig. 8-52).

SUPERFICIAL PALMAR BRANCH

The superficial palmar branch arises from the radial artery just above the wrist, where the radial artery is about to wind laterally around the carpus (Figs. 8-48; 8-50 to 8-52). It passes through, but occasionally over, the muscles of the thenar eminence, which it supplies. The vessel then anastomoses with the terminal portion of the ulnar artery, completing the superficial palmar arch (Figs. 8-48; 8-50). The superficial palmar branch of the radial artery varies considerably in size. Frequently it is very small and ends in the muscles of the thumb, but sometimes it is as large as the continuation of the radial.

DORSAL CARPAL BRANCH

The dorsal carpal branch of the radial ar¬ tery is a small vessel that arises deep to the extensor tendons of the thumb. Crossing the carpus transversely toward the medial bor¬ der of the hand, it anastomoses with the dor¬ sal carpal branch of the ulnar artery and with terminal branches of the anterior and posterior interosseous arteries to form a dor¬ sal carpal network. From this network are given off three slender dorsal metacarpal arteries, which run distally on the second, third, and fourth dorsal interosseous mus¬ cles (Fig. 8-49). The metacarpal arteries bi¬ furcate into dorsal digital branches, which then supply the adjacent sides of the index, middle, ring, and little fingers. The dorsal digital vessels anastomose with the proper palmar digital branches of the superficial palmar arch. Near their origins the dorsal metacarpal arteries anastomose with the deep palmar arch by the proximal perforat¬ ing arteries, and near their points of bifurca¬ tion, they also anastomose with the common

727

palmar digital vessels of the superficial pal¬ mar arch by the distal perforating arteries. FIRST DORSAL METACARPAL ARTERY

The first dorsal metacarpal artery arises just before the radial artery passes between the two heads of the first dorsal interosseous muscle (Fig. 8-49). It divides almost immedi¬ ately into two branches, which supply the adjacent sides of the thumb and index finger. The radial aspect of the thumb receives a branch directly from the radial artery. PRINCEPS POLLICIS ARTERY

The princeps pollicis artery arises from the radial artery as it turns medially toward the deep part of the palm (Figs. 8-48; 8-51; 8-52). It descends between the first dorsal interosseous muscle and the oblique head of the adductor pollicis, along the ulnar aspect of the metacarpal bone of the thumb to the base of the first phalanx. Here the princeps pollicis artery lies beneath the tendon of the flexor pollicis longus and divides into two branches. These make their appearance be¬ tween the medial and lateral insertions of the oblique head of the adductor pollicis muscle and run along the sides of the thumb (Figs. 8-50; 8-52). On the palmar surface of the distal phalanx, they form an arch from which branches are distributed to the skin and subcutaneous tissue of the thumb. RADIAL INDEX ARTERY

The radial index artery (arteria radialis indicis) arises from the radial artery close to the princeps pollicis artery, between the first dorsal interosseous muscle and the trans¬ verse head of the adductor pollicis muscle (Figs. 8-48; 8-50; 8-51). It courses along the radial aspect of the index finger to its ex¬ tremity, where it anastomoses with the proper digital artery supplying the ulnar aspect of the finger. At the distal border of the transverse head of the adductor pollicis, this vessel anastomoses with the princeps pollicis and gives a communicating branch to the superficial palmar arch. The princeps pollicis and radial index arteries may spring from a common trunk, which is then called the first palmar metacarpal artery.

728

THE ARTERIES

DEEP PALMAR ARCH

The deep palmar arch is the terminal part of the radial artery and it anastomoses with the deep palmar branch of the ulnar artery (Figs. 8-51; 8-52). It lies upon the carpal ex¬ tremities of the metacarpal bones and on the interosseous muscles, being covered by the oblique head of the adductor pollicis mus¬ cle, the flexor tendons of the fingers, and the lumbrical muscles. In nearly two-thirds of cases, the deep palmar arch lies deep to the ulnar nerve; in one-third of cases, it lies su¬ perficial to the nerve (to the palmar side). Occasionally it is doubled and encircles the ulnar nerve. Arising from the deep palmar arch are the palmar metacarpal arteries, per¬ forating branches, and recurrent branches. palmar metacarpal arteries. There are three or four palmar metacarpal arteries that arise from the convexity of the deep palmar arch (Figs. 8-51; 8-52). They course distally upon the interosseous muscles in the second, third, and fourth intermetacarpal spaces and anastomose, at the clefts of the fingers, with the common digital branches of the superfi¬ cial palmar arch. perforating branches. Three perforat¬ ing branches pass dorsally from the deep palmar arch, through the second, third, and fourth interosseous spaces, and between the heads of the corresponding dorsal interosse¬ ous muscles to anastomose with the dorsal metacarpal arteries. recurrent branches. The recurrent branches arise from the concavity of the deep palmar arch. They ascend on the pal¬ mar aspect of the wrist, supply the intercarpal articulations, and end in the palmar car¬ pal network.

Arteries of the Thorax and Abdomen From the aortic arch, the descending aorta courses along the posterior wall of the trunk through both the thoracic and abdominal cavities. Descending in the posterior medias¬ tinum, the vessel is called the thoracic aorta; as it penetrates the diaphragm, it becomes the posterior abdominal aorta.

THORACIC AORTA

The thoracic aorta, contained in the poste¬ rior mediastinum, descends along the poste¬ rior wall of the thorax (Fig. 8-53). It begins at the lower border of the fourth thoracic ver¬ tebra, where it is continuous with the aortic arch, and ends anterior to the lower border of the twelfth thoracic vertebra, at the aortic hiatus in the diaphragm. At its origin, the thoracic aorta is situated on the left of the vertebral column, but as it descends, it ap¬ proaches the median line. At its termination, the vessel lies directly anterior to the col¬ umn. In its descent, the thoracic aorta de¬ scribes a curve that is concave ventrally, and because its thoracic branches are small, there is no significant decrease in its diame¬ ter (Fig. 8-53). relations. The thoracic aorta is related anteri¬ orly to the root of the left lung, the pericardium, the esophagus, and the diaphragm, and posteriorly to the vertebral column and the hemiazygos veins. On the right side of the thoracic aorta are the azygos vein and thoracic duct, and on the left side, the left pleura and lung. The esophagus, with its accompa¬ nying plexus of nerves, lies to the right side of the upper thoracic aorta. More interiorly in the thorax it is placed anterior to the aorta, but as it nears the diaphragm, it is situated to the left side of the aorta.

Branches of the Thoracic Aorta

The thoracic aorta gives off visceral branches to organ structures in the thorax as well as parietal branches to the walls of the thoracic cavity. They are: Visceral Branches Pericardial Bronchial Esophageal Mediastinal Parietal Branches Posterior intercostal Subcostal Superior phrenic PERICARDIAL BRANCHES

The pericardial branches of the thoracic aorta consist of two or three small vessels that are distributed to the posterior surface

ARTERIES OF THE THORAX AND ABDOMEN

729

Left common carotid artery Left subclavian artery

Left subclavian vein_ Posterior intercostal vessels and nerve

Left phrenic nerve Pericardiacophrenic artery and vein

Vagus nerve Accessory hemiazygos vein

Ligamentum arteriosum

Left superior intercostal vein

Left pulmonary artery

Rami communicantes

Pulmonary trunk Sympathetic trunk

Left primary bronchus

Descending thoracic aorta

Left pulmonary veins

Left auricle Hemiazygos vein Thoracic aortic nerve plexus

Pericardium

Left ventricle Internal intercostal muscle

Esophagus

Greater splanchnic nerve

Diaphragm

Fig. 8-53. The aortic arch and the descending thoracic aorta viewed from the left side with the left lung removed. The pericardium has been opened to expose the left side of the heart.

of the pericardium. They also supply some of the posterior mediastinal lymph nodes and anastomose with the pericardiacophrenic branches of the internal thoracic artery. BRONCHIAL ARTERIES

The bronchial arteries vary in number, size, and origin. There is as a rule only one right bronchial artery, which arises from the third posterior intercostal artery (the first intercostal artery that comes from the aorta) or from the upper left bronchial ar¬ tery. There are usually two left bronchial arteries and these arise from the thoracic aorta. The upper left bronchial arises oppo¬

site the fifth thoracic vertebra, while the lower left bronchial artery stems from the aorta just below the level of the left bron¬ chus. Each vessel courses along the posterior surface of its bronchus, dividing and subdi¬ viding along the bronchial tubes, supplying them, the areolar tissue of the lungs, and the bronchial lymph nodes. They also send a few twigs to the esophagus, to bronchial lymph nodes, and to the pericardium. ESOPHAGEAL ARTERIES

There are four or five esophageal arteries, which arise from the ventral aspect of the aorta and pass obliquely downward to the

730

THE ARTERIES

esophagus, on which they form a chain of anastomoses. Additionally, these vessels anastomose with the esophageal branches of the inferior thyroid arteries and with as¬ cending branches from the left inferior phrenic and left gastric arteries. MEDIASTINAL BRANCHES

Numerous small mediastinal branches arise from the thoracic aorta to supply lymph nodes, vessels, nerves, and loose are¬ olar tissue in the posterior mediastinum, as well as some of the adjacent mediastinal pleura.

POSTERIOR INTERCOSTAL ARTERIES

There usually are nine pairs of posterior intercostal arteries which branch from the thoracic aorta. They arise from the dorsal aspect of the aorta and are distributed to the lower nine intercostal spaces. The first two intercostal spaces are supplied by the su¬ preme intercostal artery, which is a branch of the costocervical trunk from the subcla¬ vian artery. The right posterior intercostal arteries are longer than the left because the aorta is positioned to the left side of the ver¬ tebral column. They pass across the bodies of the vertebrae dorsal to the esophagus, tho¬ racic duct, and azygos vein and are covered by the right lung and pleura. The left poste¬ rior intercostal arteries initially course dorsally, curving along the sides of the vertebral bodies and being covered by the left lung and pleura. The two uppermost vessels are crossed by the left superior intercostal vein, the lower vessels by the accessory hemia¬ zygos and hemiazygos veins (Fig. 8-53). The further course of the posterior intercostal arteries is practically the same on both sides. Opposite the heads of the ribs, the sympa¬ thetic trunk passes anterior to them, and the splanchnic nerves descend anterior to the lower posterior intercostal arteries. Each posterior intercostal artery crosses its corresponding intercostal space ob¬ liquely toward the angle of the next rib above and is continued ventrally in the cos¬ tal groove. (This portion of the artery at one time was called the ventral ramus.) It is placed at first between the pleura and the internal posterior intercostal membrane. It then courses anteriorly around the intercos¬ tal space, lying between the internal inter¬

costal muscle and the innermost intercostal muscle. Anteriorly, it anastomoses with the anterior intercostal branch of the internal thoracic or of the musculophrenic artery. Each artery is accompanied by a vein and a nerve, the former placed above and the lat¬ ter below the artery (Fig. 8-53). This relation¬ ship exists except in the posterior part of the upper intercostal spaces, where the artery, which must ascend to the space, initially lies below the nerve and then between the nerve and vein. The third posterior intercostal ar¬ tery (first aortic) anastomoses with the su¬ preme intercostal artery, which branches from the costocervical trunk, and may form the chief supply of the second intercostal space. The lowest two posterior intercostal arteries are continued anteriorly from the intercostal spaces into the anterior abdomi¬ nal wall and anastomose with the subcostal, superior epigastric, and lumbar arteries. Branches of the Posterior Intercostal Artery

In its course from the aorta around the thoracic wall, each posterior intercostal ar¬ tery gives off several branches. These are the following: Dorsal Collateral intercostal Muscular Lateral cutaneous Mammary The dorsal branch of each posterior intercostal artery is a large vessel that courses backward through a space that is bounded above and below by the necks of the ribs, medially by the body of a vertebra, and laterally by a superior costo¬ transverse ligament. It gives off a spinal branch which enters the vertebral canal through the intervertebral foramen and is distributed to the vertebrae, the spinal cord, and its membranes. The dorsal branch then courses over the transverse process of the vertebra, accompanied by the dorsal ramus of the segmentally corresponding thoracic spinal nerve. It supplies branches to the muscles of the back and cutaneous vessels which course with corresponding cutaneous branches of the dorsal ramus of the spinal nerve. collateral intercostal branch. The col¬ lateral intercostal branch comes off from the dorsal

branch.

ARTERIES OF THE THORAX AND ABDOMEN

posterior intercostal artery near the angle of the rib and descends to the upper border of the rib below, along which it courses to anastomose with the intercostal branch of the internal thoracic artery. muscular branches. Muscular branches arise from the posterior intercostal artery to supply the intercostal and pectoral muscles and the serratus anterior. They anastomose with the supreme thoracic and lateral tho¬ racic branches of the axillary artery. LATERAL CUTANEOUS BRANCHES. Lateral cutaneous branches arise from the posterior intercostal artery at about the midaxillary line. They penetrate laterally through the intercostal and serratus anterior muscles in company with the lateral cutaneous branches of the thoracic nerves. Achieving the superficial fascia, the vessels divide into anterior and posterior branches that course in a segmental manner to supply the skin and superficial fascia overlying an intercos¬ tal space. In the third, fourth, and fifth inter¬ costal regions the anterior branches reach the lateral part of the mammary gland in the female and are sometimes called the lateral or external mammary branches. mammary branches. After giving off the lateral cutaneous branches, the posterior in¬ tercostal arteries continue around within the intercostal space, eventually to penetrate the skin and superficial fascia more anteriorly. In the third, fourth, and fifth spaces, (medial) mammary branches arise to reach the me¬ dial part of the base of the breast. They in¬ crease considerably in size during the period of lactation.

SUBCOSTAL ARTERIES

The subcostal arteries are so named be¬ cause they lie below the last ribs. As such, they cannot be considered true intercostal arteries, but they are the lowest pair of ar¬ teries derived from the thoracic aorta, and they are in series with the other pairs of pos¬ terior intercostal arteries. Each artery passes along the lower border of the twelfth rib dorsal to the kidney and ventral to the quadratus lumborum muscle; it is accompanied by the ventral ramus of the twelfth thoracic or subcostal nerve. It then pierces the poste¬ rior aponeurosis of the transversus abdomi¬ nis, and passing between this muscle and the internal oblique, it anastomoses with the superior epigastric, the lowest true intercos¬

731

tal, and the lumbar arteries. Each subcostal artery gives off a dorsal branch, which has a distribution similar to those of posterior in¬ tercostal arteries. SUPERIOR PHRENIC ARTERIES

The superior phrenic arteries are small vessels that arise from the lower part of the thoracic aorta. They are distributed to the dorsal part of the upper surface of the dia¬ phragm and anastomose with the musculo¬ phrenic and pericardiacophrenic arteries. A small aberrant artery is sometimes found aris¬ ing from the right side of the thoracic aorta near the origin of the right bronchial. It passes upward and to the right behind the trachea and the esophagus and may anastomose with the right supreme intercostal artery. It represents the remains of the right dorsal aorta, and in a small proportion of cases, it is en¬ larged to form the first part of the right subclavian artery.

abdominal aorta The abdominal aorta begins in the midline at the aortic hiatus of the diaphragm, ventral to the lower border of the body of the last thoracic vertebra. Descending anterior to the vertebral column, it ends on the body of the fourth lumbar vertebra, commonly a little to the left of the midline, by dividing into the two common iliac arteries. It diminishes rap¬ idly in size as it descends in the abdomen because of the many large vessels that branch from it. As the aorta lies upon the bodies of the vertebrae, it displays a curve that is convex anteriorly. The summit of the convexity corresponds to the third lumbar vertebra. The aortic bifurcation may be roughly judged on the surface of the abdo¬ men to occur slightly to the left of the mid¬ line at a site about 2.54 cm below the umbili¬ cus. This is approximately at the level of a line drawn between the most superior extent of the iliac crests. relations. The upper part of the abdominal aorta is covered anteriorly by the lesser omentum and stomach, dorsal to which are the branches of the celiac artery and the celiac plexus. Below these are the splenic vein, the pancreas, the left renal vein, the inferior part of the duodenum, the mesentery, and the aortic plexus. Posteriorly, the abdominal aorta is separated from the lumbar vertebrae and intervertebral discs by the anterior longitudinal liga-

732

THE ARTERIES

merit and the second, third, and fourth left lumbar veins. On its right side, the abdominal aorta is re¬ lated above to the azygos vein, cisterna chyli, tho¬ racic duct, and the right crus of the diaphragm, the latter separating it from the proximal part of the infe¬ rior vena cava and the right celiac ganglion. More caudally in the abdomen, the right side of the aorta is in contact with the inferior vena cava. On the left side, the upper part of the abdominal aorta is related to the left crus of the diaphragm and the left celiac ganglion; somewhat lower are the fourth or ascend¬ ing part of the duodenum, the duodenojejunal junc¬ tion, and some coils of the small intestine. collateral circulation. A degree of collateral circulation is provided by several anastomoses inter¬ connecting vessels that arise above the aorta with others that arise below, or anastomoses between higher and lower branching vessels from the aorta itself. Thus, an anastomosis is found on the anterior wall of the trunk between the internal thoracic artery from the subclavian and the inferior epigastric ar¬

tery, which branches from the external iliac. There is a free communication between the superior and in¬ ferior mesenteries, if an obstruction or ligature is placed between these vessels. When the point of lig¬ ature is below the origin of the inferior mesenteric (as is more common), collateral circulation is achieved between the inferior mesenteric artery and the internal pudendal artery of the pelvis. Other anastomoses exist between the lumbar arteries and the branches of the internal iliac. To these examples of collateral circulation can be added many others that protect regions of the body and organs that suf¬ fer diminished circulation.

Branches of the Abdominal Aorta

The branches of the abdominal aorta may be divided into three sets: visceral, parietal, and terminal (Fig. 8-54).

Esophagus Hepatic veins Diaphragm Cardiac end of stomach

Inferior phrenic artery

Inferior phrenic artery Suprarenal artery Celiac trunk

Inferior vena cava Right suprarenal gland Right kidney

Superior mesenteric artery Renal artery Renal vein Transversus abdominis muscle Left testicular artery Lumbar artery Quadratus lumborum muscle

Right renal artery and vein

Right testicular vein

Abdominal aorta

R ight testicular artery

Inferior mesenteric artery

Ureter Psoas major and minor muscles

Left common iliac artery Middle sacral artery

lliacus muscle Superior rectal artery

Internal iliac artery i-External iliac artery ■ - Rectum

Pelvic cavity Rectus abdominis muscle

Fig. 8-54.

■

- Urinary bladder

The abdominal aorta and its principal branches in the male.

ARTERIES OF THE THORAX AND ABDOMEN

Visceral Branches Celiac trunk Superior mesenteric Inferior mesenteric Middle suprarenal Renal Testicular Ovarian Parietal Branches Inferior phrenic Lumbar Middle sacral Terminal Branches Common iliac The visceral branches are distributed to the organs in the abdomen, and of these the celiac trunk and the superior and inferior mesenteric arteries are unpaired, whereas the middle suprarenals, renals, testicular, and ovarian are paired. The parietal branches supply the diaphragm from below as well as the posterior abdominal wall, and of these the inferior phrenics and lumbars are paired, while the middle sacral is un¬ paired. The terminal branches descend to supply the organs of the pelvis, the pelvic wall, and the lower extremities; of course, the common iliacs are paired (Fig. 8-54).

733

Hepatic Splenic VARIABILITY

IN

THE

BRANCHING

OF

THE

CELIAC

The most constant feature of this artery is the variability of its branching and of the routes by which blood reaches the organs that it principally supplies. According to Michels (1955), whose de¬ scriptions and statistics are followed in this account, the stomach, liver, pancreas, duodenum, and spleen are the organs supplied, and they can conveniently be used to designate the important variations. A gastrohepatosplenic trunk has the classic branches: a left gastric, a common hepatic, and a splenic artery. This is the usual pattern (89%), and it gives origin to all its expected sub-branches in 64.5%, and in the remainder there are supernumer¬ ary or accessory branches. An hepatosplenic trunk (3.5%) has hepatic and splenic arteries, but the left gastric arises independ¬ ently from the aorta or from the hepatic or splenic arteries. A gastrosplenic trunk (5.5%) has the left gastric and splenic arteries, but the hepatic arises from the aorta or from the superior mesenteric artery. An hepatogastric trunk (1.5%) has the left gastric and hepatic arteries, but the splenic arises from the aorta or from the superior mesenteric artery. In rare instances the celiac trunk and superior mesenteric arteries are combined. trunk.

Left Gastric Artery CELIAC TRUNK

The celiac trunk is a short thick vessel that ranges from 7 to 20 mm in diameter and arises from the aorta just below the aortic hiatus of the diaphragm (Figs. 8-54; 8-55). It is covered by the peritoneum of the dorsal wall of the lesser sac (omental bursa). On its right side are the right celiac ganglion, the right crus of the diaphragm, and the caudate lobe of the liver. On its left side are the left celiac ganglion, the left crus of the diaphragm, and the cardiac end of the stomach. Below it is related to the upper border of the pancreas and the splenic vein. A short distance below its origin from the aorta (i.e., from 1 mm to 2.2 cm, but averaging about 1.25 cm), the aorta gives origin to the superior mesenteric artery. Branches of the Celiac Trunk

After a short course of about 1 to 2 cm, the celiac trunk usually divides into three large branches (Figs. 8-55; 8-57). These are the: Left gastric

The left gastric artery most commonly is the first branch of the celiac trunk, arising near its middle part (Figs. 8-55; 8-57). Being 4 to 5 mm in diameter, it is the smallest of the three branches off the celiac trunk, but it is much larger than the right gastric artery, which usually derives from the common hepatic artery. Frequently (25%), the left gas¬ tric arises from the termination of the celiac trunk together with the hepatic and splenic arteries. The vessel is covered by that part of the parietal peritoneum of the dorsal ab¬ dominal wall which forms the dorsal layer bounding the omental bursa. Initially, the left gastric artery courses anteriorly, up¬ ward, and to the left in a gentle curve. It raises a crescentic ridge of peritoneum called the gastrophrenic fold and reaches the anterior wall of the omental bursa near the cardiac end of the stomach, accompanied by the coronary vein. Here it reverses its direc¬ tion and, lying between the two leaves of the lesser omentum, gives off a cardioesophageal branch before bifurcating into a ventral and a dorsal branch. The cardioesophageal branch arises be¬ fore the terminal bifurcation of the left gas-

734

THE ARTERIES

Left lobe of liver

Left hepatic artery

Caudate lobe of liver Right lobe of liver

Abdominal

aorta

Right hepatic artery Celiac trunk

Portal vein

Left gastric artery

Cystic artery Proper hepatic artery

Splenic artery

Inferior vena cava

Common hepatic artery

Common bile duct

Spleen Gastroduodenal artery

Stomach Lesser omentum

Pylorus Left gastroepiploic artery Right gastric artery

Greater omentum

I

4

Anterior epiploic arteries '

W'

C) The celiac trunk and its branches. The liver has been elevated to reveal the porta hepatis and the gallblad¬ der. Note that the lesser omentum and the anterior layers of the greater omentum have been cut. The arterial supply along the lesser curvature is represented by a double arcade.

Fig. 8-55.

trie artery. It is distributed to the cardia of the stomach and the lower esophagus by one to three smaller vessels. The ventral branch of the left gastric is distributed to the anterior surface of the stomach by dividing into two or three smaller arteries. The dorsal branch of the left gastric artery courses along the lesser curvature of the stomach, giving branches to the posterior surface of the stomach and usually anasto¬ mosing with the right gastric artery (Figs. 8-55; 8-57).

VARIATIONS

INVOLVING

THE

LEFT

GASTRIC

AR¬

The left gastric artery was found to be a branch of the aorta in 2.5% of cadavers studied, of a gastrosplenic trunk in 4.5%, and of an hepatogastric trunk in 1.5%. An accessory left gastric artery arose from the splenic in 6%, from the left hepatic in 3%, and from the celiac trunk in 2% of 200 bodies studied by Michels (1953). An aberrant left hepatic artery branches from the left gastric artery just proximal to its bifurcation in 23% of cadavers studied. In considering ligation of the left gastric artery, it is important to realize that these aberrant left hepatic arteries completely re¬ place the regular left hepatic artery in supplying the TERY.

ARTERIES OF THE THORAX AND ABDOMEN

735

left lobe of the liver in about half (1 1.5%) the afore¬ mentioned cases, and are accessory to the left lobe in the rest. It may be as large as 3 to 5 mm in diame¬ ter, and, lying between the two layers of the lesser omentum, it courses upward about 6 cm toward the esophagus. It then crosses the caudate lobe and en¬ ters the liver substance at the fissure for the ligamentum venosum. Because of this frequent origin of the left hepatic, the left gastric was named the gastrohepatic artery by Haller as early as 1756.1 The inferior phrenic arteries also may arise from the left gastric.

Hepatic Artery

The hepatic artery, arising from the celiac trunk, is slightly smaller (7 to 8 mm) than the splenic artery in the adult, but is the largest branch of the celiac trunk in the fetus (Figs. 8-55 to 8-57). Its first part is horizontal, run¬ ning from left to right along the upper bor¬ der of the head of the pancreas to the pylo¬ rus or first part of the duodenum, where it usually gives off the right gastric artery. Be¬ hind the duodenum, the hepatic artery gives rise to the gastroduodenal artery, and then the main stem of the vessel turns superiorly to course toward the liver. It is covered by the peritoneum of the dorsal wall of the omental bursa, which is raised thereby into the right hepatopancreatic fold. It then passes between the layers of the hepatoduo¬ denal ligament (lesser omentum) to the porta hepatis where it lies ventral to the epiploic foramen, having the common bile duct to its right and the portal vein dorsal to it. Fre¬ quently a distinction is made between two parts of the hepatic artery. That portion coursing from the celiac trunk to where the gastroduodenal artery branches is called the common hepatic artery, and the part cours¬ ing in the porta hepatis from which stem the lobar hepatic branches is called the proper hepatic artery (Figs. 8-55; 8-56). At a variable distance from the liver, the proper hepatic artery gives rise to three terminal branches, the right, left, and middle hepatic arteries. variations. Of 200 bodies, 41.5% had one or more aberrant hepatic arteries, 50.5% had none, several bodies had two, and a few three aberrants. The common hepatic arose from the aorta in three specimens of the 200, from the superior mesenteric in five, and from the left gastric in one (Michels, 1953).

'Albrecht von Haller (1708-1777): A Swiss physiologist and anatomist.

The arterial supply to the gallbladder. Ob¬ serve that the cystic artery usually branches from the right hepatic artery. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Mens chert, 1975.)

Fig. 8-56.

BRANCHES OF THE HEPATIC ARTERY. The hepatic artery gives rise to the right gastric, the gastroduodenal, the right hepatic, the left hepatic, and the middle hepatic arteries. right gastric artery. The right gastric artery is much smaller and less constant than the left gastric (Figs. 8-55; 8-57). It arises with about equal frequency from the com¬ mon hepatic artery (40%) or the left hepatic (40.5%). It may arise, however, from the gas¬ troduodenal (8%) or even the right (5.5%) or middle (5%) hepatic arteries. The vessel passes between the layers of the lesser omentum to the pylorus, which it supplies with branches. It runs to the left along the lesser curvature of the stomach, supplying an extensive area with anterior and poste¬ rior branches, and anastomoses with the dorsal branch of the left gastric artery. GASTRODUODENAL ARTERY. The gastroduodenal artery arises from the common hepatic trunk, usually about halfway between its celiac origin and its division into the hepatic branches (Figs. 8-55; 8-57). It may arise from

736

THE ARTERIES

Fig. 8 57.

The celiac artery and its branches; the stomach has been raised and the peritoneum removed.

the left hepatic artery (11%), the right hepatic (7%), the middle hepatic (1%), or more rarely from the celiac or superior mesenteric artery. It is important to note that at times the gastroduodenal artery may arise from a hepatic artery that is the sole blood supply to one of the lobes of the liver. Its ligation, therefore, should always be considered in relation to its origin. The gastroduodenal artery is a short but thick vessel, and it usually lies to the left of the common bile duct. It then crosses the duct either dorsally or ventrally and de¬ scends behind the first part of the duodenum and in front of the neck of the pancreas to the lower border of the junction between the pylorus and the first part of the duodenum. After giving off branches to the pyloric end of the stomach, the pancreas, and the supra¬ duodenal and retroduodenal branches, the gastroduodenal artery ends by dividing into the right gastroepiploic and superior pan¬ creaticoduodenal arteries.

The supraduodenal artery, when present, frequently arises from the retroduodenal or gastroduodenal (but may arise from the common or proper hepatic, the right or left hepatic, the superior pancreaticoduodenal, or the right gastric). It is distributed to the upper, anterior, and posterior surfaces of the first 3 cm of the superior (first) part of the duodenum. The retroduodenal artery also arises from the gastroduodenal above the duodenum, but may arise from one of the hepatic ar¬ teries (10%). It descends behind the duode¬ num along the left side of the common bile duct, crosses anterior to the supraduodenal portion of the duct, and forms the U-shaped dorsal pancreaticoduodenal arcade. This ar¬ cade supplies branches to all four parts of the duodenum, to the head of the pancreas, and to the common bile duct. The retroduo¬ denal artery anastomoses with a dorsal branch of the inferior pancreaticoduodenal from the superior mesenteric artery.

ARTERIES OF THE THORAX AND ABDOMEN

The right gastroepiploic artery is the larger of the two terminal branches of the gastroduodenal and is much larger than the left gastroepiploic artery (Figs. 8-55; 8-57). It passes from right to left along the greater curvature of the stomach at a somewhat var¬ iable distance from the border of the organ. It lies between the two layers of the gastro¬ colic ligament or the ventral two layers of the greater omentum when these are not adherent to the colon. It gives off a large as¬ cending pyloric branch near its origin, and at its termination usually anastomoses with the left gastroepiploic branch of the splenic artery. It supplies a number of ascending gastric branches to the stomach and de¬ scending branches to the greater omentum. These latter long anterior epiploic branches extend around the free border of the omen¬ tum and, in the dorsal layer of the omentum, may anastomose with other gastric or with pancreatic arteries. The superior pancreaticoduodenal artery arises from the gastroduodenal artery as the latter passes dorsal to the first part of the duodenum (Figs. 8-57; 8-58). It forms a loop on the anterior surface of the pancreas and runs along the groove between the pancreas and the descending (second) portion of the duodenum. The vessel is embedded within the substance of the pancreas and, dorsal to the head of the pancreas, anastomoses with the inferior pancreaticoduodenal artery, a

737

branch of the superior mesenteric artery. The loop supplies branches to the ventral surface of the distal three parts (descending, transverse, and ascending) of the duodenum. The ventral pancreaticoduodenal arcade, formed by the anastomosis of the superior and inferior pancreaticoduodenal arteries, supplies numerous branches to the pancreas and duodenum (Fig. 8-58). right hepatic artery. Near the porta hepatis and beyond the origin of the gastro¬ duodenal artery, the right hepatic artery most frequently branches from the proper hepatic artery (Figs. 8-55 to 8-57). Aberrant right hepatic arteries have been found, how¬ ever, in about one-quarter of cadavers stud¬ ied. In over three-fifths of the bodies show¬ ing an anomalous origin for the right hepatic, the vessel arises from the superior mesenteric artery. The remainder may arise directly from the aorta, the celiac trunk, the gastroduodenal, or even the left hepatic. At its origin from the proper hepatic ar¬ tery, the right hepatic artery usually lies an¬ terior to the portal vein and crosses dorsal to the hepatic duct to enter the cystic triangle (of Calot1), which is bounded by the com¬ mon hepatic duct on the left, the cystic duct on the right, and the hilum of the liver above. The right hepatic then gives off the cystic artery and finally divides into two 'Jean F. Calot (1861-1944): A French surgeon.

Common

Ant. and post, superior pancreaticoduodenal arteries

Fig. 8-58. The arterial supply to the pancreas. Note that the head of the pancreas receives the anterior and posterior superior pancreaticoduodenal arteries from the gastroduodenal, whereas the body and tail of the pancreas receive the dorsal, great, and caudal pancreatic branches from the splenic artery. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, 1975.)

738

THE ARTERIES

main branches before entering the right lobe of the liver. The cystic artery usually arises from the right hepatic artery to the right of the he¬ patic duct and within the cystic triangle (for boundaries, see p. 737). Normally it courses a short distance along the cystic duct to reach the neck of the gallbladder (Figs. 8-55; 8-56). At this site the artery divides into a superfi¬ cial branch, which supplies the free perito¬ neal surface, and a deep branch, which sup¬ plies the posterior surface of the gallbladder, embedded in the liver. The two branches anastomose and supply twigs to the adjacent liver substance. There was only a single cystic artery in 75% of the bodies studied, whereas in 25% there was an accessory cystic artery. Al¬ though 82% of the cystic arteries arose within the cystic triangle, 18% arose to the left of the hepatic duct and not in the tri¬ angle. These latter vessels had to cross (ei¬ ther in front of or behind) the hepatic duct to reach the gallbladder. In most instances in which there were two cystic arteries, they served as superficial and deep vessels, and both generally arose within the cystic tri¬ angle. However, the superficial vessel was more variable than the deep and, at times, was observed originating from the right he¬ patic to the left of the duct or from another artery. In only 5% of cases studied did the cystic artery arise from some vessel other than the right hepatic artery. In these, it arose from the proper hepatic artery or, very rarely, from the gastroduodenal artery. left hepatic artery. The left hepatic ar¬ tery usually divides into two branches, an upper and a lower, supplying twigs to the capsule of the liver and the caudate lobe be¬ fore entering the substance of the left lobe (Figs. 8-55; 8-56). Aberrant left hepatic arteries are found in about 25% of bodies studied. In these in¬ stances, the aberrant vessel was the only ar¬ tery to the left lobe of the liver in about 60%, whereas in the remaining 40% the aberrant vessel was an accessory left hepatic artery. Most of the aberrant left hepatic arteries arose from the left gastric artery. middle hepatic artery. The middle he¬ patic artery enters the fossa for the round ligament and accompanies the middle he¬ patic duct to the quadrate lobe. It is the prin¬ cipal supply for this lobe and sends twigs to the round ligament and sometimes to the left

lobe. The middle hepatic artery arises from the right hepatic in 45% of cases, from the left hepatic in 45%, and from other sources in 10%. Splenic (or Lienal) Artery

The splenic or lienal artery is the largest branch of the celiac, and it passes horizon¬ tally to the left along the pancreas to reach the spleen. It varies from 8 to 32 cm in length and is usually tortuous (Figs. 8-55; 8-57; 8-58). The first part, before it reaches the pancreas, forms a short arc, which swings down and to the right, then across the aorta to the upper border of the pancreas. The second part lies along a groove in the upper part of the dorsal surface of the body of the pancreas. It is the most tortuous and undulating part and has one or more loops or coils, but seldom courses far from the pancreas. The third part leaves the upper border of the pancreas to cross obliquely the anterior surface of the pancreas. At this point the vessel divides into its superior and inferior arteries in most subjects. The fourth part courses between the tail of the pancreas and the hilum of the spleen, and usually the superior and inferior vessels divide into five or more terminal branches at the splenic hilum. The splenic artery, lying dorsal to the stomach, is covered by the peritoneum of the dorsal wall of the omental bursa. Its fourth part crosses anterior to the upper third of the left kidney and enters the splenic hilum by passing with the splenic vein in the sub¬ stance of the lienorenal ligament. BRANCHES OF THE SPLENIC ARTERY. The splenic artery generally supplies blood to three organs—the pancreas, the stomach, and the spleen. Its branches are the pancre¬ atic, left gastroepiploic, short gastric, and splenic. pancreatic branches. In addition to numerous twiglike branches to the neck, body, and tail of the pancreas, the splenic artery gives rise to three larger pancreatic vessels: the dorsal pancreatic, the great pan¬ creatic (arteria pancreatica magna), and the caudal pancreatic (arteria caudae pancreatis) arteries (Fig. 8-58). The dorsal pancreatic artery frequently arises from the first part of the splenic (39%), but it commonly has other origins, such as from the celiac (22%), one of the hepatic ar¬ teries (19%), the superior mesenteric (14%),

ARTERIES OF THE THORAX AND ABDOMEN

or the gastroduodenal (2%). It gives a number of twigs to the neck and body of the pan¬ creas. It has two small right branches, one curving ventrally to supply the head of the pancreas and anastomosing with branches of the gastroduodenal; the other supplies the uncinate process with a plexus of vessels that anastomoses with the inferior pan¬ creaticoduodenal artery. A branch often courses interiorly to anastomose with supe¬ rior mesenteric branches below the pan¬ creas. The principal left branch is of consid¬ erable size and becomes the transverse pancreatic artery. This latter vessel takes a course to the left along the dorsocaudal sur¬ face of the pancreas for about two-thirds of its length and enters the substance of the gland to anastomose with other pancreatic branches from the splenic artery. It runs par¬ allel to the main pancreatic duct for some distance, supplying it with branches. Its other long and short branches descend in the dorsal layer of the greater omentum as the posterior epiploic arteries, which anasto¬ mose with the anterior epiploics from the gastroepiploic arcade. The great pancreatic artery (arteria pancreatica magna) arises from the second part of the splenic artery (Fig. 8-58). It is the largest pancreatic branch (2 to 4 mm diame¬ ter) and enters the left part of the body of the gland obliquely. It branches into right and left vessels. These vessels help the trans¬ verse splenic artery to supply the main pan¬ creatic duct, and they anastomose with other pancreatic arteries. The caudal pancreatic artery (arteria caudae pancreatis) arises from the third part of the splenic artery or one of its terminal branches (Fig. 8-58). It supplies vessels to the tail of the pancreas, anastomoses with the great and dorsal pancreatic branches, and supplies vessels to an accessory spleen when one is present. LEFT GASTROEPIPLOIC ARTERY. The left gastroepiploic artery is the largest branch from the splenic artery and arises from its third part or from its inferior terminal artery (Figs. 8-55; 8-57). It reaches the stomach through the pancreaticolienal and gastro¬ lienal ligaments and courses along the greater curvature of the stomach from left to right within the anterior part of the greater omentum. Its branches are distributed to both surfaces of the stomach and to the greater omentum and anastomose with both

739

gastric and epiploic branches of the right gastroepiploic artery. short gastric arteries. The short gas¬ tric arteries consist of five to seven small branches, which arise near the end of the splenic artery and from its terminal divi¬ sions (Fig. 8-57). They pass from left to right, between the layers of the gastrolienal liga¬ ment, and are distributed along the greater curvature of the fundus and cardiac end of the stomach. They anastomose with branches of the left gastric, left gastroepi¬ ploic, and inferior phrenic arteries. splenic branches. The splenic artery divides about 3.5 cm from the spleen into a superior and an inferior terminal branch. These terminal branches may divide into several branches before entering the spleen, and there may even be intermediate branch¬ ing. Division of the inferior terminal artery may be more complex than that of the supe¬ rior, and it may give origin to the left gastroepiploic and inferior polar arteries. Arteries to the poles of the spleen are of fre¬ quent occurrence. The superior polar artery usually has its origin from the main splenic artery, or it may come directly from the ce¬ liac axis. Inferior polar arteries are more fre¬ quent than superior and arise most fre¬ quently from the left gastroepiploic, but may come from the splenic or inferior terminal branches. Cross anastomoses between the larger branches at the hilum are common. SUPERIOR MESENTERIC ARTERY

The superior mesenteric artery is a large vessel that supplies the whole length of the small intestine except the superior part of the duodenum (Figs. 8-54; 8-57; 8-59; 8-62). It also supplies the cecum and the ascending part of the colon and about one-half of the transverse part of the colon (Fig. 8-59). It arises from the anterior surface of the aorta, about 1.25 cm below the celiac artery, at the level of the first lumbar vertebra, and is crossed at its origin by the splenic vein and the neck of the pancreas. The superior mes¬ enteric artery then passes downward and forward, anterior to the uncinate process of the head of the pancreas and horizontal part of the duodenum, descending between the layers of the mesentery to the right iliac fossa. Here it is considerably diminished in size and anastomoses with one of its own branches, the ileocolic artery. In its descent

740

THE ARTERIES

Fig. 8-59.

The superior mesenteric artery and its branches.

it crosses ventral to the inferior vena cava, the right ureter, and the psoas major muscle, and forms an arch, the convexity of which is directed forward and downward to the left side. It is accompanied by the superior mes¬ enteric vein, which lies to its right side (Fig. 8-59), and it is surrounded by the superior mesenteric plexus of nerves. Occasionally, the superior mesenteric artery arises from the aorta by a common trunk with the celiac trunk. Branches of the Superior Mesenteric Artery

The branches of the superior mesenteric artery supply the head of the pancreas, the duodenum, the jejunum and ileum, the cecum and appendix, the ascending and transverse colon, and about half of the de¬ scending colon. They are the:

Inferior pancreaticoduodenal Jejunal and Ileal Ileocolic Right colic Middle colic Inferior Pancreaticoduodenal Artery

The inferior pancreaticoduodenal artery arises from the superior mesenteric or from its first jejunal branch, opposite the upper border of the horizontal part of the duo¬ denum (Figs. 8-57; 8-58). It courses to the right and frequently divides into anterior and posterior superior pancreaticoduodenal branches. The anterior branch ascends in front of the head of the pancreas to anasto¬ mose with the anterior branch of the supe¬ rior pancreaticoduodenal. The posterior branch ascends on the dorsal surface of the head of the pancreas to anastomose with the

ARTERIES OF THE THORAX AND ABDOMEN

posterior branch of the superior pancreatico¬ duodenal. From these vessels branches are distributed to the head of the pancreas and to the descending and horizontal parts of the duodenum. Jejunal and Ileal Arteries

The jejunal and ileal arteries total about 12 to 15 in number (Figs. 8-59; 8-62). These intestinal vessels arise from the convex side of the superior mesenteric artery and are distributed to the jejunum and all of the ileum except its terminal portion. They run nearly parallel to one another between the layers of the mesentery, each vessel dividing into two branches. These unite with adja¬ cent branches, forming a series of arches, the convexities of which are directed toward the intestine (Fig. 8-60). Branches from this first set of arches unite with similar branches from above and below, thus forming a sec¬ ond series of arches. In the ileal region the intestinal arteries may form a third, a fourth, or even a fifth series of arches, which dimin¬

741

ish in size as they approach the intestine. In the short, upper jejunal part of the mesen¬ tery only one set of arches exists (Fig. 8-60), but more distally in the ileum, as the depth of the mesentery increases, multiple layers of arches or arcades are developed. From the terminal arches arise numerous small straight vessels, called vasa recti, which en¬ circle the intestine and ramify between its coats. From the intestinal arteries small branches are given off to the lymph nodes and other structures between the layers of the mesentery. Ileocolic Artery

The ileocolic artery is the most inferior of the vessels that arise from the right side of the superior mesenteric artery (Figs. 8-59; 8-61). It passes downward and to the right toward the right iliac fossa, where it divides into a superior and an inferior branch. The superior branch of the ileocolic artery passes to the right behind the peritoneum and ascends to about the middle of the as¬ cending colon, where it anastomoses with

Fig. 8-60. a small loop of jejunum showing the distribution of a jejunal artery coursing in the mesentery. Note that only one or two layers of arterial arches are formed by branches of the jejunal artery before the long vasa recti branch toward the intestine. (From an injected preparation of Hamilton Drummond.)

742

THE ARTERIES

the descending branch of the right colic ar¬ tery (Figs. 8-59: 8-61). The inferior branch of the ileocolic artery courses toward the supe¬ rior border of the ileocolic junction and di¬ vides into colic, cecal, appendicular, and ileal branches (Fig. 8-61). The colic branch passes upward along the ascending colon to supply several centime¬ ters of its most proximal part. The anterior and posterior cecal are distributed to the front and back of the cecum. The appendic¬ ular artery (Fig. 8-61) descends dorsal to the termination of the ileum and enters the mes¬

entery of the vermiform appendix, called the mesoappendix. Although the orientation of the appendix in the lower right quadrant is quite variable, the vessel courses along the free margin of the mesoappendix, ending in several branches that supply the organ. One of these is a recurrent branch, which sup¬ plies the posterior surface of the junction of the appendix with the cecum. The ileal branch courses to the left and upward along the distal part of the ileum, supplying it and anastomosing with the termination of the superior mesenteric.

Fig. 8-61. The branches of the iliocolic artery supplying the cecum and the appendix. Lower left insert shows that the appendix may extend in virtually any direction from the cecum. In nearly 65% of cases studied, it projects superiorly behind the cecum and in about 31% inferomedially, as drawn in the larger figure above.

ARTERIES OF THE THORAX AND ABDOMEN

743

Middle colic artery

Superior mesenteric artery

Left common iliac artery and vein

Jejunal branches Inferior mesenteric artery

Ileal branches

Sigmoid arteries

Superior rectal artery

Middle sacral artery

Middle rectal artery

Inferior rectal artery

Fig. 8-62.

The arterial supply to the large colon.

Right Colic Artery

The right colic artery arises directly from the right side of the superior mesenteric ar¬ tery, or from a stem common to it and the ileocolic (Figs. 8-59; 8-62). It passes to the right, behind the peritoneum and anterior to the right testicular or ovarian vessels, the right ureter, and the psoas major muscle, toward the middle of the ascending colon. Sometimes the vessel lies at a higher level, and crosses the descending part of the duo¬ denum and the caudal end of the right kid¬ ney. At the ascending colon, the right colic artery divides into a descending branch, which anastomoses with the ileocolic, and

an ascending branch, which anastomoses with the middle colic. These branches form arches, from the convexity of which vessels are distributed to the ascending colon, as far as the right colic flexure. Middle Colic Artery

The middle colic artery arises from the superior mesenteric just below the pancreas (Figs. 8-59; 8-62) and, passing anteriorly be¬ tween the layers of the transverse meso¬ colon, divides into right and left branches. The right branch anastomoses with the right colic, and the left branch with the left colic, which arises from the inferior mesenteric.

744

THE ARTERIES

The arches thus formed are placed about 4 cm from the transverse colon, to which they distribute branches.

the arches formed by these anastomoses, branches are distributed to the descending colon and the left part of the transverse colon.

INFERIOR MESENTERIC ARTERY

The inferior mesenteric artery supplies nearly the left half of the transverse colon, the whole of the descending colon, the sig¬ moid colon, and the greater part of the rec¬ tum (Figs. 8-54; 8-62; 8-63). It is smaller than the superior mesenteric artery and arises from the aorta, about 3 or 4 cm above its bi¬ furcation into the common iliac arteries. The origin of the inferior mesenteric artery is close to the lower border of the horizontal part of the duodenum, at the level of the middle of the third lumbar vertebra. The vessel descends behind the peritoneum, lying initially in front of, and then on the left side of, the aorta. It crosses the left common iliac artery, medial to the left ureter, and is continued into the lesser pelvis as the supe¬ rior rectal artery, descending between the two layers of the sigmoid mesocolon and ending on the upper part of the rectum.

Branches of the Inferior Mesenteric Artery

The branches of the inferior mesenteric artery are initially directed to the left or in¬ teriorly. They are the: Left colic Sigmoid Superior rectal

Left Colic Artery

The left colic artery courses to the left, deep to the peritoneum and anterior to the psoas major muscle (Fig. 8-62), and after a short but variable course, it divides into an ascending and a descending branch. The main stem of the artery or its branches cross the left ureter and left testicular or ovarian vessels. The ascending branch crosses in front of the left kidney and ends, between the two layers of the transverse mesocolon, by anastomosing with the middle colic ar¬ tery. The descending branch courses down toward the sigmoid flexure and anasto¬ moses with the highest sigmoid artery. From

Sigmoid Arteries

Two or three sigmoid arteries branch from the continuing stem of the superior mesen¬ teric artery and run obliquely downward and to the left behind the peritoneum and ventral to the psoas major muscle, the ureter, and the testicular or ovarian vessels (Figs. 8-62; 8-63). Their branches supply the caudal part of the descending colon and the sigmoid colon, anastomosing above with the left colic artery and below with the superior rec¬ tal artery.

Superior Rectal Artery

The superior rectal artery (sometimes still called the superior hemorrhoidal artery) is the continuation of the inferior mesenteric artery. It descends into the pelvis between the layers of the sigmoid mesentery and crosses the left common iliac vessels (Figs. 8-62; 8-63). Opposite the third sacral verte¬ bra, it divides into two branches, which de¬ scend one on each side of the rectum and, about 10 or 12 cm above the anus, separate into several small branches. These pierce the muscular coat of the bowel and course downward as straight vessels that are placed at regular intervals in the wall of the gut, between its muscular and mucous coats, to the level of the internal anal sphincter. From this site they form a series of loops around the lower end of the rectum and anastomose with the middle rectal branches of the in¬ ternal iliac and with the inferior rectal branches of the internal pudendal (Figs. 8-62; 8-63). clinical significance. A rich anastomosis of arterial branches that supply the large intestine is formed from the ileocolic, right colic, middle colic, left colic, and sigmoid arteries. These vessels join in the formation of a series of interconnecting arcades, the pattern of which gives rise to a continuous ves¬ sel, called the marginal artery of Drummond, which courses along the inner perimeter of the large colon, extending from the ileocolic junction to the rectum. From the marginal artery branch straight vessels (arteriae rectae), which are directed to the

ARTERIES OF THE THORAX AND ABDOMEN

745

Inferior mesenteric artery Aorta

Sigmoid arteries

Common iliac artery

Middle sacral artery —

Superior rectal artery

Lateral sacral artery External iliac artery Internal iliac artery

Coccygeus muscle Middle rectal artery Levator ani muscle Ampulla of rectum Internal pudendal artery

Inferior rectal artery Anal canal

Fig. 8-63. The inferior mesenteric artery and the blood supply to the sigmoid colon, rectum, and anal canal. Note that the rectum receives its blood supply from three different sources. These are the superior rectal artery (1) from the inferior mesenteric artery; the middle rectal artery (2) from the internal iliac artery; and the inferior rectal artery (3) from the internal pudendal artery.

organ. The clinical benefit of this vascular pattern is appreciated by the surgeon, who frequently is re¬ quired to ligate one or more branches of the mesen¬ teric vessels in the resection of bowel and yet main¬ tain the vascular integrity of the remainder of the large colon. A critical point of anastomosis for the mainte¬ nance of the vascular supply to the distal sigmoid colon, however, is found between the fields supplied by the sigmoid vessels and the superior rectal artery. The pattern of blood supply to this region must be studied carefully because high ligation of the supe¬ rior rectal artery may, in fact, result in the loss of vascularization to a portion of the distal sigmoid colon.

MIDDLE SUPRARENAL ARTERIES

Although there are three pairs of suprare¬ nal arteries—superior, middle, and inferior, only the middle set of vessels arises directly from the aorta. The superior arises from the inferior phrenic, and the inferior suprarenal arises from the renal arteries. The middle suprarenal arteries are two small vessels that arise, one from each side of the aorta, oppo¬ site the superior mesenteric artery. They pass laterally and slightly upward, over the crura of the diaphragm, to the suprarenal glands, where they anastomose with supra-

746

THE ARTERIES

renal branches from the inferior phrenic and renal arteries. In the fetus, these arteries are large. RENAL ARTERIES

The renal arteries are two large trunks that arise, one on each side of the aorta, immedi¬ ately below the superior mesenteric artery at the level of the disc between the first and second lumbar vertebrae (Fig. 8-54). Each is directed across the crus of the diaphragm of the corresponding side, thus forming nearly a right angle with the aorta. The right renal artery is longer than the left because of the position of the aorta. It passes behind the inferior vena cava, the right renal vein, the head of the pancreas, and the descending part of the duodenum. The left renal artery arises somewhat more superiorly than the right. It courses dorsal to the left renal vein, the body of the pancreas, and the splenic vein, and is itself crossed by the inferior mesenteric vein. Before reaching the hilum of the kidney, each artery divides into four or five branches, most of which lie between the renal vein and the ureter. At the renal hilum, the renal vein is most anterior and the pelvis of the kidney is most posterior. The renal artery lies between the two; however, a few of its branches usually enter the kidney behind the renal pelvic origin of the ureter. Each renal artery gives off some small in¬ ferior suprarenal branches to the suprarenal gland, the ureter, and the surrounding cellu¬ lar tissue and muscles. One or two accessory renal arteries are frequently found (23%), especially on the left side. These usually arise from the aorta and come off somewhat more frequently above the main renal artery than below. Instead of entering the kidney at the hilum, they usu¬ ally pierce the upper or lower part of the organ. TESTICULAR ARTERIES

The testicular arteries are two long slen¬ der vessels that arise from the anterior as¬ pect of the aorta a little below the renal ar¬ teries (see Fig. 8-54). Each passes obliquely downward and laterally behind the perito¬ neum, resting on the psoas major muscle. The right testicular artery lies anterior to the inferior vena cava and behind the horizontal portion of the duodenum, the middle colic and ileocolic arteries, and the terminal part

of the ileum. The left testicular artery courses behind the left colic and sigmoid arteries and the sigmoid colon. Each testicu¬ lar artery crosses obliquely over the ureter and distal part of the external iliac artery to reach the deep inguinal ring (Fig. 8-70). Pass¬ ing through the ring, the vessel accompanies the other constituents of the spermatic cord along the inguinal canal to the scrotum. Along its course, the testicular artery be¬ comes tortuous and divides into several branches. Two or three of these accompany the ductus deferens and supply the epididy¬ mis, anastomosing with the artery of the ductus deferens. Others pierce the back part of the tunica albuginea and supply the sub¬ stance of the testis. The testicular artery sup¬ plies one or two small branches to the ureter and, in the inguinal canal, gives one or two twigs to the cremaster muscle. OVARIAN ARTERIES

In the female the ovarian arteries are the homologues of the testicular arteries in the male. They are shorter than the testicular, and because they supply the ovaries, they do not pass out of the abdominal cavity. The origin and course of the first part of each ar¬ tery are the same as those described for the testicular. Arriving at the superior inlet to the lesser pelvis, the ovarian artery passes medially between the two layers of the sus¬ pensory ligament of the ovary and of the broad ligament of the uterus, to be distributed to the ovary. Small branches supply the ure¬ ter and the uterine tube, and one passes on to the side of the uterus and anastomoses with the uterine artery. Other branches are dis¬ tributed to the round ligament of the uterus, through the inguinal canal, and reach the skin of the inguinal region and the labium majus. In the early stages of development, the testes or ovaries lie by the side of the ver¬ tebral column, below the kidneys, and the testicular or ovarian arteries are short. When the gonads descend into the scrotum or lesser pelvis, their arteries gradually lengthen. INFERIOR PHRENIC ARTERIES

The inferior phrenic arteries are two small vessels that supply the diaphragm, but their origin is subject to some variation (see Fig.

ARTERIES OF THE THORAX AND ABDOMEN

8-54). They may arise separately from the anterior aspect of the aorta, immediately above the celiac artery. In an almost equal number of instances, however, these vessels have been found arising from the celiac trunk. In nearly one-third of cadavers stud¬ ied, the two inferior phrenic arteries arise by means of a common vessel instead of sepa¬ rately, and this may come from either the aorta or the celiac trunk. Less frequently these vessels may stem from the renal or ac¬ cessory renal arteries, the left gastric artery, the hepatic arteries, and even the testicular arteries. From their origin, the inferior phrenic ar¬ teries diverge from each other, cross the crura of the diaphragm, and course laterally in an oblique direction upon the abdominal surface of the diaphragm. The left phrenic artery passes behind the esophagus and then courses anteriorly on the left side of the esophageal hiatus. The right phrenic artery passes behind the inferior vena cava and then along the right side of the diaphrag¬ matic foramen, which transmits that vein. Near the dorsal part of the central tendon of the diaphragm, each vessel divides into a medial and a lateral branch. The medial branch curves ventrally and anastomoses with the same vessel of the opposite side, and with the musculophrenic and peri¬ cardiacophrenic arteries. The lateral branch passes toward the side of the thorax and anastomoses with the lower posterior inter¬ costal arteries and with the musculophrenic artery. The lateral branch of the right phrenic gives off a few vessels to supply the wall of the inferior vena cava, and the left inferior phrenic gives off some branches to the esophagus. Each inferior phrenic artery gives origin to several superior suprarenal branches to the suprarenal gland of its own side. The spleen and the liver also receive a few twigs from the left and right vessels respectively.

747

arteries take their place. The lumbar arteries run laterally and posteriorly on the bodies of the lumbar vertebrae, behind the sympa¬ thetic trunk, to the intervals between adja¬ cent transverse processes of the vertebrae and are then continued into the abdominal wall. The right lumbar arteries pass behind the inferior vena cava, and the upper two on each side course dorsal to the corresponding crus of the diaphragm. The arteries of both sides pass beneath the tendinous arches, ex¬ tending across the bodies of the lumbar ver¬ tebrae, which give origin to slips of the psoas major muscle. The vessels are then contin¬ ued behind this muscle and the lumbar plexus, and cross the quadratus lumborum, the upper three arteries running behind and the last usually in front of that muscle. At the lateral border of the quadratus lumborum. they pierce the posterior aponeurosis of the transversus abdominis and are carried ante¬ riorly between this muscle and the internal oblique. They anastomose with the lower posterior intercostal, the subcostal, the ilio¬ lumbar, the deep iliac circumflex, and the inferior epigastric arteries and with each other. BRANCHES OF THE LUMBAR ARTERIES. In the interval between the adjacent transverse processes, each lumbar artery gives off a dorsal ramus, which is continued backward between the transverse processes and is dis¬ tributed to the muscles and skin of the back. The dorsal ramus also furnishes a spinal branch, which enters the vertebral canal and is distributed similarly to spinal branches of the dorsal rami of the posterior intercostal arteries. Muscular branches are supplied from each lumbar artery and from its poste¬ rior ramus to the neighboring muscles. The lumbar arteries also send vertebral branches to the bodies of the lumbar vertebrae and small renal branches to the capsules of the kidney. MIDDLE SACRAL ARTERY

LUMBAR ARTERIES

The lumbar arteries are in series with the posterior intercostal arteries. There are usu¬ ally four on each side, and they arise from the dorsum of the aorta, opposite the bodies of the upper four lumbar vertebrae. A small fifth pair arising from the middle sacral ar¬ tery is occasionally present, but more fre¬ quently lumbar branches of the iliolumbar

The middle sacral artery is a small vessel that arises from the dorsal aspect of the aorta a short distance above the bifurcation (Figs. 8-54; 8-62; 8-63). At times it arises from one of the two fifth lumbar arteries. It descends in the midline anterior to the fourth and fifth lumbar vertebrae, the sacrum, and the coc¬ cyx. At the tip of the coccyx, the middle sac¬ ral artery reaches the coccygeal body, which

748

THE ARTERIES

is a nodular structure consisting of many ar¬ teriovenous anastomoses intermeshed in a dense connective tissue. On the last lumbar vertebra it anastomoses with the lumbar branch of the iliolumbar artery; anterior to the sacrum, it anastomoses with the lateral sacral arteries and sends small vessels into the anterior sacral foramina. It is crossed by the left common iliac vein and is accompa¬ nied by a pair of venae comitantes. These unite to form a single vessel, which opens into the left common iliac vein.

Arteries of the Pelvis, Perineum, and Gluteal Region The abdominal aorta terminates at its bi¬ furcation into the two common iliac arteries (Figs. 8-54; 8-64; 8-65; 8-75). On each side these vessels divide and subdivide, eventu¬ ally to supply the organs and walls of the pelvis, the perineum, and the gluteal region.

COMMON ILIAC ARTERIES

Just to the left side of the body of the fourth lumbar vertebra, the abdominal aorta divides into the two common iliac arteries. These vessels diverge laterally as they de¬ scend from the end of the aorta, and each divides, opposite the intervertebral fibrocartilage between the last lumbar vertebra and the sacrum, into an external and an internal iliac artery. The former vessel supplies a good deal of the lower limb, while the latter vessel supplies the viscera and walls of the pelvis. In addition to the terminal internal and external iliac branches, each common iliac artery gives off small branches to the perito¬ neum, the psoas major muscle, the ureter, and the surrounding areolar tissue, and oc¬ casionally gives origin to the iliolumbar or accessory renal arteries. Right Common Iliac Artery The right common iliac artery is usually somewhat longer than the left and passes more obliquely across the body of the last lumbar vertebra (Figs. 8-54; 8-65). It meas¬ ures about 5 cm in length, and anterior to it

are the peritoneum, the loops of small intes¬ tine, branches of sympathetic nerves, and, at its point of division, the ureter. Posteriorly, it is separated from the bodies of the fourth and fifth lumbar vertebrae and the interven¬ ing disc by the terminations of the two com¬ mon iliac veins and the commencement of the inferior vena cava. More deeply between the fifth vertebra and the psoas major mus¬ cle are the obturator nerve, the lumbosa¬ cral sympathetic trunk, and the iliolumbar branch of the internal iliac artery. Laterally, it is in relation above with the inferior vena cava and below with the right common iliac vein and the psoas major muscle. Medial to its upper part is the left common iliac vein. Left Common Iliac Artery The left common iliac artery, being a little shorter and thicker than the right, measures about 4 cm in length (see Fig. 8-54). It is re¬ lated anteriorly to the peritoneum, loops of the small intestine, branches of sympathetic nerves, and the superior rectal artery. It is crossed at its point of bifurcation by the left ureter. Posteriorly are found the bodies of the fourth and fifth lumbar vertebrae and their intervening disc, and the disc between the fifth lumbar vertebra and the sacrum. Crossing behind the vessel between the fifth lumbar vertebra and the psoas major muscle are the lumbosacral sympathetic trunk, the obturator nerve, and the iliolumbar artery. Medial to the left common iliac artery are the left common iliac vein, the hypogastric plexus, and the middle sacral artery, while lateral to it is the psoas major muscle.

VARIATIONS RELATED TO THE COMMON

ILIAC AR¬

The point of origin of the common iliac arteries varies according to the bifurcation of the aorta. In three-quarters of a large number of cases, the aorta bifurcated either anterior to the fourth lum¬ bar vertebra or upon the disc between it and the fifth. The bifurcation is located, in one case out of nine, below, and in one out of eleven, above this point. In about 80% of cases studied, the aorta bi¬ furcated within 1.25 cm above or below the level of the crest of the ilium, but more frequently below than above. The point of division of the common iliac arteries into internal and external iliac branches varies greatly. In two-thirds of the cases studied, this divi¬ sion occurred between the last lumbar vertebra and the upper border of the sacrum, being above that point in one of eight cases and below it in one of six TERIES.

ARTERIES OF THE PELVIS, PERINEUM, AND GLUTEAL REGION

749

Abdominal aorta

Right common iliac Left common iliac

Middle sacral Iliolumbar Right internal iliac

Lateral sacral

Right external iliac

Superior gluteal

Umbilical Obturator

Inferior gluteal Internal pudendal Middle rectal

Inferior epigastric

Inferior vesical A. to ductus deferens Superior vesical

Medial umbilical ligament

Fig. 8-64.

The iliac arteries and their branches.

cases. The left common iliac artery divides lower than the right more frequently. The relative lengths of the two common iliac ar¬ teries also vary. The right common iliac was the longer in 37% of cases, the left in 31%; they were equal in 32%. The length of the arteries varied from 3.5 to 7.5 cm in 72% of the cases studied. Of the remaining 28%, 1 4% were shorter than 3.5 cm and 14% were longer than 7.5 cm. The shortest com¬ mon iliac artery measured only 1.25 cm, the longest 1 1 cm. In rare instances, the right common iliac has been absent, and the external and internal iliac ar¬ teries arose directly from the aorta. collateral circulation. The principal vessels contributing to collateral circulation after the appli¬ cation of a ligature to the common iliac are the anas¬ tomoses of (1) the middle rectal branch of the inter¬ nal iliac with the superior rectal from the inferior mesenteric, (2) the uterine, ovarian, and vesical ar¬ teries of the opposite side with the same vessels on the ligated side, (3) the lateral sacral artery from the internal iliac and the middle sacral artery from the aorta, (4) the inferior epigastric artery from the ex¬ ternal iliac with the internal thoracic artery, the lower posterior intercostal arteries, and the lumbar ar¬ teries, (5) the deep iliac circumflex from the external iliac artery and the lumbar arteries from the aorta, (6) the iliolumbar artery from the internal iliac with the last lumbar artery, and (7) the obturator artery, by means of its pubic branch, with the same vessel from the opposite side and with the inferior epigas¬ tric arteries, which anastomose with the superior epigastric arteries.

Internal Iliac Artery

The internal iliac artery, also known as the hypogastric artery, begins at the bifurcation of the common iliac, anterior to the sacroil¬

iac joint at the level of the lumbosacral disc (Figs. 8-64; 8-65; 8-75). It follows a short, curved course of about 4 cm, descending toward the greater sciatic foramen. Al¬ though it is an exceedingly variable artery in terms of the pattern of its branches, in slightly more than half the bodies it divides into an anterior trunk and a posterior trunk. It supplies the walls of the pelvis, the pelvic viscera, the buttock, the genital organs, and part of the medial thigh. The internal iliac artery is covered anteri¬ orly by peritoneum and in females is related to the ovary and uterine tube. It is also crossed by the ureter. Posterior to the vessel courses the internal iliac vein, the sacroiliac joint, and the lumbar contribution to the sac¬ ral plexus, called the lumbosacral trunk. Lat¬ eral to the internal iliac artery is the internal iliac vein, which separates the artery from the psoas major and the obturator nerve. Medial to the right artery are the terminal loops of the ileum, and medial to the left ar¬ tery is the flexure of the sigmoid colon as it becomes the rectum. In the fetus, the internal iliac artery is twice as large as the external iliac; it is the direct continuation of the common iliac. It ascends along the side of the bladder and runs superiorly on the inner aspect of the anterior wall of the abdomen to reach the umbilicus, converging toward the same ves¬ sel from the opposite side. Having passed through the umbilical opening, the two ar¬ teries, which are now called umbilical ar¬ teries, enter the umbilical cord and become

750

THE ARTERIES

coiled around the umbilical vein, to ramify ultimately in the placenta. After birth, when the placental circulation ceases, only the pelvic portion of the umbili¬ cal artery remains patent, becoming in the adult the internal iliac and first part of the superior vesical artery. The remainder of the vessel is converted into a solid fibrous cord, the medial umbilical ligament, which ex¬ tends from the pelvis to the umbilicus.

means of the pubic branch of the obturator artery and the same vessel from the opposite side; (5) be¬ tween the circumflex and perforating branches of the deep femoral artery and the inferior gluteal; (6) between the superior gluteal artery and the posterior branches of the lateral sacral arteries; (7) between the iliolumbar artery and the last lumbar; (8) be¬ tween the lateral sacral artery and the middle sacral; and (9) between the iliac circumflex and the iliolum¬ bar and superior gluteal arteries.

After ligature of the internal iliac artery, collateral circulation is accom¬ plished by anastomoses (1) of the ovarian artery from the aorta and the uterine artery; (2) between the vesical arteries of the opposite side and the same vessels on the ligated side; (3) between the middle rectal branches of the internal iliac and the superior rectal artery from the inferior mesenteric; (4) be¬ tween the obturator artery and the inferior epigastric and medial femoral circumflex arteries, and by

Branches of the Internal Iliac Artery

collateral circulation.

The branches of the internal iliac artery are subject to considerable variation in their origin. The division into anterior and poste¬ rior trunks is seldom complete, and any two branches may arise from a common trunk. However, the distribution to tissues and or¬ gans of the individual branches is more con-

Abdominal aorta

Common iliac a. Deep iliac circumflex a. Middle sacral a. Right ureter Int. iliac artery Iliolumbar a. Inferior epigastric a.

Superior gluteal a. Lateral sacral a

Ext. iliac a. Obturator a. Medial umbil. lig. Ductus deferens — Superior _ vesical a.

Inferior gluteal a. Internal pudendal a Sciatic nerve Middle rectal a. Inferior vesical a. Seminal vesicle

Left ureter Bladder

Rectum

Prostate gland

Fig. 8-65.

The right internal and external iliac arteries and their branches viewed from the left side. (From Benninghoff and Goerttler, 1975.)

ARTERIES OF THE PELVIS. PERINEUM. AND GLUTEAL REGION

stant, and the different vessels may be grouped as follows: visceral, anterior parie¬ tal, and posterior parietal.

Visceral Umbilical Inferior vesical Middle rectal Uterine Vaginal Anterior Parietal Obturator Internal pudendal Posterior Parietal Iliolumbar Lateral sacral Superior gluteal Inferior gluteal VARIATIONS IN THE BRANCHING PATTERN OF THE

In a series of 1 30 consecu¬ tive dissections, Ashley and Anson (1941) recorded the pattern of variation in the branching of the inter¬ nal iliac artery. In the most common pattern (58%), the inferior gluteal and internal pudendal arteries were derived from a common stem, and the umbili¬ cal and superior gluteal arteries arose above them by separate stems. In 17%, the inferior and superior gluteal arteries arose from one stem and the umbili¬ cal and pudendal arteries arose from another stem. In 10%, the internal pudendal, inferior gluteal, and umbilical arteries arose by a common stem, and the superior gluteal branched separately. In 8%, the umbilical and internal pudendal arteries arose sepa¬ rately above a common stem for the two gluteal ar¬ teries. In these instances the internal pudendal ar¬ tery appeared to be the continuation of the internal iliac, a condition described by some authors as a more primitive type found in lower animals. Five other patterns were described, but their appearance was less frequent than the above. The obturator was probably the most variable branch, and a few of its patterns are described with that artery. internal iliac artery.

UMBILICAL ARTERY

The umbilical arteries are generally the first of the visceral branches that arise from the internal iliac arteries (Fig. 8-64). During intrauterine life, these vessels form the prin¬ cipal channels from the fetal internal iliac arteries to the umbilical cord. By adulthood, most of the vessel on each side becomes a fibrous cord called the medial umbilical lig¬ ament; however, it does retain a patent lumen for a short distance beyond the inter¬ nal iliac artery. Just proximal to the site where the umbilical artery becomes obliter¬

751

ated, the umbilical artery on each side gives rise to several superior vesical branches which supply the bladder. It also may give rise to the artery of the ductus deferens and, at times, to the middle vesical artery as well. superior vesical arteries. From one to four small superior vesical arteries arise from the umbilical artery to supply the upper part of the bladder (Figs. 8-64; 8-65). In nearly 75% of cases, there are two or three superior vesical arteries on each side. artery of the ductus deferens. This slender vessel may arise directly from the umbilical artery, or from one of the superior vesical arteries, or from the middle vesical artery (Fig. 8-64). It accompanies the ductus in its course to the testis, where it anastomo¬ ses with the testicular artery. middle vesical artery. This vessel may arise directly from the umbilical artery or as a branch of the superior vesicle. It is distrib¬ uted to the fundus of the bladder and the seminal vesicles and anastomoses with the other vesical arteries. Frequently, one or more ureteric branches arise from the mid¬ dle vesical artery or the artery to the ductus deferens to supply the lower end of the ure¬ ter. These anastomose with other vessels that supply the more superior parts of the ureter. INFERIOR VESICAL ARTERY

The inferior vesical artery sometimes arises from the anterior trunk of the internal iliac artery in common with the middle rec¬ tal. It may, however, arise from a trunk in common with the internal pudendal and superior gluteal arteries, or as a branch from the internal pudendal (Fig. 8-65). It is usually a single branch and is distributed to the fun¬ dus of the bladder, the prostate, and the sem¬ inal vesicles. The branches to the prostate communicate with the corresponding ves¬ sels of the opposite side. MIDDLE RECTAL ARTERY

The middle rectal artery may arise from the anterior trunk of the internal iliac with the inferior vesical artery, but more fre¬ quently it arises with or from the internal pudendal artery or from the inferior gluteal artery (Figs. 8-64; 8-65). Only rarely is it com¬ pletely absent. It is distributed to the rectum, anastomosing with the inferior vesical and

752

THE ARTERIES

with the superior and inferior rectal arteries. It gives branches to the seminal vesicles and the prostate.

uterus, and from its terminal portion twigs are distributed to the uterine tube and the round ligament of the uterus before anasto¬ mosing with the ovarian artery (Fig. 8-66).

UTERINE ARTERY

The uterine artery generally arises from the medial surface of the anterior trunk of the internal iliac (Fig. 8-66). It continues medially on the levator ani toward the cer¬ vix of the uterus. At about 2 cm from the cer¬ vix it crosses above and in front of the ure¬ ter, to which it supplies a small branch. Reaching the side of the uterus, it ascends in a tortuous manner between the two layers of the broad ligament to the junction of the uterine tube and uterus. It then runs laterally toward the hilum of the ovary and ends by anastomosing with the ovarian artery. It sup¬ plies branches to the uterine cervix and oth¬ ers to the vagina. These latter vessels anasto¬ mose with branches of the vaginal arteries and form with them the median longitudinal vessels called the azygos arteries of the va¬ gina. There are usually two azygos arteries, one of which courses down the ventral and the other down the dorsal surface of the va¬ gina (Fig. 8-66). The uterine artery supplies numerous branches to the body of the

Fig. 8-66.

VAGINAL ARTERIES

The vaginal arteries are represented by one, two, or even three vessels which may arise directly from the anterior trunk of the internal iliac artery (Fig. 8-66). More fre¬ quently one or more of the vaginal arteries arises from the uterine artery or even from the inferior vesical artery. Approaching the vagina at its junction with the uterine cervix, the vaginal arteries then descend upon the vagina, supplying its mucous membrane. They send branches to the bulb of the vesti¬ bule, the fundus of the bladder, and the con¬ tiguous part of the rectum, and assist in forming the azygos arteries of the vagina (Fig. 8-66). OBTURATOR ARTERY

The obturator artery arises most fre¬ quently from the ventral or medial surface of the internal iliac artery or from one of its branches (Figs. 8-64; 8-65; 8-70; 8-74). It

The arteries of the female internal organs of reproduction as seen from behind.

ARTERIES OF THE PELVIS. PERINEUM. AND GLUTEAL REGION

courses ventrally on the lateral wall of the pelvis to the obturator canal, through which it courses as it leaves the pelvic cavity to reach the thigh, where it divides into ante¬ rior and posterior branches. Lateral to the obturator artery in the pelvis is the obturator fascia covering the obturator internus mus¬ cle. The vessel is crossed medially by the ureter and ductus deferens, and it is covered by the peritoneum. The obturator nerve ac¬ companies the artery and courses above the vessel, while the obturator vein courses below. Branches of the Obturator Artery

Within the pelvis, the obturator artery gives rise to iliac, vesical, and pubic branches. Outside the pelvis, the vessel di¬ vides at the margin of the obturator foramen into an anterior and a posterior branch, which encircle the foramen under cover of the obturator externus muscle. iliac branches. The iliac branches of the obturator artery ascend in the iliac fossa and supply the iliacus muscle and send nutrient vessels to the ilium; they also anastomose with branches of the iliolumbar artery. vesical branch. The vesical branch of the obturator courses medially and back¬ ward to help supply the bladder. pubic branch. The pubic branch arises from the obturator artery just before it leaves the pelvic cavity. This branch ascends upon the inside of the pubis and communi¬ cates with the same vessel from the opposite side and with the inferior epigastric artery. anterior branch. The anterior branch of the obturator artery courses ventrally on the outer surface of the obturator membrane and then curves downward along the ante¬ rior margin of the foramen. It distributes branches to the obturator externus, pectineus, the adductor muscles, and the gracilis, anastomosing with the posterior branch and with the medial femoral circumflex artery. posterior branch. The posterior branch of the obturator artery follows the posterior margin of the foramen and divides into two branches. One branch runs anteriorly on the inferior ramus of the ischium, where it anas¬ tomoses with the anterior branch of the ob¬ turator. The other branch gives twigs to the muscles attached to the ischial tuberosity and anastomoses with the inferior gluteal. It

753

also supplies the acetabular or articular branch, which enters the hip joint through the acetabular notch, ramifies in the fat at the bottom of the acetabulum, and sends a twig deep to the transverse acetabular liga¬ ment accompanying the ligament of the head of the femur. VARIATIONS OF THE OBTURATOR ARTERY. The ob¬ turator artery was found to arise from the internal iliac or one of its branches in nearly 70% of 320 bodies studied (Pick, Anson, and Ashley, 1942). It arose from the main vessel in 23%, from the ante¬ rior trunk in 20%, from the posterior trunk in 3%, from the superior gluteal in 1 1 %, from the inferior gluteal in 9%, and from the internal pudendal or external iliac in 2 or 3%. The origin of the obturator artery from the inferior epigastric artery occurred in 27% of cases. In these instances, the artery lies in contact with the external iliac vein. Its course toward the obturator canal is relevant clinically during oper¬ ations for the repair of a femoral hernia. If its course is lateral to the lacunar ligament, repair is relatively safe. If, however, the obturator artery curves along the free margin of the lacunar ligament, it can encir¬ cle the neck of a hernial sac and be injured during the hernial repair (Fig. 8-67).

INTERNAL PUDENDAL ARTERY

The internal pudendal artery (Figs. 8-64; 8-65; 8-68) supplies the perineum and exter¬ nal organs of generation, and although the course of the artery is the same in the two sexes, the vessel is smaller in the female than in the male, and the distribution of its branches somewhat different. Internal Pudendal Artery in the Male

The internal pudendal artery in the male courses downward and laterally toward the lower border of the greater sciatic foramen and emerges from the pelvis between the

Fig. 8-67. An obturator artery is shown arising from the inferior epigastric and following the free edge of the lacunar ligament to the obturator foramen.

754

THE ARTERIES

piriform and coccygeus muscles. It then crosses the ischial spine and courses through the medial part of the lesser sciatic foramen to enter a tunnel deep to the fascia of the obturator internus muscle called the puden¬ dal canal (of Alcock1). At this point the obtu¬ rator internus forms the lateral wall of the ischiorectal fossa, and the canal courses about 4 cm above the lower margin of the ischial tuberosity. The artery gradually ap¬ proaches the margin of the inferior ramus of the ischium, and then passes ventrally be¬ tween the two layers of the fascia of the uro¬ genital diaphragm. Continuing anteriorly along the medial margin of the inferior ramus of the pubis and about 1.25 cm dorsal •Benjamin Alcock (1801-unknown): An Irish anatomist who moved to America in 1855.

to the arcuate pubic ligament, it divides into the dorsal and deep arteries of the penis, but it may pierce the superficial fascia of the urogenital diaphragm before doing so (Fig. 8-68). RELATIONS OF THE MALE INTERNAL PUDENDAL AR¬

Within the pelvis, the internal pudendal ar¬ tery lies anterior to the piriformis muscle, the sacral plexus of nerves, and the inferior gluteal artery. Crossing the ischial spine, it is covered by the glu¬ teus maximus and overlapped by the sacrotuberous ligament. At this latter side, the pudendal nerve lies medial to the artery, and the nerve to the obturator internus muscle lies lateral to the artery. In the peri¬ neum, the internal pudendal artery lies on the lateral TERY.

wall of the ischiorectal fossa in the pudendal canal, formed by the splitting of the obturator fascia. It is accompanied by a pair of companion veins and the pudendal nerve.

Scrotum Posterior scrotal artery

Perineal artery Ischiocavernosus m.

Deep transverse perineal m.

s uperficial

transverse perineal m.

Internal pudendal artery Pudendal nerve Inferior rectal artery

Deep artery of penis Dorsal artery of penis Artery to bulb and urethra Superior layer of urogenital diaphragm Internal pudendal artery External anal sphincter Levator ani m. Obturator internus m

Sacrotuberous ligament

Fig. 8-68.

The superficial branches of the internal pudendal artery in the male urogenital region.

ARTERIES OF THE PELVIS

BRANCHES OF THE MALE INTERNAL PUDENDAL

Although a few muscular branches arise from the internal pudendal artery within the pelvis, most branches supply structures in both the anal and the urogenital regions of the perineum. The branches are:

artery.

Muscular Inferior rectal Perineal Artery of the bulb of the penis Urethral Deep artery of the penis Dorsal artery of the penis muscular branches. Muscular branches from the internal pudendal artery consist of two sets: one given off in the pelvis and the other as the vessel crosses the ischial spine in the gluteal region. Within the pelvis sev¬ eral small unnamed vessels supply the leva¬ tor ani, the obturator internus, the piri¬ formis, and the coccygeus. The branches given off in the gluteal region are distributed to the adjacent parts of the gluteus maximus and to other lateral rotator muscles; they anastomose with branches of the inferior gluteal artery. INFERIOR RECTAL ARTERY. Also known as the inferior hemorrhoidal artery, this vessel arises from the internal pudendal as it passes above the ischial tuberosity. Piercing the fas¬ cial sheath forming the pudendal canal, the artery divides into two or three branches which cross the ischiorectal fossa and are distributed to the muscles and integument of the anal region (Fig. 8-68). Small branches also ascend around the lower edge of the gluteus maximus to the skin of the buttock. Branches of the inferior rectal artery anasto¬ mose with the corresponding vessels of the opposite side, with the superior and middle rectal, and with the perineal artery. perineal artery. The perineal artery arises from the internal pudendal anterior to the inferior rectal branches. It pierces the urogenital diaphragm and crosses either over or under the superficial transverse peri¬ neal muscle (Fig. 8-68). Continuing forward in the superficial perineal compartment of the urogenital region, the vessel courses an¬ teriorly, parallel to the pubic arch, in the in¬ terspace between the bulbospongiosus and ischiocavernosus muscles. It supplies both these muscles and finally divides into sev¬ eral posterior scrotal branches, which are

PERINEUM

AND GLUTEAL REGION

755

distributed to the skin and dartos tunic of the scrotum. As it pierces the urogenital dia¬ phragm, the perineal artery gives off a small transverse branch, which courses medially along the cutaneous surface of the superfi¬ cial transverse perineal muscle and anasto¬ moses with the corresponding vessel of the opposite side and with the inferior rectal ar¬ teries. The transverse branch supplies the muscle and other structures between the anus and the bulb of the penis. artery of the bulb of the penis. The ar¬ tery to the bulb is a short vessel of large cali¬ ber which arises from the internal pudendal between the two layers of fascia of the uro¬ genital diaphragm (Fig. 8-68). It passes medi¬ ally, pierces the inferior fascia of the urogen¬ ital diaphragm, and gives off branches that ramify in the bulb of the penis and in the posterior part of the corpus spongiosum penis. It gives off a small branch to the bul¬ bourethral gland (of Cowper1). urethral artery. The urethral branch of the internal pudendal artery arises a short distance anterior to the artery of the bulb of the penis. It runs medially, pierces the infe¬ rior fascia of the urogenital diaphragm, and enters the corpus spongiosum penis in which it is continued forward to the glans penis. It supplies the urethra and its sur¬ rounding tissue. deep artery of the penis. The deep ar¬ tery of the penis is one of the terminal branches of the internal pudendal artery (Fig. 8-68). It arises from that vessel while it is situated between the two fascial layers of the urogenital diaphragm. It pierces the infe¬ rior fascial layer of the urogenital dia¬ phragm and enters the crus penis obliquely. The deep artery continues distally in the center of the corpus cavernosum penis, its branches being distributed to the erectile tissue. DORSAL ARTERY OF THE PENIS. The dorsal artery of the penis is the other terminal branch of the internal pudendal artery (Fig. 8-68). It arises in the deep perineal compart¬ ment, just lateral and deep to the bulbo¬ spongiosus muscle. Piercing the inferior fas¬ cia of the urogenital diaphragm between the crus penis and the pubic arch, it then passes between the two layers of the suspensory ligament to reach the dorsum of the penis, 'William Cowper (1666-1709): An English surgeon and anatomist (London).

756

THE ARTERIES

where it runs distally to the glans, sending branches to the glans and prepuce. Along the penis, it lies between the dorsal nerve and deep dorsal vein. It supplies the skin and fi¬ brous sheath of the corpora cavernosa penis and anastomoses with the deep artery. VARIATIONS

OF

THE

MALE

INTERNAL

PUDENDAL

Sometimes the internal pudendal artery is smaller than usual or fails to give off one or two of its usual branches. In such instances, the deficiency generally is supplied by branches derived from an additional vessel, the accessory pudendal artery, which usually arises from the internal pudendal ar¬ tery before its exit from the greater sciatic foramen. The accessory vessel passes forward along the lower part of the bladder and across the side of the pros¬ tate to the root of the penis, where it perforates the urogenital diaphragm, and gives off branches usu¬ ally derived from the internal pudendal artery. The variation most frequently encountered is that in which the internal pudendal ends as the artery of the urethral bulb, while the dorsal and deep arteries of the penis arise from the accessory pudendal. The internal pudendal artery may also end as the peri¬ neal artery, the artery of the urethral bulb being de¬ rived, with the other two branches, from the acces¬ sory vessel. Occasionally the accessory pudendal artery is derived from one of the other branches of the internal iliac artery, most frequently the inferior vesical or the obturator. artery.

Internal Pudendal Artery in the Female

In the female, the internal pudendal artery is considerably smaller than in the male. Its origin and course, however, are similar and there are comparable branches for the homologous structures. Posterior labial branches of the perineal artery supply the labia majora; the artery of the bulb supplies the erectile tissue of the vestibular bulb and the vagina; the deep artery of the clitoris supplies the corpus cavernosum clitoridis; and the dorsal artery of the clitoris supplies the dorsum of that organ, ending in the glans and prepuce of the clitoris. ILIOLUMBAR ARTERY

The iliolumbar artery is a branch of the internal iliac artery, which usually comes off the posterior trunk (Figs. 8-64; 8-65). It courses upward and laterally beneath the common iliac artery, initially between the lumbosacral trunk and the obturator nerve. It then ascends between the vertebral col¬

umn and the psoas major muscle. Just above the pelvic brim and behind the psoas major muscle, the iliolumbar artery divides into a lumbar and an iliac branch. lumbar branch. The lumbar branch of the iliolumbar artery supplies the psoas major and quadratus lumborum, and anasto¬ moses with the fourth, which is the last, lum¬ bar artery. It also sends a small spinal branch through the intervertebral foramen between the last lumbar vertebra and the sacrum, into the vertebral canal, to supply the cauda equina of the spinal cord. iliac branch. The iliac branch of the ilio¬ lumbar artery descends to supply the iliacus muscle. Some branches, running between the muscle and the bone, anastomose with the iliac branches of the obturator artery. One of these enters an oblique canal to sup¬ ply the ilium, while others run along the crest of the ilium, distributing branches to the gluteal and abdominal muscles, and anastomosing in their course with the supe¬ rior gluteal, the circumflex iliac, and the lat¬ eral femoral circumflex arteries. LATERAL SACRAL ARTERIES

The lateral sacral arteries arise from the posterior trunk of the internal iliac; there are usually two, a superior and an inferior (Figs. 8-64; 8-65). SUPERIOR LATERAL SACRAL ARTERY. The superior lateral sacral artery passes medially and, after anastomosing with branches from the middle sacral, enters the first or second pelvic (anterior) sacral foramen. It supplies branches to the contents of the sacral canal and anastomoses with other spinal vessels. It then leaves the spinal canal by passing through the corresponding posterior sacral foramen, and is distributed to the skin and muscles on the dorsum of the sacrum, anas¬ tomosing with the superior gluteal artery. INFERIOR LATERAL SACRAL ARTERY. The in¬ ferior lateral sacral artery courses obliquely across the piriformis muscle and the anterior rami of the sacral nerves to the medial side of the pelvic (anterior) sacral foramina. It descends on the sacrum and anastomoses over the coccyx with the middle sacral and the opposite lateral sacral artery. In its course, it gives off branches that enter the pelvic sacral foramina. After supplying the contents of the sacral canal, these vessels emerge through the posterior sacral foram-

ARTERIES OF THE PELVIS. PERINEUM. AND GLUTEAL REGION

ina and are distributed to the muscles and skin on the dorsal surface of the sacrum. They anastomose with both the superior and inferior gluteal arteries. SUPERIOR GLUTEAL ARTERY

The superior gluteal artery is the largest branch of the internal iliac artery and is a direct continuation of its posterior trunk (Figs. 8-64; 8-65; 8-74; 8-76). It is a short artery that courses backward between the lumbo¬ sacral trunk and the first sacral nerve. Pass¬ ing out of the pelvis through the greater sci¬ atic foramen, above the superior border of the piriformis muscle, the superior gluteal artery immediately divides into a superficial and a deep branch (Fig. 8-69). Within the pel¬ vis it gives off muscular branches to the iliacus, piriformis, and obturator internus, and before leaving that cavity, it gives off a nutri¬ ent artery which enters the ilium. superficial branch. The superficial branch of the superior gluteal artery enters

Gluteus maximus m.

757

the deep surface of the gluteus maximus and divides into numerous branches (Fig. 8-69). Some of these supply the muscle and anasto¬ mose with the inferior gluteal artery; others perforate its tendinous origin and supply the skin covering the dorsal surface of the sacrum, anastomosing with the posterior branches of the lateral sacral arteries. deep branch. The deep branch of the superior gluteal artery lies deep to the glu¬ teus medius and almost immediately subdi¬ vides into a superior and an inferior division (Fig. 8-69). The superior division continues the original course of the vessel and passes along the superior border of the gluteus min¬ imus to the anterior superior spine of the ilium. It anastomoses with the deep iliac cir¬ cumflex artery and the ascending branch of the lateral femoral circumflex artery. The in¬ ferior division crosses the gluteus minimus obliquely to the greater trochanter, distrib¬ uting branches to the gluteal muscles and anastomosing with the lateral femoral cir¬ cumflex artery. Some branches pierce the

Gluteus minimus m. Muscular rami. Deep branch of superior gluteal artery

Deep branch, superior gluteal artery

*

Superficial branch.--*superior gluteal artery f

Gluteus medius m. Piriformis m. Sciatic nerve

Superior gluteal artery Deep branch, medial femoral circumflex artery Inferior gluteal artery Sacrotuberous lig. Internal pudendal a. Deep branch, medial — femoral circumflex artery

Artery of the sciatic nerve Quadratus femoris m. 1st perforating branch, femoral artery

Gluteus maximus m.

Semitendinosus m.

2nd perforating branch, femoral artery Adductor magnus m. Biceps femoris m. (long head)

The superior and inferior gluteal arteries and their branches. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, 1975.)

Fig. 8-69.

758

THE ARTERIES

gluteus minimus to supply the hip joint. Throughout most of its course, the deep branch of the superior gluteal artery ramifies between the gluteus medius and gluteus minimus muscles, helping to define the plane of separation between their fibers. INFERIOR GLUTEAL ARTERY

The inferior gluteal artery is distributed chiefly to the buttocks and back of the thigh. It passes posteriorly between the first and second sacral nerves, or between the second and third sacral nerves, and then descends between the piriformis and coccygeus mus¬ cles through the lower part of the greater sci¬ atic foramen to the gluteal region (Figs. 8-64; 8-65; 8-74; 8-76). It then descends in the inter¬ val between the greater trochanter of the femur and tuberosity of the ischium, accom¬ panied by the sciatic and posterior femoral cutaneous nerves and covered by the gluteus maximus. The inferior gluteal artery contin¬ ues down the posterior thigh, supplying the skin and anastomosing with vessels from the perforating branches of the femoral artery. Branches of the Inferior Gluteal Artery

Within the pelvis, the inferior gluteal ar¬ tery distributes branches to the piriformis, coccygeus, and levator ani. Some branches help to supply the fat around the rectum, and occasionally take the place of the mid¬ dle rectal artery. Other branches help to sup¬ ply the fundus of the bladder, the seminal vesicles, and the prostate. Outside the pelvis (Fig. 8-69), the inferior gluteal artery gives off the following branches: Muscular Coccygeal Artery of the sciatic nerve Anastomotic Articular Cutaneous Muscular branches from the inferior gluteal artery in the gluteal region supply (1) the gluteus maximus, where they anastomose with the superior gluteal artery in the substance of the muscle; (2) the smaller, lateral rotator muscles, anas¬ tomosing with the internal pudendal artery; muscular branches.

and (3) the upper part of the hamstring mus¬ cles attached to the tuberosity of the ischium. These latter vessels anastomose with the posterior branch of the obturator and the medial femoral circumflex arteries. coccygeal branches. The coccygeal branches course medially, pierce the sacrotuberous ligament, and supply the gluteus maximus, the skin, and other structures on the back of the coccyx (Fig. 8-76). ARTERY OF THE SCIATIC NERVE. This long, slender branch of the inferior gluteal artery accompanies the sciatic nerve for a short distance, then penetrates it and runs in its substance to the distal part of the thigh (Fig. 8-69). anastomotic branch. The anastomotic branch of the inferior gluteal artery de¬ scends obliquely and laterally in the gluteal region across the small external rotators of the thigh to assist in forming the so-called cruciate anastomosis. This anastomosis around the neck and greater trochanter of the femur involves the first perforating and medial and lateral femoral circumflex branches of the femoral artery in addition to the inferior gluteal artery. articular branch. An articular branch, generally arising from the anastomotic, is distributed to the capsule of the hip joint. cutaneous branches. The cutaneous branches of the inferior gluteal artery are distributed to the skin of the buttock and posterior thigh.

External Iliac Artery The external iliac artery on both the right and left sides is larger than the internal iliac. Each vessel passes obliquely downward and laterally along the medial border of the psoas major muscle. The external iliac ar¬ tery extends from the bifurcation of the common iliac artery to a point beneath the inguinal ligament, midway between the an¬ terior superior spine of the ilium and the symphysis pubis (Figs. 8-64; 8-65; 8-70; 8-74). Entering the thigh below the inguinal liga¬ ment, the vessel then becomes the femoral artery. relations. Anteriorly and medially, the external iliac artery is related to the parietal peritoneum, the subperitoneal areolar tissue, the termination of the

ARTERIES OF THE PELVIS. PERINEUM. AND GLUTEAL REGION

ileum, and, frequently, the vermiform appendix on the right side and the sigmoid colon on the left side. The origin of the artery is occasionally crossed by the ureter and, in females, by the ovarian artery and vein. The testicular vessels lie for some distance on the external iliac artery above the inguinal ligament, but near its termination. The vessel is crossed at this site by the genital branch of the genitofemoral nerve and the deep iliac circumflex vein. Curving across its medial aspect in the male is the ductus deferens, or in the female, the round ligament of the uterus. Posteriorly, the external iliac artery is related to the medial border of the psoas major muscle, from which it is separated by the iliac fascia. Proximally, the lateral portion of the external iliac vein lies be¬ hind the artery, but more distally, the vein courses entirely medial to the artery. Laterally, the external iliac artery rests on the iliac fascia overlying the psoas major muscle. Numerous lymphatic vessels and lymph nodes lie on the anterior and medial as¬ pects of the vessel. collateral circulation. The principal anasto¬ moses providing collateral circulation after the appli¬ cation of a ligature to the external iliac are: (1) the iliolumbar with the iliac circumflex, (2) the superior gluteal with the lateral femoral circumflex, (3) the obturator with the medial femoral circumflex, (4) the inferior gluteal with the first perforating and circum¬ flex branches of the profunda artery, and (5) the in¬ ternal pudendal with the external pudendal. When the obturator artery arises from the inferior epigas¬ tric, it receives blood by branches from the internal iliac or the lateral sacral or the internal pudendal ar¬ tery, and the inferior epigastric receives blood by anastomoses with the internal thoracic and lower intercostal arteries, and from the internal iliac by anastomoses of its branches with the obturator.

759

Branches of the External Iliac Artery

In addition to several small branches given to the psoas major muscle and the neighboring lymph nodes, the external iliac gives off two branches of considerable size. These are the: Inferior epigastric Deep iliac circumflex

INFERIOR EPIGASTRIC ARTERY

The inferior epigastric artery arises from the external iliac immediately above the in¬ guinal ligament (Figs. 8-70; 8-74). It curves anteriorly in the subperitoneal tissue and then ascends obliquely along the medial margin of the deep inguinal ring. Continuing its course upward, the vessel pierces the transversalis fascia, and passing anterior to the arcuate line, it ascends between the rectus abdominis muscle and the poste¬ rior layer of its sheath. The inferior epigas¬ tric artery finally divides into numerous branches, and these anastomose, above the umbilicus, with the superior epigastric branch of the internal thoracic and with the lower posterior intercostal arteries (see Fig. 8-31). As the inferior epigastric artery passes obliquely upward from its origin, it lies along the lower and medial margins of the

The inferior epigastric artery seen from the inner aspect of the lower abdominal wall. Observe also the relationships of the femoral ring and the deep inguinal ring.

Fig. 8-70.

760

THE ARTERIES

deep inguinal ring and behind the com¬ mencement of the spermatic cord. The duc¬ tus deferens in the male or the round liga¬ ment of the uterus in the female winds around the lateral and dorsal aspects of the artery. In its ascent on the inner aspect of the anterior abdominal wall, it is covered by a reflection of peritoneum called the lateral umbilical fold. The following branches arise from the inferior epigastric artery: Cremasteric Artery of the round ligament Pubic Muscular cremasteric artery. The cremasteric artery is found in males and it accompanies the spermatic cord, supplying the cremaster muscle and other coverings of the cord. It anastomoses with the testicular, the external pudendal, and the perineal arteries. ARTERY OF THE ROUND LIGAMENT. In fe¬ males, the artery that corresponds to the cremasteric is a small vessel that accompa¬ nies the round ligament of the uterus. pubic branch. The pubic branch of the inferior epigastric artery courses along the inguinal ligament. It then descends along the medial margin of the femoral ring to the in¬ ternal surface of the pubis and there anasto¬ moses with the pubic branch of the obtu¬ rator artery. In almost one-third of the cadavers, the pubic branch is much larger and actually becomes the obturator artery. muscular branches. Some of the muscu¬ lar branches of the inferior epigastric artery are distributed to the abdominal muscles and peritoneum, anastomosing with the il¬ iac circumflex and lumbar arteries. Other branches perforate the tendon of the exter¬ nal oblique muscle to supply the skin and to anastomose with branches of the superficial epigastric artery. variations. The inferior epigastric artery may arise from any part of the external iliac between the inguinal ligament and a point 6 cm above it. The vessel may also arise from the femoral artery below the inguinal ligament. Frequently it branches from the external iliac by a common trunk with the obtu¬ rator. Sometimes the inferior epigastric arises from the obturator, the latter vessel being furnished by the internal iliac, or it may be formed by two branches, one derived from the external iliac, the other from the internal iliac.

DEEP ILIAC CIRCUMFLEX ARTERY

The deep iliac circumflex artery arises from the lateral aspect of the external iliac almost opposite the inferior epigastric artery (Fig. 8-74). It ascends laterally to the anterior superior iliac spine, deep to the inguinal lig¬ ament. In its course it lies between the transversalis fascia and the peritoneum, or it is contained in a fibrous sheath formed by the union of the transversalis fascia and iliac fascia. In the lateral wall of the pelvis, the deep iliac circumflex artery anastomoses with the ascending branch of the lateral fem¬ oral circumflex artery from below. It then pierces the transversalis fascia and passes along the inner lip of the crest of the ilium to about its middle, where it perforates the transversus abdominis, and runs dorsally between that muscle and the internal oblique to anastomose with the iliolumbar and superior gluteal arteries. Opposite the anterior superior iliac spine, it gives off a large ascending branch, which courses be¬ tween the internal oblique and transversus muscles, supplying them and anastomosing with the lumbar and inferior epigastric ar¬ teries.

Arteries of the Lower Limb The artery that supplies the greater part of the lower limb is the direct continuation of the external iliac (Fig. 8-74). It courses as a single trunk from the inguinal ligament to the lower border of the popliteus muscle behind the knee joint, where it divides into two branches, the anterior and posterior tib¬ ia!. The upper part of the main trunk courses through the anterior and medial aspect of the thigh and is called the femoral artery. Below the adductor canal, the artery passes through a hiatus in the tendon of the adduc¬ tor magnus muscle in order to reach the pop¬ liteal fossa, where the vessel is called the popliteal artery. Femoral Artery

The femoral artery, being the continuation of the external iliac artery, begins immedi¬ ately below the inguinal ligament, midway

ARTERIES OF THE LOWER LIMB

Fig. 8-71.

761

Femoral sheath opened to show its three compartments.

between the anterior superior iliac spine and the symphysis pubis (Figs. 8-71 to 8-75). It passes distally along the anteromedial as¬ pect of the thigh, ending at the junction of the middle and lower thirds of the thigh, where it passes through an opening in the tendon of the adductor magnus muscle to become the popliteal artery (Fig. 8-76). In the upper part of the thigh, the femoral artery lies anterior to the hip joint, while in the lower part of its course, it lies medial to the shaft of the femur. Between these two parts, it crosses the angle between the head and shaft, remaining at some distance from the bone. The first 4 cm of the vessel are en¬ closed. together with the femoral vein, in the fibrous femoral sheath. In the upper third of the thigh, the femoral artery is contained in the femoral triangle (of Scarpa1) and in the

middle third of the thigh, in the adductor canal (of Hunter2). femoral sheath. The femoral sheath is formed by a prolongation downward under the inguinal ligament of the transversalis fascia anterior to the femoral vessels and the iliac fascia behind them (Figs. 8-71; 8-72). The sheath assumes the form of a short fun¬ nel. the wide end of which is directed supe¬ riorly, while the inferior, narrow end fuses with the adventitia of the vessels, about 4 cm below the inguinal ligament. It is strength¬ ened anteriorly by a band termed the deep crural arch. The lateral wall of the sheath is perforated by the femoral branch of the genitofemoral nerve. The medial wall is pierced by the great saphenous vein and by some lymphatic vessels. The sheath is di¬ vided into three compartments by two verti-

‘Antonio Scarpa (1747-1842): A Venetian anatomist and ophthalmologist (Pavia).

2John Hunter (1728-1793): A Scottish surgeon, anatomist and physiologist (Edinburgh and London).

762

THE ARTERIES

Lat. fem. cutan. nerve

Femoral nerve lliopectineal fascia Lumboinguinal nerve I artery Femoral sheath Femoral vein Femoral canal Lacunar ligament

Fig. 8-72.

The structures passing deep to the inguinal ligament, as seen inferiorly.

cal partitions which stretch between its an¬ terior and posterior walls. The lateral compartment contains the femoral artery, and the intermediate compartment contains the femoral vein. The medial compartment is the smallest and is called the femoral canal (Figs. 8-71; 8-72). It contains some lym¬ phatic vessels and a lymph node (of Cloquet1 or Rosenmiiller2) embedded in a small amount of areolar tissue. The femoral canal is conical and measures about 1.25 cm in length. Its base is directed superiorly and, although oval in form, is named the femoral ring (Fig. 8-70). The long diameter of the ring is directed transversely and it measures about 1.25 cm. The femoral ring (Fig. 8-70) is bounded anteriorly by the inguinal liga¬ ment, posteriorly by the pectineus muscle and its overlying pectineal fascia, medially by the crescentic base of the lacunar liga¬ ment, and laterally by the fibrous septum on the medial aspect of the femoral vein. The spermatic cord in the male and the round ligament of the uterus in the female lie im¬ mediately superior to the anterior margin of the ring, and the inferior epigastric vessels

1]ules G. Cloquet (1790-1883): A French anatomist and surgeon (Paris). 2Johann C. Rosenmiiller (1771-1820): A German anato¬ mist (Leipzig).

are close to its superior and lateral angle (Fig. 8-70). The femoral ring is closed by a somewhat condensed portion of the subperitoneal fatty tissue, called the femoral sep¬ tum, the abdominal surface of which sup¬ ports a small lymph node and is covered by the parietal layer of the peritoneum. The peritoneum presents a slight depression named the femoral fossa. The femoral sep¬ tum is pierced by numerous lymphatic ves¬ sels passing from the deep inguinal to the external iliac lymph nodes. The femoral nerve is not enclosed by the femoral sheath (Fig. 8-71). femoral triangle. The femoral triangle corresponds to the depression seen immedi¬ ately below the fold of the groin (Fig. 8-73). Its apex is directed inferiorly, and the sides are formed laterally by the sartorius, medi¬ ally by the adductor longus, and superiorly by the inguinal ligament. The floor of the space is formed from its lateral to medial aspect by the iliacus, psoas major, and pec¬ tineus muscles, and in some cases by a small part of the adductor brevis. It is divided into two nearly equal parts by the femoral ves¬ sels, which extend from near the middle of its base to its apex. The femoral artery gives off both its more superficial and deep branches, while the femoral vein receives its femoral and great saphenous tributaries. On the lateral aspect of the femoral artery is the

ARTERIES OF THE LOWER LIMB

763

Femoral nerve Superficial circumflex iliac vessels Inguinal ligament

Superficial epigastric vessels Tensor fasciae latae m.

Iliacus m. Sartorius m Femoral artery Femoral vein Deep external pudendal vessels Rectus femoris m.

Great saphenous vein

Vastus lateralis m.

Fig. 8-73.

The left femoral vessels and some of their branches, and the femoral nerve in the femoral triangle.

femoral nerve and its branches. In addition to the vessels and nerves, the femoral tri¬ angle contains some fat and lymphatics. adductor canal. The adductor canal is a fascial tunnel in the middle third of the thigh, extending from the apex of the femo¬ ral triangle to the opening in the tendon of the adductor magnus muscle, through which the femoral vessels course to the popliteal fossa (Figs. 8-75; 8-76). The canal is bounded anteriorly and laterally by the vastus medialis muscle, and posteriorly by the adductors longus and magnus. It is covered anteriorly by a strong fascia that lies deep to the sarto¬ rius and extends from the vastus medialis across the femoral vessels to the adductors longus and magnus. The canal contains the femoral artery and vein, and the saphenous nerve.

In the femo¬ the artery is situated quite superficially. Anterior to it are the skin, the superficial fascia, the superficial inguinal lymph nodes, the superficial iliac circumflex vein, the superficial layer of the fascia lata, and the anterior part of the femoral sheath. The femoral branch of the genitofemoral nerve courses for a short distance within the lateral compartment of the femoral sheath and lies at first lateral and then anterior to the artery. Near the apex of the femoral triangle, the medial cutaneous branches of the femo¬ ral nerve cross the artery from its lateral to its medial aspect. Posterior to the femoral artery are the posterior part of the femoral sheath, the pectineal fascia, the medial part of the tendon of the psoas major muscle, the pectineus muscle, and the adductor longus mus¬ cle. The artery is separated from the capsule of the hip joint by the tendon of the psoas major muscle, from the pectineus muscle by the femoral vein and RELATIONS OF THE FEMORAL ARTERY.

ral triangle,

764

the arteries

deep femoral vessels, and from the adductor longus muscle by the femoral vein. The nerve to the pectineus passes medially behind the artery. On the lateral aspect of the artery, but separated from it by some fibers of the psoas major muscle, is the femoral nerve. The femoral vein is on the medial aspect of the artery in the upper part of the femoral triangle, but is posterior to it in the lower part of the triangle. In the adductor canal (Fig. 8-75), the femoral ar¬ tery is more deeply situated, being covered by the skin, the superficial and deep fasciae, the sartorius, and the fibrous roof of the femoral canal. The saphe¬ nous nerve crosses the artery from its lateral to its medial aspect within the adductor canal. Posterior to the artery are the adductors longus and magnus, and anterolateral to it is the vastus medialis. The femoral vein lies behind the artery in the upper part of the adductor canal, but lateral to it in the distal part of the canal. variations. In rare cases the femoral artery is absent, and its place is taken by an enlarged inferior gluteal artery, which has accompanied the sciatic nerve to the popliteal fossa. When this occurs, the inferior gluteal represents the persistence of the original axis artery (Fig. 8-1 3), and the external iliac is small, terminating as the deep femoral artery. Occasionally, the femoral vein courses along the medial aspect of the artery throughout the entire ex¬ tent of the femoral triangle, or it may be split so that a large vein is placed on both sides of the artery for a greater or lesser distance through the thigh. collateral circulation. After ligature of the femoral artery, collateral circulation (Fig. 8-74) re¬ sults from anastomoses of (1) the superior and infe¬ rior gluteal branches of the internal iliac with the medial and lateral femoral circumflex and first perfo¬ rating branches of the deep femoral artery; (2) the obturator branch of the internal iliac with the medial femoral circumflex branch of the deep femoral; (3) the internal pudendal from the internal iliac with the superficial and deep external pudendal arteries off the femoral; (4) the deep iliac circumflex from the external iliac with the lateral femoral circumflex of the deep femoral and the superficial iliac circumflex of the femoral; and (5) the inferior gluteal of the internal iliac with the perforating branches of the deep femoral artery (Fig. 8-76).

Branches of the Femoral Artery

The branches of the femoral artery are: Superficial epigastric Superficial circumflex iliac Superficial external pudendal Deep external pudendal Muscular Profunda femoris Descending genicular artery

SUPERFICIAL EPIGASTRIC ARTERY

The superficial epigastric artery arises from the femoral artery about 1 cm below the inguinal ligament (Figs. 8-73; 8-75). It passes through the femoral sheath and the cribriform fascia, turns upward in front of the inguinal ligament, and ascends between the two layers of the superficial fascia, ante¬ rior to the external oblique muscle of the abdominal wall, almost to the umbilicus. It distributes branches to the superficial subinguinal lymph nodes, the superficial fascia, and the skin. It anastomoses with branches of the inferior epigastric artery and with the superficial epigastric of the other side. SUPERFICIAL CIRCUMFLEX ILIAC ARTERY

The superficial circumflex iliac artery is the smallest of the superficial branches of the femoral artery. It arises close to the su¬ perficial epigastric, pierces the fascia lata, runs laterally, parallel to the inguinal liga¬ ment, to the crest of the ilium (Figs. 8-73; 875). It divides into branches that supply the skin of the groin and the superficial subinguinal lymph nodes, and it anastomoses with the deep circumflex iliac, superior gluteal, and lateral femoral circumflex arteries. SUPERFICIAL EXTERNAL PUDENDAL ARTERY

The superficial external pudendal artery arises from the medial aspect of the femoral artery, close to the preceding vessels (Figs. 8-73; 8-75). After piercing the femoral sheath and the cribriform fascia, it courses medially across the spermatic cord (or round ligament in the female) and is distributed to the skin on the lower part of the abdomen, and to the penis and scrotum in the male, or the labium majus in the female. It anastomoses with branches of the internal pudendal artery. DEEP EXTERNAL PUDENDAL ARTERY

The deep external pudendal artery, more deeply situated than the preceding vessel, passes medially across the pectineus and adductor longus muscles (Figs. 8-73; 8-75). It is covered by the fascia lata, which it pierces at the medial aspect of the thigh, and is dis-

ARTERIES OF THE LOWER LIMB

Fig. 8-74.

765

Collateral circulation about the hip and the upper part of the right thigh. (From Eycleshymer and Jones.)

tributed to the skin of the scrotum and peri¬ neum in the male or to the labium majus in the female. Its branches anastomose with the posterior scrotal (or labial) branches of the perineal artery.

MUSCULAR BRANCHES

Muscular branches of the femoral artery supply the sartorius, vastus medialis, and adductor muscles.

DEEP FEMORAL ARTERY

The deep (or profunda) femoral artery is a large vessel that arises from the lateral and posterior part of the femoral artery, 2 to 5 cm below the inguinal ligament (Figs. 8-74; 8-75). Initially, it lies lateral to the femoral artery, but then courses behind it and the femoral vein to the medial aspect of the femur. Pass¬ ing down to the lower third of the thigh, pos¬ terior to the adductor longus muscle, the deep femoral artery ends as a small branch.

766

THE ARTERIES

Scrotum

- Saphenous nerve Descending genicular

Lateral sup. genicular

Musculoarticular br. of descending genicular Medial sup. genicular

Lateral inf, genicular — Medial inf. genicular Anterior tibial recurrent -ftT Fig. 8-75.

The femoral artery and its branches viewed from the anterior aspect of the thigh.

This branch pierces the adductor magnus and is distributed to the hamstring muscles on the posterior thigh. The terminal part of the deep femoral artery is sometimes named the fourth perforating artery, and it anasto¬ moses with upper branches of the popliteal artery. RELATIONS OF THE DEEP FEMORAL ARTERY. Poste¬ rior to the vessel, from above downward, are the iliacus, pectineus, adductor brevis, and adductor

magnus. Anteriorly, the deep femoral artery is sepa¬ rated from the femoral artery by the femoral and deep femoral veins above and by the adductor longus muscle below. Laterally, the origin of the vastus medialis intervenes between the upper part of the deep femoral artery and the femur. variations. The deep femoral artery sometimes arises from the medial side and, more rarely, from the back of the femoral artery. A more important variation, however, from a surgical point of view, is the level in the thigh at which the vessel arises. In three-fourths of a large number of specimens it

ARTERIES OF THE LOWER LIMB

arose from 2.25 to 5 cm below the inguinal liga¬ ment. In a few specimens it arose higher, more rarely opposite the inguinal ligament, and in one subject, above the ligament from the external iliac artery. Occasionally the distance between the origin of the deep femoral artery and the inguinal ligament exceeds 5 cm.

Branches of the Deep Femoral Artery

The deep femoral artery supplies much of the musculature in the anterior and medial compartments of the thigh. Some of its ves¬ sels penetrate through the musculature to the posterior compartment, thereby contrib¬ uting to the supply of the hamstrings. Its branches are: Medial femoral circumflex Lateral femoral circumflex Perforating Muscular Medial Femoral Circumflex Artery

The medial femoral circumflex artery arises from the medial aspect of the deep femoral and winds around the medial aspect of the femur (Fig. 8-74). In about 25% of ca¬ davers it arises directly from the femoral ar¬ tery. It passes first between the pectineus and psoas major muscles, and then between the obturator externus and the adductor brevis. Continuing into the gluteal region between the quadratus femoris and adduc¬ tor magnus muscles, it gives off ascending and transverse branches. The ascending branch goes to the adductor muscles, the gracilis, and the obturator externus, and it anastomoses with the obturator artery. The transverse branch descends beneath the adductor brevis to supply it and the adduc¬ tor magnus. The continuation of the medial femoral circumflex artery passes posteriorly and di¬ vides into superficial, deep, and acetabular branches. The superficial branch appears between the quadratus femoris and the proximal border of the adductor magnus. It anastomoses with the inferior gluteal, lateral femoral circumflex, and first perforating ar¬ teries, thereby contributing to the cruciate anastomosis. The deep branch runs ob¬ liquely upward upon the tendon of the obtu¬ rator externus, and in front of the quadratus

767

femoris toward the trochanteris fossa, where it anastomoses with twigs from the gluteal arteries. The acetabular branch arises oppo¬ site the acetabular notch and enters the hip joint beneath the transverse acetabular liga¬ ment in company with the acetabular branch of the obturator artery. It supplies the fat in the acetabular fossa and continues along the round ligament to the head of the femur. Lateral Femoral Circumflex Artery

The lateral femoral circumflex artery arises from the lateral aspect of the deep femoral artery (Figs. 8-74; 8-75). In nearly 20% of cadavers studied, it arises independ¬ ently from the femoral artery. It passes later¬ ally between the divisions of the femoral nerve and behind the sartorius and rectus femoris muscles, and divides into ascending, transverse, and descending branches. The ascending branch passes superiorly, deep to the tensor fasciae latae, to the lateral aspect of the hip, and anastomoses with the terminal branches of the superior gluteal and deep iliac circumflex arteries. The descending branch of the lateral fem¬ oral circumflex artery courses downward behind the rectus femoris and upon the vastus lateralis, which it supplies. One long branch descends in the vastus lateralis mus¬ cle as far as the knee and anastomoses with the superior lateral genicular branch of the popliteal artery. It is accompanied by the branch of the femoral nerve to the vastus lat¬ eralis. The transverse branch is the smallest branch, but it is often absent. It passes later¬ ally over the vastus intermedius, pierces the vastus lateralis, and winds around the femur, just below the greater trochanter. It anastomoses on the back of the thigh with the medial femoral circumflex, inferior glu¬ teal, and first perforating arteries, thereby participating in the cruciate anastomosis. Perforating Arteries

Usually three perforating arteries arise from the deep femoral artery, and the termi¬ nation of the deep femoral is frequently con¬ sidered the fourth (Figs. 8-74; 8-76). These vessels are so named because they perforate the adductor magnus muscle to reach the

768

THE ARTERIES

Gluteus medius m.

Gluteus maximus m. Superior gluteal artery and nerve Piriformis m.

Gluteus minimus m.

Pudendal n. and internal pudendal a. ^ Inferior gluteal a. Coccygeal a.

Gluteus medius m. Sciatic nerve

Ischial tuberosity Quadratus femoris m. Posterior femoral cutaneous nerve 1st perforating artery Gracilis m. Gluteus maximus m. Adductor magnus m.

2nd perforating artery

3rd perforating artery Vastus lateralis m 4th perforating artery Semimembranosus Biceps femoris m. (short head) Superior muscular branches of popliteal artery Popliteal a. Medial superior genicular a.

Lateral superior genicular a. Biceps femoris m. (long head) Sural arteries

Middle genicular a.

Gastrocnemius m. (med head)

Fig. 8-76.

Gastrocnemius m. (lat head)

The arteries of the gluteal, posterior femoral, and popliteal regions.

back of the thigh. They pass posteriorly close to the linea aspera of the femur under . cover of the small tendinous arches in the muscle. The first is given off above the ad¬ ductor brevis, the second anterior to that muscle, and the third immediately below it. The first perforating artery passes posteri¬ orly between the pectineus and adductor brevis muscles, and sometimes it perforates the latter (Figs. 8-74; 8-76). It then pierces the adductor magnus close to the linea aspera, giving branches to the adductors brevis and magnus, the biceps femoris, and the gluteus maximus. It anastomoses with the infer¬

ior gluteal, medial and lateral femoral cir¬ cumflex, and second perforating arteries (Fig. 8-74). The second perforating artery, larger than the first, pierces the tendons of the adductors brevis and magnus and divides into ascend¬ ing and descending branches, which supply the posterior femoral muscles and anasto¬ mose with the first and third perforating (Fig. 8-76). The second perforating artery frequently arises in common with the first. The nutrient artery of the femur usually branches from the second perforating artery, but when two nutrient arteries exist, they

ARTERIES OF THE LOWER LIMB

usually are derived from the first and third perforating vessels. The third perforating artery pierces the adductor magnus and divides into branches that supply the posterior femoral muscles (Fig. 8-76). These anastomose above with the higher perforating arteries and below with the terminal branches of the deep femoral artery and the muscular branches of the popliteal. The termination of the deep femo¬ ral artery, as was already described, is some¬ times termed the fourth perforating artery.

Muscular Branches

Numerous muscular branches arise from the deep femoral artery. Some of these end in the adductor muscles; others pierce the adductor magnus, give branches to the ham¬ strings, and anastomose with the medial femoral circumflex artery and with the supe¬ rior muscular branches of the popliteal ar¬ tery.

DESCENDING GENICULAR ARTERY

The descending genicular artery arises from the femoral just before the latter vessel passes through the opening in the tendon of the adductor magnus muscle (Figs. 8-74; 875). It immediately divides into a saphenous and an articular branch. saphenous branch. The saphenous branch of the descending genicular artery pierces the aponeurotic covering of the ad¬ ductor canal and accompanies the saphe¬ nous nerve to the medial aspect of the knee. It passes between the sartorius and gracilis muscles and, piercing the fascia lata, is dis¬ tributed to the skin on the upper and medial part of the leg. It anastomoses with the me¬ dial inferior genicular artery. articular branch. The articular branch of the descending genicular artery descends in the substance of the vastus medialis, ante¬ rior to the tendon of the adductor magnus, to the medial aspect of the knee (Fig. 8-75). Here it anastomoses with the medial supe¬ rior genicular artery and anterior recurrent tibial artery. Another anastomosing branch crosses the lower thigh above the patellar surface of the femur, forming an arterial arch with the lateral superior genicular ar¬ tery, from which branches supply the knee joint.

769

Popliteal Artery The popliteal artery is the continuation of the femoral artery and it courses through the popliteal fossa (Figs. 8-76; 8-77; 8-81). The vessel commences at an opening in the apo¬ neurosis of the adductor magnus muscle at the lower end of the adductor canal. Extend¬ ing from the junction of the middle and dis¬ tal thirds of the posterior thigh, the popliteal artery courses downward to the intercondy¬ lar fossa of the femur. It then continues distally to the lower border of the popliteus muscle, where it divides into anterior and posterior tibial arteries. popliteal fossa. The popliteal fossa is a diamond-shaped region posterior to the knee joint. Laterally it is bounded by the biceps femoris above, and by the plantaris and the lateral head of the gastrocnemius below. Me¬ dially it is limited by the semitendinosus and semimembranosus above, and by the medial head of the gastrocnemius below. The floor of the fossa is oriented anteriorly and is formed by the popliteal surface of the femur, the oblique popliteal ligament of the knee joint, the proximal end of the tibia, and the fascia covering the popliteus muscle. The fossa is covered posteriorly by the pop¬ liteal fascia, which is pierced by the small saphenous vein. Contents of the Popliteal Fossa. The popliteal fossa contains the popliteal vessels, the tibial and the common peroneal nerves, the termination of the small saphenous vein, the distal part of the posterior femoral cuta¬ neous nerve, the articular branch from the obturator nerve, a few small lymph nodes, and a considerable amount of fat. The tibial nerve descends through the middle of the fossa, lying most superficially beneath the deep fascia and crossing behind the popli¬ teal vessels from lateral to medial. The com¬ mon peroneal nerve descends laterally along the upper part of the fossa, close to the ten¬ don of the biceps femoris. The popliteal ves¬ sels course along the floor of the fossa. The popliteal artery is closest to the bone, and the popliteal vein, coursing superficial to the artery, is interposed between it and the nerves. The two vessels are united by dense areolar tissue. The popliteal vein is a thickwalled vessel which at first is lateral to the artery and then crosses it posteriorly to gain its medial aspect below. Sometimes the vein is doubled and interconnected by short

770

THE ARTERIES

transverse branches. In these instances, the artery courses between the veins. The artic¬ ular branch of the obturator nerve descends upon the artery to the knee joint. The poplit¬ eal lymph nodes, six or seven in number, are embedded in the fat. One node lies beneath the popliteal fascia near the termination of the external aaphenous vein, another be¬ tween the popliteal artery and the back of the knee joint, while others are aligned along the popliteal vessels. Arising from the pop¬ liteal artery and passing at right angles are its genicular branches. RELATIONS OF THE POPLITEAL ARTERY. Anterior tO the artery from above downward are the popliteal surface of the femur (which is separated from the vessel by some fat), the back of the knee joint, and the fascia covering the popliteus muscle. Posteriorly, the vessel is overlapped by the semimembranosus above, and it is covered by the gastrocnemius and plantaris muscles below. In the middle part of its course, the artery is separated from the skin and fas¬ cia by fat, and it is crossed from lateral to medial by the tibial nerve and the popliteal vein, the vein being interposed between the nerve and the artery and closely adherent to the latter. On its lateral aspect above are the biceps femoris, the tibial nerve, the popliteal vein, and the lateral condyle of the femur; below are the plantaris and the lateral head of the gastrocnemius. On its medial aspect above are the semimembranosus and the medial condyle of the femur; below are the tibial nerve, the popliteal vein, and the medial head of the gastrocnemius. variations. Occasionally the popliteal artery divides into its terminal branches opposite the knee joint. The anterior tibial under these circumstances usually passes anterior to the popliteus. Sometimes the popliteal artery divides into anterior tibial and peroneal branches, the posterior tibial being want¬ ing or very small. Occasionally it divides into three branches, the anterior and posterior tibial and the peroneal arteries.

Branches of the Popliteal Artery

In addition to its terminal branches, the popliteal artery gives rise to muscular, cuta¬ neous, and genicular vessels, the latter form¬ ing an anastomosis around the knee. The branches are: Superior muscular Sural Cutaneous Medial superior genicular Lateral superior genicular

Middle genicular Medial inferior genicular Lateral inferior genicular SUPERIOR MUSCULAR BRANCHES

Two or three superior muscular branches arise from the proximal part of the popliteal artery and are distributed to the lower parts of the adductor magnus and hamstring mus¬ cles (Fig. 8-76). These anastomose with the terminal vessels from the deep femoral ar¬ tery.

SURAL ARTERIES

The medial and lateral sural arteries are two large branches which are distributed to the gastrocnemius, soleus, and plantaris muscles of the calf (Figs. 8-77; 8-81). They arise from the popliteal artery opposite the knee joint. CUTANEOUS BRANCHES

Cutaneous branches arise either from the popliteal artery or from some of its branches. They descend between the two heads of the gastrocnemius, and piercing the deep fascia, they are distributed to the skin of the back of the leg. One branch usually accompanies the small saphenous vein. SUPERIOR GENICULAR ARTERIES

There are usually two superior genicular arteries. These arise one on each side of the popliteal artery and are therefore called medial and lateral superior genicular ar¬ teries. They wind around the femur, imme¬ diately proximal to its condyles, to the front of the knee joint. medial superior genicular artery. The medial superior genicular courses anterior to the semimembranosus and semitendinosus above the medial head of the gastrocne¬ mius (Figs. 8-76 to 8-78). Passing deep to the tendon of the adductor magnus, it divides into two branches. One of these supplies the vastus medialis, anastomosing with the de¬ scending genicular and medial inferior genicular arteries; the other ramifies close to the surface of the femur, supplying it and the knee joint, and anastomosing with the lateral superior genicular artery. The medial supe-

ARTERIES OF THE LOWER LIMB

Tibial nerve

Popliteal artery

Common peroneal nerve Medial superior genicular artery Gastrocnemius, lateral head Gastrocnemius, med. head Lateral sural artery and nerve

Med, sural artery and nerve Medial inferior genicular art. Medial sural cutaneous nerve Tendinous arch

Lateral inferior genicular artery

- Soleus

Anterior tibial artery

Tibialis posterior

Posterior tibial artery

Tibial nerve

Peroneal artery

Perforating branch Communicating artery

Medial malleolar artery I malleolar artery

Medial calcaneal artery Lateral calcaneal artery Tendo calcaneus

Fig. 8-77.

The popliteal, posterior tibial, and peroneal arteries. Right leg.

771

772

THE ARTERIES

Descending genicular Descending branch of lateral femoral circumflex Articular branch of descending genicular Saphenous branch of descending genicular Medial superior genicular Lateral superior genicular

Lateral inferior genicular

Medial inferior genicular Circumflex fibular Anterior tibial recurrent

Anterior tibial

Fig. 8-78.

The arterial anastomosis around the knee joint. Anterior view.

rior genicular artery is often small, with a resulting compensatory increase in the size of the descending genicular artery. LATERAL SUPERIOR GENICULAR ARTERY. The lateral superior genicular courses above the lateral condyle of the femur, deep to the ten¬ don of the biceps femoris, and divides into a superficial and a deep branch (Figs. 8-76; 8-78; 8-80; 8-81). The superficial branch sup¬ plies the vastus lateralis and anastomoses with the descending branch of the lateral femoral circumflex and the lateral inferior genicular arteries. The deep branch supplies the lower part of the femur and knee joint and forms an anastomotic arch across the anterior aspect of the joint with the descend¬ ing genicular, the medial superior genicular, and the inferior genicular arteries. MIDDLE GENICULAR ARTERY

The middle genicular artery is a small ves¬ sel that arises from the popliteal artery op¬ posite the back of the knee joint (Fig. 8-76). It

pierces the oblique popliteal ligament and supplies the ligaments and synovial mem¬ brane on the interior of the knee joint. INFERIOR GENICULAR ARTERIES

Two inferior genicular arteries arise from the popliteal artery below the knee joint. Under cover of the gastrocnemius muscle, one vessel branches from the medial aspect of the main vessel and the other from the lateral. MEDIAL INFERIOR GENICULAR ARTERY. The medial inferior genicular artery is usually the larger of the two lower genicular vessels (Figs. 8-77 to 8-79; 8-81). It descends medially in an oblique direction along the proximal margin of the popliteus, to which it gives branches. It then passes below the medial condyle of the tibia, deep to the tibial collat¬ eral ligament of the knee. At the anterior border of this ligament, the vessel ascends to the anterior and medial aspects of the joint, to supply the upper end of the tibia and the

ARTERIES OF THE LOWER LIMB

knee joint itself. It anastomoses with the lat¬ eral inferior and medial superior genicular arteries. LATERAL INFERIOR GENICULAR ARTERY.

The

lateral inferior genicular courses laterally above the head of the fibula to the front of the knee joint, passing deep to the lateral head of the gastrocnemius, the fibular collat¬ eral ligament of the knee joint, and the ten¬ don of the biceps femoris (Figs. 8-77 to 8-80). It ends by dividing into branches that anas¬ tomose with the medial inferior and lateral superior genicular arteries, the anterior and posterior tibial recurrent, and the circumflex fibular branch of the posterior tibial artery. ANASTOMOSIS AROUND THE KNEE JOINT. An intricate network of vessels forms a superfi¬ cial and deep plexus of arteries around the patella and on the contiguous ends of the femur and tibia (Figs. 8-78; 8-80). The super¬ ficial plexus is situated in the superficial fas¬ cia around the patella and forms three welldefined arches. One is found above the upper border of the patella, in the loose con¬ nective tissue over the quadriceps femoris muscle. The other two, distal to the patella, are situated in the fat deep to the ligamentum patellae. The deep plexus forms a close network of vessels which lies on the lower end of the femur and upper end of the tibia around their articular surfaces, sending numerous branches into the interior of the knee joint. The arteries that form this plexus are the two medial and the two lateral genicular branches of the popliteal, the de¬ scending genicular, the descending branch of the lateral femoral circumflex, the ante¬ rior and posterior tibial recurrent, and the circumflex fibular. Anterior Tibial Artery

The anterior tibial artery commences at the lower border of the popliteus muscle at the bifurcation of the popliteal artery (Figs. 8-77; 8-81). It passes anteriorly between the two heads of the tibialis posterior muscle and then through the aperture above the upper border of the interosseous membrane, to achieve the deep part of the front of the leg. Here the anterior tibial artery lies close to the medial aspect of the neck of the fibula. Descending on the anterior surface of the interosseous membrane, the vessel gradually approaches the tibia (Figs. 8-79; 8-80). In the

773

distal part of the leg it lies on the tibia, and then anterior to the ankle joint, it becomes more superficial and is called the dorsalis pedis artery.

RELATIONS OF THE ANTERIOR TIBIAL ARTERY.

|n

the upper two-thirds of its course, the anterior tibial artery rests upon the interosseous membrane. The lower one-third of the artery descends upon the front of the tibia and the anterior ligament of the ankle joint. In the upper third of the leg, it lies between the tibialis anterior and the extensor digitorum longus, and in the middle third, between the tibialis anterior and extensor hallucis longus. At the ankle the artery is crossed from lateral to medial by the tendon of the extensor hallucis longus, lying between this latter tendon and the first tendon of the extensor digi¬ torum longus. The vessel is covered in the upper two-thirds of the leg by muscles that lie on both sides and by the deep fascia. In the distal third of the leg it is covered by the skin and fascia, and by the extensor retinaculum. The anterior tibial artery is accompanied by a pair of venae comitantes which course along the sides of the artery. The deep peroneal nerve, descending obliquely around the lateral aspect of the neck of the fibula, enters the anterior compartment of the leg to lie on the lateral aspect of the anterior tibial artery. At about the middle of the leg, the nerve lies anterior to the artery, but in the lower leg it again is usually on the lateral aspect. variations. The anterior tibial artery may be small or entirely absent, its place being taken by per¬ forating branches from the posterior tibial, or by the perforating branch of the peroneal artery. Occasion¬ ally, the artery deviates toward the fibular side of the leg, regaining its usual position anterior to the ankle. More rarely, the vessel becomes superficial as high as the middle of the leg, being covered only by skin and fascia beyond that point.

Branches of the Anterior Tibial Artery

The anterior tibial artery supplies vessels to the anastomosis around the knee joint, to the muscles in the anterior compartment of the leg, and to the anastomosis around the ankle joint, becoming at that point the dorsa¬ lis pedis artery. Its branches are: Posterior tibial recurrent Anterior tibial recurrent Muscular Anterior medial malleolar Anterior lateral malleolar

774

THE ARTERIES

POSTERIOR TIBIAL RECURRENT ARTERY

The posterior tibial artery is an inconstant branch, but when present, it arises from the anterior tibial artery before that vessel achieves the anterior aspect of the leg. It as¬ cends anterior to the popliteus muscle, which it supplies, and it anastomoses with the inferior genicular branches of the popli¬ teal artery, sending a twig to the tibiofibular joint. ANTERIOR TIBIAL RECURRENT ARTERY

The anterior tibial recurrent artery arises from the anterior tibial immediately after that vessel has reached the anterior aspect of the leg (Figs. 8-78 to 8-80). It ascends in the tibialis anterior muscle, and ramifies on the front and sides of the knee joint, assisting in the formation of the arterial plexus. It anas¬ tomoses with the inferior genicular branches of the popliteal artery and with the circum¬ flex fibular artery. MUSCULAR BRANCHES

Numerous muscular branches arise from the anterior tibial artery. They are distrib¬ uted to the muscles that lie on both sides of the vessel. Some branches pierce the deep fascia to supply the skin, while others pass deeply through the interosseous membrane to anastomose with branches of the poste¬ rior tibial and peroneal arteries. ANTERIOR MEDIAL MALLEOLAR ARTERY

The anterior medial malleolar artery arises about 5 cm above the ankle joint, but it may arise lower down, even from the dor¬ salis pedis artery (Fig. 8-79). It passes behind the tendons of the extensor hallucis longus and tibialis anterior, to the medial aspect of the ankle. Its branches ramify over the me¬ dial malleolus and contribute to a network of vessels, anastomosing with branches from the posterior tibial and medial plantar ar¬ teries. ANTERIOR LATERAL MALLEOLAR ARTERY

Fig. 8-79.

Right leg.

Anterior tibial and dorsalis pedis arteries.

The anterior lateral malleolar artery is generally larger than the anterior medial vessel (Fig. 8-80). It usually arises from the

ARTERIES OF THE LOWER LIMB

anterior tibial artery distal to the lateral mal¬ leolus and may even arise from the dorsalis pedis artery. It passes deep to the tendons of the extensor digitorum longus and peroneus tertius and supplies the lateral aspect of the ankle. It anastomoses with the perforating branch of the peroneal artery and with as¬ cending twigs from the lateral tarsal artery. ANASTOMOSIS

AROUND

THE

ANKLE

JOINT.

The arteries around the ankle joint anasto¬ mose freely with one another to form net¬ works below the corresponding malleoli. The medial malleolar network is formed by the anterior medial malleolar branch of the anterior tibial, the medial tarsal branches of the dorsalis pedis, the posterior medial malleolar and medial calcaneal branches of the posterior tibial, and branches from the medial plantar artery. The lateral malleolar network is formed by the anterior lateral malleolar branch of the anterior tibial, the lateral tarsal branch of the dorsalis pedis, the perforating and the lateral calcaneal branches of the peroneal, and twigs from the lateral plantar artery (Fig. 8-80). Dorsalis Pedis Artery

The dorsalis pedis artery is the continua¬ tion of the anterior tibial artery beyond the ankle joint (Figs. 8-79; 8-80). It passes distally along the tibial side of the dorsum of the foot to the proximal part of the first intermeta¬ tarsal space. At this site the vessel divides into two terminal branches. These are the first dorsal metatarsal artery, which courses between the first and second toes, and the deep plantar artery, which penetrates be¬ tween the two heads of the first dorsal inter¬ osseous muscle to enter the sole of the foot, helping to complete the plantar arch. RELATIONS OF THE DORSALIS PEDIS ARTERY. The dorsalis pedis artery rests upon the anterior aspect of the articular capsule of the ankle joint. It continues distally in front of the talus, navicular, and interme¬ diate cuneiform bones, and the ligaments intercon¬ necting them. The artery is covered by the skin, fas¬ cia, and the inferior extensor retinaculum, and it is crossed near its termination by the first tendon of the extensor digitorum brevis. On its tibial or medial aspect is the tendon of the extensor hallucis longus. On its fibular or lateral aspect are the first tendon of the extensor digitorum longus and the termination of the deep peroneal nerve. The dorsalis pedis artery is usually accompanied by two veins. variations. The dorsalis pedis artery may be

775

larger than usual to compensate for a deficient lat¬ eral plantar artery. Its terminal branches to the toes may be absent, the toes then being supplied by the medial plantar, or its place may be taken by a large perforating branch of the peroneal artery (3%). In its descending course, the dorsalis pedis artery may lie lateral to the line between the middle of the ankle and the first interosseous space. In 12% of bodies, the dorsalis pedis is so small that it is essentially absent. The arcuate branch of the dorsalis pedis ar¬ tery is a vessel of significant size in only 54% of feet studied (Huber, 1941).

Branches of the Dorsalis Pedis Artery

The dorsalis pedis artery supplies the dor¬ sum of the foot with the following branches: Lateral tarsal Medial tarsal Arcuate First dorsal metatarsal Deep plantar LATERAL TARSAL ARTERY

The lateral tarsal artery arises most fre¬ quently from the dorsalis pedis as that vessel crosses the head of the talus (Figs. 8-79; 8-80). It passes laterally in an arched course, lying upon the tarsal bones and covered by the extensor digitorum brevis muscle. The lateral tarsal artery supplies this muscle and the articulations of the tarsus. It anastomo¬ ses with branches of the arcuate, anterior lateral malleolar, and lateral plantar arteries, and with the perforating branch of the pero¬ neal artery. MEDIAL TARSAL ARTERIES

Two or three small medial tarsal arteries ramify on the medial border of the foot and join the medial malleolar network (Fig. 8-80). ARCUATE ARTERY

The arcuate artery arises from the dorsalis pedis artery on the dorsum of the foot, be¬ tween the medial cuneiform and the base of the second metatarsal bone (Fig. 8-79). It passes laterally over the bases of the second, third, and fourth metatarsal bones, deep to the tendons of the extensor digitorum brevis, its direction being influenced by its point of origin. It anastomoses with the lateral tarsal and lateral plantar arteries. The arcuate ar-

776

THE ARTERIES

FIRST DORSAL METATARSAL ARTERY Lateral superior genicular a. Genicular anastomosis Lateral inferior genicular a. Ant. tibial recurrent a.

The first dorsal metatarsal artery courses distally on the first dorsal interosseous mus¬ cle and, at the cleft between the first and sec¬ ond toes, divides into two branches. One of these passes deep to the tendon of the exten¬ sor hallucis longus and is distributed to the medial border of the great toe; the other bi¬ furcates to supply the adjoining sides of the great and second toes.

Tibialis anterior m.

DEEP PLANTAR ARTERY Anterior tibial a.

Ext. digitorum longus m.

Peroneus longus m. Ext. hallucis longus m. Perforating branch, peroneal a. Anterior lateral malleolar a.

Dorsalis pedis a.

The deep plantar artery penetrates into the sole of the foot between the two heads of the first dorsal interosseous muscle and unites with the termination of the lateral plantar artery, thereby completing the plan¬ tar arch (Figs. 8-79; 8-80). On the plantar as¬ pect of the foot, it sends a branch along the medial side of the great toe, continuing dis¬ tally along the first interosseous space as the first plantar metatarsal artery (Figs. 8-82; 883). This latter vessel bifurcates and thereby supplies the adjacent sides of the first and second toes.

Lat. tarsal Medial tarsal aa.

Posterior Tibial Artery - Deep plantar a. Dorsal metatarsal aa. Dorsal digital aa

The right anterior tibial and dorsalis pedis arteries and their branches. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, 1975.)

Fig. 8-80.

tery gives off the second, third, and fourth dorsal metatarsal arteries (Fig. 8-80). These vessels course distally upon the correspond¬ ing dorsal interosseous muscles, and in the clefts between the toes, each divides into two dorsal digital arteries for the adjoining toes (Fig. 8-80). At the proximal parts of the interosseous spaces, the dorsal metatarsal arteries receive perforating branches from the plantar arch, and at the distal parts of the spaces they are joined by other perforating branches from the plantar metatarsal ar¬ teries. The fourth dorsal metatarsal artery gives off a branch that supplies the lateral aspect of the fifth toe.

The posterior tibial artery begins at the lower border of the popliteus muscle, oppo¬ site the interval between the tibia and fibula (Figs. 8-77; 8-81). It is larger than the anterior tibial artery, and it descends obliquely downward and medially in the posterior compartment of the leg between the superfi¬ cial and deep muscle layers. As it ap¬ proaches the tibial side of the leg, lying be¬ hind the tibia in the lower part of its course, the vessel is situated midway between the medial malleolus and the medial process of the calcaneal tuberosity. Under cover of the origin of the abductor hallucis it divides into the medial and lateral plantar arteries (Figs. 8-82; 8-83). RELATIONS OF THE POSTERIOR TIBIAL ARTERY. The posterior tibial artery lies successively upon the tibialis posterior, the flexor digitorum longus, the tibia, and the posterior part of the ankle joint. It is covered in the upper part of the leg by the deep transverse fascia that separates it from the gastro¬ cnemius and soleus, and at its entrance into the foot, it is covered by the abductor hallucis muscle. In the distal third of the leg, the artery is more superficial,

ARTERIES OF THE LOWER LIMB

being covered only by skin and fascia, and it courses parallel but anterior to the medial border of the tendo calcaneus. The posterior tibial artery is accom¬ panied by two veins and by the tibial nerve. The latter structure at first lies medial to the artery, but soon crosses the vessel posteriorly, and throughout most of its course lies lateral to the artery. Deep to the flexor retinaculum behind the medial malleolus, the tendons, blood vessels, and nerve are arranged from medial to lateral in the following order: the tendons of the tibialis posterior and flexor digitorum longus, the posterior tibial artery with a vein on each side, the tibial nerve, and, 1.25 cm nearer the heel, the tendon of the flexor hallucis longus. variation. The posterior tibial artery quite fre¬ quently is smaller than usual or even absent. In these cases its field is supplied by a large peroneal artery, which either joins the small posterior tibial artery or continues alone to the sole of the foot.

Branches of the Posterior Tibial Artery

From the posterior tibial artery arise the following branches: Circumflex fibular Peroneal Nutrient (tibial) Muscular Medial malleolar Communicating Medial calcaneal Medial plantar Lateral plantar CIRCUMFLEX FIBULAR ARTERY

The circumflex fibular artery usually arises from the upper end of the posterior tibial artery, but may arise from the popli¬ teal artery or even from the anterior tibial artery. It pierces the fibular head of the soleus muscle, winds around the neck of the fibula, and supplies the soleus along with the peroneal muscles arising from the upper fib¬ ula. It participates in the anastomosis around the lateral aspect of the knee joint (Fig. 8-78). PERONEAL ARTERY

The peroneal artery is deeply located on the fibular side of the back of the leg. It arises from the posterior tibial artery about 2.5 cm distal to the lower border of the popliteus muscle (Figs. 8-77; 8-81). It passes

777

obliquely toward the fibula and then de¬ scends along the medial aspect of that bone, contained in a fibrous canal between the tibialis posterior and the flexor hallucis longus, or in the substance of the latter mus¬ cle. The peroneal artery then runs behind the tibiofibular syndesmosis, ending in lat¬ eral calcaneal branches which ramify over the lateral and posterior surfaces of the cal¬ caneus. In the proximal part of the leg, the peroneal artery is covered by the soleus muscle and the deep transverse fascia. More distally, it lies deep to the flexor hallucis longus muscle. variations. The peroneal artery may arise from the posterior tibial artery higher than normal, or even from the popliteal artery. In contrast, it may arise as far as 7 or 8 cm below the popliteus muscle. If the vessel is larger than normal, it either reinforces the posterior tibial by joining it, or when it is very large, altogether takes the place of the posterior tib¬ ial in the distal part of the leg and foot. In the rarer instances, when the peroneal artery is smaller than normal, another branch from the posterior tibial helps to supply its muscular field, and a branch from the anterior tibial compensates for the diminished perforating artery. In 3% of specimens, the perforat¬ ing branch of the peroneal artery is considerably en¬ larged and it takes the place of the dorsalis pedis artery.

Branches of the Peroneal Artery

The peroneal artery supplies vessels to structures in the lateral aspect of the leg. The branches are: Muscular Nutrient (fibular) Perforating Communicating Lateral malleolar Lateral calcaneal Muscular branches of the peroneal artery go to the soleus, tibialis posterior, flexor hallucis longus, and peroneal muscles. nutrient artery. The nutrient artery from the peroneal is directed downward and enters the nutrient canal of the fibula. perforating branch. The perforating branch of the peroneal artery pierces the in¬ terosseous membrane about 5 cm above the lateral malleolus to reach the anterior part of muscular branches.

778

THE ARTERIES

Semitendinosus m. Biceps femoris m. Tibial n. Superior lateral genicular a.

Semimembranosus m Popliteal a. Med sural a ....

Lateral sural a. Gastrocnemius m. (medial head) — Inf. medial \ genicular a. — Plantaris m. ..

Sural n. - Tibial n. - Common peroneal n. "Anterior tibial a.

Soleus m. . t—- Post, tibial a. 4— Peroneal a. Flexor digitorum longus m. ••••*• j

Peroneus brevis m.

Tibialis posterior m.

Flexor hallucis longus m.

Peroneus longus and brevis m. Peroneal a. Medial malleolar a. Tibial n. Lateral calcaneal a.

Medial calcaneal a.

Calcaneal network

Fig. 8-81.

The right posterior tibial artery and its branches. (From Benninghoff and Goerttler, Lehrhuch der Anatomie des Menschen, 1975.)

the leg, where it anastomoses with the ante¬ rior lateral malleolar artery (Figs. 8-77; 8-79; 8-80). It then descends anterior to the tibio¬ fibular syndesmosis, gives branches to the tarsus, and anastomoses with the lateral tar¬ sal artery. communicating branch. A communicat¬ ing branch arises from the peroneal artery about 5 cm from its distal end (Fig. 8-77). It courses transversely across the leg just pos¬ terior to the interosseous membrane to join the communicating branch of the posterior tibial. LATERAL

MALLEOLAR

BRANCHES.

Several

small lateral malleolar branches arise from the peroneal artery; they wind around the lateral malleolus and join the lateral mal¬ leolar network (Fig. 8-77). LATERAL CALCANEAL BRANCHES. Lateral calcaneal branches are the terminal vessels of the peroneal artery (Figs. 8-77; 8-81). They pass to the lateral aspect of the heel and communicate with the anterior lateral malleolar branch of the anterior tibial and with the lateral malleolar branches of the peroneal artery. On the back of the heel, they anastomose with the medial calcaneal branches of the posterior tibial.

ARTERIES OF THE LOWER LIMB

NUTRIENT ARTERY

The nutrient artery of the tibia arises from the posterior tibial artery near its origin. It pierces the tibialis posterior muscle to which it gives several muscular branches, and then it descends obliquely to enter the nutrient canal of the tibia, located just below the soleal line. Within the bone, the nutrient ar¬ tery divides into an ascending branch, which supplies the superior end of the tibia, and a descending branch, which supplies the body and inferior end of the bone. It is the largest nutrient artery to a bone in the body and is accompanied to the bone by a branch of the nerve to the popliteus muscle. MUSCULAR BRANCHES

Muscular branches of the posterior tibial artery are distributed to the soleus and to the deep muscles along the back of the leg. MEDIAL MALLEOLAR ARTERY

The medial malleolar artery is a small branch of the posterior tibial artery which winds around the tibial malleolus and joins in the medial malleolar network (Figs. 8-77; 8-81). COMMUNICATING BRANCH

A communicating branch arises from the posterior tibial artery about 5 cm above the medial malleolus (Fig. 8-77). It courses trans¬ versely across the posterior aspect of the tibia and the interosseous membrane. Deep to the flexor hallucis longus muscle, it joins the communicating branch of the peroneal artery. MEDIAL CALCANEAL ARTERIES

The medial calcaneal arteries are several large vessels that arise from the poste¬ rior tibial artery just before it divides into the medial and lateral plantar arteries (Figs. 8-77; 8-80). Frequently, however, they branch from the lateral plantar rather than the posterior tibial. They pierce the flexor retinaculum and are distributed to the fat and skin behind the tendo calcaneus and about the heel, also helping to supply the muscles on the tibial side of the sole of the foot. The medial calcaneal arteries anasto¬

779

mose with the medial malleolar branches of the posterior tibial, and on the back of the heel, with the lateral calcaneal branches of the peroneal artery (Fig. 8-81).

MEDIAL PLANTAR ARTERY

The medial plantar artery is the smaller of the two terminal branches of the posterior tibial artery (Figs. 8-82; 8-83). It passes distally along the medial aspect of the foot and is at first situated deep to the abductor hallu¬ cis, and then between it and the flexor digitorum brevis, both of which it supplies. At the base of the first metatarsal bone, and much diminished in size, it passes along the medial border of the first toe, anastomosing with a branch of the first plantar metatarsal artery. Small superficial digital branches accompany the digital branches of the me¬ dial plantar nerve, and these join the plantar metatarsal arteries of the first three spaces (Fig. 8-82).

LATERAL PLANTAR ARTERY

The lateral plantar artery is much larger than the medial plantar. Initially, it passes obliquely lateralward to the base of the fifth metatarsal bone, and then it curves medially to the interval between the bases of the first and second metatarsal bones (Figs. 8-82; 883). There it unites with the deep plantar branch of the dorsalis pedis artery, which completes the formation of the plantar arch (Fig. 8-83). As the lateral plantar artery passes laterally, it is first placed between the calcaneus and abductor hallucis muscle, and then between the flexor digitorum brevis and quadratus plantae muscles. As it runs distally along the base of the little toe, it lies more superficially between the flexor digi¬ torum brevis and abductor digiti minimi, and is covered only by the plantar aponeuro¬ sis, superficial fascia, and skin. plantar arch. The remaining portion of the lateral plantar artery is the more deeply situated plantar arch (Fig. 8-83). Extending from the base of the fifth metatarsal bone, the plantar arch penetrates through the lay¬ ers of the sole of the foot to course medially, beneath the adductor hallucis. It crosses the plantar surface of the bases of the fourth, third, and second metatarsal bones and the corresponding interosseous muscles. At the

780

THE ARTERIES

Post, tibial a.

Plantar aponeurosis Abd. hallucis m. Superficial branch, medial plantar a.

Flexor digitorum brevis m.

Medial plantar a. Lat. plantar a. Flexor hallucis brevis m.

Abductor digiti minimi m. Flexor digiti minimi brevis m.

Tendon of flexor hallucis longus m. First plantar metatarsal a.

Proper digital aa. Plantar metatarsal aa.

Fig. 8-82. The more superficial branches of the plantar arteries as seen after removal of the plantar aponeurosis. Right foot. (From Benninghoff and Goerttler. Lehrbuch der Anatomie des Menschen, 1975.)

proximal part of the first interosseous space, the plantar arch is completed by its junction with the deep plantar branch of the dorsalis pedis artery. Besides distributing numerous branches to the muscles, integument, and fasciae in the sole, the plantar arch gives rise to three perforating and four plantar meta¬ tarsal arteries. The three perforating branches of the plantar arch penetrate through the proximal parts of the second, third, and fourth interos¬ seous spaces, between the heads of the dor¬ sal interosseous muscles, to anastomose with the dorsal metatarsal arteries. The four plantar metatarsal arteries course distally between the metatarsal bones and lie in contact with the interosseous mus¬

cle (Figs. 8-82; 8-83). Each vessel divides into two plantar digital arteries, which supply the adjacent sides of the toes. Near their points of division each plantar metatarsal artery gives off an anterior perforating branch to join the corresponding dorsal met¬ atarsal artery. The first plantar metatarsal artery springs from the junction between the plantar arch and the deep plantar branch of the dorsalis pedis artery (Figs. 8-82; 8-83). It sends a digi¬ tal branch to the medial aspect of the large toe. The digital branch for the lateral aspect of the little toe arises from the lateral plantar artery near the base of the fifth metatarsal bone, just as the latter vessel curves medi¬ ally to become the plantar arch.

REFERENCES

781

Post, tibial a.

Quadratus plantae m. Lat. plantar a.

Abd. hallucis m. Medial plantar a.

Plantar arch

Flexor hallucis brevis m.

Plantar metatarsal aa. Interosseous mm.

First plantar metatarsal a.

Proper digital aa.

Proper digital aa.

Fig. 8-83. The deep arteries on the plantar aspect of the right foot. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, 1975.)

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.) General Adams, W. E. 1942. The blood supply of nerves. I. Histor¬ ical review. J. Anat. (Lond.), 76:323-341. Benninghoff, A., and K. Goerttler. 1975. Lehrbuch der Anatomie des Menschen. 11th ed. Edited by H. Ferner and J. Staubesand., Urban and Schwarzenberg, Munich, 3 vols. Blomfield, L. B. 1945. Intramuscular vascular patterns in man. Proc. Roy. Soc. Med., 38:617-618 Clara, M. 1956. Die arterio-venosen Anastomosen, Anat¬ omie, Bioiogie, Pathologie. 2nd ed. Springer-Verlag, Vienna, 315 pp. Coates, A. E. 1931. Observations on the distribution of the arterial branches of the peripheral nerves. J. Anat. (Lond.), 66:499-507. Edwards, D. A. W. 1946. The blood supply and lymphatic drainage of tendons. J. Anat. (Lond.), 80:147-152.

Learmonth, J. 1950. Collateral circulation, natural and artificial. Surg. Gynec. Obstet., 90:385-392. McDonald, D. A. 1960. Blood Flow in Arteries. Williams & Wilkins, Baltimore, 328 pp. Moore, K. L. 1973. The Developing Human. W. B. Saun¬ ders Co., Philadelphia, 374 pp. Orbinson, ). L., and D. E. Smith. 1963. The Peripheral Blood Vessels. Williams & Wilkins, Baltimore, 357 pp. Quiring, D. P. 1949. Collateral Circulation (Anatomical Aspects). Lea & Febiger, Philadelphia, 142 pp. Embryology Allan, F. D. 1961. An histological study of the nerves associated with the ductus arteriosus. Anat. Rec., 139:531-537. Auer,}. 1948. The development of the human pulmonary

782

THE ARTERIES

vein and its major variations. Anat. Rec., 101:581594. Boyden, E. A. 1970. The developing bronchial arteries in a fetus of the twelfth week. Amer. J. Anat., 129:357368. Goldsmith, J. B., and H. W. Butler. 1937. The develop¬ ment of the cardiac-coronary circulatory system. Amer. J. Anat., 60:185-202. Hislop, A., and L. Reid. 1972. Intrapulmonary arterial development during fetal life: branching pattern and structure. J. Anat. (Lond.), 113:35-48. Khodadad, G. 1977. Persistent hypoglossal artery in the fetus. Acta Anat., 99:477-481. Maron, B. J., and G. M. Hutchins. 1972. Truncus arterio¬ sus malformation in a human embryo. Amer. J. Anat., 134:167-174. Moffat, D. B. 1961. The development of the posterior cer¬ ebral artery. J. Anat. (Lond.), 95:485-494. Morris, E. D., and D. B. Moffat. 1956. Abnormal origin of the basilar artery from the cervical part of the inter¬ nal carotid and its embryological significance. Anat. Rec., 125:701-712. Noback, G. ]., and I. Rehman. 1941. The ductus arteriosus in the human fetus and newborn infant. Anat. Rec., 81:505-527. Padget, D. H. 1948. Development of the cranial arteries in the human embryo. Carneg. Inst., Contr. Embryol., 32:205-262. Padget, D. H. 1954. Designation of the embryonic intersegmental arteries in reference to the vertebral ar¬ tery and subclavian stem. Anat. Rec., 119:349-356. Scammon, R. E., and E. H. Norris. 1918. On the time of the post-natal obliteration of the fetal blood-passages (foramen ovale, ductus arteriosus, ductus venosus). Anat. Rec., 15:165-180. Sciacca, A., and M. Condorelli. 1960. Involution of the Ductus Arteriosus. S. Karger, Basel, 52 pp. Senior, H. D. 1919. The development of the arteries of the human lower extremity. Amer. J. Anat., 25:55-95. Woollard, H. H. 1922. The development of the principal arterial stems in the forelimb of the pig. Carneg. Inst., Contr. Embryol., 14:139-154.

Aorta and Aortic Arches Barry, A. 1951. The aortic arch derivatives in the human adult. Anat. Rec., Ill:221-238. Blalock, A. 1946. Operative closure of patent ductus arte¬ riosus. Surg. Gynec. Obstet., 82:113-114. Congdon, E. D. 1922. Transformation of the aortic arch system during the development of the human em¬ bryo. Carneg. Inst., Contr. Embryol., 14:47-110. De Garis, C. F. 1941. The aortic arch in primates. Amer. J. Phys. Anthrop., 28:41-74. Fox, M. H., and C. M. Goss. 1958. Experimentally pro¬ duced malformations of the heart and great vessels in rat fetuses. Transposition complexes and aortic arch abnormalities. Amer. J. Anat., 102:65-92. Gross, R. E„ and P. F. Ware. 1946. The surgical signifi¬ cance of aortic arch anomalies. Surg. Gynec. Ob¬ stet., 83:435-448. Hanlon, C. R., and A. Blalock. 1948. Complete transposi¬ tion of the aorta and the pulmonary artery: Experi¬ mental observations on venous shunts as corrective features. Ann. Surg., 127:385-397. Lewis, C. W. D., and f. N. M. Parry. 1948. Double aortic arch. Anat. Rec., 101:613-615.

Me Donald, J. J., and B. J. Anson. 1940. Variations in the origin of arteries derived from the aortic arch. Amer. J. Phys. Anthrop., 27:91-108. Sealy, W. C. 1951. A report of two cases of the anoma¬ lous origin of the right subclavian artery from the descending aorta. J. Thoracic Surg., 21:319-324. Shaner, R. F. 1956. The persisting right sixth aortic arch of mammals, with a note on fetal coarctation. Anat. Rec., 125:171-184. Sinclair, J. G., and N. D. Schofield. 1944. Anomalies of the cardiopulmonary circuit compensated without a ductus arteriosus. Anat. Rec., 90:209-216. Sprang, D. H., Jr., and N. L. Cutler. 1930. A case of human right aorta. Anat. Rec., 45:365-375. Stibbe, E. P. 1929. True congenital diverticulum of the trachea in a subject showing also right aortic arch. J. Anat. (Lond.), 64:62-66. Woodburne, R. T. 1951. A case of right aortic arch and associated venous anomalies. Anat. Rec., 111:617628. Wright, N. L. 1969. Dissection study and measuration of the human aortic arch. J. Anat. (Lond.), 104:377-385.

Coronary Arteries Abramson, D. I., and H. J. Eisenberg. 1934. The coronary blood supply in the rhesus monkey. J. Anat. (Lond.), 69:520-525. Ahmed, S. H., M. T. El-Rakhawy, A. Abdalla, and R. G. Harrison. 1973. A new conception of coronary ar¬ tery preponderance. Acta Anat., 83:87-94. Chander, S., and I. Jit. 1957. Single coronary artery. J. Anat. Soc. India, 6:116-118. Chase, R. E., and C. F. De Garis. 1939. Arteriae coronariae (cordis) in the higher primates. Amer. J. Phys. Anthrop., 24:427-448. Chinn, J., and M. A. Chinn. 1961. Report of an accessory coronary artery arising from the pulmonary artery. Anat. Rec., 139:23-28. Colborn, G. L. 1966. The gross morphology of the coro¬ nary arteries of the common squirrel monkey. Anat. Rec., 155:353-368. Esperanga-Pina, J. A. 1974. Injection-corrosion-fluores¬ cence in the study of human coronary arterial anas¬ tomoses. Acta Anat., 90:481-488. Gregg, D. E. 1950. Coronary Circulation in Health and Disease. Lea & Febiger, Philadelphia, 227 pp. Gross, L. 1921. The Blood Supply of the Heart in Its Ana¬ tomical and Clinical Aspects. Paul B. Hoeber, Inc., New York, 171 pp. Gross, L., and M. A. Kugel. 1933. The arterial blood vas¬ cular distribution to the left and right ventricles of the human heart. Amer. Heart J., 9:165-177. Halpern, M. H„ and M. M. May. 1958. Phylogenetic study of the extracardiac arteries to the heart. Amer. J. Anat., 102:469-480. Hill, W. C. O. 1945. Atrial arteries in a human heart. J. Anat. (Lond.), 79:41-43. Hutchinson, M. C. E. 1978. A study of the atrial arteries in man. J. Anat. (Lond.), 125:39-54. James, T. N. 1960. The arteries of the free ventricular walls in man. Anat. Rec., 136:371-384. James, T. N. 1961. Anatomy of the Coronary Arteries. Paul B. Hoeber, Inc., New York, 211 pp. James, T. N., and G. E. Burch. 1958. The atrial coronary arteries in man. Circulation, 17:90-98. Jordan, R. A., T. J. Dry and J. E. Edwards. 1950. Cardiac

REFERENCES

clinics: CXXXVI. Anomalous origin of the right cor¬ onary artery from the pulmonary trunk. Proc. Staff Meet., Mayo Clinic, 25:673-678. Ryback, R., and N. J. Mizeres. 1965. The sinus node artery in man. Anat. Rec., 153:23-30. Tomanek, R. }. 1970. Effects of age and exercise on the extent of the myocardial capillary bed. Anat. Rec., 167:55-62. Velican, C., andD. Velican. 1977. Studies on human cor¬ onary arteries. I. Branch pads or cushions. Acta Anat., 99:377-385. Velican, D., and C. Velican. 1978. Human coronary ar¬ teries. II. Branching anatomical pattern and arterial wall microarchitecture. Acta Anat., 100:258-267. White, N. K., and J. E. Edwards. 1948. Anomalies of the coronary arteries: Report of four cases. Arch. Path., 45:766-771.

Arteries of the Head and Neck Abbie, A. A. 1932. The blood supply of the lateral genicu¬ late body with a note on the morphology of the cho¬ roidal arteries. J. Anat. (Lond.), 67:491-521. Abbie, A. A. 1933. The clinical significance of the ante¬ rior choroidal artery. Brain, 56:233-246. Abbie, A. A. 1933. The morphology of the forebrain ar¬ teries, with especial reference to the evolution of the basal ganglia. J. Anat. (Lond.), 68:433-470. Adams, W. E. 1955. The carotid sinus complex, “para¬ thyroid” III and thymo-parathyroid bodies, with special reference to the Australian opossum, Trichosurus vulpecula. Amer. [. Anat., 97.T-58. Adams, W. E. 1957. On the possible homologies of the occipital artery in mammals, with some remarks on the phylogeny and certain anomalies of the subcla¬ vian and carotid arteries. Acta Anat., 29:90-113. Ahmed, D. S., and R. H. Ahmed. 1967. The recurrent branch of the anterior cerebral artery. Anat. Rec., 157:699-700. Allan, F. D. 1952. An accessory or superficial inferior thyroid artery in a full term infant. Anat. Rec., 112:539-542. Atkinson, W. J. 1949. The anterior cerebellar artery. Its variations, pontine distribution and significance in the surgery of cerebellopontine angle tumors. J. Neurol. Psychiat., 12:137-151. Baldwin, B. A. 1964. The anatomy of the arterial supply to the cranial regions of the sheep and ox. Amer. J. Anat., 115:101-117. Baumel, J. J., and D. Y. Beard. 1961. The accessory menin¬ geal artery of man. J. Anat. (Lond.), 95:386-402. Bell, R. H., L. L. Swigart, and B. J. Anson. 1950. The rela¬ tion of the vertebral artery to the cervical vertebrae. Quart. Bull. Northwest. Univ. Med. Sch., 24:184-185. Blair, C. B., Jr., K. Nandy, and G. H. Bourne. 1962. Vascu¬ lar anomalies of the face and neck. Anat. Rec., 144:251-257. Boemer, L. C. 1937. The great vessels in deep infections of the neck. Arch. Otolaryngol., 25:465-472. Borodulya, A. V., and E. K. Pletchkova. 1973. Distribu¬ tion of cholinergic and adrenergic nerves in the in¬ ternal carotid artery: A histochemical study. Acta Anat., 86:410-425. Boyd, G. I. 1934. Abnormality of subclavian artery asso¬ ciated with presence of the scalenus minimus. J. Anat. (Lond.), 68:280-281.

783

Boyd, ]. D. 1933. Absence of the right common carotid artery. J. Anat. (Lond.), 68:551-557. Cairney, J. 1925. Tortuosity of the cervical segment of the internal carotid artery. J. Anat. (Lond.), 59:87-96. Carpenter, M. B., C. R. Noback, and M. L. Moss. 1954. The anterior choroidal artery. Its origins, course, distribution and variations. Arch. Neurol. Psychiat., 71:714-722. Chakravorty, B. G. 1971. Arterial supply of the cervical spinal cord (with special reference to the radicular arteries). Anat. Rec., 170:311-330. Chandler, S. B., and C. F. Derezinski. 1935. The varia¬ tions of the middle meningeal artery within the mid¬ dle cranial fossa. Anat. Rec., 62:309-319. Chanmugam, P. K. 1936. Note on an unusual ophthalmic artery associated with other abnormalities. J. Anat. (Lond.), 70:580-582. Curtis, G. M. 1930. The blood supply of the human para¬ thyroids. Surg. Gynec. Obstet, 51:805-809. Dahl, E. 1973. The innervation of the cerebral arteries. J. Anat. (Lond.), 115:53-64. Dandy, W. E., and E. Goetsch. 1911. The blood supply of the pituitary gland. Amer. J. Anat., 11:137-150. De La Torre, E., and M. G. Netsky. 1960. Study of persist¬ ent primitive maxillary artery in human fetus: Some homologies of cranial arteries in man and dog. Amer. J. Anat., 106:185-195. Evans, T. H. 1956. Carotid canal anomaly: Other in¬ stances of absent internal carotid artery. Med. Times, 84:1069-1072. Furlani, J. 1973. The anterior choroidal artery and its blood supply to the internal capsule. Acta Anat., 85:108-112. Gillian, L. A. 1961. The collateral circulation of the human orbit. Arch. Ophthal., 65:684-694. Gillian, L. A. 1968. The arterial and venous blood sup¬ plies to the forebrain (including the internal capsule) of primates. Neurology, 18:653-670. Hayreh, S. S. 1962. The ophthalmic artery. III. Branches. Brit. J. Ophthal., 46:212-247. Hayreh, S. S., and R. Dass. 1962. The ophthalmic artery. I. Origin and intra-cranial and intra-canalicular course. Brit. J. Ophthal., 46:65-98. Hayreh, S. S., and R. Dass. 1962. The ophthalmic artery. II. Intraorbital course. Brit. J. Ophthal., 46:165-185. Herman, L. H., A. Z. Ostrowski, and E. S. Gurdjian. 1963. Perforating branches of the middle cerebral artery; an anatomical study. Arch. Neurol., 8:32-34. Jackson, B. B. 1967. The external carotid as a brain col¬ lateral. Amer. J. Surg., 113:375-378. Jones, F. W. 1939. The anterior superior alveolar nerve and vessels. J. Anat. (Lond.), 73:583-591. Kassell, N. F., and T. W. Langfitt. 1965. Variations in the circle of Willis in Macaca mulatta. Anat. Rec., 152:257-264. Kirchner, J., E. Yanagisawa, and E. S. Crelin. 1961. Surgi¬ cal anatomy of the ethmoidal arteries. Arch. Otolaryng., 74:382-386 Krayenbiihl, H. A., and M. G. Yasargil. 1968. Cerebral Angiography. Butterworth and Co., London, 401 pp. Lasker, G. W., D. L. Opdyke, and H. Miller. 1951. The position of the internal maxillary artery and its questionable relation to the cephalic index. Anat. Rec., 109:119-126. Lazorthes, G., and G. Salamon. 1971. The arteries of the thalamus: an anatomical and radiological study. J. Neurosurg., 34:23-26.

784

THE ARTERIES

Lee, I. N. 1955. Anomalous relationship of the inferior thyroid artery. Anat. Rec., 122:499-506. Maisel, H. 1958. Some anomalies of the origin of the left vertebral artery. S. Afr. Med. )., 32:1141-1142. McCullough, A. W. 1962. Some anomalies of the cerebral arterial circle (of Willis) and related vessels. Anat. Rec., 142:537-543. Newton, T. H. 1968. The anterior and posterior menin¬ geal branches of the vertebral artery. Radiology, 91:271-279. Newton, T. H., and R. L. Mani. 1974. The vertebral artery. Chapter 67 in Radiology of the Skull and Brain. Edited by T. H. Newton and D. G. Potts. C. V. Mosby Co., St. Louis, Vol. 2, Book 2, pp.1659-1709. Newton, T. H., and D. G. Potts. 1974. In Radiology of the Skull and Brain: Angiography. C. V. Mosby Co., St. Louis, Vol. 2. Page, R. B., and R. M. Bergland. 1977. The neuro¬ hypophyseal capillary bed. I. Anatomy and arterial supply. Amer. J. Anal 148:345-357. Read, W. T., and M. Trotter. 1941. The origins of trans¬ verse cervical and transverse scapular arteries in American whites and Negroes. Amer. J. Phys. Anthrop., 28:293-247. Reed, A. F. 1943. The relations of the inferior laryngeal nerve to the inferior thyroid artery. Anat. Rec., 85:17-24. Ring, B. A. 1962. Middle cerebral artery: Anatomical and radiographic study. Acta Radiol., 57:289-300. Rogers, L. 1947. The function of the circulus arteriosus of Willis. Brain, 70:171-178. Salamon, G., J. Gonzales, ]. Faure, and G. Giudicelli. 1972. Topographic investigation of the cortical branches of the middle cerebral artery. Acta Radiol., 13:226-232. Scarlett, H. 1935. Occlusion of the central artery of the retina. Ann. Surg., 101:318-323. Scharrer, E. 1940. Arteries and veins in the mammalian brain. Anat. Rec., 78:173-196. Seydel, H. G. 1964. The diameters of the cerebral arteries of the human fetus. Anat. Rec., 150:79-88. Shanklin, W. M., and N. A. Azzam. 1963. A study of valves in the arteries of the rodent brain. Anat. Rec., 147:407-413. Smith, S. D., and R. S. Benton. 1978. A rare origin of the superior thyroid artery. Acta Anat., 101:91-93. Stephens, R. B., and D. L. Stilwell. 1969. Arteries and Veins of the Human Brain. Charles C Thomas, Springfield, 111., 181 pp. Stewart, J. D. 1932. Circulation of the human thyroid. Arch. Surg., 25:1157-1165. Sunderland, S. 1945. The arterial relations of the internal auditory meatus. Brain, 68:23-27. Taveras, J. M„ and E. H. Wood. 1964. Diagnostic Neuroradiology. Williams and Wilkins, Baltimore, 960 pp. Watt, f. C., and A. N. Me Killop. 1935. Relation of arteries to roots of nerves in the posterior cranial fossa in man. Arch. Surg., 30:336-345. Watts, J. W. 1933. A comparative study of the anterior cerebral artery and the circle of Willis in primates. J. Anat. (Lond.), 68:534-550. Westberg, G. 1963. The recurrent artery of Heubner and the arteries of the central ganglia. Acta Radiol. (Diagn.), 1:949-954. Westberg, G. 1966. Arteries of the basal ganglia. Acta Radiol. (Diagn.), 5:581-596. Williams, D. J. 1936. The origin of the posterior cerebral artery. Brain, 59:175-180.

Wilson, Me Clure. 1972. The Anatomic Foundation of Neuroradiology of the Brain. 2nd ed. Little, Brown and Co., Boston, 390 pp. Windle, W. F., F. R. Zeiss, and M. S. Adamski. 1927. Note on a case of anomalous right vertebral and subcla¬ vian arteries. J. Anat. (Lond.), 62:512-514. Wislocki, G. B. 1938. The vascular supply of the hypoph¬ ysis cerebri of the rhesus monkey and man. Res. Publ. Assn. Nerv. Ment. Dis., 17:48-68.

Arteries of the Thorax Alexander, W. F. 1946. The course and incidence of the lateral costal branch of the internal mammary ar¬ tery. Anat. Rec., 94:446. Anson, B. ]. 1936. The anomalous right subclavian artery: Its practical significance: with a report of three cases. Surg. Gynec. Obstet., 62:708-711. Anson, B. J., R. R. Wright, and J. A. Wolfer. 1939. Blood supply of the mammary gland. Surg. Gynec. Obstet., 69:468-473. Appleton, A. B. 1945. The arteries and veins of the lungs. I. Right upper lobe. J. Anat. (Lond.), 79:97-120. Boyden, E. A. 1955. Segmental Anatomy of the Lungs: A Study of the Patterns of the Segmental Bronchi and Related Pulmonary Vessels. McGraw-Hill, New York, 276 pp. Boyden, E. A. 1970. The time lag in the development of bronchial arteries. Anat. Rec., 166:611-614. Boyden, E. A., and J. G. Scannell. 1948. An analysis of variations in the bronchovascular pattern of the right upper lobe of fifty lungs. Amer. J. Anat., 82:2773. Cauldwell, E. W., R. G. Siekert, R. A. Lininger, and B. J. Anson. 1948. The bronchial arteries: An anatomic study of 150 human cadavers. Surg. Gynec. Obstet., 86:395-412. Cole, F. H., F. H. Alley, and R. S. Jones. 1951. Aberrant systemic arteries to the lower lung. Surg. Gynec. Obstet., 93:589-596. Douglass, R. 1948. Anomalous pulmonary vessels. J. Tho¬ racic Surg., 17:712-716. Ferry, R. M., Jr., and E. A. Boyden. 1951. Variations in the bronchovascular patterns of the right lower lobe of fifty lungs. J. Thoracic Surg., 22:188-201. Jackson, C. L., and J. F. Huber. 1943. Correlated applied anatomy of the bronchial tree and lungs with a sys¬ tem of nomenclature. Dis. Chest, 9:319-326. Kropp, B. N. 1951. The lateral costal branch of the inter¬ nal mammary artery. J. Thoracic Surg., 21:421-425. Maliniac, J. W. 1943. Arterial blood supply of the breast: Revised anatomic data relating to reconstructive surgery. Arch. Surg., 47:329-343. Miller, W. S. 1907. The vascular supply of the pleura pulmonalis. Amer. J. Anat., 7:389-407. O’Rahilly, R., H. Debson, and T. S. King. 1950. Subcla¬ vian origin of bronchial arteries. Anat. Rec., 108:227238. Pitel, M., and E. A. Boyden. 1953. Variations in the bron¬ chovascular patterns of the left lower lobe of fifty lungs. J. Thoracic Surg., 26:633-653. Potter, S. E., and E. A. Holyoke. 1950. Observations on the intrinsic blood supply of the esophagus. Arch. Surg., 61:944-948. Shapiro, A. L., and G. L. Robillard. 1950. The esophageal arteries. Their configurational anatomy and varia¬ tions in relation to surgery. Ann. Surg., 131:171-185.

REFERENCES

Swigart, L. L., R. G. Siekert, W. C. Hambley, and B. J. Anson. 1950. The esophageal arteries: An anatomic study of 150 specimens. Surg. Gynec. Obstet., 90:234-243. Tobin, C. E. 1952. The bronchial arteries and their con¬ nections with other vessels in the human lung. Surg. Gynec. Obstet., 95:741-750. Tobin, C. E. 1960. Some observations concerning the pulmonic vasa vasorum. Surg. Gynec. Obstet., Ill:297-303.

