Selective Anatomy: Prep Manual for Undergraduates (Vol - 1) - 2E [1, 2 ed.] 8131256936, 9788131256930

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Selective Anatomy Prep Manual for Undergraduates VOLUME I SECOND EDITION

Vishram Singh, MBBS, MS, PhD(hc), MICPS, FASI, FIMSA Adjunct Visiting Faculty, KMC, Mangalore Manipal Academy of Higher Education, Karnataka, India Editor-in-chief, Journal of the Anatomical Society of India Member of Federative International Committee for Scientific Publications (FICSP) of IFAA Former Professor and Head, Department of Anatomy, Santosh Medical College Member Academic Council and Core Committee, PhD Course, Santosh University, Ghaziabad, NCR, Delhi Examiner in National and International Universities; Member, Editorial Board, Indian Journal of Otology; Journal of Anatomy and Cell Biology Ex-Vice President, Anatomical Society of India Medicolegal Advisor, ICPS, India Consulting Editor, ABI, North Carolina, USA Associate Editor, Acta Medica International Member, COPE Council (England & Wales) Member British Association of Clinical Anatomists (BACA) Formerly at: GSVM Medical College, Kanpur King George’s Medical College, Lucknow Al-Arab Medical University, Benghazi (Libya) All India Institute of Medical Sciences, New Delhi

Table of Contents Cover image Title page Copyright Dedication Foreword to the first edition Preface to the second edition Preface to the first edition Acknowledgements

SECTION I. Upper Limb 1. Pectoral region and axilla Pectoral region Axilla 2. Back of the body and scapular region Back of the body Scapular region 3. Arm

4. Forearm 5. Hand 6. Vessels of the upper limb 7. Nerves of the upper limb 8. Joints of the upper limb

SECTION II. Head and Neck 9. Scalp, temple and face 10. Side, front and back of the neck 11. Parotid and submandibular regions Parotid region Submandibular region 12. Deep structures of the neck and prevertebral region Deep structures of the neck Prevertebral region 13. Oral cavity 14. Pharynx and palate 15. Nose and paranasal air sinuses Nose Paranasal air sinuses

16. Larynx 17. Infratemporal fossa, temporomandibular joint and pterygopalatine fossa Infratemporal fossa Temporomandibular joint Pterygopalatine fossa AN33.1 18. Ear and orbit Ear Orbit 19. Dural folds, intracranial dural venous sinuses and pituitary gland 20. Cranial nerves 21. Meninges and cerebrospinal fluid 22. Spinal cord

SECTION III. Brain 23. Overview of brain and brainstem Overview of brain Brainstem 24. Cerebellum and fourth ventricle 25. Overview of cerebrum and functional areas 26. Cerebrum 27. Basal nuclei, limbic system and lateral ventricle

Basal nuclei Limbic system Lateral ventricle 28. Diencephalon and third ventricle

SECTION IV. General Anatomy 29. Introduction and anatomical terminology 30. Skin, superficial fascia and deep fascia Skin Superficial fascia Deep fascia 31. Skeletal system 32. Joints 33. Muscles 34. Cardiovascular system 35. Lymphatic system 36. Nervous system

SECTION V. General Histology 37. Introduction to histology 38. Epithelial and connective tissues Epithelial tissue

Connective tissue AN66.1, AN66.2 39. Special connective tissues 40. Muscle tissue, blood vessels and lymphoid tissue Muscle tissue AN67.1–67.3 Blood vessels AN69.1–69.3 Lymphoid tissue AN70.2 Index

Copyright

RELX India Pvt. Ltd. Registered Office: 818, 8th Floor, Indraprakash Building, 21, Barakhamba Road, New Delhi 110001 Corporate Office: 14th Floor, Building No. 10B, DLF Cyber City, Phase II, Gurgaon-122002, Haryana, India Selective Anatomy: Prep Manual for Undergraduates, Volume I, 2nd Edition, Vishram Singh Copyright © 2020 by RELX India Pvt. Ltd. Previous edition Copyrighted 2015 by Elsevier, A division of Reed Elsevier India Private Limited. All rights reserved. ISBN: 978-81-312-5693-0 e-book ISBN: 978-81-312-5704-3 No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notice Practitioners and researchers must always rely on their own experience and knowledge

in evaluating and using any information, methods, compounds or experiments described herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made. To the fullest extent of the law, no responsibility is assumed by Elsevier, authors, editors or contributors in relation to the adaptation or for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