Arteries of the Upper Limb Blunt, M. J. 1959. The vascular anatomy of the median nerve in the forearm and hand. J. Anat. (Lond.), 93:15-22. Brockis, }. G. 1953. The blood supply of the flexor and extensor tendons of the fingers in man. J. Bone Jt. Surg., 35B.T31-138. Coleman, S. S„ and B. J. Anson. 1961. Arterial patterns in the hand based upon a study of 650 specimens. Surg. Gynec. Obstet., 113:409-424. Daseler, E. H., and B. J. Anson. 1959. Surgical anatomy of the subclavian artery and its branches. Surg. Gynec. Obstet., 108:149-174. De Garis, C. F., and W. B. Swartley. 1928. The axillary artery. Amer. J. Anat., 41:353-397. Edwards, E. A. 1960. Organization of the small arteries of the hand and digits. Amer. J. Surg., 99:837-846. Huelke, D. F. 1959. Variation in the origins of the branches of the axillary artery. Anat. Rec., 135: 33-41. Huelke, D. F. 1962. The dorsal scapular artery—A pro¬ posed term for the artery to the rhomboid muscles. Anat. Rec., 142:57-61. Marcarian. H. Q., and R. D. Smith. 1968. A quantitative study of the vasa nervorum in the ulnar nerve of cats. Anat. Rec., 161:105-110. Markee, J. E., J. Wray, J. Nork, and F. McFalls. 1961. A quantitative study of the vascular beds of the hand. J. Bone Jt. Surg., 43A.T187-1196. McCormack, L. J., E. W. Cauldwell, and B. J. Anson. 1953. Brachial and antebrachial arterial patterns. A study of 750 extremities. Surg. Gynec. Obstet., 96:43-54. Miller, R. A. 1939. Observations upon the arrangement of the axillary artery and brachial plexus. Amer. J. Anat., 64:143-163. Misra, B. D. 1955. The arteria mediana. J. Anat. Soc. India, 4:48. O’Rahilly, R„ H. Debson, and T. S. King. 1950. Subcla¬ vian origin of bronchial arteries. Anat. Rec., 108:227238. Pick, J. 1958. The innervation of the arteries in the upper limb of man. Anat. Rec., 130:103-124. Rohlich, K. 1934. Uber die Arteria transversa colli des Menschen. Anat. Anz., 79:37. Slager, R. F., and K. P. Klassen. 1958. Anomalous right subclavian artery arising distal to a coarctation of the aorta. Ann. Surg., 147:93-97. Sunderland, S. 1945. Blood supply of the nerves of the upper limb in man. Arch. Neurol. Psychiat., 53:91115. Taleisnik, J., and P. J. Kelly. 1966. The extraosseous and intraosseous blood supply of the scaphoid bone. J. Bone Jt. Surg.. 48A.T125-1137. Weathersby, H. T. 1955. The artery of the index finger. Anat. Rec., 122:57-64.

785

Weathersby, H. T. 1956. Unusual variation of the ulnar artery. Anat. Rec., 124:245-248.

Arteries of the Abdomen Anson, B. J., E. W. Cauldwell, J. W. Pick, and L. E. Beaton. 1947. The blood supply of the kidney, suprarenal gland and associated structures. Surg. Gynec. Ob¬ stet., 84:313-320. Anson, B. J., G. A. Richardson, and W. L. Minear. 1936. Variations in the number and arrangement of the renal vessels: A study of the blood supply of four hundred kidneys. J. Urol., 36:211-219. Barlow, T. E., F. H. Bentley, and D. N. Walder. 1951. Ar¬ teries, veins and arteriovenous anastomoses in the human stomach. Surg. Gynec. Obstet., 93:657-671. Basmajian, J. V. 1954. The marginal anastomoses of the arteries to the large intestine. Surg. Gynec. Obstet., 99:614-616. Baylin, G. J. 1939. Collateral circulation following an obstruction of the abdominal aorta. Anat. Rec., 75:405-408. Benton, R. S., and W. B. Cotter. 1963. A hitherto undocumented variation of the inferior mesenteric artery in man. Anat. Rec., 145:171-173. Browne, E. Z. 1940. Variations in origin and course of the hepatic artery and its branches: Importance from surgical viewpoint. Surgery, 8:424-445. Cadete-Leite, A. 1973. The arteries of the pancreas of the dog. An injection-corrosion and microangiographic study. Amer. J. Anat., 137:151-157. Cauldwell, E. W., and B. J. Anson. 1943. The visceral branches of the abdominal aorta: Topographical re¬ lationships. Amer. J. Anat., 73:27-57. Chambers, G., E. Eldred, and C. Eggett. 1972. Anatomical observations on the arterial supply to the lumbosac¬ ral spinal cord of the cat. Anat. Rec., 174:421-433. Clark, K. 1959. The blood vessels of the adrenal glands. J. Roy. Coll. Surg. Edin., 4:257-262. Clausen, H. J. 1955. An unusual variation in origin of the hepatic and splenic arteries. Anat. Rec., 123:335-340. Cokkins, A. J. 1930. Observations on the mesenteric cir¬ culation. J. Anat. (Lond.), 64:200-205. Crelin, E. S., Jr. 1948. An unusual anomalous blood ves¬ sel connecting the renal and internal spermatic ar¬ teries. Anat. Rec., 102:205-212. Daseler, E. H., B. J. Anson, W. C. Hambley, and A. F. Reimann. 1947. The cystic artery and constituents of the hepatic pedicle: A study of 500 specimens. Surg. Gynec. Obstet., 85:47-63. Drummond, H. 1914. The arterial supply of the rectum and pelvic colon. Brit. J. Surg., 1:677-685. Edwards, L. F. 1941. The retroduodenal artery. Anat. Rec., 81:351-355. El-Eishi, H. 1., S. F. Ayoub, and M. Abd-El-Khalek. 1973. The arterial supply of the human stomach. Acta Anat., 86:565-580. Elias, H., and D. Petty. 1952. Gross anatomy of the blood vessels and ducts within the human liver. Amer. J. Anat., 90:59-111. Falconer, C. W. A., and E. Griffiths. 1950. The anatomy of the blood vessels in the region of the pancreas. Brit. J. Surg., 37:334-344. Fine, H., and E. N. Keen. 1966. The arteries of the human kidney. J. Anat. (Lond.), 100:881-894. Fried, L. C., and J. Doppman. 1974. The arterial supply to the lumbosacral spinal cord in the monkey: A com¬ parison with man. Anat. Rec., 178:41-48.

786

the arteries

Fuller, P. M., and D. F. Huelke. 1973. Kidney vascular supply in the rat, cat, and dog. Acta Anat., 84:516522. George, R. 1935. Topography of the unpaired visceral branches of the abdominal aorta. J. Anat. (Lond.), 69:196-205. Goligher, J. C. 1949. The blood supply to the sigmoid colon and rectum: With reference to the technique of rectal resection with restoration of continuity. Brit. J. Surg., 37:157-162. Goligher, }. C. 1954. The adequacy of the marginal blood-supply to the left colon after high ligation of the inferior mesenteric artery during excision of the rectum. Brit. f. Surg. 41:351-353. Graves, F. T. 1956. The aberrant renal artery. J. Anat. (Lond.), 90:553-558. Graves, F. T. 1971. The Arterial Anatomy of the Kidney: The Basis of Surgicai Technique. Williams and Wil¬ kins, Baltimore, 101 pp. Greenberg, M. W. 1950. Blood supply of the rectosigmoid and rectum. Ann. Surg., 131:100-108. Harrison, R. G. 1951. A comparative study of the vascu¬ larization of the adrenal gland in the rabbit, rat and cat. J. Anat. (Lond.), 85:12-23. Healey, J., P. Schroy, and R. Sorensen. 1953. The intrahepatic distribution of the hepatic artery in man. J. Internat. Coll. Surg., 20:133-148. Laufman, H., R. E. Berggren, T. Finley, and B. J. Anson. 1960. Anatomical studies of the lumbar arteries: With reference to the safety of translumbar aortog¬ raphy. Ann. Surg., 152:621-634. Michaels, N. A. 1951. The hepatic, cystic and retroduodenal arteries and their relations to the biliary ducts: With samples of the entire celiacal blood supply. Ann. Surg., 133:503-524. Michaels, N. A. 1953. Variational anatomy of the hepatic, cystic, and retroduodenal arteries. A.M.A. Arch. Surg., 66:20-32. Michels, N. A. 1953. Collateral arterial pathways to the liver after ligation of the hepatic artery and removal of the celiac axis. Cancer, 6:708-724. Michels, N. A. 1955. Blood Supply and Anatomy of the Upper Abdominal Organs, with a Descriptive Atlas. J. B. Lippincott Co., Philadelphia, 581 pp. Michels, N. A. 1962. The anatomic variations of the arte¬ rial pancreaticoduodenal arcades: Their import in regional resection involving the gall-bladder, bile ducts, liver, pancreas, and parts of the small and large intestines. J. Int. Coll. Surg., 37:13-40. Michels, N. A., P. Siddharth, P. L. Kornblith, and W. W. Parke. 1965. The variant blood supply to the de¬ scending colon, rectosigmoid and rectum based on 400 dissections. Its importance in regional resec¬ tions: a review of medical literature. Dis. Colon Rec¬ tum, 8:251-278. Milloy, F. J., B. J. Anson, and D. K. McAffee, 1960. The rectus abdominis muscle and the epigastric arteries. Surg. Gynec. Obstet., 110:293-302. Mitra, S. K. 1966. The terminal distribution of the hepatic artery with special reference to the arterio-portal anastomosis. J. Anat. (Lond.), 100:651-663. Noer, R. J. 1943. The blood vessels of the jejunum and ileum: A comparative study of man and certain lab¬ oratory animals. Amer. J. Anat., 73:293-334. Pick, J. W., and B. J. Anson. 1940. The inferior phrenic artery: Origin and suprarenal branches. Anat. Rec., 78:413-427. Pick, J. W., and B. J. Anson. 1940. The renal vascular

pedicle: An anatomical study of 430 body-halves. J. Urol., 44:411-434. Pierson, J. M. 1943. The arterial blood supply of the pan¬ creas. Surg. Gynec. Obstet., 77:426-432. Ross, J. A. 1950. Vascular patterns of small and large intestine compared. Brit. J. Surg., 39:330-333. Shah, M. A., and M. Shah. 1946. The arterial supply of the vermiform appendix. Anat. Rec., 95:457-460. Shah, P. M., H. A. Scarton, and M. J. Tsapogas. 1978. Geometric anatomy of the aortic-common iliac bi¬ furcation. J. Anat. (Lond.), 126:451-458. Sunderland, S. 1942. Blood supply of the distal colon. Austral. New Zealand j. Surg., 11:253-263. Vandamme, J. P. J„ and G. Van Der Schuren. 1976. Reevaluation of the colic irrigation from the superior mesenteric artery. Acta Anat., 95:578-588. Wharton, G. K. 1932. The blood supply of the pancreas, with special reference to that of the islands of Langerhans. Anat. Rec., 53:55-81. Wilmer, H. A. 1941. The blood supply of the first part of the duodenum: With description of the gastroduo¬ denal plexus. Surgery, 9:679-687. Woodburne, R. T., and L. L. Olsen. 1951. The arteries of the pancreas. Anat. Rec., 111:255-270. Yule, E. 1926. The arterial supply to the duodenum. J. Anat. (Lond.), 61:344-345.

Arteries of the Pelvis Ashley, F. L., and B. J. Anson. 1941. The hypogastric ar¬ tery. Amer. J. Phys. Anthrop., 28:381-395. Braithwaite, J. L. 1952. The arterial supply of the male urinary bladder. Brit. J. Urol., 24:64-71. Braithwaite, J. L. 1953. Variations in origin of the parietal branches of the internal iliac artery. J. Anat. (Lond.), 86:423-430. Daniel, O., and R. Schackman. 1952. The blood supply of the human ureter in relation to ureterocolic anasto¬ mosis. Brit. J. Urol., 24:334-343. Dees, J. E. 1940. Anomalous relationship between ureter and external iliac artery. J. Urol., 44:207-215. Flocks, R. H. 1937. The arterial distribution within the prostate gland: Its role in transurethral prostatic resection. J. Urol., 37:524-548. Gordon, K. C. D. 1967. A comparative anatomical study of the distribution of the cystic artery in man and other species. J. Anat. (Lond.), 101:351-359. Harrison, R. G. 1949. The distribution of the vasal and cremasteric arteries of the testis and their functional importance. J. Anat. (Lond.), 83:267-282. Harrison, R. G., and A. E. Barclay. 1948. Distribution of testicular artery (internal spermatic artery) to human testis. Brit. J. Urol., 20:57-66. Lindenbaum, E„ J. M. Brandes, and ). Itskovitz. 1978. Ipsi- and contralateral anastomosis of the uterine arteries. Acta Anat., 102:157-161. Mansfield, A. O., and J. M. Howard. 1964. Absence of both common iliac arteries. A case report. Anat. Rec., 150:363-381. Shehata, R. 1976. The arterial supply of the urinary blad¬ der. Acta Anat., 96:128-134.

Arteries of the Lower Limb Assar, Y. H. 1938. The saphenous artery. J. Anat. (Lond)., 73:194. Blair, C. B. Jr., and K. Nandy. 1965. Persistence of the

REFERENCES axis artery of the lower limb. Anat. Rec., 152:161172. Chandler, S. B., and P. H. Kreuscher. 1932. A study of the blood supply of the ligamenlum teres and its rela¬ tion to the circulation of the head of the femur. J. Bone Jt. Surg., 14:834-846. Chavatzas, D. 1974. Revision of the incidence of congeni¬ tal absence of dorsalis pedis artery by an ultrasonic technique. Anat. Rec., 178:289-290. Crock, H. V. 1965. A revision of the anatomy of the ar¬ teries supplying the upper end of the human femur. J. Anat. (Lond.), 99:77-88. Howe, W. W., Jr., T. Lacey, and R. P. Schwartz. 1950. A study of the gross anatomy of the arteries supplying the proximal portion of the femur and the acetabu¬ lum. J. Bone Jt. Surg., 32A:856-866. Huber, J. F. 1941. The arterial network supplying the dor¬ sum of the foot. Anat. Rec., 80:373-391. Keen, J. A. 1961. A study of the arterial variations in the limbs, with special reference to symmetry of vascu¬ lar patterns. Amer. J. Anat., 108:245-261. Laing, P. G. 1953. The blood supply of the femoral shaft. J. Bone Jt. Surg., 35B:462-466. Mustalish, A. C., and J. Pick. 1964. On the innervation of the blood vessels in the human foot. Anat. Rec., 149:587-590. Nelson, G. E., Jr., P. J. Kelly, L. F. A. Peterson, and J. M. Janes. 1960. Blood supply of the human tibia. J. Bone Jt. Surg., 42A:625-636. Pick, J. W., B. J. Anson, and F. L. Ashley. 1942. The origin of the obturator artery. Amer. J. Anat., 70:317-343. Pierson, H. H. 1925. Seven arterial anomalies of the human leg and foot. Anat. Rec., 30:139-145. Rogers, W. M., and H. Gladstone. 1950. Vascular foram¬ ina and arterial supply of the distal end of the femur. J. Bone Jt. Surg., 32A:867-874. Rook, F. W. 1953. Arteriography of the hip joint for pre¬ dicting end results in intracapsular and intertro¬

787

chanteric fractures of the femur. Amer. J. Surg., 86:404-409. Sanders, R. J. 1963. Relationships of the common femoral artery. Anat. Rec., 145:169-170. Scapinelli, R. 1967. Blood supply of the human patella: Its relation to ischaemic necrosis after fracture. J. Bone Jt. Surg., 49B:563-570. Senior, H. D. 1919. An interpretation of the recorded anomalies of the human leg and foot. J. Anat. (Lond.), 53:130-171. Senior, H. D. 1929. Abnormal branching of the human popliteal artery. Amer. J. Anat., 44:111-120. Sevitt, S., and R. G. Thompson. 1965. The distribution and anastomoses of arteries supplying the head and neck of the femur. J. Bone Jt. Surg., 47B:560-573. Sunderland, S. 1945. Blood supply of the sciatic nerve and its popliteal divisions in man. Arch. Neurol. Psychiat., 54:283-289. Trueta, T. 1957. The normal vascular anatomy of the human femoral head during growth. J. Bone Jt. Surg., 39B.-358-394. Trueta, J., and M. H. M. Harrison. 1953. The normal vas¬ cular anatomy of the femoral head in adult man. J. Bone Jt. Surg., 35B:442-461. Vann, H. M. 1943. A note on the formation of the plantar arterial arch of the human foot. Anat. Rec., 85:269275. Weathersby, H. T. 1959. The origin of the artery of the ligamentum teres femoris. J. Bone Jt. Surg., 41A:261-263. Williams, G. D., C. H. Martin, and L. R. Mclntire. 1934. Origin of the deep and circumflex femoral group of arteries. Anat. Rec., 60:189-196. Woollard, H. H., and G. Weddell. 1934. Arterial vascular patterns. J. Anat. (Lond.), 69:25-37. Woollard, H. H., and G. Weddell. 1934. The composition and distribution of vascular nerves in the extremi¬ ties. J. Anat. (Lond.), 69:165-176.

The veins are the most variable part of the cardiovascular system. Variations in venous patterns are more frequent in vessels that drain the more superficial parts of the body than in the deeper coursing veins which often accompany the arteries. At times veins exist in pairs, one lying on each side of an artery. These are called venae comitantes and are often seen in the medium-sized ves¬ sels of the arm, forearm, and leg (brachial, radial, ulnar, and tibial). The larger arteries (axillary, femoral, and popliteal) usually have only one accompanying vein. In certain organs and body regions, however, the deep veins do not accompany arteries: this is true of the venous sinuses in the skull and verte¬ bral canal, the hepatic veins, and the large veins draining blood from the long bones.

Development of the Veins The venous system conveys blood from the capillaries to the heart. There are two distinct sets of veins, the pulmonary and the systemic. These serve two different vascular circuits: the pulmonary veins return blood to the heart from the lungs, and the systemic veins return blood to the heart from the rest of the body. The pulmonary veins return oxygenated blood from the capillaries of the lungs to the left atrium of the heart. The blood then con¬ tinues through the left ventricle and aorta to supply all the body organs. The systemic veins belong to the larger systemic circulation and convey deoxygenated blood from all the organs except the lungs to the right atrium of the heart. Blood from all the systemic veins except those of the heart eventually flows through the supe¬ rior and inferior venae cavae to the right atrium. The coronary veins flow into the cor¬ onary sinus, which then also opens into the right atrium. • The portal vein is interposed between certain abdominal viscera and the liver. Its special feature is that it both begins and ends in capillaries. The portal vein receives ve¬ nous blood from the capillaries of the diges¬ tive tube, spleen, and pancreas and delivers it to the venous capillary-like sinusoids of the liver. The blood then makes its way into the general systemic venous system through the tributaries of the hepatic veins, which flow into the inferior vena cava.

788

The development of veins actually com¬ mences when minute plexuses of vessels receive blood from the earliest developing capillaries. These plexuses give rise to tribu¬ taries that finally unite to form trunks. Pass¬ ing toward the heart, the trunks increase in size as they receive other tributaries or as they join other veins. The further development of the venous system in the human embryo will be consid¬ ered by dividing the veins into two groups: the parietal veins, which drain the body cav¬ ity, extremities, and head and form the large inferior and superior venae cavae, and the visceral veins, which drain the yolk sac and placenta and join to form the sinus venosus.

PARIETAL VEINS

The parietal veins, which drain most of the developing embryonic structures, are initially represented by four large vessels: the two anterior cardinal (or precardinal) veins and the two posterior cardinal (or postcardinal) veins (Figs. 9-1, A; 9-3). The two anterior cardinal veins, one lying on each side of the embryo, drain the more cra¬ nial venous tributaries, returning blood from the head, and soon become the primitive jugular veins. The two posterior cardinal veins, also one on each side, drain the caudal venous tributaries of the embryo, returning

Anterior cardinals Common cardinals Liver

Umbilical veins Omphalomesenteric veins Subcardinal veins

Developing subcardinal plexus in mesonephros

Posterior cardinals

Intersubcard. anastomosis

Iliac vein

5 Vi Weeks A 4 Weeks

Internal jugular

External jugular

L. brachio¬ cephalic

Subclavian

Subcardinal Inferior vena cava Post, cardinal (disappearing)

Supracardinals Intersubcardinal anastomosis

Subcardinalsupracardinal anastomosis Gonadal

Iliac vein

C

Iliac anastomosis

6 Weeks D 7 Weeks

Int. jugular

External jugular R. brachiocephalic

Right subcl.

L. brachioceph. L. subcl.

Sup. vena cava Azygos

Intercostals

Hemiazygos

Accessory hemiazygos

Inf. vena cava Suprarenal Mesonephric vessels (disappearing)

Suprarenal gland Renal vein Gonadal

Common iliac Middle sacral

Ext. iliac

F At Term E 8 Weeks

Fig. 9-1 Schematic diagrams showing certain stages in the development of the inferior vena cava between the fourth and eighth prenatal weeks and at term, based on the work of McClure and Butler (1925). Anterior and posterior cardinal veins are shown in solid black, supracardinal veins are hatched horizontally, t (in B) = vessels from the upper part of the right subcardinal vein and liver that commence forming the hepatic segment of the inferior vena cava; Ob. (in E) = oblique vein of the left atrium; * (in F) = left superior intercostal vein. (From Patten, B. M„ Human Embryol¬ ogy, 3rd ed., McGraw-Hill, New York, 1968.)

790

THE VEINS

blood from the lower body wall, the pelvis, the mesonephroi (Wolffian1 bodies), and the lower limb buds. The anterior and posterior cardinal veins on each side join to form a symmetrically arranged longitudinally ori¬ ented cardinal system (Fig. 9-1, A). Two short transverse veins, the common cardinal veins (ducts of Cuvier2), interconnect the anterior and posterior cardinal veins of each side to the corresponding horns of the sinus venosus (Figs. 9-1, B; 9-4, A). To this relatively simple pattern are added, during the fifth week of development, the subcardinal veins. These veins develop parallel and ventral to the posterior cardinal veins in the ventromedial part of the meso¬ nephric ridges and gradually take over the drainage of the mesonephroi from the poste¬ rior cardinal veins (Fig. 9-1, B). During the seventh week are added the supracardinal veins, which form dorsomedial to the poste¬ rior cardinal veins (Fig. 9-1, D). This primitive double (right and left) plan of veins then is converted to the single caval system, in which blood is returned to the heart through the inferior and superior venae cavae. inferior vena cava. The principal changes that occur to form the vena caval systems in the embryo culminate in the al¬ teration of the bilaterally symmetrical ve¬ nous plan, initiated by the formation of the anterior and posterior cardinal veins along with the subcardinal veins, into large un¬ paired vessels found on the right side of the body (the superior and inferior venae cavae). The peripheral channels in the head and limbs that flow into these centrally unpaired veins still retain much of their symmetry. The inferior vena cava, which drains blood from the lower trunk, pelvis, and lower limbs, gradually develops by replac¬ ing the various cardinal veins or by utilizing portions of them. Initially, the subcardinal veins begin to replace partially the posterior cardinal veins as the drainage channels of the mesonephroi. These channels soon form many cross connections with the posterior cardinal veins on each side (Fig. 9-1, A). As

'Kasper F. Wolff (1733-1794): A German embryologist and physiologist, who worked in St. Petersburg, Russia. -Georges L. Cuvier (1769-1832): A French zoologist and natural historian (Paris).

the mesonephroi grow, they approximate medially, and consequently the subcardinal veins of the two sides become nearly adja¬ cent. By five and one-half weeks, the two subcardinal veins establish an interconnec¬ tion called the intersubcardinal anastomosis (Fig. 9-1, B), which then enlarges to form the subcardinal sinus. Soon blood begins to flow medially into this sinus from the many small vessels that had interconnected the posterior cardinal and the subcardinal veins. This re¬ sults in a disappearance of the more caudal parts of the posterior cardinal veins (Fig. 9-1, C). As the subcardinal sinus forms, the veins of the superior pole of the right mesoneph¬ ros, which lie close to the developing liver, anastomose with some of the vessels flowing through the liver. This anastomosis occurs within a fold of mesentery called the caval fold (or mesentery), into which have grown capillaries from the liver above and some capillaries from the right subcardinal veins below (Fig. 9-1, B and C). Soon this anasto¬ mosis enlarges within the substance of the liver and becomes a principal venous chan¬ nel. It achieves the surface of the liver as the hepatic part of the inferior vena cava. The right omphalomesenteric vein enlarges to form the suprahepatic portion of the inferior vena cava, which is the segment between the liver and the right atrium. The portion of the inferior vena cava arising above the kidneys, which can be called the prerenal part, con¬ sists of the renal segment (subcardinal sinus), the hepatic segment, and the suprahe¬ patic segment. Below the level of the kidneys, the two supracardinal veins participate in the for¬ mation of the postrenal part of the inferior vena cava (Fig. 9-1, C and D). These veins arise during the seventh week, and they are seen initially as a periganglionic plexus of veins associated with the developing sympa¬ thetic ganglionic chain. The supracardinal veins develop as a pair of longitudinally ori¬ ented vessels that drain the posterior body wall dorsal to the posterior cardinal veins. Near the level of the middle part of the de¬ veloping mesonephros, the supracardinal veins merge with the subcardinal sinus. Above the subcardinal sinus, together with the persisting proximal part of the right postcardinal vein, the supracardinal vein forms the azygos system of veins (Fig. 9-1, E

DEVELOPMENT OF THE VEINS

and F). The proximal part of the left supracardinal vein, together with some of the up¬ per part of the left postcardinal vein, forms the hemiazygos, accessory hemiazygos, and the left superior intercostal vein. Below the subcardinal sinus, blood from the lower limbs is collected by the right and left iliac veins, which in the earlier stages of development open into the corresponding right and left posterior cardinal veins. Later a transverse iliac anastomosis, which at this stage connects the right and left iliac vein, eventually develops into the left common iliac vein (Fig. 9-1, C to F). Blood returning from the lower extremities increasingly is shunted from the lower end of the right post¬ cardinal vein to the right supracardinal vein. As the postcardinal vein gradually disap¬ pears, the lower part of the right supra¬ cardinal vein enlarges and forms the postrenal part of the inferior vena cava (Fig. 9-1, E and F). Above the subcardinal sinus, the left pos¬ terior cardinal-subcardinal vein disappears, except the part immediately above the renal vein, which is retained as the left suprarenal vein. The fate of the left posterior cardinalsubcardinal system also accounts for the fact that the left gonadal vein (testicular or ovar¬ ian) opens into the left renal vein, while the vein on the right side drains into the postrenal segment of the inferior vena cava (Fig. 9-1, E and F). superior vena cava. The superior vena cava develops at the junction of the two brachiocephalic veins, which in turn receive blood from the head by way of the internal and external jugular veins and from the

791

upper limb by means of the subclavian vein. The primitive internal jugular veins, which drain the cranial end of the embryo on each side, initially are simply the anterior cardi¬ nal veins, whereas the external jugular veins develop in the region of the mandible by the junction of a number of smaller, more super¬ ficial vessels (Fig. 9-1, B to D). At four weeks the lower portion of the an¬ terior cardinal vein joins the posterior cardi¬ nal vein to form the common cardinal vein (Figs. 9-1, A; 9-2, A). Because the heart as well as the common cardinal veins lie far to the cranial end of the developing embryo at the time that the upper limb buds appear, the initial veins that drain the upper limb buds flow into the posterior cardinal veins (Fig. 9-1, B). As development continues, the heart descends relative to the upper limb buds, and soon the limb bud veins (axillary) begin to drain into the more caudal part of the anterior cardinal vein (internal jugular). When this occurs (sixth to seventh weeks), the primitive pattern of two brachiocephalic veins (right and left superior venae cavae) is formed (Figs. 9-1, C; 9-2, B). About this same time, an anastomosis forms between the two anterior cardinal veins, which re¬ sults in the formation of a transverse con¬ necting vein in front of the trachea as a con¬ fluence of thymic and thyroid veins. This anastomosis becomes the left brachioce¬ phalic vein, and it allows blood returning from the cranial left side of the embryo to be shunted to the right side of the heart, where it must enter the right atrium (Figs. 9-1, D; 9-2, B). The junction of the two brachioce¬ phalic veins eventually forms the superior

Fig. 9-2. Diagrams showing the transformation of the cardinal veins into the superior vena cava in human embryos at six weeks (A), eight weeks (B), and in the adult (C). H.I. = left superior intercostal vein (highest intercostal); O.V. = oblique vein of the left atrium; S = left subclavian vein. (From Arey, L. B„ Developmental Anatomy, 7th ed., W. B. Saunders Co., Philadelphia, 1974.)

792

THE VEINS

vena cava (Fig. 9-1, D to F). The remainder of the left anterior cardinal vein, below the left brachiocephalic, becomes much smaller, but it contributes to the formation of the left superior intercostal vein, in conjunction with the small remaining cranial end of the left posterior cardinal vein. The right ante¬ rior cardinal vein between the azygos vein and the union with the left brachiocephalic vein becomes the upper part of the adult su¬ perior vena cava. The lower part of the su¬ perior cava, that is, the part between the azy¬ gos vein and the heart, is formed by the original right common cardinal vein (duct of Cuvier). The left anterior cardinal vein, cau¬ dal to the transverse left brachiocephalic vein and left superior intercostal vein, and the left common cardinal vein regress. The upper part becomes the vestigial fold of Marshall1 (Figs. 9-1, E and F; 9-2), and the proximal part of the left common cardinal vein becomes the oblique vein of the left atrium (of Marshall). The oblique vein of the left atrium drains across the dorsal surface of the left atrium to open into the coronary 'John Marshall (1818-1891): An English anatomist and surgeon (London).

Fig. 9-3.

sinus, which represents the persistent left horn of the sinus venosus. Both the right and left superior venae cavae are present in some animals, and occasionally are found as anomalies in adult human beings.

VISCERAL VEINS

The visceral veins are the two vitelline or omphalomesenteric veins which bring blood to the embryo from the yolk sac, and the two umbilical veins which return oxygenated fetal blood to the embryo from the placenta. These four veins open into the sinus venosus. vitelline veins. The paired vitelline veins follow the stalk of the yolk sac, and thereby enter the body of the embryo. They course cranially, at first ventral to and then on either side of the developing foregut, each on its way to its respective horn of the sinus venosus. The vitelline veins unite on the ventral aspect of the intestinal canal, and more cranially, they are connected to each other by two anastomotic branches, one on the dorsal and the other on the ventral as¬ pect of the duodenal portion of the intestine,

Semischematic diagram showing the basic vascular plan of the human embryo at the end of first month. For the sake of simplicity, the paired vessels are shown only on the side toward observer. (From Patten, B. M., Human Embryology, 3rd ed„ McGraw-Hill, New York, 1968.)

DEVELOPMENT OF THE VEINS

793

Heart

Liver

Anastomosis of omph. veins within liver Umb. vein (allantoic)

Anastomoses forming

Superior vena cava (rt. com. card.)

Ductus venosus

Coronary sinus (proximal part of left com. card, vein)

Right hepatic vein (omph.) Portal sinus

Anastomoses of omph. veins

Portal vein (omph.)

Umb. veins fused in belly-stalk

Left umbilical vein

Duodenum

Right \!> umbilical —5 vein

Diagrams showing steps in the development of the hepatic-portal circulation from the omphalomesenteric veins, and the changes by which blood returning in the umbilical veins from the placenta is rerouted through the liver. A, fourth week; B, fifth week; C, sixth week; D, seventh week and older. The asterisk in C indicates the hepatic part of the inferior vena cava. (From Patten, B. M., Human Embryology, 3rd ed., McGraw-Hill, New York, 1968.) Fig. 9-4.

which is thus encircled by two venous rings (Fig. 9-4, B). Into the middle or dorsal anasto¬ mosis opens the superior mesenteric vein, which arises in the dorsal mesentery of the intestine. Within the 9eptum transversum, the portions of the veins above the upper ring are interrupted by the developing liver and are broken up by it into a plexus of small capillary-like vessels termed sinu¬ soids. The vessels conveying blood to this plexus become the tributaries of the portal

vein, while the vessels draining the plexus from the liver into the sinus venosus form the future hepatic veins (Figs. 9-4, C and D; 9-5). Ultimately the left vitelline (hepatic) veins no longer communicate directly with the sinus venosus, but open into the devel¬ oping right hepatic veins. The persistent part of the upper venous ring, above the opening of the superior mesenteric vein, forms the trunk of the portal vein. umbilical veins. The two umbilical veins

794

THE VEINS

Right anterior cardinal

Left anterior cardinal

Right posterior cardinal vein Left posterior cardinal vein Right common cardinal

Sinus venosus

Left common cardinal

Right hepatic vein Left hepatic vein

Portal vein

Left umbilical vein

Portal vein

Right umbilical vein Left umbilical vein

Umbilical cord

Fig. 9-5. Human embryo with heart and anterior body wall removed to show the sinus venosus and its tributaries. (After His.)

return oxygenated blood to the embryo from the placenta. They form a single trunk in the body stalk, but remain separate within the embryo and pass forward to the sinus veno¬ sus in the side walls of the embryonic body (Fig. 9-4, B). Like the vitelline veins, their di¬ rect connection with the sinus venosus be¬ comes interrupted by the developing liver, and thus at this stage (6 mm, fifth week), all the blood from the yolk sac and placenta passes through the substance of the liver before reaching the heart. During the sixth week, the two umbilical veins commence to fuse in the umbilical cord, and the left um¬ bilical channel becomes the principal course for the returning blood (Figs. 9-4, C; 9-5). In the embryo the right umbilical and right vi¬ telline veins shrivel and disappear, while the left umbilical vein enlarges and opens into the upper venous ring of the vitelline veins. When the yolk sac atrophies, the left vitel¬ line vein also undergoes atrophy and disap¬ pears (Fig. 9-5). Finally, a direct branch is established between this ring and the right

hepatic vein. This branch enlarges rapidly into a wide channel named the ductus veno¬ sus (Fig. 9-4, C and D). Through the ductus venosus most of the blood is returned from the placenta and carried directly to the heart without passing through the liver. The left umbilical vein and the ductus venosus un¬ dergo atrophy and obliteration after birth, and form respectively the ligamentum teres and ligamentum venosum of the liver.

The Pulmonary Veins The pulmonary veins, two from each lung, return oxygenated blood to the left atrium of the heart (Fig. 9-6). The capillary networks in the walls of the air sacs join together to form one vessel for each lobule. These vessels unite successively to form a single trunk for each lobe, three for the right and two for the left lung. The vein from the middle lobe of the right lung usually unites with that from the superior lobe so that ultimately two

THE PULMONARY VEINS

795

Fig. 9-6.

Diagrammatic representation of the branches of the superior and inferior pulmonary veins on each side of the body. (Redrawn after Nomina Anatomica, 1968, Excerpta Medica Foundation.)

trunks are formed from each lung. Near the heart, the four pulmonary veins perforate the fibrous layer of the pericardium and open separately into the superior part of the left atrium (Fig. 9-7). The three veins from the right lung may remain separate, and at times the two left veins join and enter the heart by a common opening. At the roots of the lungs, the superior pul¬ monary veins lie anterior and a little inferior to the pulmonary arteries. The inferior veins are situated in the most caudal part of the hilum on a plane posterior to the superior veins. The pulmonary veins are about 1.5 cm in length, and on the right side they pass behind the right atrium and superior vena cava to reach the left atrium. The left pulmo¬ nary veins course anterior to the descending thoracic aorta on their way to the heart. Within the lung the ramifications of the veins do not always accompany the bronchi and arteries in the central regions of the bronchopulmonary segments. More superfi¬ cially near the pleura, they are found be¬ tween bronchopulmonary segments, or more deeply, they are found intrasegmentally. The

branchings of both the larger and the smaller tributaries are quite variable. A list of the bronchopulmonary segments is found in Chapter 15.

RIGHT SUPERIOR PULMONARY VEIN

The right superior pulmonary vein has three tributaries for the superior lobe and one for the middle lobe (Fig. 9-6). apical segmental vein. The apical seg¬ mental vein lies near the mediastinal pleura. It has an intrasegmental tributary draining the apex and an infrasegmental tributary separating the apical from the anterior seg¬ ments. posterior segmental vein. The posterior segmental vein is the largest vein of the su¬ perior lobe and has both intralobar and infralobar parts. The intralobar part has an apical, a posterior, and an intersegmental tributary, which is a prominent vein of the posterior surface. The infralobar part lies near the pleura between the superior and middle lobes.

796

THE VEINS

anterior segmental vein. The anterior segmental vein has two tributaries, intrasegmental and infrasegmental. These accom¬ pany the two branches of the anterior seg¬ mental bronchus of the right superior lobe. right middle lobe vein. The right middle lobe vein is usually a single tributary of the right superior pulmonary vein, but its two segmental veins may remain separate. The lateral segmental vein splits into a tributary for the lateral segment and a tributary sepa¬ rating the segments. The medial segmental vein lies near the mediastinal surface and has two tributaries, one subpleural and one intrasegmental.

RIGHT INFERIOR PULMONARY VEIN

The right inferior pulmonary vein occu¬ pies the most inferior part of the hilum of the right lung, and has two main tributaries, a superior (or apical) segmental vein and a common basal vein (Fig. 9-6). SUPERIOR

(OR

APICAL)

SEGMENTAL

VEIN.

The superior segmental vein begins near the medial side of the middle lobe bronchus and is formed by two or three tributaries with intrasegmental and infrasegmental tribu¬ taries. common basal vein. The common basal vein is a large short trunk that drains the four basal segments of the lower lobe of the right lung. It has two principal tributaries, a superior basal and an inferior basal. The su¬ perior basal tributary lies deep to the sur¬ face of the inferior lobe and drains both its anterior basal and lateral basal bronchopul¬ monary segments by intrasegmental and infrasegmental tributaries. The inferior basal tributary drains the posterior basal and lateral basal bronchopulmonary seg¬ ments. The medial basal bronchopulmonary segment is drained by several tributaries that open into both the superior basal and inferior basal veins.

LEFT superior pulmonary vein

The left superior pulmonary vein drains blood from the two bronchopulmonary seg¬ ments of the superior lobe, as well as from the two segments of the lingula of the supe¬ rior lobe. It is formed by a confluence of the

apicoposterior segmental vein, the anterior segmental vein, and the lingular division vein. The latter vein is formed by the junc¬ tion of the superior and inferior lingular veins (Fig. 9-6). apicoposterior segmental vein. The apicoposterior segmental vein is formed by the junction of an intrasegmental tributary and an infrasegmental tributary. anterior segmental vein. The anterior segmental vein drains the anterior segment of the left superior lobe, and is formed by intrasegmental and infrasegmental tribu¬ taries. lingular division vein. The lingular di¬ vision vein drains the superior lingular and inferior lingular segments. The superior lingular vein has posterior and anterior intersegmental tributaries. The tributaries of the inferior lingular vein are superior and inferior. The latter drains into the inferior pulmonary vein in some instances.

LEFT INFERIOR PULMONARY VEIN

The left inferior pulmonary vein receives a smaller apical superior segmental vein and a larger common basal segmental vein (Fig. 9-6). APICAL SUPERIOR SEGMENTAL VEIN. The apical superior segmental vein lies on the medial side of the superior lobe bronchus and is itself formed by a central intraseg¬ mental and two intersegmental tributaries, the latter separating the segment from its neighbors. common basal vein. The common basal vein receives the superior basal vein, which largely drains the anterior basal segment by intrasegmental and infrasegmental tributar¬ ies, and the inferior basal vein, which drains the posterior basal and lateral basal seg¬ ments by intrasegmental and infraseg¬ mental tributaries. The medial basal bron¬ chopulmonary segment is drained by two venous channels, one intrasegmental and the other intersegmental; the latter separates the medial basal segment from the posterior basal segment. One or both of these veins drains into the common basal vein. The anterior basal vein, which drains into the superior basal division of the common basal vein, has an intrasegmental and an infrasegmental tributary; the latter usually

THE SYSTEMIC VEINS

lies deep to the pulmonary ligament and sep¬ arates the medial basal from the lateral basal bronchopulmonary segments. The lateral basal vein, which drains into the inferior basal division of the common basal vein, is primarily an intersegmental vessel in the depth of the lobe between the lateral basal and posterior basal bronchi, but it also has an intrasegmental tributary. The posterior basal vein, which also drains into the infe¬ rior basal division of the common basal vein, is intrasegmental; it lies in the hollow be¬ tween the branches of the posterior basal segmental bronchus and drains these regions by two tributaries.

The Systemic Veins The veins commence as minute plexuses that receive blood from the capillaries. The tributaries arising from these plexuses unite into trunks, and these, in their passage to¬ ward the heart, constantly increase in size as they receive tributaries or join other veins. The veins are larger in caliber and more numerous than the arteries, giving the ve¬ nous system a larger capacity than that of the arterial system. The capacity of the pul¬ monary veins, however, only slightly ex¬ ceeds that of the pulmonary arteries. The veins, when full, are cylindrical like the ar¬ teries, but their walls are thin and they col¬ lapse when empty. In the cadaver, they may be interrupted at intervals by nodular en¬ largements that indicate the existence of valves in their interior. Veins anastomose freely, especially in cer¬ tain regions of the body. These communica¬ tions exist between large trunks as well as between smaller branches. Between the ve¬ nous sinuses of the cranium, and between the veins of the neck, where obstruction would bring imminent danger to the cere¬ bral venous system, large and frequent anas¬ tomoses are found. The same free communi¬ cation exists between the veins throughout the entire extent of the vertebral canal, and between the veins composing the various venous plexuses in the abdomen and pelvis. Three types of venous channels can be iden¬ tified according to their location in the body: superficial veins, deep veins, and venous si¬ nuses. superficial veins. The superficial veins

797

are found within the substance of the super¬ ficial fascia immediately beneath the skin. They drain the capillary networks near the surface of the body and return this blood to deeper veins by perforating the deep fascia. Some of the larger superficial veins include the facial vein, which drains the superficial structures of the face, the cephalic and basilic veins of the upper extremity, the thoracoepigastric vein of the anterior trunk, and the great and small saphenous veins of the lower extremity. deep veins. The deep veins generally ac¬ company the deeper coursing arteries and usually are enclosed in the same sheaths as the vessels. The larger arteries, such as the axillary, subclavian, popliteal, and femoral, usually have only one accompanying vein. In the case of the smaller arteries, such as the radial, ulnar, brachial, tibial, and pero¬ neal, the veins exist generally in pairs, one lying on each side of the vessel, and are called venae comites or venae comitantes. In certain organs of the body, however, the deep veins do not accompany the arteries. Examples of these are the veins in the skull and vertebral canal, the hepatic veins in the liver, and the larger veins that return blood from the bones. VENOUS sinuses. Throughout the body are veins to which the term sinus has been given. At times a sinus is a vessel that does not have the same layers in its walls as other veins, but this definition cannot be applied consistently. Within the cranial cavity of the skull are found venous sinuses that consist of canals formed by a separation of the two layers of the dura mater. Their outer coat consists of fibrous tissue, their inner of an endothelial layer continuous with the lining of the veins. The coronary sinus is the vessel into which drain the veins of the heart. Small venous capillary channels in the liver are called venous sinusoids. The sinus venosus is a venous channel found in the embry¬ onic heart. The systemic veins may be arranged in four groups: (1) the cardiac veins or veins of the heart; (2) the superior vena cava and its tributaries, which include the veins of the head, neck, upper limbs, and thorax; (3) the inferior vena cava and its tributaries, which include the veins of the lower limbs, some veins of the abdomen, and the veins of the pelvis; and (4) the portal system of veins.

798

THE VEINS

Veins of the Heart

the coronary sinus. These tributaries in¬ clude the:

The veins of the heart, or the cardiac veins, with the exception of certain small vessels that open directly into the chambers, are tributaries of the coronary sinus.

Great cardiac vein Small cardiac vein Middle cardiac vein Posterior vein of the left ventricle Oblique vein of the left atrium

CORONARY SINUS

The coronary sinus is a wide venous chan¬ nel, about 2.25 cm in length, situated in the posterior part of the coronary sulcus of the heart, and usually covered by muscular fi¬ bers from the left atrium (Fig. 9-7). It ends in the right atrium, between the opening of the inferior vena cava and the atrioventricular aperture; its orifice is guarded by a single semilunar valve, the valve of the coronary sinus (valve of Thebesius1). This valve does not appear to have any functional signifi¬ cance in the adult heart. Most of the venous blood returning from heart tissue courses in veins that open into ^dam C. Thebesius (1686-1732): A German physician and anatomist.

Each of these veins, except the last, is pro¬ vided with a valve at its orifice. great cardiac vein. The great cardiac vein begins at the apex of the heart and as¬ cends along the anterior interventricular sul¬ cus to the base of the ventricles (Figs. 8-16; 8-18). It then curves to the left in the coro¬ nary sulcus, and reaching the back of the heart, opens into the left extremity of the coronary sinus (Fig. 9-7). It receives tributar¬ ies from the left atrium and from both ven¬ tricles. One of these, the left marginal vein, is of considerable size and ascends along the left margin of the heart (Fig. 9-7). small cardiac vein. The small cardiac vein courses in the coronary sulcus between the right atrium and ventricle. It flows into the right extremity of the coronary sinus,

Azygos vein

Left pulmonary veins Right pulmonary veins Oblique vein of left atrium Great cardiac vein Left marginal vein

Inferior vena cava

Post, vein of left ventricle

Small cardiac vein Right ventricle Middle cardiac vein Fig. 9-7.

Base and diaphragmatic surface of heart.

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

near the site where the coronary sinus termi¬ nates in the right atrium (Fig. 9-7). The small cardiac vein receives blood from the back of the right atrium and ventricle. The right marginal vein, which ascends from near the apex and along the right margin of the heart, joins the small cardiac vein in the coronary sulcus, or opens directly into the right atrium. middle cardiac vein. The middle cardiac vein commences at the apex of the heart, ascends in the posterior interventricular sul¬ cus, receives tributaries from both ventri¬ cles, and ends in the coronary sinus near its right extremity (Fig. 9-7). POSTERIOR

VEIN

OF

THE

LEFT

799

Most of them open into the atria, but a few end in the ventricles.

Superior Vena Cava and its Tributaries Draining into the superior vena cava are venous tributaries that collect blood from the head, neck, upper extremity, the thorax (including the thoracic wall), and even from much of the abdominal wall.

SUPERIOR VENA CAVA

VENTRICLE.

Ascending along the diaphragmatic surface of the left ventricle, the posterior vein of the left ventricle accompanies the circumflex branch of the left coronary artery. Usually it opens into the coronary sinus to the left of the middle cardiac vein, but it may course farther to the left and open into the great cardiac vein (Fig. 9-7). OBLIQUE VEIN OF THE LEFT ATRIUM. The oblique vein of the left atrium is a small ves¬ sel that descends obliquely on the back of the left atrium and ends in the coronary sinus near its left extremity (Fig. 9-7). It is continuous superiorly with the ligament of the left vena cava, and the two structures form the remnant of the left common cardi¬ nal vein. Several cardiac veins do not end in the coronary sinus, but are directed into the chambers of the heart. These are the: Anterior cardiac veins Smallest cardiac veins ANTERIOR CARDIAC VEINS

The anterior cardiac veins consist of three or four small vessels that collect blood from the ventral aspect of the right ventricle and open into the right atrium. The right mar¬ ginal vein frequently opens into the right atrium, and is therefore sometimes regarded as belonging to this group.

SMALLEST CARDIAC VEINS

The superior vena cava drains venous blood from the superior half of the body (Fig. 9-8). Its caliber of about 2 cm in diame¬ ter is second in size in the human body only to the inferior vena cava, which is slightly larger. The superior vena cava measures about 7 cm in length and is formed by the junction of the two brachiocephalic veins at the level of the first intercostal space, close behind the sternum on the right side. From this junction the superior vena cava trans¬ ports blood inferiorly, lying deep to the sec¬ ond rib cartilage and intercostal space at the right border of the sternum, and empties into the upper part of the right atrium at the level of the third right costal cartilage. As it de¬ scends, the superior vena cava curves gently with its convexity to the right. The part of the vessel nearer the heart, amounting to about half its length, lies within the pericar¬ dial sac and it is covered by the serous peri¬ cardium. relations of the superior vena cava. Ante¬ rior to the superior vena cava are the anterior mar¬ gins of the right lung and pleura, with the pericar¬ dium intervening below. These separate it from the first and second intercostal spaces and from the sec¬ ond and third right costal cartilages. Posterior to it are the root of the right lung and the right vagus nerve. On the right side of the superior vena cava are the phrenic nerve and right pleura, and on its left side, is the commencement of the brachiocephalic artery and the ascending aorta, the latter overlap¬ ping the large vein. Just before piercing the pericar¬ dium, the superior vena cava receives the azygos vein and several small veins from the pericardium and other structures in the mediastinum. The supe¬ rior vena cava has no valves.

These vessels (also called the venae cordis minimi) consist of a number of minute veins that arise in the muscular wall of the heart.

variations in the superior vena cava.

At

times the brachiocephalic veins open separately into the right atrium. In these cases the right brachioce-

800

THE VEINS

, Ophthalmic v.

Cavernous sinus -- Sigmoid sinus Facial v. ..

Submental v Thyroid ima v.

‘ Retromandibular v.

Internal jugular v. Superior thyroid v. External jugular v. Subclavian v.

Right brachiocephalic v.

-—

Brachial v.

Superior vena cava --

-- Thoracoepigastric v

Hepatic vv Splenic v. Portal v. Superior mesenteric v. Inferior mesenteric v. Ileum Common iliac v. Internal iliac v. - External iliac v. Femoral v.

Superficial dorsal vein of penis - • Lateral femoral circumflex v.

-Great saphenous v.

FJG 9 9 ^ Jar8e ve*ns body. Note that the portal system of veins in the abdomen is represented in black. (From Benninghoff and Goerttler, Lohrbuch der Anotomic des Menschen, Urban and Schwarzenberg, 1975.)

phalic vein follows the normal course of the superior vena cava, while the left vein, called the left supe¬ rior vena cava, passes ventral to the root of the left lung, and turning to the dorsum of the heart, ends in the right atrium. This occasional condition in the adult is due to the persistence of the early fetal con¬ dition (see Fig. 9-1, C and D), but is normal in adult birds and some mammals. In some instances of per¬ sistent left superior vena cava, a small branch may interconnect the two large veins. TRIBUTARIES OF THE SUPERIOR VENA CAVA.

The two brachiocephalic veins join to form

the superior vena cava (Fig. 9-8). Addition¬ ally, the superior vena cava receives the azy¬ gos vein and several small veins from the mediastinum and pericardium. Further dis¬ cussion of the tributaries of the superior vena cava relates to its regional drainage. Thus, the following sections are described sequentially: Veins of the head and neck Veins of the upper limb Veins of the thorax

SUPERIOR VENA CAVA AND ITS TRIBUTARIES VEINS OF THE HEAD AND NECK

The veins of the head and neck may be divided into the following groups: Veins of the face Superficial veins of the face Deep veins of the face Veins of the cranium Veins of the brain Sinuses of the dura mater Diploic veins Emissary veins Veins of the neck External jugular vein Internal jugular vein Vertebral vein

Superficial Veins of the Face Facial Superficial temporal Posterior auricular Occipital Retromandibular These veins are tributaries of the internal and external jugular veins. FACIAL VEIN

The facial vein drains blood from the su¬ perficial structures of the face (Figs. 9-9 and 9-10). Its first part, named the angular vein, perficial temporal vein Middle temporal vein Supratrochlear vein Supraorbital vein Communication with ophthalmic vein Angular vein Inferior palpebral vein External nasal veins Superior labial veins

Deep facial vein Masseter muscle Inferior labial vein Occipital vein

Facial vein

Anterior auricular vein

Submental vein

Transverse facial vein Lingual vein Posterior auricular vein

Pharyngeal vein

Maxillary vein

Internal jugular vein Superior thyroid vein

Retromandibular vein Anterior jugular vein Sternocleidomastoid muscle External jugular vein Posterior external jugular vein

Sternocleidomastoid muscle

Platysma muscle

Transverse cervical vein Suprascapular vein

Fig. 9-9.

801

The superficial veins of the head and neck.

802

THE VEINS

begins at the medial angle of the eye by a trochlear veins communicate by means of a union of the supratrochlear and supraorbital transverse nasal arch before each joins the veins. It accompanies the facial artery along supraorbital vein of that side. Occasionally the lateral border of the nose, but has a less . the two supratrochlear veins join on the tortuous course. Descending on the face, upper forehead to form a prominent single deep to the zygomaticus major and minor vein that bifurcates at the root of the nose muscles, the facial vein follows the border of and joins the two angular veins. the masseter muscle to the inferior border of supraorbital vein. The supraorbital vein the body of the mandible. It then curves also begins by anastomosing with a frontal around this bone to enter the neck. In the tributary of the superficial temporal vein neck, the facial vein communicates with the (Fig. 9-9). It lies superficial to the frontal anterior jugular vein and with the external belly of the occipitofrontalis muscle, which jugular before emptying into the internal it drains, and joins the supratrochlear vein at jugular at about the level of the hyoid bone. the medial angle of the orbit. As it passes Formerly, the communication with the ex¬ over the supraorbital notch in the frontal ternal jugular was named the posterior fa¬ bone, the supraorbital vein forms an anasto¬ cial and the segment emptying into the inter¬ mosis with the superior ophthalmic vein, nal jugular was named the common facial and it also receives the frontal diploic vein, vein. The facial vein anastomoses with the which perforates a foramen at the bottom of cavernous sinus by way of the angular, su¬ the notch. praorbital, and superior ophthalmic veins deep facial vein. The deep facial vein (Fig. 9-10), and also by way of its tributary, empties into the facial vein where the zygo¬ the deep facial vein, to the pterygoid plexus maticus major muscle crosses the anterior and inferior ophthalmic vein. border of the masseter muscle (Figs. 9-9; 9-10). It begins as a large anastomosis with the clinical correlation. The facial vein has no pterygoid plexus (Fig. 9-10), and receives valves. In cases of infections about the nose and small tributaries from the buccinator, zygo¬ mouth, the blood in the vein may become throm¬ maticus major, and masseter muscles, as bosed. An infected thrombus can progress against well as from other neighboring structures. the flow of blood, finally reaching the cavernous sinus through its anastomoses and causing menin¬ Other tributaries of the facial vein as it gitis. courses across the face are: The angular vein, formed by the junction of the supratrochlear and supraorbital veins at the root of the nose, becomes the facial vein near the level of the zygomaticus major muscle (Fig. 9-9). During its course the angular vein receives the fol¬ lowing tributaries: angular vein.

superior palpebral vein, which arises in the upper eyelid and opens into the lateral aspect of the angular vein; inferior palpebral vein, which arises in the lower eyelid and passes downward and medially to open into the angular vein; and external nasal veins, which course up¬ ward and laterally from the alae of the nose and open into the angular vein (Fig. 9-9). supratrochlear vein. The supratrochlear vein commences from a venous plexus on the forehead and scalp that communicates with the frontal tributaries of the superficial temporal vein (Fig. 9-9). It lies near the vein of the opposite side in its course to the root of the nose. At this site, the two supra¬

superior labial vein, which is formed from a venous plexus on the upper lip and drains laterally and superiorly to join the facial vein (Fig. 9-9); inferior labial vein, which is formed along the lower lip and drains laterally to the fa¬ cial vein (Fig. 9-9); parotid veins, which are small vessels that drain the parotid and masseteric regions and course medially to join the facial vein; external palatine vein, which drains the soft palate near the superior pole of the ton¬ sil. It courses downward and forward in the tonsillar bed, penetrates the superior con¬ strictor muscle, and joins the facial vein just below the body of the mandible. In the neck, the facial vein receives the: submental vein, which courses posteriorly along the mylohyoid muscle to join the fa¬ cial vein below the body of the mandible (Fig. 9-9); and submandibular vein, which drains the submandibular gland and courses laterally to join the facial vein.

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

SUPERFICIAL TEMPORAL VEIN

The superficial temporal vein begins from a broad plexus of veins on the vertex and side of the head, where it anastomoses with the supratrochlear, supraorbital, posterior auricular, and occipital veins (Fig. 9-9). Over the crown of the skull, it anastomoses with the superficial temporal vein of the other side. Anterior and posterior tributaries unite in front of the ear to form the trunk of the superficial temporal vein, which then crosses the posterior root of the zygomatic arch and enters the substance of the parotid gland. Here it unites with the maxillary vein to form the retromandibular vein. TRIBUTARIES OF THE SUPERFICIAL TEMPORAL

The superficial temporal vein re¬ ceives the following tributaries: vein.

middle temporal vein, which receives smaller vessels in the lateral orbital region, courses deep to the temporal fascia, and joins the superficial temporal vein just above the zygomatic arch (Fig. 9-9); transverse facial vein, which courses lat¬ erally across the face superficial to the masseter muscle and joins the superficial tempo¬ ral vein at about the level of the ear lobe (Fig. 9-9); and anterior auricular vein, which returns blood from the external ear and joins the superficial temporal vein from behind (Fig. 9-9). POSTERIOR AURICULAR VEIN

The posterior auricular vein begins on the side of the head from a venous plexus that includes anastomoses with the occipital and superficial temporal veins (Fig. 9-9). It de¬ scends behind the external ear and joins the retromandibular vein within or below the parotid gland to form the external jugular vein. The posterior auricular vein receives tributaries from the back of the ear and the stylomastoid vein.

803

them pierces the cranial attachment of the trapezius muscle. It enters the suboccipital triangle, and forming a plexus, joins the deep cervical and vertebral veins. The parie¬ tal emissary vein connects it with the supe¬ rior sagittal sinus, the mastoid emissary vein connects it with the transverse sinus, and through the occipital diploic vein it is con¬ nected with the confluens sinuum. Occa¬ sionally the occipital vein follows the occip¬ ital artery as far as the carotid sheath and empties into the internal jugular, or it may join the posterior auricular vein and drain into the external jugular vein.

RETROMANDIBULAR VEIN

The retromandibular vein is formed from the junction of the superficial temporal and maxillary veins (Figs. 9-9; 9-10). It courses through the substance of the parotid gland between the ramus of the mandible and the upper part of the anterior border of the sternocleidomastoid muscle. The retro¬ mandibular vein lies superficial to the exter¬ nal carotid artery, but deep to the facial nerve. The retromandibular vein has a large communicating branch with the facial vein that was formerly called the posterior facial vein, and the common trunk from these two veins was called the common facial vein (Fig. 9-10). It receives small tributaries from the parotid gland and the masseter muscle, and joins the posterior auricular vein to form the beginning of the external jugular vein.

Deep Veins of the Face Maxillary Pterygoid plexus These veins are tributaries of the internal and external jugular veins.

MAXILLARY VEIN OCCIPITAL VEIN

The occipital vein begins in a plexus on the posterior part of the scalp, where it anas¬ tomoses with posterior auricular and super¬ ficial temporal venous tributaries (Fig. 9-9). From this plexus the occipital vein becomes a single vessel that courses with the occipital artery and greater occipital nerve, and with

The maxillary vein is a short trunk that accompanies the first part of the maxillary artery; it passes backward between the neck of the mandible and the sphenomandibular ligament. It is formed by a confluence of the veins in the pterygoid plexus and ends by joining the superficial temporal vein to form the retromandibular vein (Fig. 9-10).

804

THE VEINS

PTERYGOID PLEXUS

The pterygoid plexus is an extensive net¬ work of veins situated between the tempo¬ ralis and lateral pterygoid muscles and be¬ tween the two pterygoid muscles, and it extends outward between surrounding structures in the infratemporal fossa (Fig. 9-10). It receives tributaries that correspond to branches of the maxillary artery. These include the: inferior alveolar vein, which drains the lower jaw and lower teeth; middle meningeal vein, which drains the dura mater located within the cranial cavity; deep temporal veins, through which the pterygoid plexus anastomoses with the tem¬ poral plexus; masseteric vein, which drains the masseter muscle;

buccal vein, which drains the buccinator muscle; posterior superior alveolar veins, which drain the upper posterior teeth and gums; pharyngeal veins, which drain the supe¬ rior pharyngeal constrictor and the upper pharynx; descending palatine vein, which drains the palate; infraorbital vein, which assists in the drainage of the inferior structures of the orbit and the infraorbital region of the face; vein of the pterygoid canal, which links the pterygopalatine fossa with the cranial cavity; and sphenopalatine vein, which helps to drain the nasal cavity and nasal septum. The sphenopalatine vein, accompanying the artery, drains the veins of the nasal sep-

Junction of supraorbital and supratrochlear veins

Superior ophthalmic vein — Angular vein Interior ophthalmic vein

Cavernous sinus

Pterygoid plexus

Superficial temporal v. — Deep facial vein

Maxillary vein Retromandibular v. —

External jugular vein (Posterior facial vein)

Submental vein Internal jugular vein

(Common facial vein)

Fig. 9-10. Principal veins of face and orbit. Two labels in parentheses utilize old terminology for which new terms were not included in the Nomina Anatomica. (From Eycleshymer and Jones.)

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

turn and the extensive plexuses of the erec¬ tile tissue in the mucous membrane of the nasal conchae. Its tributaries anastomose with the inferior ophthalmic and ethmoidal veins and may communicate through the cribriform plate and foramen cecum of the ethmoid bone with the superior sagittal sinus. The pterygoid plexus communicates with the cavernous sinus through the foramen of Vesalius, the rete foraminae ovalis, emissary veins of the foramen lacerum, and inferior ophthalmic vein. It communicates with the facial vein through the deep facial and angu¬ lar veins. Veins of the Brain

The veins of the brain are tributaries of the venous sinuses that flow into the inter¬ nal jugular veins. They possess no valves, and their walls, due to the absence of mus¬ cular tissue, are extremely thin. As they

Superior cerebral vein (of central sulcus) Superior anastomotic vein (of Trolard)

805

leave the brain, they pierce the arachnoid membrane and the inner or meningeal layer of the dura mater, and open into the cranial venous sinuses. The veins of the brain do not accompany the arteries. They may be subdi¬ vided into the: Cerebral veins Cerebellar veins Veins of the brainstem

CEREBRAL VEINS

The cerebral veins include both external veins, which drain the outer surfaces of the brain and empty into the venous sinuses, and the internal veins, which drain the inner parts of the cerebral hemispheres and empty into the great cerebral vein (of Galen1). The external veins are the superior, superficial middle, and inferior cerebral veins. Claudius Galen (120-210 A.D.): A Greek physician, phys¬ iologist, and anatomist who practiced in Rome.

Superior sagittal sinus

Superior cerebral vein

Superior cerebral veins

Superficial middle cerebral vein

Inferior cerebral veins (of occipital lobe)

Inferior cerebral vein (of temporal lobe)

Inferior anastomotic vein (of Labbe)

Fig. 9-11. The superficial cerebral veins as seen from the right side of the brain. (From Crosby, E. C„ Humphrey, T. and Lauer, E. W„ Correlative Anatomy of the Nervous System, Macmillan Publishing Co., Inc., New York, 1962.)

806

THE VEINS

Superior Cerebral Veins

The superior cerebral veins, 10 to 16 in number, drain the superolateral and medial surfaces of the hemispheres (Fig. 9-11). Most are lodged in the sulci of the cerebral cortex, but some run across the gyri. All of the supe¬ rior cerebral veins open into the superior sagittal sinus after a course of one or more centimeters in the dural wall. The anterior veins course nearly at right angles to the sinus, while the posterior and larger veins are directed more obliquely forward and open into the sinus in a direction opposed to the current of the blood contained within it (this may be of little functional significance).

cavernous, sphenoparietal, superior petro¬ sal, and transverse sinuses. Located more deeply in the brain and draining the internal structures of the cere¬ bral hemispheres are the great cerebral vein and its principal tributaries, the internal cer¬ ebral veins, and the basal vein. Great Cerebral Vein

The inferior cerebral veins are small and drain the inferior surfaces of the hemi¬ spheres (Fig. 9-11). Those on the orbital sur¬ face of the frontal lobe join the superior cer¬ ebral veins, and through these open into the superior sagittal sinus. Others, which drain the temporal lobe, anastomose with the mid¬ dle cerebral and basal veins, and join the

The great cerebral vein is formed by the union of the two internal cerebral veins (Figs. 9-12; 9-13). It is a short (about 2 cm) median trunk into which flow the veins that drain the deep, medially oriented structures of the basal ganglia, thalamus, hypothala¬ mus, and midbrain. It curves posteriorly and upward around the splenium of the corpus callosum, and ends by joining the inferior sagittal sinus at the anterior extremity of the straight sinus. internal cerebral veins. The two inter¬ nal cerebral veins drain the deep parts of the hemisphere (Figs. 9-12; 9-13). Each is formed near the interventricular foramen by the union of the thalamostriate and choroid veins. The internal cerebral veins run back¬ ward, parallel with one another, between the layers of the tela choroidea of the third ven¬ tricle, and beneath the splenium of the cor¬ pus callosum, where they unite to form the great cerebral vein. Just prior to their union, each internal cerebral vein receives the cor¬ responding basal vein of that side. thalamostriate vein. The thalamostriate vein commences in the groove between the corpus striatum and thalamus, and receives numerous veins from both of these regions (Figs. 9-12; 9-13). On each side the thalamo¬ striate vein unites behind the anterior col¬ umns of the fornix with the choroid vein, to form the corresponding internal cerebral vein. choroid vein. The choroid vein courses along the entire length of the choroid plexus, and receives veins from the hippocampus, the fornix, and the corpus callosum. Ascend¬ ing to the interventricular foramen (of Monro3), the choroid vein is joined by the thalamostriate vein to form the internal cer¬ ebral vein.

'Paulin Trolard (1842-1910): A French anatomist. 2Leon Labbe (1832-1916): A French surgeon (Paris).

3 Alexander Monro II (1733-1817): A Scottish anatomist (Edinburgh).

Superficial Middle Cerebral Vein

The superficial middle cerebral vein be¬ gins on the lateral surface of the hemisphere and usually ends in the cavernous sinus (Fig. 9-11). It drains most of the lateral surface of the cerebral cortex, and courses in the lat¬ eral (Sylvian) sulcus. Although there may be multiple veins of smaller diameter within the sulcus, the superficial middle cerebral vein anastomoses both superiorly toward the midline and inferolaterally over the tem¬ poral lobe. It is connected above with the superior sagittal sinus by way of the supe¬ rior anastomotic vein (of Trolard1), which then becomes one of the superior cerebral veins that open into the sinus. Inferolaterally, the superficial middle cerebral vein is joined to the transverse sinus by the inferior anas¬ tomotic vein (of Labbe2). Thus, the superfi¬ cial middle cerebral vein is directly con¬ nected with the cavernous, superior sagittal, and tranverse venous sinuses of the skull.

Inferior Cerebral Veins

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

807

Septal vein

— Thalamostriate vein

_ Internal cerebral vein

Choroid vein

Great cerebral vein (of Galen)

Fig. 9-1 2. The internal cerebral veins and their tributaries draining the deep cerebral structures. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, Urban and Schwarzenberg, 1975.)

BASAL VEIN

The basal vein is formed at the anterior perforated substance by the union of a small anterior cerebral vein which accompanies the anterior cerebral artery, the deep middle cerebral vein which receives tributaries from the insula and neighboring gyri and runs in the lower part of the lateral cerebral sulcus, and the inferior striate veins which leave the corpus striatum through the ante¬ rior perforated substance (Fig. 9-13). The basal vein passes posteriorly around the cer¬ ebral peduncle, and ends either in the inter¬ nal cerebral vein near its junction with the great cerebral vein, or in the great cerebral vein itself. It receives tributaries from the interpeduncular fossa, the inferior horn of

the lateral ventricle, the parahippocampal gyrus, and the midbrain.

CEREBELLAR VEINS

The cerebellar veins are located on the surface of the cerebellum and consist of two sets, superior and inferior. Certain of the su¬ perior cerebellar veins pass forward and medially, across the superior vermis, and end in the straight sinus or in the great cere¬ bral vein, while others course laterally to the transverse and superior petrosal sinuses. The inferior cerebellar veins are larger than the superior cerebellar; some course anteri¬ orly and laterally and end in the superior petrosal or transverse sinuses, while others

808

THE VEINS

Anastomotic veins Thalamostriate vein Longitudinal caudate vein Transverse caudate vein

Choroid vein

Inferior sagittal sinus

Straight sinus

Anterior terminal vein

Septal vein Transverse sinus

Basal vein

Great cerebral vein (of Galen)

Internal cerebral vein

Fig. 9-1 3. Midsagittal view of the deeply located veins of the cerebrum. Note the relationship of the internal cerebral veins, the great cerebral vein, and the straight sinus. (Adapted from Truex, R. C. and Carpenter, M. B., Human Neuroanatomy, 6th ed., Williams and Wilkins, Baltimore, 1969.)

course directly backward and open into the occipital sinus.

superiorly toward the great cerebral vein or the basal vein. Sinuses of the Dura Mater

VEINS OF THE BRAINSTEM

The veins of the midbrain, pons, and me¬ dulla form a superficial plexus which lies deep to the arteries. From the plexus ante¬ rior and posterior median longitudinal chan¬ nels form along the medulla oblongata. The anterior vein drains superiorly into the pon¬ tine plexus, interiorly into the vertebral veins and the corresponding veins of the spi¬ nal cord, and laterally into radicular veins which leave the cranial cavity with the lower cranial nerves. The posterior vein drains into the inferior petrosal and basilar sinuses, as well as along the cranial nerve rootlets. Over the pons, the superficial ve¬ nous channels form more laterally situated longitudinal veins. These drain laterally into the inferior petrosal sinuses or through the foramina with the cranial nerves. The ve¬ nous drainage of the midbrain is directed

The sinuses of the dura mater are venous channels which drain blood from the brain and the bones that form the cranial cavity and carry it into the internal jugular vein. Situated between the two layers of the dura mater, they are devoid of valves but are lined by endothelium continuous with that of the veins into which they drain. They may be divided into a posterosuperior and an anteroinferior group. The posterosuperior group of intracranial venous sinuses consists of the following: Superior sagittal sinus Inferior sagittal sinus Straight sinus Transverse sinuses Sigmoid sinuses Petrosquamous sinuses Occipital sinus Confluence of sinuses

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

809

Dural vein Superior sagittal sinus

Venous lacuna

Venous lacuna

Fig. 9-14. Superior sagittal sinus laid open after removal of the skull cap. The fibrous cords (of Willis) are clearly seen. The venous lacunae are also well shown; from two of them probes have been passed into the superior sagittal sinus. (From Poirier and Charpy.)

The superior sagittal sinus occupies the attached convex margin of the falx cerebri (Figs. 9-14; 9-15; 9-19). Commencing at the foramen cecum, through which it may re¬ ceive a vein from the nasal cavity, the sinus is directed posteriorly, grooving the inner surface of the frontal bone, the adjacent margins of the two parietal bones, and the inner aspect of the squamous part of the oc¬ cipital bone along the superior part of the cruciate eminence. Near the internal occipi¬ tal protuberance, it deviates to one side, usu¬ ally the right, and is continued as the corre¬ sponding transverse sinus. The superior sagittal sinus is triangular in cross section, and gradually enlarges as it passes posteri¬ orly. Its inner surface presents the openings of the superior cerebral veins. Their orifices are concealed by fibrous folds and numerous fibrous bands (chords of Willis1) that extend

transversely across the inferior angle of the sinus (Fig. 9-14). Small openings in the wall communicate with irregularly shaped spaces, called lateral venous lacunae, in the dura mater near the sinus. There are usually three lacunae on each side, a small frontal, a large parietal, and an occipital which is in¬ termediate in size. Most of the cerebral veins from the outer surface of the hemisphere open into these lacunae, and numerous arachnoid granulations (Pacchionian2 bod¬ ies) project into them. These latter struc¬ tures, evaginations of arachnoid mesothelium into the sinus, communicate with the subarachnoid space, and provide a pathway by which cerebrospinal fluid can flow di¬ rectly into the venous blood. The superior sagittal sinus receives the superior cerebral veins and veins from the diploe, and near the posterior extremity of the sagittal suture, also the anastomosing emissary veins from the pericranium, which pass through the

'Thomas Willis (1621-1675): An English physician (Lon¬ don).

2Antonio Pacchioni (1665-1726): An Italian anatomist (Rome).

SUPERIOR SAGITTAL SINUS

810

THE VEINS

parietal foramina, and veins from the dura mater. Numerous anastomoses exist be¬ tween this sinus and the veins of the nose and scalp.

sides receiving blood from the inferior sagit¬ tal sinus, the straight sinus receives the great cerebral vein and the superior cerebellar veins. A few transverse fibrous bands cross its interior.

INFERIOR SAGITTAL SINUS

The inferior sagittal sinus is contained in the posterior half or two-thirds of the free margin of the falx cerebri. This is found in the deepest region of the longitudinal fissure that separates the two hemispheres of the brain, and just above the white commissure, called the corpus callosum, which intercon¬ nects the two hemispheres across the mid¬ line. The inferior sagittal sinus is cylindrical, increases in size as it passes posteriorly, and ends in the straight sinus (Figs. 9-15; 9-19). It receives several veins from the falx cerebri, and occasionally a few from the medial sur¬ face of the hemispheres. STRAIGHT SINUS

The straight sinus is situated at the line of junction of the falx cerebri and the tento¬ rium cerebelli (Figs. 9-13; 9-15; 9-19). It is tri¬ angular in cross section, and it enlarges as it proceeds posteriorly from the end of the in¬ ferior sagittal sinus. It opens into the trans¬ verse sinus of the side opposite that in which the superior sagittal sinus terminates. Be¬

TRANSVERSE SINUSES

The transverse sinuses are large and begin at the internal occipital protuberance (Figs. 9-15; 9-16; 9-19). One, generally the right, is the direct continuation of the superior sagit¬ tal sinus, the other of the straight sinus. Each transverse sinus passes horizontally lateralward and then forward, describing a slight curve, to the base of the petrous portion of the temporal bone. In this part of its course, it lies in the attached margin of the tento¬ rium cerebelli. As it leaves the tentorium, it becomes the sigmoid sinus. The transverse sinuses are frequently of unequal size, the one formed by the superior sagittal sinus being the larger. At the base of the petrous portion of the temporal bone, where the transverse sinuses become the sigmoid si¬ nuses, they receive the superior petrosal si¬ nuses. During their course, the transverse sinuses receive some of the inferior cerebral veins and the inferior anastomotic veins from the cerebral cortex, and some of the inferior cerebellar veins, as well as the pos¬ terior temporal and occipital diploic veins.

Superior sagittal sinus Falx cerebri

Inferior sagittal sinus

Great cerebral vein (Galen) Straight sinus Left tentorium cerebelli Right tentorium cerebelli (cut) Confluence of the sinuses

Transverse sinus Occipital sinus Superior petrosal sinus Fig. 9-15.

sinus

Sagittal section of the skull with the brain removed, showing the sinuses of the dura.

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

SIGMOID SINUSES

The sigmoid sinuses are directly continu¬ ous with the transverse sinuses and com¬ mence where the transverse sinuses emerge from the tentorium cerebelli. Each sigmoid sinus curves inferiorly and medially in an S-shaped manner, in order to reach the pos¬ terior part of the jugular foramen, where it ends in the internal jugular vein (Fig. 9-16). In its course it rests initially on the mastoid part of the temporal bone, and then just be¬ fore its termination, on the jugular process of the occipital bone. As it passes through the jugular foramen, the sigmoid sinus is sepa¬ rated by the vagus and spinal accessory nerves from the inferior petrosal sinus, which emerges through the anterior part of the jugular foramen.

81 1

sagittal, the straight, and the occipital, with the two large transverse sinuses (Fig. 9-15). It is situated on the inner surface of the cra¬ nium, usually just to the right of the internal occipital protuberance. The direction of cur¬ rents within the confluence is such that the right transverse sinus usually receives the greater part of its blood from the superior sagittal sinus, and the left transverse sinus receives blood from the straight sinus. The anteroinferior group of intracranial venous sinuses includes the following: Cavernous sinuses Ophthalmic veins Sphenoparietal sinuses Intercavernous sinus Superior petrosal sinuses Inferior petrosal sinuses Basilar plexus

PETROSQUAMOUS SINUSES

The petrosquamous sinuses are found only occasionally. When present, each is located in a groove that courses along the junction of the squamous and petrous parts of the temporal bone. On each side this sinus opens posteriorly into the transverse sinus, close to where the latter becomes the sig¬ moid sinus. Anteriorly the petrosquamous sinus communicates with the retroman¬ dibular vein behind the ramus of the man¬ dible. OCCIPITAL SINUS

The occipital sinus is one of the smallest of the cranial sinuses (Figs. 9-15; 9-19). It is situated in or near the midline, along the at¬ tached margin of the falx cerebelli, and is generally single but occasionally paired. It commences around the margin of the fora¬ men magnum by several small venous channels, one of which joins the terminal part of the sigmoid sinus. Inferiorly it com¬ municates with the internal vertebral ve¬ nous plexuses, and superiorly it opens into one of the transverse sinuses or, more fre¬ quently, into the confluence of sinuses.

CONFLUENCE OF SINUSES

The confluence of sinuses (also known as the torcular Herophili1) is the dilated junc¬ tion of three tributary sinuses, the superior ^erophilus (about 350 b.c.): A Greek physician and anatomist, who worked in Alexandria, Egypt.

CAVERNOUS SINUSES

The cavernous sinuses are situated to the right and left of the body of the sphenoid bone, and communicate with each other both in front of and behind the hypophysis (Fig. 9-16). They are about 1 cm wide and are traversed by numerous interlacing fibrous filaments which present them with irregular venous spaces internally, and a trabeculated, spongy character that slows the flow of ve¬ nous blood. They are larger behind than in front, and each sinus extends about 2 cm from the superior orbital fissure anteriorly to the apex of the petrous portion of the tempo¬ ral bone posteriorly. Each cavernous sinus drains posteriorly into the superior petrosal and inferior petrosal sinuses. Along the medial wall of each cavernous sinus courses the internal carotid artery, sur¬ rounded by the carotid plexus of sympa¬ thetic nerve fibers (Fig. 9-17), and just infe¬ rior and lateral to the artery is found the abducens nerve. On the lateral wall of the sinus are the oculomotor and trochlear nerves, along with the ophthalmic and max¬ illary divisions of the trigeminal nerve (Fig. 9-17). These structures are separated from the blood flowing through the sinus by the endothelial lining of the sinus wall. The cavernous sinus receives the superior and inferior ophthalmic veins, the superfi¬ cial middle cerebral vein, several of the infe¬ rior cerebral veins, and the small spheno¬ parietal sinus. It communicates with the transverse sinus by means of the superior

812

THE VEINS

Levator palpebrae Rectus superior

Sup. oph¬ thalmic vein

Sphenoparietal sinus

Sigmoid sinus

Vertebral artery

End of straight sinus

Superior sagittal sinus Fig. 9-16.

The venous sinuses at the base of the skull.

petrosal sinus; with the internal jugular vein by way of the inferior petrosal sinus; with the pterygoid plexus by veins that pass through the sphenoidal emissary foramen (of Vesalius1), the foramen ovale, and fora¬ men lacerum; and with the angular and fa¬ cial veins through the superior ophthalmic vein. The two cavernous sinuses anastomose with each other through the anterior and posterior intercavernous sinuses. Superior Ophthalmic Vein

9-16; 9-19). It passes posteriorly through the superior part of the orbit, and receives tribu¬ taries that correspond to the branches of the ophthalmic artery. Forming a short single trunk, it passes between the two heads of the Internal carotid artery Cavernous sinus Oculomotor nerve Trochlear nerve Ophthalmic nerve Abducent nerve

The superior ophthalmic vein begins at the medial angle of the upper eyelid by a confluence of tributaries of the supratroch¬ lear, supraorbital, and angular veins (Figs. Andreas Vesalius (1514-1564): A great Flemish anato¬ mist who did his finest work in Padua, Italy.

Fig. 9-17.

Oblique section through the cavernous sinus.

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

lateral rectus muscle and then through the medial part of the superior orbital fissure below the abducens nerve, and opens into the cavernous sinus. Inferior Ophthalmic Vein

The inferior ophthalmic vein begins in a venous network on the anterior part of the floor and medial wall of the orbit (Fig. 9-19). It receives veins from the inferior rectus and inferior oblique muscles, as well as from the lacrimal sac and eyelids. Coursing posteri¬ orly in the inferior part of the orbit, it di¬ vides into two branches. One of these passes through the inferior orbital fissure and joins the pterygoid venous plexus. The other en¬ ters the cranial cavity through the superior orbital fissure and ends in the cavernous sinus, either separately, or more frequently in common with the superior ophthalmic vein. SPHENOPARIETAL SINUSES

Each of the two sphenoparietal sinuses, one on each side, begins from a small menin¬ geal vein near the lateral tip of the lesser wing of the sphenoid bone. It then courses medially in a groove on the inferior surface of the lesser wing of the sphenoid bone and drains into the anterior part of the cavernous sinus. In addition to receiving a few small meningeal venous tributaries, it usually re¬ ceives the anterior temporal diploic vein. INTERCAVERNOUS SINUSES

The anterior and posterior intercavernous sinuses interconnect the cavernous sinuses across the midline. The anterior inter¬ cavernous sinus passes in front of the hy¬ pophysis, while the posterior passes behind the gland (Fig. 9-16). Together with the cav¬ ernous sinuses, they form a venous circle, sometimes called the circular sinus, around the hypophysis. The anterior intercavernous sinus is usually the larger of the two, but ei¬ ther one may be absent. SUPERIOR PETROSAL SINUSES

The superior petrosal sinuses are small and narrow, and on each side they connect the cavernous with the transverse sinus (Figs. 9-15; 9-16; 9-19). Each superior petrosal

81 3

sinus courses laterally and backward from the posterior end of the cavernous sinus. Passing over the trigeminal nerve, it lies in the attached margin of the tentorium cerebelli, along a groove in the superior border of the petrous portion of the temporal bone. It joins the transverse sinus where the latter curves downward and becomes the sigmoid sinus on the inner surface of the mastoid part of the temporal. It receives certain of the cerebellar and inferior cerebral veins, and veins from the tympanic cavity.

INFERIOR PETROSAL SINUSES

Each of the two inferior petrosal sinuses is situated in the corresponding inferior petro¬ sal sulcus that is formed by the junction of the petrous part of the temporal bone and the basilar part of the occipital bone (Figs. 9-15; 9-16; 9-19). Commencing at the posteroinferior part of the cavernous sinus, the infe¬ rior petrosal sinus passes to the anterior part of the jugular foramen, and it ends in the superior bulb of the internal jugular vein. The inferior petrosal sinus receives the laby¬ rinthine veins, and also veins from the me¬ dulla oblongata, pons, and inferior surface of the cerebellum. The relationship of the vessels and nerves passing through the jugular foramen is as follows: the inferior petrosal sinus lies anteromedially, with the meningeal branch of the ascending pharyngeal artery, and is directed obliquely downward and back¬ ward; the sigmoid sinus is situated at the lat¬ eral and posterior part of the foramen, with a meningeal branch of the occipital artery; between the two sinuses are the glossopha¬ ryngeal, vagus, and accessory nerves. These three sets of structures are separated by two processes of fibrous tissue. The junction of the inferior petrosal sinus and the internal jugular vein takes place on the lateral aspect of the nerves.

BASILAR PLEXUS

The basilar plexus consists of several in¬ terlacing venous channels located between the layers of the dura mater over the basilar part of the occipital bone (Fig. 9-16). It serves to connect the two inferior petrosal sinuses, and it communicates with the anterior verte¬ bral venous plexus.

814

the veins

Diploic Veins

The diploe of the cranial bones contain bone marrow and are drained by venous channels called the diploic veins. These veins are large and at irregular intervals ex¬ hibit pouch-like dilatations. Their walls are thin, consisting only of endothelium resting on a layer of elastic tissue. While the cranial bones are separated from one another, these veins are confined to particular bones, but when the sutures are obliterated, the veins unite and generally increase in size. Thus, they are enlarged in the elderly, but virtually nonexistent in the newborn, only gradually developing during early childhood. The diploic veins communicate with the menin¬ geal veins and the sinuses of the dura mater, with the veins of the pericranium, and with each other. Usually the following diploic veins are found in the skull: Frontal Anterior temporal Posterior temporal Occipital FRONTAL DIPLOIC VEIN

The frontal diploic vein is found in the anterior part of the frontal bone (Fig. 9-18). Through the inner table of the skull, it com¬ municates with the superior sagittal sinus. The veins of the two sides usually join ante¬

Fig. 9-18.

riorly to form a single vessel, which per¬ forates the outer table in the roof of the su¬ praorbital notch and anastomoses with the supraorbital vein. ANTERIOR TEMPORAL DIPLOIC VEIN

There are usually two anterior temporal diploic veins, one found in front of the coro¬ nal suture in the frontal bone, and the other behind the suture in the parietal bone (Fig. 9-18). Internally they communicate with the sphenoparietal sinus, while externally they anastomose with one of the deep temporal veins through an aperture in the great wing of the sphenoid bone. POSTERIOR TEMPORAL DIPLOIC VEIN

The posterior temporal diploic vein courses downward in the parietal bone to¬ ward the mastoid region of the temporal bone (Fig. 9-18). It either perforates the inner table through an aperture at the mastoid angle of the parietal bone, or it courses through the mastoid foramen and terminates in the transverse sinus. OCCIPITAL DIPLOIC VEIN

The occipital diploic vein, the largest of the diploic veins, is confined to the occipital bone (Fig. 9-18). It opens either externally

The diploic veins displayed after removal of the outer table of the skull.

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

into the occipital vein, or internally into the transverse sinus or the confluence of sinuses. Emissary Veins

The emissary veins pass through various foramina and openings in the cranial wall and establish anastomoses between the si¬

81 5

nuses of the dura inside the skull and the veins on the exterior of the skull (Fig. 9-19). Some of the following emissary veins are always present, others only occasionally. mastoid emissary vein. The mastoid emissary vein is usually present. It courses through the mastoid foramen and may traLateral ventricle

Fig. 9-19. The veins of the head and neck projected onto the skull and brain. The cerebral ventricles are shown in red. The extracranial portions of the veins are shown in solid blue, while the intracranial portions of the veins are in hatched blue. Numbers identify the foramina through which veins traverse the cranium. 1, Superior orbital fissure. 2, Inferior orbital fissure. 3, Foramen ovale. 4, Foramen spinosum. 5, Foramen lacerum. 6, Carotid canal. 7, Jugular foramen. 8, Hypoglossal canal. 9, Condyloid canal. Black inverted crescents indicate openings through which emissary veins pass. (From Eycleshymer and Jones.)

816

the veins

verse a diploic vein for a short distance, con¬ necting the sigmoid sinus with the posterior auricular or with the occipital vein. occipital emissary vein. The occipital emissary vein courses through a small fora¬ men at the occipital protuberance and links the confluence of sinuses with the occipital vein. parietal emissary vein. The parietal em¬ issary vein passes through the parietal fora¬ men, anastomoses with the diploic veins, and interconnects the superior sagittal sinus with the veins of the scalp. VENOUS

PLEXUS

OF

THE

HYPOGLOSSAL

This network of small veins tra¬ verses the hypoglossal canal and joins the sigmoid sinus with the vertebral vein or the internal jugular vein. condylar emissary vein. The condylar emissary vein is inconstant, but when pres¬ ent, it passes through the condylar canal and connects the sigmoid sinus with the deep veins in the upper neck. canal.

VENOUS

PLEXUS

OF

THE

FORAMEN

OVALE.

This plexus of small veins interconnects the cavernous sinus with the pterygoid plexus through the foramen ovale. EMISSARY VEINS OF THE FORAMEN LACERUM.

Two or three small veins course through the foramen lacerum and connect the cavernous sinus with the pterygoid plexus. EMISSARY VEIN OF THE SPHENOID FORAMEN.

In about half of the skulls, an emissary vein courses through the sphenoidal foramen (of Vesalius), which also connects the cavernous sinus with the pterygoid plexus. internal carotid venous plexus. An in¬ ternal carotid plexus of veins accompanies the internal carotid artery and traverses the carotid canal between the cavernous sinus and the internal jugular vein. EMISSARY VEIN OF THE FORAMEN CECUM.

In

some specimens a vein is transmitted through the foramen cecum, which connects the superior sagittal sinus with the veins of the nasal cavity. Other anastomoses between the dural sinus and veins outside the cranial cavity that are not classed as emissary veins are the connection between the cavernous sinus and the facial vein through the superior ophthal¬ mic and angular veins, and the communica¬ tion between the inferior petrosal sinus and the vertebral veins by way of the basilar plexus.

External Jugular Vein

The external jugular vein is one of three large veins that course in the neck and re¬ turn blood from structures in the cranial cavity, face, and neck. The other two are the vertebral vein and the internal jugular vein. The external jugular vein flows into the sub¬ clavian vein, as does the vertebral vein, whereas the internal jugular vein is a tribu¬ tary of the brachiocephalic vein. The external jugular vein receives the greater part of the blood from the exterior of the cranium, including the scalp and the superficial and deep regions of the face. It is formed by the junction of the retromandi¬ bular and the posterior auricular veins (Figs. 9-20; 9-22). It commences in the substance of the parotid gland, on a level with the angle of the mandible. Descending perpendicu¬ larly in the neck, the external jugular vein obliquely crosses the superficial surface of the sternocleidomastoid muscle, along a line between the angle of the mandible and the middle of the clavicle. At the clavicle, it lies near the posterior border of the sterno¬ cleidomastoid muscle, and within the sub¬ clavian triangle it perforates the deep fascia and ends in the subclavian vein, lateral or ventral to the anterior scalene muscle. It is separated from the sternocleidomastoid muscle by the investing layer of deep cervi¬ cal fascia, and is covered by the platysma, the superficial fascia, and skin. The external jugular vein crosses the transverse cervical nerve, and its upper half courses parallel to the great auricular nerve. The vein varies in size, in inverse proportion to the other veins of the neck; it is occasionally doubled. It is provided with two pairs of valves, the lower pair being placed at its entrance into the subclavian vein; the upper pair in most cases is about 4 cm above the clavicle. The portion of vein located between the two sets of valves is often dilated, and is sometimes termed the sinus of the external jugular vein. These valves do not prevent the regur¬ gitation of blood, or the passage of injected substances distally. TRIBUTARIES

OF

THE

EXTERNAL

JUGULAR

The external jugular vein receives the posterior external jugular vein, and near its termination, the anterior jugular, transverse scapular, and suprascapular veins. It also is joined by a large communicating branch

vein.

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

from the internal jugular vein, and occasion¬ ally it receives the occipital vein. POSTERIOR EXTERNAL JUGULAR VEIN

The posterior external jugular vein begins in the occipital region and returns blood from the skin and superficial muscles in the upper and posterior part of the neck. It lies between the splenius and trapezius muscles (Fig. 9-23), runs down the posterior part of the neck, and opens into the middle third of the external jugular vein. Anterior Jugular Vein

The anterior jugular vein begins near the hyoid bone, and is formed by the confluence of several superficial veins from the sub¬ mandibular region (Fig. 9-20). It descends between the midline of the neck and the an¬ terior border of the sternocleidomastoid muscle. In the lower neck, the anterior jugu¬ lar vein passes deep to the sternocleidomas¬

Mylohyoid muscle Stylohyoid muscle

81 7

toid muscle and opens into the terminal part of the external jugular, or in some instances, into the subclavian vein (Fig. 9-20). It varies considerably in size, usually in inverse pro¬ portion to the size of the external jugular vein. Most frequently there are two anterior jugular veins, a right and left, but sometimes only one. It usually receives tributaries from some laryngeal veins and occasionally from a small thyroid vein, and it communicates with the internal jugular vein. Just above the sternum the two anterior jugular veins are united by a transverse trunk and form the jugular venous arch, which receives tribu¬ taries from the inferior thyroid veins. The anterior jugular vein contains no valves. TRANSVERSE CERVICAL VEIN

The transverse cervical vein forms from tributaries that drain from beneath the tra¬ pezius (Figs. 9-20; 9-22). It is directed anteromedially, across the posterior triangle of the neck, and opens into the external jugular

Anterior belly of digastric muscle Facial vein

Internal carotid Anterior jugular vein

Retromandibular vein

Thyroid cartilage Internal jugular vein Sternohyoid muscle

Superior thyroid vein (also receiving lingual and laryngeal branches) External jugular vein

Trapezius muscle

Omohyoid muscle (superior belly)

External jugular

Sternocleidomastoid muscle

Transverse cervical

Thyroid gland

Brachiocephalic vein Subclavian vein

Jugular venous arch Inferior thyroid vein Clavicle Pectoralis major muscle

Fig. 9-20. The superficial veins of the neck. The right sternocleidomastoid muscle has been removed to reveal the course of the internal jugular vein. (After Sobotta.)

818

the veins

vein near its termination, but it may drain into the subclavian vein. It usually accompa¬ nies the transverse cervical artery.

pair of valves that are placed about 2.5 cm above the termination of the vessel. TRIBUTARIES

OF

THE

INTERNAL

JUGULAR

During its course, the internal jugular vein receives the inferior petrosal sinus and the facial, lingual, pharyngeal, superior and middle thyroid, and sometimes occipital veins. The thoracic duct on the left side and the right lymphatic duct on the right side open into the angle of union of the internal jugular and subclavian veins. Because the inferior petrosal sinus and the facial and occipital veins were described earlier in the chapter, they will not be elabo¬ rated on further here. However, note that the inferior petrosal sinus leaves the skull through the anterior part of the jugular fora¬ men, and joins the superior bulb of the inter¬ nal jugular vein; the facial vein joins the in¬ ternal jugular vein just below the angle of the mandible; and the occipital vein usually joins the posterior auricular vein and flows into the external jugular vein, but at times it follows the course of the occipital artery and flows directly into the internal jugular vein near the level of the hyoid bone. vein.

SUPRASCAPULAR VEIN

The suprascapular (or transverse scapu¬ lar) vein accompanies the artery of the same name and usually opens into the external jugular near its termination. It may empty into the subclavian vein. Internal Jugular Vein

The internal jugular vein collects blood from the brain, the superficial parts of the face, and the neck (Figs. 9-20: 9-22). It is di¬ rectly continuous with the sigmoid sinus in the posterior compartment of the jugular foramen at the base of the skull. At its origin is a dilatation called the superior jugular bulb. The internal jugular vein courses downward in the neck, lying at first lateral to the internal carotid artery, and then lateral to the common carotid artery. At the root of the neck, it unites with the subclavian vein to form the brachiocephalic vein. A little above its termination is a second dilatation, the inferior jugular bulb. Superiorly near its origin, the internal jug¬ ular vein lies on the rectus capitis lateralis muscle, and behind the internal carotid ar¬ tery and the nerves emerging from the jugu¬ lar foramen. Just above the posterior belly of the digastric muscle, the internal jugular vein and the internal carotid artery lie nearly in the same plane as the glossopha¬ ryngeal and hypoglossal nerves, which pass anteriorly between them. The vagus nerve descends between the vein and the artery, and the accessory nerve runs obliquely backward, superficial to the internal jugular vein and toward the sternocleidomastoid muscle. It is frequently stated that the inter¬ nal jugular vein is surrounded throughout its course by the carotid sheath. The vein, how¬ ever, is usually superficial to the sheath, which in fact does surround the internal ca¬ rotid artery and vagus nerve. At the root of the neck, the right internal jugular vein is placed at a little distance from the common carotid artery, and crosses the first part of the subclavian artery, whereas the left inter¬ nal jugular vein usually overlaps the com¬ mon carotid artery. The left vein is generally smaller than the right, and each contains a

LINGUAL VEIN

The lingual vein opens into the internal jugular vein near the hyoid bone. It receives blood primarily from its dorsal lingual tribu¬ taries. Additionally, blood from the tip of the tongue drains into the deep lingual vein. dorsal lingual veins. Two or more dor¬ sal lingual veins drain the dorsum and sides of the tongue (Fig. 9-21). Coursing downward and posteriorly, they join together to form the lingual vein, which accompanies the lin¬ gual artery. The lingual vein then courses posteriorly between the genioglossus and hyoglossus muscles and empties into the in¬ ternal jugular vein just above the greater horn of the hyoid bone. deep lingual vein. The deep lingual vein commences at the tip of the tongue, where it forms an anastomosis with the same vein from the opposite side (Fig. 9-21). Traveling downward and backward just deep to the mucous membrane of the tongue, it receives the small sublingual vein, and near the ante¬ rior border of the hyoglossus muscle, it be¬ comes adjacent to the hypoglossal nerve. At this point it is called the accompanying vein of the hypoglossal nerve, also known as the ranine vein. Passing backward with the hy-

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

81 9

Dorsal lingual artery Deep lingual vein Dorsal lingual veins

Hypoglossal and accompanying (ranine) vein

Fig. 9-21.

Veins of the tongue. The hypoglossal nerve has been displaced downward. (From Testut.)

poglossal nerve along the lateral (superficial) border of the hyoglossus muscle, this vein usually opens into the facial vein, but it may join the lingual vein or even open directly into the internal jugular vein.

PHARYNGEAL VEINS

The pharyngeal veins begin in the pharyn¬ geal plexus on the outer surface of the phar¬ ynx, and after receiving some posterior me¬ ningeal veins and the vein coursing with the artery of the pterygoid canal, they end in the internal jugular vein. They occasionally open into the facial, lingual, or superior thy¬ roid vein.

SUPERIOR THYROID VEIN

The superior thyroid vein begins in the substance and on the surface of the thyroid gland by tributaries that correspond to the branches of the superior thyroid artery, and ends in the middle part of the internal jugu¬ lar vein, just below the hyoid bone (Figs. 9-20; 9-22). It receives the superior laryngeal and cricothyroid veins. At times the superior thyroid vein opens into the facial vein.

MIDDLE THYROID VEIN

The middle thyroid vein collects blood from the lower lateral part of the thyroid gland, and is joined by some veins from the larynx and trachea. It crosses laterally in front of the common carotid artery and deep

to the strap muscles, and opens into the in¬ ternal jugular vein just above the level of the lower border of the thyroid gland. Vertebral Vein

The vertebral vein does not emerge from the cranial cavity through the foramen mag¬ num with the vertebral artery. Instead, it is formed in the suboccipital triangle from numerous small tributaries that spring from the internal vertebral venous plexuses and leave the vertebral canal above the posterior arch of the atlas (Fig. 9-23). These vessels unite with small veins from the deep mus¬ cles in the upper part of the dorsal neck, and form a vessel that enters the foramen in the transverse process of the atlas. Forming a dense plexus around the vertebral artery, they descend in a canal formed by the trans¬ verse foramina of the cervical vertebrae. This plexus ends in a single trunk, the verte¬ bral vein, which emerges usually from the transverse foramen of the sixth (but occa¬ sionally from the seventh) cervical vertebra. In the root of the neck, the vertebral artery opens into the dorsal part of the brachioce¬ phalic vein near its origin, its opening being guarded by a pair of valves. On the right side, the vertebral vein crosses the first part of the subclavian artery. TRIBUTARIES OF THE VERTEBRAL VEIN. The vertebral vein communicates with the sig¬ moid sinus by a vein that passes through the condylar canal, when that canal exists. It also receives tributaries from the occipital

820

THE VEINS

Digastric muscle (anterior belly) Facial vein

Mylohyoid muscle

Retromandibular vein

Stylohyoid muscle

External jugular vein Superior thyroid vein (also receives lingual vein) Internal jugular vein

Omohyoid muscle

Sternohyoid muscle Sternocleidomastoid muscle

Thyroid gland Right vagus nerve

Trapezius muscle

Phrenic nerve Middle thyroid vein Common carotid artery

Inferior thyroid vein Left subclavian artery

Superficial cervical vein Transverse cervical vein

Left recurrent laryngeal nerve

Right subclavian vein

Aorta

Fig. 9-22.

The internal jugular system of veins in the deeper neck. Note the superior middle and inferior thyroid veins. (After Sobotta.)

vein, the prevertebral muscles, the internal and external vertebral venous plexuses, and the anterior vertebral and the deep cervical veins. Near its termination it is sometimes joined by the first intercostal vein.

from the deep muscles at the back of the neck. It receives tributaries from the plex¬ uses around the spines of the cervical verte¬ brae, and terminates in the inferior part of the vertebral vein.

ANTERIOR VERTEBRAL VEIN

ACCESSORY VERTEBRAL VEIN

The anterior vertebral vein (ascending cervical vein) commences in a plexus around the transverse processes of the cra¬ nial cervical vertebrae (Fig. 9-23). It de¬ scends in the neck with the ascending cervi¬ cal artery, between the anterior scalene and longus capitis muscles, and opens into the terminal part of the vertebral vein.

The accessory vertebral vein, when pres¬ ent, arises as a small vein from the venous plexus surrounding the vertebral artery, in the canal formed by the transverse foramina of the cervical vertebrae. It emerges from the transverse foramen of the seventh cervical vertebra, courses anteriorly in the lower neck, and opens into the terminal part of the vertebral vein.

DEEP CERVICAL VEIN

The deep cervical vein accompanies its artery between the semispinalis capitis and cervicis (Fig. 9-23). It begins in the suboccipital region as communicating branches from the occipital vein and as small veins

VEINS OF THE UPPER LIMB

The veins of the upper limb can be di¬ vided into two sets, superficial and deep. Distinguished by their topographic position.

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

821

Vertebral vein

Posterior external jugular vein

Vertebral vein

Anterior vertebral vein

Deep cervical vein

Fig. 9-23.

The vertebral vein and other veins in the neck, lateral view. (From Poirier and Charpy.)

they anastomose with each other at frequent sites, and thus form several parallel chan¬ nels of drainage from any single region. The superficial veins are distributed immediately beneath the skin, within the superficial fas¬ cia. The deep veins accompany the arteries, are the venae comitantes, and usually have the same name as their arteries. Both sets of veins are provided with valves, which are more numerous in the deep veins than in the superficial. Superficial Veins of the Upper Limb

Two large veins, the cephalic and the basilic, receive blood from the smaller su¬ perficial veins of the upper limb, and convey it to the axillary vein and then into the sub¬ clavian and brachiocephalic veins (Fig. 924). The cephalic vein courses along the ra¬ dial side of the forearm and the lateral side of the arm. The basilic vein occupies the ulnar aspect of the forearm and medial side of the arm. The superficial veins of the upper limb are: Cephalic Basilic Median antebrachial Venous network of the dorsal hand Superficial venous palmar arch

CEPHALIC VEIN

The cephalic vein begins on the radial aspect of the dorsal venous network of the hand (Fig. 9-24). As it ascends, it winds around the radial border of the forearm, thereby receiving tributaries from both pal¬ mar and dorsal surfaces of the hand. Just below the antecubital fossa, it communi¬ cates with the basilic vein by means of the median cubital vein, which also receives a branch from the deep forearm veins. The main stem of the cephalic vein then contin¬ ues proximally, along the lateral side of the antecubital fossa in the groove between the brachioradialis and the biceps brachii mus¬ cles, where it crosses superficial to the lat¬ eral antebrachial cutaneous branch of the musculocutaneous nerve. Its ascent in the arm continues in the groove along the lateral border of the biceps brachii. In the proximal third of the arm, it passes between the pectoralis major and deltoid muscles, where it is accompanied by the deltoid branch of the thoracoacromial artery. From the interval between these two muscles and the clavicle, called the deltopectoral triangle, the ce¬ phalic vein passes behind the clavicular head of the pectoralis major muscle. It then pierces the clavipectoral fascia, and crossing the axillary artery, it enters the axillary vein

822

THE VEINS

vein may spring from the cephalic vein, proximal to the wrist, and join it once again higher in the forearm. A large oblique anas¬ tomosis frequently connects the basilic and cephalic veins on the back of the forearm.

BASILIC VEIN

Cephalic vein

Basilic vein

Median cubital vein Lateral antebrachial cutaneous nerve Cephalic vein Accessory cephalic vein

Basilic vein

Medial antebrachial cutaneous nerve

Median antebrachial vein

The basilic vein begins on the ulnar aspect of the dorsal venous network of the hand. It ascends on the posterior surface of the ulnar side of the forearm, and is inclined toward the anterior surface just below the elbow, where it is joined by the median cubital vein (Fig. 9-24). It then courses obliquely upward in the groove between the biceps brachii and pronator teres and crosses the brachial ar¬ tery, from which it is separated by the bicip¬ ital aponeurosis. Filaments of the medial antebrachial cutaneous nerve pass both in front of and behind this portion of the vein. Continuing upward in the arm. the basilic vein then travels along the medial border of the biceps brachii. It perforates the deep fas¬ cia a little below the middle of the arm, and ascending on the medial side of the brachial artery to the lower border of the teres major, it joins the brachial vein to form the axillary vein (Fig. 9-27).

MEDIAN ANTEBRACHIAL VEIN

Fig. 9-24. The superficial veins of the upper limb. Note the radial or lateral course of the cephalic vein and the ulnar or medial ascent of the basilic vein.

just below the clavicle (Fig. 9-27). Sometimes it communicates with the external jugular vein by a tributary that ascends in front of the clavicle. accessory cephalic vein. The accessory cephalic vein arises either from a small trib¬ utary plexus on the dorsum of the forearm or from the ulnar side of the dorsal venous network (Fig. 9-24). It remains on the radial side of the cephalic vein and joins it just below the elbow. The accessory cephalic

The median antebrachial vein drains the venous plexus on the palmar surface of the hand (Fig. 9-24). It ascends slightly toward the ulnar side of the anterior forearm, and ends either in the basilic vein or in the me¬ dian cubital vein. At times it divides into two vessels, one of which joins the basilic vein and the other the cephalic vein below the antecubital fossa. The median antebra¬ chial vein also anastomoses with the deep veins of the forearm. There is great variation in the pattern of the superficial veins of the forearm. Fre¬ quently there is a reciprocal relationship in the size of the cephalic and basilic veins. Ei¬ ther one may predominate or even be lack¬ ing. The median antebrachial vein may be absent as a definite vessel. The median cubi¬ tal vein may split into a distinct Y, with one arm of the Y draining into the cephalic and the other into the basilic vein. In this case, one branch is called the median cephalic vein, the other the median basilic vein.

SUPERIOR VENA CAVA AND ITS TRIBUTARIES clinical considerations. The veins of the proximal forearm are usually the ones employed in venipuncture. One of the veins of the median cubital complex regularly has a large vessel anastomosing with the deep veins (Fig. 9-27). This anastomosis holds the superficial vein in place and prevents it from slipping away from the point of the needle.

VENOUS NETWORK OF THE DORSAL HAND

The venous network of the dorsal hand forms initially from dorsal digital veins which pass along the sides of the fingers. These are joined to one another by oblique communicating branches, and the digital veins from the adjacent sides of the fingers unite to form three dorsal metacarpal veins which end in the venous network on the

Fig. 9-25.

823

back of the hand (Fig. 9-25). The radial part of the network is joined by the dorsal digital vein from the radial side of the index finger and by the dorsal digital veins of the thumb; it is prolonged proximally as the cephalic vein. The ulnar part of the network receives the dorsal digital vein of the ulnar side of the little finger, and is continued proximally as the basilic vein. An anastomosing vein fre¬ quently makes an additional connection with either the cephalic or basilic vein in the middle of the forearm.

SUPERFICIAL VENOUS PALMAR ARCH

The superficial venous palmar arch is more delicate than the venous network of the dorsal hand and is formed by palmar

The veins on the dorsum of the hand.

824

the veins

digital veins that drain into venous networks situated over the thenar and hypothenar eminences. These, in turn, flow proximally over the palmar surface of the wrist and help to form the median antebrachial vein. The palmar digital veins also are interconnected in the folds between the fingers to the ve¬ nous network of the dorsal hand by the intercapitular veins. Deep Veins of the Upper Limb

The deep veins follow the course of the arteries, accompanying them as their venae comitantes. Accompanying veins are gener¬ ally arranged in pairs, situated on both sides of the corresponding artery, and several short, transverse anastomotic channels gen¬ erally interconnect them. The deep veins of the upper limb include the following: Deep veins of the hand Deep veins of the forearm Brachial veins Axillary veins Subclavian vein DEEP VEINS OF THE HAND

The superficial and deep palmar arterial arches are each accompanied by a pair of venae comitantes that form the superficial and deep palmar venous arches and receive the veins corresponding to the branches of the arterial arches. Thus, the common pal¬ mar digital veins, formed by the union of the proper palmar digital veins, open into the superficial venous arch, and the palmar met¬ acarpal veins flow into the deep palmar ve¬ nous arch. The dorsal metacarpal veins re¬ ceive perforating branches from the palmar metacarpal veins, and end in the radial veins and the superficial veins on the dorsum of the wrist.

Fig. 9-26. The deep veins of the upper forearm and lower arm in the left upper limb.

than the ulnar, and also receive the dorsal metacarpal veins. The ulnar veins also re¬ ceive small tributaries from the deep palmar venous arch and communicate with the su¬ perficial veins at the wrist. Near the elbow the ulnar veins receive the anterior and pos¬ terior interosseous veins and send a large communicating branch to the median cubi¬ tal vein. BRACHIAL VEINS

DEEP VEINS OF THE FOREARM

The deep veins of the forearm are the venae comitantes of the radial and ulnar ar¬ teries and constitute the vessels into which the palmar venous arches flow. The deep venous palmar arch drains principally into the radial veins, while the superficial venous palmar arch drains into the ulnar veins. The radial and ulnar venae comitantes all unite at the bend of the elbow to form the brachial veins (Fig. 9-26). The radial veins are smaller

The two brachial veins are placed on the medial and lateral sides of the brachial ar¬ tery, and receive tributaries that correspond to the branches given off by the artery (Fig. 9-26). Near the lower margin of the subscapularis muscle, they join the axillary vein. The medial brachial vein frequently flows into the basilic vein. During the re¬ mainder of its ascent into the axillary vein, the basilic vein takes the place of the medial brachial accompanying vein. These deep

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

veins have numerous anastomoses, not only with each other, but also with the superficial veins. AXILLARY VEIN

The axillary vein begins at the junction of the basilic and brachial veins, which is lo¬ cated usually near the lower border of the teres major muscle, and it ends at the outer border of the first rib, where it becomes the subclavian vein (Fig. 9-27). In addition to the tributaries that correspond to the branches of the axillary artery, it receives the cephalic vein near its termination. It lies on the me¬ dial side of the artery, which it partly over¬ laps. Between the two vessels are the medial cord of the brachial plexus, the median, the ulnar, and the medial pectoral nerves. Adja¬ cent to the axillary vein are the medial brachial and antebrachial cutaneous nerves, and closely related to the axillary neurovas¬ cular bundle are the lateral axillary lymph nodes. The axillary vein is provided with a pair of valves opposite the distal border of the subscapularis muscle, and valves also are found at the ends of the cephalic and subscapular veins.

825

SUBCLAVIAN VEIN

The subclavian vein is the continuation of the axillary vein, and it extends from the lat¬ eral border of the first rib to the sternal end of the clavicle, where it unites with the inter¬ nal jugular vein and forms the brachioce¬ phalic vein. It is in relation anteriorly with the clavicle and subclavius muscle, and pos¬ teriorly and superiorly with the subclavian artery, from which it is separated medially by the anterior scalene muscle, and on the right side, by the phrenic nerve. Inferiorly it rests in a depression on the first rib and on the pleura. It usually is provided with a pair of valves that are situated about 2.5 cm from its termination. The subclavian vein occa¬ sionally ascends in the neck to the level of the third part of the subclavian artery, and at times passes with this vessel behind the an¬ terior scalene muscle. TRIBUTARIES OF THE SUBCLAVIAN VEIN. The subclavian vein usually receives only the external jugular vein, but sometimes it also receives the anterior jugular vein, and occa¬ sionally also a small tributary from the ce¬ phalic vein, which ascends ventral to the clavicle. At its angle of junction with the in-

Pectoralis minor muscle

Axillary artery

Deltoid muscle Cephalic vein Musculocutaneous nerve Brachial vein Coracobrachialis muscle

Biceps brachii muscle

Subscapular vein Long thoracic vein Circumflex scapular vein Latissimus dorsi muscle Subscapularis muscle Fig. 9-27.

The veins of the right axilla, showing their relationship to the axillary artery and some of the nerves and muscles of the region.

826

the veins

ternal jugular, the left subclavian vein re¬ ceives the thoracic duct, and the right sub¬ clavian vein receives the right lymphatic duct.

VEINS OF THE THORAX

The special vein of the thorax that drains the blood from the thoracic wall and inter¬ costal spaces is the azygos vein (Fig. 9-28). It is the first tributary of the superior vena cava, joining the latter as it passes ventral to the root of the lung. The other principal trib¬ utaries of the superior vena cava are the brachiocephalic veins, two large collecting trunks that receive blood from the head, neck, and upper limbs (Fig. 9-28). Because the anatomy of the superior vena cava, pulmonary veins, and cardiac veins has already been discussed, only the follow¬ ing veins of the thorax, which contribute blood to the superior vena cava, will be de¬ scribed at this point: Azygos Brachiocephalic Right brachiocephalic Left brachiocephalic Internal thoracic Inferior thyroid Superior intercostal Veins of the vertebral column Azygos Vein

the thorax it lies on the right posterior inter¬ costal arteries, to the right of the aorta and thoracic duct, and is partly covered by pleura. TRIBUTARIES OF THE AZYGOS VEIN. The azygos vein receives the following tributaries: Right superior intercostal vein Right fifth to eleventh posterior intercostal veins Right subcostal vein Hemiazygos vein Accessory hemiazygos vein Esophageal, mediastinal, and pericardial veins A few imperfect valves are found in the azy¬ gos vein, but the valves of its tributaries are complete. RIGHT SUPERIOR INTERCOSTAL VEIN

Generally the right first intercostal vein drains into the right brachiocephalic vein or into one of its tributaries, such as the verte¬ bral vein or the right subclavian vein. The second, third, and fourth right intercostal veins (and sometimes also the first) join to form a single trunk, called the right superior intercostal vein, which usually empties into the azygos vein as the latter arches over the hilum of the right lung. As will be described, the left superior intercostal vein drains into the left brachiocephalic vein. RIGHT FIFTH TO ELEVENTH POSTERIOR INTERCOSTAL VEINS

The azygos vein in the adult is the vessel that persists from the fetal right posterior cardinal and right supracardinal veins (Figs. 9-1; 9-2). It usually commences opposite the first or second lumbar vertebra by a union of the ascending lumbar vein and the right sub¬ costal vein, but it also may be joined at times by a tributary from the right renal vein, or a tributary from the inferior vena cava (Fig. 928). The azygos vein may enter the thorax through the aortic hiatus of the diaphragm, or it may pass into the thorax separately, through or behind the right crus of the dia¬ phragm. It then ascends along the right side of the vertebral column to the fourth thoracic vertebra, where it arches anteriorly over the root of the right lung, and ends in the supe¬ rior vena cava, just before that vessel pierces the pericardium. When the azygos vein tra¬ verses the aortic hiatus, it lies on the right side of the aorta, with the thoracic duct. In

The right fifth to eleventh posterior inter¬ costal veins drain directly into the azygos vein at their respective segmental levels (Fig. 9-28). The posterior intercostal veins are so named to distinguish them from the anterior intercostal veins, which are tribu¬ taries of the internal thoracic veins. Accom¬ panying the intercostal arteries (one in each intercostal space), the intercostal veins lie along the upper border of the space, in a groove along the lower margin of the rib and in a position superior to the artery. Each vein receives a dorsal tributary from the muscles and cutaneous area of the back, and a spinal tributary that anastomoses with the plexuses of the vertebral column and spinal cord. The posterior intercostal veins also anastomose with the anterior veins of the internal thoracic, and with the lateral tho¬ racic or thoracoepigastric veins.

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

827

Anterior jugular Superior thyroid

M iddle thyroid

External jugular

I nternal thoracic L. Superior Intercostal

I nferior phrenic

Suprarenal Suprarenal

Deep iliac circumflex

W Infr. epigastric

Fig. 9-28. The venae cavae and azygos veins, with their tributaries. This pattern shows an expanded left superior intercostal vein, no accessory hemiazygos vein, and the left seventh posterior intercostal vein (not labeled) draining directly into the azygos vein.

828

THE VEINS

RIGHT SUBCOSTAL VEIN

ESOPHAGEAL. MEDIASTINAL AND PERICARDIAL VEINS

The right subcostal vein corresponds to the twelfth intercostal vein. It commences in the anterior abdominal wall on the right side and courses posteriorly around the trunk along the lower border of the twelfth rib. Dorsally, as it approaches the right lateral side of the body of the first lumbar vertebra, the right subcostal vein usually joins the right ascending lumbar vein to form the azy¬ gos vein. The left subcostal vein usually joins the hemiazygos vein.

Esophageal veins, draining the thoracic portion of the esophagus, open into the azy¬ gos and hemiazygos veins. These veins anas¬ tomose with upper esophageal vessels that drain into the left brachiocephalic vein, and with lower esophageal veins that also com¬ municate with branches from the left gas¬ tric vein. Many small posterior mediastinal veins drain into the azygos and hemiazygos veins. In addition to draining into the inter¬ nal thoracic and inferior phrenic veins, the pericardial veins communicate with the azy¬ gos and hemiazygos veins.

HEMIAZYGOS VEIN

The hemiazygos vein is even more variable in its origin than the azygos vein, but most frequently it begins by the junction of the left subcostal vein and the ascending lumbar vein (Fig. 9-28). Either of these two vessels alone, however, may form the origin of the hemiazygos vein. It then enters the thorax through the left crus of the diaphragm with the left greater splanchnic nerve, but it may go through the aortic hiatus. Ascending on the left side of the vertebral column as high as the ninth thoracic vertebra, the hemiazygos vein passes horizontally across the vertebral column, dorsal to the aorta, esophagus, and thoracic duct, and ends in the azygos vein. It receives the caudal four or five left posterior intercostal veins, the subcostal vein of the left side, and some esophageal and mediasti¬ nal veins. ACCESSORY HEMIAZYGOS VEIN

The accessory hemiazygos vein descends on the left side of the vertebral column. Typ¬ ically, it receives the fourth to the eighth left posterior intercostal veins, and either crosses the body of the eighth thoracic verte¬ bra to join the azygos vein or ends in the hemiazygos vein. It varies inversely in size with the left superior intercostal vein; when it is small, or altogether wanting, the left superior intercostal vein may extend as low as the fifth or sixth intercostal space. clinical note.

During obstruction of the inferior

vena cava, the azygos and hemiazygos veins, as well as the vertebral veins, form important routes by which venous blood can be returned to the heart. These veins connect the superior and inferior venae cavae and communicate below with the common iliac veins via the ascending lumbar veins and with many of the tributaries of the inferior vena cava.

BRONCHIAL VEINS

There are usually two bronchial veins on each side, and these vessels return blood from the structures at the roots of the lungs. The right bronchial veins open into the azy¬ gos vein near its termination, while the left bronchial veins drain into the left superior intercostal or the accessory hemiazygos vein. A large quantity of the blood that is carried to the lungs through the bronchial arteries is returned to the left side of the heart through the pulmonary veins. Brachiocephalic Veins The brachiocephalic veins are two large trunks, right and left, located one on each side of the root of the neck (Fig. 9-28). They are formed by the junction of the internal jugular and subclavian veins of the corre¬ sponding side, and they terminate by uniting to form the superior vena cava. Because the superior vena cava is situated toward the right, the left brachiocephalic vein is longer than the right.

RIGHT BRACHIOCEPHALIC VEIN

The right brachiocephalic vein is a short vessel, about 2.5 cm in length, that begins behind the sternal end of the clavicle (Figs. 9-8; 9-28). It passes almost vertically down¬ ward and joins the left brachiocephalic vein to form the superior vena cava just below the cartilage of the first rib, close to the right border of the sternum. The right brachioce¬ phalic vein lies anterior and to the right of the brachiocephalic artery; on its right side are the phrenic nerve and the pleura, which

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

are interposed between it and the apex of the lung. This vein, at its commencement, receives the right vertebral vein, and more caudally, the right internal thoracic and right inferior thyroid veins, and occasionally the vein from the first intercostal space.

LEFT BRACHIOCEPHALIC VEIN

The left brachiocephalic vein measures about 6 cm in length. From deep to the ster¬ nal end of the left clavicle, it courses ob¬ liquely downward and to the right, behind the upper half of the manubrium sterni (Fig. 9-28). At the sternal end of the first right cos¬ tal cartilage, it unites with the right brachio¬ cephalic vein to form the superior vena cava. It is separated from the manubrium sterni by the sternohyoid and sternothyroid muscles, the thymus or its remains, and some loose areolar tissue. Dorsal to the left brachiocephalic vein are the large brachio¬ cephalic, left common carotid, and left sub¬ clavian arteries which arise from the aortic arch. Also behind the vein are the trachea and the left vagus and phrenic nerves. At times the brachiocephalic vein courses more superiorly and lies in the root of the neck at the level of the jugular notch. TRIBUTARIES

OF

THE

BRACHIOCEPHALIC

Both brachiocephalic veins receive as tributaries the vertebral, the internal tho¬ racic, and the inferior thyroid veins. The left brachiocephalic vein also receives the left superior intercostal veins, and occasionally some thymic and pericardiac veins. The right brachiocephalic vein may receive the vein from the first intercostal space. Because the vertebral vein was described with the deep veins of the neck, the following vessels will be considered now also:

veins.

Internal thoracic vein Inferior thyroid veins Superior intercostal veins

829

phrenic vein, which accompanys the peri¬ cardiacophrenic artery, usually flows into the internal thoracic vein.

Inferior Thyroid Veins

Usually there are at least two, but fre¬ quently three or four, inferior thyroid veins. These arise in the venous plexus of the thy¬ roid gland and communicate with the mid¬ dle and superior thyroid veins (Fig. 9-28). At the level of the jugular notch, they form a plexus anterior to the trachea and deep to the sternothyroid muscles. From this plexus a left inferior thyroid vein descends and joins the left brachiocephalic vein, and a right vein passes obliquely downward and to the right across the brachiocephalic ar¬ tery, and opens into the right brachioce¬ phalic vein, close to its junction with the superior vena cava. Sometimes both inferior thyroid veins open by a common trunk, ei¬ ther into the left brachiocephalic vein or into the superior vena cava. The inferior thy¬ roid veins drain the esophageal, tracheal, and inferior laryngeal veins, and are pro¬ vided with valves at their terminations.

Superior Intercostal Veins

The right and left superior intercostal veins drain blood from the upper two or three intercostal spaces. The right superior intercostal vein passes downward and opens into the azygos vein. The left superior inter¬ costal vein runs across the arch of the aorta and the origins of the left subclavian and left common carotid arteries, and opens into the left brachiocephalic vein (Fig. 9-28). It usu¬ ally receives the left bronchial vein, and sometimes the left pericardiacophrenic vein. It has a prominent anastomosis with the ac¬ cessory hemiazygos vein, and when the lat¬ ter is missing, it drains all the upper left spaces.

Internal Thoracic Veins

On each side the internal thoracic vein is the accompanying vein of the internal tho¬ racic artery, and it receives tributaries corre¬ sponding to the branches of the artery (Fig. 9-28). Uniting to form a single trunk just below the manubriosternal joint, the inter¬ nal thoracic vein ascends on the medial side of its artery and opens into the correspond¬ ing brachiocephalic vein. The pericardiaco¬

Veins of the Vertebral Column

The veins that drain blood from the verte¬ bral column, some adjacent musculature, and the meninges of the spinal cord form intricate plexuses that extend along the en¬ tire length of the column. These plexuses may be divided into two groups, external and internal, according to whether they are located outside or within the vertebral canal.

830

the veins

nt. external vertebral plexus

Vertebral body

Basivertebral vein nt. internal vertebral plexus Intervertebral vein Ant. radicular vei

Post, radicular vein

Transverse process st. internal vertebral plexus Post, external vertebral plexus

Spinous process

Fig. 9-29.

Transverse section through the body of a thoracic vertebra, showing the vertebral venous plexuses. (After

Netter.)

The plexuses of the two groups anastomose freely with each other and terminate in the intervertebral veins. The plexuses and veins of the vertebral system are: External vertebral venous plexuses Internal vertebral venous plexuses Basivertebral veins Intervertebral veins Veins of the spinal cord EXTERNAL VERTEBRAL VENOUS PLEXUSES

The external vertebral venous plexuses are best developed in the cervical region and consist of anterior and posterior plexuses which anastomose freely with each other (Figs. 9-29; 9-30). The anterior external plex¬ uses lie ventral to the bodies of the verte¬ brae, communicate with the basivertebral and intervertebral veins, and receive tribu¬ taries from the bodies of the vertebrae. The posterior external plexuses are placed partly on the dorsal surface of the vertebral arches and their processes, and partly be¬ tween the deep dorsal muscles. In the cervi¬ cal region the external vertebral plexuses

anastomose with the vertebral, occipital, and deep cervical veins. More inferiorly along the vertebral column, the external plexuses anastomose with the posterior in¬ tercostal veins of the thorax and with the lumbar veins of the posterior abdominal wall. INTERNAL VERTEBRAL VENOUS PLEXUSES

The internal vertebral venous plexuses lie within the vertebral canal between the dura mater and the vertebrae, and receive tribu¬ taries from the bones and the spinal cord (Figs. 9-29; 9-30). They form a closer network than the external plexuses, and course mainly in a vertical direction, forming four longitudinal veins, two anterior and two posterior. The anterior internal plexuses consist of two large veins that lie along the posterior surface of the vertebral bodies and intervertebral discs on each side of the pos¬ terior longitudinal ligament. Under cover of this ligament, they are connected by trans¬ verse branches into which the basivertebral veins open. The two posterior internal plex¬ uses are placed on each side of the midline

SUPERIOR VENA CAVA AND ITS TRIBUTARIES

831

Basivertebral vein

Posterior internal vertebral plexus Anterior internal vertebral plexus ntervertebral vein

Anterior external vertebral plexus

Posterior external vertebral plexus

Vertebral body Intervertebral vein

Spinous process

Fig. 9-30.

Median sagittal section of three thoracic vertebrae, showing the vertebral venous plexuses.

ventral to the vertebral arches and ligamenta flava, and they anastomose by veins that pass through these ligaments with the poste¬ rior external plexuses. The anterior and pos¬ terior plexuses communicate freely with each other within the vertebral canal by a series of venous rings, one opposite each vertebra. Around the foramen magnum, the internal plexuses form an intricate network that opens into the vertebral veins and is connected above with the occipital and sig¬ moid sinuses, the basilar plexus, the condy¬ lar emissary vein, and the venous plexus in the hypoglossal canal.

channels in the cancellous tissue of the bod¬ ies of the vertebrae, similar in every respect to those found in the diploe of the cranial bones. They communicate through small openings anteriorly and laterally on the bod¬ ies of the vertebrae with the anterior exter¬ nal vertebral plexuses. They also converge posteriorly in the vertebral canal as single or doubled vessels that join the transverse branches uniting the anterior internal verte¬ bral plexuses. The openings of the basiverte¬ bral veins are valved, and these vessels be¬ come greatly enlarged in advanced age. INTERVERTEBRAL VEINS

BASIVERTEBRAL VEINS

The basivertebral veins emerge from the foramina on the dorsal surface of the verte¬ bral bodies (Figs. 9-29; 9-30). They are thinwalled vessels contained in large, tortuous

The intervertebral veins accompany the spinal nerves through the intervertebral fo¬ ramina (Figs. 9-29; 9-30). They receive blood from the veins of the spinal cord, drain the internal and external vertebral plexuses,

832

The veins

and flow into the vertebral, posterior inter¬ costal, lumbar, and lateral sacral veins; their orifices are provided with valves.

VEINS OF THE SPINAL CORD

The veins of the spinal cord are situated in the pia mater, within which they form a tor¬ tuous venous plexus. They emerge chiefly from the median fissures of the cord and are largest in the lumbar region. In this plexus there are two median longitudinal spinal veins, one in front of the anterior median fis¬ sure and the other behind the posterior me¬ dian sulcus of the cord. Additionally, there are two anterolateral and two posterolateral longitudinal spinal veins that course along the outer surface of the cord, deep to the dorsal and ventral roots. They drain into the intervertebral veins. Near the base of the skull they unite and form two or three small trunks. These communicate with the verte¬ bral veins and then end in the inferior cere¬ bellar veins or in the inferior petrosal si¬ nuses. clinical considerations. Batson (1940) dis¬ covered that the venous plexuses of the vertebral column constitute a system that parallels the caval system, and that if he injected a radiopaque sub¬ stance into the dorsal vein of the penis in a cadaver, the substance found its way readily into the veins of the entire vertebral column, the skull, and the inte¬ rior of the cranium. The material drained from the dorsal vein of the penis into the prostatic plexus and then followed communications with the veins of the sacrum, ilium, lumbar vertebrae, upper femur, and the venae vasorum of the large femoral blood ves¬ sels, without traversing the main caval tributaries. Similarly, material injected into a small breast vein found its way into the veins of the clavicle, the inter¬ costal veins, the head of the humerus, cervical verte¬ brae, and dural sinuses, without following the caval paths. Radiopaque material injected into the dorsal vein of the penis of an anesthetized monkey drained into the caval system when the animal was undis¬ turbed, but if its abdomen was put under pressure, simulating the increased intra-abdominal pressure of coughing or straining, the material drained into the veins of the vertebrae. There are certain instances in which metastases from pelvic organ tumors appear earlier in the pelvic bones, bodies of vertebrae, and central nervous sys¬ tem regions than in the lungs. According to Batson, this occurs during periods of increased abdominopelvic pressure (such as coughing, urination, and defecation), when considerable blood returns through the vertebral plexuses rather than through the inferior caval system.

Inferior Vena Cava and its Tributaries Draining into the inferior vena cava are most of the veins of the abdomen and pelvis and all of the veins of the lower extremities. Certain veins that receive blood from the lower anterior abdominal wall (inferior epi¬ gastric vein, superficial epigastric vein, ex¬ ternal pudendal vein, and superficial cir¬ cumflex iliac vein) drain inferiorly into the femoral or great saphenous vein, and thereby achieve the inferior vena cava. However, the superficial and deep veins, which drain the upper anterior abdominal and thoracic wall (superior epigastric vein, lateral thoracic vein), as well as the ascend¬ ing lumbar veins that drain the posterior abdominal wall, flow into tributaries that drain into the superior vena cava.

INFERIOR VENA CAVA

The inferior vena cava returns blood from structures below the diaphragm to the right atrium of the heart (Fig. 9-31). It is formed by the junction of the two common iliac veins, anterior and slightly to the right of the body of the fifth lumbar vertebra. It ascends in front of the vertebral column, on the right side of the aorta, and when it reaches the liver, it lies in a groove on the dorsal surface of that organ. The inferior vena cava then perforates the diaphragm between the me¬ dian and right portions of its central tendon. Subsequently, it inclines ventrally and me¬ dially for about 2.5 cm, and after piercing the fibrous pericardium, it becomes covered by a reflection of serous pericardium and opens into the right atrium near the level of the ninth thoracic vertebra. Anterior to its atrial orifice is a semilunar valve, the valve of the inferior vena cava, which is rudimen¬ tary in the adult but is large and exercises an important function in the fetus. relations of the inferior vena cava. The ab¬ dominal portion of the inferior vena cava is overlaid anteriorly at its commencement by the right com¬ mon iliac artery. It is crossed by the root of the mes¬ entery and by the right ovarian or testicular artery. It is covered anteriorly by peritoneum in its ascent along the posterior abdominal wall as far as the hori¬ zontal (third) part of the duodenum. Losing its peri¬ toneum, the inferior vena cava courses behind the

INFERIOR VENA CAVA AND ITS TRIBUTARIES

833

Inferior phrenic arteries

Testicular vessels

Fig 9*31.

The inferior vena cava and some of its tributaries.

horizontal part of the duodenum, as well as behind the head of the pancreas, the superior (first) part of the duodenum, the common bile duct, and the por¬ tal vein. Behind the hilum of the liver, it is again briefly covered by peritoneum until it achieves the posterior surface of the liver, which then partly over¬ laps and occasionally completely surrounds it. Pos¬ terior to the inferior vena cava are the bodies of the upper four lumbar vertebrae, the right psoas major muscle, the right crus of the diaphragm, the right inferior phrenic, suprarenal, renal, and lumbar ar¬ teries, right sympathetic trunk and right celiac gan¬ glion, and the medial part of the right suprarenal gland. On the right side, the inferior vena cava is related to the right kidney and ureter (Fig. 9-31), while on the left side it is related to the aorta, right crus of the diaphragm, and the caudate lobe of the liver. The thoracic portion is only about 2.5 cm in length and is situated partly inside and partly outside

the pericardial sac. The extrapericardial part of the inferior vena cava is separated from the right pleura and lung by the phrenic nerve and by a fibrous band, the right phrenicopericardiac ligament. This liga¬ ment, often feebly marked, is attached to the margin of the caval opening in the diaphragm and to the pericardium at the root of the right lung. The intrapericardiac part of the inferior vena cava is short, and is covered by the serous layer of the pericar¬ dium. VARIATIONS IN THE INFERIOR VENA CAVA. Because the inferior vena cava is formed by a rather complex series of developmental changes, it is not surprising that it has many structural anomalies. Cases have been reported in which there is an absence of the hepatic or prerenal part of the inferior vena cava.

This results from the failure of the tributaries of the right subcardinal vein to join the veins of the liver between the fifth and sixth prenatal week. In these instances, the postrenal part of the inferior vena

834

THE VEINS

cava joins the azygos or hemiazygos vein, which is then large. Thus, except for the hepatic veins, which pass directly to the right atrium, the superior vena cava receives all of the blood from the body before transmitting it to the right atrium. More frequently, however, anomalies of the infe¬ rior vena cava involve the postrenal portion. These include double inferior vena cava, which results from persistence of the left subcardinal vein; per¬ sistent left inferior vena cava, with the absence of the right vessel; preureteral inferior vena cava, in which the right ureter passes behind and around the inferior vena cava to reach the bladder; and persist¬ ent renal collar, which is seen in cases of double venae cavae and involves two left renal veins inter¬ connecting the venae cavae, one passing in front of and the other behind the aorta to form a ring (Gray and Skandalakis, 1972). collateral circulation. The inferior vena cava below the renal arteries is sometimes ligated be¬ cause of thrombosis. Channels of anastomosis for collateral circulation under these circumstances in¬ clude the following: (1) the vertebral veins, (2) anas¬ tomoses between the lumbar veins of the inferior vena caval system and the ascending lumbar of the azygos system, (3) anastomoses between the supe¬ rior, middle, and inferior rectal veins, (4) the thoracoepigastric vein, which connects the superfi¬ cial inferior epigastric with the lateral thoracic vein, and (5) several anastomoses between vessels in the portal system of veins with vessels in the superior vena caval system, including left gastric-esophageal anastomosis and anastomosis between hepatic and diaphragmatic vessels along the bare area of the liver.

VEINS OF THE ABDOMEN

The veins of the abdomen flow directly into the inferior vena cava, or achieve the inferior vena cava indirectly by draining into the portal system of veins that courses through the liver and out the hepatic veins to the inferior vena cava. Thus, the abdominal veins will be described under two headings: the parietal and posterior abdominal vis¬ ceral veins, and the portal system of veins.

Parietal and Posterior Abdominal Visceral Veins

The inferior vena cava receives blood from the two common iliac veins and from the following vessels: Lumbar Testicular Ovarian

Renal Suprarenal Inferior phrenic Hepatic

LUMBAR VEINS

The lumbar veins, four on each side, col¬ lect blood by dorsal tributaries from the muscles and integument of the lumbar re¬ gion of the back, and by abdominal tributar¬ ies from the walls of the abdomen, where they communicate with the epigastric veins. Adjacent to the vertebral column, they re¬ ceive veins from the vertebral plexuses, and then pass anteriorly around the sides of the bodies of the vertebrae, posterior to the psoas major muscle, and end in the dorsal part of the inferior vena cava. The left lum¬ bar veins are longer than the right, and pass behind the aorta to reach the inferior vena cava. The lumbar veins are connected by a longitudinal vein, called the ascending lum¬ bar vein (Fig. 9-28), which passes anterior to the transverse processes of the lumbar verte¬ brae. It is most frequently the origin of the azygos vein on the right side and of the hemiazygos vein on the left. These vessels provide anastomoses between the common iliac and iliolumbar veins of the inferior vena caval system, and between the azygos and hemiazygos veins of the superior vena caval system.

TESTICULAR VEINS

The testicular veins emerge from the back of the testis, receive tributaries from the epi¬ didymis, and unite to form a convoluted mass of vessels called the pampiniform plexus, which constitutes the greater part of the spermatic cord (Fig. 9-32). The numerous vessels composing this plexus ascend along the cord, anterior to the ductus deferens. Just below the superficial inguinal ring, the ves¬ sels unite to form three or four veins that pass along the inguinal canal. Entering the abdomen through the deep inguinal ring, the veins coalesce to form two vessels that as¬ cend on the psoas major. Under cover of the peritoneum and lying on either side of the testicular artery, the two veins unite to form a single testicular vein on each side. The right testicular vein opens into the inferior vena cava at an acute angle, while the left testicular vein flows into the left renal vein

INFERIOR VENA CAVA AND ITS TRIBUTARIES

835

Pampiniform plexus

Fig. 9-32.

Testicular veins. (From Testut.)

at a right angle (Figs. 9-28; 9-31). The testicu¬ lar veins are provided with valves. The left testicular vein passes behind the lower por¬ tion of the descending colon, and thus is exposed to pressure from the contents of that part of the bowel. The right testicular vein passes behind the distal part of the ileum and the horizontal or third part of the duodenum on its path to the inferior vena cava. OVARIAN VEINS

The ovarian veins correspond to the testic¬ ular veins in the male. Each forms a plexus in the broad ligament near the ovary and uterine tube, which communicates freely with the uterovaginal plexus of veins. From the ovarian plexus in the broad ligament on each side emerge at least two vessels which unite to form a single vein. These terminate in a manner similar to that of the testicular veins, the right ovarian vein opening into the

inferior vena cava, and the left ovarian vein flowing into the left renal vein. Valves are usually found in these veins, especially near their junctures with the inferior vena cava and left renal vein. Like the uterine veins, the ovarian veins become much enlarged during pregnancy. RENAL VEINS

The renal veins are large and pass anterior to the renal arteries (Figs. 9-28; 9-31). The left renal vein is longer (8.5 cm) than the right (3.5 cm), and it passes in front of the aorta, just below the origin of the superior mesen¬ teric artery. It receives the left testicular (or ovarian) and left inferior phrenic veins, and usually the left suprarenal vein. The left renal vein, due to the more superior position of the left kidney, opens into the inferior vena cava at a slightly higher level than the right renal vein. The short, thick right renal vein courses medially to the inferior vena

836

THE VEINS

cava behind the descending (second) part of the duodenum. At times it sends a communi¬ cating tributary that helps to form the origin of the azygos vein. SUPRARENAL VEINS

Usually a single suprarenal vein emerges from each suprarenal gland, even though multiple arteries supply the glands (Fig. 928). The short right suprarenal vein passes transversely and opens directly into the infe¬ rior vena cava on its posterior aspect, while the longer left suprarenal vein courses inferomedially, behind the body of the pan¬ creas, and opens into the left renal vein from above. INFERIOR PHRENIC VEINS

The inferior phrenic veins follow the course of the inferior phrenic arteries along the inferior surface of the diaphragm. The right vein ends in the inferior vena cava, while the left vein is represented by two branches, one of which opens into the left renal or suprarenal vein, and the other of which passes anterior to the esophageal hia¬ tus in the diaphragm and empties into the inferior vena cava. HEPATIC VEINS

The hepatic veins commence in the sub¬ stance of the liver by the coalescence of many hepatic sinusoids in the center of the hepatic lobules to form the central or intra¬ lobular veins. These latter vessels, as they leave the hepatic lobules, join one another to form the sublobular veins, which are the tributaries to the hepatic veins. The hepatic veins become arranged in two groups and emerge from the posterior surface of the liver to flow into the inferior vena cava. The upper group usually consists of three large veins: left, middle, and right. These converge toward the posterior surface of the liver and open into the inferior vena cava, which courses along its groove on the dorsal part of the liver (Figs. 9-28; 9-31). The veins of the lower group vary in number, are small, and come from the right and caudate lobes. The tributaries that form these hepatic veins run singly, are in direct contact with the hepatic tissue, and do not contain valves.

Portal System of Veins

The portal system (Fig. 9-33) includes all of the veins that drain blood from the ab¬ dominal part of the digestive tube (except the lower part of the rectum) and from the spleen, pancreas, and gallbladder. From these, visceral blood is conveyed to the liver by the portal vein. In the liver this vein rami¬ fies like an artery and ends in capillary-like vessels termed sinusoids, from which the blood is conveyed to the inferior vena cava by the hepatic veins. Thus, the blood in the portal system passes through two sets of minute vessels that allow an exchange of substances: (a) the capillaries of the diges¬ tive tube, spleen, pancreas, and gallbladder, and (b) the sinusoids of the liver. In the adult, the portal vein and its tributaries do not have valves, but in the fetus and for a short time after birth, valves can be demonstrated in the tributaries of the portal vein. As a rule these valves soon atrophy and disappear, but in some subjects their remnants can still be observed. PORTAL VEIN

The portal vein, about 8 cm in length, is formed at the level of the second lumbar vertebra, anterior to the inferior vena cava and behind the neck of the pancreas, by the junction of the superior mesenteric and sple¬ nic veins (Fig. 9-33). It passes behind the su¬ perior or first part of the duodenum and then ascends in the right border of the lesser omentum to the right portion of the porta hepatis. At this point it divides into a right and a left branch, each accompanying the corresponding branches of the hepatic ar¬ tery into the substance of the liver. Within the lesser omentum, the portal vein lies pos¬ terior to the common bile duct and the he¬ patic artery, positioned in a plane between the two structures, with the duct oriented more to the right and the artery to the left. The portal vein is surrounded by the hepatic plexus of nerves, and is accompanied by numerous lymphatic vessels and some lymph nodes. The right branch of the portal vein courses almost transversely to the right at the porta hepatis, and generally receives the cystic vein from the gallbladder before entering the right lobe of the liver. The left branch is longer but of smaller caliber than the right. It ascends more vertically in the

INFERIOR VENA CAVA AND ITS TRIBUTARIES

porta hepatis, gives branches to the caudate and quadrate lobes, and then enters the left lobe of the liver. In its ascent, the left branch of the portal vein is joined anteriorly by a fibrous cord, the ligamentum teres, which represents the remains of the obliterated umbilical vein. The left branch is also united with the left hepatic vein, which then flows into the inferior vena cava by a second fi¬ brous cord, the ligamentum venosum, which is the remnant of the fetal ductus venosus. The fetal umbilical vein is the principal channel by which oxygenated blood is re¬ turned to the fetus from the placenta. Blood is shunted to the inferior vena cava by means of the ductus venosus so that placen¬ tal blood can reach the heart for distribution to the rest of the body. TRIBUTARIES OF THE PORTAL VEIN. The por¬ tal vein forms at the junction of the splenic and superior mesenteric veins, but it also directly receives vessels that drain the lesser curvature of the stomach and the gallblad¬ der. Additionally, communicating veins from the umbilical region of the anterior abdominal wall drain into the portal vein. Its tributaries include the following: Splenic (lienal) Superior mesenteric Left gastric Right gastric Prepyloric Cystic Paraumbilical Splenic Vein

The splenic (or lienal) vein commences as five or six tributaries that return blood from the spleen (Fig. 9-33). These unite to form a single vessel located medial to the hilum of the spleen; initially the vessel lies, with the splenic artery and the tail of the pancreas, between the leaves of the phrenicosplenic (lienorenal) ligament. The splenic vein then passes across the posterior abdominal wall, anterior to the upper third of the left kidney and behind the body of the pancreas, which it grooves and from which it receives many small veins. In its course it lies caudal to the lienal artery, and ends posterior to the neck of the pancreas by uniting at a right angle with the superior mesenteric vein to form the portal vein. The splenic vein is large, but is not tortuous like the artery.

837

TRIBUTARIES OF THE SPLENIC VEIN. The splenic vein receives the short gastric veins, the left gastroepiploic vein, the pancreatic veins, and the inferior mesenteric veins. Short Gastric Veins. The short gastric veins, four or five in number, drain the fun¬ dus and left part of the greater curvature of the stomach (Fig. 9-33). These pass between the two layers of the gastrosplenic ligament and end in the splenic vein or in one of its large tributaries. Left Gastroepiploic Vein. The left gastro¬ epiploic vein receives tributaries from both the ventral and dorsal surfaces of the stom¬ ach and from the greater omentum (Fig. 933). It courses from right to left along the greater curvature of the stomach, with the left gastroepiploic artery, and usually flows into the splenic vein near its junction with the superior mesenteric vein. Pancreatic Veins. The pancreatic veins consist of several small vessels that drain the body and tail of the pancreas and open into the trunk of the splenic vein. Inferior Mesenteric Vein. The inferior mesenteric vein returns blood from the rec¬ tum and from the sigmoid and descending parts of the colon (Fig. 9-33). It begins in the rectum as the superior rectal vein, with its origin in the rectal plexus, and through"' this plexus it communicates with the middle and inferior rectal veins. The superior rectal vein then receives the sigmoid veins and leaves the lesser pelvis, accompanied by the supe¬ rior rectal artery. After ascending across the common iliac vessels, the superior rectal vein receives the large left colic vein, which drains the left colic flexure and descending colon, and then continues its ascent as the inferior mesenteric vein. This vein lies to the left of its artery, and ascends under cover of the peritoneum, ventral to the left psoas major muscle. It then passes behind the body of the pancreas and opens into the splenic vein. Sometimes (10% of cases) the inferior mesenteric vein ends in the angle of union of the splenic and superior mesenteric veins, or it drains into the superior mesen¬ teric vein.

Superior Mesenteric Vein

The superior mesenteric vein returns blood from the small intestine, the cecum, and the ascending and transverse portions of

838

the veins

Spleen Left gastric vein (coronary vein) Cystic vein Hepatic artery Common bile duct Portal vein

Short gastric veins Splenic vein Left gastroepiploic vein Pancreas

Duodenum Superior mesenteric vein

Rt. gastroepiploic vein Ant. sup. pancreatico¬ duodenal vein Inferior mesenteric vein

Right colic vein

Descending colon Left colic vein Jejunum

Ascending colon

Ileum

Fig. 9-33. The portal vein and its tributaries. Note that the pyloric end of the stomach and the transverse colon have been removed to reveal the underlying mesenteric veins.

the colon (Fig. 9-33). It begins in the right iliac fossa by the union of the veins that drain the terminal part of the ileum, the cecum, and the vermiform appendix, and it ascends between the two layers of the mes¬ entery on the right side of the superior mes¬ enteric artery. In its upward course, the su¬ perior mesenteric vein passes in front of the right ureter, the inferior vena cava, the hori¬ zontal part of the duodenum, and the uncinate process of the pancreas. Behind the neck of the pancreas it unites with the sple¬ nic vein to form the portal vein. TRIBUTARIES OF THE SUPERIOR MESENTERIC

In addition to the tributaries that cor¬ respond to the branches of the superior mes¬ enteric artery (the jejunal, ileal, ileocolic, right colic, and middle colic veins), the supe¬ vein.

rior mesenteric vein is joined by the right gastroepiploic and the pancreaticoduodenal veins. Right Gastroepiploic Vein. The right gastroepiploic vein receives tributaries from the greater omentum, parts of both ventral and dorsal surfaces of the stomach, and the anterior superior pancreaticoduodenal vein. It anastomoses with the left gastroepiploic vein and courses from left to right between the anterior two layers of the greater omen¬ tum, along the greater curvature of the stom¬ ach (Fig. 9-33). Pancreaticoduodenal Veins. The superior and inferior pancreaticoduodenal veins cor¬ respond to their accompanying arteries and form venous arcades anterior and posterior to the head of the pancreas. The anterior

INFERIOR VENA CAVA AND ITS TRIBUTARIES

superior pancreaticoduodenal vein drains into the right gastroepiploic vein, while the posterior superior pancreaticoduodenal vein flows directly into the portal vein (Fig. 9-33). The anterior and posterior inferior usually drain singly or as a common trunk into the superior mesenteric vein or its first jejunal branch. Left Gastric Vein

The left gastric vein frequently is called the coronary vein of the stomach, and it courses upward and from right to left along the lesser curvature (Fig. 9-33). It lies be¬ tween the two layers of the lesser omentum and receives venous tributaries from both the anterior and posterior surfaces of the stomach. As the left gastric vein reaches the esophageal end of the stomach, it receives lower esophageal veins and then turns to the right and courses inferiorly, behind the peri¬ toneum of the lesser omental sac (lesser omentum), and terminates in the portal vein. Right Gastric Vein

The right gastric vein, at times called the pyloric vein, is a small vessel coursing be¬ tween the two layers of the lesser omentum, along the lesser curvature of the stomach with the right gastric artery. It anastomoses with the left gastric vein midway along the lesser curvature, and it flows toward the right to empty most often into the portal vein. It may, however, terminate in the supe¬ rior mesenteric vein or even in the right gastroepiploic vein. It is frequently joined by the prepyloric vein, which drains the stomach in the region of the pyloric canal. Cystic Veins

The cystic veins consist of a number of small vessels that vary considerably in their drainage pattern of the gallbladder. As many as six or eight individual vessels flow di¬ rectly along the attached (to the liver) ante¬ rior surface of the organ into the substance of the liver. The vessels draining the ex¬ posed serosal or posterior surface join at the neck of the gallbladder to form either single or double cystic veins (Fig. 9-33). These flow along the cystic duct and upward along the hepatic ducts and drain into the liver. Inferi¬ orly, they anastomose with veins that drain

839

the common bile duct, and only rarely do the cystic veins drain directly into the portal vein or its main branches. Paraumbilical Veins

The paraumbilical veins extend along the ligamentum teres of the liver and the median umbilical ligament. They are small vessels that establish an anastomosis between the veins of the anterior abdominal wall and the portal and internal iliac veins. The best marked of these small veins is one that com¬ mences at the umbilicus and courses dorsally and upward, between the layers of the falciform ligament along the surface or within the ligamentum teres, and ends in the left branch of the portal vein. COLLATERAL CIRCULATION

BETWEEN THE

PORTAL

Clinical conditions, such as cirrhosis of the liver, valvular heart disease, or the physical pressure of tumors, may obstruct or diminish the portal circulation through the liver. In these situations several collateral routes become available for the return of portal venous blood: (a) Tributaries of the left gastric veins of the portal system anastomose with tributaries of the lower esophageal veins that drain through the azygos and hemiazygos veins into the superior vena cava. (b) The superior rectal branches of the inferior mes¬ enteric vein (portal system) anastomose with the middle rectal veins and the inferior rectal branches of the internal pudendal veins, which are tributaries of the internal iliac veins (inferior vena caval sys¬ tem). (c) In the umbilical region, small venous tribu¬ taries of the portal vein course along the ligamentum teres and the falciform ligament. These paraumbilical vessels anastomose with the superior epigastric and internal thoracic veins (superior vena cava) and with the inferior epigastric veins (inferior vena cava). Vari¬ cosities of these paraumbilical veins, radiating from the umbilicus, constitute a clinical condition called caput medusae, (d) Veins along the surface of the bare area of the liver (portal system) anastomose with small tributaries of the inferior phrenic veins that drain the inferior surface of the diaphragm (infe¬ rior vena cava), (e) Tributaries of intestinal veins that course in the roots of the mesenteries (portal system) anastomose with tributaries of retroperitoneal veins that drain the posterior abdominal wall. AND CAVAL venous systems.

VEINS OF THE PELVIS AND PERINEUM

Venous blood from of the pelvic wall and external genitalia in into veins that join on

the organs and much from the muscles and the perineum drains each side to form the

840

THE VEINS

internal iliac vein. This vessel joins its corre¬ sponding external iliac vein to form the common iliac vein. At the junction of the right and left common iliac veins, the infe¬ rior vena cava is formed (Figs. 9-28; 9-34). Common Iliac Veins The common iliac veins, formed by the union of the internal and external iliac veins, commence anterior to the sacroiliac joint. Passing obliquely upward to the right side of the aorta and the body of the fifth lumbar vertebra, the two common iliac veins end by uniting with each other at an acute angle to form the inferior vena cava. The right common iliac vein is shorter than the left, nearly vertical in direction, and ascends dorsal and then lateral to its corresponding artery. The left common iliac vein is longer and more oblique in its course, and is situ¬ ated at first on the medial side of its corre¬ sponding artery and later dorsal to the right common iliac artery. Each common iliac vein receives the iliolumbar vein, and some¬ times the lateral sacral veins. Additionally, the left common iliac vein receives the me¬ dian sacral vein. No valves are found in these veins. VARIATIONS OF THE COMMON ILIAC VEINS. The left common iliac vein, instead of joining the right in its usual position, occasionally ascends on the left side of the aorta as high as the kidney, where, after receiving the left renal vein, it crosses over the aorta and joins the right vein to form the inferior vena cava. In these bodies, the two common iliacs are connected by a small communicating branch at the site where usually they are united. This variation rep¬ resents a persisting left posterior cardinal or supracardinal vein (Fig. 9-1, C and D).

Iliolumbar Vein

The iliolumbar vein, coursing on each side with its corresponding artery, commences superiorly in the lower part of the posterior abdominal wall, where it anastomoses with the lower lumbar veins, and laterally in the iliac fossa just below the iliac crest (Fig. 934). Its lumbar tributary passes downward into the pelvis deep to the psoas major mus¬ cle, while its iliac tributary drains medially over the iliacus muscle. The two tributaries join to form the iliolumbar vein, which then courses inferiorly and medially and empties into the lateral aspect of the common iliac vein.

Median Sacral Vein

The median sacral vein is formed by the junction of smaller vessels on each side that drain medially within the hollow on the an¬ terior aspect of the sacrum. The vein ascends with its accompanying artery nearly in the midline and ends in the left common iliac vein, sometimes in the angle of junction of the two iliac veins.

INTERNAL ILIAC VEIN

The internal iliac vein, formerly called the hypogastric vein, begins near the upper part of the greater sciatic foramen. It passes up¬ ward and backward in the pelvis, slightly medial to the corresponding artery. At the brim of the pelvis and anterior to the sacroil¬ iac joint, the internal iliac vein joins the ex¬ ternal iliac to form the common iliac vein (Fig. 9-34). TRIBUTARIES OF THE

INTERNAL ILIAC VEIN.

With the exception of the iliolumbar vein which usually joins the common iliac vein, the tributaries of the internal iliac vein cor¬ respond to the branches of the internal iliac artery. It receives the following: Superior gluteal Inferior gluteal Internal pudendal Obturator Lateral sacral Middle rectal Dorsal veins of penis and clitoris Vesical Uterine Vaginal Superior Gluteal Veins

The superior gluteal veins are venae comitantes of the superior gluteal artery. They receive tributaries corresponding with the branches of the artery from the gluteal struc¬ tures, and enter the pelvis above the piri¬ formis muscle through the greater sciatic foramen. Frequently the venae comitantes unite as a single vessel on each side before ending in the internal iliac vein. Inferior Gluteal Veins

The inferior gluteal veins are venae comi¬ tantes of the inferior gluteal artery. They begin on the proximal part of the posterior thigh, where they anastomose with the me-

INFERIOR VENA CAVA AND ITS TRIBUTARIES

841

Inferior vena cava Third lumbar vein Abdominal aorta Ascending lumbar vein Right testicular vein

Iliolumbar vein Right common iliac vein Right ureter

Right external iliac vein Inferior epigastric v. Obturator v.

Right internal iliac vein

Ductus deferens

Superior rectal vein Rectum

Bladder

Left ureter Rectal venous plexus Vesical venous plexus Middle rectal vein

Prostatic venous plexus Deep dorsal vein of penis Prostate gland

Levator ani muscle —— Internal pudendal vein

Posterior scrotal veins

— Inferior rectal veins

Penis

—

Fig. 9-34.

The veins in the right half of the male pelvis viewed from the left side. (After Spalteholz.)

dial femoral circumflex and first perforating veins. Entering the pelvis through the lower part of the greater sciatic foramen, below the piriformis muscle, they join to form a single stem that opens on each side into the distal part of the internal iliac vein. Internal Pudendal Veins

The internal pudendal veins are the venae comitantes of the internal pudendal artery. Venous blood draining the corpora caver¬ nosa penis along the deep dorsal veins usu¬ ally flows directly posteriorly and enters the prostatic plexus of veins. From this plexus arise the vessels that become the internal pudendal veins, accompanying the internal pudendal artery from this point and then uniting on each side to form a single vessel, which ends in the internal iliac vein. At times the deep dorsal veins of the penis tend

to drain laterally, following more closely the deep arterial supply to the penis. In these instances tributaries of the deep dorsal veins themselves form the origin of the internal pudendal veins. The internal pudendal veins receive tributaries from the crura and bulb of the penis, as well as from the scrotal (or labial) and inferior rectal veins. Frequently the portion of the internal pudendal vein that extends from the penis to the opening of the pudendal canal in the ischiorectal fossa is called the perineal vein. Obturator Vein

The obturator vein begins in the adductor region of the thigh and enters the pelvis through the upper part of the obturator fora¬ men (Fig. 9-34). It courses dorsally and supe¬ riorly on the lateral wall of the pelvis below the obturator artery, then passes between

842

the veins

the ureter and the internal iliac artery, and ends in the internal iliac vein.

Lateral Sacral Veins

The lateral sacral veins accompany the lateral sacral arteries on the anterior surface of the sacrum and open into the internal iliac vein. As the lateral sacral veins ascend along the posterolateral pelvic wall, they are joined by vessels that emerge through the pelvic (anterior) sacral foramina. The veins of the two sides anastomose and join in the formation of the sacral venous plexus.

Middle Rectal Vein

The middle rectal vein originates in the rectal plexus and receives tributaries from the bladder, prostate, and seminal vesicle (Fig. 9-34). It courses laterally on the pelvic surface of the levator ani muscle and ends in the internal iliac vein. rectal venous plexus. The rectal venous plexus surrounds the rectum and communi¬ cates anteriorly with the vesical plexus in the male or the uterovaginal plexus in the female (Fig. 9-34). It consists of two parts, an internal rectal plexus in the submucosa, and an external rectal plexus outside the muscu¬ lar coat. The internal plexus presents a se¬ ries of dilated pouches that are connected by transverse vessels and are arranged in a cir¬ cle around the tubular rectum, immediately above the anal orifice. The lower part of the external plexus is drained by the inferior rectal veins into the internal pudendal vein; the middle part drains into the middle rectal vein which joins the internal iliac vein; and the upper part is drained by the superior rectal vein which forms the commencement of the inferior mesenteric vein, a tributary of the portal vein. A free communication be¬ tween the portal and systemic venous sys¬ tems is established through the rectal plexus.

Dorsal Veins of the Penis and Clitoris

On the dorsum of the penis are located both superficial and deep veins (Fig. 9-35). The superficial dorsal vein drains the pre¬ puce and skin of the penis. It courses proximally in the subcutaneous tissue, inclines to the right or left, and opens into the corre¬ sponding superficial external pudendal vein, a tributary of the great saphenous vein. The deep dorsal vein lies beneath the deep fascia of the penis, but superficial to the tunica al¬ buginea of the corpora cavernosa. It receives blood from the glans penis and from the corpora cavernosa by way of the deep veins of the penis. It courses proximally in the midline between the two dorsal arteries. Near the root of the penis it enters the pelvis by passing between the two parts of the sus¬ pensory ligament and then through an aperture just below the arcuate pubic liga¬ ment of the symphysis pubis. The deep dor¬ sal vein then divides into two branches that enter the prostatic plexus, one on each side. The deep dorsal vein also anastomoses with the internal pudendal vein, distal to the sym¬ physis pubis. The dorsal vein of the clitoris drains the erectile tissue of that organ and courses backward into the pelvis in a manner similar to that in the male. It terminates in the ve¬ nous plexus around the bladder, the vesical venous plexus. In contrast, the venous blood from the vestibular bulb and the other struc¬ tures in the urogenital region of the female, along with the tissue within the ischiorectal fossa and surrounding the anus, drains back¬ ward and laterally into the internal puden¬ dal veins. Thus, venous blood from most of the female perineum enters the pelvis along routes comparable to those in the male (Fig. 9-36). Superficial and deep dorsal veins

Lfui^di

ai

ici y

and nerve Integument Dartos tunic

The veins that form the internal rectal plexus are contained in very loose connective tissue; thus they get less support from surrounding structures than do most other veins, and are less capable of resisting increased blood pressure. Frequently they become dilated and varicosed, forming internal hemorrhoids or piles. Varicosities of the external rectal veins also cause painful external hemorrhoids. Enlargement of these veins can occur when the portal vein is obstructed or in childbearing women. clinical correlation.

„ Deep penile fascia (Buck) ■ Corpus cavernosum penis Central artery Septum penis Tunica albuginia Urethra Corpus spongiosum penis

The penis in transverse section, showing the blood vessels.

Fig. 9-35.

INFERIOR VENA CAVA AND ITS TRIBUTARIES

843

Dorsal vein of clitoris

Labial veins

Internal pudendal vein (perineal vein)

Ischiocavernosus muscle

Vestibular bulb

Bulbospongiosus muscle

Veins of the vestibular bulb

Superficial transverse perineal muscle

Deep transverse perineal muscle ■ Levator ani muscle

Internal pudendal vein Inferior rectal veinsExternal anal plexus _ of veins

Fig. 9-36.

Gluteus maximus muscle

The veins of the anal and urogenital regions of the female perineum.

The prostatic venous plexus lies behind the arcuate pubic ligament and the symphysis pubis, and in front of the bladder and prostate. Its chief tributary is the deep dorsal vein of the penis, but it also receives tributaries from the blad¬ der and prostate. It anastomoses with the vesical plexus, the internal pudendal vein, and the vertebral veins, and drains into the vesical and internal iliac veins. The prostatic plexus lies partly in the fascial sheath of the prostate and partly between the sheath and the prostatic capsule.

A complex network of uterine veins courses along the sides of the uterus be¬ tween the two layers of the broad ligament (Fig. 9-37). The veins form the uterine ve¬ nous plexuses and anastomose with the ovarian and vaginal plexuses. From the infe¬ rior part of the uterine plexuses, at the level of the external orifice of the cervix, arises a pair of uterine veins on each side. These course laterally and posteriorly and open into the corresponding internal iliac vein.

Vesical Veins

Vaginal Veins

The vesical veins envelop the caudal part of the bladder and the base of the prostate. They form the vesical venous plexus and anastomose with the prostatic plexus in the male or with the uterine and vaginal plex¬ uses in the female. The vesical venous plexus drains by means of several vesical veins that frequently unite into one or two vessels on each side before entering the in¬ ternal iliac vein.

The venous drainage of the vagina occurs by means of vaginal plexuses along the sides of the vagina (Fig. 9-37). These are in conti¬ nuity with the uterine plexuses and they also communicate with the vesical and rectal plexuses. The vaginal plexuses are drained by at least one, and at times two vaginal veins on each side that flow into the internal iliac veins either directly or through connec¬ tions with the internal pudendal veins.

prostatic venous plexus.

Uterine Veins

844

THE VEINS

Fig. 9-37. The blood vessels of the female pelvis, showing the chief source of blood supply to the uterus and vagina. (From Eycleshymer and Jones.)

EXTERNAL ILIAC VEIN

The external iliac vein is the upward con¬ tinuation of the femoral vein and therefore receives blood from the lower limb (Figs. 9-28; 9-34). It also drains the lower part of the anterior abdominal wall. The femoral vein becomes the external iliac vein at the level

of the inguinal ligament. Passing superiorly along the brim of the lesser pelvis, the exter¬ nal iliac vein ends opposite the sacroiliac joint by uniting with the internal iliac vein to form the common iliac vein. On the right side, it lies at first medial to the external iliac artery, but as it passes upward it gradually inclines behind the artery. On the left side, it

INFERIOR VENA CAVA AND ITS TRIBUTARIES

lies altogether on the medial side of the ar¬ tery. It frequently contains one, sometimes two, valves.

845

also found in the veins of the lower limb than in veins of the upper limb.

TRIBUTARIES OF THE EXTERNAL ILIAC VEIN.

As it ascends, the external iliac vein receives the following veins: Inferior epigastric Deep circumflex iliac Pubic Inferior Epigastric Vein

The inferior epigastric vein is formed by the union of the venae comitantes of the in¬ ferior epigastric artery. At their source supe¬ riorly, the venae comitantes anastomose with the superior epigastric vein. The infe¬ rior epigastric vein joins the external iliac vein about 1.25 cm above the inguinal liga¬ ment. Deep Circumflex Iliac Vein

The deep circumflex iliac vein is formed by the union of the venae comitantes of the deep circumflex iliac artery, and joins the external iliac vein about 2 cm above the in¬ guinal ligament.

Superficial Veins of the Lower Limb

The superficial veins of the lower limb are the great and small saphenous veins, their tributaries, and the superficial veins of the foot. GREAT SAPHENOUS VEIN

The great saphenous vein is the longest vein in the body, beginning in the superficial vein that courses along the dorsomedial margin of the foot. It terminates in the femo¬ ral vein about 3 cm below the inguinal liga¬ ment (Fig. 9-38). It ascends anterior to the tibial malleolus and along the medial side of the leg together with the saphenous nerve. Passing upward behind the medial condyles of the tibia and femur, it then ascends along the medial side of the anterior thigh to a point about 3 cm below the inguinal liga¬ ment, where it dips through the saphenous hiatus (fossa ovalis), penetrates the lower end of the femoral sheath, and opens into the femoral vein. The great saphenous vein contains between 10 and 20 valves. These are more numerous in the leg than in the thigh. Fre¬ quently this vein and its branches become dilated and then varicosed. This results when valves that normally prevent the flow of venous blood from the long deep veins to those more superficial in the lower limb become incompetent. Dangerous thrombi may develop, especially from the portion of the great saphenous vein which extends from the midregion of the calf to the upper third of the thigh clinical correlation.

Pubic Vein

The pubic vein interconnects the obtura¬ tor vein in the obturator foramen and the external iliac vein. It ascends on the inner aspect of the pubis and -accompanies the pubic branch of the obturator artery. In about 33% of cases, it is enlarged, function¬ ally taking the place of the obturator vein. In these instances it becomes a dangerous ves¬ sel when operations are made in the region of the femoral ring.

VEINS OF THE LOWER LIMB

The veins of the lower limb are subdi¬ vided into superficial and deep sets in a manner similar to those of the upper limb. The superficial veins course in the superfi¬ cial fascia just beneath the skin, while the deep veins accompany the arteries. Both sets of veins are provided with valves, which are more numerous in the deep veins than in the superficial. A greater number of valves is

TRIBUTARIES OF THE GREAT SAPHENOUS VEIN.

At the ankle, the great saphenous vein re¬ ceives tributaries from the sole of the foot by way of the medial marginal vein. In the leg, it anastomoses freely with the small saphe¬ nous vein, communicates with the anterior and posterior tibial veins from deeper in the leg, and receives many cutaneous veins. In the thigh, it anastomoses with the femoral vein and receives numerous tributaries. Those from the medial and posterior parts of the thigh frequently unite to form a large ac¬ cessory saphenous vein that joins the main vein at a variable level. Near the saphenous hiatus it is joined by the superficial external

846

THE VEINS

Accessory saphenous Superficial external pudendal Superficial circumflex iliac Superficial epigastric Thoracoepigastric

Accessory Saphenous Vein

The accessory saphenous vein is the name frequently given to the superficial vein that arises along the posteromedial border of the thigh. It ascends around the medial aspect of the thigh, receiving tributaries primarily from the posterior surface, and joins the sa¬ phenous vein on its medial aspect. At times this vessel is called the medial accessory saphenous vein, to differentiate it from the lateral accessory saphenous vein, which arises anteriorly just above the knee (Fig. 938). Receiving tributaries from the lateral and anterior surfaces of the thigh, the lateral accessory saphenous vein ascends on the front of the thigh and opens into the saphe¬ nous vein on its lateral aspect (Daseler et al„ 1946). Superficial External Pudendal Vein

The superficial external pudendal vein forms from tributaries that laterally drain the superficial fascia from the upper medial thigh, the lower medial inguinal region, and the scrotum (or labia majora) (Fig. 9-38). It usually (90% of cases) opens into the great saphenous vein, but at times (10%) flows into the medial accessory saphenous vein. Superficial Circumflex Iliac Vein

The superficial circumflex iliac vein forms from tributaries that drain the superficial fascia over the uppermost lateral surface of the anterior thigh, extending even from the anterior abdominal wall above the lateral part of the inguinal ligament (Fig. 9-38). The vein descends medially in an oblique course and opens directly into the great saphenous vein (60% of cases) or into the lateral acces¬ sory saphenous vein (40%). pudendal, superficial circumflex iliac, and superficial epigastric veins (Fig. 9-38). Addi¬ tionally, through the superficial epigastric vein it forms an anastomosis with veins of the upper limb by means of the thoraco¬ epigastric vein. Of these tributaries the fol¬ lowing will be described further:

Superficial Epigastric Vein

The superficial epigastric vein arises from tributaries that drain the superficial fascia over a rather wide region of the lower ante¬ rior abdominal wall (Fig. 9-38). These tribu-

INFERIOR VENA CAVA AND ITS TRIBUTARIES

taries descend directly from the pubic region or obliquely from the more lateral inguinal region, and become a single vessel that opens into the lateral (80% of cases) or me¬ dial (20%) aspect of the great saphenous vein or into the corresponding accessory saphe¬ nous vein. The superficial epigastric vein anastomoses by way of the thoracoepigastric vein with vessels draining superiorly over the thoracic wall. thoracoepigastric vein. The thoracoepigastric vein is a longitudinally oriented vessel whose tributaries form an anastomo¬

sis over the anterior abdominal and thoracic walls (Fig. 9-39). It connects venous channels that drain into the axillary vein, usually by means of the lateral thoracic vein, with oth¬ ers that drain into the superficial epigastric and superficial circumflex iliac veins, which flow into the great saphenous-femoral ve¬ nous complex. Normally the vein is a rela¬ tively small vessel that simply contributes to the drainage of the superficial fascia. How¬ ever, the thoracoepigastric vein provides an important collateral channel in clinical con¬ ditions that obstruct either the inferior vena

V

Axillary Lateral thoracic vein

Thoracoepigastric vein Thoracoepigastric vein

Paraumbilical veins

Superficial epigastric vein Superficial circumflex iliac vein Great saphenous vein

Fig. 9-39.

847

The thoracoepigastric vein and other superficial veins of the anterior thoracic wall.

848

THE VEINS

cava or the portal vein. Under these circum¬ stances this vein can become greatly en¬ larged and tortuous. SMALL SAPHENOUS VEIN

The small saphenous vein begins behind the lateral malleolus as a continuation of the marginal vein that courses along the dorso¬ lateral aspect of the foot. At first it ascends along the lateral border of the calcaneal ten¬ don and then crosses this tendon to reach the middle of the back of the leg. Running di¬ rectly upward, it perforates the deep fascia in the distal part of the popliteal fossa, and ends in the popliteal vein between the two heads of the gastrocnemius muscle (Fig. 940). It anastomoses with the deep veins on the dorsum of the foot, and receives numer¬ ous large tributaries from the superficial fas¬ cia on the back of the leg. Before the small

saphenous vein pierces the deep fascia, it joins a vessel that courses superiorly and anteriorly to anastomose with the great sa¬ phenous vein. In its ascent, the small saphe¬ nous vein possesses from 9 to 12 valves, one of which is always found near its termina¬ tion in the popliteal vein. In the distal third of the leg the small saphenous vein is accom¬ panied by the sural nerve, and in the proxi¬ mal two-thirds by the medial sural cutane¬ ous nerve. SUPERFICIAL VEINS OF THE FOOT

On the dorsum of the foot, the dorsal digi¬ tal veins communicate with the plantar digi¬ tal veins in the clefts between the toes. The adjacent dorsal digital veins join to form the dorsal metatarsal veins. These latter vessels unite across the distal ends of the metatarsal bones in a dorsal venous arch (Fig. 9-38). Proximal to this arch is an irregular venous network that receives tributaries from the deep veins. This network is joined at the sides of the foot by medial and lateral mar¬ ginal veins, which are formed mainly by the union of branches from the superficial parts of the sole of the foot. On the sole of the foot, the superficial veins form a plantar cutaneous venous arch that extends across the roots of the toes and opens at the sides of the foot into the medial and lateral marginal veins. Proximal to this arch is a plantar cutaneous venous network that is especially dense in the fat beneath the heel. This network communicates with the cutaneous venous arch and with the deep veins, but drains chiefly into the medial and lateral marginal veins. Deep Veins of the Lower Limb

The deep veins and their tributaries in the lower limb accompany the arteries and their branches, and they possess numerous valves. Sequentially they include: Deep veins of the foot Deep veins of the leg Popliteal vein Deep veins of the thigh DEEP VEINS OF THE FOOT

Fig. 9-40.

The small saphenous vein.

The plantar digital veins arise from plex¬ uses on the plantar surfaces of the digits, and after sending communicating vessels to join

INFERIOR VENA CAVA AND ITS TRIBUTARIES

849

the dorsal digital veins, they unite to form four plantar metatarsal veins. These course proximally in the metatarsal spaces and anastomose by means of perforating veins with the veins on the dorsum of the foot. The plantar metatarsal veins unite to form the deep plantar venous arch, which accompa¬ nies the plantar arterial arch across the plan¬ tar aspect of the foot between the oblique part of the adductor hallucis muscle and the interossei muscles. From the deep plantar venous arch, the medial and lateral plantar veins run proximally near their correspond¬ ing arteries. They communicate by anasto¬ mosing vessels with the great and small sa¬ phenous veins on the two sides of the foot. The medial and lateral plantar veins then unite to form the posterior tibial veins be¬ hind the medial malleolus.

DEEP VEINS OF THE LEG

The deep veins of the leg ascend with their accompanying arteries in both the anterior and posterior compartments. The principal deep veins include: Posterior tibial Peroneal Anterior tibial

Fig. 9-41. The popliteal vein and the junction of the peroneal and posterior tibial veins.

Anterior Tibial Veins Posterior Tibial Veins

The posterior tibial veins accompany the posterior tibial artery. Paired as venae comitantes in the lower leg, the vessels at times join to form a single vein, which with its ar¬ tery ascends in the fascial plane between the superficial and deep muscles of the posterior compartment. The posterior tibial veins drain blood from these posterior compart¬ ment muscles and also receive communicat¬ ing vessels from the more superficial veins. Two-thirds of the way up the leg, the poste¬ rior tibial veins receive the peroneal veins (Fig. 9-41). peroneal veins. The peroneal veins as¬ cend obliquely in the same plane as the pos¬ terior tibial veins from the lateral aspect of the leg. They accompany the peroneal artery and open into the posterior tibial veins distal to the popliteal fossa, just below the lower border of the popliteus muscle (Fig. 9-41). The peroneal veins drain the lateral com¬ partment muscles and also muscles of the posterior compartment.

The anterior tibial veins accompany the anterior tibial artery and deep peroneal nerve, and they are the upward continuation of the venae comitantes of the dorsalis pedis artery. Ascending above the ankle joint in the lower leg between the tibialis anterior and extensor hallucis longus muscles, the anterior tibial veins course deeply on the interosseous membrane. In the upper leg the neurovascular bundle lies between the tibialis anterior and the extensor digitorum longus. The veins leave the anterior leg by passing between the tibia and fibula through the upper part of the interosseous mem¬ brane. They unite with the posterior tibial veins just below the popliteal fossa in the posterior compartment to form the popliteal vein. POPLITEAL VEIN

The popliteal vein is formed by the junc¬ tion of the anterior and posterior tibial veins at the distal border of the popliteus muscle.