Content Strategist - Education Solutions: Arvind Koul Content Project Manager: Goldy Bhatnagar Production Executive: Dhan Singh Sr Graphic Designer: Milind Majgaonkar

Typeset by GW India Printed and bound at

Dedication Dedicated to My Mother, Late Smt. Ganga Devi Singh My Father, Late Shri Hari Ram Singh My Students, Past, and Present

Foreword to the first edition Professor (Dr) VK Arora, MD, DCD, CTC&E (JAPAN) FNCCP, FIMSA, FGSI, Vice Chancellor, Santosh Medical College, Santosh University, Ghaziabad, NCR, Delhi, ExAdditional Director General, of Health Services Government of India

It gives me a great pleasure to write the Foreword for Professor Vishram Singh’s book Selective Anatomy Prep Manual for Undergraduates. There was a long-felt need for a suitable book on anatomy in question-answer format to help students not only to revise vast course of anatomy before examination in limited time but also present their knowledge in an easy format. It is a herculean task to select the frequently asked questions in examinations of various universities and answer them in a manner as expected by an examiner. Professor Vishram Singh is an eminent and highly regarded Anatomist. He has authored about a dozen books and published a number of research papers in national and international journals. This book is in two volumes in question-answer format. Volume I covers the complete syllabus of Paper I and Volume II, the syllabus of Paper II. The book is profusely illustrated by four-color line diagrams which can be easily reproduced by the students during examination. This book is an appropriate comprehensive manual for university examination, thus I strongly recommend it to the undergraduate medical students. Wishing Professor Vishram Singh for his future endeavor.

Preface to the second edition Vishram Singh

It is with great pleasure that I present the second edition of Selective Anatomy: Prep Manual for Undergraduates, which is widely used by the undergraduate medical students as well as dental, paramedical and nursing students. This book is in question–answer format and set in 2 volumes – Volume I covers the syllabus of Paper I and Volume II the syllabus of Paper II. The popularity of this book reflects the appeal of its concept-building approach written with my vast experience of teaching about 45 years. Efforts have been made very carefully to present the text in concise manner that will be acceptable to most of the examiners. In fact, the huge syllabus of anatomy is beyond the comprehension of students in 1 year. The main purpose of this book is to relieve the students of pre-examination stress while revising the syllabus paper-wise in short available time. However, the students should be aware that this book is meant only for the purpose of revision and does not replace the standard textbook. This book is liked and well appreciated by the students all over India. Based on enormous suggestions from the students and fellow academicians, many new questions and answers along with figures and tables have been added in this edition. The previous text has been thoroughly revised and most of the diagrams have been completely revised for easy understanding and reproducibility in the examination by the students. I strongly feel that the book in its present form will be more useful than the previous one to students and teachers alike. I will highly appreciate the comments and suggestions from both students and teachers for further improvement of this book. “Nothing is permanent in life except change.”

Preface to the first edition Vishram Singh

The Medical Council of India has reduced the duration of teaching of 1st year MBBS course from 1½ years to 1 year. It has also introduced the specific pattern of questions such as long and short answer questions, short notes, drawing and labeling of diagrams, providing anatomical, embryological, and genetic basis of clinical problems and MCQs. Each student tries his/her best to clear the examination. However, many students do not know how to present the answers considering the marks allotted. This book is in question-answer format in 2 volumes. Volume I covers the syllabus of Paper I, while Volume II will deal with the syllabus of Paper II. Having 40 years of teaching experience and being an examiner in various medical colleges and institutions, I have put my best effort in selecting frequently asked questions (FAQs) and tried to answer them in a concise manner acceptable to most of the examiners. Most of the diagrams are drawn by myself to ensure the accuracy and to see that they can be easily reproduced by the students in examination. Although, initially I was a bit hesitant to write a book in question and answer format but later my conscience allowed me to do so because the sole aim of a teacher is to solve the problems faced by the students and inspire them to become good doctors. I hope that this book will definitely solve the problems of students and relieve them from pre-examination stress. However, the student should be aware that this book is meant only for revision purpose and not to replace the standard textbook. I am confident this book will serve the purpose for which it meant. Lastly I will highly appreciate comments both good and bad about the book from both students and faculty because that will help me to improve the book in future. “Necessity is the mother of invention.”

Acknowledgements I sincerely thank my colleagues in the Department, especially Prof. Mangla M. Pai (HOD) and Prof. Latha V. Prabhu and Associate Prof. Murli Manju for their cooperation and appreciation of my work. I highly appreciate the help provided by Associate Prof. Preeti Srivastava, NDMC Medical College and Hindu Rao Hospital, Delhi, for going through the proofs of this book. I am also thankful to Assistant Prof. Krishna G., Department of Anatomy, Rajarajeswari Medical College, Bengaluru, Karnataka for providing feedback from students. I gratefully acknowledge the feedback and support of all my fellow colleagues in Anatomy throughout India, particularly: • Prof. N.C. Goel (Vice principal and former Head of the Department), Hind Institute of Medical Sciences, Barabanki, Lucknow, Uttar Pradesh. • Prof. Punita Manik (Head of the Department), King George Medical College, Lucknow, Uttar Pradesh. • Prof. P.K. Sharma (Head of the Department), Era Medical College, Lucknow, Uttar Pradesh. • Prof. Poonam Kharb (Head of the Department), ITS Dental College, Ghaziabad, Uttar Pradesh. • Prof. T.C. Singel, Zydus Medical College, Dahod, Gujarat. • Prof. T.S. Roy (Head of the Department), AIIMS, New Delhi. • Profs Vandana Mehta (Head of the Department) and Hitendra Lohiya, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi. • Prof. Vanita Gupta (Head of the Department), Rama Medical College, Hapur, Uttar Pradesh. • Profs Deepa Singh (Head of the Department) and Akshya Dubey, Himalayan Institute of Medical Sciences, Jolly Grant, Dehradun, Uttarakhand. • Prof. W.M.S. Johnson (Dean), Sree Balaji Medical College, Chennai. • Prof. Suniti Pandey (Head of the Department), GSVM Medical College, Kanpur. • Prof. (Dr) S.L. Jethani (Medical Superintendent and Former Head of the Department of Anatomy), Himalayan Institute of Medical Sciences, Dehradun, Uttarakhand. • Prof. G.M. Mahesh (Head of the Department), Basaveshwara Medical College, Chitradurga, Karnataka. • Profs Avinash Chandra Agrawal (Head of the Department) and A.K. Srivastava, Prasad Institute of Medical Sciences, Banthra, Lucknow. • Prof. Sneh Agrawal (Head of the Department), Lady Harding Medical College,

New Delhi. • Prof. Sneha Guruprasad Kalthur (Head of the Department) and Dr Prakash Babu, KMC, Manipal, Karnataka. • Prof. Emeritus S.D. Joshi, Sri Aurobindo Institute of Medical Sciences, Indore, Madhya Pradesh. Lastly, I thank my daughter Dr Rashi Singh, son Dr Gaurav Singh and daughter-inlaw Anupama Singh for helping me in the preparation of this manuscript. I gratefully acknowledge the help and cooperation received from the staff of RELX India Pvt Ltd, especially Arvind Koul (Content Strategist), Shabina Nasim (Head of Content Project Management) and Goldy Bhatnagar (Content Project Manager), in completing the project on time.

SECTION I

Upper Limb OUTLINE 1. 2. 3. 4. 5. 6. 7. 8.