850

THE VEINS

It ascends through the popliteal fossa to the aperture in the adductor magnus muscle, called the adductor hiatus, where it becomes the femoral vein in the adductor canal. In the lower part of its course within the poplit¬ eal fossa, it is placed medial to the popliteal artery (Fig. 9-41); between the heads of the gastrocnemius muscle, it lies superficial to that vessel; above the knee joint, it remains superficial to the popliteal artery but courses along its lateral side. The popliteal vein re¬ ceives tributaries corresponding to the branches of the popliteal artery, as well as the small saphenous vein, and in its course it usually contains four valves. DEEP VEINS OF THE THIGH

The deep veins of the thigh accompany the deep arteries. The principal deep vein is the femoral vein, and into this flow the deep femoral vein, the saphenous vein, and the medial and lateral femoral circumflex veins. Additionally, the perforating veins which drain the posterior structures of the thigh are large tributaries of the deep femoral vein. Femoral Vein

The femoral vein, accompanying the fem¬ oral artery, ascends from the superior end of the popliteal fossa through the adductor canal, lateral to and somewhat behind the artery. Proximal to the adductor canal in the lower part of the femoral triangle, the femo¬ ral vein lies behind the artery and as it as¬ cends, it gradually crosses to the medial side of the artery. At the level of the inguinal liga¬ ment it occupies the medial compartment of the femoral sheath, and the femoral vein becomes the external iliac vein above the ligament. The femoral vein receives numer¬ ous muscular tributaries, and about 4 cm or more below the inguinal ligament, it is joined on its posterior aspect by the deep femoral vein and somewhat higher on its anterior aspect by the saphenous vein. Also the medial and lateral femoral circumflex veins may open either into the femoral vein or into the deep femoral vein. There are usu¬ ally three or four valves in the femoral vein; one is generally found (in 90% of cases) just below the entrance of the deep femoral vein (Basmajian, 1952). deep femoral vein. The deep femoral vein is formed by the junction of three or

four perforating veins that correspond to the perforating branches of the deep femoral artery. Through the perforating veins, anas¬ tomoses are established by the femoral vein with the inferior gluteal vein above and with the popliteal vein below. The perforating veins return blood from muscles in all three compartments of the thigh, as well as from the femur. MEDIAL AND LATERAL FEMORAL CIRCUMFLEX

The medial and lateral femoral cir¬ cumflex veins do not terminate in a pattern consistent with the origin of the correspond¬ ing arteries. In 86% of cases studied, the two femoral circumflex veins terminate in the femoral vein, whereas in 2% both veins term¬ inate in the deep femoral vein. In the re¬ maining 12% either the medial or the lateral femoral circumflex vein joins the femoral vein, while the other joins the deep femoral vein (Baird and Cope, 1933).

veins.

Histology of the Blood Vessels ARTERIES

The arterial system consists of an elabo¬ rate system of tubular structures that con¬ ducts blood away from the heart. All arteries are composed of three coats: an inner coat called the tunica intima, an intermediate coat, the tunica media, and an external coat, the tunica adventitia (Fig. 9-42). The compo¬ sition and relative thickness of these coats differ in arteries of different size; however, in all of these the functional cell type of the tunica intima is the endothelial cell, that of the tunica media is the smooth muscle cell, while the principal cell type of the tunica adventitia is connective tissue. tunica intima. The tunica intima, or in¬ nermost coat, consists of a thin lining of en¬ dothelial cells that is longitudinally oriented and continuous with the endothelium of capillaries on the one hand and with the endocardium of the heart on the other. The endothelium is a single layer of simple squa¬ mous or plate-like cells, polygonal, oval, or fusiform in shape, with rounded oval or flat¬ tened nuclei. Although the outlines of the cells can be brought out by treatment with silver nitrate, studies in recent years utiliz¬ ing the electron microscope have shown that

HISTOLOGY OF THE BLOOD VESSELS

endothelial cells are closely apposed, being separated by only about 200 A, and contain little or no intercellular cement at their junc¬ tions. The endothelial cells rest on a basal lamina, and in arteries larger than arteriolar capillaries, delicate strands of connective tissue form a subendothelial layer that in¬ tervenes between the endothelium and the internal elastic membrane. The latter is eas¬ ily identified in muscular arteries. It consists of a network of elastic fibers arranged more or less longitudinally, leaving elongated ap¬ ertures or perforations that give it a fenes¬ trated appearance. Fine cytoplasmic proc¬ esses on the basal surface of the endothelial cells project through the fenestrations of the internal elastic membrane to achieve contact with the overlying smooth muscle cells of the tunica media. The internal elastic mem¬ brane forms the chief thickness of the tunica intima, and it is thrown into folds when ar¬ teries are fixed histologically. In microscopic

851

cross sections the internal elastic membrane appears as a wavy line, glassy and almost unstained when using routine histological techniques such as hematoxylin and eosin; however, it stains heavily with special sub¬ stances such as orcein, which characteristi¬ cally reacts with elastic tissue. tunica media. The tunica media, or mid¬ dle coat, is principally composed of thin, cylindrical smooth muscle cells and elastic tissue, and it accounts for the bulk of the wall of most arteries. The smooth muscle cells are disposed in circular layers around the vessel, and the thickness of the tunica media, as well as its composition, varies with the size of the vessel. The smooth mus¬ cle cells are held together by an abundant amount of intercellular glycoprotein, which contains collagen fibrils and reticular and elastic fibers. The intercellular material is probably formed by the smooth muscle cells themselves, because virtually no other cells

Tunica adventitia

Tunica media

Endothelium of tunica intima

Tunica adventitia

Ext. elastic membrane

Tunica media

Int. elastic membrane Endothelium of tunica intima

Fig. 9-42. right.

Cross section of parts of the walls of adjacent medium-sized artery and vein. Artery, lower left; vein, upper

852

THE VEINS

are found in the tunica media. The external margin of the tunica media frequently is marked by a prominent layer of elastic tissue called the external elastic membrane. tunica adventitia. The tunica adventitia, or outer coat, consists of areolar connective tissue that contains fibroblasts within a fine meshwork of elastic fibers and bundles of collagen. As described previously, the elas¬ tic tissue is more abundant adjacent to the tunica media, where it is called the external elastic membrane. The tunica adventitia var¬ ies in thickness in different types of arteries, but usually it is not as thick as the tunica media. The tunica adventitia contains the vasa vasorum, which are the arteries and veins that supply the vessel walls. It also contains fine lymphatic vessels, as well as the nerve fibers that supply the arteries. The latter appear to terminate near or within the exter¬ nal elastic membrane. As arteries extend distally, there is a grad¬ ual transition in their size. Certain features characterize arteries of different sizes. Large Elastic Arteries

Large elastic arteries such as the aorta and its major branches, as well as the pulmonary trunk and its two principal branches, con¬

duct blood from the heart to the smaller dis¬ tributing arteries (Fig. 9-43). They have a thick tunica intima, and although the endo¬ thelium is still only a single layer in thick¬ ness, the subendothelial layer contains con¬ siderable connective tissue that is composed of bundles of collagen and some smooth muscle cells along with occasional macro¬ phages. Surrounding the subendothelial connective tissue is a fenestrated elastic tis¬ sue layer, which in smaller vessels is consid¬ ered to be the internal elastic membrane. In large arteries, however, it is difficult to deter¬ mine the external boundary between the tunica intima and the internal border of the tunica media, because the tunica media con¬ tains many concentric layers of fenestrated elastic tissue (Fig. 9-43). There may be 50 or more elastic laminae in the tunica media, and interspersed between these elastic fibers are smooth muscle cells, collagenous fibers, and extracellular ground substance (Fig. 9-44). The tunica adventitia of large arteries is thin relative to the tunica media and the line of transition may not be easily apparent. Characteristically, the connective tissue of the external coat is more fibrous in nature and contains more collagen and less elastic tissue. The tunica adventitia of large ves¬ sels also contains numerous small vessels

Tunica intima Internal elastic membrane

Tunica media

Tunica adventitia

Blood vessels

Fig 9-43. Photomicrograph of a section of the wall of the aorta, stained for elastic fibers. Note the relative widths of the three layers. 24 x.

HISTOLOGY OF THE BLOOD VESSELS

853

Fig. 9-44. Photomicrograph of the tunica media of the human aorta showing many lamellae of elastic fibers, which characterize the microscopic anatomy of that coat in the walls of large elastic arteries. 144 X-

and nerves, the vasa vasorum and nervi vasorum, and its external layers gradu¬ ally merge with the surrounding connective tissue. Medium-Sized Muscular Arteries The medium-sized arteries include most of the named arteries that distribute blood to the different organs and parts of the body. The tunica intima is formed by a single layer of endothelium resting on a basal lamina. Deep to this is a thin subendothelial layer that lies adjacent to a well-defined fenes¬ trated internal elastic lamina. The muscular coat, or tunica media, is especially well de¬ veloped and the physiology of the smooth muscle cells is under the influence of neurohumors liberated by the vasomotor nerves. This mechanism controls the flow of blood by altering the diameter of the lumen of these arteries. In the somewhat smaller ar¬ teries the tunica media is almost entirely muscular, but in larger ones more and more elastic tissue is interposed with the smooth muscle cells (Fig. 9-45). The thickness of the tunica adventitia is variable. In arteries lo¬ cated in well-protected sites such as those in the abdominal or cranial cavities, it is rela¬ tively thin, but it is much thicker in exposed regions such as the limbs. The bundles of

nerve fibers are numerous in the tunica ad¬ ventitia of many muscular arteries, and on some arteries supplying the abdominal or¬ gans they are so profuse that they form ex¬ tensive plexuses that coat the vessels almost completely. Small Arteries and Arterioles As the named muscular arteries are dis¬ tributed peripherally, they branch into smaller muscular arteries; these divide into muscular arterioles, which then branch into terminal arterioles less than 50 fim in diame¬ ter (Figs. 9-46; 9-47). The tunica intima of ar¬ terioles consists of a layer of flattened, elon¬ gated endothelial cells resting on a basal lamina. In cross sections of larger arterioles, a corrugated internal elastic membrane sur¬ rounds the endothelium; however in arteri¬ oles of small diameter, less elastic tissue is seen and this membrane is incomplete. In the smallest terminal arterioles, the elastic tissue disappears completely (Fig. 9-47). The tunica media of arterioles consists of smooth muscle cells, and its thickness varies directly with the diameter of the vessels. In the larger arterioles, perhaps three or more layers of smooth muscle cells surround the endothelium in a circumferential pattern, whereas in the terminal arterioles the tunica

854

THE VEINS

Fig. 9-45. Photomicrographs of intercostal artery (A, C) and vein (B, D). A and B are stained with hematoxylin and eosin, while C and D are stained for elastic fibers. Arrows mark the boundary between the tunica media (above) and ■ tunica adventitia (below) in each photomicrograph. 130 x. (From Windle, W. F„ Textbook of Histology, 4th ed., McGraw-Hill, New York, 1969.)

media consists of only a single layer of smooth muscle. The tunica adventitia of larger arterioles consists of loose connective tissue with some collagenous and elastic fi¬ bers and fibroblasts, but this outer coat be¬ comes less well defined and greatly reduced in the smallest arterioles (Fig. 9-47).

Capillaries

From the smallest arteriolar vessels, fine networks of endothelium-lined tubes perme¬ ate most tissues and organs (Fig. 9-48). These minute tubes are the capillaries and their networks form the functional and morpho-

HISTOLOGY OF THE BLOOD VESSELS

Fig. 9-46. Small artery and vein, pia mater of sheep. 250 X- Surface view above the interrupted line; longitu¬ dinal section below. Artery in red; vein in blue.

logic connections between the arterial and venous systems. Frequently and closely as¬ sociated with the outer surface of endothe¬ lial cells are macrophages or mesenchymal perivascular cells called pericytes. Although there is some variation in their size, the aver¬ age diameter of capillaries is about 8jum, roughly equivalent to that of a red blood cor¬ puscle (Fig. 9-48). Functionally, capillaries carry nutrient substances to tissues and or¬ gans and take away the metabolic products of cells. These processes require the transfer of substances across the capillary wall, uti¬ lizing the permeable nature of the endothe¬ lial lining. The anatomical basis of capillary permeability and the sites through which substances pass across the endothelial lining has been a subject of intensive study both physiologically and with the electron micro¬ scope. On morphological grounds, two types of capillaries have been described, the con¬ tinuous and the fenestrated. continuous capillaries. Continuous capillaries are usually seen in muscle, skin, and connective tissue and in the brain and spinal cord. Along both the luminal and outer surfaces of the endothelial cells in this type of capillary are found numerous pinocytotic vesicular invaginations, called caveolae, which measure between 500 and 700 A (Fig. 9-49). It is theorized that these vesicles may be sites for the entrapment of large molecules, and that the vesicles then pinch off and traverse the endothelial cell

855

cytoplasm to the opposite surface, where they fuse with the membrane again and their contents are discharged outside the endothe¬ lial cell. Continuous capillaries have walls of endothelial cells whose basal laminae are continuous and whose intercellular junc¬ tions are of the occludens type. These junc¬ tional complexes have intercellular spaces that measure only about 150 to 200 A; these narrow spaces are believed to be wide enough to allow water and simple solutions to pass through them, but not larger mole¬ cules such as proteins (Fig. 9-50). fenestrated capillaries. Fenestrated capillaries are found in the glomeruli of the kidney, the intestinal villi, the endocrine glands, and other tissues and organs where rapid transfer of fluids occurs. In addition to containing the pinocytic vesicular caveolae, the endothelial cells that form these capillar¬ ies have cytoplasmic zones, frequently adja¬ cent to the nuclei of the cells, that character¬ istically are exceedingly narrow. At these sites the endothelial cells are so thin that a series of fenestrations or pores about 1,000 A in diameter perforates the cells. The perfora¬ tions are actually covered by a fine dia¬ phragm, which is thinner than the cell mem¬ brane and effectively allows water and solutions to pass readily through the cell.

VEINS

The veins return blood to the heart from tissues and organs throughout the body. Their walls are thinner but their lumina are larger than those of their accompanying ar¬ teries, and although the structure of veins varies, usually they have the same three lay¬ ers as do arteries: tunica intima, tunica media, and tunica adventitia. Venous blood is under less pressure than arterial blood and it flows more slowly; therefore, at vari¬ ous sites veins contain thin membranous valves to prevent the blood from flowing backward toward the capillary bed and away from the heart. Like arteries, veins are supplied with nutrient vessels, the vasa vasorum. They also are innervated, but they receive fewer nerve fibers than arteries. Generally, veins are distinguished by size as either small-caliber venules, medium-sized veins, or large venous trunks.

856

the veins

9-47. Electron micrograph of an arteriole from the human pyloric antrum. The lumen of the arteriole (Alu) is lined by two endothelial cells interconnected at junctions (j). A smooth muscle cell is shown outside the basal lamina (Bl) of the endothelium. Surrounding this are the basal lamina and collagenous connective tissue layer (Cf). N, nucleus; v, vesicles; Cp, cytoplasmic processes; c, centrioles; m, mitochondria; Fc, fibrocyte; Gl, glycogen; Mm, smooth muscle of stomach wall; R, red blood cell. (From Ebe, T. and Kobayashi, S., Fine Structure of Human Cells and Tissue, John Wiley and Sons, New York, 1972.)

Fig.

HISTOLOGY OF THE BLOOD VESSELS

Fig. 9-48.

857

Cross section of a capillary in the lamina propria of the gastric mucosa. The capillary is formed by an endothelial cell surrounded by a basement membrane (Bm). Note the numerous pinocytotic vesicles (Pi) along the membrane of the endothelial cell and the fenestrations (Fe), each of which is bridged by a thin diaphragm. Nu, nucleus; Go, Golgi complex; Mi, mitochondria; Er, erythrocyte; Th, thrombocyte. 30,000 X- (From Rhodin, J. A. G., An Atlas of Ultrastructure, W. B. Saunders Co., Philadelphia, 1963.)

858

THE VEINS

Fig. 9-49.

Electron micrograph of a portion of endothelial membrane in a capillary, showing surface pinocytotic vesicles (V1( V2) bridged by diaphragms consisting of a single layer (dj) or probably more than one layer (d2). A closed vesicle within the endothelial cytoplasm is shown as V3. (From Bruns and Palade, ]. Cell Biol., 37: 244-276, 1968.)

Fig. 9-50. Intercellular junctions between pairs of endothelial cells, showing regions of constriction (X), the base¬ ment membrane (BM), the external (EL) and internal (IL) leaflets of the unit membrane. The lumen of the capillary is indicated by L. 160.000 x • (From Luft, J. H., Capillary Permeability in The Inflammatory Process, 2nd ed., Zweifach, B. W., Grant, L., and McCluskey, R. T. (eds.), Vol. 2, Academic Press, New York, 1973.)

HISTOLOGY OF THE BLOOD VESSELS

Venules The venules are the smallest veins, and they are formed by the union of several cap¬ illaries. They are larger than capillaries, measuring as much as 20 or 25 ju,m, and they are importantly involved in the transfer of substances between the body fluids and the vascular system. Although their walls re¬ semble those of capillaries, there is a thin layer of collagenous fibrils and fibroblasts oriented longitudinally outside the endothe¬ lium. It is difficult, however, to distinguish the three separate layers in the walls of the smallest venules. In the walls of slightly larger venules (i.e., those with diameters of 50 to 60 /im) are found a few smooth muscle cells interposed between the endothelial cells and the connective tissue strands that form the tunica adventitia. In many of these larger venules the smooth muscle cells do not form a complete layer around the endo¬ thelium. In veins that measure 200 to 400 gm in diameter, the three coats become recog¬ nizable and even thin elastic fibers are seen interwoven with the collagenous fibers of the tunica adventitia. Veins of Medium Size The walls of medium-sized veins may vary somewhat in their structure, but usu¬ ally the three coats can be identified (Figs. 9-42; 9-51). The endothelial cells of the tu¬ nica intima in these veins contain nuclei that are more oval and less flattened than those in arteries. These cells are supported by deli¬ cate connective tissue, external to which is a network of elastic fibers that takes the place of the fenestrated membrane of the arteries. The tunica media is usually thinner than that of accompanying arteries, and it is com¬ posed of circularly arranged smooth muscle cells, intermingled with collagenous and elastic fibers (Fig. 9-45). At times there is a blending of the connective tissue elements of the innermost and middle coats, and a true definition of the border between them is not readily seen. The tunica adventitia con¬ sists of loose connective tissue with longitu¬ dinal elastic fibers, and it is usually the thickest coat (Figs. 9-42; 9-45). Large Veins In large veins the tunica adventitia may be several times thicker than the tunica media and it constitutes a major part of the vessel

859

wall. The tunica adventitia consists of loose connective tissue that contains elastic fibers and longitudinally oriented collagenous fi¬ bers. Within the adventitia are also found layers of longitudinally coursing smooth muscle fibers. These are most distinct in the inferior vena cava (especially at its termina¬ tion in the heart), in the trunks of hepatic veins, in all the large trunks of the portal vein, and in the external iliac, renal, and azygos veins. In the inferior vena cava, renal, and portal veins, the muscle fibers ex¬ tend through the whole thickness of the outer coat, but in the other veins mentioned, a layer of connective and elastic tissue is found external to the muscular fibers. The large veins that open into the heart are cov¬ ered for a short distance by a layer of car¬ diac muscle from the heart. Muscular tissue is lacking in the following: (a) veins of the maternal part of the placenta, (b) venous si¬ nuses of the dura mater and veins of the pia mater of the brain and spinal cord, (c) veins of the retina, (d) veins of the cancellous tis¬ sue of bones, and (e) venous spaces of the corpora cavernosa. Veins at these sites con¬ sist of an internal endothelial lining sup¬ ported on one or more layers of loose con¬ nective tissue. valves of the veins. Many veins are pro¬ vided with valves to prevent the reflux of blood (Fig. 9-52). Each valve is formed by a reduplication of the tunica intima which is strengthened by connective tissue and elas¬ tic fibers. The valve is covered on both sur¬ faces with endothelium, the arrangement of which differs on the two surfaces. On the surface of the valve next to the wall of the vein, the endothelial cells are arranged transversely, while on the other surface, over which the current of blood flows, the cells are arranged longitudinally in the di¬ rection of the current. Most commonly two such valves are found placed opposite each other. This is especially so in the smaller veins or in the larger trunks at the points where they are joined by smaller tributaries; occasionally there are three valves and sometimes only one. The valves are semilu¬ nar, and are attached by their convex edges to the wall of the vein. The concave margins are free, directed in the course of the venous current, and lie in close apposition with the wall of the vein so long as the current of blood flows in its natural course toward the heart. If, however, any regurgitation occurs, the valves become distended, their opposed

860

THE VEINS

t

Vlu

¥ ti i mPiIP UrT Fig. 9-51.

WmEB£*#fr''

m

Electron micrograph of a posterior abdominal vein in a seven-month-old fetus. This vein shows quite clearly the three layers forming the wall of the vessel. The endothelial cells (E) of the tunica intima rest upon a basal lamina (Bl). Surrounding these is a single layer of smooth muscle cells (Sm) that forms the tunica media. The tunica adventitia is a thicker layer of collagenous connective tissue fibers (Cf), among which are fibrocytes (Fc). Vlu, lumen; Vv, vas vasorum; j, junction between endothelial cells. 15,000 X- (From Ebe, Y. and Kobayashi, S., Fine Structure of Human Cells and Tissues, John Wiley and Sons, Inc., New York, 1972.)

REFERENCES

Fig. 9-52. The proximal portions of the femoral and great saphenous veins laid open to show the valves. About two-thirds natural size.

861

edges are brought into contact, and the back¬ ward (low is interrupted. The wall of the vein on the cardiac side of the point of at¬ tachment of each valve is expanded into a pouch or sinus that gives the vessel a knotted appearance when injected or distended with blood. Valves are numerous in the veins of the limbs, especially the lower limbs, be¬ cause these vessels must conduct blood against the force of gravity. They are absent in the very small veins and also in the venae cavae, hepatic, renal, uterine, and ovarian veins. A few valves are found in the testicu¬ lar veins, and one also at their points of junc¬ tion with the renal vein or inferior vena cava. The cerebral and spinal veins, the veins of cancellous bone, the pulmonary veins, and the umbilical vein and its branches are also destitute of valves. A few valves arc occasionally found in the azygos and intercostal veins. Rudimentary valves are found in the tributaries of the portal ve¬ nous system.

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.)

Development of Veins Arey, L. B. 1974. Developmental Anatomy. Rev. 7th ed. W. B. Saunders, Philadelphia, 695 pp. Auer, J. 1948. The development of the human pulmonary vein and its major variations. Anat. Rec., 101:581594. Bremer, J. L. 1914. The earliest blood vessels in man. Amer. J. Anat., 16:447-476. Butler, E. G. 1927. The relative role played by the great embryonic veins in the development of the mamma¬ lian vena cava posterior. Amer. J. Anat., 39:267-353. Butler, H. 1957. The development of certain human dural venous sinuses. J. Anat., (Lond.), 91:510-526. Dickson, A. D. 1957. The development of the ductus venosus in man and the goat. J. Anat. (Lond.), 91:358368. Fraser, R. S., J. Dvorkin, R. E. Rossall, and R. Eidem. 1961. Left superior vena cava. A review of associ¬ ated congenital heart lesions, catheterization data and roentgenologic findings. Amer. J. Med., 31:711716. Friedman, S. M. 1945. Report of two unusual venous abnormalities (left postrenal inferior vena cava; postaortic left innominate vein). Anal. Rcc., 92:7176. Gladstone, R. ). 1910. A case in which the right ureter passed behind the inferior vena cava. [. Anat. (Lond.), 45:225-231. Gladstone, R. J. 1929. Development of the inferior vena cava in the light of recent research, with especial reference to certain abnormalities, and current de¬

scriptions of the ascending lumbar and azygos veins. J. Anat. (Lond.), 64:70-93. Gray, S. W., and J. E. Skandalakis. 1972. Embryology for Surgeons. W. B. Saunders Co., Philadelphia, 918 pp. Karrer, H. E. 1960. Electron microscope study of devel¬ oping chick embryo aorta. J. Ultrastruct. Res., 4:420-454. Kessler, R. E., and D. S. Zimmon. 1966. Umbilical vein angiography. Radiology, 87:841-844. Me Clure, C. F. W., and C. G. Butler. 1925. The develop¬ ment of the vena cava inferior in man. Amer. J. Anat., 35:331-383. Neil, C. A. 1956. Development of the pulmonary veins. Pediatrics, 18:880-887. Padget, D. H. 1956. The cranial venous system in man in reference to development, adult configuration, and relation to the arteries. Amer. J. Anat., 98:307-356. Padget, D. H. 1957. The development of cranial venous system in man, from the viewpoint of comparative anatomy. Carneg. Inst., Contr. Embryol., 36:79-140. Patten, B. M. 1966. Human Embryology. 3rd ed., McGraw-Hill Book Co., New York, 651 pp. Reagan, F. P. 1927. The supposed homology of vena azy¬ gos and vena cava inferior considered in the light of new facts concerning.their development. Anat. Rec., 35:129-148. Reis, R. H., and G. Esenther. 1959. Variations in the pat¬ tern of renal vessels and their relation to the type of posterior vena cava in man. Amer. J. Anat., 104:295318. Rosenquist, G. C. 1971. The common cardinal veins in the chick embryo: their origin and development as

862

THE VEINS

studied by radioautographic mapping. Anat. Rec., 169:501-508. Shaner, R. F. 1961. The development of the bronchial veins, with special reference to anomalies of the pulmonary veins. Anat. Rec., 140:159-165. Stewart, W. B. 1923. The ductus venosus in the fetus and in the adult. Anat. Rec., 25:225-235. Streeter, G. L. 1915. The development of the venous si¬ nuses of the dura mater in the human embryo. Amer. J. Anat., 18:145-178. Williams, A. F. 1953. The formation of the popliteal vein. Surg. Gynecol. Obstet., 97:769-772. Veins of the Deep Head, Face, Neck and Upper Extremity Armstrong, L. D., and A. Horowitz. 1971. The brain ve¬ nous system of the dog. Amer. J. Anat., 132:479-490. Balo, J. 1950. The dural venous sinuses. Anat. Rec., 106:319-326. Batson, O. V. 1942. Veins of the pharynx. Arch. Otolar¬ yngol., 36:212-219. Bedford, T. H. B. 1934. The great vein of Galen and the syndrome of increased intracranial pressure. Brain, 57:1-24. Boemer, L. C. 1937. The great vessels in deep infection of the neck. Arch. Otolaryngol., 25:465-472. Bol’shakov, O. P. 1964. Macroscopic and microscopic structural features of cavernous sinus. Fed. Proc., 23:308-311 Browder, )., A. Browder, and H. A. Kaplan. 1973. Ana¬ tomical relationships of the cerebral and dural ve¬ nous systems in the parasagittal area. Anat. Rec., 176:329-332. Brown, S. 1941. The external jugular vein. Amer. J. Phys. Anthrop., 28:213-226. Browning, H. C. 1953. The confluence of dural venous sinuses. Amer. J. Anat., 93:307-330. Campbell, E. H. 1933. The cavernous sinus: anatomical and clinical considerations. Ann. Otol. Rhinol. Laryngol., 42:51-63. Charles, C. M. 1932. On the arrangement of the superfi¬ cial veins of the cubital fossa. Anat. Rec., 54:9-14. Clark, W. E. Le Gros. 1920. On the Pacchionian bodies. J. Anat. (Lond.), 55:40-48. Coates, A. E. 1934. A note on the superior petrosal sinus and its relation to the sensory root of the trigeminal nerve. J. Anat. (Lond.), 68:428. Hayner, J. C. 1949. Variations in the torcular Herophili and transverse sinuses. Anat. Rec., 103:542. Holdorff, B., and G. B. Bradac. 1974. The intrapanencymatous ponto-mesencephalic veins. A radio-anatomical study. Acta Anat., 89:333-344. Jefferson, G., and D. Stewart. 1928. On the veins of the diploe. Br. J. Surg., 16:70-88. Kaplan, T., and A. Katz. 1937. Thrombosis of the axillary vein: case report with comments on etiology, pa¬ thology and diagnosis. Amer. J. Surg., 37:326-333. Krayenbtihl, H. A., and M. G. Yasargil. 1968. Cerebral Angiography. Butterworths and Co. Ltd., London, 401 pp. Kumar, A. J., G. M. Hochwald, and I. Kricheff. 1976. An angiographic study of the carotid arterial and jugu¬ lar venous systems in the cat. Amer. J. Anat., 145:357-369. Neuhof, H. 1938. Excision of the axillary vein in the radi¬ cal operation for carcinoma of the breast. Ann. Surg., 108:15-20.

Newton, T. H., and D. G. Potts. 1974. Veins. In Radiology of the Skull and Brain, Vol. 2: Angiography. Book 3, Part XIII. C. V. Mosby, St. Louis, pp. 1851-2254. O’Connell, J. E. A. 1934. Some observations on cerebral veins. Brain, 57:484-503. Pikkieff, E. 1937. On subcutaneous veins of the neck. J. Anat. (Lond.), 72:119-127. Sargent, P. 1910. Some points in the anatomy of the in¬ tracranial blood sinuses. J. Anat. (Lond.), 45:69-72. Schlesinger, B. 1939. The venous drainage of the brain, with special reference to the galenic system. Brain, 62:274-291. Schwadron, L., and B. C. Moffett. 1950. Relationships of cranial nerves to Meckel’s cave and the cavernous sinus. Anat. Rec., 106:131-137. Stopford, J. S. B. 1929. The functional significance of the arrangement of the cerebral and cerebellar veins. J. Anat. (Lond.), 64:257-261. Woodhall, B., and A. E. Seeds. 1936. Cranial venous si¬ nuses: correlation between skull markings and roentgenograms of the occipital bone. Arch. Surg., 33:867-875. Pulmonary Veins, Superior Vena Cava, and Other Veins of the Thorax Appleton, A. B. 1945. The arteries and veins of the lungs: I. Right upper lobe. J. Anat. (Lond.), 79:97-120. Atwell, W. J., and P. Zoltowski. 1938. A case of left supe¬ rior vena cava without a corresponding vessel on the right side. Anat. Rec., 70:525-532. Brody, H. 1942. Drainage of the pulmonary veins into the right side of the heart. Arch. Pathol., 33:221-240. Butler, H. 1951. The veins of the esophagus. Thorax, 6:276-296. Carlson, H. A. 1934. Obstruction of the superior vena cava: an experimental study. Arch. Surg., 29:669677. Chouke, K. S. 1939. A case of bilateral superior vena cava in an adult. Anat. Rec., 74:151-157. Coakley, J. B., and T. S. King. 1959. Cardiac muscle rela¬ tion of the coronary sinus, the oblique vein of the left atrium and the left precaval vein in mammals. J. Anat. (Lond.), 93:30-35. Conn, L. C., J. Calder, J. W. Mac Gregor, and R. F. Shaner. 1942. Report of a case in which all the pulmonary veins from both lungs drain into the superior vena cava. Anat. Rec., 83:335-340. Esperanqa-Pina, J. A. 1975. Morphological study of the human anterior cardiac veins, venae cardis anteriores. Acta Anat., 92:145-159. Esperanqa-Pina, J. A., and A. Dos Santos Ferreira. 1974. Microangiographic aspects of the thebisian veins. Acta Anat., 88:156-160. Esperanqa-Pina, J. A., M. Correia, and J. G. O’Neill. 1975. Morphological study on the thebisian veins of the right cavities of the heart in the dog. Acta Anat., 92:310-320. Fieldstein, L. E., and J. Pick. 1942. Drainage of the coro¬ nary sinus into the left auricle: report of a rare con¬ genital cardiac anomaly. Amer. J. Clin. Pathol., 12:66-69. Kegaries, D. L. 1934. The venous plexus of the oeso¬ phagus: its clinical significance. Surg. Gynecol. Ob¬ stet., 58:46-51. Lindsay, H. C. 1925. An abnormal vena hemiazygos. J. Anat. (Lond.), 59:438. Massopust, L. C., and W. D. Gardner. 1950. Infrared pho-

REFERENCES tographic studies of the superficial thoracic veins in the female. Surg. Gynecol. Obstet., 91:717-727. Me Cotter, R. E. 1916. Three cases of the persistence of the left superior vena cava. Anat. Rec., 10:371-383. Morton, W. R. M. 1948. Pre-aortic drainage of the hemiazygos veins: Report of two cases. Anat. Rec., 101:187-191. Nandy, K., and C. B. Blair, Jr. 1965. Double superior venae cavae with completely paired azygos veins. Anat. Rec., 151:1-9. Papez, J. W. 1938. Two cases of persistent left superior vena cava in man. Anat. Rec., 70:191-198. Prows, M. S. 1943. Two cases of bilateral superior venae cavae, one draining a closed coronary sinus. Anat. Rec., 87:99-106. Reeves, J. T. 1967. Microradiography of intrapulmonary bronchial veins of the dog. Anat. Rec., 159:255-262. Sanders, J. M. 1946. Bilateral superior vena cavae. Anat. Rec., 94:657-662. Smith, W. C. 1916. A case of a left superior vena cava without a corresponding vessel on the right side. Anat. Rec., 11:191-198. Thompson, I. M. 1929. Venae cavae superiores dextra et sinistra of equal size in an adult. J. Anat. (Lond.), 63:496-497. Troyer, J. R. 1961. A multiple anomaly of the human heart and great veins. Anat. Rec., 139:509-513. Truex, R. C., and A. W. Angulo. 1952. Comparative study of the arterial and venous systems of the ventricular myocardium with special reference to the coronary sinus. Anat. Rec., 113:467-491. Vajda, J., M. Tomcsik, and W. J. Van Doorenmaalen. 1973. Connections between the venous system of the heart and the epicardiac lymphatic network. Acta Anat., 83:262-274. Inferior Vena Cava and Veins of the Abdomen, Pelvis, Perineum, and Lower Extremity Amsler, F. R., Jr., and M. C. Wilber. 1967. Intraosseous vertebral venography as a diagnostic aid in evaluat¬ ing intervertebral-disc disease of the lumbar spine. J. Bone Joint Surg., 49-A:703-712. Anson, B. J., E. W. Cauldwell, J. W. Pick, and L. E. Beaton. 1948. The anatomy of the pararenal system of veins, with comments on the renal arteries. J. Urol., 60:714-737. Baird, R. D., and J. S. Cope. 1933. On the termination of the circumflex veins of the thigh and their relations to the origins of the circumflex arteries. Anat. Rec., 57:325-337. Barlow, T. E., F. H. Bentley, and D. N. Walder. 1951. Arteries, veins and arteriovenous anastomoses in the human stomach. Surg. Gynecol. Obstet., 93:657-671. Batson, O. V. 1940. The function of the vertebral veins and their rfile in the spread of metastases. Ann. Surg., 112:138-149. Batson, O. V. 1942. The role of the vertebral veins in metastatic processes. Ann. Intern. Med., 16:38-45. Batson, O. V. 1957. The vertebral vein system. Amer. J. Roentgenol., 78:195-212. Becker, F. F. 1962. A singular left sided inferior vena cava. Anat. Rec., 143:117-120. Blasingame, F. J. L., and C. H. Burge. 1937. A case of left postrenal inferior vena cava without transposition of viscera. Anat. Rec., 69:465-470.

863

Boruchow, I. B., and J. Johnson. 1972. Obstructions of the vena cava. Review. Surg. Gynecol. Obstet., 134:115-121. Boyer, C. C. 1953. Anomalous inferior vena cava formed from supracardinal complexes. Anat. Rec., 117:829839. Brantigan, O. C. 1947. Anomalies of the pulmonary veins; their surgical significance. Surg. Gynecol. Obstet., 84:653-658. Brunschwig, A., and T. S. Walsh. 1949. Resection of the great veins on the lateral pelvic wall. Surg. Gynecol. Obstet., 88:498-500. Charles, C. M., T. L. Finley, R. D. Baird, and J. S. Cope. 1930. On the termination of the circumflex veins of the thigh. Anat. Rec., 46:125-132. Conn, L. C., J. Calder, J. W. Mac Gregor, and R. F. Shaner. 1942. Report of a case in which all pulmonary veins from both lungs drain into the superior vena cava. Anat. Rec., 83:335-340. Crock, H. V. 1962. The arterial supply and venous drain¬ age of the bones of the human knee joint. Anat. Rec., 144:199-217. Daniel, P. M., and M. M. L. Prichard. 1951. Variations in the circulation of the portal venous blood within the liver. J. Physiol. (Lond.), 114:521-537. Daseler, E. H., B. J. Anson, A. F. Reimann, and L. E. Beaton. 1946. The saphenous venous tributaries and related structures in relation to the technique of high ligation: based chiefly upon a study of 550 dis¬ sections. Surg. Gynecol. Obstet., 82:53-63. Di Dio, L. J. A. 1961. The termination of the vena gastrica sinistra in 220 cadavers. Anat. Rec., 141:141-144. Douglass, B. E., A. H. Baggestoss, and W. H. Hollinshead. 1950. The anatomy of the portal vein and its tribu¬ taries. Surg. Gynecol. Obstet., 91:562-576. Edwards, E. A., and J. D. Robuck, Jr. 1947. Applied anat¬ omy of the femoral vein and its tributaries. Surg. Gynecol. Obstet., 85:547-557. Ferraz De Carvalho, C. A. 1971. Considerations on the muscularis mucosae and its relations with veins at the esophago-gastric transition zone. Acta Anat., 78:559-573. Gerber, A. B., M. Lev, and S. L. Goldberg. 1951. The surgi¬ cal anatomy of the splenic vein. Amer. J. Surg., 82:339-343. Gibson, J. B. 1959. The hepatic veins in man and their sphincter mechanisms. J. Anat. (Lond.)., 93:368-379. Glasser, S. T. 1943. An anatomic study of venous varia¬ tions at the fossa ovalis. The significance of recur¬ rences following ligation. Arch. Surg., 46:289-295. Gonzalo-Sanz, L. M., and R. Insansti. 1976. The structure of the suprarenal venous system and its possible functional significance. Acta Anat., 95:309-318. Grady, E. D., and E. M. Colvin. 1953. Treatment of ve¬ nous insufficiency of the lower extremities with a note on the use of ascending phlebography. Amer. Surg., 19:936-945. Heath, T., and B. House. 1970. Origin and distribution of portal blood in the cat and rabbit. Amer. J. Anat., 127:71-80. Heller, R. E. 1942. The circulation in normal and varicose veins. Surg. Gynecol. Obstet., 74:1118-1127. Hollinshead, W. H., and J. A. Me Farlane. 1953. The col¬ lateral venous drainage from the kidney following occlusion of the renal vein in the dog. Surg. Gynecol. Obstet., 97:213-219. Huseby, R. A., and E. A. Boyden. 1941. Absence of the hepatic portion of the inferior vena cava with bilat-

864

the veins

eral retention of the supracardinal system. Anat. Rec., 81:537-544. Keck, S. W., and P. J. Kelly. 1965. The effect of venous stasis on intraosseous pressure and longitudinal bone growth in the dog. J. Bone joint Surg., 47A.539-544. Keen, J. A. 1941. The collateral venous circulation in a case of thrombosis of the inferior vena cava, and its embryological interpretation. Br. J. Surg., 29:105114. Kosinki, C. 1926. Observations on the superficial venous system of the lower extremity. J. Anat. (Lond.), 60:131-142. Kreider, P. G. 1933. The anatomy of the veins of the gall bladder. Their relation to an impacted stone. Surg. Gynecol. Obstet., 57:475-482. Kuster, G., E. F. Lofgren, and W. H. Hollinshead. 1968. Anatomy of the veins of the foot. Surg. Gynecol. Obstet., 127:817-823. Mavor, G. E., and J. M. D. Galloway. 1967. Collaterals of the deep venous circulation of the lower limb. Surg. Gynecol. Obstet., 125, 561-571. Mullarky, R. E. 1965. The Anatomy of Varicose Veins. Charles C Thomas, Springfield, Ill., 89 pp. O’Keeffe, A. F., R. Warren, and G. A. Donaldson. 1951. Venous circulation in lower extremities following femoral vein interruption. Surgery, 29:267-270. Pollack, A. A., and E. H. Wood. 1949. Venous pressure in the saphenous vein at the ankle in man during exer¬ cise and changes in posture. J. Appl. Physiol., 1:649662. Schnug, E. 1943. Ligation of the superior mesenteric vein. Surgery, 14:610-616. Severn, C. B. 1972. A morphological study of the devel¬ opment of the human liver. II. Establishment of liver parenchyma, extrahepatic ducts and associ¬ ated venous channels. Amer. J. Anat., 133:85-107. Shah, A. C., and Srivastava. 1966. Fascial canal for the small saphenous vein. J. Anat. (Lond.), 100:411-413. Simonds, J. P. 1936. Chronic occlusion of the portal vein. Arch. Surg., 33:397-424. Suh, T. H., and L. Alexander. 1939. Vascular system of the human spinal cord. Arch. Neurol. Psychiat., 41:659-677. Van Cleave, C. D. 1931. A multiple anomaly of the great veins and interatrial septum in a human heart. Anat. Rec., 50:45-51. Wagner, J. B.. Jr., and P. A. Herbut. 1949. Etiology of primary varicose veins: histologic study of one hun¬ dred saphenofemoral junctions. Amer. J. Surg., 7&876-880. Wermuth, E. G. 1939. Anastomoses between the rectal and uterine veins forming a connexion between the somatic and portal venous system in the rectouter¬ ine pouch. J. Anat. (Lond.), 74:116-126. Yelin, G. 1940. Retroaortic renal vein. J. Urol.. 44:406-410. Histology and Ultrastructure of Arteries and Veins Abraham, A. 1969. Microscopic Innervation of the Heart and Blood Vessels in Vertebrates Including Man. Pergamon Press, Oxford, 433 pp. Bennett, H. S., Luft, J. H., and J. C. Hampton. 1957. Mor¬ phological classification of vertebrate blood capil¬ laries. Amer. J. Physiol., 196:381-390. Bierring, F., and T. Kobayashi. 1963. Electron microscopy

of the normal rabbit aorta. Acta Path. Microbiol. Scand., 57:154-168. Brightman, M. W., and T. S. Reese. 1969. Junctions be¬ tween intimately apposed cell membranes in the vertebrate brain. J. Cell Biol., 40:648-677. Bruns, R. R., and G. E. Palade. 1968. Studies on blood capillaries. I. General organization of blood capil¬ laries in muscle, j. Cell Biol., 37:244-276. Bruns, R. R., and G. E. Palade. 1968. Studies on blood capillaries. II. Transport of ferritin molecules across the wall of muscular capillaries. J. Cell Biol., 37:277-299. Buck, R. C. 1958. The fine structure of endothelium of large arteries. J. Biophys. Biochem. Cytol., 4:187-190. Chambers, R., and B. W. Zweifach. 1944. Topography and function of the mesenteric capillary circulation. Amer. J. Anat., 75:173-205. Chambers, R., and B. W. Zweifach. 1947. Intercellular cement and capillary permeability. Physiol. Rec., 27:436-463. Clark, E. R„ and E. L. Clark. 1943. Caliber changes in minute blood-vessels observed in the living mam¬ mal. Amer. J. Anat., 73:215-250. Ebe, T., and S. Kobayashi. 1972. Fine Structure of Human Cells and Tissues. John Wiley & Sons, New York, 266 pp. Epling, G. E. 1966. Electron microscopic observations of pericytes of small blood vessels in the lungs and hearts of normal cattle and swine. Anat. Rec., 155:513-530. Farquhar, M. 1961. Fine structure and function in capil¬ laries of the anterior pituitary gland. Angiology, 12:270-292. Fawcett, D. W. 1959. The fine structure of capillaries, arterioles and small arteries. In The Microcircula¬ tion. Edited by S. R. M. Reynolds and B. W. Zweifach. Univ. Illinois Press, Urbana, pp. 1-27. Fawcett, D. W. 1963. Comparative observations on the fine structure of blood capillaries. In The Peripheral Blood Vessels. Edited by J. L. Orbison and D. E. Smith. Internat. Acad. Pathol. Monograph No. 4. Williams & Wilkins, Baltimore, pp. 17-44. Fernando, N. V. P., and H. Z. Movat. 1964. The capillar¬ ies. Exp. Mol. Pathol., 3:87-97. Fernando, N. V. P., and H. Z. Movat. 1964. The smallest arterial vessels: terminal arterioles and metarterioles. Exp. Mol. Pathol., 3:1-9. Florey, H. 1961. Exchange of substances between the blood and tissues. Nature, 192:908-912. Florey, H. 1966. The endothelial cell. Br. Med. J., 2:487490. Haust, M. D., R. H. More, S. A. Bencosme, and J. V. Balis. 1965. Elastogenesis in human aorta: an electron mi¬ croscope study. Exp. Mol. Pathol., 4:508-524. Hibbs, R. G., G. E. Burch, and J. H. Phillips. 1958. The fine structure of the small blood vessels of normal human dermis and subcutis. Amer. Heart J., 56:662670. Hiittner, I., M. Boutet, and R. H. More. 1973. Gap junc¬ tions in arterial endothelium. J. Cell Biol., 57:247252. Iwayama, T. 1971. Nexuses between areas of the surface membrane of the same arterial smooth muscle cell. J. Cell Biol., 49:521-525. Kaech, M. K. 1960. Electron microscopy of the normal rat aorta. J. Biophys. Biochem. Cytol., 7:533-538. Karnovsky, M. J. 1967. The ultrastructural basis of capil-

REFERENCES

lary permeability studied with peroxide as a tracer. J. Cell Biol., 35:213-236. Karnovsky, M. J., and R. S. Cotran. 1966. The intercellu¬ lar passage of exogenous peroxidase across endo¬ thelium and mesothelium. Anat. Rec., 154:365. Luft, J. H. 1963. The fine structure of the vascular wall. In Evolution of the Arteriosclerotic Plaque. Edited by R. J. Jones., Univ. Chicago Press, Chicago, pp. 3-28. Luft. J. H. 1973. Capillary permeability. In The Inflam¬ matory Process. Vol. 2. Edited by B. W. Zweifach, L. Grant, and R. T. Me Cluskey. 2nd ed. Academic Press, New York, pp. 47-93. Majno, G. 1965. Ultrastructure of the vascular mem¬ brane. In Handbook of Physiology. Sect. 2, Circula¬ tion, Vol. 3. Edited by W. F. Hamilton and P. Dow. American Physiological Society, Washington, D.C., pp. 2293-2376. Movat, H. Z., and N. V. P. Fernando. 1963. Small arteries with an internal elastic lamina. Exp. Mol. Pathol., 2:549-563. Movat, H. Z., and N. V. P. Fernando. 1964. The venules and their perivascular cells. Exp. Mol. Pathol., 3:98-114. Palade, G. E. 1960. Transport in quanta across the endo¬ thelium of blood capillaries. Anat. Rec., 136:254. Palade, G. E. 1961. Blood capillaries of the heart and other organs. Circulation, 24:368-384. Palade, G. E. 1968. Small pore and large pore systems in capillary permeability. In Hemorheology. Edited by A. L. Copley. Pergamon Press, New York, pp. 703720. Parker, F. 1958. An electron microscope study of coro¬ nary arteries. Amer. J. Anat., 103:247-273. Paule, W. J. 1965. Electron microscopy of the newborn rat aorta. J. Ultrastruct. Res., 8:219-235. Pease, D. C., and S. Molinari. 1960. Electron microscopy of muscular arteries: pial vessels of the cat and monkey. J. Ultrastruct. Res., 3:447-468. Pease, D. C., and W. J. Paule. 1960. Electron microscopy of elastic arteries: the thoracic aorta of the rat. j. Ultrastruct. Res., 3:469-483. Phelps, P. C., and J. H. Luft. 1969. Electron microscopical study of relaxation and constriction in frog arteri¬ oles. Amer. J. Anat., 125:399-428. Rhodin, J. A. G. 1962. The diaphragm of capillary endo¬ thelial fenestrations. J. Ultrastruct. Res., 6:171-185. Rhodin, J. A. G. 1962. Fine structure of the vascular wall in mammals, with special reference to the smooth muscle component. Physiol. Res., 42 (Suppl. 5):4881. Rhodin, J. A. G. 1963. An Atlas of Ultrastructure. W. B. Saunders Co., Philadelphia, 222 pp. Rhodin, J. A. G. 1967. The ultrastructure of mammalian arterioles and precapillary sphincters. J. Ultrastruct. Res., 18:181-223. Rhodin, J. A. G. 1968. Ultrastructure of mammalian ve¬ nous capillaries, venules and small collecting veins. J. Ultrastruct. Res., 25:452-500. Schwartz, S. M., and E. P. Benditt. 1972. Studies on

865

aortic intima. Amer. J. Pathol., 66:241-264. Shea, S. M., and M. S. Karnovsky. 1966. Brownian move¬ ment: a theoretical explanation for the movement of vesicles across endothelium. Nature, 212:353-355. Simionescu, M., N. Simionescu, and G. E. Palade. 1974. Morphometric data on the endothelium of blood capillaries. J. Cell Biol., 60:128-152. Smith, V., J. W. Ryan, D. D. Michie, and D. Smith. 1971. Endothelial projections, as revealed by scanning electron microscopy. Science, 173:925-927. Takada, M. 1970. Fenestrated venules of the large sali¬ vary glands. Anat. Rec., 166:605-610. Takada, M., and I. Gore. 1968. Capillary endothelial fen¬ estrations in the lamina propria of the guinea pig tongue. Anat. Rec., 161:465-469. Takada, M., and S. Hattori. 1972. Presence of fenestrated capillaries in the skin. Anat. Rec., 173:213-220. Windle, W. F. 1976. Textbook of Histology. 5th ed. McGraw-Hill Book Co., New York, 561 pp. Zweifach, B. W. 1959. The microcirculation of the blood. Sci. Amer., 200:54-60. Zweifach, B. W., L. Grant, and R. T. Me Cluskey (eds.) 1973. The Inflammatory Process. 2nd ed. Academic Press, New York, 3 vols.

Valves in Veins Basmajian, J. V. 1952. The distribution of valves in the femoral, external iliac, and common iliac veins and their relationship to varicose veins. Surg. Gynecol. Obstet., 95:537-542. Edwards, E. A. 1936. The orientation of venous valves in relation to body surfaces. Anat. Rec., 64:369-385. Edwards, E. A., and J. E. Edwards. 1943. The venous valves in thromboangiitis obliterans. Arch. Pathol., 35:242-252. Kampmeier, O. F., and C. Birch. 1927. The origin and development of the venous valves, with particular reference to the saphenous district. Amer. J. Anat., 38:451-499. Kelly, R. E. 1930. Is it true that the valves in a vein neces¬ sarily become incompetent when the vein dilates? Br. J. Surg., 18:53. Lofgren, E. P., T. T. Meyers, K. A. Lofgren, and G. Kuster. 1968. The venous valves of the foot and ankle. Surg. Gynecol. Obstet., 127:289-290. Luke, J. C. 1951. The deep vein valves: a venographic study in normal and postphlebetic states. Surgery, 29:381-386. Powell, T., and R. B. Lynn. 1951. The valves of the exter¬ nal iliac, femoral, and upper third of the popliteal veins. Surg. Gynecol. Obstet., 92:453-455. Reuther, T. F. 1940. The valves and anastomoses of the hemorrhoidal and related veins. Amer. J. Surg., 49:326-334. Van Cleave, C. D., and R. L. Holman. 1954. A preliminary study of the number and distribution of valves in normal and varicose veins. Amer. Surg., 20:533-537.

The Lymphatic

The lymphatic system is a vascular net¬ work of thin-walled capillaries and larger lymphatic vessels that drains lymph from the tissue spaces of most organs and returns it to the venous system for recirculation. Pe¬ ripherally, the lymphatic vessels do not communicate with the blood vessels, but the lymph eventually empties into the blood¬ stream at the junction of the jugular and subclavian veins at both sides of the neck. The endothelium of the veins at these points of junction is continuous with that of the lymphatic vessels. Lymphatic fluid is an ultrafiltrate of blood that contains plasma proteins, and during its course it circulates through lymphatic tissue and lymph nodes that are lined with phago¬ cytes capable of removing foreign matter. Additionally, many lymphocytes enter the lymphatic fluid at these nodes, as do the immunoglobulins or antibodies that are so important for immunologic protection. Lymph draining from different organs can vary significantly in its constituents. From the intestines it may have a white milky ap¬

866

pearance and contain a high level of di¬ gested fatty substances, whereas from the liver it may be rich in proteins. The pervasive nature of the lymphatic capillary system, so vital for the system to perform its beneficial functions, may also prove to be dangerous because its channels serve as a means by which bacteria are able to spread quickly throughout the body, with the result of generalized infection. Likewise, the lymphatic system furnishes pathways for the spread of malignant diseases, allow¬ ing routes for the establishment of meta¬ static tumors in other tissues and organs from a primary cancer site. The enormous clinical importance of the lymphatic system is widely recognized today, and yet the study of the system in the dissecting room is unsatisfactory because the thinness of its vascular walls and the small size of its chan¬ nels make them indistinguishable from the surrounding connective tissues. Thus, most of the information concerning the anatomy of the system has been obtained by labori¬ ous special investigations using the injection of colored substances into the minute ves¬ sels. Injection into the larger vessels is inef¬ fective because of the presence of numerous valves. The lymphatic system consists of: (1) an extensive capillary network that collects lymph peripherally from various organs and tissues; (2) an elaborate system of collecting vessels that carries the lymph from the lym¬ phatic capillaries to the bloodstream through an opening into the great veins at the root of the neck; (3) a number of firm, rounded bodies called lymph nodes, placed like fil¬ ters in the paths of the collecting vessels; (4) certain lymphatic organs that resemble the lymph nodes, such as the tonsils and the aggregated lymphatic tissue found in the walls of the alimentary tract; (5) the spleen; and (6) the thymus. Another element that might be added is the lymphoid tissue, rec¬ ognizable only with the aid of a microscope and consisting of reticular or areolar con¬ nective tissue that contains an accumulation of lymphocytes but lacks the organization of lymphatic nodules. The spleen serves as an important lymph¬ oid organ, performing phagocytic functions as well as being an organ in which circulat¬ ing antigens activate appropriate lympho¬ cytes to become functioning immunologic cells. The thymus, important early in life as a

DEVELOPMENT OF LYMPHATIC SYSTEM

lymphoid organ, produces the so-called T lymphocytes, which participate in cellmediated immunologic responses. Providing for the proper development of a competent immunologic system, the organ is of greater significance for the maturing child than for the adult. The lymphatic capillaries and collecting vessels are lined throughout by a continuous layer of endothelial cells, thus forming a closed system. The lymphatic vessels of the small intestine receive the special designa¬ tion of lacteals because they transport the milk-white fluid called chyle, but they do not differ morphologically from other lym¬ phatic vessels. Lymphatic vessels are not found in avas¬ cular structures such as the nails, hair, cor¬ nea, or epidermis, nor are they found in the central nervous system, meninges, eyeball, internal ear, or spleen.

Development of Lymphatic System The precise manner by which the devel¬ opment of the lymphatic system commences is still incompletely understood; however, two views have been forwarded. According to one view, the earliest lymphatic vessels arise from the endothelium of veins as sprouts that coalesce to form primitive lymph sacs. Proponents of this view feel that these initial lymphatic .plexuses, derived from the veins, then spread to surrounding tissues and organs to form a lymphatic net¬ work (Sabin, 1902, 1904, 1912, 1916; Yoffey and Courtice, 1970). Another view maintains that the initial lymphatic sacs arise in mes¬ enchyme independent of the veins, and only secondarily establish venous connections (Huntington and McClure, 1910; Huntington, 1908). Regardless of the specific manner by which the earliest lymphatic sacs are formed, the two jugular lymph sacs, one on each side, form during the sixth week near the junction of the subclavian and anterior cardinal veins (Fig. 10-1). From these sacs lymphatic capillary plexuses spread to the neck, head, arms, and thorax. The more di¬ rect channels of the plexuses enlarge and form the lymphatic vessels. The larger ves¬ sels acquire smooth muscular coats with nerve connections and exhibit contractility. Each jugular sac establishes at least one con-

867

Left brachiocephalic v. Internal jugular v. External jugular v. Jugular lymph sac Rt . brachiocephalic v. Superior vena cava

Left common cardinal v. Left postcardinal v.

Prerenal part of inferior vena cava

Cisterna chyli Left renal v.

Postrenal part of inferior vena cava

Retroperitoneal lymph sac

Left common iliac v. Posterior lymph sac

External iliac v. Internal iliac v.

Fig. 10-1. Schema showing relative positions of pri¬ mary lymph sacs based on the description given by Sabin (1916).

nection with its jugular vein, and from the left sac the upper part of the thoracic duct develops. At a slightly later stage (eighth week), an¬ other lymphatic sac, the retroperitoneal lymph sac, forms near the primitive inferior vena cava and mesonephric veins. From it lymphatics spread to the abdominal viscera and diaphragm, and the sac establishes con¬ nections with the cisterna chyli by the end of the ninth week. Also during the eighth week, another unpaired lymphatic sac, the cisterna chyli, forms near the Wolffian bodies. Giving rise to the adult cisterna chyli and the lower part of the thoracic duct, it joins that part of the duct that develops from the left jugular sac (Fig. 10-2). By the end of the eighth week, the paired posterior lymph sacs appear near the junc¬ tions of the primitive iliac veins and the pos¬ terior cardinal veins. From these sacs, lym¬ phatics spread to the abdominal wall, pelvic region, and legs. The posterior lymphatic sacs join each other by the end of the ninth week and also link superiorly with the cis¬ terna chyli (Fig. 10-2). The adult main lym¬ phatic duct forms by means of a diagonal junction of the inferior part of the right lym¬ phatic trunk (connected caudally with the dilated cisterna chyli) and the upper part of the left lymphatic trunk (continuous superi¬ orly with the left jugular sac).

868

THE LYMPHATIC SYSTEM

Jugular sac

Superficial lymphatics

Sup. vena cava

Jugular lymph sac Subclavian lymph sac

Thoracic duct

Lymph node Deep lymphatics Retroper. sac Thoracic duct

Cisterna chyli

Retroperitoneal lymph sac

Cisterna chyli Posterior lymph sac Posterior sac Superficial lymphatics

Lymph node

A

B

Fig. 10-2. Development of the primary lymphatic vessels in man. A, Profile reconstruction of the lymphatic system in a nine-week-old human embryo (Sabin, 1916). B, Diagram of the definitive thoracic duct emerging from a lymphatic plexus. (From Arey, L. B., Developmental Anatomy, 7th ed., W. B. Saunders Co., Philadelphia, 1965.)

development of lymph nodes. The pri¬ mary lymph nodes begin to develop during the third month in capillary lymphatic plex¬ uses that are formed from the large lymph sacs. Secondary lymph nodes develop later, and even after birth, in peripherally located capillary lymphatic plexuses. Lymphocytes are already present in the bloodstream and tissues long before lymph nodes begin to appear. The earliest stages of lymph node development are obscure, but it seems prob¬ able that lymphocytes lodge in special re¬ gions of the capillary plexuses and multiply to form larger and larger masses that become the cortical lymphoid nodules and medul¬ lary cords. Parallel with this multiplication of lymphocytes, the surrounding mesen¬ chyme forms a connective tissue capsule from which trabeculae carrying blood ves¬ sels grow into the lymphoid tissue. Collage¬ nous fibers form in the larger trabeculae, and these continue as reticular fibrils into the smaller trabeculae. The mesenchymal cells

of the larger trabeculae become fibroblasts, and those accompanying the reticular fibrils are known as reticular cells. Just what hap¬ pens to the lymphatic endothelium of the capillary plexus within the developing node is obscure. Some authors believe that it forms the cortical and medullary sinuses. Others believe that the endothelial lining becomes incomplete and that the reticular cells are washed by the lymph. With this idea goes the theory that some of the reticu¬ lar cells become spherical to form the first lymphocytes of the developing node and that they retain this potency throughout life.

Distribution of Lymphatic Vessels The vessels that form the lymphatic sys¬ tem consist of extensive capillary plexuses that drain into an intricate system of collect-

DISTRIBUTION OF LYMPHATIC VESSELS

ing lymphatic vessels. These, in turn, flow into larger lymphatic trunks that end in the cisterna chyli, the thoracic duct, or the right lymphatic duct (Fig. 10-3). lymphatic capillary plexuses. The capil¬ lary plexuses that collect lymph from the intercellular fluid constitute the beginning of the lymphatic system, because it is from these plexuses that the lymphatic collecting vessels arise. These collecting vessels con¬ duct the lymph centrally through one or more lymph nodes to the lymphatic trunks, cisterna chyli, thoracic duct, or right lym¬ phatic duct. The number, size, and richness of the capillary plexuses differ in different regions and organs. Where abundant, they usually are arranged in two or more anasto¬ mosing layers. Most lymphatic capillaries do not contain valves. Lymphatic capillaries are especially abun¬ dant in the dermis of the skin. They form a continuous network beneath the epidermis throughout the entire body, with the excep¬ tion of the cornea. The dermis has a superfi¬ cial plexus, without valves, that is connected by many anastomoses to a somewhat wider, coarser deep plexus with a few valves. The superficial plexus sends blind ends into the dermal papillae. The plexuses are especially rich over the palmar surface of the hands

869

and fingers, the plantar surface of the feet and toes, the conjunctiva, the scrotum, the vulva, and around orifices where the skin becomes continuous with mucous mem¬ branes (Fig. 10-4). Lymphatic capillary plexuses are abun¬ dant in the mucous membranes of the respi¬ ratory and digestive systems. They form a continuous network from the nares and lips to the anus. In most places there is a subepithelial plexus in the mucosa that anastomo¬ ses freely with a coarser plexus in the submu¬ cosa. Blind ends extend between the tubular glands of the stomach and into the villi of the intestine. The latter are the lacteals. They have a smooth muscle coat and are contractile. Those portions of the alimentary canal that are covered by peritoneum have a subserous capillary plexus beneath the mesothelium that anastomoses with the submu¬ cosal set. The lungs have a rich subserous plexus that connects with the deep plexuses within the lungs. The latter accompany the bronchi and bronchioles but their capillaries do not extend to the alveoli. The salivary glands, pancreas, and liver possess deep lymphatic plexuses. They are perilobular and do not extend between the epithelial cells. The gallbladder, and the cys-

Fig. 10-3. Schema of the larger lymphatic channels in the body. (From Benninghoff and Goerttler, Lehrbuch tier Anatomie des Menschen, 10th ed., Urban and Schwarzenberg, 1975.)

870

THE LYMPHATIC SYSTEM

Fig. 10-4. Lymphatic capillaries of the dermis from the medial border of the sole of the human foot. Note the finer capillaries of the superficial plexus (a) and the larger vessels in the deeper plexus (b). 30 X- (From Teichmann.)

tic, hepatic, and common bile ducts have rich plexuses in the mucosa. The deep lym¬ phatics of the liver deliver a copious supply of lymph. The liver and gallbladder have rich subserous plexuses. The kidney has a rich network in the cap¬ sule and a deep plexus between the tubules of the parenchyma. The renal pelvis and the ureters have rich networks in the mucosa and muscular layer that are continuous with similar plexuses of the urinary bladder. The male urethra has a dense plexus in the mu¬ cosa. The lymphatic capillaries are espe¬ cially abundant around the navicular fossa. The testis, epididymis, ductus deferens, seminal vesicles, and prostate have superfi¬ cial capillary plexuses. Both the testis and prostate have deep interstitial plexuses. The ovary has a rich capillary plexus in the parenchyma. Capillaries are absent in the tunica albuginea. The uterine tubes and uterus have mucous and muscular plexuses, as well as serous and subserous ones. The vagina has a rich fine-meshed plexus in the mucosa and a coarser one in the muscular layer. Lymphatic capillary plexuses are abun¬ dant beneath the mesothelial lining of the pleural, peritoneal, and pericardial cavities and the joint capsules. The dense connective tissues of tendons, ligaments, and perios¬ teum are richly supplied with plexuses. Very fine capillary plexuses around the fibers of

skeletal muscle have been described. Their occurrence in bone and bone marrow is not settled. The heart has a rich subepicardial plexus as well as a subendocardial plexus. The myocardium has a uniform capillary plexus that anastomoses with both the subendocar¬ dial and subepicardial ones. There are no collecting trunks in the myocardium. COLLECTING

LYMPHATIC

VESSELS

AND

LYM¬

PHATIC trunks. Lymph drains from the lymphatic capillary plexuses into collecting lymphatic channels that resemble venules and enter lymph nodes as afferent vessels. From these initial nodes, several collecting lymphatic vessels join to form slightly larger collecting channels, which then accompany larger blood vessels and enter a series of lymph nodes in succession and anastomose frequently. These larger collecting lym¬ phatic vessels often extend over long dis¬ tances without a change of caliber. They are exceedingly delicate, and their coats are so transparent that lymph can readily be seen through them. The walls of collecting vessels are interrupted at intervals by constrictions, which correspond to the location of valves on their interior, and give the vessels a knot¬ ted or beaded appearance. At certain sites in the body, groups of col¬ lecting vessels course in a parallel manner to form lymphatic trunks. These are especially seen along routes leading to the cisterna

MICROSCOPIC STRUCTURE OF LYMPHATIC VESSELS AND LYMPH NODES

chyli and toward the termination of the right lymphatic and thoracic ducts. Leading into the cisterna chyli are the intestinal trunk and the right and left lumbar trunks, while the right lymphatic duct and the thoracic duct both receive the bronchomediastinal, jugular, and subclavian trunks on their re¬ spective sides, near the junctions of the two ducts with the venous system. Lymphatic vessels are arranged in superfi¬ cial and deep sets. The superficial lymphatic vessels are placed immediately beneath the integument, accompanying the superficial veins. They join the deep lymphatic vessels at certain sites by perforating the deep fas¬ cia. The deep lymphatic vessels, fewer in number but larger than the superficial, ac¬ company the deep blood vessels. In the interior of the body, lymphatic ves¬ sels lie in the submucous areolar tissue throughout the whole length of the digestive, respiratory, and genitourinary tracts, and in the subserous tissue of the thoracic and ab¬ dominal walls. Plexiform networks of mi¬ nute lymphatic vessels are found inter¬ spersed among the parenchymal elements and blood vessels of the several tissues. The lymphatic vessels that compose the network, as well as the meshes between them, are much larger than those of the capillary plexus. From these networks small vessels emerge and pass either to a neighboring node or join some larger lymphatic trunk. The lymphatic vessels in any region of the body or in any organ exceed the veins in number, but they are much smaller in diam¬ eter. Their anastomoses, especially those of the large trunks, are also more frequent. These anastomoses are effected by vessels equal in diameter to those that they connect, and the continuing trunks retain the same diameter.

Microscopic Structure of Lymphatic Vessels and Lymph Nodes The lymphatic vessels are channels through which lymphatic fluid from tissue spaces passes in a one-way direction into the venous system. Along the course of the lym¬ phatic vessels are located encapsulated ac¬ cumulations of lymphatic tissue, the lymph nodes, within which the lymphocytes are formed.

871

STRUCTURE OF LYMPHATIC VESSELS lymphatic capillaries. Lymphatic capil¬ laries are thin, endothelial-lined channels whose walls are even more delicate than those of capillaries of the blood vascular system (Fig. 10-5). Frequently the contiguous edges of adjacent endothelial cells overlap, and fine anchoring filaments of collagen appear to attach the outer surface of the en¬ dothelium to the surrounding tissue. Lym¬ phatic capillaries do not possess a welldeveloped basal lamina, and not only do they allow the passage of extracellular fluids through their walls, but they also ab¬ sorb back into the circulation considerable amounts of proteins that have escaped into the interstitial spaces. larger lymphatic vessels. Lymphatic vessels whose diameters measure 1 to 2 mm are considered to be collecting vessels, and their walls are somewhat thicker and better defined than those of lymphatic capillaries. Nonetheless, they are readily distinguisha¬ ble from blood vessels because their walls are considerably thinner than those of ar¬ teries and veins of comparable diameter. The walls of lymphatic vessels that measure more than 2 mm in diameter are composed of three layers, similar to those of blood ves¬ sels, but the boundaries of these tunics are not easily distinguishable. The internal coat is thin, transparent, and slightly elastic, consisting of a layer of elon¬ gated endothelial cells with wavy margins by which the contiguous cells are dove¬ tailed. The endothelial cells are supported on an elastic membrane. The middle coat is composed of smooth muscle cells that are disposed in a circular or oblique manner, and fine elastic fibers that are oriented in a transverse direction. The external coat is fairly well developed and consists of con¬ nective tissue intermixed with smooth mus¬ cle fibers that course longitudinally or ob¬ liquely. This adventitia forms a protective covering over the other coats, and connects the vessel with the neighboring structures. The thoracic duct is the largest of the lym¬ phatic vessels, measuring about 0.5 cm in diameter. Its wall is somewhat more com¬ plex than that of other lymphatic vessels, having a tunica intima that consists of endo¬ thelial cells, deep to which are collagenous and elastic fibers. The subendothelial elastic fibers form an internal elastic membrane

872

THE LYMPHATIC SYSTEM

Fig. 10-5. An electron micrograph of a lymphatic capillary in cross-section. Note the close association of the sur¬ rounding connective tissue (CT) with the capillary wall which is maintained by anchoring filaments (af). The extreme narrowing (arrows) achieved by the endothelium is illustrated at several regions of the capillary wall. Observe that the nucleus (n) protrudes into the capillary lumen, nu: nucleolus; i: several intercellular junctions; m: mitochondria. 11,000 X- (From Leak, 1970).

MICROSCOPIC STRUCTURE OF LYMPHATIC VESSELS AND LYMPH NODES

similar to that found in the arteries. In the tunica media there is, in addition to muscu¬ lar and elastic fibers, a layer of connective tissue with longitudinally arranged fibers. The tunica adventitia consists of both con¬ nective tissue and bundles of smooth muscle fibers, and it tends to blend with surround¬ ing connective tissue. The larger lymphatic vessels are supplied by nutrient vessels, which are distributed to their outer and middle coats, as well as by unmyelinated nerve fibers, which form fine plexuses in their wall. The valves of lymphatic vessels are formed by thin layers of fibrous connective tissue, covered on both surfaces by endothe¬ lium, and having the same arrangement as the valves in veins. The valves consist of semilunar cusps that are attached by their convex edges to the wall of the vessel, the concave edges being free and directed along the course of the contained current. Usually two such cusps of equal size are found oppo¬ site each other, but occasionally exceptions occur, especially at or near the anatomoses of lymphatic vessels. In such cases one cusp may be small and the other proportionately larger. At times, a valve may consist of three cusps. Valves are placed at much shorter in¬ tervals in lymphatic vessels than in the veins. They are most numerous near lymph nodes, and are found more frequently in lymphatic vessels of the neck and upper ex¬ tremity than in those of the lower extremity. The wall of the lymphatic vessel immedi¬ ately above the point of attachment of each cusp of a valve is expanded into a pouch or sinus that gives to these vessels, when dis¬ tended, a characteristic knotted or beaded appearance. Valves are wanting in the capil¬ laries that compose the plexiform network, from which the larger lymphatic vessels originate. Lymph is propelled by contrac¬ tions of the walls in the larger lymphatic vessels, or by the motion of surrounding structures in smaller vessels. The valves pre¬ vent the backward flow of lymph.

STRUCTURE OF LYMPH NODES

Lymph nodes are small oval or bean¬ shaped bodies that are situated along the course of lymphatic vessels so that lymph will filter through them on its way to the blood. Each node generally has a slight de¬

873

pression on one side, the hilus, through which the blood vessels enter and leave (Figs. 10-6; 10-7). The efferent lymphatic ves¬ sels also emerge from the hilus, while the afferent lymphatic vessels enter lymph nodes at various places on the periphery. When a fresh lymph node is transected, it displays a lighter, outer cortex, surrounding an inner, darker medulla. The boundary be¬ tween these is indefinite, but at the hilus the cortex is deficient and the medulla extends to the nodal surface (Fig. 10-6). The afferent lymph vessels carry fluid to the nodal pe¬ riphery, where it achieves the cortex, and after traversing the node, lymph leaves the medulla by way of the efferent lymphatic vessels at the hilus (Fig. 10-7). Lymph nodes measure 1 to about 30 mm in diameter, and each consists of enormous numbers of lymphocytes, plasma cells, and macrophages, densely packed into masses that are partially subdivided into a series of cortical nodules and medullary cords by anastomosing connective tissue trabeculae, bordered by lymph sinuses. The trabeculae extend into the node from the collagenous connective tissue capsule and the hilus. An intricate network of reticular fibers extends from the trabeculae to form a supporting meshwork for the lymphoid elements (Fig. 10-8). A continuous narrow channel, proba¬ bly lined by endothelial cells and macro¬ phages, is found just beneath the capsule. From this subcapsular or marginal sinus arise other radially-oriented sinuses that border the trabeculae; these course through the cortex and medulla and are appropri¬ ately called cortical sinuses and medullary sinuses (Figs. 10-6 to 10-8). The afferent lym¬ phatic vessels open into the subcapsular sinus, and the efferent vessels arise from the medullary sinuses. As lymph slowly passes through this system of channels from affer¬ ent to efferent vessels, its flow is retarded by the large numbers of reticular fibers that project across the sinuses in all directions. The elegantly intricate architecture of the lymph node allows the lymphatic fluid an abundant exposure to the lymphoid ele¬ ments that surround the sinuses, thereby creating an effective means by which foreign elements in the tissue fluids may be de¬ tected, attacked, and phagocytosed. Numer¬ ous flattened stellate endothelial cells and macrophages cling to the reticular fibers. The supporting stromal structures of a

874

THE LYMPHATIC SYSTEM

> Pericapsular (at and connective tissue

Capsule

Lymphatic tissue

Capsule and afterent lymphatics

Cortex

Medulla

Trabeculae

Blood vessels in trabeculae

'SI* Marginal (subcapsular)-f

^

A cross-section view through a lymph node. Stained with hematoxylin and eosin. 32 Atlas of Human Histology, 5th ed., Lea & Febiger, Philadelphia, 1981.)

Fig. 10-6.

x

• (From di

MICROSCOPIC STRUCTURE OF LYMPHATIC VESSELS AND LYMPH NODES

875

Trabecula Capsule Afferent lymphatic vessel Primary lymphoid follicle

Subcapsular sinus

Diffuse cortical lymphoid tissue

Cortical sinus Germinal centers

Medullary cord Medullary sinus

Lymphatic vessels in hilus Artery Efferent lymphatic vessel

Fig. 10-7. Diagram of a lymph node indicating how the afferent lymphatic vessels open into the subcapsular sinus. Lymph then flows through the cortical sinuses and the medullary sinuses before leaving by way of the efferent lymphatic vessels. (After Bloom and Fawcett, A Textbook of Histology, 9th ed., 1968.)

lymph node include the collagenous connec¬ tive tissue capsule, which also contains net¬ works of elastic fibers and a few smooth muscle cells, its trabecular extensions, and the finer reticular fibers (Figs. 10-8; 10-9). The capsule is thicker at the hilum, where blood vessels enter and leave the node along with their accompanying vasomotor nerve fibers. The parenchymal tissue of a lymph node is organized within the cortex into dense spherical masses of lymphoid cells, called primary lymphoid follicles or primary nod¬ ules (Figs. 10-6 to 10-8). Within these follicles are frequently found central areas where mitotic nuclei indicate multiplication of the lymphocytes. These areas are termed germi¬ nal centers or secondary nodules. The cells that compose them have more abundant pro¬ toplasm than the peripheral cells, and con¬ sist of large and medium-sized lymphocytes. Other, more diffusely disseminated lymph¬ oid tissue is found between the primary fol¬ licles in the cortex of the node (Figs. 10-8; 10-9). Within the medulla, the lymph¬

oid tissue is even more diffuse and helps to form the medullary cords that are oriented toward the hilus. These cords are aggrega¬ tions of lymphocytes, plasma cells, and mac¬ rophages that usually surround blood ves¬ sels and reticular fibers. hemal nodes. Although a few red blood cells are normally found in lymph nodes, hemal nodes contain exceptionally large numbers of erythrocytes. They are found in certain animals, notably ruminants, but probably only occur as pathologic structures in man. Hemal nodes are quite small and resemble lymph nodes in structure, but are likely to be without afferent and efferent lymphatic vessels and are engorged with blood. lymph. Although lymph should be de¬ fined as the fluid within the walls of a closed system consisting of the lymphatic vessels, it should be understood that the composition of the lymph found in a regional set of lym¬ phatics is nearly identical with that of the interstitial or tissue fluid of the region being

876

THE LYMPHATIC SYSTEM

Capsule

Trabecula

Subcapsular sinus

Primary lymphoid follicle

Fig. 10-8. This is a photomicrograph of a human lymph node showing the capsule, the subcapsular sinus and portions of two primary lymphoid follicles which are separated by a darkly impregnated connective tissue trabecula. 360 X- (Counterstained silver preparation.)

drained. Thus, lymphatic fluids derived from different parts of the body have differ¬ ent chemical compositions. Interstitial fluid has an average protein concentration of 2gm/100ml, as does lymph; however, lymph drained from the liver and intestines may have protein levels two to three times higher, and after a fatty meal, lymph from the intestinal lacteals may have a fat concen¬ tration high enough to make the fluid milky white. Frequently, lymph has been called an ul¬ trafiltrate of blood plasma, but the important issue is that lymphatic capillaries are capa¬ ble of reabsorbing proteins, a process that does not occur to any appreciable degree at the venule end of the blood capillary system. Although venules reabsorb water, the pro¬ teins that leak into the interstitial spaces remain behind in the tissues. Unless reab¬ sorption of proteins by the lymphatic capil¬

laries occurs, death can follow in one or two days. Lymph that drains from the limbs is gener¬ ally a colorless or slightly yellow watery fluid with a specific gravity slightly over 1. When examined under the microscope, leu¬ kocytes of the lymphocyte class are found floating in the transparent fluid. They always increase in number after the passage of the lymph through lymphoid tissue, as in lymph nodes.

Large Lymphatic Vessels THORACIC DUCT

The thoracic duct conveys a greater part of the lymph in the body back into the blood vascular system (Figs. 10-10; 10-22). It is the

LARGE LYMPHATIC VESSELS

877

Trabecula

Subcapsular sinus

Reticular fibers

Primary lymphoid follicle

Fig. 10-9. High magnification of a portion of the subcapsular sinus and primary lymphoid follicle in the lymph node shown in Figure 10-8. Note the meshwork of reticular fibers and dense masses of lymphoid tissue which characterize the follicle and the looser lymphoid elements in the subcapsular sinus. 900 X- (Counterstained silver preparation.) *

common trunk of all the lymphatic vessels except those on the right side of the head, neck, and thorax, the right upper limb, the right lung, right side of the heart, and the diaphragmatic surface of the liver. In the adult, the thoracic duct varies in length from 38 to 45 cm and extends from the second lumbar vertebra to the root of the neck. It begins in the abdomen by a dilatation, the cisterna chyli, which is situated on the ante¬ rior surface of the body of the first and sec¬ ond lumbar vertebrae, to the right side of and behind the aorta, and adjacent to the right crus of the diaphragm. The duct then enters the thorax through the aortic hiatus of the diaphragm, and ascends through the pos¬ terior mediastinum between the aorta and azygos vein. Dorsal to it in this region are the vertebral column, the right intercostal ar¬ teries, and the hemiazygos veins, which cross the midline to open into the azygos

vein. Ventral to it are the diaphragm, the esophagus, and the pericardium, the latter being separated from the duct by a recess in the right pleural cavity. Opposite the fifth thoracic vertebra, the thoracic duct inclines toward the left side and enters the superior mediastinum. Its ascent in the thorax continues to the tho¬ racic inlet, dorsal to the aortic arch and the thoracic part of the left subclavian artery, and between the left side of the esophagus and the left pleura.Passing into the root of the neck on the left side, the thoracic duct forms an arch that rises about 3 or 4 cm above the clavicle, crossing anterior to the subclavian artery, the vertebral artery and vein, and the thyro¬ cervical trunk or its branches. It also passes ventral to the phrenic nerve and the medial border of the scalenus anterior muscle, and dorsal to the left common carotid artery,

878

THE LYMPHATIC SYSTEM

termination. It is generally flexuous and con¬ stricted at intervals and presents a varicose appearance. Not infrequently, it divides in the middle of its course into two vessels of unequal size that soon reunite, or into sev¬ eral branches that form a plexiform inter¬ lacement. It occasionally divides in the upper part of its course into two branches, right and left, the left ending in the usual manner, while the right opens into the right subclavian vein with the right lymphatic duct. The thoracic duct has several valves. At its junction with the venous system, it has a bi¬ cuspid valve, and the free borders of the cusps of this valve are directed toward the vein to prevent the reflux of venous blood into the duct. cisterna chyli. The cisterna chyli is a dilated sac anterior to the bodies of the two uppermost lumbar vertebrae; it forms the origin of the thoracic duct (Figs. 10-10; 1011). It lies lateral to the right crus of the dia¬ phragm, and it receives the right and left lumbar lymphatic trunks, along with the in¬ testinal lymphatic trunks. The lumbar trunks are formed by the union of the effer¬ ent vessels from the lateral aortic lumbar lymph nodes. They receive lymph from the lower limbs, the walls and viscera of the pel¬ vis, the kidneys, suprarenal glands, ovaries or testes, and the deep lymphatics of the greater part of the abdominal wall. The in¬ testinal trunks consist of large lymphatic vessels that receive lymph from the stomach and intestine, the pancreas and spleen, and the visceral surface of the liver. Tributaries of the Thoracic Duct

Fig. 10-10.

The thoracic and right lymphatic ducts.

vagus nerve, and internal jugular vein. It terminates by opening into the angle of junc¬ tion of the left subclavian vein and the left internal jugular vein. The thoracic duct is about 3 to 5 mm in diameter at its commencement, but its cali¬ ber diminishes considerably in the middle of the thorax, and again dilates just before its

Opening into the thoracic duct near the cisterna chyli, on each side, is a descending trunk from the posterior intercostal lymph nodes that drains the lower six or seven in¬ tercostal spaces. On each side of the thorax, the duct is joined by a trunk that drains the upper lumbar lymph nodes and pierces the crus of the diaphragm. It also receives effer¬ ent vessels from the posterior mediastinal lymph nodes and from the posterior inter¬ costal lymph nodes of the upper six spaces on the left side. In the neck, it is frequently joined by the left jugular trunk, which drains the left side of the head and neck, and the left subclavian trunk from the left upper extremity. Sometimes it also receives the left

I

LYMPHATIC VESSELS AND NODES OF THE HEAD AND NECK

879

Modes of origin of thoracic duct, a, Thoracic duct, a’, Cisterna chyli. b, c, Efferent trunks from lateral aortic node, d, An efferent vessel which pierces the left crus of the diaphragm, e, f, Lateral aortic nodes, h, Retroaortic nodes, i, Intestinal trunk, j, Descending branch from intercostal lymphatics. (Poirier and Charpy.) Fig. 10-11.

bronchomediastinal trunk; however, this vessel usually opens independently into the junction of the left subclavian and internal jugular veins. RIGHT LYMPHATIC DUCT

The right lymphatic duct measures about 1.25 cm in length. It courses along the medial border of the right scalenus anterior muscle at the root of the neck, and ends in the right subclavian vein, at its angle of junction with the right internal jugular vein. Its orifice is guarded by a bicuspid valve, the two semilu¬ nar cusps of which prevent the passage of venous blood into the duct. Tributaries of the Right Lymphatic Duct

The right lymphatic duct receives lymph from the right side of the head and neck through the right jugular trunk, from the

right upper extremity through the right sub¬ clavian trunk, and from the right side of the thorax, right lung, right side of the heart, and part of the convex surface of the liver through the right bronchomediastinal trunk. Although a single right lymphatic duct, formed by the junction of these three trunks, occurs at times, more frequently these trunks open separately near the angle of junction of the right internal jugular and right subclavian veins (Fig. 10-12).

Lymphatic Vessels and Nodes of the Head and Neck For the most part, lymph that drains from the superficial structures in the head initially flows into superficial vessels and nodes in the upper neck (Fig. 10-13). It is then directed into the deep cervical nodes, which also re-

a

d c

e

Fig. 10-12. Terminal collecting trunks of right side, a, Jugular trunk, b, Subclavian trunk, c, Bronchomediastinal trunk, d, Right lymphatic trunk, e, Node of internal mammary chain, f, Node of deep cervical chain. (Poirier and Charpy.)

880

the lymphatic system

Maxillary

Superficial parotid

Retroauricular

Buccal

Mandibular Superficial cervical

Submandibular Submental

Superior deep cervical

Inferior deep cervical

Fig. 10-13.

Superficial lymph nodes and lymphatic vessels of head and neck.

ceive lymphatic channels from deeper struc¬ tures in the face and head, as well as from the deeper viscera of the neck. In the deep neck the lymphatic vessels join to form the jugular trunk, which on the right side joins the right lymphatic duct or opens directly into the right subclavian vein, and on the left side joins the thoracic duct. The following description will consider first the lymphatic vessels and lymph nodes of the head, and then the lymphatic vessels and nodes of the neck.

LYMPHATIC VESSELS OF THE HEAD

The lymphatic vessels of the head include those that drain the scalp, external ear, face, walls of the nasal cavity, and mouth, as well as those of the walls of the oral cavity, pala¬ tine tonsils, and tongue.

LYMPHATIC

VESSELS

OF

THE

SCALP.

The

lymphatic vessels that drain the scalp in¬ clude those from the temporoparietal region and those that drain the occipital region (Fig. 10-13). The temporoparietal vessels end in superficial parotid and retromandibular nodes, while the occipital vessels terminate partly in the occipital nodes and partly in a trunk that runs downward along the poste¬ rior border of the sternocleidomastoid mus¬ cle and ends in the inferior deep cervical nodes. Lymphatic vessels that drain the frontal region of the scalp above the nose will be considered with the facial channels. LYMPHATIC VESSELS OF THE

EXTERNAL EAR.

The lymphatic vessels draining the auricula of the external ear and the walls of the exter¬ nal acoustic meatus are also divisible into three groups: anterior, posterior, and infe¬ rior. The anterior auricular vessels drain the lateral surface of the pinna and the anterior

LYMPHATIC VESSELS AND NODES OF THE HEAD AND NECK

wall of the meatus and flow to the anterior auricular nodes, situated immediately in front of the tragus. The posterior auricular vessels drain the margin of the auricula and the upper part of its cranial surface, and the internal surface and posterior wall of the meatus, and flow to the posterior auricular and superior deep cervical nodes. The infe¬ rior auricular vessels from the floor of the external acoustic meatus and the lobule of the auricula drain downward into superfi¬ cial and superior deep cervical nodes. lymphatic vessels of the face. The lym¬ phatic vessels of the face are more numerous than those of the scalp. The palpebral ves¬ sels from the eyelids and the conjunctival vessels drain partly downward to the sub¬ mandibular nodes, but principally laterally and posteriorly to the parotid nodes (Figs. 10-13; 10-14). Lymphatic vessels from the posterior part of the cheek also pass to the parotid nodes, while those from the anterior portion of the cheek, the side of the nose, the upper lip, and the lateral portions of the lower lip end in the submandibular nodes. The deep temporal and infratemporal ves¬ sels pass to the deep facial and superior deep cervical nodes. The deeper vessels of the cheek and lips, like the more superficial lymphatics, terminate in the submandibular nodes. Both superficial and deep labial ves¬

sels from the central part of the lower lip course to the submental nodes. LYMPHATIC VESSELS OF THE

NASAL

CAVITY.

From the anterior parts of the walls of the nasal cavity, lymphatic vessels communi¬ cate with channels from the integument of the nose, and therefore, end in the subman¬ dibular nodes. Lymphatic vessels from the posterior two-thirds of the nasal cavity and the paranasal air sinuses pass partly to the retropharyngeal and partly to the superior deep cervical nodes. lymphatic vessels of the mouth. Lym¬ phatic vessels of the gums pass to the sub¬ mandibular nodes. Channels that drain the hard palate are continuous in front with those of the upper gum, but pass backward to pierce the superior pharyngeal constrictor muscle and end in the superior deep cervical and subparotid nodes. Lymphatic vessels of the soft palate pass backward and laterally, and end partly in the retropharyngeal and subparotid nodes, and partly in the superior deep cervical nodes. The vessels of the ante¬ rior part of the floor of the mouth pass either directly to the inferior nodes of the superior deep cervical group, or indirectly through the submental nodes. Lymphatics from the remainder of the floor of the mouth pass to the submandibular and superior deep cervi¬ cal nodes.

Parotid

Facial

Submandibular Superficial cervical

Deep cervical

Fig. 10-14.

881

The lymphatics and lymph nodes of the lateral aspect of the face. (After Kiittner.)

882

THE LYMPHATIC SYSTEM

Lymphatic Vessels from Palatine Tonsil.

Usually three to five lymphatic vessels arise from the palatine tonsil. These pierce the buccopharyngeal fascia and the superior pharyngeal constrictor muscle, and pass be¬ tween the stylohyoid muscle and the inter¬ nal jugular vein to the most superior deep cervical node (Fig. 10-15). They end in a node, called the jugulodigastric node, which lies at the side of the posterior belly of the digastric muscle and adjacent to the internal jugular vein. Occasionally one or two addi¬ tional vessels course to small nodes on the lateral side of the internal jugular vein, under cover of the sternocleidomastoid muscle. Lymphatic

Vessels

from

the

Tongue.

Lymphatic vessels that arise in the tongue drain chiefly into the deep cervical nodes that lie between the posterior belly of the digastric muscle and the superior belly of the omohyoid muscle (Fig. 10-15). One lymph node, situated at the bifurcation of

the common carotid artery and posterior to the internal jugular vein and the omohyoid muscle, is intimately associated with these vessels; it is called the jugulo-omohyoid node and has frequently been referred to as the principal node of the tongue. The lym¬ phatic vessels of the tongue can be divided into four groups: apical (vessels from the tip of the tongue that course to the suprahyoid nodes and the jugulo-omohyoid node); lat¬ eral or marginal (vessels from the margin of the tongue, some of which pierce the mylo¬ hyoid muscle and end in the submandibular nodes, while others pass downward on the hyoglossus muscle to the superior deep cer¬ vical nodes) (Fig. 10-16); basal (channels from the region of the vallate papillae that travel to the superior deep cervical nodes); and median or central (a few vessels from the more anterior central region) that perfo¬ rate the mylohyoid muscle to reach the submental and submandibular nodes, although the majority turn around the posterior bor-

Submandibular gland

Submandibular node Stylohyoid muscle Digastric muscle

Hyoid bone

Superior deep cervical nodes

Omohyoid muscle Internal jugular

Common carotid artery Inferior deep cervical nodes

Sternohyoid muscle

Fiq. 10-15. The deep cervical lymphatic nodes and vessels of the right upper cervical triangle. The lymphatic drainage of the tongue is shown. (Eycleshymer and Jones.)

LYMPHATIC VESSELS AND NODES OF THE HEAD AND NECK

der of the muscle and enter both the supe¬ rior and inferior deep cervical lymph nodes. It is important to realize that lymphatics from the apical, median, and basal parts of the tongue course to deep cervical nodes on both sides of the neck, whereas lymphatic vessels from the lateral margins of the tongue initially flow to nodes on the same side (Fig. 10-16). LYMPH NODES OF THE HEAD

The lymph nodes of the head are arranged in the following groups: Occipital Retroauricular Superficial parotid Deep parotid Facial Deep facial Lingual Retropharyngeal occipital lymph nodes. The occipital lymph nodes, one to three in number, are located on the back of the head, close to the margin of the trapezius muscle, and rest on the insertion of the semispinalis capitis (Figs. 10-13; 10-18). Their afferent vessels drain the occipital region of the scalp, while their ef¬ ferent vessels pass to the superior deep cer¬ vical nodes. RETROAURICULAR LYMPH NODES. The retroauricular lymph nodes, usually two in num¬ ber, are situated on the mastoid insertion of

883

the sternocleidomastoid muscle, deep to the posterior auricular muscle (Figs. 10-13; 1018). Their afferent vessels drain the posterior part of the temporoparietal region, the upper part of the cranial surface of the auricula or pinna, and the posterior part of the external acoustic meatus; efferent vessels pass to the superior deep cervical nodes. SUPERFICIAL PAROTID LYMPH NODES. The superficial parotid or preauricular nodes usually number three or more, and they lie immediately anterior to the tragus of the ex¬ ternal ear (Figs. 10-13; 10-14). Their afferent vessels drain the lateral surface of the au¬ ricula, external acoustic meatus, root of the nose, eyelids, and frontotemporal region of the scalp, while their efferent vessels pass to the superior deep cervical nodes. DEEP PAROTID LYMPH NODES. The deep parotid lymph nodes are arranged in two groups. One group is embedded in the sub¬ stance of the parotid gland, and a second group, the subparotid nodes, is located deep to the gland and lies on the lateral wall of the pharynx. These deep parotid nodes receive lymphatic afferents from the parotid gland, the posterior parts of the palate, the floor of the nasal cavity, and the walls of the tym¬ panic cavity of the middle ear; the efferent vessels of these nodes pass to the superior deep cervical nodes. Other afferent vessels to the subparotid nodes drain the nasal part of the pharynx and the posterior parts of the nasal cavities, while the efferent vessels also pass to the superior deep cervical nodes.

SubmandibularUpper — deep cervical

Lower — deep cervical

10-16. A diagram to show the course of the marginal and central lymphatic vessels of the tongue to the lymph nodes on both sides of the neck. (Jamieson and Dobson.)

Fig.

884

THE LYMPHATIC SYSTEM

The facial lymph nodes consist of maxillary, buccal, and man¬ dibular nodes (Fig. 10-13). The maxillary nodes are scattered over the infraorbital re¬ gion, from the groove between the nose and cheek to the zygomatic arch. The buccal nodes, one or more, are placed over the buc¬ cinator muscle, opposite the angle of the mouth. The mandibular nodes lie on the outer surface of the mandible, in front of the masseter muscle and in contact with the fa¬ cial artery and vein. Their afferent vessels drain the eyelids, the conjunctiva, and the skin and mucous membrane of the nose and cheek, and their efferent vessels pass to the submandibular nodes (Figs. 10-13; 10-14). deep facial lymph nodes. The deep facial or internal maxillary nodes are placed deep to the ramus of the mandible, on the outer surface of the lateral pterygoid muscle, in relation to the maxillary artery. Their affer¬ ent vessels drain the temporal and infratem¬ poral fossae and the nasal part of the phar¬ ynx, while their efferents pass to the superior deep cervical nodes. lingual lymph nodes. Two or three small lingual nodes are located along the surface of the hyoglossus muscle and under the genioglossus muscle. They serve as substations in the course of the lymphatic vessels of the tongue to the deep cervical nodes. retropharyngeal lymph nodes. The ret¬ ropharyngeal lymph nodes, one to three in number, lie in the buccopharyngeal fascia, facial

lymph

nooes.

behind the upper part of the pharynx and anterior to the arch of the atlas, from which they are separated by the longus capitis mus¬ cle (Fig. 10-17). Their afferent vessels drain the nasal cavity, nasal part of the pharynx, and auditory tubes, while their efferent ves¬ sels pass to the superior deep cervical nodes.

LYMPHATIC VESSELS OF THE NECK

In addition to draining the skin and mus¬ cles of the neck, the lymphatic vessels of this region serve the pharynx and upper esopha¬ gus, the larynx and upper trachea, and the thyroid gland. Lymphatics from the skin and strap muscles of the anterolateral neck drain into the deep cervical nodes. The lymphatic vessels from the pharynx generally drain backward, laterally, and downward, while those from the nasophar¬ ynx and pharyngeal tonsil drain to the lat¬ eral retropharyngeal nodes (Fig. 10-17). From the oropharynx and palatine tonsil, lym¬ phatics drain to the superior deep cervical chain of nodes, and especially to the jugulodigastric node (Figs. 10-15; 10-18). From the laryngeal pharynx and upper esophagus, lymphatic vessels course in the piriform sinus and paratracheal region to the inferior deep cervical nodes. Numerous lymphatic vessels drain the lar¬ ynx. They are divided into two sets, a supe¬ rior and an inferior, by the vocal fold, which

Lat. retropharyngeal lymph nodes Afferent vessels to retropharyngeal v nodes

Afferent vesse superior deep cervical lymph node

Retropharyngeal node A superior deep cervical lymph node Efferent vessels of retro¬ pharyngeal nodes

Fig. 10-17.

Lymphatics and lymph nodes of the pharynx. (Poirier and Charpy.)

LYMPHATIC VESSELS AND NODES OF THE HEAD AND NECK

885

Temporoparietal lymph vessels

Parotid node Retroauricular nodes

Occipital nodes — Submandibular nodes Submental node Jugulodigastric lymph node Internal jugular vein Deep superior cervical nodes

Jugulo-omohyoid lymph node Deep inferior cervical nodes

I Jugular lymphatic trunk Subclavian lymphatic trunl

_Subclavian vein

\

\

-Axillary nodes

Mammary plexus

Fig. 10-18.

The deep lymphatic vessels and nodes on the right side of the head, neck, and axilla.

itself does not contain numerous vessels. The vessels of the superior set pierce the thyrohyoid membrane, course with the su¬ perior laryngeal artery, and join the superior deep cervical nodes. The inferior set of la¬

ryngeal lymphatic vessels courses along branches of the inferior thyroid artery. Some pierce the conus elasticus and join the pre¬ tracheal and prelaryngeal nodes, while oth¬ ers course between the cricoid and first tra-

886

THE LYMPHATIC SYSTEM

cheal ring and descend to the inferior deep cervical nodes. The lymphatic vessels of the thyroid gland also consist of superior and inferior sets; these follow the branches of the superior and inferior thyroid artery. The superior set drains the upper margin of the isthmus and the upper parts of the lateral lobes of the gland, and enters the superior deep cervical nodes. The inferior set drains most of the isthmus and the lower parts of the lateral lobes. Both sets descend to the deep inferior cervical nodes by way of both the pretra¬ cheal and paratracheal nodes, the latter ac¬ companying the recurrent laryngeal nerves. Lymphatic vessels from the cervical portion of the trachea also drain into these paratracheal nodes. Some lymphatic vessels of the thyroid gland may open directly into the large veins in the root of the neck, or into the thoracic duct.

LYMPH NODES OF THE NECK

The lymph nodes of the neck include the following groups: Submandibular Submental Superficial cervical Anterior cervical Deep cervical submandibular lymph nodes. The sub¬ mandibular chain of lymph nodes, three to six in number, are located beneath the body of the mandible in the submandibular tri¬ angle (Figs. 10-13 to 10-15; 10-18). They usu¬ ally rest on the superficial surface of the sub¬ mandibular salivary gland, but may extend as far forward as the border of the anterior belly of the digastric muscle. One node, which lies on the facial artery as it turns over the mandible, is the largest and most constant of the series. Additional small lymph nodes are sometimes found on the deep surface of the submandibular salivary gland. Afferent lymphatic vessels to the sub¬ mandibular nodes drain the medial palpe¬ bral commissure of the eye, the cheek, the side of the nose, the upper lip, the lateral part of the lower lip, the gums and teeth, the an¬ terior part of the margin of the tongue (ex¬ cept the tip), the frontal, maxillary, and eth¬ moidal sinuses, as well as the efferent vessels from the facial and submental nodes. Thus,

not only superficial integumentary struc¬ tures, but also mucous membranes, drain into the submandibular nodes, and in turn, their efferent vessels pass to both superficial cervical and superior deep cervical nodes. submental lymph nodes. Three or four small submental lymph nodes are found in the submental triangle between the anterior bellies of the digastric muscles (Figs. 10-13; 10-18). Their afferents drain a centrally placed wedge of tissue that includes the inci¬ sor region of the lower gum and lips, tip of the tongue, central part of the floor of the mouth, and skin of the chin. Efferent vessels from the submental nodes pass partly to the submandibular nodes, and partly to the deep cervical chain, especially the juguloomohyoid node. SUPERFICIAL CERVICAL LYMPH NODES. The superficial cervical lymph nodes lie in close relationship with the external jugular vein as it emerges from the parotid gland, and therefore are located superficial to the sterno¬ cleidomastoid muscle (Figs. 10-13; 10-14). Their afferent vessels drain the lower parts of the external ear and parotid region, while their efferent channels pass around the ante¬ rior margin of the sternocleidomastoid mus¬ cle to join the superior deep cervical nodes. ANTERIOR CERVICAL LYMPH NODES. The anterior cervical lymph nodes form an irreg¬ ular and inconstant group located below the hyoid bone and in front of the larynx, trachea, and thyroid gland. They may be divided into a superficial and a deep set. The superficial set is placed on the anterior jugular vein and drains the skin of the anterior region of the neck below the hyoid bone. The deep set is further subdivided into prelaryngeal nodes, which lie on the middle cricothyroid liga¬ ment, and pretracheal nodes, which are lo¬ cated ventral to the trachea. This deeper set drains the lower part of the larynx, the thy¬ roid gland, and the cervical part of the tra¬ chea. Its efferent vessels pass to the most in¬ ferior of the superior deep cervical nodes. DEEP CERVICAL LYMPH NODES. The deep cervical lymph nodes are numerous and large, forming a chain of 20 to 30 nodes along the carotid sheath and around the internal jugular vein. Lying by the side of the phar¬ ynx, esophagus, and trachea, the deep cervi¬ cal nodes extend from the base of the skull to the root of the neck. They are usually de¬ scribed in two groups, the superior and infe¬ rior deep cervical nodes.

LYMPHATIC VESSELS AND NODES OF THE UPPER LIMB

Superior Deep Cervical Lymph Nodes. The superior deep cervical nodes are located above the level at which the omohyoid mus¬ cle crosses the common carotid artery (Figs. 10-13 to 10-15; 10-17; 10-18). They lie deep to the sternocleidomastoid muscle, in close re¬ lationship to the accessory nerve and the in¬ ternal jugular vein; some of the nodes lie anterior, and others posterior, to the vessel. The superior deep cervical nodes drain the occipital portion of the scalp, the auricula, the back of the neck, a considerable part of the tongue, and the larynx, thyroid gland, trachea, nasal part of the pharynx, nasal cav¬ ities, palate, and esophagus. They also re¬ ceive the efferent vessels from all the other nodes of the head and neck, except the infe¬ rior deep cervical nodes. The most superior, and one of the most important of these deep cervical nodes, lies just below the site where the posterior belly of the digastric muscle crosses the internal jugular vein and internal carotid artery. It is called the jugulodigastric lymph node and is located in a rather super¬ ficial position that allows it to be palpated with ease in the living patient (Fig. 10-18). It is sometimes called the subdigastric or ton¬ sillar node, and it becomes swollen when the tonsil or pharynx is inflamed, or when there is a cancer on the posterior third of the tongue or the palatine tonsil. Inferior Deep Cervical Lymph Nodes. The inferior deep cervical nodes extend beyond the posterior margin of the sternocleido¬ mastoid muscle and into the supraclavicular triangle, where they are in close relationship to the brachial plexus and subclavian vein (Figs. 10-13; 10-15; 10-18). One large and rela¬ tively constant node in this group is the jugulo-omohyoid lymph node (Fig. 10-18). It lies on or immediately behind the internal jugular vein, just superior to the tendon of the omohyoid muscle. The inferior deep cer¬ vical nodes drain the back of the scalp and neck, the superficial pectoral region, part of the arm, and occasionally part of the supe¬ rior surface of the liver. In addition, they receive vessels from the tongue and the su¬ perior deep cervical nodes. These latter nodes pass partly to the inferior deep cervi¬ cal nodes, and partly to a trunk that unites with the efferent vessel of the inferior deep cervical nodes to form the jugular trunk. On the right side, this trunk ends in the junction of the internal jugular and subclavian veins, while on the left side it joins the thoracic

887

duct. A few minute paratracheal nodes are situated alongside the recurrent laryngeal nerves on the lateral aspects of the trachea and esophagus.

Lymphatic Vessels and Nodes of the Upper Limb The lymphatic drainage of the upper limb is directed along the routes of the major blood vascular channels. The superficial lymphatics generally follow the veins, while the deep lymphatics course with the arteries. For the most part, lymph from the upper limb drains to axillary nodes because the arm, forearm, and hand possess very few nodes and those few are exceedingly small.

LYMPHATIC VESSELS OF THE UPPER LIMB

The lymphatic vessels of the upper limb consist of two sets, superficial and deep. superficial lymphatic vessels. The su¬ perficial lymphatic vessels of the upper ex¬ tremity commence in the complex lym¬ phatic plexus that pervades the skin throughout the entire limb. The meshes of the plexus are much denser in the palm of the hand and on the flexor aspect of the dig¬ its than elsewhere. The digital plexuses are drained by vessels that course along the sides of each finger and incline backward to reach the dorsum of the hand (Fig. 10-19). From the dense palmar plexus, vessels pass in different directions, proximally toward the wrist, distally to join the digital vessels, medially to join the vessels on the ulnar bor¬ der of the hand, and laterally to those on the thumb. Several vessels from the central part of the palmar plexus unite to form a trunk that passes around the metacarpal bone of the index finger to join the vessels on the back of that digit and on the back of the thumb. Continuing proximally from around the wrist, the lymphatic vessels are col¬ lected, more or less as parallel channels, into radial, median, and ulnar groups, which ac¬ company, respectively, the cephalic, me¬ dian, and basilic veins in the forearm (Fig. 10-20). A few of the ulnar lymphatics end in the small supratrochlear nodes that are lo¬ cated superficially just above the medial aspect of the cubital fossa, but the majority

888

THE LYMPHATIC SYSTEM

LYMPH NODES OF THE UPPER LIMB

Fig. 10-19. Lymphatic vessels of the dorsal surface of the hand. (Sappey.)

pass directly to the lateral group of axillary nodes. Some of the radial vessels are col¬ lected into a trunk that ascends with the ce¬ phalic vein to the deltopectoral nodes (Figs. 10-20; 10-21). The efferents from this group may penetrate the clavipectoral fascia, with the cephalic vein, to enter the apical group of axillary nodes in the infraclavicular re¬ gion, or they may ascend as far as the lower deep cervical nodes above the clavicle. deep lymphatic vessels. The deep lym¬ phatic vessels accompany the deep blood yessels. In the forearm, they consist of four sets, which correspond to the radial, ulnar, anterior, and posterior interosseous arteries. They communicate at intervals with the su¬ perficial lymphatics, and some channels end in nodes that are occasionally found with these arteries. Along their ascent proximally in the arm. these deeper lymphatic vessels follow the course of the brachial artery. A few may even terminate in small nodes along these vessels, but most of them pass to the lateral group of axillary nodes.

For the most part the lymph nodes of the upper limb are grouped in the axilla. How¬ ever, there exists a set of somewhat isolated, outlying, and more superficial nodes, which are small and receive afferent lymphatic ves¬ sels from some of the ascending channels of the forearm and arm. Therefore, the lymph nodes of the upper extremity will be de¬ scribed as consisting of superficial and deep sets. superficial lymph nodes. The super¬ ficial lymph nodes in the upper extremity are few and small, and they are located either deep to the epidermis or in the underlying superficial fascia, closely associated with large superficial veins. They include both supratrochlear and deltopectoral nodes. Supratrochlear Nodes. One or as many as five small supratrochlear nodes are present in the superficial fascia, above the medial epicondyle of the humerus, medial to the basilic vein (Fig. 10-20). Their afferents drain the middle, ring, and little fingers, the medial portion of the hand, and the superficial area over the ulnar side of the forearm, but these vessels are in free communication with the other lymphatic vessels of the forearm. Their efferent vessels also accompany the basilic vein and some join the deeper ves¬ sels. Deltopectoral Nodes. One or two delto¬ pectoral nodes are found beside the cephalic vein and within the deltopectoral triangle, between the pectoralis major and deltoid muscles, immediately below the clavicle. deep lymph nodes. The deep lymph nodes are chiefly grouped in the axilla, al¬ though a few tiny nodes may be found in the forearm, along the course of the radial, ulnar, and interosseous arteries, and in the arm along the medial side of the brachial ar¬ tery. The Axillary Nodes. The axillary lymph nodes (Fig. 10-21) are large, vary from 20 to 30 in number, and are arranged in the fol¬ lowing groups: Lateral Pectoral (anterior) Subscapular (posterior) Central Apical (subclavicular) Lateral Group. The lateral group consists of four to six axillary nodes that are located

LYMPHATIC VESSELS AND NODES OF THE UPPER LIMB

Fig. 10-20.

889

The superficial lymph nodes and lymphatic vessels of the upper limb.

medial and posterior to the axillary vein (Fig. 10-21). The afferents of these nodes drain the whole upper limb with the excep¬ tion of that part whose vessels accompany the cephalic vein. The efferent vessels pass partly to the central and apical groups of axillary nodes, and partly to the inferior deep cervical nodes. Pectoral Group. The pectoral or anterior group of four or five nodes lies along the lat¬ eral border of the pectoralis minor muscle, in relationship to the lateral thoracic artery (Fig. 10-21). Their afferent vessels drain the skin and muscles of the anterior and lateral thoracic walls, and the central and lateral parts of the mammary gland; their efferent vessels pass partly to the central and partly to the apical groups of axillary nodes.

Subscapular Group. The subscapular or posterior group consists of six or seven axil¬ lary nodes placed along the lower margin of the posterior wall of the axilla in the course of the subscapular artery (Fig. 10-21). The afferents of this group drain the skin and muscles of the dorsal part of the neck and the posterior thoracic wall. Their efferents pass to the central group of axillary nodes. Central Group. A central group of three or four large axillary lymph nodes is embed¬ ded in the adipose tissue near the base of the axilla (Fig. 10-21). This group of nodes does not drain any specific part of the upper limb directly, but receives vessels from the lateral pectoral and subscapular groups of nodes. Its efferent vessels pass upward and medi¬ ally to the apical nodes.

890

THE LYMPHATIC SYSTEM

Apical Group. The apical or subclavicular group consists of 6 to 12 axillary lymph nodes situated partly behind the upper part of the pectoralis minor and partly in the apex of the axilla, medial and superior to the upper border of that muscle (Fig. 10-21). Its only direct territorial afferents are those that accompany the cephalic vein, and one or more that drain the upper peripheral part of the mammary gland; however, it receives the efferent vessels from all the other axillary nodes. The efferent vessels of the subclavicular group unite to form the subclavian trunk, which opens either directly into the junction of the internal jugular and subcla¬ vian veins or into the jugular lymphatic trunk; on the left side it may end in the tho¬ racic duct. A few efferents from the apical nodes usually pass to the inferior deep cervi¬ cal nodes.

Lymphatic Vessels and Nodes of the Thorax In considering the lymphatic drainage of the thorax, initially the lymphatic vessels and then the lymph nodes will be described.

LYMPHATIC VESSELS OF THE THORAX

The lymphatic vessels of the thorax drain both the thoracic wall and the viscera lo¬ cated within the thoracic cavity. Lymphatic Vessels of the Thoracic Wall The lymphatic vessels of the thoracic wall include the more superficial lymphatic channels that drain the skin and superficial fascia (which on the anterior thoracic wall includes the mammary gland) and the deeper lymphatic vessels that drain the mus¬ culature of the thorax, the intercostal spaces, and the diaphragm. SUPERFICIAL LYMPHATIC VESSELS OF THE THO¬ wall. The superficial lymphatic channels of the thoracic wall ramify beneath the skin and converge on the axillary nodes. These vessels drain the back region superfi¬ cial to the trapezius and latissimus dorsi muscles, and they course anteriorly and unite to form about 10 or 12 trunks that ter¬ minate in the subscapular group of axillary RACIC

lymph nodes (Fig. 10-21). The vessels that drain the pectoral region, including channels from the skin covering the peripheral part of the mammary gland, course dorsally, but those over the serratus anterior muscle course superiorly, to the pectoral group of axillary nodes. Others near the lateral mar¬ gin of the sternum pass inward, between the rib cartilages, and end in the parasternal nodes; the vessels of the two sides anasto¬ mose across the anterior surface of the ster¬ num. A few vessels from the upper part of the pectoral region ascend over the clavicle to the supraclavicular group of cervical nodes. Lymphatic Vessels of the Mammary Gland. The lymphatic vessels that drain the mammary gland are numerous and their great clinical importance stems from their role in the spread of malignant cells from carcinoma of the breast. Within the struc¬ ture of the gland, the lymphatic vessels origi¬ nate as channels that course along the interlobular spaces and the walls of the lac¬ tiferous ducts. Those vessels that drain the glandular tissue and overlying skin of the central part of the breast pass to an intricate plexus situated beneath the areola called the subareolar plexus (Fig. 10-21). This plexus also receives lymphatic vessels from the areola, as well as from the nipple. Efferent collecting vessels from both the superior and inferior aspects of the subareolar plexus course laterally and then superiorly to the pectoral group of axillary lymph nodes. Other vessels may bypass the pecto¬ ral nodes and course laterally and dorsally to the subscapular group of axillary nodes, while a few channels from the superior part of the breast may course to the apical group of nodes (Fig. 10-21). Because most of the lymph draining the breast courses initially to the various groups of axillary nodes, this route is considered the primary direction of drainage. However, some lymphatic vessels from the medial part of the gland are directed medially, pierce the thoracic wall, and end in para¬ sternal lymph nodes that course retrosternally with the internal thoracic artery and vein. Some channels communicate directly with the intercostal nodes, and other efferent ves¬ sels from the lower part of the breast may communicate interiorly with diaphragmatic and abdominal lymphatic channels, as well as with some from the opposite breast.

LYMPHATIC VESSELS AND NODES OF THE THORAX

891

Lateral group Deltopectoral

Apical group

Mammary lymphatic ending in subclavicular

Subscapular group

Pectoral group Mammary collecting trunks Pectoral group Subareolar plexus Cutaneous collecting trunk from the thoracic wall

trunks

Fig. 10-21.

Lymphatics of the mammary gland and the axillary nodes. (Poirier and Charpy.)

DEEP LYMPHATIC VESSELS OF THE THORACIC

The deep lymphatic vessels of the thoracic wall collect lymph from the deeper tissues of the thoracic cage, including chan¬ nels from the following three sources: tho¬ racic muscles, intercostal spaces, and the diaphragm. Lymphatic Vessels from Thoracic Mus¬ cles. Most of the lymphatic vessels that are derived from muscles attached to the ribs end in the axillary nodes, but some vessels from the medial part of the pectoralis major muscle pass to the parasternal lymph nodes. Lymphatic Vessels from Intercostal Spaces. Lymphatic vessels within the inter¬ costal spaces drain the intercostal muscles and the parietal pleura. Those vessels that drain the external intercostal muscles course dorsally, and after receiving the vessels that accompany the posterior branches of the in¬ tercostal arteries, end in the intercostal nodes (Fig. 10-22). Those lymphatic vessels that drain the internal intercostal muscles and parietal pleura consist of a single trunk in each space. Coursing ventrally around the intercostal spaces in the subpleural tissue, the upper six trunks open separately into parasternal nodes or into the vessels that unite them. Those of the lower spaces unite wall.

trunks passing to internal thoracic

to form a single trunk that terminates in the most caudal of the parasternal nodes. Lymphatic Vessels of the Diaphragm. The lymphatic vessels of the diaphragm form two plexuses, one on its thoracic and an¬ other on its abdominal surface. These plex¬ uses anastomose freely with each other, and are most numerous on the parts covered, re¬ spectively, by the pleura and peritoneum. On the thoracic surface of the diaphragm, the lymphatic vessels communicate with those of the costal and mediastinal parts of the pleura. Their efferents consist of three groups: anterior, passing to anterior dia¬ phragmatic nodes that lie near the junction of the seventh rib and its cartilage; middle, coursing to nodes on the esophagus and to those around the termination of the inferior vena cava; and posterior, which terminate in nodes that surround the aorta at the point where this vessel leaves the thoracic cavity. On the abdominal surface of the diaphragm, a plexus of fine lymphatic vessels anastomo¬ ses with those of the liver, and at the periph¬ ery of the diaphragm, with those of the subperitoneal tissue. The efferents from the right half of this plexus terminate partly in a group of nodes on the trunk of the corre¬ sponding inferior phrenic artery, while oth-

892

THE LYMPHATIC SYSTEM

Right jugular trunk Right subclavian trunk

Superior deep cervical node Left jugular trunk Inferior deep cervical node — Thoracic duct (opening)

Right lymphatic ductAnterior mediastinal nodes

Left bronchomediastinal trunk

Posterior mediastinal nodes Intercostal nodes and vessels Thoracic duct ■

Cisterna chyli

Preaortic nodes and vessels

Lateral aortic nodes

Lateral aortic nodes

Lateral sacral nodes Internal iliac nodes-(-

/

Median sacral nodes and vessel External iliac nodes

Fig. 10-22. Diagrammatic view of the deep nodes of the thorax and abdomen. Observe the cisterna chyli in the gbdomen and the ascending courses of the thoracic duct and the right lymphatic duct.

ers end in the right lateral aortic nodes. Those from the left half of the plexus pass to preaortic and left lateral aortic nodes, and to the nodes on the terminal portion of the esophagus. Visceral Lymphatic Vessels of the Thorax Within the thoracic cavity, visceral plex¬ uses of lymphatic vessels drain the heart, lungs, pleura, thymus, and esophagus.

LYMPHATIC VESSELS OF THE HEART. The lymphatic vessels of the heart are arranged in three plexuses, one located deep to the endocardium, one in the myocardium, and one beneath the epicardium (deep to the vis¬ ceral pericardium). Drainage occurs from deeper lymphatic vessels toward the more superficial surfaces of the heart; thus, the subendocardial vessels drain into the myo¬ cardial lymphatics, which, in turn, drain into the subepicardial plexus. Efferent vessels

LYMPHATIC VESSELS AND NODES OF THE THORAX

from the subepicardial plexus form right and left collecting lymphatic trunks. The left trunks, two to three in number, ascend in the anterior interventricular sulcus, and receive lymphatic vessels from both ventricles. When they reach the coronary sulcus, they are joined by a large lymphatic trunk that ascends in the posterior interventricular sul¬ cus on the diaphragmatic surface of the heart. The junction of these two lymphatic channels, which primarily drain the left side of the heart, forms a single vessel that as¬ cends between the pulmonary artery and the left atrium and ends in one of the right supe¬ rior tracheobronchial lymph nodes. The right trunk receives its afferents from the right atrium, and from the right border and diaphragmatic surface of the right ventricle. It courses upward in the coronary sulcus, adjacent to the right coronary artery, and then continues its ascent in front of the as¬ cending aorta and terminates in one of the upper left anterior mediastinal nodes. LYMPHATIC VESSELS OF THE LUNGS. The lymphatic vessels of the lungs originate in superficial and deep plexuses. The superfi¬ cial plexus is located on the surface of the lung just beneath the pulmonary pleura, while the deep plexus accompanies the branches of the pulmonary vessels and the ramifications of the bronchi. In the case of the larger bronchi, the deep plexus consists of a submucous network, located in the walls of the bronchi beneath the mucous membrane, and a peribronchial network found outside the walls of the bronchi. In the smaller bronchi there is only a single plexus, which extends as far as the bronchi¬ oles but fails to reach the alveoli, in the walls of which there are no lymphatic vessels. Ef¬ ferents from the superficial plexus course around the borders of the lungs and along the margins of the fissures separating the lobes. The lymphatics converge to end in bronchopulmonary nodes situated at the hilum. Efferents of the deep lymphatics are conducted to the hilum along the pulmonary vessels and bronchi, and end in both bron¬ chopulmonary and tracheobronchial nodes (Fig. 10-23). Little or no anastomosis occurs between the superficial and deep lymphatics of the lungs, except in the region of the hilum. LYMPHATIC VESSELS OF THE PLEURA. The lymphatic vessels of the pleura consist of channels located in both the visceral and parietal layers. The visceral set of lymphat¬

893

ics drains into the superficial efferent vessels of the lungs, deep to the visceral pleura. The parietal set of lymphatics has three modes of termination: lymphatics of the costal pleura join the lymphatics of the internal intercos¬ tal muscles and so reach the parasternal nodes; those of the diaphragmatic pleura are drained by the efferent vessels on the thoracic surface of the diaphragm (see “Lymphatic Vessels of the Diaphragm”); those of the mediastinal pleura terminate in the posterior mediastinal lymph nodes. LYMPHATIC VESSELS OF THE THYMUS. The lymphatic vessels of the thymus end in the anterior mediastinal, tracheobronchial, and parasternal nodes. LYMPHATIC

VESSELS

OF

THE

ESOPHAGUS.

The efferent lymphatic vessels from the cer¬ vical part of the esophagus drain into paratracheal and deep cervical nodes; those from the thoracic part end in posterior me¬ diastinal nodes; and those from the abdomi¬ nal part drain into the left gastric lymph nodes.

LYMPH NODES OF THE THORAX

The lymph nodes of the thorax are divided into nodes that drain the thoracic wall and those that drain the thoracic viscera. Lymph Nodes of the Thoracic Wall The lymph drain the soft racic cage, and parietal nodes the following:

nodes of the thoracic wall and hard tissues of the tho¬ are at times referred to as the of the thorax. They include

Parasternal nodes Intercostal nodes Diaphragmatic nodes parasternal nodes. The parasternal lymph nodes are located at the anterior ends of the intercostal spaces, and form a longitu¬ dinal chain of four to six nodes along the course of the internal thoracic artery. These important nodes derive afferent vessels from the mammary gland, from the deeper struc¬ tures of the anterior abdominal wall above the level of the umbilicus, from the dia¬ phragmatic surface of the liver through a small group of nodes that lies behind the xiphoid process, and from the deeper parts of the anterior thoracic wall. Their efferent

894

the lymphatic system

vessels usually unite to form a single trunk on each side of the sternum. This trunk may open directly into the junction of the subcla¬ vian and internal jugular veins, or, on the right side, it may join the main lymphatic duct on the subclavian duct, and on the left side, the thoracic duct. At times it may join lymphatic vessels from the tracheobronchial and anterior mediastinal nodes to form the bronchomediastinal trunk, which then enters the venous system either directly or through the large lymphatic ducts at the root of the neck. intercostal nodes. The intercostal lymph nodes are located in the dorsal part of the thorax, within the intercostal spaces near the heads of the ribs (Fig. 10-22). There are one or more in each interspace and they lie in relationship to the intercostal vessels. The intercostal lymph nodes receive the deep lymphatics from the posterolateral as¬ pect of the chest, as well as from certain channels from the breast; some of these ves¬ sels are interrupted by small lateral intercos¬ tal nodes. The efferent vessels of the nodes in the lower four or five spaces unite to form a trunk that descends and opens either into the cisterna chyli or into the commencement of the thoracic duct. The efferent channels of the nodes in the upper spaces of the left side end in the thoracic duct, and those of the corresponding right spaces, in the right lym¬ phatic duct. diaphragmatic nodes. The diaphrag¬ matic nodes lie on the thoracic aspect of the diaphragm and consist of three sets: anterior, lateral, and posterior. Anterior Diaphragmatic Nodes. The ante¬ rior diaphragmatic set consists of two or three small nodes, located dorsal to the base of the xiphoid process, that receive afferents from the convex surface of the liver, and one or two nodes, located on each side near the junction of the seventh rib with its cartilage, that receive lymphatic vessels from the ante¬ rior part of the diaphragm. The efferent ves¬ sels of the anterior set pass to the parasternal nodes. Lateral Diaphragmatic Nodes. The lateral diaphragmatic set consists of two or three small nodes on each side, close to the site where the phrenic nerves enter the dia¬ phragm. On the right side, some of the nodes of this group lie within the fibrous sac of the pericardium, anterior to the termination of the inferior vena cava; on the left side, they

extend to the esophageal hiatus. The afferent vessels of the lateral diaphragmatic nodes are derived from the middle region of the diaphragm; those on the right side also re¬ ceive afferents from the convex surface of the liver. Their efferents pass to the para¬ sternal nodes by way of the anterior dia¬ phragmatic nodes, to the upper anterior mediastinal nodes by a vessel that courses superiorly with the phrenic nerve, and to the posterior mediastinal nodes. Posterior Diaphragmatic Nodes. The pos¬ terior diaphragmatic set consists of a few nodes situated on the back of the crura of the diaphragm, and communicates on the one hand with the lateral aortic set of lumbar nodes, and on the other with the posterior mediastinal nodes. Lymph Nodes of the Thoracic Viscera Lymphatic vessels that drain the organs of the thorax pass initially through groups of visceral nodes. Usually three groups are described: Anterior mediastinal Posterior mediastinal Tracheobronchial anterior mediastinal nodes. The ante¬ rior mediastinal nodes are located in the an¬ terior part of the superior mediastinum, in front of the brachiocephalic veins, the aortic arch, and the large arterial trunks that arise from the aorta (Fig. 10-22). They receive af¬ ferent lymphatic vessels from the thymus, heart, and pericardium, and from the lower end of the thyroid gland. Additionally, the anterior mediastinal nodes receive lymph from the mediastinal pleura and anterior part of the hilus of the lung, from the parasternal nodes, and from the diaphragm and liver by way of the lateral diaphrag¬ matic nodes. Their efferent vessels unite with those of the tracheobronchial nodes to form the right and left bronchomediastinal trunks, which ascend in the thorax to open into the main lymphatic ducts or into the venous system directly in the root of the neck. posterior mediastinal nodes. The pos¬ terior mediastinal nodes lie behind the peri¬ cardium in relationship to the esophagus and descending thoracic aorta. There are eight to ten nodes in this group, and their

LYMPHATIC VESSELS AND NODES OF THE THORAX

afferent vessels are derived from the esopha¬ gus, the posterior part of the pericardium, the diaphragm, and the convex surface of the liver. Their efferent channels mostly end in the thoracic duct, but some join the tra¬ cheobronchial nodes. tracheobronchial nodes. The tracheobronchial nodes are assembled in five groups: Tracheal Superior tracheobronchial Inferior tracheobronchial Bronchopulmonary Pulmonary The tracheal nodes ex¬ tend along both sides of the thoracic part of the trachea, and are therefore sometimes called the paratracheal nodes (Fig. 10-23). Superior Tracheobronchial Nodes. The superior tracheobronchial nodes are found Tracheal Nodes.

L. recurrent nerve

895

on each side, superior and lateral to the angle at which the trachea bifurcates into the two primary bronchi. The chains con¬ tinue laterally along the superior border of the two principal bronchi (Fig. 10-28). Inferior Tracheobronchial Nodes. The in¬ ferior tracheobronchial nodes lie in the angle below the bifurcation of the trachea, and their chains continue inferolaterally along the lower border of the principal bron¬ chi (Fig. 10-23). Bronchopulmonary Nodes. The broncho¬ pulmonary nodes are found at the hilus of each lung, at the site of division of the prin¬ cipal bronchi and pulmonary vessels into the lobar bronchi and vessels (Fig. 10-23). Pulmonary Nodes. The pulmonary lymph nodes are found in the lung substance along the course of the segmental bronchi. The tracheal nodes in the thorax receive afferent vessels that drain the trachea and

R. recurrent nerve Paratracheal nodes

Paratracheal nodes

Brachiocephalic artery

Right superior and inferior ial nodes

Left superior and inferior tracheobronchial nodes R. bronchopulmo¬ nary nodes

L. bronchopulmo¬ nary nodes

Fig. 10-23. Posterior view of the deep visceral nodes of the thorax. Note the right and left superior and inferior tracheobronchial nodes. The superior nodes of these groups lie above the tracheobronchial angle on each side, while the inferior tracheobronchial nodes are located below the angle of division of the trachea into the two primary bronchi. (After Hall6.)

896

THE LYMPHATIC SYSTEM

the upper thoracic portion of the esophagus. The remaining groups of tracheobronchial nodes form continuous chains, and it is diffi¬ cult to define the limits of each group. Cer¬ tainly, however, the superficial and deep lymphatics of the lungs and the bronchial trees drain into the pulmonary and broncho¬ pulmonary nodes, which, in turn, drain into the superior and inferior tracheobronchial nodes. The latter also receive some afferent vessels from other posterior mediastinal or¬ gans. The efferent vessels from the tracheobron¬ chial nodes ascend with those of the tracheal nodes, which unite with efferents of the parasternal and anterior mediastinal nodes to form the right and left bronchomediastinal trunks. The right bronchomediastinal trunk may join the right lymphatic duct, and the left may join the thoracic duct. More fre¬ quently, however, they open independently of these ducts into the junction of the inter¬ nal jugular and subclavian veins of their own side.

clinical note. There are continually being swept into the bronchi and alveoli of all city dwellers large quantities of inhaled dust and black carbona¬ ceous pigment. Particles that are not picked up by dust cells, caught in the mucus, and discharged are taken up by phagocytes and transported in the lym¬ phatic vessels to the lymph nodes. This results in an enlargement and a blackened coloration of the lymph nodes in the tracheobronchial groups. The work environment can markedly enhance this condi¬ tion. The lymph nodes and lungs of coal miners in¬ variably contain large amounts of entrapped black particles (anthracosis). Other types of dust particles may also be inhaled chronically as a result of occu¬ pational activities and entrapped in these lymph nodes. Thus, the lungs of iron workers show depos¬ its of iron particles (siderosis), and those of stone masons show stone dust or sand (silicosis).

Lymphatic Vessels and Nodes of the Abdomen and Pelvis In describing the lymphatic vessels and nodes of the abdomen and pelvis, initially the lymphatic vessels and then the lymph nodes will be considered.

LYMPHATIC VESSELS OF THE ABDOMEN AND PELVIS

The lymphatic vessels of the abdomen pelvis include the parietal channels drain the abdominal and pelvic walls, the visceral vessels of the abdominal pelvic organs.

and that and and

Lymphatic 1/esse/s of the Abdominal and Pelvic Wall

Both superficial and deep lymphatic ves¬ sels drain the walls of the abdomen and pel¬ vis. Together they constitute the parietal ves¬ sels of these regions of the trunk. SUPERFICIAL LYMPHATIC VESSELS OF THE AB¬ DOMINAL and pelvic walls. The lymphatic vessels in the skin and superficial fascia of the anterior abdominal wall above the um¬ bilicus drain upward, into the superficial collecting channels of the anterior thoracic wall and therefore into the axillary nodes. Below the umbilicus, the superficial lym¬ phatic vessels follow the course of the super¬ ficial blood vessels and converge to the superficial inguinal nodes. Lymphatic chan¬ nels from the superficial tissue overlying the rectus abdominis muscle follow the course of the superficial epigastric vessels; those from the lateral regions of the abdominal wall pass along the crest of the ilium with the superficial iliac circumflex vessels. The superficial lymphatic vessels of the glu¬ teal region turn horizontally around the but¬ tock, and join the upper and lower groups of superficial inguinal lymph nodes. DEEP LYMPHATIC VESSELS OF THE ABDOMINAL

The deep lymphatic ves¬ sels of the abdominal and pelvic walls also accompany the principal blood vessels. Those of the parietes of the pelvis accom¬ pany the branches of the internal iliac artery and drain into the internal iliac and common iliac nodes, and eventually into the lateral aortic group of lumbar lymph nodes on each side (Figs. 10-24; 10-34 to 10-36). and pelvic walls.

Lymphatic Vessels of the Abdominal and Pelvic Viscera

The visceral lymphatic vessels of the ab¬ domen and pelvis include the lymphatic channels of the:

LYMPHATIC VESSELS AND NODES OF THE ABDOMEN AND PELVIS

897

Left lateral aortic Right lateral aortic Common iliac

fllHIIIlHlW'*’

Node in front of sacral promontory

I Common " iliac

Common iliac External iliac

External iliac

Obturator nerve Obturator artery

External iliac

Obturator artery Obturator

Fig. 10-24.

The parietal lymph nodes of the pelvis. (Cundo and Marcille.)

Subdiaphragmatic portion of the digestive tube and its associated glands Spleen and suprarenal glands Urinary tract Reproductive organs Perineum and external genitalia

LYMPHATIC VESSELS FROM THE SUBDIAPHRAGMATIC PORTION OF THE DIGESTIVE TUBE AND ITS ASSOCIATED GLANDS

The lymphatic vessels of the digestive tube below the level of the diaphragm are situated partly in the mucosa and partly in the submucosal, muscular, and serosal coats. Because the vessels in the mucosa drain into the deeper layers, the lymphatics will be considered as a single system in any part of

the gastrointestinal tube. The following re¬ gional visceral lymphatics will be described: Stomach Duodenum Greater omentum Jejunum and ileum Appendix and cecum Colon Rectum and anal canal Liver Gallbladder Pancreas The lymphatic vessels of the stomach are contin¬ uous at the cardiac orifice with those of the esophagus, and at the pylorus with those of the duodenum (Figs. 10-25; 10-26). They LYMPHATIC VESSELS OF THE STOMACH.

898

THE LYMPHATIC SYSTEM

mainly follow the blood vessels and are ar¬ ranged in four sets. Lymphatic vessels of the first set accompany the branches of the left gastric artery, receive tributaries from a large area on both anterior and posterior surfaces of the stomach, and terminate in the left gastric lymph nodes. Lymphatic chan¬ nels of the second set drain the fundus and body of the stomach to the left of a line drawn vertically from the esophagus. They accompany, more or less closely, the short gastric and left gastroepiploic arteries and end in the pancreaticosplenic lymph nodes. The vessels of the third set drain the right portion of the greater curvature of the stom¬ ach as far as the pylorus, and end in the right gastroepiploic nodes, the efferents of which pass to the pyloric nodes. Lymphatic vessels of the fourth set drain the pyloric portion and pass to the hepatic, pyloric, and left gas¬ tric lymph nodes (Figs. 10-25; 10-26). LYMPHATIC

VESSELS

OF

THE

DUODENUM.

The lymphatic vessels of the duodenum con¬ sist of anterior and posterior sets that open into a series of small pyloric nodes, located on the anterior and posterior aspects of the groove between the head of the pancreas and the duodenum (Figs. 10-25; 10-26). The efferents of these nodes course in two direc¬

tions, superiorly to the hepatic nodes and inferiorly to the preaortic group of lumbar nodes, around the origin of the superior mesenteric artery. LYMPHATIC VESSELS OF THE GREATER OMEN¬

The lymphatic vessels of the greater omentum course longitudinally with the omental blood vessels that branch from the right and left gastroepiploic arteries and veins. The lymphatic channels ascend to empty into lymphatic vessels and nodes along the greater curvature of the stomach. On the right side these drain into the right gastroepiploic and pyloric nodes, but on the left side they drain into the pancreatico¬ splenic nodes.

TUM.

LYMPHATIC

VESSELS

OF

THE

JEJUNUM

AND

The lymphatic vessels of the jejunal and ileal regions of the small intestine are termed lacteals because of the milk-white lymph they contain during intestinal diges¬ tion after a fatty meal. They course between the layers of the mesentery and enter the mesenteric nodes, the efferents of which end in the superior mesenteric set of preaortic nodes.

ileum.

LYMPHATIC VESSELS

OF

THE

APPENDIX

AND

The ileocolic, appendicular, and cecal regions of the gastrointestinal tract

cecum.

Paracardial nodes

Left gastric nodes Stomach

Spleen Hepatic nodes — Right gastric nodes

Pylorus

Pancreaticosplenic nodes

Pyloric nodes

Pancreas Right gastroepiploic nodes Duodenum

Fig. 10-25.

Lymphatic vessels and nodes of the stomach. (Redrawn after Jamieson and Dobson,1907.)

LYMPHATIC VESSELS AND NODES OF THE ABDOMEN AND PELVIS

899

Stomach

Right gastroepiploic nodes

Left gastric nodes Paracardial nodes

Right gastric node Celiac nodes Pylorus

Pancreaticosplenic nodes Pyloric nodes

Pancreaticoduodenal nodes

Inferior vena cava Aorta

Fig. 10-26. The lymphatic vessels of the stomach, duodenum, and pancreas demonstrated with the stomach turned upward. (After Jamieson and Dobson, 1907b.)

contain many lymphatic vessels because there is much lymphoid tissue in the walls of these parts of the gastrointestinal tract. From the body and tail of the vermiform appen¬ dix, 8 to 15 vessels ascend between the lay¬ ers of the mesentery of the appendix, several being interrupted by the small (appendicu¬ lar) nodes that lie between the peritoneal layers. These vessels unite to form three or four channels that end partly in the lower and partly in the upper nodes of the ileocolic chain (Figs. 10-27; 10-28). The vessels from the root of the appendix and from the cecum form anterior and posterior groups. The an¬ terior vessels pass in front of the cecum, and end in the anterior ileocolic nodes and in the upper and lower nodes of the ileocolic chain (Fig. 10-27). The posterior vessels ascend over the dorsal aspect of the cecum, and terminate in the posterior ileocolic nodes and in the lower nodes of the ileocolic chain (Fig. 10-28).

LYMPHATIC

VESSELS

OF

THE

COLON.

The

lymphatic vessels of the ascending and transverse colon drain through nodes lo¬ cated along the course of the marginal artery (paracolic nodes), as well as through the right colic and middle colic nodes, on their way to the superior mesenteric set of preaortic nodes (Fig. 10-29). Those of the de¬ scending and sigmoid parts of the colon are interrupted by the small nodes on the branches of the left colic and sigmoid ar¬ teries, and ultimately end in the inferior mesenteric set of preaortic nodes. LYMPHATIC

VESSELS

OF

THE

RECTUM

AND

The lymphatic vessels of the rectum have important clinical significance because of the high incidence of carcinoma in this lower region of the large intestine. As in other parts of the intestinal tract, the rec¬ tum contains both submucosal and muscular networks of lymphatic vessels. The mucocu¬ taneous or pectinate line forms a boundary anal canal.

900

THE LYMPHATIC SYSTEM

Duodenum

Upper group of ileocolic

Lower group of ileocolic

Cecum Fig. 10-27.

Vermiform appendix

The lymphatics of cecum and vermiform appendix from the front. (Jamieson and Dobson, 1907a.)

Upper group of ileocolic

Lower group of ileocolic

Vermiform appendix Cecum Fig. 10-28.

The lymphatics of cecum and vermiform appendix from behind. (Jamieson and Dobson, 1907a.)

LYMPHATIC VESSELS AND NODES OF THE ABDOMEN AND PELVIS

901

Paracolic nodes

Inferior mesenteric artery

Duodenum Superior mesenteric nodes

Left colic nodes

Inferior mesenteric nodes

Right colic nodes Ileocolic nodes Ileum

Superior rectal node

Cecum

Sigmoid nodes Appendix

Sigmoid colon

Fig. 10-29.

Lymphatic vessels and nodes of the large intestine. (After Jamieson and Dobson, 1909.)

between those lymphatics above, which drain into pelvic and lower abdominal nodes, and those lymphatics below, which drain outside the pelvis and with the peri¬ neal lymphatics to the superficial inguinal nodes. The lymphatic vessels of the rectum can be divided into superior, middle, and inferior channels. The superior lymphatics of the rectum join those of the sigmoid colon and drain ini¬ tially through pararectal nodes, which lie parallel to the rectum, and then superiorly along the course of the superior rectal artery and vein, to end in the inferior mesenteric group of preaortic nodes. The middle group of lymphatics drains approximately 10 cm of rectum above the mucocutaneous line. These channels run downward, along the course of the inferior rectal blood vessels, and terminate in nodes that accompany their branches; laterally, along the course of the middle rectal artery and vein, to terminate in

the internal iliac nodes; and superiorly, to join the uppermost channels of the rectum. The inferior group of rectal lymphatics drains the anal canal distal to the mucocuta¬ neous line. These vessels descend to the skin and superficial fascia of the perineum, and course to the superficial inguinal nodes. From these nodes lymphatic vessels enter the pelvis by way of the external and com¬ mon iliac nodes. lymphatic vessels of the liver. The lym¬ phatic vessels of the liver are divisible into two sets, superficial and deep. Superficial Lymphatic Vessels. The su¬ perficial lymphatic vessels of the liver course beneath the peritoneum and over the entire surface of the organ; they may be grouped into those located on the convex di¬ aphragmatic surface and those on the vis¬ ceral surface. Diaphragmatic Surface. The dorsal part of the diaphragmatic surface of the liver is

902

THE LYMPHATIC SYSTEM

drained by lymphatic vessels on its right, middle, and left aspects. One or two vessels along the right side course backward on the abdominal surface of the diaphragm, and after crossing the right crus, they end in the celiac group of preaortic nodes. Five or six channels along the middle part of the dia¬ phragmatic surface pass through the vena caval foramen in the diaphragm, and end in one or two lymph nodes that are situated around the terminal part of the inferior vena cava. A few lymphatic vessels from the left side pass dorsally, toward the esophageal hiatus, and terminate in the paracardial group of left gastric nodes. From the ventral part of the diaphrag¬ matic surface of the right and left lobes adja¬ cent to the falciform ligament, the lymphatic vessels converge to form two trunks. One of these accompanies the inferior vena cava through the diaphragm and ends in the nodes around the terminal part of this ves¬ sel, while the other courses downward and anteriorly, and turning around the inferior sharp margin of the liver, accompanies the upper part of the ligamentum teres to end in the hepatic nodes. A few additional vessels from this anterior surface also turn around the inferior sharp margin to reach the he¬ patic nodes. Visceral Surface. The lymphatic vessels from the visceral surface of the liver mostly converge toward the porta hepatis. They accompany the deep lymphatics that emerge from the liver at this site, and end in the he¬ patic nodes. One or two channels from the posterior parts of the right and caudate lobes accompany the inferior vena cava through the diaphragm and end in nodes near the ter¬ mination of this vein. Deep Lymphatic Vessels. The deep lym¬ phatic vessels from the internal substance of the liver join to form ascending and de¬ scending trunks. The ascending trunks ac¬ company the hepatic veins and pass through the diaphragm, to end in lymph nodes around the terminal part of the vein. The descending trunks emerge from the porta hepatis and end in the hepatic nodes. LYMPHATIC

VESSELS

OF

THE

GALLBLADDER.

The lymphatic vessels that drain the gall¬ bladder pass to the hepatic nodes in the porta hepatis. There is evidence that inter¬ connections exist between lymphatic chan¬ nels of the gallbladder and the liver, which possibly helps to explain the spread of infec¬

tions and other diseases between these two organs. Lymphatic vessels of the common bile duct course to the hepatic nodes, along¬ side the duct, and to the upper pancreatico¬ duodenal nodes. LYMPHATIC

VESSELS

OF

THE

PANCREAS.

The lymphatic vessels of the pancreas fol¬ low the course of its blood vessels (Fig. 10-26). Most of them enter the pancreaticosplenic nodes, but some end in nodes lo¬ cated along the pancreaticoduodenal ves¬ sels. Other pancreatic lymphatic channels open into the superior mesenteric set of preaortic nodes. LYMPHATIC VESSELS FROM THE SPLEEN AND SUPRARENAL GLANDS LYMPHATIC VESSELS OF THE SPLEEN. The lymphatic vessels of the spleen are princi¬ pally derived from the capsule and from the connective tissue that forms the trabeculae. These pass to splenic nodes, located be¬ tween the layers of the gastrosplenic liga¬ ment at the hilus, and to pancreaticosplenic nodes, located along the superior border of the tail of the pancreas (Fig. 10-25). LYMPHATIC

VESSELS

OF

THE

SUPRARENAL

glands. The lymphatic vessels of the su¬ prarenal glands usually accompany the su¬ prarenal veins and end in the lateral aortic set of lumbar nodes. Occasionally some ves¬ sels pierce the crura of the diaphragm and end in the posterior mediastinal nodes.

LYMPHATIC VESSELS OF THE URINARY TRACT LYMPHATIC

VESSELS

OF THE

KIDNEY.

The

lymphatic vessels of the kidney form three plexuses: one in the substance of the renal cortex, a second beneath the fibrous capsule of the kidney, and a third in the perineph¬ ric fat. The subcapsular and perinephric plexuses communicate freely with each other. The lymphatic vessels from the plexus in the substance of the kidney converge to form four or five trunks that emerge at the hilus. Here they are joined by vessels from the subcapsular plexus, and following the course of the renal vein, they end in the lat¬ eral aortic set of lumbar nodes. The peri¬ nephric plexus drains directly into the more superior of the lateral aortic nodes. LYMPHATIC VESSELS OF THE URETER. The lymphatic vessels of the ureter commence in

LYMPHATIC VESSELS AND NODES OF THE ABDOMEN AND PELVIS

plexuses within the muscular and adventi¬ tial layers of the organ. The channels from the proximal portion end partly in the effer¬ ent vessels of the kidney, and in part directly in the lateral aortic set of lumbar nodes. Those from the middle portion (above the pelvic brim) drain into common iliac nodes, whereas the vessels from the intrapelvic portion of the tube (below the pelvic brim) drain into external and internal iliac nodes, and more distally may join efferent vessels from the bladder. LYMPHATIC VESSELS OF THE BLADDER. The lymphatic vessels of the bladder commence in muscular and extramuscular plexuses, and it is claimed that the mucous membrane is devoid of lymphatic channels. The effer¬ ent vessels emerge from the bladder in three groups: those from the anterior aspect, the

903

posterior aspect, and the region of the trigone. The vessels from the anterior part of the inferolateral surface and the anterior part of the superior surface pass laterally along the course of the obliterated umbilical artery and end in the external iliac nodes (Fig. 1030). Located along their course are minute nodes that are arranged in front of the blad¬ der in an anterior vesical group, and a lateral vesical group, adjacent to the lateral umbili¬ cal ligament. Most of the vessels from the posterior part of the inferolateral surface pass laterally and backward to common iliac and internal iliac nodes, but a few vessels course backward, even beyond the bifurcation of the aorta, to one or two nodes in front of the sacral prom¬ ontory (Fig. 10-30). The channels from the

Lateral aortic nodes (lumbar)

Aorta

Common iliac nodes Common iliac nodes (medial group in front of promontory) Common iliac artery

Internal iliac nodes

External iliac nodes

Sacral nodes

Ureter

-Lymphatics from bladder

Rectum

Bladder

Prostate

Fig. 10-30.

Lymphatic vessels from the bladder.

904

the lymphatic system

posterior part of the superior surface also course laterally to the common iliac and in¬ ternal iliac nodes. Lymphatic vessels from the trigone of the bladder course upward and laterally to both the external and internal iliac nodes. LYMPHATIC VESSELS OF THE URETHRA. The lymphatic vessels of nearly the entire female urethra and of the prostatic and membra¬ nous parts of the male urethra pass prin¬ cipally to the internal iliac lymph nodes. Lymphatics from the distal extremity of the female urethra drain with those from the skin of the female external genitalia to the superficial inguinal nodes. Lymphatic vessels from the spongy por¬ tion of the male urethra accompany those of the glans penis and terminate in the deep inguinal nodes, adjacent to the femoral ar¬ tery. Other vessels course upward along the inguinal canal and drain into the external iliac nodes. LYMPHATIC VESSELS OF THE MALE REPRODUCTIVE ORGANS

The lymphatic vessels of the testis consist of two sets, superficial and deep. The superficial vessels commence on the surface of the tu¬ nica vaginalis, while the deep vessels are derived from the epididymis and body of the testis. They form four to eight collecting trunks that ascend with the testicular blood vessels in the spermatic cord. At the abdomi¬ nal inguinal ring, they continue upward on the anterior surface of the psoas major mus¬ cle to the point where the testicular artery and vein cross the ureter, and they end in the lateral and preaortic sets of lumbar nodes. LYMPHATIC

VESSELS

OF

THE

TESTIS.

LYMPHATIC VESSELS OF THE DUCTUS DEFER¬ ENS and seminal vesicles. Only superficial lymphatic vessels that drain the ductus deferens have been described, and these ter¬ minate in the external iliac nodes. Both superficial and deep lymphatic ves¬ sels drain the seminal vesicles, and these drain into the external iliac and internal iliac lymph nodes (Fig. 10-31). LYMPHATIC VESSELS OF THE PROSTATE. The lymphatic vessels of the prostate gland ter¬ minate principally in the internal iliac and sacral lymph nodes (Fig. 10-31). One lymph vessel from the posterior surface of the pros¬ tate, however, courses laterally and ends in

the external the anterior vessels that the urethra iliac nodes.

iliac nodes, while another from surface of the gland joins the drain the membranous part of and terminates in the internal

LYMPHATIC VESSELS OF THE FEMALE REPRODUCTIVE ORGANS LYMPHATIC VESSELS OF THE OVARY. A rich plexus of lymphatic vessels drains each ovary, and when they leave the hilum, they follow the course of the ovarian artery and vein to terminate in the lateral and preaortic sets of the lumbar nodes. LYMPHATIC VESSELS OF THE

UTERINE TUBE.

The lymphatic vessels of the upper and mid¬ dle parts of the uterine tube follow those from the ovary and end in the lateral and preaortic sets of lumbar nodes. Channels that drain the lowest part of the uterine tube course laterally between the leaves of the broad ligament to the internal iliac nodes, and with the round ligament, through the inguinal canal to the superficial inguinal nodes. LYMPHATIC VESSELS OF THE UTERUS. The lymphatic vessels of the uterus consist of two sets, superficial and deep, the former placed beneath the peritoneum, the latter in the wall of the uterus. Efferent vessels from the cervix of the uterus course in three directions: laterally with the uterine artery to the external iliac nodes; posterolaterally, passing behind the ureter, to the internal iliac nodes; and poste¬ riorly, to the common iliac and lateral sacral nodes (Figs. 10-32; 10-33). The majority of the lymphatic vessels of the body and fundus of the uterus pass later¬ ally in the broad ligaments with the uterine artery to internal iliac nodes. Others are con¬ tinued superiorly with the ovarian vessels and end in the lateral and preaortic sets of lumbar nodes. A few channels course to the external iliac nodes, and one or two vessels traverse the inguinal canal and end in the superficial inguinal nodes. In the nongravid uterus, the lymphatic vessels are very small, but during gestation they are greatly en¬ larged. LYMPHATIC VESSELS OF THE VAGINA. Three groups of lymphatic vessels drain the vagina (Fig. 10-33). The upper (cervicovaginal) channels course laterally with branches of

LYMPHATIC VESSELS AND NODES OF THE ABDOMEN AND PELVIS

905

Lateral aortic (lumbar) nodes

\

External iliac nodes

Common iliac nodes (medial group in front of promontory)

—^-Sacral nodes (lateral)

Vessels draining into lateral sacral nodes Middle rectal artery Middle rectal lymphatic vessels

Collecting vessels and visceral nodes of seminal vesicle and prostate

Fig. 10-31

Lymphatic vessels of the prostate and middle rectal region.

the uterine artery to the external and inter¬ nal iliac nodes. Lymphatic vessels from the middle region of the vagina follow the branches of the vaginal artery to the internal iliac nodes, along the course of which are interspersed other minute nodes. Some lym¬ phatic vessels from the lower part of the va¬ gina join those of the middle portion and course toward nodes in the lateral wall of the pelvis, while others near the vaginal ori¬ fice join those of the vulva and pass to the superficial inguinal nodes. The lymphatics of the vagina interconnect with those of the cervix of the uterus, the rectum, and the ex¬ ternal genitalia, but not with those of the bladder.

LYMPHATIC VESSELS OF THE PERINEUM AND EXTERNAL GENITALIA LYMPHATIC VESSELS OF THE UROGENITAL RE¬ GION. The lymphatic vessels of the skin and superficial fascia in the urogenital region of the perineum, along with the superficial lymphatic vessels from the skin of the scro¬ tum and penis and those of the labia majora and labia minora, course laterally with the external pudendal artery and vein and ter¬ minate in the upper and lower superficial in¬ guinal nodes. The lymphatic vessels of the glans penis and clitoris course with the deep dorsal vein and drain laterally to the deep inguinal

906

THE LYMPHATIC SYSTEM

Uterine tube iliac nodes (medial group, in front of promontory)

External iliac nodes Internal iliac nodes Uterine vessels of external iliac nodes

Sacral node (lateral group) Uterine vessels .draining into internal iliac nodes

Lymphatic network in lateral aspect of cervix

Uterine vessel passing to sacral nodes

Fig. 10-32.

Lymphatic vessels draining the uterus.

nodes (Fig. 10-34). These vessels may extend superiorly, even through the femoral canal, to the external iliac nodes. Other channels course upward through the inguinal canal also to achieve the external iliac nodes. LYMPHATIC

VESSELS

OF

THE

ANAL

REGION.

The superficial lymphatic vessels in the anal region of the perineum also course to the su¬ perficial inguinal lymph nodes. Some chan¬ nels, those deeper in the ischiorectal fossa, follow the course of the inferior rectal and internal pudendal hlood vessels and thereby enter the pelvis and end in the internal iliac nodes.

LYMPH NODES OF THE ABDOMEN AND PELVIS

The lymph nodes of the abdomen and pel¬ vis may be divided, according to their loca¬ tion, into those nodes that lie behind the

peritoneum, adjacent to the walls of the abdominopelvic cavity in close association with the large blood vessels, and those lymph nodes that are more intimately re¬ lated to the abdominopelvic viscera and to the vessels more directly supplying the or¬ gans.

Lymph Nodes of the Abdominal and Pelvic Walls The lymph nodes located adjacent to the walls of the abdominal and pelvic cavities are frequently referred to as parietal nodes. These nodes include the following groups: External iliac Common iliac Epigastric Circumflex iliac Internal iliac

LYMPHATIC VESSELS AND NODES OF THE ABDOMEN AND PELVIS

907

Preaortic nodes (lumbar)

Aorta Inferior vena cava

Common iliac nodes

Rectum

Internal iliac nodes

External iliac node

Ovary

Uterine tube

Fornix of vagina Round ligament of uterus

Cervix of uterus

Vagina

Fig. 10-33.

Lymphatic vessels of the vagina and uterus.

Sacral Lumbar Lateral aortic Preaortic Retroaortic external iliac nodes. The external iliac nodes, eight to ten in number, lie along the external iliac vessels (Figs. 10-24; 10-35; 1036). They are arranged in three groups, one on the lateral aspect, another on the medial aspect, and a third, which is sometimes ab¬ sent, on the anterior aspect of the vessels. The external iliac nodes receive afferent ves¬ sels from:

(a) the lower extremity, by way of the su¬ perficial and deep inguinal nodes, as well as from some lymphatics from the adductor region of the thigh; (b) the lower anterior abdominal wall, by way of the epigastric and circumflex iliac nodes; (c) the perineum, by way of lymphatic channels from the glans penis or clitoris that reach the external iliac nodes through the inguinal canal, and by means of vessels that course laterally from the genitalia and then superiorly through the femoral canal; (d) the pelvis, through direct channels from the fundus of the bladder, the prostate,

908

THE LYMPHATIC SYSTEM

Internal iliac node

Common iliac node (medial group in front of sacral promontory)

Sacral node (lateral group)

External iliac-. Internal iliac Satellite trunk of internal puden¬ dal vessels

V.

Internal lymphatics of bladder

Trunk of middle rectal vessels

Lymphatic from penis Lymphatics of

collecting trunk ral collecting trunks

Glandular nodule

Fig. 10-34.

Prostatic collecting trunk

Lymphatic vessels draining the glans penis and the spongy and membranous portions of the urethra.

and membranous urethra in the male, or from the upper vagina and uterine cervix in the female. Efferent vessels leave the external iliac nodes and ascend to common iliac and lum¬ bar nodes. common iliac nodes. The six to eight common iliac nodes are located medial, lateral, and posterior to the common iliac vessels (Figs. 10-24; 10-35; 10-36), and they extend from the external iliac nodes to the bifurcation of the aorta. Several of the me¬ dial nodes are located in front of the fifth lumbar vertebra and the promontory of the sacrum; these extend downward from the bifurcation of the aorta. The lateral and pos¬ terior nodes directly extend the chain of parietal pelvic nodes from the external and internal iliac sets to the lateral lumbar nodes. epigastric nodes. Three or four epigas¬ tric nodes follow the course of the lower part of the inferior epigastric vessels, and their efferent channels drain into the exter¬ nal iliac nodes. circumflex iliac nodes. Two to four cir-

cumflex iliac nodes, when present, are situ¬ ated along the course of the deep circumflex iliac vessels. Their efferent channels also drain into the external iliac nodes. internal iliac nodes. The internal iliac nodes surround the internal iliac vessels, and they receive lymphatics that correspond to the distribution of the branches of the in¬ ternal iliac artery (Figs. 10-30; 10-32 to 10-36). Lying deep to the pelvic fascia, they receive lymphatics from all the pelvic viscera, from the deeper parts of the perineum, including the membranous and spongy portions of the urethra, and from the gluteal region and dorsum of the thigh. An obturator node is sometimes seen in the upper part of the ob¬ turator foramen. The efferent vessels of the internal iliac group end in the common iliac nodes. sacral nodes. Five or six sacral nodes lie in the cavity of the sacrum, in relationship to the median and lateral sacral arteries (Figs. 10-30 to 10-32; 10-34). They receive lymphat¬ ics from the rectum and posterior wall of the pelvis, and pass to the internal iliac and lum¬ bar nodes.

LYMPHATIC VESSELS AND NODES OF THE ABDOMEN AND PELVIS

909

Inferior diaphragmatic nodes Thoracic duct Lumbar lymphatic trunks Right lateral aortic nodes (lumbar) Preaortic nodes (renal) Right lateral aortic nodes (lumbar)

Common iliac nodes (medial group anterior to the sacral promontory)

Preaortic nodes (renal)

Left lateral aortic nodes (lumbar)

Preaortic nodes (inferior mesenteric) Left lateral aortic nodes (lumbar) Common iliac nodes (lateral chain) Common iliac nodes (posterior chain)

External iliac nodes (adjacent to femoral ring)

External iliac nodes (lateral chain) External iliac nodes (adjacent to femoral rin 9) Internal iliac nodes

LymphaLic nodes of Lhe pelvis and posterior abdominal wall. (From Rouvier, H., Anatomie Humaine, 7th ed., Masson, Paris, 1954.)

Fig. 10-35.

lumbar nodes. The lumbar nodes are numerous and consist of right and left lateral aortic, preaortic, and retraaortic groups. Right and Left Lateral Aortic Nodes. The right lateral aortic nodes are situated partly anterior to the inferior vena cava, near the termination of the renal vein, and partly pos¬ terior to it on the origin of the psoas major muscle, and on the right crus of the dia¬ phragm. The left lateral aortic nodes form a chain on the left side of the abdominal aorta, in front of the origin of the psoas major and left crus of the diaphragm (Figs. 10-22; 10-24; 10-30; 10-31; 10-35; 10-36). On both sides of the midline, the lateral aortic nodes receive lymphatic vessels from the common iliac nodes; from the testis in the male or from the ovary, uterine tube, and body of the uterus in the female; from the kidney and suprarenal glands; and from lymphatics draining the lateral abdominal muscles and accompanying the lumbar veins. Most of the efferent vessels of the lat¬ eral aortic nodes converge to form the right

and left lumbar trunks, which join the cisterna chyli, but some enter the preaortic and retroaortic .nodes, and others pierce the crura of the diaphragm to join the lower end of the thoracic duct. Preaortic Nodes. The preaortic nodes are divided into celiac, superior mesenteric, and inferior mesenteric groups, arranged around the origins of the corresponding arteries (Figs. 10-22; 10-33; 10-35; 10-36). They receive a few vessels from the lateral aortic nodes, but their principal afferent vessels are de¬ rived from the viscera supplied by the three arteries with which they are associated. Some of their efferent vessels pass to the retroaortic nodes, but the majority unite to form the intestinal trunk, which enters the cisterna chyli. Retroaortic Nodes. The retroaortic nodes are placed below the cisterna chyli on the bodies of the third and fourth lumbar verte¬ brae. They receive lymphatic trunks from the lateral and preaortic nodes, and their ef¬ ferent vessels end in the cisterna chyli.

910

THE LYMPHATIC SYSTEM

Fig. 10-36. Lymphadenogram showing the parietal lymph nodes of the pelvis and of the posterior abdominal wall. 1, External iliac nodes; 2, internal iliac nodes; 3, common iliac nodes; 4, lateral aortic (lumbar) nodes; 5, preaortic (lumbar) nodes. (From Gooneratne, B. W. M., Lymphography—Clinical and Experimental, Butterworth and Co. Ltd., London, 1974.)

Lymph Nodes of the Abdominal Organs

The lymph nodes of the abdominal organs are frequently referred to as the visceral nodes of the abdomen. They are closely as¬ sociated with the blood vessels, either being clustered in groups at the origin of the ves¬

sels, or forming chains along the courses of their branches. The three principal groups of nodes into which lymph from most of the abdominal visceral nodes eventually drains before entering the cisterna chyli or the tho¬ racic duct are the celiac, superior mesen¬ teric, and inferior mesenteric sets of

LYMPHATIC VESSELS AND NODES OF THE ABDOMEN AND PELVIS

preaortic nodes. These surround the roots of the large and similarly named unpaired ar¬ teries, allowing convenient classification of the outlying chains of nodes along branches or subbranches of these vessels (Fig. 10-22). CELIAC NODES

The celiac nodes include those nodes that drain the stomach, greater omentum, liver, gallbladder, and spleen, and most but not all of the lymph from the pancreas and duode¬ num. The celiac nodes are divided into the following sets: Left gastric Right gastric Hepatic Pyloric Pancreaticosplenic LEFT gastric nodes. The left gastric nodes follow the course of the left gastric artery and consist of the following three groups: upper, lower, and paracardial (Figs. 10-25; 10-26). The upper left gastric nodes lie at the root of the left gastric artery, where it branches from the celiac trunk. The lower left gastric nodes accompany the descending branches of the artery along the cardiac half of the lesser curvature of the stomach, be¬ tween the two layers of the lesser omentum. The paracardial group of celiac nodes is lo¬ cated around the cardiac end of the stomach in a radial manner, comparable to a chain of beads. The left gastric nodes receive afferent vessels from the stomach, and their efferent channels pass to the celiac group of preaortic nodes. RIGHT gastric nodes. The right gastric nodes lie between the leaves of the lesser omentum, along the course of the right gas¬ tric artery. They drain the lower end of the lesser curvature and their efferent vessels pass to the hepatic nodes (Figs. 10-25; 10-26). hepatic nodes. The hepatic nodes are located between the two layers of the lesser omentum and course along the common hepatic artery and its right and left hepatic branches as far as the porta hepatis (Fig. 1025). One node of this group is placed near the neck of the gallbladder and is known as the cystic node. A few additional nodes descend along the common bile duct as far as the head of the pancreas. The nodes of the he¬ patic chain receive afferent vessels from the stomach, duodenum, liver, gallbladder, the

91 1

bile ducts, and pancreas. Their efferent channels join the celiac group of preaortic nodes. pyloric nodes. The pyloric nodes lie ad¬ jacent to the head of the pancreas and along the medial border of the superior end of the descending part of the duodenum (Figs. 1025; 10-26). They are located in close relation¬ ship to the pylorus of the stomach, and at the site of bifurcation of the gastroduodenal ar¬ tery. They receive afferent vessels from the pylorus of the stomach, the superior part of the duodenum, as well as from the right gastroepiploic nodes, which course between the layers of the greater omentum, along the greater curvature of the stomach with the right gastroepiploic artery (Fig. 10-25). Their efferent channels drain to the hepatic nodes and the celiac group of preaortic nodes, as well as to the superior mesenteric group of preaortic nodes. pancreaticosplenic nodes. The pancreaticosplenic nodes accompany the splenic artery and are located adjacent to the poste¬ rior surface and upper border of the pan¬ creas (Figs. 10-25; 10-26). One or two nodes of this group are found in the gastrosplenic lig¬ ament. The nodes at the hilus of the spleen, in addition to receiving channels from the splenic hilum, receive lymphatic vessels from the left gastroepiploic nodes. These lat¬ ter nodes course between the layers of the greater omentum, along the greater curva¬ ture of the stomach. Thus, the pancreatico¬ splenic nodes receive afferent vessels from the stomach, spleen, and pancreas, and their efferent vessels join the celiac group of preaortic nodes. SUPERIOR MESENTERIC NODES

The superior mesenteric nodes, located around the root of the superior mesenteric artery, are numerous and large. They drain the visceral field supplied by branches of the superior mesenteric artery, and this includes part of the head of the pancreas, a portion of the duodenum, the entire jejunum, ileum, appendix, cecum, ascending colon, and most of the transverse colon. These nodes can be divided into the following groups: Mesenteric Ileocolic Right colic Middle colic

912

THE LYMPHATIC SYSTEM

The mesenteric nodes lie between the layers of the mesen¬ tery. They vary in number from 100 to 200, and may be grouped into three sets: one lying close to the wall of the small intestine, among the terminal twigs of the superior mesenteric artery; a second in relation to the loops and primary branches of the vessels: and a third along the proximal portion of the inferior mesenteric arterial trunk. They drain the jejunum and ileum along the intes¬ tinal branches of the superior mesenteric artery. Also, a part of the head of the pan¬ creas and a portion of the duodenum are drained by nodes that course along the infe¬ rior pancreaticoduodenal branch of the su¬ perior mesenteric artery. Efferent vessels from the more proximal mesenteric nodes drain into the superior mesenteric group of preaortic nodes. ileocolic nodes. Ten to twenty ileocolic lymph nodes form a chain around the ileocolic artery (Figs. 10-27; 10-28), but show a tendency to divide into two groups, one near the duodenum and another on the lower part of the trunk of the artery. Where the ileocolic artery divides into its terminal branches, the chain is broken up into several groups: ileal, in relation to the ileal branch of the artery; anterior ileocolic, usually three nodes in the ileocecal fold near the wall of the cecum; posterior ileocolic, mostly placed in the angle between the ileum and the colon, but partly lying dorsal to the cecum at its junction with the ascending colon; and a single appendicular node, between the lay¬ ers of the mesenteriole of the vermiform appendix. These nodes receive lymph from the terminal portion of the ileum, the appen¬ dix and cecum, and from several inches of the proximal portion of the ascending colon. Their efferent channels drain into the infe¬ rior mesenteric group of pancreatic nodes. right colic nodes. The right colic group of superior mesenteric nodes follows the course of the right colic artery and its branches as far as the medial border of the ascending colon. These nodes receive affer¬ ent vessels from paracolic nodes that are spaced along the medial border of the as¬ cending colon. Their efferent vessels pass to the superior mesenteric group of preaortic nodes. middle colic nodes. The middle colic nodes are numerous and accompany the middle colic artery and its branches to the mesenteric

nodes.

transverse colon, between the layers of the transverse mesocolon (Fig. 10-29). They are best developed in the area of the right and left colic flexures. The middle colic nodes receive afferent vessels from the para¬ colic nodes that lie along the mesenteric bor¬ der of the transverse colon. Their efferent vessels course to the superior mesenteric group of preaortic nodes. INFERIOR MESENTERIC NODES

The inferior mesenteric nodes are clus¬ tered around the stem of the inferior mesen¬ teric artery and its branches. They drain the descending colon, sigmoid colon, and the upper part of the rectum, a field consistent with the blood supply of the inferior mesen¬ teric artery. They are divided into the fol¬ lowing groups: Left colic Sigmoid Superior rectal left colic nodes. The left colic nodes lie along the course of the left colic branch of the inferior mesenteric artery, as far as the wall of the descending colon (Fig. 10-29). Along the medial border of the descending colon are found the paracolic nodes, which directly drain the large intestine. Efferent vessels from these nodes lead to the left colic nodes, which, in turn, send their efferent branches to the inferior mesenteric group of preaortic nodes. sigmoid nodes. The sigmoid lymph nodes are located between the layers of the sigmoid mesocolon, along the sigmoid branches of the inferior mesenteric artery (Fig. 10-29). They drain the sigmoid colon through the paracolic nodes that are located along the mesenteric border of the viscus. Efferent vessels from the sigmoid nodes terminate in the inferior mesenteric group of preaortic nodes. superior rectal nodes. The superior rectal group of lymph nodes courses along the superior rectal branch of the inferior mesenteric artery (Fig. 10-29). Lymphatic vessels from the rectum course to pararectal nodes, which are oriented longitudinally along the rectum and in contact with its muscular coat. From these nodes, efferent vessels pass to the superior rectal nodes, which then drain to the inferior mesenteric group of preaortic nodes.

LYMPHATIC VESSELS AND NODES OF THE LOWER LIMB

Lymphatic Vessels and Nodes of the Lower Limb Most of the lymphatic vessels of the lower limb ascend either superficial or deep to groups of inguinal lymph nodes that lie in the upper anterior thigh, just below the in¬ guinal ligament. Intermediate nodes are also found in the anterior leg and popliteal fossa, along the course of major blood vessels. In this section are described initially the lym¬ phatic vessels of the lower limb and then the groups of lymph nodes.

LYMPHATIC VESSELS OF THE LOWER LIMB

The lymphatic vessels of the lower limb consist of two sets, superficial and deep, and their distribution corresponds closely to that of the veins. superficial lymphatic vessels. The su¬ perficial lymphatic vessels of the lower limb lie in the superficial fascia, and are most numerous on the sole of the foot. They are divisible into two groups: a medial, which follows the course of the great saphenous vein, and a lateral, which accompanies the small saphenous vein.

Tibial nerve Semitendinosus muscle Popliteal vein

Semimembranosus muscle

artery

Gracilis muscle

peroneal nerve

Popliteal lymph nodes

Biceps femoris muscle

Small saphenous vein

Semimembranosus muscle

Lateral head of gastrocnemius muscle

Medial head of gastrocnemius muscle

Fig. 10-37.

91 3

Lymph nodes of the popliteal fossa.

914

THE LYMPHATIC SYSTEM

Fig. 10-38.

Lateral view of the right popliteal region. A contrast medium was injected into a superficial lymphatic vessel behind the lateral malleolus. This outlined one of the lymphatic vessels ascending to a popliteal lymph node (marked by a cross) in the upper superficial region of the popliteal fossa. (From Battezzati and Ippolito, The Lymphatic System, John Wiley and Sons, New York, 1972.)

The medial group of superficial vessels is larger and more numerous than the lateral group, and commences on the tibial side and dorsum of the foot (Fig. 10-39). The vessels ascend both anterior and posterior to the me¬

dial malleolus, course up the leg with the great saphenous vein, and pass with it behind the medial condyle of the femur to the groin. These vessels end in the lower set of superficial in¬ guinal lymph nodes (Figs. 10-39; 10-40).

LYMPHATIC VESSELS AND NODES OF THE LOWER LIMB

The lateral group of superficial vessels commences on the fibular side of the foot. Some of these vessels ascend on the anterior aspect of the leg, cross the tibia just below the knee, join the lymphatics on the medial side of the thigh, and end in the lower set of superficial inguinal nodes. Others pass behind the lateral malleolus, and accompa¬ nying the small saphenous vein, enter the popliteal nodes (Figs. 10-37; 10-38). The superficial lymphatic vessels of the dorsal thigh curve around both the lateral and medial aspects of the limb to open into the upper and lower sets of the superficial inguinal nodes. From the lateral gluteal re¬ gion, superficial lymphatic vessels course around the lateral hip region to reach the upper superficial inguinal nodes, while ves¬ sels from the anus and external genitalia (ex¬ cept the glans penis or clitoris) pass medially to the lower set of superficial inguinal nodes. deep lymphatic vessels. The deep lym¬ phatic vessels are few in number and accom¬ pany the deep blood vessels. In the leg, they consist of three sets, the anterior tibial, pos¬ terior tibial, and peroneal, that accompany the corresponding blood vessels. Each of the sets consists of two or three lymphatic chan¬ nels, and these enter the popliteal lymph nodes. The deep lymphatic vessels of the gluteal and ischial regions follow the course of the corresponding blood vessels. Those accom¬ panying the superior gluteal vessels end in a node that lies on the intrapelvic portion of the superior gluteal artery, near the upper border of the greater sciatic foramen. Those following the inferior gluteal vessels tra¬ verse one or two small nodes that lie below the piriformis muscle and end in the internal iliac nodes.

91 5

Superficial inguinal (upper group) Superficial inguinal (lower group)

Great saphenous vein

lymph nodes of the lower limb

The lymph nodes of the lower limb consist of the following: Anterior tibial node Popliteal nodes Superficial inguinal nodes Upper group Lower group Deep inguinal nodes The anterior tibial node is small and inconstantly found. When present, it lies on the interosseous memanterior tibial node.

Fig. 10-39. The superficial inguinal lymph nodes and lymphatic vessels of the lower limb.

916

the lymphatic system

sels to the deep inguinal nodes, but a few may accompany the great saphenous vein and end in the superficial inguinal nodes.

INGUINAL NODES

Fig. 10-40.

Normal lymphogram of the right inguinal region. 1, Superficial upper inguinal nodes; 2, deep ingui¬ nal nodes; 3, superficial lower inguinal nodes. (From de Roo, T., Atlas of Lymphography, J. B. Lippincott, Phila¬ delphia, 1975.)

brane, between the tibia and fibula, adjacent to the anterior tibial vessels. It constitutes a substation in the course of the anterior tibial lymphatic trunks. popliteal nodes. Six or seven small pop¬ liteal nodes are embedded in the fat of the popliteal fossa (Figs. 10-37; 10-38). One lies immediately beneath the popliteal fascia, near the terminal part of the small saphe¬ nous vein, and drains the region from which this vein derives its tributaries. Another is placed between the popliteal artery and the posterior surface of the knee joint; it re¬ ceives the lymphatic vessels from the knee joint, together with those that accompany the genicular arteries. The others lie at the sides of the popliteal vessels, and receive as afferents the trunks that accompany the an¬ terior and posterior tibial blood vessels. Most of the efferent channels of the popliteal nodes course upward along the femoral ves¬

The inguinal lymph nodes are located below the inguinal ligament in the upper anterior and medial thigh (Figs. 10-39; 10-40). These are the principal terminal nodes of the lower limb and they receive most of the ef¬ ferent lymphatic channels from the foot, leg, and thigh. There are 12 to 20 inguinal nodes and they are divided into superficial and deep inguinal sets. Of these, the superficial inguinal nodes are more numerous and con¬ sist of upper and lower groups. superficial inguinal nodes. The superfi¬ cial inguinal lymph nodes lie in the fat be¬ tween the skin and deep fascia, distal to the inguinal ligament. These nodes are divided into an upper group, forming a chain paral¬ lel to the inguinal ligament and extending from the anterior superior iliac spine to the femoral vessels, and a lower group, found in the superficial fascia surrounding the termi¬ nal part of the great saphenous vein (Figs. 10-39; 10-40). The upper group of superficial inguinal nodes, consisting of five or six nodes, re¬ ceives afferent lymphatic channels from the superficial structures of the gluteal region and from the superficial fascia of the ante¬ rior abdominal wall, below the umbilicus. Additionally, they receive superficial affer¬ ent channels from both the external geni¬ talia and from the perianal region of the perineum. The lower group of four or five superficial inguinal nodes (formerly called superficial subinguinal nodes) receives most of the su¬ perficial afferent lymphatic channels of the lower limb, as well as a few superficial ves¬ sels from both the urogenital and anal re¬ gions of the perineum. Some efferent vessels from the superficial inguinal nodes drain to the deep inguinal nodes through the cribriform fascia, but most efferent channels pass into the pelvis by way of the femoral canal to the external iliac nodes. deep inguinal nodes. The deep inguinal lymph nodes vary from one to three in num¬ ber, and are located deep to the fascia lata, on the medial side of the femoral vein (Fig.

THE SPLEEN

10-40). When three are present, the lowest node is situated just below the junction of the great saphenous and femoral veins, the intermediate node lies within the femoral canal, and the highest node (also known as the node of Cloquet1 or Rosenmuller2) is lo¬ cated in the lateral part of the femoral ring. Of these, the intermediate node is the most inconstant of the three, but the highest is also frequently absent. The deep inguinal nodes receive afferent channels from the deep lymphatic vessels that accompany the femoral artery and vein, other lymphatic vessels from the glans penis or glans clitoris, and some efferent channels from the lower group of superficial lymph nodes. Efferent channels from the deep inguinal nodes pass through the femoral canal to the external iliac nodes.

The Spleen The spleen, a freely movable organ that is largely invested by peritoneum, is situated principally in the left hypochondriac region of the abdomen. Its posterior extremity ex¬ tends into the epigastric region, and it is usually located between the fundus of the stomach and the diaphragm. It is soft and friable, highly vascular, and dark purplish. Although during fetal life and shortly after birth the spleen gives rise to new red blood corpuscles, this is not thought to occur nor¬ mally in the adult human organ. Hemopoie¬ sis does occur, however, in the spleens of many other adult vertebrates. The spleen, like certain other lymphoid organs, trans¬ forms lymphocytes into cells that produce antibodies or participate in cell-mediated immunologic reactions. Additionally, the spleen contains many macrophages that de¬ stroy old red blood cells, the hemoglobin of which is transformed into bilirubin and re¬ used by the body. The size and weight of the spleen are li¬ able to extreme variations at different peri¬ ods of life, in different individuals, and in the same individual under different condi¬ tions. In the adult, it is usually about 12 cm

'Jules Germain Cloquet (1790-1883): A French anatomist and surgeon (Paris). 2Johann Christian Rosenmuller (1771-1820): A German anatomist and surgeon (Leipzig).

91 7

in length, 7 cm in breadth, and 3 or 4 cm in thickness. The spleen increases in weight from 17 gm or less during the first year after birth to 170 gm at 20 years, and then slowly decreases to 122 gm at 76 to 80 years of age. Male spleens weigh more than female, and the variation in weight of adult spleens is from 100 to 250 gm, and in extreme in¬ stances, 50 to 400 gm. The size of the spleen increases during and after digestion, and varies according to the state of nutrition of the body, being large in well fed, and small in starved animals. In a patient with malarial fever it becomes much enlarged, weighing occasionally as much as 9 kg.1

DEVELOPMENT OF THE SPLEEN

The spleen appears initially as several clusters of mesenchymal cells between the layers of the dorsal mesogastrium, near the tail of the pancreas during the fifth week (6-mm stage). These cellular aggregates be¬ come vascularized and soon fuse to form a lobulated structure. Evidence of this lobulation is still indicated in the adult spleen by notches usually present along the superior margin. With the rotation of the stomach, which results in the greater curva¬ ture being directed toward the left, the spleen is also carried to the left, and lies be¬ hind the stomach and in contact with the left kidney. The part of the dorsal mesogastrium that intervened between the spleen and the kidney becomes the lienorenal ligament, while that part between the spleen and the greater curvature of the stomach forms the gastrosplenic ligament.

Simple agen¬ of the spleen, splenic agenesis associ¬ ated with cardiac defects, the occurrence of several spleens, each of good size (poly¬ splenia), the existence of a normal spleen with accessory small spleens, and the ec¬ topic location of splenic tissue in the scro¬ tum (splenogonadal fusion) that descended with the testis are abnormalities in develop¬ ment that have been described (Gray and Skandalakis, 1972). anomalies in development.

esis

1 These data are taken from the monograph entitled The Structure and Use of the Spleen by Henry Gray, which was published in 1854 and won the triennial "Astley Cooper Prize” of £300 in 1853.

918

THE LYMPHATIC SYSTEM

Fig. 10-41.

The visceral surface of the spleen.

RELATIONSHIPS OF THE ADULT SPLEEN

The spleen has two surfaces, diaphrag¬ matic and visceral; two margins, superior and inferior; and two extremities, anterior and posterior (Figs. 10-41; 10-42). diaphragmatic surface. The diaphrag¬ matic surface of the spleen is smooth, con¬ vex, and directed upward, backward, and to the left, except toward its posterior extrem¬ ity, where it is directed slightly medially. This surface is adjacent to the abdominal aspect of the diaphragm, which separates the spleen from the ninth, tenth, and elev¬ enth ribs of the left side, and the intervening caudal border of the left lung and pleura (Fig. 10-42,C). visceral surface. The visceral surface of the spleen is oriented toward the abdominal cavity, and it has gastric, renal, and colic areas (Fig. 10-41). Gastric Area. The gastric area of the vis¬ ceral surface of the spleen is directed anteri¬ orly, upward, and medially (Fig. 10-41). It is broad and concave, and is in contact with the dorsal wall of the stomach, and below this, with the tail of the pancreas. It has near

its medial border a long fissure, or more fre¬ quently a series of depressions, termed the hilus. This is pierced by several irregular apertures for the entrance and exit of vessels and nerves. Renal Area. The renal area of the visceral surface of the spleen is somewhat flattened and separated from the gastric area by an elevated ridge along the hilus. It is directed medially and downward and it is considera¬ bly narrower than the gastric area (Fig. 1041). It is in anatomic relationship to the upper part of the anterior surface of the left kidney and occasionally with the upper as¬ pect of the left suprarenal gland. Colic Area. The colic area of the visceral surface of the spleen is flat and triangular. It rests on the left flexure of the large colon and the phrenicocolic ligament, and it is fre¬ quently in contact with the tail of the pan¬ creas (Fig. 10-41). borders of the spleen. The superior border is free, sharp, thin, and often notched, and it separates the diaphragmatic surface from the gastric area of the visceral surface. The inferior border is more rounded and more blunt than the superior border

THE SPLEEN

(Fig. 10-41). It separates the renal area of the visceral surface from the diaphragmatic sur¬ face, and it corresponds to the lower border of the eleventh rib, lying between the dia¬ phragm and left kidney. extremities of the spleen. The posterior extremity is rounded and directed toward the vertebral column. The anterior extremity is broader and more expanded than the pos¬ terior (Fig. 10-41), extending between the superior and inferior borders and separating the colic area of the visceral surface from the diaphragmatic surface. PERITONEAL ATTACHMENTS. The Capsule of the spleen is completely covered, except at the hilus, by a closely adherent layer of vis¬ ceral peritoneum. Developing between the layers of the dorsal mesogastrium, the spleen divides this mesentery into two portions. One extends between the stomach and the spleen and is called the gastrosplenic liga¬ ment. The other is interposed between the spleen and the dorsal body wall and is called the phrenicolienal ligament (Fig. 10-42,A). The lower part of the phrenicolienal liga¬ ment, called the lienorenal ligament, extends to the left kidney, and between its layers are found the tail of the pancreas and the sple¬ nic vessels and nerves that course through the hilus of the spleen (Fig. 10-42,B). Be¬ tween the leaves of the gastrosplenic liga¬ ment are found the short gastric and left gastroepiploic vessels. Because these ligaments form the left boundary of the omental bursa (lesser sac), their outer surfaces are covered by perito¬ neum that surrounds the greater sac and their inner surfaces are covered by perito¬ neum that lines the omental bursa. The spleen itself is covered by greater sac perito¬ neum only, unless the gastrolienal and phrenicolienal ligaments fail to meet at the hilum, in which condition a small area within the hilum may be covered by perito¬ neum that lines the omental bursa. As pointed out previously, near the spleen are frequently found small nodules of sple¬ nic tissue. This is especially so in the gastro¬ splenic ligament and greater omentum, and these nodules may be either isolated or con¬ nected to the spleen by thin bands of splenic tissue. These are called accessory spleens, and their size varies from that of a pea to that of a plum.

919

MICROSCOPIC STRUCTURE OF THE SPLEEN

The spleen is an encapsulated lymphatic organ, but it is unlike the lymph nodes be¬ cause through the sinuses of the spleen venous blood filters, whereas through the sinuses of the lymph nodes the lymphatic fluid filters. CAPSULE AND TRABECULAE

The spleen is invested by two coats: an external serous layer and an internal fibroelastic capsule. From the latter, connective tissue trabeculae penetrate the substance of the spleen, separating it into many small compartments (Fig. 10-43). external serous coat. The external se¬ rous coat is not an intrinsic part of the spleen because it is derived from the peritoneum. It is a thin, smooth layer of mesothelial cells, and it is intimately adherent to the underly¬ ing fibroelastic capsule. It invests the entire organ, except at the hilum and along the lines of reflection of the phrenicolienal and gastrosplenic ligaments. splenic capsule. The spleen is enclosed in a rather heavy fibroelastic capsule that is composed of dense fibrous connective tis¬ sue, is rich in elastic fibers, and contains scattered fibroblasts and some smooth mus¬ cle cells. The capsule closely invests the organ, and at the hilum is prolonged inward upon the vessels in the form of sheaths. From these sheaths, as well as from the inner surface of the fibroelastic capsule, numerous small fibrous bands, called trabeculae, are given off in all directions. Because of the high content of elastic fibers in the capsule, the vascular sheaths, and the trabeculae, the spleen possesses a considerable ability to undergo variations in size. trabeculae. The trabeculae are flattened strands of connective tissue that divide the spleen into many small intercommunicating compartments, each several millimeters in diameter (Fig. 10-43). Containing an even higher number of elastic fibers than the cap¬ sule, the trabeculae are scattered throughout the spleen, thereby forming a complex meshwork. The trabeculae arise from the branching of larger connective tissue sheaths that penetrate the organ at the hilus, while other trabecular strands branch from

920

THE LYMPHATIC SYSTEM

Short gastric vessels (vasa brevia)

Gastrosplenic

!>g.

Spleen

Phrenicocolic

lifl.

Splenic vessels

Left gastro¬ epiploic vessels

Aorta Inf. vena cava " Spleen B Gastro\ splenic lig Lienorenal lig.

I Splenic | pedicle

J

Lesser omentum Greater omentum Gastrosplenic lig. containing: 1 -short gastric vessels 2-left gastro¬ epiploic vessels C

Lienorenal lig containing: 1 -splenic vessels 2-tail of pan¬ creas

Fig. 10-42

The splenic ligaments. A, The gastrosplenic ligament (part of the greater omentum) has been opened to reveal the splenic vessels and the short gastric vessels. B, Cross section through the spleen and fundus of the stomach; observe the gastrosplenic ligament oriented anteriorly and the lienorenal ligament oriented posteriorly. C, The spleen in relationship to the ninth, tenth, and eleventh ribs. Note the cut edges of the gastrosplenic and lienorenal ligaments. (From Thorek, P., Anatomy in Surgery, 2nd ed., J. B. Lippincott, Philadelphia, 1962.)

THE SPLEEN

921

Fig. 10-43.

Transverse section of the spleen, showing the trabecular tissue and the splenic vein and its tributaries. (From Henry Gray, 1854).

the internal capsular surface. Within the compartments outlined by the trabeculae is found the splenic pulp.

SPLENIC PULP

In a cross section of freshly cut spleen, small whitish to gray regions, measuring 0.25 to 1 mm in diameter, are seen scattered throughout a mass of soft, dark reddishbrown tissue. These lighter regions are collectively called the white pulp and indi¬ vidually are known as lymphatic nodules (or Malpighian1 bodies), while the surrounding larger mass of darker tissue is called the red pulp (Fig. 10-44). white pulp. The white pulp of the spleen consists of many small masses of periarterial lymphocytes and other related cells. Arteries that enter the hilum of the spleen course along the trabecular meshwork and branch into smaller vessels. Supporting these smaller vessels are sheaths of reticular fi¬ bers, in the meshes of which are infiltrations of lymphocytes. As the arteries branch, they leave the trabeculae and eventually pene¬ trate the red pulp. As the periarterial lym¬ phatic sheaths surrounding the vessels leave the trabeculae, they become enlarged at cer¬ tain sites to form the lymphatic nodules of Marcello Malpighi (1628-1694): A great Italian micro¬ scope anatomist and embryologist (Bologna, Pisa, and Messina).

the white pulp (Fig. 10-44). The microscopic structure of these nodules, which have com¬ pact masses of lymphocytes enmeshed within a network of reticular fibers, is not significantly different from that of the germi¬ nal centers of lymph nodes. red pulp. The red pulp forms the main substance of the spleen (Fig. 10-44). It is com¬ posed of rich plexuses of tortuous venous sinuses. Between the sinuses are splenic cords that contain diffuse lymphatic cells, which include many macrophages, all the white blood cell types, many erythrocytes, and plasma cells, all enmeshed in a fine net¬ work formed by the processes of stellate re¬ ticular cells. Attached by perpendicular processes to the outer endothelial walls of the venous sinuses, the reticular cell bodies lie suspended within the splenic cords, and come into direct contact with the free cellu¬ lar elements. The macrophages are often large and contain ingested and partly di¬ gested red blood cells and pigment. Between the lymphoid tissue of the white pulp and the sinuses and splenic cords of the red pulp is a marginal zone that shows char¬ acteristics transitional between the two types of splenic tissue. BLOOD VESSELS OF THE SPLEEN arteries. Derived as one of the branches of the celiac trunk, the splenic artery is re¬ markable for its size, being quite large in

922

THE LYMPHATIC SYSTEM

Peritoneum and capsule Lymphatic nodule

Tangential section of a splenic nodule

Splenic nodules (white pulp)

Central arteries (t.s.) in splenic nodules

Trabeculae

Venous sinuses in the red pulp

Trabecular artery

Trabecular veins Splenic cords in the red pulp Trabeculae (t.s.) Sheathed artery Pulp arteries (arterioles)

Central artery (I s ).

Fig. 10-44.

A section through a portion of the human spleen, stained with hematoxylin and eosin. 50 Fiore, M„ Atlas of Human Histology, 5th ed., Lea & Febiger, Philadelphia, 1981.)

proportion to the size of the organ, and also for its tortuous course. It divides into six or more branches, which enter the hilum and ramify throughout its substance. Each of these branches supplies chiefly that region of the spleen in which it ramifies, having no anastomosis with the majority of other branches. They course in the transverse axis of the organ and diminish in size during transit. These initial branches of the splenic ar¬ tery further subdivide into smaller muscular trabecular arteries, which course along the trabecular system (Fig. 10-45). Their adventi¬ tial coat blends with the connective tissue of the trabeculae, and they frequently are de¬ scribed as having trabecular sheaths, which similarly invest the veins emerging at the hilum and the incoming nerves. The trabec¬ ular arteries ultimately leave the trabecular sheaths and their tunica adventitia is re¬ placed by packs of lymphocytes, enmeshed in reticular fibers, which form the white pulp. These vessels are then called the cen¬ tral (or follicular) arteries, and they contain one or two layers of smooth muscle. Central arteries are not accompanied by veins, and despite their name they are usually dis¬

x

• (From di

placed to an eccentric position in the splenic lymphatic nodules (Figs. 10-44: 10-45). As the central arteries branch, they be¬ come reduced in diameter, and their sheaths of lymphoid tissue become considerably thinner. When central arteries become re¬ duced to about 50 jti in diameter, each vessel divides into two to six straight branches called penicillar arteries. These latter ves¬ sels. still surrounded by a single or double layer of lymphocytes, enter the red pulp, course for less than 1 mm. and branch into two or three arterial capillaries. At this point, the arterial capillaries are lined by endothelial cells and have no muscle or adventitial coats, but they do acquire a charac¬ teristic thick sheath that consists of concen¬ trically arranged macrophages and reticular fibers. The diameter of these sheathed capil¬ laries is about 6 to 8 ju. Although found in the human spleen, these capillaries are more prominent in other animals, such as the dog. After a short course, sheathed capillaries branch into normal capillaries. Blood from these fine arterial capillaries reaches the venous sinuses, but exactly how this occurs is still conjectural. Some authors claim that the arterial capillaries are connected with

THE SPLEEN

Gives off capillaries to white pulp.

4.

923

Arteriole continues on to enter red pulp.

Arteriole branch enters primary nodule. According to "open theory," arteriole opens into mesh (pulp cords) between sinusoids.

3. Each branch is ensheathed with dense accumulations of lymphocytes.

Sinusoids.

8. According to "closed theory," arteriole opens directly into sinusoids.

Artery leaves trabecula to enter pulp.

9. Sinusoids empty into veins of red pulp.

Trabecula from hilus with artery

10. These drain into trabecular veins.

and vein.

Fig. 10-45. This diagram illustrates the course of blood within the spleen from arteries at the hilus, through the splenic pulp, the sinusoids, and back through the veins. The labels should be read sequentially from 1 to 10. (From Ham, A. W., Histology, 7th ed„ J. B. Lippincott, Philadelphia, 1974.)

the venous sinuses in a closed system, and that the endothelial lining between them is complete. Other authors maintain that the endothelial connections are incomplete and in this open type of circulation, the arterial blood is thought to enter the splenic lym¬ phatic cords and then to diffuse through the endothelium and into the venous sinuses (Fig. 10-45). The flow through the splenic pulp is controlled by rhythmic contraction and relaxation of individual and groups of arterioles. venous sinuses. The venous sinuses of the red pulp are tortuous channels measur¬ ing 12 to 40 n in diameter. Their walls are formed by long, narrow endothelial cells that are oriented longitudinally along the sinusoid wall. Their nuclei bulge into the lumen; however, their cytoplasmic processes do not form true intercellular junctions. More recent evidence indicates that they do not behave as fixed macrophages, as was

once thought. The endothelial cells are sup¬ ported by circularly arranged reticular fi¬ bers that are continuous with the collagen fibers of the trabeculae. The reticular fibers form rings around the sinusoids. veins. The venous sinuses open into the slender, thin-walled veins of the splenic pulp. These join to form the trabecular veins, which in turn unite to form the six or more branches of the splenic vein emerging from the hilus (Fig. 10-45). LYMPHATIC VESSELS AND NERVES

Although few, if any, lymphatic vessels have been found in the lymphoid tissue of the splenic pulp in the human spleen, they have been described in some other mammals. Lymphatic vessels do exist in the capsule of the human spleen and along the larger trabeculae. They emerge at lymphatic vessels.

924

THE LYMPHATIC SYSTEM

the hilus with the veins and open into sple¬ nic nodes found at the hilus and into pancreaticosplenic nodes along the superior border of the pancreas. nerves. Nerve fibers to the spleen are derived from the celiac plexus and course along the splenic artery to the hilus. These are primarily unmyelinated postganglionic sympathetic fibers that are vasomotor in function. Some fibers from the right vagus nerve, however, also have been found cours¬ ing to the spleen. The nerve fibers enter the spleen at the hilus and course along the ar¬ teries as far as their trabecular and central branches. They terminate not only along the smooth musculature of the vessel walls, but within the splenic pulp as well.

The Thymus The thymus in an infant is a prominent organ, occupying the anterior superior medi¬ astinum, but the thymus in an adult of ad¬ vanced years may be scarcely recognizable because of atrophic changes (Fig. 10-46). It is situated between the sternum and great ves¬ sels, resting on the pericardium and overlap¬ ping somewhat the upper anterior borders of both lungs. At one time, the thymus was thought simply to function as a producer of lymphocytes. Only since the 1960s has the enormous importance of the thymus in the maturation of a competent immunologic sys¬ tem come to light. Although much still needs to be learned, the thymus is now recognized

Trachea Thyroid veins Right vagus Superior vena cava

Fig

10-46.

as perhaps the key organ that contributes to the ability of the body to produce antibodies and to reject foreign tissues and cells.

DEVELOPMENT OF THE THYMUS

During the latter part of the fifth prenatal week, when the developing embryo is only about 10 mm long, the primordia of the thy¬ mus appear on the anterior aspect of the third pharyngeal pouch, one on each side. At this same time, the inferior parathyroid glands develop as small solid masses on the dorsal aspect of the third pouch. Between the sixth and eighth weeks the developing thymus is initially recognized as two hollow endodermal elongations that descend into the thorax and then fuse in front of the de¬ veloping great vessels. At this time, the infe¬ rior parathyroid glands usually separate from the thymus and come to rest on the posterior surface of the thyroid gland. Some¬ times, however, the inferior parathyroid glands do not separate and their continued development occurs within the substance of the thymus, where they come to lie in the anterior mediastinum. The fusion medially of the two thymic diverticula involves only the mesenchymal connective tissue into which the thymic tis¬ sue has grown, and there is no fusion of the parenchyma of the two developing lobes. The pharyngeal opening of each diverticu¬ lum, the thymopharyngeal duct, is soon obliterated, but this stalk may persist for a period of time as a cellular cord. Some in-

Thyroid gland Left common carotid artery Left internal jugular vein Left subclavian vessels

The thymus of a full-term fetus; exposed in situ.

THE THYMIJS

vestigators have claimed that the anterior aspect of the fourth pharyngeal pouch also develops into a small amount of thymic tis¬ sue, but this has not been definitely estab¬ lished as a routine occurrence. As the lobules continue to increase in size, their peripheral zones form the cortex of the thymus, in which many small lymphocytes are concentrated, and their central zones form the medulla, in which the cellular re¬ ticulum predominates. The thymus attains a weight of 12 to 14 gm before birth, but it does not reach its greatest relative size until the age of two years. It continues to grow until puberty, at which time it reaches its greatest absolute size, weighing about 35 gm. After adolescence it begins its process of involu¬ tion. histogenesis of the thymus. The cellu¬ lar differentiation of the thymus commences when endodermal epithelial cells form solid cords that grow caudally into the surround¬ ing mesenchyme tissue. Soon the tubular masses of epithelial cells are penetrated by blood vessels, and the cells change their shape into stellate cells. They still remain attached to each other by cellular processes, but what results is a cytoreticular meshwork arrangement. Some of the epithelial cells, instead of contributing to the cytoreticular meshwork, become arranged in concentric, spherical clusters called thymic corpuscles (or Hassall’s1 bodies), the centers of which appear to show degenerative changes (Fig. 10-49). At about the eighth prenatal week, lym¬ phocytes appear in the developing epithelial cytoreticular meshwork, filling the intersti¬ tial spaces between the epithelial cells. At one time some investigators believed that these lymphocytes were derived from the epithelial cells themselves, while others thought that they came from the mesen¬ chymal cells. The weight of evidence now indicates, however, that the thymus (like the developing spleen, liver, and bone marrow) receives stem cells from the yolk sac in the embryo, whereas after birth the stem cells come from the bone marrow. These reach the thymus by way of the blood stream and they begin to differentiate into small lym¬ phocytes, which in the thymus are called thymocytes. During embryogenesis, the pro1 Arthur H. Hassall (1817-1894): An English physician and botanist (London).

925

liferation of thymocytes occurs at a high rate and large numbers of these leave the thymus to reside at many sites elsewhere in the body.

relationships of the thymus

The thymus consists of two lateral lobes that are held in close contact by connective tissue, which also encloses the whole organ in a distinct capsule. It is situated partly in the thorax and partly in the neck, extending from the fourth costal cartilage to the lower border of the thyroid gland (Fig. 10-46). In the neck, it lies anterior and lateral to the trachea, and deep to the origins of the ster¬ nohyoid and sternothyroid muscles. In the thorax, it occupies the anterior portion of the superior mediastinum; superficial to it is the sternum, and deep to it are the great ves¬ sels and the upper part of the fibrous peri¬ cardium. The two lobes generally differ in size and shape, the right frequently overlap¬ ping the left. The thymus has a pinkish gray color, is soft and tabulated, and at birth measures approximately 5 cm in length, 4 cm in width, and 6 mm in thickness. Of greater importance, however, is its weight at differ¬ ent periods of maturation from birth through adulthood and senility (described previ¬ ously), at which times the organ alters signif¬ icantly in size.

MICROSCOPIC STRUCTURE OF THE THYMUS

The two lobes of the thymus are com¬ posed of numerous lobules, varying from 0.5 to 2 mm in diameter, which are incompletely separated from each other by delicate con¬ nective tissue. The parenchymal cells of one lobule are joined to those of adjacent ones by thin cellular interconnections. The lob¬ ules can be seen on stained sections with the unaided eye. Using low power magnifica¬ tion, two zones of tissue can be seen within each lobule, an outer cortex and an inner medulla (Fig. 10-47). The cortical part consists primarily of a network of stellate reticular cells and their processes, which differentiated from endo¬ dermal epithelial cells, and numerous closely packed aggregations of lymphocytes called thymocytes, which occupy the spaces within the cytoreticulum (Fig. 10-48). The

926

THE LYMPHATIC SYSTEM

Interlobar connective tissue Cortex Medulla Capsule

Fig. 10-47.

Section of thymus from full-term fetus, lightly stained with hematoxylin. 5 X-

medullary portion of a thymic lobule con¬ tains reticular cells of varying shapes. Whereas some maintain the stellate charac¬ teristics of reticular cells found in the cortex, others become elongated, somewhat flat¬ tened, and circularly arranged in lamellae to form the thymic corpuscles, which measure 0.03 to 0.10 mm in diameter (Fig. 10-49). The central core of these corpuscles consists of granular cells that appear to be degenerat¬ ing. The medulla contains many fewer lym¬ phocytes than the cortex. The stroma of the thymus consists of a thin investing capsule and interlobular con¬ nective tissue septa, in which are found the blood vessels and nerves supplying the organ. vessels and nerves. The thymic arteries are derived from mediastinal branches of the internal thoracic artery, and from branches of the inferior thyroid arteries. The thymic veins drain into the left brachioce¬ phalic, the internal thoracic, and the inferior thyroid veins. From the interlobular septa, smaller arteries enter the depths of the lobu¬ lar parenchyma along the cortical-medullary border. From these vessels capillaries pene¬ trate and ramify within the cortex, while other small vessels course into the medulla. The returning capillaries and venules merge in a comparable manner and return to the interlobular septa in a similar course. The lymphatic vessels that drain the thy¬ mus terminate in parasternal, anterior medi¬ astinal. and tracheobronchial lymph nodes. The nerves that supply the thymus are very small and are derived from both sym¬

pathetic and vagal branches. Also distrib¬ uted to the capsule of the thymus, but not penetrating the substance of the gland, are small branches from the phrenic nerves and from the superior root of the ansa cervicalis. involution of the thymus. The thymus commences gradual involutionary changes in early childhood, and this process is accel¬ erated after puberty. This is a normal change and it is called age involution, but it may be superseded by a rapid accidental involution due to excessive stress, starvation, ionizing radiation, or acute disease. The small lym¬ phocytes of the cortex disappear and the reticular tissue becomes compressed. The disappearing thymic tissue is likely to be replaced by adipose tissue, but the connec¬ tive tissue capsule persists, retaining its orig¬ inal shape. With age the weight of the thy¬ mus is usually reduced significantly, and in an older individual what appears to be a yel¬ lowish-colored thymus, when sectioned, will reveal only small islands of thymic tissue surrounded by fat. functions of the thymus. Only recently has the importance of the thymus been ap¬ preciated. One of the most exciting fields of research in the latter half of the twentieth century has been the work that has eluci¬ dated the cellular and humoral mechanisms by which the body achieves and maintains its immunologic defense. At one time it was thought that the thymus quite simply pro¬ duced lymphocytes. Although this is one of its most important functions, it was not then realized how essential these specific lym¬ phocytes, and probably certain humoral se-

THE THYMUS

927

Capsule

Secondary (incomplete) trabeculae

Interlobular trabeculae

edulla continuous in three lobules

obule sectioned tangentially Cortex

Thymic corpuscles (Hassall’s corpuscles)

Medulla

Cortex

Lobule

;lnterlobular trabeculae

Blood vessels in trabeculae

Fig. 10-48. Low power view of the thymus showing its lobular structure. Note the darker cortical regions of each lobule surrounding the lighter medullary regions. Hematoxylin and eosin, 40 X- (From di Fiore, M., Atlas of Human Histology, 5th ed., Lea & Febiger, Philadelphia, 1981.)

Venule

Capillary

Medulla (thymic lymphocytes and stroma) Aggregations of epithelial reticular cells Thymic corpuscle (Hassall's corpuscle)

Trabecula-

Cortex lymphocytes)

Degenerating center of thymic corpuscle Epithelial reticular cells in continuity with cells of the thymic corpuscle Epithelial reticular cells in the stroma

Fig. 10-49. A medium-power view of the medullary region of a thymic lobule showing a thymic corpuscle (Hassall's body). Hematoxylin and eosin, 250 X- (From di Fiore, M., Atlas of Human Histology, 5th ed. Lea & Febiger, Philadel¬ phia, 1981.)

928

THE LYMPHATIC SYSTEM

cretions liberated by thymic cells, were to the maturation of the immunologic system. Removal of the thymus at birth results in animals that are immunologically incompe¬ tent. They cannot reject transplanted grafts, and being defenseless to the normal anti¬ genic challenges of the environment, they soon die. Further, these animals show a defi¬ ciency of lymphocytes in the spleen, lymph nodes, and blood.

The epithelial (reticular) cells of the thy¬ mus probably have an endocrine function. It is thought that these cells secrete a hormone(s) that induces a capacity in lympho¬ cytes, both of the thymus itself and elsewhere, and in plasma cells to form anti¬ bodies in response to antigens.

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.) Embryology of the Lymphatic System Ackerman, G. A. 1967. Developmental relationship be¬ tween the appearance of lymphocytes and lympho¬ poietic activity in the thymus and lymph nodes of the fetal cat. Anat. Rec., 158:387-392. Bailey, R. P., and L. Weiss. 1975. Ontogeny of human fetal lymph nodes. Amer. J. Anat., 142:15-28. Cash,). R. 1921. On the development of the lymphatics in the stomach of the embryo pig. Carneg. Inst., Contr. Embryol., 13:1-15. Clark, E. R., and E. L. Clark. 1920. On the origin and early development of the lymphatic system in the chick. Carneg. Inst., Contr. Embryol., 45:449-482. Clark, E. R., and E. L. Clark. 1932. Observations on the new growth of lymphatic vessels as seen in trans¬ parent chambers introduced into the rabbit’s ear. Amer. J. Anat., 51:49-87. Gray, S. W.. and J. E. Skandalakis. 1972. Embryology for Surgeons. W. B. Saunders Co., Philadelphia, 918 pp. Huntington, G. S. 1908. The genetic interpretation of the development of the mammalian lymphatic system. Amer. J. Anat., 2:19-45. Huntington, G. S. 1911. The Anatomy and Development of the Systemic Lymphatic Vessels in the Domestic Cat. American Anatomical Memoir No. 1, Wistar Institute of Anatomy and Biology, Philadelphia, 175 pp. Huntington, G. S„ and C. F. W. McClure. 1910. The anat¬ omy and development of the jugular lymph sac in the domestic cat (Felis domestica). Amer. J. Anat., 10:177-311. Kampmeier, O. F. 1928. The genetic history of the valves in the lymphatic system of man. Amer. J. Anat., 40:413-457. Kampmeier, O. F. 1928. On the lymph flow of the human heart, with reference to the development of chan¬ nels and first appearance, distribution, and physiol¬ ogy of their valves. Amer. Heart J., 4:210-222. Lewis, F. T. 1906. The development of the lymphatic sys¬ tem in rabbits. Amer. J. Anat., 5:95-111. Lewis, F. T. 1909. On the cervical veins and lymphatics in four human embryos. With an interpretation of anomalies of the subclavian and jugular veins in the adult. Amer. J. Anat., 9:33-42. McClure, C. F. W. 1915. The development of the lym¬ phatic system in the light of the more recent investi¬

gations in the field of vasculogenesis. Anat. Rec., 9:563-579. Sabin, F. R. 1902. On the origin of the lymphatic system from the veins, and the development of the lymph hearts and thoracic duct in the pig. Amer. J. Anat., 1:367-389. Sabin, F. R. 1904. On the development of the superficial lymphatics in the skin of the pig. Amer. J. Anat., 3:183-195. Sabin, F. R. 1916. The origin and development of the lym¬ phatic system. Johns Hopkins Hosp. Rep., 17:347440.

Lymph Nodes and Lymphocytes Bailey, R. P., and L. Weiss. 1975. Light and electron mi¬ croscopic studies of postcapillary venules in devel¬ oping human fetal lymph nodes. Amer. J. Anat., 143:43-58. Baker, B. L., D. J. Ingle, and C. R. Li. 1951. The histology of the lymphoid organs of rats treated with adrenocorticotropin. Amer. J. Anat., 88:313-349. Borum, K., and M. H. Claesson. 1971. Histology of the induction phase of the primary immune response in lymph nodes of germfree mice. Acta Pathol. Micro¬ biol. Scand. (A), 79:561-568. Brahim, F., and D. G. Osmond. 1973. The migration of lymphocytes from bone marrow to popliteal lymph nodes demonstrated by selective bone marrow la¬ beling with 3H-thymidine in vivo. Anat. Rec., 175:737-746. Clark, S. L., Jr. 1962. The reticulum of lymph nodes in mice studied with the electron microscope. Amer. J. Anat., 110:217-258. Cohen, S., P. Vassalli, B. Benacerraf, and R. T. McCluskey. 1966. The distribution of antigenic and nonantigenic compounds within draining lymph nodes. Lab. In¬ vest., 15:1143-1155. Conway, E. A. 1937. Cyclic changes in lymphatic nod¬ ules. Anat. Rec., 69:487-508. Ehrich, W. E. 1929. Studies on lymphoid tissue, I: The anatomy of secondary nodules and some remarks on the lymphatic and lymphoid tissues. Amer. J. Anat., 43:347-384. Farr, A. G., and P. P. H. De Bruyn. 1975. Macrophagelymphocyte clusters in lymph nodes: a possible sub-

REFERENCES

strate for cellular interactions in the immune re¬ sponse. Amer. J. Anat., 144:209-232. Farr, A. G., and P. P. H. De Bruyn. 1975. The mode of lymphocyte migration through postcapillary venule endothelium in lymph node. Amer. j. Anat., 143:59-92. Ford, W. L., and J. L. Gowans. 1969. The traffic of lym¬ phocytes. Semin. Hematol., 6:67-83. Fujita, T., M. Miyoshi, and T. Murakami. 1972. Scanning electron microscope observation of the dog mesen¬ teric lymph node. Z. Zellforsch. mikrosk. Anat., 133:147-162. Furuta, W. J. 1948. The histologic structure of the lymph node capsule at the hilum. Anat. Rec., 102:213-223. Gowans, J. L. 1966. Lifespan, recirculation and trans¬ formation of lymphocytes. Internat. Rev. Exp. Pa¬ thol., 5:1-24. Gowans, J. L„ and E. J. Knight. 1964. The route of re¬ circulation of lymphocytes in the rat. Proc. Roy. Soc. Lond. B, 159:257-282. Han, S. S. 1961. The ultrastructure of the mesenteric lymph node of the rat. Amer. J. Anat., 109:183-225. Handley, R. S., and A. C. Thackray. 1947. Invasion of the internal mammary lymph glands in carcinoma of the breast. Brit. J. Cancer, 1:15-20. Handley, R. S., and A. C. Thackray. 1949. The internal mammary lymph chain in carcinoma of the breast. Lancet, 2:276-278. Harris, T. N., K. Hummeler, and S. Harris. 1966. Electron microscopic observations on the antibody-produc¬ ing lymph node cells. ). Exp. Med., 123:161-172. Kelly, R. H„ B. M. Balfour, J. A. Armstrong, and S. Grif¬ fiths. 1978. Functional anatomy of lymph nodes. II. Peripheral lymph-borne monocular cells. Anat. Rec., 190:5-22. Marchesi, V. T., and}. L. Gowans. 1964. The migration of lymphocytes through the endothelium of venules and lymph nodes. Proc. Roy. Soc. Lond. B, 159:283290. Meyer, A. W. 1917. Studies on hemal nodes. VII. The development and function of hemal nodes. Amer. J. Anat., 21:375-406. Pinto, S. 1946. Technica de la injection de linfaticos en el animal vivo. Medicine, Madrid, 14:453. Pressman,}.)., and M. B. Simon. 1961. Experimental evi¬ dence of direct communications between lymph nodes and veins. Surg. Gynecol. Obstet., 113:537541. Pressman, J. J., M. B. Simon, K. Hand, and J. Miller. 1962. Passage of fluids, cells and bacteria via direct com¬ munications between lymph nodes and veins. Surg. Gynecol. Obstet., 115:207-214. Reinhardt, W. O. 1946. Growth of lymph nodes, thymus and spleen, and output of thoracic duct lympho¬ cytes in the normal rat. Anat. Rec., 94:197-211. Roitt, I. M., M. F. Greaves, G. Torrigiani, J. Brostoff, and J. H. L. Playfair. 1969. The cellular basis of immuno¬ logical responses. Lancet, 2:367-371. Slonecker, C. E. 1969. H3-leucine incorporation in antigenically stimulated rat popliteal lymph node cells. Anat. Rec., 165:363-378. Sorenson, G. D. 1960. An electron microscopic study of popliteal lymph nodes from rabbits. Amer. I. Anat., 107:73-96. Stibbe, E. P. 1918. The internal mammary lymphatic glands. J. Anat. (Lond.), 52:257-264.

929

Turner, D. R. 1969. The vascular tree of the haemal node in the rat. J. Anat. (Lond.), 104:481-494. White, A., andT. F. Dougherty. 1946. The role of lympho¬ cytes in normal and immune globulin production and the mode of release of globulin from lympho¬ cytes. Ann. N.Y. Acad. Sci., 46:859-882. Yoffey, J. M. 1964. The lymphocyte. Ann. Rev. Med., 15:125-148.

Lymphatic System and Vessels Allen, L. 1943. The lymphatics of the parietal tunica vagi¬ nalis propria of man. Anat. Rec., 85:427-433. Allen, L. 1967. Lymphatics and lymphoid tissue. Ann. Rev. Physiol., 29:197-224. Bartlett, R. W., G. Crile, Jr., and E. A. Graham. 1935. A lymphatic connection between the gall bladder and liver. Surg. Gynecol. Obstet., 61:363-365. Batlezzati, M., and D. Ippolito. 1972. The Lymphatic Sys¬ tem. [ohn Wiley & Sons, New York, 496 pp. Blair, J. B., E. A. Holyoke, and R. R. Best. 1950. A note on the lymphatics of the middle and lower rectum and anus. Anat. Rec., 108:635-644. Boggon, R. P., and A. J. Palfrey. 1973. The microscopic anatomy of human lymphatic trunks. J. Anat. (Lond.), 114:389-406. Burch, G. E. 1939. Superficial lymphatics of human eye¬ lids observed by injection in vivo. Anat. Rec., 73:443-446. Busch, F., and E. S. Sayegh. 1963. Roentgenographic vis¬ ualization of human testicular lymphatics: A pre¬ liminary report. J. Urol., 89:106-110. Butler, H., and K. Balankura. 1952. Preaortic thoracic duct and azygos veins. Anat. Rec., 113:409-419. Cain, J. C„ J. H. Grindlay, J. L. Bollman, E. V. Flock, and F. C. Mann. 1947. Lymph from liver and thoracic duct: An experimental study. Surg. Gynecol. Ob¬ stet., 85:559-562. Coller, F. A., E. B. Kay, and R. S. McIntyre. 1941. Re¬ gional lymphatic metastases of carcinoma of the stomach. Arch. Surg., 43:748-761. Cuneo, B., and L. Marcille. 1901. Lymphatiques de l’ombilic. Bull. Mem. Soc. Anat. (Paris), 76:580-583. Cuneo, B., and L. Marcille. 1901. Note surles lymphatiques du clitoris. Bull. Mdm. Soc. Anat. (Paris), 76:624-625. Cuneo, B., and L. Marcille. 1901. Topographie des gangli¬ ons ilio-pelviens. Bull. Mem. Soc. Anat. (Paris), 76:653-663. Davis, H. K. 1915. A statistical study of the thoracic duct in man. Amer. J. Anat., 17:211-244. De Roo, T. 1975. Atlas of Lymphography. J. B. Lippincott, Philadelphia, 190 pp. Dixon, F. W., and N. L. Hoerr. 1944. Lymphatic drainage of paranasal sinuses. Laryngoscope, 54:165-175. Edwards, D. A. W. 1946. The blood supply and lymphatic drainage of tendons. J. Anat. (Lond.), 80:147-152. Eliska, O., and M. Eliskova. 1976. Lymph drainage of sinu-atrial node in man and dog. Acta Anat., 96:418-428. Engeset, A. 1959. The route of peripheral lymph to the blood stream. An x-ray study of the barrier theory. J. Anat. (Lond.), 93:96-100. Gilchrist, R. K., and V. C. David. 1938. Lymphatic spread of carcinoma of the rectum. Ann. Surg., 108:621-642. Glover, R., and J. M. Waugh. 1946. The retrograde lym¬ phatic spread of carcinoma of the “rectosigmoid

930

THE LYMPHATIC SYSTEM

region”: Its influence on surgical problems. Surg. Gynecol. Obstet., 82:434-448. Gooneratne, B. W. M. 1972. Lymphatic system in cats outlined by lymphography. Acta Anat., 81:36-41. Gooneratne, B. W. M. 1972. The lymphatic system in rhe¬ sus monkeys (Macaco mulatto) outlined by lower limb lymphography. Acta Anat., 81:602-608. Gooneratne, B. W. M. 1974. Lymphography—Clinical and Experimental. Butterworths, London, 194 pp. Gray, J. H. 1937. The lymphatics of the stomach. J. Anat. (Lond.), 71:492-496. Gray, J. H. 1939. Studies of the regeneration of lymphatic vessels. J. Anat. (Lond.), 74:309-335. Grinnell, R. S. 1942. The lymphatic and venous spread of carcinoma of the rectum. Ann. Surg., 116:200-216. Grinnell, R. S. 1950. Lymphatic metastases of carcinoma of the colon and rectum. Ann. Surg., 131:494-506. Gusev, A. M. 1964. Lymph vessels of human conjunctiva. Fed. Proc., 23.T1099-T1102. Halsell, J., R. Smith, C. Bentlage, O. Park, and J. Hum¬ phreys. 1965. Lymphatic drainage of the breast dem¬ onstrated by vital dye staining and radiography. Ann. Surg., 162:221-226. Holmes, M. )., P. J. O'Morchoe, and C. C. O’Morchoe. 1977. Morphology of the intrarenal lymphatic sys¬ tem. Capsular and hilar communications. Amer. J. Anat., 149:333-351. Jamieson, J. K., and J. F. Dobson. 1907a. The lymphatic system of the cecum and appendix. Lancet, 1:11371143. Jamieson, J. K., and J. F. Dobson. 1907b. The lymphatic system of the stomach. Lancet, 1:1061-1066. Jamieson, J. K., and J. F. Dobson. 1909. The lymphatics of the colon. Proc. Roy. Soc. Med., 2 (Part 3):149-174. Jamieson, J. K„ and J. F. Dobson. 1920. The lymphatics of the tongue: with particular reference to the removal of lymphatic glands in cancer of the tongue. Brit. J. Surg., 8:80-87. Kampmeier, O. F. 1969. Evolution and Comparative Morphology of the Lymphatic System. Charles C Thomas, Springfield, Ill., 620 pp. Kinmonth, J. B. 1952. Lymphangiography in man. A method of outlining lymphatic trunks at operation. Clin. Sci., 11:13-20. Kinmonth, J. B. 1964. Some general aspects of the inves¬ tigation and surgery of the lymphatic system. J. Cardiovasc. Surg., 5:680-682. Leak, L. V. 1970. Electron microscopic observations of lymphatic capillaries and the structural components of the connective tissue-lymph interface. Microvasc. Res., 2:361-391. Leak, L. V. 1972. The transport of exogenous peroxidase across the blood-tissue-lymph interface. J. Ultrastruct. Res., 39:24-42. Leak. L. V., and J. F. Burke. 1968. Ultrastructural studies on the lymphatic anchoring filaments. J. Cell Biol., 36:129-149. Leak, L. V., A. Schannahan, H. Scully, and W. M. Daggett. 1978. Lymphatic vessels of the mammalian heart. Anat. Rec., 191:183-202. Lee, F. C. 1923. On the lymph vessels of the liver. Carneg. Inst., Contr. Embryol., 15:63-72. Miller, W. S. 1896. The lymphatics of the lung. Anat. Anz., 12:110-114. Nesselrod, J. P. 1936. An anatomic restudy of the pelvic lymphatics. Ann. Surg., 104:905-916. Papp, M., P. Rohlich, I. Rusznydk, and I. Toro. 1964. Cen¬ tral chyliferous vessel of intestinal villus. Fed. Proc., 23.T155-T158.

Parker. A. E. 1936. The lymph collectors from the urinary bladder and their connections with the main poste¬ rior lymph channels of the abdomen. Anat. Rec., 65:443-460. Parker, A. E. 1936. The lymph vessels from the posterior urethra, their regional lymph nodes and relation¬ ships to the main posterior abdominal lymph chan¬ nels. J. Urol., 36:538-557. Parker, A. E. 1940. Lymph collectors from the ureters, their regional nodes and relations to posterior ab¬ dominal lymph channels. J. Urol., 43:811-830. Patek, P. R. 1939. The morphology of the lymphatics of the mammalian heart. Amer. J. Anat., 64:203-249. Pflug, J. J., and J. S. Calnin. 1971. The normal anatomy of the lymphatic system in the human leg. Brit. J. Surg., 58:925-930. Pierce, E. C. 1944. Renal lymphatics. Anat. Rec., 90:315335. Powell, T. O. 1944. Studies in the lymphatics of the fe¬ male urinary bladder. Surg. Gynecol. Obstet., 78:605-609. Reiffenstuhl, G. 1964. The Lymphatics of the Female Genital Organs. J. B. Lippincott, Philadelphia, 165 pp. Roenberger, A., and H. Abrams. 1971. Radiology of the thoracic duct. Amer. J. Roentgenol., 111:807-820. Rouviere, H. 1954. Anatomie Humaine, Descriptive et Topographique. 7th ed. vol. 2. Masson, Paris. Rusznyak, I., M. Foldi, and G. Szabo. 1960. Lymphatics and Lymph Circulation, Physiology and Pathology. Pergamon Press, New York, 853 pp. Schatzki, P. F. 1978. Electron microscopy of lymphatics of the porta hepatis. Acta Anat., 102:54-59. Shore, L. R. 1929. The lymphatic drainage of the human heart. J. Anat. (Lond.), 63:291-313. Shrewsbury, M. M., Jr., and W. O. Reinhardt. 1955. Rela¬ tionships of adrenals, gonads, and thyroid to thy¬ mus and lymph nodes, and to blood and thoracic duct leukocytes. Blood, 10:633-645. Simer, P. H. 1935. Omental lymphatics in man. Anat. Rec., 63:253-262. Spirin, B. A. 1964. Internal lymphatic system of penis. Fed. Proc., 23:T159-T167. Teichmann, L. 1861. Das Saugadersystem von anatomischen Standpunkte. W. P. Engelmann, Leipzig. Tobin, C. E. 1957. Human pulmonic lymphatics. Anat. Rec., 127:611-624. Turner-Warwick, R. T. 1959. The lymphatics of the breast. Brit. J. Surg., 46:574-582. Vadja, J., and M. Tomcsik. 1971. The structure of the valves of the lymphatic vessels. Acta Anat., 78:521531. Vadja, J., M. Tomcsik, and W. J. Van Doorenmaalen. 1973. Connections between the venous system of the heart and the epicardiac lymphatic network. Acta Anat., 83:262-274. Van Pernis, P. A. 1949. Variations of the thoracic duct. Surgery, 26:806-809. Wallace, S., et al. 1961. Lymphangiograms: their diagnos¬ tic and therapeutic potential. Radiology, 76:179-199. Weinberg, J., and E. M. Greaney. 1950. Identification of regional lymph nodes by means of a vital staining dye during surgery of gastric cancer. Surg. Gynecol. Obstet., 90:561-567. Wislocki, G. B., and E. W. Dempsey. 1939. Remarks on the lymphatics of the reproductive tract of the fe¬ male rhesus monkey (Macaca mulatta). Anat. Rec., 75:341-362. Yoffey, J. M., and F. C. Courtice. 1956. Lymphatics,

REFERENCES

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Spleen Barcroft, J., and J. G. Stephens. 1936. Observations on the size of the spleen. J. Physiol. (Lond.), 64.T-22. Bennett-Jones, M. J„ and C. A. St. Hill. 1952. Accessory spleen in the scrotum. Brit. J. Surg., 40:259-262. Braithwaite, J. L., and D. J. Adams. 1957. The venous drainage of the rat spleen. J. Anat. (Lond.), 91:352357. Burke, J. S., and G. T. Simon. 1970. Electron microscopy of the spleen. I. Anatomy and microcirculation. Amer. J. Pathol., 58:127-155. Burke, J. S., and G. T. Simon. 1970. Electron microscopy of the spleen. II. Phagocytosis of colloidal carbon. Amer. J. Pathol., 58:157-181. Chen, L. T., and L. Weiss. 1972. Electron microscopy of the red pulp of human spleen. Amer. J. Anat., 134:425-458. Curtis, G. M., and D. Movitz. 1946. The surgical signifi¬ cance of the accessory spleen. Ann. Surg., 123:276298. Edwards, V. D., and G. T. Simon. 1970. Ultrastructural aspects of red cell destruction in the normal rat spleen. J. Ultrastruct. Res., 33:187-201. Galindo, B., and J. A. Freeman. 1963. Fine structure of splenic pulp. Anat. Rec., 147:25-29. Galindo, B., and T. Imaeda. 1962. Electron microscope study of the white pulp of the mouse spleen. Anat. Rec., 143:399-416. Gray, H. 1854. On the Structure and Use of the Spleen. J. W. Parker & Son, London, 380 pp. Halpert, B., and F. Gyorkey. 1959. Lesions observed in the accessory spleens of 311 patients. Amer. J. Clin. Pathol., 32:165-168. Holyoke, E. A. 1936. The role of the primitive mesothelium in the development of the mammalian spleen. Anat. Rec., 65:333-349. Jacobsen, G. 1971. Morphological-histochemical com¬ parison of dog and cat splenic ellipsoid sheaths. Anat. Rec., 169:105-113. Knisely, M. H. 1936. Spleen studies. I. Microscopic obser¬ vations of the circulatory system of living unstimu¬ lated mammalian spleens. Anat. Rec., 65:23-50. Knisely, M. H. 1936. Spleen studies. II. Microscopic ob¬ servations of the circulatory system of living trau¬ matized spleens, and of dying spleens. Anat. Rec., 65:131-148. Krumbhaar, E. B., and S. W. Lippincott. 1939. Postmor¬ tem weight of “normal” human spleen at different ages. Amer. J. Med. Sci., 197:344-358. Lewis, O. J. 1957. The blood vessels of the adult mamma¬ lian spleen. J. Anat. (Lond.), 91:245-250. Mac Kenzie, D. W., Jr., A. O. Whipple, and M. P. Wintersteiner. 1941. Studies on microscopic anat¬ omy and physiology of living trans-illuminated mammalian spleens. Amer. J. Anat., 68:397-456. Mall, F. P. 1900. The architecture and blood vessels of the dog’s spleen. Z. Morphol., 2:1-42. Mall, F. P. 1903. On the circulation through the pulp of the dog’s spleen. Amer. J. Anat., 2:315-332. Michels, N. A. 1942. The variational anatomy of the spleen and splenic artery. Amer. [. Anat., 70:21-72. Miyoshi, M., and T. Fujita. 1971. Stereo-fine structure of

931

the splenic red pulp. A combined scanning and transmission electron microscope study on dog and rat spleen. Arch. Histol. Jpn., 33:225-246. Miyoshi, M., T. Fujita, and J. Tokunaga. 1970. The red pulp of the rabbit spleen studied under the scanning electron microscope. Arch. Histol. Jpn., 32:289-306. Murphy, J. W., and W. A. Mitchell. 1957. Congenital ab¬ sence of the spleen. Pediatrics, 20:253-256. Peck, H. M., and N. L. Hoerr. 1951. The intermediary circulation in the red pulp of the mouse spleen. Anat. Rec., 109:447-477. Sneath, W. A. 1912. An apparent third testicle consisting of scrotal spleen. J. Anat. (Lond.), 47:340-342. Snook, T. 1950. A comparative study of the vascular ar¬ rangements in mammalian spleens. Amer. J. Anat., 87:31-77. Thiel, G. A., and H. Downey. 1921. The development of the mammalian spleen, with special reference to its hematopoietic activity. Amer. J. Anat., 28:279-339. Thomas, C. E. 1967. An electron and light microscopic study of sinus structure in perfused rabbit and dog spleens. Amer. J. Anat., 120:527-552. Weiss, L. 1957. A study of the structure of splenic sinuses in man and the albino rat with the light microscope and the electron microscope. J. Biophys. Biochem. Cytol., 3:599-610. Weiss, L. 1963. The structure of the intermediate vascu¬ lar pathways in the spleen of rabbits. Amer. J. Anat., 113:51-91. Weiss, L. 1973. The development of the primary vascular reticulum in the spleen of human fetuses (38- to 57-mm crown-rump length). Amer. J. Anat., 136:315-338. Williams, R. G. 1961. Studies of the vasculature in living autografts of spleen. Anat. Rec., 140:109-121.

Thymus Abe, K., and T. Ito. 1970. Fine structure of small lympho¬ cytes in the thymus of the mouse: qualitative and quantitative analysis by electron microscopy. Z. Zellforsch. mikrosk. Anat., 110:321-335. Ackerman, G. A., and J. R. Hostetler. 1970. Morphologi¬ cal studies of the embryonic rabbit thymus: The in situ epithelial versus the extrathymic derivation of the initial population of lymphocytes in the embry¬ onic thymus. Anat. Rec., 166:27-46. Ackerman, G. A., and R. A. Knuoff. 1964. Lymphocyte formation in the thymus of the embryonic chick. Anat. Rec., 149:191-215. Auerbach, R. 1961. Experimental analysis of the origin of cell types in the development of the mouse thymus. Devel. Biol., 3:336-354. Burnet, F. M. 1962. The immunological significance of the thymus: an extension of the clonal selection theory of immunity. Australas. Ann. Med., 11:79-91. Castlemann, B. 1966. The pathology of the thymus gland in myasthenia gravis. Ann. N.Y. Acad. Sci., 135:496505. Clark, S. L., Jr. 1963. The thymus in mice of strain 129/J, studied with the electron microscope. Amer. J. Anat., 112:1-33. Colley, D. G., A. Malakian, and B. H. Waksman. 1970. Cellular differentiation in the thymus. II. Thymusspecific antigens in rat thymus and peripheral lymphoid cells. J. Immunol., 104:585-592. Colley, D. G., A. Y. Shih Wu, and B. H. Waksman. 1970. Cellular differentiation in the thymus. III. Surface properties of rat thymus and lymph node cells sepa-

932

THE LYMPHATIC SYSTEM

rated on density gradients. J. Exp. Med., 132:11071121. Csaba, G. Y., I. Toro, and E. Kapa. 19(30. Provoked tissue reaction of the thymus in tissue culture. Acta Morphol. Acad. Sci. Hung., 9:197-202. Dung, H. C. 1973. Electron microscopic study of involuting thymus of “lethargic” mutant mice. Anat. Rec., 177:585-606. Goldschneider, 1., and D. D. McGregor. 1968. Migration of lymphocytes and thymocytes in the rat. I. The route of migration from blood to spleen and lymph nodes. J. Exp. Med., 127:155-168. Good, R. A., et al. 1962. The role of the thymus in the development of immunologic capacity in rabbits and mice. J. Exp. Med., 116:773-795. Good, R. A., and A. E. Gabrielsen (eds.). 1964. The Thy¬ mus in Immunobiology. P. B. Hoeber, New York, 778 pp. Gregoire, C. 1943. Regeneration of the involuted thymus after adrenalectomy. J. Morphol., 72:239-261. Hoshino, T., M. Takeda, K. Abe, and T. Ito. 1969. Early development of thymic lymphocytes in mice, stud¬ ied by light and electron microscopy. Anat. Rec., 164:47-66. Izard, J. 1966. Ultrastructure of thymic reticulum in guinea pig. Cytological aspects of the problem of the thymic secretion. Anat. Rec., 155:117-132. Karetzky, M., and L. E. Rudolf. 1964. Current status of the thymus gland. Surg. Gynecol. Obstet., 119:129138. Keynes, G. 1954. The physiology of the thymus gland. Brit. Med. J., 2:659-663. Mandel, T. 1968. The development and structure of Hassall’s corpuscles in the guinea pig. Z. Zellforsch. mikrosk. Anat., 89:180-192. Mandel, T. 1968. Ultrastructure of epithelial cells in the cortex of guinea pig thymus. Z. Zellforsch. mikrosk. Anat., 92:159-168. Miller, J. F. A. P. 1962. Effect of neonatal thymectomy on the immunological responsiveness of the mouse. Proc. Roy. Soc. Biol. (Lond.), 156:415-428. Miller, J. F. A. P. 1963. Role of the thymus in immunity. Brit. Med. J„ 5355:459-464. Miller, J. F. A. P. 1964. The thymus and the development of immunologic responsiveness. Science, 144:15441551. Miller, J. F. A. P., and D. Osoba. 1967. Current concepts of the immunological function of the thymus. Physiol. Rev., 47:437-520.

Mitchell, G. F., and J. F. A. P. Miller. 1968. Immunological activity of thymus and thoracic-duct lymphocytes. Proc. Nat. Acad. Sci. (USA). 59:296-303. Moore, M. A. S., and J. J. T. Owen. 1967. Experimental studies on the development of the thymus. J. Exp. Med., 126:715-726. Murray, R. G., A. Murray, and A. Pizzo. 1965. The fine structure of the thymocytes of young rats. Anat. Rec., 151:17-40. Norris, E. H. 1938. The morphogenesis and histogenesis of the thymus gland in man. Carneg. Inst., Contr. Embrvol., 27:191-207. Osoba, D. 1972. Thymic function, immunologic defi¬ ciency and autoimmunity. Med. Clin. North Amer., 56:319-335. Sainte-Marie, G. 1974. Tridimensional reconstruction of the rat thymus. Anat. Rec., 179:517-526. Sainte-Marie, G., and F. S. Peng. 1971. Emigration of thymocytes from the thymus. A review and study of the problem. Rev. Canad. Biol., 30:51-78. Sanel, F. T„ 1967. Ultrastructure of differentiating cells during thymus histogenesis. A light and electron microscopic study of epithelial and lymphoid cell differentiation during thymus histogenesis in C57 black mice. Z. Zellforsch. mikrosk. Anat., 83:8-29. Shier, K. J. 1963. The morphology of the epithelial thy¬ mus: Observations on the lymphocyte-depleted and fetal thymus. Lab. Invest., 12:316-326. Small, M., and N. Trainin. 1971. Contribution of a thymic humoral factor to the development of an immunologically competent population from cells of mouse bone marrow, f. Exp. Med., 134:786-800. Smith, C., and H. T. Parkhurst. 1949. Studies on the thy¬ mus of the mammal. II. A comparison of the stain¬ ing properties of Hassall's corpuscles and of thick skin of the guinea pig. Anat. Rec., 103:649-673. Toro, I. 1961. The cytology of the thymus gland. Folia Biol. (Krakow), 7:145-149. Weissman, I. L. 1967. Thymus cell migration. J. Exp. Med., 126:291-304. Weller, G. L., Jr. 1933. Development of the thyroid, para¬ thyroid, and thymus glands in man. Carneg. Inst., Contr. Embryol., 24:93-142. Wilson, A., A. R. Obrist, and H. Wilson. 1953. Some ef¬ fects of extracts of thymus glands removed from patients with myasthenia gravis. Lancet, 2:368-371.

Developmental and Gross

Anatomy of the Central Nervous System

all others. In addition to these more abstract functions of the human brain, which are common to all healthy members of our spe¬ cies, our individualities and the distinctive characteristics that give to each of us an identity and separate us, one from another, are also based in the structure and functions of our own personal nervous system. In this chapter emphasis is placed on the developing nervous system and the gross anatomy of the spinal cord and brain. The detailed internal structure of the nervous system and the broad discipline of neurobi¬ ology and the other neurosciences will not be extensively recounted, for there are many excellent specialized textbooks in which these fascinating fields are handled more appropriately.

Development of the Nervous System The architectural and functional develop¬ ment of the nervous system and the underly¬ ing principles involved collectively form one of the most exciting chapters in all of biology. The descriptive and experimental neuroembryologist has had the task of ex¬ plaining how and why the nervous system develops its infinite complexity. Similarities among the early developmental stages of many of the higher vertebrates have allowed us to gain much information about early human neurogenesis. Formation of Presumptive Neural Derivatives

The human nervous system, having evolved from that of lower animals, accounts more nearly for the behaviors characteristic of people than does any other organ system in the body. Its role in the control and manage¬ ment of most functions of other organs and tissues allows for appropriate reactions to alterations in the environment and, thus, for survival. In this latter respect it functions comparably to the nervous systems of other mammals, but in its highly evolved integra¬ tive, communicative, reflective, creative, and acutely perceptive functions, the human nervous system lends to Man those abilities that have truly elevated our species above

Each of us develops from the single-celled, fertilized ovum. Through successive mitotic divisions, the ovum becomes a fluid-filled ball of cells known as the blastula, within which exists an inner cell mass that is des¬ tined to become the embryo proper. This mass of cells is surrounded by an outer, flat¬ tened, cellular shell known as the trophoblast, which rapidly proliferates and invades the maternal uterine tissue. The use of vital staining techniques has made possible the discovery of regions of the living blastula that become the three primary germ layers: the ectoderm, mesoderm, and endoderm. Along the mid-dorsal line of the embryo at this early stage, there appears a primitive streak, an area of ectoderm where a faster

933

934

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

EMBRYONIC ECTODERM

NEURAL GROOVE

NEURO-ECTODERMAL JUNCTION NEURAL GROOVE

Fig. 11-1. Schematic sections through the neural groove and neural tube in successively older embryos. (Redrawn after W. J. Hamilton and H. W. Mossman, Human Embryology, 4th ed., Williams and Wilkins, Bal¬ timore, 1972.)

proliferation of cells occurs. Because the entire nervous system is ectodermal in ori¬ gin, it is at this time (15 to 17 days after fertilization) that the presumptive neural re¬ gions of the human embryo commence dif¬ ferential transformation. In front of the primitive streak appears the primitive knot (Hensen’s1 node), from which extends the developing notochord. The flat¬ tened layer of ectoderm on the dorsal aspect of the embryo now becomes stratified, and this unequal growth of the neural plate leads to an infolding of the ectoderm and thus the formation of the neural groove (Fig. 11-1,A

1 Victor Hensen (1835-1924): A German embryologist and physiologist (Kiel).

and B). Coursing along the longitudinal axis of the embryo, the neural groove then be¬ comes surrounded by the neural folds. As the process of invagination continues, the neural folds fuse to form the neural tube, the rostral part of which is broader and eventu¬ ally develops into the brain, while the nar¬ row caudal part forms the spinal cord (Fig. 11-1,C and D). The central lumen of the neu¬ ral tube is retained as the ventricular system rostrally and as the central canal of the spi¬ nal cord caudally. neural induction. At these early devel¬ opmental stages, the organization of the por¬ tion of the embryo that is destined to be¬ come the nervous system, i.e. essentially the neural plate and folds, appears to be under the inductive influence of underlying meso¬ dermal elements. In their classic experi¬ ments, Spemann and Mangold (1924) first emphasized the necessity for the mainte¬ nance of physical contact between the neu¬ ral ectoderm and the subjacent mesodermal tissue for normal neural development. When a particular part of an embryo is capable of liberating a chemical substance that causes the surrounding tissue to develop in a cer¬ tain manner, the process is called induction. The biochemical substance is called the evocator, and the property exhibited by the surrounding tissue in response to the evocator is called competence. Because mesoderm at the dorsal lip of the blastopore (and probably tissue in other re¬ gions of the primitive streak) is capable of directly inducing the formation of central neural tissue in the embryo, it is called a pri¬ mary organizer. Although the chemical na¬ ture of the evocator is still unknown, several types of substances have been shown to have inductive effects. The great significance of these early peri¬ ods to the normal development of the com¬ plete mature central nervous system should be stressed. The shifting of only a few cells in the wrong direction, or the failure in growth or closure of a small part of the neu¬ ral tube in an embryo 2 to 3 mm long, can result in embryonic death or serious malfor¬ mation. For example, if the neural groove fails to close, or if having closed, it fails to separate completely from the overlying ecto¬ derm, the development of the associated ver¬ tebrae is also abnormal, and a condition known as spina bifida results.

DEVELOPMENT OF THE NERVOUS SYSTEM

Histogenesis of the Neural Tube

The neural tube eventually separates from the layer of ectoderm that is destined to be¬ come skin and continues to develop subcu¬ taneously. Rapid division and growth in the cephalic end of the neural tube occurs and soon the accumulations of nuclear masses in the walls of the neural tube become recog¬ nizable as forebrain, midbrain, and hind¬ brain. In recent decades the histogenesis of the cellular elements that comprise the central nervous system has become a subject of en¬ hanced scientific interest. For many years the pseudostratified, columnar, neuroepithe¬ lial structure of the very early neural tube, even before its closure, was described as consisting of several cell types. His (1889, 1904) proposed that from these cell types three layers develop: ependymal, mantle, and marginal. In His’ schema, the innermost ependymal layer contains germinal cells that divide to form neuroblasts. These mi¬ grate through a wider layer of spongioblasts (precursors to the neuroglia) to form the mantle layer or gray matter region. The out¬ ermost marginal layer does not contain many cell bodies, but instead consists of many nerve processes (fibers) that eventu¬ ally form the white matter.

935

A more recent and welcome clarification of the terminology, and a variation on the classic schema of His regarding histogenesis of the neural tube, is based on modern electron microscopic and autoradiographic findings (Boulder Committee, 1970). This proposal states that four geographic zones form in the developing vertebrate central nervous sys¬ tem: ventricular, subventricular, intermedi¬ ate, and marginal (Fig. 11-2). Within the ventricular zone, which bor¬ ders the central lumen, a single pseudostrati¬ fied columnar cell type called the ventricu¬ lar cell exists (Fig. 11-2,A). This cellular element is the source of all neurons and macroglia (astrocytes and oligodendroglia) in the central nervous system. The germinal cells and the spongioblasts, which His con¬ sidered different cell types, are in fact mi¬ totic and intermitotic forms of the ventricu¬ lar cell. The Fugitas (1963a, b; 1964) and others have shown that as cells in this inner¬ most ventricular zone (Fugita’s matrix layer) pass through intermitotic and mitotic phases, their nuclei “elevate” away from and then return to the innermost region of the neural tube. During their intermitotic period (DNA synthetic phase), the ventricular cells have an elongated columnar form, and the nuclei are located away from the lumen in FOUR-ZONE

SCHEMA

RECOMMENDED.

Fig 11-2. Schematic drawing of five stages (A-E) in the development of the vertebrate central nervous system, as described in the text. Abbreviations: CP, cortical plate; I, intermediate zone; M, marginal zone; S, subventricular zone; V, ventricular zone. (From Boulder Committee, Anat. Rec„ 116:257-262, 1970.)

936

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

the outer limit of the ventricular zone. When these columnar cells are ready to divide, thereby replicating their DNA, the cells be¬ come spherical, the nuclei move inward toward the surface of the ventricular lumen, and at this deepest portion in the wall of the neural tube, the cells divide. Shortly after the formation of the ventric¬ ular zone, an outermost marginal zone, com¬ posed principally of the cytoplasmic proc¬ esses of the ventricular cells, is recognizable (Fig. 11-2,B). As the ventricular cells con¬ tinue to divide, some newly formed cells migrate outward from the ventricular zone to create an intermediate zone, interposed between the marginal and ventricular zones (Fig. 11-2,C). Certain cells that form this in¬ termediate zone are immature nerve cells that have ceased to divide. As they mature, these cells develop axons and dendrites that course either within the intermediate zone or enter the more outlying marginal zone. In certain parts of the developing neuraxis, such as the anterior region of the spinal cord, the intermediate zone remains rela¬ tively uniform. In the developing cerebrum and cerebellum, however, cell bodies within this zone migrate to form other layers, such as the cortical plate illustrated in Figure 112,D and E. This more recent description of the proc¬ ess also recognizes a subventricular zone that eventually forms between the ventricu¬ lar and intermediate zones (Fig. 11-2,D and E). Migrating to the subventricular zone are round proliferating cells that do not elevate and descend during their intermitotic and mitotic phases. These cells give rise to the adult subependymal neuronal elements, as well as to the adult astrocytes and oligodendroglia, but not to the ependymal cells. From this subventricular zone, the neuroglial ele¬ ments are thought to migrate to all other zones of the embryonic neuraxis. Development of the Spinal Cord

As a result of the proliferation and migra¬ tion of ventricular cells into the intermediate zone, the lateral walls of the neural tube in¬ crease in thickness. In contrast, the roof plate and floor plate become quite thin, and the central lumen is rather narrow and slitlike (Fig. 11-3,B). The ventral part of each lateral wall further enlarges, and the middle portion of the lumen becomes altered on

ROOF PLATE ALAR LAMINA

SULCUS LIMITANS

EPENDYMA BASAL • LAMINA FLOOR PLATE

POST. '•HORN

POST. SEPTUM

DORSAL COLUMN

LAT SR Al COLUMN

EPENDYMA GENERAL VISCERAL EFFERENT ANT HORN ANT. FISSURE

VENTRAL COLUMN

Fig. 11-3. Diagrams illustrating four successive stages in the development of the alar (in black) and basal (in red) laminae of the spinal cord region. (From W. J. Ham¬ ilton and H. W. Mossman, Human Embryology, 4th ed., Williams and Wilkins, Baltimore, 1972.)

each side by the formation of a longitudinal groove, the sulcus limitans (Fig. 11-3). The sulcus indicates the area on the wall of the neural tube at which the dorsal or alar lam¬ ina is separated from the ventral or basal lamina. These laminae represent an early functional differentiation: the alar lamina or alar plate will become the sensory portion of the gray substance, and the basal lamina or basal plate will become the motor portion (Figs. 11-3; 11-4). The basal lamina thickens, and in a cross section the intermediate zone (mantle layer) appears as an expanded region between the marginal and ventricular zones. This thick¬ ening is the rudiment of the ventral gray col¬ umn or ventral horn. Its immature nerve cells send their axons out through the mar¬ ginal layer to form the ventral roots of the spinal nerves (Fig. 11-4). The alar lamina also thickens gradually, becoming the dorsal gray column or dorsal horn. Later, axons from many of these cells grow rostrally and assist in the formation of the dorsal and lat¬ eral white columns or funiculi (Fig. 11-4). A few fibers cross to the opposite side and form the ventral white commissure.

DEVELOPMENT OF THE NERVOUS SYSTEM

937

Roof plate Alar lamina Oval bundle

Dorsal nerve root Central canal Ependymal zone Lateral funiculus Basal lamina

Ventral nerve root Ventral funiculus Floor plate A Fig 11-4. Transverse sections through the spinal cords of human embryos. A, Age about four and a half weeks; B, age about three months. (W. His.)

At the end of about the fourth week, nerve fibers begin to appear in the marginal layer. The first to develop are the short intersegmental fibers, which come from differentiat¬ ing nerve cells in the intermediate zone. Fi¬ bers from the cells in the spinal ganglia also grow into the marginal zone and by the sixth week have formed a well-defined oval bun¬ dle in the peripheral part of the alar lamina (Fig. 11-4). This bundle gradually increases in size and spreads toward the midline from each side; it forms the rudiments of the dor¬ sal funiculi, which are separated by the dor¬ sal median sulcus. Long intersegmental fi¬ bers appear about the third month, and corticospinal fibers appear about the fifth month. Initially, all the nerve fibers are de¬ void of myelin, and the various bundles of fibers become myelinated at different times. Thus, the dorsal and ventral roots acquire myelin about the fifth month, and the corti¬ cospinal fibers, after the ninth month. The expanding growth of the ventral horn and ventral funiculus of the two sides causes these parts to bulge laterally beyond the floor plate, leaving a deep groove, the ventral median fissure, between the two ventral fu¬ niculi. segmentation. Segmentation is the repe¬ tition of structural patterns at successive lev¬ els and is one of the earliest vertebrate char¬ acteristics of the human embryo. The first somites that are formed are the most ce¬

phalic ones; they appear behind the auditory placode during the third week of develop¬ ment. Thereafter, the number of somites in¬ creases rapidly, so that by the fifth week there are already 38 pairs. The most constant of these developing myotomes are the eight cervical, twelve thoracic, five lumbar, and five sacral somites. These become inner¬ vated by the developing spinal nerves and create the segmental organization of the body, providing the basis for segmental re¬ flex activities. Corresponding to the development of the somites, the thickening of the wall of the neural tube is not uniform. This enlargement is somewhat greater at the sites at which the spinal nerves attach to the cord than in be¬ tween, producing a beaded appearance and establishing the neuromeres or segments. The relative thickness of the spinal segments varies according to the size of the nerves and the bulk of the peripheral field that the nerve supplies. There exists no valid evidence to indicate that segmentation is a characteristic inherent in the early neuraxis. In contrast, experimental evidence has shown that seg¬ mentation in the nervous system is deter¬ mined to a large extent by segmentation of the mesodermal somites. On the basis of the segmentation of the axial mesoderm, it is generally accepted that spinal nerve and ganglion segmentation is acquired secondar¬ ily. In later development, the long projection

938

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Body of vertebra

Spinal cord

Cerebrospinal fluid (in subarachnoid space)

Dura mater

Pia mater

Root of first sacral nerve

Arachnoid

Dorsal root ganglion

11-5. Diagrams showing four successive stages in the differential growth of the spinal cord in relation to the vertebral column and meninges. Note the elevation in the position of the caudal end of the cord and the increasing length and obliquity of the first sacral nerve, used here for reference. A, Eighth prenatal week; B, twenty-fourth prenatal week; C, newborn infant; D, adult. (From K. L. Moore, The Developing Human, W. B. Saunders, Philadel¬ phia, 1973.) Fig

tracts grow into the marginal zone, thereby obliterating the segmental appearance of the spinal cord. GROWTH

OF THE

SPINAL CORD WITHIN THE

canal. In embryos during the somite stages and until the third prenatal month, the spinal cord forms a long, slender tube curved to the shape of the embryo and extending its entire length as far as the coc¬ cygeal region (Fig. 11-5). The segmentally arranged spinal nerve roots emerge and enter the spinal cord at levels directly in line with their sites of origin. By the sixth month the caudal end of the cord reaches only as far as the upper part of the sacrum, while at birth it is on a level with the third lumbar vertebra. These positional changes continue during postnatal maturation, so that in the adult, the end of the spinal cord lies at the level of the intervertebral disc between the first and second lumbar vertebrae (Fig. 11-5). This uneven growth and the marked ce¬ phalic flexure of the brain keep the rostral end of the maturing nervous system within vertebral

the cranial cavity. The adult spinal cord gives the appearance of having been pulled upward in the spinal canal, and the spinal nerves below the cervical level become more and more longitudinally displaced within the vertebral canal. Because these nerves must still emerge at their somatic structures through their respective interver¬ tebral foramina, the lower end of the verte¬ bral canal becomes filled with the long coursing roots of the lower spinal segments. These roots are located intradurally, and this region of the cord is called the cauda equina. The finely tapered end of the cord itself, still attached to the most distal part of the vertebral canal in the coccyx, is called the filum terminale (Fig. 11-5). Development of the Spinal Nerves

The continued maturation of young nerve cells in the ventrolateral portion of the inter¬ mediate zone of the spinal cord results in the formation of the ventral roots, whereas the

DEVELOPMENT OF THE NERVOUS SYSTEM

939

Ectoderm Neural crest migrating

Third somite Neural tube Blood vessel

Fig. 11-6.

Neural crest formation. Transverse section through third somite of nine somite rat embryo.

immature neurons in the dorsal root ganglia grow into the cord to form the dorsal roots. ventral roots. As groups of nerve cells that form the gray matter in the basal plate continue to differentiate during the fifth week, they sprout delicate processes that emerge from the ventral horn and form the rudiments of the ventral roots. Many of these fibers, motor in function, course toward masses of differentiating striated muscle cells and eventually make contact. dorsal roots. The dorsal roots, which develop differently than the ventral roots, form differentiating nerve cells in the dorsal root ganglia. During the sixth and seventh prenatal weeks, these young neurons send processes both centrally into the poste¬ rior gray matter of the spinal cord and pe¬ ripherally to structures that are developing within their respective myotomes. The tissue

that forms the spinal ganglia is a ridge of neuroectodermal cells called the neural crest or ganglion ridge. The Neural Crest. The neural crest forms from bands of ectodermal cells that originate early during the development of the nervous system and are located on the sides of the neural folds (Figs. 11-6; 11-7). As the folds begin to fuse, the neural crest cells from both sides form an aggregation of cells along the midline, dorsal to the neural tube and ex¬ tending from the caudal part of the cephalic region all along the developing neuraxis (Fig. 11-7). After a short period of time, the neural crest cells once again become dis¬ placed bilaterally, undergo metameric seg¬ mentation, and begin to differentiate. The proliferating neural crest cells are gathered into paired spherical groups that correspond to each segment and will become the primiNeural crest

Neural crest

Fig. 11 -7. Development of the human neural crest. A, 2.5 mm; B, 5.0 mm; C, 7.5 mm; D, longitudinal diagram of the early spinal cord showing the neural crest as a plate of tissue overlying the neural tube. The neural crest then divides into right and left portions, each of which will further subdivide segmentally. (After L. B. Arey, Developmental Anatomy, revised 7th ed., W. B. Saunders, Philadelphia, 1974.)

940

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

five spinal ganglia. Some of the neural crest cells from the ventral part of each primitive ganglion separate and migrate peripherally to form the sympathetic ganglia and other neural crest derivatives. In addition to the spinal ganglia and the ganglia of the sympathetic system, the neu¬ ral crest gives origin to the parasympathetic ganglia in the head, along with the sensory ganglia associated with the trigeminal, fa¬ cial, glossopharyngeal, and vagus nerves. Also derived from the neural crest are the neurilemma sheath cells of the peripheral nerves. Other neural crest cells become dis¬ persed with the general mesenchyme and are responsible for the melanocytes in the skin, the cells of the adrenal medulla, the chromaffin cell system, and probably certain cartilages in the head. Neurons of the Spinal Ganglia. As just stated, proliferation of the neural crest re¬ sults in the formation of cellular aggrega¬ tions, lateral to the neural tube, that are des¬ tined to become the sensory ganglia (Fig. 11-8,A). The developing neurons within these segmentally arranged ganglia give rise to the sensory fibers of the spinal nerves. During differentiation these nerve cells are initially bipolar due to the development of a primary process at either end. As their matu¬ ration continues, a majority of the cells in

mammals become unipolar as the two pri¬ mary processes fuse into a single stem, which emerges from the neuronal soma (Fig. 11-8,B). Beyond the point of fusion, the axon divides like a T into two primary branches, one of which is directed centrally, and the other, peripherally. The centrally oriented branch grows into the neural tube as a sen¬ sory root fiber. As they penetrate the dorso¬ lateral wall of the neural tube, the sensory fibers bifurcate into ascending and descend¬ ing branches within the marginal zone of the spinal cord. The fibers then enter the devel¬ oping intermediate zone (gray matter) and come into synaptic connection with other maturing nerve cells there. The peripherally directed branches of the spinal ganglion cells become the afferent fibers in the cere¬ brospinal nerves. Within the ganglia, some of the neural crest cells form capsules that surround the ganglion cell bodies. These supporting ele¬ ments, which are disc-like and flattened, are called satellite cells. In contrast to what oc¬ curs in other ganglia, note that neurons in the sensory ganglia of the vestibulocochlear nerve remain bipolar throughout life. NERVE fiber sheaths. The axis cylinders in the developing peripheral nerves soon become surrounded by protective sheaths that are also ectodermal in origin. In the path

Commissural neuron Dorsal funiculus Dorsal (sensory) root

Sensory neuron in spinal ganglion

Lateral funiculus

Inter¬ mediate stages

Motor neuron Unipola Ventral (motor) root Spinal nerve trunk

Ventral funiculus Root fibers

Ventral commissure A

Development of a human spinal nerve. A, Transverse section of the spinal cord and the dorsal and ventral roots in a 7-mm embryo. B, Longitudinal section of a spinal ganglion in an embryo of ten weeks, showing the transfor¬ mation of bipolar ganglion cells into unipolar cells. These two figures come from the studies of S. Ramon y Cajal. (From L. B. Arey, Developmental Anatomy, revised 7th ed„ W. B. Saunders, Philadelphia, 1974.)

Fig. 11-8.

DEVELOPMENT OF THE NERVOUS SYSTEM

of the outgrowing axons can be seen numer¬ ous spindle-shaped ectodermal cells that have migrated from the neural tube and the neural crest along the course of the ventral and dorsal roots. These are the Schwann1 cells; they form not only a prominent morpho¬ logic feature in a developing peripheral nerve, but they also have an important role in the differentiation of the nerve fibers. They form the nucleated sheath, or neuri¬ lemma, of the peripheral nerve, and because they form myelin, they are comparable to the oligodendroglia of the central nervous system. The layers of myelin that form around the developing nerve fibers have been shown by electron microscopy not to be an extracellular substance, as was once believed, but alternating layers of lipids and protein which are plasma membranes of the Schwann cells wrapped around the axis cyl¬ inders in a spiral manner. Although there is no question that the Schwann cells associated with the dorsal roots have a neural crest origin, it has been experimentally inferred that certain sheath cells accompanying the ventral root fibers may originate in the neural tube. Development of the Brain

The cephalic portion of the neural tube enlarges and begins to change its shape even before it is completely closed. The unequal growth in size and thickness of the different parts, together with the formation of certain flexures, establishes at an early stage three recognizable regions within the primitive brain: the rhombencephalon (or hindbrain), the mesencephalon (or midbrain), and the prosencephalon (or forebrain). During the fourth prenatal week in embryos of 3 to 4 mm, the first of the flexures to appear is the midbrain (or cephalic) flexure in the region of the mesencephalon (Fig. 11-9,A). By means of this flexure the forebrain makes a U-shaped bend ventrally over the rostral end of the notochord and foregut, causing the midbrain for a period of time to protrude dorsally as the most prominent part of the brain. The second bend, the cervical flexure, appears at the junction of the hindbrain and spinal cord at nearly the same time as does •Theodore Schwann (1810-1882): A German histologist and physiologist who was a professor at Liege in Bel¬ gium.

941

the midbrain flexure. The cervical flexure continues to develop until the hindbrain and spinal cord form a right angle with each other (Fig. 11-9,A). It then gradually dimin¬ ishes as the body posture changes and the head becomes erect, and it disappears some time after the sixth week. The third bend is named the pontine flexure because it occurs in the region of the future pons (Fig. 11-9,B). In contrast to the midbrain and cervical flex¬ ures, the convexity of the pontine flexure is directed anteriorly. The sulci limitans, which divide the lat¬ eral walls of the spinal cord into alar and basal laminae, clearly extend rostrally through the hindbrain and midbrain. They also divide these brain stem regions of the neuraxis into alar (or dorsal) and basal (or ventral) laminae. The early developing brain, being tubular in nature, contains a cavity that is continu¬ ous throughout the entire neuraxis, from the forebrain above to the lowest regions of the spinal cord. As development progresses and changes occur in the external shape of dif¬ ferent regions of the central nervous system, the shape of the inner cavity also undergoes regional changes. In the forebrain the cavity becomes the lateral ventricles of the cere¬ bral hemispheres and the third ventricle of the diencephalon (Fig. 11-9,C). The lumen narrows throughout the midbrain, eventu¬ ally becoming the cerebral aqueduct, and opens once again as the fourth ventricle in the hindbrain. At the rostral end of the hind¬ brain, a constriction of the cavity results from a transverse invagination called the dorsal rhombencephalic sulcus. This region of the neuraxis is sometimes known as the rhombencephalic isthmus, and its cavity is continuous caudally with the fourth ventri¬ cle, which, in turn, becomes the central canal of the spinal cord (Fig. 11-9,C). THE RHOMBENCEPHALON

When the midbrain flexure appears, the rhombencephalon, or hindbrain, is as long as the forebrain and midbrain combined (Figs. 11-11; 11-12). For descriptive purposes, the rhombencephalon is divided into a more caudal portion called the myelencephalon, which forms the medulla oblongata, and a more cranial part, the metencephalon, which forms the cerebellum and pons. the myelencephalon. The caudal part of

942

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Cervical flexure

A, Flexures of the human brain in 6-mm embryo (early part of fifth week). B, Flexures of the human brain in 14-mm embryo (early part of sixth week). C, Longitudinal hemisection of human brain in an 11-mm embryo (end of fifth week), showing the internal cavities. (Redrawn after L. B. Arey, Developmental Anatomy, revised 7th ed., W. B. Saunders, Philadelphia, 1974.) Fig. 11-9

the hindbrain is the myelencephalon, and it forms the medulla oblongata. At first the medulla is similar to the spinal cord, consist¬ ing of a roof plate, floor plate, and lateral plates of alar and basal laminae. The roof plate becomes greatly stretched and thinned at an early stage (Fig. 11-10,B and C), but the floor plate holds the lateral plates together so that they diverge and flatten simultaneously. The sulcus limitans persists, but now it sepa¬ rates a laterally placed alar lamina from a more medially placed basal lamina. The functional pattern remains similar to the spi¬ nal cord with a sensory alar plate, a motor basal plate, and autonomic nuclei along the sulcus limitans (Fig. 11-10,C, D, and E). Sensory fibers from the neural crest gan¬ glia of the glossopharyngeal and vagus nerves form a bundle opposite the sulcus limitans. Called the tractus solitarius (Fig. 11-10,B), it corresponds to the oval bundle of the primitive spinal cord (Fig. 11-4,A). At first it is in contact with the outer surface of

the alar lamina, but it later is buried by the overgrowth of neighboring parts (Fig. 11-10,0). At about five weeks, the part of the alar lam¬ ina next to the floor plate bends over later¬ ally, forming the rhombic lip (Figs. 11-10,E; 11-13). The rhombic lip folds downward, over the main part of the alar lamina, fuses with it, and buries the tractus solitarius and spinal root of the trigeminal nerve. Later, the nodulus and flocculus of the cerebellum develop from the rhombic lip. Although the basal plate corresponds in function to the ventral horn of the spinal cord because both give rise to motor fibers, in the basal plate the cells become arranged in groups or nuclei instead of continuous columns. In addition, neuroblasts migrate from the alar plate and rhombic lip into the basal lamina and become aggregated in the olivary nuclei (Fig. 11-10,D). Many of the fi¬ bers from these cells cross the midline of the floor plate and thus constitute the rudiment of the raphe of the medulla. The accumula-

DEVELOPMENT OF THE NERVOUS SYSTEM

Sulcus limitans Dorsal root

Nucleus & Fasciculus solitarius

Som. aff. col.

Ventricular zone

943

Nuc. desc root n.V.

Vise. aff. col.

Dorsal eff. nuc. n.X.

Intermed. zone

Marginal zone

Hypoglossal nucleus N XII

Somatic aff. column (nuc. desc. root n.V)

Visceral eff. column (dorsal eff. nucleus n.X)

Fasc. sol.

Vise. aff. column (nuc. of fasc. sol.

N.a.

Som. eff. column (hypoglossal nuc.)

Desc. root V

Dorsal acc. olive Medial lemniscus Medial acc. olive Pyramidal tract

Som, eff. column (abducens nucleus)

Genu of n.VII

Genu of n.VII

Sup. salivatory nucleus

Abducens nuc.

Med. long, fasciculus

Nerve VI Rhomb lip Nuc. desc root n.V. Fasc. sol.

Fasc. sol. Nuc. desc. root V & root

Superior olive Medial lemniscus

Sp. vise. eff. cal. (motor, nuc. n.VII) Pyramidal tract

Pontine gray

Cross sections of cord and medulla comparing manner of origin of spinal and cranial nerves. A, Thoracic cord of 14.8-mm embryo to show origin of typical spinal nerve. B, Lower part of medulla for comparison with cord structure. C, Medulla of 15-mm embryo at level of upper rootlets of nerves X and XII. D, Medulla of 73-mm embryo at level of upper rootlets of nerves X and XII. Compare with C. E, Medulla of 15-mm embryo at level of pons, showing the roots of nerves VI and VII. F, Medulla of 73-mm embryo at level of pons, showing the roots of nerves VI and VII. Compare with E. Abbreviations: Acc., accessory; Aff., afferent; Col., column; Desc., descending; Eff., efferent; Fasc. Sol., fasciculus solitarius; Gn., ganglion; Inf., inferior; Jug., jugular; N.A., nucleus ambiguus (note that in the younger stage (C), it is not separated from the general afferent column as happens later (D) and since it supplies skeletal muscle of branchiomeric origin rather than smooth muscle it is classified as a special visceral efferent nucleus); Nuc., nucleus; R., restiform body; Rhomb., rhombic; Sp., special; Vise., visceral. (Courtesy of B. M. Patten, Human Embryology, 3rd ed., McGraw-Hill, New York, 1968.) Fig. 11-10.

tion of these cells and fibers in the ventral part of the basal plate pushes the motor nu¬ clei deep into the interior, and in the adult they are found close to the interior lumen. The change is further accentuated by the

development of the pyramids at about the fourth month and by the fiber connections of the cerebellum. On the floor of the fourth ventricle, the rhomboid fossa—a series of six temporary transverse rhombic grooves—ap-

944

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Brain of a human embryo of about four and one-half weeks, showing the interior of the forebrain. (From a model by W. His.)

Fig

11-11. Exterior of brain of human embryo of about four and one-half weeks. (From a model by W. His.)

Fig. 11-12

pears. The most cephalic, or first and second, grooves lie over the trigeminal nucleus; the third groove lies over the facial nucleus; the fourth, over the abducent nucleus; the fifth, over the glossopharyngeal nucleus; and the sixth, over the nucleus of the vagus nerve. the metencephalon. The metencephalon is the rostral portion of the hindbrain, and it extends from the pontine flexure to the rhombencephalic isthmus. Its cavity is the rostral part of the fourth ventricle. Two re¬ gions of the neuraxis, the pons ventrally and the cerebellum dorsally, are derived from the metencephalon (Fig. 11-14). The Pons. The pons consists of a dorsal, more primitive, and phylogenetically older part called the pontine tegmentum, which forms a thick floor for the fourth ventricle. Its structure in many ways resembles that of the medulla oblongata and it contains the upward continuation of many structures found in the medulla. In contrast, the basilar or ventral portion of the pons is a more re¬ cent and distinctly mammalian acquisition, since through it course fiber systems that in¬ terconnect the cerebral cortex and the cere¬ bellar regions.

The roof plate of the embryonic pons forms a thin sheet of white matter in front of the cerebellar cortex called the medullary velum. The basal plates, located ventral to the sulci limitans, as in the myelencephalon and spinal cord, form motor neurons (Fig. 11-15). In the pons these contribute general somatic efferent fibers for the abducens nerve, which supplies the lateral rectus mus¬ cle in the orbit, and special visceral efferent neurons for the trigeminal and facial nerves, which supply the muscles derived from the first and second branchial arches. Addition¬ ally, preganglionic parasympathetic general visceral motor neurons are formed in the su¬ perior salivatory nucleus. Their axons also emerge with the facial nerve to synapse pe¬ ripherally in the pterygopalatine and sub¬ mandibular ganglia. The basal plate also contributes neuronal elements to the reticu¬ lar formation. The alar plates, located dorsal to the sulci limitans, form the relay nuclei for sensory components in the trigeminal, facial, and vestibulocochlear nerves (Fig. 11-15). The sensory nucleus of the trigeminal nerve, found in the pontine tegmentum and also

DEVELOPMENT OF THE NERVOUS SYSTEM

Fig. 11-13.

945

Exterior of the brain of a human embryo of about five weeks. (From a model by W. His.

extending caudally into the medulla oblong¬ ata, receives general sensory afferent trigem¬ inal fibers. Special and general visceral af¬ ferent fibers course in the pons with the facial nerve to enter the tractus and nucleus solitarius, and the vestibular and cochlear nuclei receive special sensory afferent fibers from the vestibulocochlear nerve. The floor plate of the developing pons forms a midline raphe, as it does in the myelencephalon. The ventrally located basilar portion of the pons contains the large pontine nuclei, which are formed by cells that migrate from the alar plates of both the myelencephalon and metencephalon. Fibers from the cere¬ bral cortex enter these nuclei, whereas fibers from the pontine nuclei cross the midline and course to the cerebellum by way of the middle cerebellar peduncles. The Cerebellum. Principally due to the pontine flexure, the dorsolateral parts of the alar plates in the cephalic portion of the hindbrain bend laterally and posteriorly to form the rhombic lips (Figs. 11-13; 11-16). The rostral part of each rhombic lip be¬ comes thickened and, together with the alar plates in the rostral rhombencephalon,

forms the rudiments of the cerebellum (Fig. 11-14). Initially, the two rhombic lips partially project into the fourth ventricle and partially onto the dorsal surface of the metencephalon above the attachment of the roof plate. As the pontine flexure deepens, the rhombic lips become compressed, which causes them to fuse, thereby forming the transverse cerebellar plate. After the third month, this plate becomes differentiated into an unpaired midline portion, which be¬ comes the vermis, and symmetrically shaped lateral portions, which develop into the cerebellar hemispheres. At this stage the developing cerebellum assumes a “dumb¬ bell” appearance, and further growth is prin¬ cipally the result of enlargement of its extra¬ ventricular part. Because of this so-called eversion, the cerebellum becomes essen¬ tially an extraventricular structure, overly¬ ing the fourth ventricle. The outer surface of the cerebellum is ini¬ tially smooth. Soon after the third month, however, the first of the cerebellar fissures appears, separating the nodulus and the floc¬ culus from the rest of the vermis and the lat¬ eral cerebellar lobes. This is called the pos-

946

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Choroidal fissure

Interventricular foramen Lamina terminalis Optic

gland

Fig. 11-14.

Interior of the brain of a human embryo of about five weeks. (From a model by W. His.)

terolateral fissure, behind which is the phylogenetically older flocculonodular node, importantly related to the vestibular system, and in front of which is the more rapidly growing cerebellar hemispheres. During the fourth and fifth months this rapid growth results in the formation of a number of fis¬ Superficial cerebellar cortex

sures that separate newly formed lobules in the cerebellar hemispheres. These include the primary fissure, which courses trans¬ versely and deeply to separate the paleocerebellar anterior lobe from the neocerebellar posterior lobe, as well as several other transverse fissures, including (from back to front) the secondary fissure, the prepyramidal fissure, the horizontal fissure, and the posterior superior fissure.

Roof plate

THE MESENCEPHALON

Rhombic lip

Somatic afferent (V, VIII) Visceral afferent (VII)

Pontine nuclei

Visceral efferent (V.VII) Somatic efferent (VI)

Diagrammatic representation of the basal and alar plates of the metencephalon. Note the motor nuclei of the basal plates, the sensory nuclei of the alar plates, and the pontine nuclei located more ventrally. (From J. Langman, Medical Embryology, Williams and Wilkins, Baltimore, 1963.)

Fig. 11-15.

The mesencephalon, or midbrain, devel¬ ops around a primitive neural cavity that eventually is reduced in diameter to form the cerebral aqueduct (of Sylvius1). The nar¬ row canal joins the lumen of the diencepha¬ lon (the third ventricle) rostrally with that of the rhombencephalon (the fourth ventricle) caudally. Three major regions of the embry¬ onic neural tube become differentiated in 'Franciscus Sylvius (Latinized form of Frangois Dubois, or de la Boe (1614-1672): A Dutch physician and anato¬ mist (Leyden).

DEVELOPMENT OF THE NERVOUS SYSTEM

Taenia Rhombic lip

Fig 11 16. Hindbrain of a human embryo of three months—viewed from behind and partly from the left side. (From a model by W. His.)

this part of the brain stem. These are the tec¬ tum, which develops dorsal to the cerebral aqueduct, and the midbrain tegmentum and cerebral peduncles, which form ventral and lateral to the aqueduct. The midbrain tectum develops from the two alar laminae that invade the roof plate of the original neural tube. As in other re¬ gions of the neuraxis, cells from the alar plates develop into structures related to sen¬ sory functions, and in the midbrain tectum, they form the corpora quadrigemina. These four bodies are the paired inferior and supe¬ rior colliculi, which serve as important relay centers for the integration of reflexes initi¬ ated by both auditory and visual impulses (Fig. 11-17). The basal plate forms the tegmentum of the midbrain and from it originate the motor

Fig. 11-17.

947

nuclei of the oculomotor and trochlear nerves (Fig. 11-17). These general somatic efferent fibers supply the extraocular mus¬ culature that is formed within the preotic myotomes. Also formed by the basal plate are the general visceral efferent neurons of the Edinger'M/Vestphal3 nucleus, pregangli¬ onic parasympathetic nerve cells that emerge with the oculomotor nerve to syn¬ apse in the ciliary ganglion. From this gan¬ glion, postganglionic fibers supply the sphincter of the pupil. The ventrolateral aspect of the basal plates receives large numbers of descending corticofugal fibers destined for the pons, medulla oblongata, and spinal cord. These form the crura cerebri or cerebral pedun¬ cles, which are separated from the tegmental region on both sides by nuclear masses called the substantia nigra (Fig. 11-17). The cells that form the mesencephalic reticular formation, as well as the red nucleus, are thought by some investigators to migrate from the alar plates into the tegmental re¬ gions. Others have claimed that these mid¬ brain elements develop in situ from basal plate cells. There is also conjecture relating to the origin of the cells that form the sub¬ stantia nigra. THE PROSENCEPHALON

At early stages, transverse sections of the prosencephalon, or forebrain, display the same parts as those that are seen at similar 2Ludwig Edinger (1855-1918): A German anatomist and neurologist (Frankfurt-am-Main). 3Karl F. O. Westphal (1833-1890): A German neurologist and psychiatrist (Berlin).

Diagrams showing the differentiation of midbrain structures from alar and basal plates. The arrows in A indicate the migration of alar plate cells, which form the red nucleus and substantia nigra. (From J. Langman, Medical Embryology, Williams and Wilkins, Baltimore, 1963.)

948

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

stages of development in the spinal cord and medulla: namely, thick lateral walls con¬ nected by thin roof and floor plates. Al¬ though many investigators believe that the sulcus limitans does not extend forward beyond the midbrain and that the prosen¬ cephalon is formed primarily from the alar laminae, others believe that the hypothala¬ mus is derived from the basal laminae and that the rest of the forebrain forms from the alar laminae. The latter point to the hypo¬ thalamic sulcus, which continues forward as far as the optic recess and might be consid¬ ered analogous to the sulcus limitans. Irre¬ spective of this matter, the telencephalon gives origin to all of the central nervous sys¬ tem cranial to the midbrain. At a very early period, even before the clo¬ sure of the cranial part of the neural tube, the optic vesicles appear as diverticula on each side of the forebrain. Initially they communicate with the forebrain vesicle by relatively wide openings. Later the proximal part of the vesicle is narrowed into the optic stalk (Figs. 11-11 to 11-14), and the peripheral part is expanded into the optic cup. The cav¬ ity of the vesicle eventually disappears, and the stalk is invaded by nerve fibers and be¬ comes the optic nerve and tract. The optic cup becomes the retina. After closure of the neural tube, the lateral walls of the forebrain grow anteriorly and ventrally much more rapidly than the me¬ dian portion, resulting in the formation of a large pouch on each side, the cerebral hemi¬ spheres (Figs. 11-11; 11-13). The cavities within the pouches are the rudiments of the lateral ventricles and their intercommuni¬ cations become the future interventricular foramina of Monro4 (Figs. 11-12; 11-14). The median portion of the wall of the forebrain vesicle, formed by the anterior part of the roof plate, consists of a thin lamina that stretches from the interventricular foramina to the recess at the base of the optic stalk called the lamina terminalis. The rostral part of the forebrain, including the hemispheres, is the telencephalon or endbrain, and the caudal part is called the diencephalon or in¬ termediate brain. The cavity of the median part of the forebrain vesicle becomes the third ventricle. the di encephalon . The diencephalon 4Alexander Monro Secundus (1733-1817): A Scottish anatomist and surgeon (Edinburgh).

gives rise to the thalamus, metathalamus, epithalamus, and hypothalamus (Figs. 11-12; 11-14; 11-18). A groove in the lateral wall of this part of the forebrain vesicle, the hypo¬ thalamic sulcus, separates the epithalamus, metathalamus, and thalamus, located more dorsally, from the hypothalamus, located ventrally. The caudal extent of the dien¬ cephalon consists of a plane drawn between the posterior commissure dorsally and the mammillary bodies ventrally, while rostrally it extends to the cerebral hemispheres and forms the telencephalon. At the base of the brain the diencephalon extends rostrally to a site a few millimeters anterior to the optic chiasma. The thalamus arises as a thickening of the cephalic two-thirds of the alar plate. For some time it is visible as a prominence on the external surface of the brain (Figs. 11-11; 11-13), but it later becomes buried by the overgrowth of the hemispheres (Fig. 11-18). The thalami of the two sides protrude medi¬ ally into the ventricular cavity and eventu¬ ally join across the midline in a small com¬ missure-like junction of gray substance called the interthalamic adhesion. This was formerly termed the massa intermedia. The metathalamus consists of the medial and lateral geniculate bodies, which appear as slight prominences on the outer surface of the alar lamina. The medial geniculate bod¬ ies are relay stations for the transmission of auditory impulses, while the lateral genicu¬ late bodies function as relay centers in the visual pathways. The epithalamus includes the pineal body, the posterior commissure, and the habenular trigone. The pineal body arises as an evagination of the roof plate between the thalamus and the colliculi (Fig. 11-18). The habenular trigone, consisting of the habenular nuclei and the habenular commissure, de¬ velops in the roof plate just rostral to the pineal gland, and the posterior commissure develops just caudal to it. The roof plate of the diencephalon rostral to the pineal gland remains thin and epithelial in character and becomes invaginated by the choroid plexus of the third ventricle. The choroid plexus consists of modified ependymal cells that form a close functional relationship with blood vessels in the pia mater, and as else¬ where in the ventricular system, it secretes cerebrospinal fluid. The hypothalamus is formed from the

DEVELOPMENT OF THE NERVOUS SYSTEM Choroidal fissure

Fig. 11-18.

Median sagittal section of brain of human embryo of three months. (From a model by W. His.)

portion of the lateral walls of the diencepha¬ lon located below the hypothalamic sulcus (Figs. 11-12; 11-14; 11-18). One group of hypo¬ thalamic nuclei that develops becomes im¬ portantly related to many visceral and endo¬ crine functions, as well as to the innate behaviors of feeding, drinking, and sleep¬ ing. Caudally the mammillary bodies are formed; initially these arise as a single ventrally protruding structure that later during the third prenatal month becomes divided by a midline furrow (Figs. 11-13; 11-14). Anterior to the mammillary bodies the tuber cinereum is formed, and in front of this a diverticulum develops in the hypotha¬ lamic floor and gives rise to the infundibu¬ lum and posterior lobe of the pituitary gland (Fig. 11-18). In contrast, the anterior lobe of the pituitary gland develops from an ecto¬ dermal diverticulum called Rathke’s1 pouch. This latter outgrowth appears in the roof of the stomodeum during the middle of the third week. It extends upward toward the floor of the hypothalamus, and as it makes contact with the posterior lobe, it loses its !Martin H. Rathke (1793-1860): A German anatomist and zoologist (Konigsburg).

949

attachment on the pharyngeal roof during the sixth week. The optic part of the hypothalamus ini¬ tially is represented by two diverticula, the optic vesicles. Peripherally the optic cup forms the retina, whereas the optic stalk is retained as the pathway through which the ingrowing optic nerve fibers from the gangli¬ onic layer of the retina form the optic chiasma and optic tract. The optic chiasma, lo¬ cated rostrally in the hypothalamic floor, forms the boundary between the diencepha¬ lon and telencephalon at the base of the brain. the telencephalon. The telencephalon is the most rostral portion of the developing neuraxis, and early during its formation it consists of two lateral diverticula and an interconnecting median part, the lamina terminalis, which is continuous with the dien¬ cephalon. The cavities of the diverticula rep¬ resent the lateral ventricles and their walls become thickened to form the substance of the cerebral hemispheres. The cavity of the median portion is the most rostral extent of the third ventricle. Initially, the lateral ventricles widely communicate with the third ventricle, but eventually, as the cere¬ bral hemispheres grow, these communica¬ tions become the slit-like interventricular foramina. The cerebral hemispheres expand rapidly after the sixth week, and by the fourth month almost completely cover the dien¬ cephalon, mesencephalon, and cerebellum (Fig. 11-18). The medial surfaces of the two hemispheres come into contact, which ac¬ counts for their flattened appearance and results in the formation of the longitudinal cerebral fissure, which intervenes between the hemispheres. This enormous growth of the cerebral hemispheres is characteristic of mammalian brains, especially the human brain. It is convenient and functionally rele¬ vant to describe the further development of the following principal parts of each cere¬ bral hemisphere: the rhinencephalon and archeopallium, the corpus striatum, and the neopallium. Rhinencephalon and Archeopallium. Con¬ tinued use of the term rhinencephalon (olfactory brain) can be justified only when the structures incorporated within its defini¬ tion are clearly stated. Confusion arises be¬ cause authors have frequently used the term loosely to include many structures that are

950

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

not directly related to olfaction, but are asso¬ ciated instead with emotional and visceral functions (such as mating behavior, feeding, aggressivity, and fear)—functions that, espe¬ cially in lower vertebrates, depend impor¬ tantly on olfactory cues. In this book, the term rhinencephalon is used strictly to in¬ clude the olfactory bulb and those forebrain regions that receive nerve fibers directly from it. Thus, in addition to the olfactory bulb, the rhinencephalon includes the olfac¬ tory tracts, the medial, intermediate, and lat¬ eral olfactory striae, the olfactory trigone (formed where the striae diverge), the ante¬ rior olfactory nucleus, the olfactory tubercle (anterior perforated substance), the corticomedial group of nuclei in the amygdaloid complex, and the prepiriform and periamygdaloid cortex of the piriform lobe. In es¬ sence, this represents the olfactory bulb, its tracts, and the paleopallium, the so-called olfactory cortex. Because the hippocampal formation in mammals does not appear to receive major projections of olfactory fibers directly, its structures are included in the term archeopallium. The rhinencephalon and archeopallium are phylogenetically the oldest portions of the telencephalon, and in fishes, amphibia, and reptiles they constitute virtually the en¬ tire cerebral hemisphere. The rhinencephalic primordia first appear on the medial aspect of the anteroventral surface of each develop¬ ing cerebral hemisphere during the latter part of the fifth week (Figs. 11-13; 11-14). Ex¬ ternally, a slight longitudinal ridge or diver¬ ticulum appears which corresponds to a fur¬ row that forms on the inner aspect of the hemisphere, close to the lamina terminalis. The rhinencephalon is separated from the lateral surface of the hemisphere by the rhinal sulcus and is continuous caudally with the portion of the hemisphere that will form the anteromedial end of the temporal lobe. As development continues, the longitu¬ dinal ridge becomes divided by a groove into an anterior and a posterior part. The rostral part of the ridge is the primitive olfactory lobe, while the caudal part is the piriform lobe (Fig. 11-19). From the rostral part of the longitudinal ridge, a hollow shaft grows for¬ ward, the cavity of which initially retains a communication with the lateral ventricle. During the third month, the stalk loses its cavity and becomes solid, forming the primi¬ tive olfactory bulb and tract. The proximal

Fig. 11-19. Inferior surface of brain of embryo at be¬ ginning of fourth month. (From Kollmann.)

part of the primitive olfactory lobe is con¬ nected with the parolfactory or subcallosal area, adjacent to the lamina terminalis on the medial surface of the hemisphere, by the medial olfactory gyrus (Fig. 11-19). From the caudal part of the primitive ol¬ factory ridge develop the anterior perforated substance and piriform lobe (Fig. 11-19). At the beginning of the fourth month, the piriform lobe forms a curved elevation that is continuous behind with the medial sur¬ face of the future temporal lobe. Intercon¬ nected rostrally to the olfactory lobe by the lateral olfactory gyrus (or prepiriform re¬ gion), the surface of the piriform lobe is marked at this stage by the gyrus ambiens and the gyrus semilunaris (Fig. 11-19). These develop into the corticomedial part of the amygdala and the lumen insulae. The adult piriform lobe, bounded laterally by the rhinal sulcus, is divided into the prepiriform, periamygdaloid, and entorhinal regions. The prepiriform and periamygdaloid regions re¬ ceive direct olfactory bulb fibers by way of the lateral olfactory tract, while the entorhi¬ nal region, which forms a large part of the parahippocampal gyrus, receives projec¬ tions from the prepiriform cortex, but none directly from the olfactory bulb. The adult archeopallium consists of the hippocampus (cornu ammonis), the dentate gyrus, and the subicular part of the para¬ hippocampal gyrus. Together these struc¬ tures are also frequently called the hippo¬ campal formation, and before the appear-

DEVELOPMENT OF THE NERVOUS SYSTEM

ance of the corpus callosum, they develop on the medial wall of the cerebral hemi¬ sphere along a line parallel with, but above and in front of, the choroid fissure. Becom¬ ing folded into the cavity of the lateral ven¬ tricle, so that the prominence bulging into the ventricle forms the hippocampus, the invagination is accompanied by the develop¬ ment of a corresponding fissure, the hippo¬ campal sulcus, on the medial surface of the cerebral hemisphere. Soon the marginal zone of the invagination differentiates to form the dentate gyrus, while inferiorly and laterally the hippocampus merges with the cortex of the parahippocampal gyrus by means of the subiculum. As the infolding proceeds, the hippocampal fissure is elon¬ gated; the subiculum becomes located on one side of the hippocampal sulcus and the dentate gyrus on the other side. Eventually, the hippocampus (cornu ammonis) curves around the hippocampal fissure, and the dentate gyrus lies within the concave aspect of the curve. The outer gray substance of the primordium of the archeopallial cortex ends within the bulging prominence between the hippo¬ campal fissure and the choroid fissure, leav¬ ing the white matter, called the alveus, ex¬ posed along the edge of the hippocampus adjacent to the epithelial cells of the epen¬ dyma. These fibers join to form the fimbria of the fornix. With the downward and for¬ ward growth of the temporal lobe, the hip¬ pocampal fissure and parts associated with it extend from the interventricular foramen to the end of the inferior horn of the lateral ventricle. Corpus Striatum. The corpus striatum appears as a thickening in the floor of the tel¬ encephalon between the optic stalk and the interventricular foramen, adjacent to the thalamus (Figs. 11-12; 11-14; 11-20; 11-21). By the second month it has increased in size and bulges from the floor of the lateral ven¬ tricle into the ventricular lumen, extending as far as the occipital pole of the primitive hemisphere. As the expansion of the cerebral hemi¬ spheres gradually covers the diencephalon, a part of the corpus striatum is carried into the lateral ventricular wall and downward into the roof of the inferior horn of the lat¬ eral ventricle as the tail of the caudate nu¬ cleus. During the fourth and fifth months, the corpus striatum is invaded and incom¬

951

pletely subdivided by large numbers of fi¬ bers of the internal capsule into two masses: an inner or dorsomedial part adjacent to the ventricle, the caudate nucleus, and an outer part, ventrolateral to the fibers of the inter¬ nal capsule, the lentiform nucleus (Fig. 1121). This latter nucleus develops into the larger putamen laterally and the smaller glo¬ bus pallidus medially. The Neopallium. The neopallium, or non¬ olfactory part of the cerebral cortex, forms the greater part of the hemisphere. Early in development its cavity is the primitive lat¬ eral ventricle. This is enclosed by a thin wall of neural tissue from which the cortex of the hemisphere is derived, and it expands in all directions but especially dorsally and caudally. By the third month the hemispheres cover the diencephalon; by the sixth month they overlap the midbrain; and by the eighth month they reach the hindbrain. The median lamina uniting the two hemispheres does not share in their expansion and remains as the thin roof of the third ventricle. Thus, be¬ tween the hemispheres there develops a deep cleft, the forerunner of the longitudinal cerebral fissure. The cleft becomes occupied by a septum of mesodermal tissue that constitutes the primitive falx cerebri. As the cerebral hemispheres expand, each lateral ventricle is gradually drawn outward onto three prolongations that represent the future anterior, inferior, and posterior horns. The part of the wall along the medial bor¬ der of the primitive lateral ventricle, which is immediately continuous with the roof plate of the diencephalon, lies over the prim¬ itive interventricular foramen and extends caudally. This border remains thin and has an ependymal or epithelial character. It is invaginated into the medial wall of the lat¬ eral ventricle to form the choroid fissure (Figs. 11-14; 11-22). Mesodermal tissue from the outer surface of the hemisphere, the rudiment of the pia mater, spreads into the fissure between the two layers of the epen¬ dyma to form the rudiment of the tela choroidea. The blood vessels accompanying the mesoderm form the choroid plexus, which almost completely fills the cavity of the ventricle for several months (Figs. 11-20; 11-21). The tela choroidea, lying over the roof of the diencephalon, also invaginates the thin epithelial covering to form the cho¬ roid plexus of the third ventricle. As described previously, the medial wall

952

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM ROOF OF THIRD VENTRICLE LATERAL VENTRICLE

CHOROIDAL INVAGINATION

INTER¬ VENTRICULAR FORAMEN

THIRD VENTRICLE

ROOF OF THIRD VENTRICLE HIPPOCAMPAL CORTEX

THIRD VENTRICLE

NEOPALLIAL CORTEX

LATERAL VENTRICLE CHOROID PLEXUS CORPUS STRIATUM LATERALE

INTERVENTRICULAR FORAMEN

CORPUS STRIATUM MEDIALE

B.

LATERAL VENTRICLE ROOF OF THIRD VENTRICLE

NEOPALLIAL CORTEX

CHOROID PLEXUS

CORPUS STRIATUM THIRD VENTRICLE

INTERVENTRICULAR FORAMEN

ANTERIOR LOBE OF HYPOPHYSIS C. Fig 11 -20

INFUNDIBULUM

Frontal sections through the forebrain of (A) 15-mm, (B) 17-mm, and (C) 19-mm human embryos, showing various stages in the development of the lateral ventricles and the choroid plexuses. Embryonic ages: early, mid, and latter part of the sixth week. (From W. ). Hamilton and H. W. Mossman, Human Embryology, 41h ed., Williams and Wilkins, Baltimore, 1972.)

DEVELOPMENT OE THE NERVOUS SYSi I M EPENDYMAL LAYER

953

MANTLE LAYER

SUPERIOR SAGITTAL SINUS

NEOPALLIAL CORTEX

MARGINAL LAYER INFERIOR SAGITTAL SINUS CHOROID PLEXUS

HIPPOCAMPAL CORTEX

LATERAL VENTRICLE ROOF OF THIRD VENTRICLE CAUDATE NUCLEUS THIRD VENTRICLE LENTICULAR NUCLEUS

INTERNAL CAPSULE PRE-OPTIC RECESS

ANTERIOR COMMISSURE

Frontal section through the left cerebral hemisphere of a 73-mm human fetus (fourth month). Observe the developing ventricular system and the corpus striatum. (From W. J. Hamilton, and H. W. Mossman, Human Embryol¬ ogy, 4th ed., Williams and Wilkins, Baltimore, 1972.) Fig. 11-21.

of the cerebral hemisphere becomes folded into the cavity of the lateral ventricle and develops as the rudiment of the hippocam¬ pal formation. Growth of the remaining cer¬ ebral cortex is so great that the structure is thrown into folds or convolutions (gyri) be¬ tween which are formed the sulci or fissures. Additionally, groups of nerve fibers pass from one hemisphere to the other, forming the commissures. The Commissures. The development of the posterior commissure was mentioned in the section describing the embryology of the diencephalon. The other commissures inter¬ connecting the two hemispheres are the large corpus callosum, the anterior commis¬ sure, and the small commissure of the fornix, which all arise from the lamina terminalis (Fig. 11-22). At about the fourth month a small thickening appears in this lam¬ ina, immediately in front of the interventric¬ ular foramen. The lower part of this thicken¬ ing soon becomes constricted, and fibers grow into it to form the anterior commissure. These fibers interconnect the two olfactory bulbs and certain other paleopallial struc¬ tures of the two sides, such as the piriform and prepiriform regions and the amygdaloid

nuclei. The upper part continues to grow caudally with the hemispheres and is in¬ vaded by two sets of fibers. Transverse fi¬ bers, extending between the two cerebral hemispheres, pass into its dorsal part and become differentiated as the corpus callo¬ sum. Longitudinal fibers from the hippocam¬ pus pass into the ventral part of the lamina terminalis, and arching over the thalamus to the mammillary bodies, develop into the fornix. The anterior portion between the corpus callosum and fornix is not invaded by commissural fibers and becomes the sep¬ tum pellucidum. Sulci and Gyri. The outer surface of the cerebral hemisphere is at first smooth. Later it exhibits a number of convolutions, or gyri, that are separated from each other by sulci, which appear during the sixth or seventh month of fetal life. The term complete sulcus is applied to grooves that involve the entire thickness of the cerebral wall and thus pro¬ duce corresponding eminences in the ven¬ tricular cavity. The other sulci affect only the superficial part of the wall and therefore leave no impressions in the ventricle. The complete sulci are the ctioroidal and hippocampal, which have already been de-

954

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Choroidal fissure Gyrus dentatus Taenia thalami Thalamus Corpus callosum Septum pellucidum

Post, commissure

Anterior commissure Corpora quadrigemina

Lamina terminalis

Cerebral aqueduct Cerebral peduncle

Rhinencephalon Optic chiasma

Cerebellum

Hypophysis III. ventricle Pons IV. ventricle Medulla oblongata

Fig. 11-22.

Median sagittal section of brain of human embryo of four months. (Marchand.)

scribed; the calcarine, which produces the swelling known as the calcar avis in the pos¬ terior horn of the ventricle; and the collat¬ eral sulcus, with its corresponding eminence in the ventricular cavity. The central sulcus (the fissure of Rolando1) develops in two parts; the intraparietal sulcus, in four parts; and the cingulate sulcus, in two or three parts. The lateral cerebral (or Sylvian) sul¬ cus differs from all the other sulci in its mode of development. It appears toward the end of the third month as a depression, the Sylvian fossa, on the lateral surface of the hemisphere (Fig. 11-23). The floor of this fossa becomes the insula, and its adherence to the subjacent corpus striatum prevents this part of the cortex from expanding at the same rate as the portions that surround it. The neighboring parts of the hemisphere, therefore, gradually grow over and cover the insula, constituting the temporal, parietal, frontal, and orbital opercula of the adult brain. The frontal and orbital opercula are the last to form, but by the end of the first year after birth, the insula is completely sub¬ merged. The sulci separating the opposed margins of the opercula constitute the adult lateral cerebral sulcus.

the cell body of the first, or preganglionic, neuron lies within the substance of the brain or spinal cord, while the cell body of the sec¬ ond, or postganglionic, neuron is located more peripherally in one of the autonomic ganglia outside the central nervous system. SYMPATHETIC NERVOUS SYSTEM. The Cell bodies of the preganglionic neurons in the sympathetic division of the autonomic nerv¬ ous system are located in the lateral gray matter of the spinal cord in a column ex¬ tending from the first thoracic segment through the second lumbar segment. Occu¬ pying a position between the afferent groups of the dorsal horn and the somatic efferent groups of the ventral horn, the preganglionic Parietal operculum

Development of the Autonomic Nervous System

The autonomic nervous system consists of sympathetic and parasympathetic divisions. It is a two-motor neuron system, of which 'Luigi Rolando (1773-1831): An Italian anatomist (Turin).

Temporal operculum Sylvian fossa Frontal operculum Fig. 11-23. Outer surface of cerebral hemisphere of human embryo of about five months.

DEVELOPMENT OF THE NERVOUS SYSTEM

sympathetic neurons develop axons that grow out through the ventral roots with the somatic motor fibers. Eventually these pre¬ ganglionic elements leave the spinal nerves by way of the white rami communicantes to synapse with postganglionic sympathetic neurons within the ganglia of the sympa¬ thetic trunk or in the other outlying collat¬ eral ganglia found in the abdomen. Sympathetic Ganglia. Most investigators today believe that the ganglion cells that form the sympathetic ganglia are derived from the neural crest. These cells commence migrating along the dorsal roots of the spinal nerves during the fifth prenatal week, and they eventually form segmentally paired neuronal groups in the embryonic thoracic region dorsolateral to the aorta. Soon the fi¬ bers grow between the masses of cells to form the sympathetic chains. Other ganglion cells grow from the cervical and lumbar re¬ gions of the neural crest to form the cervical and lumbosacral ganglia. Certain sympa¬ thetic ganglion cells migrate beyond the sympathetic trunk to form ganglia adjacent to the branches of the abdominal aorta. These outlying collateral ganglia develop shortly after those of the sympathetic trunk and include the celiac, superior mesenteric, and inferior mesenteric ganglia. The nerve fibers of the postganglionic sympathetic neurons are either unmyelinated or sur¬ rounded by very thin myelin sheaths. PARASYMPATHETIC NERVOUS SYSTEM. The parasympathetic nervous system consists of preganglionic nerve cells that arise in the visceral efferent nuclei of the brain, and their axons grow out of the brain by way of the oculomotor, facial, glossopharyngeal, and vagus nerves. Additionally, other pre¬ ganglionic parasympathetic neurons de¬ velop in the lateral gray column of the sec¬ ond, third, and fourth sacral segments and leave the spinal cord in the ventral roots of the sacral nerves. The oculomotor, facial, and glossopharyngeal parasympathetic neu¬ rons course to ganglia in the orbit, deep face, and lower jaw, from which postganglionic parasympathetic fibers course to the viscera in the head. The vagus nerve descends to supply preganglionic fibers to terminal gan¬ glia within or near the viscera of the neck, thorax, and abdomen. Sacral parasympa¬ thetic fibers grow as far as terminal ganglia in the lower part of the gastrointestinal tract and in the pelvic organs. Parasympathetic Ganglia. The precise

955

origin of the ganglion cells that form the ciliary, pterygopalatine, submandibular, and otic ganglia of the head is still not com¬ pletely understood. Some believe that the ganglion cells migrate from the trigeminal ganglion along the developing divisions of the trigeminal nerve. Others feel that all the cells are derived from the central nervous system and migrate along the specific cranial nerves that carry the preganglionic fibers. Still other investigators feel that the para¬ sympathetic ganglia in the head receive cells not only from the sensory ganglion of the tri¬ geminal nerve, but also from the geniculate ganglion of the facial nerve and the inferior ganglion of the glossopharyngeal nerve. The origin of the postganglionic neurons that synapse with the preganglionic vagal fibers is also uncertain. It has been proposed that they derive from several sources, in¬ cluding the ganglia of the vagus nerve, and from the central nervous system by migrat¬ ing along the vagal trunks. The ganglion cells associated with the sacral parasympathetic fibers are thought to arise from the neural crest, which forms adjacent to the sacral seg¬ ments of the neural tube. Development of the Cranial Nerves

The development of the olfactory, optic, and vestibulocochlear nerves is described in more detail in Chapter 13. The pattern of development of the other cranial nerves is quite similar to that of the spinal nerves. The cranial sensory or afferent nerves are de¬ rived from cells in the ganglion rudiments of the neural crest. Evidence from research in lower animal forms also indicates that ecto¬ dermal thickenings that overlie the ganglia make some contribution to the formation of the sensory ganglia of the trigeminal, facial, glossopharyngeal, and vagus nerves. These have been called epibranchial placodes. The central processes of these ganglion cells grow into the brain and form the sensory elements in the roots of the nerves, while the peripheral processes extend distally to their sensory fields of distribution. In considering the development of the medulla oblongata, it appears that the tractus solitarius (Fig. 11-10) is derived from the fibers that grow inward from the ganglion rudiments of the glosso¬ pharyngeal and vagus nerves, and that it is the homologue of the oval bundle in the cord, which has its origin in the dorsal nerve roots. During the development of the bulbar

956

DEVELOPMENTAL AND GROSS ANATOMY OE THE CENTRAL NERVOUS SYSTEM

Acoustic gn Semilunar gn Metencephalon

N.V.

Superior gn N.Vl

Petrosal gn., n.lX Jugular gn., n.X.

Froriep's gn

Hypoglossal n. XII N.lll 1st cervical gn.

N.IV

Accessory n. XI Nodose gn., n.X

Br. Fr.

Descending cervical Hyoid branches

Br. Na.-c.

Musculo cutaneous Axillary Phrenic

Max. div. n.V.

Median n. Radial n. Ulnar n.

Mand. div. n.V. Gen. gn., n.VII Ch. tymp. n.VII

1 st thoracic gn.

Heart Septum transversum Liver

Tibial n. Peroneal n

Dorsal ramus

Gut

Femoral n. Obturator n.

cutaneous br. L.1 Ventral cutaneous br. Mesonephros llio-inguinal & hypogastric n.

Fig 11 -24. Reconstruction of the nervous system in a 10-mm human embryo during the fifth prenatal week (from the studies of G. L. Streeter). Note the developing cranial and spinal nerves. (Taken from B. M. Patten, Human Embryol¬ ogy, 3rd ed., McGraw-Hill, New York, 1968.)

part of the accessory nerve and the hypo¬ glossal nerve, strands of ganglion cells ex¬ tend along the rootlets of these cranial nerves. These are derived from an embry¬ onic sensory ganglion, known as Froriep’s2 ganglion, which develops between the jugu¬ lar ganglion of the vagus and the first cervi¬ cal ganglion (Fig. 11-24). Most of Froriep's ganglion disappears in the adult, although occasionally ganglion cells can be observed 2August von Froriep (1849-1917): A German anatomist.

along the course of the accessory and hypo¬ glossal nerves. The motor or efferent components of the cranial nerves arise as outgrowths of the neuroblasts that are situated in the basal laminae of the midbrain and hindbrain. In contrast to the spinal motor nerve rootlets that develop from the basal lamina in single sets at each segmental level, the motor root¬ lets of the cranial nerves form two sets as they emerge from the brainstem. One group of rootlets develops from the medial and the

GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Forebrain

Hindbrain

Midbrain Midbrain Hindbrain

Optic vesicle

957

Auditory vesicle

DienAuditory ceph. pit Optic vesicle Spinal cord

Telencephalon

B Hindbrain Mesencephalon Midbrain

Metencephalon Rhombic lip

Dien¬ cephalon

Myelenceph.

Dien¬ cephalon

Telencephalic vesicle

Spinal cord

Telencephalic vesicle

D Fig. 11-25. Four stages in the development of the brain and cranial nerves (adapted from various sources, but principally from the studies of G. L. Streeter). A, 20-somite stage (about three and one-half weeks); B, 4-mm stage (about four weeks); C, 8-mm stage (about four and one-half weeks); D, 17-mm stage (about six and one-half weeks). The cranial nerves are indicated by the appropriate Roman numerals. Abbreviations: Hy., hyoid arch; Md., mandibular arch. (Taken from B. M. Patten, Human Embryology, 2nd ed., McGraw-Hill, New York, 1953.)

other from the lateral parts of the basal lam¬ ina. From the medial part of the basal lamina develop the somatic efferent fibers of the oculomotor, trochlear, abducent, and hypo¬ glossal nerves that supply the striated mus¬ culature formed from the somites (Fig. 1124). The lateral part of the basal lamina forms the accessory nerve and the branchial motor fibers of the trigeminal, facial, glosso¬ pharyngeal and vagus nerves that supply the voluntary musculature formed from the branchial arches (Figs. 11-24; 11-25).

Gross Anatomy of the Central Nervous System The central nervous system, divided for convenience of description into the spinal cord (or medulla spinalis) and brain (or en¬ cephalon), is a single, continuous organ sys¬ tem from which also are derived the 12 pairs of cranial nerves and the 31 pairs of spinal nerves (Fig. 11-26). The cranial and spinal

nerves, along with their ganglia and those of the autonomic nervous system, constitute the peripheral nervous system. The central nervous system functions to integrate infor¬ mation that it receives from the environment by way of receptors and the sensory nerves. Its reactions are transmitted to the effectors through the motor nerves. The spinal cord and brain are composed of groups of neuron cell bodies, which to¬ gether with their dendritic processes form the gray substance. Elongated processes, fre¬ quently myelinated and extending from the nerve cells, collect in bundles to form the white substance and the tracts. Enmeshed among the neurons and the processes are large numbers of neuroglial cells and capil¬ laries that maintain the appropriate chemi¬ cal environment and provide the nutrients necessary for proper neuronal metabolism. Because the internal neuroanatomy of the central nervous system is a subject more appropriately handled in specialized text¬ books and taught as a discipline separate from gross anatomy, most of the remainder

958

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

1st cervical n.

lii -Ant arch of atlas

• Spinal ganglia

-Arch of 7th cervical vertebra 8th cervical n. -Arch of 1st thoracic vertebra 1st thoracic n.-Third rib

rDura mater

—Arch of 12th thoracic vertebra 12th thoracic n."

-Arch of 1st lumbar vertebra

1st lumbar n.-

“Spinal ganglion

"Arch of 5th lumbar vertebra 5th lumbar n.

1 st sacral n. ■

^Sacrum

-Filum terminale externum

11-26 The dorsal aspect of the spinal cord exposed within the vertebral canal. The spinous processes and the laminae of the vertebrae have been removed and the dura mater has been opened longitudinally. (Redrawn after Sobotta.) Fig

of this chapter deals with the external and gross anatomy of the spinal cord and brain. Reference is made to the internal anatomy of the central nervous system on those occa¬

sions when it will lead to a better under¬ standing or description of the external form. The principal subdivisions of the central nervous system include the spinal cord,

GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

959

rhombencephalon (hindbrain), mesencepha¬ lon (midbrain), and prosencephalon (fore¬ brain). The rhombencephalon consists of the myelencephalon (medulla oblongata) and the metencephalon (pons and cerebellum), while the prosencephalon includes the dien¬ cephalon (thalamus and hypothalamus) and telencephalon (cerebral hemispheres).

SPINAL CORD

The spinal cord (medulla spinalis) is the elongated, nearly cylindrical part of the cen¬ tral nervous system that lies within most of the vertebral canal (Fig. 11-26). The diameter of the spinal cord in the midthoracic region is about 1 cm, but it is significantly greater at the lower cervical and midlumbar levels. Its average length in the male is about 45 cm, and in the female, from 42 to 43 cm, while its weight amounts to about 30 gm. The spinal cord extends from the upper border of the atlas, where it is continuous through the fo¬ ramen magnum with the medulla oblongata of the brain stem, to the lower border of the first or upper border of the second lumbar vertebra, where it tapers to a point, forming the conus medullaris (Figs. 11-27; 11-30). The position of the spinal cord varies somewhat with the movements of the verte¬ bral column, being drawn upward slightly when the column is flexed. The degree to which the spinal cord fills the vertebral col¬ umn also varies at different periods of life. Until the third prenatal month the spinal cord is as long as the vertebral column, but from this stage onward the vertebral column elongates more rapidly than the spinal cord. By the end of the fifth prenatal month, the spinal cord terminates at the base of the sac¬ rum, and at birth it ends at about the third lumbar vertebra. It gradually recedes during childhood until it reaches the adult position (Fig. 11-5). Surrounding the spinal cord are three protective membranes called menin¬ ges—the dura mater, the arachnoid, and the pia mater (Figs. 11-29; 11-31). Between the latter two is found the cerebrospinal fluid. These membranes are described more completely elsewhere in this chapter. The filum terminale is a delicate filament that continues down the vertebral canal from the apex of the conus medullaris to the first segment of the coccyx (Figs. 11-26; 1127; 11-30). It is approximately 20 cm in length. Its upper 15 cm, contained within the

Fig. 11-27. The cauda equina of the spinal cord show¬ ing the conus medullaris, the filum terminale internum, and the filum terminale externum. (From Benninghoff and Goerttler, Lehrbuch der Anatomie des Menschen, Vol. 3,9th ed., Urban and Schwarzenberg, Munich, 1975.)

tubular sheath of the dura mater and sur¬ rounded by the nerves of the cauda equina, is called the filum terminale internum. The lower part, the filum terminale externum, is closely invested by the dura mater to which it adheres. Extending beyond the apex of the sheath, it finally attaches to the dorsal part of the first coccygeal segment (Fig. 11-27). The filum consists mainly of fibrous tissue con¬ tinuous with the pia mater. A few nerve fi¬ bers adherent to the outer surface probably represent rudimentary second and third coc¬ cygeal nerves. The central canal of the spi¬ nal cord continues down into the filum for 5 or 6 cm.

960

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Relationships and Form of the Spinal Cord VERTEBRAL COLUMN ANO CAUDA EQUINA. It was just stated that the neural substance of the adult spinal cord does not occupy the entire length of the vertebral canal, as was the case during the third month of prenatal development, because the vertebral column grows at a faster pace than the spinal cord. Because the cord is continuous with the de¬ veloping brain, and thereby firmly anchored rostrally, this differential growth pattern causes the spinal cord to be drawn upward in the vertebral canal. There results a great intravertebral lengthening of the lumbar and sacral nerve roots because they still emerge from the vertebral column through their segmentally appropriate intervertebral foram¬ ina below (Fig. 11-28). These caudally placed nerve roots are directed in a progressively more oblique manner, so that they pass al¬ most vertically downward within the dura mater for some distance before reaching their foramina of exit. The resulting collec¬ tion of rootlets beyond the termination of the neural substance of the cord is called the cauda equina (Figs. 11-26 to 11-28). epidural space. The dimensions of the vertebral canal within the spinal column are considerably greater than the diameter of the enclosed spinal cord and its meningeal coverings. This permits the required move¬ ments of the cord during flexion and exten¬ sion of the vertebral column without a re¬ sultant spinal contusion or compression. Between the bony inner wall of the vertebral canal and the outer surface of the dura mater is found the epidural space, and this is loosely packed with strands of epidural fat. Closely adhering to the wall of the verte¬ bral canal are the internal vertebral venous plexuses. Additionally, fine dorsal and ven¬ tral epidural branches of the spinal arteries ramify within the epidural fat to supply the vertebrae and the external surface of the spi¬ nal dura mater. ENLARGEMENTS OF THE CORD. The Spinal cord is slightly flattened dorsoventrally and its diameter is increased by enlargements in two regions: cervical and lumbar (Fig. 11-30). The cervical enlargement extends from about the fifth cervical to the second tho¬ racic vertebra, its maximum circumference (about 38 mm) being at the level of the sixth pair of cervical nerves. It corresponds to the origin of the large nerves that supply the upper limbs. The lumbar enlargement be-

Fig. 11-28. Diagram showing the relationship of the spinal cord segments and the level of emergence of the spinal nerves to the bodies and spinous processes of the vertebrae. (From W. Haymaker and B. Woodhall, Pe¬ ripheral Nerve Injuries, 2nd ed., W. B. Saunders, Phila¬ delphia, 1953.)

GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

961

Anterior Median Fissure. The anterior median fissure traverses the entire extent of the anterior surface of the spinal cord along its midline (Figs. 11-30 to 11-32). It penetrates an average depth of about 3 mm, being somewhat deeper more caudally. It contains adjacent folds of pia mater and the floor of the fissure is formed by a band of trans¬ versely crossing white fibers, the ventral

Fig 11-29. The dura mater has been opened to reveal the dorsal aspect of the spinal cord. Note that the thin arachnoid membrane has been left intact in the upper part of the exposure. (From P. Thorek, Anatomy in Sur¬ gery, 2nd ed., }. B. Lippincott, Philadelphia, 1962.)

gins at the level of the ninth thoracic verte¬ bra and reaches its maximum circumference (about 33 mm) opposite the last thoracic ver¬ tebra, after which it tapers rapidly into the conus medullaris. These vertebral levels cor¬ respond to the sites of attachment of nerve roots that extend from the first lumbar to the third sacral segment. From these segments arise the nerves that supply the lower limb. fissures and sulci. After removal of the meningeal coverings, especially the pia mater, the surface of the spinal cord is marked by several longitudinal furrows. Two of these, the anterior median fissure and the posterior median sulcus, nearly di¬ vide the spinal cord longitudinally into sym¬ metrical right and left halves. The two sides of the cord remain interconnected, however, by commissural bands of gray and white matter. Within the gray commissural bands is located the central canal. The dorsal sur¬ face of the cord also shows a posterolateral sulcus, as well as a posterior intermediate sulcus (Figs. 11-30 to 11-32).

ANTERIOR Fig 11-30.

nal cord.

POSTERIOR

Anterior and posterior diagrams of the spi¬

962

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Anterior median fissure

White matter Gray matter

Posterior median sulcus Posterior intermediate sulcus Posterolateral sulcus

Denticulate ligament

Dorsal fi bers

"Dura mater

Arachnoid membrane

Spinal ganglion

nerve

f'g I1;31 T^e d°rsaI asPect of the spinal cord. In the lower region the dura mater is intact, while in the upper region all of the meningeal coverings have been removed. (After Sobotta.)

white commissure. This commissure is per¬ forated by branches of the anterior spinal vessels, which serve the central part of the spinal cord. Posterior Median Sulcus. The posterior median sulcus is a shallow groove from which a thin sheet of neuroglial tissue, the posterior median septum, penetrates more than half way into the substance of the cord, effectively separating the dorsal portion into right and left halves (Fig. 11-32). This septum varies in depth from 4 to 6 mm, but dimin¬

ishes considerably in the lower part of the spinal cord. Posterolateral Sulcus. The posterolateral sulcus is a longitudinal furrow located on each side of the posterior median sulcus along the line of attachment of the dorsal roots of the spinal nerves (Figs. 11-30; 11-32). Between the posterolateral sulcus and the posterior median sulcus on each side is found the posterior funiculus. Together the posterior funiculi are frequently called the posterior white columns of the spinal cord.

GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

963

Posterior median sulcus Posterior intermediate sulcus Posterior median septum Posterior funiculus Dorsal nerve root Posterolateral sulcus Dorsolateral fasciculus (Lissauer) Dorsal horn (gray column)

Substantia gelatinosa Dorsal gray commissure

Lateral funiculus Reticular formation

Central canal

Lateral horn (gray column) Ventral gray commissure Ventral horn (gray column)

Ventral white commissure

Anterolateral sulcus Ventral nerve roots

Anterior median fissure

Anterior funiculus

Fig. 11-32.

Transverse section of the spinal cord in the midthoracic region.

Posterior Intermediate Sulcus. The poste¬ rior intermediate sulcus is a groove found in the upper thoracic and cervical regions of the spinal cord and interposed between the posterior median sulcus and the posterolat¬ eral sulcus along the posterior funiculus (Figs. 11-30; 11-32). It marks the line of sepa¬ ration between two ascending large tracts of white nerve fibers, the more medially lo¬ cated fasciculus gracilis, and the fasciculus cuneatus found more laterally. Another less prominent groove, the anter¬ olateral sulcus, is sometimes described as being in relationship to the emerging ventral roots (Figs. 11-30; 11-32). The relationship is frequently indistinct, however, because the ventral rootlets arise in bundles and not in a linear series and they emerge over an area of some slight width. The white matter of the spinal cord between the posterolateral sul¬ cus and the anterior median fissure is di¬ vided into a lateral funiculus and an anterior funiculus by the ventral roots (Fig. 11-32). In the upper part of the cervical spinal cord, in addition to the dorsal and ventral roots, a series of nerve roots passes outward through the lateral funiculus. These unite to form the spinal portion of the accessory nerve (XI), which ascends through the foramen mag¬ num to enter the cranial cavity. There it con¬ tributes the motor fibers of the eleventh

cranial nerve that supply the sternocleido¬ mastoid and trapezius muscles. segments of the spinal cord. Thirty-one pairs of spinal nerves originate from the spi¬ nal cord, each with a ventral (or anterior) root and a dorsal (or posterior) root. The pairs are grouped as follows: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal (Fig. 11-28). The cord itself also is divided for convenience of description into cervical, thoracic, lumbar, and sacral regions to corre¬ spond with the nerve roots. It is customary also to speak of the part of the cord giving rise to each pair of nerves as a spinal seg¬ ment or neuromere, although the distin¬ guishing marks, except for the roots, are not retained after embryonic life. Arbitrarily defined, each spinal segment is considered to extend from the uppermost filament of one root to the uppermost filament of the next root. The segments vary in their extent along the cord; in the cervical region they average 13 mm and in the midthoracic region, 26 mm, whereas their length diminishes rapidly in the lumbar and sacral regions from 15 to 4 mm. spinal nerve roots. Each spinal nerve has two roots: a dorsal (or posterior) root, also called the sensory root because its fibers transmit impulses to the cord, and a ventral (or anterior) root, also called the motor root

964

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

because its fibers carry impulses outward from the cord to muscles and other struc¬ tures. Dorsal (Posterior) Roots. The dorsal roots are attached in linear series along the poster¬ olateral sulcus of the cord, and each segmen¬ tal root consists of six or eight rootlets (fila radicularia) (Fig. 11-31). They contain the central processes of spinal ganglion cells whose peripheral processes extend outward to the sensory endings in the skin, muscles, tendons, and viscera. The rootlets are di¬ vided into two groups as they enter the cord: a medial bundle containing mainly large myelinated fibers and a lateral bundle con¬ taining finely myelinated and unmyelinated fibers. Arising from the spinal ganglion cells, the roots are accompanied by delicate radic¬ ular branches of the spinal arteries and veins. Within the vertebral canal, the dorsal roots penetrate the dura mater and the un¬ derlying arachnoid membrane and then course for varying distances, depending on their seg¬ mental level, within the subarachnoid space before entering the spinal cord at the root-cord junction. Ventral (Anterior) Roots. The ventral roots emerge from the spinal cord in two or three irregular rows of rootlets spread over a strip about 2 or 3 mm wide. Like the dorsal roots, the ventral roots are usually accompa¬ nied by branches of the spinal vessels. They course within the subarachnoid space prior to becoming surrounded by the tubular pro¬ longations of the dura mater and arachnoid, which encase the spinal nerves and the dor¬ sal root ganglia at the intervertebral foram¬ ina. The ventral roots join the dorsal roots to form the mixed spinal nerve at each segmen¬ tal level. The ventral roots contain the axons of the cells in the anterior and lateral cell columns of the central gray matter of the cord.

Arterial Blood Supply of the Spinal Cord

The basic pattern of the arterial blood supply to the spinal cord consists of three longitudinally coursing vessels that arise just rostral to the cervical region of the cord and descend on its surface as far as the conus medullaris, and numerous feeder ar¬ teries and radicular vessels that gain en¬ trance to the vertebral canal segmentally by coursing through the intervertebral foram¬ ina with the spinal nerves (Figs. 11-33 to 11-

36). Anastomoses between the longitudinally oriented and the segmentally derived vessels occur on the surface of the spinal cord and result in the formation of a rich vascular plexus from which medullary vessels pene¬ trate the substance of the cord to reach both the white and gray matter. Vessels that pene¬ trate the spinal cord substance are thought, for the most part, to be end arteries and, therefore, they do not anastomose further. Although there is significant variation with respect to the segmental levels at which the feeder vessels enter the vertebral canal, there is a general consistency in the overall vascular pattern, namely, that longitudinally oriented vessels descending from above are supplemented by branches from the medi¬ ally coursing spinal arteries at varying seg¬ mental levels.

LONGITUDINAL ARTERIES SUPPLYING THE SPINAL CORD

There are usually three longitudinally ori¬ ented spinal arteries. These are a single ante¬ rior spinal artery, which descends in the an¬ terior median fissure, and two posterior spinal arteries, which descend along or near the posterolateral sulci of the spinal cord (Figs. 11-33 to 11-36). anterior spinal artery. The anterior spi¬ nal artery is sometimes called the anterior median longitudinal artery of the spinal cord. It usually forms rostrally from the junction of two anterior spinal branches, one derived from each of the two vertebral arteries (Figs. 11-33; 11-34). The union of these two vessels generally occurs intracranially at or near the midline on the anterior aspect of the medulla oblongata at about the level of the olivary nuclei. From this site, the anterior spinal artery descends without in¬ terruption to the tip of the conus medullaris, lying just ventral to the anterior median fis¬ sure. Slightly dorsal and to one side of the artery courses the anterior median longitudi¬ nal venous trunk of the spinal cord (Suh and Alexander, 1939). Frequently the anterior spinal artery is duplicated in the cervical cord region because of an incomplete fusion of its two fetal precursors (Aminoff, 1976). Occasionally, one of the paired vertebral branches is much smaller or even absent, and at other times two or more very slender spinal vessels may branch from one of the vertebral arteries to unite with a large

GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

965

artery

artery

Anterior spinal artery

Vertebral a

Spinal branch of vertebral artery

Thyrocervical trunk Subclavian artery

Costocervical trim

5th Intercostal artery (spinal branch)

10th Intercostal artery (spinal branch)

Anterior-spinal artery

Renal artery

Common iliac artery

S

Fig. 11-33. derived from thyrocervical derived from

Diagrammatic representation of the anterior spinal artery. Note that the anterior feeder vessels are the intercostal and vertebral arteries, as well as from spinal branches from vessels coming off the and costocervical trunks. Rostrally, the anterior spinal artery is formed from anterior spinal branches each vertebral artery. (After Sobotta.)

966

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Fig. 11 -34. The vascular pattern of the anterior spinal artery and the anterior medullary feeder arteries in three adult human specimens. The numbers within the figure indicate the approximate diameters of the different vessels in micrometers. V.A., vertebral artery; S.I., superior intercostal artery. (From G. F. Dommisse, The Arteries and Veins of the Human Spinal Cord from Birth, Churchill-Livingstone, Edinburgh, 1975.)

branch from the other side (Tveten, 1976). Along its course the anterior spinal artery varies considerably in its diameter, but its caliber is consistently larger in the cervical and lower thoracic regions. Along the mid¬ portion of the thoracic spinal cord (i.e., be¬ tween T3 and T9), the vessel is quite slender (0.35 to 0.50 mm), and this region of the cord has been considered a vulnerable zone with

respect to its circulation (Dommisse, 1975). At the conus medullaris and along the filum terminale, the anterior spinal artery is re¬ duced in size to a tiny vessel that frequently communicates by anastomotic branches with the posterior longitudinal arteries. The anterior spinal artery is reinforced at a number of segmental levels by feeder arte¬ rial branches from the segmental arteries

GROSS ANATOMY OF THE CENTRAL NERVOUS SYS! I M

967

Basilar artery

Vertebral artery Anterior spinal artery

Posterior inferior artery

Vertebral artery

Dorsal radicular artery

Posterior spinal rtery

Posterior spinal artery Spinal rami of segmental spinal arteries from vessels in the neck

Artery of the dura mater (formed by branches of segmental spinal arteries)

Fig. 11-35. The arterial blood supply of the spinal cord is derived from anterior and posterior spinal arteries, which usually branch from the vertebral artery, as well as from radicular and medullary feeder branches coming from segmental vessels. (Redrawn after Netter.)

that enter the vertebral canal, accompanying the spinal nerves and their roots (Fig. 11-34). The largest of these feeder vessels invariably increases the diameter of the anterior spinal artery beyond its point of junction. POSTERIOR SPINAL ARTERIES. The two posterior spinal arteries are sometimes called the paired posterolateral longitudinal arterial trunks of the spinal cord. On each side the vessel usually originates directly from the intracranial part of the vertebral

artery, somewhat lower than the origins of the branches that unite to form the anterior spinal artery (Figs. 11-35; 11-36). At times the posterior spinal arteries do not arise directly from the vertebral arteries, but from their posterior inferior cerebellar branches in¬ stead. Each vessel descends on the posterior surface of the spinal cord along the postero¬ lateral sulcus in close relationship to the line of entrance of the dorsal roots. They are smaller in diameter and more irregular than

968

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Fig 11 36. The vascular pattern of the posterior spinal arteries and the posterior medullary feeder arteries in three human specimens (15 months, 22 years, 15 years). The numbers within the figures indicate the approximate diameters of the different vessels in micrometers. V.A., vertebral artery; D.C., deep cervical artery; S.I., superior intercostal artery. (From G. F. Dommisse, The Arteries and Veins of the Human Spinal Cord from Birth, Churchill-Livingstone, Edinburgh, 1975.)

the anterior spinal artery and communicate by many anastomosing channels with in¬ coming segmental arteries and across the midline with each other. To some extent the pattern thus formed resembles an embry¬ onic plexus, but usually the longitudinal continuity of the vessels can be discerned throughout the length of the cord (see Fig.

11-37). Along the conus medullaris, the pos¬ terior spinal arteries communicate freely with branches from the anterior spinal ar¬ tery to form what is frequently called the cruciate anastomosis of the conus medul¬ laris. Throughout its course, each posterior spinal artery gives off branches that pene¬ trate the cord to supply the white matter of

969

GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

plying the spinal cord come from the poste¬ rior intercostal arteries, which stem directly from the posterior aspect of the thoracic aorta. In the lumbar region, they branch from the lumbar arteries, while the segmen¬ tal arteries supplying the sacral region usu¬ ally stem from the lateral sacral arteries or, less commonly, from the middle sacral ar¬ tery (Gillilan, 1958). RADICULAR

AND

MEDULLARY

FEEDER

As they enter the intervertebral foramina, the segmental spinal arteries at every level give rise to the true dorsal and ventral radicular branches, which course with and supply the dorsal and ventral roots. Additionally, at certain of the vertebral levels, medullary feeder branches arise from the segmental spinal arteries to join the anterior and pos¬ terolateral longitudinally coursing spinal arteries (Figs. 11-34 to 11-38). These reinforce the circulation descending from above and are most important in maintaining an appro¬ priate level of blood supply to the cord. The medullary feeder arteries vary both in num¬ ber and in the levels at which they arise in different individuals. Anterior Medullary Feeder Arteries. There is an average total of eight anterior medul¬ lary feeder arteries (both sides included in the total) that enter the vertebral canal segmentally to join the anterior (longitudinal) spinal artery (Fig. 11-34); however, the num¬ ber varies from 2 to 17 in different individu¬ als (Dommisse, 1975). Their diameter varies from 0.2 to 0.8 mm. One especially large (1.0 to 1.3 mm) and important vessel, the great anterior medullary artery (or artery of Adamkiewicz1), which reinforces the circu¬ lation to the lumbar enlargement, usually enters the vertebral canal at the lower tho¬ racic or upper lumbar level. This vessel, however, has been observed to enter as high as the seventh thoracic and as low as the fourth lumbar level. It is a unilateral artery and in 77% of the specimens studied it en¬ tered the spinal cord from the left side (Dommisse, 1975). Three anterior medullary feeder arteries (range one to six) join the ventral spinal ar¬ tery in the cervical region. The largest of these is most frequently at the fifth or sixth BRANCHES OF THE SEGMENTAL ARTERIES.

Fag. 11-37 A posterior view of the cervical spinal cord snowing an arterial injection of the posterior spinal ar¬ teries, certain radicular arteries, several larger vessels along the roots which are posterior medullary feeder ar¬ teries, and the anastomotic network of the dorsal cord. (Maillot and Koritke, 1970.)

the posterior columns, the dorsal gray mat¬ ter, and the superficial dorsal aspect of the lateral columns. SEGMENTAL ARTERIES SUPPLYING THE SPINAL CORD

The spinal cord receives segmental ar¬ teries bilaterally at every intervertebral level and these vessels enter the spinal canal by way of the intervertebral foramina. In the upper three to five cervical segments, they are medially coursing branches of the verte¬ bral artery, whereas in the lower cervical region, they may be derived from the as¬ cending cervical branch of the inferior thy¬ roid artery or from the deep cervical branch of the costocervical trunk (Fig. 11-35). In the thoracic region, the segmental vessels sup¬

1 Albert Adamkiewicz (1850-1921): A Polish experimen¬ tal pathologist (Krakow).

970

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

Sulcal artery Dorsolateral longitudinal arterial trunk

Ventral longitudinal arterial trunk

Supe rficial coronal artery

Dorsal radicular artery

Ventral medullary feeder artery

Segmental artery

radicular artery

Fig 11-38. Diagram of the arterial vascular pattern of a spinal cord segment. Note the difference between the medullary feeder branches and the radicular branches of the segmental spinal arteries. (From W. F. Windle, ed„ The Spinal Cord and Its Reaction to Injury, Marcel Dekker, New York, 1980.)

cervical level. The thoracic region receives an average of three feeder arteries (range one to five), and the lumbar spinal cord, an average of two feeder vessels. Posterior Medullary Feeder Arteries. The posterior medullary feeder arteries are smaller in diameter but more numerous and more evenly distributed than the anterior (Fig. 11-36). In the series of dissections re¬ ported by Dommisse (1975), the average total of posterior feeder arteries observed (both sides included) was 12, with a range from 6 to 25. Gillilan (1958) reported a range of 10 to 20 vessels, while Tveten (1976) found a range of 14 to 25. Thus, in the cervical region, an average number of three posterior medul¬ lary feeder arteries can be expected, with the highest incidence of vessels found at ver¬ tebral levels C6 to C8. An average of five posterior feeder vessels has been found be¬ tween spinal segments T2 to T9, and four vessels between T10 and S5. The diameter of the posterior medullary feeder arteries ranges from 0.05 to 0.35 mm.

INTRAMEDULLARY ARTERIES OF THE SPINAL CORD

Most of the gray and white substance of the spinal cord receives arterial blood by way of branches from the anterior and pos¬ terior spinal arteries. A small amount of the parenchyma of the cord, however, is sup¬ plied by the five radicular branches of the segmental spinal arteries that course inti¬ mately with the dorsal and ventral roots. Some of these latter vessels penetrate the surface of the cord and accompany the roots through the root-cord junction (Figs. 11-38; 11-39). INTRAMEDULLARY BRANCHES FROM THE ANTE¬

The anterior spinal ar¬ tery gives rise to many short and straight branches that frequently stem at right angles to the main trunk and course posteriorly through the anterior median fissure to reach the anterior commissural region of the spi¬ nal cord. These are called sulcal (or central) arteries, and most arise singly (Fig. 11-38). Reaching the cord at the depth of the fissure. RIOR spinal artery.

GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

971

the anterior and lateral columns are sup¬ plied by sulcal vessels, while the more su¬ perficial regions of white substance are sup¬ plied by branches from the coronal vessels and the surface pial plexus. INTRAMEDULLARY BRANCHES FROM THE POS¬

The two posterior spinal arteries, coursing in the posterolateral sulci, give off penetrating branches that sup¬ ply the posterior one-third of the spinal cord (Fig. 11-39). At each level, some of these ves¬ sels accompany the fibers of the dorsal roots into the posterior gray substance of the dor¬ sal horn. Entering the spinal cord, they branch at an acute angle and quickly subdi¬ vide into precapillary and capillary vessels (Gillilan, 1958). Other branches from the posterior spinal artery are directed medially on the surface of the cord, and from these vessels stem small penetrating arteries that supply the white matter of the posterior col¬ umn on each side. Some of these vessels enter the cord directly on its posterior sur¬ face, while others enter the posterior median sulcus to penetrate the posterior columns medially. Although there may be some anatomic continuity between a few capillaries derived from the anterior spinal artery and those derived from the posterior spinal artery, the intramedullary branches from these vessels do not form significant functional anastomo¬ ses. During life, their “functional distribu¬ tion is as if they were end arteries” (Gillilan, 1958). radicular arteries. Many authors pre¬ sent a confusing description of the radicular arteries because they do not differentiate between the anterior and posterior medul¬ lary feeder branches and the true dorsal and ventral radicular branches, all of which stem from the segmentally derived spinal vessels after the latter have entered the interverte¬ bral foramina. The true radicular arteries, which nourish the nerve roots, are found at every level and on both sides of the cord (Fig. 11-38). At times some of these vessels achieve the root-cord junction and penetrate the spinal cord to assist in the supply of the most superficial parts of the gray matter in both the dorsal and ventral horns. TERIOR spinal arteries.

Fig. 11-39. Diagram of a cross section of the spinal cord showing the regions supplied by the various intra¬ medullary arteries. A, Region of distribution of the sulcal (central) artery; D, region supplied by the penetrating arteries from the lateral and ventral pial plexus; ad,the region that may be supplied by either the sulcal artery or the lateral and ventral penetrating arteries; B, the region supplied by the penetrating arteries from the posterior plexus; ab, the region that may be supplied by either the sulcal or the posterior penetrating arteries. (L. A. Gillilan, 1958.)

each sulcal artery turns to the left or right but does not bifurcate to supply both sides. Successive sulcal arteries frequently turn alternately, but occasionally consecutive vessels turn to the same side. The number of sulcal arteries supplying each segment var¬ ies from five to nine, being more numerous in those segments that form the spinal cord enlargements. Counts ranging from 184 to 228 sulcal arteries (average 210) for all 31 segments of the cord have been reported (Tvetan, 1976). In addition to the sulcal branches, the an¬ terior spinal artery gives rise to a number of delicate coronal arteries, which course later¬ ally around the outer surface of the cord (Fig. 11-38). They help to form a superficial pial plexus and they anastomose with each other and with superficial branches from the posterior spinal arteries. From the coronal arteries and the pial plexus, penetrating branches enter the white matter of the ven¬ tral and lateral columns. The sulcal arteries and the penetrating branches from the coronal arteries together supply the anterior two-thirds of the spinal cord (Fig. 11-39). The anterior gray column, the base of the posterior gray column, and the deeper portions of the white matter in

Venous Drainage of the Spinal Cord

The veins that drain the spinal cord pa¬ renchyma are described as two principal groups: the intramedullary veins, which

972

DEVELOPMENTAL AND GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

form from the intrinsic capillaries of the spi¬ nal cord, and the intradurally located sur¬ face veins of the spinal cord, which receive the intramedullary veins and drain extradurally into veins in the neck, thorax, abdo¬ men, pelvis, and spinal column, as well as the communicating venous sinuses of the cranial cavity. In general, the veins of the spinal cord follow a pattern consistent with that of the spinal arteries, but a number of differences exist. The veins of the spinal cord should not be confused with the veins of the vertebral column. These latter include the internal and external vertebral plexuses (of Batson1), which are extradural but com¬ municate with the veins that drain the neu¬ ral tissue of the spinal cord on the one hand and the systemic veins of the thorax, abdo¬ men, and pelvis, as well as the dural sinuses of the skull on the other. INTRAMEDULLARY VEINS OF THE SPINAL CORD

Venous blood from the spinal cord drains from within the neural tissue to the more superficial channels located on the surface

Radial vein

of the cord by means of an anterior median group of sulcal (or central) veins, which opens into the longitudinally coursing ante¬ rior median vein, and by a radial group of veins, which arises from the periphery of the gray matter or from the white matter and courses radially toward the superficial coro¬ nal plexus of veins in the pia mater (Fig. 1140) (Gillilan, 1970). sulcal (or central) veins. Each sulcal (or central) vein is formed by the confluence of several venules just deep to the anterior median sulcus (fissure) within the substance of the anterior white commissure (Figs. 1140; 11-41). Their location corresponds to the sulcal arteries, but contrary to the unilater¬ ally directed arteries, the sulcal veins re¬ ceive blood from both halves of the cord and even anastomose above and below with ven¬ ules that form adjacent sulcal veins. The sulcal veins are less numerous and smaller than the sulcal arteries, and they open into the anterior median spinal vein, which is 1Oscar V. Batson (1894-1979): An American anatomist at the University of Pennsylvania (Philadelphia).

Epidural veins

Dura mater

From external vertebral plexus

Arachnoid

Intervertebral foramen

Central vein

Spinal nerve

Radicular veins

From external vertebral plexus

Intervertebral vein

Coronal plexus Anterior median spinal vein

Medullary vein

11 40. This figure shows the sulcal (central) and radial veins within the spinal cord and their relationship to the pial and epidural venous plexuses. Convergence of the intramedullary, radicular, and epidural veins at the interverte¬ bral foramen is shown on the right. (L. A. Gillilan, 1970).

Fig

GROSS ANATOMY OF THE CENTRAL NERVOUS SYSTEM

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Fig. 12-3.

THE PERIPHERAL NERVOUS SYSTEM

The left optic nerve and the optic tracts.

coats through the many small foramina of the lamina cribrosa sclerae to form the optic nerve. The optic nerve, as it courses posteri¬ orly toward the brain, traverses the central region of the orbit, passes through the optic canal (foramen), and then, approaching the nerve of the other side, joins it to form the optic chiasma. From the chiasma, the fibers continue in the optic tracts, which diverge from each other and reach the base of the brain near the cerebral peduncle. The cen¬ tral connections of the fibers are described in Chapter 11. Parts of the Optic Nerve The optic nerve has four portions, con¬ tained in: (a) the bulb, (b) the orbit, (c) the optic canal, and (d) the cranial cavity. intraocular portion. The intraocular portion is very short, about 1 mm, and the nerve fibers within it are unmyelinated until they pass through the lamina cribrosa, at which point they become myelinated and supported by neuroglia. orbital portion. The orbital portion, 3 to 4 mm in diameter, is 20 to 30 mm long; its course is slightly sinuous, which allows greater length for unrestricted movement of the eyeball. It is invested by sheaths derived from the dura, arachnoid, and pia mater, all three of which fuse and become continuous with the sclera at the lamina cribrosa; the dura extends as far back as the cranial cav¬ ity, the arachnoid somewhat farther, and the pia all the way to the chiasma. The pia

closely ensheathes the nerve and sends nu¬ merous septa into its substance, carrying the blood supply. Between the sheaths are sub¬ arachnoid and subdural spaces similar to and continuous with those of the cranial cavity, the subarachnoid ends in a cul-de-sac at the lamina cribrosa. As it traverses the orbit, the optic nerve is surrounded by the posterior part of the fascia bulbi (Tenon’s capsule1), the orbital fat, and, in its anterior two-thirds, by the ciliary nerves and arteries. Toward the posterior part of the orbit, it is crossed obliquely by the nasociliary nerve, the ophthalmic artery, the superior ophthal¬ mic vein, and the superior division of the oculomotor nerve. Farther toward the roof of the orbit are the rectus superior and leva¬ tor palpebrae superioris muscles, and the trochlear and frontal nerves. Inferior to it are the inferior division of the oculomotor nerve and the rectus inferior muscle; medial to it is the rectus medialis muscle; and lateral to it are the abducent nerve and rectus later¬ alis muscle. In the posterior part of the orbit are the ciliary ganglion and the ophthalmic artery (Fig. 12-6). As it passes into the optic canal, accompanied by the ophthalmic ar¬ tery, it is surrounded by the common anular tendon (of Zinn2), which serves as the origin of the ocular muscles. A short distance be¬ hind the bulb, the optic nerve is pierced by the central artery of the retina and its ac¬ companying vein. These vessels enter the bulb through an opening in the lamina cribrosa and supply the retina. optic canal portion. Within the optic canal, the ophthalmic artery lies inferior to the nerve, just after it has branched from the internal carotid artery. Medially, separated by a thin plate of bone, is the sphenoidal air sinus. If the pneumatization of the bone is extensive, the nerve may be almost com¬ pletely surrounded by the sphenoidal sinus or the posterior ethmoidal cells. Superior to the nerve, the three sheaths—dura, arach¬ noid, and pia—are fused to each other, to the nerve, and to the periosteum of the bone, thereby fixing the nerve and preventing it from being forced back and forth in the fora¬ men. The subarachnoid and subdural spaces are present only below the nerve. 'Jacques Rene Tenon (1724-1816): A French pathologist and surgeon (Paris). 2Johann Gottfried Zinn (1727-1759): A German professor of medicine and botanist (Gottingen).

CRANIAL NERVES

The intracranial portion of the nerve (Fig. 12-1) rests on the anterior part of the cavernous sinus and on the diaphragma sellae, which overlies the hypophysis. The part of the brain above the nerve is the anterior perforated substance. The internal carotid artery approaches the nerve laterally and then is directly inferior to it at the origin of the ophthalmic artery. The anterior cerebral artery crosses superior to it. intracranial portion.

Optic Chiasma

The optic chiasma (Fig. 12-3), as the name indicates, resembles the Greek letter “X” from the convergence of the optic nerves in front and the divergence of the optic tracts behind. It rests upon the tuberculum sellae of the sphenoid bone and on the diaphragma sellae of the dura. It is continuous superiorly with the lamina terminalis, and posteriorly, with the tuber cinereum and the infundibu¬ lum of the hypophysis. Lateral to the optic chiasma, on each side, are the anterior perfo¬ rated substance and the internal carotid ar¬ tery. Optic Tract

The optic tract leaves the chiasma and diverges from its fellow of the opposite side until it reaches the cerebral peduncle, where it winds obliquely across the undersurface. It is adjacent to the tuber cinereum and pe¬ duncle, thus having contact with the third ventricle. As it terminates, a shallow groove divides it into a medial and lateral root. The lateral root contains fibers of visual function and ends in the lateral geniculate body. The medial root carries fibers that decussate (commissure of Gudden1 and probably other nonvisual commissures, those of Meynert2 and Darkschewitsch3). The fibers lying medially in the optic nerve cross in the chiasma and continue in the optic tract of the other side. The lateral fibers are uncrossed and continue to the brain in the optic tract of the same side. The

'Bernhard Aloys von Gudden (1824-1886): A Swiss pro¬ fessor of psychiatry (Zurich). 2Theodor Herman Meynert (1833-1892): An Austrian professor of neurology and psychiatry (Vienna). 3Liverij Osipovich Darkschewitsch (1858-1925): A Rus¬ sian neurologist (St. Petersburg).

1155

fibers from the two sides become intermin¬ gled in the tract. The optic nerve corresponds to a tract of fibers within the brain rather than to the other cranial nerves because of its embryologic development and its structure. It devel¬ ops from a diverticulum of the lateral aspect of the forebrain; its fibers probably are third in the chain of neurons from the receptors to the brain. The fibers are supported by neu¬ roglia instead of neurilemmal sheaths, and the nerve has three sheaths prolonged from the corresponding meninges of the brain (see Chapter 13).

III.

OCULOMOTOR NERVE

The oculomotor nerve (Figs. 12-6; 12-7) supplies the levator palpebrae superioris muscle, the extrinsic muscles of the eye ex¬ cept the obliquus superior and rectus lat¬ eralis, and the intrinsic muscles with the exception of the dilator pupillae. Its super¬ ficial origin is from the midbrain at the ocu¬ lomotor sulcus on the medial side of the cer¬ ebral peduncle. Its deep origin and central connections within the brain are described in Chapter 11. The oculomotor nerve is tra¬ ditionally considered a motor nerve, con¬ taining special somatic efferent fibers for the ocular muscles and parasympathetic fibers for the ciliary ganglion, but experimental evidence indicates that it contains proprio¬ ceptive fibers from cells in the brain stem near the motor cells (Corbin and Oliver, 1942). As it emerges from the brain into the pos¬ terior cranial fossa, the nerve is invested with pia mater, and is bathed in the cerebro¬ spinal fluid of the cisterna interpeduncularis (basalis). It passes between the superior cer¬ ebellar and posterior cerebral arteries near the termination of the basilar artery. It is cov¬ ered with arachnoid lateral to the posterior clinoid process, and between the anterior and posterior clinoid processes it pierces the dura (Fig. 12-1) by passing between the free and attached borders of the tentorium cerebelli. It runs anteriorly, embedded in the lat¬ eral wall of the cavernous sinus (Fig. 12-13), superior to the other orbital nerves. It enters the superior orbital fissure between the two heads of the rectus lateralis (Fig. 12-4) in two divisions, a superior and an inferior. Within the fissure, the trochlear, lacrimal, and fron-

1156

THE PERIPHERAL NERVOUS SYSTEM

Levator palpebrae Frontal nerve Sup ramus of oculomotor nerve

Nasociliary nerve Trochlear nerve

Sup. orbital fissure Lacrimal nerve

Abducent nerve Inf. ramus of oculomotor nerve

Inf. orbital fissure

Optic canal

Fig. 12-4. Dissection showing origins of right ocular muscles, and nerves entering through the superior orbital fissure.

tal nerves lie superior to it, the abducent nerve lies inferior and lateral to it, and the nasociliary nerve passes between its two divisions. Two communications join the oculomotor nerve as it runs along the wall of the cavern¬ ous sinus: (1) one from the cavernous plexus of the sympathetic system, carrying postgan¬ glionic fibers from the superior cervical gan¬ glion: and (2) one from the ophthalmic divi¬ sion of the trigeminal nerve. The superior division (Fig. 12-6), smaller than the inferior, passes medialward across the optic nerve and sends branches to the rectus superior and the levator palpebrae superioris muscles. The branch to the leva¬ tor contains sympathetic postganglionic fi¬ bers from the cavernous plexus, which con¬ tinue anteriorly to reach the nonstriated muscle attached to the superior tarsus. The inferior division has four branches: to the rectus medialis, passing inferior to the optic nerve; to the rectus inferior; and to the obliquus inferior. The latter runs forward between the inferior and lateral recti mus¬ cles and gives off a short, rather thick branch, the root of the ciliary ganglion. ciliary ganglion. The ciliary ganglion (ophthalmic or lenticular ganglion) (Figs. 12-5; 12-6) is a small parasympathetic gan¬

glion (1 or 2 mm in diameter) whose pregan¬ glionic fibers come from the oculomotor nerve and whose postganglionic fibers carry motor impulses to the ciliaris and sphincter pupillae muscles. It is situated about 1 cm from the posterior boundary of the orbit, close to the lateral surface of the optic nerve and between it and the rectus lateralis mus¬ cle and the ophthalmic artery. The parasympathetic motor root (radix oculomotorii; short root) of the ganglion is a rather short, thick nerve, which may be dou¬ ble. It comes from the branch of the inferior division of the oculomotor nerve that sup¬ plies the obliquus inferior and is connected with the posterior inferior angle of the gan¬ glion. It contains preganglionic parasympa¬ thetic fibers from the Edinger-Westphal group of cells of the third nerve nucleus, which form synapses in the ganglion with cells whose postganglionic fibers pass through the short ciliary nerves into the bulb. Two communications were formerly called roots of the ganglion: (1) a communication with the nasociliary nerve (long root; sen¬ sory root) joins the posterior superior angle of the ganglion; it contains sensory fibers that traverse the short ciliary nerves on their way from the cornea, iris, and ciliary body,

CRANIAL NERVES

1157

Short ciliary nerve to ciliary muscle

Fig. 12-5. Autonomic connections of the ciliary and superior cervical ganglia. Parasympathetic blue; sympathetic red.

Long ciliary Anterior ethmoidal Ciliary ganglion Lacrimal

Nasociliary

Cavernous plexus on internal carotid artery

Sensory root

\

I

Oculomotor Trochlear Sensory root Motor root

Motor root Sympathetic root Abducent

Zygomatic Short ciliary

Fig. 12-6.

Nerves of the orbit, side view.

1 1 58

THE PERIPHERAL NERVOUS SYSTEM

without forming synapses in the ganglion; (2) a communication with the sympathetic system (sympathetic root) that is a slender filament from the cavernous plexus which frequently blends with the communication with the nasociliary nerve. It contains post¬ ganglionic fibers from the superior cervical ganglion that pass through the ciliary gan¬ glion without forming synapses and reach the dilator pupillae muscle and the blood vessels of the bulb through the short ciliary nerves. The branches of the ganglion are the short ciliary nerves, which are six to ten delicate filaments that leave the anterior part of the ganglion in two bundles, superior and infe¬ rior. They run anteriorly with the ciliary ar¬ teries in a wavy course, one set above and the other below the optic nerve, and they are accompanied by the long ciliary nerves from the nasociliary. They pierce the sclera at the posterior part of the bulb, pass anteriorly in delicate grooves on the inner surface of the sclera, and are distributed to the ciliary body, iris, and cornea. The parasympathetic post¬ ganglionic fibers supply the ciliaris and sphincter pupillae muscles. The short ciliary nerves also carry sympathetic postgangli¬ onic fibers to the dilator pupillae muscle, and sensory fibers from the cornea, iris, and ciliary body.

IV. TROCHLEAR NERVE

The trochlear nerve (Fig. 12-7) is the small¬ est of the cranial nerves and supplies the obliquus superior oculi muscle. Its superfi¬ cial origin is from the surface of the anterior medullary velum at the side of the frenulum veli, immediately posterior to the inferior colliculus. Its deep origin and central con¬ nections are described in Chapter 11. The nerve is directed laterally across the superior cerebellar peduncle, and it winds around the cerebral peduncle near the pons. It runs anteriorly along the free border of the tentorium cerebelli for 1 or 2 cm (Fig. 12-1), pierces the dura just posterior to the poste¬ rior clinoid process, and without changing the direction of its course, takes its place in the lateral wall of the cavernous sinus (Fig. 12-13) between the oculomotor nerve and the ophthalmic division of the trigeminal nerve, to which it becomes firmly attached

Supratrochlear Supraorbital Trochlea Infratrochlear Anterior ethmoidal

Nasociliary Lacrimal

t

Zygomatic

Trochlear Cavernous plexus Internal carotid artery Oculomotor Dura mater Motor root of trigeminal

Fig. 12-7.

Recurrent meningeal Sensory root

Nerves of the orbit, seen from above.

by connective tissue. It crosses the oculomo¬ tor r.erve in a slightly upward course, enters the orbit through the superior orbital fissure, and becomes superior to the other nerves. In the orbit it passes medialward, above the origin of the levator palpebrae superioris (Fig. 12-4), and finally enters the orbital sur¬ face of the obliquus superior. In the lateral wall of the cavernous sinus the trochlear nerve forms communications with the cavernous plexus of the sympa¬ thetic and with the ophthalmic division of the trigeminal nerve. variations. Occasionally sensory branches ap¬ pear to come from the trochlear nerve, but they are probably aberrant fibers that have come from the ophthalmic nerve.

V. TRIGEMINAL NERVE

The trigeminal nerve is the largest of the cranial nerves. It is the great cutaneous sen¬ sory nerve of the face, the sensory nerve to the mucous membranes and other internal structures of the head, and the motor nerve of the muscles of mastication.

CRANIAL NERVES

Roots

The trigeminal nerve traditionally has two roots, a larger sensory root and a smaller motor root (Fig. 12-6). Investigations have also revealed a third or intermediate root. The sensory root is composed of a large number of fine bundles in close association with each other that enter the pons through the lateral part of its ventral surface. The nerve fibers in the sensory root are the cen¬ tral processes of the ganglion cells in the tri¬ geminal (semilunar) ganglion. The motor root emerges in several bundles from the surface of the pons approximately 2 to 5 mm medial and anterior (rostral) to the sensory root. In addition to the motor fibers, the motor root includes proprioceptive sen¬ sory fibers from the mesencephalic central nucleus of the nerve (Corbin and Harrison, 1940). The intermediate root, composed of one or more bundles, has an origin from the surface of the pons quite distinct from that of the other two roots (Jannetta and Rand, 1966). The bundles arise between the motor and sensory roots and are separated from them by 1 to 5 mm (Vidic and Stephanos, 1969). The internal fiber connections, function, and surgical importance of this root are not yet explained. The three roots pass anteriorly in the pos¬ terior cranial fossa, under the shadow of the tentorium where the latter is attached to the petrous portion of the temporal bone, to the trigeminal ganglion. The deep origin and central connections of these roots are de¬ scribed in Chapter 11. Trigeminal Ganglion

The trigeminal ganglion (ganglion semilunare; Gasserian ganglion1) (Fig. 12-8) lies in a pocket of dura mater (cavum Meckelii2) that occupies the trigeminal impression near the apex of the petrous portion of the tempo¬ ral bone (Burr and Robinson, 1925). The gan¬ glionic mass is flat and has a semilunar shape; it is approximately 1 cm x 2 cm (Fig. 12-8). The central processes of the cells leave

'Johann Laurenz Gasser (7—1765): An Austrian anatomist (Vienna). 2Johann Friedrich Meckel (the Elder, 1714-1774): A Ger¬ man anatomist and obstetrician (Berlin).

1159

the concavity and the peripheral fibers leave the convexity of the crescent. The ganglion is lateral to the posterior part of the cavernous sinus and the internal ca¬ rotid artery at the foramen lacerum, and the central fibers pass inferior to the superior petrosal sinus. The motor root, being medial to the sensory, passes beneath the ganglion (that is, between it and the petrous bone), and leaves the skull through the foramen ovale with the mandibular nerve. The greater petrosal nerve also passes between the ganglion and the bone. The ganglion re¬ ceives filaments from the carotid plexus of the sympathetic system, and it gives off min¬ ute branches to the tentorium cerebelli and to the dura mater of the middle cranial fossa. The peripheral fibers from the ganglion are collected into three large divisions: (1) the ophthalmic, (2) the maxillary, and (3) the mandibular nerves. The ophthalmic and maxillary nerves remain sensory, but the mandibular nerve becomes mixed, being joined by the motor root just outside the skull. Four small ganglia are associated with these nerves: the ciliary ganglion with the ophthalmic, the pterygopalatine with the maxillary, and the otic and submandibular with the mandibular. These ganglia are not a part of the trigeminal complex functionally, however, and the trigeminal fibers that com¬ municate with them pass through without synapses. The ganglia are parasympathetic and are therefore described with the nerves that supply their motor roots with pregangli¬ onic fibers (viz., the ciliary ganglion with the oculomotor nerve, the pterygopalatine and submandibular ganglia with the facial nerve, and the otic ganglion with the glossopharyn¬ geal nerve. Ophthalmic Nerve

The ophthalmic nerve (Figs. 12-6; 12-7), or first division of the trigeminal, leaves the anterior superior part of the trigeminal gan¬ glion and enters the orbit through the supe¬ rior orbital fissure. It is a flat band about 2.5 cm long and lies in the lateral wall of the cavernous sinus, inferior to the oculomotor and trochlear nerves (Fig. 12-13). It is a sen¬ sory nerve, supplying the bulb of the eye, conjunctiva, lacrimal gland, part of the mu¬ cous membrane of the nose and paranasal

1 1 60

THE PERIPHERAL NERVOUS SYSTEM

sinuses, and the skin of the forehead, eye¬ lids, and nose. The ophthalmic nerve is joined by com¬ municating sympathetic filaments from the cavernous plexus and communicates with the oculomotor, trochlear, and abducent nerves. It gives off a recurrent filament to the dura mater, and just before it passes through the superior orbital fissure it divides into three other branches: frontal, lacrimal, and nasociliary.

BRANCHES AND COMMUNICATIONS OF OPHTHALMIC NERVE

Tentorial Branch

The tentorial branch (Fig. 12-7, recurrent filament) arises near the ganglion, passes across and adheres to the trochlear nerve, and runs between the layers of the tento¬ rium, to which it is distributed.

Lacrimal Nerve

The lacrimal nerve (Fig. 12-7) is the small¬ est of the three branches of the ophthalmic nerve. It passes anteriorly in a separate tube of dura mater, and enters the orbit through the narrowest part of the superior orbital fis¬ sure. In the orbit it runs along the superior border of the rectus lateralis muscle close to the periorbita, and enters the lacrimal gland with the lacrimal artery, giving off filaments to supply the gland and adjacent conjunc¬ tiva. Finally, it pierces the orbital septum and ends in the skin of the upper eyelid, joining with filaments of the facial nerve. In the orbit, through a communication with the zygomatic branch of the maxillary nerve (Figs. 12-6; 12-8), it receives postgangli¬ onic parasympathetic fibers, which are the secretomotor fibers for the lacrimal gland. These fibers pass from their cells of origin in the pterygopalatine ganglion through the pterygopalatine nerves to the maxillary nerve, then along the zygomatic and zygo¬ maticotemporal nerves, finally traversing the communication just mentioned and being distributed with the branches of the lacrimal nerve to the gland. The preganglionic fibers reach the ganglion from the facial nerve by way of the greater petrosal nerve.

variations. The lacrimal nerve is occasionally absent, and its place is then taken by the zygo¬ maticotemporal branch of the maxillary nerve. Sometimes the latter is absent and a communication of the lacrimal is substituted for it.

Frontal Nerve

The frontal nerve (Fig. 12-7) is the largest branch of the ophthalmic nerve, and may be regarded, both from its size and direction, as the continuation of the nerve. It enters the orbit through the superior orbital fissure, continues rostrally between the levator palpebrae superioris and the periorbita, and at a variable distance approximately half¬ way to the supraorbital margin, it divides into a large supraorbital and a small supra¬ trochlear branch. supratrochlear nerve. The supratrochlear nerve (Fig. 12-7) bends medially to pass superior to the pulley of the obliquus supe¬ rior muscle and gives off a filament that communicates with the infratrochlear branch of the nasociliary nerve. It pierces the orbital fascia, sends filaments to the conjunctiva and skin of the medial part of the upper lid, passes deep to the corrugator and frontalis muscles, and divides into branches that pierce the muscles to supply the skin of the lower and mesial part of the forehead (Fig. 12-10). supraorbital nerve. The supraorbital nerve (Fig. 12-7), the continuation of the frontal nerve, leaves the orbit through the supraorbital notch or foramen. It gives fila¬ ments to the upper lid and continues upon the forehead, dividing into medial and lat¬ eral branches beneath the frontalis muscle (Fig. 12-10). The medial branch, sometimes called the frontal branch, is smaller; it pierces the muscle and supplies the scalp as far as the parietal bone. The larger lateral branch pierces the galea aponeurotica and supplies the scalp nearly as far back as the lambdoidal suture (Fig. 12-18). The supraor¬ bital nerve may divide before leaving the orbit, in which case the lateral branch occu¬ pies the supraorbital notch or foramen and the medial or frontal branch may have a notch of its own. frontal sinus branch. In the supraorbital notch, a small filament pierces the bone to supply the mucous membrane of the fron¬ tal sinus.

CRANIAL NERVES

Nasociliary Nerve

The nasociliary nerve (Fig. 12-7) is inter¬ mediate in size between the frontal and lac¬ rimal nerves and is more deeply placed in the orbit. It enters the orbit between the two heads of the rectus lateralis muscle, and be¬ tween the superior and inferior divisions of the oculomotor nerve. It passes across the optic nerve and runs obliquely inferior to the rectus superior and obliquus superior muscles to the medial wall of the orbital cav¬ ity. Here it passes through the anterior eth¬ moidal foramen as the anterior ethmoidal nerve and enters the cranial cavity just supe¬ rior to the cribriform plate of the ethmoid bone. It runs along a shallow groove on the lateral margin of the plate, and penetrating the bone through a slit at the side of the crista galli, it enters the nasal cavity. It sup¬ plies branches to the mucous membrane of the nasal cavity (Figs. 12-2; 12-12). Finally, it emerges between the inferior border of the nasal bone and the lateral nasal cartilage as the external nasal branch. BRANCHES OF THE NASOCILIARY NERVE. The communication with the ciliary ganglion {long or sensory root of the ganglion) (Fig. 12-6) usually arises from the nasociliary nerve between the two heads of the rectus lateralis muscle. It runs anteriorly on the lat¬ eral side of the optic nerve and enters the posterior superior angle of the ciliary gan¬ glion. It contains sensory fibers that pass through the ganglion without synapses and continue on into the bulb by way of the short ciliary nerves. It is sometimes joined by a filament from the cavernous plexus of sympathetic fibers or from the superior ramus of the oculomotor nerve. The ciliary ganglion is described with the oculomotor nerve. Two or three long ciliary nerves are given off from the nasociliary nerve as it crosses the optic nerve. They accompany the short ciliary nerves from the ciliary ganglion, pierce the posterior part of the sclera, and running anteriorly between it and the cho¬ roid, are distributed to the iris and cornea. In addition to afferent fibers, the long ciliary nerves probably contain sympathetic fibers from the superior cervical ganglion to the dilator pupillae muscle, which passes through the communication between the cavernous plexus and the ophthalmic nerve.

1161

The infratrochlear nerve (Fig. 12-7) is given off from the nasociliary nerve just be¬ fore it enters the anterior ethmoidal fora¬ men. It runs anteriorly along the superior border of the rectus medialis muscle and is joined near the pulley of the obliquus supe¬ rior by a filament from the supratrochlear nerve. It then passes to the medial angle of the eye and supplies the skin of the eyelids and side of the nose, the conjunctiva, the lac¬ rimal sac, and the caruncula lacrimalis (Fig. 12-10). The ethmoidal branches supply the mu¬ cous membrane of the sinuses. The posterior ethmoidal nerve leaves the orbit through the posterior ethmoidal foramen and supplies the posterior ethmoidal and the sphenoidal sinuses. The anterior ethmoidal branches are filaments that are given off as the nerve passes through the anterior ethmoidal fora¬ men; they supply the anterior ethmoidal and frontal sinuses. The internal nasal branches supply the mucous membrane of the anterior part of the septum and lateral wall of the nasal cavity (Figs. 12-2; 12-12). The external nasal branch emerges be¬ tween the nasal bone and the lateral nasal cartilage, passes deep to the nasalis muscle, and supplies the skin of the ala and the apex of the nose (Fig. 12-8).

Maxillary Nerve

The maxillary nerve (superior maxillary nerve) (Fig. 12-8), or second division of the trigeminal, arises from the middle of the tri¬ geminal ganglion. It is intermediate between the other two divisions in size and position, and like the ophthalmic nerve, it is entirely sensory. It supplies the skin of the middle portion of the face, lower eyelid, side of the nose, and the upper lip (Fig. 12-10); the mu¬ cous membrane of the nasopharynx, maxil¬ lary sinus, soft palate, tonsil and roof of the mouth; and the upper gums and teeth. It passes horizontally rostralward, at first in the inferior part of the lateral wall of the cavernous sinus and then beneath the dura to the foramen rotundum, through which it leaves the cranial cavity. From the foramen rotundum, it crosses the pterygopalatine fossa, inclines lateralward in a groove on the posterior surface of the maxilla, and enters the orbit through the inferior orbital fissure.

1 162

the peripheral nervous system

Fig. 12-8.

Distribution of the maxillary and mandibular nerves, and the submandibular ganglion.

In the posterior part of the orbit it becomes the infraorbital nerve, lies in the infraorbital groove, and, continuing rostralward, dips into the infraorbital canal. It emerges into the face through the infraorbital foramen, where it is deep to the levator labii superioris, and divides into branches for the skin of the face, nose, lower eyelid, and upper lip. The branches of the maxillary nerve may be divided into four groups, those given off: (1) in the cranium, (2) in the pterygopalatine fossa, (3) in the infraorbital canal, and (4) in the face.

BRANCHES IN THE CRANIUM

The middle meningeal nerve (meningeal or dural branch) is given off from the maxil¬ lary nerve directly after its origin from the trigeminal (semilunar) ganglion: it accompa¬ nies the middle meningeal artery and sup¬ plies the dura mater.

BRANCHES IN THE PTERYGOPALATINE FOSSA

Zygomatic Nerve

The zygomatic nerve (temporomalar nerve; orbital nerve) (Fig. 12-6) arises in the pterygopa¬ latine fossa, enters the orbit by the inferior orbital fissure, and divides into two branches, zygomaticotemporal and zygomaticofacial. ZYGOMATICOTEMPORAL BRANCH. The ZygOmaticotemporal branch runs along the lat¬ eral wall of the orbit in a groove in the zygo¬ matic bone, and passing through a small foramen or through the sphenozygomatic suture, enters the temporal fossa. It runs upward between the bone and substance of the temporalis muscle, pierces the temporal fascia about 2.5 cm above the zygomatic arch, is distributed to the skin of the side of the forehead, and communicates with the facial nerve and with the auriculotemporal branch of the mandibular nerve. As it

CRANIAL NERVES

pierces the temporal fascia, it gives off a slender twig, which runs between the two layers of the fascia to the lateral side of the orbit (Fig. 12-18). Before it leaves the orbit, it sends a com¬ munication to the lacrimal nerve through which the postganglionic parasympathetic fibers from the pterygopalatine ganglion reach the lacrimal gland (Fig. 12-8). zygomaticofacial branch. The zygomaticofacial branch (molar branch) passes along the inferior lateral angle of the orbit, through the zygomatic bone by way of the zygomat¬ icoorbital and zygomaticofacial foramina, emerges upon the face, and perforating the orbicularis oculi muscle, supplies the skin on the prominence of the cheek. It joins with the facial nerve and with the inferior palpe¬ bral branches of the infraorbital nerve (Fig. 12-18).

variations. The two branches vary in size, a deficiency in one being made up by the other or by the lacrimal or infraorbital nerves.

Pterygopalatine Nerves

The pterygopalatine nerves (sphenopala¬ tine nerves) (Figs. 12-8; 12-9) are two short trunks that unite at the pterygopalatine gan¬ glion and then are redistributed into branches. Formerly these trunks were called the sensory

1163

roots of the ganglion, and their peripheral branches were listed as the branches of dis¬ tribution of the ganglion. Since most fibers in the trunks are trigeminal somatic afferents that merely pass beside or through the gan¬ glion without synapses, the branches are listed here as belonging to the maxillary nerve rather than the ganglion. The ganglion is described with the facial nerve. The pterygopalatine nerves serve also as important functional communications be¬ tween the ganglion and the maxillary nerve. Postganglionic parasympathetic secretomotor fibers from the ganglion pass through them and back along the main maxillary nerve to the zygomatic nerve, through which they are routed to the lacrimal nerve and lacrimal gland. Other fibers from the gan¬ glion accompany the branches of distribu¬ tion of the maxillary nerve to the glands of the nasal cavity and palate. The branches of distribution from the pterygopalatine nerves are divisible into four groups: (1) orbital, (2) palatine, (3) poste¬ rior superior nasal, and (4) pharyngeal. orbital branches. The orbital branches (ascending branches) are two or three deli¬ cate filaments that enter the orbit by the in¬ ferior orbital fissure and supply the perios¬ teum. Filaments pass through foramina in the frontoethmoidal suture to supply the mucous membrane of the posterior ethmoi¬ dal and sphenoidal sinuses.

Nerve of pterygoid canal Greater petrosal nerve petrosal nerve petrosal nerve Nerve to tens. tymp.

Pter, pal. gang.

Tensor tymp.

Otic ganglion

Mid. men. art. Auric, temp. n. Maxil. art.

Greater pal. a. Lesser pal. n. Chorda tymp. Mylohyoid n.

Fig. 12-9.

The pterygopalatine ganglion and nasal and palatine nerves.

1 1 64

THE PERIPHERAL NERVOUS SYSTEM

greater palatine nerve. The greater pal¬ atine nerve (anterior palatine nerve; de¬ scending branch) (Figs. 12-9; 12-12) passes through the pterygopalatine canal, emerges upon the hard palate through the greater pal¬ atine foramen, and divides into several branches, the longest of which passes anteri¬ orly in a groove in the hard palate nearly as far as the incisor teeth. It supplies the gums and mucous membrane of the hard palate and adjacent parts of the soft palate, and communicates with the terminal filaments of the nasopalatine nerve. Posterior Inferior Nasal Branches. These branches leave the nerve while it is in the canal, enter the nasal cavity through open¬ ings in the palatine bone, and ramify over the inferior nasal concha and middle and inferior meatuses. Lesser Palatine Nerves. These nerves (Fig. 12-9) emerge through the lesser palatine foramina and distribute branches to the soft palate, uvula, and tonsil. They join with the tonsillar branches of the glossopharyngeal nerve to form a plexus around the tonsil (circulus tonsillaris). Many of the somatic affer¬ ent fibers contained in the lesser palatine nerves belong to the facial nerve, have their cells in the geniculate ganglion, and traverse

the greater petrosal nerve and the nerve of the pterygoid canal (Vidian1 nerve). POSTERIOR SUPERIOR NASAL BRANCHES. The posterior superior nasal branches enter the posterior part of the nasal cavity by the sphenopalatine foramen and supply the mucous membrane covering the superior and middle conchae, the lining of the poste¬ rior ethmoid sinuses, and the posterior part of the septum. One branch, longer and larger than the others, and named the nasopala¬ tine nerve, passes across the roof of the na¬ sal cavity inferior to the ostium of the sphe¬ noidal sinus to reach the septum. It runs obliquely forward and downward, lying between the mucous membrane and perios¬ teum of the septum, to the incisive canal (Fig. 12-2). It passes through the canal and communicates with the corresponding nerve of the opposite side and with the greater palatine nerve. pharyngeal branch. The pharyngeal branch (pterygopalatine nerve) (Fig. 12-9) leaves the posterior part of the pterygopala¬ tine ganglion. It passes through the pharyn-

^idus Vidius (Guido Guidi, 1500-1569): An Italian phy¬ sician and professor of medicine (Pisa).

Lacrimal n.

Supratrochlear n Supraorbital n

Infratrochlear n

Temporal br. of temporomalar

Nasal nerve Infraorbital nerve Buccal nerve

r br of temporomalar Auriculotemporal nerve

Mental ne

Fig. 12-10. Sensory areas of the head, showing the general distribution of the three divisions of the fifth nerve. (Modified from Testut.)

CRANIAL NERVES

geal canal with the pharyngeal branch of the maxillary artery, and is distributed to the mucous membrane of the nasal part of the pharynx posterior to the auditory tube. Posterior Superior Alveolar Branches

The posterior superior alveolar branches (posterior superior dental branches) (Fig. 12-8) arise from the trunk of the nerve just before it enters the infraorbital groove; there are generally two, but sometimes they arise by a single trunk. They cross the tuberosity of the maxilla and give off several twigs to the gums and neighboring parts of the mu¬ cous membrane of the cheek. They then enter the posterior alveolar canals on the infratemporal surface of the maxilla, and passing anteriorly in the substance of the bone, communicate with the middle supe¬ rior alveolar nerve. They give off branches to the lining membrane of the maxillary sinus and three twigs to each molar tooth; these twigs enter the foramina at the apices of the roots of the teeth.

1165

BRANCHES IN THE FACE inferior palpebral branches. The infe¬ rior palpebral branches (Fig. 12-8) pass supe¬ riorly, deep to the orbicularis oculi muscle. They supply the skin and conjunctiva of the lower eyelid, joining at the lateral angle of the orbit with the facial and zygomaticofacial nerves. external nasal branches. The external nasal branches (Fig. 12-8) supply the skin of the side of the nose and of the septum mo¬ bile nasi. They join with the terminal twigs of the nasociliary nerve. superior labial branches. The superior labial branches (Fig. 12-8), the largest and most numerous, pass deep to the levator labii superioris muscle and are distributed to the skin of the upper lip, to the mucous membrane of the mouth, and to the labial glands. They communicate immediately in¬ ferior to the orbit with filaments from the facial nerve, forming with them the infraor¬ bital plexus.

Mandibular Nerve BRANCHES IN INFRAORBITAL CANAL MIDDLE SUPERIOR ALVEOLAR BRANCH. The middle superior alveolar branch (middle superior dental branch) is given off from the nerve in the posterior part of the infraor¬ bital canal, and runs downward and forward in a canal in the lateral wall of the maxil¬ lary sinus to supply the two premolar teeth. It forms a superior dental plexus with the anterior and posterior superior alveolar branches. ANTERIOR SUPERIOR ALVEOLAR BRANCH. The large anterior superior alveolar branch (an¬ terior superior dental branch) (Fig. 12-8) is given off from the nerve just before its exit from the infraorbital foramen; it courses in a canal in the anterior wall of the maxillary sinus, and divides into branches that supply the incisor and canine teeth. It communi¬ cates with the middle superior alveolar branch and gives off a nasal branch, which passes through a minute canal in the lateral wall of the inferior meatus and supplies the mucous membrane of the anterior part of the inferior meatus and the floor of the nasal cavity, communicating with the nasal branches from the pterygopalatine nerves. The infraorbital nerve emerges through the infraorbital foramen and supplies the branches to the face (Fig. 12-10).

The mandibular nerve (inferior maxillary nerve) (Figs. 12-8; 12-11; 12-12), or third and largest division of the trigeminal, is a mixed nerve and has two roots: a large sensory root arising from the inferior angle of the trigemi¬ nal ganglion, and a small motor root (the entire motor root of the trigeminal nerve). The sensory fibers supply the skin of the temporal region, auricula, external meatus, cheek, lower lip, and lower part of the face; the mucous membrane of the cheek, tongue, and mastoid air cells; the lower teeth and gums; the mandible and temporomandibular joint; and part of the dura mater and skull. The motor fibers supply the muscles of mas¬ tication (masseter, temporalis, pterygoid), the mylohyoid and anterior belly of the di¬ gastric, and the tensores tympani and veli palatini. The two roots leave the middle cra¬ nial fossa through the foramen ovale, the motor part medial to the sensory, and unite just outside the skull. The main trunk thus formed is short, 2 or 3 mm, and divides into a smaller anterior and a larger posterior divi¬ sion. The otic ganglion lies close against the medial surface of the nerve, just outside the foramen ovale where the two roots fuse, and it surrounds the origin of the medial ptery¬ goid nerve (Fig. 12-20). A communication to the otic ganglion

1166

THE PERIPHERAL NERVOUS SYSTEM

Deep temporal nerves

Auriculotemporal nerve Buccal nerve Communicating nerve

Facial nerve Inferior alveolar and mylohyoid nerves

Lingual nerve Parotid duct

Mental nerve Fig. 12-11.

Mandibular division of the trigeminal nerve.

from the internal pterygoid nerve was for¬ merly called a root of the ganglion, but the fibers pass through without synapses. variations. The two divisions are separated by a fibrous band, the pterygospinous ligament, which may become ossified, and the anterior division then passes through a separate opening in the bone, the pterygospinous foramen (foramen of Civinini1).

The branches of the main trunk of the nerve are the meningeal branch, the medial pterygoid nerve, the anterior trunk, and the posterior trunk. MENINGEAL BRANCH

The meningeal branch (nervus spinosus, recurrent branch) enters the skull through the foramen spinosum with the middle men¬ ingeal artery. It divides into two branches, 'Filippo (Pisa).

Civinini (1805-1844):

An

Italian

anatomist

which accompany the anterior and posterior divisions of the artery and supply the dura mater. The anterior branch communicates with the meningeal branch of the maxillary nerve; the posterior sends filaments to the mucous membrane of the mastoid air cells. MEDIAL PTERYGOID NERVE

The medial pterygoid nerve (Fig. 12-20) is a slender branch that penetrates the otic ganglion and, after a short course, enters the deep surface of the muscle. It has two small branches that have a close association with the otic ganglion and have been described as branches of the ganglion, but their fibers pass through the ganglion without interrup¬ tion. These are the nerve to the tensor veli palatini (Fig. 12-9), which enters the muscle near its origin, and the nerve to the tensor tympani, which lies close to and nearly par¬ allel with the lesser superficial petrosal nerve and penetrates the cartilage of the auditory tube to supply the muscle.

CRANIAL NERVES

ANTERIOR TRUNK

The anterior division of the mandibular nerve (Fig. 12-8) receives a small contribu¬ tion of sensory fibers and all of the motor fibers from the motor root except those in the medial pterygoid and mylohyoid nerves. The following branches supply the muscles of mastication and the skin and mucous membrane of the cheek. masseteric nerve. The masseteric nerve (Fig. 12-11) passes lateralward, above the lateral pterygoid, to the mandibular notch, which it crosses with the masseteric artery to enter the masseter muscle near its origin from the zygomatic arch. It gives a filament to the temporomandibular joint. DEEP temporal nerves. The deep tempo¬ ral nerves (Fig. 12-11) are usually two, ante¬ rior and posterior, but a third or interme¬ diate may be present. The anterior deep temporal frequently is given off from the buccal nerve; it emerges with the latter be¬ tween the two heads of the lateral pterygoid muscle and turns superiorly into the anterior portion of the temporalis muscle. The poste¬ rior deep temporal nerve, and the intermedi¬ ate nerve if present, pass over the superior border of the lateral pterygoid close to the bone of the temporal fossa and enter the deep surface of the muscle. The posterior branch sometimes arises in common with the masseteric nerve. lateral pterygoid nerve. The lateral pter¬ ygoid nerve enters the deep surface of the muscle. It frequently arises in conjunction with the buccal nerve. buccal nerve. The buccal nerve (bucci¬ nator nerve; long buccal nerve) (Fig. 12-11) passes between the two heads of the lateral pterygoid muscle to reach its superficial sur¬ face; it follows or penetrates the inferior part of the temporalis muscle and emerges from under the anterior border of the masseter muscle. It ramifies on the surface of the buc¬ cinator muscle, forming a plexus of commu¬ nications with the buccal branches of the facial nerve; it supplies the skin of the cheek over this muscle and sends penetrating branches to supply the mucous membrane of the mouth and part of the gums in the same area. variations. The buccal nerve may supply a branch to the lateral pterygoid as it passes through that muscle, and frequently it gives off the anterior deep temporal nerve. It may arise from the trigemi¬

1167

nal ganglion, passing through its own foramen; it may be a branch of the inferior alveolar nerve; or it may be replaced by a branch of the maxillary nerve.

POSTERIOR TRUNK

The posterior division of the mandibular nerve is mainly sensory, but it has a small motor component. The following are its branches. auriculotemporal nerve. The auriculo¬ temporal nerve (Fig. 12-8) generally arises by two roots that join after encircling the mid¬ dle meningeal artery close to the foramen spinosum. It runs posteriorly, deep to the lat¬ eral pterygoid muscle, along the medial side of the neck of the mandible, and it turns su¬ periorly with the superficial temporal artery, between the auricula and the condyle of the mandible, under cover of the parotid gland. Escaping from beneath the gland, it passes over the root of the zygomatic arch and di¬ vides into superficial temporal branches (Fig. 12-18). The branches and communica¬ tions of the auriculotemporal nerve are sev¬ eral. The communications with the facial nerve (Fig. 12-11), usually two large communica¬ tions, pass anteriorly from behind the neck of the mandible and join the facial nerve in the substance of the parotid gland at the pos¬ terior border of the masseter muscle. They carry sensory fibers that accompany the zy¬ gomatic, buccal, and mandibular branches of the facial nerve and supply the skin of these areas. Communications with the otic ganglion (Fig. 12-20) join the roots of the auriculo¬ temporal nerve close to their origin. They carry postganglionic parasympathetic fibers whose preganglionic fibers come from the glossopharyngeal nerve and supply the pa¬ rotid gland with secretomotor fibers. The anterior auricular branches (Fig. 1211), usually two, supply the skin of the ante¬ rior superior part of the auricula, principally the helix and tragus. The two branches to the external acoustic meatus (Fig. 12-11) enter the meatus between its bony and cartilaginous portions and sup¬ ply the skin lining it; the upper one sends a filament to the tympanic membrane. The articular branches consist of one or two twigs that enter the posterior part of the temporomandibular joint. The parotid branches supply the parotid

1 1 68

THE PERIPHERAL NERVOUS SYSTEM

gland, carrying the parasympathetic post¬ ganglionic fibers transmitted by the com¬ munication between the auriculotemporal nerve and the otic ganglion. The superficial temporal branches accom¬ pany the superficial temporal artery to the vertex of the skull; they supply the skin of the temporal region and communicate with the facial and zygomaticotemporal nerves. lingual nerve. The lingual nerve (Figs. 12-8; 12-12; 12-36) is at first deep to the lateral pterygoid muscle, running parallel with the inferior alveolar nerve and lying medial and anterior to it. It is frequently joined to the inferior alveolar nerve by a branch that may cross the maxillary artery. The chorda tympani nerve joins it here also. The lingual nerve runs between the medial pterygoid muscle and the mandible, and then crosses obliquely over the superior constrictor of

the pharynx and the styloglossus to reach the side of the tongue. It passes between the hyoglossus and the deep part of the subman¬ dibular gland. Finally, crossing the lateral side of the submandibular duct, it runs along the undersurface of the tongue to its tip, lying immediately beneath the mucous mem¬ brane (Fig. 12-12). The chorda tympani (Figs. 12-8; 12-12), a branch of the facial nerve, joins the lingual nerve posteriorly at an acute angle, 1 or 2 cm from the foramen ovale. It carries special sensory fibers for taste and parasympathetic preganglionic fibers for the submandibular ganglion. The communications with the subman¬ dibular ganglion are usually two or more short nerves by which the ganglion seems to be suspended (Fig. 12-12). The proximal nerves carry the preganglionic parasympa-

Olfactory bulb

Fig 12-12. Deep dissection of the region of the face viewed from its medial aspect, showing the pterygopalatine, otic, and submandibular ganglia and associated structures. (Redrawn from Tondury.)

CRANIAL NERVES

thetic fibers communicated to the lingual by the chorda tympani. The distal communica¬ tion contains postganglionic fibers for distri¬ bution to the sublingual gland. Communications with the hypoglossal nerve (Fig. 12-36) form a plexus at the ante¬ rior margin of the hyoglossus muscle. The branches of distribution supply the mucous membrane of the anterior twothirds of the tongue, the adjacent mouth and gums, and the sublingual gland. The taste buds of the anterior two-thirds of the tongue are supplied by the fibers communicated through the chorda tympani. inferior alveolar nerve. The inferior al¬ veolar nerve (inferior dental nerve) (Fig. 12-11) accompanies the inferior alveolar ar¬ tery, at first deep to the lateral pterygoid muscle and then between the sphenomandibular ligament and the ramus of the man¬ dible, to the mandibular foramen. It enters the mandibular canal through the foramen, and passes anteriorly within the bone as far as the mental foramen, where it divides into two terminal branches. The mylohyoid nerve (Fig. 12-8) leaves the inferior alveolar nerve just before it enters the mandibular foramen, and it continues inferiorly and anteriorly in a groove on the deep surface of the ramus of the mandible to reach the mylohyoid muscle. It supplies this muscle and crosses its superficial surface to reach the anterior belly of the digastric mus¬ cle (Fig. 12-8), which it also supplies. The dental branches form a plexus within the bone and supply the molar and premolar teeth. Filaments enter the pulp canal of each root through the apical foramen and supply the pulp of the tooth. The incisive branch is one of the terminal branches. It continues anteriorly within the bone, after the mental nerve separates from it, and forms a plexus that supplies the ca¬ nine and incisor teeth. The mental nerve (Fig. 12-11), the other terminal branch, emerges from the bone at the mental foramen and divides beneath the depressor anguli oris muscle into three branches: one is distributed to the skin of the chin: the other two, to the skin and mucous membrane of the lower lip. These branches communicate freely with branches of the facial nerve. The otic and submandibular ganglia, al¬ though closely associated with the mandibu¬ lar nerve, are not connected functionally,

1169

and are described, therefore, with the nerves that supply them with preganglionic fibers: the otic ganglion with the glossopharyngeal nerve, and the submandibular with the fa¬ cial nerve. variations. The inferior alveolar and lingual nerves may form a single trunk or they may have communications of variable size; the chorda tympani may appear to join the inferior alveolar nerve, with a later communication carrying the fibers to the lin¬ gual nerve. The inferior alveolar nerve is occasion¬ ally perforated by the maxillary artery. It may have accessory roots from other branches of the mandib¬ ular nerve or a separate root from the trigeminal ganglion. The mylohyoid nerve may communicate with the lingual nerve, and it has been described as sending filaments to the depressor anguli oris, the platysma, the submandibular gland, and the integu¬ ment below the chin. TRIGEMINAL NERVE PAIN (TIC DOULOUREUX). The trigeminal nerve is more frequently the seat of se¬ vere neuritic or neuralgic pain than any other nerve in the body. The pain of a localized infection or irrita¬ tion may be confined to that area, but commonly this is not the case. Involvement of an internal branch is likely to cause severe distress in a related cutaneous area by referred pain. As a general rule the diffusion of pain over the branches of the nerve is confined to one of the main divisions, although in severe cases it may radiate over the other main divi¬ sions. The commonest example of this condition is the neuralgia that is often associated with dental caries. Although the tooth itself may not appear to be pain¬ ful, the most distressing referred pains are experi¬ enced, which are relieved at once by treatment of the affected tooth. With the ophthalmic nerve, se¬ vere supraorbital pain is commonly associated with acute glaucoma or with frontal or ethmoidal sinusi¬ tis. Malignant growths or empyema of the maxillary sinus and diseased conditions in the nasal cavity, as well as dental caries, may cause neuralgia of the sec¬ ond division. Pain in the mandibular division is likely to occur in the ear or other distribution of the auricu¬ lotemporal nerve, although the actual disease may involve one of the lower teeth or the tongue. When a focus of infection or irritation cannot be found, as is all too frequently the case, various measures may be taken to interrupt the pain fibers. Local injection of alcohol into the painful nerve may give temporary relief, and injection of a main divi¬ sion close to the ganglion has been performed with a certain measure of success. The main divisions have been incised surgically, and the entire ganglion has been removed in intractable cases. In the latter oper¬ ation, bleeding is likely to be dangerous and the nerves to the muscles of mastication may be para¬ lyzed. In other operations, the motor root is spared by cutting the sensory root inside the cranium before it reaches the ganglion.

1 1 70 VI.

THE PERIPHERAL NERVOUS SYSTEM

VII.

ABDUCENT NERVE

The abducent nerve (sixth nerve) (Fig. 12-6) supplies the rectus lateralis oculi mus¬ cle. Its superficial origin is in the furrow be¬ tween the inferior border of the pons and the superior end of the pyramid of the medulla oblongata. It pierces the dura mater on the dorsum sellae of the sphenoid bone, runs through a notch below the posterior clinoid process, and traverses the cavernous sinus lateral to the internal carotid artery. It enters the orbit through the superior orbital fissure, superior to the ophthalmic vein, from which it is separated by a lamina of dura mater. After passing between the two heads of the rectus lateralis muscle, it enters its ocular surface. Communication with the sympathetic sys¬ tem is by several filaments from the carotid and cavernous plexuses. Through a filament from the ophthalmic nerve, the abducent nerve communicates with the trigeminal nerve. RELATION

OF

ORBITAL

NERVES

TO

CAVERNOUS

Embedded in the lateral wall of the cavern¬ ous sinus, in order beginning with the most supe¬ rior, are the oculomotor, trochlear, ophthalmic, and maxillary nerves (Fig. 1 2-1 3). The abducent nerve is suspended by connective tissue trabeculae within the sinus, lateral to the internal carotid artery and medial to the ophthalmic nerve. The maxillary nerve is related to the posterior portion of the sinus and it soon diverges from the other nerves. As the nerves approach the superior orbital fissure, the oculomotor and ophthalmic nerves divide into branches, and the abducent nerve approaches the others, so that their relative positions are considerably changed. sinus.

Internal carotid artery Cavernous sinus Oculomotor nerve Trochlear nerve Ophthalmic nerve Abducent nerve

Maxillary nerve

FACIAL NERVE

The facial nerve (seventh nerve) has two roots of unequal size (Fig. 12-14). The larger is the motor root; the smaller, lying between the motor root and the vestibulocochlear nerve, is called the nervus intermedius (nerve of Wrisberg1), and contains special sensory fibers for taste and parasympathetic fibers. The superficial origin of both roots is at the inferior border of the pons in the re¬ cess between the olive and the inferior cere¬ bellar peduncle, the motor root being me¬ dial, the vestibulocochlear nerve lateral, and the nervus intermedius between. The facial nerve is the motor nerve to the muscles of facial expression, to muscles in the scalp and external ear, and to the bucci¬ nator, platysma, stapedius, stylohyoid, and posterior belly of the digastric muscles. The sensory part supplies the anterior two-thirds of the tongue with taste, and parts of the ex¬ ternal acoustic meatus, soft palate, and adja¬ cent pharynx with general sensation. The parasympathetic part supplies secretomotor fibers for the submandibular, sublingual, lacrimal, nasal, and palatine glands. From their superficial attachment, the two roots pass lateralward, with the vestibulo¬ cochlear nerve, into the internal acoustic meatus (Fig. 12-1). At the fundus of the mea¬ tus, the facial nerve separates from the ves¬ tibulocochlear nerve and enters the sub¬ stance of the petrous portion of the temporal bone, through which it runs a serpentine course in the facial canal (aqueductus Fallopii2). At first it continues lateralward in the region between the cochlea and semicircular canals (Fig. 13-58); near the tympanic cavity it makes an abrupt bend posteriorly, runs in the medial wall of the cavity just above the oval window (Fig. 13-50), covered by a thin plate of bone that causes a slight prominence in the wall (Fig. 13-51), and then dips down beside the mastoid air cells to reach the stylomastoid foramen. Where it changes its course abruptly, there is an exaggeration of the bend into a U-shaped structure named the geniculum; at this point also, the two roots become fused and the nerve is swollen ‘Heinrich August Wrisberg (1739-1808): A German anat¬

Fig. 12-13. ous sinus.

Oblique section through the right cavern¬

omist (Gottingen). 2Gabriele Fallopius (1523-1552): An Italian anatomist (Padua).

CRANIAL NERVES

1171

Nucleus salivatorius superior

Efferent division of n. Intermedius

Genu

Superior maxillary n N. intermedius I Geniculate ganglion

Nucleus of facial n.

Vidian n. Large petrosal

External petrosal fAfferent division of n. intermedius ending in nucleus of tractus solitarius To auricular branch of vagus n.

Tympanic br of IX

'petrosal

J}-,

\ Pterygo-- palatine ? » ganglion

S-Otic ganglion

.r ✓

Tympanic plexus

Communicating branch

tymPar"

Post. auricular br

Lingual n Temporal Zygomatic

To digastric To stylohyoid

Infraorbital

Afferent (taste) fibers

Buccal Mandibular Cervical

Efferent (excito-glandular) fibers to submandibular and sublingual ganglia and glands

Fig. 12-14.

Plan of the facial and intermediate nerves and their communication with other nerves.

by the presence of the geniculate ganglion (Fig. 12-15). As it emerges from the stylomastoid fora¬ men, the nerve runs anteriorly in the sub¬ stance of the parotid gland, crosses the ex¬ ternal carotid artery, and divides at the posterior border of the ramus of the man¬ dible into two primary branches—a supe¬ rior branch, the temporofacial, and an infe¬ rior branch, the cervicofacial. Numerous branches come off the cervicofacial branch in a plexiform arrangement to form the pa¬ rotid plexus; these are distributed over the head, face, and upper part of the neck, sup¬ plying the superficial muscles in these re¬ gions. Geniculate Ganglion

The geniculate ganglion (Fig. 12-15) is a small fusiform swelling of the geniculum, where the facial nerve bends abruptly back¬ ward at the hiatus of the facial canal. It is the sensory ganglion of the facial nerve. The central processes of its unipolar ganglion

cells reach the brain stem through the nervus intermedius; the majority of the pe¬ ripheral processes pass to the taste buds of the anterior two-thirds of the tongue through the chorda tympani and lingual nerves; many peripheral processes pass through the greater superficial petrosal and lesser pala¬ tine nerves to the soft palate; and a smaller number join the auricular branch of the vagus nerve to supply the skin of the exter¬ nal acoustic meatus and mastoid process (Foley et al., 1946). The glossopalatine nerve is the name given by some authors (Hardesty, 1933) to that portion of the facial nerve contributed by the nervus intermedius. It comprises, therefore, the sensory part, including the geniculate ganglion, the chorda tympani, and greater petrosal nerve; and the parasym¬ pathetic part, including the submandibular and pterygopalatine ganglia and their branches. Although this separation is sug¬ gested by the similarity between this com¬ plex and the glossopharyngeal nerve, it has not been generally adopted.

1172

THE PERIPHERAL NERVOUS SYSTEM

Communications of the Facial Nerve

In the internal acoustic meatus, communi¬ cations with the vestibulocochlear nerve probably contain fibers that leave the facial nerve, run with the vestibulocochlear nerve for a short distance, and return to the facial nerve. At the geniculate ganglion, the facial nerve communicates with the otic ganglion by filaments that join the lesser petrosal nerve, and with the sympathetic fibers on the middle meningeal artery (external su¬ perficial petrosal nerve). In the facial canal, just before it leaves the stylomastoid foramen, the facial nerve com¬ municates with the auricular branch of the vagus as the latter runs across it in the sub¬ stance of the bone. After its exit from the stylomastoid fora¬ men, the facial nerve communicates with the glossopharyngeal nerve, the vagus nerve, and the great auricular nerve from the cervi¬ cal plexus. The auriculotemporal nerve from the mandibular division of the trigeminal usually sends two large communications that pass anteriorly from behind the neck of the mandible to join the facial nerve in the substance of the parotid gland (Fig. 12-11). They carry sensory fibers that accompany the terminal zygomatic, buccal, and mandib¬ ular branches to the skin of these areas. Peripheral branches of the facial nerve communicate behind the ear, with the lesser occipital nerve; on the face, with trigeminal branches; and in the neck, with the cervical cutaneous nerve. Branches of Facial Nerve from the Geniculate Ganglion

External petrosal To lesser petrosal Greater petrosal Geniculate ganglion

Facial Vestibulocochlear

Fig. 12 15. The geniculate ganglion and facial nerve in the temporal bone.

form the nerve of the pterygoid canal (Vidian nerve) (Figs. 12-9; 12-12). The greater petrosal nerve is a mixed nerve, containing sensory and parasympathetic fibers. The parasympathetic fibers, from the nervus intermedius, become the motor root of the pterygopalatine ganglion. The bulk of the nerve consists of sensory fibers, which are the peripheral processes of cells in the genic¬ ulate ganglion and are distributed to the soft palate through the lesser palatine nerves, with a few filaments to the auditory tube. Nerve of Pterygoid Canal

The nerve of the pterygoid canal (Vidian nerve) (Fig. 12-9), formed by the union of the greater petrosal and deep petrosal nerves at the foramen lacerum, enters the posterior opening of the pterygoid canal with the cor¬ responding artery and is joined by a small ascending sphenoidal branch from the otic ganglion. The bony wall of the canal com¬ monly causes a ridge in the floor of the sphe¬ noidal sinus, and while the nerve is in the canal it gives off one or two filaments for the mucous membrane of the sinus. From the anterior opening of the canal, the nerve crosses the pterygopalatine fossa and enters the pterygopalatine ganglion.

GREATER PETROSAL NERVE

The greater petrosal nerve (greater super¬ ficial petrosal nerve) arises from the genicu¬ late ganglion (Fig. 12-15), and after a short course in the bone, it emerges through the hiatus of the facial canal into the middle cra¬ nial fossa. It runs rostralward beneath the dura mater and the trigeminal ganglion in a sulcus on the anterior surface of the petrous portion of the temporal bone, passes supe¬ rior to the cartilage of the auditory tube (which fills the foramen lacerum), crosses the lateral side of the internal carotid artery, and unites with the deep petrosal nerve to

Pterygopalatine Ganglion

The pterygopalatine ganglion (sphenopal¬ atine ganglion; Meckel's ganglion) (Figs. 12-9; 12-12) is deeply placed in the pterygo¬ palatine fossa, just inferior to the maxillary nerve as the latter crosses the fossa close to the pterygopalatine foramen. It is triangular or heartshaped and about 5 mm long. It is embedded in the fibrous tissue between the neighboring bones and is closely attached to the pterygopalatine branches of the maxil¬ lary division of the trigeminal nerve. It is a parasympathetic ganglion relaying chiefly

CRANIAL NERVES

1173

Lacrimal gland

Fig. 12 16. Autonomic connections of the pterygopalatine and superior cervical ganglia. Parasympathetic blue; sympathetic red.

secretomotor impulses from the facial nerve (Fig. 12-16). The parasympathetic root (visceral effer¬ ent) of the pterygopalatine ganglion is the greater petrosal nerve, and its continuation, the nerve of the pterygoid canal. The fibers are preganglionic parasympathetic fibers, which leave the brain stem in the nervus intermedius. COMMUNICATIONS OF THE PTERYGOPALATINE

Maxillary Nerve. Two short trunks from the maxillary nerve, the ptery¬ gopalatine nerves, are commonly called the sensory root of the ganglion although they have no such functional connection with it. They contain mainly sensory fibers from the trigeminal ganglion that pass through or be¬ side the pterygopalatine ganglion without synapses and continue on their way to the mucous membrane of the nasal cavity and

ganglion

palate. These trunks are important commu¬ nications for the ganglion, however, since they are traversed by the postganglionic fi¬ bers of distribution on their way to the max¬ illary nerve, whence they reach the lacrimal gland and the small glands of the nasal cav¬ ity and palate. Deep Petrosal Nerve The deep petrosal nerve is commonly called the sympathetic root of the pterygopalatine ganglion, al¬ though it is merely a communication be¬ tween the ganglion and the sympathetic sys¬ tem. It contains postganglionic fibers from the superior cervical sympathetic ganglion, by way of the carotid plexus, and passes through the pterygopalatine ganglion with¬ out synapses and accompanies the branches of the pterygopalatine nerves (trigeminal branches) to their destination in the mucous membrane of the nasal cavity and palate.

1 1 74

THE PERIPHERAL NERVOUS SYSTEM

BRANCHES FROM THE PTERYGOPALATINE GAN¬ GLION. The branches of distribution from the pterygopalatine ganglion, containing the postganglionic fibers of the cells within the ganglion, are not independent nerves for the most part, but find their way to their destina¬ tions by accompanying other nerves, mainly the branches of the maxillary nerve. The fibers for the lacrimal gland pass back to the main trunk of the maxillary nerve through the pterygopalatine nerves. They leave the maxillary through the zygomatic and zygomaticotemporal nerves, pass through a communication between the latter and the lacrimal nerve in the orbit, and are then distributed to the gland (Fig. 12-6). Fibers for the small glands of the mucous membrane of the nasal cavity, pharynx, and palate join the greater and lesser palatine nerves, the posterior superior nasal branches, and the pharyngeal branch, and are distributed with them.

Branches of Facial Nerve Within the Facial Canal

NERVE TO STAPEDIUS MUSCLE

The nerve to the stapedius muscle arises from the facial nerve as it passes downward in the posterior wall of the tympanum. It reaches the muscle through a minute open¬ ing in the base of the pyramid (see Middle Ear, Chapter 13). CHORDA TYMPANI NERVE

The chorda tympani nerve (Figs. 12-8; 1212) arises from the part of the facial nerve that runs vertically downward in the poste¬ rior wall of the tympanum just before it reaches the stylomastoid foramen. Entering its own canal in the hone about 6 mm above the stylomastoid foramen, the chorda passes back cranialward almost parallel with the facial nerve but diverges toward the lateral wall of the tympanum. It emerges through an aperture in the posterior wall of the tympa¬ num (iter chordae posterius) between the base of the pyramid and the attachment of the tympanic membrane. It runs horizon¬ tally along the lateral wall of the tympanum covered by the thin mucous membrane, and, lying against the tympanic membrane, it crosses the attached manubrium of the mal¬

leus (Fig. 13-49). It leaves the tympanic cav¬ ity near the anterior border of the membrane through the iter chordae anterius, traverses a canal in the petrotympanic fissure (canal of Huguier1), and emerges from the skull on the medial surface of the spine of the sphe¬ noid bone. After crossing the spine, usually in a groove, and being joined by a small communication from the otic ganglion, it unites with the lingual nerve at an acute angle between the medial and lateral ptery¬ goid muscles. The bulk of the fibers of the chorda tym¬ pani are special visceral afferents for taste, which are distributed with the branches of the lingual nerve to the anterior two-thirds of the tongue. It also contains preganglionic parasympathetic fibers (secretomotor) from the nervus intermedius, which terminate in synapses with cells in the submandibular ganglion (Foley, 1945). submandibular ganglion. The subman¬ dibular ganglion (submaxillary ganglion) (Figs. 12-8; 12-12) is a small mass, 2 to 5 mm in diameter, situated above the deep portion of the submandibular gland on the hyoglossus muscle, near the posterior border of the my¬ lohyoid muscle and suspended from the lower border of the lingual nerve by two fil¬ aments approximately 5 mm long. The prox¬ imal filament is the parasympathetic root, which conveys fibers originating in the nervus intermedius and is communicated to the lingual nerve by the chorda tympani. These are preganglionic visceral efferent fi¬ bers (secretomotor) whose postganglionic fibers innervate the submandibular, sublin¬ gual, lingual, and neighboring small salivary glands (Fig. 12-17). The branches of distribution are (a) five or six filaments distributed to the submandibu¬ lar gland and its duct, (b) to the small glands about the floor of the mouth, and (c) the dis¬ tal filament attaching the ganglion to the lin¬ gual nerve, which communicates the fibers distributed to the sublingual and small lin¬ gual glands with the terminal branches of the lingual nerve. Small groups of ganglion cells are constantly found in the stroma of the submandibular gland, usually near the larger branches of the duct, and functionally are considered a part of the submandibular ganglion. 'Pierre Charles Huguier (1804-1873): A French surgeon (Paris).

CRANIAL NERVES

1175

Fig. 12-17. Autonomic connections of the submandibular and superior cervical ganglia. Parasympathetic blue; sympathetic red.

A communication with the sympathetic bundles on the facial artery has been called the sympathetic root of the ganglion, but the fibers are postganglionic and have no synap¬ ses in the ganglion. Visceral afferent fibers passing through the root to the lingual and thence to the chorda tympani have been called the sen¬ sory root, but they have no synapses in the ganglion and their cell bodies are in the ge¬ niculate ganglion. Branches of Facial Nerve in the Face and Neck

posterior auricular nerve. The poste¬ rior auricular nerve (Fig. 12-18) arises close to the stylomastoid foramen and runs cranialward anterior to the mastoid process; here it is joined by a filament from the auric¬ ular branch of the vagus, and communicates

with the posterior branch of the great auric¬ ular nerve and with the lesser occipital nerve. Between the external acoustic meatus and the mastoid process it divides into auric¬ ular and occipital branches. The auricular branch supplies the auricularis posterior and the intrinsic muscles on the cranial sur¬ face of the auricula. The occipital branch, the larger of the two, passes backward along the superior nuchal line of the occipital bone and supplies the occipitalis muscle. digastric branch. The digastric branch arises close to the stylomastoid foramen, and divides into several filaments, which supply the posterior belly of the digastric muscle. stylohyoid branch. The stylohyoid branch frequently arises in conjunction with the digastric branch; it is long and slender, and enters the stylohyoid muscle near its middle. parotid plexus. The terminal portion of

1176

THE PERIPHERAL NERVOUS SYSTEM

Termination: of supratrochlear of infratrochlear of nasociliary

Fig. 12-18.

The nerves of the scalp, face, and side of neck.

the facial nerve, within the substance of the parotid gland, divides into a temporofacial and a cervicofacial division which in turn, either within the gland or after leaving it, break up into a plexus and supply the facial muscles in different regions. Temporal Branches. The temporal branches (Fig. 12-18) cross the zygomatic arch to the temporal region, supplying the auriculares anterior and superior. They communicate with the zygomaticotemporal branch of the maxillary nerve and with the auriculotemporal branch of the mandibular division of the trigeminal nerve. The more anterior branches supply the frontalis, the orbicularis oculi, and the corrugator muscles and join the supraorbital and lacrimal branches of the ophthalmic nerve.

Zygomatic Branches. The zygomatic branches (malar branches) run across the face in the region of the zygomatic arch to the lateral angle of the orbit, where they sup¬ ply the orbicularis oculi, and communicate with filaments from the lacrimal nerve of the ophthalmic division and the zygomaticofa¬ cial branch of the maxillary division of the trigeminal nerve. The lower zygomatic branches commonly join the deep buccal branches and assist in forming the infraor¬ bital plexus. Buccal Branches. The buccal branches (infraorbital branches), larger than the rest, pass horizontally rostralward to be distrib¬ uted inferior to the orbit and around the mouth. The superficial branches run be¬ neath the skin and superficial to the muscles

CRANIAL NERVES

of the face, which they supply; some are dis¬ tributed to the procerus muscle, communi¬ cating at the medial angle of the orbit with the infratrochlear and nasociliary branches of the ophthalmic nerve. The deep branches, commonly reinforced by zygomatic branches, pass deep to the zygomaticus and the levator labii superioris muscles, supply¬ ing them and forming an infraorbital plexus with the infraorbital branch of the maxillary division of the trigeminal nerve (Fig. 12-18). These branches also supply the small mus¬ cles of the nose. The more inferior deep branches supply the buccinator and orbicu¬ laris oris muscles, and communicate with filaments of the buccal branch of the man¬ dibular division of the trigeminal nerve. Mandibular Branch. The mandibular branch (r. marginalis mandibuiae) passes rostralward deep to the platysma and de¬ pressor anguli oris supplying the muscles of the lower lip and chin and communicating with the mental branch of the inferior alveo¬ lar nerve. Cervical Branch. The cervical branch (r. colli) runs rostralward deep to the platysma, which it supplies, and forms a series of arches across the side of the neck over the suprahyoid region. One branch joins the cer¬ vical cutaneous nerve from the cervical plexus.

VIII.

VESTIBULOCOCHLEAR NERVE

The vestibulocochlear nerve (n. statoacusticus; n. octavius; eighth nerve) (Fig. 11-62) consists of two distinct sets of fibers, the cochlear and vestibular nerves, which differ in their peripheral endings, central connec¬ tions, functions, and time of myelination. These two portions of the vestibulocochlear nerve are joined into a common trunk that enters the internal acoustic meatus with the facial nerve (Fig. 12-15). Centrally, the ves¬ tibulocochlear nerve divides into a lateral (cochlear) root and a medial (vestibular) root. As it passes distally in the internal au¬ ditory meatus, it divides into the various branches, which are distributed to the recep¬ tor areas in the membranous labyrinth (see Chapter 13). Both divisions of this nerve are sensory and the fibers arise from bipolar ganglion cells.

1177

COCHLEAR NERVE. The cochlear nerve or root, the nerve of hearing, arises from bi¬ polar cells in the spiral ganglion of the cochlea, situated near the inner edge of the osseous spiral lamina. The peripheral fibers pass to the organ of Corti.1 The central fibers pass through the modiolus and then through the foramina of the tractus spiralis foraminosus or through the foramen centrale into the lateral or outer end of the internal acous¬ tic meatus. The nerve passes along the inter¬ nal acoustic meatus with the vestibular nerve and across the subarachnoid space, just above the flocculus, almost directly medialward toward the inferior peduncle to terminate in the cochlear nuclei. The cochlear nerve is placed lateral to the vestibular root. Its fibers end in two nuclei: one, the ventral cochlear nucleus, lies imme¬ diately in front of the inferior cerebellar peduncle; the other, the dorsal cochlear nu¬ cleus, tuberculum acusticum, somewhat lat¬ eral to it (see Chapter 11). vestibular nerve. The vestibular nerve or root, the nerve of equilibration, arises from bipolar cells in the vestibular ganglion (ganglion of Scarp a2) which is situated in the superior part of the lateral end of the in¬ ternal acoustic meatus. The peripheral fibers divide into three branches: the superior branch passes through the foramina in the area vestibularis superior and ends in the utricle and in the ampullae of the anterior and lateral semicircular ducts; the fibers of the inferior branch traverse the foramina in the area vestibularis inferior and end in the saccule; the posterior branch runs through the foramen singulare and supplies the am¬ pulla of the posterior semicircular duct. The fibers of the vestibular nerve enter the medulla oblongata, pass between the infe¬ rior cerebellar peduncle and the spinal tract of the trigeminal nerve, and bifurcate into ascending and descending branches. The descending branches form the spinal root of the vestibular nerve and terminate in the associated nucleus. The ascending branches pass to the medial, lateral, and superior ves¬ tibular nuclei, and to the nucleus fastigii and the vermis of the cerebellum. 'Alfonso Corti (1822-1888): An Italian anatomist (born in Sardinia, worked in Germany). 2Antonio Scarpa (1747-1832): An Italian anatomist and surgeon (Pavia).

1178 IX.

the peripheral nervous system

GLOSSOPHARYNGEAL NERVE

The glossopharyngeal nerve (ninth nerve) (Fig. 12-22), as its name implies, is distrib¬ uted to the tongue and pharynx. It is a mixed nerve, its sensory fibers being both visceral and somatic, and its motor fibers both gen¬ eral and special visceral efferents. The so¬ matic afferent fibers supply the mucous membrane of the pharynx, fauces, palatine tonsil, and posterior part of the tongue; spe¬ cial visceral afferents supply the taste buds of the posterior part of the tongue; general visceral afferents supply the blood pressure receptors of the carotid sinus. The special vis¬ ceral efferent fibers supply the stylopharyngeus muscle; the general visceral efferents are mainly secretomotor for the parotid and small glands in the mucous membrane of the posterior part of the tongue and neighboring pharynx. The superficial origin is by three or four rootlets in series with those of the vagus nerve, attached to the superior part of the medulla oblongata in the groove between the olive and the inferior peduncle. From its superficial origin, the nerve passes lateralward across the flocculus to the jugular foramen, through which it passes, lateral and anterior to the vagus and acces¬ sory nerves (Fig. 12-22), in a separate sheath of dura mater and lying in a groove on the lower border of the petrous portion of the temporal bone. After its exit from the skull, it runs anteriorly between the internal jugu¬ lar vein and the internal carotid artery, su¬ perficial to the latter vessel and posterior to the styloid process and its muscles. It fol¬ lows the posterior border of the stylopharyngeus muscle for 2 or 3 cm, then curves across its superficial surface to the posterior border of the hyoglossus muscle, where it penetrates more deeply to be distributed to the palatine tonsil, the mucous membrane of the fauces and base of the tongue, and the glands of that region. The portion of the nerve that lies in the jugular foramen has two enlargements, the superior and the infe¬ rior ganglia. The superior ganglion (jugular ganglion) is situated in the upper part of the groove in which the nerve is lodged during its passage through the jugular foramen. It is very small, may be absent, and is usually regarded as a detached portion of the inferior ganglion.

The inferior ganglion (petrous ganglion) is situated in a depression in the lower border of the petrous portion of the temporal bone. These ganglia contain the cell bodies for the sensory fibers of the nerve (Fig. 12-21). Communications of Glossopharyngeal Nerve

(1) The communications with the vagus nerve are two filaments, one joining the au¬ ricular branch, the other the superior gan¬ glion. (2) The superior cervical sympathetic ganglion communicates with the inferior ganglion. (3) The communication with the facial nerve is between the trunk of the glos¬ sopharyngeal nerve below the inferior gan¬ glion and the facial nerve after its exit from the stylomastoid foramen; it perforates the posterior belly of the digastric muscle.

Branches of Glossopharyngeal Nerve

TYMPANIC NERVE

The tympanic nerve (nerve of Jacobson) (Fig. 12-19) supplies parasympathetic fibers to the parotid gland through the otic gan¬ glion and sensory fibers to the mucous mem¬ brane of the middle ear. It arises from the inferior ganglion and enters a small canal through an opening in the bony ridge that separates the carotid canal from the jugular fossa on the inferior surface of the petrous portion of the temporal bone. After a short cranialward course in the bone, it enters the tympanic cavity by an aperture in its floor near the medial wall. It continues upward in a groove on the surface of the promontory (Fig. 13-50), helps to form the tympanic plexus, reenters a canaliculus at the level of the processus cochleariformis, passes inter¬ nal to the semicanal for the tensor tympani, and continues as the lesser petrosal nerve (Rosen, 1950). tympanic plexus. The tympanic plexus lies in grooves on the surface of the promon¬ tory and is formed by the junction of the tympanic and caroticotympanic nerves. The caroticotympanic nerves, superior and infe¬ rior, are communications from the carotid plexus of the sympathetic, which enter the tympanic cavity by perforating the wall of the carotid canal. The plexus communicates

CRANIAL NERVES

1179

fissure between the petrous portion and the great wing of the sphenoid, or through a small opening in the latter bone, and termi¬ nates in the otic ganglion as its visceral motor or parasympathetic root. In the canal it is joined by a filament from the geniculate ganglion of the facial nerve. OTIC GANGLION

The otic ganglion (Figs. 12-12; 12-20) is a flat, oval, or stellate ganglion, 2 to 4 mm in diameter, closely approximated to the me¬ dial surface of the mandibular division of the trigeminal, immediately outside of the foramen ovale, and it has the origin of the medial pterygoid nerve embedded in it. It is lateral to the cartilaginous portion of the auditory tube, anterior to the middle menin¬ geal artery, and posterior to the origin of the tensor veli palatini muscle. The root of the otic ganglion, which is par¬ asympathetic, is the lesser petrosal nerve. It contains preganglionic fibers from the nu¬ cleus salivatorius inferior in the medulla oblongata, principally through the glosso¬ pharyngeal nerve but probably partly also through the facial nerve. COMMUNICATIONS OF THE OTIC GANGLION.

Fig. 12-19. Autonomic connections of the otic and superior cervical ganglia. Parasympathetic blue; sym¬ pathetic red.

with the greater petrosal nerve by a filament that passes through an opening on the labyrinthic wall, in front of the fenestra vestibuli. Sensory branches are distributed through the plexus to the mucous membrane of the fenestra ovalis, fenestra rotunda, tympanic membrane, auditory tube, and mastoid air cells. The lesser petrosal nerve (Figs. 12-9; 12-20) is the terminal branch or continuation of the tympanic nerve beyond the plexus. After penetrating the bone medial to the tensor tympani muscle, it emerges into the cranial cavity on the superior surface of the petrous portion of the temporal bone, immediately lateral to the hiatus of the facial canal. It leaves the cranial cavity again through the

A communication with the sympathetic net¬ work on the middle meningeal artery has been called the sympathetic root of the gan¬ glion, but these fibers are already postgangli¬ onic and pass through the ganglion without synapses. A communication with the medial ptery¬ goid nerve has been described as a motor root, and the continuation of the fibers to the tensor veli palatini and tensor tympani mus¬ cles has been described as branches of the ganglion, but they are trigeminal fibers that pass through the ganglion. A communication with the mandibular nerve has been called a sensory root, but the fibers have no functional connection with the ganglion. A slender filament, the sphenoidal branch, connects with the nerve of the pterygoid canal, and a small branch communicates with the chorda tympani. BRANCHES

OF

DISTRIBUTION

OF THE

OTIC

The postganglionic fibers arising in the otic ganglion pass mainly through a communication with the auriculotemporal nerve and are distributed with its branches ganglion.

1 1 80

the peripheral nervous system

Middle meningeal a

Auriculotemporal n

Fig. 12-20.

The otic ganglion and its branches.

to the parotid gland. Other filaments proba¬ bly accompany other nerves to reach small glands in the mouth and pharynx.

CAROTID SINUS NERVE

The carotid sinus nerve (nerve of Hering1) (Fig. 12-21) arises from the main trunk of the glossopharyngeal nerve just beyond its emergence from the jugular foramen; it com¬ municates with the nodose ganglion or the pharyngeal branch of the vagus nerve near its origin. Its continuation or principal branch runs down the anterior surface of the internal carotid artery to the carotid bifurca¬ tion, and it terminates in the wall of the dila¬ ted portion of the artery—the carotid sinus—supplying it with afferent fibers for its blood pressure receptors. It has a rather constant branch that joins the intercarotid plexus, formed principally by vagus and sympathetic branches, or it communicates with these nerves independently and reaches the carotid body. Glossopharyngeal fibers may traverse the plexus and its branches to the carotid body on their way to the ca¬ rotid sinus (Sheehan et al., 1941). Its func¬ tional association with the carotid body is questionable. 'Heinrich Ewald Hering (1866-1948): A German physiol¬ ogist (Cologne).

PHARYNGEAL BRANCHES

The pharyngeal branches are three or four filaments that join pharyngeal branches of the vagus and sympathetic nerves opposite the constrictor pharyngis medius muscle to form the pharyngeal plexus (Fig. 12-21). Branches from the plexus penetrate the mus¬ cular coat of the pharynx and supply its muscles and mucous membrane; the exact contribution of the glossopharyngeal nerve is uncertain. BRANCH TO STYLOPHARYNGEUS

The branch to the stylopharyngeus is the only muscular branch of the glossopharyn¬ geal nerve. TONSILLAR BRANCHES

The tonsillar branches supply the palatine tonsil, forming around it a network from which filaments are distributed to the soft palate and fauces, where they communicate with the lesser palatine nerves.

LINGUAL BRANCHES

The lingual branches one supplies the vallate ent fibers for taste, and the mucous membrane

are two in number; papillae with affer¬ general afferents to at the base of the

CRANIAL NERVES

1181

Small petrosal n.

Vagus n Internal carotid art. Accessory nMj Glossopharyngeal n. Hypoglossal n

Pharyngeal branch Lingual branch

Superior cervical sympathetic ganglion

Pharyngeal plexus Hypoglossal n.

Carotid sinus n. C3

Thyrohyoid n.

Carotid sinus-T Lingual art. Superior laryngeal n. cs ^

Superior thyroid art.

Middle cervical -" sympathetic ganglion C6 $ Phrenic n. ■

External branch Ansa cervicalis

C7 £

Inferior cervical C8

ni

Fig. 12-21.

Carotid sinus nerve, carotid body, internal carotid artery, and neighboring cranial, spinal, and sympa¬ thetic nerve connections. Diagrammatic.

tongue; the other supplies the mucous mem¬ brane and glands of the posterior part of the tongue, and communicates with the lingual nerve. clinical comment. Neuralgic pain or "tic douloreux" of the glossopharyngeal nerve occurs in the ear, throat, base of the tongue, rim of the palate, and the lower lateral and posterior part of the phar¬ ynx. The most common trigger zone is the tonsillar fossa (Pastore and Meredith, 1949).

X. THE VAGUS NERVE

The vagus nerve (tenth nerve; pneumogastric nerve) (Figs. 12-22; 12-37), named from its wandering course, is the longest of the cranial nerves and has the most exten¬ sive distribution, passing through the neck and thorax into the abdomen. It has both

somatic and visceral afferent fibers, and gen¬ eral and special visceral efferent fibers. The somatic sensory fibers supply the skin of the posterior surface of the external ear and the external acoustic meatus; the visceral affer¬ ent fibers supply the mucous membrane of the pharynx, larynx, bronchi, lungs, heart, esophagus, stomach, intestines, and kidney. General visceral efferent fibers (parasympa¬ thetic) are distributed to the heart, and sup¬ ply the nonstriated muscle and glands of the esophagus, stomach, trachea, bronchi, bili¬ ary tract, and most of the intestine. Special visceral efferent fibers supply the voluntary muscles of the larynx, pharynx, and palate (except the tensor), but most of the latter fi¬ bers originate in the cranial part of the ac¬ cessory nerve. The superficial origin of the vagus is com¬ posed of eight or ten rootlets attached to the medulla oblongata in the groove between

1182

the peripheral nervous system

jugular foramen. The nerve leaves the cra¬ nial cavity through this opening, accompa¬ nied by the accessory nerve and contained in the same dural sheath, but separated by a septum from the glossopharyngeal nerve, which lies anteriorly. This portion of the vagus has two enlargements, the superior and inferior ganglia, which are the sensory ganglia of the nerve. superior ganglion. The superior gan¬ glion (g. of the root; jugular ganglion) (Fig. 12-21) is a spherical swelling, about 4 mm in diameter, of the vagus nerve as it lies in the jugular foramen. The central processes of its unipolar (sensory) ganglion cells enter the medulla, usually in three or four large inde¬ pendent rootlets, slightly dorsal to the motor rootlets. Most of the peripheral processes of the ganglion cells enter the auricular branch of the vagus, but a few probably are distrib¬ uted with the pharyngeal branches. inferior ganglion. The inferior ganglion (g. of the trunk; nodose ganglion) (Fig. 12-23) forms a fusiform swelling about 2.5 cm long on the vagus nerve after its exit from the jug¬ ular foramen and about 1 cm distal to the superior ganglion. The central processes of its unipolar (sensory) cells pass through the superior ganglion without traversing the re¬ gion occupied by cells, and frequently ac¬ company motor fibers in the rootlets for a short distance but enter the medulla slightly dorsal to them, in line with the superior root¬ lets. Some of the peripheral processes of the ganglion cells make up the internal ramus of the superior laryngeal nerve, and the rest are distributed with other branches of the vagus to the larynx, trachea, bronchi, eso¬ phagus, and other thoracic and abdominal viscera. Communications of the Vagus Nerve

Fig. 12-22.

Course and distribution of the glossopha¬ ryngeal, vagus, and accessory nerves.

the olive and the inferior peduncle, inferior to those of the glossopharyngeal nerve and superior to those of the accessory nerve. The rootlets unite into a flat cord that passes be¬ neath the flocculus of the cerebellum to the

At the superior ganglion, several delicate filaments communicate (1) with the cranial portion of the accessory nerve; (2) with the inferior ganglion of the glossopharyngeal nerve; (3) with the facial nerve by means of the auricular branch; and (4) with the supe¬ rior cervical ganglion of the sympathetic system (jugular nerve). The cranial part of the accessory nerve joins the vagus just proximal to the inferior ganglion. It is the source of the greater part of the fibers in the motor branches of the vagus to the pharynx and larynx.

CRANIAL NERVES

Oculomotor ■

1 1 83

0-^

Trigeminal ■ Abducens ■ VII & VIII Jugular bulb IX, X & XI Inferior ganglion (nodose) vagus -Occipital artery Ascending pharyngeal art." Glossopharyngeal nerve

Internal carotid nerve Super, cerv. symp. gang. ■ Hypoglossal nerve

Vagus nerve Accessory nerve Super, laryngeal nerve

Super, laryn. art. Arytenoid, obi. Arytenoid, trans. ■ Cricoaryten. poster. Infer, laryn. art.Infer. laryn. ner. .

Mid. cerv. sym. gang.

Vertebral arteryInf. cerv. sym. gang Recurrent laryn nerve

Brachial plexus Thyrocervical trunk

Fig. 12-23. Dorsal view of the pharynx and associated nerves and blood vessels after removal of the cervical vertebrae and part of the occipital bone. (Redrawn from Tondury.)

At the inferior ganglion, communication is (1) with the hypoglossal nerve, (2) with the superior cervical sympathetic ganglion, and (3) with the loop between the first and sec¬ ond cervical spinal nerves. The resulting vagus nerve trunk, after it

has been joined by the cranial part of the accessory nerve just distal to the inferior ganglion, passes vertically down the neck within the carotid sheath, deep to and be¬ tween the internal jugular vein and the inter¬ nal and common carotid arteries. Beyond the

1 1 84

THE PERIPHERAL NERVOUS SYSTEM

root of the neck the course of the nerve dif¬ fers on the two sides of the body. The right vagus nerve crosses the first part of the subclavian artery, lying superficial to it and between it and the brachiocephalic vein (Fig. 12-24). It continues along the side of the trachea to the dorsal aspect of the root of the lung, where it spreads out in the poste¬ rior pulmonary plexus (Fig. 12-25). Below this plexus, it splits into cords that enter into the formation of the plexus on the dor¬ sal aspect of the esophagus. After sending communications to the left vagus, these cords unite with each other and with com¬

Thyrocervical artery Inferior thyroid nerve Subclavian artery and vein Phrenic nerve Pleura

munications from the left vagus to form a single trunk, the posterior vagus nerve, be¬ fore passing through the esophageal hiatus in the diaphragm (Fig. 12-25). Below the dia¬ phragm, the posterior vagus continues along the lesser curvature of the stomach on its posterior surface for a short distance and divides into a celiac and several gastric branches. The left vagus enters the thorax between the left carotid and subclavian arteries, deep to the left brachiocephalic vein (Fig. 12-37). It crosses the left side of the arch of the aorta (Fig. 12-24), angling dorsally in its caudal-

Vertebral artery and vein Mid. cerv. symp. ganglion Thoracic duct Brachial plexus Int. thoracic artery Subclavian artery Com. carotid artery

Vagus nerve Azygos vein

Pulmonary arteries

Vagus nerve Recurrent nerve Pulmonary plexus

Pulmonary artery Bronchial artery Pulmonary veins Pulmonary veins

Azygos vein

Esophageal plexus

Thoracic duct Greater splanchnic nerve

Inferior vena cava

Fig. 12-24

Pleura

The mediastinal organs and the roots of the lungs after removal of the heart and pericardium. (Redrawn

from Tondury.)

CRANIAL NERVES

Common carotid artery Thyrocervical trunk Cupula pleura Thoracic / ill,

Scalenus anterior ■ First rib _ Inferior thyroid artery , Subclavian artery

•SSL,. IPte

artery

1185

Mi

Recurrent nerve ' Right lung

, Azygos vein

_ Bronchial artery

Dorsal pulmonary_ plexus

Pleura Thoracic duct

12-25. Dorsal view of the mediastinal structures and roots of the lungs, after removal of the vertebral column, ribs, and thoracic aorta. (Redrawn from Tondury.) Fig.

ward course. It passes between the aorta and the left pulmonary artery just distal to the ligamentum arteriosum, and reaches the dorsal aspect of the root of the lung, where it flattens into the posterior pulmonary plexus (Fig. 12-25). It reaches the esophagus as a

variable number of strands; these follow the ventral aspect of the esophagus, send com¬ munications to the right vagus, and usually unite with each other and with substantial communications from the right vagus to form a single trunk, the anterior vagus

1 1 86

THE peripheral nervous system

nerve, before passing through the dia¬ phragm. Below the diaphragm, the anterior vagus nerve, on the anterior aspect of the stomach, divides into an hepatic and several gastric branches (Jackson, 1949). Branches in the Jugular Fossa meningeal branch. The meningeal branch (dural branch) is a recurrent filament that arises at the superior ganglion and is distributed to the dura mater in the posterior cranial fossa. auricular branch. The auricular branch (nerve of Arnold1) arises from the superior ganglion and soon communicates by a fila¬ ment with the inferior ganglion of the glos¬ sopharyngeal nerve. It passes posterior to the internal jugular vein, and when it reaches the lateral wall of the jugular fossa, it enters the mastoid canaliculus, which crosses the facial canal in the bone about 4 mm superior to the stylomastoid foramen and communicates with the facial nerve. It is a somatic afferent nerve and it reaches the surface by passing through the tympanomas¬ toid fissure. It divides into two branches: (a) one joins the posterior auricular nerve, and (b) the other is distributed to the skin of the back of the auricula and to the posterior part of the external acoustic meatus.

Branches of the Vagus Nerve in the Neck

The pharyngeal branches, usually two, arise at the upper part of the inferior ganglion; they contain sensory fibers from the ganglion and motor fibers from the communication with the ac¬ cessory nerve. They pass across the internal carotid artery to the superior border of the constrictor pharyngis medius where they divide into several bundles that join branches of the glossopharyngeal, sympa¬ thetic, and external branch of the superior laryngeal nerves to form the pharyngeal plexus (Fig. 12-21). Through the plexus, branches are distrib¬ uted to the muscles and mucous membrane of the pharynx, and to the muscles of the soft palate, except the tensor veli palatini. pharyngeal branches.

'Philipp Friedrich Arnold (1803-1890): A German anato¬ mist (Zurich, Freiburg, Tubingen, and Heidelberg).

The nerves to the carotid body are fila¬ ments from the pharyngeal and possibly from the superior laryngeal branches, which join with similar filaments from the glosso¬ pharyngeal nerve and the superior cervical sympathetic ganglion to form the intercarotid plexus between the internal and external carotid arteries at the bifurcation. The vagus fibers are visceral afferents that terminate in the carotid body, which is a chemoreceptor sensitive to changes in oxygen tension of the blood. This is located at the carotid bifurca¬ tion (Sheehan et al., 1941). superior laryngeal nerve. The superior laryngeal nerve (Fig. 12-22) arises near the lower end of the inferior ganglion and passes caudalward and medialward deep to the internal carotid artery and along the pharynx toward the superior cornu of the thyroid cartilage. It has a communication with the superior cervical sympathetic gan¬ glion and may contribute to the intercarotid plexus. It terminates by dividing into a smaller external and a larger internal branch. The external branch (Fig. 12-22) continues caudalward beside the larynx, deep to the sternothyroid muscle and supplies motor fibers to the cricothyroid muscle and part of the constrictor pharyngis inferior. It contrib¬ utes fibers to the pharyngeal plexus and communicates with the superior sympa¬ thetic cardiac nerve. The internal branch swings anteriorly to reach the thyrohyoid membrane, which it pierces with the superior laryngeal artery. It supplies sensory fibers to the mucous mem¬ brane and parasympathetic secretomotor fibers to the associated glands through branches to the epiglottis, base of the tongue, aryepiglottic fold, and the larynx as far cau¬ dalward as the vocal folds. A filament passes caudalward beneath the mucous membrane on the inner surface of the thy¬ roid cartilage and joins the recurrent nerve (Fig. 12-23). SUPERIOR

CARDIAC

BRANCHES.

TWO

Or

three superior cardiac branches arise from the vagus at the superior and inferior parts of the neck. The superior branches are small and communicate with the cardiac branches of the sympathetic. They can be traced to the deep part of the cardiac plexus. The inferior branch arises at the root of the neck just era-

CRANIAL NERVES

nial to the first rib. On the right side it passes ventral or lateral to the brachiocephalic ar¬ tery and joins the deep part of the cardiac plexus. On the left side it passes across the left side of the arch of the aorta and joins the superficial part of the cardiac plexus. recurrent nerve. The recurrent nerve (inferior or recurrent laryngeal nerve) (Fig. 12-25), as its name implies, arises far caudally and runs back cranialward in the neck to its destination, the muscles of the larynx. The origin and early part of its course are different on the two sides. On the right side, it arises in the root of the neck, as the vagus crosses superficial to the first part of the sub¬ clavian artery. It loops under the arch of this vessel and passes dorsal to it to the side of the trachea and esophagus (Fig. 12-74). On the left side, the recurrent nerve arises in the cranial part of the thorax, as the vagus crosses the left side of the arch of the aorta (Fig. 12-75). Just distal to the ligamentum arteriosum, it loops under the arch and passes around it to the side of the trachea. The fur¬ ther course on the two sides is similar; it passes deep to the common carotid artery and along the groove between the trachea and esophagus, medial to the overhanging deep surface of the thyroid lobe. Here it comes into close relationship with the termi¬ nal portion of the inferior thyroid artery. It runs under the caudal border of the constric¬ tor pharyngis inferior muscle, enters the lar¬ ynx through the cricothyroid membrane deep to the articulation of the inferior cornu of the thyroid with the cricoid cartilage, and is distributed to all the muscles of the larynx except the cricothyroid. Its branches are as follows: Cardiac branches are given off as the nerve loops around the subclavian artery or the aorta. These are described below as the inferior cardiac branches of the vagus. Tracheal and esophageal branches, more numerous on the left than on the right, are distributed to the mucous membranes and muscular coats (Fig. 12-23). Pharyngeal branches are filaments to the constrictor pharyngis inferior. Sensory and secretomotor filaments, which reach the recurrent through the com¬ munication with the internal branch of the superior laryngeal, supply the mucous mem¬ brane of the larynx below the vocal folds.

1187

The inferior laryngeal nerves are the ter¬ minal branches that supply motor fibers to all the intrinsic muscles of the larynx except the cricothyroid. variations. When the right subclavian artery arises from the descending aorta, the recurrent nerve arises in the neck and passes directly to the larynx.

Branches of Vagus Nerve in the Thorax inferior cardiac branches. The inferior cardiac branches (thoracic cardiac branches) arise on the right side from the trunk of the vagus as it lies by the side of the trachea and from the recurrent nerve, and on the left side from the recurrent nerve only. They end in the deep part of the cardiac plexus. The visceral efferent fibers to the heart in all the cardiac branches are preganglionic. After passage through the cardiac and coro¬ nary plexuses, these fibers form synapses with groups of ganglion cells in the heart wall, and the postganglionic fibers terminate about the conduction system and muscula¬ ture of the heart. The visceral afferent fibers from cells in the inferior ganglion traverse the cardiac plexus and cardiac nerves, supplying the heart and great vessels. The visceral afferent fibers that supply the aortic bodies (glomera aortica) are carried mainly by the cardiac branches of the right vagus, and those that supply the supracardial bodies (aortic paraganglia) are carried mainly by those of the left vagus. These bod¬ ies are chemoreceptors similar to the carotid body; the cell bodies of the afferent fibers are in the inferior ganglion (Hollinshead; 1939, 1940). DEPRESSOR NERVE OR NERVE OF CYON. In Some animals, the afferent fibers of the vagus from the heart and great vessels are largely contained in a separate nerve whose stimulation causes depression of the activity of the heart. In man, these fibers are probably contained in the inferior cardiac branches (Mitchell, 1953).

anterior bronchial branches. The ante¬ rior bronchial branches (anterior or ventral pulmonary branches) are two or three small

1 188

THE- PERIPHERAL NERVOUS SYSTEM

nerves on the ventral surface of the root of the lung that join with filaments from the sympathetic to form the anterior pulmonary plexus. From this plexus, filaments follow the ramifications of the bronchi and pulmo¬ nary vessels, or communicate with the car¬ diac or posterior pulmonary plexuses. POSTERIOR BRONCHIAL BRANCHES. The posterior bronchial branches (posterior or dorsal pulmonary branches) (Fig. 12-25) are numerous offshoots from the main trunk of the vagus as it passes dorsal to the root of the lung. The vagus itself in this region is flat and spread out so that it combines with the bronchial branches and with the sympa¬ thetic communications to form what is called the posterior pulmonary plexus. The plexus has communications with the car¬ diac, aortic, and esophageal plexuses and its branches follow the ramifications of the bronchi and pulmonary vessels. The visceral efferent fibers form synapses with small groups of ganglion cells in the walls of the bronchi, and the postganglionic fibers terminate in the nonstriated muscle and glands of the bronchi. Afferent fibers supply the lungs and bron¬ chi. esophageal branches. The esophageal branches (Fig. 12-25) consist of superior fila¬ ments from the recurrent nerve and inferior branches from the trunk of the vagus and the esophageal plexus. They contain both vis¬ ceral efferent (parasympathetic pregangli¬ onic) and visceral afferent fibers. esophageal plexus. The fibers of the vagus caudal to the root of the lung split into several bundles (Fig. 12-25), usually two to four larger bundles and a variable number of smaller parallel and communicating strands on each side, which spread out on the esophagus and become partly embedded in its adventitial coat. Filaments are given off for the innervation of the esophagus and there are communications with the splanchnic nerves and sympathetic trunk, forming as a whole the esophageal plexus. The bundles from the left vagus (Fig. 12-24) gradually swing around to the ventral surface of the esophagus; those from the right vagus (Fig. 12-25) swing to the dorsal surface. Just cra¬ nial to the diaphragm, the larger bundles from the left vagus usually combine with one or two strands from the right on the ven¬ tral surface of the esophagus to form a single

trunk, and this newly constituted vagus, which is not strictly the equivalent of the left vagus, passes through the esophageal hiatus of the diaphragm as the anterior vagus. A similar combination on the dorsal surface of the esophagus, mostly right vagus but with a communication from the left, passes through the esophageal hiatus as the posterior vagus (Jackson, 1949). Branches of the Anterior and Posterior Vagi in the Abdomen

The branches in the abdomen (Figs. 12-71; 12-72) contain both visceral efferent (para¬ sympathetic preganglionic) and visceral af¬ ferent fibers. The cells of the postganglionic fibers of the stomach and intestines are in the myenteric plexus (of Auerbach1) and the submucous plexus (of Meissner2); those of the glands are either in small local groups of ganglion cells or possibly in the celiac plexus. gastric branches. Usually four to six branches are given off by both anterior and posterior vagi at the cardiac end of the stom¬ ach. They fan out over their respective sur¬ faces of the fundus and body and penetrate the wall to be distributed to the myenteric and submucous plexuses. On both anterior and posterior surfaces, one branch, longer than the others, follows along the lesser cur¬ vature and has been called the principal nerve of the lesser curvature; it is distributed to the pyloric vestibule rather than the pylo¬ rus itself. hepatic branches. The hepatic branches from the anterior vagus are larger than those from the posterior vagus. They cross from the stomach to the liver in the lesser omen¬ tum and continue along the fissure for the ductus venosus to the porta hepatis, where they give off right and left branches to the liver. The large hepatic branch of the ante¬ rior vagus contributes to the plexus on the hepatic artery and has the following branches: (1) Branches to the gallbladder and bile ducts come from the hepatic branches or the plexus on the artery. 'Leopold Auerbach (1828-1897): A German anatomist and neuropathologist (Breslau). 2Georg Meissner (1829-1905): A German physiologist (Basle and Gottingen).

CRANIAL NERVES

(2) A pancreatic branch runs dorsalward to its destination. (3) A branch along the right gastric artery is distributed to the pylorus and the first part of the duodenum. (4) A branch accompanies the gastroduo¬ denal artery and right gastroepiploic artery and is distributed to the duodenum and stomach. celiac branches. A large terminal divi¬ sion of the posterior vagus follows the left gastric artery or runs along the crus of the diaphragm to the celiac plexus. The terminal branches cannot be followed once the nerve has entered the plexus, but the vagus fibers, through the secondary plexuses, reach the duodenum, pancreas, kidney, spleen, small intestine, and large intestine as far as the splenic flexure. Before the nerve enters the plexus it may give a branch to the superior mesenteric artery or to the aortic plexus (see Celiac Plexus).

XI. THE ACCESSORY NERVE

The accessory nerve (eleventh nerve; spi¬ nal accessory nerve) (Fig. 12-22) is a motor nerve consisting of two parts, a cranial and a spinal part. cranial part. The cranial part (r. internus; accessory portion) arises by four or five deli¬ cate cranial rootlets from the side of the medulla oblongata, inferior to and in series with those of the vagus. From its deep origin and from its destination, it might well be considered a part of the vagus. It runs lateralward to the jugular foramen, where it interchanges fibers with the spinal part or becomes united with it for a short distance, and has one or two filaments of communica¬ tion with the superior ganglion of the vagus. It then passes through the jugular foramen, separates from the spinal part and joins the vagus as the ramus internus, just proximal to the inferior ganglion. Its fibers are distributed through the pharyngeal branch of the vagus to the uvula, levator veli palatini, and the pharyngeal constrictor muscles, and through the superior and inferior laryngeal branches of the vagus to the muscles of the larynx and the esophagus. spinal part. The spinal part (r. externus; spinal portion) originates from motor cells in the lateral part of the ventral column of

1189

gray substance of the first five cervical seg¬ ments of the spinal cord. The fibers pass through the lateral funiculus, emerge on the surface as the spinal rootlets, and join each other seriatim as they follow up the cord between the ligamentum denticulatum and the dorsal rootlets of the spinal nerves. The nerve passes through the foramen magnum into the cranial cavity, crosses the occipital bone to the jugular notch, and penetrates the dura mater over the jugular bulb as the ramus externus (Fig. 12-1). It passes through the jugular foramen in the same sheath of dura as the vagus, but is separated from it by a fold of the arachnoid. In the jugular fora¬ men, it interchanges fibers with the cranial part or joins it for a short distance and sepa¬ rates from it again. At its exit from the fora¬ men, it turns dorsalward, lying ventral to the internal jugular vein in two-thirds and dor¬ sal to it in one-third of the bodies. It passes posterior to the stylohyoid and digastric muscles to the cranial part of the sterno¬ cleidomastoid muscle, which it pierces, and then courses obliquely caudalward across the posterior triangle of the neck to the ven¬ tral border of the trapezius muscle (Fig. 1222). In the posterior triangle it is covered only by the outer investing layer of deep fas¬ cia, the subcutaneous fascia and the skin (Fig. 12-35). COMMUNICATIONS AND BRANCHES. The accessory nerve communicates with the sec¬ ond, third, and fourth cervical nerves, and assuming a plexiform arrangement, it con¬ tinues on the deep surface of the trapezius almost to its caudal border (Fig. 12-22). Ex¬ perimental observations with monkeys indi¬ cate that the communications with the cervi¬ cal nerves carry proprioceptive sensory fibers from cells in the dorsal root ganglia of the spinal nerves. The branches of the acces¬ sory nerve are as follows: (1) Sternocleidomastoid branches are given off as the nerve penetrates this muscle. (2) Trapezius branches are supplied from the part of the nerve lying deep to the mus¬ cle. variations. The lower limit of the origin of the spinal part may vary from C3 to C7. It may pass beneath the sternocleidomastoid muscle without piercing it, and in one instance it ended in that mus¬ cle, the trapezius being supplied by the third and fourth cervical nerves.

1 1 90

XII.

THE PERIPHERAL nervous system

HYPOGLOSSAL NERVE

The hypoglossal nerve (twelfth nerve) (Figs. 12-21; 12-36) is the motor nerve of the tongue. Its superficial origin from the me¬ dulla oblongata is by a series of rootlets in the ventrolateral sulcus between the pyra¬ mid and the olive. The rootlets are collected into two bun¬ dles that perforate the dura mater sepa¬ rately, opposite the hypoglossal canal in the occipital bone, and unite after their passage through it; in some instances the canal is di¬ vided by a small bony spicule. As the nerve emerges from the skull, it is deeply placed beneath the internal carotid artery and the internal jugular vein and is closely bound to the vagus nerve. It runs caudalward and for¬ ward between the vein and artery, becomes superficial to them near the angle of the mandible, loops around the occipital artery, and passes anteriorly across the external carotid and lingual arteries caudal to the tendon of the digastric muscle (Fig. 12-36). It curves slightly cranialward above the hyoid bone, and passes deep to the tendon of the digastric and the stylohyoid muscle, be¬ tween the mylohyoid and the hyoglossus muscles, and continues anteriorly among the fibers of the genioglossus as far as the tip of the tongue, distributing branches to the in¬ trinsic muscles. communications. The communications with the vagus nerve occur close to the skull; numerous filaments pass between the hypo¬ glossal and the inferior ganglion of the vagus through the mass of connective tissue that binds the two nerves together. As the nerve winds around the occipital artery, it commu¬ nicates by a filament with the pharyngeal plexus. The communication with the sympa¬ thetic system takes place opposite the atlas by branches of the superior cervical gan¬ glion. The lingual nerve communicates with the hypoglossal nerve near the anterior border of the hyoglossus muscle by numerous fila¬ ments that lie upon the muscle. The commu¬ nication that occurs opposite the atlas, be¬ tween the hypoglossal nerve and the loop connecting the anterior primary divisions of the first and second cervical nerves is especially significant because it contains the motor fibers for the nerves to the supraand infrahyoid muscles. This communica¬ tion probably also contains sensory fibers

from the cranialmost cervical dorsal root ganglia. branches. Meningeal branches are min¬ ute filaments that are given off in the hypo¬ glossal canal and pass back to the dura mater of the posterior cranial fossa. They probably contain sensory fibers communi¬ cated to the hypoglossal nerve from the loop between the first and second cervical nerves. The superior root of the ansa cervicalis (descending hypoglossal) (Figs. 12-26; 12-36) is a long slender branch that leaves the hy¬ poglossal nerve as it loops around the occip¬ ital artery. It runs along the superficial sur¬ face of the carotid sheath to the middle of the neck, gives a branch to the superior belly of the omohyoid muscle, and becomes the medial arm of a loop, the ansa cervicalis (ansa hypoglossi*). The lateral arm of the loop is the inferior root of the ansa cervicalis (descending cervical) from the second and third cervicals. The branches from the loop supply (1) the inferior belly of the omohyoid, (2) the sternohyoid, and (3) the sternothyroid muscles. The fibers in the descending hypo¬ glossal nerve originate in the first cervical spinal segment, not in the hypoglossal nu¬ cleus, and pass through the communication between the first cervical nerve and the hy¬ poglossal nerve described previously. The thyrohyoid branch and the geniohy¬ oid branch are also made up of fibers from the first cervical nerve. They leave the hypo¬ glossal nerve near the posterior border of the hyoglossus muscle. The thyrohyoid branch runs obliquely across the greater cornu of the hyoid bone to reach the muscle it sup¬ plies. The muscular branches that contain true hypoglossal fibers are distributed to the styloglossus, hyoglossus, genioglossus, and intrinsic muscles of the tongue. At the un¬ dersurface of the tongue, numerous slender

‘The Paris Nomenclature has changed the name of this loop from ansa hypoglossi to ansa cervicalis. The names ansa hypoglossi, descending hypoglossal, and descend¬ ing cervical are still important to mention because (1) there usually are several cervical loops and (2) the great¬ est importance of the name, ansa hypoglossi, is to the surgeon, who would identify it by its connection with the hypoglossal nerve rather than the cervical nerves. Knowledge of its cervical origin has been obtained largely through clinical observations and animal experi¬ mentation, not from dissection.

SPINAL NERVES

Fig. 12-26.

1191

Plan of hypoglossal and first three cervical nerves.

branches pass cranialward into the sub¬ stance of the organ to supply its intrinsic muscles. The branches of the hypoglossal nerve to the tongue probably contain propri¬ oceptive sensory fibers with cells of origin in the first (if present) and second cervical dor¬ sal root ganglia.

Spinal Nerves The spinal nerves arise from the spinal cord within the spinal canal and pass out through the intervertebral foramina. The 31 pairs are grouped as follows: 8 cervical; 12 thoracic; 5 lumbar; 5 sacral; 1 coccygeal. The first cervical leaves the vertebral canal be¬ tween the occipital bone and the atlas and is therefore called the suboccipital nerve; the eighth cervical nerve leaves between the seventh cervical and first thoracic verte¬ brae.

Each spinal nerve is attached to the spinal cord by two roots, a ventral or motor root, and a dorsal or sensory root (Figs. 11-21; 12-27). The ventral root (anterior root; motor root) emerges from the ventral surface of the spinal cord as a number of rootlets or fila¬ ments (fila radicularia), which usually com¬ bine to form two bundles near the interver¬ tebral foramen. The dorsal root (posterior root; sensory root) is larger than the ventral root because of the greater size and number of its rootlets; these are attached along the ventral lateral furrow of the spinal cord and unite to form two bundles, which enter the spinal gan¬ glion. The dorsal and ventral roots unite imme¬ diately beyond the spinal ganglion to form the spinal nerve, which then emerges through the intervertebral foramen. Both nerve roots receive a covering from the pia roots of the spinal nerves.

1192

THE PERIPHERAL nervous system

Spinal ganglion

Posterior nerve root

Blood vessel

Skin

Somatic afferent Visceral afferent Spinal nerve

Somatic efferent White ramus

Visceral efferent postganglionic

Anterior nerve root Gray ramus Visceral efferent preganglionic Visceral efferent postganglionic

Sympathetic ganglion Muscle spindle Skeletal muscle

Visceral afferent Viscera

Fig. 12 27.

Parietal peritoneum

Schema showing structure of a typical spinal nerve.

mater and are loosely invested by the arach¬ noid, the latter being prolonged as far as the points where the roots pierce the dura mater. The two roots pierce the dura separately, each receiving from this membrane a sheath which becomes continuous with the connec¬ tive tissue of the epineurium after the roots join to form the spinal nerve. The spinal ganglion (ganglion spin ale, dorsal root ganglion) is a collection of nerve cells on the dorsal root of the spinal nerve. It is oval and proportional in size to the dor¬ sal root on which it is situated; it is bifid medially where it is joined by the two bun¬ dles of rootlets. The ganglion is usually placed in the intervertebral foramen, imme¬ diately outside the dura mater, but there are exceptions to this rule; the ganglia of the first and second cervical nerves lie on the verte¬ bral arches of the axis and atlas respectively, those of the sacral nerves are inside the ver¬ tebral canal, and that of the coccygeal nerve is within the sheath of the dura mater. Size and Direction. In the cervical region, the roots of the first four nerves are small, the last four, large, and the dorsal roots, three times as large as the ventral, a larger proportion than in any other

region; their individual filaments are also larger than in the ventral roots. The first cervical is an exception; its dorsal root is smaller than its ventral root. The roots of the first and second cervical nerves are short and run nearly horizontally to their exits from the vertebral canal. The roots of the third to the eighth nerves run obliquely caudalward, the obliquity and length successively increasing. In the thoracic region the roots, with the exception of the first, are small, and the dorsal root is only slightly larger than the ventral root. They increase successively in length, and in the more caudal tho¬ racic region they descend in contact with the spinal cord for a distance equal to the height of at least two vertebrae before they emerge from the vertebral canal. The largest roots with the most numerous individ¬ ual filaments are found in the lumbar and superior sacral regions. The roots of the coccygeal nerve are the smallest. The roots of the lumbar, sacral, and coccygeal nerves run vertically caudalward, and since the spinal cord ends near the lower border of the first lumbar vertebra, the roots of the successive segments are increasingly long. The name cauda equina is given to the resulting collection of nerve roots below the termination of the spinal cord. The largest nerve roots, and consequently the largest spinal nerves, are attached to the cervical and to the lumbar swellings of the spinal cord; these are the nerves largely distributed to the upper and lower limbs.

SPINAL NERVES

gray rami communicantes. The gray rami communicantes (postganglionic rami) contain the postganglionic fibers from the adjacent sympathetic chain ganglia. These fibers are visceral efferents that run in the nerves and their branches toward the pe¬ riphery, where they supply the smooth mus¬ cle in the blood vessel walls, the arrectores pilorum muscles, and the sweat glands. Since there are not as many sympathetic ganglia as there are spinal nerves, some gan¬ glia supply rami to more than one nerve. Al¬ though variations are common, a simple plan may be given as follows: The first four cervical nerves receive their rami from the superior cervical ganglion; the fifth and sixth cervical nerves, from the middle ganglion; and the seventh and eighth cervical nerves, from the inferior cervical ganglion. The first ten thoracic nerves receive rami from corre¬ sponding ganglia, but the eleventh and twelfth receive rami from a single coalesced ganglion. The lumbar and sacral nerves re¬ ceive their rami from a variable number of ganglia that correspond only approximately with the nerves. Each spinal nerve usually receives two or three sympathetic gray rami communicantes. They join the nerve just distal to the union between the dorsal and ventral roots, and in the thoracic and upper lumbar region are regularly medial to the white rami com¬ municantes. The latter are the branches of the spinal nerves that carry preganglionic fibers to the sympathetic chain. The ventral and dorsal primary divisions may each re¬ ceive a ramus, but if the rami join the ventral division only, some of the fibers course back centrally until they can reach the dorsal di¬ vision (Dass, 1952). WHITE RAMUS COMMUNICANTES. The white ramus communicans (preganglionic ramus) is the branch of the spinal nerve through which the preganglionic fibers from the spi¬ nal cord reach the sympathetic chain and are thus the roots of the sympathetic ganglia. They arise from the twelve thoracic and first two lumbar nerves only and usually join the sympathetic chain at or near a ganglion. They leave the ventral primary division of the spinal nerve soon after it has emerged from the intervertebral foramen. A small meningeal branch is given off from each spinal nerve immediately after it emerges from the intervertebral foramen. This branch reenters the vertebral canal

1 1 93

through the foramen, supplies afferent fibers to the vertebrae and their ligaments, and car¬ ries sympathetic postganglionic fibers to the blood vessels of the spinal cord and its mem¬ branes. primary divisions. The spinal nerve splits into its two primary divisions, ventral and dorsal, almost as soon as the two roots join, and both divisions receive fibers from both roots.

DORSAL PRIMARY DIVISIONS OF THE SPINAL NERVES

The dorsal primary divisions are smaller, as a rule, than the ventral divisions. As they arise from the spinal nerve, they are directed dorsalward, and with the exception of those of the first cervical, the fourth and fifth sac¬ ral, and the coccygeal, divide into medial and lateral branches for the supply of the muscles and skin of the dorsal part of the neck and trunk (Fig. 12-52). Cervical Nerves

In the first cervical or suboccipital nerve the dorsal primary division is larger than the ventral. It emerges from the spinal canal superior to the posterior arch of the atlas and inferior to the vertebral artery to enter the suboccipital triangle. It supplies the muscles that bound this triangle, namely, the rectus capitis posterior major and the obliqui superior and inferior, and it gives branches to the rectus capitis posterior minor and the semispinalis capitis (Fig. 1228). A filament from the branch to the obliquus inferior joins the dorsal division of the second cervical nerve. variations. The first nerve occasionally has a cutaneous branch that accompanies the occipital artery to the scalp and communicates with the greater and lesser occipital nerves.

The dorsal division of the second cervical nerve is much larger than the ventral divi¬ sion and is the greatest of the cervical dorsal divisions. It emerges between the posterior arch of the atlas and the lamina of the axis, caudal to the obliquus inferior muscle, which it supplies. It communicates with the first cervical and then divides into a large medial branch and a small lateral branch.

1 1 94

THE PERIPHERAL NERVOUS SYSTEM

Greater occipital nerve Third occipital Rectus capitis minor Rectus major Suboccipital nerve Vertebral artery

2nd cervical nerve

3rd cervical nerve

Fig. 12-28.

Dorsal primary divisions of the upper three cervical nerves.

The greater occipital nerve (Figs. 12-28; 12-35) is the name given to the medial branch because of its size and distribution. It crosses obliquely between the obliquus infe¬ rior and the semispinalis capitis muscles, pierces the latter and the trapezius near their attachments to the occipital bone, and be¬ comes subcutaneous (Fig. 12-28). It commu¬ nicates with the third cervical nerve, runs upward on the back of the head with the occipital artery, and divides into branches that supply the scalp over the vertex and top of the head, communicating with the lesser occipital nerve. It gives muscular branches to the semispinalis capitis. The lesser occipital nerve is described with the ventral primary divisions. The lateral branch (external branch) sup¬ plies branches to the splenius and semispi¬ nalis capitis muscles and often communi¬ cates with the lateral branch of the third nerve. The dorsal division of the third cervical nerve is intermediate in size between the second and fourth. Its medial branch runs between the semispinalis capitis and cervicis muscles, pierces the splenius and the trape¬ zius, and gives branches to the skin. The third occipital nerve (least occipital

nerve) is the cutaneous part of the third nerve. It pierces the trapezius medial to the greater occipital nerve, with which it com¬ municates, and is distributed to the skin of the lower part of the back of the head (Fig. 12-28). The lateral branch communicates with that of the second cervical nerve, sup¬ plies the same muscles, and gives a branch to the longissimus capitis muscle. The dorsal primary divisions of the fourth to eighth cervical nerves divide into medial and lateral branches. The medial branches of the fourth and fifth cervical nerves run between the semispinalis capitis and cervicis, which they supply; near the spinous proc¬ esses of the vertebrae they pierce the splenius and trapezius muscles to end in the skin (Fig. 12-31). Those of the lower three nerves are small and end in the semispinalis cervicis and capitis, the multifidus, and the interspinales. The lateral branches of the lower five nerves supply the splenius, iliocostalis cervicis, and the longissimus capitis and cervicis muscles. variations. The dorsal division of the first cervi¬ cal nerve and the medial branches of the dorsal divi¬ sions of the second and third cervical nerves are sometimes joined by the communicating loops to

SPINAL NERVES

form a posterior cervical plexus (of Cruveilhier).1 The greater and lesser occipital nerves vary recipro¬ cally with each other; the greater may communicate with the great auricular or posterior auricular nerves, and a branch to the auricula has been observed. The cutaneous branch of the fifth nerve may be lacking and the lower cervical nerves occasionally have cu¬ taneous twigs. Thoracic Nerves

The dorsal primary divisions of all the thoracic nerves have medial and lateral branches, but the cutaneous branches in the more cranial thorax are different from those in the more caudal thorax. The medial branch (internal branch) (Fig. 12-52) from the dorsal divisions of the upper six thoracic nerves passes between and sup¬ plies the semispinalis and multifidus mus¬ cles, pierces the rhomboidei and trapezius, and approaching the surface close to the spi¬ nous process of the vertebra (Fig. 12-31), ex¬ tends out laterally to the skin over the back. The medial branches of the lower six nerves end in the transversospinales and longissimus muscles, usually without cutaneous branches. The lateral branches (external branches) run through or deep to the longissimus to the interval between it and the iliocostalis mus¬ cles, which they supply. They gradually in¬ crease in size from the first to the twelfth; the cranial six nerves end in the muscles, but the more caudal six have cutaneous branches that pierce the serratus posterior inferior and the latissimus dorsi along the junction between the fleshy and aponeurotic portions of the latter muscle (Fig. 12-31). The cutaneous portions of both medial and lateral branches have a caudalward course that becomes more pronounced caudally, so that the twelfth nerve reaches down to the skin of the buttocks. The cutaneous part of the first thoracic nerve may be lack¬ ing. Both medial and lateral branches of some nerves may have cutaneous fibers, es¬ pecially those of the sixth, seventh, and eighth thoracic nerves (Fig. 12-32). Lumbar Nerves

The medial branches of the dorsal pri¬ mary divisions of the lumbar nerves run close to the articular processes of the verte¬ brae and end in the multifidus muscle. 'Jean Cruveilhier (1791-1874): A French (Paris).

pathologist

1195

The lateral branches supply the sacrospinalis muscle. The upper three give off cuta¬ neous nerves that pierce the aponeurosis of the latissimus dorsi at the lateral border of the sacrospinalis and cross the posterior part of the iliac crest to be distributed, as the su¬ perior clunial nerves, to the skin of the but¬ tocks as far as the greater trochanter (Fig. 12-31). Sacral and Coccygeal Nerves

The dorsal divisions of the sacral nerves are small and diminish in size distally; they emerge, except the last, through the poste¬ rior sacral foramina under cover of the multifidus muscle. The medial branches of the first three are small and end in the multifidus. The lateral branches of the first three nerves join with one another and with the last lumbar and fourth sacral nerves to form loops on the dorsal surface of the sacrum (Fig. 12-33). From these loops branches run to the dorsal surface of the sacrotuberous ligament and form a second series of loops under the gluteus maximus. From this sec¬ ond series two or three cutaneous branches pierce the gluteus maximus along a line from the posterior superior iliac spine to the tip of the coccyx, and they supply the skin over the medial part of the buttocks. The dorsal divisions of the last two sacral nerves and the coccygeal nerves do not di¬ vide into medial and lateral branches, but unite with each other on the back of the sac¬ rum, to form loops that supply the skin over the coccyx. VENTRAL PRIMARY DIVISIONS OF THE SPINAL NERVES

The ventral primary divisions of the spi¬ nal nerves supply the ventral and lateral parts of the trunk and all parts of the limbs. They are, for the most part, larger than the dorsal divisions. In the thoracic region they remain independent of one another, but in the cervical, lumbar, and sacral regions they unite near their origins to form plexuses. Cervical Nerves

The ventral division of the first cervical or suboccipital nerve issues from the vertebral canal cranial to the posterior arch of the

1 196

THE PERIPHERAL NERVOUS SYSTEM

Fig. 12-29.

Distribution of cutaneous nerves. Ventral aspect.

SPINAL NERVES

Fig. 12-30.

1 1 97

Distribution of cutaneous nerves. Dorsal aspect.

Fig. 12-29. 12-30. These figures (and others like them) show areas of distribution on the skin supplied by each of the spinal nerves. The work of Sherrington has demonstrated that the “sensory root field” of a particular dorsal root ganglion overlaps that of the zones or “dermatomes” supplied by the ganglion above and below (Fig. 12-32). In fact, fibers carrying different modalities, i.e., pain and touch, vary in the amount of this overlap.

1198

THE peripheral nervous system

Fig. 12-32. Areas of distribution of the cutaneous branches of the dorsal divisions of the spinal nerves. The areas of the medial branches are in black; those of the lateral, in red. (H. M. Johnston.)

Fig. 12-31. Diagram of the distribution of the cutane¬ ous branches of the dorsal divisions of the spinal nerves.

atlas and runs rostralward around the lateral aspect of the superior articular process, medial to the vertebral artery. In most in¬ stances it is medial and anterior to the rectus capitis lateralis, but occasionally it pierces the muscle. The ventral divisions of the other cervical nerves pass outward between the anterior and posterior intertransversarii, lying on the grooved cranial surfaces of the transverse processes of the vertebrae. The first four cer-

vical nerves form the cervical plexus; the last four, together with the first thoracic, form the brachial plexus. They all receive gray rami communicantes from the sympa¬ thetic chain. Cervical Plexus

The cervical plexus (Fig. 12-34) is formed by the ventral primary divisions of the first four cervical nerves; each nerve, except the first, divides into a superior and inferior branch, and the branches unite to form three loops. The sympathetic rami may join the nerves or the loops. The plexus is situated opposite the cranial four cervical vertebrae,

SPINAL NERVES

Fig. 12-33.

The dorsal divisions of the sacral nerves.

ventrolateral to the levator scapulae and scalenus medius and deep to the sternocleido¬ mastoid muscle. The cervical plexus has communications with certain cranial nerves and muscular and cutaneous branches, which may be ar¬ ranged in tabular form as follows; the num¬ bers indicate the segmental components.

A. Communications of the Cervical Plexus 1. With vagus nerve 2. With hypoglossal nerve 3. With accessory nerve

C 1, 2 C 1, 2 C2, 3,4

B. Superficial or Cutaneous Branches 1. Lesser occipital 2. Great auricular

C2 C 2, 3

3. Anterior cutaneous* 4. Supraclavicular

C 2, 3 C 3, 4

C. Deep or Muscular Branches 5. Rectus capitis anterior and lateralis 6. Longus capitus and colli

C C C C

1, 2 1 1, 2, 3 2, 3, 4

1199

7. Geniohyoid Thyrohyoid Omohyoid (superior) 8. Sternohyoid Sternothyroid Omohyoid (inferior) 9. Phrenic 10. Sternocleidomastoid 11. Trapezius 12. Levator scapulae 13. Scalenus medius

C 1, (2) C 1, (2) C C C C C C C C C

1, 2, 2, 2, 3, 2, 3, 3, 3,

(2) 3 3 3 4, 5 3 4 4 4

‘This name conforms with names in more caudal seg¬ ments.

COMMUNICATIONS OF THE CERVICAL PLEXUS

The communication with the vagus nerve is between the loop connect¬ ing the first and second nerves and the infe¬ rior ganglion. hypoglossal nerve. The communication with the hypoglossal nerve (Figs. 12-26; 1234) is a short bundle that leaves the loop be¬ tween the first and second nerves. The great bulk of its fibers are from the first nerve; it runs distally with hypoglossal nerve for 3 or 4 cm and leaves it again as the superior root (descending hypoglossal). It contains motor vagus nerve.

1 200

THE PERIPHERAL NERVOUS SYSTEM

and proprioceptive fibers for certain hyoid muscles and is described later as part of the ansa cervicalis (ansa hypoglossi). accessory nerve. The communications with the accessory nerve (Fig. 12-34) leave the cervical plexus at several points: (a) one leaves the loop between the second and third nerves, frequently appearing to come from the lesser occipital nerve (C 2), and joins the fibers of the accessory, which sup¬ ply the sternocleidomastoid; (b) a bundle leaves the third nerve, sometimes in associa¬ tion with the great auricular nerve, and joins the accessory fibers to the trapezius; (c) one or two bundles leave the fourth nerve and join the accessory nerve directly or enter into a network on the deep surface of the trapezius. These communications contain proprioceptive sensory fibers (Corbin and Harrison, 1939).

SUPERFICIAL OR CUTANEOUS BRANCHES OF THE CERVICAL PLEXUS lesser occipital nerve. The lesser occip¬ ital nerve (Fig. 12-35) arises from the second cervical nerve or the loop between the second and third nerves and ascends along the sternocleidomastoid muscle, curv¬ ing around its posterior border. Near the in¬ sertion of the muscle on the cranium, it perforates the deep fascia and continues upward along the side of the head behind the ear, supplying the skin and communicat¬ ing with the greater occipital nerve, the great auricular nerve, and the posterior auricular branch of the facial nerve. It has an auricu¬ lar branch that supplies the upper and back part of the auricula, communicating with the mastoid branch of the great auricular nerve.

SPINAL NERVES

1201

Termination: of supratrochlear of infratrochlear of nasociliary

Fig. 12-35.

The nerves of the scalp, face, and side of neck.

variations. The lesser occipital nerve varies re¬ ciprocally with the greater occipital nerve; it is fre¬ quently duplicated or may be wanting.

The great auric¬ ular nerve (Fig. 12-35), larger than the pre¬ ceding, arises from the second and third nerves, winds around the posterior border of the sternocleidomastoid muscle, and after perforating the deep fascia, ascends on the surface of that muscle but deep to the platysma and divides into an anterior and a posterior branch. The anterior branch (facial branch) is dis¬ tributed to the skin of the face over the pa¬ rotid gland. It communicates in the sub¬ stance of the gland with the facial nerve. great auricular nerve.

The posterior branch (mastoid branch) supplies the skin over the mastoid process and back of the auricula except its upper part; a filament pierces the auricula to reach its lateral surface, where it is distributed to the lobule and lower part of the concha. It communicates with the smaller occipital nerve, the auricular branch of the vagus, and the posterior auricular branch of the facial nerve. anterior cutaneous nerve. The anterior cutaneous nerve (Fig. 12-35) arises from the second and third cervical nerves and bends around the posterior border of the sterno¬ cleidomastoid at its middle. Crossing the surface of the muscle obliquely as it runs horizontally ventralward, it perforates the

1 202

THE PERIPHERAL NERVOUS SYSTEM

deep fascia, passing deep to the external jug¬ ular vein, pierces the platysma, and divides into ascending and descending branches. The ascending branches (rr. superiores) pass cranialward to the submandibular re¬ gion, pierce the platysma, and are distrib¬ uted to the cranial, ventral, and lateral parts of the neck. One filament accompanies the external jugular vein toward the angle of the mandible and communicates with the cervi¬ cal branch of the facial nerve under cover of the platysma. The descending branches (rr. inferiores) pierce the platysma and are distributed to the skin of the ventral and lateral parts of the neck as far down as the sternum. supraclavicular nerves. The supraclavicular nerves (descending branches) (Fig. 12-35) arise from the third and fourth (mainly the fourth) cervical nerves. They emerge from under the posterior border of the sternocleidomastoid muscle and cross the posterior triangle of the neck under cover of the investing layer of deep fascia. Near the clavicle they perforate the fascia and platysma in three bundles or groups— medial, intermediate and lateral. The medial supraclavicular nerves (ante¬ rior supraclavicular nerves; suprasternal nerves) cross the external jugular vein, the clavicular head of the sternocleidomastoid muscle, and the clavicle to supply the skin of the medial infraclavicular region as far as the midline. They furnish one or two fila¬ ments to the sternoclavicular joint. The intermediate supraclavicular nerves (middle supraclavicular nerves) cross the clavicle and supply the skin over the pectoralis major and the deltoid and they commu¬ nicate with the cutaneous branches of the more cranial intercostal nerves. The lateral supraclavicular nerves (poste¬ rior supraclavicular nerves; supracromial nerves) pass obliquely across the outer sur¬ face of the trapezius and the acromion, and supply the skin of the cranial and dorsal parts of the shoulder. variations. One of the middle supraclavicular nerves may perforate the clavicle.

DEEP OR MUSCULAR BRANCHES OF THE CERVICAL PLEXUS

Branches to the rectus capitis anterior and rectus capitis rectus

capitis

branches.

lateralis come from the loop between the first and second nerves. LONGUS

CAPITIS

AND

COLLI

BRANCHES.

Branches to the longus capitis and longus colli are given off separately; for the capitis from the first, second, and third; for the colli from the second, third, and fourth nerves. hyoid musculature branches. Branches to the hyoid musculature (Fig. 12-36) are de¬ scribed previously as branches of the hypo¬ glossal nerve, but the fibers do not come from the hypoglossal nucleus in the brain; they originate instead from the cervical seg¬ ments of the spinal cord. Fibers communi¬ cated to the hypoglossal nerve from the first cervical nerve or from the loop between the first and second nerves leave the hypoglossal nerve again to appear as (1) individual branches to the geniohyoid, thyrohyoid or superior belly of the omohyoid, or (2) as the superior root (descendens hypoglossi) to join the inferior root (descendens cervicalis) from the second and third cervical nerves to form the ansa cervicalis (ansa hy¬ poglossi). The nerve to the geniohyoid leaves the hypoglossal nerve distally and has a course similar to that of the thyrohyoid nerve. The nerve to the thyrohyoid (Fig. 12-36) leaves the hypoglossal nerve near the poste¬ rior border of the hyoglossus and runs ob¬ liquely across the greater cornu of the hyoid bone and enters the muscle as a slender fila¬ ment. It leaves the hypoglossal distal to the origin of the root superior of the ansa. The fibers for the superior belly of the omohyoid leave the superior root before it forms the ansa and reach the muscle as a slender filament. ansa cervicalis. The ansa cervicalis (ansa hypoglossi) is a loop of slender nerves that may be somewhat plexiform, ventral and lateral to the common carotid artery and internal jugular vein. It is formed by fibers from the first cervical spinal segment that leave the hypoglossal nerve as the superior root (descendens hypoglossi), and the infe¬ rior root (descendens cervicalis) from the second and third cervical nerves. It usually lies superficial to the carotid sheath at about the level of the cricoid cartilage. The nerves to the sternohyoid and sterno¬ thyroid muscles leave the convexity of the loop and run down the superficial surface of the carotid artery to enter the muscles at the root of the neck. They may be separate fila-

SPINAL NERVES

merits or combined into a single nerve for a variable distance. The nerve to the inferior belly of the omohyoid leaves the convexity of the loop and runs lateralward across the neck deep to the intermediate tendon of the muscle to reach the inferior belly. variations. The ansa is quite variable in posi¬ tion; it may occur at various levels. Frequently it is high near the bifurcation of the carotid, in which circumstance it may be within the carotid sheath. The superior root may appear to arise wholly or in part from the vagus. A branch to the sternoclei¬ domastoid and filaments entering the thorax to join the vagus or sympathetic have been described.

phrenic nerve. The phrenic nerve (inter¬ nal respiratory nerve of Bell1) (Fig. 12-37) is generally known as the motor nerve to the lSir Charles Bell (1774-1842): A Scottish physiologist who worked in London.

1203

diaphragm, but it contains about half as many sensory as motor fibers, and it should not be forgotten that the lower thoracic nerves also contribute to the innervation of the diaphragm. The phrenic nerve originates chiefly from the fourth cervical nerve but is augmented by fibers from the third and fifth nerves. It lies on the ventral surface of the scalenus anterior, gradually crossing from its lateral to its medial border (Fig. 12-36). Under cover of the sternocleidomastoid, it is crossed by the inferior belly of the omohyoid and the transverse cervical and suprascapu¬ lar vessels. It continues with the scalenus anterior between the subclavian vein and artery, and as it enters the thorax, it crosses the origin of the internal thoracic artery and is joined by the pericardiacophrenic branch of this artery. It passes caudalward over the cupula of the pleura and ventral to the root of the lung, then along the lateral aspect of

1 204

THE peripheral nervous systfm

Anterior primary division of fourth cervical Phrenic Brachial plexus

Inferior laryngeal

Vagus

Root of lung Pericardial branch

Inferior cervical ganglion Inferior laryngeal Nerve to subclavius muscle Communicating branch from branchial plexus Thoracic cardiac branch of vagus Inferior laryngeal Anterior pulmonary Anterior pulmonary plexus

Ramifications of phrenic Fig. 12-37.

The phrenic nerve and its relations with the vagus nerve.

the pericardium, between it and the medias¬ tinal pleura, until it reaches the diaphragm, where it divides into its terminal branches. At the root of the neck it is joined by a com¬ munication from the sympathetic trunk. The right nerve is more deeply placed, is shorter, and runs more vertically caudalward than the left. In the upper part of the thorax it is lateral to the right brachioce¬ phalic vein and the superior vena cava (Figs. 12-37; 12-78). The left nerve is longer than the right be¬ cause of the inclination of the heart toward the left and because of the more caudal posi¬ tion of the diaphragm on this side. At the

root of the neck it is crossed by the thoracic duct, and in the superior mediastinum it lies between the left common carotid and the subclavian arteries, and is lateral to the vagus as it crosses the left side of the arch of the aorta (Figs. 12-37; 12-79). The pleural branches of the phrenic nerve are very fine filaments supplied to the costal and mediastinal pleura over the apex of the lung. The pericardial branches are delicate fila¬ ments to the upper part of the pericardium. The terminal branches pass through the diaphragm separately, and diverging from each other, are distributed on the abdominal

SPINAL NERVES

1 205

nerve. They are proprioceptive sensory rather than motor nerves and are derived from the second and third nerves (Corbin and Harrison, 1938). The branches to the trapezius are like those to the sternocleidomastoid and are derived from the third and fourth nerves. Muscular branches to the levator scapulae are supplied by the third and fourth nerves. Branches to the scalenus medius are from the third and fourth nerves.

surface to supply the diaphragm muscle and sensory fibers to the peritoneum. On the right side, a branch near the inferior vena cava communicates with the phrenic plexus, which accompanies the inferior phrenic ar¬ tery from the celiac plexus, and where they join there is usually a small phrenic gan¬ glion. On the left, there is a communication with the phrenic plexus also, but without a ganglion. The accessory phrenic nerve is described later.

Brachial Plexus The phrenic nerve may receive fi¬ bers from the inferior root of the ansa cervicalis, or from the second or sixth nerves. At the root of the neck or in the thorax it may be joined by an acces¬ sory phrenic from the fifth nerve or from the nerve to the subclavius. It may arise from the nerve to the subclavius or give a branch to that muscle. It may pass ventral to the subclavian vein or perforate it. variations.

The brachial plexus (Figs. 12-38; 12-39), as its name implies, supplies the nerves to the upper limb. It is formed by the ventral pri¬ mary divisions of the fifth to eighth cervical nerves and the first thoracic nerves. A com¬ municating loop from the fourth to the fifth cervical nerve and one from the second to the first thoracic nerve also usually contrib¬ ute to the plexus. It lies in the lateral part of the neck in the clavicular region, extending from the scalenus anterior to the axilla.

other branches. The branches to the sternocleidomastoid may be independent or partly communicate with the accessory

nerves

cords

divisions

trunks

roots from 4th cervical

Dorsal scapular 5th cervical Nerve to subclavius and accessory phrenic

to Scaleni to Longus 6th cervical

Suprascapular

7th cervical M usculocutaneous

- Long thoracic Axillary

8th cervical

Radial

Median 1st thoracic

Ulnar Med. antebrachial cutaneous

from 2nd thoracic Medial brachial cutaneous

Superior subscapular Thoracodorsal

Inferior subscapular

Fig

12-38

Plan of brachial plexus.

1 206

THE PERIPHERAL NERVOUS SYSTEM

COMPONENTS

The brachial plexus is composed of roots, trunks, divisions, cords, and terminal nerves. The roots of the brachial plexus are pro¬ vided by the anterior primary divisions of the last four cervical nerves and the first tho¬ racic nerve. The trunks are formed from these roots and are named according to their position relative to each other. The superior trunk is formed by the union of the fifth and sixth cervical nerves as they emerge be¬ tween the scalenus medius and anterior. The middle trunk is formed by the seventh cervi¬ cal nerve alone. The inferior trunk is formed by the union of the eighth cervical and first thoracic nerves. The trunks, after a short course, split into anterior and posterior divisions. The ante¬ rior and posterior divisions of the superior and middle trunks are about equal in size, but the posterior division of the inferior trunk is much smaller than the anterior divi¬ sion because it receives a very small or no contribution from the first thoracic nerve. The cords, formed from these divisions, are named according to their relation to the axil¬ lary artery: lateral, medial, and posterior. The anterior divisions of the superior and middle trunks are united into the lateral cord. The anterior division of the inferior trunk becomes the medial cord. The poste¬ rior divisions of all three trunks are united into the posterior cord. The cords in turn break up into the nerves, which are the ter¬ minal branches.

SYMPATHETIC CONTRIBUTIONS TO THE BRACHIAL PLEXUS

The ventral primary divisions of the spi¬ nal nerves that enter into the brachial plexus obtain their sympathetic fibers in the form of the gray rami communicantes from the sym¬ pathetic chain. The fifth and sixth nerves receive fibers from the middle cervical gan¬ glion; the sixth, seventh, and eighth nerves, from the inferior cervical or stellate gan¬ glion; the first and second thoracic nerves, from the stellate or the first and second tho¬ racic ganglia. relations. In the neck, the brachial plexus lies in the posterior triangle, being covered by the skin, platysma, and deep fascia; it is crossed by the supra¬ clavicular nerves, the inferior belly of the omohyoid, the external jugular vein, and the transverse cervical artery. The roots emerge between the scaleni ante¬

rior and medius, cranial to the third part of the sub¬ clavian artery, while the trunk formed by the union of the eighth cervical and first thoracic nerves is placed dorsal to the artery. The plexus next passes dorsal to the clavicle, the subclavius, and the trans¬ verse scapular vessels, and lies upon the first digitation of the serratus anterior and the subscapularis. In the axilla it is placed lateral to the first por¬ tion of the axillary artery; it surrounds the second part of the artery, one cord lying medial to it, one lateral to it, and one dorsal to it. In the axilla it gives off its terminal branches to the upper limb. variations. Variations of the brachial plexus are of several types: (a) variations in the contributions of the spinal nerves to the roots of the plexus, (b) varia¬ tions in the formation of the trunks, divisions, or cords, (c) variations in the origin or combination of the branches, (d) variations in the relation to the ar¬ tery. (a) The fourth cervical nerve contributes to twothirds of the plexuses, and T 2 contributes to more than one-third. When the contribution from C 4 is large and that from T 2 lacking, the plexus appears to have a more cranial position and has been termed prefixed. Similarly, when the contribution from T 2 is large and from C 4 lacking, the plexus appears to have a more caudal position and has been termed postfixed. It is doubtful whether this shifting of posi¬ tion is more common than one in which the plexus is spread out to include both C 4 and T 2, or con¬ tracted to exclude both. Variations in the contribu¬ tion to the plexus may be correlated with the posi¬ tion of the limb bud at the time the nerves first grow into it in the embryo (Miller and Detwiler, 1936), and many variations are similar to the usual condi¬ tions found in the different primates. (b) The trunks vary little in their formation from the cervical roots, but the superior and inferior trunks especially may appear to be absent because the nerves split into dorsal and ventral divisions be¬ fore they combine into trunks. The cords in these instances are formed from the divisions of the nerves but the sources of the fibers can be readily traced and made to correspond with the usual pattern. Many of these instances may be the result of too vigorous a removal of the connective tissue sheaths of the nerves in dissection. The medial cord may receive a contribution from the middle trunk and the lateral cord may receive fibers from C 8 or the lower trunk. (c) The median nerve may have small heads, either medial or lateral, in addition to the usual two. It ap¬ pears to receive fibers from all segments entering the plexus in most instances. Many peculiarities in¬ volve combined origins of the median and muscu¬ locutaneous nerves, with separation into definitive nerves or branches farther down the arm; thus the musculocutaneous nerve gives a branch to the me¬ dian in the arm in a fourth of the bodies, but a branch from the median to the ulnar is much less frequent. The musculocutaneous nerve frequently receives fibers from C 4 in addition to the usual C 5 and C 6, and appears to receive fibers from C 7 in

SPINAL NERVES

only two-thirds. The nerve to the coracobrachialis muscle is a branch of the lateral cord or some part of the plexus (exclusive of C 8 and T 1) other than the musculocutaneous nerve in almost half of the bod¬ ies. The ulnar nerve may have a lateral head from the lateral cord, the lateral head of the median, or from C 7; in two-thirds of the plexuses the ulnar nerve may receive fibers from C 7 or possibly more cranial segments. The radial and axillary nerves may be formed from the trunks and divisions without the presence of a true posterior cord. The radial nerve appears to receive fibers from all segments contrib¬ uting to the plexus in most instances, but participa¬ tion of C 4 and T 1 is probably incidental because C 4 may not enter the plexus and in a few instances T 1 can be definitely excluded. The axillary nerve probably receives no fibers from C 8 and T 1 and the contribution from C 7 is undetermined. (d) Among tiid variations m xne relationship be¬ tween the axillary artery and the brachial plexus, the most common is an artery superficial to the median nerve; also, the median nerve may be split by a branch of the artery. An aberrant axillary artery, i.e., one not derived from the seventh segmental artery, has a different relation to the roots of the plexus depending on whether it was derived from a seg¬ mental artery cranial or caudal to the seventh. The cords of the plexus may be split by arterial branches, and communicating loops of nerves may be formed around the artery or its branches.

A. Branches from the Cervical Nerves 1. To the phrenic nerve 2. To longus colli and the scaleni 3. Accessory phrenic

C 5 C 5, 6, 7, 8 C 5

B. Branches from the Roots 4. Dorsal scapular 5. Long thoracic

C 5, 6 C 5, 6

10. Thoracodorsal 11. Axillary 12. Medial brachial cutaneous

C C C C C

13. Medial antebrachial cutaneous

C 8, T 1

5, 5, 6, 5, 8,

6, 7, 8, T 1 6 7, 8 6 T1

E. Terminal Nerves 14. 15. 16. 17.

Musculocutaneous Median Ulnar Radial

The ventral primary divisions of the fifth to eighth cervical nerves give branches be¬ fore they enter into the plexus, and the brachial plexus may be divided into the branches that arise from the roots, from the trunks, or from the cords ~nd into ihe terminal nerves. From their topograpnic re¬ lation to the clavicle, the branches may be divided into supra- and infraclavicular branches. Branches from the Cervical Nerves

Branches of the anterior primary divisions of the last four cervical and first thoracic nerves before they enter the brachial plexus include: 1. The fifth cervical nerve may contribute to the phrenic nerve at its origin. 2. Muscular branches from each of the four lower cervical nerves are supplied to the longus colli and the scalenus anterior, medius, and posterior. 3. The accessory phrenic nerve (Fig. 1237) is an inconstant branch that may come from the nerve to the subclavius or from the fifth nerve. It passes ventral to the subcla¬ vian vein and joins the phrenic nerve at the root of the neck or in the thorax, forming a loop around the vein. surgical considerations. Resection of the phrenic nerve for immobilization of the diaphragm may be only partially successful if the accessory is not resected also. In avulsion of the phrenic nerve, the subclavian vein is in danger of being torn by the loop between the accessory and the phrenic nerves.

Branches from the Roots (Supraclavicular Branches)

D. Branches from the Cords 8. Pectoral 9. Subscapular

BRANCHES OF THE BRACHIAL PLEXUS

C5 C 5, 6, 7

C. Branches from the Trunks 6. Nerve to the subclavius 7. Suprascapular

1207

C C C C

5, 6, 8, 5,

6, 7, T 6,

7 8, T 1 1 7, 8 (T 1)

dorsal scapular nerves. The dorsal scapular nerve (nerve to the rhomboidei; posterior scapular nerve) (Fig. 12-38) arises from the fifth cervical nerve near the inter¬ vertebral foramen, frequently in common with a root of the long thoracic nerve. It pierces the scalenus medius and runs dorsally as well as caudalward on the deep sur¬ face of the levator scapulae to the vertebral border of the scapula. It supplies the rhomboideus major and minor, and along with the third and fourth nerves, gives a branch to the levator scapulae muscle. LONG thoracic nerve. The long thoracic nerve (external respiratory nerve of Bell; posterior thoracic nerve) (Fig. 12-39) is the

1 208

THE PERIPHERAL NERVOUS SYSTEM

Musculocutaneous nerve

Intercostobrachial

Medial antebrachial cutaneous nerve

Medial brachial cutaneous nerves

Lateral cutaneous branch of fourth intercostal

Thoracodorsal nerve

Subscapular nerves

Lateral cutaneous branch of third intercostal Long thoracic nerve

Fig. 12-39. The right brachial plexus (infraclavicular portion) in the axillary fossa; viewed from below and in front. The pectoralis major and minor muscles have been largely removed; their attachments have been reflected. (Spalteholz.)

Anterior branch of axillary

Posterior branch of axillary

Branches of lateral brachial cutaneous nerve

Fig. 12-40.

Suprascapular and axillary nerves of right side, seen from behind. (Testut.)

SPINAL NERVES

nerve to the serratus anterior muscle. It arises by three roots: from the fifth, sixth, and seventh cervical nerves. Those from the fifth and sixth join just after they pierce the scalenus medius; the seventh joins them at the level of the first rib. The nerve runs caudalward dorsal to the brachial plexus and axillary vessels and continues along the lat¬ eral surfaces of the serratus anterior, under cover of the subscapularis muscle. It sends branches to all the digitations of the serratus; the fibers from the fifth nerve supply the upper part, the sixth the middle, and the sev¬ enth the lower part of the muscle. variations. The root from the fifth nerve may remain independent; the root from the seventh may be lacking.

Branches from the Trunks (Supraclavicular)

nerve to subclavius muscle. The nerve to the subclavius is a small branch that arises from the superior trunk, although its fibers are mainly from the fifth nerve, and passes ventral to the distal part of the plexus, the subclavian artery, and the sub¬ clavian vein to reach the subclavius muscle (Fig. 12-37). variations. The accessory phrenic nerve may arise from the subclavius nerve, or the phrenic nerve may supply the branch to the subclavius muscle.

suprascapular nerve. The suprascapular nerve (Fig. 12-40) arises from the superior trunk and takes a more or less direct course across the posterior triangle to the scapular notch, passing dorsal to the inferior belly of the omohyoid muscle and the anterior bor¬ der of the trapezius. It passes through the notch, under the superior transverse liga¬ ment, runs deep to the supraspinatus muscle and around the lateral border of the spine of the scapula into the infraspinous fossa. In the supraspinous fossa it gives a branch to the supraspinatus and an articular filament to the shoulder joint. In the infraspinous fossa, it gives two branches to the infraspi¬ natus and filaments to the shoulder joint and scapula. Branches from the Cords (Infraclavicular Branches)

The infraclavicular branches arise from the three cords of the brachial plexus, but it should be emphasized that a particular

1 209

branch of any cord need not contain fibers from all the cervical nerves contributing to that cord. For example, the axillary nerve, from the posterior cord, contains fibers from C 5 and 6 only, not from C 5, 6, 7, 8, and T 1. Likewise, a branch from one of the larger terminal nerves may not contain fibers from all the cervical segments contributing to that nerve; the branch of the radial nerve to the supinator muscle, for example, contains only fibers from C 6. pectoral nerves. The pectoral nerves (Fig. 12-46) are two nerves, one lateral and one medial to the axillary artery, that arise at the level of the clavicle and supply the pec¬ toral muscles. The lateral (superior) pectoral nerve is so named because it is lateral to the artery and arises from the lateral cord of the brachial plexus or from the anterior divisions of the superior and middle trunks just before they unite into the cord. It passes superficial to the first part of the axillary artery and vein, sends a communicating branch to the infe¬ rior pectoral branch, and then pierces the clavipectoral fascia to reach the deep sur¬ face of the clavicular and cranial sternocos¬ tal portions of the pectoralis major muscle. The medial (inferior) pectoral nerve is so named because its origin is from the medial cord of the brachial plexus, medial to the artery. Its origin is more lateral in position with respect to the midline of the body than that of the superior branch. It passes be¬ tween the axillary artery and vein, gives a branch that joins the communication from the superior branch to form a plexiform loop around the artery, and enters the deep sur¬ face of the pectoralis minor muscle. It sup¬ plies this muscle and two or three of its branches continue through the muscle to supply the more caudal part of the pectoralis major. The most distal branch may pass around the border of the minor. The loop gives off branches that supply both muscles. subscapular nerves. The subscapular nerves (Fig. 12-39), usually two in number, arise from the posterior cord of the brachial plexus, deep in the axilla. The superior subscapular nerve (short subscapular), the smaller of the two, enters the superior part of the subscapularis mus¬ cle; it is frequently double. The inferior subscapular nerve supplies the distal part of the subscapularis and ends in the teres major muscle.

1210

THE PERIPHERAL NERVOUS SYSTEM

variations. The nerve to the teres major may be a separate branch of the posterior cord, or rarely, of the axillary nerve.

thoracodorsal nerves. The thoracodorsal nerve (middle or long subscapular nerve) (Fig. 12-39) is a branch of the posterior cord of the brachial plexus; it usually arises be¬ tween the two subscapular nerves. It follows the course of the subscapular and thoraco¬ dorsal arteries along the posterior wall of the axilla, under cover of the ventral border of the latissimus dorsi, and terminates in branches that supply this muscle. axillary nerve. The axillary nerve (cir¬ cumflex nerve) (Fig. 12-40) is the last branch of the posterior cord of the brachial plexus before the latter becomes the radial nerve. It passes over the insertion of the subscapularis muscle dorsal to the axillary artery, crosses the teres minor, and leaves the axilla, accompanied by the posterior humeral cir¬ cumflex artery, by passing through the quad¬ rilateral space bounded by the surgical neck of the humerus, the teres major, the teres minor, and the long head of the triceps. It divides into two branches. The posterior branch (lower branch) sup¬ plies the teres minor and the posterior part of the deltoid. It then pierces the deep fascia at the posterior border of the deltoid as the lateral brachial cutaneous nerve, to supply the skin over the distal two-thirds of the pos¬ terior part of this muscle and over the adja¬ cent long head of the triceps brachii. The anterior branch (upper branch) winds around the surgical neck of the humerus with the posterior humeral circumflex ves¬ sels, under cover of the deltoid as far as its anterior border. It supplies this muscle and sends a few small cutaneous filaments to the skin covering its distal part. Articular filaments leave the nerve near its origin and in the quadrilateral space; these . supply the anterior inferior part of the cap¬ sule of the shoulder joint. MEDIAL BRACHIAL CUTANEOUS NERVE. The medial brachial cutaneous nerve (nerve of Wrisberg), a small nerve, arises from the medial cord of the brachial plexus and is distributed to the medial side of the arm. It passes through the axilla, at first lying dorsal and then medial to the axillary vein and brachial artery. It pierces the deep fascia in the middle of the arm and is distributed to the skin of the arm as far as the medial epi-

condyle and olecranon. A part of it forms a loop with the intercostobrachial nerve in the axilla, and there is a reciprocal relationship in size between these two nerves. It also communicates with the ulnar branch of the medial antebrachial cutaneous nerve or it may be a branch of the latter nerve. MEDIAL

ANTEBRACHIAL

CUTANEOUS

NERVE.

The medial antebrachial cutaneous nerve (Figs. 12-41 to 12-44; 12-46) arises from the medial cord of the brachial plexus, medial to

Fig. 12-41. Cutaneous nerves of right upper limb. Anterior view.

SPINAL NERVES

1211

Fig. 12-42.

Diagram of segmental distribution of the cutaneous nerves of the right upper limb. Anterior view.

Fig.

12-43. Cutaneous nerves of right upper limb, Posterior view.

the axillary artery. Near the axilla, it gives off a filament that pierces the fascia and sup¬ plies the skin over the biceps nearly as far as the elbow. The nerve runs down the ulnar side of the arm medial to the brachial artery, pierces the deep fascia with the basilic vein about the middle of the arm, and divides into an anterior and an ulnar branch. The ulnar branch (posterior branch) passes obliquely distalward on the medial

side of the basilic vein, anterior to the me¬ dial epicondyle of the humerus to the dor¬ sum of the forearm, and continues on its ulnar side as far as the wrist, supplying the skin. It communicates with the medial brachial cutaneous, the dorsal antebrachial cutaneous, and the dorsal branch of the ulnar nerve. The anterior branch is larger and passes, usually superficial but occasionally deep, to

1212

THE PERIPHERAL NERVOUS SYSTEM

Fig. 12-44.

Diagram of segmental distribution of the cutaneous nerves of the right upper limb. Posterior view.

the median basilic vein. It continues on the anterior part of the ulnar side of the forearm, distributing filaments to the skin as far as the wrist, and communicating with the palmar cutaneous branch of the ulnar nerve. Terminal Branches

The terminal branches of the brachial plexus are the musculocutaneous, median, ulnar, and radial nerves.

musculocutaneous nerve. The musculocutaneous nerve (Fig. 12-46) is formed by the splitting of the lateral cord of the brach¬ ial plexus at the inferior border of the pectoralis minor into two branches, the other branch being the lateral root of the median nerve. It pierces the coracobrachialis mus¬ cle, and lying between the brachialis and the biceps brachii, crosses to the lateral side of the arm. A short distance above the elbow it pierces the deep fascia lateral to the tendon of the biceps and continues into the forearm as the lateral antebrachial cutaneous nerve. The branch to the coracobrachialis leaves the nerve close to its origin. Muscular branches are supplied to the bi¬ ceps and the greater part of the brachialis. An articular filament given off from the nerve to the brachialis supplies the elbow joint. A filament to the humerus enters the nutri¬ ent foramen with the artery. The lateral antebrachial cutaneous nerve (Figs. 12-41 to 12-44) passes deep to the ce¬ phalic vein and divides opposite the elbow joint into an anterior and a dorsal branch. The anterior branch (volar branch) fol¬ lows along the radial border of the forearm to the wrist and supplies the skin over the radial half of its anterior surface. At the wrist it is superficial to the radial artery, and some of its filaments pierce the deep fascia to follow the vessel to the dorsal surface of the carpus. It terminates in cutaneous fila¬ ments at the thenar eminence after commu¬ nicating with the superficial branch of the radial and the palmar cutaneous branch of the median nerve. The dorsal branch (posterior branch) passes distally along the dorsal part of the radial surface of the forearm, supplying the skin almost to the wrist, and communicating with the dorsal antebrachial cutaneous nerve and the superficial branch of the ra¬ dial nerve. Variations. The musculocutaneous and median nerves present frequent irregularities in their origins from the lateral cord of the plexus. The branch to the coracobrachialis muscle may be a separate nerve. In this condition the musculocutaneous nerve may continue with the median for a variable distance be¬ fore it passes under the biceps. Some of the fibers of the median nerve may run for some distance in the musculocutaneous nerve before they join their proper trunk; less frequently the reverse is the case and fibers of the musculocutaneous nerve run with

SPINAL NERVES

1213

Fig. 12-45. Dermatome chart of the upper limb of man outlined by the pattern of hyposensitivity from loss of function of a single nerve root. (From Keegan and Garrett, Anat. Rec., 102:415, 1948.)

the median. The musculocutaneous nerve may give a branch to the pronator teres or it may supply the dorsum of the thumb in the absence of the superfi¬ cial branch of the radial nerve. ¥

The median nerve (Fig. 12-46) is the nerve to the radial side of the flexor portion of the forearm and hand. It takes its origin from the brachial plexus by two large roots, one from the lateral and one from the medial cord. The roots at first lie on each side of the third part of the axillary ar¬ tery, then embracing it, they unite on its ven¬ tral surface to form the trunk of the nerve. In its course down the arm it accompanies the brachial artery, to which it is at first lateral, but gradually it crosses the ventral surface of the artery in the middle or distal part of the arm and lies medial to it at the bend of the elbow, where it is deep to the bicipital fascia and superficial to the brachialis muscle. In the forearm, the median nerve passes between the two heads of the pronator teres, being separated from the ulnar artery by the deep head. It continues distally between the median

nerve.

flexores digitorum superficialis and profun¬ dus almost to the flexor retinaculum, where it becomes more superficial and lies between the tendons of the flexor digitorum superfi¬ cialis and the flexor carpi radialis. It is deep to the tendon of the palmaris longus and slightly ulnarward of it, and it is the most superficial of the structures that pass through the tunnel under the flexor reti¬ naculum. In the palm of the hand, the median nerve is covered only by the skin and the palmar aponeurosis and rests on the tendons of the flexor muscles (Fig. 12-47). Immediately after emerging from under the retinaculum, it becomes enlarged and flattened and splits into muscular and digital branches. Branches. The median nerve has no branches above the elbow joint unless, as occasionally happens, the nerve to the pro¬ nator teres arises there. Articular branches to the elbow joint are one or two twigs given off as the nerve passes the joint. Muscular branches leave the nerve near the elbow and supply all the superficial mus-

1214

THE PERIPHERAL NERVOUS SYSTEM

Superior pectoral

Inferior pectoral

Musculocutaneous

Median

Radial Deep br. of radial

Superfic. br. of radial

Palmar interosseous

Fig. 12-46.

Nerves of the left upper limb.

SPINAL NERVES

1215

Digital arteries gital nerves

Ulnar nerve Palmaris brevis Super! palmar of radial artery Ulnar artery Palmaris longus

Fig. 12-47.

Superficial dissection of the palm of the hand. (Redrawn from Tondury.)

cles of the anterior part of the forearm ex¬ cept the flexor carpi ulnaris, i.e., the prona¬ tor teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis. The anterior interosseous nerve (Fig. 1246) accompanies the anterior interosseous artery along the anterior surface of the inter¬ osseous membrane in the interval between the flexor pollicis longus and the flexor digi¬

torum profundus, ending in the pronator quadratus and the wrist joint. It supplies all the deep anterior muscles of the forearm except the ulnar half of the profundus, i.e., the radial half of the flexor digitorum pro¬ fundus, the flexor pollicis longus, and the pronator quadratus. The palmar branch of the median nerve (Fig. 12-42) pierces the antebrachial fascia

1216

THE PERIPHERAL NERVOUS SYSTEM

distal to the wrist and divides into a medial and a lateral branch. The medial branch supplies the skin of the palm and communi¬ cates with the palmar cutaneous branch of the ulnar nerve. The lateral branch supplies the skin over the thenar eminence and com¬ municates with the lateral antebrachial cu¬ taneous nerve. The muscular branch in the hand (Fig. 1248) is a short stout nerve that leaves the ra¬ dial side of the median nerve, sometimes in company with the first common palmar digi¬

tal nerve, just after the former passes under the flexor retinaculum. It supplies the mus¬ cles of the thenar eminence with the excep¬ tion of the deep head of the short flexor, i.e., the abductor pollicis brevis, the opponens pollicis and the superficial head of the flexor pollicis brevis. The first common palmar digital nerve (Figs. 12-48; 12-50) divides into three proper palmar digital nerves (digital collaterals), two of which supply the sides of the thumb; the third gives a twig to the first lumbrical

12-48. Dissection of the palm of the hand, showing the superficial palmar arch, median and ulnar nerves, and synovial sheaths. (Redrawn from Tondury.) Fig.

SPINAL NERVES

and continues as the proper palmar digital nerve for the radial side of the index finger. The second common palmar digital nerve gives a twig to the second lumbrical, and continuing to the web between the index and middle fingers, splits into proper digital nerves for the adjacent sides of these fingers. The third common palmar digital nerve occasionally gives a twig to the third lumbrical, in which case it has a double innervation; it communicates with a branch of the ulnar nerve, and continues to the web between the middle and the ring fingers, where it splits into proper digital nerves for the adjacent sides of these digits. The proper digital nerves (digital collater¬ als) (Figs. 12-47; 12-48; 12-50) supply the skin of the palmar surface and the dorsal surface over the terminal phalanx of their digits. At the end of the digit each nerve terminates in two branches, one of which ramifies in the skin of the ball, the other in the pulp under the nail. They communicate with the dorsal digital branches of the superficial radial nerve, and in the fingers they are superficial to the corresponding arteries. Variations. In 1 6 per cent of bodies studied, the relation of the median nerve to the two heads of the pronator teres varies from that described; it may pass deep to the humeral head in the absence of an ulnar head, or deep to the ulnar head, or split the humeral head (Jamieson and Anson, 1952). There is overlapping of territory in the innervation of the flexor digitorum profundus by the median and ulnar nerves in 50 per cent of bodies; it is twice as com¬ mon for the median to encroach on the ulnar. The portion of the profundus attached to the index finger is the only part of that muscle constantly supplied by one nerve, the median. In the majority of cases the profundus and the lumbrical of a particular digit are innervated by the same nerve. Encroachment of the median on the ulnar is less common for the lumbricals than the profundus. The median nerve may sup¬ ply the first dorsal interosseus (Sunderland 1945, 1946).

The ulnar nerve (Fig. 12-46) occupies a superficial position along the medial side of the arm and is the nerve to the muscles and skin of the ulnar side of the forearm and hand. It is the terminal continu¬ ation of the medial cord of the brachial plexus, after the medial head of the median nerve has separated from it. It is medial, at first to the axillary artery and then to the brachial artery as far as the middle of the ulnar nerve.

1217

arm, and is parallel with and not far distant from the median and medial antebrachial cutaneous nerves. In the middle of the arm it angles dorsally, pierces the medial intermus¬ cular septum, and follows along the medial head of the triceps muscle to the groove be¬ tween the olecranon and the medial epicondyle of the humerus. In this position it is covered only by the skin and fascia and can readily be palpated as the “funny bone” of the elbow. The ulnar nerve is accompanied in its course through the distal half of the arm by the superior ulnar collateral artery and the ulnar collateral branch of the radial nerve. It enters the forearm between the two heads of the flexor carpi ulnaris and continues be¬ tween this muscle and the flexor digitorum profundus half way down the forearm. In the proximal part of the forearm it is sepa¬ rated from the ulnar artery by a considera¬ ble distance, but in the distal half it lies close to its ulnar side, radialward from the flexor carpi ulnaris, and covered only by the skin and fascia. Proximal to the wrist it gives off a large dorsal branch and continues into the hand, where it has muscular and digital branches. Branches. The ulnar nerve usually has no branches proximal to the elbow. Distal to the elbow its branches are as follows: The articular branches to the elbow joint are several small filaments that leave the nerve as it lies in the groove between the olecranon and the medial epicondyle of the humerus. Two muscular branches arise near the elbow and supply the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus. The palmar cutaneous branch of the ulnar nerve arises near the middle of the forearm and accompanies the ulnar artery into the hand. It gives filaments to the artery, per¬ forates the flexor retinaculum, and ends in the skin of the palm, communicating with the palmar branch of the median nerve. The dorsal branch (Figs. 12-43; 12-46) arises in the distal half of the forearm and reaches the dorsum of the wrist by passing between the flexor carpi ulnaris and the ulna. It pierces the deep fascia and divides into two dorsal digital nerves and a metacar¬ pal communicating branch. The more me¬ dial digital nerve supplies the ulnar side of the little finger; the other digital branch, the

1218

THE PERIPHERAL NERVOUS SYSTEM

adjacent sides of the little and ring fingers. The metacarpal branch supplies the skin of that area and continues toward the web be¬ tween the ring and middle fingers, where it joins a similar branch of the superficial ra¬ dial nerve to supply the adjacent sides of these two fingers. On the little finger the dor¬ sal digital branches extend only as far as the base of the terminal phalanx, and on the ring finger as far as the base of the second pha¬ lanx; the more distal parts of these digits are supplied by the dorsal branches of the proper palmar digital nerves from the ulnar nerve. The palmar branch or terminal portion of the ulnar nerve crosses the ulnar border of the wrist in company with the ulnar artery, superficial to the flexor retinaculum and under cover of the palmaris brevis, and di¬ vides into a superficial and deep branch. The superficial branch (Figs. 12-48; 12-50) supplies the palmaris brevis and the skin of

the hypothenar eminence and divides into digital branches. A proper palmar digital branch goes to the ulnar side of the little fin¬ ger; a common palmar digital branch divides into proper digital branches for the adjacent sides of the little and ring fingers and com¬ municates with the branches of the median nerve. The proper digital branches are dis¬ tributed to the fingers in the same manner as those of the median nerve. The deep branch (Figs. 12-49; 12-50) passes between the abductor digiti minimi and flexor digiti minimi brevis accompanied by the deep branch of the ulnar artery; it then pierces the opponens digiti minimi and fol¬ lows the course of the deep palmar arch across the interossei, deep to the midpalmar and thenar fascial clefts. Near its origin it gives branches to the three small muscles of the little finger, and as it crosses the hand it supplies the third and fourth lumbricals and all the interossei, both palmar and dor-

Ulnar artery & nerve Deep branch ulnar art. Deep branch ulnar nerve Flexor tendons Radial artery Median nerve Princeps poll, art

Flex. poll, brevis Flex. poll. long. Adduct, poll.

Deep palmar arch Palmar metacarp. art. Deep flex, tendon Superf. flex, tendon

Lumbricales Proper digital artery & nerve

Deep dissection of the palm of the hand, showing the deep palmar arch and the deep palmar branch of the ulnar nerve. (Redrawn from Tondury.)

Fig. 12-49.

SPINAL NERVES

1219

Palmar interosseous Radial Ulnar nerve

Medial branch of superficial radial Branch of anterior interosseous to joint

Lateral branch of superficial radial

Superficial branch of ulnar Deep branch of ulnar Nerve to palmaris

Deep branch of ulnar Nerve to third and fourth lumbricals

Termination of ulnar in thumb muscles

Digital collateral branches

Fig. 12-50.

Deep palmar nerves. (Testut.)

sal. It ends by supplying the adductores pollicis and the deep head of the flexor pollicis brevis. It also sends articular fila¬ ments to the wrist joint.

ciencies on the dorsum of the hand that are supplied by the radial nerve or it may encroach upon the area usually supplied by that nerve. See variations of the median nerve and brachial plexus.

Variations. The ulnar nerve may pass in front of the medial epicondyle. It frequently has a communi¬ cation with the median nerve in the forearm and rarely with the medial antebrachial cutaneous, me¬ dian, or musculocutaneous nerves in the arm. It may send muscular branches to the medial head of the triceps, the flexor digitorum superficialis, the first and second lumbricals and the superficial head of the flexor pollicis brevis muscles. It may have defi¬

radial nerve. The radial nerve (musculospiral nerve) (Fig. 12-51), the largest branch of the brachial plexus, is the continuation of the posterior cord; it supplies the extensor muscles of the arm and forearm as well as the skin covering them. It crosses the tendon of the latissimus dorsi, deep to the axillary artery, and after passing the inferior border

1 220

Fig. 12-51. nerves.

the peripheral nervous system

The suprascapular, axillary, and radial

of the teres major, it winds around the me¬ dial side of the humerus and enters the sub¬ stance of the triceps between the medial and long heads. It takes a spiral course down the arm close to the humerus in the groove that separates the origins of the medial and lat¬ eral heads of the triceps, accompanied by the deep brachial artery. Having reached the lateral side of the arm, it pierces the lateral intermuscular septum and runs between the

brachialis and the brachioradialis anterior to the lateral epicondyle, where it divides into superficial and deep branches (Fig. 12-46). Branches in the Arm. Both muscular and cutaneous branches of the radial nerve are found in the arm. The medial muscular branches arise in the axilla and supply the medial and long heads of the triceps. The branch to the medial head is a long filament that accompanies the ulnar nerve and superior ulnar collateral artery as far as the lower third of the arm and is there¬ fore named the ulnar collateral nerve. The posterior brachial cutaneous nerve (internal cutaneous branch of the musculospiral) arises in the axilla to the medial side of the arm, supplying the skin on the dorsal surface nearly as far as the olecranon. In its course it crosses dorsal to, and communi¬ cates with, the intercostobrachial nerve. The posterior muscular branches arise from the nerve as it lies in the spiral groove of the humerus; they supply the medial and lateral heads of the triceps and the anco¬ neus. The nerve to the latter muscle is a long, slender filament that lies buried in the sub¬ stance of the medial head of the triceps. The posterior antebrachial cutaneous nerve (external cutaneous branch of the musculospiral) perforates the lateral head of the triceps at its attachment to the humerus and divides into proximal and distal branches. The smaller proximal branch lies close to the cephalic vein and supplies the skin of the dorsal part of the distal half of the arm. The distal branch pierces the deep fas¬ cia below the insertion of the deltoid and continues along the lateral side of the arm and elbow and the dorsal side of the forearm to the wrist. It supplies the skin in its course, and near its termination, it communicates with the dorsal branch of the lateral antebra¬ chial cutaneous nerve. The lateral muscular branches supply the brachioradialis, the extensor carpi radialis longus, and the lateral part of the brachialis. Articular branches to the elbow come from the radial nerve between the brachialis and brachioradialis, from the ulnar collat¬ eral nerve, and from the nerve to the anco¬ neus. Branches in the Forearm. The superficial branch of the radial nerve (Fig. 12-46) runs along the lateral border of the forearm under cover of the brachioradialis muscle. In the proximal third of the forearm it gradually

SPINAL NERVES

approaches the radial artery; in the middle third it lies just radialward to the artery; and in the lower third it quits the artery and an¬ gles dorsally under the tendon of the brachioradialis toward the dorsum of the wrist, where it pierces the deep fascia and divides into two branches. The lateral branch is smaller, supplies the skin of the radial side and ball of the thumb, and communicates with the palmar branch of the lateral antebrachial cutaneous nerve. The medial branch communicates above the wrist, with the dorsal branch of the lat¬ eral antebrachial cutaneous nerve, and on the dorsum of the hand, with the dorsal branch of the ulnar nerve. It then divides into four dorsal digital nerves (Fig. 12-43), which are distributed as follows: (1) to the ulnar side of the thumb, (2) to the radial side of the index finger, (3) to the adjacent sides of the index and middle fingers, and (4) to the dorsal branch of the ulnar nerve to form a communication, and to the adjacent sides of the middle and ring fingers. The deep branch of the radial nerve (pos¬ terior interosseous nerve) (Fig. 12-51) winds to the dorsum of the forearm around the ra¬ dial side of the radius between the planes of fibers of the supinator muscle and continues between the superficial and deep layers of muscles to the middle of the forearm. Considerably diminished in size, and named the dorsal interosseous nerve, it lies on the dorsal surface of the interosseous mem¬ brane, and under cover of the extensor pollicis longus, it continues to the dorsum of the carpus, where it ends. Muscular branches of the deep branch of the radial nerve to the extensor carpi radialis brevis and the supinator are given off be¬ fore the nerve turns dorsally. After passing through the supinator, branches are given to the extensor digitorum, extensor digiti min¬ imi, extensor carpi ulnaris, the two extensores and abductor longus pollicis, and the exten¬ sor indicis. Articular filaments from a terminal plexus of the radial nerve are distributed to the liga¬ ments and articulations of the carpus and metacarpus. variations. The radial nerve may pass through the quadrilateral space with the axillary nerve, and when the profunda brachii supplies the nutrient ar¬ tery of the humerus, it may be accompanied by a filament from the radial. The nerve to the brachialis

1221

muscles is inconstant. The deep branch may pass superficial to the entire supinator. There is great var¬ iation in the distribution and overlapping of the ra¬ dial and ulnar nerves on the back of the hand; the most frequent arrangement appears to be that the radial supplies three and a half digits, the ulnar, one and a half digits (Sunderland, 1945, 1946). Thoracic Nerves

The ventral primary divisions (anterior divisions) (Fig. 12-52) of the thoracic nerves number 12 on each side. The first eleven, sit¬ uated between the ribs, are termed intercostals; the twelfth lies below the last rib and is called the subcostal nerve. The intercostal nerves are distributed chiefly to the parietes of the thorax and abdomen, and they differ from the other spinal nerves in that each pursues an independent course, i.e., they do not enter into a plexus. The first two contrib¬ ute to the upper limb as well as to the thorax; the next four are limited in their distribution to the thorax; the lower five supply the parietes of the thorax and the abdomen. The twelfth thoracic nerve is distributed to the abdominal wall and the skin of the buttock. RAMI COMMUNICANTES Each thoracic nerve contributes pregangli¬ onic sympathetic fibers to the sympathetic chain through a white ramus communicans, and receives postganglionic fibers from the chain ganglia through gray rami communicantes. Both rami are attached to the spinal nerves near their exit from the intervertebral foramina, the gray rami being more medial than the white. For more details see the sec¬ tion on the Sympathetic System. FIRST THORACIC NERVE The ventral primary division of the first thoracic nerve divides immediately into two parts: (1) the larger part leaves the thorax ventral to the neck of the first rib and be¬ comes one of the roots of the brachial plexus (described previously); (2) the smaller part becomes the first intercostal nerve. The first intercostal nerve runs along the first inter¬ costal space to the sternum, perforates the muscles and deep fascia, and ends as the first anterior cutaneous nerve of the thorax. It has no lateral cutaneous branch, as a rule, but it may have a communication with the intercostobrachial branch of the second

1222

THE PERIPHERAL NERVOUS SYSTEM

Posterior cutaneous n.

Fig. 12-52.

Plan of a typical intercostal nerve.

nerve. A communication between the first and second nerves inside the thorax occurs frequently and contains postganglionic sym¬ pathetic fibers from the second or even the third thoracic sympathetic ganglion. SUPERIOR THORACIC NERVES

The ventral primary divisions of the sec¬ ond to the sixth thoracic nerves and the in¬ tercostal portion of the first thoracic are known as the thoracic intercostal nerves (Figs. 12-53; 12-54; 12-78). They pass ventralward in the intercostal spaces with the inter¬ costal vessels; from the vertebral column to the angles of the ribs, they lie between the pleura and the posterior intercostal mem¬

brane; from the angle to the middle of the ribs, they pass between the intercostales interni and externi. They then enter the sub¬ stance of the intercostales interni, where they remain concealed until they reach the costal cartilages; here they again emerge on the inner surface of the muscle and lie between it and the pleura. The nerves are inferior to the vessels and, like them, are at first close to the rib above, but as they pro¬ ceed ventrally they may approach the mid¬ dle of the intercostal space. Near the ster¬ num they pass ventral to the transversus thoracis and the internal thoracic vessels, and near the sternum they pierce the intercostalis internus, the anterior intercostal membrane, the pectoralis major and the pec-

SPINAL NERVES

1223

Intercost obrachial

Anterior cutaneous nerves of thorax

Anterior cutaneous nerves of abdomen

Lateral cutaneous of III to XI thoracic

Lateral cutaneous of iliohypogastric Ant. cutaneous of X, XI, and XII thoracic

Lateral cutaneous of XII thoracic

Fig. 12-53.

Cutaneous distribution of thoracic nerves. (Testut.)

toral fascia, terminating as the anterior cuta¬ neous nerves of the thorax. They have short medial and longer lateral branches that sup¬ ply the skin and mamma. muscular branches. Muscular branches supply the intercostales interni and externi, the subcostales, the levatores costarum, the

serratus posterior superior, and the transversus thoracis. At the ventral part of the thorax some of these branches cross the costal carti¬ lages from one intercostal space to another. cutaneous branches. The lateral cuta¬ neous nerves (Figs. 12-53; 12-54) arise from the intercostal nerves about midway be-

1224

THE PERIPHERAL NERVOUS SYSTEM

Internal

Intercostobrachial

Lateral cutaneous branches of III to XI thoracic

Lateral cutaneous of XII thoracic

Iliohypogastric

Fig. 12 54.

Intercostal nerves, the superficial muscles having been removed. (Testut.)

tween the vertebral column and the ster¬ num, pierce the intercostales externi and serratus anterior, and divide into anterior and posterior branches. The anterior branches supply the skin of the lateral and ventral part of the chest and mammae; those of the fifth and sixth nerves also supply the cranial digitations of the obliquus externus abdominis. The posterior branches supply the skin over the latissimus dorsi and the scapular region.

The intercostobrachial nerve (Figs. 12-39; 12-41; 12-46) arises from the second intercos¬ tal nerve as if it were a lateral cutaneous nerve, but it fails to divide into an anterior and a posterior branch. After piercing the imercostales and the serratus anterior, it crosses the axilla, embedded in the adipose tissue, to reach the medial side of the arm. It forms a loop of communication with the medial brachial cutaneous nerve of the brachial plexus and assists it in supplying

SPINAL NERVES

the skin of the medial and posterior part of the arm. It also communicates with the pos¬ terior brachial cutaneous branch of the ra¬ dial nerve. An intercostobrachial branch frequently arises from the third intercostal nerve, sup¬ plying the axilla and medial side of the arm. LOWER THORACIC NERVES

The ventral primary divisions of the sev¬ enth to eleventh thoracic nerves are contin¬ ued beyond the intercostal spaces into the anterior abdominal wall and are named the thoracoabdominal intercostal nerves (Figs. 12-53; 12-54). They have the same arrange¬ ment as the upper nerves as far as the ante¬ rior ends of the intercostal spaces, where they pass dorsal to the costal cartilages. They run ventralward between the obliquus internus and transversus abdominis mus¬ cles, pierce the sheath of the rectus abdomi¬ nis, which they supply, and terminate as the anterior cutaneous branches. muscular branches. Muscular branches supply the intercostales, the obliqui, and transversus abdominis muscles; the last three also supply the serratus posterior infe¬ rior. cutaneous branches. The lateral cuta¬ neous branches (Figs. 12-53; 12-54) arise mid¬ way along the nerves, pierce the intercostales externi and the obliquus externus in line with the lateral cutaneous branches of the upper intercostals, and divide into anterior and posterior branches. The anterior branches give branches to the digitations of the obliquus externus and extend caudalward and ventralward nearly as far as the margin of the rectus abdominis, supplying the skin. The posterior branches pass dorsally to supply the skin over the latissimus dorsi. The anterior cutaneous branches pene¬ trate the anterior layer of the sheath of the rectus abdominis and divide into medial and lateral branches that supply the skin of the anterior part of the abdominal wall.

TWELFTH THORACIC NERVE

The anterior primary division of the twelfth thoracic (Figs. 12-53; 12-54; 12-57) or subcostal nerve is larger than those above it. It runs along the inferior border of the twelfth rib, often communicates with the first lumbar nerve, and passes under the lat¬ eral lumbocostal arch. It crosses the ventral

1225

surface of the quadratus lumborum, pene¬ trates the transversus abdominis, and con¬ tinues ventralward to be distributed in the same manner as the lower intercostal nerves. It communicates with the iliohypogastric nerve of the lumbar plexus and gives a branch to the pyramidalis. The lateral cuta¬ neous branch is large and does not divide into anterior and posterior branches. It perforates the obliqui muscles, passes down¬ ward over the crest of the ilium ventral to a similar branch of the iliohypogastric nerve, and is distributed to the skin of the anterior part of the gluteal region, some filaments ex¬ tending as far down as the greater trochanter. Lumbar Nerves and Lumbosacral Plexus

The ventral primary divisions are increas¬ ingly large as they are placed more caudally in the lumbar region. Their course is lateralward and caudalward, either under cover of the psoas major muscle or between its fas¬ ciculi. The first three nerves and the larger part of the fourth nerve are connected by communicating loops, and they are fre¬ quently joined by a communication from the twelfth thoracic nerve, forming the lumbar plexus. The smaller part of the fourth nerve joins the fifth to form the lumbosacral trunk, which enters the sacral plexus. The fourth nerve, because it is divided between the two plexuses, is sometimes called the nervus furcalis. Only the first two lumbar nerves contrib¬ ute preganglionic sympathetic fibers to the sympathetic chain through white rami communicantes. All the lumbar nerves re¬ ceive postganglionic fibers from the sympa¬ thetic chain through gray rami communi¬ cantes. For more details see the section on the Sympathetic Nervous System. Muscular branches are supplied to the psoas major and the quadratus lumborum from the ventral primary divisions of the lumbar nerves before they enter the lumbar plexus. The lumbosacral plexus is the name given to the combination of all the ventral primary divisions of the lumbar, sacral, and coccyg¬ eal nerves. The lumbar and sacral plexuses supply the lower limb, but in addition the sacral nerves supply the perineum through the pudendal plexus and the coccygeal re¬ gion through the coccygeal plexus. For con¬ venience in description, these plexuses will be considered separately.

1226

THE PERIPHERAL NERVOUS SYSTEM

LUMBAR PLEXUS

The lumbar plexus (Fig. 12-55) is formed by the ventral primary divisions of the first three and the greater part of the fourth lum¬ bar nerves, with a communication from the twelfth thoracic usually joining the first lum¬ bar nerve. It is situated on the inside of the posterior abdominal wall, either dorsal to the psoas major or among its fasciculi, and ventral to the transverse processes of the lumbar vertebrae. The lumbar plexus is not an intricate interlacement like the brachial plexus, but its branches usually arise from two or three nerves, so that the resulting junctions between adjacent nerves have the appearance of loops. The manner in which the plexus is formed is the following (Figs. 12-55; 12-56): the first lumbar nerve, usually supplemented by a communication from the twelfth thoracic nerve, splits into a cranial and a caudal branch. The cranial branch forms the iliohy¬ pogastric and ilioinguinal nerves; the caudal and smaller branches unite with a branch from the second lumbar nerve to form the

genitofemoral nerve. The remainder of the second nerve and the third and fourth nerves each split into a small ventral and a large dorsal portion; the ventral portions unite into one nerve, the obturator. The dor¬ sal portions of the second and third nerves each divide again into unequal branches; the two smaller branches unite to form the lat¬ eral femoral cutaneous nerve; the two larger branches join the dorsal portion of the fourth nerve to form the femoral nerve. The accessory obturator nerve, which is present in about one out of five individuals, comes from the third and fourth nerves. A consid¬ erable part of the fourth nerve joins the fifth lumbar nerve in the lumbosacral trunk. The branches of the lumbar plexus are as follows: 1. Iliohypogastric 2. Ilioinguinal

L 1, (T 12) L1

3. 4. 5. 6. 7.

L 1, L 2, L 2, L 3, L 2,

Genitofemoral Lateral femoral cutaneous Obturator Accessory obturator Femoral

From 12th thoracic

1 st lumbar

Iliohypogastric Ilioinguinal 2nd lumbar Genitofemoral

3rd lumbar Lat. femoral cutaneous

4th lumbar

To psoas and iliacus 5th lumbar Femoral Accessory obturator Obturator

Lumbosacral trunk Fig. 12-55.

Plan of lumbar plexus.

2 3 3, 4 4 3, 4

SPINAL NERVES

Subcostal nerve

1227

Celiac ganglion Superior mesen plexus

Iliohypogastric nerve

Ilioinguinal nerve

Inferior mesen. plexus

Hypogastric plexus

Lateral femoral cutaneous nerve

Lumbosacral trunk

Genitofemoral nerve

Anterior sup. spine Obturator nerve Circumflex t- iliac artery 4-Femoral nerve Femoral branch

Genital branch Inguinal ligament Iliohypogastric

Sacral parasym pathetics

Ilioinguinal Spermatic cord Hiatus saphen.

Superficial inguinal ring

Gr. saphen. vein-L

Fig. 12-56.

The lumbar plexus and its branches.

These branches may be divided into two groups according to their distribution. The first three supply the caudal part of the parietes of the abdominal wall; the last four supply the anterior thigh and medial part of the leg. iliohypogastric imerve. The iliohypogastric nerve (Figs. 12-56; 12-58) arises from the first lumbar nerve and from the communica¬ tion with the twelfth thoracic nerve, when this is present. It emerges from the upper part of the lateral border of the psoas major, crosses the quadratus lumborum to the crest of the ilium, and penetrates the posterior part of the transversus abdominis near the crest of the ilium. Between the transversus and the obliquus internus it divides into a lateral and anterior cutaneous branch. The lateral cutaneous branch (iliac

branch) pierces the obliqui internus and externus immediately above the iliac crest, and is distributed to the skin of the gluteal region posterior to the lateral cutaneous branch of the twelfth thoracic nerve (Figs. 12-57; 1264); these two nerves are inversely propor¬ tional in size. The anterior cutaneous branch (hypogas¬ tric branch) (Figs. 12-54; 12-58) continues its course between the obliquus internus and tranversus, pierces the former, and becomes subcutaneous by passing through a perfora¬ tion in the aponeurosis of the obliquus externus about 2 cm above the superficial in¬ guinal ring. It is distributed to the skin of the hypogastric region (Fig. 12-27). Muscular branches are supplied to the obliquus internus and transversus. ilioinguinal nerve. The ilioinguinal

1228

THE PERIPHERAL NERVOUS SYSTEM

Lumbar portion of sympathetic

Twelfth thoracic n

Twelfth thoracic n.

First lumbar n. Nerve to quadratus lumborum

Iliohypogastric n.

Transversalis Obliqus internus Obliqus externus Second lumbar n.

Ilioinguinal n

Iliohypogastric n. Genitofemoral n Ramus communicans

Third lumbar n. Iliac branch of iliohypogastric Abdominal branch of iliohypo.

Lat. femoral cutaneous n.

Fourth lumbar n. Fifth lumbar n. Ilioinguinal n.

Genitofemoral n.

Lateral femoral cutaneous n.

Femoral branch

Obturator nerve External spermatic branch of genito¬ femoral n. Lumboinguinal branch of genitofemoral n. Posterior branch of lateral femoral cutaneous n. Anterior branch of lateral femoral cutaneous n.

Genital branch

Aponeurosis of external oblique Fig. 12-57.

Dorsal nerve of penis

Deep and superficial dissection of the lumbar plexus. (Testut.)

nerve (Figs. 12-56; 12-57) arises from the lat¬ eral border of the psoas major just caudal to the iliohypogastric nerve and follows a simi¬ lar course obliquely across the fibers of the quadratus lumborum to the crest of the ilium. It penetrates the transversus muscle near the anterior part of the crest, communi¬ cates with the iliohypogastric nerve, and pierces the obliquus internus, distributing filaments to it. It then accompanies the sper¬ matic cord through the superficial inguinal ring, and is distributed to the skin over the proximal and medial part of the thigh, the

root of the penis, and the scrotum in the male (Fig. 12-57), or the mons pubis and the labium majus in the female. Muscular twigs are supplied to the obliquus internus and transversus. clinical comment. The optimal point for block¬ ing the iliohypogastric and ilioinguinal nerves with local anesthesia is 4 to 6 cm posterior to the anterior superior spine of the ilium, along the lateral aspect of the external lip of the crest, where the nerves per¬ forate the transversus abdominis muscle (Jamieson eta!.. 1952).

SPINAL NERVES

1229

genitofemoral nerve. The genitofemoral nerve (genitocrural nerve) (Figs. 12-56; 12-57; 12-59) arises from the first and second lum¬ bar nerves and passes caudalward through the substance of the psoas major until it emerges on its ventral surface opposite the third or fourth lumbar vertebra, where it is covered by transversalis fascia and perito¬ neum. On the surface of the muscle, or occa¬ sionally within its substance, it divides into a genital and a femoral branch. The genital branch (external spermatic nerve) continues along the psoas major to the inguinal ligament, where it either pierces the transversalis and internal spermatic fas¬ cia or passes through the internal inguinal ring to reach the spermatic cord. It lies against the dorsal aspect of the cord, sup¬ plies the cremaster muscle, and is distrib¬ uted to the skin of the scrotum and adjacent thigh. In the female it accompanies the round ligament of the uterus. The femoral branch (lumboinguinal nerve) lies on the psoas major, lateral to the genital branch, and passes under the ingui¬ nal ligament with the external iliac artery. It enters the femoral sheath, superficial and lateral to the artery, then pierces the sheath and fascia lata to supply the skin of the proximal part of the anterior surface of the thigh. It gives a filament to the femoral ar¬ tery and communicates with the anterior cutaneous branches of the femoral nerve (Figs. 12-58; 12-59). variations. The iliohypogastric or ilioinguinal nerves may arise from a common trunk, or the ilioinguinal nerve may join the iliohypogastric at the iliac crest, with the latter nerve then supplying the missing branches. The ilioinguinal nerve may be lacking and the genital branch supplies its branches, or the genital branch may be absent and the ilioinguinal substitutes for it. The femoral branch and lateral femoral cutaneous nerves or the anterior cutaneous branches of the femoral nerve may sub¬ stitute for each other to a greater or lesser extent.

The lateral femoral cutaneous nerve (external cutaneous nerve) (Figs. 12-55; 12-58) arises from the dorsal portion of the ventral pri¬ mary divisions of the second and third lum¬ bar nerves. It emerges from the lateral bor¬ der of the psoas major about its middle, and runs across the iliacus muscle obliquely toward the anterior superior iliac spine. It LATERAL FEMORAL CUTANEOUS NERVE.

Fig. 12-58. Cutaneous nerves of right lower limb. Anterior view.

1230

the peripheral nervous system

Diagram of segmental distribution of the cutaneous nerves of the right lower limb. Anterior view.

Fig. 12-59.

then passes under the inguinal ligament and over the sartorius muscle into the subcuta¬ neous tissues of the thigh, dividing into an anterior and a posterior branch (Fig. 12-57). The anterior branch becomes superficial about 10 cm distal to the inguinal ligament and is distributed to the skin of the lateral and anterior parts of the thigh as far as the knee (Fig. 12-58). The terminal filaments communicate with the anterior cutaneous branches of the femoral nerve and the infra¬ patellar branches of the saphenous nerve, forming the patellar plexus. The posterior branch pierces the fascia lata and subdivides into filaments that pass posteriorly across the lateral and posterior surfaces of the thigh, supplying the skin from the level of the greater trochanter to the middle of the thigh (Fig. 12-64). obturator nerve. The obturator nerve (Figs. 12-55; 12-56), the motor nerve to the adductores muscles, arises by three roots from the ventral portions of the second, third, and fourth lumbar nerves; the root from the third lumbar nerve is the largest, and that from the second is often very small. The obturator emerges from the medial bor¬ der of psoas major near the brim of the pel¬ vis, under cover of the common iliac vessels, and passes lateral to the hypogastric vessels and the ureter. It runs along the lateral wall of the lesser pelvis to enter the upper part of the obturator foramen with the obturator vessels. As it enters the thigh it divides into anterior and posterior branches, which are separated by some of the fibers of the obtu¬ rator externus muscle and the adductor brevis muscle. Anterior Branch. The anterior or superfi¬ cial branch (Fig. 12-60) communicates with the accessory obturator nerve, when this is present, and passes over the superior border of the obturator externus, deep to the pectineus and adductor longus and superficial to the adductor brevis. At the distal border of the adductor longus it communicates with the anterior cutaneous and saphenous branches of the femoral nerve, forming the subsartorial plexus, and terminates in fila¬ ments accompanying the femoral artery. An articular branch to the hip joint is given off near the obturator foramen. Mus¬ cular branches are supplied to the adductor longus, gracilis, and usually to the adductor brevis; in rare instances it gives a branch to the pectineus muscle.

SPINAL NERVES

Lateral femoral cutaneous n.

Iliacus muscle Femoral n Psoas major muscle

Ant. cutaneous branch

.Anterior division of obturator n. . Med. br. of ant. cutaneous n. FEMORIJ

■ Saphenous n.

V

Superficial. peroneal n.

Deep peroneal n.'

1231

A cutaneous branch is occasionally found as a continuation of the communication with the anterior cutaneous and saphenous branches. It emerges from beneath the infe¬ rior border of the adductor longus and con¬ tinues along the posterior margin of the sartorius to the medial side of the knee, where it pierces the deep fascia, communicates with the saphenous nerve, and is distributed to the skin of the medial side of the proximal half of the leg. Posterior Branch. The posterior branch pierces the anterior part of the obturator externus, passes posterior to the adductor brevis and anterior to the adductor magnus, and divides into muscular and articular branches. Muscular branches are given to the obtu¬ rator externus as it passes between its fibers, to the adductor magnus, and to the adductor brevis when it is not supplied by the anterior branch. The articular branch for the knee joint ei¬ ther perforates the adductor magnus or passes under the arch through which the femoral artery passes and enters the poplit¬ eal fossa. It accompanies the popliteal ar¬ tery, supplying it with filaments, and reaches the back of the knee joint, where it perforates the oblique popliteal ligament and is distrib¬ uted to the synovial membrane. accessory obturator nerve. The acces¬ sory obturator nerve (Fig. 12-56) is a small nerve present in about 29% of cases. It arises from the ventral part of the third and fourth lumbar nerves, follows along the medial bor¬ der of the psoas major, and crosses over the superior ramus of the pubis instead of going through the obturator foramen with the ob¬ turator nerve. It passes deep to the pectineus muscle, supplying it with branches, commu¬ nicates with the anterior branch of the obtu¬ rator nerve, and sends a branch to the hip joint. variations. When the obturator nerve has a cu¬ taneous branch, the medial cutaneous branch of the femoral nerve is correspondingly small. When the accessory obturator is lacking, the obturator nerve supplies two nerves to the hip joint; the accessory may be very small and be lost in the capsule of the hip joint.

Fig. 12-60. view.

Nerves of the right lower limb. Anterior

femoral nerve. The femoral nerve (ante¬ rior crural nerve) (Figs. 12-55 to 12-60), the largest branch of the lumbar plexus and the

1232

THE PERIPHERAL NERVOUS SYSTEM

principal nerve of the anterior part of the thigh, arises from the dorsal portions of the ventral primary divisions of the second, third, and fourth lumbar nerves. It emerges through the fibers of the psoas major at the distal part of its lateral border and passes down between it and the iliacus, being cov¬ ered by the iliac portion of the transversalis fascia. The femoral nerve passes under the inguinal ligament, lateral to the femoral ar¬ tery, and breaks up into branches soon after it enters the thigh. Muscular branches to the iliacus are given off within the abdomen. The anterior cutaneous branches are two large nerves: the intermediate and medial cutaneous nerves (Fig. 12-58). Intermediate Cutaneous Nerve. The in¬ termediate cutaneous nerve (middle cutane¬ ous nerve) pierces the fascia lata (and gener¬ ally the sartorius) about 7.5 cm distal to the inguinal ligament. It divides into two branches that descend in immediate proxim¬ ity along the anterior thigh to supply the skin as far distally as the anterior knee. Here they communicate with the medial cutaneous nerve and the infrapatellar branch of the saphenous, thereby forming the patellar plexus. In the proximal part of the thigh the lateral branch of the intermediate cutaneous nerve communicates with the femoral branch of the genitofemoral nerve. Medial Cutaneous Nerve. The medial cutaneous nerve (internal cutaneous nerve) passes obliquely across the proximal part of the sheath of the femoral artery, and divides into two branches, an anterior and a pos¬ terior, anterior to or at the medial side of that vessel. Before dividing, it gives off a few filaments that accompany the great saphe¬ nous vein and pierce the fascia lata to supply the integument of the medial side of the thigh. One of these filaments passes through the saphenous opening: a second becomes subcutaneous about the middle of the thigh; a third pierces the fascia at its lower third. The anterior branch runs distalward on the sartorius, perforates the fascia lata at the dis¬ tal third of the thigh, and divides into two branches: one supplies the integument as far distally as the medial side of the knee; the other crosses to the lateral side of the patella, communicating in its course with the infra¬ patellar branch of the saphenous nerve. The posterior branch descends along the medial border of the sartorius muscle to the knee, where it pierces the fascia lata, communi¬

cates with the saphenous nerve, and gives off several cutaneous branches. It then passes down to supply the integument of the medial side of the leg. Beneath the fascia lata, at the lower border of the adductor longus, it forms a plexiform network (subsartorial plexus) with branches of the saphenous and obturator nerves. Variations. When the communicating branch from the obturator nerve is large and continues to the integument of the leg, the posterior branch of the medial cutaneous nerve is small and terminates in the plexus, occasionally giving off a few cutane¬ ous filaments.

Nerve to Pectineus. The nerve to the pectineus arises immediately below the inguinal ligament, and passes deep to the femoral sheath to enter the anterior surface of the muscle; it is often double. Nerve to Sartorius. The nerve to the sar¬ torius arises in common with the intermedi¬ ate cutaneous nerve and enters the deep sur¬ face of the proximal part of the muscle. Saphenous Nerve. The saphenous nerve (Figs. 12-58; 12-60; 12-64) is the largest and longest branch of the femoral nerve; it sup¬ plies the skin of the medial side of the leg. It passes deep to the sartorius in company with the femoral artery, and lies anterior to the artery, crossing from its lateral to its medial side, within the fascial covering of the ad¬ ductor canal (Fig. 8-61). At the tendinous arch in the adductor magnus, it quits the ar¬ tery, penetrates the fascial covering of the adductor canal, continues along the medial side of the knee deep to the sartorius, and pierces the fascia lata between the tendons of the sartorius and the gracilis to become subcutaneous. It then accompanies the great saphenous vein along the tibial side of the leg, and at the medial border of the tibia in the distal third of the leg, it divides into two terminal branches. One branch joins the medial cutaneous and obturator nerves in the middle of the thigh to form the subsartorial plexus. A large infrapatellar branch, given off at the medial side of the knee, pierces the sarto¬ rius and fascia lata and is distributed to the skin in front of the patella. Above the knee it communicates with the anterior cutaneous branches of the femoral nerve; below the knee it communicates with other branches of the saphenous nerve; and on the lateral

SPINAL NERVES

side of the joint, it communicates with branches of the lateral femoral cutaneous nerve to form the patellar plexus. Branches below the knee are distributed to the skin of the anterior and medial side of the leg, communicating with the medial cu¬ taneous nerve and the cutaneous branch of the obturator, if present. One branch contin¬ ues along the margin of the tibia, and ends at the ankle. The other terminal branch passes anterior to the ankle and is distributed to the medial side of the foot, as far as the ball of the great toe, communicating with the me¬ dial branch of the superficial peroneal nerve. Branches to the Quadriceps Femoris. The branch to the rectus femoris enters the prox¬ imal part of the deep surface of the muscle (Fig. 12-60). The large branch to the vastus lateralis accompanies the descending branch

of the lateral femoral circumflex artery to the distal part of the muscle. The branch to the vastus medialis muscle runs parallel with the saphenous nerve, lateral to the femoral vessels and outside of the adductor canal, and it enters the muscle near its middle. The two or three branches to the vastus intermedius, enter the anterior surface of the muscle about the middle of the thigh; a filament from one of these de¬ scends through the muscle to the articularis genu and the knee joint. Articular Branches. The articular branch to the hip joint is derived from the nerve to the rectus femoris. Articular branches to the knee joint are three in number. (1) A long slender filament derived from the nerve to the vastus lateralis penetrates the capsule of the joint on its an¬ terior aspect. (2) A filament derived from the nerve to the vastus medialis can usually be

Sympathetic runk

Fig. 12-61.

1233

Dissection of side wall of pelvis showing sacral and pudendal plexuses. (Testut.)

1 234

THE PERIPHERAL NERVOUS SYSTEM

Fig. 12-62. Dermatome chart of the lower limb of man outlined by the pattern of hyposensitivity from loss of function of a single nerve root. (From Keegan and Garrett, Anat. Rec., 102:417, 1948.)

traced downward on the surface of this mus¬ cle; it pierces the muscle and accompanies the articular branch of the descending genicular artery to the medial side of the ar¬ ticular capsule, which it penetrates, to sup¬ ply the synovial membrane. (3) The branch to the vastus intermedius, which supplies the articularis genu, also is distributed to the knee joint. Sacral and Coccygeal Nerves and Sacral Plexus

The ventral primary divisions of the sacral coccygeal nerves enter into the formation of the sacral and pudendal plexuses. Those from the first four sacral nerves enter the pelvis through the anterior sacral foramina; the fifth enters between the sacrum and coc¬ cyx, and the coccygeals enter below the first

piece of the coccyx. The first and second sacrals are large; the third, fourth, and fifth diminish progressively in size. The sacral plexus (Figs. 12-61; 12-63; 12-70) is formed by the lumbosacral trunk from the fourth and fifth lumbar nerves and by the first, second, and third sacral nerves. They converge toward the caudal part of the greater sciatic foramen and unite into a large flat band, most of which is continued into the thigh as the sciatic nerve. The plexus lies against the posterior and lateral walls of the pelvis, between the piriformis and the inter¬ nal iliac vessels, which are embedded in the pelvic subserous fascia. The nerves that enter the plexus, with the exception of the third sacral, split into ventral and dorsal por¬ tions, and the branches that arise from them are listed in the chart that appears at the top of page 1236.

SPINAL NERVES

1235

4th Lumbar

5th Lumbar

1st Sacral

Superior gluteal n

2nd Sacral Inferior gluteal n Visceral br. To piriformis

3rd Sacral

Visceral br.

Sciatic

I Common Peroneal.

I

4th Sacral

Tibial

Visceral br.

5th Sacral

To quadratus femoris and inferior gemellus To obturator internus and superior gemellus Post. fern, cutaneous n

Coccygeal Perforating cutaneous n. Pudendal n To levator ani, coccygeus and sphincter ani externus Fig. 12-63.

Plan of sacral and coccygeal plexuses.

NERVE TO QUADRATUS FEMORIS AND GEMELLUS INFERIOR

The nerve to the quadratus femoris and gemellus inferior, from the ventral portions of L 4, 5, and S 1, leaves the pelvis through the greater sciatic foramen, distal to the piri¬ formis and ventral to the sciatic nerve. It runs ventral or deep to the tendon of the ob¬ turator internus and gemelli and enters the

deep surface of the quadratus and gemellus inferior. An articular branch is given to the hip joint. NERVE TO OBTURATOR INTERNUS AND GEMELLUS SUPERIOR

The nerve to the obturator internus and gemellus superior (Fig. 12-66), from the ven¬ tral portions of L 5, and S 1, 2, leaves the pel-

1236

THE PERIPHERAL NERVOUS SYSTEM

Branches From the Sciatic Plexus

Ventral Portions Nerve to quadratus femoris and gemellus inferior Nerve to obturator internus and gemellus superior Nerve to piriformis Superior gluteal Inferior gluteal Posterior femoral cutaneous Perforating cutaneous Sciatic a. Tibial b. Common peroneal (Pudendal)

vis through the greater sciatic foramen distal to the piriformis. It gives off the branch to the gemellus superior, then crosses the spine of the ischium, reenters the pelvis through the lesser sciatic foramen, and enters the pelvic surface of the obturator internus.

NERVE TO PIRIFORMIS

The nerve to the piriformis, from the dor¬ sal portions of S 2 or S 1, 2, enters the ventral surface of the muscle; it may be double.

SUPERIOR GLUTEAL NERVE

The superior gluteal nerve (Figs. 12-66; 12-70), from the dorsal portions of L 4, 5, and S 1, leaves the pelvis through the greater sci¬ atic foramen proximal to the piriformis, and accompanying the superior gluteal vessels and their branches, divides into a superior and an inferior branch. The superior branch is distributed to the gluteus minimus muscle. The inferior branch crosses the gluteus minimus, gives filaments to the gluteus medius and mini¬ mus, and ends in a branch to the tensor fas¬ ciae latae.

INFERIOR GLUTEAL NERVE

The inferior gluteal nerve, from the dorsal portions of L 5, and S 1, 2, leaves the pelvis through the greater sciatic foramen distal to the piriformis and enters the deep surface of the gluteus maximus.

Dorsal Portions

L 4, 5, S 1 L 5, S 1, 2

S 2, 3

S (1), 2 L 4, 5, S 1 L 5, S 1, 2 S 1, 2 S 2, 3

L 4, 5, S 1, 2, 3 L 4, 5, S 1, 2 S 2, 3, 4

POSTERIOR FEMORAL CUTANEOUS NERVE

The posterior femoral cutaneous nerve (small sciatic nerve) (Figs. 12-64 to 12-66) is distributed to the skin of the perineum and the posterior surface of the thigh and leg. It arises from the dorsal portions of S 1 and 2 and from the ventral divisions of S 2 and 3, and leaves the pelvis through the greater sci¬ atic foramen distal to the piriformis. It ac¬ companies the inferior gluteal artery to the inferior border of the gluteus maximus and runs down the posterior thigh, superficial to the long head of the biceps femoris and deep to the fascia lata to the back of the knee. It pierces the deep fascia and accompanies the small saphenous vein to the middle of the back of the leg, its terminal twigs communi¬ cating with the sural nerve. The three or four inferior clunial branches (gluteal branches) turn upward around the lower border of the gluteus maximus and supply the skin covering the lower and lat¬ eral part of that muscle. The perineal branches (Fig. 12-66) arise at the lower border of the gluteus maximus, run medially over the origin of the ham¬ strings toward the groove between the thigh and perineum, and pierce the deep fascia to supply the skin of the external genitalia and adjacent proximal medial surface of the thigh. One long branch, the inferior puden¬ dal (long scrotal nerve) (Fig. 12-70), runs ventrally in the fascia of the perineum to the skin of the scrotum and base of the penis in fhe male or to the skin of the labium majus in the female, communicating with the pos-

SPINAL NERVES

Cutaneous nerves of right lower limb. Posterior view. Fig.

12-64.

1237

Fig. 12-65. Diagram of the segmental distribution of the cutaneous nerves of the right lower limb. Posteri¬ or view.

1 238

THE PERIPHERAL NERVOUS SYSTEM

Superior gluteal Pudendal. Nerve to obturator internus

Greater Troth.

Perineal ■ branch

terior scrotal and inferior rectal branches of the pudendal nerve. The femoral branches consist of numer¬ ous filaments from both sides of the nerve that are distributed to the skin of the poste¬ rior and medial sides of the thigh and the popliteal fossa (Fig. 12-64). The sural branches are usually two termi¬ nal twigs that supply the skin of the poste¬ rior leg to a varying extent and communicate with the sural nerve. variations. When the tibial and peroneal nerves arise separately, the posterior femoral cutaneous nerve also arises from the sacral plexus in two parts. The ventral portion accompanies the tibial nerve and gives off the perineal and medial femoral branches; the dorsal portion passes through the piriformis with the peroneal nerve and supplies the gluteal and lat¬ eral femoral branches. The inferior pudendal branch may pierce the sacrotuberous ligament. The sural branches may be lacking or may extend down as far as the ankle.

Descending cutaneous V' n

Tibial -

PERFORATING CUTANEOUS NERVE Common peroneal

Med. sural cutaneous ■ Tibial ■

m

The perforating cutaneous nerve (n. clunium inferior medialis) arises from the posterior surface of the second and third sacral nerves. It pierces the caudal part of the sacrotuberous ligament, winds around the inferior border of the gluteus maximus, and is distributed to the skin over the medial and caudal parts of that muscle. variations. The perforating cutaneous nerve is lacking in one third of the bodies; its place may be taken by a branch of the posterior femoral cutaneous nerve, or by a branch from S 3 and 4, or S 4 and 5. It may pierce the gluteus maximus as well as the ligament, or instead of piercing the ligament it may accompany the pudendal nerve or go between the muscle and the ligament. It may arise in common with the pudendal nerve.

SCIATIC NERVE

Medial calcaneal.

Fig. 12-66. Nerves of the right lower limb. Posterior view. (In this diagram the medial and lateral sural cuta¬ neous are not in their normal position. They have been displaced by the removal of the superficial muscles.)

The sciatic nerve (n. ischiadicus; great sci¬ atic nerve) (Fig. 12-66) is the largest nerve in the body. It supplies the skin of the foot and most of the leg, the muscles of the posterior thigh, all the muscles of the leg and foot, and contributes filaments to all the joints of the lower limb. It is the continuation of the main part of the sacral plexus, arising from L 4, 5 and S 1, 2, 3. It passes out of the pelvis through the greater sciatic foramen and ex¬ tends from the inferior border of the piri-

SPINAL NERVES

formis to the distal third of the thigh, where it splits into two large terminal divisions, the tibial and common peroneal nerves. In the proximal part of its course it rests upon the posterior surface of the ischium, between the ischial tuberosity and the greater tro¬ chanter of the femur, and crosses the obtura¬ tor internus, gemelli, and quadratus femoris. It is accompanied by the posterior femoral cutaneous nerve and the inferior gluteal ar¬ tery and is covered by the gluteus maximus. More distally it lies upon the adductor magnus and is crossed obliquely by the long head of the biceps femoris. The tibial and common peroneal nerves represent two divisions within the sciatic nerve that are manifest at the origin of the nerve and preserve their identity throughout its length, although combined into one large nerve by a common connective tissue sheath. The tibial division takes its origin in the sacral plexus from the ventral divisions of L4, 5, and S 1, 2, 3; the peroneal division originates from the dorsal divisions of L 4, 5 and S 1, 2. In some bodies these two divi¬ sions remain separate throughout their course, no true sciatic nerve being formed. Articular Branches

Articular branches arise from the proxi¬ mal part of the nerve and supply the hip joint, perforating the posterior part of the capsule. They may arise from the sacral plexus. Muscular Branches

The muscular branches to the hamstrings, viz., the long head of the biceps femoris, the semitendinosus, and the semimembranosus muscles, and to the adductor magnus come from the tibial division; the branch to the short head of the biceps comes from the common peroneal division. Tibial Nerve

The tibial nerve (medial popliteal nerve) (Fig. 12-66), the larger of the two terminal divisions of the sciatic nerve, is composed of fibers from the ventral portions of L 4, 5 and S 1, 2, 3. It continues in the same direction as the sciatic nerve, at first deep to the long head of the biceps, then through the middle of the popliteal fossa covered by adipose tis¬

1239

sue and fascia. After crossing the popliteus muscle, it passes between the heads of the gastrocnemius and under the soleus. It re¬ mains deep to these muscles down to the medial margin of the tendo calcaneus, along which it runs to the flexor retinaculum and there divides into the medial and lateral plantar nerves. At its origin it is some dis¬ tance lateral to the popliteal artery and vein, but as it continues in a straight course it crosses superficial to the vessels in the pop¬ liteal fossa, and, lying medial to them, passes with them under the tendinous arch formed by the soleus. It accompanies the posterior tibial artery, at first being medial but soon crossing the artery and lying lateral to it down to the ankle. ARTICULAR BRANCHES OF TIBIAL NERVE. Ar¬ ticular branches supply the knee and ankle joints. Three branches, accompanying the supe¬ rior and inferior medial genicular and the middle genicular arteries, pierce the liga¬ ments and supply the knee joint. The supe¬ rior branch is inconstant. Just proximal to the bifurcation at the flexor retinaculum, an articular branch is given off to the ankle joint. MUSCULAR

BRANCHES

OF

TIBIAL

NERVE.

Muscular branches are supplied to the mus¬ cles of the posterior leg. Branches that arise as the nerve lies between the two heads of the gastrocnemius are distributed to both heads of the gastrocnemius, plantaris, so¬ leus, and popliteus; the latter branch turns around the distal border and is distributed to the deep surface of the muscle. Arising more distally, either separately or by a common trunk, are branches to the soleus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus; the branch to the last muscle accompanies the peroneal artery; that to the soleus enters the deep surface of the muscle. MEDIAL SURAL CUTANEOUS NERVE. The medial sural cutaneous nerve (n. communicans tibialis) remains superficial in the groove between the two heads of the gas¬ trocnemius, accompanied by the small sa¬ phenous vein. Near the middle of the back of the leg, it pierces the deep fascia and is joined by the communicating ramus of the lateral sural cutaneous branch of the pero¬ neal nerve to form the sural nerve. sural nerve. The sural nerve (short sa¬ phenous nerve) (Fig. 12-64) is formed by the union of the medial sural cutaneous nerve

1 240

the peripheral nervous system

and the communicating ramus of the lateral sural cutaneous nerve (peroneal anasto¬ motic). Lying with the small saphenous vein near the lateral margin of the tendo calca¬ neus, it continues distally to the interval be¬ tween the lateral malleolus and the calca¬ neus, supplying branches to the skin of the back of the leg and communicating with the posterior femoral cutaneous nerve. The nerve turns anteriorly below the lateral mal¬ leolus and is continued as the lateral dorsal cutaneous nerve along the lateral side of the foot and little toe (Fig. 12-58). It communi¬ cates on the dorsum of the foot with the in¬ termediate dorsal cutaneous nerve, a branch of the superficial peroneal nerve. medial calcaneal branches. The medial calcaneal branches (internal calcaneal branches) (Fig. 12-66) perforate the flexor retinaculum and are distributed to the skin of the heel and medial side of the sole of the foot. medial plantar nerve. The medial plan¬ tar nerve (internal plantar nerve) (Fig. 1267), the larger of the two terminal branches of the tibial nerve, accompanies the medial

plantar artery. From its origin under the flexor retinaculum, it passes deep to the ab¬ ductor hallucis, and appearing between this muscle and the flexor digitorum brevis, it gives off the proper plantar digital nerve to the great toe. It finally divides opposite the bases of the metatarsal bones into three common digital nerves. Branches of the Medial Plantar Nerve. The plantar cutaneous branches pierce the plantar aponeurosis between the abductor hallucis and the flexor digitorum brevis and are distributed to the skin of the sole of the foot (Fig. 12-68). Muscular branches for the abductor hallu¬ cis and flexor digitorum brevis arise from the trunk of the nerve and enter the deep surfaces of the muscles. A branch for the flexor hallucis brevis springs from the proper digital nerve to the medial side of the great toe. A branch for the first lumbrical comes from the first common digital nerve. The articular branches supply the joints of the tarsus and metatarsus. The proper digital nerve of the great toe pierces the plantar aponeurosis posterior to the tarsometatarsal joint, sends a branch to the flexor hallucis brevis, and is distributed to the skin of the medial side of the great toe (Fig. 12-67). The three common digital nerves pass be¬ tween the divisions of the plantar aponeuro¬ sis; each splits into the two proper digital nerves. Those of the first common digital supply the adjacent sides of the great and

Fig. 12-68.

Fig. 12-67.

The plantar nerves.

Diagram of the segmental distribution of the cutaneous nerves of the sole of the foot.

SPINAL NERVES

second toes; those of the second, the adja¬ cent sides of the second and third toes; those of the third, the adjacent sides of the third and fourth toes. The first common digital nerve gives a twig to the first lumbrical. The third communicates with the lateral plantar nerve. Each proper digital nerve gives off cutaneous and articular filaments along the digit, finally terminating in the ball of the toe, and opposite the distal phalanx sends a dorsal branch that is distributed to the structures around the nail. lateral plantar nerve. The lateral plan¬ tar nerve (external plantar nerve) (Figs. 1267; 12-68) supplies the skin of the fifth and lateral half of the fourth toes, as well as most of the deep muscles of the foot; its distribu¬ tion is similar to that of the ulnar nerve in the hand. It passes distally with the lateral plantar artery to the lateral side of the foot, lying between the flexor digitorum brevis and the quadratus plantae, and in the inter¬ val between the former muscle and the ab¬ ductor digiti minimi, it divides into a super¬ ficial and a deep branch. Branches of the Lateral Plantar Nerve. Muscular branches to the quadratus plantae and the abductor digiti minimi are given off before the division into superficial and deep branches. The superficial branch splits into a com¬ mon digital nerve and a nerve that supplies the proper digital for the lateral side of the little toe, and muscular branches to the flexor digiti minimi brevis and the two interossei of the fourth intermetatarsal space. The common digital nerve has a communi¬ cation with the third common digital branch of the medial plantar nerve and divides into two proper digital nerves that are distrib¬ uted to the adjacent sides of the fourth and fifth toes. The deep branch accompanies the lateral plantar artery on the deep surface of the ten¬ dons of the flexors longi and the adductor hallucis. It supplies all the interossei except those in the fourth intermetatarsal space, the second, third, and fourth lumbricals, and the adductor hallucis. Common Peroneal Nerve

The common peroneal nerve (lateral popliteal nerve; peroneal nerve) (Fig. 12-66), the smaller of the two terminal divisions of the sciatic nerve, is composed of fibers from the dorsal portions of L 4, 5 and S 1, 2. It runs

1241

obliquely along the lateral side of the poplit¬ eal fossa, close to the medial border of the biceps femoris and between that muscle and the lateral head of the gastrocnemius, to the head of the fibula. It winds around the neck of the fibula and passes deep to the peroneus longus, where it divides into the superficial and deep peroneal nerves. articular branches. There are three ar¬ ticular branches to the knee: (a) one accompanies the superior lateral genicular artery to the knee, occasionally arising from the trunk of the sciatic nerve; (b) one accom¬ panies the inferior lateral genicular artery to the joint; and (c) the third (recurrent) articu¬ lar nerve is given off at the point of division of the common peroneal nerve and accom¬ panies the anterior tibial recurrent artery through the substance of the tibialis anterior to the anterior part of the knee (Fig. 12-60, not labeled). lateral sural cutaneous nerve. The lat¬ eral sural cutaneous nerve (lateral cutane¬ ous branch) is distributed to the skin of the posterior and lateral surfaces of the leg (Fig. 12-65) and has an important communicating ramus. The communicating ramus (peroneal anastomotic nerve) (Figs. 12-64; 12-66) arises near the head of the fibula, crosses superfi¬ cial to the lateral head of the gastrocnemius, and in the middle of the leg joins the medial sural cutaneous nerve to form the sural nerve. deep peroneal nerve. The deep peroneal nerve (anterior tibial nerve) (Figs. 12-60; 1269), arising from the bifurcation of the com¬ mon peroneal nerve between the fibula and the peroneus longus, continues deep to the extensor digitorum longus to the anterior surface of the interosseous membrane. It meets the anterior tibial artery in the proxi¬ mal third of the leg and continues with it distally, passes under the extensor retinacu¬ lum, and terminates at the ankle in a medial and a lateral branch. Muscular branches are supplied in the leg to the tibialis anterior, extensor digitorum longus, peroneus tertius, and extensor hallu¬ cis longus. An articular branch is supplied to the ankle joint. The lateral terminal branch (external or tarsal branch) passes across the tarsus deep to the extensor digitorum brevis, and having become enlarged like the dorsal interosseous nerve at the wrist, supplies the extensor digi¬ torum brevis. Three minute interosseous

1 242

THE PERIPHERAL NERVOUS SYSTEM

Common peroneal nerve Articular branches Anterior tibial recurrent artery Infrapatellar branch Saphenous nerve

Anterior tibial artery Deep peroneal nerve

Superficial peroneal nerve

Medial dorsal cutaneous nerve—f Intermedial dorsal cutaneous nerve Dorsalis pedis artery

Lateral terminal branch Sural nerve Medial terminal branch Extensor digitorum brevis Dorsal digital nerves

Fig. 12-69.

Deep nerves of the anterior leg.

branches are given off from the enlargement; they supply the tarsal joints and the meta¬ tarsophalangeal joints of the second, third, and fourth toes. A muscular filament is sent to the second interosseus dorsalis from the first of these interosseous branches. The medial terminal branch (internal branch) accompanies the dorsalis pedis ar¬

tery along the dorsum of the foot, and at the first interosseous space, divides into two dorsal digital nerves (Fig. 12-70) which sup¬ ply adjacent sides of the great and second toes, communicating with the medial dorsal cutaneous branch of the superficial peroneal nerve. An interosseous branch, given off be¬ fore it divides, enters the first space, supply-

SPINAL NERVES

ing the metatarsophalangeal joint of the great toe and sending a filament to the first interosseus dorsalis. superficial peroneal nerve. The super¬ ficial peroneal nerve (musculocutaneous nerve) (Figs. 12-69; 12-70) passes distally be¬ tween the peronei and the extensor digitorum longus, pierces the deep fascia in the lower third of the leg, and divides into a medial and intermediate dorsal cutaneous nerve. Muscular branches are given off in its course between the muscles to the peroneus longus and brevis. Cutaneous filaments are supplied to the skin of the lower part of the leg. The medial dorsal cutaneous nerve (inter¬ nal dorsal cutaneous branch) (Fig. 12-69) passes in front of the ankle joint and divides into two dorsal digital branches. The medial one supplies the medial side of the great toe and communicates with the deep peroneal nerve. The lateral one supplies the adjacent sides of the second and third toes. It also supplies the skin of the medial side of the foot and ankle and communicates with the saphenous nerve. The intermediate dorsal cutaneous nerve (external dorsal cutaneous branch) (Fig. 1269) passes along the lateral part of the dor¬ sum of the foot, supplying the skin of the lateral side of the foot and ankle and com¬ municating with the sural nerve. It termi¬ nates by dividing into two dorsal digital branches, one of which supplies the adja¬ cent sides of the third and fourth toes, the other the adjacent sides of the fourth and lit¬ tle toes. Frequently some of the lateral branches of the superficial peroneal nerve are absent and their places are then taken by branches of the sural nerve. Pudendal Plexus

The pudendal plexus (Figs. 12-63; 12-70) is formed from the anterior branches of the second and third and all of the fourth sacral nerves. It is sometimes considered a part of the sacral plexus. It lies in the posterior hol¬ low of the pelvis on the ventral surface of the piriformis muscle. VISCERAL BRANCHES

The visceral branches arise from the sec¬ ond, third, and fourth sacral nerves. They contain (1) parasympathetic visceral efferent

1 243

preganglionic fibers, which form synapses with the cells in the small scattered ganglia located in or near the walls of the pelvic vis¬ cera, and (2) visceral afferent fibers from the pelvic organs. These nerves join branches of the hypogastric plexus of the sympathetic and the sympathetic chain to form the pelvic plexus, which lies in the deeper portion of the pelvic subserous fascia (Ashley and Anson, 1946). The various elements of the pelvic plexus cannot be followed by dissection, but the destination of the sacral parasympathetic fibers has been traced by clinical observa¬ tion and animal experimentation. The branches to the bladder, prostate and seminal vesicles approach these organs from their posterior and lateral sides and termi¬ nate in groups of ganglion cells in the pelvic plexus or in the walls of the organs. The postganglionic fibers are efferents to the muscles and glands, except the sphincters, to which they are inhibitory. The branches to the uterus reach the gan¬ glia in the uterine plexus. The postgangli¬ onic fibers are inhibitory except during pregnancy, when their function is said to be reversed. The branches to the external genitalia leave the pelvic plexus to join the pudendal nerve. They are distributed through its branches to the corpora cavernosa, causing active dilatation of the cavernous blood si¬ nuses. The branches to the alimentary tract con¬ sist of (a) filaments that go directly to the rectum from the pelvic plexus, and (b) fibers that pass through the hypogastric plexus, the hypogastric nerves, and the inferior mesen¬ teric plexus to reach the descending and sig¬ moid colon. These are preganglionic fibers that have synapses with the cells in the my¬ enteric and submucous plexuses and are ef¬ ferent to this part of the intestine, except for the sphincter ani internus, to which they are inhibitory. MUSCULAR BRANCHES

The muscular branches (Fig. 12-61), de¬ rived mainly from the fourth (sometimes from the third and fifth) sacral, enter the pel¬ vic surfaces of the levator ani and coccygeus. The nerve to the sphincter ani externus (perineal branch) reaches the ischiorectal fossa by piercing the coccygeus or by pass¬ ing between it and the levator.

1 244

THE PERIPHERAL NERVOUS SYSTEM

Sympathetic ganglion Genitofemoral nerve Lumbosacral trunk

Superior gluteal artery

Internal iliac artery

A\

First 7 sacral nerve

Inferior epigastric artery and vein

Obturator artery and vein Fourth sacral nerve Visceral nerves Suspensory ligament Pudendal nerve

Dorsal nerve of penis

Posterior femoral cutaneous nerve Posterior scrotal nerves

Cluneal nerves Fig. 12-70

Pudendal nerve, and sacral and pudendal plexus of the right side.

PUDENDAL NERVE

The pudendal nerve (internal pudic nerve) (Fig. 12-70) arises from S 2, 3 and 4, and pass¬ ing between the piriformis and coccygeus, leaves the pelvis through the distal part of the greater sciatic foramen. It then crosses the spine of the ischium and reenters the pel¬ vis through the lesser sciatic foramen. It ac¬ companies the internal pudendal vessels along the lateral wall of the ischiorectal fossa in a tunnel formed by a splitting of the obturator fascia (Alcock’s canal1), and as it approaches the urogenital diaphragm, it splits into two terminal branches. inferior rectal nerve. The inferior rec¬ tal nerve (inferior hemorrhoidal nerve) arises from the pudendal nerve before its terminal division or occasionally directly

‘Benjamin Alcock (1801-?): An Irish professor of anat¬ omy (Cork, then went to America).

from the sacral plexus. Coursing medially across the ischiorectal fossa with the inferior rectal vessels, it breaks up into branches that are distributed to the sphincter ani externus and the integument around the anus. Branches of this nerve communicate with the perineal branch of the posterior femoral cutaneous nerve and with the posterior scrotal nerves. perineal nerve. The perineal nerve (Fig. 12-70), the larger and more superficial of the two terminal branches of the pudendal, ac¬ companies the perineal artery and at the urogenital diaphragm divides into superfi¬ cial and deep branches. The two superficial branches of the peri¬ neal nerve are the medial and the lateral posterior scrotal (or labial) nerves. They pierce the fascia of the urogenital diaphragm and run ventrally along the lateral part of the urogenital triangle in company with the posterior scrotal branches of the perineal

VISCERAL NERVOUS SYSTEM

artery. They are distributed to the skin of the scrotum in the male or to the skin of the la¬ bium majus in the female. The lateral branch communicates with the perineal branch of the posterior femoral cutaneous nerve. The deep branch is mainly muscular, sup¬ plying branches to the transversus perinei superficialis, bulbocavernosus, ischiocavernosus, transversus perinei profundus, and sphincter urethrae membranacea. The nerve to the bulb is given off from the nerve to the bulbocavernosus; it pierces this muscle, and supplies the corpus cavernosum urethrae and the mucous membrane of the urethra. dorsal nerve of penis. The dorsal nerve of the penis (Fig. 12-70), the deeper terminal branch of the pudendal nerve, accompanies the internal pudendal artery along the ramus of the ischium, and then runs ventrally along the margin of the inferior ramus of the pubis, lying between the superficial and deep lay¬ ers of fascia of the urogenital diaphragm. Piercing the superficial layer, it gives a branch to the corpus cavernosum penis, and continuing forward in company with the dorsal artery of the penis between the layers of the suspensory ligament, it runs along the dorsum of the penis and is distributed to the skin of that organ, ending in the glans penis. The dorsal nerve of the clitoris is smaller and has a distribution corresponding to that of the penis in the male. Coccygeal Plexus

The coccygeal plexus (Fig. 12-63) is formed by the coccygeal nerve with commu¬ nications from the fourth and fifth sacral nerves. From this delicate plexus, a few fine filaments, the anococcygeal nerves, pierce the sacrotuberous ligament and supply the skin in the region of the coccyx.

Visceral Nervous System The visceral nervous system or visceral portion of the peripheral nervous system (vegetative nervous system; involuntary ner¬ vous system; major sympathetic system; plexiform nervous system) comprises the whole complex of fibers, nerves, ganglia, and plexuses by means of which impulses are conveyed from the central nervous system to the viscera and from the viscera to

1 245

the central nervous system. It has the usual two groups of fibers necessary for reflex con¬ nections: (a) afferent fibers, receiving stimuli and carrying impulses toward the central nervous system, and (b) efferent fibers, car¬ rying impulses from the appropriate centers to the active effector organs, which in this instance are the nonstriated muscle, cardiac muscle, and glands of the body. Attention is called to the use of the term sympa¬ thetic system in this edition. In former editions it was used for the visceral nervous system and included both afferent and efferent, autonomic and parasym¬ pathetic components. Although the central nervous system is involved in all nervous or reflex control of the viscera, with the possible exception of the en¬ teric plexus, it is more convenient for the purposes of description to separate the peripheral from the central portions. It must be emphasized, however, that the separation is artificial and should not be car¬ ried over into physiologic considerations. In the present edition the term sympathetic is used in the restricted meaning of the thoracolumbar division of the visceral efferent system. The terms sympathetic afferent and autonomic afferent are replaced by vis¬ ceral afferent.

VISCERAL AFFERENT FIBERS

The visceral afferent fibers cannot be sep¬ arated into a morphologically independent system because, like the somatic sensory fi¬ bers, their cell bodies are situated in the sen¬ sory ganglia of the cerebrospinal nerves. The distinction between somatic and visceral afferent fibers is one of peripheral distribu¬ tion rather than one of fundamental ana¬ tomic and physiologic significance. The vis¬ ceral afferents, however, commonly have modalities of sensation different from those of somatic afferents, and most of them are either vaguely localized or have no repre¬ sentation in consciousness. The visceral ef¬ ferent fibers make reflex connections with visceral afferents. The number and extent of the visceral afferents are not clearly estab¬ lished, and the peripheral processes reach the ganglia by various routes. Many traverse the branches and plexuses of the autonomic system, most of them accompany blood ves¬ sels for at least a part of their course, and some run in the cerebrospinal nerves. referred pain. Although many, perhaps most, of the physiologic impulses carried by visceral affer¬ ent fibers fail to reach consciousness, pathologic

1246

THE PERIPHERAL NERVOUS SYSTEM

conditions or excessive stimulation may activate those that carry pain. The central nervous system has a poorly developed power of localizing the source of such pain, and by some mechanism not clearly understood, the pain may be referred to the region supplied by the somatic afferent fibers whose central connections are the same as those of the vis¬ ceral afferents. For example, the visceral afferents from the heart enter the upper thoracic nerves, and impulses traversing them may cause painful sensa¬ tions in the axilla, down the ulnar surface of the arm, and in the precardial region. The study of clinical cases of referred pain has been useful in tracing the path of afferent fibers from the various viscera, and a knowledge of these paths may assist the diagnosti¬ cian in locating a pathologic process.

The visceral afferent fibers are summa¬ rized below; for more complete descriptions of the individual nerves mentioned, consult the accounts given elsewhere. head. Visceral afferents from endings on the peripheral blood vessels of the face and scalp probably accompany the branches of the external carotid artery to the superior cervical ganglion and through communicat¬ ing rami to the spinal nerves. Afferents on the blood vessels of the brain and meninges may accompany the branches of the inter¬ nal carotid and vertebral arteries, passing through the upper cervical spinal nerves or possibly the ninth and tenth cranial nerves. imose and nasal cavity. There is evidence that a few visceral afferent fibers from the nose are brought to the brain by the nervus terminalis (Larsell, 1950). Others traverse the branches of the sphenopalatine and palatine nerves to reach the facial nerve through the Vidian and greater superficial petrosal nerves. mouth and pharynx. The visceral affer¬ ents from the mouth, pharynx, and salivary glands pass through the pharyngeal plexus to the glossopharyngeal, vagus, and facial nerves. neck. Visceral afferents from the larynx, trachea, esophagus, and thyroid gland are carried by the vagus or reach the sympa¬ thetic trunk through the pharyngeal plexus and pass through rami communicantes to the cervical or upper thoracic nerves. The carotid sinus nerve carries the vis¬ ceral afferents from the pressoreceptor end¬ ings in the carotid sinus through the glos¬ sopharyngeal nerve. The chemoreceptor afferents from the carotid body reach the vagus nerve through branches of the pharyn¬ geal or superior laryngeal nerves.

The visceral afferents from the thoracic wall and parietal pleura join the intercostal nerves, after following the ar¬ teries for variable distances, and thus enter the spinal ganglia. Those from the parietal pericardium join either the phrenic nerve or the intercostal nerves. Visceral afferents from the heart and the origins of the great vessels enter the cardiac plexus and either join the branches of the vagus or reach the upper thoracic spinal nerves and their ganglia by way of sympa¬ thetic branches, the sympathetic trunk, and rami communicantes. The aortic bodies (glomera aortica) are chemoreceptors similar to the carotid bod¬ ies; their afferent fibers run in the right vagus and have cell bodies in the inferior ganglion. The supracardial bodies (aortic paraganglia) are also chemoreceptors with their afferent fibers in the left vagus and cell bodies in the inferior ganglion. depressor nerve. In some animals, the afferent fibers of the vagus from the heart and great vessels are contained in a separate nerve whose stimulation depresses the activ¬ ity of the heart. In man, these fibers are prob¬ ably contained in the cardiac branches of the recurrent nerves. Visceral afferents from the lungs, bronchi, and pulmonary pleura reach either the vagus nerve through the pulmonary plexuses or the spinal nerves and their ganglia through the sympathetic branches and rami com¬ municantes. abdomen. Visceral afferent fibers from the abdominal wall and parietal peritoneum probably accompany the arteries in part of their course and finally reach the spinal gan¬ glia through the spinal nerves. The myeli¬ nated fibers from the Pacinian1 corpuscles in the mesentery and pancreas at its base run in the thoracic splanchnic nerves, then through the sympathetic trunk, and finally over the white rami communicantes to the spinal nerves and ganglia. Visceral afferent fibers from the stomach, small intestine, cecum, appendix, ascending and transverse colon, liver, gallbladder, bile ducts, pancreas, and suprarenals traverse the celiac plexus and its secondary plexuses and branches. They accompany the arter¬ ies, pass through the splanchnic nerves, the thorax.

'Filippo Pacini (1812-1883): An Italian anatomist (Flor¬ ence).

VISCERAL NERVOUS SYSTEM

sympathetic trunk, and rami communicantes to reach the spinal nerves and ganglia. Some of these afferents may enter the va¬ gus nerve. The visceral afferents from the kidney, ureter, testis, ductus deferens, ovary, and uterine tube traverse the renal and celiac plexuses or parts of their secondary plex¬ uses, pass through the lower thoracic and upper lumbar splanchnic nerves to the sym¬ pathetic trunk, and thence through white rami communicantes to the spinal nerves and ganglia. pelvis. The visceral afferent fibers from the descending colon, sigmoid, and rectum traverse the pelvic plexus, hypogastric nerves and plexus, inferior mesenteric plexus, ce¬ liac plexus, and lumbar splanchnic nerves on their way to the sympathetic trunk, white rami communicantes, and spinal nerves and ganglia. Others from the rectum pass through the pelvic plexus into the visceral branches of the second, third, and fourth sacral nerves and their ganglia. Visceral afferents from the bladder, pros¬ tate, seminal vesicles, and urethra pass through the pelvic plexus and through the hypogastric nerves and plexuses, splanchnic nerves, and sympathetic rami into the lum¬ bar ganglia, or through the visceral branches of the sacral nerves into the sacral ganglia. Visceral afferents from the uterus traverse the pelvic plexus, hypogastric nerves and plexus, lumbar splanchnic nerves, sympa¬ thetic trunk, rami communicantes, and lum¬ bar spinal nerves and their ganglia. Visceral afferent fibers from the external genitalia pass through either the pelvic plexus or the pudendal nerve and reach the sacral nerves and their ganglia. upper extremity. Visceral afferent fibers accompany the peripheral blood vessels for some distance, but may join the larger branches of the brachial plexus and reach the dorsal root ganglia through the spinal nerves, or they may follow the paths of the sympathetic fibers and reach the dorsal gan¬ glia, especially the first two or three thoracic, through the white rami communicantes. lower extremity. Visceral afferents ac¬ company the peripheral vessels and the fem¬ oral artery to the aortic plexus, then through the lumbar splanchnic nerves to the rami communicantes, spinal nerves and ganglia. Others may join the tibial or peroneal nerves and traverse the sacral and lumbar sym¬

1 247

pathetic trunk and rami communicantes to reach the lumbar nerves and their gan¬ glia.

AUTONOMIC or visceral efferent system

The visceral efferent portions of the pe¬ ripheral nervous system are combined into a morphologic and physiologic entity called the autonomic nervous system (systema ner¬ vosum autonomicum) (Fig. 12-71). The fun¬ damental morphologic difference between the visceral and somatic motor systems is that two neurons are required to transmit an impulse from the central nervous system to the active effector organ in the viscera, whereas only a single neuron is required to carry an impulse from the central nervous system to a skeletal muscle fiber. As the name autonomic implies, this system has a certain amount of independence because, in most individuals, it is not under direct vol¬ untary command. It is controlled by neurons within the central nervous system, neverthe¬ less, and is connected with the latter at vari¬ ous levels. The enteric plexus is the only portion of the visceral system that seems to carry out reflex responses without involving the central nervous system (Kuntz, 1953). The autonomic nervous system is com¬ posed of two divisions or systems that differ from each other morphologically and which for the most part are antagonistic to each other physiologically. The morphologic dif¬ ferences have to do (a) with the manner in which the two systems are connected with the central nervous system, and (b) with the location of their ganglia. The sympathetic or thoracolumbar system is connected with the central nervous system through the thoracic and upper lumbar segments of the spinal cord, and its ganglia tend to be placed near the spinal column rather than near the vis¬ cera innervated. The parasympathetic or craniosacral system is connected with the central nervous system through certain cra¬ nial nerves and through the middle three sacral segments of the spinal cord, and its ganglia tend to be placed peripherally near the organs innervated. The sympathetic and parasympathetic sys¬ tems both innervate many of the same organs, and in this double innervation the two sys¬ tems are usually antagonistic to each other

1 248

THF PERIPHERAL NERVOUS SYSTEM

Fig. 12 71 Diagram of efferent autonomic nervous system. Blue, cranial and sacral outflow, parasympathetic. Red, thoracolumbar outflow, sympathetic. Interrupted lines designate postganglionic fibers to spinal and cranial nerves to supply vasomotor innervation to head, trunk and limbs, motor fibers to smooth muscles of skin and fibers to sweat glands. (Modified after Meyer and Gottlieb.) This is only a diagram and does not accurately portray all the details of distribution.

VISCERAL NERVOUS SYSTEM

physiologically. No consistent rule can be given for the effect of each, but in general the sympathetic system mobilizes the energy for sudden activity such as that in rage or flight; for example, the pupils dilate, the heart beats faster, the peripheral blood ves¬ sels constrict, and the blood pressure rises. The parasympathetic system aims more to¬ ward restoring the reserves; for example, the pupils contract, the heart beats more slowly, and the alimentary tract and its glands be¬ come active. The two systems frequently travel to¬ gether, especially in the thorax, abdomen, and pelvis, forming extensive plexuses that contain the fibers of both. The arrangement of the bundles within these plexuses is very complicated and the identity of individual fibers cannot be determined with certainty. For purposes of description, therefore, a third subdivision of the autonomic system is recognized—the great autonomic plexuses. Parasympathetic System

The parasympathetic system is the cranio¬ sacral portion of the autonomic nervous sys¬ tem and contains visceral efferent fibers that originate in certain cranial nerves and in the sacral portion of the spinal cord. CRANIAL PORTION OF THE PARASYMPATHETIC SYSTEM

The cranial outflow includes fibers in the oculomotor, facial, glossopharyngeal, and vagus nerves. These nerves have been de¬ scribed previously and the details are re¬ peated here only insofar as they apply to the visceral efferent fibers. oculomotor nerve. The oculomotor nerve contains efferent fibers for the nonstriated muscle making up the ciliaris and sphincter pupillae muscles of the eyeball (for diagram, see Fig. 12-5). The preganglionic fibers arise from the cells in the Edinger-Westphal nu¬ cleus1,2 located in the anterior part of the oculomotor nucleus in the tegmentum of the midbrain. They run in the inferior division of the oculomotor nerve to the ciliary ganTudwig Edinger (1855-1918): A German neurologist and anatomist (Frankfurt-am-Main). 2Karl Friedrich Otto Westphal (1833-1890): A German psychiatrist and anatomist (Berlin).

1 249

glion (Fig. 12-6) and there form synapses with the ganglion cells. The postganglionic fibers proceed in the short ciliary nerves to the eyeball, penetrate the sclera, and reach the muscles just named. facial nerve. The facial nerve contains efferent fibers for the lacrimal gland, the submandibular and sublingual glands, and the many small glands in the mucous mem¬ brane of the nasal cavity, palate, and tongue (for diagrams, see Figs. 12-16; 12-17). The preganglionic fibers arise from cells in the superior salivatory nucleus in the reticular formation, dorsomedial to the facial nucleus in the pons, and leave the brain in the nervus intermedius. Pterygopalatine Ganglion. Certain pre¬ ganglionic fibers branch from the facial nerve at the geniculum via the greater petro¬ sal nerve, course through the pterygoid ca¬ nal, and terminate by forming synapses with the cells in the pterygopalatine ganglion (Fig. 12-12). Some of the postganglionic fibers reach the lacrimal gland via the maxillary, zygomatic, and lacrimal nerve route; others accompany the branches of the maxillary nerve to the glands in the mucous mem¬ brane of the nasal cavity and nasopharynx; and still others accompany the palatine nerves to the glands of the soft palate, ton¬ sils, uvula, roof of the mouth, and upper lip. Submandibular Ganglion. Other pregan¬ glionic fibers leave the facial nerve in the chorda tympani and with it join the lingual nerve to reach the submandibular ganglion (Fig. 12-12). They form synapses in the gan¬ glion or with groups of ganglion cells in the substance of the gland. The postganglionic fibers form the secretomotor supply to the submandibular and the sublingual glands. Otic Ganglion. Filaments communicating with the otic ganglion may contribute pre¬ ganglionic fibers which join those from the glossopharyngeal nerve to supply the pa¬ rotid gland. GLOSSOPHARYNGEAL NERVE. The gloSSOpharyngeal nerve contains efferent fibers for the parotid gland and small glands in the mucous membrane of the tongue and floor of the mouth (for diagram, see Fig. 1221) The preganglionic fibers arise in the infe¬ rior salivatory nucleus in the medulla ob¬ longata, traverse the tympanic and lesser petrosal nerves, and form synapses in the otic ganglion (Fig. 12-12). Most of the post-

1 250

THE PERIPHERAL NERVOUS SYSTEM

ganglionic fibers join the auriculotemporal nerve and are distributed with its branches to the parotid gland, providing its secretomotor fibers. Other postganglionic fibers are said to supply the glands of the mucous mem¬ brane of the tongue and floor of the mouth. vagus nerve. The vagus nerve contains efferent fibers for the nonstriated muscle and glands of the bronchial tree, of the ali¬ mentary tract as far as the transverse colon, of the gallbladder and bile ducts, the pan¬ creas, and inhibitory fibers for the heart. The preganglionic fibers arise from cells in the dorsal motor nucleus of the vagus in the medulla oblongata; they run in the vagus nerve and its branches to ganglia situated in or near the organs innervated. Heart. The preganglionic fibers for the heart reach the cardiac plexus by way of the superior and inferior cardiac nerves of the vagus, and are distributed by branches of the plexus to the ganglion cells in the heart wall (Fig. 12-77). The ganglion cells form numer¬ ous clusters in the connective tissue of the epicardium on the surface of the atrium, on the auricular appendages, and in the inter¬ atrial septum. The postganglionic fibers terminate in relation to specialized muscular elements in the sinoatrial and atrioventricu¬ lar nodes, and atrioventricular bundle and its branches as far as the Purkinje1 fibers (Stotler and McMahon, 1947). Lungs. The preganglionic fibers from the bronchi leave the main trunk of the vagus nerve in the thorax as the anterior and poste¬ rior bronchial branches. They traverse the anterior and posterior pulmonary plexuses (Figs. 12-24; 12-25) and terminate in the clus¬ ters of ganglion cells scattered along the ramifications of the bronchial tree. The post¬ ganglionic fibers are distributed to the bron¬ chial musculature and bronchial glands. Alimentary Tract. The alimentary tract receives, through various branches, pregan¬ glionic fibers that end in the myenteric plexus of Auerbach and the submucous plexus of Meissner, forming synapses with the ganglion cells scattered in groups throughout these plexuses. The postgangli¬ onic fibers are the efferents from the muscu¬ lar walls and the secreting cells of the tunica mucosa. 'Johannes Evangelista Purkinje (1787-1869): A Bohemian anatomist and physiologist (Breslau and Prague).

The preganglionic fibers reach the upper part of the esophagus through the recurrent nerve, and the lower part, below the hilum of the lung, through branches from the esophageal plexus (Fig. 12-76). The stomach receives an average of four branches from the anterior vagus and six from the posterior vagus. The pylorus and duodenum receive fibers from the hepatic branch of the anterior vagus. The small intestine, cecum, appendix vermiformis, ascending and transverse colon receive fibers from the posterior vagus that join the celiac plexus (Fig. 12-80) and accom¬ pany the branches of the superior mesen¬ teric artery (Jackson, 1949). The gallbladder and bile ducts receive pre¬ ganglionic fibers through the vagus branches in the celiac plexus, which traverse the gastrohepatic ligament and terminate in the small clusters of ganglion cells in the wall of the gallbladder and in the region adjacent to the bile ducts. The postganglionic fibers are the efferents for the muscular walls and mucous membrane. The pancreas receives fibers through the hepatic branches of the anterior and poste¬ rior vagi and, through the branches of the celiac plexus that accompany the arteries, supply this organ. SACRAL PORTION OF THE PARASYMPATHETIC SYSTEM

The cells that give rise to the sacral out¬ flow are in the second, third, and fourth sac¬ ral segments of the spinal cord and pass out with the corresponding sacral nerves. They leave the sacral nerves in the visceral branches and join the pelvic plexus (Fig. 1281) in the deeper portions of the pelvic subserous fascia. Branches from this plexus contain preganglionic fibers for the scattered ganglia in or near the walls of the various pelvic viscera (Ashley and Anson, 1946). The branches to the bladder, prostate and seminal vesicles supply efferent fibers to these organs, except for the fibers to the sphincter, which are inhibitory. The branches to the uterus and vagina reach ganglia in the uterovaginal plexus; the postganglionic fibers are inhibitory except during pregnancy, when their function is said to be reversed. The branches of the pelvic plexus, which join the pudendal nerve and are distributed

VISCERAL NERVOUS SYSTEM

to the external genitalia, cause active dilata¬ tion of the cavernous blood sinuses of the erectile corpora. The visceral branches of the sacral nerves in laboratory animals are concentrated in a single trunk called the “nervus erigens” be¬ cause of this function, but the term is not directly applicable to the conditions in man because there is no single nerve such as that used for experimentation in the animals. Branches from the pelvic plexus contain¬ ing preganglionic fibers join the hypogastric nerve, and through it and the inferior mesen¬ teric plexus are distributed to the descend¬ ing and sigmoid colon and rectum. They are efferent to this part of the intestine except for the sphincter ani internus, for which they are inhibitory. Small branches from the pelvic plexus go directly to the rectum. Sympathetic System

The sympathetic system (Fig. 12-72) re¬ ceives its fibers that connect with the central nervous system through the thoracolumbar outflow of visceral efferent fibers. These fi¬ bers are the axons of cells in the lateral col¬ umn of gray matter in the thoracic and upper lumbar segments of the spinal cord. They leave the cord through the ventral roots of the spinal nerves and traverse short commu¬ nications to reach the sympathetic trunk, where they may terminate in the chain gan¬ glia of the trunk itself, or may continue into the collateral ganglia of the prevertebral plexuses. They are the preganglionic fibers and are mostly the small myelinated variety (3 yin or less in diameter). The postgangli¬ onic fibers are the axons of the cells in these chain and collateral ganglia and are gener¬ ally unmyelinated. They are distributed to the heart, nonstriated muscle, and glands all over the body, which they reach by way of communications with the cerebrospinal nerves, by way of various plexuses, and by their own visceral branches of distribution. variations. Variability is a prominent character¬ istic of the sympathetic system, and although a de¬ scription that will correspond with even the majority of individuals is impossible, certain general princi¬ ples of organization can be recognized. These are incorporated in the account that follows and the general description is supplemented and made spe¬ cific by giving a few of the common variations. Many of the details concerning the paths taken by

1251

the fibers are still unknown, and we must rely heav¬ ily upon information obtained from animal experi¬ mentation, although it may not have been confirmed by clinical observations with human patients.

trunk. The sympathetic consists of a series of ganglia called the central or chain ganglia (Fig. 12-76), which are connected by intervening cords and extend along the lateral aspect of the vertebral column from the base of the skull to the coccyx. The cranial end of the trunk proper is formed by the superior cervical ganglion (Fig. 12-72), but there is a direct continuation into the head, the internal ca¬ rotid nerve. The caudal ends of the two trunks converge at the coccyx and may merge into a single ganglion—the ganglion impar. Cross connections between the two cords in the sacral region are frequent, but rarely occur above the fifth lumbar. The trunk contains, in addition to the gan¬ glia, the preganglionic fibers, which are small (1 to 3 gm in diameter) and myelinated; the postganglionic fibers, which are mostly unmyelinated; and a smaller number of af¬ ferent fibers, which are both myelinated (medium, 5 gm, and large, 10 gm) and unmy¬ elinated. All types of fibers may run up or down in the trunk for the distance between two or many segments. The cords interven¬ ing between the ganglia are usually single except in the lower cervical region, but dou¬ bling is frequent in any part of the trunk al¬ though it rarely extends farther than be¬ tween two adjacent ganglia. Numerous small collections of ganglion cells occur outside of the major ganglia; these may be microscopic in size or grossly visible. They are called in¬ termediary ganglia, and are found in the roots or branches of the trunk and even in the spinal nerves close to these communicat¬ ing rami (Kuntz and Alexander, 1950). ganglia. The central or chain ganglia of the sympathetic trunk are rounded, fusiform or irregular in shape, with diameters usually ranging from 1 to 10 mm, but neighboring ganglia may fuse into larger masses and the superior cervical ganglion is always larger. They contain multipolar neurons whose processes are the postganglionic fibers. The roots of the ganglia of the sympathetic trunk are commonly called the white rami communicantes (rami communicantes alhi) because of the whitish color imparted to sympathetic

trunk

1252

THE PERIPHERAL NERVOUS SYSTEM

Maxillary nerve Ciliary ganglion Pterygopalatine ganglion Superior cervical ganglion of sympathetic

Cervical plexus Pharyngeal plexus

Brachial plexus

Middle cervical ganglion of sympathetic Inferior cervical ganglion of sympathetic Recurrent nerve Bronchial plexus

Cardiac plexus

Esophageal plexus Coronary plexuses

Left vagus nerve

Gastric plexus Greater splanchnic nerve Lesser splanchnic nerve

Celiac plexus Superior mesenteric plexus

Aortic plexus Lumbar plexus -

Inferior mesenteric plexus

Hypogastric plexus

Sacral plexus

- Pelvic plexus Bladder Vesical plexus

Fig. 12-72. The right sympathetic chain and its connections with the thoracic, abdominal, and pelvic plexuses. (After Schwalbe.)

them by the preponderance of myelinated fibers they contain. These myelinated fibers are mainly the small (1 to 3 /xm in diameter) preganglionic axons of the thoracolumbar outflow, whose cell bodies are in the lateral

column of gray matter in the spinal cord. They emerge from the spinal cord with the somatic motor fibers in the ventral roots of the spinal nerves of the thoracic and the first and second lumbar segments. Many of the

VISCERAL NERVOUS SYSTEM

preganglionic fibers in each root fail to make synaptic connections in the ganglia at the level of entrance; some travel cranialward to the cervical ganglia, some caudalward to the lumbar and sacral ganglia, and many in the lower thoracic and upper lumbar levels pass out of the trunk and reach the celiac and re¬ lated collateral ganglia through the splanch¬ nic nerves. One preganglionic fiber may give collaterals to several of the chain ganglia and may terminate on as many as 15 to 20 ganglionic neurons.

The sympathetic trunk has branches of distribution, containing the postganglionic fibers that originate in the ganglia, and branches of communication, containing pre¬ ganglionic fibers that pass through the trunk without synapses on their way to the collat¬ eral ganglia in the abdomen. branches of oistribution. The branches of distribution are of several types: (1) branches to the spinal nerves, (2) branches to the cranial nerves, (3) branches accompany¬ ing arteries, (4) separate branches to individ¬ ual organs, and (5) branches to the great au¬ tonomic plexuses. 1. The branches to the spinal nerves are commonly called the gray rami communi¬ cantes (Fig. 12-73) because the preponder¬ ance of unmyelinated fibers gives them a more grayish cast than the roots or white rami, which are adjacent to them in the tho¬ racic area. These branches contribute post¬ ganglionic fibers, most of which accompany the cutaneous branches of the spinal nerves to supply the arrectores pilorum muscles, the sweat glands, and the vasoconstrictor fibers of the peripheral blood vessels.

The roots of the ganglia or white rami communicantes are to be distinguished from the branches to the spinal nerves or gray rami communicantes with which they are closely related. The white rami leave the anterior primary divisions of the spinal nerves close outside of the intervertebral foramina, but are regularly more distal than the gray rami. They con¬ tain medium and large myelinated fibers, probably afferents, and some unmyelinated fibers in addition to the small myelinated preganglionic fibers. In the lower thoracic and upper lumbar regions the white rami take an oblique course from the nerve of one segment to the ganglion of the segment below and have been called, therefore, the oblique rami, as opposed to the transverse gray rami. They are more likely to be attached to the intervening cords than the gray rami. The white rami, varying from 0.5 to 2 cm, are longer in the lower thoracic and lumbar region, where they are also usually double or triple. Posterior nerve root

Gray rami join all the spinal nerves, while the white rami arise only from the thoracic and first two lumbar segments. The gray ramus usually leaves the

Spinal ganglion

Blood vessel

Skin

Somatic afferent Visceral afferent Spinal nerve

A 71-----\-

Somatic efferent White ramus

Visceral efferent postganglionic

Anterior nerve root Visceral efferent preganglionic Visceral efferent postganglionic

Sympathetic ganglion Visceral afferent

•Viscera

Fig. 12-73.

1253

Muscle spindle Skeletal muscle

Parietal peritoneum

Schema showing structure of a typical spinal nerve. Afferent, blue: efferent, red.

1 254

THE PERIPHERAL NERVOUS SYSTEM

trunk at a ganglion near the same level as the spinal nerve, and in the thoracic and lumbar regions, where there are both gray and white rami, it is regu¬ larly proximal to the white.

Branches to the cranial nerves may go di¬ rectly to the nerves or they may pass through plexuses on blood vessels. Direct communi¬ cations are encountered to the superior and inferior ganglia of the vagus, the inferior ganglion of the glossopharyngeal, and the hypoglossal nerves. Branches accompanying the arteries are too numerous to list here, but are given with the detailed descriptions of the different parts of the system in later pages. Prominent examples are the nerves on the internal and external carotid arteries and their branches. Branches to individual organs may take an independent course but they commonly pass through plexuses (for example, the cardiac branches), or accompany blood vessels for some distance (for example, those to the bulb of the eye). Branches to the cardiac, pulmonary, and pelvic plexuses probably contain postgan¬ glionic fibers, but most of the branches from the trunk to the abdominal plexuses proba¬ bly contain preganglionic fibers. branches of communication. The prin¬ cipal branches of communication containing preganglionic fibers are the splanchnic nerves. They branch from the ganglia or the trunk of the thoracic and lumbar regions and supply the fibers that are the roots to the celiac, aorticorenal, and mesenteric ganglia. The post¬ ganglionic fibers from these ganglia supply the various abdominal and pelvic organs.

DIVISIONS OF THE SYMPATHETIC SYSTEM

The sympathetic nervous system is di¬ vided into portions according to topographic position as follows: (1) cephalic, (2) cervical, (3) thoracic, (4) abdominal or lumbar, and (5) pelvic. These parts are not independent and are chosen merely for convenience in de¬ scription. In addition to these portions, con¬ cerned primarily with the sympathetic trunk and ganglia, there are autonomic plexuses, which are described separately. Cephalic Portion of the Sympathetic System

The cephalic portion of the sympathetic system contains no part of the ganglionated cord, but is formed largely by a direct ce¬

phalic prolongation from the superior cervi¬ cal ganglion, named the internal carotid nerve. In addition, there are nerves accom¬ panying the vertebral artery and the various branches of the external carotid artery that supply fibers to many structures in the head, such as the pilomotor muscles, sweat glands, and peripheral arteries of the face, and the salivary and other glands. internal carotid nerve. The internal carotid nerve (Fig. 12-23), arising from the cephalic end of the superior cervical gan¬ glion, accompanies the internal carotid ar¬ tery, and after entering the carotid canal in the petrous portion of the temporal bone, divides into two branches that lie against the medial and lateral aspects of the artery. The lateral branch, the larger of the two, distrib¬ utes filaments to the carotid artery and forms the internal carotid plexus. The medial branch also distributes filaments to the ar¬ tery, and following the artery to the cavern¬ ous sinus, forms the cavernous plexus. Internal Carotid Plexus. The internal ca¬ rotid plexus (carotid plexus) (Fig. 12-21) is the continuation of the lateral branch of the internal carotid nerve. It surrounds the lat¬ eral aspect of the artery, occasionally con¬ taining a small carotid ganglion. In addition to filaments to the artery, it has the following branches: A communication with the trigeminal nerve joins the latter at the trigeminal gan¬ glion. A communication joins the abducent nerve as it lies near the lateral aspect of the internal carotid artery. The deep petrosal nerve (Fig. 12-9) leaves the plexus at the lateral side of the artery, passes through the cartilage of the auditory tube which fills the foramen lacerum, and joins the greater petrosal nerve to form the nerve of the pterygoid canal (Vidian nerve). In the pterygopalatine fossa, the Vidian nerve joins the pterygopalatine ganglion, and its contribution through the deep petro¬ sal nerve has been called the sympathetic root of the ganglion. However the sympa¬ thetic fibers, already postganglionic, pass through or beside the ganglion without syn¬ apses and are distributed to the glands and blood vessels of the pharynx, nasal cavity, and palate by accompanying the branches of the maxillary nerve (Fig. 12-16). The caroticotympanic nerves are two or three filaments that pass through foramina in the bony wall of the carotid canal and join

VISCERAL NERVOUS SYSTEM

the tympanic plexus on the promontory of the middle ear. Cavernous Plexus. The cavernous plexus (Fig. 12-12) is the continuation of the medial branch of the internal carotid nerve. It lies inferior and medial to the part of the internal carotid artery enclosed by the cavernous sinus. It communicates with the adjacent cranial nerves and continues along the ar¬ tery to its terminal branches. The communication with the oculomotor nerve enters the orbit and joins the nerve at its point of division. A communication joins the trochlear nerve as it lies in the lateral wall of the cav¬ ernous sinus. The communication with the ophthalmic division of the trigeminal joins the latter nerve at its inferior surface. Fibers to the dilator pupillae muscle of the iris traverse the communication with the ophthalmic nerve and accompany the naso¬ ciliary nerve and the long ciliary nerves to the posterior part of the bulb, where they penetrate the sclera and run forward to the iris (for diagram, see Fig. 12-4). The communication with the ciliary gan¬ glion leaves the anterior part of the cavern¬ ous plexus and enters the orbit through the superior orbital fissure. It may join the nasociliary nerve and reach the ganglion through the latter’s branch to the ganglion, or it may take an independent course to the ganglion. Filaments to the hypophysis accompany its blood vessels. The terminal filaments from the internal carotid and cavernous plexuses continue along the anterior and middle cerebral ar¬ teries and the ophthalmic artery. Fibers on the cerebral arteries may be traced to the pia mater; those on the ophthalmic artery ac¬ company all its branches in the orbit. The filaments on the anterior communicating ar¬ tery may connect the sympathetic nerves of the right and left sides. External Carotid Nerves. The external carotid nerves send filaments out along all the branches of the external carotid artery. The filaments on the facial artery join the submandibular ganglion; they have formerly been called the sympathetic root of the gan¬ glion, but they pass through it without form¬ ing synapses and supply the submandibular and probably the sublingual glands (for dia¬ gram, see Fig. 12-17). The network of fila¬ ments on the middle meningeal artery gives

1255

off the small deep petrosal nerve, which has been called the sympathetic root of the otic ganglion, but its fibers pass through the gan¬ glion without synapses, some accompanying the auriculotemporal nerve to the parotid gland (for diagram, see Fig. 12-19), others forming the external superficial petrosal nerve which is a communication with the geniculate ganglion. Filaments on the facial, superficial temporal, and other arteries that are distributed to the skin supply the arrectores pilorum muscles and sweat glands, as well as the muscles constricting the arteries themselves. Cervical Portion of the Sympathetic System

The cervical portion of the sympathetic trunk consists of three ganglia—superior, middle, and inferior—connected by inter¬ vening cords (Fig. 12-74). It is ventral to the transverse processes of the vertebrae, close to the carotid artery, being embedded in the fascia of the carotid sheath itself or in the connective tissue between the sheath and the longus colli and capitis muscles. It re¬ ceives no roots or white rami communicantes from the cervical spinal nerves; its pregan¬ glionic fibers enter the trunk through the white rami from the upper five thoracic spi¬ nal nerves, mainly the second and third, and travel cranialward in the trunk to the three ganglia. The trunk also contains postgangli¬ onic fibers from various sources and visceral afferent fibers with their cell bodies in the dorsal root ganglia. superior cervical ganglion. The supe¬ rior cervical ganglion (Fig. 12-22), much larger than the other cervical ganglia and usually the largest of all the trunk ganglia, is approximately 28 mm long and 8 mm wide, fusiform in shape, frequently broad and flat, and occasionally constricted into two or more parts. It is embedded in the connective tissue between the carotid sheath and the prevertebral fascia over the longus capitis, at the level of the second cervical vertebra. It is the cephalic end of the sympathetic chain and is connected with the middle ganglion caudally by a rather long interganglionic cord. It is believed to be formed by the coa¬ lescence of sympathetic primordia from the cranial four cervical segments of the body. Its branches follow. Internal and External Carotid Nerves. The internal and external carotid nerves (de¬ scribed previously) leave the cephalic pole

1256

mi

PERIPHERAL NERVOUS SYSTEM

Suprascapular artery

Fig. 12 74 Cervical portion of the sympathetic nervous system on the right side, with the common carotid artery and internal jugular vein removed and with the vagus nerve and thyroid gland drawn aside. (Redrawn from Tondury.)

of the ganglion, and serve as direct continua¬ tions of the sympathetic trunk into the head. Cranial Nerves. Communications with the cranial nerves are delicate filaments that • join (a) the inferior ganglion of the glosso¬ pharyngeal nerve, (b) the superior and infe¬ rior ganglia of the vagus, and (c) the hypo¬ glossal nerve. The jugular nerve is a filament that passes cranialward to the base of the skull and divides to join the inferior gan¬ glion of the glossopharyngeal and the supe¬ rior ganglion of the vagus nerve. Cervical Nerves. Branches to the upper two to four cervical spinal nerves are the gray rami communicantes of these nerves. They course lateralward and dorsalward,

and have been called the lateral or external branches of the ganglion. The branches to any one nerve are variable and may be mul¬ tiple or absent. Variations. The branches to the first and sec¬ ond nerves are constantly present. Since the spinal nerves in the neck are connected by loops, as parts of the cervical plexus, the branch to the first nerve may join the loop between the first and second nerves, and the branch to the second may join the loop between the second and third nerves. There may be two to four branches to each of these nerves. The third cervical nerve receives a branch (ramus) from the ganglion in the majority of individ¬ uals, but in many instances it comes from the trunk below the superior ganglion. A branch for the third

VISCERAL NERVOUS SYSTEM

nerve often forms a loop with a lower branch, which then supplies roots to both the third and fourth nerves. Branches may join the third nerve itself or the loop between it and the fourth nerve. The fourth nerve receives a branch from the gan¬ glion only occasionally. Its rami frequently arise in common with those of either the third, fifth, or even the sixth nerves, and may come from the trunk or from nerves accompanying the vertebral artery. Pharyngeal Branches. Pharyngeal branches, commonly four to six, leave the medial as¬ pect of the ganglion, and in their course to¬ ward the pharynx, communicate with pha¬ ryngeal branches of the glossopharyngeal and vagus nerves opposite the constrictor pharyngis medius to form the pharyngeal plexus. Some of the filaments form a plexus on the lateral wall of the pharynx, others travel in the substance of the prevertebral fascia to the dorsum of the pharynx and form a posterior pharyngeal plexus. Fila¬ ments communicate with the superior laryn¬ geal nerve. Intercarotid Plexus. The intercarotid plexus receives one or two branches, either from the ganglion or from the external carotid nerves. They communicate with filaments from the pharyngeal branch of the vagus and the carotid branch of the glossopharyngeal nerve in the region of the carotid bifurca¬ tion, and are distributed in the plexus to the carotid sinus and the carotid body, where they probably serve a vasomotor function. Superior Cardiac Nerve. The superior car¬ diac nerve (Figs. 12-74; 12-75) arises by two or three filaments from the ganglion, and occasionally also by a filament from the trunk between the superior and middle gan¬ glia. It runs down the neck in the connective tissue of the posterior layers of the carotid sheath superficial to the longus colli, and crosses ventral or dorsal to the inferior thy¬ roid artery and recurrent nerve. The course of the nerves on the two sides then differs. The right nerve, at the root of the neck, passes either ventral or dorsal to the subcla¬ vian artery, and along the brachiocephalic artery to the deep part of the cardiac plexus. The left nerve passes ventral to the common carotid and across the left side of the arch of the aorta to reach the superficial part of the cardiac plexus. The superior cardiac nerves may communicate with the middle and infe¬ rior cardiac sympathetic nerves, with the cardiac branches of the vagus, the external branch of the superior laryngeal nerve, the

1257

recurrent nerve, the thyroid branch of the middle ganglion, the nerves on the inferior thyroid artery, and the tracheal and anterior pulmonary plexuses. middle cervical ganglion. The middle cervical ganglion (Fig. 12-75), the smallest of the three cervical ganglia, varies in size, form, and position, and may be either absent or doubled. It probably represents a fusion of the two sympathetic primordia corre¬ sponding to the fifth and sixth cervical nerves. When single, the ganglion may have a high position, at the level of the transverse process of the sixth cervical vertebra (the ca¬ rotid or Chassaignac’s tubercle1), or a low position nearer the level of the seventh cer¬ vical vertebra. In the high position it lies on the longus colli above the cranial bend of the inferior thyroid artery. In the low position it lies in close association with the ventral or ventromedial aspect of the vertebral artery, 1 to 3 cm from the latter's origin. The middle cervical ganglion has no white ramus communicans; its preganglionic fibers probably leave the spinal cord through the white rami of the second and third thoracic nerves and reach the ganglion through the intervening sympathetic trunk. Variations. The middle cervical ganglion was absent in 5, single in 10 and double in 1 0 of 25 dissections (Pick and Sheehan, 1946). It was pres¬ ent in 53 and double in two of 100 body halves (Jamieson et at., 1 952), with 64% in the high posi¬ tion. A small ganglion in the low position may have no branches. Several small thickenings may occur along the trunk between the superior and inferior ganglia. The ganglion may be split, surrounding the inferior thyroid artery (Axford, 1928). The intermediate cervical sympathetic gan¬ glion (of Jonnesco, 1 923) corresponds to a middle ganglion in the low position described above. Ac¬ cording to Saccomanno (1 943), it appears more con¬ stantly than a middle ganglion in the high position. A ganglion in the low position has been called the thyroid ganglion because of its close relationship to the inferior thyroid artery (Jamieson et al., 1952). The vertebral ganglion is a name given to a gan¬ glion in the low position, on the deep part of the loop of the ansa subclavia, included as part of the stellate ganglionic configuration (Pick and Sheehan, 1 946). Cervical Nerves. The branches (gray rami communicantes) are constantly supplied to the fifth and sixth nerves. A ganglion in the 'Charles Marie Edouard Chassaignac (1805-1879): A French surgeon (Paris).

1258

THE PERIPHERAL NERVOUS SYSTEM

Phrenic nerve

Lateral pectoral nerve Inferior thyroid artery Recurrent nerve Thoracoacrom ial artery

Superficial cardiac plexus Recurrent nerve Ligamentum arteriosum Phrenic nerve

Sympathetic trunk Left pulmonary artery

Fig. 12-75. Cervical portion of the sympathetic system on the left side, with the common carotid artery, internal jugular vein, vagus nerve, and subclavian artery partly removed, and the thyroid gland drawn forward. (Redrawn from Tondury.)

high position may send branches to the fourth nerve. The gray rami of the fifth cervical nerve number from one to three. (1) The most con¬ stant arises from the middle ganglion or the trunk just above it, runs upward and later¬ ally across the scalenus anterior, winds around the carotid tubercle and along a groove in the transverse process of the fifth cervical vertebra to the fifth nerve. It may pierce the scalenus anterior and it may di¬ vide, one branch going to the sixth nerve, or it may be prolonged to give a branch to the fourth or even the third nerve (Axford, 1928). (2) A ramus present in the majority of indi¬ viduals leaves the trunk just above the ca¬

rotid tubercle, pierces the longus colli either medial or lateral to the vertebral artery, and receives a communication from the nerve of the vertebral artery. (3) An inconstant ramus is a branch of that of the sixth nerve which accompanies the vertebral artery. The rami of the sixth cervical nerve may be two to four in number, one from the mid¬ dle and one from the inferior ganglion being constant. (1) A short ramus from the middle ganglion runs cranialward through the lon¬ gus colli just above the carotid tubercle to join the sixth nerve as it lies in its groove, medial to the vertebral artery. (2) A long fine branch from the middle ganglion or the trunk just above it crosses the vertebral ar-

VISCERAL NERVOUS SYSTEM

tery and scalenus anterior and joins the nerve lateral to the carotid tubercle, some¬ times continuing on to the fifth nerve. Middle Cardiac Nerve. The middle car¬ diac nerve (great cardiac nerve) (Fig. 12-75), the largest of the three cardiac nerves in the neck, arises from the middle cervical gan¬ glion, from the trunk between the middle and inferior ganglia, or both. As it descends dorsal to the common carotid artery, it com¬ municates with the superior cardiac nerve and the inferior laryngeal nerve. On the right side, at the root of the neck, it goes either deep or superficial to the subclavian artery, continues along the trachea, communicates with the recurrent nerve, and joins the right side of the deep part of the cardiac plexus. The left nerve enters the thorax between the common carotid and subclavian arteries and joins the left side of the deep part of the car¬ diac plexus. Thyroid Nerves. Branches from the mid¬ dle cervical ganglion form a plexus on the inferior thyroid artery, supply the thyroid gland, join the plexus on the common ca¬ rotid artery, and may communicate with the inferior laryngeal and external branch of the superior laryngeal nerves (Braeucker, 1922). The trunk between the middle and infe¬ rior cervical ganglia is constantly double, the two strands enclosing the subclavian ar¬ tery. The superficial strand is usually much longer than the deep strand and forms a loop about the artery, supplying it with branches; it is called the ansa subclayia (of Vieusens1) (Fig. 12-75). Since it is a rather constant fea¬ ture, it may be used to identify and distin¬ guish the middle and inferior ganglia or the components representing them. Occasion¬ ally the loop is formed about the vertebral artery instead of the subclavian, or there may be individual loops about both. inferior cervical ganglion. The inferior cervical ganglion (Fig. 12-75) is situated be¬ tween the base of the transverse process of the seventh cervical vertebra and the neck of the first rib, on the medial side of the costocervical artery. In most instances it is incompletely separated from or fused with the first thoracic ganglion, but it will be de¬ scribed as it appears when discrete, and the fused ganglion, called the stellate, also will be described below. It is larger than the midRaymond de Vieussens (1641-1715): A French anatomist (Montpellier).

1259

die ganglion, has an irregular shape, and probably represents the fusion of sympa¬ thetic primordia corresponding to the sev¬ enth and eighth cervical nerves. It has no white ramus, but receives its preganglionic fibers from the thoracic part of the trunk through its connection with the first thoracic ganglion. Variations. The inferior cervical ganglion was independent in 5 out of 25 cases (Pick and Sheehan, 1 946) and in 1 8 out of 1 00 cases (Jamie¬ son et al., 1 952). A white ramus has been described joining the eighth cervical nerve and the sympa¬ thetic (Pearson, 1952).

Branches (gray rami communicantes) are constantly supplied to the sixth, seventh, and eighth cervical nerves. Cervical Nerves.

The sixth cervical nerve commonly receives branches from the inferior cervical ganglion as well as from the middle cervical ganglion. (1) A constant, rather thick ramus from the deep part of the inferior cervical ganglion runs cranialward along the medial aspect of the vertebral artery, ventral to the vertebral veins and lateral to the longus colli, and enters the foramen in the transverse process of the sixth cervi¬ cal vertebra with the vertebral artery. It communi¬ cates with the plexus on the vertebral artery and sup¬ plies rami for the sixth and seventh, sometimes the fifth or even more cephalic nerves. (2) An inconstant ramus from the inferior ganglion is similar to the last, but pierces the scalenus anterior instead of passing through the foramen (Axford, 1928). The seventh cervical nerve receives two to five branches (gray rami) from the inferior cervical gan¬ glion. (1) A constant, well-defined branch 15 to 25 mm long crosses ventral to the eighth cervical nerve, either deep to, superficial to, or piercing the scalenus anterior. It may be composed of two or three parallel filaments. (2) A constant branch ac¬ companies the vertebral artery and is shared by the sixth nerve. (3) A frequent branch lies close to the vertebral vein, crosses the eighth cervical nerve, to which it may give filaments, and enters the foramen in the seventh cervical vertebra with the vein (Axford, 1928). The eighth cervical nerve receives two to five rather short branches (averaging 10 mm in length) from the inferior cervical ganglion. (1) A constant, well-defined, thick branch runs cranialward and lateralward, often across the neck of the first rib, and joins the eighth cervical nerve deep to the scalenus anterior. It is dorsal to the first part of the subclavian artery and is intimately related to the superior inter¬ costal artery. It may be represented by two to four parallel filaments. (2) A constant short thick branch from the upper pole of the inferior ganglion runs

1260

THE PERIPHERAL NERVOUS SYSTEM

vertically cranialward, medial and dorsal to the ver¬ tebral artery, a few millimeters lateral to the longus colli. It passes ventral to the transverse process of the first thoracic vertebra and medial to the first costocentral articulation, and joins the eighth cervi¬ cal nerve as it emerges from its foramen. (3) A fre¬ quent ramus accompanies the vertebral vein with a similar branch to the seventh nerve. Inferior Cardiac Nerve. The inferior car¬ diac nerve (Fig. 12-75) arises from either the inferior cervical ganglion, the first thoracic ganglion, the stellate ganglion, or the ansa subclavia. It passes deep to the subclavian artery and along the anterior surface of the trachea to the deep cardiac plexus. It com¬ municates with the middle cardiac nerve and the recurrent laryngeal nerve, and sup¬ plies twigs to various cervical structures (Saccomanno, 1943). Vertebral Nerve. The branches that ac¬ company the vertebral artery through the vertebral foramina are large. They join simi¬ lar branches from the first thoracic ganglion to form the vertebral nerve, which continues into the cranial cavity on the basilar, poste¬ rior cerebral, and cerebellar arteries. Com¬ munications between the vertebral nerve and the cervical spinal nerves frequently serve as rami of these nerves (Christensen et al., 1952).

Junction of Cervical and Thoracic Portions

The junction of the cervical with the tho¬ racic portion of the sympathetic trunk re¬ quires special consideration, first, because the lowest cervical and highest thoracic gan¬ glia are usually fused, and second, because the trunk makes an abrupt change of direc¬ tion at this point. The cervical portion of the trunk lies upon the ventral aspect of the transverse processes, but is also in a plane ventral to the vertebral bodies because of the latter’s small size and the presence of the longus colli muscle. The trunk drops back dorsalward as it enters the thorax, winding around the transverse process of the seventh cervical vertebra to reach the neck of the first rib. stellate ganglion. The stellate ganglion (cervicothoracic ganglion) (Fig. 12-75) is the name given to the ganglionic mass that re¬ sults when, as is usually the case, the inferior cervical and first thoracic ganglia are fused. It varies in size and form, occasionally in¬ cluding the middle cervical or the second

thoracic ganglia, and is located between the eighth cervical and first thoracic nerves. Its branches and communications are modifica¬ tions of those that would be found if the component ganglia remained separate. The white ramus communicans, therefore, comes from the first thoracic nerve, or from the sec¬ ond also, if the mass includes the second ganglion. The branches of the stellate ganglion that supply the gray rami to the spinal nerves include: a frequent branch to the sixth nerve, a constant branch to the seventh nerve, and constant double or multiple branches to the eighth cervical, first thoracic, and second thoracic nerves. The large branch to the ver¬ tebral artery leaves the superior border of the ganglion and forms the major portion of the vertebral nerve. Other branches are simi¬ lar to those described for the independent ganglia (Kirgis and Kuntz, 1942). Variations. In 25 bodies, the inferior cervical ganglion was independent in 5, fused with the first thoracic in 1 7, and fused with both the first and second thoracic in 3 (Pick and Sheehan, 1946). A stellate ganglion was present in 82 of 100 bodies (Jamieson et al., 1952). When the second thoracic is fused with the first, the inferior cervical is more likely to be independent. Surgical Considerations. The branches (gray rami) from the stellate ganglion to the eighth cervical and first thoracic nerves carry the bulk of the sympa¬ thetic fibers to the upper limb (Kirgis and Kuntz, 1942) . Other branches also carry fibers, however, and Woollard and Norish (1933) recommend that the middle cervical and second thoracic ganglia be included in the "stellate complex," and that the de¬ scription of the independent ganglia be abandoned. The sympathetic rami of the brachial plexus are de¬ scribed in more detail in the discussion of the brach¬ ial plexus. Comparative Anatomic Considerations. The stellate ganglion in cats includes the inferior cer¬ vical and first three thoracic ganglia (Saccomanno, 1943) and in rhesus monkeys the inferior cervical and first two thoracic ganglia (Sheehan and Pick, 1 943). The function of the stellate ganglion in con¬ trol of the heart, as it is revealed by animal experi¬ mentation with dogs, cats, and monkeys, does not agree entirely with that revealed by clinical observa¬ tions. A partial explanation for this is provided by the fact that more thoracic ganglia are included in the stellate complex and a much greater bulk of the ac¬ celerator nerve arises from the ganglion in these ani¬ mals than in man.

VISCERAL NERVOUS SYSTEM

Thoracic Portion of the Sympathetic System

The thoracic portion of the sympathetic trunk (Figs. 12-76; 12-77) contains a series of ganglia that correspond approximately to the thoracic spinal nerves, but the coales¬ cence of adjacent ganglia commonly reduces the number to fewer than 12. The ganglia are oval, fusiform, triangular, or irregular in shape. They lie against the necks of the ribs in the upper thorax, gradually become more ventrally placed in the lower thorax, and finally lie at the sides of the bodies of the lowest thoracic vertebrae. The trunk is cov¬ ered by the costal portion of the parietal pleura, and the interganglionic cords are between the pleura and the intercostal ves¬ sels, which they cross.

1261

The roots of the ganglia are the white rami communicantes supplied by each spinal nerve to the corresponding ganglion or the trunk nearby. They contain predominantly small myelinated fibers (1 to 3 ju.m in diame¬ ter), which leave the spinal cord through the ventral roots of the spinal nerves; the cell bodies are in the lateral column of gray mat¬ ter in the spinal cord. Many of the pregangli¬ onic fibers fail to make synapses in their ganglia of entrance. From the upper five roots, these fibers take a cranial direction in the trunk, and for the most part, terminate in the cervical ganglia. Many of the fibers in the caudal six or seven rami traverse the trunk for a variable distance and then emerge into the splanchnic nerves, which are the roots of the celiac and related ganglia.

Phrenic nerve Common carotid artery

Brachial plexus Subclavian artery Subclavian vein

%

Scalenus anterior Internal jugular vein

Internal thoracic artery and vein

A—Superior vena cava Ramus communicans •

■ Posterior pulmonary plexus Pulmonary ■ vessels

Intercostal vein, jyvjfir artery and nerve

Pericardiacophrenic artery

Thoracic duct-

Esophageal • plexus

Greater splanchnic nerveLesser splanchnic nerve'

Fig.

12-76.

The mediastinum from the right side. (Redrawn from Tondury.)

1262

THE PERIPHERAL NERVOUS SYSTEM

Scalenus anterior Brachial plexus Common carotid Subclavian artery First rib Subclavian vein Cardiac nerve _ Highest intercostal vein

Vagus nerve

Highest inter¬ costal artery

Int. thoracic vein

Cardiac ner. Superficial cardiac plexus Recurrent nerve

Intercost, v., art., nerve

Pulmonary art Access, hemiazyg. v.

Pulmonary plexus

Sympathetic trunk

Phrenic nerve Pulmon. vein

Branch. artery

Pharyng plexus

Great, splan. nerve

Fig. 12-77.

The mediastinum from the left side. (Redrawn from Tondury.)

FIRST THORACIC GANGLION. The first thoracic ganglion, when independent, is larger than the rest. It has an elongated or crescen¬ tic shape. Because of the change in direction of the trunk as it passes from the neck into the thorax, the ganglion is elongated dorsoventrally. It lies at the medial end of the first intercostal space or ventral to the neck of the first rib, medial to the costocervical arterial trunk. It is usually combined with the infe¬ rior cervical ganglion into a stellate ganglion

(as discussed previously), or it may coalesce with the second thoracic ganglion. The sec¬ ond to the tenth ganglia lie opposite the in¬ tervertebral disc or the cranial border of the next more caudal vertebra, slightly lower than the corresponding spinal nerve. In most individuals, the last thoracic ganglion, lying on the body of the twelfth vertebra, is larger, and by its connection to both the eleventh and twelfth nerves, takes the place of these two ganglia.

VISCERAL NERVOUS SYSTEM

Variations. The first thoracic ganglion was inde¬ pendent of the stellate in 5 instances, and the sec¬ ond thoracic was independent in 22 out of 25 in¬ stances. Fusion occurred between the third and fourth three times; fourth and fifth five times; fifth and sixth once; sixth and seventh once; seventh and eighth four times; eighth and ninth twice; ninth and tenth twice (Pick and Sheehan, 1946). Small accessory ganglia occur at or near the junction of the communicating rami with the thoracic nerves, espe¬ cially the upper four. Those at the white rami may provide sympathetic pathways to spinal nerves with¬ out traversing the sympathetic trunk (Ehrlich and Alexander, 1951).

The branches of the thoracic trunk are of three varieties: gray rami communicantes, vis¬ ceral branches, and the splanchnic nerves. gray rami communicantes. The branches that form the gray rami communicantes are supplied to each spinal nerve. Usually two or three short branches are sent to each cor¬ responding spinal nerve, and occasionally a slender branch reaches the next more caudal ganglion. When there are two or more branches to a single nerve, one branch may go to the anterior and one to the posterior primary division of the nerve. When the branches go only to the anterior primary division, the fibers turn back within the nerve to reach the posterior division (Dass, 1952). The gray rami are regularly proximal and transverse; the white rami, distal and oblique. visceral branches. Visceral branches are supplied to the cardiac, pulmonary, esophageal, and aortic plexuses. Cardiac Plexus. Branches to the cardiac plexus from the first five thoracic ganglia vary in number both in different individuals and between the two sides in the same indi¬ vidual; there may be 15 or 20 in some cases. Larger ones usually come from ganglia; smaller ones, from intervening cords. They course medially close to the intercostal ar¬ tery and vein, usually between the vessels and in the same connective tissue sheath, supplying filaments to them and communi¬ cating with the esophageal and pulmonary plexuses. From the right side they approach the deep part of the plexus, between the esophagus and the lateral aspect of the aorta. From the left side, they pass dorsal to the aorta and approach the deep part of the plexus from the right (Kuntz and More¬ house, 1930). Branches from the third, fourth, and fifth ganglia are more abundant than those from the first two; branches may

1263

come from the sixth and seventh ganglia, but these usually enter the aortic network. The cross-sectional area of the thoracic cardiac nerves, as they enter the plexus, is twice as large as that of the cervical cardiac nerves (Saccomanno, 1943). Esophageal Branches. Delicate esopha¬ geal branches from several of the thoracic ganglia, both upper and lower, may follow the intercostal vessels to the esophagus and join the plexus formed by the vagus, or fila¬ ments may be supplied by the cardiac and aortic plexuses, or by the splanchnic nerves. Posterior Pulmonary Plexus. The poste¬ rior pulmonary plexus receives twigs from the second, third, and fourth ganglia that fol¬ low the intercostal arteries to the hilum of the lung. Aortic Network. Branches to the aortic network come from the last five or six tho¬ racic ganglia, from the cardiac plexus, and from the splanchnic nerves. Branches from these bundles accompany the branches of the artery, and probably supplement the splanchnic nerves. splanchnic nerves. The splanchnic nerves arise from the caudal six or seven thoracic and first lumbar ganglia. They are not, strictly speaking, true branches of the ganglia, since they contain only a small number of postganglionic fibers. They are composed principally of myelinated fibers, and accordingly have a whitish color and firm consistency similar to those of the so¬ matic nerves. The small myelinated fibers (1 to 3 gm in diameter), which predominate, are the preganglionic fibers that pass through the chain ganglia without synapses to be¬ come the roots of the celiac and related gan¬ glia. Also present are large myelinated fi¬ bers, which are probably visceral afferents with their cell bodies in the dorsal root gan¬ glia of the spinal nerves. Many of the fibers of all types probably come from spinal cord segments higher than the ganglia from which the branches arise. Greater Splanchnic Nerve. The greater splanchnic nerve (Figs. 12-76; 12-77) is formed by contributions from the fifth (or sixth) to the ninth (or tenth) thoracic ganglia, which leave the ganglia in a medial direction and angle across the vertebral bodies ob¬ liquely in their caudalward course. They are combined into a single nerve that pierces the crus of the diaphragm and, after making an abrupt bend or loop ventralward, ends in the celiac ganglion by entering the lateral

1 264

THE PERIPHERAL NERVOUS SYSTEM

border of its principal mass (Fig. 12-78). A small splanchnic ganglion occurs commonly in the nerve at the level of the eleventh or twelfth thoracic vertebra; it is considered part of the celiac ganglion formed by cells that failed to migrate as far as the large gan¬ glion during embryonic development. Pre¬ ganglionic fibers to the suprarenal glands are conveyed by the splanchnic nerves and pass through the celiac plexus without synapses in the ganglion. Lesser Splanchnic Nerve. The lesser splanchnic nerve (Fig. 12-77) is formed by branches of the ninth and tenth thoracic ganglia or from the cord between them. It pierces the crus of the diaphragm with the greater splanchnic nerve and ends in the aorticorenal ganglion. Lowest Splanchnic Nerve. The lowest splanchnic nerve (least splanchnic nerve), when present, is a branch of the last thoracic ganglion or of the lesser splanchnic nerve. It passes through the diaphragm with the sym¬ pathetic trunk and ends in the renal plexus. Variations. The uppermost branch to the splanchnics in 25 dissections was the fourth gan¬ glion once; fifth, twice; sixth, eleven times; seventh, seven times; eighth, four times (Pick and Sheehan, 1 946). Filaments from the upper thoracic and stel¬ late ganglia, from the cardiac nerves, or from the branches to the pulmonary and aortic plexuses sometimes continue downward to join the celiac plexus and have been considered a fourth splanchnic nerve. Lumbar splanchnic nerves are described below.

Abdominal Portion of the Sympathetic System

The abdominal portion of the sympathetic trunk (Fig. 12-79) is situated ventral to the bodies of the lumbar vertebrae, along the medial margin of the psoas major. The cord connecting the last thoracic and first lumbar ganglia bends ventrally as it passes under the medial lumbocostal arch of the dia¬ phragm, bringing the trunk rather abruptly into its ventral relationship with the lumbar vertebrae. The left trunk is partly concealed by the aorta; the right, by the inferior vena cava. lumbar ganglia. The lumbar ganglia have no fixed pattern. The number varies from two to six, with four or five occurring in three-fourths of the trunks, but massive fusions are frequent and two specimens with four ganglia may bear no resemblance to

each other. Although the five individual lumbar ganglia should not be expected in any particular instance, each one occurs with sufficient frequency to make an ana¬ tomic description possible. The numbering of the ganglia is based upon the spinal nerves with which they are connected as well as upon the relationship to the verte¬ brae (Pick and Sheehan, 1946). The roots of the lumbar ganglia (white rami communicantes) are found only as far as the second lumbar spinal nerve, the cau¬ dal limit of the thoracolumbar outflow. The preganglionic fibers for the rest of the lum¬ bar and for the sacral and coccygeal ganglia run caudally in the trunk, mainly from these first two lumbar roots. One or two roots (white rami) are supplied to each of the first three lumbar ganglia (or their representa¬ tives in fused ganglia) by the spinal nerve one segment above; the roots take an oblique course caudalward while the branches to the spinal nerves (gray rami) take a transverse course (Botar, 1932). Thus the twelfth tho¬ racic nerve sends roots to the first lumbar ganglion; the first lumbar nerve, to the sec¬ ond ganglion; and the second lumbar nerve, to the third ganglion. The ganglia of the lumbar trunk, when independently represented, lie on the bodies of the corresponding vertebrae or the inter¬ vertebral discs caudally. The first ganglion is close to or partly concealed by the medial lumbocostal arch. The ganglion on the sec¬ ond lumbar vertebra is the most constant, largest, and most easily palpated and identi¬ fied by the surgeon. The fifth ganglion is rel¬ atively inaccessible to the surgeon because of the common iliac vessels. Variations. In 25 bodies, the first lumbar gan¬ glion (identified by its rami) was independent in 1 3, fused with other ganglia in 10, and separated into two parts in 2; the second ganglion was missing in 2, independent in 1 2, fused in 7, and split in 4; the third ganglion was independent in 2, fused in 17, split in 4, and connected only with L 3 nerve in 3; the fourth ganglion was independent in one, fused in 1 2, split in 1 2, and of these 1 1 connected with L 4 only; the fifth ganglion was independent in 4, fused in 3, split in 18, and of these 15 connected with L 5 only (Pick and Sheehan, 1946).

The branches of the lumbar trunk may be divided into three groups: (1) the gray rami communicantes, (2) the lumbar splanchnic

VISCERAL NERVOUS SYSTEM

1265

Superior suprarenal artery Inferior phrenic artery

Suprarenal plexus Middle suprarenal artery

Celiac ganglion Greater splanchnic nerve

Lesser splanchnic nerve 1 2th thoracic nerve

Inferior suprarenal artery

Renal

artery

Sympathetic -i trunk

Iliohypogastric nerve Ilioinguinal nerve

Lumbar artery Lumbar vein

Lateral femoral cutaneous nerve

Genitofemoral nerve

Fig. 12-78. The lumbar portion of the right sympathetic trunk, the celiac ganglion, splanchnic nerves, suprarenal gland, and kidney. (Redrawn from Tondury.)

nerves, and (3) the visceral branches through the celiac plexus. gray rami communicantes. The branches that are the gray rami communicantes are supplied to each of the lumbar nerves. They take a transverse path, in contrast to the oblique path of the white rami, and they are more proximal than the white rami in the segments where both are present. They are longer than those in the thoracic region be¬ cause the lumbar trunk is more ventrally

placed, at some distance from the spinal nerves, and they commonly accompany the lumbar arteries under the fibrous arches of the psoas, frequently splitting, doubling, and rejoining (Kuntz and Alexander, 1950). lumbar splanchnic nerves. The lumbar splanchnic nerves are two to four relatively short branches of the lumbar trunk at the level of the first, second, and third lumbar vertebrae, and are, therefore, caudal to the last root of the lesser splanchnic nerve. They

1 266

THE PERIPHERAL NERVOUS SYSTEM

Anterior vagus nerve Esophagus Inferior phrenic artery

Posterior vagus nerve Superior suprarenal artery

Suprarenal plexus Greater splanchnic n.

Celiac ganglion Lesser splanchnic n. Subcostal n. Renal plexus Sympathetic trunk Iliohypogastric nerve

Inferior mesenteric artery

Inferior mesenteric ganglion Aortic plexus Ovarian artery Common iliac artery Genitofemoral nerve

Hypogastric plexus

Fig. 12-79. The lumbar portion of the left sympathetic trunk, celiac and mesenteric ganglia, splanchnic nerves, hypogastric plexus, suprarenal gland, and kidney. (Redrawn from Tondury.)

pass either medialward, caudalward, and ventralward to join the aortic network, or, in the case of the most caudal lumbar splanch¬ nic, caudalward and ventralward around the aorta to the inferior mesenteric ganglion or the hypogastric nerve. On the right side they pass between the aorta and the inferior vena cava (Trumble, 1934). Frequently they con¬ tain small groups of ganglion cells that are believed to be displaced from the sympa¬ thetic trunk (Harris, 1943).

celiac ganglion.

The celiac ganglion

(semilunar ganglion) (Fig. 12-80) comprises

two masses of ganglionic tissue approxi¬ mately 2 cm in diameter, superficially re¬ sembling lymph nodes, which lie ventral and lateral to the abdominal aorta on each side at the level of the first lumbar vertebra. The ganglia are irregular in shape, are usu¬ ally partly dispersed into several small gan¬ glionic masses, and are connected with each other across the midline by a dense network

VISCERAL NERVOUS SYSTEM

1267

Inferior vena cava Anterior vagus

Inferior phrenic artery

Posterior vagus Inferior phrenic artery Celiac artery

Superior mesenteric artery Capsular artery Suprarenal vein

Renal plexus on renal artery

Testicular artery Sympathetic trunk Iliohypogastric n. Ilioinguinal n. Lateral femoral cutaneous n

Testicular veins

Renal artery and plexus

12th thoracic n. Inferior mesenteric artery Iliohypogastric n. Lateral femoral cutaneous n. Testicular artery Testicular vein Hypogastric plexus Femoral branch Genital branch of genitofemoral n.

View of the posterior abdominal wall, showing the celiac, aortic, and hypogastric plexuses of autonomic nerves. (Redrawn from Tondury.) Fig. 12-80.

of bundles, especially caudal to the celiac artery. The ganglia lie on the ventral surface of the crura of the diaphragm, close to the medial border of the suprarenal glands. The right ganglion is covered by the inferior vena cava; the left is covered by the peritoneum of the lesser sac in close relation to the pan¬ creas. AORTICORENAL AND SUPERIOR MESENTERIC ganglia. The aorticorenal and superior mesenteric ganglia are masses that are more or less completely detached from the caudal portion of the celiac ganglion but represent portions of the larger celiac ganglionic com¬ plex. The aorticorenal ganglion lies at the origin of the renal artery; the superior mes¬ enteric ganglion, at the origin of the corre¬ sponding artery. The roots of these ganglia

are the splanchnic nerves (discussed previ¬ ously). Each greater splanchnic nerve enters the dorsal and lateral border of the main celiac ganglion (Fig. 12-80); the lesser splanchnic nerve enters the aorticorenal ganglion (Fig. 12-78), and the lowest splanchnic joins the renal plexus. They con¬ tain preganglionic fibers from the last six or seven thoracic spinal cord segments, which pass through the sympathetic trunk without synapses. The postganglionic fibers that arise in the celiac ganglia form an extensive plexus (the celiac plexus) of nerve bundles and fila¬ ments, which branch off into subsidiary plexuses, in general following the branches of the abdominal aorta. The nerves from the celiac plexus pass down the aorta in the

1268

THE PERIPHERAL NERVOUS SYSTEM

form of a network that is penetrated by the inferior mesenteric artery. The more cranial lumbar splanchnic nerves make a stout con¬ tribution to this network and join the caudal lumbar splanchnic nerves to form thick ganglionated nerve bundles on each side of the midline. These bundles converge and meet at the bifurcation of the aorta, with a free decussation of fibers, and then continue as the right and left hypogastric nerves. Small ganglionic nodes are present, especially if the network is compressed (Trumble, 1934). inferior mesenteric ganglion. The infe¬ rior mesenteric ganglion is more difficult to define in man than in many animals, but a considerable amount of ganglionic tissue is almost invariably present at the origin of the inferior mesenteric artery. The roots of the ganglion are provided by nerves from the celiac plexus, the celiac roots, and by the lumbar splanchnic nerves. The inferior mesenteric ganglion in cats (Harris, 1943) is composed of three distinct masses arranged in a triangle about the ori¬ gin of the inferior mesenteric artery. Ganglia are found in dogs, guinea pigs, rabbits, and monkeys also (Trumble, 1934). Branches. The branches of the inferior mesenteric ganglion are (a) nerves that ac¬ company the inferior mesenteric artery and its branches to supply the colon, and (b) fi¬ bers that join each hypogastric nerve and continue from the bifurcation to join the pel¬ vic plexus. The hypogastric nerve crosses the medial side of the ureter and contributes to the ureteric network of nerves. It contains mainly fine unmyelinated fibers but has many medium myelinated fibers (4 to 6 jum) and a few large ones, probably afferent. The hypogastric nerves fan out into an extensive network just under the parietal peritoneum in the subserous fascia. They supply the rec¬ tal, vesical, prostatic, ureteric, and ductus deferens nerves (Ashley and Anson, 1946). Pelvic Portion of the Sympathetic System

The pelvic portion of the sympathetic trunk (Fig. 12-81) lies against the ventral sur¬ face of the sacrum, medial to the sacral fo¬ ramina. It is the direct continuation of the lumbar trunk and contains four or five gan¬ glia, smaller than those in other parts of the chain. Fusion of adjacent ganglia is common and cords connecting the trunks of the two sides across the midline occur regularly.

There are no white rami communicantes in the sacral region; small myelinated pregan¬ glionic fibers from the second, third, and fourth sacral nerves enter the pelvic plexus but they belong to the parasympathetic or craniosacral outflow rather than the sympa¬ thetic. The coccygeal ganglion is the most caudal ganglion of the sympathetic trunk; it is commonly a single ganglion, the ganglion impar, representing a fusion of the ganglia of the two sides, and usually lies in the midline but may be at one side. The branches of the sacral and coccygeal ganglia which are the gray rami communi¬ cantes of the sacral spinal nerves are sup¬ plied to each of the sacral and the coccygeal nerves. In most instances, each ganglion, or its representative in a fused ganglion, sup¬ plies rami to two adjacent spinal nerves (Pick and Sheehan, 1946). Visceral branches in variable numbers join the hypogastric and pelvic plexuses, and are supplied through them to the pelvic viscera and blood vessels (Trumble, 1934). Great Autonomic Plexuses

The two subdivisions of the autonomic nervous system, the sympathetic and para¬ sympathetic, are combined into extensive plexuses in the thorax, abdomen, and pelvis, named respectively the cardiac plexus, the celiac plexus, and the pelvic plexus. Experi¬ mental and clinical observations have made it possible to trace the sympathetic and para¬ sympathetic components to some extent, but on the morphologic evidence of dissections, it is almost impossible to distinguish the ulti¬ mate paths of the fibers belonging to the two systems. These plexuses also contain vis¬ ceral afferent fibers, described in earlier pages. CARDIAC PLEXUS

The cardiac plexus (Fig. 7-19) is situated at the base of the heart, close to the arch of the aorta, and is traditionally subdivided into a superficial and a deep part for topographic reasons, although the functional associations do not justify this division. The sympathetic contribution is largely postganglionic; the parasympathetic, largely preganglionic, with scattered groups of ganglion cells. superficial part. The superficial part of the cardiac plexus (Fig. 12-77) lies in the arch

VISCERAL NERVOUS SYSTEM

1 269

Sympathetic trunk

Lateral sacral art. Super, gluteal art.

£r«il

Infer, gluteal art. Sacral plexus Int. pudend. art. Visceral branch

Inferior vesical art

Urinary bladder

Vagina

Fig. 12-81.

Sagittal section of an adult female pelvis, with the peritoneum and subserous fascia partially dissected

away to show the pelvic plexus of autonomic nerves. (Redrawn from Tondury.)

of the aorta somewhat on the left side be¬ tween it and the bifurcation of the pulmo¬ nary artery. It is formed by the superior cer¬ vical cardiac branch of the left sympathetic and the lower of the two superior cardiac branches of the left vagus. A small ganglion, the cardiac ganglion (of Wrisberg1), is occa¬ sionally found in this plexus at the right side of the ligamentum arteriosum; it is probably a parasympathetic ganglion receiving pre¬ ganglionic fibers from the vagus. The branches of the superficial cardiac plexus are as follows: (a) to the deep cardiac plexus, (b) to the anterior coronary plexus, and (c) to the left anterior pulmonary plexus. deep part. The deep part of the cardiac plexus is situated deep to the arch of the aorta, between it and the bifurcation of the trachea and cranial to the pulmonary artery. Heinrich August Wrisberg (1739-1808): A German anat¬ omist (Gottingen)

It is much more extensive than the superfi¬ cial part and receives all the cardiac branches of both vagi and sympathetic trunks, except the two mentioned previously which enter the superficial part (left superior sympa¬ thetic and left lower superior of the vagus). It also receives the lower cardiac branches of the vagus and the recurrent nerve, vis¬ ceral rami from the upper cranial thoracic sympathetic ganglia, and communications from the superficial part of the cardiac plexus. The branches of the deep part of the car¬ diac plexus may be divided into right and left halves. The right half of the deep cardiac plexus gives branches that follow the right pulmo¬ nary artery. Those ventral to the artery are more numerous, and after contributing a few filaments to the anterior pulmonary plexus, continue into the anterior coronary plexus; those dorsal to the artery distribute a few hi-

1270

THE PERIPHERAL NERVOUS SYSTEM

aments to the right atrium and are then con¬ tinued onward to form part of the posterior coronary plexus. The left half of the deep cardiac plexus communicates with the superficial plexus, gives filaments to the left atrium and to the anterior pulmonary plexus, and is then con¬ tinued into the greater part of the posterior coronary plexus. The posterior coronary plexus (left coro¬ nary plexus) is larger than the anterior, and accompanies the left coronary artery. It is formed chiefly by filaments from the left half and by a few filaments from the right half of the deep plexus. It is distributed to the left atrium and ventricle. The anterior coronary plexus (right cor¬ onary plexus) is formed partly from the superficial and partly from the deep parts of the cardiac plexus. It accompanies the right coronary artery and is distributed to the right atrium and ventricle (Stotler and McMahon, 1947).

CELIAC PLEXUS

The celiac plexus (solar plexus) (Figs. 1278; 12-80) is situated at the level of the upper part of the first lumbar vertebra. It contains two large ganglionic masses and a dense net¬ work of fibers surrounding the roots of the celiac and superior mesenteric arteries. The denser part of the plexus lies between the suprarenal glands, on the ventral surface of the crura of the diaphragm and abdominal aorta, and dorsal to the stomach and the omental bursa, but it has extensive prolon¬ gations caudalward on the aorta and out along its branches. The celiac ganglia are described with the abdominal portion of the sympathetic system. The preganglionic para¬ sympathetic fibers reach the plexus through the anterior (left) and posterior (right) vagi on the stomach. The preganglionic sympa¬ thetic fibers reach the celiac, aorticorenal, and superior mesenteric ganglia through the greater and lesser splanchnic nerves. These nerves also supply preganglionic fibers to the cells in the medulla of the suprarenal glands, which correspond developmentally to postganglionic neurons. secondary plexuses. The secondary plex¬ uses and prolongations from the celiac plexus follow. The phrenic plexus (Fig. 12-80) accompa¬ nies the inferior phrenic artery to the dia¬

phragm. It arises from the superior part of the celiac plexus and is larger on the right side than on the left. It communicates with the phrenic nerve; at the point of junction with the right phrenic nerve, near the vena caval foramen in the diaphragm, there may be a small ganglion, the phrenic ganglion. The phrenic plexus gives filaments to the inferior vena cava, the inferior phrenic ar¬ teries, and the suprarenal and hepatic plex¬ uses. The hepatic plexus accompanies the he¬ patic artery, ramifying upon its branches and upon those of the portal vein in the sub¬ stance of the liver. A large network accom¬ panies the gastroduodenal artery and is con¬ tinued as the inferior gastric plexus on the right gastroepiploic artery along the greater curvature of the stomach, communicating with the splenic plexus. Extensions from the hepatic plexus supply the pancreas and gall¬ bladder, and there is a communication with the phrenic plexus. The splenic plexus, containing mainly fi¬ bers from the left celiac ganglion and the anterior (left) vagus, accompanies the sple¬ nic artery to the spleen and in its course sends filaments along its branches, espe¬ cially to the pancreas. The superior gastric plexus (gastric or coronary plexus) accompanies the left gas¬ tric artery along the lesser curvature of the stomach and communicates with the ante¬ rior (left) vagus. The suprarenal plexus (Fig. 12-78) is com¬ posed principally of short, rather stout, branches from the celiac ganglion, with some contributions from the greater splanch¬ nic nerve and the phrenic plexus. The fibers that it contains are predominantly pregangli¬ onic sympathetics, which pass through the celiac ganglion without synapses and are distributed to the medulla of the suprarenal gland, where the cells are homologous with postganglionic neurons. Postganglionic fi¬ bers to the blood vessels are also present (Swinyard, 1937). The renal plexus (Fig. 12-78) is formed by filaments from the celiac plexus, the aorti¬ corenal ganglion, the aortic plexus, and the smallest splanchnic nerve. It accompanies the renal artery into the kidney, giving some filaments to the spermatic plexus and to the inferior vena cava on the right side (Chris¬ tensen et al., 1951). The spermatic plexus receives filaments

VISCERAL NERVOUS SYSTEM

from the renal and aortic plexuses and ac¬ companies the testicular artery to the testis. In the female, the ovarian plexus arises from the renal plexus, accompanies the ovarian artery, and is distributed to the ovary, uter¬ ine tubes, and the fundus of the uterus. The superior mesenteric plexus is essen¬ tially the lower part of the celiac plexus; it may appear more or less detached from the rest of the plexus and frequently it contains a separate ganglionic mass, the superior mesenteric ganglion. Its vagus fibers come principally from the posterior vagus. It sur¬ rounds and accompanies the superior mes¬ enteric artery, being distributed with the lat¬ ter’s pancreatic, intestinal, ileocolic, right colic, and middle colic branches, which sup¬ ply the corresponding organs. The abdominal aortic plexus (aortic plexus) (Fig. 12-80) is formed from both right and left celiac plexuses and ganglia and from the lumbar splanchnic nerves. It lies upon the ventral and lateral surfaces of the aorta between the origins of the superior and inferior mesenteric arteries. From this plexus arise the spermatic, inferior mesenteric, ex¬ ternal iliac, and hypogastric plexuses, and filaments to the inferior vena cava. The inferior mesenteric plexus surrounds the origin of the inferior mesenteric artery and contains a ganglion (Fig. 12-80), the infe¬ rior mesenteric ganglion, or thickened bun¬ dles that contain ganglion cells. It is derived from the aortic plexus, through whose celiac and lumbar splanchnic contributions it re¬ ceives preganglionic as well as postgangli¬ onic fibers. It surrounds the inferior mesen¬ teric artery, and divides into a number of subsidiary plexuses that accompany its branches—the left colic, sigmoid, and supe¬ rior rectal—to the corresponding organs (Harris, 1943). The superior hypogastric plexus (presac¬ ral nerve) (Fig. 12-80) is the caudalward con¬ tinuation of the aortic and inferior mesen¬ teric plexuses. It extends from the level of the fourth lumbar to the first sacral verte¬ brae and lies in the subserous fascia just un¬ der the peritoneum. It is at first ventral to the aorta, then lies between the common iliac arteries; crosses the left common iliac vein, and enters the pelvis to lie against the mid¬ dle sacral vessels and the vertebrae. At the first sacral vertebra it divides into two parts, the right and left hypogastric nerves. The hypogastric nerve may be a single

1271

rather large nerve or several bundles form¬ ing a parallel network. It lies medial and dorsal to the common and internal iliac ar¬ teries, crosses the branches of the latter, and enters the inferior hypogastric plexus. The inferior hypogastric plexus is a fan¬ like expansion from the hypogastric nerves at the proximal part of the rectum and blad¬ der in the subserous fascia just above the sacrogenital fold. It receives filaments from the sacral portion of the sympathetic chain and from the deeper parts of the pelvic plexus. PELVIC PLEXUS

The pelvic plexus (Fig. 12-81) of the auto¬ nomic system is formed by the hypogastric plexus, by rami from the sacral portion of the sympathetic chain, and by the visceral branches of the second, third, and fourth sacral nerves. Through its secondary plex¬ uses it is distributed to all the pelvic viscera. secondary plexuses. The middle rectal plexus (middle hemorrhoidal plexus) is con¬ tained in the tissue of the sacrogenital fold and is therefore the most superficial part of the pelvic plexus with relation to the perito¬ neum. It is usually independent of the mid¬ dle rectal artery, and except for its terminal filaments to the caudal sigmoid colon and rectum, it is several centimeters from the bowel itself. From its superficial position, it appears to be the continuation of the inferior hypogastric plexus, but the latter has a num¬ ber of other continuations and the rectal plexus supplies the lower bowel with par¬ asympathetic fibers through contributions from the visceral branches of the sacral nerves. It communicates with the superior rectal branches from the inferior mesenteric plexus (Ashley and Anson, 1946). The vesical plexus arises from the ante¬ rior part of the pelvic plexus, its fibers de¬ rived from the superficial or hypogastric net¬ work and the deeper bundles from the sacral nerves. The filaments are divisible into peri¬ ureteric, prostatic, seminal vesicle, and lat¬ eral vesical groups. The prostatic plexus, from the deeper ven¬ tral part of the pelvic plexus, is composed of large nerves that are distributed to the pros¬ tate, seminal vesicles, and corpora caver¬ nosa. The nerves supplying the corpora con¬ sist of two sets, the greater and lesser cavernous nerves, which arise from the ven-

1272

THE PERIPHERAL NERVOUS SYSTEM

tral part of the prostatic plexus, join with branches of the pudendal nerve, and pass beneath the pubic arch. Filaments at the base of the gland supply the prostatic and membranous urethra, the ejaculatory ducts, and the bulbourethral glands. The greater cavernous nerve passes distalward along the dorsum of the penis, joins the dorsal nerve of the penis, and is distributed to the corpus cavernosum penis. The lesser cavernous nerves perforate the fibrous covering of the penis near its root, and are distributed to the corpus spongio¬ sum penis and the penile urethra.

The vaginal plexus arises from the caudal part of the pelvic plexus. It is distributed to the walls of the vagina and to the erectile tissue of the vestibule and clitoris. The uterine plexus arises from the caudal portion of the pelvic plexus. It approaches the uterus from its caudal and lateral aspect in the base of the broad ligament, in the same region as the uterine artery. It is dis¬ tributed to its musculature, supplies fila¬ ments to the uterine tube, and communicates with the ovarian plexus (Curtis et al., 1942).

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.)

Cranial Nerves I. Nervus Terminalis; Olfactory Nerve Bojsen-Moller, F. 1975. Demonstration of terminalis, ol¬ factory, trigeminal and perivascular nerves in the rat nasal septum. J. Comp. Neurol., 159:245-256. Brookover, C. 1914. The nervus terminalis in man. J. Comp. Neurol., 24:131-136. de Lorenzo, A. J. 1957. Electron microscopic observa¬ tions of the olfactory mucosa and olfactory nerve. J. Biophys. Biochem. Cytol., 3:839-850. Graziadei, G. A., M. S. Karlan, J. J. Bernstein, and P. P. C. Graziadei. 1980. Reinnervation of the olfactory bulb after section of the olfactory nerve in monkey (Saimiri sciureus). Brain Res., 189:343-354. Larsell, O. 1950. The nervus terminalis. Ann. Otol., 59:414-438. Loo, S. K. 1977. Fine structure of the olfactory epithelium in some primates. J. Anat. (Lond.), 123:135-146. Pearson, A. A. 1941. The development of the nervus ter¬ minalis in man. J. Comp. Neurol., 75:39-66. Rao, V. S. 1948. The lateral olfactory root in the human embryo. Anat. Rec., 101:617-620. Schultz, E. W. 1941. Regeneration of olfactory cells. Proc. Soc. Exp. Biol. Med., 46:41-43. Smith, C. G. 1942. Age incidence of atrophy of olfactory nerves in man: A contribution to the study of the process of aging. J. Comp. Neurol., 77:589-596. Smith, C. G. 1951. Regeneration of sensory olfactory epi¬ thelium and nerves in adult frogs. Anat. Rec., 109:661672. II. Optic Nerve Anderson, D. R., and W. Hoyt. 1969. Ultrastructure of intraorbital portion of human and monkey optic nerve. Arch. Ophthalmol., 82:506-530. Arees, E. A. 1978. Growth patterns of axons in the optic nerve of chick during myelogenesis. J. Comp. Neurol., 180:73-84. Arey, L. B. 1916. The function of the efferent fibers of the optic nerve of fishes. J. Comp. Neurol., 26:213-245, Bruesch, S. R., and L. B. Arey. 1942. The number of mye¬ linated and unmyelinated fibers in the optic nerve of vertebrates. J. Comp. Neurol., 77:631-665.

Donovan, A. 1967. The nerve fiber composition of the cat optic nerve. J. Anat. (Lond.), 101:1-11. Francois, J„ and A. Neetens. 1969. Physioanatomy of the axial vascularisation of the optic nerve. Documenta Ophthalmol., 26:38-49. Goldberg, S., and M. Kotani. 1967. The projection of optic nerve fibers in the frog Rana catesbiana as studied by radioautography. Anat. Rec., 158:325331. Henkind, P., and M. Levitsky. 1969. Angioarchitecture of the optic nerve. I. The papilla. Amer. J. Ophthalmol., 68:979-986. Hokoc, J. N„ and E. Oswaldo-Cruz. 1978. Quantitative analysis of the opossum’s optic nerve: An electron microscope study. J. Comp. Neurol., 178:773-782. Hughes, A. 1977. The pigmented-rat optic nerve: Fibre count and fibre diameter spectrum. J. Comp. Neurol., 176:263-268. Hughes, A., and H. Wassle. 1976. The cat optic nerve: Fibre total count and diameter spectrum. J. Comp. Neurol., 169:171-184. Jayatilaka, A. D. P. 1967. A note on arachnoid villi in relation to human optic nerves. J. Anat. (Lond.), 101:171-173. Kupfer, C., L. Chumbley, and J. de C. Downer. 1967. Quantitative histology of optic nerve, optic tract and lateral geniculate nucleus of man. J. Anat. (Lond.), 101:393-402. Lieberman, M. F., A. E. Maumenee, and W. R. Green. 1976. Histologic studies of the vasculature of the anterior optic nerve. Amer. J. Ophthalmol., 82:405423. Rogers, K. T. 1957. Early development of the optic nerve in the chick. Anat. Rec., 129:97-107. Steele, E. J., and M. }. Blunt. 1956. The blood supply of the optic nerve and chiasma in man. J. Anat. (Lond.), 90:486-493. Stone, J., and J. E. Campion. 1978. Estimate of the num¬ ber of myelinated axons in the cat’s optic nerve. J. Comp. Neurol., 180:799-806. Sturrock, R. R. 1975. A light and electron microscopic study of proliferation and maturation of fibrous as¬ trocytes in the optic nerve of the human embryo. J. Anat. (Lond.), 119:223-234.

REFERENCES

Tennekoon. G. I.. S. R. Cohen, D. L. Price, and G. M. McKhann. 1977. Myelinogenesis in optic nerve. A morphological, autoradiographic and biochemical analysis. J. Cell Biol., 72:604-616. Turner,}. W. A. 1943. Indirect injuries of the optic nerve. Brain, 66:140-151. Vaney, D. I., and A. Hughes. 1976. The rabbit optic nerve. Fibre diameter spectrum, fibre count and compari¬ son with retinal ganglion cell count. }. Comp. Neurol., 170:241-251. Vaughn, J. E., P. L. Hinds, and R. P. Skoff. 1970. Electron microscopic studies of Wallerian degeneration in rat optic nerves. I. The multipotential glia. J. Comp. Neurol., 140:175-206. Vaughn, J. E., and D. C. Pease. 1970. Electron micro¬ scopic studies of Wallerian degeneration in rat optic nerves. II. Astrocytes, oligodendrocytes and adven¬ titial cells. J. Comp. Neurol., 140:207-226. III. Oculomotor Nerve Abd-El-Malek, S. 1938. On the localization of nerve cen¬ tres of the extrinsic ocular muscles in the oculomo¬ tor nucleus. J. Anat. (Lond.), 72:518-523. Abd-El-Malek, S. 1938. On the presence of sensory fibers in the ocular nerves. J. Anat. (Lond.), 72:524-530. Bach y Rita, P., and F. Ito. 1966. Properties of stretch receptors in cat extra-ocular muscles. J. Physiol. (Lond.), 186:663-688. Bortolami, R., A. Veggetti, E. Callegari, M. L. Lucchi, and G. Palmieri. 1977. Afferent fibers and sensory gan¬ glion cells with the oculomotor nerve in some mam¬ mals and man. I. Anatomical investigations. Arch. Ital. Biol., 115:355-385. Clark, W. E. Le Gros. 1926. The mammalian oculomotor nucleus. J. Anat. (Lond.), 60:426-448. Corbin, K. B., and R. K. Oliver. 1942. The origin of fibers to the grape-like endings in the insertion third of the extra-ocular muscles. J. Comp. Neurol., 77:171-186. Manni, E„ R. Bortolami, V. E. Pettorossi, M. L. Lucchi, and E. Callegari. 1978. Afferent fibers and sensory ganglion cells within the oculomotor nerve in some mammals and man. II. Electrophysiological investi¬ gations. Arch. Ital. Biol., 116:16-24. Pearson, A. A. 1944. The oculomotor nucleus in the human fetus. J. Comp. Neurol., 80:47-63. Sunderland, S., and E. S. R. Hughes. 1946. The pupilloconstrictor pathway and the nerves to the ocular muscles in man. Brain, 69:301-309. Warwick, R. 1954. The ocular parasympathetic nerve supply and its mesencephalic sources. J. Anat. (Lond.), 88:71-93. IV. Trochlear Nerve Batini, C., C. Buisseret-Delmas, and R. T. Kado. 1979. On the fibers of the III, IV and VI cranial nerves in the cat. Arch. Ital. Biol., 117:111-122. Gacek, R. R. 1979. Location of trochlear vestibuloocular neurons in the cat. Exp. Neurol., 66:135-145. Kerns, J. M., and L. A. Rothblat. 1981. The effects of mo¬ nocular deprivation on the development of the rat trochlear nerve. Brain Res., 230:367-371. Kerns, R. M. 1980. Postnatal differentiation of the rat trochlear nerve. J. Comp. Neurol., 189:291-306. Mustafa, G. Y., and H. J. Gamble. 1979. Changes in axo¬ nal numbers in developing human trochlear nerve. J. Anat. (Lond.), 128:323-330. Nathan. H., and Y. Goldhammer. 1973. The rootlets of the trochlear nerve. Anatomical observations in human bodies. Acta Anat., 84:590-596.

1273

Pearson, A. A. 1943. The trochlear nerve in human fe¬ tuses. J. Comp. Neurol., 78:29-43. Sherif, M. F., N. J. Papadopoulos, and E. N. Albert. 1981. Fiber contribution from the mesencephalic nucleus of the trigeminal nerve to the trochlear nerve in the cat: a histological quantitative study. Anat. Rec., 201:669-678. Sohal, G. S. 1976. An experimental study of cell death in the developing trochlear nucleus. Exp. Neurol., 51: 684-698. Sohal, G. S., and R. K. Holt. 1978. Identification of troch¬ lear motoneurons by retrograde transport of horse¬ radish peroxidase. Exp. Neurol., 59:509-514. Sohal. G. S., and T. A. Weidman. 1978. Development of the trochlear nerve: loss of axons during normal ontogenesis. Brain Res., 142:455-465. Sohal. G. S., T. A. Weidman, and S. D. Stoney. 1978. Development of the trochlear nerve: effects of early removal of periphery. Exp. Neurol., 59:331-341. Stoney, S. D., Jr., and G. S. Sohal. 1978. Development of the trochlear nerve: neuromuscular transmission and electrophysiologic properties. Exp. Neurol., 62: 798-803. Weidman, T. A., and G. S. Sohal. 1977. Cell and fiber composition of the trochlear nerve. Brain Res., 125:340-344. Zaki, W. 1960. The trochlear nerve in man. Study relative to its origin, its intracerebral traject and its struc¬ ture. Arch. Anat. Histol. Embryol., 43:105-120. V. Trigeminal Nerve Anderson, K. V., and H. S. Rosing. 1977. Location of fe¬ line trigeminal ganglion cells innervating maxillary canine teeth: a horseradish peroxidase analysis. Exp. Neurol., 57:302-306. Arvidsson, J. 1975. Location of cat trigeminal ganglion cells innervating dental pulp of upper and lower canines studied by retrograde transport of horserad¬ ish peroxidase. Brain Res., 99:135-139. Augustine, J. R., B. Vidic, and P. A. Young. 1971. An inter¬ mediate root of the trigeminal nerve in the dog. Anat. Rec., 169:697-703. Baumel, J. J., J. P. Vanderheiden, and J. E. McElenney. 1971. The auriculotemporal nerve of man. Amer. J. Anat., 130:431-440. Beasley, W. L., and G. R. Holland. 1978. A quantitative analysis of the innervation of the pulp of the cat’s canine tooth. J. Comp. Neurol., 179:487-494. Bernick, S. 1948. Innervation of the human tooth. Anat. Rec., 101:81-107. Burr, H. S., and G. B. Robinson. 1925. An anatomical study of the Gasserian ganglion, with particular ref¬ erence to the nature and extent of Meckel’s cave. Anat. Rec., 29:269-282. Carter, R. B., and E. N. Keen. 1971. The intramandibular course of the inferior alveolar nerve. J. Anat. (Lond.), 108:433-440. Christensen, K. 1934. The innervation of the nasal mu¬ cosa, with special reference to its afferent supply. Ann. Otol. Rhinol. Laryngol., 43:1066-1083. Corbin, K. B. 1940. Observations on the peripheral distri¬ bution of fibers arising in the mesencephalic nucleus of the fifth cranial nerve. J. Comp. Neurol., 73:153177. Corbin, K. B., and F. Harrison. 1940. Function of mesen¬ cephalic root of fifth cranial nerve. J. Neurophysiol., 3:423-435. Cushing, H. 1904. The sensory distribution of the fifth cranial nerve. Bull. Johns Hopkins Hosp., 15:213232.

1274

THE PERIPHERAL NERVOUS SYSTEM

Fitzgerald, M. J. T. 1956. The occurrence of a middle su¬ perior alveolar nerve in man. J. Anat. (Lond.), 90:520522. Foley, J. O., H. R. Pepper, and W. H. Kessler. 1946. The ratio of nerve fibers to nerve cells in the geniculate ganglion. J. Comp. Neurol., 85:141-148. Frazier, C. H., and E. Whitehead. 1925. The morphology of the gasserian ganglion. Brain, 48:458-475. Gasser, R. F., and D. M. Wise. 1972. The trigeminal nerve in the baboon. Anat. Rec.,172:511-522. Henderson, W. R. 1965. The anatomy of the gasserian ganglion and the distribution of pain in relation to injection and operation for trigeminal neuralgia. Ann. Roy. Coll. Surg. (Lond.), 37:346-373. Holland, G. R. 1978. Fibre numbers and sizes in the infe¬ rior alveolar nerve of the cat. J. Anat. (Lond.), 127: 343-352. Jannetta, P. J., and R. W. Rand. 1966. Transtentorial retrogasserian rhizotomy in trigeminal neuralgia by microneurosurgical technique. Bull. Los Angeles Neurol. Soc., 31:93-99. Jones, F. W. 1939. The anterior superior alveolar nerves and vessels. J. Anat. (Lond.), 73:583-591. Mohuiddin, A. 1951. The postnatal development of the inferior dental nerve of the cat. J. Anat. (Lond.), 85:24-35. Pearson, A. A. 1949. The development and connections of the mesencephalic root of the trigeminal nerve in man. J. Comp. Neurol., 90:1-46. Pearson, A. A. 1977. The early innervation of the devel¬ oping deciduous teeth. J. Anat. (Lond.), 123:563-578. Roberts, W. H., and N. B. Jorgensen. 1962. A note on the distribution of the superior alveolar nerves in rela¬ tion to the primary teeth. Anat. Rec., 141:81-84. Starkie, C., and D. Stewart. 1931. The intra-mandibular course of the inferior dental nerve. J. Anat. (Lond.), 65:319-323. Szentagothai, J. 1949. Functional representation in the motor trigeminal nucleus. J. Comp. Neurol., 90:111120. Vidic, B., and J. Stefanatos. 1969. The roots of the trigem¬ inal nerve and their fiber components. Anat. Rec., 163:330. Wedgwood, M. 1966. The peripheral course of the infe¬ rior dental nerve. J. Anat. (Lond.), 100:639-650. Young, R. F., and R. Stevens. 1979. Unmyelinated axons in the trigeminal motor root of human and cat. J. Comp. Neurol., 183:205-214. VI. Abducent Nerve Bronson, R. T., and E. T. Hedley-Whyte. 1977. Morpho¬ metric analysis of the effects of exenteration and enucleation on the development of the third and sixth cranial nerves in the rat. J. Comp. Neurol.. 176:315-330. Cushing, H. 1911. Strangulation of the nervi abducentes by lateral branches of the basilar artery in cases of brain tumour. Brain, 33:204-235. Gacek, R. R. 1979. Location of abducens afferent neurons in the cat. Exp. Neurol., 64:342-353. Konigsmark, B. W„ U. P. Kalyanarama, P. Corey, and E. A. Murphy. 1969. An evaluation of techniques in neuronal population estimates: the sixth nerve nu¬ cleus. Bull. Johns Hopkins Hosp., 125:146-158. Sivanandasingham, P. 1978. Peripheral pathway of pro¬ prioceptive fibres from feline extra-ocular muscles. I. A histological study. Acta Anat., 100:173-184.

Spencer, R. F., and J. D. Porter. 1981. Innervation and structure of extraocular muscles in the monkey in comparison to those of the cat. J. Comp. Neurol., 198:649-665. Spencer, R. F„ and P. Sterling. 1977. Study of motoneurones and interneurones in the cat abducens nucleus iden¬ tified by retrograde intraaxonal transport of horse¬ radish peroxidase. J. Comp. Neurol., 176:65-86. Vijayashanker, N., and H. Brody. 1977. A study of aging in the human abducens nucleus. J. Comp. Neurol., 173:433-438. Wolff, E. 1928. A bend of the sixth cranial nerve, and its clinical significance. J. Anat. (Lond.), 63:150-151. Wolff, E. 1928. A bend in the sixth nerve and its probable significance. Brit. J. Ophthalmol., 12:22-24. VII. Facial Nerve Blevins, C. E. 1964. Studies on the innervation of the stapedius muscle of the cat. Anat. Rec., 149:157-171. Blunt, M. J. 1954. The blood supply of the facial nerve. J. Anat. (Lond.), 88:520-526. Bosman, D. H. 1978. The distribution of the chorda tympani in the middle ear area in man and two other primates. J. Anat. (Lond.), 127:443-446. Bowden, R. E. M., and Z. Y. Mahran. 1960. Experimental and histological studies of the extrapetrous portion of the facial nerve and its communications with the trigeminal nerve in the rabbit. J. Anat. (Lond.), 94:375-386. Bruesch, S. R. 1944. The distribution of myelinated affer¬ ent fibers in the branches of the cat’s facial nerve. J. Comp. Neurol., 81:169-191. Bunnell, S. 1937. Surgical repair of the facial nerve. Arch. Otolaryngol., 25:235-259. Coleman, C. C. 1944. Surgical lesions of the facial nerve: With comments on its anatomy. Ann. Surg., 119: 641-655. de Lorenzo, A. S. 1958. Electron microscopic observa¬ tions on the taste buds of the rabbit. J. Biophys. Biochem. Cytol., 4.T43-150. Dobozi, M. 1975. Surgical anatomy of the geniculate gan¬ glion. Acta Otolaryngol. (Stockholm), 80:116-119. Durcan, D. J„ J. J. Shea, and J. P. Sleeckx. 1967. Bifurca¬ tion of the facial nerve. Arch. Otolaryngol.. 86:619631. Foley, J. O. 1945. The sensory and motor axons of the chorda tympani. Proc. Soc. Exp. Biol. Med., 60:262267. Foley, J. O., and F. S. Dubois. 1943. An experimental study of the facial nerve. J. Comp. Neurol., 79:79105. Gasser, R. F. 1970. The early development of the parotid gland around the facial nerve and its branches in man. Anat. Rec., 167:63-78. Gomez, H. 1961. The innervation of lingual salivary glands. Anat. Rec., 139:69-76. Higbee, D. 1949. Functional and anatomic relation of the sphenopalatine ganglion to the autonomic nervous system. Arch. Otolaryngol., 50:45-58. Jannetta, P. J., M. Abbasy, J. C. Maroon, F. M. Ramos, and M. S. Alvin. 1977. Etiology and definitive microsurgical treatment of hemifacial spasm. Operative techniques and results in 47 patients. J. Neurosurg., 47:321-328. Kubota, K., and T. Masegi. 1972. Proprioceptive afferents in facial nerves of some insectivores. Anat. Rec., 173:353-363.

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Kudo, H., and S. Nori. 1974. Topography of the facial nerve in the human temporal bone. Acta Anat., 90:467-480. Laurenson, R. D. 1964. A rapid exposure of the facial nerve. Anat. Rec., 150:317-318. McCormack, L. J., E. W. Cauldwell, and B. J. Anson. 1945. The surgical anatomy of the facial nerve with spe¬ cial reference to the parotid gland. Surg. Gynecol. Obstet., 80:620-630. McKenzie, }. 1948. The parotid gland in relation to the facial nerve. J. Anat. (Lond.), 82:183-186. Miller, I. J., Jr. 1974. Branched chorda tympani neurons and interactions among taste receptors. J. Comp. Neurol., 158:155-166. Olmsted, J. M. D. 1922. Taste fibers and the chorda tym¬ pani nerve. J. Comp. Neurol., 34:337-341. Podvinec, M., and C. R. Pfaltz. 1976. Studies on the anatomy of the facial nerve. Acta Otolaryngol. (Stockholm), 81:173-177. Rhoton, A. L„ Jr., S. Kobayashi, and W. H. Hollinshead. 1968. Nervus intermedius. J. Neurosurg., 29:609-618. Ruskell, G. L. 1970. An ocular parasympathetic nerve pathway of facial nerve origin and its influence on intraocular pressure. Exp. Eye Res., 10:319-330. Ruskell, G. L. 1971. The distribution of autonomic post¬ ganglionic nerve fibres in the lacrimal gland in the rat. J. Anat. (Lond.), 109:229-242. Shimazawa, A. 1971. Quantitative studies of the greater petrosal nerve of the mouse with the electron micro¬ scope. Anat. Rec., 170:303-308. Shimazawa, A. 1973. An electron microscopic analysis of the nerve of the pterygoid canal in the mouse. Anat. Rec., 175:631-637. Sunderland, S., and D. F. Cossar. 1953. The structure of the facial nerve. Anat. Rec., 116:147-165. Vidic, B. 1968. The origin and the course of the communi¬ cating branch of the facial nerve to the lesser petro¬ sal nerve in man. Anat. Rec., 162:511-515. Vidic, B. 1970. The connections of the intra-osseous seg¬ ment of the facial nerve in baboon (papio sp.). Anat. Rec., 168:477-490. Vidic, B., and P. A. Young. 1967. Gross and microscopic observations on the communicating branch of the facial nerve to the lesser petrosal nerve. Anat. Rec., 158:257-261. Wind, J. 1977. The facial nerve and human evolution. Adv. Otorhinolaryngol., 22:215-219.

Engstrom, H., and H. Wersall. 1958. Structure and inner¬ vation of the ear sensory epithelia. Internat. Rev. Cytol., 6:535-585. Fernandez, C. 1951. The innervation of the cochlea (guinea pig). Laryngoscope, 61:1152-1172. Gacek, R„ and G. L. Rasmussen. 1957. Fiber analysis of the acoustic nerve of the cat, monkey and guinea pig. Anat. Rec., 127:417 (Abstract). Gacek, R. R., and G. L. Rasmussen. 1961. Fiber analysis of the statoacoustic nerve of guinea pig, cat, and monkey. Anat. Rec., 139:455-463. Galambos, R., and H. Davis. 1943. The response of single auditory nerve fibers to acoustic stimulation. J. Neu¬ rophysiol., 6:39-57. Hardy, M. 1934. Observations on the innervation of the macula sacculi in man. Anat. Rec., 59:403-418. Osen, K. K. 1970. Course and termination of the primary afferents in the cochlear nuclei of the cat. An experi¬ mental anatomical study. Arch. Ital. Biol., 108:21-51. Petroff, A. E. 1955. An experimental investigation of the origin of efferent fiber projections to the vestibular neuroepithelium. Anat. Rec., 121:352-353. Rasmussen, A. T. 1940. Studies of the eighth cranial nerve of man. Laryngoscope, 50:67-83. Rasmussen, G. L., and R. Gacek. 1958. Concerning the question of an efferent component of the vestibular nerve of the cat. Anat. Rec., 130:361-362. Rasmussen, G. L., and W. F. Windle. 1960. Neural Mech¬ anisms of the Auditory and Vestibular Systems. Charles C Thomas, Springfield, Ill., 422 pp. Romand, R., A. Sans, M. R. Romand, and R. Marty. 1976. The structural maturation of the stato-acoustic nerve in the cat. J. Comp. Neurol., 170:1-16. Ross, M. D. 1969. The general visceral efferent compo¬ nent of the eighth cranial nerve. J. Comp. Neurol., 135:453-478. Stopp, P. E., and S. D. Comis. 1978. Afferent and efferent innervation of the guinea-pig cochlea: a light micro¬ scopic and histochemical study. Neuroscience, 3:1197-1206. Tasaki, I. 1954. Nerve impulses in individual auditory nerve fibers of the guinea pig. J. Neurophysiol., 17: 97-122. Wersall, J. 1956. Studies on the structure and innervation of the sensory epithelium of the cristae ampullares in the guinea pig. Acta Otolaryngol. (Stockholm), Suppl., 126:1-85.

VIII. Vestibulocochlear Nerve Arnesen, A. R., and K. K. Osen. 1978. The cochlear nerve in the cat: Topography, cochleotopy and fiber spec¬ trum. J. Comp. Neurol., 178:661-678. Davis, H. 1954. The excitation of nerve impulses in the cochlea. Ann. Otol. Rhinol. Laryngol., 63:469-480. Davis, H. 1958. Transmission and conduction in the cochlea. Laryngoscope, 68:359-382. Dohlman, G., J. Farkashidy, and F. Salonna. 1958. Cen¬ trifugal nerve fibers to the sensory epithelium of the vestibular labyrinth. J. Laryngol. Otol. (Lond.), 72:984-991. Dunn, R. F. 1978. Nerve fibers of the eighth nerve and their distribution to the sensory nerves of the inner ear in the bullfrog. J. Comp. Neurol., 182:621-636. Engstrom, H. 1958. On the double innervation of the sen¬ sory epithelia of the inner ear. Acta Otolaryngol. (Stockholm), 49:109-118.

IX. Glossopharyngeal Nerve Abbot, P. C., M. D. B. Daly, and A. Howe. 1972. Early ultrastructural changes in the carotid body after degenerative section of the carotid sinus nerve in the cat. Acta Anat., 83:161-184. Boyd, J. D. 1937. Observations on the human carotid sinus and its nerve supply. Anat. Anz., 84:386-399. Dixon, J. S. 1966. The fine structure of parasympathetic nerve cells in the otic ganglia of the rabbit. Anat. Rec., 156:239-251. Erickson, T. C. 1936. Paroxysmal neuralgia of the tym¬ panic branch of the glossopharyngeal nerve: Report of a case in which relief was obtained by intracra¬ nial section of the glossopharyngeal nerve. Arch. Neurol. Psychiat., 35:1070-1075. Eyzaguirre, C., and J. Lewin. 1961. Effect of sympathetic stimulation on carotid nerve activity. J. Physiol. (Lond.), 159:251-267.

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THE PERIPHERAL NERVOUS SYSTEM

Frenckner, P. 1951. Observations on the anatomy of the tympanic plexus and technique of tympanosympathectomy. Arch. Otolaryngol., 54:347-355. Guth, L. 1957. The effects of glossopharyngeal nerve transection on the circumvallate papilla of the rat. Anat. Rec„ 128:715-731. Heymans, C., and J. J. Bouckaert. 1939. Les chemorecepteurs du sinus carotidien. Ergebn. der Physiol., 41:28-55. Kienecker, E.-W., H. Knoche, and D. Bingmann. 1978. Functional properties of regenerating sinus nerve fibres in the rabbit. Neuroscience, 3:977-988. Lawn, A. M. 1966. The localization, in the nucleus ambiguus of the rabbit, of the cells of origin of mo¬ tor nerve fibers in the glossopharyngeal nerve and various branches of the vagus nerve by means of retrograde degeneration. J. Comp. Neurol., 127:293305. Mitchell, R. A., A. Sinha, and D. M. McDonald. 1972. Chemoreceptive properties of regenerated endings of the carotid sinus nerve. Brain Res., 28:681-685. Nishio, J., T. Matsuya, K. Ibuki, and T. Miyazaki. 1976. Roles of the facial, glossopharyngeal and vagus nerves in velopharyngeal movement. Cleft Palate J., 13:201-214. Partridge, E. J. 1918. The relations of the glossopharyn¬ geal nerve at its exit from the cranial cavity. J. Anat. (Lond.), 52:332-334. Pastore, P. N., and J. M. Meredith. 1949. Glossopharyn¬ geal neuralgia. Arch. Otolaryngol., 50:789-794. Reichert, F. L., and E. J. Poth. 1933. Recent knowledge regarding the physiology of the glossopharyngeal nerve in man with analysis of its sensory, motor, gustatory and secretory functions. Bull. Johns Hop¬ kins Hosp., 53:131-139. Ripley, R. C., J. W. Hollifield, and A. S. Nies. 1977. Sus¬ tained hypertension after section of the glossopha¬ ryngeal nerve. Amer. J. Med., 62:297-302. Rosen, S. 1950. The tympanic plexus. Arch. Otolaryngol., 52:15-18. Sheehan, D., J. H. Mulholland, and B. Shafiroff. 1941. Surgical anatomy of the carotid sinus nerve. Anat. Rec., 80:431-442. Sprague, J. M. 1944. The innervation of the pharynx in the Rhesus monkey, and the formation of the pha¬ ryngeal plexus in primates. Anat. Rec., 90:197-208. State, F. A., and R. E. M. Bowden. 1974. The effect of transection of the glossopharyngeal nerve upon the structure, cholinesterase activity and innervation of taste buds in rabbits. J. Anat. (Lond.), 118:77-100. Tarlov, I. M. 1940. Sensory and motor roots of the glosso¬ pharyngeal nerve and the vagus-spinal accessory complex. Arch. Neurol. Psychiat.. 44:1018-1021. von Euler, U. S., and Y. Zotterman. 1942. Action potenti¬ als from the baroceptive and chemoceptive fibres in the carotid sinus nerve of the dog. Acta Physiol. Scandinav., 4:13-22. Willis, A. G., and J. D. Tange. 1959. Studies on the inner¬ vation of the carotid sinus of man. Amer. J. Anat., 104:87-113. Zapata, P., L. J. Stensaas, and C. Eyzaguirre. 1976. Axon regeneration following a lesion of the carotid nerve. Electrophysiological and ultrastructural observa¬ tions. Brain Res., 113:235-253. X. Vagus Nerve Armstrong, W. G„ and J. W. Hinton. 1951. Multiple divi¬ sions of the recurrent laryngeal nerve: an anatomic study. Arch. Surg., 62:532-539.

Berlin, D. D., and F. H. Lahey. 1929. Dissections of the recurrent and superior laryngeal nerves: The rela¬ tion of the recurrent to the inferior thyroid artery and the relation of the superior to abductor paraly¬ sis. Surg. Gynecol. Obstet., 49:102-104. Bowden, R. E. M. 1955. Surgical anatomy of the recurrent laryngeal nerve. Brit. J. Surg., 43:153-163. Brocklehurst, R. J., and F. H. Edgeworth. 1940. The fibre components of the laryngeal nerves of Macaca mu¬ latto. J. Anat. (Lond.), 74:386-389. Chamberlin, J. A., and T. Winship. 1947. Anatomic varia¬ tions of the vagus nerves—their significance in vagus neurectomy. Surgery, 22:1-19. Chase, M. R„ and S. W. Ranson. 1914. The structure of the roots, trunk and branches of the vagus nerve. J. Comp. Neurol., 24:31-60. Dragstedt, L. R., H. J. Fournier, E. R. Woodward, E. B. Tovee, and P. V. Harper, Jr. 1947. Transabdominal gastric vagotomy: A study of the anatomy and sur¬ gery of the vagus nerves at the lower portion of the esophagus. Surg. Gynecol. Obstet., 85:461-466. Dubois, F. S., and J. O. Foley. 1936. Experimental studies on the vagus and spinal accessory nerve in the cat. Anat. Rec., 64:285-307. Evans, D. H. L., and J. G. Murray. 1954. Histological and functional studies on the fibre composition of the vagus nerve of the rabbit. J. Anat. (Lond.), 88:320337. Foley, J. O., and F. S. Dubois. 1937. Quantitative studies of the vagus nerve in the cat: I. The ratio of sensory to motor fibers. J. Comp. Neurol., 67:49-67. Gordon, T., N. Niven-Jenkins, and G. Vrbova. 1980. Ob¬ servations on neuromuscular connection between the vagus nerve and skeletal muscle. Neuroscience, 5:597-610. Hoffman, H. H., and A. Kuntz. 1957. Vagus nerve compo¬ nents. Anat. Rec., 127:551-568. Hoffman, H. H., and H. N. Schnitzlein. 1961. The num¬ bers of nerve fibers in the vagus nerve of man. Anat. Rec., 139:429-435. Hollinshead, W. H. 1939. The origin of the nerve fibers to the glomus aorticum of the cat. J. Comp. Neurol., 71:417-426. Hollinshead, W. H. 1940. The innervation of the supracardial bodies in the cat. J. Comp. Neurol., 73:37-48. Jackson, R. G. 1949. Anatomy of the vagus nerves in the region of the lower esophagus and the stomach. Anat. Rec., 103.T-18. Johnson, F. E., and E. A. Boyden. 1952. The effect of dou¬ ble vagotomy on the motor activity of the human gallbladder. Surgery, 32:591-601. Kyosola, K., L. Rechardt, L. Veijola, T. Waris, and O. Penttila. 1980. Innervation of the human gastric wall. J. Anat. (Lond.), 131:453-470. Legrand, M. C., G. H. Paff, and R. J. Boucek. 1966. Initia¬ tion of vagal control of heart rate in the embryonic chick. Anat. Rec., 155:163-166. Lemere, F. 1932. Innervation of the larynx: I. Innervation of the laryngeal muscles. Amer. J. Anat., 51:417-437. Lemere, F. 1932. Innervation of the larynx. II. Ramus anastomoticus and ganglion cells of the superior la¬ ryngeal nerve. Anat. Rec., 54:389-407. Mitchell, G. A. G., and R. Warwick. 1955. The dorsal vagal nucleus. Acta Anat., 25:371-395. Mohr, P. D. 1969. The blood supply of the vagus nerve. Acta Anat., 73:19-26. Morrison, L. F. 1952. Recurrent laryngeal nerve paralysis. A revised conception based on the dissection of one

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hundred cadavers. Ann. Otol. Rhinol. Laryngol., 61: 567-592. Peden, J. K., C. F. Schneider, and R. D. Bikel. 1950. Ana¬ tomic relations of the vagus nerves to esophagus. Amer. J. Surg., 80:32-34. Ranson, S. W., and P. Mihalik. 1932. The structure of the vagus nerve. Anat. Rec., 54:355-360. Reed, A. F. 1943. The relations of the inferior laryngeal nerve to the inferior thyroid artery. Anat. Rec., 85:17-23. Rethi, A. 1951. Histological analysis of the experimen¬ tally degenerated vagus nerve. Acta Morphol., 1:221230. Richardson, A. P., and J. C. Hinsey. 1933. Functional studies of the nodose ganglion of the vagus with degeneration methods. Proc. Soc. Exp. Biol. Med., 30:1141-1143. Schnitzlein, H. N., L. C. Rowe, and H. H. Hoffman. 1958. The myelinated component of the vagus nerves in man. Anat. Rec., 131:649-667. Sunderland, S., and W. E. Swaney. 1952. The intraneural topography of the recurrent laryngeal nerve in man. Anat. Rec., 114:411-426. Tarlov, I. M. 1942. Section of the cephalic third of the vagus-spinal accessory complex: Clinical and histo¬ logic results. Arch. Neurol. Psychiat., 47:141-148. Teitelbaum, H. A. 1933. The nature of the thoracic and abdominal distribution of the vagus nerves. Anat. Rec., 55:297-317. Todo, K., T. Yamamoto, H. Satomi, H. Ise, H. Takatama, and K. Takahashi. 1977. Origins of vagal pregan¬ glionic fibers to the sinoatrial and atrioventri¬ cular node regions in the cat heart as studied by the horseradish peroxidase method. Brain Res., 130: 545-550.

XI. Accessory Nerve Balagura, S., and R. G. Katz. 1980. Undecussated inner¬ vation to the sternocleidomastoid muscle: a rein¬ statement. Ann. Neurol., 7:84-85. Black, D. 1914. On the so-called “bulbar” portion of the accessory nerve. Anat. Rec., 8.T10-112. Corbin, K. B., and F. Harrison. 1938. Proprioceptive com¬ ponents of cranial nerves. The spinal accessory nerve. J. Comp. Neurol., 69:315-328. Corbin, K. B., and F. Harrison. 1939. The sensory inner¬ vation of the spinal accessory and tongue muscula¬ ture in the rhesus monkey. Brain, 62:191-197. Gordon, S. L., W. P. Graham, J. T. Black, and S. H. Miller. 1977. Accessory nerve function after surgical proce¬ dures in the posterior triangle. Arch. Surg., 112:264268. Hill, J. H., and N. R. Olson. 1979. The surgical anatomy of the spinal accessory nerve and the internal branch of the superior laryngeal nerve. Laryngoscope, 89: 1935-1942. Pearson, A. A. 1938. The spinal accessory nerve in human embryos. J. Comp. Neurol., 68:243-266. Pearson, A. A., R. W. Sauter, and G. R. Herrin. 1964. The accessory nerve and its relation to the upper spinal nerves. Amer. J. Anat., 114:371-391. Romanes, G. J. 1940. The spinal accessory nerve in the sheep. J. Anat. (Lond.), 74:336-347. Straus, W. L., Jr., and A. B. Howell. 1936. The spinal accessory nerve and its musculature. Quart. Rev. Biol., 11:387-402. Windle, W. F. 1931. The sensory component of the spinal accessory nerve. J. Comp. Neurol., 53:115-127.

1277

Yee, J., F. Harrison, and K. B. Corbin. 1939. The sensory innervation of the spinal accessory and tongue mus¬ culature in the rabbit. J. Comp. Neurol., 70:305-314. XII. Hypoglossal Nerve Allen, W. F. 1929. Effect of repeated traumatization of the central stump of the hypoglossal nerve on de¬ generation and regeneration of its fibers and cells. Anat. Rec., 43:27-32. Barnard, J. W. 1940. The hypoglossal complex of verte¬ brates. J. Comp. Neurol., 72:489-524. Downman, C. B. B. 1939. Afferent fibres of the hypoglos¬ sal nerve. J. Anat. (Lond.), 73:387-395. Pearson, A. A. 1939. The hypoglossal nerve in human embryos. J. Comp. Neurol., 71:21-39. Pearson, A. A. 1943. Sensory type neurons in the hypo¬ glossal nerve. Anat. Rec., 85:365-375. Scotti, D., D. Melancon, and A. Oliver. 1978. Hypoglossal paralysis due to compression by a tortuous internal carotid artery in the neck. Neuroradiology, 14:263265. Shaia, F. T., and M. D. Graham. 1977. The hypoglossal nerve. Its relationship to the temporal bone and jug¬ ular foramen. Laryngoscope, 87:1137-1139. Tarkhan, A. A., and I. Abou-el-naga. 1947. Sensory fibres in the hypoglossal nerve. J. Anat. (Lond.), 81:23-32. Tarkhan, A. A., and S. Abd El-Malek. 1950. On the pres¬ ence of sensory nerve cells on the hypoglossal nerve. J. Comp. Neurol., 93:219-228. Vij, S., and R. Kanagasuntheram. 1972. Development of the nerve supply to the human tongue. Acta Anat., 81:466-477. Weddell, G., J. A. Harpman, D. Lambley, and L. Young. 1940. The innervation of the musculature of the tongue. J. Anat. (Lond.), 74:255-267. Zimny, R., T. Sobusiak, and Z. Mattosz. 1970/1971. The afferent components of the hypoglossal nerve. An experimental study with toluidine blue and silver impregnation methods. J. fur Hirnforsch., 12:83-100.

Spinal Nerves A. General Barry, A. 1956. A quantitative study of the prenatal changes in angulation of the spinal nerves. Anat. Rec., 126:97-110. Cave, A. J. E. 1929. The distribution of the first intercos¬ tal nerve and its relation to the first rib. J. Anat. (Lond.), 63:367-379. Collis, J. L., L. M. Satchwell, and L. D. Abrams. 1954. Nerve supply to the diaphragm. Thorax, 9:22-25. Corbin, K. B., and F. Harrison. 1939. The sensory inner¬ vation of the spinal accessory and tongue muscula¬ ture in the rhesus monkey. Brain, 62:191-197. Corbin, K. B., and J. C. Hinsey. 1935. Intramedullary course of the dorsal root fibers of each of the first four cervical nerves. J. Comp. Neurol., 63:119-126. Davies, F., R. J. Gladstone, and E. P. Stibbe. 1932. The anatomy of the intercostal nerves. J. Anat. (Lond.), 66:323-333. Emery, D. G., H. Ito, and R. E. Coggeshall. 1977. Unmye¬ linated axons in thoracic ventral roots of the cat. J. Comp. Neurol., 172:37-48. Fraher, J. P. 1978. Quantitative studies on the maturation of central and peripheral parts of individual ventral motoneuron axons. I. Myelin sheath and axon cali¬ bre. J. Anat. (Lond.), 126:509-534. Fraher, J. P. 1978. Quantitative studies on the maturation

1278

THE PERIPHERAL NERVOUS SYSTEM

of central and peripheral parts of individual ventral motoneuron axons. II. Internodal length. J. Anat. (Lond.), 127:1-16. Gershenbaum, M. R., and F. J. Roisen. 1978. A scanning electron microscopic study of peripheral nerve de¬ generation and regeneration. Neuroscience, 3:12411250. Hidayet, M. A., H. A. Wahid, and A. S. Wilson. 1974. Investigations on the innervation of the human dia¬ phragm. Anat. Rec., 179:507-516. Hinsey, J. C. 1933. The functional components of the dor¬ sal roots of spinal nerves. Quart. Rev. Biol., 8:457464. Hogg, I. D. 1941. Sensory nerves and associated struc¬ tures in the skin of human fetuses of 8 to 14 weeks of menstrual age correlated with functional capability. J. Comp. Neurol., 75:371-410. Horwitz, M. T., and L. M. Tocantins. 1938. An anatomical study of the role of the long thoracic nerve and the related scapular bursae in the pathogenesis of local paralysis of the serratus anterior muscle. Anat. Rec., 71:375-385. Keegan, f. J„ and F. D. Garrett. 1948. The segmental dis¬ tribution of the cutaneous nerves in the limbs of man. Anat. Rec., 102:409-437. Kelley, W. O. 1950. Phrenic nerve paralysis: Special con¬ sideration of the accessory phrenic nerve. }. Tho¬ racic Surg., 19:923-928. Kiss, F., and H. C. Ballon. 1929. Contribution to the nerve supply of the diaphragm. Anat. Rec., 41:285-298. Kozlov, V. I. 1969. Formation and structure of the spinal nerve. Acta Anat., 73:321-350. Langford, L. A., and R. E. Coggeshall. 1979. Branching of sensory axons in the dorsal root and evidence for the absence of dorsal root efferent fibers. J. Comp. Neurol., 184:193-204. McKinniss, M. E. 1936. The number of ganglion cells in the dorsal root ganglia of the second and third cervi¬ cal nerves in human fetuses of various ages. Anat. Rec., 65:255-259. Merendino, K. A., R. J. Johnson, H. H. Skinner, and R. X. Maguire. 1956. Intradiaphragmatic distribution of the phrenic nerve with particular reference to place¬ ment of diaphragmatic incisions and controlled seg¬ mental paralysis. Surg. Gynecol. Obstet., 39:189-198. Mesulam, M.-M., and T. M. Brushart. 1979. Transganglionic and anterograde transport of horseradish per¬ oxidase across dorsal root ganglia: a tetramethylbenzidine method for tracing central sensory connections of muscles and peripheral nerves. Neu¬ roscience, 4:1107-1117. Moyer, E. K., and B. F. Kaliszewski. 1958. The number of nerve fibers in motor spinal nerve roots of young, mature and aged cats. Anat. Rec., 131:681-699. • Moyer, E. K., and D. L. Kimmel. 1948. The repair of sev¬ ered motor and sensory spinal nerve roots by the arterial sleeve method of anastomosis. J. Comp. Neurol., 88:285-317. Pallie, W., and J. K. Manuel. 1968. Intersegmental anasto¬ moses between dorsal spinal rootlets in some verte¬ brates. Acta Anat., 70:341-351. Pearson, A. A., and J. J. Bass. 1961. Cutaneous branches of the posterior primary rami of the cervical nerves. Anat. Rec., 139:263 (Abstract). Pearson, A. A., R. W. Sauter, and J. J. Bass. 1963. Cutane¬ ous branches of the dorsal primary rami of the cer¬ vical nerves. Amer. J. Anat., 112:169-180. Pearson, A. A., R. W. Sauter, and T. F. Buckley. 1966.

Further observations on the cutaneous branches of the dorsal primary rami of the spinal nerves. Amer. J. Anat., 118:891-903. Perera, H., and F. R. Edwards. 1957. Intradiaphragmatic course of the left phrenic nerve in relation to dia¬ phragmatic incisions. Lancet, 2:75-77. Roofe, P. G. 1940. Innervation of the annulus fibrosus and posterior longitudinal ligament. Arch. Neurol. Psychiat., 44:100-103. Schlaepfer, K. 1926. A further note on the motor innerva¬ tion of the diaphragm. Anat. Rec., 32:143-150. Sindou, M., C. Quoex, and C. Baleydier. 1974. Fiber orga¬ nization at the posterior spinal cord-rootlet junction in man. J. Comp. Neurol., 153:15-26. Stilwell, D. L., Jr. 1956. The nerve supply of the vertebral column and its associated structures in the monkey. Anat. Rec., 125:139-169. Stilwell, D. L„ Jr. 1957. Regional variations in the inner¬ vation of deep fasciae and aponeuroses. Anat. Rec., 127:635-653. Sunderland, S., and K. C. Bradley. 1949. The cross-sec¬ tional area of peripheral nerve trunks devoted to nerve fibers. Brain, 72:428-449. Tarlov, I. M. 1937. Structure of the nerve root: I. Nature of the junction between the central and the periph¬ eral nervous system. Arch. Neurol. Psychiat., 37: 555-583. Tarlov, I. M. 1937. Structure of the nerve root: II. Differ¬ entiation of sensory from motor roots; observations on identification in roots of mixed cranial nerves. Arch. Neurol. Psychiat., 37:1338-1355. Thornton, M. W., and M. R. Sweisthal. 1969. The phrenic nerve; its terminal divisions and supply to the crura of the diaphragm. Anat. Rec., 164:283-290. Wilson, A. S. 1968. Investigations on the innervation of the diaphragm in cats and rodents. Anat. Rec., 162:425-432. Wilson, A. S. 1970. Experimental studies on the innerva¬ tion of the diaphragm in cats. Anat. Rec., 168:537547. Yee, J„ and K. B. Corbin. 1939. The intramedullary course of the upper five cervical dorsal root fibers in the rabbit. J. Comp. Neurol., 70:297-304.

B. Brachial Plexus and Nerves of Upper Limb Beaton, L. E., and B. J. Anson. 1939. The relation of the median nerve to the pronator teres muscle. Anat. Rec., 75:23-26. Blunt, M. J. 1959. The vascular anatomy of the median nerve in the forearm and hand. J. Anat. (Lond.), 93: 15-22. Capener, N. 1966. The vulnerability of the posterior in¬ terosseous nerve of the forearm. A case report and an anatomical study. J. Bone Jt. Surg., 48B:770-773. Clausen, E. G. 1942. Postoperative "anesthetic” paralysis of the brachial plexus: A review of the literature and report of nine cases. Surgery, 12:933-942. Davis, L., J. Martin, and G. Perret. 1947. The treatment of injuries of the brachial plexus. Ann. Surg., 125:647657. De Jong, R. N. 1943. Syndrome of involvement of poste¬ rior cord of the brachial plexus. Arch. Neurol. Psy¬ chiat., 49:860-862. Farber, J. S., and R. S. Bryan. 1968. The anterior interos¬ seous nerve syndrome. J. Bone Jt. Surg., 50A.-521523. Fullerton, P. M. 1963. The effect of ischaemia on nerve

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conduction in the carpal tunnel syndrome. J. Neurol. Neurosurg. Psychiat., 26:385-397. Gardner, E. 1948. The innervation of the elbow joint. Anat. Rec., 102.T61-174. Gardner, E. 1948. The innervation of the shoulder joint. Anat. Rec., 102:1-18. Gitlin, G. 1957. Concerning the gangliform enlargement (‘Pseudoganglion’) on the nerve to the teres minor muscle. J. Anat. (Lond.), 91:466-470. Gore, D. R. 1971. Carpometacarpal dislocation producing compression of the deep branch of the ulnar nerve. J. Bone Jt. Surg., 53A.T387-1390. Gray, D. J., and E. Gardner. 1965. The innervation of the joints of the wrist and hand. Anat. Rec., 151:261-266. Harness, D., and E. Sekeles. 1971. The double anasto¬ motic innervation of thenar muscles. J. Anat. (Lond.), 109:461-466. Harris, W. 1939. The Morphology of the Brachial Plexus. Oxford University Press, London, 117 pp. Ip, M. C., and K. S. F. Chang. 1968. A study on the radial supply of the brachialis muscle. Anat. Rec., 162:363371. Jamieson, R. W., and B. J. Anson. 1952. The relation of the median nerve to the heads of origin of the prona¬ tor teres muscle. Quart. Bull. Northwestern Univ. Med. Sch., 26:34-35. Johnson, R. K., and M. M. Shrewsbury. 1970. Anatomical course of the thenar branch of the median nerve— usually in a separate tunnel through the transverse carpal ligament. J. Bone Jt. Surg., 52A:269-273. Kasai, T. 1963. About the N. cutaneous brachii lateralis inferior. Amer. J. Anat., 112:305-309. Keegan, J. J., and F. D. Garrett. 1948. The segmental dis¬ tribution of the cutaneous nerves in the limbs of man. Anat. Rec., 102:407-437. Kerr, A. T. 1918. The brachial plexus of nerves in man, the variations in its formation and branches. Amer. J. Anat., 23:285-395. Latarjet, M., J. H. Neidhart, A. Morrin, and J. M. Autissier. 1967. L’entree du nerf musculo-cutane dans le mus¬ cle coraco-brachial. Comp. Rend. Assn. Anat., 138: 755-765. Linell, E. A. 1921. The distribution of nerves in the upper limb, with reference to variabilities and their clini¬ cal significance. J. Anat. (Lond.), 55:79-112. Linscheid, R. L. 1965. Injuries to the radial nerve at the wrist. Arch. Surg., 91:942-946. Marble, H. C., E. Hamlin, Jr., and A. L. Watkins. 1942. Regeneration in the ulnar, median and radial nerves. Amer. J. Surg., 55:274-294. Miller, M. R., H. J. Ralston, III, and M. Kasahara. 1958. The pattern of cutaneous innervation of the human hand. Amer. J. Anat., 102:183-217. Miller, R. A. 1939. Observations upon the arrangement of the axillary artery and brachial plexus. Amer. J. Anat., 64:143-163. Miller, R. A., and S. R. Detwiler. 1936. Comparative stud¬ ies upon the origin and development of the brachial plexus. Anat. Rec., 65:273-292. Millesi, H., G. Meissl, and A. Berger. 1976. Further expe¬ rience with interfascicular grafting of the median, ulnar and radial nerves. J. Bone Jt. Surg., 58A.209218. Ogden, J. A. 1972. An unusual branch of the median nerve. J. Bone Jt. Surg., 54A.T779-1781. Olson, I. A. 1968. The origin of the lateral cutaneous nerve of forearm and its anaesthesia for modified brachial plexus block. J. Anat. (Lond.), 105:381-382.

1279

Papathanassion, B. T. 1968. A variant of the motor branch of the median nerve in the hand. J. Bone Jt. Surg., 50B: 156-157. Rowntree, T. 1949. Anomalous innervation of the hand muscles. J. Bone Jt. Surg., 31B.505-510. Singer, E. 1933. Human brachial plexus united into a sin¬ gle cord: Description and interpretation. Anat. Rec., 55:411-419. Spinner, M. 1970. The anterior interosseous nerve syn¬ drome with special attention to its variations. J. Bone Jt. Surg., 52A.84-94. Stilwell, D. L., Jr. 1957. The innervation of deep struc¬ tures of the hand. Amer. J. Anat., 101:75-99. Sunderland, S. 1945. The innervation of the flexor digitorum profundus and lumbrical muscles. Anat. Rec., 93:317-321. Sunderland, S. 1945. The intraneural topography of the radial, median and ulnar nerves. Brain, 68:243-299. Sunderland, S. 1946. The innervation of the first dorsal interosseous muscle of the hand. Anat. Rec., 95:7-10. Sunderland, S. 1948. The distribution of sympathetic fi¬ bres in the brachial plexus in man. Brain, 71:88-102. Sunderland, S., and G. M. Bedbrook. 1949. The relative sympathetic contribution to individual roots of the brachial plexus in man. Brain, 72:297-301. Taleisnik, J. 1973. The palmar cutaneous branch of the median nerve and the approach to the carpal tunnel. An anatomical study. J. Bone ft. Surg., 55A.T2121217. Tracey, J. F., and E. W. Brannon. 1958. Management of brachial plexus injuries (traction type). J. Bone Jt. Surg., 40A.T031-1042. Wallace, W. A., and R. E. Coupland. 1975. Variations in the nerves of the thumb and index finger. J. Bone Jt. Surg., 576:491-494. Wallace, W. A., and P. A. M. Weston. 1974. The arrange¬ ment of the digital nerves within the human thumb and index fingers. J. Anat. (Lond.), 118:381-382. Wood, V. E., and G. K. Frykman. 1978. Unusual branch¬ ing of the median nerve at the wrist. A case report. J. Bone Jt. Surg., 60A:267-268.

C. Lumbosacral Plexus and Nerves of Lower Limb Beaton, L. E., and B. J. Anson. 1937. The relation of the sciatic nerve and of its subdivisions to the piri¬ formis muscle. Anat. Rec., 70:1-5. Beaton, L. E., and B. J. Anson. 1938. The sciatic nerve and the piriformis muscle: their interrelation a possible cause of coccygodynia. J. Bone Jt. Surg., 20:686-688. Bordeen, C. R., and A. W. Elting. 1901. A statistical study of the variations in the formation and position of the lumbo-sacral plexus in man. Anat. Anz., 19:124135 and 209-238. Champetier, J., and C. Descours. 1968. The branches of the posterior tibial nerve in the tibiotarsal joint. Comp. Rend. Assn. Anat., 141:677-685. Coggeshall, R. C., J. D. Coulter, and W. D. Willis, Jr. 1974. Unmyelinated axons in the ventral roots of the cat lumbosacral enlargement. J. Comp. Neurol., 153:39-58. Davies, F. 1935. A note on the first lumbar nerve. J. Anat. (Lond.), 70:177-178. Day, M. H. 1964. The blood supply of the lumbar and sacral plexuses in the human foetus. J. Anat. (Lond.), 98:105-116. Dempsher, J., and J. M. Sprague. 1948. A study of the distribution of sensory and motor fibers in the lum-

1 280

THE PERIPHERAL NERVOUS SYSTEM

bosacral plexus and in the thoracic nerves of the cat. Anat. Rec., 102:195-204. Gardner, E. 1944. The distribution and termination of nerves in the knee joint of the cat. J. Comp. Neurol., 80:11-32. Gardner, E. 1948. The innervation of the knee joint. Anat.

Rec., 101:109-130. Gardner, E. 1948. The innervation of the hip joint. Anat. Rec., 101:353-371. Gardner, E., and D. Gray. 1968. The innervation of the joints of the foot. Anat. Rec., 161:141-148. Garnjobst, W. 1964. Injuries to the saphenous nerve fol¬ lowing operations for varicose veins. Surg. Gynecol. Obstet., 119:359-361. Gutrecht, J. A., and P. J. Dyck. 1970. Quantitative teased-fiber and histologic studies of human sural nerve during postnatal development. }. Comp. Neurol., 138:117-130. Harrison, V. F., and O. A. Mortensen. 1962. Identification and voluntary control of single motor unit activity in the tibialis anterior muscle. Anat. Rec., 144:109116. Horwitz, M. T. 1939. The anatomy of the lumbosacral nerve plexus—its relation to variations of vertebral segmentation and the posterior sacral nerve plexus. Anat. Rec., 74:91-107. Huelke, D. F. 1957. A study of the formation of the sural nerve in adult man. Amer. j. Phys. Anthrop., 15: 137-147. Huelke, D. F. 1958. The origin of the peroneal communi¬ cating nerve in adult man. Anat. Rec., 132:81-92. Ip, M. C., G. Vrbova, and D. R. Westbury. 1977. The sen¬ sory reinnervation of hind limb muscles of the cat following denervation and de-efferentation. Neuro¬ science, 2:423-434. Jamieson, R. W„ L. L. Swigart, and B. J. Anson. 1952. Points of parietal perforation of the ilioinguinal and iliohypogastric nerves in relation to optimal sites for local anesthesia. Quart. Bull. Northwest. Univ. Med. Sch., 26:22-26. Kaiser, R. A. 1949. Obturator neurectomy for coxalgia. An anatomical study of the obturator and the acces¬ sory obturator nerve. J. Bone Jt. Surg., 31A.-815-819. Keegan, J. J. 1947. Relations of nerve roots to abnormali¬

ties of lumbar and cervical portions of the spine. Arch. Surg., 55:246-270. Miller, M. R., and M. Kasahara. 1959. The pattern of cu¬ taneous innervation of the human foot. Amer. J. Anat., 105:233-255. Ochoa, J. 1971. The sural nerve of the human fetus: elec¬ tron microscope observations and count of axons. J. Anat. (Lond.), 108:231-245. Ochoa, J., and W. E. P. Mair. 1969. The normal sural nerve in man. I. Ultrastructure and numbers of fi¬ bres and cells. Acta Neuropathol., 13:197-216. Oelrich, T. M., and D. A. Moosman. 1977. The aberrant course of the cutaneous component of the ilioingui¬ nal nerve. Anat. Rec., 189:233-236. Roberts, W. H. B., and W. H. Taylor. 1973. Inferior rectal nerve variations as it relates to pudendal block. Anat. Rec., 177:461-464. Stilwell, D. L., Jr. 1957. The innervation of deep struc¬ tures of the human foot. Amer. J. Anat., 101:59-73. Sunderland, S. 1948. The intraneural topography of the sciatic nerve and its popliteal divisions in man. Brain, 71:242-273. Sunderland. S., and E. S. R. Hughes. 1946. Metrical and non-metrical features of the muscular branches of

the sciatic nerve and its medial and lateral popliteal divisions. J. Comp. Neurol., 85:205-222. Trotter, M. 1932. The relation of the sciatic nerve to the piriformis muscle. Anat. Rec., 52:321-323. Ueyama, T. 1978. The topography of root fibres within the sciatic nerve trunk of the dog. J. Anat. (Lond.), 127:277-290. Wertheimer, L. G. 1952. The sensory nerves of the hip joint. J. Bone Jt. Surg., 34A:477-487. Wilson, A. S„ P. G. Legg, and J. C. McNeur. 1969. Studies on the innervation of the medial meniscus in the human knee joint. Anat. Rec., 165:485-491. Woodburne, R. T. 1960. The accessory obturator nerve and the innervation of the pectineus muscle. Anat. Rec., 136:367-369.

D. Visceral Afferent and Autonomic Nerves (Sympathetic and Sacral Parasympathetic) Aim, P., J. Alumets, E. Brodin, R. Hakanson, G. Nilsson, N.-O. Sjoberg, and F. Sundler. 1978. Peptidergic (substance P) nerves in the genito-urinary tract. Neuroscience, 3:419-426. Aim, P„ J. Alumets, R. Hakanson, and F. Sundler. 1977. Peptidergic (vasoactive intestinal peptide) nerves in the genito-urinary tract. Neuroscience, 2:751-754. Ashley, F. L., and B. J. Anson. 1946. The pelvic autonomic nerves in the male. Surg. Gynecol. Obstet., 82:598608. Axford, M. 1928. Some observations on the cervical sym¬ pathetic ganglia. J. Anat. (Lond.), 62:301-318. Barlow, C. M., and W. S. Root. 1949. The ocular sympa¬ thetic path between the superior cervical ganglion and the orbit in the cat. J. Comp. Neurol., 91:195-208. Becker, R. F., and J. A. Grunt. 1957. The cervical sympa¬ thetic ganglia. Anat. Rec., 127:1-14. Bojsen-Miller, F., and J. Tranum-Jensen. 1969. On nerves and nerve endings in the conducting system of the moderator band (septomarginal trabecula). J. Anat. (Lond.), 108:387-395. Chiba, T. 1978. Monoamine fluorescence and electron microscopic studies on small intensely fluorescent (granule-containing) cells in human sympathetic ganglia. J. Comp. Neurol., 179:153-168. Christensen, K., E. Lewis, and A. Kuntz. 1951. Innerva¬ tion of the renal blood vessels in the cat. J. Comp. Neurol., 95:373-385. Christensen, K., E. H. Polley, and E. Lewis. 1952. The nerves along the vertebral artery and innervation of the blood vessels of the hindbrain of the cat. J. Comp. Neurol., 96:71-91. Cleveland, D. A. 1932. Afferent fibers in the cervical sym¬ pathetic trunk, superior cervical ganglion and inter¬ nal carotid nerve. J. Comp. Neurol., 54:35-43. Coggeshall, R. E., and S. L. Galbraith. 1978. Categories of axons in mammalian rami communicantes, Part II. J. Comp. Neurol., 181:349-360. Coggeshall, R. E., M. B. Hancock, and M. L. Applebaum. 1976. Categories of axons in mammalian rami com¬ municantes. J. Comp. Neurol., 167:105-124. Curtis, A. H., B. J. Anson, F. L. Ashley, and T. Jones. 1942. The anatomy of the pelvic autonomic nerves in rela¬ tion to gynecology. Surg. Gynecol. Obstet., 75:743750. Dass, R. 1952. Sympathetic components of the dorsal pri¬ mary divisions of human spinal nerves. Anat. Rec., 113:493-501. Ebbesson, S. O. E. 1963. A quantitative study of human

REFERENCES

superior cervical sympathetic ganglia. Anat. Rec., 146:353-356. Edwards, E. A. 1951. Operative anatomy of the lumbar sympathetic chain. Angiology, 2:184-198. Edwards, L. F., and R. C. Baker. 1940. Variations in the formation of the splanchnic nerves in man. Anat. Rec., 77:335-342. Ehrlich, E., Jr., and W. F. Alexander. 1951. Surgical impli¬ cations of upper thoracic independent sympathetic pathways. Arch. Surg., 62:609-614. Elftman, A. G. 1943. The afferent and parasympathetic innervation of the lungs and trachea of the dog. Amer. J. Anat., 72:1-27. Ellison, J. P., and T. H. Williams. 1969. Sympathetic nerve pathways to the human heart and their varia¬ tions. Amer. J. Anat., 124:149-162. Foley, J. O., and H. N. Schnitzlein. 1957. The contribution of individual thoracic spinal nerves to the upper cervical sympathetic trunk. J. Comp. Neurol., 108: 109-120. Forbes, H. S., and S. Cobb. 1938. Vasomotor control of cerebral vessels. Brain, 61:221-233. Gardner, E. 1943. Surgical anatomy of the external ca¬ rotid plexus. Arch. Surg., 46:238-244. Gardner, E., and R. O’Rahilly. 1976. The nerve supply and conducting system of the human heart at the end of the embryonic period proper. J. Anat. (Lond.), 121:571-587. Gernandt, B., and Y. Zotterman. 1946. The splanchnic efferent outflow of impulses in the light of ergotamine action. Acta Physiol. Scand., 11:301-317. Gray, D. J. 1947. The intrinsic nerves in the testis. Anat. Rec., 98:325-335. Harris, A. J. 1943. An experimental analysis of the infe¬ rior mesenteric plexus. J. Comp. Neurol., 79:1-17. Hinsey, J. C., K. Hare, and G. A. Wolf. 1942. Structure of the cervical sympathetic chain in the cat. Anat. Rec., 82:175-183. Jamieson, R. W., D. B. Smith, and B. J. Anson. 1952. The cervical sympathetic ganglia. Quart. Bull. North¬ west. Univ. Med. Sch., 26:219-227. Jonnesco, T. 1923. Le Sympathjque Cervico-thoracique. Masson, Paris, 91 pp. Kirgis, H. D., and A. Kuntz. 1942. Inconstant sympathetic neural pathways; their relation to sympathetic de¬ nervation of upper extremity. Arch. Surg., 44:95-102. Kisner, W. H., and H. Mahorner. 1952. An evaluation of lumbar sympathectomy. Amer. Surg., 18:30-35. Kuntz, A. 1953. The Autonomic Nervous System. 4th ed. Lea & Febiger, Philadelphia, 605 pp. Kuntz, A., and W. F. Alexander. 1950. Surgical implica¬ tions of lower thoracic and lumbar independent sympathetic pathways. Arch. Surg., 61:1007-1018. Kuntz, A., H. H. Hoffman, and E. M. Schaeffer. 1957. Fiber components of the splanchnic nerves. Anat. Rec., 128:139-146. Kuntz, A., and A. Morehouse. 1930. Thoracic sympa¬ thetic cardiac nerves in man. Their relation to cer¬ vical sympathetic ganglionectomy. Arch. Surg., 20:607-613. Kuntz, A., and R. E. Morris, Jr. 1946. Components and distribution of the spermatic nerves and the nerves of the vas deferens. J. Comp. Neurol., 85:33-44. Langworthy, O. R. 1965. Commissures of autonomic fi¬ bers in the pelvic organs of rats. Anat. Rec., 151: 583-587. Lannon, J., and E. Weller. 1947. The parasympathetic supply of the distal colon. Brit. J. Surg., 34:373-378.

1281

Larsell, O., and R. A. Fenton. 1936. Sympathetic innerva¬ tion of the nose: Research report. Arch. Otolaryn¬ gol., 24:687-695. Lever, J. D. 1976. Studies on sympathetic ganglia. J. Anat. (Lond.), 121:430-431. Mitchell, G. A. G. 1938. The innervation of the ovary, uterine tube, testis and epididymis. [. Anat. (Lond.), 72:508-517. Mitchell, G. A. G. 1951. The intrinsic renal nerves. Acta Anat., 13:1-15. Mitchell, G. A. G. 1953. Anatomy of the Autonomic Nervous System. Williams & Wilkins Co., Balti¬ more, 356 pp. Mizeres, N. J. 1963. The cardiac plexus in man. Amer. J. Anat., 112:141-151. Mustalish, A. C., and J. Pick. 1964. On the innervation of the blood vessels in the human foot. Anat. Rec., 149:587-590. Nadelhaft, I., W. C. Degroat, and C. Morgan. 1980. Loca¬ tion and morphology of parasympathetic pregangli¬ onic neurons in the sacral spinal cord of the cat re¬ vealed by retrograde axonal transport. J. Comp. Neurol., 193:265-282. Nonidez, J. F. 1939. Studies on the innervation of the heart. I. Distribution of the cardiac nerves, with spe¬ cial reference to the identification of the sympa¬ thetic and parasympathetic postganglionics. Amer. J. Anat., 65:361-413. Nonidez, J. F. 1941. Studies on the innervation of the heart. II. Afferent nerve endings in the large arteries , and veins. Amer. J. Anat., 68:151-189. Pearson, A. A. 1952. The connections of the sympathetic trunk in the cervical and upper thoracic levels in the human fetus. Anat. Rec., 106:231. Pearson, A. A., and A. L. Eckhardt. 1960. Observations on the gray and white rami communicantes in human embryos. Anat. Rec., 138:115-127. Pearson, A. A., and R. W. Sauter. 1970. Nerve contribu¬ tions to the pelvic plexus and the umbilical cord. Amer. J. Anat., 128:485-498. Perlow, S„ and K. L. Vehe. 1935. Variations in the gross anatomy of the stellate and lumbar sympathetic ganglia. Amer. J. Surg., 30:454-458. Pick, J., and D. Sheehan. 1946. Sympathetic rami in man. J. Anat. (Lond.), 80:12-20. Randall, W. C., J. A. Armour, D. C. Randall, and O. A. Smith. 1971. Functional anatomy of the cardiac nerves in the baboon. Anat. Rec., 170:183-198. Ray, B. S., J. C. Hinsey, and W. A. Geohegan. 1943. Ob¬ servations on the distribution of the sympathetic nerves to the pupil and upper extremity as deter¬ mined by stimulation of the anterior roots in man. Ann. Surg., 118:647-655. Reed, A. F. 1951. The origins of the splanchnic nerves. Anat. Rec., 109:341. Richardson, K. C. 1960. Studies on the structure of auto¬ nomic nerves in the small intestine. J. Anat. (Lond.), 94:457-472. Richardson, K. C. 1962. The fine structure of autonomic nerve endings in smooth muscle of the rat vas defer¬ ens. J. Anat. (Lond.), 96:427-442. Rubin, E., and D. Purves. 1980. Segmental organization of sympathetic preganglionic neurons in the mam¬ malian spinal cord. J. Comp. Neurol., 192:163-174. Saccomanno, G. 1943. The components of the upper tho¬ racic sympathetic nerves. J. Comp. Neurol., 79:355378. Shashirina, M. I. 1964. Structural organization of supe-

1 282

THE PERIPHERAL NERVOUS SYSTEM

rior cervical sympathetic ganglion of the cat. Fed. Proc., 23.T711-T714. Shimazawa, A. 1972. Quantitative studies of the deep petrosal nerve of the mouse with the electron micro¬ scope. Anat. Rec., 372:483-488. Smith, R. B. 1971. The occurrence and location of intrin¬ sic cardiac ganglia and nerve plexuses in the human neonate. Anat. Rec., 169:33-40. Southam, J. A. 1959. The inferior mesenteric ganglion. J. Anat. (Lond.), 93:304-308. Stotler, W. A., and R. A. McMahon. 1947. Innervation and structure of conductive system of human heart. J. Comp. Neurol., 87:57-83. Sulkin, N. M., and A. Kuntz. 1950. A histochemical study of the autonomic ganglia of the cat following pro¬ longed preganglionic stimulation. Anat. Rec., 308: 255-277.

Swinyard, C. A. 1937. The innervation of the suprarenal glands. Anat. Rec., 68:417-429. Thompson, S. A., and J. A. Gosling. 1977. Morphological and histochemical observations on human fetal and postnatal pelvic autonomic ganglia. J. Anat. (Lond.), 124:259-260. Trumble, H. C. 1934. The parasympathetic nerve supply to the distal colon. Med. ). Australia, II: 149-151. Webber, R. H. 1958. A contribution on the sympathetic nerves in the lumbar region. Anat. Rec., 330:581-604. Woodburne, R. T. 1956. The sacral parasympathetic in¬ nervation of the colon. Anat. Rec., 324:67-76. Woollard, H. H., and R. E. Norrish. 1933. Anatomy of the peripheral sympathetic nervous system. Brit. J. Surg., 23:83-103. Wrete, M. 1959. The anatomy of the sympathetic trunks in man. J. Anat. (Lond.), 93:448-459.

Endings of the sensory nerves of the pe¬ ripheral nervous system are found in end organs which may be divided into two large groups: (1) the organs of the special senses of smell, taste, sight, and hearing, and (2) the sensory endings of general sensation of heat, cold, touch, pain, pressure, etc. This chapter considers only the organs of the special senses.

for the sense of smell and they are customar¬ ily referred to by clinicians as the upper res¬ piratory tract. The olfactory region is located in the most superior part of both nasal fossae and occu¬ pies the mucous membrane covering the superior nasal concha and the septum oppo¬ site (Fig. 13-1). Thus it is confined to an area of the fossa whose walls are formed by the ethmoid bone. The olfactory sensory endings are the least specialized of the special senses. They are modified epithelial cells liberally scattered within the columnar epithelium of the mu¬ cous membrane. The sensory cells are known as olfactory cells and the other epi¬ thelial cells, as supporting cells. Although the epithelium appears pseudostratified, the supporting cells are not ciliated and there are no goblet cells (Fig. 13-2). The olfactory cells are bipolar, with a small amount of cytoplasm surrounding a large spherical nucleus. The slender periph¬ eral or superficial process extends to the sur¬ face of the epithelial membrane and sends out a tuft of fine processes known as olfac¬ tory hairs. The central or deep process pene¬ trates the basement membrane and in the underlying connective tissue joins neighbor¬ ing processes to form the bundles of unmye¬ linated fibers of the olfactory nerves (Fig. 13-3). Mingled with the nerve bundles in the subepithelial tissue are numerous branched tubular glands of a serous secreting type (glands of Bowman1), which keep the mem¬ brane protected with moisture. The bundles of nerve fibers form a plexus in the submucosa and finally collect into about 20 nerves that pass through the open¬ ings in the cribriform plate of the ethmoid bone as the fila olfactoria. The nerve fibers end by forming synapses with processes of the mitral cells in the glomeruli of the olfac¬ tory bulb (Fig. 13-3; also see page 1050).

Organ of Smell

Organ of Taste

The sensory endings for the sense of smell are located in the nose, and for this reason the entire nose has, by long tradition, been described in this chapter. In this edition, however, all but the olfactory area are de¬ scribed in Chapter 15, the Respiratory Sys¬ tem, because the nose and nasal cavity are more important for the passage of air than

The peripheral taste organs (gustatory or¬ gans) are the taste buds (gustatory caliculi) distributed over the tongue and occasionally on adjacent parts. They are spherical or ovoid nests of cells embedded in the strati'Sir William Bowman (1816-1892): An English anato¬ mist, ophthalmologist, and physiologist (London).

1283

1 284

ORGANS OF THE SPECIAL SENSES

Nasociliary nerve

Posterior superior nasal branches Nasopalatine nerve

Fig. 13-1.

The nerves of the right side of the septum of the nose.

fied squamous epithelium (Fig. 13-4), and are present in large numbers on the sides of the vallate papillae and to a lesser extent on the opposed walls of the fossae around them (Fig. 13-5). They are also found over the sides and back of the tongue, especially on the fungiform papillae (Fig. 16-36). They are plentiful over the lingual fimbria and are occasionally present on the oral surface of the soft palate and on the posterior surface of the epiglottis. Each taste bud occupies an ovoid pocket that extends through the thickness of the

epithelium. It has two openings—one at the surface and the other at the basement mem¬ brane. There are two types of cells within the bud: gustatory cells and supporting cells (Fig. 13-4). The supporting cells are elon¬ gated and extend between the basement membrane and the surface; they form an outer shell for the taste bud, arranged like the staves of a wooden cask. Supporting cells are also scattered through the bud be¬ tween the gustatory cells. The gustatory cells occupy the interior portion of the bud; they are spindle-shaped and have a large round

Epithelium

Nerve bundles

Glands of Bowman bundles

Fig. 13-2.

Section of the olfactory mucous membrane (Cadiat).

ORGAN OF SIGHT THE EYE

Gustatory cell

1285

Supporting cell

13-4. Section through a taste bud. Semidiagrammatic 450 XFig.

central nucleus. At the peripheral end of each gustatory cell protrudes a delicate hair-like process, the gustatory hair, through an opening at the surface, the gustatory pore. The central end of the gustatory cell does not end in an axon, as in the case of the ol¬ factory cell, but remains within the taste bud, where it is in intimate contact with many fine terminations of nerves that pass into the taste bud through an opening in the basement membrane. The nerves are myeli¬ nated until they reach the taste buds but lose their sheaths as they enter the bud. nerves. The posterior third of the tongue, in¬ cluding the taste buds on the vallate papillae, is sup¬ plied by the glossopharyngeal nerve. The fibers for

taste to the anterior two-thirds leave the brain in the nervus intermedius, continue in the chorda tympani, and reach the tongue in the branches of the lingual nerve. It is believed that taste buds on the epiglottis are supplied by the vagus nerve.

Organ of Sight: The Eye The bulb of the eye, or organ of sight, is contained in a bony cavity, the orbit, which is composed of parts of the frontal, maxil¬ lary, zygomatic, sphenoid, ethmoid, lacri¬ mal, and palatine bones. The bulb is embed¬ ded in the orbital fat but separated from it by a thin membranous sac, the fascia bulbi.

Con. pap. Vallate papilla Filif. pap.

Lenticular papilla

Circular furrow

Ling, tonsil Epithel.

Lymph nodule Tonsillar crypt Mucous gland Muscle fibers

Duct of gland WatTut^

13-5. Section of posterior part of dorsum of tongue showing circumvallate papillae and lingual tonsil. (Redrawn from Braus.)

Fig.

1286

ORGANS OF THE SPECIAL SENSES

Associated with it are certain accessory structures—the muscles, fasciae, eyebrows, eyelids, conjunctiva, and lacrimal apparatus.

DEVELOPMENT

The retina and optic nerve develop from the forebrain, the lens, from the overlying ectoderm, and the accessory structures, from the mesenchyme. The eyes begin to develop as a pair of diverticula from the lateral as¬ pects of the forebrain. These diverticula make their appearance before the closure of the anterior end of the neural tube; after clo¬ sure of the tube they are known as the optic vesicles. They project toward the sides of the head, and the peripheral part of each vesicle expands to form a hollow bulb, while the proximal part remains narrow and con¬ stitutes the optic stalk. When the peripheral part of the optic vesicle comes in contact with the overlying ectoderm, the latter thick¬ ens, invaginates, becomes severed from the ectoderm, and forms the lens vesicle. At the same time the optic vesicle partially encir¬ cles the lens vesicle, forming the optic cup. Its two layers are continuous with each other at the cup margin, which ultimately overlaps the front of the lens except for the future aperture of the pupil (Figs. 13-6 to 139). The process of invagination also causes an infolding of the posterior surface of the vesicle and the optic stalk, producing the choroidal fissure (Fig. 13-10). Mesenchyme and the retinal blood vessels (hyaloid artery) grow into the fissure. The fissure closes dur¬ ing the seventh week and the two-layered optic cup and optic stalk become complete. Sometimes the choroidal fissure persists, and when this occurs the choroid and iris in the region of the fissure remain undevel¬ oped, giving rise to the condition known as coloboma of the choroid or iris. retina. The retina is developed from the optic cup. The outer stratum of the cup per¬ sists as a single layer of cells which assume a columnar shape, acquire pigment, and form the pigmented layer of the retina; the pig¬ ment first appears in the cells near the edge of the cup. The cells of the inner stratum proliferate and form a layer of considerable thickness from which the nervous elements and the sustentacular fibers of the retina are developed. In the portion of the cup that overlaps the lens, the inner stratum is not differentiated into nervous elements, but

Fig. 13-6. Brain of 3.9-mm human embryo, 22-23 som¬ ites. C.CR., neural crest of nerves VII and VIII; N.P., neuropore; OT., otic vesicle; RH, rhombencephalon; V.OI., optic vesicle. (Carnegie embryo No. 8943. Bartelmez and Dekeban, Contribution to Embryology, Vol. 37, 1962.

13-7. Brain of 6.7-mm human embryo. C.OP., conus opticus; DEN., diencephalon; L„ lens; MS., mesen¬ cephalon; S.DM., sulcus di-mesencephalicus; V.OP., optic vesicle. (Carnegie Embryo No. 6502. Bartelmez and Dekaban, 1962.

Fig.

ORGAN OF SIGHT: THE EYE

Fig. 13-8. Brain of 7.5-mm human embryo. C.OP., conus opticus; HYP., hypophysis; L.CBL., lamina cerebellaris; L.T., lamina terminalis; V.C., cerebral vesicle; V.IV., fourth ventricle. (Carnegie Embryo No. 6506. Bartelmez and Dekeban, 1962.)

1 287

forms a layer of columnar cells that is ap¬ plied to the pigmented layer; these two strata form the pars ciliaris and pars iridica retinae. The cells of the inner or retinal layer of the optic cup become differentiated into spongioblasts and germinal cells, and the lat¬ ter by their subdivisions give rise to neuro¬ blasts. From the spongioblasts are formed the sustentacular fibers of Muller,1 the outer and inner limiting membranes, and the groundwork of the molecular layers of the retina. The neuroblasts form the ganglionic and nuclear layers. The layer of rods and cones first develops in the central part of the optic cup and from there gradually extends toward the cup margin. All the layers of the retina are completed by the eighth month of fetal life. optic nerve. The optic stalk is converted into the optic nerve by the obliteration of its cavity and the growth of nerve fibers into it. Most of these fibers are centripetal and grow backward into the optic stalk from the nerve cells of the retina, but a few extend in the opposite direction and are derived from nerve cells in the brain. The fibers of the optic nerve receive their myelin sheaths about the tenth week after birth. The optic chiasma is formed by the meeting and par¬ tial decussation of the fibers of the two optic nerves. Behind the chiasma, the fibers grow Heinrich

Muller (1820-1864):

A German

anatomist

(Wurzburg).

Edge of optic cup

Optic stalk

Lens vesicle

Optic (choroidal) fissure

Central artery and vein of the retina (hyaloid vessels)

Fig. 13-9. Optic cup and lens vesicle, 8-mm human embryo. EC, ectoderm; L, lens; NR, neural part of retina; OS, optic stalk; OV, optic vesicle; PR, pigment layer of retina. (Courtesy of Doctor Aeleta Barber.)

Fig. 13-10. The optic cup and lens vesicle in a human embryo during the fifth week. Note the optic fissure and the developing central vessels of the retina (hyaloid ves¬ sels).

1288

ORGANS OF THE SPECIAL SENSES

backward as the optic tracts to the thalamus and midbrain. crystalline lens. The crystalline lens is developed from the lens vesicle, which re¬ cedes within the margin of the cup and be¬ comes separated by mesoderm from the overlying ectoderm. The cells forming the posterior wall of the vesicle lengthen and are converted into the lens fibers, which grow forward and fill the cavity of the vesicle (Fig. 13-11). The cells forming the anterior wall retain their cellular character and form the epithelium on the anterior surface of the adult lens. hyaloid artery. A capillary net continu¬ ous with the primitive choroid net enters the choroid fissure. As the fissure closes, con¬ nections with the choroid net are cut off ex¬ cept at the edge of the cup. The vessel en¬ closed in the optic stalk is the hyaloid artery. Its branches surround the deep surface of the lens and drain into the choroid net at the margin of the cup. As the vitreous body in¬ creases, the hyaloid supplies branches to it. By the second month, the lens is invested by a vascular mesodermal capsule, the capsula vasculosa lentis. The blood vessels supply¬ ing the posterior part of this capsule are de¬ rived from the hyaloid artery; those for the

anterior part, from the anterior ciliary ar¬ teries. The portion of the capsule that covers the front of the lens is named the pupillary membrane. By the sixth month all the ves¬ sels of the capsule have atrophied except the hyaloid artery, which disappears during the ninth month; the position of this artery is indicated in the adult by the hyaloid canal, which extends from the optic disc to the pos¬ terior surface of the lens. With the loss of its blood vessels, the capsula vasculosa lentis disappears, but sometimes the pupillary membrane persists at birth, giving rise to the condition termed congenital atresia of the pupil. CENTRAL ARTERY OF THE RETINA. By the fourth month, branches of the hyaloid artery and veins that have developed during the third month begin to spread out in the retina and reach the ora serrata by the eighth month. After atrophy of the vitreous part of the hyaloid vessels, the proximal part in the optic nerve and retina becomes the central artery of the retina. choroid. The choroid is analogous to the leptomeninges of the brain and spinal cord. It develops from mesenchyme between the sclera (dura) and the optic cup (an extension of the brain wall). The mesenchyme is in-

Rudiment of c Rectus muscle

Optic nerve

Retina Pigmented layer Vitreous body (shrunken)

Cornea Membrana pupillaris Eyelid

Iris Pars ciliaris and pars iridica retinae

Fig. 13-11.

Horizontal section through the eye of an 18-day-old rabbit embryo. 30 X- (Kolliker.)

ORGAN OF SIGHT

vaded by capillaries from the ciliary vessels. They form a rich plexus over the outer sur¬ face of the optic cup and connect with the hyaloid capillary plexus in the pupillary re¬ gion. The mesenchyme forms a loose net¬ work of fibroblasts, pigmented cells, and col¬ lagenous fibrils, partially separated by mesothelial-lined, fluid-containing spaces. canalof schlemm. The canal of Schlemm1 (sinus venosus sclerae) and the circular ves¬ sels of the iris develop from the anterior ex¬ tension of the plexus of the choroid. The former is analogous to a venous sinus of the dura mater; the anterior chamber is analo¬ gous to the subarachnoid spaces. The drain¬ age of aqueous humor by way of the pecti¬ nate villi into the canal of Schlemm is analogous to the drainage of the subarach¬ noid fluid by way of the arachnoid granula¬ tions into the dural sinuses. 1Friedrich S. Schlemm (1795-1858): A German anatomist (Berlin).

Upper eyelid

Pigmented layer of retina

THE EYE

vitreous body. The vitreous body (Fig. 13-12) develops between the lens and the optic cup as the two structures become sepa¬ rated. Some authors believe that initially the retina and perhaps the lens as well play roles in the formation of the vitreous body; others believe that the retina plays the sole role; and still others believe that both retina and invading mesenchyme are involved. Fixed and stained preparations show throughout the vitreous body a delicate network of fi¬ brils continuous with the long processes of stellate mesenchymal cells and with the ret¬ ina. Later the fibrils are limited to the ciliary region, where they are supposed to form the zonula ciliaris. sclera. The sclera (Fig. 13-12) is derived from the mesenchyme surrounding the optic cup. Fibroblasts form a dense layer of col¬ lagenous fibers continuous with the sheath of the optic nerve. The sclera is analogous to the dura mater. cornea. Most of the cornea (Fig. 13-12) is

Mesodermal part of vitreous body

Rudiment of sclera

’1*' « «*"v Vi' ^ \

Mesoderm

Fig. 13-12.

1289

Ectodermal part of vitreous body

Nervous layer of retina

Sagittal section of eye of human embryo of six weeks. (Kollmann/

1 290

ORGANS OF THE SPECIAL SENSES

derived from mesenchyme that invades the region between the lens and ectoderm. The overlying ectoderm becomes the corneal epithelium. The endothelial (mesothelial) layer comes from mesenchymal cells that line the corneal side of the cleft (anterior chamber), which develops between the cor¬ nea and pupillary membrane. The factors responsible for the transparency of the cor¬ nea are unknown. anterior chamber. The anterior cham¬ ber of the eye appears as a cleft in the meso¬ derm separating the lens from the overlying ectoderm. The layer of mesoderm anterior to the cleft forms the substantia propria of the cornea, that posterior to the cleft forms the stroma of the iris and the pupillary mem¬ brane. pupillary membrane. In the fetus, the pupil is closed by a delicate vascular mem¬ brane, the pupillary membrane, which di¬ vides the space in which the iris is sus¬ pended into two distinct chambers. The vessels of this membrane are derived partly from those of the capsule of the margin of the iris and partly from those of the capsule of the lens; they have a looped arrangement and converge toward each other without anastomosing. About the sixth month, the membrane begins to disappear by absorp¬ tion from the center toward the circumfer¬ ence, and at birth only a few fragments are present; in exceptional cases it persists. The fibers of the ciliary muscle are de¬ rived from the mesoderm, but those of the sphincter and dilatator pupillary muscles are of ectodermal origin, being developed from the cells of the pupillary part of the optic cup. eyelids. The eyelids are formed as small cutaneous folds (Figs. 13-11; 13-12) which, about the middle of the third month, come together and unite in front of the cornea. They remain united until about the end of the sixth month. lacrimal apparatus. The lacrimal sac and nasolacrimal duct develop from a thicken¬ ing of the ectoderm in the groove known as the nasooptic furrow, between the lateral nasal and maxillary processes. This thicken¬ ing forms a solid cord of cells that sinks into the mesoderm; during the third month the central cells of the cord break down, and a lumen, the nasolacrimal duct, is established. The lacrimal ducts arise as buds from the upper part of the cord of cells and secondar¬

ily establish openings (puneta lacrimalia) on the margins of the lids. The epithelium of the cornea and conjunctiva, and that which lines the ducts and alveoli of the lacrimal gland, is of ectodermal origin, as are also the eyelashes and the lining cells of the glands that open on the lid margins.

BULB OF THE EYE

The bulb of the eye is composed of seg¬ ments of two spheres of different sizes. The transparent anterior segment, the cornea, is from a small sphere and forms about onesixth of the bulb. The opaque posterior seg¬ ment is from a larger sphere and forms about five-sixths of the bulb. The term anterior pole is applied to the central point of the an¬ terior curvature of the bulb, and posterior pole, to the central point of its posterior cur¬ vature; a line joining the two poles forms the optic axis. The axes of the two bulbs are nearly parallel, and therefore do not corre¬ spond to the axes of the orbits, which di¬ verge lateralward. The optic nerves follow the direction of the axes of the orbits and therefore are not parallel; each leaves its eyeball 3 mm to the nasal side and a little below the level of the posterior pole. The transverse and anteroposterior diameters of the bulb are somewhat greater than its verti¬ cal diameter; the former amounts to about 24 mm and the latter, to about 23.5 mm. In the female, all three diameters are rather less than those in the male. The anteroposterior diameter at birth is about 17.5 mm, and at puberty, 20 to 21 mm.

Tunics of the Eye The bulb is composed of three tunics: (1) an outer fibrous tunic, consisting of the sclera posteriorly and the cornea anteriorly; (2) an intermediate vascular, pigmented tunic, comprising the choroid, ciliary body, and iris; and (3) an internal neural tunic, the retina (Fig. 13-13).

FIBROUS TUNIC

The sclera is opaque, and constitutes the posterior five-sixths of the tunic; the cornea is transparent, and forms the anterior sixth (Fig. 13-13).

ORGAN OF SIGHT

THE EYE

1291

Sinus venosus sclerae

Sulcus sclerae Posterior chamber

Ciliary body

Conjunctiva

Zonular spaces

Hyaloid canal

Rectus lateralis

Rectus medialis

Sclera Choroid Retina

Central retinal artery Fovea centralis

Optic nerve

Nerve sheath Fig. 13-13.

Horizontal section of the eyeball.

sclera. The sclera received its name from its density and hardness; it is a tough, inelastic membrane that maintains the size and form of the bulb. Its thicker posterior part measures 1 mm. Its external surface is white and smooth, except at the points at which the recti and obliqui muscles are inserted. Its anterior part is covered by the conjunctival membrane; the rest of the sur¬ face is separated from the fascia bulbi (cap¬ sule of Tenon1) by the loose connective tis¬ sue of a fascial cleft (see p. 1307), which permits rotation of the eyeball within the fascia. Its inner surface is brown and marked by grooves, in which the ciliary nerves and ves¬ sels are lodged; it is loosely attached to the pigmented suprachoroid lamina of the cho¬ roid. Posteriorly it is pierced by the optic nerve, and is continuous through the fibrous sheath of this nerve with the dura mater. The optic nerve passes through the lamina cribrosa sclerae (Fig. 13-14), in which minute orifices transmit the neural filaments, and the fibrous septa dividing them from one

another are continuous with those that sepa¬ rate the bundles of nerve fibers. One of these openings, larger than the rest and occupying the center of the lamina, transmits the cen¬ tral artery and vein of the retina. Around the exit of the optic nerve are numerous small apertures for the transmission of the ciliary vessels and nerves, and about midway be¬ tween the cribrosa and the sclerocorneal junction are four or five large apertures from the transmission of the vorticose veins. The sclera is directly continuous with the cornea anteriorly, the line of union being termed the sclerocorneal junction. Near the junction, the inner surface of the sclera pro¬ jects into a circular ridge called the scleral spur, to which the ciliary muscle and the iris are attached. Anterior to this ridge is a cir¬ cular depression, the scleral sulcus, which is crossed by trabecular tissue that separates the angle of the anterior chamber from the canal of Schlemm. The spaces of the trabec¬ ular tissue (spaces of Fontana2) connect on one side with the anterior chamber of the eye and on the other with the pectinate villi.

’Jacques Rene Tenon (1724-1816): A French surgeon and pathologist (Paris).

2Felice Fontana (1720-1805): An Italian physiologist and philosopher (Pisa and Florence).

1292

ORGANS OF THE SPECIAL SENSES Lamina cribrosa

Discus nervi optici

Retina Choroid

Sclera

Posterior short ciliary artery and vein Pial sheath Arachnoid sheath Dural sheath Intervaginal spaces Bundles of optic nerve

Fig. 13-14.

Central artery and vein of retina

The terminal portion of the optic nerve as it traverses the lamina cribrosa of the sclera.

The aqueous humor filters through the walls of the villi into the canal of Schlemm. cornea. The cornea, the transparent part of the external tunic, is almost circular in outline, occasionally a little broader in the tranverse than in the vertical direction. It is convex anteriorly and projects like a dome beyond the sclera. Its degree of curvature varies in different individuals, and in the same individual at different periods of life, being more pronounced in youth than in advanced life. The cornea is dense and of uniform thickness throughout; its posterior circumference is perfectly circular in out¬ line, and exceeds the anterior slightly in di¬ ameter. Immediately anterior to the sclerocorneal junction the cornea bulges inward as a thickened rim.

vascular membrane, dark brown or choco¬ late-colored, investing the posterior fivesixths of the bulb; it is pierced posteriorly by the optic nerve, and in this location is firmly adherent to the sclera. Its outer surface is loosely connected by the lamina suprachoroidea with the sclera; its inner surface is at¬ tached to the pigmented layer of the retina. ciliary body. The ciliary body extends from the ora serrata of the retina to the outer edge of the iris and the sclerocorneal junc¬ tion. It consists of the thickened vascular tunic of the eye and the ciliary muscle. Its

VASCULAR TUNIC

The vascular tunic (uvea) (Figs. 13-15; 1316; 13-17) of the eye is composed of the cho¬ roid, the ciliary body, and the iris. The choroid invests the posterior fivesixths of the bulb and extends as far anteri¬ orly as the ora serrata of the retina. The ciliary body connects the choroid to the circumference of the iris. The iris is a circular diaphragm behind the cornea and presents near its center a rounded aperture, the pupil. choroid. The choroid is a thin, highly

Fig. 13-15. The arteries of the choroid and iris. The greater part of the sclera has been removed. (Enlarged.)

ORGAN OF SIGHT THE EYE

Fig. 13-16.

The veins of the choroid. (Enlarged.)

inner surface is covered by the thin, pig¬ mented ciliary part of the retina. The sus¬ pensory ligament of the lens is attached to the ciliary body. The ciliary body comprises two zones, the orbiculus ciliaris and the cili¬ ary processes (Fig. 13-18). The orbiculus ciliaris is 4 mm wide and extends from the ora serrata to the ciliary processes. Its thickness increases as it ap¬ proaches the ciliary processes owing to the

1293

increase in thickness of the ciliary muscle. The choroid layer is thicker here than over the optical part of the retina. Its inner sur¬ face presents numerous small, radially ar¬ ranged ridges, the ciliary processes. The ciliary processes are formed by the inward folding of the various layers of the choroid, i.e., the choroid proper and the lam¬ ina basalis; the layers are received between corresponding foldings of the suspensory ligament of the lens. The ciliary processes are arranged radially on the posterior sur¬ face of the iris, forming a sort of frill around the margin of the lens (Fig. 13-18). Their numbers vary from 60 to 80; the larger ones are about 2.5 mm long, and the smaller ones, consisting of about one-third of the entire number, are situated in spaces between the larger processes, but with no regular ar¬ rangement. They are attached by their pe¬ riphery to three or four ridges of the orbic¬ ulus ciliaris and are continuous with the layers of the choroid. Their other extremities are free and rounded, and are directed to¬ ward the circumference of the lens. Anteri¬ orly, they are continuous with the periphery of the iris. Their posterior surfaces are con¬ nected with the suspensory ligament of the lens. The ciliaris muscle (ciliary muscle) con¬ sists of unstriated fibers. It forms a grayish, semitransparent, circular band, about 3 mm broad, on the outer surface of the anterior part of the choroid. It is thickest anteriorly and consists of two sets of fibers, meridional

Retina Choroid Sclera

Orbiculus ciliaris Ciliary process Pars ciliaris retinae Ora serrata

Fig. 13-17.

The choroid and iris. (Enlarged.)

Fig. 13-18.

Interior of anterior half of bulb of eye.

1 294

ORGANS OF THE SPECIAL SENSES

and circular. The meridional fibers, much more numerous than the circular fibers, arise from the posterior margin of the scleral spur; they run posteriorly and are attached to the ciliary processes and orbiculus ciliaris. The circular fibers are internal to the meridional ones, and in a meridional section they ap¬ pear as a triangular zone behind the filtra¬ tion angle and close to the circumference of the iris. They are well developed in hyper¬ metropic eyes, but are rudimentary or ab¬ sent in myopic eyes. The ciliaris muscle is the chief agent in accommodation, i.e., in adjusting the eye to the vision of near ob¬ jects. When it contracts, it draws the ciliary processes centripetally, relaxes the suspen¬ sory ligament of the lens, and thus allows the lens to become more convex. iris. The iris has received its name from its various colors in different individuals. It is a circular, contractile disc suspended in the aqueous humor between the cornea and lens; it is perforated a little to the nasal side of its center by a circular aperture, the pupil. At its periphery it is continuous with the cil¬ iary body, and it is also connected with the posterior elastic lamina of the cornea by means of the pectinate ligament. Its flat sur¬ faces are anterior, toward the cornea, and posterior, toward the ciliary processes and lens. The iris divides the space between the lens and the cornea into an anterior and a posterior chamber. The anterior chamber of the eye is bound anteriorly by the posterior surface of the cornea and posteriorly by the iris and the central part of the lens. The pos¬ terior chamber is a narrow cleft posterior to the peripheral part of the iris and anterior to the suspensory ligament of the lens and the ciliary processes (Fig. 13-13). In the adult, the two chambers communicate through the pupil, but in the fetus, until the seventh month, they are separated by the pupillary membrane (p. 1288). INTERNAL TUNIC

The internal tunic is a continuous mem¬ brane, but has a posterior nervous part, the retina proper, and an anterior non-neural part, the pars ciliaris and pars iridica retinae. retina. The retina is a delicate neural membrane upon which the images of exter¬ nal objects are received. Its outer surface is in contact with the choroid; its inner surface,

with the vitreous body. Posteriorly, it is con¬ tinuous with the optic nerve. It gradually diminishes in thickness anteriorly and ex¬ tends nearly as far as the ciliary body, where it appears to end in a jagged margin, the ora serrata. Here the neural tissue of the ret¬ ina ends, but a thin prolongation of the mem¬ brane extends anteriorly over the back of the ciliary processes and iris, forming the pars ciliaris retinae and pars iridica retinae already referred to. This forward prolonga¬ tion consists of the pigmented layer of the retina together with a stratum of columnar epithelium. The retina is soft and semitrans¬ parent. It has a purple tint in the fresh state, owing to the presence of a coloring material named rhodopsin or visual purple, but it soon becomes clouded, opaque, and bleached when exposed to sunlight. Exactly in the center of the posterior part of the retina, cor¬ responding to the optical axis of the eye and at a point in which the sense of vision is most perfect, is an oval yellowish area, the macula; in the macula is a central depres¬ sion, the fovea centralis (Fig. 13-18). At the fovea centralis the retina is exceedingly thin, and the dark color of the choroid is dis¬ tinctly seen through it. About 3 mm to the nasal side of the macula is the optic disc, which marks the exit of the optic nerve. A depression in the center of the disc, the porus opticus, marks the point of entrance of the central retinal artery. The disc is the only part of the surface of the retina that is insensitive to light, and it is termed the blind spot (Fig. 13-19).

Structure of the Tunics of the Bulb STRUCTURE OF THE SCLERA

The sclera is formed of bundles and lami¬ nae of collagenous fibers intermixed with fine elastic fibers, fibroblasts, and other con¬ nective tissue cells. Its vessels are not nu¬ merous, the capillaries being small and unit¬ ing at long and wide intervals. Its nerves are derived from the ciliary nerves. STRUCTURE OF THE CORNEA

The cornea consists of five layers: (1) the corneal epithelium, continuous with that of the conjunctiva; (2) the anterior lamina; (3) the substantia propria; (4) the posterior lam-

ORGAN OF SIGHT: THE EYE

1295

Macula _

Fovea centralis Optic disc

Interior of posterior half of right eye as viewed through an ophthalmoscope. The distribution of central vessels of the retina is shown (veins darker than arteries) and their relation to the optic disc. The area of most acute vision, the macula, is shown. (Eycleshymer and Jones.) Fig. 13-19.

ina; and (5) the endothelium (mesothelium) of the anterior chamber (Fig. 13-20). The corneal epithelium (anterior layer) covers the front of the cornea and consists of several layers of cells. The cells of the deep¬ est layer are columnar; then follow two or three layers of polyhedral cells, the majority of which are prickle cells similar to those found in the stratum mucosum of the cuticle. Lastly, there are three or four layers of squa¬ mous cells, with flat nuclei. The anterior lamina (anterior limiting layer; Bowman’s membrane) consists of closely interwoven fibrils, similar to those found in the substantia propria but contain¬ ing no corneal corpuscles. It may be re¬ garded as a condensed part of the substantia propria. The substantia propria corneae is fibrous, tough, unyielding, and perfectly transparent. It is composed of about 60 flat superimposed lamellae made up of bundles of modified connective tissue, the fibers of which are di¬ rectly continuous with those of the sclera. The fibers of each lamella are for the most part parallel with one another, but at right

angles to those of adjacent lamellae, and fre¬ quently pass from one lamella to the next. The lamellae are held together by an inter¬ stitial cement substance, except for the cor¬ neal spaces which contain the corneal cor¬ puscles, modified fibroblasts resembling the space in form, but not entirely filling them. The posterior elastic lamina (membrane of Descemet1; membrane of Demours2) cov¬ ers the posterior surface of the substantia propria. It is an elastic, transparent, homoge¬ neous membrane of extreme thinness, which is not rendered opaque by either water, alco¬ hol, or acids. When stripped from the sub¬ stantia propria it curls up, or rolls upon itself with the attached surface innermost. At the margin of the cornea, the posterior elastic lamina breaks up into fibers that form the trabecular tissue already described. Some of the fibers of this trabecular tissue are continued into the substance of the iris, 1Jean Descemet (1732-1810): A French anatomist and surgeon (Paris). 2Pierre Demours (1702-1795): A French ophthalmologist (Paris).

1296

ORGANS OF THE SPECIAL SENSES vessels and nerves. The cornea is a nonvascular structure. The capillary vessels, which end in loops at its circumference, are derived from the an¬ terior ciliary arteries. Lymphatic vessels have not yet been demonstrated in it, but are represented by the channels in which the bundles of nerves run; these channels are lined by an endothelium. The nerves are numerous and are derived from the ciliary nerves. Around the periphery of the cor¬ nea they form an annular plexus, from which fibers enter the substantia propria. They lose their myelin sheaths and ramify throughout its substance in a delicate network, and their terminal filaments form a firm and close plexus on the surface of the cornea proper, beneath the epithelium. This is termed the subepithelialplexus, and from it fibrils are given off that ramify between the epithelial cells, forming an intraepithelial plexus.

STRUCTURE OF THE CHOROID

Vertical section of human cornea from near the margin. (Waldeyer.) Magnified. 1. Epithelium. 2. An¬ terior lamina. 3. Substantia propria. 4. Posterior elastic lamina. 5. Endothelium of the anterior chamber, a, Oblique fibers in the anterior layer of the substantia pro¬ pria. b, Lamellae, the fibers of which are cut across, pro¬ ducing a dotted appearance, c, Corneal corpuscles ap¬ pearing fusiform in section, d, Lamellae, the fibers of which are cut longitudinally, e, Transition to the sclera, with more distinct fibrillation, and surmounted by a thicker epithelium, f, Small blood vessels cut across near the margin of the cornea. Fig. 13-20.

forming the pectinate ligament of the iris, while others are connected with the forepart of the sclera and choroid. The endothelium of the anterior chamber (posterior layer; corneal endothelium) is a mesothelial, rather than an endothelial, layer that covers the posterior surface of the elastic lamina. It is reflected onto the front of the iris, and also lines the spaces of the angle of the iris. It consists of a single stratum of polygonal, flattened, nucleated cells.

The choroid consists mainly of a dense capillary plexus and of small arteries and veins that carry blood to and from this plexus. On its external surface is a thin mem¬ brane, the lamina suprachoroidea, composed of delicate nonvascular lamellae—each la¬ mella consisting of a network of fine elastic fibers, among which are branched pigment cells. The potential spaces between the la¬ mellae are lined by mesothelium and open freely into the perichoroidal space. Internal to this lamina is the choroid proper, consisting of two layers: an outer layer, composed of small arteries and veins with pigment cells interspersed between them; and an inner layer, consisting of a cap¬ illary plexus. The outer layer (lamina vasculosa) con¬ sists partly of the larger branches of the short ciliary arteries that run between the veins before they bend inward to end in the capillaries, but primarily this layer is formed of veins, named the venae vorticosae from their arrangement (Figs. 13-16; 13-17). The veins converge to four or five equidistant trunks, which pierce the sclera midway be¬ tween the sclerocorneal junction and the exit of the optic nerve. Interspersed between the vessels are dark, star-shaped pigment cells, the processes of which, communicat¬ ing with those of neighboring cells, form a delicate network or stroma, which loses its pigmented character toward the inner sur¬ face of the choroid. The inner layer (lamina choriocapillaris) consists of an exceedingly fine capillary

ORGAN OF SIGHT

plexus formed by the short ciliary vessels; the network is closer and finer in the poste¬ rior than in the anterior part of the choroid. About 1.25 cm behind the cornea, the meshes of the plexus become larger and are continuous with those of the ciliary proc¬ esses. These two laminae are connected by a stratum intermedium, which consists of fine elastic fibers. On the inner surface of the lamina choriocapillaris is a thin, structure¬ less, or faintly fibrous membrane called the lamina basalis; it is closely connected with the stroma of the choroid and separates it from the pigmented layer of the retina. One of the functions of the choroid is to provide nutrition for the retina and to con¬ vey vessels and nerves to the ciliary body and iris. tapetum. This name is applied to the outer and posterior part of the choroid, which in many animals has an iridescent appearance. STRUCTURE OF THE CILIARY PROCESSES

The structure of the ciliary processes (Fig. 13-18) is similar to that of the choroid, but the vessels are larger and have chiefly a lon¬ gitudinal direction. Their posterior surfaces are covered by a bilaminar layer of black pigment cells, which is continued anteriorly from the retina and is named the pars ciliaris retinae. In the stroma of the ciliary processes are also stellate pigment cells, but these are not as numerous as in the choroid itself. STRUCTURE OF THE IRIS

The iris is composed of the following structures: 1. A layer of flat mesothelial cells is placed on a delicate hyaline basement mem¬ brane on the anterior surface. This layer is continuous with the mesothelium covering the posterior elastic lamina of the cornea, and in individuals with dark-colored irises, the cells contain pigment granules. 2. The stroma of the iris consists of fibers and cells. The former are made up of deli¬ cate collagenous bundles. A few fibers at the circumference of the iris have a circular di¬ rection, but the majority radiate toward the pupil, forming delicate meshes in which the vessels and nerves are contained. Inter¬ spersed between the bundles of connective tissue are numerous branched cells with fine

THE EYE

1297

processes. In dark eyes, many of these cells contain pigment granules, but in blue eyes and the eyes of albinos, they are unpigmented. 3. The muscular fibers are involuntary and consist of circular and radiating fibers. The circular fibers form the sphincter pupillae; they are arranged in a narrow band about 1 mm wide that surrounds the margin of the pupil toward the posterior surface of the iris. The fibers near the free margin are closely aggregated; those near the periphery of the band are somewhat separated and form incomplete circles. The radiating fibers form the dilatator pupillae; they converge from the circumference toward the center and blend with the circular fibers near the margin of the pupil. 4. The posterior surface of the iris has a deep purple tint, being covered by two lay¬ ers of pigmented columnar epithelium that are continuous at the periphery of the iris with the pars ciliaris retinae. This pigmented epithelium is named the pars iridica retinae. The color of the iris is produced by the reflection of light from dark pigment cells underlying a translucent tissue, and it is de¬ termined, therefore, by the amount of the pigment and its distribution throughout the texture of the iris. The number and the situa¬ tion of the pigment cells differ in different irises. In the albino, pigment is absent; in the various shades of blue eyes, the pigment cells are confined to the posterior surface of the iris, whereas in gray, brown, and black eyes, pigment is found also in the cells of the stroma and in those of the endothelium on the front of the iris. clinical note. The iris may be absent, either in part or altogether, as a congenital condition, and in some instances the pupillary membrane persists, al¬ though it is rarely complete. The iris may be the seat of a malformation termed a coloboma, which con¬ sists of a deficiency or cleft, due in a great number of cases to an arrest in development. In these cases the cleft is found at the lower aspect, extending directly downward from the pupil, and the gap frequently extends through the choroid to the porus opticus. In some rare cases the gap is found in other parts of the iris, and is not then associated with any deficiency of the choroid. vessels and nerves. The arteries of the iris are derived from the long and anterior ciliary arteries and from the vessels of the ciliary processes (see p. 1292). Each of the two long ciliary arteries, having reached the attached margin of the iris, divides into an upper and lower branch. These anastomose with

1 298

ORGANS OF THE SPECIAL SENSES

corresponding branches from the opposite side and thus encircle the iris. Into this vascular circle, the circulus arteriosus major, the anterior ciliary ar¬ teries pour their blood, and from it vessels converge to the free margin of the iris, where they communi¬ cate to form a second circle, the circulus arteriosus minor (Fig. 1 3-21). The nerves of the choroid and iris (Fig. 13-16) are the long and short ciliary nerves; the former are branches of the nasociliary nerve, and the latter are branches of the ciliary ganglion. They pierce the sclera around the entrance of the optic nerve, run forward in the perichoroidal space, and supply the blood vessels of the choroid. After reaching the iris, they form a plexus around its attached margin; from this are derived unmyelinated fibers that end in the sphincter and dilatator pupillae. Other fibers from the plexus end in a network on the anterior surface of the iris. The fibers, derived through the motor root of the ciliary ganglion from the oculomotor nerve, supply the sphincter pupillae, while those derived from the sympathetic root supply the dilatator pupillae.

STRUCTURE OF THE RETINA

Fig. 13-22. Section of human retina. e.I.m., external limiting membrane; g.L, ganglionic layer; i.l.m., internal limiting membrane; i.n., inner nuclear layer; i.p., inner plexiform layer; o.n., outer nuclear layer; o.p., outer plexiform layer; pig., pigment cell layer; r.c., layer of rods and cones; s.o., stratum opticum. 500 X- (Redrawn from Sobotta.)

The retina consists of an outer pigmented layer and an inner neural stratum or retina proper (Figs. 13-22; 13-23). retina proper. The neural structures of the retina proper are supported by a series of nonneural or sustentacular fibers. In histo¬ logic sections made perpendicularly to the surface of the retina, ten layers are identified and named from within outward as follows:

1. Internal limiting membrane 2. Stratum opticum, layer of nerve fibers 3. Ganglion cell layer 4. Inner plexiform layer 5. Inner nuclear layer 6. Outer plexiform layer 7. Outer nuclear layer 8. External limiting membrane 9. Layer of rods and cones 10. Pigmented layer

Fig. 13-21.

1. The internal limiting membrane is a thin cribriform layer formed by the susten¬ tacular fibers (p. 1301). 2. The stratum opticum or layer of nerve fibers is formed by the expansion of the fi¬ bers of the optic nerve; it is thickest near the porus opticus, gradually diminishing toward the ora serrata. As the nerve fibers pass through the lamina cribrosa sclerae, they lose their myelin sheaths and continue on¬ ward through the choroid and retina as sim¬ ple axons. When they reach the internal sur¬ face of the retina, they radiate as a group of bundles from their point of entrance, and in many places they are arranged in plexuses. Most of the fibers are centripetal and are the direct continuations of the axons of the cells of the ganglionic layer, but a few of them are centrifugal and ramify in the inner plexi¬ form and inner nuclear layers, where they end in enlarged extremities.

Iris, anterior view.

ORGAN OF SIGHT: THE EYE

1299

Internal limiting membrane... Stratum opticum-Ganglionic layer —

Inner plexiform layer Centrifugal fiber Diffuse amacrine cell Inner nuclear layer

*'i Amacrine cells

Fiber of Muller •••Horizontal cell Outer plexiform --layer -T—; Rod granules

Outer nuclear layer

Cone granules

External limiting membrane""/ Layer of rods and cones

,! piiiii, • o I o I o r Fig. 13-23.

Pigmented layer

Plan of retinal neurons. (After Cajal.)

3. The ganglion cell layer consists of a sin¬ gle layer of large ganglion cells, except in the macula, where there are several strata. The cells are somewhat flask-shaped; the rounded internal surface of each rests on the stratum opticum and sends an axon into the fiber layer. From the opposite end numerous dendrites extend into the inner plexiform layer, where they branch and form flat ar¬ borizations at different levels. The ganglion cells vary much in size, and the dendrites of the smaller ones usually arborize in the inner plexiform layer as soon as they enter it, while those of the larger cells ramify close to the inner nuclear layer. 4. The inner plexiform layer is made up of a dense reticulum of minute fibrils formed by the interlacement of the dendrites of the ganglion cells with those of the cells of the inner nuclear layer. Within this reticulum, a few branched spongioblasts are embedded. 5. The inner nuclear layer is made up of closely packed cells, of which there are three varieties: bipolar cells, horizontal cells and amacrine cells. The bipolar cells, by far the most numer¬ ous, are round or oval, and each is prolonged

into an inner and an outer process. They are divisible into rod bipolars and cone bipolars. The inner processes of the rod bipolars run through the inner plexiform layer and arbo¬ rize around the bodies of the cells of the gan¬ glionic layer; their outer processes end in the outer plexiform layer in tufts of fibrils around the button-like ends of the inner processes of the rod granules. The inner processes of the cone bipolars ramify in the inner plexiform layer in contact with the dendrites of the ganglionic cells. The horizontal cells lie in the outer part of the inner nuclear layer and have somewhat flattened cell bodies. Their dendrites divide into numerous branches in the outer plexi¬ form layer, while their axons run horizon¬ tally for some distance and finally ramify in the same layer. The amacrine cells are in the inner part of the inner nuclear layer and are so named because it has not yet been shown that they possess axons. Their dendrites ramify exten¬ sively in the inner plexiform layer. The cell bodies and nuclei of the sustentacular fibers are in this layer. 6. The outer plexiform layer is much thin-

1 300

ORGANS OF THE SPECIAL SENSES

ner than the inner layer but, like it, consists of a dense network of minute fibrils derived from the processes of the horizontal cells of the preceding layer and the outer processes of the rod and cone bipoplar cells, which ramify in it, forming arborizations around the enlarged ends of the rod fibers and with the branched foot plates of the cone fibers. 7. The outer nuclear layer, like the inner nuclear layer, contains strata of oval cell bodies. The latter are of two types: rod or cone nuclei, so named because they are con¬ nected respectively with the rods and cones of the next layer. The rod nuclei are much more numerous and are placed at different levels throughout the layer. Prolonged from either extremity of each cell is a fine process. The outer process is continuous with a sin¬

gle rod of the layer of rods and cones; the inner process ends in the outer plexiform layer in an enlarged extremity and is embed¬ ded in the tuft into which the outer proc¬ esses of the rod bipolar cells break up. In its course it has numerous varicosities. The cone nuclei, fewer in number than the rod nuclei, are placed close to the external limiting membrane, through which they are continuous with the cones of the layer of rods and cones. They contain a piriform nu¬ cleus that almost completely fills the cell. From the inner extremity, a thick process passes into the outer plexiform layer, and there expands into a pyramidal enlargement or foot plate from which numerous fine fi¬ brils are given off and come in contact with the outer processes of the cone bipolars.

Posterior limiting membrane (of Descemet) Anterior epithelium of cornea

Anterior chamber of eye ^apsule of lens ^Sphincter of pupil

Cornea

Pars iridica retinae Iris Dilator of pupil Posterior chamber of eye Canal of Schlemm Conjunctiva Anterior ciliary vessel Episcleral connective tissue

Sclera

Zonular fibers' Ciliary process

Pars ciliaris retinae Perichoroidal space

{Circular fibers' Meridional fibers Radial fibers

Ora serrata/

Insertion of tendon of lateral rectus muscle

Choroid

Pars optica retinae Pigmented layer of retina

Fig. 13-24.

A horizontal section through half of the anterior part of the eyeball.

ORGAN OF SIGHT

8. The external limiting membrane is formed by the sustentacular cells (see below). 9. The layer of rods and cones (Jacob’s membrane1).—The elements composing this layer are of two types, rods and cones, the former being much more numerous than the latter, except in the macula (Figs. 13-22; 13-23). The rods are cylindrical, 40 to 60 y long, 2 n thick and arranged perpendicular to the surface. Each rod consists of an outer and an inner segment of about equal length. The outer segment is more slender than the inner segment, is strongly refractive and has trans¬ verse striae; it tends to break up into a num¬ ber of thin discs superimposed on one an¬ other. It also exhibits faint longitudinal markings. The inner part of the inner seg¬ ment is indistinctly granular and is called the myoid; its outer part presents a longitu¬ dinal striation and represents the ellip¬ soid, which is composed of fine, bright, highly refracting fibrils. The visual purple or rhodopsin, found in the outer segments, gives a purple or reddish color in a darkadapted eye, and is the pigment for detection of low light intensity. The cones are conical or flask-shaped; their broad ends rest upon the external lim¬ iting membrane, and the narrow, pointed extremity is turned to the choroid. Like the rods, each is made up of two segments, outer and inner; the outer segment is a short coni¬ cal process, which, like the outer segment of the rod, exhibits transverse striae. The inner segment resembles the inner segment of the rods in structure, but it has a larger, thicker ellipsoid and a bulging deep granular part. The pigment in the outer segment of the cones is iodopsin, which is for color vision. 10. The pigmented layer consists of a sin¬ gle stratum of cells. When viewed from the outer surface, these cells are smooth and hexagonal; when seen in section, each cell consists of an outer nonpigmented part con¬ taining a large oval nucleus and an inner pig¬ mented portion that extends as a series of straight thread-like processes between the rods, especially when the eye is exposed to light. In the eyes of albinos, the cells of this layer have no pigment. Arthur Jacob (1790-1874): Irish ophthalmologist and anatomist (Dublin).

THE EYE

1301

SUPPORTING FRAMEWORK OF THE RETINA. The neural layers of the retina are con¬ nected by a supporting framework formed by the sustentacular fibers of Muller; these fibers pass through all the neural layers except that of the rods and cones. Each be¬ gins on the inner surface of the retina by an expanded, often forked base, which some¬ times contains a spheroidal body that stains deeply with hematoxylin. The edges of the bases of adjoining fibers unite to form the internal limiting membrane. As the fibers pass through the nerve fiber and ganglionic layers, they give off a few lateral branches; in the inner nuclear layer they give off nu¬ merous lateral processes for the support of the bipolar cells, while in the outer nuclear layer they form a network around the rod and cone fibrils, and unite to form the exter¬ nal limiting membrane at the bases of the rods and cones. At the level of the inner nu¬ clear layer, each sustentacular fiber contains a clear oval nucleus. MACULA AND FOVEA CENTRALIS. In the macula, the nerve fibers are wanting as a contin¬ uous layer, the ganglionic layer consists of several strata of cells, and the rods are lack¬ ing. The cones are longer and narrower than in other parts, and in the outer nuclear layer there are only cone nuclei, the processes of which are very long and arranged in curved lines. In the fovea centralis, the only parts pres¬ ent are (1) the cones; (2) the outer nuclear layer, the cone fibers of which are directed almost horizontally; (3) an exceedingly thin inner plexiform layer. The pigmented layer is thicker and its pigment more pronounced than elsewhere. The color of the macula seems to imbue all the layers except that of the cones; it is a rich yellow and deepest toward the center of the macula. ora serrata. At the ora serrata (Fig. 1318), the neural layers of the retina end ab¬ ruptly, and the retina continues onward as a single layer of columnar cells covered by the pigmented layer. This double layer is known as the pars ciliaris retinae, and can be traced forward from the ciliary processes on to the back of the iris, where it is termed the pars iridica retinae. vessels. The central retinal artery (Fig. 13-19) and its accompanying vein pierce the optic nerve and enter the bulb of the eye through the porus

1 302

ORGANS OF THE SPECIAL SENSES

opticus. The artery immediately bifurcates into an upper and a lower branch, and each of these again divides into a medial or nasal and a lateral or tempo¬ ral branch. These branches first run between the hyaloid membrane and the neural layer, but they soon enter the neural layer and pass anteriorly, di¬ viding dichotomously. From these branches a min¬ ute capillary plexus is given off that does not extend beyond the inner nuclear layer. The macula receives two small branches (superior and inferior macular arteries) from the temporal branches and small twigs directly from the central artery; these do not, how¬ ever, reach as far as the fovea centralis, which has no blood vessels. The branches of the central retinal artery do not anastomose with each other—in other words, they are terminal arteries. In the fetus, a small vessel, the hyaloid artery, passes forward as a continuation of the central retinal artery through the vitreous humor to the posterior surface of the cap¬ sule of the lens.

Zonula Ciliaris

The zonula ciliaris (zonule of Zinn,1 sus¬ pensory ligament of the lens) consists of a series of straight fibrils that radiate from the ciliary body to the lens. It is attached to the capsule of the lens a short distance anterior to its equator. Scattered delicate fibers are also attached to the region of the equator it¬ self. This ligament retains the lens in posi¬ tion, and is relaxed by the contraction of the meridional fibers of the ciliary muscle, so that the lens is allowed to become more con¬ vex. Posterior to the suspensory ligament there is a sacculated canal, the spatia zonularia (canal of Petit2), which encircles the equator of the lens; it can be easily in¬ flated through a fine blowpipe inserted under the suspensory ligament.

REFRACTING MEDIA

Crystalline Lens

The refracting media are five: Cornea (see p. 1292) Aqueous humor Vitreous body Zonula ciliaris Crystalline lens Aqueous Humor

The aqueous humor fills the anterior and posterior chambers. It is small in quantity, has an alkaline reaction, and consists mainly of water. The aqueous humor is secreted by the ciliary process. The fluid passes through the posterior chamber and the pupil into the anterior chamber. From the angle of the an¬ terior chamber it passes into the spaces of Fontana to the pectinate villi, through which it is filtered into the venous canal of Schlemm. Vitreous Body

The vitreous body fills the concavity of the pars optica retinae, to which it is firmly ad¬ herent, especially at the ora serrata. It is transparent, semigelatinous, and is hollowed anteriorly for the lens. Some indications of the hyaloid canal between the optic nerve and lens may persist. No blood vessels penetrate the vitreous body, so that its nutrition must be carried on by vessels of the retina and ciliary processes, situated upon its exterior.

The crystalline lens, enclosed in its cap¬ sule, is situated immediately between the iris and the vitreous body and is encircled by the ciliary processes, which slightly over¬ lap its margin. The capsule of the lens (capsula lentis) is a transparent, structureless membrane that closely surrounds the lens and is thicker in front than behind. It is brittle but highly elastic, and when ruptured the edges roll up, with the outer surface innermost. It rests in the hyaloid fossa in the anterior part of the vitreous body posteriorly and is in contact with the free border of the iris anteriorly, but recedes from it at the circumference, thus forming the posterior chamber of the eye. It is retained in its position chiefly by the suspensory ligament of the lens, already described. The lens is a transparent, biconvex body; the convexity of its anterior surface is less than that of its posterior surface. The central points of these surfaces are termed, respec¬ tively, the anterior and posterior poles; a line connecting the poles constitutes the axis of the lens, while the marginal circumfer¬ ence is termed the equator.

’ Johann Gottfried Zinn (1727-1759): A German physician and botanist (Gottingen). 2Frangois Pourfour du Petit (1664-1741): French surgeon and anatomist (Paris).

ORGAN OF SIGHT THE EYE

1 303

STRUCTURE OF THE LENS

The lens is made up of a soft cortical sub¬ stance and a firm, central part, the nucleus (Fig. 13-25). Faint lines (radii lentis) radiate from the poles to the equator. In the adult there may be six or more of these lines, but in the fetus there are only three, and they diverge from each other at angles of 120° (Fig. 13-26). On the anterior surface, one line ascends vertically and the other two diverge downward; on the posterior surface, one ray descends vertically and the other two di¬ verge upward. They correspond with the free edges of an equal number of septa that are composed of an amorphous substance. These septa dip into the substance of the lens and mark the interruptions of a series of concentrically arranged laminae (Fig. 13-25). Each lamina is built up of a number of hex¬ agonal, ribbon-like lens fibers, the edges of which are more or less serrated. The serra¬ tions fit between those of neighboring fibers, while the ends of the fibers come into appo¬ sition at the septa. The fibers run in a curved manner from the septa on the anterior sur¬ face to those on the posterior surface. No fi¬ bers pass from pole to pole; they are ar¬ ranged in such a way that those beginning near the pole on one surface of the lens end near the peripheral extremity of the plane on the other, and vice versa. The fibers of the outer layers of the lens are nucleated, and together they form a nuclear layer, most dis¬ tinct toward the equator. The anterior sur¬ face of the lens is covered by a layer of transparent, columnar, nucleated epithe¬ lium. At the equator the cells become elon¬ gated, and their gradual transition into lens fibers can be traced (Fig. 13-27). In the fetus, the lens is nearly spherical, and has a slightly reddish tint; it is soft and breaks down readily on the slightest pres-

Diagram showing the direction and ar¬ rangement of the radiating lines on the front and back of the fetal lens. A, From the front. B, From the back.

Fig. 13-26.

sure. A small branch from the central retinal artery runs forward, as already mentioned, through the vitreous body to the posterior part of the capsule of the lens, where its branches radiate and form a plexiform net¬ work that covers the posterior surface of the capsule. The branches are continuous around the margin of the capsule with the vessels of the pupillary membrane and with those of the iris. In the adult, the lens is col¬ orless, transparent, firm, and devoid of ves¬ sels. In old age it becomes flattened on both surfaces and slightly opaque, has an amber tint, and increases in density (Fig. 13-28). VESSELS AND NERVES OF THE BULB (Fig. 13-15). The arteries of the eye are the long, short, and ante¬ rior ciliary arteries and the central retinal artery. They have already been described (see p. 688). The ciliary veins are seen on the outer surface of the choroid and are named, because of their ar¬ rangement, the venae vorticosae (Fig. 13-16). The veins converge to four or five equidistant trunks that pierce the sclera midway between the sclerocorneal junction and the porus opticus. Another set of veins accompanies the anterior ciliary arteries. All these veins open into the ophthalmic veins. The ciliary nerves are derived from the nasociliary nerve and from the ciliary ganglion.

ACCESSORY ORGANS OF THE EYE

The accessory organs of the eye include the ocular muscles, the fasciae, the eye¬ brows, the eyelids, the conjunctiva, and the lacrimal apparatus. Ocular Muscles The ocular muscles are:

Fig. 13-25.

(Enlarged.)

The crystalline lens, hardened and divided.

Levator palpebrae superioris Rectus superior Rectus inferior

1 304

ORGANS OF THE SPECIAL SENSES

o0 2

Profile views of the lens at different periods of life. 1. In the fetus. 2. In adult life. 3. In old age.

Fig. 13-28.

Section through the margin of the lens, showing the transition of the epithelium into the lens fibers. (Babuchin.)

Fig. 13-27.

Rectus medialis Rectus lateralis Obliquus superior Obliquus inferior The levator palpebrae superioris (Fig. 13-29) is a thin, flat muscle arising from the

inferior surface of the small wing of the sphenoid, where it is separated from the optic foramen by the origin of the rectus superior. At its origin it is narrow and tendi¬ nous, but it becomes broad and fleshy and ends anteriorly in a wide aponeurosis that splits into three lamellae. The superficial lamella blends with the superior part of the orbital septum, and is prolonged over the superior tarsus to the palpebral part of the orbicularis oculi and to the deep surface of the skin of the upper eyelid. The middle lamella, largely made up of nonstriated mus¬ cular fibers, is inserted into the superior margin of the superior tarsus, while the deepest lamella blends with an expansion from the sheath of the rectus superior and with it is attached to the superior fornix of the conjunctiva. The four recti muscles (Fig. 13-30) arise from a fibrous ring (anuius tendineus com¬ munis) that surrounds the superior, medial, and inferior margins of the optic foramen and encircles the optic nerve (Fig. 13-31). The ring is completed by a tendinous bridge prolonged over the inferior and medial part of the superior orbital fissure and attached to a tubercle on the margin of the great wing of the sphenoid, bounding the fissure. Two specialized parts of this fibrous ring may be made out: a lower, the ligament or tendon of Zinn, which gives origin to the rectus infe¬ rior, part of the rectus medialis, and the lower head of origin of the rectus lateralis; and an upper part which gives origin to the rectus superior, the rest of the rectus medi¬ alis, and the upper head of the rectus later¬ alis. This upper band is sometimes termed the superior tendon of Lockwood.1 Each muscle passes anteriorly in the position im¬ plied by its name, to be inserted by a tendi1 Charles Barrett Lockwood (1856-1914): An English sur¬ geon (London).

ORGAN OF SIGHT

THE EYE

1305

Tendon of superior oblique m Levator palpebrae superiors m. Central retinal artery Rectus superior m.

Orbicularis oculi m.

Superior tarsus

Upper eyelid

Inferior tarsus Optic nerve Lower eyelid Rectus inferior m. Orbicularis oculi m.

Roof of maxillary sinus Inferior oblique m

Fig. 13-29.

Sagittal section of the right orbital cavity.

nous expansion into the sclera, about 6 mm from the margin of the cornea. Between the two heads of the rectus lateralis is a narrow interval through which pass the two divi¬ sions of the oculomotor nerve, the nasocil¬ iary nerve, the abducens nerve, and the oph¬ thalmic vein. Although these muscles have a common origin and are inserted in a similar manner into the sclera, there are certain dif¬ ferences between their length and breadth. The rectus medialis is the broadest, the rec¬ tus lateralis the longest, and the rectus supe¬ rior the thinnest and narrowest. The obliquus superior oculi (superior oblique) is a fusiform muscle placed at the superior and medial side of the orbit. It arises immediately above the margin of the optic foramen, superior and medial to the origin of the rectus superior, and passing anteriorly, it ends in a rounded tendon that plays in a fibrocartilaginous ring or pulley attached to the trochlear fovea of the frontal bone. The contiguous surfaces of the tendon and ring are lined by a delicate synovial sheath and are enclosed in a thin fibrous

investment. The tendon bends around the pulley at more than a right angle, passes be¬ neath the rectus superior to the lateral part of the bulb of the eye, and is inserted into the sclera, posterior to the equator of the eye¬ ball; the insertion of the muscle lies between the rectus superior and the rectus lateralis. The obliquus inferior oculi (inferior oblique) is a thin, narrow muscle placed near the anterior margin of the floor of the orbit. It arises from the orbital surface of the max¬ illa, lateral to the lacrimal groove. Passing lateralward, at first between the rectus infe¬ rior and the floor of the orbit and then be¬ tween the bulb and the rectus lateralis, it is inserted into the lateral part of the sclera between the rectus superior and the rectus lateralis, near but somewhat posterior to the insertion of the obliquus superior. nerves. The levator palpebrae superiors, the obliquus inferior, and the recti superior, inferior, and medialis are supplied by the oculomotor nerve; the obliquus superior is supplied by the trochlear nerve, and the rectus lateralis, by the abducens nerve (Fig.

13-31).

1306

ORGANS OF THE SPECIAL SENSES

Levator palpebrae superioris

Superior oblique m.

Superior rectus m.

Medial rectus m.

Lateral rectus m.

(

Upper head Lower head

Sphenoid bone Lateral rectus m. Roof of maxillary sinus Inferior rectus m. Fig. 13-30.

Muscles of the right orbit.

Levator palpebrae Frontal nerve Sup. ramus of oculomotor nerve Sup orbital fissure

Nasociliary nerve Trochlear nerve Trochlea

Lacrimal nerve

Abducent nerve Inf. ramus of oculomotor nerve

Fig. 13-31.

i

Inf. orbital fissure

Optic canal

Dissection showing origins of right ocular muscles and the nerves entering the orbit through the superior orbital fissure.

ORGAN OF SIGHT

actions. The levator palpebrae raises the upper eyelid and is the direct antagonist of the orbicularis oculi. The four recti are attached to the bulb of the eye in such a manner that, acting singly, they turn its corneal surface in the direction corresponding to their names. The movement produced by the rectus superior or rectus inferior is not a simple one be¬ cause the axis of the orbit, and hence their direction of pull, diverges from the median plane, causing their pull to be accompanied by a certain deviation medialward, with a slight amount of rotation. These latter movements are corrected by the obliqui; the obliquus inferior corrects the medial deviation caused by the rectus superior and the obliquus supe¬ rior corrects the deviation caused by the rectus infe¬ rior. The contraction of the rectus lateralis or rectus medialis, on the other hand, produces a purely hori¬ zontal movement. If any two neighboring recti of one eye act together, they carry the globe of the eye diagonally in these directions: upward and medialward, upward and lateralward, downward and medialward, or downward and lateralward. Some¬ times the corresponding recti of the two eyes act in unison, and at other times the opposite recti act together. Thus, in turning the eyes to the right, the rectus lateralis of the right eye will act in unison with the rectus medialis of the left eye, but if both eyes are directed to an object in the midline at a short distance, the two recti mediales will act in uni¬ son. The movement of circumduction, as in looking around a room, is performed by the successive ac¬ tions of the four recti. The obliqui rotate the eyeball on its anteroposterior axis, the superior muscle di¬ recting the cornea downward and lateralward, and the inferior muscle directing it upward and lateral-

Periorbita Levator palpebrae superioris Rectus _ superior Vagina bulbi (Tenon's capsule)

THE EYE

1307

ward. These movements are required for the correct viewing of an object when the head is moved laterally, as from shoulder to shoulder, in order that the picture may fall in all respects on the same part of the retina of either eye.

A layer of nonstriped muscle, the orbitalis muscle (of H. Muller), bridges the inferior orbital fissure.

Fasciae and Ligaments The fascia bulbi (vagina bulbi; capsule of Tenon) (Fig. 13-32) is a thin membrane that envelops the eyeball from the optic nerve to the ciliary region, separating it from the or¬ bital fat and forming a socket in which it plays. Its inner surface is smooth and is sep¬ arated from the outer surface of the sclera by the periscleral fascial cleft. This space be¬ tween the fascia and sclera (spatium intervaginale) is continuous with the subdural and subarachnoid cavities; it is traversed by delicate bands of connective tissue that ex¬ tend between the fascia and the sclera. The fascia is perforated by the ciliary vessels and nerves, and it fuses with the sheath of the optic nerve and with the sclera around the lamina cribrosa. Anteriorly it blends with the ocular conjunctiva, with which it is at¬ tached to the ciliary region of the bulb. The fascia bulbi is prolonged over tendons

Orbital septum Vagina bulbi Fornix conjunctivae

Spatium intervaginale

Orbital fat

Rectus inferior

Obliquus infe_

Vagina bulbi Check ligament Orbital septum

Fascia bulbi (capsule of Tenon). Sagittal section, semidiagrammatic. (Redrawn from Surgical Anatomy of the Human Body by J. B. Deaver, P. Blakiston’s Son & Co., 1926.)

Fig. 13-32.

1 308

ORGANS OF THE SPECIAL SENSES

of the individual ocular muscles as a tubular sheath (fascia musculares). The sheath of the tendon of the obliquus superior is car¬ ried as far as the fibrous pulley of that mus¬ cle; the sheath of the obliquus inferior reaches as far as the floor of the orbit, to which it gives off a slip. The sheaths of the recti are gradually lost in the perimysium, but they give off important expansions. The expansion from the rectus superior blends with the tendon of the levator palpebrae; that of the rectus inferior is attached to the inferior tarsus. The expansions from the sheaths of the recti medialis and especially the rectus lateralis are strong and are at¬ tached to the lacrimal and zygomatic bones respectively. As they probably check the actions of the two recti, these structures have been named the medial and lateral check ligaments. A thickening of the lower part of the fascia bulbi, named the suspen¬ sory ligament of the eye, is slung like a ham¬ mock below the eyeball, and is expanded in the center and narrow at the ends, and at¬ tached to the zygomatic and lacrimal bones respectively. The periorbita is the name given to the periosteum of the orbit. It is loosely con¬ nected to the bones and can be readily sepa¬ rated from them. It is continuous with the dura mater by processes that pass through the optic foramen and superior orbital fis¬ sure and with the sheath of the optic nerve. At the margin of the orbit, a process from the periorbita assists in forming the orbital sep¬ tum. The periorbita has two other processes: one to enclose the lacrimal gland, the other to hold the pulley of the obliquus superior in position. The orbital septum (palpebral ligament) (Fig. 13-32) is a membranous sheet that is continuous with the part of the periorbita that is attached to the edge of the orbit. In the upper eyelid, the orbital septum blends by its peripheral circumference with the ten¬ don of the levator palpebrae superioris and the superior tarsus; in the lower eyelid, the orbital septum blends with the inferior tar¬ sus . Medially it is thin, and after separating from the medial palpebral ligament, it is fixed to the lacrimal bone immediately be¬ hind the lacrimal sac. The septum is perfo¬ rated by the vessels and nerves that pass from the orbital cavity to the face and scalp. The eyelids are richly supplied with blood.

Eyebrows

The eyebrows (supercilia) are two arched eminences that surmount the superior mar¬ gins of the orbits. The eyebrows consist of thickened integument that is connected be¬ neath with the orbicularis oculi, corrugator, and frontalis muscles. They support numer¬ ous short, thick hairs.

Eyelids

The eyelids (palpebrae) are two thin, mov¬ able covers placed in front of the eye that protect it from injury by their closure. The upper eyelid is larger and more movable than the lower, and is furnished with an ele¬ vator muscle, the levator palpebrae superi¬ oris. When the eyelids are open, an elliptical space, the palpebral fissure (rima palpebra¬ rum), is left between their margins, the angles of which correspond to the junctions of the upper and lower eyelids. These angles are called the palpebral commissures or canthi. The lateral palpebral commissure (exter¬ nal or lateral canthus) is more acute than the medial commissure, and the eyelids here lie in close contact with the bulb of the eye. The medial palpebral commissure (internal or medial canthus) is prolonged for a short distance toward the nose, and the two eye¬ lids are separated by a triangular space, the lacus lacrimalis (Fig. 13-37). At the basal angles of the lacus lacrimalis, on the margin of each eyelid, is a small conical elevation, the lacrimal papilla, the apex of which is pierced by a small orifice, the punctum lacrimale. This opening is the commence¬ ment of the lacrimal duct. STRUCTURE OF THE EYELIDS. (Fig. 13-33). The eyelids are composed of the following structures, from outer to inner surfaces: in¬ tegument, areolar tissue, fibers of the orbi¬ cularis oculi, tarsus, orbital septum, tarsal glands, and conjunctiva. The upper eyelid, in addition, has the aponeurosis of the leva¬ tor palpebrae superioris (Fig. 13-34). The integument is extremely thin and con¬ tinuous at the margins of the eyelids with the conjunctiva. The subcutaneous areolar tissue is lax, delicate, and seldom contains any fat. The palpebral fibers of the orbicularis oculi are thin, pale, and have an involuntary as well as a voluntary action.

ORGAN OF SIGHT

Sagittal section through the upper eyelid. (After Waldeyer.) a, Skin, b, Orbicularis oculi. b', Mar¬ ginal fasciculus of orbicularis (ciliary bundle), c, Levator palpebrae. d, Conjunctiva, e, Tarsus, f, Tarsal gland, g, Ciliary gland, h, Eyelashes, i, .Small hairs of skin, j, Sweat glands, k, Posterior tarsal glands. Fig. 13-33.

Lacrimal artery and nerve

Lateral palpebral raphe

Fig. 13-34.

THE EYE

1 309

The tarsi (tarsal plates) (Fig. 13-34) are two thin, elongated plates of dense connec¬ tive tissue about 2.5 cm long; one is placed in each eyelid and contributes to its form and support. The superior tarsus, the larger, is semilunar, about 10 mm in breadth at the center, and gradually narrows toward its extremities. To the anterior surface of this plate the aponeurosis of the levator palpebrae superioris is attached. The inferior tarsus, the smaller plate, is thin, elliptical, and has a vertical diameter of about 5 mm. The free or ciliary margins of these plates are thick and straight. The attached or orbital margins are connected to the circumference of the orbit by the orbital septum. The lateral angles are attached to the zygomatic bone by the lateral palpebral raphe. The medial angles of the two plates end at the lacus lacrimalis and are attached to the frontal process of the maxilla by the medial palpebral ligament. eyelashes. The eyelashes (cilia) are at¬ tached to the free edges of the eyelids; they are short, thick, curved hairs, arranged in a double or triple row: those of the upper eye¬ lid, more numerous and longer than those of the lower, curve upward; those of the lower eyelid curve downward, so that they do not interlace when the lids are closed. Near the attachment of the eyelashes are the openings of the ciliary glands, which are arranged in several rows close to the free margin of the lid. These are regarded as enlarged and mod¬ ified sudoriferous glands.

Supraorbital vessels and nerve

Lacrimal sac Medial palpebral ligament

The tarsi and their ligaments. Right eye; anterior view.

1310

ORGANS OF THE SPECIAL SENSES

tarsal glands. The tarsal glands (Meibo¬ mian1 glands) (Figs. 13-35; 13-36) are situated on the inner surfaces of the eyelids between the tarsi and conjunctiva. They may be seen distinctly through the conjunctiva when the eyelids are everted, having an appearance similar to parallel strings of pearls. There are about 30 glands in the upper eyelid and somewhat fewer in the lower. They are em¬ bedded in grooves in the inner surfaces of the tarsi and correspond in length with the breadth of these plates; they are, conse¬ quently, longer in the upper than in the lower eyelid. Their ducts open on the free margins of the lids by minute apertures. STRUCTURE OF THE TARSAL GLANDS. The tarsal glands are modified sebaceous glands; each consists of a single straight tube or fol¬ licle with numerous small lateral divertic¬ ula. The tubes are supported by a basement membrane and are lined at their mouths by stratified epithelium; the deeper parts of the tubes and the lateral offshoots are lined by a layer of polyhedral cells.

Conjunctiva

The conjunctiva is the mucous membrane of the eye. It lines the inner surfaces of the eyelids or palpebrae and is reflected over the anterior part of the sclera. The palpebral portion (tunica conjunctiva palpebrarum) is thick, opaque, highly vascu¬ lar, and covered with numerous papillae; the deeper part has a considerable amount of 1 Heinrich Meibom (1638-1700): A German physician and anatomist (Helmstadt).

Puncta lacrimalia

Punctum lacrimale Plica semilunaris Caruncula Punctum lacrimale Openings of tarsal glands

Anterior view of left eye with eyelids sepa¬ rated to show medial canthus.

Fig. 13-36.

lymphoid tissue. At the margins of the lids, the conjunctiva becomes continuous with the lining membrane of the ducts of the tar¬ sal glands; through the lacrimal ducts, it is continuous with the lining membrane of the lacrimal sac and nasolacrimal duct. At the lateral angle of the upper eyelid, the ducts of the lacrimal gland open on the free surface of the conjunctiva, and at the medial angle it forms a semilunar fold, the plica semilunaris (Fig. 13-36). The line of reflection of the con¬ junctiva from the upper eyelid onto the bulb of the eye is named the superior fornix, and that from the lower lid is named the inferior fornix. The bulbar portion (tunica conjunctiva bulbi) of the conjunctiva is loosely con¬ nected over the sclera; it is thin, transparent, destitute of papillae, and only slightly vascu¬ lar. At the circumference of the cornea, the conjunctiva becomes the epithelium of the cornea, already described (see p. 1295). Lym¬ phatics arise in the conjunctiva in a delicate zone around the cornea; these vessels run to the scleral conjunctiva. Lymphoid follicles are found in the conjunctiva, chiefly near the medial palpebral commissure. They were first described by Bruch1, in his description of Peyer’s patches2 of the small intestine, as “identical structures existing in the under eyelid of the ox.”

^arl Wilhelm Ludwig Bruch (1819-1884): A German Fig. 13-35. The tarsal glands seen from the inner sur¬ face of the eyelids.

anatomist (Basel and Giessen). 2Johann Conrad Peyer (1653-1712): Swiss anatomist and logician (Schaffhausen).

ORGAN OF SIGHT

In and near the fornices, but more plenti¬ ful in the upper than in the lower eyelid, sev¬ eral convoluted tubular glands open on the surface of the conjunctiva. caruncula lacrimalis. The caruncula lacrimalis is a small, reddish protuberance situated at the medial palpebral commissure and filling up the lacus lacrimalis. It consists of a small island of skin containing seba¬ ceous and sudoriferous glands, and it is the source of the whitish secretion that con¬ stantly collects in this region. A few slender hairs are attached to its surface. Lateral to the caruncula is a slight semilunar fold of conjunctiva, the concavity of which is di¬ rected toward the cornea; this is called the plica semilunaris. Smooth muscular fibers have been found in this fold, and in some of the domesticated animals it contains a thin plate of cartilage.

nerves. The nerves in the conjunctiva are nu¬ merous and form rich plexuses. They appear to terminate in a peculiar form of tactile corpuscle called terminal bulbs.

THE EYE

1311

Lacrimal Apparatus

The lacrimal apparatus (Fig. 13-37) con¬ sists of (a) the lacrimal gland, which secretes the tears, and its excretory ducts, which con¬ vey the fluid to the surface of the eye; and (b) the lacrimal ducts, the lacrimal sac, and the nasolacrimal duct, by which the fluid is con¬ veyed into the cavity of the nose. lacrimal gland. The lacrimal gland (Figs. 13-34; 13-35) is superior and lateral to the bulb and is lodged in the lacrimal fossa on the medial side of the zygomatic process of the frontal bone. It is oval, about the size and shape of an almond, and consists of two por¬ tions. The orbital part (pars orbitalis; supe¬ rior lacrimal gland) is connected to the peri¬ osteum of the orbit by a few fibrous bands and rests upon the tendons of the recti superioris and lateralis, which separate it from the bulb of the eye. The palpebral part (pars palpebralis; inferior lacrimal gland) is separated from the orbital part by a fibrous septum and projects into the back part of the upper eyelid, where its deep surface is re- . lated to the conjunctiva. The ducts of the

Puncta lacrimalia

Caruncula lacrimalis Ductus lacrimalis

Plica semilunaris conjunctivae ,Fornix sacci lacrimalis Glandulae tarsales. Ductuli excretorii [gl. lacrimalis] Maxilla [processus frontalis]

Glandula lacrimalissuperior y. Glandula lacrimalis inferior

-Saccus lacrimalis Cavum nasi

Bulbus oculi

Concha nasalis media —Ductus nasolacrimalis Conjunctiva

-Meatus nasi inferior

Lacus lacrimalis^

Concha nasalis inferior

Papilla lacrimalis

'-f—;

Septum nasi

Ampulla ductus lacrimalis N. infraorbitalis Corpus adiposum orbitae Maxilla . '"".TV— Fig. 13-37. Topography of the lacrimal apparatus. The lacrimal and tarsal glands are shown in blue. The nose and a portion of the face have been cut away. (Eycleshymer and Jones.)

1312

ORGANS

OF IHF SPECIAL SENSES

glands, numbering six to twelve, run ob¬ liquely beneath the conjunctiva for a short distance and open along the upper and lat¬ eral half of the superior conjunctival fornix. lacrimal ducts. The lacrimal ducts (lac¬ rimal canals), one in each eyelid, commence at minute orifices, termed puncta lacrimalia, on the summits of the papillae lacrimales, which are on the margins of the lids at the lateral extremity of the lacus lacrimalis. The superior duct, the smaller and shorter of the two, at first ascends and then bends at an acute angle and passes medialward and downward to the lacrimal sac. The inferior duct at first descends and then runs almost horizontally to the lacrimal sac. At the an¬ gles they are dilated into ampullae; their walls are dense, and their mucous lining is covered by stratified squamous epithelium placed on a basement membrane. Outside the basement membrane is a layer of striped muscle that is continuous with the lacrimal part of the orbicularis oculi; at the base of each lacrimal papilla the muscular fibers are circularly arranged and form a kind of sphincter. lacrimal sac. The lacrimal sac is the upper dilated end of the nasolacrimal duct. It is lodged in a deep groove formed by the lacrimal bone and the frontal process of the maxilla. It is oval and measures 12 to 15 mm long; its upper end is closed and round, and its lower end continues into the nasolacrimal duct. The superficial surface of the lacrimal sac is covered by a fibrous expansion de¬ rived from the medial palpebral ligament, and its deep surface is crossed by the lacri¬ mal part of the orbicularis oculi (p. 441), which is attached to the crest on the lacrimal bone. nasolacrimal duct. The nasolacrimal duct (nasal duct) is a membranous canal, about 18 mm long, that extends from the lower part of the lacrimal sac to the inferior meatus of the nose, where it ends in a some¬ what expanded orifice that is provided with an imperfect valve, the plica lacrimalis (Hasneri1), which is formed by a fold of the mucous membrane. The nasolacrimal duct is contained in an osseous canal that is formed by the maxilla, the lacrimal bone, and the inferior nasal concha. It is narrower in the middle than at either end, and is directed downward, backward, and a little lateral-

ward. The mucous lining of the lacrimal sac and nasolacrimal duct is covered with co¬ lumnar epithelium, which is ciliated in places. STRUCTURE OF THE LACRIMAL GLAND. In structure and general appearance the lacri¬ mal gland resembles the serous salivary glands. structure of the lacrimal sac. The lac¬ rimal sac consists of a fibrous elastic coat that is lined internally by mucous mem¬ brane. The mucous membrane is continuous through the lacrimal ducts with the conjunc¬ tiva, and through the nasolacrimal duct with the mucous membrane of the nasal cavity.

Organ of Hearing and Equilibration: The Ear The ear (organum vestibulocochleare; organum oticum; organum stato-acousticum), or organ of hearing and equilibra¬ tion, is divisible into three parts: the external ear, the middle ear or tympanic cavity, and the internal ear or labyrinth. development

The first rudiment of the internal ear ap¬ pears shortly after that of the eye in the form of a patch of thickened ectoderm, the audi¬ tory plate, over the region of the hindbrain. The auditory plate becomes depressed and converted into the auditory pit (Fig. 13-38). The mouth of the pit is then closed, and the auditory vesicle is formed (Fig. 13-39); from this the epithelial lining of the membranous labyrinth is derived. From the vesicle certain diverticula are given off that form the var¬ ious parts of the membranous labyrinth (Figs.

Cavity of hindbrain

Section through the head of a human em¬ bryo, about 12 days old, in the region of the hindbrain. (Kollmann.) Fig. 13-38

1 Joseph Ritter von Artha Hasner (1819-1892): A Bohe¬ mian ophthalmologist (Prague).

ORGAN OF HEARING AND EQUILIBRATION

Hindbrain

Section through hindbrain and auditory vesicles of an embryo more advanced than that of Figure 13-38. (After His.) Fig. 13-39.

13-40; 13-41). One from the middle part forms the ductus and saccus endolymphaticus; another from the anterior end gradually elongates, and forming a tube coiled on it¬ self, becomes the cochlear duct, the vestibu¬ lar extremity of which is subsequently con¬ stricted to form the canalis reuniens. Three other diverticula appear as disc-like evaginations on the surface of the vesicle. The central parts of the walls of the discs coa¬ lesce and disappear, while the peripheral portions persist to form the semicircular ducts; of these, the anterior is the first and the lateral is the last to be completed. The central part of the vesicle represents the membranous vestibule, and this is subdi¬ vided by a constriction into a smaller ventral part, the saccule, and a larger dorsal and posterior part, the utricle. This subdivision is effected by a fold that extends deeply into the proximal part of the ductus endolym¬ phaticus, so that the utricle and saccule ulti¬ mately communicate with each other by means of a Y-shaped canal. The saccule opens into the cochlear duct through the canalis reuniens, and the semicircular ducts communicate with the utricle. The mesodermal tissue surrounding the various parts of the epithelial labyrinth is converted into a cartilaginous capsule, and this is finally ossified to form the bony laby¬ rinth. Between the cartilaginous capsule and the epithelial structures is a stratum of meso¬ dermal tissue that is differentiated into three layers: an outer layer, which forms the peri¬ osteal lining of the bony labyrinth; an inner layer, which is in direct contact with the epi¬ thelial structures; and an intermediate layer, which consists of gelatinous tissue. The perilymphatic spaces are developed by the absorption of this gelatinous tissue. The modiolus and osseous spiral lamina of the cochlea are not preformed in cartilage but are ossified directly from connective tissue.

THE EAR

1313

The middle ear and auditory tube are de¬ veloped from the first pharyngeal pouch. The entodermal lining of the dorsal end of this pouch is in contact with the ectoderm of the corresponding pharyngeal groove; by the extension of the mesoderm between these two layers, the tympanic membrane forms. During the sixth or seventh month, the tym¬ panic antrum appears as an upward and backward expansion of the tympanic cavity. There is some difference of opinion regard¬ ing the exact mode of development of the ossicles of the middle ear. The view gener¬ ally held is that the malleus develops from the proximal end of the mandibular (Meck¬ el’s) cartilage (Fig. 2-48); the incus develops in the proximal end of the mandibular arch; and the stapes develops from the proximal end of the hyoid arch. The malleus, with the exception of its anterior process, is ossified from a single center that appears near the neck of the bone; the anterior process is ossi¬ fied separately in membrane and joins the main part of the bone about the sixth month of fetal life. The incus is ossified from one center that appears in the upper part of its long crus and ultimately extends into its len¬ ticular process. The stapes first appears as a ring (anulus stapedius) encircling a small vessel, the stapedial artery, which subse¬ quently atrophies; it is ossified from a single center in its base. The external ear and external acoustic meatus develop from the first branchial groove. The lower part of this groove ex¬ tends inward as a funnel-shaped tube (pri¬ mary meatus), from which the cartilaginous portion and a small part of the roof of the osseous portion of the meatus are developed. From the lower part of the funnel-shaped tube, an epithelial lamina extends down¬ ward and inward along the inferior wall of the primitive tympanic cavity; by the split¬ ting of this lamina the inner part of the mea¬ tus (secondary meatus) is produced, while the inner portion of the lamina forms the cutaneous stratum of the tympanic mem¬ brane. The auricula or pinna develops by the gradual differentiation or tubercles that ap¬ pear around the margin of the first branchial groove (see Chapter 2 and Fig. 2-57). The acoustic nerve rudiment appears about the end of the third week as a group of ganglion cells closely applied to the cranial edge of the auditory vesicle. Whether these cells are derived from the ectoderm adjoin-

1314

ORGANS OF THE SPECIAL SENSES

d. sc. post. d. sc. ant *

’

Hr- Lateral groove

B ■ d. sc. lat.

4.3 mm front

' Cochlea

6.6 mm lateral 9 mm lateral

absorpt. focu.

20 mm lateral

30 mm lateral

Lateral views of membranous labyrinth and acoustic complex. 25 x dia. (Streeter.) absorpt. focu, Area of wall where absorption is complete; amp., ampulla membranacea; crus, crus commune; d. sc. lat., ductus semicircularis lateralis; d. sc. post., ductus semicircularis posterior; d. sc. ant., ductus semicircular anterior; coch. or cochlea, ductus cochlearis; duct, endolymph, ductus endolymphaticus; d. reuniens, ductus reuniens Henseni; endol. or endolymphs, appendix endolymphaticus; rec. utr., recessus utriculi; sacc., sacculus; sac endol., saccus endolymphaticus; sinu utr. lat., sinus utriculi lateralis; utric., utriculus; vestib. p., vestibular pouch.

Fig. 13-40.

ing the auditory vesicle or whether they have migrated from the wall of the neural tube is not yet certain. The ganglion gradu¬ ally splits into two parts: the vestibular gan¬ glion and the spiral ganglion. The peripheral branches of the vestibular ganglion pass in two divisions; the pars superior gives rami to

the superior ampulla of the anterior semicir¬ cular duct, to the lateral ampulla, and to the utricle; the pars inferior gives rami to the saccule and the posterior ampulla. The prox¬ imal fibers of the vestibular ganglion form the vestibular nerve; the proximal fibers of the spiral ganglion form the cochlear nerve.

ORGAN OF HEARING AND EQUILIBRATION

THE EAR

1315

Endolymph Vestib. pouch.N

—Utic.-sacc.

6.6 mm median

Cochlea 9 mm median

1 1 mm median

1 3 mm median

20 mm median Fig. 13-41.

30 mm median

Median views of membranous labyrinth and acoustic complex in human embryos. 25

x

dia. (Streeter.)

EXTERNAL EAR

Auricula

The external ear consists of the expanded portion named the auricula or pinna and the external acoustic meatus. The former pro¬ jects from the side of the head and collects the vibrations of the air by which sound is produced; the latter leads inward from the bottom of the auricula and conducts the vi¬ brations to the tympanic cavity.

The auricula or pinna (Fig. 13-42) is ovoid, with its larger end directed upward. Its lat¬ eral surface is irregularly concave, directed slightly anteriorly, and has numerous emi¬ nences and depressions, to which names have been assigned. The prominent rim of the auricula is called the helix. Where the helix turns inferiorly, a small tubercle, the auricu-

1316

Fig. 13-42.

ORGANS OF THE SPECIAL SENSES

The auricula, lateral surface.

lar tubercle of Darwin, is frequently seen; this tubercle is evident about the sixth month of fetal life, when the whole auricula closely resembles that of some adult mon¬ keys. Another curved prominence, parallel with and anterior to the helix, is called the antihelix; this divides above into two crura, between which is a triangular depression, the fossa triangularis. The narrow curved depression between the helix and the anti¬ helix is called the scapha. The antihelix de¬ scribes a curve around a deep, capacious cavity, the concha, which is partially di¬ vided into two parts by the crus or com¬ mencement of the helix; the superior part is termed the cymba conchae, and the inferior part is called the cavum conchae. Anterior to the concha and projecting posteriorly over the meatus is a small pointed eminence, the tragus, so called because it is generally cov¬ ered on its undersurface with a tuft of hair resembling a goat’s beard. Opposite the tra¬ gus and separated from it by the intertragic notch is a small tubercle, the antitragus. Below this is the lobule, which is composed of areolar and adipose tissues and lacks the firmness and elasticity of the rest of the auricula. The cranial surface of the auricula pres¬ ents elevations that correspond to the de¬ pressions on its lateral surface, after which they are named, e.g., eminentia conchae, eminentia triangularis.

parts by ligaments and muscles and to the commencement of the external acoustic meatus by fibrous tissue. integument. The skin is thin, closely adherent to the cartilage, and covered with fine hairs furnished with sebaceous glands, which are most numerous in the concha and scaphoid fossa. On the tragus and antitragus, the hairs are strong and numerous. The skin of the auricula is continuous with that lining the external acoustic meatus. cartilage. The cartilage of the auricula (cartilago auriculae; cartilage of the pinna) (Figs. 13-42; 13-43) consists of a single piece; it gives form to this part of the ear, and upon its surface are found the eminences and de¬ pressions just described. It is absent from the lobule; it is also deficient between the tragus and beginning of the helix, the gap being filled by dense fibrous tissue. At the front of the auricula, where the helix bends upward, is a small projection of cartilage called the spina helicis; in the lower part of the helix, the cartilage is prolonged down¬ ward as a tail-like process, the cauda helicis; this is separated from the antihelix by a fissure, the fissura antitragohelicina. The cranial aspect of the cartilage exhibits a transverse furrow, the sulcus antihelicis transversus, which corresponds with the inferior crus of the antihelix and separates the eminentia conchae from the eminentia triangularis. The eminentia conchae is crossed by a vertical ridge (ponticulus), which gives attachment to the auricularis posterior muscle. In the cartilage of the auri¬ cula are two fissures, one behind the crus helicis and another in the tragus.

STRUCTURE OF THE AURICULA

The auricula is composed of a thin plate of yellow elastic cartilage covered with integu¬ ment; it is connected to the surrounding

Fig. 13-43.

cula.

Cranial surface of cartilage of right auri¬

ORGAN OF HEARING AND EQUILIBRATION

The ligaments of the auricula (ligamenta auricularia [Valsalva1]; liga¬ ments of the pinna) consist of two sets: (1) extrinsic, connecting the auricula to the side of the head; (2) intrinsic, connecting various parts of the cartilage together. The extrinsic ligaments are two, anterior and posterior. The anterior ligament ex¬ tends from the tragus and spina helicis to the root of the zygomatic process of the tempo¬ ral bone. The posterior ligament passes from the posterior surface of the concha to the outer surface of the mastoid process. The chief intrinsic ligaments are: (1) a strong fibrous band that stretches from the tragus to the commencement of the helix, completing the meatus in front and partly encircling the boundary of the concha; and (2) a band between the antihelix and the cauda helicis. Other less important bands are found on the cranial surface of the pinna. muscles. The muscles of the auricula (Fig. 13-44) consist of two sets: (1) extrinsic, which connect the auricula with the skull and scalp and move it as a whole; and (2) intrinsic, which extend from one part of the auricle to another. ligaments.

Antonio Maria Valsalva (1666-1723): An Italian anato¬ mist (Bologna).

THE EAR

1317

The extrinsic muscles are the auriculares anterior, superior, and posterior, described with the facial muscles in Chapter 6. The intrinsic muscles are: Helicis major Helicis minor Tragicus Antitragicus Transversus auriculae Obliquus auriculae The helicis major is a narrow vertical band situated upon the anterior margin of the helix. It arises from the spina helicis and is inserted into the anterior border of the helix, where the helix is about to curve backward. The helicis minor is an oblique fasciculus that covers the crus helicis. The tragicus is a short, flat vertical band on the lateral surface of the tragus. The antitragicus arises from the outer part of the antitragus and is inserted into the cauda helicis and antihelix. The transversus auriculae is placed on the cranial surface of the pinna. It consists of scattered fibers, partly tendinous and partly muscular, that extend from the eminentia conchae to the prominence corresponding with the scapha. The obliquus auriculae, also on the cra¬ nial surface, consists of a few fibers that extend from the upper and back part of the concha to the convexity immediately above it. vessels. The arteries of the auricula are the posterior auricular from the external carotid, the an¬ terior auricular from the superficial temporal, and a branch from the occipital artery. The veins accompany the corresponding arteries. nerves. The auriculares anterior and superior and the intrinsic muscles on the lateral surface are supplied by the temporal branch of the facial nerve. The auricularis posterior and the intrinsic muscles on the cranial surface are supplied by the posterior au¬ ricular branch of the same nerve. The sensory nerves are: the great auricular, from the cervical plexus; the auricular branch of the vagus; the auriculotemporal branch of the mandibu¬ lar nerve; and the lesser occipital from the cervical plexus.

External Acoustic Meatus

Fig.

13-44.

The muscles of the auricula.

The external acoustic meatus (external auditory canal or meatus) extends from the bottom of the concha to the tympanic mem-

1318

ORGANS OF THE SPECIAL SENSES

Cartilage of auricula Attic Incus Malleus Tympanic cavity Tensor tympani

Nasal

part pharynx

Tympanic membrane Cartilaginous part of ext. acoustic meatus

Bony part of ext. acoustic meatus

Fig. 13-45.

External and middle ear, opened anteriorly; right side.

brane (Figs. 13-45; 13-46). It is about 4 cm long if measured from the tragus; from the bottom of the concha it is about 2.5 cm long. It forms an S-shaped curve, and is directed at first inward, forward, and slightly upward (pars externa); it then passes inward and backward (pars media), and lastly is carried

inward, forward, and slightly downward (pars interna). It is an oval cylindrical canal, the greatest diameter being directed down¬ ward and backward at the external orifice, but nearly horizontal at the inner end. It has two constrictions, one near the inner end of the cartilaginous portion, and another, the

Auditory tube of mandible

Internal carotid artery

Part of parotid gland Tragus External acoustic meatus

Internal acoustic meatus

Tympanic cavity Tympanic membran Mastoid air-cells

Transverse sinus

Fig. 13-46.

Horizontal section through left ear; upper half of section.

ORGAN OF HEARING AND EQUILIBRATION

isthmus, in the osseous portion about 2 cm from the bottom of the concha. The tym¬ panic membrane, which closes the inner end of the meatus, is directed obliquely, so the floor and anterior wall of the meatus are longer than the roof and posterior wall. The external acoustic meatus is formed partly by cartilage and membrane and partly by bone, and it is lined with skin. The cartilaginous portion is about 8 mm long; it is continuous with the cartilage of the auricula and firmly attached to the cir¬ cumference of the auditory process of the temporal bone. The cartilage is deficient at the cranial and posterior part of the meatus, where it is replaced by fibrous membrane; two or three deep fissures are present in the anterior part of the cartilage. The osseous portion is about 16 mm long and is narrower than the cartilaginous por¬ tion. It is directed inward and a little for¬ ward, forming in its course a slight curve, the convexity of which is upward and back¬ ward. The inner end is smaller than the outer end and is sloped; the anterior wall projects beyond the posterior for about 4 mm. This end is marked, except at its cra¬ nial part, by a narrow groove, the tympanic sulcus, in which the circumference of the tympanic membrane is attached. Its outer end is dilated and rough in the greater part of its circumference for the attachment of the cartilage of the auricula. The anterior and inferior parts of the osseous portion are formed by a curved plate'of bone—the tym¬ panic part of the temporal bone—which in the fetus exists as a separate ring (anulus tympanicus) that is incomplete at its cranial part (Chapter 4). The skin lining the meatus is very thin; it adheres closely to the cartilaginous and os¬ seous portions of the tube and covers the outer surface of the tympanic membrane. After maceration, the thin pouch of epider¬ mis, when withdrawn, preserves the form of the meatus. In the thick subcutaneous tissue of the cartilaginous part of the meatus are numerous ceruminous glands that secrete the ear wax; their structure resembles that of the sudoriferous glands. RELATIONS of the meatus. Anterior to the osse¬ ous part is the condyle of the mandible, but the latter is frequently separated from the cartilaginous part by a portion of the parotid gland. The movements of the jaw influence to some extent the lumen of this

THE EAR

1319

latter portion. Posterior to the osseous part are the mastoid air cells, which are separated from the mea¬ tus by a thin layer of bone. vessels. The arteries supplying the walls of the meatus are branches from the posterior auricular, maxillary, and superficial temporal arteries. nerves. The nerves are chiefly derived from the auriculotemporal branch of the mandibular nerve and the auricular branch of the vagus.

MIDDLE EAR OR TYMPANUM

The middle ear or tympanic cavity (drum; tympanum) is an irregular, laterally com¬ pressed space within the temporal bone. It is filled with air, which is conveyed to it from the nasal part of the pharynx through the auditory tube. The cavity contains a chain of tiny movable bones that bridge from its lateral to its medial wall and convey the vibrations communicated to the tym¬ panic membrane across the cavity to the in¬ ternal ear. The tympanic cavity consists of two parts; the tympanic cavity proper, opposite the tympanic membrane, and the attic or epitympanic recess, cranial to the level of the membrane which contains the upper half of the malleus and the greater part of the incus. Including the attic, the vertical and antero¬ posterior diameters of the cavity are each about 15 mm. The transverse diameter meas¬ ures about 6 mm superiorly and 4 mm interi¬ orly; opposite the center of the tympanic membrane it is only about 2 mm. The tym¬ panic cavity is bounded laterally by the tym¬ panic membrane; medially, by the lateral wall of the internal ear. It communicates posteriorly with the tympanic antrum and through it with the mastoid air cells; anteri¬ orly, the tympanic cavity communicates with the auditory tube (Fig. 13-45). Tegmental Wall or Roof

The roof is formed by a thin plate of bone, the tegmen tympani, which separates the tympanic from the cranial cavity. It is situ¬ ated on the anterior surface of the petrous portion of the temporal bone close to its angle of junction with the squama tempo¬ ralis. It is prolonged posteriorly to roof in the tympanic antrum, and anteriorly to cover the semicanal for the tensor tympani muscle. Its lateral edge corresponds with the remains of the petrosquamous suture.

1320

ORGANS OF

THE SPECIAL SENSES

Jugular Wall or Floor

The floor is narrow and consists of a thin plate of bone (fundus tympani), which sepa¬ rates the tympanic cavity from the jugular fossa. It has, near the labyrinthic wall, a small aperture for the passage of the tym¬ panic branch of the glossopharyngeal nerve. Membranous or Lateral Wall

The lateral wall (outer wall) is formed mainly by the tympanic membrane and partly by the ring of bone into which this membrane is inserted. The ring of bone is incomplete at its upper part, forming a notch (of Rivinus1), close to which are three small apertures: the iter chordae posterius, the petrotympanic fissure, and the iter chordae anterius. The iter chordae posterius (apertura tympanica canaliculi chordae) is situated in the angle of junction between the mastoid and membranous wall of the tympanic cavity, 1Augustus Quirinus Rivinus (1652-1723): A German anatomist and botanist (Leipzig).

immediately posterior to the tympanic mem¬ brane and on a level with the superior end of the manubrium of the malleus. It leads into a minute canal in the mastoid bone that de¬ scends almost parallel with the facial nerve and meets the facial canal at an acute angle near the stylomastoid foramen. Through it the chorda tympani nerve enters the tym¬ panic cavity (Fig. 13-47). The petrotympanic fissure (Giaserian fis¬ sure2) (Fig. 13-47) opens just superior and anterior to the ring of bone into which the tympanic membrane is inserted; in this situ¬ ation it is a mere slit about 2 mm long. It lodges the anterior process and anterior liga¬ ment of the malleus and gives passage to the anterior tympanic branch of the maxillary artery. The iter chordae anterius (canal of Huguier3) is at the medial end of the petro¬ tympanic fissure; through it the chorda tym¬ pani nerve leaves the tympanic cavity. 2Johann Heinrich Glaser (1629-1675): A Swiss anatomist (Basel). 3Pierre Charles Huguier (1804-1874): A French surgeon (Paris).

Superior ligament of malleolus

Epitympanic recess

Articular surface for body of incus

Neck of malleus Anterior ligament and anterior process of malleolus

Flaccid portion of membrana tympani Posterior tympanic spine

Insertion of tensor tympani muscle

Tympanic orifice of canal for chorda tympani nerve

Giaserian fissure

Eustachian tube

Tense portion of membrana tympani Fig. 13 47.

The right membrana tympani with the malleus and the chorda tympani, viewed from within. (Spalteholz.)

ORGAN OF HEARING AND EQUILIBRATION

Tympanic Membrane

The tympanic membrane (Figs. 13-47; 1348) separates the tympanic cavity from the bottom of the external acoustic meatus. It is a thin, semitransparent membrane, nearly oval, directed very obliquely inferiorly and medially to form an angle of about 55° with the floor of the meatus. Its longest diameter, almost vertical, measures 9 to 10 mm; its shortest diameter measures 8 to 9 mm. The greater part of its circumference is thick and forms a fibrocartilaginous ring, which is fixed in the tympanic sulcus at the inner end of the meatus. This sulcus is deficient superi¬ orly at the notch of Rivinus, and from the ends of this notch two bands, the anterior and posterior malleolar folds, are prolonged to the lateral process of the malleus. The small, somewhat triangular part of the mem¬ brane situated superior to these folds is lax

THE EAR

1321

and thin and is named the pars flaccida, as opposed to the rest of the membrane, which is called the pars tensa. The manubrium of the malleus is firmly attached to the medial surface of the membrane as far as its center, which it draws inward toward the tympanic cavity. The lateral surface of the membrane is thus concave, and the most depressed part of this concavity is named the umbo. STRUCTURE OF THE TYMPANIC MEMBRANE

The tympanic membrane is composed of three strata: lateral (cutaneous), intermedi¬ ate (fibrous), and medial (mucous). The cuta¬ neous stratum is derived from the integu¬ ment lining the meatus. The fibrous stratum consists of two layers: a radiate stratum, the fibers of which diverge from the manubrium of the malleus, and a circular stratum, the fibers of which are plentiful around the cir-

Flaccid portion of the tympanic membrane

Posterior malleolar fold Anterior malleolar fold

Long limb of incus Malleolar prominence

Malleolar stria Promontory Tense portion of the tympanic membrane

Umbo Tympanic ring

Fibrocartilaginous ring

Fig. 13-48.

The lateral aspect of the right tympanic membrane as seen through an otoscope. The membrane is oval and measures about 11 mm in its long diameter and about 9 mm across. (Redrawn after Sobotta.)

1322

ORGANS OF THE SPECIAL SENSES

ontory, and the prominence of the facial canal (Fig. 13-49). The fenestra vestibuli (fenestra ovalis; oval window) is a reniform opening leading from the tympanic cavity into the vestibule of the internal ear. Its long diameter is hori¬ zontal, and its convex border is upward. In the intact body it is occupied by the base of the stapes, the circumference of which is secured by the annular ligament to the mar¬ gin of the foramen (Fig. 13-50). The fenestra cochleae (fenestra rotunda; round window) is situated inferior and a lit¬ tle posterior to the fenestra vestibuli, from which it is separated by a rounded elevation, the promontory. It is placed at the bottom of a funnel-shaped depression and, in the mac¬ erated bone, leads into the cochlea of the in¬ ternal ear; in the intact body it is closed by a membrane, the secondary tympanic mem¬ brane, which is concave toward the cochlea. This membrane consists of three layers: an external or mucous layer derived from the mucous lining of the tympanic cavity; an in¬ ternal layer from the lining membrane of the cochlea; and an intermediate or fibrous layer. The promontory (promontorium) is a rounded prominence formed by the outward

cumference but sparse and scattered near the center of the membrane. Branched or dendritic fibers are also present, especially in the posterior half of the membrane. The mucous stratum is the internal surface of the membrane derived from the lining of the cavity. vessels and nerves. The arteries of the tym¬ panic membrane are derived from the deep auricular branch of the maxillary artery, which ramifies be¬ neath the cutaneous stratum, and from the stylo¬ mastoid branch of the posterior auricular artery and the tympanic branch of the maxillary artery, which are distributed on the mucous surface. The superfi¬ cial veins open into the external jugular; those on the deep surface drain partly into the transverse sinus and veins of the dura mater, and partly into a plexus on the auditory tube. The membrane receives its chief nerve supply from the auriculotemporal branch of the mandibular nerve; the auricular branch of the vagus and the tympanic branch of the glossopharyngeal nerve also supply it.

Labyrinthic or Medial Wall The medial wall (inner wall) is directed vertically and presents for examination the fenestrae vestibuli and cochleae, the prom¬

Tympanic antrum Tegmen tympani Prominence of lateral semicircular canal Prominence of facial canal Fenestra vestibuli Bristle in semicanal for tensor tympani Septum canalis musculotubarii Bristle in hiatus of facial canal

Carotid canal Bony part of auditory tube Promontory Bristle in pyramid Fenestra cochleae Sulcus tympanicus Mastoid cells Bristle in stylomastoid foramen Fig. 13-49.

Coronal section of right temporal bone.

ORGAN OF HEARING AND EQUILIBRATION: THE EAR

Junction between mas¬ toid antrum and epitympanic recess

1323

Epitympanic recess Prominence of lateral semicircular canal Prominence of facial canal Tendon of stapedius muscle Plica stapedius Processus cochleariformis Tensor tympani muscle (cut through) Wall of labyrinth

Fossa incudis Posterior sinus Pyramidal eminence Tympanic sinus

Fossula of fenestra rotunda

Jugular wall

Tympanic plexus

The medial wall and part of the posterior and anterior walls of the right tympanic cavity, lateral view. (Spalteholz.) (See Fig. 13-49.)

Fig. 13-50.

projection of the first turn of the cochlea. It is placed between the fenestrae, and its sur¬ face is furrowed by small grooves for the nerves of the tympanic plexus. A minute spicule of bone frequently connects the promontory to the pyramidal eminence. The prominence of the facial canal (promi¬ nentia canalis facialis; prominence of aque¬ duct of Fallopius1) indicates the position of the bony canal in which the facial nerve is contained; this canal traverses the labyrinthic wall of the tympanic cavity superior to the fenestra vestibuli, and posterior to that opening, curves nearly vertically interiorly along the mastoid wall (Fig. 13-51). Mastoid or Posterior Wall The posterior wall presents for examina¬ tion the entrance to the tympanic antrum, the pyramidal eminence, and the fossa incudis. The entrance to the antrum is a large, ir'Gabriele Falloppio (1523-1563): An Italian anatomist and surgeon (Padua).

regular aperture that leads posteriorly from the epitympanic recess into a considerable air space, the tympanic or mastoid antrum (see Chapter 4). The antrum leads posteri¬ orly and interiorly into the mastoid air cells, which vary greatly in number, size, and form. The antrum and mastoid air cells are lined by mucous membrane that is continu¬ ous with that which lines the tympanic cav¬ ity. On the medial wall of the entrance to the antrum is a rounded eminence, situated su¬ perior and posterior to the prominence of the facial canal; it corresponds with the posi¬ tion of the ampullated ends of the anterior and lateral semicircular canals. The pyramidal eminence (pyramid) is sit¬ uated immediately posterior to the fenestra vestibuli and anterior to the vertical portion of the facial canal. It is hollow but contains the stapedius muscle. Its summit projects anteriorly toward the fenestra vestibuli and is pierced by a small aperture that transmits the tendon of the muscle. The cavity in the pyramidal eminence is prolonged posteri¬ orly toward the facial canal and communi¬ cates with it by a minute aperture that trans-

1 324

ORGANS OF THE SPECIAL SENSES

Fig. 13-51.

View of the medial wall of the tympanum (enlarged). (See Fig. 13-49.)

mits a branch of the facial nerve to the stapedius muscle. The fossa incudis is a small depression in the inferior and posterior part of the epitympanic recess; it lodges the short crus of the incus. Carotid or Anterior Wall The anterior wall corresponds with the carotid canal, from which it is separated by a thin plate of bone that is perforated by the tympanic branch of the internal carotid ar¬ tery and the caroticotympanic nerve, which connects the sympathetic plexus on the in¬ ternal carotid artery with the tympanic plexus on the promontory. At the superior part of the anterior wall are the orifice of the semicanal for the tensor tympani muscle and the tympanic orifice of the auditory tube, separated from each other by a thin horizon¬ tal plate of bone, the septum canalis musculotubarii. These canals run from the tym¬ panic cavity medialward to the retiring angle between the squama and the petrous portion of the temporal bone. The semicanal for the tensor tympani (semicanalis m. tensoris tympani) is the su¬ perior and the smaller of the two canals; it is cylindrical and lies beneath the tegmen tym¬ pani. It extends to the labyrinthic wall of the tympanic cavity and ends immediately above the fenestra vestibuli. The septum canalis musculotubarii (processus cochleariformis) passes posteriorly, forming its lateral wall and floor; it expands above the anterior end of the fenestra vestibuli and terminates there by curving laterally to form a pulley over which the tendon of the muscle passes.

Auditory Tube The auditory tube (tuba auditiva; Eusta¬ chian tube1) is the channel through which the tympanic cavity communicates with the nasal part of the pharynx. Its length is about 36 mm, and in its medialward course it forms an angle of about 45° with the sagittal plane and an angle of 30 to 40° with the hori¬ zontal plane. Its walls are composed partly of bone and partly of cartilage and fibrous tissue (Fig. 13-45). The osseous portion is about 12 mm long. It begins in the carotid wall of the tympanic cavity, inferior to the septum canalis musculotubarii, and gradually narrowing, ends at the angle of junction of the squama and the petrous portion of the temporal bone. Its extremity has a jagged margin that serves for the attachment of the cartilagi¬ nous portion. The cartilaginous portion, about 24 mm long, is contained in a triangular plate of elastic fibrocartilage, the apex of which is attached to the margin of the medial end of the osseous portion of the tube, while the base lies directly under the mucous mem¬ brane of the nasal part of the pharynx, where it forms an elevation, the torus tubarius or cushion, posterior to the pharyn¬ geal orifice of the tube. The superior edge of the cartilage is bent over laterally, forming a groove or furrow that is open inferiorly and laterally. The part of the canal lying in this furrow is completed by fibrous membrane. The cartilage lies in a groove between the petrous part of the temporal and the great 'Bartolommeo Eustachio (15207-1574): An Italian anato¬ mist (Rome).

ORGAN OF HEARING AND EQUILIBRATION

wing of the sphenoid, and it ends opposite the middle of the medial pterygoid plate. The cartilaginous and bony portions of the tube are not in the same plane, the former inclining inferiorly a little more than the lat¬ ter. The diameter of the tube is not uniform throughout; it is greatest at the pharyngeal orifice, least at the junction of the bony and cartilaginous portions, and again increases toward the tympanic opening. The narrow¬ est part of the tube is termed the isthmus. The position and relations of the pharyngeal orifice are described with the nasal part of the pharynx. The mucous membrane of the tube is con¬ tinuous with that of the nasal part of the pharynx and the tympanic cavity. It is cov¬ ered with ciliated epithelium and is thin in the osseous portion, while in the cartilagi¬ nous portion it contains many mucous glands and, near the pharyngeal orifice, a considerable amount of adenoid tissue, the tubal tonsil. The tube is opened during de¬ glutition by the salpingopharyngeus and dilatator tubae muscles. The latter arises from the hook of the cartilage and from the membranous part of the tube and blends below with the tensor veli palatini. Auditory Ossicles The tympanic cavity contains a chain of three movable ossicles, the malleus, incus, and stapes. The first is attached to the tym¬ panic membrane, the last’ to the circumfer¬ ence of the fenestra vestibuli, the incus being placed between and connected to both by delicate articulations (Fig. 13-55). malleus. The malleus (Fig. 13-52), so named from its fancied resemblance to a hammer, consists of a head, neck, and three

THE EAR

1325

processes, viz., the manubrium and the ante¬ rior and lateral processes. The head is the large superior extremity of the bone; it is oval and articulates posteri¬ orly with the incus, being free in the rest of its extent. The facet for articulation with the incus is constricted near the middle and con¬ sists of a superior larger and an inferior smaller part, which are bent nearly at a right angle to each other. Opposite the constric¬ tion, the inferior margin of the facet projects in the form of a process, the cog-tooth or spur of the malleus. The neck is the narrow contracted part joining the head with a prominence to which the anterior and posterior processes are at¬ tached. The manubrium mallei is connected by its lateral margin with the tympanic membrane. It is directed slightly posteriorly as well as inferiorly; it decreases in size toward its free end, which is slightly curved and flattened transversely. On its medial side, near the head end, is a slight projection into which the tendon of the tensor tympani is inserted. The anterior process is a delicate spicule directed anteriorly toward the petrotym¬ panic fissure, to which it is connected by lig¬ amentous fibers. In the fetus this is the long¬ est process of the malleus, and it is directly continuous with the cartilage of Meckel.1 The lateral process is a slight conical pro¬ jection that springs from the root of the ma¬ nubrium. It is directed laterally and is at¬ tached to the superior part of the tympanic membrane and, by means of the anterior and posterior malleolar folds, to the extremities of the notch of Rivinus. incus. The incus (Fig. 13-53) received its name from its resemblance to an anvil, but it looks more like a premolar tooth with two Johann Friedrich Meckel (the Younger) (1781-1833): A

Head

German anatomist and surgeon (Halle).

Facet for incus Lateral process

Neck

Facet for malleus Anterior process

Manu¬ brium

Short crus Body

Fig. 13-52.

view.

Left malleus. A, Posterior view. B, Medial

Fig.

13-53.

view.

Left incus. A, Medial view. B, Anterior

1326

ORGANS OF THE SPECIAL SENSES

roots that differ in length and are widely sep¬ arated from each other. It consists of a body and two crura. The body is somewhat cubical but com¬ pressed transversely. On its anterior surface is a deeply concavo-convex facet that articu¬ lates with the head of the malleus. The two crura diverge from each other nearly at right angles. The short crus, which is somewhat conical, projects almost hori¬ zontally backward and is attached to the fossa incudis in the posterior part of the epitympanic recess. The long crus descends nearly vertically parallel to the manubrium of the malleus and, bending medialward, ends in a rounded projection, the lenticular process, which is tipped with cartilage and articulates with the head of the stapes. stapes. The stapes (Fig. 13-54), so called from its resemblance to a stirrup, consists of a head, neck, two crura, and a base. The head has a depression, which is cov¬ ered by cartilage; it articulates with the len¬ ticular process of the incus. The neck, the constricted part of the bone succeeding the head, has the insertion of the tendon of the stapedius muscle attached to it. The two crura diverge from the neck and are connected at their ends by a flattened oval plate, the base, which forms the foot¬ plate of the stirrup and is fixed to the margin of the fenestra vestibuli by a ring of ligamen¬ tous fibers. Of the two crura, the anterior is shorter and less curved than the posterior.

LIGAMENTS OF THE OSSICLES. The OSSicleS are connected with the walls of the tym¬ panic cavity by ligaments: three for the mal¬ leus and one each for the incus and stapes (Fig. 13-55). The anterior ligament of the malleus is at¬ tached by one end to the neck of the malleus, just above the anterior process, and by the other end to the anterior wall of the tym¬ panic cavity, close to the petrotympanic fissure. Some of its fibers are prolonged through the fissure to reach the spine of the sphenoid bone. The superior ligament of the malleus is a delicate, round bundle that descends from the roof of the epitympanic recess to the head of the malleus. The lateral ligament of the malleus is a tri¬ angular band passing from the posterior part of the notch of Rivinus to the head of the malleus. Helmholtz described the anterior ligament and the posterior part of the lateral ligament as forming together the axis liga¬ ment, around which the malleus rotates. The posterior ligament of the incus is a short, thick band connecting the end of the short crus of the incus to the fossa incudis. A superior ligament of the incus has been described, but it is little more than a fold of mucous membrane. The vestibular surface and the circumfer-

ARTICULATIONS OF THE AUDITORY OSSICLES.

The incudomcilleolar joint is a saddleshaped diarthrosis; it is surrounded by an articular capsule, and the joint cavity is incompletely divided into two by a wedgeshaped articular disc or meniscus. The incudostapedial joint is an enarthrosis surrounded by an articular capsule. Some observers have described an articular disc or meniscus in this joint; oth¬ ers regard the joint as a syndesmosis.

Head

B Fig. 13-54.

surface.

A, Left stapes. B, Base of stapes, medial

Fig. 13-55. Chain of ossicles and their ligaments, ante¬ rior view of a vertical transverse section of the tympa¬ num. (Testut.)

ORGAN OF HEARING AND EQUILIBRATION

ence of the base of the stapes are covered with hyaline cartilage. The cartilage that encircles the base is attached to the margin of the fenestra vestibuli by a fibrous ring, the annular ligament of the base of the stapes. Muscles of the Tympanic Cavity

These are the tensor tympani and the sta¬ pedius (Figs. 13-45; 13-50). The tensor tympani is contained in the bony canal above the osseous portion of the auditory tube, from which it is separated by the septum canalis musculotubarii. It arises from the cartilaginous portion of the audi¬ tory tube and the adjoining part of the great wing of the sphenoid, as well as from the osseous canal in which it is contained. Pass¬ ing posteriorly through the canal, it ends in a slender tendon that enters the tympanic cav¬ ity, makes a sharp bend around the extrem¬ ity of the septum, the processus cochleariformis, and is inserted into the manubrium of the malleus, near its root. It is supplied by a branch of the mandibular nerve that passes through the otic ganglion. The stapedius arises from the wall of the conical cavity inside the pyramid. Its tendon emerges from the orifice at the apex of the eminence, and is inserted into the posterior surface of the neck of the stapes. It is sup¬ plied by a branch of the facial nerve. actions. The tensor tympani draws the tym¬ panic membrane medialward, and thus increases its tension. The stapedius pulls the head of the stapes posteriorly, tilting the base and possibly increasing the tension of the fluid within the internal ear. Both muscles have a snubbing action, reducing the oscil¬ lations of the ossicles and thereby protecting the inner ear from injury during a loud noise, such as that of a riveting machine.

Mucous Membrane of the Tympanic Cavity

This membrane is continuous with that of the pharynx through the auditory tube. It invests the auditory ossicles, the muscles, and the nerves contained in the tympanic cavity. It forms the medial layer of the tym¬ panic membrane and the lateral layer of the secondary tympanic membrane, and is re¬ flected into the tympanic antrum and mas¬ toid cells, which it lines throughout. It forms several folds that extend from the walls of the tympanic cavity to the ossicles. Of these,

THE EAR

1327

one descends from the roof of the cavity to the head of the malleus and superior margin of the body of the incus; a second invests the stapedius muscle. Other folds invest the chorda tympani nerve and the tensor tym¬ pani muscle. These folds separate pouch¬ like cavities and give the interior of the tym¬ panum a somewhat honey-combed appear¬ ance. One of these pouches, the pouch of Prussak1, is well marked and lies between the neck of the malleus and the membrana flaccida. Two other recesses may be men¬ tioned: they are formed by the mucous mem¬ brane that envelops the chorda tympani nerve and are named the anterior and poste¬ rior recesses of Troltsch2. In the tympanic cavity this membrane is pale, thin, slightly vascular, and covered for the most part with columnar ciliated epithelium, but over the pyramidal eminence, ossicles, and tympanic membrane it possesses a flat, nonciliated epithelium. In the tympanic antrum and mastoid cells, its epithelium is also non¬ ciliated. In the osseous portion of the audi¬ tory tube the membrane is thin, but in the cartilaginous portion it is thick, highly vas¬ cular, and provided with numerous mucous glands. The epithelium that lines the tube is columnar and ciliated. vessels and nerves. There are six arteries, two of which are larger than the others, viz., the tym¬ panic branch of the maxillary artery, which supplies the tympanic membrane and the stylomastoid branch of the posterior auricular artery, which sup¬ plies the back part of the tympanic cavity and mas¬ toid cells. The smaller arteries include the following: the petrosal branch of the middle meningeal artery, which enters through the hiatus of the facial canal; a branch from the ascending pharyngeal artery and another from the artery of the pterygoid canal, which accompany the auditory tube; and the tym¬ panic branch from the internal carotid, which is given off in the carotid canal and perforates the thin anterior wall of the tympanic cavity. The veins term¬ inate in the pterygoid plexus and the superior petro¬ sal sinus. The nerves constitute the tympanic plexus, which ramifies upon the surface of the promontory, and the chorda tympani, which merely passes through the cavity. The plexus is formed by (1) the tympanic branch of the glossopharyngeal nerve; (2) the caroti¬ cotympanic nerves; (3) the lesser petrosal nerve; 'Alexander Prussak (1839-1897): A Russian otologist (St. Petersburg). 2Anton Friedrich von Troltsch (1829-1890): A German otologist (Wurzburg).

1 328

ORGANS OF THE SPECIAL SENSES

and (4) a branch that joins the greater petrosal nerve. The tympanic branch of the glossopharyngeal [Jacobson s nerve1) enters the tympanic cavity by an aperture in its floor close to the labyrinthic wall; it divides into branches that ramify on the promontory and enter into the formation of the tympanic plexus. The superior and inferior caroticotympanic nerves from the carotid plexus of sympathetic fibers pass through the wall of the carotid canal and join the tympanic plexus. The branch to the greater pe¬ trosal passes through an opening on the labyrinthic wall, anterior to the fenestra vestibuli. The lesser petrosal nerve is a continuation of the tympanic branch of the glossopharyngeal nerve beyond the tympanic plexus. It penetrates the bone near the geniculate ganglion of the facial nerve, with which it communicates by a filament. It continues through the bone and enters the middle cranial fossa through a small aperture situated lateral to the hia¬ tus of the facial canal on the anterior surface of the petrous portion of the temporal bone. It leaves the middle fossa through a fissure or foramen of its own or through the foramen ovale, and ends in the otic ganglion, constituting its root and supplying it with preganglionic parasympathetic fibers. The branches of distribution of the tympanic plexus supply the mucous membrane of the tym¬ panic cavity, the fenestra vestibuli, the fenestra cochleae, and the auditory tube. The lesser petrosal may be looked upon as the continuation of the tym¬ panic branch of the glossopharyngeal nerve through the plexus to the otic ganglion. In addition to the tympanic plexus, there are nerves that supply the muscles. The tensor tympani is supplied by a branch from the mandibular nerve that passes through the otic ganglion, and the stape¬ dius is supplied by a branch from the facial nerve. The chorda tympani nerve crosses the tympanic cavity (Fig. 13-47). It leaves the facial canal about 6 mm before the facial nerve emerges from the stylomastoid foramen. It runs back upward in a canal of its own, almost parallel with the facial canal, and enters the tympanic cavity through the iter chor¬ dae posterius, where it becomes invested with mu¬ cous membrane. It traverses the tympanic cavity across the medial surface of the tympanic mem¬ brane and over the upper part of the manubrium of the malleus to the carotid wall, where it makes exit through the iter chordae anterius (canal of Huguier).

labyrinth, from the complexity of its shape, and consists of two parts: the osseous laby¬ rinth, a series of cavities within the petrous part of the temporal bone, and the membra¬ nous labyrinth, a series of communicating membranous sacs and ducts contained within the bony cavities. Osseus Labyrinth The osseous labyrinth (Figs. 13-56; 13-57) consists of three parts: vestibule, semicircu¬ lar canals, and cochlea. These are cavities hollowed out of the substance of the bone and lined by periosteum; they contain a clear fluid, the perilymph, in which the membranous labyrinth is suspended. vestibule. The vestibule is the central part of the osseous labyrinth. It is situated medial to the tympanic cavity, posterior to the cochlea, and anterior to the semicircular canals. It is somewhat ovoid but flat trans¬ versely; it measures about 5 mm sagittally and vertically, and about 3 mm across. In its lateral or tympanic wall is the fenestra ves¬ tibuli, which in the intact body is closed by the base of the stapes and annular ligament. On its medial wall is a small circular depres¬ sion, the recessus sphericus, which is perfo¬ rated at its anterior and inferior part by sev¬ eral minute holes (macula cribrosa media) for the passage of filaments of the vestibulo¬ cochlear nerve to the saccule. Posterior to this depression is an oblique ridge, the crista vestibuli, the anterior end of which is named the pyramid of the vestibule. This ridge bi¬ furcates to enclose a small depression, the

INTERNAL EAR OR LABYRINTH

The internal ear is the essential part of the organ of hearing, the ultimate distribution of the vestibulocochlear nerve. It is called the

‘Ludwig Levin Jacobson (1783-1843): A Danish anato¬ mist and physician (Copenhagen).

Fig. 13-56. Right osseous labyrinth with spongy bone removed. Lateral view.

ORGAN OF HEARING AND EQUILIBRATION

fossa cochlearis, which is perforated by a number of holes for the passage of filaments of the vestibulocochlear nerve that supply the vestibular end of the ductus cochlearis. At the posterior part of the medial wall is the orifice of the aquaeductus vestibuli, which extends to the posterior surface of the pet¬ rous portion of the temporal bone. It trans¬ mits a small vein and contains a tubular pro¬ longation of the membranous labyrinth, the ductus endolymphaticus, which ends in a cul-de-sac between the layers of the dura mater within the cranial cavity. On the superior wall or roof is a trans¬ versely oval depression, the recessus ellipticus, which is separated from the recessus sphericus by the crista vestibuli already mentioned. The pyramid and adjoining part of the recessus ellipticus are perforated by a number of holes (macula cribrosa superior). The apertures in the pyramid transmit the nerves to the utricle; those in the recessus ellipticus transmit the nerves to the ampul¬ lae of the anterior and lateral semicircular

THE EAR

1329

ducts. Posteriorly are the five orifices of the semicircular canals. Anteriorly is an ellipti¬ cal opening that communicates with the scala vestibuli of the cochlea. boimy semicircular canals. There are three bony semicircular canals: anterior, posterior, and lateral; these are situated su¬ perior and posterior to the vestibule. They are unequal in length and compressed from side to side; each describes the greater part of a circle. Each measures about 0.8 mm in diameter, and presents a dilatation at one end, called the ampulla, which measures more than twice the diameter of the tube. They open into the vestibule by five orifices, with one of the apertures being common to two of the canals. The anterior semicircular canal (superior semicircular canal); 15 to 20 mm long, is ver¬ tical in direction and is placed transversely to the long axis of the petrous portion of the temporal bone (Fig. 13-58), on the anterior surface of which its arch forms a round pro¬ jection. It describes about two-thirds of a

semicircular canal

Internal opening of endolymphatic duct ptical recess Margin of vestibular window Lateral semicircular canal

crest Scala vestibuli

Scala tympani

ina of modiolus

Hamulus of spiral lamina Bony spiral lamina Posterior semicircular canal Ampulla of posterior semicircular canal

Secondary spiral lamina Cochlear canal Med. cribriform macula

Spherical recess Cochlear recess Crest of cochlear window

Fig. 13-57.

The right bony labyrinth with the semicircular canals and the cochlea opened. (Redrawn after Sobotta.)

1 330

ORGANS OF THE SPECIAL SENSES

Recessus ellipticus Recessus sphaericus Cochlea

Orifice of aquaeductus vestibuli Fossa cochlearis

Orifice of aquaeductus cochleae

Cochlear fenestra

Fig. 13-58.

Interior of right osseous labyrinth.

circle. Its lateral extremity is ampullated and opens into the superior part of the vestibule; the opposite end joins with the superior part of the posterior canal to form the crus com¬ mune, which opens into the superior and medial part of the vestibule. The posterior semicircular canal, also ver¬ tical, is directed posteriorly, nearly parallel to the posterior surface of the petrous bone. It is the longest of the three canals, measur¬ ing from 18 to 22 mm. Its inferior or ampullated end opens into the inferior and posterior part of the vestibule; its superior end opens into the crus commune already mentioned. The lateral or horizontal canal (external semicircular canal) is the shortest of the three canals. It measures 12 to 15 mm, and its arch is directed horizontally lateralward; thus, each semicircular canal stands at right angles to the other two. Its ampullated end corresponds to the superior and lateral angle of the vestibule, just above the fenestra ves¬ tibuli, where it opens close to the ampullated end of the superior canal. Its opposite end opens at the superior and posterior part of the vestibule. The lateral canal of one ear is very nearly in the same plane as that of the other, while the anterior canal of one ear is nearly parallel to the posterior canal of the other. cochlea (Figs. 13-56; 13-57). The cochlea bears some resemblance to a common snail shell. It forms the anterior part of the laby¬ rinth, is conical, and is placed almost hori¬

zontally in front of the vestibule. Its apex (cupula) is directed anteriorly and laterally, with a slight inclination interiorly, toward the labyrinthic wall of the tympanic cavity. Its base corresponds with the bottom of the internal acoustic meatus and is perforated by numerous apertures for the passage of the cochlear division of the vestibulocochlear nerve. The cochlea measures about 5 mm from base to apex, and its breadth across the base is about 9 mm. It consists of: (1) a conical¬ shaped central axis, the modiolus; (2) a ca¬ nal, the inner wall of which is formed by the central axis, wound spirally around it for two and three-quarter turns, from the base to the apex; and (3) a delicate lamina, the osseous spiral lamina, which projects from the modiolus, and, following the windings of the canal, partially subdivides it into two. In the intact body, the basilar membrane stretches from the free border of this lamina to the outer wall of the bony cochlea and completely separates the canal into two pas¬ sages, which, however, communicate with each other at the apex of the modiolus by a small opening, named the helicotrema (Fig. 13-59). The modiolus is the conical central axis or pillar of the cochlea. Its base is broad and appears at the bottom of the internal acous¬ tic meatus, where it corresponds with the area cochleae; it is perforated by numerous orifices that transmit filaments of the coch¬ lear division of the vestibulocochlear nerve.

ORGAN OF HEARING AND EQUILIBRATION

The nerves for the first turn and a half pass through the foramina of the tractus spiralis foraminosus; those for the apical turn pass through the foramen centrale. The canals of the tractus spiralis foraminosus pass through the modiolus and successively bend out¬ ward to reach the attached margin of the lamina spiralis ossea. Here they become en¬ larged and by their apposition form the spi¬ ral canal of the modiolus, which follows the course of the attached margin of the osseous spiral lamina and lodges the spiral ganglion (ganglion of Corti1). The foramen centrale is continued into a canal that runs through the middle of the modiolus to its apex. The mo¬ diolus diminishes rapidly in size in the sec¬ ond and succeeding coil. The bony canal of the cochlea takes two and three-quarter turns around the modio¬ lus. It is about 30 mm long and diminishes gradually in diameter from the base to the summit, where it terminates in the cupula, which forms the apex of the cochlea (Fig. 13-59). The beginning of this canal is about 3 mm in diameter; it diverges from the modi¬ olus toward the tympanic cavity and vesti¬ bule and presents three openings. One open1 Alfonso Corti (1822-1888): An Italian anatomist (Sar¬ dinia).

Helicotrema

THE EAR

1331

ing, the fenestra cochleae, communicates with the tympanic cavity; in the intact body this aperture is closed by the secondary tym¬ panic membrane. Another opening has an elliptical form and opens into the vestibule. The third opening is the aperture of the aquaeductus cochleae, which leads to a min¬ ute, funnel-shaped canal that opens on the inferior surface of the petrous part of the temporal bone. It transmits a small vein, and also forms a communication between the subarachnoid cavity and the scala tympani. The osseous spiral lamina is a bony shelf or ledge that projects from the modiolus into the interior of the canal, and like the canal, takes two and three-quarter turns around the modiolus. It reaches about half way toward the outer wall of the tube and partially di¬ vides its cavity into two passages or scalae, of which the superior is named the scala vestibuli, while the inferior is termed the scala tympani (Fig. 13-59). Near the summit of the cochlea, the lamina ends in a hook¬ shaped process, the hamulus laminae spi¬ ralis; this assists in forming the boundary of a small opening, the helicotrema, through which the two scalae communicate with each other. From the spiral canal of the modiolus numerous canals pass outward through the osseous spiral lamina as far as

Lamina spiralis ossea Tympanic cavity

Cupula

Vestibular fenestra Fissura vestibuli Recessus sphericus Fossa cochlearis Cochlea Lat. semicircular canal

Scala vestibuli Scala

Vestibule Post semicircular canal Aquaeductus vestibuli Recessus ellipticus

Fig. 13-59. The cochlea and vestibule, viewed from above. All the hard parts that form the roof of the internal ear have been removed with a saw.

1 332

ORGANS OF THE SPECIAL SENSES

its free edge. In the inferior part of the first turn a second bony lamina, the secondary spiral lamina, projects inward from the outer wall of the bony tube; it does not, how¬ ever, reach the primary osseous spiral lam¬ ina, so that if viewed from the vestibule a narrow fissure, the vestibule fissure, is seen between them. The osseous labyrinth is lined by an ex¬ ceedingly thin fibrous membrane. The at¬ tached surface is rough, fibrous, and closely adherent to the bone; its free surface is smooth, pale, covered with a layer of epithe¬ lium, and secretes a thin, limpid fluid, the perilymph. A delicate tubular process of this membrane is prolonged along the aqueduct of the cochlea to the inner surface of the dura mater. Membranous Labyrinth

The membranous labyrinth (Figs. 13-60; 13-61; 13-62) is lodged within the bony cavi¬ ties just described, and has the same general form as these; it is, however, considerably smaller, and is partly separated from the bony walls by a fluid, the perilymph. In cer¬ tain places it is fixed to the walls of the cav¬ ity. The membranous labyrinth also contains fluid, the endolymph, and the ramifications of the vestibulocochlear nerve are distrib¬ uted on its walls. Within the osseous vestibule the membra¬ nous labyrinth does not quite preserve the form of the bony cavity, but consists of two membranous sacs, the utricle and the sac¬ cule.

Fig. 13-60.

The membranous labyrinth. (Enlarged.)

utricle. The utricle, the larger of the two sacs, is oblong, compressed transversely, and occupies the superior and posterior part of the vestibule, lying in contact with the recessus ellipticus and the part inferior to it. That portion which is lodged in the recess forms a sort of pouch or cul-de-sac, the floor and anterior wall of which are thick and form the macula of the utricle, which re¬ ceives the utricular filaments of the vestibu¬ locochlear nerve. The cavity of the utricle communicates behind with the semicircular ducts by five orifices. From its anterior wall is given off the ductus utriculosaccularis, which opens into the ductus endolymphaticus. saccule. The saccule is the smaller of the two vestibular sacs; it has a globular shape and lies in the recessus sphericus near the opening of the scala vestibuli of the cochlea. Its anterior part exhibits an oval thickening, the macula of the saccule, to which are dis¬ tributed the saccular filaments of the vestib¬ ulocochlear nerve. Its cavity does not di¬ rectly communicate with that of the utricle. From the posterior wall a canal, the ductus endolymphaticus, is given off; this duct is joined by the ductus utriculosaccularis, and then passes along the aquaeductus vestibuli and ends in a blind pouch (saccus endolymp¬ haticus) on the posterior surface of the pet¬ rous portion of the temporal bone, where it is in contact with the dura mater. From the inferior part of the saccule a short tube, the ductus reuniens (canalis reuniens of Hensen1) passes inferiorly and opens into the ductus cochlearis near its vestibular ex¬ tremity (Fig. 13-60). semicircular ducts. The semicircular ducts (membranous semicircular canals) (Figs. 13-61; 13-62) are about one-fourth of the diameter of the osseous canals, but in number, shape, and general form they are precisely similar, and each has an ampulla at one end. They open by five orifices into the utricle, one opening being common to the medial end of the anterior duct and the su¬ perior end of the posterior duct. In each ampulla, the wall is thickened and projects into the cavity as a fiddle-shaped, trans¬ versely placed elevation, the ampullary crest, in which the nerves end. The utricle, saccule, and semicircular ducts are held in position by numerous fi1 Victor Hensen (1835-1924): German anatomist and physiologist (Kiel).

ORGAN OF HFARING AND EQUILIBRATION

THE EAR

1333

Fig. 13-61. Right human membranous labyrinth, removed from its bony enclosure and viewed from the anterolateral aspect. (G. Retzius.)

12

23

11 8,9,1010' 5

5 3'6

1' 4

3

Fig. 13-62. The same from the posteromedial aspect. 1. Lateral semicircular canal; 1', its ampulla; 2. Posterior canal; 2', its ampulla. 3. Anterior canal; 3', its ampulla. 4. Conjoined limb of anterior and posterior canals (sinus utriculi superior). 5. Utricle; 5', recessus utriculi; 5", sinus utriculi posterior. 6. Ductus endolymphaticus. 7. Canalis utriculosaccularis. 8. Nerve to ampulla of anterior canal. 9. Nerve to ampulla of lateral canal. 10. Nerve to recessus utriculi (in Fig. 13-61, the three branches appear conjoined); 10', ending of nerve in recessus utriculi. 11. Facial nerve. 12. Lagena cochleae. 13. Nerve of cochlea within spiral lamina. 14. Basilar membrane. 15. Nerve fibers to macula of saccule. 16. Nerve to ampulla of posterior canal. 17. Saccule. 18. Secondary membrane of tympanum. 19. Canalis reuniens. 20. Vestibular end of ductus cochlearis. 23. Section of the facial and acoustic nerves within internal acoustic meatus. The separation between them is not apparent in this section. (G. Retzius.)

1 334

ORGANS OF THE SPECIAL SENSES

brous bands that stretch across the space between them and the bony walls. STRUCTURE OF THE UTRICLE, SACCULE, AND semicircular ducts (Fig. 13-63). The walls of the utricle, saccule, and semicircular ducts consist of three layers. The outer layer is a loose and flocculent structure, appar¬ ently composed of ordinary fibrous tissue containing blood vessels and some pigment cells. The middle layer, thicker and more transparent than the outer, forms a homoge¬ neous membrana propria and has numerous papilliform projections on its internal sur¬ face, especially in the semicircular ducts, which exhibit an appearance of longitudinal fibrillation on the addition of acetic acid. The inner layer is formed of polygonal nu¬ cleated epithelial cells. In the maculae of the utricle and saccule and in the ampullary crests of the semicircular ducts, the middle coat is thick and the epithelium is columnar and consists of supporting cells and hair cells. The supporting cells are fusiform; their deep ends are attached to the membrana propria while their free extremities are united to form a thin cuticle. The neuroepi¬ thelium or hair cells are flask-shaped, and their deep, rounded ends do not reach the membrana propria, but lie between the sup¬ porting cells. The deep part of each contains

a large nucleus, while its more superficial part is granular and pigmented. The free end is surmounted by a long, tapering, hair-like filament that projects into the cavity. The fil¬ aments of the vestibulocochlear nerve enter these parts, and having pierced the outer and middle layers, they lose their myelin sheaths and their axons ramify between the hair cells. Numerous small round bodies termed otoconia (statoconia), each consisting of a mass of minute crystalline grains of carbon¬ ate of lime held together in a mesh of gelati¬ nous tissue, are suspended in the endolymph in contact with the free ends of the hairs pro¬ jecting from the maculae. COCHLEAR DUCT. The cochlear duct (duc¬ tus cochlearis; membranous cochlea; scala media) consists of a spirally arranged tube enclosed in the bony canal of the cochlea and lying along its outer wall. As already stated, the osseous spiral lam¬ ina extends only part of the distance be¬ tween the modiolus and the outer wall of the cochlea, while the basilar membrane (membrana spiralis) stretches from its free edge to the outer wall of the cochlea and completes the roof of the scala tympani. A second and more delicate membrane, the vestibular membrane (Reissner’s mem-

Connective tissue binding duct to periosteum

Semicircular duct Fibrous band uniting free surface of duct to periosteum

Semicircular canal

Periosteum Fig. 13-63.

Transverse section of a human semicircular canal and duct. (After Riidinger.)

ORGAN OF HEARING AND EQUILIBRATION

brane1), extends from the thickened perios¬ teum covering the osseous spiral lamina to the outer wall of the cochlea, where it is at¬ tached at some little distance above the outer edge of the basilar membrane. A canal is thus shut off between the scala tympani and the scala vestibuli; this is the cochlear duct or scala media (Figs. 13-64; 13-65). It is triangular on transverse section, its roof being formed by the vestibular membrane, its outer wall of the periosteum lining the bony canal, and its floor by the membrana spiralis and the outer part of the osseous spi¬ ral lamina. Its extremities are closed, the upper is termed the lagena and is attached to the cupula at the upper part of the helico-

1Ernst Reissner (1824-1878): A German anatomist (Dorpat, then Breslau).

Fig. 13-64.

THE EAR

1335

trema; the inferior is lodged in the recessus cochlearis of the vestibule. Near the inferior end, the ductus cochlearis becomes con¬ tinuous with the sacculus by means of a narrow, short canal, the ductus reuniens (Fig. 13-60). The spiral organ of Corti rests upon the basilar membrane. The vestibular mem¬ brane is thin, homogeneous, and covered on its superior and inferior surfaces by a layer of epithelium. The periosteum, forming the outer wall of the cochlear duct, is greatly thickened and altered in character, and is called the spiral ligament. It projects inward below as a triangular prominence, the basi¬ lar crest, which gives attachment to the outer edge of the basilar membrane; imme¬ diately above the crest is a concavity, the sulcus spiralis externus. The upper portion of the spiral ligament contains numerous

A section through the left temporal bone. (Drawn from a section prepared at the Fehrens Institute, kindly lent by Prof. J. Kirk.)

1336

ORGANS OF THE SPECIAL SENSES

capillary loops and small blood vessels, and it is termed the stria vascularis. The osseous spiral lamina consists of two plates of bone, and between these are the canals for the transmission of the filaments of the vestibulocochlear nerve. On the upper plate of that part of the lamina which is out¬ side the vestibular membrane, the perios¬ teum is thickened to form the limbus lami¬ nae spiralis. This ends externally in a concavity. The sulcus spiralis internus (Fig. 13-65) represents, in section, the form of the letter C; the upper part, formed by the over¬ hanging extremity of the limbus, is named the vestibular lip; the lower part, prolonged and tapering, is called the tympanic lip, and is perforated by numerous foramina for the passage of the cochlear nerve fibers. The upper surface of the vestibular lip is inter¬ sected at right angles by a number of fur¬ rows, between which are numerous eleva¬

tions; these present the appearance of teeth along the free surface and margin of the lip, and they have been named dentes acoustici. The limbus is covered by a layer of what appears to be squamous epithelium, but the deeper parts of the cells with their contained nuclei occupy the intervals between the ele¬ vations and between the auditory teeth. This layer of epithelium is continuous on the one hand with that lining the sulcus spiralis internus, and on the other with that covering the undersurface of the vestibular mem¬ brane. basilar membrane. The basilar mem¬ brane stretches from the tympanic lip of the osseous spiral lamina to the basilar crest and consists of two parts, an inner and an outer. The inner part is thin and is named the zona arcuata; it supports the spiral organ of Corti. The outer is thicker and striated and is termed the zona pectinata. The undersurface

Scala vestibuli *'* Ductus cochlearis

Vestibular membrane

Sulcus spiralis externus Membrana tectoria

Osseous spiral lamina

Scala tympani Basilar membrane

Spiral organ

Sulcus spiralis internus

Spiral ganglion

Fig. 13-65.

A section through the second turn of the cochlea indicated in the previous figure. (Mallory’s stain.)

ORGAN OF HEARING AND EQUILIBRATION: THE EAR

of the membrane is covered by a layer of vascular connective tissue; one of the vessels in this tissue is somewhat larger than the rest, and is named the vas spirale. STRUCTURE OF THE ORGAN OF CORTI. The spiral organ or organ of Corti (Fig. 13-66) is composed of a series of epithelial structures placed upon the inner part of the basilar membrane. The average length is 31.5 mm. The more central of these structures are two rows of rod-like bodies, the inner and outer rods or pillars of Corti. The bases of the rods are supported on the basilar membrane, those of the inner row at some distance from those of the outer row. The two rows incline toward each other, and coming into contact superiorly, enclose between them and the basilar membrane a triangular tunnel, the tunnel of Corti. On the inner side of the inner rods is a single row of hair cells, and on the outer side of the outer rods are three or four rows of similar cells, together with certain supporting cells termed the cells of Deiters and Hensen. The free ends of the outer hair cells occupy a series of apertures in a net-like membrane, the reticular mem¬ brane, and the entire organ is covered by the tectorial membrane. Rods of Corti. Each consists of a base or foot-plate and elongated part or body, and an upper end or head. The body of each rod is finely striated, but in the head there is an oval, nonstriated portion that stains deeply with carmine. Occupying the angles be¬ tween the rods and the basilar membrane are nucleated cells that partly envelop the

rods and extend onto the floor of Corti’s tun¬ nel; these may be looked upon as the undif¬ ferentiated parts of the cells from which the rods have been formed. The inner rods number nearly 6000, and their bases rest on the basilar membrane close to the tympanic lip of the sulcus spi¬ ralis internus. The shaft or body of each is sinuously curved and forms an angle of about 60° with the basilar membrane. The head resembles the proximal end of the ulna and presents a deep concavity that accom¬ modates a convexity on the head of the outer rod. The headplate, or portion overhanging the concavity, overlaps the headplate of the outer rod. The outer rods, numbering nearly 4000, are longer and more obliquely set than the inner rods, forming with the basilar mem¬ brane an angle of about 40°. Their heads are convex internally; they fit into the concavi¬ ties on the heads of the inner rods and are continued outward as thin flattened plates, termed phalangeal processes, which unite with the phalangeal processes of Deiters’ cells to form the reticular membrane. Hair Cells. The hair cells are short colum¬ nar cells; their free ends are on a level with the heads of Corti’s rods, and each is sur¬ mounted by about 20 hair-like processes ar¬ ranged in the form of a crescent with its con¬ cavity directed inward. The deep ends of the cells reach about half way along Corti’s rods, and each contains a large nucleus; in contact with the deep ends of the hair cells are the terminal filaments of the cochlear division

Outer hair cells Membrana tectoria

Limbus

Cells of Deiters Outer rod Nerve fibers Fig. 13-66.

1 337

Basilar membrane

Section through the spiral organ of Corti. Magnified. (G. Retzius.)

1338

ORGANS OF THE SPECIAL SENSES

of the vestibulocochlear nerve. The inner hair cells, about 3500 in number, are ar¬ ranged in a single row on the medial side of the inner rods. Because their diameters are greater than those of the rods, each hair cell is supported by more than one rod. The free ends of the inner hair cells are encircled by a cuticular membrane that is fixed to the heads of the inner rods. Adjoining the inner hair cells are one or two rows of columnar supporting cells, which, in turn, are continu¬ ous with the cubical cells lining the sulcus spiralis internus. The outer hair cells num¬ ber about 12,000 and are nearly twice as long as the inner. In the basal coil of the cochlea they are arranged in three regular rows; in the apical coil, in four somewhat irregular rows. The receptors for high tones are lo¬ cated in the basal turn of the cochlea. Supporting Cells. Between the rows of the outer hair cells are rows of supporting cells, called the cells of Deiters1; their ex¬ panded bases are planted on the basilar membrane, while the opposite end of each presents a clubbed extremity or phalangeal process. Immediately to the outer side of Deiters’ cells are five or six rows of colum¬ nar cells, the supporting cells of Hensen. Their bases are narrow, while their upper parts are expanded and form a rounded ele¬ vation on the floor of the ductus cochlearis. The columnar cells lying outside Hensen’s cells are termed the cells of Claudius.2 A space exists between the outer rods of Corti and the adjacent hair cells; this is called the space of Nuel.3 Reticular Lamina. The reticular lamina is a delicate framework perforated by rounded holes which are occupied by the free ends of the outer hair cells. It extends from the heads of the outer rods of Corti to the exter¬ nal row of the outer hair cells, and is formed by several rows of minute fiddle-shaped cu¬ ticular structures, called phalanges, between which are circular apertures containing the free ends of the hair cells. The innermost row of phalanges consists of the phalangeal processes of the outer rods of Corti; the outer rows are formed by the modified free ends of Deiters’ cells. ’Otto Friedrich Carl Deiters, (1834-1863): A German anatomist (Bonn). 2Friedrich Matthias Claudius (1822-1869): An Austrian anatomist. 3Jean Pierre Nuel (1847-1920): A Belgian physiologist and otologist (Ghent and Li6ge).

Tectorial Membrane. Covering the sulcus spiralis internus and the spiral organ of Corti is the tectorial membrane, which is attached to the limbus laminae spiralis close to the inner edge of the vestibular membrane. Its inner part is thin and overlies the auditory teeth of Huschke;4 its outer part is thick, and along its lower surface, opposite the inner hair cells, is a clear band, named Hensen’s stripe owing to the intercrossing of its fibers. The lateral margin of the membrane is much thinner. It consists of fine, colorless fibers embedded in a transparent matrix of a soft col¬ lagenous, semisolid character with marked adhesiveness; the matrix may be a variety of soft keratin. The general transverse di¬ rection of the fibers inclines from the radius of the cochlea toward the apex. Nerves. The vestibulocochlear nerve (acoustic nerve; n. statoacusticus; nerve of hearing) divides near the bottom of the internal acoustic meatus into an anterior or cochlear branch and a posterior or vestibular branch. The vestibular nerve supplies the utricle, the sac¬ cule, and the ampullae of the semicircular ducts. On the trunk of the nerve, within the internal acoustic meatus, is the vestibular ganglion (ganglion of Scarpa5); the fibers of the nerve arise from the cells of this ganglion. On the distal side of the ganglion the nerve splits into a superior, an inferior, and a posterior branch. The filaments of the superior branch are transmitted through the foramina in the area vestibularis superior, and end in the macula of the utricle and in the ampullae of the anterior and lateral semicircular ducts. Those of the inferior branch traverse the foramina in the area vestibularis inferior and end in the macula of the saccule. The posterior branch runs through the foramen singulare at the posteroinferior part of the bottom of the mea¬ tus and divides into filaments to supply the ampulla of the posterior semicircular duct. The cochlear nerve divides into numerous fila¬ ments at the base of the modiolus. Those for the basal and middle coils pass through the foramina in the tractus spiralis foraminosus and those for the api¬ cal coil pass through the canalis centralis; the nerves bend outward to pass between the lamellae of the osseous spiral lamina. Occupying the spiral canal of the modiolus is the spiral ganglion of the cochlea (ganglion of Corti) (Fig. 13-65), which consists of bipolar nerve cells that constitute the cells of origin of this nerve. Reaching the outer edge of the osse¬ ous spiral lamina, the fibers of the nerve pass through the foramina in the tympanic lip. Some end 4Emil Huschke (1797-1858): A German anatomist (Jena). 5 Anthony Scarpa (1747-1832): Italian anatomist and sur¬ geon (Pavia).

REFERENCES

by arborizing around the bases of the inner hair cells, while others pass between Corti's rods and across the tunnel to end in a similar manner in rela¬ tion to the outer hair cells. The cochlear nerve gives off a vestibular branch to supply the vestibular end of the ductus cochlearis; the filaments of this branch pass through the foramina in the fossa cochlearis. Vessels. The arteries of the labyrinth are the internal auditory artery, which comes from the basi¬ lar artery, and the stylomastoid artery, which comes from the posterior auricular artery. The internal audi¬ tory artery divides at the bottom of the internal

1339

acoustic meatus into two branches: cochlear and vestibular. The cochlear branch subdivides into 12 or 1 4 twigs that traverse the canals in the modiolus and are distributed, in the form of a capillary net¬ work, in the lamina spiralis and basilar membrane. The vestibular branches are distributed to the utri¬ cle, saccule, and semicircular ducts. The veins of the vestibule and semicircular canals accompany the arteries, and, receiving those of the cochlea at the base of the modiolus, unite to form the internal auditory veins, which end in the poste¬ rior part of the superior petrosal sinus or in the trans¬ verse sinus.

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.)

Organ of Smell Arstila, A., and J. Wersall. 1967. The ultrastructure of the olfactory epithelium of the guinea pig. Acta Oto¬ laryngol., 64: 187-204. Bloom, G. 1954. Studies on the olfactory epithelium of the frog and the toad with the aid of light and elec¬ tron microscopy. Z. Zellforsch., 41:89-100. deLorenzo, A. J. 1957. Electron microscopic observations of the olfactory mucosa and olfactory nerve. ]. Biophys. Biochem. Cytol., 3:839-850. Doty, R. L., ed. 1976. Mammalian Olfaction, Reproduc¬ tive Processes and Behavior. Academic Press, New York, 344 pp. Frisch, D. 1967. Ultrastructure of mouse olfactory mu¬ cosa. Amer. J. Anat., 121:87-120. Gasser, H. S. 1956. Olfactory nerve fibers. J. Gen. Phys¬ iol., 39:473-498. Graziadei, P. P. C. 1971. The olfactory mucosa of verte¬ brates. In Handbook of Sensory Physiology, Vol. 4, Chemical Senses. Edited by L. M. Beidler. SpringerVerlag, Berlin, pp. 27-58. Gross, G. W., and L. M. Beidler. 1973. Fast axonal trans¬ port in the c-fibers of the garfish olfactory nerve. }. Neurobiol., 4:413-428. Gross, G. W., and L. M. Beidler. 1975. A quantitative analysis of isotope concentration profiles and rapid transport velocities in the c-fibers of the garfish ol¬ factory nerve. J. Neurobiol., 6:213-232. Mathews, D. F. 1972. Response patterns of single neurons in the tortoise olfactory epithelium and olfactory bulb. J. Gen. Physiol., 60:166-180. Moulton, D. G., and L. M. Beidler. 1967. Structure and function of the peripheral olfactory system. Physiol. Rev., 47:1-52. Moulton, D. G., G. Celebi, and R. P. Fink. 1970. Olfaction in mammals—two aspects: proliferation of cells in the olfactory epithelium and sensitivity to odours. In Taste and Smell in Vertebrates. Edited by G. E. W. Wolstenholme and J. Knight. Ciba Foundation Symposium, W. and A. Churchill, London, pp. 227-245. Mozell, M. M. 1966. The spatiotemporal analysis of odorants at the level of the olfactory receptor sheet. J. Gen. Physiol., 50:25-42.

Reese, T. 1965. Olfactory cilia in the frog. J. Cell Biol., 25:209-230. Reese, T., and M. W. Brightman. 1970. Olfactory surface and central olfactory connections in some verte¬ brates. In Taste and Smell in Vertebrates. Edited by G. E. W. Wolstenholme and J. Knight. Ciba Founda¬ tion Symposium, W. and A. Churchill, London, pp. 115-143. Smith, C. G. 1941. Incidence of atopy of olfactory nerves in man. Arch. Otolaryngol., 34: 533-539. Smith, C. G. 1951. Regeneration of sensory olfactory epi¬ thelium and nerves in adult frogs. Anat. Rec., 109: 661-672.

Organ of Taste Beidler, L. M. 1954. A theory of taste stimulation. J. Gen. Physiol., 38:133-148. Beidler, L. M., and R. L. S. Smallman. 1965. Renewal of cells within taste buds. J. Cell Biol., 27:263-272. Benjamin, R. M., and H. Burton. 1968. Projection of taste nerve afferents to anterior opercular insular cortex in squirrel monkey (Saimiri sciureus). Brain Res., 7:221-231. Benjamin, R. M., R. Emmers, and A. J. Blomquist. 1968. Projection of tongue nerve afferents to somatic sen¬ sory area I in squirrel monkey (Saimiri sciureus). Brain Res., 7:208-220. Bradley, R. M., and I. B. Stern. 1967. The development of the human taste bud during the fetal period. J. Anat. (Lond.), 101:743-752. deLorenzo, A. J. 1958. Electron microscopic observations on the taste buds of the rabbit. J. Biophys. Biochem. Cytol., 4:143-150. Farbman, A. I. 1965. Electron microscope study of the developing taste bud in rat fungiform papilla. Devel. Biol., 11:110-135. Farbman, A. I. 1965. Fine structure of the taste bud. J. Ultrastruct. Res., 12:328-350. Fishman, I. Y. 1957. Single fiber gustatory impulses in rat and hamster. J. Cell. Comp. Physiol., 49:319-334. Frank, M. 1973. An analysis of hamster afferent taste nerve response functions. J. Gen. Physiol., 61: 588-618.

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Mechanisms of the Auditory and Vestibular Sys¬ tems. Charles C Thomas, Springfield, Ill., 422 pp. Saito, R„ M. Igarashi, B. R. Alford, and F. R. Guilford. 1971. Anatomical measurement of the sinus tympani. A study of horizontal serial sections of the human temporal bone. Arch. Otolaryngol., 94: 418-425. Sando, I. 1965. The anatomical interrelationships of the cochlear nerve fibers. Acta Otolaryngol., 59:417-436. Schuknecht, H. K. 1950. A clinical study of auditory damage following blows to the head. Ann. Otolar¬ yngol., 59:331-358. Smith, C. A. 1968. Electron microscopy of the inner ear. Ann. Otol. Rhinol. Laryngol., 77:629-643. Smith, C. A. 1975. The inner ear: Its embryological devel¬ opment and microstructure. In The Nervous Sys¬ tem. Edited by D. B. Tower. Vol. 3, Human Commu¬ nication and Its Disorders. Raven Press, New York, pp. 1-18. Smith, C. A., and E. W. Dempsey. 1957. Electron micros¬ copy of the organ of Corti. Amer. J. Anat., 100:337-368. Spector, B. 1944. Storage of trypan blue in the internal ear of the rat. Anat. Rec., 88:83-89. Spoendlin, H. 1969. Innervation patterns in the organ of Corti of the cat. Acta Otolaryngol., 67:239-254. Spoendlin, H. 1972. Innervation densities of the cochlea. Acta Otolaryngol., 73:235-248. Sunderland, S. 1945. The arterial relations of the internal auditory meatus. Brain, 68:23-27. Tasaki, I. 1954. Nerve impulses in individual auditory nerve fibers of guinea pig. J. Neurophysiol., 17:97-122. Tonndorf, J., and S. M. Khanna. 1970. The role of the tympanic membrane in middle ear transmission. Ann. Otol. Rhinol. Laryngol., 79:743-753.

von Bekesy, G. 1956. Current status of theories of hear¬ ing. Science, 123:779-783. Wersall, J. 1956. Studies on the structure and innervation of the sensory epithelium of the cristae ampullares in the guinea pig. Acta Otolaryngol., Suppl., 126:1-85. Wersall, J., and A. Flock. 1964. Physiological aspects of the structure of vestibular end organs. Acta Otolar¬ yngol., Suppl., 192:85-89. Wersall, J., A. Flock, and P. G. Lindquist. 1965. Structural basis for directional sensitivity in cochlear and ves¬ tibular sensory receptors. Cold Spring Harbor Symp. Quant. Biol., 30:115-132. Wiggers, H. C. 1937. The functions of the intra-aural muscles. Amer. J. Physiol., 120:771-780. Winerman, I., H. Nathan, and B. Arensburg. 1980. Poste¬ rior ligament of the incus: variations in its compo¬ nents. Ear Nose Throat J., 59:227-231. Wislocki, G. B., and A. J. Ladman. 1955. Selective histochemical staining of the otolithic membranes, cupulae and tectorial membrane of the inner ear. J. Anat. (Lond.), 89:1-12. Wolff, D., R. J. Bellucci, and A. A. Eggston. 1957. Micro¬ scopic Anatomy of the Temporal Bone. Williams and Wilkins, Baltimore, 414 pp. Yntema, C. L. 1933. Experiments on the determination of the ear ectoderm in the embryo of Amblystoma punctatum. J. Exp. Zool., 65:317-357. Yoko, Y. 1971. Early formation of nerve fibers in the human otocyst. Acta Anat. (Basel), 80:99-106. Zorzetto, N., and O. J. Tamega. 1979. The anatomical re¬ lationship of the middle ear and the jugular bulb. Anat. Anz., 146:470-480.

The Integument Covering the surface of the body and shel¬ tering it from injurious influences in the en¬ vironment is the skin or integument. It pro¬ tects the deeper tissues from injury, from drying, and from invasion by foreign orga¬ nisms; it contains the peripheral endings of many of the sensory nerves. It plays an im¬ portant part in the regulation of the body temperature and also has limited excretory and absorbing powers. It consists princi¬ pally of a layer of dense connective tissue, named the dermis (corium, cutis vera), and an external covering of epithelium, termed the epidermis or cuticle. On the surface of the former layer are sensitive and vascular papillae; within or beneath it are certain or¬ gans with special functions, namely, the su¬ doriferous and sebaceous glands and the hair follicles.

Development The epidermis and its appendages (hairs, nails, sebaceous and sweat glands) are de¬ veloped from the ectoderm; the corium or true skin is of mesodermal origin. About the fifth week of fetal development, the epider¬ mis consists of two layers of cells, the deeper one corresponding to the rete mucosum. The

subcutaneous fat appears about the fourth month, and the papillae of the true skin, about the sixth month. A considerable des¬ quamation of epidermis takes place during fetal life, and this desquamated epidermis, mixed with sebaceous secretion, constitutes the vernix caseosa, with which the skin is smeared during the last three months of fetal life. The nails are formed at the third month and begin to project from the epidermis about the sixth month. The hairs appear be¬ tween the third and fourth months in the form of solid downgrowths of the deeper layer of the epidermis, the growing extremi¬ ties of which become inverted by papillary projections from the corium. The central cells of the solid downgrowths undergo al¬ teration to form the hair, while the periph¬ eral cells are retained to form the lining cells of the hair follicle. About the fifth month the fetal hairs (lanugo) appear first on the head and then on the other parts; they drop after birth and give place to the permanent hairs. The cellular structures of the sudoriferous and sebaceous glands are formed from the ectoderm, whereas the connective tissue and blood vessels are derived from the meso¬ derm. All the sweat glands are fully formed at birth; they begin to develop as early as the fourth month.

Structure epidermis. The epidermis, cuticle, or scarf skin is nonvascular, consists of strati¬ fied epithelium, and is accurately molded over the papillary layer of the dermis. It var¬ ies in thickness in different parts of the body. In some situations, as in the palms of the hands and soles of the feet, it is thick, hard, and horny in texture. The more superficial layers of cells, called the horny layer (stra¬ tum corneum), may be separated by macera¬ tion from a deeper stratum, which is called the stratum mucosum and which consists of several layers of differently shaped cells. The free surface of the epidermis is marked by a network of linear furrows of variable size, dividing the surface into polygonal or lozenge-shaped areas. Some of these furrows are large, such as those opposite the flexures of the joints, and they correspond to folds in the dermis. In other situations, as upon the back of the hand, they are exceedingly fine and intersect one another at various angles. 1345

1 346

the integument

Upon the palmar surfaces of the hands and fingers and upon the soles of the feet, the epidermal ridges are distinct and disposed in curves; they depend upon the large size and peculiar arrangements of the papillae upon which the epidermis is placed. These ridges increase friction between contact surfaces to prevent slipping in walking or prehension. The direction of the ridges is at right angles to the force that tends to produce slipping or to the resultant of such forces when these forces vary in direction. In each individual the lines of the tips of the fingers and thumbs form distinct patterns unlike those of any other person. A method of determining the identity of a person is based on this fact by making impressions or fingerprints of these lines. The deep surface of the epidermis is accurately molded upon the papillary layer of the dermis, the papillae being covered by a basement membrane. When the epidermis is lifted off by maceration and inverted, it presents on its undersurface pits or depres¬ sions that correspond to the papillae, and ridges corresponding to the intervals be¬ tween them. Fine tubular prolongations are continued from this layer into the ducts of the sudoriferous and sebaceous glands. The stratified squamous epithelium of the epidermis is composed of several layers named according to various properties such as shape of cells, texture, composition and

position. Beginning with the deepest, they are: (a) stratum basale, (b) stratum spinosum, (c) stratum granulosum, (d) stratum lucidum, and (e) stratum corneum. The stratum basale, the deepest layer, is composed of columnar or cylindrical cells, giving it an alternate name stratum cylindricum. The ends of the cells in contact with the basement membrane have toothlike pro¬ toplasmic projections that fit into sockets in the membrane and appear to anchor the cells to the underlying dermis. The cells of this layer undergo division by mitosis, sup¬ plying new cells to make up for the contin¬ ual loss of surface layers from abrasion. This layer has been appropriately named the stra¬ tum germinativum (Fig. 14-1). The stratum spinosum is composed of several layers of polygonal cells, the number depending upon the area of the body from which the skin is taken. As a result of the slight shrinkage caused by technical proce¬ dures, these cells in ordinary histologic preparations appear to have cytoplasmic bridges connecting them with their neigh¬ bors. When they are pulled apart, they ap¬ pear to have minute spines on their surface, giving them the name prickle cells. Electron microscopic studies have shown that each cell adheres to its neighbors at particular points called desmosomes, and that these points are drawn out into the spines by

/ Hair shaft Epidermis Strat. corn. Strat. germ.

Sebaceous gland Arr. pill muscle

Derma Sweat gland

Blood vessel

Bulb 1 Hair Papilla ) root

Subcut. adipose tissue

Galea aponeurotica

Cranial periost.

Fig. 14-1.

Section through scalp of adult cadaver. 5 x.

STRUCTURE

shrinkage. Ultrastructural studies have also shown that the cytoplasm of these cells con¬ tains minute fibrils, some of which are ori¬ ented toward the desmosomes. In light mi¬ croscopic preparations these fibrils may be visible, and since they are associated with the desmosomes, they give the impression of running between cells and are called tonofibrils. The stratum granulosum is composed of two or three rows of flat cells that lie parallel with the surface. They contain numerous large granules that stain deeply with hema¬ toxylin. They are composed of keratohyalin, a substance that apparently is transformed into keratin in more superficial layers. The stratum lucidum appears to be a ho¬ mogenous translucent band, much thinner than the strata on either side of it. The cells contain droplets of eleidin and their nuclei and cell boundaries are not visible. The stratum corneum is composed of squamous plates of scales fused together to make the outer horny layer. These plates are the remains of the cells and contain a fibrous protein, keratin. The most superficial layer sloughs off or desquamates. The thickness of this layer is correlated with the trauma to which an area is subjected, being very thick on the palms and soles but thin over pro¬ tected areas. pigmentation. The black color of the skin in the Negro and the tawny color among some of the white races are due to the pres¬ ence of pigment in the cells of the epidermis. This pigment is especially distinct in the cells of the stratum basale and is similar to that found in the cells of the pigmented layer of the retina. As the cells approach the surface and desiccate, the color becomes partially lost; the disappearance of the pig¬ ment from the superficial layers of the epi¬ dermis, however, is difficult to explain. The pigment (melanin) consists of small dark brown or black granules, closely packed together within the cells, but not in¬ volving the nucleus. The main purpose of the epidermis is pro¬ tection. As the surface is worn away, new cells are supplied, and thus the true skin, the vessels, and the nerves that it contains are defended against damage. dermis. The dermis, corium, cutis vera or true skin is tough, flexible, and elastic. Its thickness varies in different parts of the body. Thus it is very thick in the palms of

1347

the hands and soles of the feet. It is thicker on the dorsal aspect of the body than on the ventral aspects, and on the lateral sides of the limbs than on the medial sides. In the eyelids, scrotum, and penis, it is exceedingly thin and delicate. The dermis consists of felted connective tissue, with a varying amount of elastic fi¬ bers and numerous blood vessels, lymphat¬ ics, and nerves. The connective tissue is ar¬ ranged in two layers: a deeper or reticular layer, and a superficial or papillary layer (Fig. 14-2). Smooth muscle cells are found in the der¬ mis and the subcutaneous layers of the scro¬ tum, penis, labia majora, and nipples. In the mammary papilla, the smooth muscle cells are disposed in circular bands and radiating bundles arranged in superimposed laminae. Where there are hairs, discrete bundles of smooth muscle called the arrectores pilorum are attached in the superficial layers of the corium and near the base of each hair fol¬ licle. The papillary layer (stratum papillare; superficial layer; corpus papillare of the corium) consists of numerous small, highly sensitive, and vascular eminences, the papil¬ lae, which rise perpendicularly from its sur¬ face. The papillae are minute conical emi¬ nences with rounded or blunted extremities; occasionally they are divided into two or more parts and are received into corre¬ sponding pits on the undersurface of the cu¬ ticle. On the general surface of the body, especially in parts endowed with slight sen¬ sibility, they are few in number and exceed¬ ingly minute, but in some situations, as upon the palmar surfaces of the hands and fingers and the plantar surfaces of the feet and toes, the papillae are long, large, closely aggre¬ gated, and arranged in parallel curved lines, forming the elevated ridges seen on the free surface of the epidermis. Each ridge con¬ tains two rows of papillae, between which the ducts of the sudoriferous glands pass outward to open on the summit of the ridge. Each papilla consists of small and closely interlacing bundles of finely fibrillated tis¬ sue with a few elastic fibers; within this tissue is a capillary loop, and in some papil¬ lae, especially in the palms of the hand and the fingers, there are tactile corpuscles (Fig. 14-3). The reticular layer (stratum reticulare; deep layer) consists of fibroelastic connec-

1 348

THE INTEGUMENT

Duct of sweat gland

Meissner s corpuscle

f1*?' I*'?' Section through the skin of the human foot, cut perpendicularly to the surface. (From Rauber-Kopsch Lehrbuch u. Atlas d. Anatomie d. Menschen, 19th ed„ Vol. II, Georg Thieme Verlag, Stuttgart, 1955.)

Meissner's corpuscle

Fig. 14-3. Vascular and sensory papillae in the skin of the human foot. (From Rauber-Kopsch, Lehrbuch u. Atlas d. Anatomie d. Menschen, 19th ed„ Vol. II, Georg Thieme Verlag, Stuttgart, 1955.)

five tissue, which is composed chiefly of col¬ lagenous bundles but contains yellow elastic fibers in varying number in different parts of the body. The cells are principally fibro¬ blasts and histiocytes, but other types may be found. Near the papillary layer the collag¬ enous bundles are small and compactly ar¬ ranged; in the deeper layers they are larger and coarser, and between their meshes are sweat glands, sebaceous glands, hair shafts or follicles, and small collections of fat cells. The deep surface of the reticular layer merges with the adipose tissue of the subcu¬ taneous fascia. CLEAVAGE LINES OF THE SKIN (Langer’s lines1). When a sharp conical instrument is used to make a penetrating wound, it does not leave a round hole in the skin, as might be expected, but a slit such as would be ex¬ pected from a flat blade. Maps of the direc¬ tions of these slits from puncture wounds over all parts of the body have been made from dissecting room material (Figs. 14-4; 1 Carl Ritter von Eldenbeig von Langer (1819-1887): Aus¬ trian anatomist (Vienna).

STRUCTURE

Fig. 14-4.

1 349

Cleavage lines (Langer’s lines) of the skin. Trunk and extremities. (Eller.)

14-5). These maps indicate that there are def¬ inite lines of tension or cleavage lines within the skin that are characteristic for each part of the body. In microscopic sections cut par¬ allel with these lines, most of the collage¬ nous bundles of the reticular layer are cut longitudinally, while in sections cut across the lines, the bundles are in cross section. The cleavage lines correspond closely with the crease lines on the surface of the skin in most parts of the body. The pattern of the cleavage lines, according to Cox (1941), var¬ ies with body configuration, but is constant for individuals of similar build regardless of age. There are limited areas of the body in which the orientation of the bundles is irreg¬ ular and confused. The cleavage lines are of particular interest to the surgeon because an incision made parallel to the lines heals with a fine linear scar, while an incision across the lines may set up irregular tensions that result in an unsightly scar.

Fig. 14-5. Cleavage lines (Langer’s lines) of the skin. Head and neck. (Eller.)

1350

THE INTEGUMENT

vessels and nerves. The arteries supplying the skin form a network in the subcutaneous tissue, branches of which supply the sudoriferous glands, the hair follicles, and the fat. Other branches unite in a plexus immediately beneath the dermis; from this plexus, fine capillary vessels pass into the papillae, forming, in the smaller ones, a single capillary loop, but in the larger, a more or less convoluted vessel. The lymphatic vessels of the skin form two net¬ works, superficial and deep, which communicate with each other and with those of the subcutaneous tissue by oblique branches. The nerves of the skin terminate partly in the epi¬ dermis and partly in the corium; at their terminals are found various types of nerve endings.

Appendages of the Skin The appendages of the skin are the nails, the hairs, and the sudoriferous and seba¬ ceous glands with their ducts. nails. The nails (ungues) (Fig. 14-6) are flattened, elastic structures of a horny tex¬ ture placed upon the dorsal surfaces of the

terminal phalanges of the fingers and toes. Each nail is convex on its outer surface, con¬ cave within, and is implanted by a portion called the root into a groove in the skin. The exposed portion is called the body, and the distal extremity, the free edge. The nail is firmly adherent to the corium, being accu¬ rately molded upon its surface; the part be¬ neath the body and root of the nail is called the nail matrix, because from it the nail is produced. Under the greater part of the body of the nail, the matrix is thick and raised into a series of longitudinal ridges that are highly vascular, and the color is seen through the transparent tissue. Near the root of the nail, the papillae are smaller, less vascular, and have no regular arrangement, and here the tissue of the nail is not firmly adherent to the connective tissue stratum but only in contact with it; hence this portion is whiter and is called the lunula because of its shape. The cuticle as it passes forward on the dorsal surface of the finger or toe is attached to the surface of the nail a little in advance

Hyponychium

Stratum corneum

Malpighian layer Nail bed

Malpighian layer

Derma

Derma Periosteum Eponychium

Marrow cavity Nail root

Nail matrix

Fig. 14-6.

Median longitudinal section through finger of adult cadaver. The marrow has been removed to show bony trabeculae. 5 X-

APPENDAGES OF THE SKIN

of its root. At the extremity of the finger, it is connected with the undersurface of the nail: both epidermic structures are thus directly continuous with each other. The superficial, horny part of the nail consists of a greatly thickened stratum lucidum; the stratum corneum forms merely the thin cuticular fold (eponychium) that overlaps the lunula; and the deeper part consists of the stratum mucosum. The cells in contact with the papillae of the matrix are columnar and arranged perpendicularly to the surface; those that succeed them are round or polygonal, with the more superficial ones becoming broad, thin, flattened, and so closely packed as to make the limits of the cells indistinct. The nails grow in length by the proliferation of the cells of the stratum germinativum at the root of the nail, and they grow in thickness from the part of the stratum germinativum that underlies the lunula. hair. Hairs (pili) are found on nearly every part of the body’s surface, but are ab¬ sent from the palms of the hands, the soles of the feet, the dorsal surfaces of the terminal phalanges, the glans penis, the inner surface of the prepuce, and the inner surfaces of the labia. They vary much in length, thickness,

1351

and color in different parts of the body and among different races of mankind. In some parts, as in the skin of the eyelids, they are so short that they do not project beyond the fol¬ licles containing them; in others, as upon the scalp, they are of considerable length. Some hairs, such as the eyelashes, the pubic hairs, and the whiskers and beard, are remarkable for their thickness. Straight hairs are stronger than curly hairs, and present on transverse section a cylindrical or oval out¬ line; curly hairs, on the other hand, are flat. A hair consists of a root, which is the part implanted in the skin, and a shaft or scapus, which is the portion projecting from the sur¬ face. The root of the hair (radix pili) ends in an enlargement, the hair bulb, which is whiter and softer than the shaft, and is lodged in a follicular involution of the epidermis called the hair follicle (Fig. 14-7). The follicle of a very long hair extends into the subcutaneous cellular tissue. The hair follicle commences on the surface of the skin with a funnelshaped opening and passes inward in an oblique direction for straight hairs or curved for curly hairs; it is dilated at its deep ex¬ tremity, where it corresponds with the hair

Arrector pili muscle

Epi¬ dermis

Corium Extruding club hair

Sebac. gland Arr. pili. m.

Gland coil Outer root sheath

Sweat gland j-

Inner root sheath Connective tissue sheath

Tela subcut.

Hair bulb with papilla

Fig. 14-7. Section of human scalp with hairs cut longitudinally. (From Rauber-Kopsch, Lehrhuch u. Atlas d. Anatomie d. Menschen, 19th ed., Vol. II, Georg Thieme Verlag, Stuttgart, 1955.)

1352

THE INTEGUMENT

bulb. Opening into the follicle near its free extremity are the ducts of one or more seba¬ ceous glands. At the bottom of each hair fol¬ licle is a small conical, vascular eminence or papilla, similar in every respect to those found upon the surface of the skin; it is con¬ tinuous with the dermic layer of the follicle and supplied with nerve fibrils. The hair fol¬ licle consists of two coats—an outer or dermic, and an inner or epidermic. The outer or dermic coat is formed mainly of fibrous tissue; it is continuous with the dermis, highly vascular, and supplied with numerous minute nervous filaments. It con¬ sists of three layers (Fig. 14-8). The most in¬ ternal is a hyaline basement membrane, which is well marked in the larger hair folli¬ cles but not very distinct in the follicles of minute hairs. This membrane is limited to the deeper part of the follicle. Outside this is a compact layer of fibers and spindle-shaped cells arranged circularly around the follicle; this layer extends from the bottom of the fol¬ licle as high as the entrance of the ducts of the sebaceous glands. Externally a thick layer of connective tissue is arranged in lon¬ gitudinal bundles, forming a more open tex¬ ture and corresponding to the reticular part of the dermis; in this are contained the blood vessels and nerves. The inner or epidermic coat adheres closely to the root of the hair and consists of

two strata, named respectively the outer and inner root sheaths. The outer sheath corre¬ sponds with the stratum mucosum of the epidermis and resembles it in the rounded form and soft character of its cells; at the bottom of the hair follicle these cells become continuous with those of the root of the hair. The inner root sheath consists of (1) a deli¬ cate cuticle next to the hair, composed of a single layer of imbricated scales with atro¬ phied nuclei; (2) one or two layers of horny, flat nucleated cells, known as Huxley’s layer1; and (3) a single layer of cubical cells with clear, flat nuclei, called Henle’s layer.2 The hair bulb is molded over the papilla and composed of polyhedral epithelial cells, which become elongated and spindleshaped as they pass upward into the root of the hair. Some, however, remain polyhedral in the center. Some of these latter cells con¬ tain pigment granules, which are responsible for the color of the hair. It occasionally hap¬ pens that these pigment granules completely fill the cells in the center of the bulb. This causes the dark tract of pigment, of greater or lesser length, that often is found in the axis of the hair. 'Thomas Henry Huxley (1825-1895): An English physiol¬ ogist and naturalist (London). 2Friedrich Gustav Jakob Henle (1809-1885): A German anatomist and histologist (Gottingen).

--Connective tissue sheath - Vitreous membrane -Cylindrical "Polyhedral J

Cells of outer root sheath

enle's layer —Huxley's layer •--Cuticle — Cortex of hair

Fig 14-8. Cross section through hair and root sheath. The red granules in Huxley’s layer are keratohyalin. The space between hair and sheath is an artifact. (From Rauber-Kopsch, Lehrbuch u. Atlas d. Anatomie d. Menschen, 19th ed., Vol. II, Georg Thieme Verlag, Stuttgart, 1955.)

APPENDAGES OF THE SKIN

The shaft of the hair (scapus pili) consists, from within outward, of three parts: the medulla, the cortex, and the cuticle. The me¬ dulla is usually wanting in the fine hairs cov¬ ering the surface of the body, and commonly in those of the head. It is more opaque and deeply colored than the cortex when viewed by transmitted light, but when viewed by reflected light it is white. It is composed of rows of polyhedral cells that contain gran¬ ules of eleidin and frequently air spaces. The cortex constitutes the chief part of the shaft; its cells are elongated and united to form flat fusiform fibers that contain pigment gran¬ ules in dark hair and air in white hair. The cuticle consists of a single layer of flat scales that overlap one another from deep to super¬ ficial. Connected with the hair follicles are min¬ ute bundles of involuntary muscular fibers, termed the arrectores pilorum. They arise from the superficial layer of the dermis and are inserted into the hair follicle, deep to the entrance of the duct of the sebaceous gland. They are placed on the side toward which the hair slopes, and by their action they di¬ minish the obliquity of the follicle and make the hair stand erect (Fig. 14-7). The seba¬ ceous gland is situated in the angle formed by the arrector muscle with the superficial portion of the hair follicle, and contraction of the muscle thus tends to squeeze the seba¬ ceous secretion from the duct of the gland. sebaceous glands. The sebaceous glands are small, sacculated, glandular or¬ gans lodged in the substance of the dermis. They are found in most parts of the skin, but are especially abundant in the scalp and face; they are also numerous around the ap¬ ertures of the anus, nose, mouth, and exter¬ nal ear, but are wanting in the palms of the hands and soles of the feet. Each gland con¬ sists of a single duct, more or less capacious, which emerges from a cluster of oval or flask-shaped alveoli. The number of alveoli may vary from two to five in number, but in some instances there may be as many as 20. Each alveolus is composed of a transparent basement membrane enclosing epithelial cells. The outer or marginal cells are small, polyhedral, and continuous with the cells lining the duct. The remainder of the alveo¬ lus is filled with larger cells that contain lipid, except in the center, where the cells have disintegrated, leaving a cavity filled with their debris and a mass of fatty matter,

1 353

Sweat gland Epidermis

Epithelium

Sudoriferous duct

Tela subcutanea

Secreting tubule of sudoriferous gland

Fig. 14-9.

Sweat gland from the sole of the human foot. (From Rauber-Kopsch, Lehrbuch u. Atlas d. Anatomie d. Menschen, 19th ed., Vol. II, Georg Thieme Verlag, Stutt¬ gart, 1955.)

1 354

the integument

which constitute the sebum cutaneum. The ducts open most frequently into the hair fol¬ licles, but occasionally upon the general sur¬ face, as in the labia minora and the free mar¬ gin of the lips. On the nose and face the glands are large, distinctly lobulated, and often become much enlarged from the accu¬ mulation of pent-up secretion. The tarsal glands of the eyelids are elongated seba¬ ceous glands with numerous lateral diver¬ ticula. sudoriferous glands. The sudoriferous or sweat glands (glandulae sudoriferae) (Fig. 14-9) are found in almost every part of the skin. Each consists of a single tube, the deep part of which is irregularly coiled into an oval or spherical ball, named the body of the gland, while the superficial part, or duct, tra¬ verses the dermis and cuticle and opens on the surface of the skin by a funnel-shaped aperture. In the superficial layers of the der¬ mis the duct is straight, but in the deeper lay¬ ers it is convoluted or even twisted. Where the epidermis is thick, as in the palms of the hands and soles of the feet, the part of the duct that passes through it is spirally coiled. The size of the glands varies. They are espe¬ cially large in those regions where the amount of perspiration is great, as in the ax¬ illae, where they form a thin, mammillated layer of a reddish color, which corresponds exactly to the situation of the hair in this re¬ gion; the glands are also large in the groin. The number of glands varies. They are plentiful on the palms of the hands and on the soles of the feet, where the orifices of the ducts are exceedingly regular and open on the curved ridges. They are least numerous in the neck and back. The palm has about 370 glands per square centimeter; the back of the hand, about 200; the forehead, 175; the breast, abdomen, and forearm, 155, and the

leg and back, 60 to 80. It has been estimated that the total number is about 2,000,000. The following shows the average number of sweat glands per square centimeter of skin on the fingers in various races (Clark and Llamon, 1917): American (white). 558.2 American (Negro). 597.2 Filipino. 653.6 Moro. 684.4 Negrito (adult).709.2 Hindu. 738.2 Negrito (youth).950.0

Sweat glands are absent in the deeper por¬ tion of the external auditory meatus, the pre¬ puce, and the glans penis. The tube, both in the body of the gland and in the duct, consists of two layers—an outer layer of fine areolar tissue and an inner layer of epithelium. The outer layer is thin and continuous with the superficial stratum of the dermis. In the body of the gland, the epithelium consists of a single layer of cubical cells, between the deep ends of which the basement membrane is a layer of longitudinally or obliquely arranged nonstriped muscular fibers. The ducts are destitute of muscular fibers and are com¬ posed of a basement membrane lined by two or three layers of polyhedral cells; the lumen of the duct is coated by a thin cuticle. When the epidermis is carefully removed from the surface of the dermis, the ducts may be pulled out from the dermis in the form of short, thread-like processes. The ceruminous glands of the external acoustic meatus, the ciliary glands at the margins of the eyelids, the circumanal glands and probably the mammary glands are modified sudoriferous glands. The average quantity of sweat se¬ creted in 24 hours varies from 700 to 900 gm.

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.)

Skin Billingham, R. E., and P. B. Medawar. 1953. A study of the branched cells of mammalian epidermis with special reference to the fate of their division prod¬ ucts. Philos. Trans. Roy. Soc. Lond. (Biol.), 237151169. Billingham, R. E„ and W. K. Silvers. 1960. The melano¬ cytes of mammals. Q. Rev. Biol., 35:1-40.

Breathnach, A. S. 1964. Observations on cytoplasmic organelles in Langerhans cells of human epidermis. J. Anat. (Lond.), 98:265-270. Breathnach, A. S. 1965. The cell of Langerhans. Int. Rev. Cytol., 18:1-28. Breathnach, A. S. 1968. The epidermal Langerhans cell. Brit. J. Dermatol., 80:688-689. Breathnach, A. S. 1971. An Atlas of the Ultrastructure of Human Skin. Churchill, London, 406 pp.

REFERENCES

Breathnach, A. S. 1981. Ultrastructure of embryonic skin. Curr. Probl. Dermatol., 9:1-28. Brody, I. 1959. The keratinization of epidermal cells of normal guinea pig skin as revealed by electron mi¬ croscopy. J. Ultrastruct. Res., 2:482-511. Brody, 1.1960. The ultrastructure of the tonofibrils in the keratinization process of normal human epidermis. J. Ultrastruct. Res., 4:264-297. Brody, 1. 1977. Ultrastructure of stratum corneum. Int. J. Dermatol., 16:245-256. Champion, R. H., T. Gillman, A. J. Rook, and R. T. Sims (eds.). 1970. An Introduction to the Biology of the Skin. Blackwell, Oxford, 450 pp. Cox, H. T. 1941. The cleavage lines of the skin. Brit. J. Surg., 29:234-240. Cummins, H., and C. Midlo. 1961. Finger prints, Palms and Soles. Dover Publications, New York, 319 pp. Danielson, D. A. 1977. Wrinkling of the human skin. J. Biomech., 10:201-204. Drochmans, P. 1963. Melanin granules: Their fine struc¬ ture, formation, and degradation in normal and pathological tissues. Int. Rev. Exp. Pathol., 2:357422. Eady, R. A. J., et al. 1979. Mast cell population density, blood vessel density and histamine content in nor¬ mal human skin. Brit. }. Dermatol., 100:623-633. Enna, C. D., and R. F. Dyer. 1979. The histomorphology of the elastic tissue system in the skin of the human hand. Hand, 11:144-150. Farquhar, M. G., and G. E. Palade. 1965. Cell junctions in amphibian skin. J. Cell Biol., 26:263-291. Felsher, Z. 1947. Studies on the adherence of the epider¬ mis to the corium. J. Invest. Dermatol., 8:35-47. Fitzpatrick, T. B., and G. Szabo. 1959. The melanocyte: Cytology and cytochemistry. J. Invest. Dermatol., 32:197-209. Forbes, G. 1938. Lymphatics of the skin, with a note on lymphatic watershed areas. J. Anat. (Lond.), 72:399410. Green, H. 1980. The keratinocyte as differentiated cell type. Harvey Lect., 74:101-139. Haertsch, P. A. 1981. The blood supply to the skin of the leg; A post-mortem investigation. Brit. J. Plast. Surg., 34:470-477. Hibbs, R. G., G. E. Burch, and J. H. Phillips. 1958. The fine structure of the small blood vessels of the normal human dermis and subcutis. Amer. Heart J., 56:662670. Hibbs, R. G., and W. H. Clark, Jr. 1959. Electron micro¬ scope studies of the human epidermis. The cell boundaries and topography of the stratum Malpighii. J. Biophys. Biochem. Cytol., 6:71-76. Holbrook, K. A. 1979. Human epidermal embryogenesis. Int. J. Dermatol., 18:329-356. Holbrook, K. A., and G. F. Odland. 1980. Regional devel¬ opment of the human epidermis in the first trimester embryo and the second trimester fetus (ages related to the timing of amniocentesis and fetal biopsy). J. Invest. Dermatol., 74:161-168. Katzberg, A. A. 1958. The area of the dermo-epidermal junction in human skin. Anat. Rec., 131:717-726. Lavker, R. M., and A. G. Matoltsy. 1970. Formation of horny cells. The fate of cell organelles and differen¬ tiation products in ruminal epithelium. J. Cell Biol., 44:501-512. Leder, L. D. 1981. Intraepidermal mast cells and their origin. Amer. }. Dermatopathol., 3:247-250. Marks, R. 1981. Measurement of biological ageing in human epidermis. Brit. J. Dermatol., 104:627-633.

1355

Matoltsy, A. G. 1966. Membrane-coating granules of the epidermis, j. Ultrastruct. Res., 15:510-515. Matoltsy, A. G., and S. J. Sinesi. 1957. A study of the mechanism of keratinization of human epidermal cells. Anat. Rec., 128:55-68. Medawar, P. B. 1953. The micro-anatomy of the mamma¬ lian epidermis. Q. J. Micr. Sci., 94:481-506. Meyer, W., K. Neurand, and B. Radke. 1982. Collagen fibre arrangement in the skin of the pig. J. Anat. (Lond.), 134:139-148. Montagna, W. 1965. The skin. Sci. Amer., 212(2):56-66. Montagna, W„ and W. C. Lobitz, Jr. (eds.). 1964. The Epidermis. Academic Press, New York, 646 pp. Montagna, W., and P. F. Parakkal. 1974. The Structure and Function of the Skin. 3rd ed. Academic Press, New York, 433 pp. Munger, B. L. 1982. Multiple afferent innervation of pri¬ mate facial hairs—Henry Head and Max von Frey revisited Brain Res., 257.T-43. Odland, G. F. 1950. The morphology of the attachment between the dermis and the epidermis. Anat. Rec., 108:399-413. Odland, G. F. 1958. The fine structure of the interrela¬ tionship of cells in the human epidermis.}. Biophys. Biochem. Cytol., 4:529-538. Okajima, M. 1979. Dermal and epidermal structures of the volar skin. Birth Defects, 15:179-198. Sagebiel, R. W. 1972. In vivo and in vitro uptake of ferri¬ tin by Langerhans cells of the epidermis. J. Invest. Dermatol., 58:47-54. Sarkany, I., and G. A. Caron. 1965. Microtopography of the human skin. ). Anat. (Lond.), 99:359-364. Selby, C. C. 1955. An electron microscope study of the epidermis of mammalian skin in thin sections. I. Dermo-epidermal junction and basal cell layer. J. Biophys. Biochem. Cytol., 1:429-444. Selby, C. C. 1957. An electron microscopic study of thin sections of human skin. II. Superficial cell layers of footpad epidermis. J. Invest. Dermatol., 29:131-149. Southwood, W. F. W. 1955. The thickness of the skin. Plast. Reconstr. Surg., 15:423-429. Spearman, R. I. C. 1973. The Integument: A Textbook of Skin Biology. Cambridge University Press, London, 208 pp. Taussig, J., and G. D. Williams. 1940. Skin color and skin cancer. Arch. Pathol., 30:721-730. Tsuji, T. 1982. Scanning electron microscopy of dermal elastic fibres in transverse section. Brit. j. Dermatol., 106:545-550. Zelickson, S. A. (ed.). 1967. Ultrastructure of Normal and Abnormal Skin. Lea & Febiger, Philadelphia, 431 pp.

Hair, Nails and Glands Baker, B. L. 1951. The relationship of the adrenal, thy¬ roid, and pituitary glands to the growth of hair. Ann. N. Y. Acad. Sci., 53:690-707. Baran, R. 1981. Nail growth direction revisited. Why do nails grow out instead of up? J. Amer. Acad. Derma¬ tol., 4:78-84. Bean, W. B. 1980. Nail growth. Thirty-five years of obser¬ vation. Arch. Intern. Med., 140:73-76. Bell, M. 1971. A comparative study of sebaceous gland ultrastructure in subhuman primates. III. Ma¬ caques: Ultrastructure of sebaceous glands during fetal development of rhesus monkeys (Macaca mulatto). Anat. Rec., 170:331:342. Birbeck, M. S. C., E. H. Mercer, and N. A. Barnicot. 1956.

1 356

THE INTEGUMENT

The structure and formation of pigment granules in human hair. Exp. Cell Res., 10:505-514. Birbeck, M. S. C., and E. H. Mercer. 1957. The electron microscopy of the human hair follicle. I. Introduc¬ tion and the hair cortex. II. The hair cuticle. III. The inner root sheath and trichohyaline.}. Biophys. Biochem. Cytol., 3:203-230. Butcher, E. 0.1946. Hair growth and sebaceous glands in skin transplanted under the skin and into the perito¬ neal cavity in the rat. Anat. Rec., 96:101-109. Butcher, E. O. 1951. Development of the pilary system and the replacement of hair in mammals. Ann. N. Y. Acad. Sci., 53:508-516. Chase, H. B. 1954. Growth of the hair. Physiol. Rev., 34:113-126. Chase, H. B., W. Montagna, and J. D. Malone. 1953. Changes in the skin in relation to the hair growth cycle. Anat. Rec., 116:75-81. Clark, E., and R. H. Lhamon. 1917. Observations on the sweat glands of tropical and northern races. Anat. Rec., 12:139-147. Dawber, R. P. 1980. The ultrastructure and growth of human nails. Arch. Dermatol. Res., 269:197-204. Dixon, A. D. 1961. The innervation of hair follicles in the mammalian lip. Anat. Rec., 140:147-158. Duggins, O. H. 1954. Age changes in head hair from birth to maturity. IV. Refractive indices and birefringence of the cuticle of hair of children. Amer. J. Phys. Anthrop., N.S., 12:89-114. Ellis, R. A. 1967. Eccrine, sebaceous and apocrine glands. In Ultrastructure of Normal and Abnormal Skin. Edited by A. S. Zelickson. Lea & Febiger, Philadel¬ phia, pp. 132-162. Hamilton, J. B. 1942. Male hormone stimulation is pre¬ requisite and an incitant in common baldness. Amer. J. Anat., 71:451-480. Hamilton, J. B. 1951. Patterned loss of hair in man: Types and incidence. Ann. N. Y. Acad. Sci., 53:708-728. Hibbs, R. G. 1958. The fine structure of human eccrine sweat glands. Amer. J. Anat., 103:201-217. Holbrook, K. A., and G. F. Odland. 1978. Structure of the human fetal hair canal and initial hair eruption. J. Invest. Dermatol., 71:385-390. Inaba, M., C. T. McKinstry, and F. Umezawa. 1981. Clini¬ cal observations on the development and eventual character of hair in the axillae of human beings. J. Dermatol. Surg. Oncol., 7:340-342. Ito, T., and S. Shibasaki. 1966. Electron microscopic study on human eccrine sweat glands. Arch. Histol. Jap., 27:81-115. Johnson, P. L„ and G. Bevelander. 1946. Glycogen and phosphatase in the developing hair. Anat. Rec., 95:193-199. Mahler, F., et al. 1979. Blood pressure fluctuations in human nailfold capillaries. Amer. J. Physiol., 236.H888-H893. Montagna, W., H. B. Chase, and W. C. Lobitz, Jr. 1953. Histology and cytochemistry of human skin. IV. The eccrine sweat glands. J. Invest. Dermatol., 20:415423. Munger, B. L. 1961. The ultrastructure and histophysiology of human eccrine sweat glands. J. Biophys. Biochem. Cytol., 11:385-402. Munger, B. L., and S. W. Brusilow. 1961. An electron mi¬

croscopic study of eccrine sweat glands of the cat foot and toe pads—Evidence for ductal reabsorp¬ tion in the human. J. Biophys. Biochem. Cytol., 11:403-417. Prakkal, P. F. 1966. The fine structure of the dermal pa¬ pilla of the guinea pig hair follicle. J. Ultrastruct. Res., 14:133-142. Riggott, J. M., and E. H. Wyatt. 1980. Scanning electron microscopy of hair from different regions of the body of the rat. J. Anat. (Lond.), 130:121-126. Rogers, G. E. 1957. Electron microscope observations on the structure of sebaceous glands. Exp. Cell Res., 13:517-520. Rogers, G. E. 1958. Some aspects of the structure of the inner root sheath of hair follicles revealed by light and electron microscopy. Exp. Cell Res., 14: 378-387. Runne, U., and C. E. Orfanos. 1981. The human nail: Structure, growth and pathological changes. Curr. Probl. Dermatol., 9.T02-149. Singh, J. D. 1982. Distribution of hair on the phalanges of the hand in Nigerians. Acta Anat., 112:31-35. Sulzberger, M. B., F. Herrmann, R. Keller, and B. V. Pisha. 1950. Studies of sweating: III. Experimental factors in influencing the function of the sweat ducts. J. Invest. Dermatol., 14:91-112. Sunderland, S., and L. J. Ray. 1952. The effect of denerva¬ tion on nail growth. J. Neurol. Neurosurg. Psychia¬ try, 15:50-53. Szabo, G. 1967. The regional anatomy of the human in¬ tegument, with special reference to the distribution of hair follicles, sweat glands and melanocytes. Philos. Trans. Roy. Soc. Lond. (Biol.), 252:447-485. Thomas, P. K., and D. G. Ferriman. 1957. Variation in facial and pubic hair growth in white women. Amer. J. Phys. Anthrop., N.S., 15:171-180. Trotter, M. 1938. A review of the classifications of hair. Amer. J. Phys. Anthrop., 24:105-126. Trotter, M. 1939. Classifications of hair color. Amer. J. Phys. Anthrop., 25:237-260. Trotter, M., and O. H. Duggins. 1948. Age changes in head hair from birth to maturity. 1. Index and size of hair of children. Amer. J. Phys. Anthrop., N.S., 6:489-506. Trotter, M., and O. H. Duggins. 1950. Age changes in head hair from birth to maturity. III. Cuticular scale counts of hair of children. Amer. J. Phys. Anthrop., N.S., 8:467-484. Uno, H., and W. Montagna. 1982. Reinnervation of hair follicle end organs and Meissner corpuscles in skin grafts of macaques. J. Invest. Dermatol., 78:210-214. Weiner, J. S., and K. Hellmann. 1960. The sweat glands. Biol. Rev., 35:141-186. Weinstein, G. D., and K. M. Mooney. 1980. Cell prolifera¬ tion kinetics in the human hair root. J. Invest. Der¬ matol., 74:43-46. Young, R. D. 1980. Morphological and ultrastructural aspects of the dermal papilla during the growth cycle of the vibrissal follicle in the rat. J. Anat. (Lond.), 131:355-365. Zaias, N., and J. Alvarez. 1968. The formation of the pri¬ mate nail plate. J. Invest. Dermatol., 51:120-136. Zimmermann, A. A., and C. Cornbleet. 1948. The devel¬ opment of epidermal pigmentation in the negro fetus. J. Invest. Dermatol., 11:383-395.

The Respiratory

Respiration, or exchange of gaseous sub¬ stance between the air and the blood stream, is brought about in the respiratory system (respiratory apparatus): the nose, nasal pas¬ sages, nasopharynx, larynx, trachea, bron¬ chi, and lungs. The pleura, pleural cavities, and the topography of other structures in the thorax are also described in this chapter. The muscular actions associated with respi¬ ration are discussed with the description of the diaphragm in Chapter 6.

Development The development of the nose is described in Chapter 2, Embryology. The primordium of the principal respira¬ tory organs appears as a median longitudinal groove in the ventral wall of the pharynx in an embryo of the third week (3 to 4 mm). The groove deepens and its lips fuse to form the laryngotracheal tube (Fig. 15-1), the cranial end of which opens into the pharynx by a slit-like aperture formed by the persistent

ventral part of the groove. The tube is lined by endoderm, from which the epithelial lin¬ ing of the respiratory tract is developed. The cranial part of the tube becomes the larynx, its next succeeding part the trachea, and from its caudal end two lateral outgrowths arise, the right and left lung buds, from which the bronchi and lungs develop. The first rudiment of the larynx consists of two arytenoid swellings, which appear on either side of the cranial end of the laryngo¬ tracheal groove and are continuous ventrally with a transverse ridge (furcula of His1) that lies between the ventral ends of the third branchial arches and from which the epi¬ glottis is subsequently developed (Figs. 16-4; 16-5). After the separation of the trachea from the esophagus the arytenoid swellings come into contact with each other and with the back of the epiglottis, and the entrance to the larynx assumes the form of a T-shaped cleft. The margins of the cleft adhere to each other and the laryngeal entrance is occluded for a time. The mesodermal wall of the tube con¬ denses to form the cartilages of the larynx and trachea. The arytenoid swellings differ¬ entiate into the arytenoid and corniculate cartilages, and the folds joining them to the epiglottis form the aryepiglottic folds, in which the cuneiform cartilages develop as derivatives of the epiglottis. The thyroid car¬ tilage appears as two lateral plates, each chondrified from two centers and united in the ventral midline by membrane in which an additional center of chondrification de¬ velops. The cricoid cartilage arises from two cartilaginous centers that soon unite ven¬ trally and gradually grow around to fuse on the dorsal aspect of the tube. The right and left lung buds grow out dor¬ sal to the common cardinal veins and are at first symmetrical, but their ends soon become lobulated, three lobules appearing on the right, and two on the left. These subdivisions are the early indications of the correspond¬ ing lobes of the lungs (Figs. 15-2; 15-3). The buds undergo further subdivision and rami¬ fication, and ultimately end in minute ex¬ panded extremities—the infundibula of the lung. After the sixth month the air sacs begin to appear on the infundibula in the form of minute pouches. Vilhelm His (1831-1904): A German anatomist and physiologist (Basel and Leipzig).

1357

1 358

THE RESPIRATORY SYSTEM

Mouth of olfactory pit Median part of fronto¬ nasal process Eye

Processus globulari

Maxillary process

Hypophysis

Mandibular arch

1st branchial pouch

Future tympanic membrane

Sinus cervicalis Hyoid arch Laryngotracheal tube Third arch Lung Fourth arch

The head and neck of a 32-day-old human embryo seen from the ventral surface. The floor of the mouth and pharynx has been removed. (His.)

Fig. 15-1.

During the course of their development the lungs migrate in a caudal direction, so that by the time of birth the bifurcation of the trachea is opposite the fourth thoracic vertebra. As the lungs grow, they project into the part of the celom that will ultimately form the pleural cavities, and the superficial layer of the mesoderm enveloping the lung rudiment expands on the growing lung and is converted into the pulmonary pleura. The pulmonary arteries are derived from the sixth aortic arches (Figs. 8-6 to 8-9).

Upper Respiratory Tract NOSE

External Nose

nares or nostrils is provided with stiff hairs, or vibrissae, which arrest the passage of for¬ eign substances carried with the current of air intended for respiration. The lateral sur¬ faces of the nose form, by their union in the midline, the dorsum nasi, the direction of which varies considerably in different indi¬ viduals. The upper part of the dorsum is sup¬ ported by the nasal bones and is named the bridge. The lateral surface ends below in rounded eminences, the alae nasi. structure. The framework of the exter¬ nal nose is composed of bones and carti¬ lages; it is covered by the integument and is lined by mucous membrane. Bones and Cartilage. The bony frame¬ work occupies the upper part of the organ; it consists of the nasal bones and the frontal processes of the maxillae. The cartilaginous framework consists of

The external nose is shaped like a pyra¬ mid, its free angle termed the apex. The two elliptical orifices, the nares, are separated from each other by a median septum, the columna. The interior surface of the anterior

Lung buds from a human embryo of about four weeks, showing commencing lobulations. (His.)

Fig. 15-2.

Fig. 15-3.

Lungs of a human embryo more advanced in development. (His.)

UPPER RESPIRATORY TRACT

five large pieces: the septal cartilage, the two lateral and the two greater alar cartilages, and several smaller pieces, the lesser alar cartilages (Figs. 15-4 to 15-7). The various cartilages are connected to each other and to the bones by a tough fibrous membrane. The septal cartilage is thicker at its mar¬ gins than at its center and separates the nasal cavities. Its anterior margin is connected with the nasal bones, and is continuous with the anterior margins of the lateral cartilages. Inferiorly, it is connected to the medial crura of the greater alar cartilages by fibrous tis¬ sue. Its posterior margin is connected with the perpendicular plate of the ethmoid; its inferior margin, with the vomer and the pal¬ atine processes of the maxillae. The septal cartilage may be prolonged posteriorly (especially in children) for some distance between the vomer and perpendic¬ ular plate of the ethmoid as a narrow proc¬ ess, the sphenoidal process. The septal car¬ tilage does not reach as far as the lowest part of the nasal septum. This is formed by the medial crura of the greater alar carti¬ lages. The lateral cartilage (upper lateral carti¬ lage) is situated below the inferior margin of the nasal bone; it is flat and triangular. Its anterior margin is thicker than the posterior, and is continuous above with the cartilage of the septum, but separated from it below by a narrow fissure. Its superior margin is at¬ tached to the nasal bone and the frontal process of the maxilla; its inferior margin is connected by fibrous tissue with the greater alar cartilage. The greater alar cartilage (lower lateral cartilage) is a thin, flexible plate situated

1359

Greater alar cartilage

Septal cartilage Tela subcutanea cutis

Cartilages of the nose. Inferior view.

Fig. 15-5.

immediately below the lateral cartilage and bent upon itself in such a manner that it forms the medial and lateral walls of the naris of its own side. The portion that forms the medial wall is loosely connected with the corresponding portion of the opposite cartilage, the two forming, together with the thickened integument and subjacent tissue, the septum mobile nasi. The part that forms the lateral wall is curved to correspond with the ala of the nose. It is oval, flat, and nar¬ row posteriorly where it is connected with the frontal process of the maxilla by a tough fibrous membrane, in which are found three or four small cartilaginous plates, the lesser alar cartilages (sesamoid cartilages). Superi¬ orly, the greater alar cartilage is connected by fibrous tissue to the lateral cartilage and anterior part of the cartilage of the septum; inferiorly, it falls short of the margin of the naris, the ala being completed by fatty and fibrous tissue covered by skin. Anteriorly, the greater alar cartilages are separated by a notch that corresponds with the apex of the nose.

Crista gall Cribriform plate

Frontal sinus Nasal bone

Lesser alar

Palatine bone

Greater alar

Fig. 15-6. Fig. 15-4.

Cartilages of the nose. Side view.

side.

Vomeronasal cartilage

Bones and cartilages of septum of nose. Right

1 360

THE RESPIRATORY SYSTEM

Septal cartilage Lateral cartilage Lesser alar cartilage Greater alar cartilage

Fig. 15-7.

Cartilages of the nose. Anterior view.

Muscles. The muscles acting on the ex¬ ternal nose are described in Chapter 6. Integument. The integument of the dor¬ sum and sides of the nose is thin and loosely connected with the subjacent parts, but over the tip and alae it is thicker and more firmly adherent, and is furnished with a large num¬ ber of sebaceous follicles, the orifices of which are usually quite distinct. Vessels and Nerves. The arteries of the exter¬ nal nose are the alar and septal branches of the facial artery, which supply the alae and septum. The dor¬ sum and sides are supplied from the dorsal nasal branch of the ophthalmic artery and the infraorbital branch of the maxillary artery. The veins end in the facial and ophthalmic veins. The nerves for the muscles of the nose are de¬ rived from the facial nerve. The skin receives branches from the infratrochlear and nasociliary branches of the ophthalmic nerve and from the infra¬ orbital branch of the maxillary nerve. Nasal Cavity The nasal cavity is divided by the median septum into two symmetrical and approxi¬ mately equal chambers, the nasal fossae. They have their external openings through the nostrils or nares, and they open into the nasopharynx through the choanae. The nares are oval apertures measuring about 1.5 cm anteroposteriorly and 1 cm trans¬ versely. The choanae are two oval openings

measuring approximately 2.5 cm vertically and 1.5 cm transversely. The bony boundaries of the nasal cavity are described in Chapter 4, Osteology. Inside the aperture of the nostril is a slight dilatation, the vestibule, which is bounded laterally by the ala and lateral crus of the greater alar cartilage and medially by the medial crus of the same cartilage. It is lined by skin containing hairs and sebaceous glands, and it extends as a small recess to¬ ward the apex of the nose. Each nasal fossa is divided into two parts: an olfactory region, consisting of the superior nasal concha and the opposed part of the septum, and a respi¬ ratory region, which comprises the rest of the cavity. lateral WALL(Figs. 15-8; 15-9). On the lat¬ eral wall are the superior, middle, and in¬ ferior nasal conchae, overhanging the corre¬ sponding nasal passages or meatuses. Above the superior concha is a narrow recess, the sphenoethmoidal recess, into which the sphenoidal sinus opens. The superior mea¬ tus is a short oblique passage that extends about half way along the superior border of the middle concha; the posterior ethmoidal cells open into the anterior part of this mea¬ tus. The middle meatus is continued anteri¬ orly into a shallow depression situated above the vestibule and named the atrium of the middle meatus. The lateral wall of this meatus is fully displayed only by raising or removing the middle concha. On it is a rounded elevation, the bulla ethmoidalis, and anterior and inferior to this is a curved cleft, the hiatus semilunaris. The bulla ethmoidalis (Fig. 15-9) is caused by the bulging of the middle ethmoi¬ dal cells, which open on or immediately above it, and the size of the bulla varies with that of its contained cells. The hiatus semilunaris is the narrow curved opening into a deep pocket, the in¬ fundibulum. It is bounded inferiorly by the sharp concave margin of the uncinate proc¬ ess of the ethmoid bone, and superiorly, by the bulla ethmoidalis. The anterior ethmoi¬ dal cells open into the anterior part of the infundibulum. In slightly over 50% of sub¬ jects, the infundibulum is directly continu¬ ous with the frontonasal duct or passage leading from the frontal air sinus. When the anterior end of the uncinate process fuses with the anterior part of the bulla, this conti¬ nuity is interrupted, and the frontonasal

UPPER RESPIRATORY TRACT

Sphenoethmoidal recess

Agger nasi Fornix pharyngis

Limen nasi Nasopharyngeal meatus

Pharyngeal orifice of auditory tube Fig. 15-8.

Pharyngeal recess

Lateral wall of nasal cavity.

Bristle in infundibulum Cut edge of middle concha Hiatus semilunaris Bulla ethmoidalis Opening of middle ethmoidal cells Cut edge of superior concha Openings of posterior ethmoidal cells Bristle in opening of sphenoidal sinus

Uncinate process

Bristle in nasolacrimal canal Bristle in opening of maxillary sinus Fig. 15-9.

cut edge ot inferior concha

auditory tube

Pharyngeal rece:

Lateral wall of nasal cavity; the three nasal conchae have been removed.

1361

1362

THE RESPIRATORY SYSTEM

duct then opens directly into the anterior end of the middle meatus. In the bottom of the infundibulum, below the bulla ethmoidalis and partly hidden by the inferior end of the uncinate process, is the ostium maxillare, or opening from the maxillary sinus. This opening is placed near the roof of the sinus. An accessory opening from the sinus is frequently present below the posterior end of the middle nasal con¬ cha. The inferior meatus is inferior and lat¬ eral to the inferior nasal concha; the naso¬ lacrimal duct opens into this meatus under cover of the anterior part of the concha. medial wall (Fig. 15-6). The medial wall or septum is frequently deflected from the median plane, thus lessening the size of one nasal fossa and increasing that of the other; ridges or spurs of bone growing into one or the other fossa from the septum are also sometimes present. Immediately over the incisive canal at the inferior edge of the car¬ tilage of the septum is a depression, the na¬ sopalatine recess. In the septum close to this recess a minute orifice may be discerned; it leads posteriorly into a blind pouch, the ru¬ dimentary vomeronasal organ of Jacobson,1 which is supported by a strip of cartilage, the vomeronasal cartilage. This organ is well developed in many of the lower animals, where it apparently plays a part in the sense of smell, since it is supplied by twigs of the olfactory nerve and is lined by epithelium similar to that in the olfactory region of the nose. roof. The roof of the nasal cavity is nar¬ row from side to side, except at its posterior part, and may be divided into sphenoidal, ethmoidal, and frontonasal parts, after the bones that form it. floor. The floor is concave from side to side. Its anterior three-fourths are formed by the palatine process of the maxilla; its poste¬ rior fourth is formed by the horizontal proc¬ ess of the palatine bone. mucous membrane. The nasal mucous membrane lines the nasal cavity and adheres intimately to the periosteum or perichon¬ drium. It is continuous with the skin through the nares, and with the mucous membrane of the nasal part of the pharynx through the choanae. From the nasal fossa its continuity with the conjunctiva may be traced through the nasolacrimal and lacrimal ducts; it is Ludwig Levin Jacobson (1783-1843): A Danish anato¬ mist and physician (Copenhagen).

continuous with the frontal, ethmoidal, sphenoidal, and maxillary sinuses through the several openings in the meatuses. Conti¬ nuity with the middle ear is established with the nasopharynx through the auditory tube. The mucous membrane is thickest and most vascular over the nasal conchae. It is also thick over the septum, but very thin in the meatuses, on the floor of the nasal cavity, and in the various sinuses. Owing to the thickness of the greater part of this membrane, the nasal cavities are much narrower and the middle and inferior nasal conchae appear larger and more prom¬ inent than in the skeleton; the various aper¬ tures communicating with the meatuses also are considerably narrowed. Structure of the Mucous Membrane. The mucous membrane covering the respiratory portion of the nasal cavity has a pseudostratified, ciliated, columnar epithelium, liberally interspersed with goblet cells. Beneath the basement membrane of the epithelium, the areolar connective tissue is infiltrated with lymphocytes, which may be so numerous that they form a diffuse lymphoid tissue. The lamina propria is composed of a layer of glands toward the surface and a layer of blood vessels next to the periosteum. The glands may be large or small and contain ei¬ ther mucous or serous alveoli. They have individual openings on the surface, and their secretion forms a protective layer over the membrane which serves to warm and moisten the inspired air. In the deeper layers of the lamina propria, especially over the conchae, the dilated veins and blood spaces form a rich plexus that bears a superficial resemblance to erectile tissue; these areas easily become engorged as the result of irri¬ tation or inflammation, causing the mem¬ brane to swell and encroach upon the lumen of the meatuses, and even occlude the ostia of the sinuses. The mucous membrane of the paranasal sinuses is columnar ciliated, similar to that of the nasal fossae, but is much thinner and for the most part lacking in glands in the lamina propria. The olfactory portion of the mucous mem¬ brane of the nasal cavity is described at the beginning of Chapter 13. Vessels and Nerves. The arteries of the nasal cavities are the anterior and posterior ethmoidal branches of the ophthalmic artery, which supply the ethmoidal cells, frontal sinuses, and roof of the

UPPER RESPIRATORY TRACT

1363

Lateral cartilage of nose Cartilage of septum Mid. nasal concha

Angular vein Infraorbital nerve Zygomatic proc. Inf. nasal meatus Inf. nasal concha

Nasopharyngeal meatus

Nasal portion of pharynx

Fig. 15-10. Transverse section through the anterior part of the head at a level just inferior to the apex of the dens (odontoid process). Inferior view.

nose; the sphenopalatine branch of the maxillary ar¬ tery, which supplies the mucous membrane cover¬ ing the conchae, the meatuses, and septum; the sep¬ tal ramus of the superior labial branch of the facial artery; the infraorbital and alveolar branches of the maxillary artery, which supply the lining membrane of the maxillary sinus; and the pharyngeal branch of the maxillary artery, which is distributed to the sphe¬ noidal sinus. The ramifications of these vessels form a close plexiform network beneath and in the sub¬ stance of the mucous membrane. Some veins open into the sphenopalatine vein; others join the facial vein. Some accompany the eth¬ moidal arteries and end in the ophthalmic veins, and a few communicate with the veins on the orbital sur¬ face of the frontal lobe of the brain through the fo¬ ramina in the cribriform plate of the ethmoid bone. When the foramen cecum is patent, it transmits a vein to the superior sagittal sinus. The lymphatics are described in Chapter 10. The nerves of ordinary sensation are: the naso¬ ciliary branch of the ophthalmic nerve, filaments from the anterior alveolar branch of the maxillary nerve, the nerve of the pterygoid canal, the nasopal¬ atine nerve, the anterior palatine nerve, and nasal branches of the pterygopalatine nerve. The nasociliary branch of the ophthalmic nerve distributes filaments to the anterior part of the sep¬ tum and lateral wall of the nasal cavity. Filaments from the anterior alveolar nerve supply the inferior meatus and inferior concha. The nerve of the ptery¬

goid canal supplies the upper and back part of the septum and superior concha; the upper nasal branches from the pterygopalatine nerve have a sim¬ ilar distribution. The nasopalatine nerve supplies the middle of the septum. The anterior palatine nerve supplies the lower nasal branches to the middle and inferior conchae. The olfactory nerves, the nerves of the special sense of smell, are a number of fine filaments distrib¬ uted to the mucous membrane of the olfactory re¬ gion. Their fibers arise from the bipolar olfactory cells and lack medullary sheaths. They unite into fas¬ ciculi that form a plexus beneath the mucous mem¬ brane and then ascend in grooves or canals in the ethmoid bone. They pass into the skull through the foramina in the cribriform plate of the ethmoid and enter the olfactory bulb, in which they ramify and form synapses with the dendrites of the mitral cells (see Chapter 1 3).

Accessory Sinuses of the Nose The accessory sinuses or air cells of the nose (paranasal sinuses) (Figs. 15-9 to 15-12) are the frontal, ethmoidal, sphenoidal, and maxillary. They vary in size and form in dif¬ ferent individuals and are lined by ciliated mucous membrane directly continuous with that of the nasal cavity. frontal sinuses. The frontal sinuses, sit-

1364

THE RESPIRATORY SYSTEM

Superior concha Ethmoidal air cell

Contents of Orbit

Superior meatus

11

Middle concha Middle meatus Septum nasi Inferior concha Maxillary sinus Inferior meatus

'Havd'tlictla te

Fig. 15-11.

Coronal section of nasal cavities.

uated behind the superciliary arches, are rarely symmetrical, and the septum between them frequently deviates to one side or the other of the midline. Their average measure¬ ments are: height. 3 cm; breadth, 2.5 cm; depth, 2.5 cm. A large frontal sinus may ex¬ tend out over most of the orbit. Each opens into the anterior part of the corresponding middle meatus of the nose through the fron¬ tonasal duct, which enters the anterior part of the middle meatus. Absent at birth, the frontal sinuses are generally fairly well de¬ veloped between the seventh and eighth years, but reach their full size only after puberty. ethmoidal air cells. The ethmoidal air cells consist of numerous small, thin-walled cavities occupying the ethmoidal labyrinth and completed by the frontal, maxillary, lac¬ rimal, sphenoidal, and palatine bones. They lie between the upper parts of the nasal cavi¬ ties and the orbits, and are separated from these cavities by thin bony laminae. On ei¬ ther side they are arranged in three groups: anterior, middle, and posterior. The anterior and middle groups open into the middle meatus of the nose, the former by way of the infundibulum, the latter on or above the

bulla ethmoidalis. The posterior cells open into the superior meatus under cover of the superior nasal concha; sometimes one or more open into the sphenoidal sinus. The ethmoidal cells begin to develop after fetal life. sphenoidal sinuses. The sphenoidal si¬ nuses (Fig. 15-9), contained within the body of the sphenoid, vary in size and shape, and owing to the lateral displacement of the in¬ tervening septum, they are rarely symmetri¬ cal. Their average measurements are: verti¬ cal height, 2.2 cm; transverse breadth, 2 cm; depth 2.2 cm. When exceptionally large, they may extend into the roots of the ptery¬ goid processes or great wings, and may in¬ vade the basilar part of the occipital bone. Each sinus communicates with the spheno¬ ethmoidal recess by means of an ostium in the upper part of its anterior wall. The sphe¬ noidal sinuses are present as minute cavities at birth, but their main development takes place after puberty. maxillary sinus. The maxillary sinus (antrum of Highmore1), the largest of the Nathaniel Highmore (1613-1685): An English physician (Sherborne).

UPPER RESPIRATORY TRACT

1365

Radiograph of adult skull, frontal view, showing the frontal sinus (F), the ethmoid air cells (E), and the maxillary sinus (M). (From Juhl, J.H., Essentials of Roentgen Interpretation, 4th ed., Harper and Row Publishers, Hagerstown, Md., 1981.)

Fig. 15-12.

accessory sinuses of the nose, is a pyramidal cavity in the body of the maxilla. Its base is formed by the lateral wall of the nasal cav¬ ity, and its apex extends into the zygomatic process. Its roof or orbital wall is frequently ridged by the bony wall of the infraorbital canal; its floor is formed by the alveolar process and is usually 1 to 10 mm below the level of the floor of the nose. Projecting into the floor are several conical elevations corre¬ sponding with the roots of the first and sec¬ ond molar teeth, and in some cases the floor is perforated by one or more of these roots. The size of the sinus varies in different skulls and even on the two sides of the same skull. The adult capacity varies from 9.5 cc to 20 cc (average about 14.75 cc). The measurements of an average-sized sinus are: vertical height opposite the first molar tooth, 3.75 cm; trans¬ verse breadth, 2.5 cm; anteroposterior depth, 3 cm. In the superior part of its medial wall is an ostium through which it communicates with the lower part of the infundibulum; a second or accessory orifice is frequently

present in the middle meatus posterior to the first. The maxillary sinus appears as a shal¬ low groove on the medial surface of the bone about the fourth month of fetal life, but does not reach its full size until after the second dentition.

LARYNX

The larynx or organ of voice is the part of the air passage that connects the pharynx with the trachea. It produces a considerable projection in the midline of the neck called the Adam’s apple. It forms the inferior part of the anterior wall of the pharynx, and is covered by the mucous lining of that cavity. Its vertical extent corresponds to the fourth, fifth, and sixth cervical vertebrae, but it is placed somewhat higher in the female and also during childhood; on either side of it lie the great vessels of the neck. The average measurements of the adult larynx in both males and females appear on page 1366.

1366

THE RESPIRATORY SYSTEM

Males (mm) Length. 44 Transverse diameter. 43 Anteroposterior diameter. 36 Circumference.136

Females (mm) 36 41 26 112

EPIGLOTTIS

Until puberty the larynx of the male differs little in size from that of the female. In the female its increase after puberty is only slight; in the male it undergoes considerable increase; all the cartilages are enlarged and the thyroid cartilage becomes prominent in the midline of the neck, while the length of the rima glottidis is nearly doubled.

The larynx is broad above, where it pre¬ sents the form of a triangular box flattened dorsally and at the sides, and it is bounded ventrally by a prominent vertical ridge. Caudally, it is narrow and cylindrical. It is com¬ posed of cartilages, which are connected together by ligaments and moved by numer¬ ous muscles. It is lined by mucous mem¬ brane continuous with that of the pharynx and the trachea. Cartilages of the Larynx

THYROID

uormcuiaie carriages Cuneiform cartilage

ARYTENOID Posterior surface

Insertion of Cricoarytenoideus posterior Arytenoid cartilages, base

There are nine cartilages of the larynx (Fig. 15-13), three single and three paired, as follows: Thyroid Cricoid Arytenoid (two) Corniculate (two) Cuneiform (two) Epiglottis thyroid cartilage. The thyroid cartilage (Fig. 15-13) is the largest cartilage of the lar¬ ynx. It consists of two laminae, the anterior borders of which are fused with each other at an acute angle in the midline of the neck; these form a subcutaneous projection named the laryngeal prominence (Adam’s apple). This prominence is most distinct at its cra¬ nial part and is larger in the male than in the female. Immediately above it, the lami¬ nae are separated by a V-shaped notch, the superior thyroid notch. The laminae are ir¬ regularly quadrilateral in shape, and their posterior angles are prolonged into proc¬ esses termed the superior and inferior cornua. On the outer surface of each lamina an oblique line runs caudalward and ventral-

CRICOID Articular facet for arytenoid cartilage Articular facet for inferior cornu of thyroid cartilage

Fig. 15-13.

The cartilages of the larynx. Posterior view.

ward from the superior thyroid tubercle, sit¬ uated near the root of the superior cornu, to the inferior thyroid tubercle on the caudal border. This line gives attachment to the sternothyroid, thyrohyoid, and the inferior pharyngeal constrictor. The inner surface is smooth; cranially and dorsally it is slightly concave and covered by mucous membrane. Ventrally, in the angle formed by the junc¬ tion of the laminae, are attached the stem of the epiglottis, the ventricular and vocal liga¬ ments, the thyroarytenoid, thyroepiglotticus, and vocalis muscles, and the thyroepiglottic ligament. The cranial border is concave dorsally and convex ventrally; it gives attachment to the corresponding half of the thyrohyoid

UPPER RESPIRATORY TRACT

membrane. The caudal border is concave dorsally and nearly straight ventrally, the two parts being separated by the inferior thyroid tubercle. A small part of it in and near the midline is connected to the cricoid cartilage by the middle cricothyroid liga¬ ment. The dorsal border, thick and rounded, receives the insertions of the stylopharyngeus and palatopharyngeus. It ends cranially, in the superior cornu, and caudally, in the inferior cornu. The superior cornu is long and narrow, directed cranialward, and ends in a conical extremity, which gives attach¬ ment to the lateral thyrohyoid ligament. The inferior cornu is short and thick; it is di¬ rected caudalward, with a slight inclination, and presents, on the medial side of its tip, a small oval articular facet for articulation with the side of the cricoid cartilage. During infancy, the laminae of the thyroid cartilage are joined to each other by a nar¬ row, lozenge-shaped strip named the intra¬ thyroid cartilage. This strip extends from the cranial to the caudal border of the cartilage in the midline, and is distinguished from the laminae by being more transparent and more flexible. cricoid cartilage. The cricoid cartilage (Fig. 15-13) is smaller but thicker and stronger than the thyroid, and forms the cau¬ dal and dorsal parts of the wall of the larynx. It consists of two parts: a posterior quadrate lamina and a narrow anterior arch, onefourth or one-fifth of the depth of the lamina. The lamina of the cricoid cartilage is deep and broad and measures about 2 or 3 cm craniocaudally. On its dorsal surface, in the midline, is a vertical ridge, to the caudal part of which are attached the longitudinal fibers of the esophagus, and on either side of this ridge is a broad depression for the posterior cricoarytenoid. The arch is narrow, convex, and measures vertically from 5 to 7 mm; it affords attach¬ ment externally, ventrally, and at the sides to the cricothyroid muscle, and dorsally, to part of the inferior constrictor of the pharynx. On either side, at the junction of the lam¬ ina with the arch, is a small round articular surface for articulation with the inferior cornu of the thyroid cartilage. The caudal border of the cricoid cartilage is horizontal and connected to the highest ring of the trachea by the cricotracheal liga¬ ment. The cranial border runs obliquely

1 367

cranialward and dorsalward, owing to the great depth of the lamina. It gives attach¬ ment, ventrally, to the middle cricothyroid ligament and at the side, to the conus elasticus and the lateral cricoarytenoids. Dorsally, it has a shallow notch in the mid¬ dle, and on either side of this a smooth, oval convex surface for articulation with the base of an arytenoid cartilage. The inner surface of the cricoid cartilage is smooth and lined by mucous membrane. arytenoid cartilage. The arytenoid carti¬ lages (Fig. 15-13) are two in number, situated at the cranial border of the lamina of the cri¬ coid cartilage, at the dorsum of the larynx. Each is pyramidal and has three surfaces, a base, and an apex. The dorsal surface is triangular, smooth, concave, and gives attachment to the oblique and transverse arytenoid. The ven¬ trolateral surface is somewhat convex and rough. On it, near the apex of the cartilage, is a rounded elevation (colliculus) from which a ridge (crista arcuata) curves at first dorsalward and then caudalward and ventralward to the vocal process. The caudal part of this crest intervenes between two depressions or foveae: an upper triangular depression and a lower oblong depression. The latter gives attachment to the vocalis muscle. The me¬ dial surface is narrow, smooth, and flat. It is covered by mucous membrane and forms the lateral boundary of the intercartilaginous part of the rima glottidis. The base of each cartilage is broad, and has a concave smooth surface for articula¬ tion with the cricoid cartilage. Its lateral angle is short, round, and prominent; it pro¬ jects dorsalward, and is termed the muscular process. It receives the insertion of the pos¬ terior cricoarytenoid dorsally and the lateral cricoarytenoid ventrally. Its anterior angle, also prominent but more pointed, projects horizontally ventralward; it gives attach¬ ment to the vocal ligament and is called the vocal process (Fig. 15-16). The apex of each cartilage is pointed, curved dorsalward and medialward, and surmounted by a small conical, cartilaginous nodule, the corniculate cartilage. corniculate cartilage. The corniculate cartilages (cartilages of Santorini1) are two small conical nodules consisting of yellow Giovanni Domenico Santorini (1681-1737): An Italian anatomist (Venice).

1368

THE RESPIRATORY SYSTEM

elastic cartilage, which articulate with the summits of the arytenoid cartilages and serve to prolong them dorsalward and medialward. They are situated in the poste¬ rior parts of the aryepiglottic folds of mu¬ cous membrane, and they are sometimes fused with the arytenoid cartilages. cuneiform cartilage. The cuneiform cartilages (cartilages of Wrisberg2) are two small, elongated pieces of yellow elastic car¬ tilage, placed one on either side, in the aryepiglottic fold, where they give rise to small 2Heinrich August Wrisberg (1739-1808): A German anat¬ omist (Gottingen).

whitish elevations on the surface of the mu¬ cous membrane, just ventral to the arytenoid cartilages. epiglottis. The epiglottis (Fig. 15-13) is a thin lamella of yellow elastic cartilage, shaped like a leaf. It projects obliquely up¬ ward behind the root of the tongue and ven¬ tral to the entrance of the larynx. The free extremity is broad and round; the attached part or stem is long, narrow, and connected by the thyroepiglottic ligament to the angle formed by the two laminae of the thyroid cartilage, a short distance caudal to the supe¬ rior thyroid notch. The caudal part of its an¬ terior surface is connected to the cranial

Lateral thyrohyoid ligament Triticea cartilage

Superior cornu

Hyoid bone

Internal laryngeal nerve Superior laryngeal artery Superior laryngeal vein Thyrohyoid membrane

Thyroid cartilage

Inferior cornu

Conus elasticus Middle cricothyroid ligament Cricoid cartilage

Trachea

Fig. 15-14.

The ligaments of the larynx. Anterolateral view.

UPPER RESPIRATORY TRACT

border of the body of the hyoid bone by an elastic ligamentous band, the hyoepiglottic ligament. The anterior or lingual surface is curved ventralward and is covered on its cranial, free part by mucous membrane, which is re¬ flected onto the sides and root of the tongue, forming a median and two lateral glossoepi¬ glottic folds. The lateral folds are partly at¬ tached to the wall of the pharynx. The de¬ pressions between the epiglottis and the root of the tongue, on either side of the median fold, are named the valleculae (Fig. 15-18). The caudal part of the anterior surface lies dorsal to the hyoid bone, the hyothyroid membrane, and the upper part of the thyroid cartilage, but is separated from these struc¬ tures by a mass of fatty tissue. The posterior or laryngeal surface is smooth, concave from side to side, and concavoconvex vertically; its caudal part projects dorsalward as an elevation, the tu¬ bercle or cushion. The surface of the carti¬ lage is indented by a number of small pits in which mucous glands are lodged. To its sides the aryepiglottic folds are attached. structure. The corniculate and cunei¬ form cartilages, the epiglottis, and the apices of the arytenoids at first consist of hyaline cartilage, but later elastic fibers are depos¬ ited in the matrix, converting them into yel¬ low elastic cartilage that shows little tend¬ ency to calcification. The thyroid, cricoid, and the greater part of the arytenoids consist of hyaline cartilage and become more or less ossified as age advances. Ossification com¬ mences about the twenty-fifth year in the thyroid cartilage and somewhat later in the cricoid and arytenoids; by the sixty-fifth year these cartilages may be completely con¬ verted into bone. Ligaments The ligaments of the larynx (Figs. 15-14; 15-15) are extrinsic (those that connect the thyroid cartilage and epiglottis with the hyoid bone, and the cricoid cartilage with the trachea) and intrinsic (those that connect the several cartilages of the larynx to each other). extrinsic ligaments. The ligaments that connect the thyroid cartilage with the hyoid bone are the thyrohyoid membrane and a middle and two lateral thyrohyoid ligaments.

1 369

The thyrohyoid membrane (hyothyroid membrane) is a broad, fibroelastic layer at¬ tached to the cranial border of the thyroid cartilage and to the front of its superior cornu, and to the cranial margin of the dor¬ sal surface of the body and greater cornua of the hyoid bone. It thus passes dorsal to the posterior surface of the body of the hyoid, and is separated from it by a bursa that facil¬ itates the upward movement of the larynx during deglutition. Its middle thicker part is termed the middle thyrohyoid ligament (middle hyothyroid ligament); its lateral thinner portions are pierced by the superior laryngeal vessels and the internal branch of the superior laryngeal nerve. Its anterior sur¬ face is in relation with the thyrohyoid, ster¬ nohyoid, and omohyoid muscles, and with the body of the hyoid bone. The thyrohyoid ligament (lateral hyothy¬ roid ligament) is a round elastic cord that forms the posterior border of the thyrohyoid membrane and passes between the tip of the superior cornu of the thyroid cartilage and the extremity of the greater cornu of the hyoid bone. A small cartilaginous nodule (cartilago triticea), sometimes bony, is fre¬ quently found in it. The epiglottis is connected with the hyoid bone by an elastic band, the hyoepiglottic ligament, which extends from the anterior surface of the epiglottis to the upper border of the body of the hyoid bone. The glossoepi¬ glottic folds of mucous membrane may also be considered extrinsic ligaments of the epi¬ glottis. The cricotracheal ligament connects the cricoid cartilage with the first ring of the tra¬ chea. It resembles the fibrous membrane that connects the cartilaginous rings of the tra¬ chea to each other. intrinsic ligaments. Beneath the mu¬ cous membrane of the larnyx is a broad sheet of fibrous tissue that contains many elastic fibers and is termed the elastic mem¬ brane of the larynx. It is subdivided on ei¬ ther side by the interval between the ven¬ tricular and vocal ligaments. The cranial portion extends between the arytenoid carti¬ lage and the epiglottis and is often poorly defined; the caudal part is a well-marked membrane that forms, with its fellow of the opposite side, the conus elasticus, which connects the thyroid, cricoid, and arytenoid cartilages to one another.

1 370

THE RESPIRATORY SYSTEM

Epiglottis

Triticea cartilage Hyoid bone

Thyrohyoid membrane

Corniculate cartilage

Thyroid cartilage

Vestibular ligament

Arytenoid cartilage

Vocal ligament Posterior cricoarytenoid ligament

Cricothyroid joint Cricoid cartilage

Trachea

The ligaments of the larynx viewed from the posterior aspect. Note that the right half of the thyrohyoid membrane has been removed to show the contours of the thyroid cartilage, the epiglottis, and the hyoid bone.

Fig. 15-15.

The conus elasticus (cricothyroid mem¬ brane) is composed mainly of yellow elastic tissue. It consists of an anterior and two lat¬ eral portions. The anterior part or middle cricothyroid ligament (ligamentum cricothyroideum medium; central part of cricothy¬ roid membrane) is thick, strong, and con¬ nects the ventral parts of the contiguous margins of the thyroid and cricoid cartilages. It is overlapped on either side by the crico¬

thyroid muscles, but between these it is sub¬ cutaneous; it is crossed horizontally by a small anastomotic arterial arch formed by the junction of the two cricothyroid arteries, branches of which pierce it. The lateral portions are thinner and lie close under the mucous membrane of the larynx; they ex¬ tend from the superior border of the cricoid cartilage to the inferior margin of the vocal ligaments, with which they are continuous.

UPPER RESPIRATORY TRACT

These ligaments may, therefore, be regarded as the free borders of the lateral portions of the conus elasticus, and they extend from the vocal processes of the arytenoid carti¬ lages to the angle of the thyroid cartilage about midway between its cranial and cau¬ dal borders. An articular capsule, strengthened poste¬ riorly by a well-marked fibrous band, en¬ closes the articulation of the inferior cornu of the thyroid with the cricoid cartilage on either side. Each arytenoid cartilage is connected to the cricoid by a capsule and a posterior cricoarytenoid ligament. The capsule is thin and loose and is attached to the margins of the articular surfaces. The posterior crico¬ arytenoid ligament extends from the cricoid to the medial and dorsal part of the base of the arytenoid. The thyroepiglottic ligament is a long, slender, elastic cord that connects the stem of the epiglottis with the angle of the thyroid cartilage immediately beneath the superior thyroid notch and cranial to the attachment of the ventricular ligaments. movements. The articulation between the infe¬ rior cornu of the thyroid cartilage and the cricoid cartilage on either side is diarthrodial and permits rotatory and gliding movements. During the rotatory movement, the cricoid cartilage rotates upon the in¬ ferior cornua of the thyroid cartilage around an axis that passes transversely through both joints. The gliding movement consists of a limited shifting of the cricoid on the thyroid in different directions. The articulation between the arytenoid cartilages and the cricoid is also diarthrodial and permits two varieties of movement: one is rotation of the aryte¬ noid on a vertical axis, whereby the vocal process is moved lateralward or medialward and the rima glottidis is increased or diminished; the other is a gliding movement, which allows the arytenoid carti¬ lages to approach or recede from each other. From the direction and slope of the articular surfaces, lat¬ eral gliding is accompanied by a forward and down¬ ward movement. The two movements of gliding and rotation are associated, the medial gliding being con¬ nected with the medialward rotation, and the lateral gliding with lateralward rotation. The posterior cricoarytenoid ligaments limit the forward move¬ ment of the arytenoid cartilages on the cricoid.

Interior of the Larynx The cavity of the larynx extends from the laryngeal entrance to the caudal border of the cricoid cartilage, where it is continuous with that of the trachea. It is divided into

1371

two parts by the projection of the vocal folds, between which is a narrow triangular fissure or opening, the rima glottidis. The portion of the cavity of the larynx above the vocal folds is called the vestibule. It is wide and triangular; about the center of its base or anterior wall, however, is the backward pro¬ jection of the tubercle of the epiglottis. It contains the ventricular folds, and between these and the vocal folds are the ventricles of the larynx. The portion caudal to the vocal folds is at first elliptical, but widens out, assumes a circular form, and is continu¬ ous with the tube of the trachea (Figs. 15-16; 15-17). entrance of the larynx. The entrance of the larynx (Fig. 15-18) is bounded ventrally by the epiglottis; dorsally, by the apices of the arytenoid cartilages, the corniculate car¬ tilages, and the interarytenoid notch; and on either side, by a fold of mucous membrane, enclosing ligamentous and muscular fibers, which is stretched between the side of the epiglottis and the apex of the arytenoid car¬ tilage. This is the aryepiglottic fold, on the posterior part of the margin of which the cuneiform cartilage forms a more or less dis¬ tinct whitish prominence, the cuneiform tubercle. vestibular folds. The vestibular folds (plicae verrtriculares; superior or false vocal cords) are two thick folds of mucous mem¬ brane, each of which encloses a narrow band of fibrous tissue, the vestibular liga¬ ment, which is attached ventrally to the angle of the thyroid cartilage, immediately below the attachment of the epiglottis, and dorsally to the ventrolateral surface of the arytenoid cartilage, a short distance above the vocal process. The caudal border of this ligament, enclosed in mucous membrane, forms a free crescentic margin, which con¬ stitutes the upper boundary of the ventricle of the larynx. vocal folds. The vocal folds (plicae vocales; inferior or true vocal cords) enclose two strong bands named the vocal ligaments or vocal cords (inferior thyroarytenoid). Each ligament consists of a band of yellow elastic tissue attached ventrally to the angle of the thyroid cartilage and dorsally to the vocal process of the arytenoid. Its caudal border is continuous with the thin lateral part of the conus elasticus. Its cranial border forms the boundary of the ventricle of the larynx. Laterally, the vocalis muscle lies paral-

1 372

THE RESPIRATORY SYSTEM

A dissection to show the right half of the conus elasticus. The right lamina of the thyroid cartilage and the subjacent muscles have been removed. Fig. 15-16.

Epiglottic cartilage

Aryepiglottic fold

Thyrohyoid ligament

Trans, aryt. mus. Ventricle

Vocal fold

Cricothyroid ligament Cricoid arch

Cricoid lamina

Tracheal cartilage

Fig. 15-17.

Sagittal section of larynx, right half.

UPPER RESPIRATORY TRACT

1373

Sulcus terminalis Foramen cecum

Median glossoepiglottic fold

Vallecula Lateral glossoepiglottic fold

Greater cornu of hyoid bone

• Tubercle - Aryepiglottic fold - Ventricle Vocal fold Cuneiform cartilage

Corniculate cartilage

dtrOJioJ-T

Fig. 15-18.

The entrance to the larynx, posterior view.

lei with it. The ligament is covered medially by mucous membrane that is extremely thin and closely adheres to its surface. ventricle. The ventricle of the larynx (ventricuius laryngis [Morgagnii1]; laryn¬ geal sinus) is a fusiform fossa, bounded by the free crescentic edge of the ventricular fold, by the straight margin- of the vocal fold and by the mucous membrane covering the corresponding thyroarytenoid muscle. The anterior part of the ventricle leads by a nar¬ row opening into a cecal pouch of mucous membrane of variable size called the ap¬ pendix. appendix. The appendix of the laryngeal ventricle (appendix ventriculi laryngis; laryngeal saccule) is a membranous sac placed between the ventricular fold and the inner surface of the thyroid cartilage, occa¬ sionally extending as far as its cranial border or even higher. On the surface of its mucous membrane are the openings of 60 or 70 mu¬ cous glands, which are lodged in the submu¬ cous areolar tissue. This sac is enclosed in a fibrous capsule that is continuous caudally with the ventricular ligament. Its medial sur¬

face is covered by a few delicate muscular fasciculi that arise from the apex of the ary¬ tenoid cartilage and become lost in the aryepiglottic fold of mucous membrane; later¬ ally it is separated from the thyroid cartilage by the thyroepiglotticus. These muscles compress the sac and express the secretion it contains upon the vocal folds to lubricate their surfaces. rima glottidis. The rima glottidis (Fig. 15-19) is the elongated fissure or opening

Median glossoepiglottic fold Vallecula

Epiglottis Tubercle of epiglottis Vocal fold Ventricular fold

Aryepiglottic fold

Cuneiform cartilage

Corniculate cartilage Trachea

1 Giovanni Battista Morgagni (1682-1771): An

anatomist and pathologist (Padua).

Italian Fig. 15-19.

Laryngoscopic view of interior of larynx.

1374

THE RESPIRATORY SYSTEM

between the vocal folds ventrally and the bases and vocal processes of the arytenoid cartilages dorsally. It is therefore subdivided into a larger anterior intramembranous part (glottis vocalis), which measures about three-fifths of the length of the entire aper¬ ture, and a posterior intercartilaginous part (glottis respiratoria). Posteriorly it is limited by the mucous membrane passing between the arytenoid cartilages. The rima glottidis is the narrowest part of the cavity of the lar¬ ynx, and its level corresponds with the bases of the arytenoid cartilages. Its length, in the male, is about 23 mm; in the female, from 17 to 18 mm. The width and shape of the rima glottidis vary with the movements of the vocal cords and arytenoid cartilages during respiration and phonation. In the condition of rest, i.e., when these structures are unin¬ fluenced by muscular action, as in quiet res¬ piration, the intermembranous part is trian¬ gular, with its apex in front and its base behind (the latter is represented by a line, about 8 mm long, connecting the anterior ends of the vocal processes, while the medial surfaces of the arytenoids are parallel to each other, and hence the intercartilaginous part is rectangular). During extreme adduc¬ tion of the vocal folds, as in the emission of a high note, the intermembranous part is re¬ duced to a linear slit by the apposition of the vocal folds, while the intercartilaginous part is triangular, its apex corresponding to the anterior ends of the vocal processes of the arytenoids, which are approximated by the medial rotation of the cartilages. Conversely, in extreme abduction of the vocal folds, as in forced inspiration, the arytenoids and their vocal processes are rotated lateralward and the intercartilaginous part is triangular, but with its apex directed backward. In this condition the entire glottis is somewhat loz¬ enge-shaped, the widest part of the aperture corresponding with the attachments of the vocal folds to the vocal processes.

Lateral cricoarytenoid Arytenoid Thyroarytenoid cricothyroid. The triangular cricothy¬ roid muscle (Fig. 15-20) arises from the front and lateral part of the cricoid cartilage; its fibers are arranged in two groups. The cau¬ dal fibers constitute a pars obliqua and slant backward to the anterior border of the infe¬ rior cornu; the anterior fibers, forming a pars recta, run cranialward, backward, and lateralward to the posterior part of the lower border of the lamina of the thyroid cartilage. The medial borders of the muscles on the two sides are separated by a triangular inter¬ val, occupied by the middle cricothyroid lig¬ ament. posterior cricoarytenoid. The poste¬ rior cricoarytenoid (Fig. 15-20) arises from the broad depression on the corresponding half of the posterior surface of the lamina of the cricoid cartilage; its fibers run cranialward and lateralward, and converge to be inserted into the back of the muscular proc¬ ess of the arytenoid cartilage. The upper¬ most fibers are nearly horizontal, the middle are oblique, and the lowest are almost vertical. lateral cricoarytenoid. The lateral cricoarytenoid (Fig. 15-22) is oblong and

Muscles

The muscles of the larynx are extrinsic, passing between the larynx and parts around (described in Chapter 6), and intrin¬ sic, confined entirely to the larynx. The intrinsic muscles are: Cricothyroid Posterior cricoarytenoid

Fig. 15-20.

attachments.

Side view of the larynx, showing muscular

UPPER RESPIRATORY TRACT

smaller than the posterior cricoarytenoid muscle. It arises from the cranial border of the arch of the cricoid cartilage, and passing obliquely upward and backward, is inserted into the front of the muscular process of the arytenoid cartilage. arytenoid. The arytenoid (Fig. 15-21) is a single muscle that fills up the posterior con¬ cave surfaces of the arytenoid cartilages. It arises from the posterior surface and lateral border of one arytenoid cartilage, and is in¬ serted into the corresponding parts of the opposite cartilage. It consists of oblique and transverse parts. The oblique arytenoid, the more superficial, forms two fasciculi that pass from the base of one cartilage to the apex of the opposite one, and therefore cross each other like the limbs of the letter X. A few fibers are continued around the lateral margin of the cartilage, and are prolonged into the aryepiglottic fold; they are some¬ times described as a separate muscle, the aryepiglotticus. The transverse arytenoid crosses transversely between the two carti¬ lages. thyroarytenoid. The thyroarytenoid (Figs. 15-22; 15-23) is a broad, thin, muscle that lies parallel with and lateral to the vocal fold and supports the wall of the ventricle and its appendix. It arises from the caudal

1375

Corniculate cartilages

Articular facet for inferior cornu of thyroid cartilage

Muscles of larynx, side view. Right lamina of thyroid cartilage removed. Fig. 15-22.

half of the angle of the thyroid cartilage and from the middle cricothyroid ligament. Its fibers pass dorsalward and lateralward, to be inserted into the base and anterior sur¬ face of the arytenoid cartilage. The more medial fibers of the muscle can be differenti-

Tubercle of epiglottis Cuneiform cartilage Corniculate cartilage lAryte/noid

Posterior cricoaryte¬ noid

Fig. 15-23. Fig. 15-21.

Muscles of larynx, posterior view.

(Enlarged.)

Muscles of the larynx, seen from above.

1376

the respiratory system

ated as a band that is inserted into the vocal process of the arytenoid cartilage and into the adjacent portion of its anterior surface; it is termed the vocalis, and lies parallel with the vocal ligament, to which it adheres. Many fibers of the thyroarytenoid are pro¬ longed into the aryepiglottic fold, where some of them become lost, while others are continued to the margin of the epiglottis. They have received a distinctive name, thyroepiglotticus, and are sometimes de¬ scribed as a separate muscle. A few fibers extend along the wall of the ventricle from the lateral wall of the arytenoid cartilage to the side of the epiglottis and constitute the ventricularis muscle. actions. The actions of the muscles of the larynx may be conveniently divided into two groups: (1) those that open and close the glottis; (2) those that regulate the degree of tension of the vocal folds. The posterior cricoarytenoids separate the vocal folds and, consequently, open the glottis by rotating the arytenoid cartilages outward around a vertical axis passing through the cricoarytenoid joints, so that their vocal processes and the vocal folds at¬ tached to them become widely separated. The lateral cricoarytenoids close the glottis by ro¬ tating the arytenoid cartilages inward, so as to ap¬ proximate their vocal processes. The arytenoid approximates the arytenoid carti¬ lages, and thus closes the opening of the glottis, especially at its back part. The cricothyroids produce tension and elongation of the vocal folds by drawing up the arch of the cri¬ coid cartilage and tilting back the upper border of its lamina; the distance between the vocal processes and the angle of the thyroid is thus increased and the folds are elongated. The thyroarytenoids, consisting of two parts hav¬ ing different attachments and different directions, have a rather complicated action. Their main action is to draw the arytenoid cartilages forward toward the thyroid and thus shorten and relax the vocal folds. Their lateral portions rotate the arytenoid carti¬ lage inward and thus narrow the rima glottidis by bringing the two vocal folds together. Certain min¬ ute fibers of the vocalis division, inserting obliquely upon the vocal ligament and designated as the aryvocalis muscle, are considered by Strong (1935) to be chiefly responsible for the control of pitch, through their ability to regulate the length of the vibrating part of the vocal folds. The manner in which the entrance of the larynx is closed during deglutition is discussed in Chapter 1 6.

Structure The mucous mem¬ brane of the larynx is continuous with that lining the mouth, pharynx, trachea and MUCOUS membrane.

bronchi, and is prolonged into the lungs. It lines the posterior surface and the upper part of the anterior surface of the epiglottis, to which it is closely adherent, and helps to form the aryepiglottic folds, which bound the entrance of the larynx. It lines the whole of the cavity of the larynx; by its reduplica¬ tion, it forms the chief part of the vestibular fold, and from the ventricle, it is continued into the ventricular appendix. It is then re¬ flected over the vocal ligament, where it is thin and intimately adherent, covers the inner surface of the conus elasticus and cri¬ coid cartilage, and is ultimately continuous with the lining membrane of the trachea. The anterior surface and the upper half of the posterior surface of the epiglottis, the upper part of the aryepiglottic folds, and the vocal folds are covered by stratified squa¬ mous epithelium; all the rest of the laryngeal mucous membrane is covered by columnar ciliated cells, but patches of stratified squa¬ mous epithelium are found in the mucous membrane above the glottis. glands. The mucous membrane of the larynx is furnished with numerous mucussecreting glands, the orifices of which are found in nearly every part; they are plentiful upon the epiglottis, being lodged in little pits in its substance; they are also found in large numbers along the margin of the aryepiglot¬ tic fold in front of the arytenoid cartilages, where they are termed the arytenoid glands. They exist also in large numbers in the ven¬ tricular appendages. None are found on the free edges of the vocal folds. vessels. The chief arteries of the larynx are the laryngeal branches derived from the superior and inferior thyroid arteries. The veins accompany the arteries; those accompanying the superior laryngeal artery join the superior thyroid vein, which opens into the internal jugular vein, while those accompa¬ nying the inferior laryngeal artery join the inferior thyroid vein, which opens into the brachiocephalic vein. The lymphatic vessels consist of two sets, superior and inferior. The former accompany the superior laryngeal artery and pierce the thyrohyoid membrane, to end in the nodes situated near the bifurcation of the common carotid artery. Of the latter, some pass through the middle cricothyroid ligament and open into nodes lying in front of that ligament or in front of the upper part of the trachea, while others pass to the deep cervical nodes and to the nodes accompanying the inferior thyroid artery. nerves. The nerves are derived from the vagus nerve by way of the internal and external branches of the superior laryngeal nerve and from the recur¬ rent nerve. The internal laryngeal branch is sensory.

UPPER RESPIRATORY TRACT

It enters the larynx by piercing the posterior part of the thyrohyoid membrane above the superior laryn¬ geal vessels, and divides into three branches: one is distributed to both surfaces of the epiglottis; a sec¬ ond, to the aryepiglottic fold; and a third, the larg¬ est, supplies the mucous membrane over the back of the larynx and communicates with the recurrent nerve. The external laryngeal branch supplies the cricothyroid muscle. The recurrent nerve passes cranialward beneath the caudal border of the con¬ strictor pharyngis inferior immediately dorsal to the cricothyroid joint. It supplies all the muscles of the larynx except the cricothyroid. The sensory branches of the laryngeal nerves form subepithelial plexuses, from which fibers end between the cells covering the mucous membrane. Over the posterior surface of the epiglottis, in the aryepiglottic folds, and less regularly in some other

Fig. 15-24.

1377

parts, taste buds similar to those in the tongue are found. Fibers from the sympathetic nerves supply the blood vessels and glands.

TRACHEA AND BRONCHI

Trachea The trachea or windpipe (Fig 15-24) is a car¬ tilaginous and membranous tube, that ex¬ tends from the larynx, on a level with the sixth cervical vertebra, to the cranial border of the fifth thoracic vertebra, where it di¬ vides into the two bronchi. The trachea is nearly but not quite cylindrical, being flat-

Front view of cartilages of larynx, trachea, and bronchi.

1378

THE RESPIRATORY SYSTEM

tened dorsally; its length measures about 11 cm; its diameter, from side to side, is from 2 to 2.5 cm, being always greater in the male than in the female. In the child the trachea is smaller, more deeply placed, and more mov¬ able than in the adult. relations. The ventral surface of the trachea is covered, in the neck, by the isthmus of the thyroid gland, the inferior thyroid veins, the thyroid ima ar¬ tery (when that vessel exists), the sternothyroid and sternohyoid muscles, the cervical fascia, and, more superficially, by the anastomosing branches be¬ tween the anterior jugular veins. In the thorax, it is covered by the manubrium sterni, the remains of the thymus, the left brachiocephalic vein, the aortic arch, the brachiocephalic and left common carotid arteries, and the deep cardiac plexus. Dorsally it is in contact with the esophagus. Laterally, in the neck, it is in relation with the common carotid arteries, the right and left lobes of the thyroid gland, the inferior thyroid arteries, and the recurrent nerves; in the thorax, it lies in the superior mediastinum, and is in relation on the right side with the pleura and right vagus, and near the root of the neck with the brachi¬ ocephalic artery; on its left side are the left recurrent nerve, the aortic arch, and the left common carotid and subclavian arteries. clinical considerations. The operation for tracheotomy, when performed as an emergency, is best carried out by piercing the neck 1 cm below the cricoid cartilage and opening the trachea between the second and third cartilaginous rings. The thyroid and cricoid cartilages are avoided because of subse¬ quent scarring of the larynx. The isthmus of the thy¬ roid gland is usually caudal to the first two tracheal cartilages and no blood vessels of appreciable size are present. Caudal to the thyroid gland, the trachea is situated much deeper than above it because of Burns's space,1 and large veins are likely to be present.

Right Bronchus The right bronchus is wider, shorter, and less abrupt in its divergence from the tra¬ chea than the left. It is about 2.5 cm long and enters the right lung nearly opposite the fifth thoracic vertebra. The azygos vein arches over it and the pulmonary artery lies at first inferior and then ventral to it. It gives rise to three subsidiary bronchi, one to each of the lobes. The superior lobe bronchus comes off above the pulmonary artery and has been called, therefore, the eparterial bronchus. The bronchi to the middle and inferior lobes ‘Allen Burns (1781-1813): A Scottish anatomist (Glas¬ gow).

separate below the pulmonary artery and are accordingly hyparterial in position. The right superior lobe bronchus divides into three branches named, according to the bronchopulmonary segments that they enter, the bronchus for the apical segment, for the posterior segment, and for the ante¬ rior segment. The right middle lobe bron¬ chus divides into two branches, the bron¬ chus for the lateral and for the medial segments. The right inferior lobe bronchus first gives off the bronchus to the superior segment, and then divides into four bronchi for the basal segments: the medial basal, an¬ terior basal, lateral basal, and posterior basal segments. Left Bronchus The left bronchus is smaller in caliber but about twice as long as the right (5 cm). It passes under the aortic arch and crosses ven¬ tral to the esophagus, thoracic duct, and de¬ scending aorta. It is superior to the pulmo¬ nary artery at first, then dorsal, and finally passes inferior to the artery before it divides into the bronchi for the superior and inferior lobes. Both lobar bronchi, therefore, are hyparterial in position. The left superior lobe bronchus divides into two branches, one of which is distrib¬ uted to a portion of the left lung correspond¬ ing to the right superior lobe; the other, to a portion corresponding to the right middle lobe. These two branches are called the su¬ perior division and inferior division bronchi to differentiate them from segmental bron¬ chi. The superior division bronchus of the left superior lobe divides into branches for the apical posterior segment and the anterior segment. The inferior division bronchus di¬ vides into bronchi for the superior and infe¬ rior segments. The left inferior lobe bron¬ chus gives off first the bronchus for the superior segment and then divides into three branches for basal segments: the anterior medial basal, lateral basal, and posterior basal segments. The picture seen through a bronchoscope may be reproduced if a section is made across the trachea and a bird’s-eye view taken of its interior (Fig. 15-25). At the bot¬ tom of the trachea, the septum that separates the two bronchi is visible as a spur (in bronchoscopic terminology) and is named the carina. The carina is placed to the left of the

UPPER RESPIRATORY TRACT Right

Fig. 15-25. Bifurcation of the trachea, viewed from above, with the interior showing the carina as it would be seen through a bronchoscope.

middle line and the right bronchus appears as a more direct continuation of the trachea than the left. Because of this asymmetry and because the right bronchus is larger in diam¬ eter than the left, foreign bodies that enter the trachea have a tendency to drop into the right bronchus rather than into the left. Structure

The trachea and extrapulmonary bronchi are composed of imperfect rings of hyaline cartilage, fibrous tissue, muscular fibers, mucous membrane, and glands (Fig. 15-26). cartilages. The cartilages of the trachea number from 16 to 20; each forms an imper¬ fect ring, which occupies the anterior twothirds or so of the circumference of the tra¬

chea, being deficient behind, where the tube is completed by fibrous tissue and non-striated muscular fibers. The cartilages are placed horizontally above each other, sepa¬ rated by narrow intervals. They measure about 4 mm deep and 1 mm thick. Their outer surfaces are flattened in a vertical di¬ rection, but internally, they are convex, the cartilages being thicker in the middle than at the margins. Two or more of the cartilages often unite, partially or completely, and they are sometimes bifurcated at their extremi¬ ties. They are highly elastic, but may become calcified in advanced life. In the right bron¬ chus the cartilages vary in number from six to eight; in the left, from nine to twelve. They are shorter and narrower than those of the trachea, but have the same shape and arrangement. The special tracheal cartilages are the first and the last (Fig. 15-24). The first cartilage is broader than the rest and often divided at one end; it is connected by the cricotracheal ligament with the cau¬ dal border of the cricoid cartilage, with which or with the succeeding cartilage it is sometimes blended. The last cartilage is thick and broad in the middle, because its lower border is pro¬ longed into a triangular hook-shaped proc¬ ess that curves downward and backward between the origins of the two bronchi. It

Tunica fibrosa Tracheal gland

Cartilage ring

Epithelium Lamina propria

Sub¬ mucosa

Trachealis muscle

Blood vessel

Fig. 15-26.

1379

Cross section of trachea, adult cadaver. 5 X-

1380

the respiratory system

ends on each side in an imperfect ring, which encloses the commencement of each bronchus. The cartilage above the last is somewhat broader than the others at its center. fibrous membrane. The cartilages are enclosed in an elastic fibrous membrane that consists of two layers; one, the thicker, passes over the outer surface of the ring, and the other passes over the inner surface. At the cranial and caudal margins of the carti¬ lages the two layers blend together to form a single membrane that connects the rings with one another. In the space between the ends of the rings dorsally, the membrane forms a single layer also. muscular tissue. The muscular tissue consists of two layers of nonstriated muscle, longitudinal and transverse, between the ends of the cartilages. The longitudinal fi¬ bers are external and consist of a few scat¬ tered bundles. The transverse fibers (trachealis muscle) are arranged internally in branching and anastomosing bands that ex¬ tend more or less transversely (Fig. 15-26). mucous membrane. The mucous mem¬ brane is continuous above with that of the larynx and below with that of the bronchi. It consists of areolar and lymphoid tissue and has a well-marked basement membrane that supports a stratified epithelium, the surface layer of which is columnar and ciliated, while the deeper layers are composed of oval or rounded cells. Beneath the basement membrane is a distinct layer of longitudinal elastic fibers with a small amount of inter¬ vening areolar tissue. The submucous layer is composed of a loose meshwork of connec¬ tive tissue that contains large blood vessels, nerves, and mucous glands; the ducts of the latter pierce the overlying layers and open on the surface (Fig. 15-27). vessels and nerves. The trachea is supplied with blood by the inferior thyroid arteries. The veins end in the thyroid venous plexus. The nerves are derived from the vagus and the recurrent nerves and from the sympathetic trunk; they are distributed to the trachealis muscles and between the epithelial cells.

PLEURA

Each lung is invested by an exceedingly delicate serous membrane, the pleura, which is arranged in the form of a closed invagi-

Fig. 15-27. Section through wall of human trachea, c, Cartilage; e.p., pseudostratified ciliated epithelium; g.c., goblet cell; m.g., mucous gland. 8 x. (Sobotta.)

nated sac. A portion of the serous membrane covers the surface of the lung and dips into the fissures between its lobes; it is called the pulmonary pleura. The rest of the membrane lines the inner surface of the chest wall, cov¬ ers the diaphragm, and is reflected over the structures occupying the middle of the tho¬ rax; this portion is termed the parietal pleura. The two layers are continuous with each other around and below the root of the lung; in health they are in actual contact with each other, but the potential space be¬ tween them is known as the pleural cavity. When the lung collapses or when air or fluid collects between the two layers, the cavity becomes apparent. The right and left pleural sacs are entirely separate from each other; between them are all the thoracic viscera except the lungs, and they touch each other only for a short distance ventrally, behind the upper part of the body of the sternum; the interval in the middle of the thorax be¬ tween the two sacs is termed the mediasti¬ num. Different portions of the parietal pleura have received special names that indicate their position: thus, that portion which lines the inner surfaces of the ribs and intercostal muscles is the costal pleura; that clothing the convex surface of the diaphragm is the dia-

UPPER RESPIRATORY TRACT

phragmatic pleura; that which rises into the neck, over the summit of the lung, is the cu¬ pula of the pleura (cervical pleura); and that which is applied to the other thoracic vis¬ cera is the mediastinal pleura. Parietal Pleura

Commencing at the sternum, the pleura passes lateralward, lining the costal carti¬ lages, ribs, and intercostal muscles (Figs. 1528; 15-29). At the dorsal part of the thorax, it passes over the sympathetic trunk and its branches and is reflected upon the sides of the bodies of the vertebrae, where it is sepa¬ rated by a narrow interval, the posterior mediastinum, from the opposite pleura. From the vertebral column the pleura passes to the side of the pericardium, which it cov¬ ers to a slight extent before it covers the dor¬ sal part of the root of the lung, from the cau¬ dal border of which a triangular sheet descends vertically toward the diaphragm. This sheet is the posterior layer of a fold known as the pulmonary ligament.

Fig. 15-28.

1381

From the dorsal portion of the lung root, the pleura may be traced over the costal sur¬ face of the lung, over its apex and base, and also over the sides of the fissures between the lobes, onto its mediastinal surface and the ventral part of its root. It is continued from the caudal margin of the root as the anterior layer of the pulmonary ligament, and from this it is reflected onto the pericar¬ dium (pericardial pleura), and then to the dorsal surface of the sternum. Cranial to the level of the root of the lung, however, the mediastinal pleura passes uninterruptedly from the vertebral column to the sternum over the structures in the superior mediasti¬ num. It covers the cranial surface of the dia¬ phragm and extends, ventrally, as low as the costal cartilage of the seventh rib; at the side of the chest, it extends to the caudal border of the tenth rib on the left side and to the cranial border of the same rib on the right side. Dorsally, it reaches as low as the twelfth rib, and sometimes even to the trans¬ verse process of the first lumbar vertebra. The cupula projects through the superior

Front view of thorax, showing the relations of the pleurae and lungs to the chest wall. Phrenicocostal and costomediastinal sinus in blue; lungs in purple.

1382

THE RESPIRATORY SYSTEM

Fig. 15-29. Lateral view of thorax, showing the rela¬ tions of the pleurae and lungs to the chest wall. Phreni¬ cocostal and costomediastinal sinus in blue; lungs in purple.

opening of the thorax into the neck, extend¬ ing from 2.5 to 5 cm above the sternal end of the first rib; this portion of the sac is strengthened by a dome-like expansion of fascia (Sibson’s1 fascia), which is attached ventrally to the inner border of the first rib and dorsally to the anterior border of the transverse process of the seventh cervical vertebra. This is covered and strengthened by a few spreading muscular fibers derived from the scalene muscles called the scalenus minimus. In the ventral part of the chest, the two pleural sacs behind the manubrium are sep¬ arated by an angular interval; the reflection is represented by a line drawn from the ster¬ noclavicular articulation to the midpoint of the junction of the manubrium with the body of the sternum. From this point the two pleurae descend in close contact to the level of the fourth costal cartilages. The line of reflection on the right side is continued cau1 Francis Sibson (1814-1876): An English physician (Lon¬ don).

dalward in nearly a straight line to the xiph¬ oid process, and then turns lateralward, while on the left side the line of reflection diverges lateralward and is continued caudalward, close to the left border of the ster¬ num, as far as the sixth costal cartilage. The caudal limit of the pleura is on a considera¬ bly lower level than the corresponding limit of the lung, but does not extend to the at¬ tachment of the diaphragm, so that caudal to the line of reflection from the chest wall on to the diaphragm, the pleura is in direct con¬ tact with the rib cartilages and the inter¬ costales interni. Moreover, in ordinary inspi¬ ration the thin inferior margin of the lung does not extend as far as the line of the pleu¬ ral reflection, so that the costal and dia¬ phragmatic pleurae are in contact here, the intervening narrow slit being termed the costodiaphragmatic recess (phrenicocostal sinus). A similar condition exists behind the sternum and rib cartilages, where the ante¬ rior thin margin of the lung falls short of the line of pleural reflection, and where the slit¬ like cavity between the two layers of pleura forms the costomediastinal recess (costo¬ mediastinal sinus). The line along which the right pleura is reflected from the chest wall to the dia¬ phragm starts ventrally, immediately below the seventh sternocostal joint, and runs caudalward and dorsalward behind the seventh costal cartilage, thus crossing the tenth rib in the midaxillary line, from which it is pro¬ longed to the level of the spinous process of the twelfth thoracic vertebra. The reflection of the left pleura follows at first the ascend¬ ing part of the sixth costal cartilage, and in the rest of its course is slightly lower than that of the right side. The free surface of the pleura is smooth, glistening, and moistened by a serous fluid; its attached surface adheres intimately to the lung and to the pulmonary vessels as they emerge from the pericardium; it also adheres to the cranial surface of the diaphragm. Throughout the rest of its extent it is easily separable from the adjacent parts. The right pleural sac is shorter, wider, and reaches higher in the neck than the left. Pulmonary Ligament

The root of the lung is covered by pleura, except at its caudal border where the invest¬ ing layers come into contact. Here they form

UPPER RESPIRATORY TRACT

a sort of mesenteric fold, the pulmonary lig¬ ament, which extends between the mediasti¬ nal surface of the lung and the pericardium. Just above the diaphragm the ligament ends in a free falciform border. It retains the lower part of the lung in position.

Structure

Like other serous membranes, the pleura is composed of a single layer of flattened mesothelial cells resting upon a delicate con¬ nective tissue membrane, beneath which lies a stroma of collagenous tissue containing several prominent networks of yellow elas¬ tic fibers. Blood vessels, lymphatics, and nerves are distributed in the substance of the pleura. VESSELS AND nerves. The arteries of the pleura are derived from the intercostal, internal thoracic, musculophrenic, thymic, pericardiac, pulmonary, and bronchial vessels. The veins correspond to the arteries. The lymphatics are described in Chap¬ ter 10. The nerves of the parietal pleura are derived from the phrenic, intercostal, vagus, and sympathetic nerves; those of the pulmonary pleura, from the vagus and sympathetic nerves through the pulmo¬

Left brachiocephalic vein

1 383

nary plexuses at the hilum of the lung. It is believed that nerves accompany the ramifications of the bron¬ chial arteries in the pulmonary pleura. MEDIASTINUM

The mediastinum is interposed as a parti¬ tion in the median portion of the thorax, sep¬ arating the parietal pleural sacs of the two lungs (Fig. 15-31). It extends from the ster¬ num ventrally to the vertebral column dorsally and comprises all the thoracic viscera, except the lungs and pleurae, embedded in a thickening and expansion of the subserous fascia of the thorax. It is divided arbitrarily, for the purposes of description, into cranial and caudal parts by a plane that extends from the sternal angle to the caudal border of the fourth thoracic vertebra. The cranial part is named the superior mediastinum; the caudal part is again subdivided into three parts: the anterior mediastinum, ventral to the pericardium: the middle mediastinum, containing the pericardium: and the poste¬ rior mediastinum, dorsal to the pericardium. The superior mediastinum (Fig. 15-30) is bounded by the superior aperture of the tho¬ rax; by the plane of the superior limit of the pericardium: by the manubrium: by the

Lt. carotid Thymus art.

Vagus nerve

/

t

Vagus nerve

Int. thoracic ^'artery

Rt. brachio-cephalic v. rst rib -Trachea Vertebral art. Lt. subcla- vian art Esoph¬ agus Second rib

Third rib

Fig. 1 5-30. Transverse section through the upper margin of the second thoracic vertebra, showing the superior mediastinum. (Braune.)

1 384

THE RESPIRATORY SYSTEM

Transversus thoracis

Thoracic duct

Vagus nerves

Fig. 15-31. A transverse section of the thorax showing the contents of the middle and the posterior mediastinum. The pleural and pericardial cavities are exaggerated since normally there is no space between parietal and visceral pleurae and between pericardium and heart.

upper four thoracic vertebrae; and laterally, by the mediastinal pleurae of the two lungs. It contains the origins of the sternohyoid and sternothyroid muscles and the lower ends of the longus colli muscles; the aortic arch; the brachiocephalic artery and the thoracic por¬ tions of the left common carotid and the left subclavian arteries; the brachiocephalic veins and the upper half of the superior vena cava; the left highest intercostal vein; the vagus, cardiac, phrenic, and left recurrent nerves; the trachea, esophagus, and thoracic duct; and the remains of the thymus, and some lymph nodes. The anterior mediastinum (Fig. 15-31) is bounded ventrally by the body of the ster¬ num and because of the position of the heart, the left transversus thoracis muscle and parts of the fourth, fifth, sixth, and seventh costal cartilages. It is bounded dorsally by the parietal pericardium and extends caudalward as far as the diaphragm. Besides a few lymph nodes and vessels, it contains only a thin layer of subserous fascia which is separated from the endothoracic or deep fas¬ cia superiorly by a fascial cleft, but there is a firm attachment in its caudal part that forms the pericardiosternal ligament.

The middle mediastinum (Fig. 15-31) is the broadest part of the interpleural septum. It contains the heart enclosed in the pericar¬ dium, the ascending aorta, the lower half of the superior vena cava with the azygos vein opening into it, the pulmonary trunk dividing into its two branches, the right and left pulmonary veins, and the phrenic nerves. The posterior mediastinum (Fig. 15-31) is an irregularly shaped mass running parallel with the vertebral column and, because of the slope of the diaphragm, it extends caudally beyond the pericardium. It is bounded ventrally, by the pericardium and, more caudally, by the diaphragm; dorsally, by the ver¬ tebral column from the lower border of the fourth to the twelfth thoracic vertebra; and on either side, by the mediastinal pleurae. It contains the thoracic part of the descending aorta, the azygos and hemiazygos veins, the vagus and splanchnic nerves, the bifurcation of the trachea and the two bronchi, the esophagus, the thoracic duct, and many large lymph nodes. Some authorities include the bifurcation of the trachea, the two bronchi, and the roots of the two lungs in the middle mediastinum.

LUNGS (PULMONES)

Lungs (Pulmones) The lungs are the essential organs of respi¬ ration; they are placed on either side within the thorax and are separated from each other by the heart and other contents of the mediastinum (Fig. 12-76). The substance of the lung has a light, porous, spongy texture; it floats in water and crepitates when han¬ dled owing to the presence of air in the alve¬ oli. It is also highly elastic, hence the re¬ tracted state of these organs when they are removed from the closed cavity of the tho¬ rax. The surface is smooth, shiny, and marked out into numerous polyhedral areas that indicate the lobules of the organ: each of these areas is crossed by numerous lighter lines. At birth the lungs are pinkish-white in color; in adult life the color is a slaty gray, mottled in patches, and as age advances, this mottling assumes a black color. The coloring matter consists of granules of carbon depos¬ ited in the areolar tissue near the surface of the organ. It increases in quantity as age ad¬ vances, and is more abundant in males than in females. As a rule, the posterior border of the lung is darker than the anterior. The right lung usually weighs about 625 gm, the left weighs 567 gm, but much varia¬ tion is met according to the amount of blood or serous fluid they may contain. The lungs are heavier in males than in females, their proportion to the body being 1 to 37 in the former and 1 to 43 in the latter. The vital capacity, the quantity of air that can be ex¬ haled by the deepest expiration after making the deepest inspiration, varies greatly with the individual; an average for an adult man is 3700 ml. The total volume of the fully ex¬ panded lungs is about 6500 ml; this includes both tissues and contained air. The tidal air, the amount of air breathed in or out during quiet respiration, is about 500 ml for the adult man. Various calculations indicate that the total epithelial area of the respiratory and nonrespiratory surfaces during ordinary deep inspiration of the adult is not greater than 70 square meters. Each lung is conical and presents for ex¬ amination an apex, a base, three borders, and two surfaces. The apex is rounded and extends into the root of the neck, reaching 2.5 to 5 cm above the level of the sternal end of the first rib. A sulcus is produced by the subclavian artery as it curves ventral to the pleura and runs

1 385

cranialward and lateralward immediately below the apex. The base is broad, concave, and rests upon the convex surface of the diaphragm, which separates the right lung from the right lobe of the liver, and the left lung from the left lobe of the liver, the stomach, and the spleen. Since the diaphragm extends higher on the right than on the left side, the concav¬ ity on the base of the right lung is deeper than that on the left. Laterally and dorsally, the base is bounded by a thin, sharp margin that projects for some distance into the phrenicocostal sinus of the pleura, between the lower ribs and the costal attachment of the diaphragm. The base of the lung de¬ scends during inspiration and ascends dur¬ ing expiration.

SURFACES

The costal surface (external or thoracic surface) is smooth, convex, of considerable extent, and corresponds to the form of the cavity of the chest, being deeper dorsally than ventrally. It is in contact with the costal pleura and presents, in specimens that have been hardened in situ, slight grooves corre¬ sponding with the overlying ribs. The mediastinal surface (inner surface) is divided into a mediastinal and a vertebral portion. The mediastinal portion is in con¬ tact with the mediastinal pleura. It has a deep concavity, the cardiac impression, which accommodates the pericardium. Dor¬ sal and cranial to this concavity is a slight depression named the hilum, through which the structures that form the root of the lung enter and leave. On the right lung (Fig. 15-33), immediately cranial to the hilum, is an arched furrow that accommodates the azygos vein. Running cranialward and then arching lateralward some little distance below the apex is a wide groove for the superior vena cava and right brachiocephalic vein. Dorsal to the hilum and the attachment of the pulmonary ligament is a vertical groove for the esophagus; this groove becomes less distinct caudally, owing to the inclination of the lower part of the esophagus to the left of the midline. Ventral and to the right of the lower part of the esophageal groove is a deep concavity for the extrapericardiac portion of the thoracic part of the inferior vena cava. On the left lung (Fig. 15-34), immediately

1386

THE RESPIRATORY SYSTEM

Fig. 15-32.

Front view of heart and lungs.

cranial to the hilum, is a well-marked curved furrow produced by the aortic arch, and running cranialward from this toward the apex is a groove that accommodates the left subclavian artery; a slight impression ven¬ tral to the latter and close to the margin of the lung lodges the left innominate vein. Dorsal to the hilum and pulmonary ligament is a vertical furrow produced by the de¬ scending aorta, and ventral to this, near the base of the lung, the lower part of the esoph¬ agus causes a shallow impression.

The anterior border is thin and sharp and overlaps the ventral surface of the heart and pericardium. The anterior border of the right lung is almost vertical and projects into the costomediastinal sinus; that of the left lung has an angular notch, the cardiac notch, in which the pericardium comes into contact with the sternum. Opposite this notch, the anterior margin of the left lung is situated a little distance lateral to the line of reflection of the corresponding part of the pleura.

FISSURES AND LOBES BORDERS

The right lung is divided into three lobes (superior, middle, and inferior) by two interlobar fissures. The oblique fissure separates the inferior from the middle and superior lobes and cor¬ responds with the oblique fissure in the left lung. Its direction is more vertical, however, right lung.

The inferior border is thin and sharp where it separates the base from the costal surface and extends into the phrenicocostal sinus; medially, where it divides the base from the mediastinal surface, it is blunt and rounded.

LUNGS (PULMONES)

1387

Groove for subclavian artery

Groove for sup. vena cava Groove for azygos vein Eparterial bronchus

Pulmonary artery

Hyparterial bronchus Pulmonary veins Groove for esophagus

Concavity for inf. vena cava Pulmonary ligament

Fig. 15-33.

Mediastinal surface of right lung.

and it cuts the lower border about 7.5 cm dorsal to its extremity. The horizontal fissure separates the supe¬ rior from the middle lobe. It begins in the previous fissure near the dorsal border of the lung, and running horizontally, cuts the ven¬ tral border on a level with the sternal end of the fourth costal cartilage; on the mediasti¬ nal surface it may be traced dorsal to the hilum. The middle lobe, the smallest lobe of the right lung, is wedge-shaped and includes the lower part of the ventral border and the ventral part of the base of the lung. The right lung is shorter by 2.5 cm than the left because the diaphragm rises higher on the right side, and it is broader because of the inclination of the heart to the left side. Its total capacity is greater, however, and it weighs more than the left lung. left lung. The left lung is divided into two lobes, a superior and an inferior, by an oblique fissure that extends from the costal to the mediastinal surface of the lung both above and below the hilum. As seen on the surface, this fissure begins on the mediasti¬

nal surface of the lung at the hilum, and runs dorsalward and cranialward to the posterior border, which it crosses at a point about 6 cm below the apex. It then extends caudalward and ventralward over the costal surface, to reach the lower border near its extremity, and its further course can be fol¬ lowed across the mediastinal surface as far as the hilum. The superior lobe includes the apex, the anterior border, a considerable part of the costal surface, and the greater part of the mediastinal surface of the lung. The inferior lobe is larger than the superior and comprises almost the whole of the base, a large portion of the costal surface, and the greater part of the vertebral part of the me¬ dial surface.

ROOT

The root of the lung (radix pulmonis) (Figs. 15-33; 15-34) is formed by the bron¬ chus, pulmonary artery, pulmonary veins, bronchial arteries and veins, pulmonary

1 388

the respiratory system

Groove for left subclavian artery Groove for left innominate vein

Pulmonary artery Pulmonary veins

Bronchus

Posterior border

Cardiac notch

Pulmonary ligament

Lingula

Fig. 15-34.

Mediastinal surface of left lung.

plexuses of nerves, lymphatic vessels, and bronchial lymph nodes. These structures are all embedded in mediastinal connective tis¬ sue and the entire mass is encircled by a re¬ flection of the pleura. It corresponds to the hilum, which is near the center of the medi¬ astinal surface of the lung, dorsal to the car¬ diac impression and closer to the posterior than the anterior border. The root of the right lung lies dorsal to the superior vena cava and the right atrium, and the azygos vein arches over it (Fig. 12-76). The root of the left lung is ventral to the descending aorta and inferior to the aortic arch (Fig. 1277). The phrenic nerve, the pericardiophrenic artery and vein, and the anterior pulmonary plexus of nerves are ventral, while the vagus nerve and its posterior pulmonary plexus are dorsal to the root of the lung on both sides. Caudal to the root of each lung, the reflection of the pleura from mediastinum to lung is prolonged downward toward the dia¬ phragm as the pulmonary ligament (p. 1382). The chief structures of the roots of both lungs have a similar relation to each other in a dorsoventral direction, but there is a dif¬ ference in their superior and inferior rela¬ tions on the two sides. Thus the pulmonary

veins are ventral, the bronchi dorsal, and the pulmonary arteries between, on both sides. On the right side, the superior lobe bronchus is superior and the pulmonary artery is slightly lower; next are the bronchi to the middle and inferior lobes, and most inferior is the pulmonary vein (Fig. 15-33). On the left side, the pulmonary artery is superior, the pulmonary veins inferior, and the bron¬ chus between (Fig. 15-34).

FURTHER SUBDIVISION OF THE LUNG

The importance of certain smaller units of structure of the lungs, called bronchopul¬ monary segments, has been emphasized by the thoracic surgeon, bronchoscopist, and radiologist. To interpret these units cor¬ rectly, one should give particular attention to the concept that the lung is fundamentally the aggregate of all the branchings of the bronchus. According to this concept, a bron¬ chopulmonary segment is that portion of the lung to which any particular bronchus is dis¬ tributed, and the term might conceivably be applied to the lobule supplied by its lobular bronchus. In actual practice, however, it is

LUNGS (PULMONES)

customary to restrict the term bronchopul¬ monary segment to the portion of the lung supplied by the direct branches of the lobar bronchi (and of the division bronchi in the case of the left superior lobe). These seg¬ ments are as definite as the lobes, and their relative extent and position can be demon¬ strated by introducing different colored gel¬ atin into their bronchi. It is possible, in many cases, to follow the delicate connective tis¬ sue between the segments and dissect them apart. That the majority of extra fissures fol¬ low the planes of separation between the segments also demonstrates their fundamen¬ tal nature. BRONCHOPULMONARY SEGMENTS (Fig. 1535). The bronchopulmonary segments are named according to their positions in the lobes, and the bronchus to each is named after its segment. The right superior lobe has three segments: apical, posterior, and ante¬ rior. The right middle lobe has a lateral and a medial segment. The right inferior lobe has a superior and four basal segments: the me¬ dial basal, anterior basal, lateral basal, and posterior basal. The left superior lobe is first separated into two divisions, the superior division corresponding to the right superior lobe, and an inferior division corresponding to the right middle lobe. The superior divi¬ sion of the left superior lobe has an apical posterior and an anterior segment. The infe¬ rior division of the left superior lobe has a superior and an inferior segment. The left inferior lobe has a superior and three basal segments: anteromedial basal, lateral basal, and posterior basal. variations. The branching of the lobar bronchi to form segmental bronchi is reasonably constant. The superior lobe bronchus is somewhat more con¬ stant than the inferior lobe bronchus. In approxi¬ mately 95% of the specimens, it is possible to iden¬ tify three segmental bronchi coming from the right superior lobe bronchus, although in some of these cases, two segmental bronchi may seem to arise from a short common stem. The size of the lung segment supplied by a particular bronchus may be larger or smaller than expected, even when the branching appears at first glance to follow the usual pattern, because it may have exchanged a smaller branch bronchus with an adjacent segmental bron¬ chus. In the case of the lower lobe bronchus, the superior and the medial basal segmental bronchi are about as constant as the branches in the superior lobe, but there is more variation in the anterior basal, lateral basal, and posterior basal segments. In somewhat less than 50% of the specimens, branches come from the posterior aspect of the infe¬

1389

rior lobe bronchus between the superior segmental and the basal segmental bronchi, or from the stem below the anterior basal segmental bronchus.

The branchings of the bronchi are desig¬ nated according to the parts of the lungs that they ventilate. The two main bronchi corre¬ spond to the right and left lungs. The right bronchus is subdivided into three lobar bronchi for the superior, middle, and in¬ ferior lobes; the left bronchus is subdivided into two, for the superior and inferior lobes. Each lobar bronchus is subdivided into branchings for the bronchopulmonary seg¬ ments depicted in Figure 15-36. For the purpose of relating the smaller branchings of the bronchi to the ramifica¬ tions of the pulmonary arteries and veins, they have been named and numbered by Boyden (1955) (see Fig. 15-36). In the lists of segmental bronchi, arteries, and veins, corre¬ sponding structures of the right and left lungs are placed opposite each other.

BLOOD VESSELS OF THE LUNGS

The vessels that serve the special function of the lungs, that is, of aerating the blood, are the pulmonary arteries and veins and their connecting capillaries (Figs. 15-36 to 15-41). The blood supply for the purpose of nutri¬ tion to the tissues of the lungs is provided by the bronchial arteries and veins; these are discussed on page 1398. pulmonary vessels. The right and left pulmonary arteries, formed by the bifurca¬ tion of the pulmonary trunk, convey the deoxygenated blood to the right and left lungs. They divide into branches that accompany the bronchi, coursing chiefly along their dor¬ sal surface. The bronchopulmonary seg¬ ments are supplied by main intrasegmental branches of the pulmonary arteries, which are single for the most part, but which may arise as common trunks for adjacent seg¬ ments (Boyden, 1955). The artery for one seg¬ ment is likely to supply small branches to the neighboring segments. Distal to the alve¬ olar duct, branches are distributed to each atrium, from which arise smaller radicles terminating in a dense capillary network in the walls of the alveoli. The pulmonary veins are described in Chapter 9. The segmental veins are listed here according to the same classification used for the segmental arteries.

1390

THE RESPIRATORY SYSTEM

Left Lung

Right Lung Lobes Superior

Middle

( j

Apical Posterior Anterior

( Lateral Medial

V

Superior Medial basal Anterior basal Lateral basal Posterior basal

Segments

Lobes Superior division

{Apical-posterior Anterior

Superior Inferior (lingular) division

(Superior Inferior

(Superior Anteromedial basal Lateral basal Posterior basal

inferior lobe

Inferior

Segments

Medial and Basal View

Medial and Basal View

The bronchopulmonary segments. The segmental branches of the bronchi are shown in corresponding colors. (After J. F. Huber, 1947.)

Fig. 15-35.

LUNGS (PULMONES)

1391

SEGMENTAL BRONCHI

Right Superior Lobe

B’-Apical bronchus B^-apical ramus B’b-anterior ramus B2-Anterior bronchus B2a-posterior ramus B2a1-superior subramus B2a2-inferior subramus B2b-anterior ramus B3-Posterior bronchus B3a-apical ramus B3b-posterior ramus

Left Superior Lobe Superior Divison

B1+3_Apical posterior bronchus B’a, B3a-apical rami B'b, B3b-anterior and posterior rami B2-Anterior bronchus B2a-posterior ramus

B2b-anterior ramus

Right Middle Lobe

Left Superior Lobe Inferior (Lingular) Division

B4-Lateral bronchus B4a-posterior ramus B4b-anterior ramus B5-Medial bronchus B5a-superior ramus B5b-inferior ramus

B4-Superior lingular bronchus B4a-posterior ramus B4b-anterior ramus B5-lnferior lingular bronchus B5a-superior ramus B5b-inferior ramus

Right Inferior Lobe

Left Inferior Lobe

B6-Superior bronchus B6a-medial ramus B6a1-paravertebral subramus B6a2-posterior subramus B6b-superior ramus B6c-lateral ramus B*-Subsuperior bronchus BX* (10)-accessory subsuperior bronchus B7-Medial basal bronchus B7a-anterior ramus B7b-medial ramus B3-Anterior basal bronchus B8a-lateral ramus B8b-basal ramus B9-Lateral basal bronchus B9a-lateral ramus B9b-basal ramus B10-Posterior basal bronchus BV* (10)-accessory subsuperior ramus B10a-laterobasal ramus B10b-mediobasal ramus

B6-Superior bronchus B6a-medial ramus B6a 1-paravertebral subramus B6a2-posterior subramus B6b-superior ramus B6c-lateral ramus B*-Subsuperior bronchus BX* (9), BX* (1 0)-accessory subsuperior bronchus B7-Medial basal bronchus B7a-lateroanterior ramus B7b-medioanterior ramus B8-Anterior basal bronchus B8a-lateral ramus B8b-basal ramus B9-Lateral basal bronchus BX* (9)-accessory subsuperior ramus B9b-basal ramus = B9 B10-Posterior basal bronchus BX* (10)-accessory subsuperior ramus B10a-laterobasal ramus B10b-mediobasal ramus

1392

THE RESPIRATORY SYSTEM

SEGMENTAL ARTERIES

Right Superior Lobe A4-Apical segmental artery A^-apical ramus A^-anterior ramus A2-Anterior segmental artery A2a-posterior ramus A2al-superior subramus A2a2-inferior subramus A2b-anterior ramus A3-Posterior segmental artery A3a-apical ramus A3b-posterior ramus

Middle Lobe

Left Superior Lobe Superior Divison A1 + 3-Apical posterior segmental artery A'a-apical ramus A4b-anterior ramus A3a-apical ramus A3b-posterior ramus A2-Anterior segmental artery A2a-posterior ramus A2b-anterior ramus

Left Superior Lobe Inferior or Lingular Division

A5a-superior ramus A5b-inferior ramus

A4-Superior lingular artery (a. lingularis superior) A4a-posterior ramus A4b-anterior ramus A5-Inferior lingular artery (a. lingularis inferior) A5a-superior ramus A5b-inferior ramus

Right Inferior Lobe

Left Inferior Lobe

A6-Superior segmental artery A6a-medial ramus A6b-superior ramus A6c-lateral ramus A7-Medial basal artery A7a-anterior ramus A7b-medial ramus A8-Anterior basal artery A8a-lateral ramus A8b-basal ramus A9-Lateral basal artery A9a-lateral ramus A9b-basal ramus A10-Posterior basal artery A10a-laterobasal ramus A10b-mediobasal ramus

A6-Superior segmental artery A6a-medial ramus A6b-superior ramus A6c-lateral ramus A7-Medial basal artery A7a-anterior ramus A7b-medial ramus A8-Anterior basal artery A8a-lateral ramus A8b-basal ramus A9-Lateral basal artery A9a-lateral ramus A9b-basal ramus A10-Posterior basal artery A10a-laterobasal ramus A10b-mediobasal ramus

A4-Lateral segmental artery A4a-posterior ramus A4b-anterior ramus A5-Medial segmental artery

LUNGS (PULMONES)

1393

SEGMENTAL VEINS

Right Superior Lobe

V^Apical segmental vein V1a-apical ramus V^b-anterior ramus V3-Posterior segmental vein V3a-apical ramus V3b-posterior ramus V3c-posterior intersegmental ramus V3d-anterior ramus V2-Anterior segmental vein V2a-superior ramus V2b-Inferior ramus

Left Superior Lobe Superior Division V1 + 3-Apical posterior segmental vein Vx-Apical vein V1a-apical ramus V1b-anterior ramus V3-Posterior vein V3a-apical ramus V3b-posterior ramus V3c-posterior intersegmental ramus V2-Anterior segmental vein V2a-superior ramus V2b-inferior ramus V2c-posterior ramus

Middle Lobe

Inferior Division

V4-Lateral segmental vein V4a-posterior ramus V4b-anterior ramus V5-Medial segmental vein V5a-superior ramus V5b-inferior ramus

V4-Superior lingular segmental vein V4a-posterior ramus V4b-anterior ramus V5-Inferior lingular segmental vein V5a-superior ramus V5b-inferior ramus

Right Inferior Lobe

Left Inferior Lobe

V6-Superior segmental vein V6a-medial ramus V6b-superior ramus V6c-lateral ramus V7-Medial basal segmental vein V7a-anterior ramus V7b-medial ramus V8-Anterior basal segmental vein V8a-lateral ramus V8b-basal ramus V9-Lateral basal segmental vein V9a-lateral ramus V9b-basal ramus V10-Posterior basal segmental vein V10a-laterobasal ramus V10b-mediobasal ramus

V6-Superior segmental vein V6a-medial ramus V6b-superior ramus V6c-lateral ramus V7-Medial basal segmental vein V7a-lateroanterior ramus V7b-medioanterior ramus V8-Anterior basal segmental vein V8a-lateral ramus V8b-basal ramus V9-Lateral basal segmental vein V9a-lateral ramus V9b-basal ramus V10-Posterior basal segmental vein V10a-laterobasal ramus V10b-mediobasal ramus

1394

THE RESPIRATORY SYSTEM

Right superior lobe bronchus

Apical posterior segmental br. Apical segmental bronchus Post, segmental bronchus Anterior segmental bronchus

Left superior lobe bronchus

Super, seg bronchus Middle lobe bronchus

Superior seg. br. Anterior seg. br.

Lateral segment

-Inferior lobe br. Ant. bas. seg. br

Medial segment

Med. bas. seg. br.

Ant. bas. seg. br. Lat. bas. seg. br.

Lat. bas seg. br.

Post. bas. seg. br.

Med. bas. seg. br.

Ventral view of bronchial tree illustrating prevailing mode of branching. (Redrawn from E. A. Boyden, 1955, Segmental Anatomy of the Lungs, courtesy of Blakiston Division, McGraw-Hill Book Co., Inc.)

Fig. 15-36.

Dissection of mediastinal surface of right superior lobe showing the prevailing pattern. The con¬ ventional colors are followed: red for arteries, blue for veins, and black for bronchi. (Redrawn from E. A. Boyden, 1955, Segmental Anatomy of the Lungs, cour¬ tesy of Blakiston Division, McGraw-Hill Book Co., Inc.)

Fig. 15-37.

Dissection of mediastinal surface of middle lobe. (Redrawn from E. A. Boyden, 1955, Segmental Anat¬ omy of the Lungs, courtesy of Blakiston Division, McGraw-Hill Book Co., Inc.)

Fig. 15-38.

LUNGS (PULMONES)

1395

Dissection of mediastinal surface of right inferior lobe; the mode of branching of the inferior pul¬ monary vein is atypical. (Redrawn from E. A. Boyden, 1955, Segmental Anatomy of the Lungs, courtesy of Blakiston Division, McGraw-Hill Book Co., Inc.) Fig. 15-39.

Fig. 15-41. Dissection of mediastinal surface of fairly typical left inferior lobe. (Redrawn from E. A. Boyden, 1955, Segmental Anatomy of the Lungs, courtesy of Blakiston Division, McGraw-Hill Book Co., Inc.)

Serous Coat The serous coat is the pulmonary pleura (p. 1380). It is thin, transparent, and invests the entire organ as far as the root. Subserous Alveolar Tissue The subserous areolar tissue contains a large proportion of elastic fibers. It invests the entire surface of the lung and extends inward between the lobules. Parenchyma Dissection of mediastinal surface of left superior lobe. (Redrawn from E. A. Boyden, 1955, Seg¬ mental Anatomy of the Lungs, courtesy of Blakiston Division, McGraw-Hill Book Co., Inc.) Fig. 1 5-40.

STRUCTURE

The lungs are composed of an external serous coat, a subserous areolar tissue, and the pulmonary substance or parenchyma.

The parenchyma is composed of second¬ ary lobules which, although closely con¬ nected together by an interlobular areolar tissue, are quite distinct from one another, and in the fetus may be teased asunder with¬ out much difficulty. The secondary lobules vary in size; those on the surface are large and pyramidal, with the base turned toward the surface; those in the interior are smaller and variously shaped. Each secondary lob¬ ule is composed of several primary lobules,

1396

THE RESPIRATORY SYSTEM

the anatomic units of the lung. The primary lobule consists of an alveolar duct, the air spaces connected with it, and blood vessels, lymphatics, and nerves (Fig. 15-42). intrapulmonary bronchi. The intrapulmonary bronchi divide and subdivide throughout the entire organ, the smallest subdivisions constituting the lobular bron¬ chioles. The larger divisions consist of: (1) an outer coat of fibrous tissue, in which irregu¬ lar plates of hyaline cartilage are found at intervals, with the most developed appear¬ ing at the points of division; (2) internal to the fibrous coat, an interlacing network of circularly disposed smooth muscle fibers, the bronchial muscle; and (3) most inter¬ nally, the mucous membrane, which is lined by columnar ciliated epithelium resting on a basement membrane. The corium of the mucous membrane contains numerous elas¬ tic fibers that run longitudinally and a cer¬ tain amount of lymphoid tissue; it also con¬ tains the ducts of mucous glands, the acini of which lie in the fibrous coat. In the lobular bronchioles (terminal bron¬ chioles), the ciliated epithelial cells become cuboidal, and cartilage plates cease to exist

when the diameter of the bronchiole reaches about 1 mm. Branching and anastomosing bands of smooth muscle fibers, continuous with those of the intrapulmonary bronchi, invest the bronchiole and its subdivisions to the point of junction between alveolar duct and atrium (Fig. 15-43). Each bronchiole, according to Miller (1947), divides into two or more respiratory bronchioles, with scattered alveoli, and each of these again divides into several alveolar ducts, with a greater number of alveoli con¬ nected with them (Fig. 15-44). Each alveolar duct is connected with a variable number of irregularly spherical spaces, which also pos¬ sess alveoli, the atria. With each atrium, a

s

View of a reconstruction, from a dog’s lung, of the musculature of a noncartilaginous bronchiolus (lobular bronchiole), 0.565 mm in diameter, its branches, and its termination in a primary lobule of which only a single alveolar sac is shown completely reconstructed. B, bronchiolus; B.R. bronchiolus respiratorius; D.AI., ductulus alveolaris; S.Al., sacculus alveolaris. 125 x and reduced to 8. (Miller, The Lung, courtesy of Charles C Thomas.)

Fig. 15-43.

Part of a secondary lobule from the depth of a human lung, showing parts of several primary lob¬ ules. 1, bronchiole; 2, respiratory bronchiole; 3, alveolar duct; 4, atria; 5, alveolar sac; 6, alveolus or air cell; m, smooth muscle; a, branch pulmonary artery; v, branch pulmonary vein; s, septum between secondary lobules. Camera drawing of one 50-/1 section. 20 x diameters. (Miller, Jour. Morph.)

Fig. 15-42.

LUNGS (PULMONES)

1397

General scheme of a primary lobule, showing the subdivisions of (B) a respiratory bronchiole into two alveolar ducts; and the atria (A), alveolar sacs (S.AL.) of one of these ducts. ALV', alveoli scattered along the bronchi¬ oles; P, pleura, 1, pulmonary artery, dividing into smaller radicles for each atrium, one of which terminates in a capillary plexus on the wall of an alveolus; 2, its branches to the respiratory bronchiole and alveolar duct; 3, pulmo¬ nary vein with its tributaries from the pleura 6, capillary plexus of alveolus, and wall of the atrium 9 and alveolar duct 10; 4, lymphatics; dotted areas at 7, 8, 9 and 10, indicating areas of lymphoid tissue; 5, bronchial artery terminating in a plexus on the wall of the bronchiole; 5', bronchial artery terminating in pleura. (Miller, The Lung, courtesy of Charles C Thomas.) Fig. 15-44.

variable number (2 to 5) of alveolar sacs are connected which bear alveoli or air spaces on all parts of their circumference. alveoli. The alveoli are lined by a con¬ tinuous layer of pulmonary alveolar epithe¬ lium. The nuclei of the epithelial cells pro¬ trude into the air spaces, and the perinuclear cytoplasm attenuates abruptly into thin sheets of cytoplasm. The cytoplasmic sheets, averaging about 0.2 jam in thickness, rest on a basement membrane and face on the alveo¬ lar air spaces. The alveolar walls contain blood capillaries and collagenous, reticular, and elastic connective tissue fibers. The bar¬

rier between the capillary blood and alveo¬ lar air includes two thin layers of cytoplasm, alveolar epithelium and capillary endothe¬ lium with adherent basement membranes for each. Tissue space between these two membranes may be potential or real, but they are not adherent and variable amounts of interstitial elements may separate them. The fetal lung resembles a gland in that the alveoli have a small lumen and are lined by cubical epithelium. After the first respira¬ tion the alveoli become distended, and the epithelium takes on the characteristics of the adult.

1 398

THE RESPIRATORY SYSTEM

The bronchial arteries supply blood for the nutrition of the lung; the right lung usually receives a single artery and the left lung receives two. They are derived from the ventral side of the upper part of the thoracic aorta or from the upper aortic intercostal arteries. Some are distributed to the bronchial glands and to the walls of the bronchi and pulmonary vessels; those supplying the bronchi extend as far as the respiratory bronchioles, where they form capillary plexuses that unite with similar plexuses formed by the pulmonary artery, both of which give rise to small venous trunks forming one of the sources of the pulmonary vein. Others are distributed in the interlobular areolar tissue and end partly in the deep and partly in the superficial bron¬ chial veins. Lastly, some ramify upon the surface of the lung, beneath the pleura, where they form a cap¬ illary network. vessels.

The bronchial vein is formed at the root of the lung. It receives superficial and deep veins from a limited area about the hilum; the larger part of the blood supplied by the bronchial arteries is returned by the pulmonary veins. The bronchial vein ends on the right side in the azygos vein, and on the left side in the highest intercostal vein or in the accessory hemiazygos vein. The lymphatics are described on page 894. nerves. The lungs are supplied from the anterior and posterior pulmonary plexuses, formed chiefly by branches from the sympathetic and vagus nerves. The filaments from these plexuses accompany the bronchial tubes, supplying efferent fibers to the bronchial muscle and afferent fibers to the bronchial mucous membrane and probably to the alveoli of the lung. Small ganglia are found upon these nerves.

References (References are listed not only to those articles and books cited in the text, but to others as well which are considered to contain valuable resource information for the student who desires it.) Nose and Paranasal Sinuses Ali, M. Y. 1965. Histology of the human nasopharyngeal mucosa, J. Anat. (Lond.), 99:657-672. Allison, A. C. 1953. The morphology of the olfactory sys¬ tem in the vertebrates. Biol. Rev., 28:195-244. Blanton, P. L., and N. L. Biggs. 1969. Eighteen hundred years of controversy: The paranasal sinuses. Amer. J. Anat., 124:135-147. Brain, J. D. 1970. The uptake of inhaled gases by the nose. Ann. Otol. Rhinol. Laryngol., 79:529-539. Bridger, M. W., and A. W. P. van Nostrand. 1978. The nose and paranasal sinuses—applied surgical anat¬ omy. A histologic study of whole organ sections in three planes. J. Otolaryngol. (Suppl. 6), 7:1-33. Burnham, H. H. 1935. An anatomical investigation of blood vessels of the lateral nasal wall and their rela¬ tion to turbinates and sinuses. J. Laryngol. Otol., 50.-569--593. Cauna, N., and K. H. Hinderer. 1969. Fine structure of blood vessels of the human nasal respiratory mu¬ cosa. Ann. Otol. Rhinol. Laryngol., 78:865-879. Cauna, N„ K. H. Hinderer, and R. T. Wentges. 1969. Sen¬ sory receptor organs of the human nasal respiratory mucosa. Amer. J. Anat., 124:187-209. Clark, G. M. 1971. The structural support of the nose. ). Otolaryngol. Soc. Austral., 3:235-240. Dawes, J. D. K., and M. M. L. Prichard. 1953. Studies of the vascular arrangements of the nose. J. Anat. (Lond.), 87:311-322. Dion, M. C., B. W. Jafek, and C. E. Tobin. 1978. The anat¬ omy of the nose. External support. Arch. Otolaryn¬ gol., 104:145-150. Drettner, B. 1979. The role of the nose in the functional unit of the respiratory system. Rhinology, 17:3-11. Drumheller, G. W. 1973. Topology of the lateral nasal cartilages: The anatomical relationship of the lateral nasal to the greater alar cartilage, lateral crus. Anat. Rec., 176:321-327. Fabricant, N. D., and G. Conklin. 1965. The Dangerous Cold—Its Cures and Complications. Macmillan Publishing Company, New York, 179 pp.

Jacobs, M. H. 1947. Anatomic study of the maxillary sinus from the standpoint of the oral surgeon. J. Oral Surg., 5:282-291. Lucas, A. M. 1932. The nasal cavity and direction of fluid by ciliary movement in Macacus rhesus. Amer. J. Anat., 50:141-177. Negus, V. E. 1958. The Comparative Anatomy and Phys¬ iology of the Nose and Paranasal Sinuses. Living¬ stone, Edinburgh, 402 pp. Revskoi, Y. K. 1965. Variations in frontal sinus structure and their significance in selection of pilots. Fed. Proc., 24.T948-T950. Ritter, F. N. 1970. The vasculature of the nose. Ann. Otol. Rhinol. Laryngol., 79:468-474. Rose, J. M., C. M. Pomerat, and B. Danes. 1949. Tissue culture studies of ciliated nasal mucosa in man. Anat. Rec., 104:409-419. Rosen, M. D., and B. G. Sarnat. 1954. A comparison of the volume of the left and right maxillary sinuses in dogs. Anat. Rec., 120:65-71. Schaeffer, J. P. 1920. The Nose, Paranasal Sinuses, Nasolacrimal Passageways, and Olfactory Organ in Man. Blakiston Company, Philadelphia, 370 pp. Sellers, L. M. 1949. The frontal sinus—A problem in diag¬ nosis and treatment. The Mississippi Doctor, 27: 317-320. Stamm, W. K. 1981. Anatomy of the pterygopalatine fo¬ ramen and the fontanella in the lateral nasal wall. Rhinology, 19:87-91. Vidic, B. 1971. The morphogenesis of the lateral nasal wall in the early prenatal life of man. Amer. J. Anat., 130:121-139. Warbrick, J. G. 1960. The early development of the nasal cavity and upper lip in the human embryo. J. Anat. (Lond.), 94:351-362. Larynx, Trachea, and Bronchi Baken, R. J., and C. R. Noback. 1971. Neuromuscular spindles in intrinsic muscles of a human larynx. J. Speech Hear. Res., 14:513-518. Beck, C., and W. Mann. 1980. The inner laryngeal lym-

REFERENCES

phatics. A lymphangioscopical and electron micro¬ scopical study. Acta Otolaryngol., 89:265-270. Blanding, J. D„ Jr., R. W. Ogilvie, C. L. Hoffman, and W. H. Knisely. 1964. The gross morphology of the arte¬ rial supply to the trachea, primary bronchi, and esophagus of the rabbit. Anat. Rec., 148:611-614. Boyden, E. A. 1971. The structure of the pulmonary aci¬ nus in a child of six years and eight months. Amer. ]. Anat., 132:275-299. Boyden, E. A. 1974. The mode of origin of pulmonary acini and respiratory bronchioles in the fetal lung. Amer. J. Anat., 141:317-328. Campbell, A. H., and A. G. Liddelow. 1967. Significant variations in the shape of the trachea and large bronchi. Med. ). Austral., 1:1017-1020. Cauldwell, E. W., R. G. Siekert, R. E. Lininger, and B. J. Anson. 1948. The bronchial arteries. An anatomic study of 150 human cadavers. Surg. Gynecol. Obstet., 86:395-412. English, D. T., and C. E. Blevins. 1969. Motor units of laryngeal muscles. Arch. Otolaryngol., 89:778-784. Falk, D. 1975. Comparative anatomy of the larynx in man and the chimpanzee: Implications for language in Neanderthal. Amer. J. Phys. Anthropol., 43:123-132. Fisher, A. W. F. 1964. The intrinsic innervation of the trachea. J. Anat. (Lond.), 98:117-124. Gay, T., H. Hirose, M. Strome, and M. Sawashima. 1972. Electromyography of the intrinsic laryngeal muscles during phonation. Ann. Otol. Rhinol. Laryngol., 81:401-409. Gray, G. W., and C. M. Wise. 1959. The Bases of Speech. 3rd Edition. Harper and Brothers, New York, 562 pp. Greene, M. C. L. 1980. The Voice and Its Disorders. 4th Edition. J. B. Lippincott Co., Philadelphia, 484 pp. Inoue, S., and G. P. Dionne. 1977. Tonofilaments in nor¬ mal human bronchial epithelium and in squamous cell carcinoma. Amer. }. Pathol., 88:345-354. Kahane, J. C. 1978. A morphological study of the human prepubertal and pubertal larynx. Amer. J. Anat., 151:11-19. Keene, M. F. L. 1961. Muscle spindles in human laryngeal muscles. J. Anat. (Lond.), 95:25-29. King, B. T„ and R. L. Gregg. 1948. An anatomical reason for the various behaviors of paralyzed vocal cords. Ann. Otol. Rhinol. Laryngol., 57:925-944. Kirchner, J. A., and B. D. Wyke. 1965. Articular reflex mechanisms in the larynx. Ann. Otol. Rhinol. Laryngol., 74:749-768. Kotby, M. N., and L. K. Haugen. 1970. The mechanics of laryngeal function. Acta Otolaryngol., 70:203-211. Latarje, M. 1954. La vascularisation sanguinea des bronches. Les bronches, 4.T45. von Leden, H., and P. Moore, 1961. Vibratory pattern of the vocal cords in unilateral laryngeal paralysis. Acta Otolaryngol., 53:493-506. Lucier, G. E., J. Daynes, and B.}. Sessle. 1978. Laryngeal reflex regulation: Peripheral and central neural analyses. Exp. Neurol., 62:200-213. MacKenzie, C. F., T. C. McAslan, B. Shin, D. Schellinger, and M. Helrich. 1978. The shape of the human adult trachea. Anesthesiology, 49:48-50. Macklin, C. C. 1929. The musculature of the bronchi and lungs. Physiol. Rev., 9:1-60. Marchand, P., J. C. Gilroy, and V. H. Wilson. 1950. An anatomical study of bronchial vascular system and its variations in disease. Thorax, 5:207-221. Maue, W. M., and D. R. Dickson. 1971. Cartilages and ligaments of the adult human larynx. Arch. Otolar¬ yngol., 94:432-439.

1399

Miller, R. A. 1941. The laryngeal sacs of an infant and an adult gorilla. Amer. J. Anat., 69:1-17. Miserocchi, G„ J. Mortola, and G. Sant’Ambrogio. 1973. Localization of pulmonary stretch receptors in the airways of the dog. J. Physiol. (Lond.), 235:775-782. Monkhouse, W. S., and W. F. Whimster. 1976. An ac¬ count of the longitudinal mucosal corrugations of the human tracheo-bronchial tree, with observa¬ tions on those of some animals. J. Anat. (Lond.), 122:681-695. Mortola, J. P., and G. Sant’Ambrogio. 1979. Mechanics of the trachea and behaviour of its slowly adapting stretch receptors. J. Physiol. (Lond.), 286:577-590. Negus, V. E. 1931. The Mechanism of the Larynx. C. V. Mosby, St. Louis, 528 pp. Negus, V. E. 1949. The Comparative Anatomy and Phys¬ iology of the Larynx. Heinemann, London, 230 pp. O’Donnell, S. R., and N. Saar. 1973. Histochemical locali¬ zation of adrenergic nerves in the guinea-pig tra¬ chea. Brit. J. Pharmacol., 47:707-710. Phalen, R. F., H. C. Yeh, G. M. Schum, and O. G. Raabe. 1978. Application of an idealized model to mor¬ phometry of the mammalian tracheobronchial tree. Anat. Rec., 190:167-176. Pressman, J. J. 1942. Physiology of the vocal cords in phonation and respiration. Arch. Otolaryngol., 35: 355-398. Reid, L. 1979. Basic aspects of bronchial anatomy—and further knowledge of pulmonary neuro-anatomy. Scand. J. Respir. Dis. (Suppl.), 103:13-18. Rhodin, J., and T. Dalhamm. 1956. Electron microscopy of the tracheal ciliated mucosa in rats. Z. Zellforsch., 44:345-412. Salassa, J. R., B. W. Pearson, and W. S. Payne. 1977. Gross and microscopical blood supply of the tra¬ chea. Ann. Thorac. Surg., 24:100-117. Schreider, J. P., and O. G. Raabe. 1981. Structure of the human respiratory acinus. Amer. J. Anat., 162:221-232. Sellars, I. E., and E. N. Keen. 1978. The anatomy and movements of the cricoarytenoid joint. Laryngo¬ scope, 88:667-674. Smith, E. I. 1957. The early development of the trachea . and esophagus in relation to atresia of the esophaghus and tracheoesophageal fistula. Carneg. Instn., Contr. Embryol., 36:41-58. Sram, F., and J. Syka. 1977. Firing pattern of motor units in the vocal muscle during phonation. Acta Otolar¬ yngol., 84:132-137. Stell, P. M., I. Gregory, and J. Watt. 1980. Morphology of the human larynx. II. The subglottis. Clin. Otolaryn¬ gol., 5:389-395. Stell, P. M., R. Gudrun, and J. Watt. 1981. Morphology of the human larynx. III. The supraglottis. Clin. Oto¬ laryngol., 6:389-393. Strong, L. H. 1935. The mechanism of laryngeal pitch. Anat. Rec., 63:13-28. Tanabe, M., N. Isshiki, and K. Kitajima. 1972. Vibratory pattern of the vocal cord in unilateral paralysis of the cricothyroid muscle. An experimental study. Acta Otolaryngol., 74:339-345. Turner, R. S. 1962. A note on the geometry of the tracheal bifurcation. Anat. Rec., 143:189-194. Wessels, N. K. 1970. Mammalian lung development: In¬ teractions in formation and morphogenesis of tra¬ cheal buds. J. Exp. Zool., 175:455-466. Williams, A. F. 1951. The nerve supply of laryngeal mus¬ cles. J. Laryngol. Otol., 65:343-348. Williams, A. F. 1954. The recurrent laryngeal nerve and the thyroid gland. ). Laryngol. Otol., 68:719-725.

1 400

THE RESPIRATORY SYSTEM

Lungs, Bronchopulmonary Segments, and Pleura Adams, F. H. 1966. Functional development of the fetal lung. J. Pediat., 68:794-801. Alexander, H. L. 1933. The autonomic control of the heart, lungs, and bronchi. Ann. Intern. Med., 6:1033-1043. Altman, P. L., J. F. Gibson, Jr., and C. C. Wang. 1958. Handbook of Respiration. Edited by D. S. Dittmer, and R. M. Grebe. W. B. Saunders, Philadelphia, 403 pp. Appleton, A. B. 1944. Segments and blood-vessels of the lungs. Lancet, 2:592-594. Avery, M. E. 1962. The alveolar lining layer. A review of studies on its role in pulmonary mechanics and in the pathogenesis of atelectasis. Pediatrics, 30:324330. Bloomer, W. E., A. A. Liebow, and M. R. Hales. 1960. Surgical Anatomy of the Bronchovascular Seg¬ ments. Charles C Thomas, Springfield, Ill., 273 pp. Boyden, E. A. 1953. A critique of the international no¬ menclature on bronchopulmonary segments. Dis. Chest, 23:266-269. Boyden, E. A. 1955. Segmental Anatomy of the Lungs. The Blakiston Division, McGraw-Hill Book Co., New York, 276 pp. Boyden, E. A. 1961. The nomenclature of the broncho¬ pulmonary segments and their blood supply. Dis. Chest, 39.T-6. Boyden, E. A. 1965. The terminal air sacs and their blood supply in a 37-day infant lung. Amer. J. Anat., 116:413-427. Boyden, E. A. 1967. Notes on the development of the lung in infancy and early childhood. Amer. J. Anat., 121:749-762. Boyden, E. A. 1969. The pattern of the terminal air spaces in a premature infant of 30-32 weeks that lived nine¬ teen and a quarter hours. Amer. J. Anat., 126:31-40. Boyden, E. A., and J. F. Hartman. 1946. An analysis of the variations in the bronchopulmonary segments of the left upper lobes of fifty lungs. Amer. J. Anat., 79:321-360. Boyden, E. A., and D. H. Tompsett. 1965. The changing patterns in the developing lungs of infants. Acta Anat., 61:164-192. Bradley, G. W. 1977. Control of the breathing pattern. Internat. Rev. Physiol., 14:185-217. Brock, R. C. 1954. The Anatomy of the Bronchial Tree. 2nd Edition. Oxford University Press, London, „ 243 pp. Cech, S. 1969. Adrenergic innervation of blood vessels in the lung of some mammals. Acta Anat., 74:169-182. Clements, J. A. 1970. Pulmonary surfactant. Amer. Rev. Resp. Dis., 101:984-990. Drinker, C. K. 1954. The Clinical Physiology of the Lungs. Charles C Thomas, Springfield, Ill., 84 pp. Dunnill, M. S. 1962. Postnatal growth of the lung. Tho¬ rax, 17:329-333. Elftman, A. G. 1943. The afferent and parasympathetic innervation of the lungs and trachea of the dog. Amer. J. Anat., 72:1-27. Elliott, F. M., and L. Reid. 1965. Some new facts about the pulmonary artery and its branching pattern. Clin. Radiol., 16:193-198. Empey, D. W. 1978. Diseases of the respiratory system. Introduction: Structure and function of the lungs. Brit. Med. J., 1:631-633. Engel, S. 1962. Lung Structure. Charles C Thomas, Springfield, Ill., 300 pp.

Fenn, W. O., and H. Rahn. 1965. Handbook of Physiology-Respiration. Section 3, Vol. 2. American Physiological Society, Williams and Wilkins, Balti¬ more, pp. 927-1696. Findlay, C. W., Jr., and H. C. Maier. 1951. Anomalies of the pulmonary vessels and their surgical signifi¬ cance. Surgery, 29:604-641. Gaylor, J. B. 1934. The intrinsic nervous mechanism of the human lung. Brain, 57:143-160. Harbord, R. P., and R. Woolner. 1959. Symposium on Pulmonary Ventilation. Williams and Wilkins, Bal¬ timore, 109 pp. Hasleton, P. S. 1972. The internal surface area of the adult human lung. J. Anat. (Lond.), 112:391-400. von Hayek, H. 1960. The Human Lung. Translated by Vernon E. Krahl. Hafner Publishing Co., New York, 372 pp. Heitzman, E. R., J. V. Scrivani, J. Martino, and J. Moro. 1971. The azygos vein and its pleural reflections. I. Normal roentgen anatomy. Radiology, 101:249-258. Heuck, F. 1959. Die Streifenatelektasen der Lunge. Georg Thieme Verlag, Stuttgart, 108 pp. Huber, J. F. 1949. Practical correlative anatomy of the bron¬ chial tree and lungs. J. Nat. Med. Assoc., 41:49-60. Hughes, G. M. 1974. Comparative Physiology of Verte¬ brate Respiration. 2nd Edition. Heinemann, Lon¬ don, 144 pp. Jackson, C. L., and J. F. Huber. 1943. Correlated applied anatomy of the bronchial tree and lungs with a sys¬ tem of nomenclature. Dis. Chest, 9:319-326. Kendall, M. W., and E. Eissmann. 1980. Scanning elec¬ tron microscopic examination of human pulmonary capillaries using a latex replication method. Anat. Rec., 196:275-283. Kikkawa, Y. 1970. Morphology of alveolar lining layer. Anat. Rec., 167:389-400. Kirks, D. R., P. E. Kane, E. A. Free, and H. Taybi. 1976. Systemic arterial supply to normal basilar segments of the left lower lobe. Amer. J. Roentgenol., 126:817821. Kohn, K„ and M. Richter. 1958. Die Lungenarterienbahn bei angeborenen Herz/ehiern. Georg Thieme Verlag, Stuttgart, 112 pp. Krahl, V. E. 1955. Current concept of the finer structure of the lung. Arch. Intern. Med., 96:342-356. Krahl, V. E. 1964. Anatomy of the mammalian lung. In Handbook of Physiology—Respiration. Section 3, Vol. 1. Edited by W. O. Fenn and H. Rahn. American Physiological Society, Williams and Wilkins, Balti¬ more, pp. 213-284. Lachman, E. 1942. A comparison of the posterior bound¬ aries of lungs and pleura as demonstrated on the cadaver and on the roentgenogram of the living. Anat. Rec., 83:521-542. Lachman, E. 1946. The dynamic concept of thoracic topography: A critical review of present day teach¬ ing of visceral anatomy. Amer. J. Roentgenol., 56:419-440. Larsell, O. 1922. The ganglia, plexuses, and nerve-termi¬ nations of the mammalian lung and pleura pulmonalis. J. Comp. Neurol., 35:97-132. Larsell, O., and R. S. Dow. 1933. The innervation of the human lung. Amer. J. Anat., 52:125-146. Levin, D. L., A. M. Rudolph, M. A. Heymann, and R. H. Phibbs. 1976. Morphological development of the pulmonary vascular bed in fetal lambs. Circulation, 53:144-151. Loosli, C. G., and R. F. Baker. 1962. The human lung: Microscopic structure and diffusion. In Pulmonary

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1401

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lacteal vessels. Finally the small intestine ends in the large intestine, made up of cecum, colon, rectum, and anal canal, the last terminating on the surface of the body at the anus. The accessory organs are the teeth, for purposes of mastication; the three pairs of salivary glands—the parotid, the subman¬ dibular, and the sublingual—the secretion from which mixes with the food in the mouth and converts it into a bolus and acts chemically on one of its constituents; the liver and pancreas, two large glands in the abdomen, the secretions of which, in addi¬ tion to that of numerous minute glands in the walls of the alimentary canal, assist in the process of digestion.

Development of the Digestive System The primitive digestive tube consists of two parts: (1) the foregut, within the cephalic flexure and dorsal to the heart; and (2) the hindgut, within the caudal flexure (Fig. 16-1).

Thalamencephalon

The digestive system, which provides the apparatus for the digestion of food, consists of the digestive tube and certain accessory organs. The digestive tube (alimentary canal) is a musculomembranous tube, about 9 meters long, that extends from the mouth to the anus; it is lined throughout its entire extent by mucous membrane. Different names have been applied to the various parts of its course: at its commencement is the mouth, where provision is made for the mechanical division of the food (mastication), and for its admixture with a fluid secreted by the sali¬ vary glands (insalivation). Beyond this are the pharynx and esophagus, which convey food into the stomach, where it is stored for a time and where the first stages of the diges¬ tive process take place. The stomach is fol¬ lowed by the small intestine, which is di¬ vided for purposes of description into three parts: the duodenum, the jejunum, and the ileum. In the small intestine the process of digestion is completed and the resulting products are absorbed into the blood and 1402

Fig. 16-1.

Human embryo about 15 days old. Brain and heart represented from right side. Digestive tube and yolk sac in median section. (After His.)

DEVELOPMENT OF THE DIGESTIVE SYSTEM

Between these is the wide opening of the yolk sac, which is gradually narrowed and reduced to a small foramen leading into the vitelline duct. At first the foregut and hindgut end blindly. The anterior end of the foregut is separated from the stomodeum by the buccopharyngeal membrane (Fig. 16-1); the hindgut ends in the cloaca, which is closed by the cloacal membrane.

1 403

Future apex of nose Medial nasal process Olfactory pit Lateral nasal process Globular process Maxillary process Stomodeum Mandibular arch

MOUTH AIMD ASSOCIATED STRUCTURES

mouth. The mouth is developed partly from the stomodeum and partly from the floor of the anterior portion of the foregut. By the growth of the head end of the embryo and the formation of the cephalic flexure, the pericardial area and the buccopharyn¬ geal membrane come to lie on the ventral surface of the embryo. With the further ex¬ pansion of the brain and the forward bulging of the pericardium, the buccopharyngeal membrane is depressed between these two prominences. This depression constitutes the stomodeum (Fig. 16-1), which is lined by ectoderm and is separated from the anterior end of the foregut by the buccopharyngeal membrane. This membrane is devoid of mesoderm, being formed by the apposition of the stomodal ectoderm with the foregut entoderm; at the end of the third week it dis¬ appears, and thus a communication is estab¬ lished between the mouth and the future pharynx. No trace of the membrane is found in the adult, and the communication just mentioned must not be confused with the permanent isthmus faucium. The lips, teeth, and gums are formed from the walls of the stomodeum, but the tongue develops in the floor of the pharynx. The visceral arches extend ventrally be¬ tween the stomodeum and the pericardium, and with the completion of the mandibular arch and the formation of the maxillary processes, the mouth assumes the appear¬ ance of a pentagonal orifice. The orifice is bounded cranially by the frontonasal proc¬ ess, caudally by the mandibular arch, and laterally by the maxillary processes (Fig. 16-2). With the inward growth and fusion of the palatine processes (Figs. 2-55; 2-56), the stomodeum is divided into an upper nasal and a lower buccal part. Along the free mar¬ gins of the processes bounding the mouth cavity a shallow groove appears; this is

Fig. 16-2. Head end of human embryo about 30 to 31 days old. (From model by Peters.)

termed the primary labial groove, and from the bottom of it ectoderm grows downward into the underlying mesoderm. The central cells of the ectodermal downgrowth degen¬ erate and a secondary labial groove forms, and as this deepens, the lips and cheeks sep¬ arate from the alveolar processes of the maxillae and mandible. salivary glands. The salivary glands arise as buds from the epithelial lining of the mouth. The parotid gland appears during the fourth week in the angle between the maxil¬ lary process and the mandibular arch. The submandibular gland appears in the sixth week, and the sublingual gland appears dur¬ ing the ninth week in the hollow between the tongue and the mandibular arch. tongue. The tongue (Figs. 16-3 to 16-6) develops in the floor of the pharynx, and consists of an anterior or buccal part and a posterior or pharyngeal part, which are sep¬ arated in the adult by the V-shaped sulcus terminalis. During the third week there ap¬ pears, immediately dorsal to the ventral ends of the two halves of the mandibular arch, a rounded swelling named the tuberculum impar, which may help to form the buc¬ cal part of the tongue or may be purely a transitory structure. From the ventral ends of the fourth arch there arises a second and larger elevation, in the center of which is a median groove or furrow. This elevation was

1 404

THE DIGESTIVE SYSTEM

Lateral tongue swellings Future apex of nose Medial nasal process Olfactory pit Lateral nasal process Globular process Maxillary process

Entrance to larynx

Roof of pharynx

Arytenoid swellings

Hypophyseal diverticulum Dorsal wall of pharynx

Fig. 16-5. Floor of pharynx of human embryo at the end of the fourth week. (From model by Peters.)

Fig. 16-3. Same embryo as shown in Figure 16-2, with front wall of pharynx removed.

named the furcula by His1 and at first it is separated from the tuberculum impar by a depression, but later by a ridge, the copula, which is formed by the forward growth and fusion of the ventral ends of the second and third arches. The posterior or pharyngeal part of the tongue develops from the copula, which extends forward in the form of a V, to embrace between its two limbs the buccal part of the tongue. At the apex of the V, a pit-like invagination occurs to form the thy¬ roid gland, and this depression is repre¬ sented in the adult by the foramen cecum of the tongue. In the adult the union of the an¬ terior and posterior parts of the tongue is ‘Wilhelm His (1831-1904): A German anatomist and physiologist (Basel and Leipzig).

Lateral tongue swellings

marked by the V-shaped sulcus terminalis, the apex of which is at the foramen cecum, while the two limbs run lateralward and for¬ ward, parallel to, but a little behind, the vallate papillae. palatine tonsils. The palatine tonsils develop from the dorsal angles of the second branchial pouches. The entoderm that lines these pouches grows into the surrounding mesoderm in the form of solid buds. These buds become hollowed out by the degenera¬ tion and casting off of their central cells, forming the tonsillar crypts. Lymphoid cells accumulate around the crypts and become grouped to form the lymphoid follicles; the latter, however, are not well defined until after birth.

PHARYNX AND POSTPHARYNGEAL ALIMENTARY TUBE

The cranial part of the foregut becomes dilated to form the pharynx (Fig. 16-1), in re¬ lation to which the branchial arches are de¬ veloped (see p. 45); the succeeding part re-

Thyroid diverticulum

Entrance to larynx

Fig. 16-4. Floor of pharynx of human embryo about 26 days old. (From model by Peters.)

Arytenoid swellings

Fig. 16-6. Floor of pharynx of human embryo about 30 days old. (From model by Peters.)

DEVELOPMENT OF THE DIGESTIVE SYSTEM

mains tubular, and with the descent of the stomach is elongated to form the esophagus. About the fourth week a fusiform dilatation appears, which is the future stomach, and beyond this the gut opens freely into the yolk sac (Fig. 16-7, A and B). The opening is wide at first, but it gradually narrows into a tubular stalk, the yolk stalk or vitelline duct.

Between the stomach and the mouth of the yolk sac the liver diverticulum appears. From the stomach to the rectum the alimentary canal is attached to the notochord by a band of mesoderm, from which the common mes¬ entery of the gut subsequently develops. The stomach is also attached to the ventral abdominal wall as far as the umbilicus by

Notochord

Fig. 16-7.

1405

Rathke's pouch

Sketches in profile of two stages in the development of the human digestive tube. (His.) A, 30 x; B, 20 X-

1 406

THE DIGESTIVE SYSTEM

the septum transversum. The cranial portion of the septum takes part in the formation of the diaphragm, whereas the caudal portion, into which the liver grows, forms the ventral mesogastrium (Fig. 16-10). As the stomach undergoes further dilatation, its two curva¬ tures become recognizable (Figs. 16-7, B; 16-8), the greater curvature oriented toward the vertebral column and the lesser curva¬ ture toward the anterior wall of the abdo¬ men, with its two surfaces facing to the right and left respectively. Caudal to the stomach the gut undergoes great elongation and forms a V-shaped loop that projects ventralward; from the bend or angle of the loop the vitelline duct passes into the umbil¬ icus (Fig. 16-9). For a time a large part of the loop extends beyond the abdominal cavity into the umbilical cord, but by the end of the third month it has been drawn back into the cavity. With the lengthening of the tube, the mesoderm that attaches it to the future ver¬ tebral column and carries the blood vessels to supply the gut, becomes thinner and drawn out to form the posterior common mesentery. The portion of this mesentery that is attached to the greater curvature of the stomach is named the dorsal mesogas¬ trium, and the part that suspends the colon is termed the mesocolon (Fig. 16-10). About the sixth week, a diverticulum of the gut appears just caudal to the opening of the vitelline duct and indicates the future

cecum and vermiform appendix. The part of the loop on the distal side of the cecal diver¬ ticulum increases in diameter and forms the future ascending and transverse portions of the large intestine. Until the fifth month the cecal diverticulum has a uniform caliber, but from this time onward its distal part remains rudimentary and forms the vermi¬ form appendix, while its proximal part ex¬ pands to form the cecum. Changes also take place in the shape and position of the stom¬ ach. Its dorsal part or greater curvature, to which the dorsal mesogastrium is attached, grows much more rapidly than its ventral part or lesser curvature, to which the ventral mesogastrium is fixed. Also, the greater cur¬ vature swings toward the left, so that the right surface of the stomach becomes di¬ rected dorsalward and the left surface ventralward (Fig. 16-11), a change in position that explains why the left vagus nerve is found on the ventral surface of the stomach and the right vagus on the dorsal surface. The dorsal mesogastrium, being attached to the greater curvature, must necessarily fol¬ low this movement, and hence it becomes greatly elongated and drawn lateralward and ventralward from the vertebral column; as in the case of the stomach, the right surfaces of both the dorsal and ventral mesogastria are now directed dorsalward, and the left ventralward. In this way a pouch, the lesser sac (omental bursa), is

in the development of the digestive tube. (His.)

DEVELOPMENT OF THE DIGESTIVE SYSTEM

Septum transversum

Aorta Dorsal mesogastrium

Falciform ligament of liver

Stomach

Lesser omentum

Umbilical vein Intestinal V-shaped loop Mesentery

Umbilical cord

Colon

The primitive mesentery of a six-week-old human embryo, half schematic. (Kollmann.)

Fig. 16-9.

formed dorsal to the stomach. This increases in size as the digestive tube undergoes fur¬ ther development, and the entrance to the pouch becomes the future epiploic foramen or foramen of Winslow.1 The duodenum develops from the part of 'Jacob Benignus Winslow (1669-1760): A Danish anato¬ mist who worked in Paris.

1407

the tube that immediately succeeds the stom¬ ach; it undergoes little elongation, being more or less fixed in position by the liver and pancreas, which arise as diverticula from it. The duodenum is first suspended by a mesentery and projects ventralward in the form of a loop. The loop and its mesentery are subsequently displaced by the transverse colon, so that the right surface of the duode¬ nal mesentery is directed dorsalward, and adhering to the parietal peritoneum, is lost. The remainder of the digestive tube be¬ comes greatly elongated, and as a conse¬ quence the tube is coiled on itself. This elon¬ gation demands a corresponding increase in the width of the intestinal attachment of the mesentery, which becomes folded. At this stage the small and large intestines are attached to the vertebral column by a continuous common mesentery, with the coils of the small intestine falling to the right of the midline and the large intestine falling to the left (Fig. 16-11). Sometimes this condition persists throughout life, and it is then found that the duodenum does not cross from the right to the left side of the vertebral column, but lies entirely on the right side of the

Aorta

Spleen

Ventral mesogastrium

Dorsal mesogastrium Celiac artery

Pancreas Duodenum

Superior mesenteric artery

Mesentery

Cecum

Inferior mesenteric artery

Hindgut

Fig. 16-10. Abdominal part of digestive tube and its attachment to the primitive or common mesentery. Human embryo of six weeks. (After Toldt.)

1408

THE DIGESTIVE SYSTEM

Dorsal mesogastrium Dorsal mesogastrium

Greater curvature of stomach

Greater curvature of stomach

Bile duct Duodenum

Duodenum reater omentum

Greater omentum

Mesentery Mesocolon Cecum

Small intestine

Point where intestinal loops cross each other

Point where intestinal loops cross each other Mesocolon

Cecum Large intestine

Vermiform appendix Mesentery

Vitelline duct

Large intestine Small intestine

Vitelline duct Rectum Rectum

Fig. 16-11. Diagrams to illustrate two stages in the development of the digestive tube and its mesentery. The arrow indicates the entrance to the bursa omentalis. The ventral mesogastrium has been eliminated.

median plane, where it is continued into the jeju¬ num; the arteries to the small intestine also arise from the right instead of the left side of the superior mesenteric artery.

The gut is now rotated counterclockwise upon itself, so that the large intestine is car¬ ried ventral to the small intestine, and the cecum is placed immediately caudal to the liver. About the sixth month the cecum de¬ scends into the right iliac fossa, and the large intestine forms an arch consisting of the as¬ cending, transverse, and descending por¬ tions of the colon; the transverse portion crosses ventral to the duodenum and lies just caudal to the greater curvature of the stom¬ ach, the coils of the small intestine being dis¬ posed within this arch (Fig. 16-12). Some¬ times the caudalward progress of the cecum is arrested, so that in the adult it may lie im¬ mediately caudal to the liver instead of in the right iliac region. Further changes that take place in the lesser sac (omental bursa) and in the common mes¬ entery give rise to the peritoneal relations seen in the adult. The omental bursa, which at first reaches only as far as the greater cur¬ vature of the stomach, grows caudalward to form the greater omentum; this extension lies ventral to the transverse colon and the coils of the small intestine (Fig. 16-13). Be¬

fore the pleuroperitoneal opening is closed, the omental bursa sends a diverticulum cranialward on either side of the esophagus; the left diverticulum soon disappears, but the right diverticulum becomes constricted

Final disposition of the intestines and their vascular relations. (Jonnesco.) A, Aorta. H, Hepatic ar¬ tery. M, Col., Branches of superior mesenteric artery, m, m', Branches of inferior mesenteric artery. S, Splenic ar¬ tery. Fig. 16-12.

DEVELOPMENT OF THE DIGESTIVE SYSTEM

1409

attachment characteristic of its adult condi¬ tion. The lesser omentum is formed, as indi¬ cated previously, by the mesoderm or ventral mesogastrium, which attaches the stomach and duodenum to the anterior abdominal wall. The subsequent growth of the liver separates this leaf into two parts: the lesser omentum between the stomach and liver, and the falciform and coronary ligaments between the liver and the abdomi¬ nal wall and diaphragm (Fig. 16-13).

RECTUM AND ANAL CANAL

Fig. 16-13. Schematic figure of the omental bursa, etc. Human embryo of eight weeks. (Kollmann.)

and persists in most adults as a small sac lying within the thorax on the right side of the caudal end of the esophagus. The ventral layer of the transverse meso¬ colon is at first distinct from the dorsal layer of the greater omentum, but ultimately the two blend, and hence the greater omentum appears to be attached to the transverse colon (Fig. 16-14). The mesenteries of the ascending and descending parts of the colon disappear in the majority of cases, while that of the small intestine assumes the oblique

The hindgut is at first prolonged caudalward into the body stalk as the tube of the allantois. With the growth and flexure of the caudal end of the embryo, the body stalk, with its allantoic tube, is carried cranialward to the ventral aspect of the body, and conse¬ quently a bend is formed at the junction of the hindgut and allantois. This bend be¬ comes dilated into a pouch that constitutes the entodermal cloaca; the hindgut opens into its dorsal part and the allantois extends out ventrally from its ventral part. At a later stage the mesonephric (Wolffian)1 and paramesonephric (Mullerian)2 ducts open into its ventral portion. The cloaca is, for a time, 1Kaspar Friedrich Wolff (1733-1794): A Russian anato¬ mist and physiologist (St. Petersburg). 2Johannes Peter Muller (1801-1858): A German anato¬ mist and physiologist (Berlin).

Diaphragm «

\

Liver

Lesser omentum -- Omental bursa - - Stomach — Pancreas

0)