Pectoral region and axilla Back of the body and scapular region Arm Forearm Hand Vessels of the upper limb Nerves of the upper limb Joints of the upper limb

1

Pectoral region and axilla Pectoral region Breast ❖ What is breast? Describe its structure in brief.  AN9.2 The breast is a modified sweat gland (apocrine type). It is rudimentary in male and well developed in female at puberty. In adult female, it is seen as a soft hemispherical protruding organ one on either side in the pectoral region.

Structure The breast is composed of three components: skin, parenchyma and fibrofatty stroma (Fig. 1.1).

FIG. 1.1 Structure of the breast: A, parenchyma of the breast (lobes and ducts); B, fibrofatty (lobes and ducts of the breast); and stroma of the breast (fat and suspensory ligaments of Cooper).

Skin: It presents nipple and areola. • Nipple: It is a dark conical projection of skin in the centre of breast. It is pierced by 10–15 lactiferous ducts and contains smooth muscle fibres. • Areola: It is circular blackish discolouration around the nipple. It contains

numerous modified sebaceous glands. They secrete oily secretion which lubricates and prevents the nipple from drying and cracking. Parenchyma: It consists of glandular part made up of alveoli, lactiferous ducts and lactiferous sinuses. Fibrofatty stroma: It consists of fibrofatty tissue. • Fibrous stroma, consists of fibrous septa (ligaments of Cooper), which extends from skin to the pectoral fascia and divides the gland into 10–15 lobes. • Fatty stroma, lies between fibrous septa and glandular part.

N.B. To drain breast abscess, the incision is given radially to avoid damage to the lactiferous ducts. ❖ Describe the female breast under the following headings: (a) location and extent, (b) relations, (c) blood supply, (d) lymphatic drainage and (e) applied anatomy.  AN9.2

Location (fig. 1.2) The breast is hemispherical in shape and located one on either side in the superficial fascia of the pectoral region.

FIG. 1.2 Location and extent of breast.

Extent (fig. 1.2) • Vertically: It extends from 2nd to 6th rib in midclavicular line. • Horizontally: It extends from lateral border of the sternum to the midaxillary line.

Relations Superficial relations • Skin • Superficial fascia Deep relations • Pectoral fascia (deep fascia covering the pectoralis major). • Three muscles: pectoralis major (medially), serratus anterior (laterally) and external oblique (inferomedially). • Loose areolar tissue of the retromammary space intervenes between the breast and pectoral fascia.

N.B. • The structures forming deep relations together constitute the mammary bed. • Glandular tissue of the breast can be freely moved on deeper structures, i.e. pectoralis major covered by pectoral fascia. • The breast prostheses are often inserted in the retromammary space.

Blood supply Arterial supply: The breast is highly vascular organ and is supplied by the following arteries: • Internal thoracic artery through its 2nd, 3rd and 4th perforating branches. • Lateral thoracic, superior thoracic and acromiothoracic branches of the axillary artery. • Lateral branches of the posterior intercostal arteries.

N.B. Lateral thoracic artery is the main artery supplying the breast. Venous drainage: The main veins draining area around areola and parenchyma (glandular tissue) are

deep veins. They form the circular venous plexus at the base of the gland. From here, they drain into: • Axillary vein • Internal mammary vein • Intercostal veins

Lymphatic drainage (fig. 1.3) The lymph vessels draining the breast are divided into two sets: (a) A set draining the parenchyma, nipple and areola; (b) A set draining overlying skin, excluding nipple and areola.

FIG. 1.3 Mode of lymphatic drainage of the breast.

• Those draining the parenchyma including areola and nipple form subareolar plexus of Sappey, which drains as follows: ■ Seventy-five per cent (75%) into axillary group of lymph nodes chiefly into anterior (or pectoral) group. Some reach posterior (subscapular) group. Efferents from these pass to central and thence into apical group. ■ Twenty per cent (20%) drain into parasternal (internal mammary) nodes. ■ Five per cent (5%) drain into posterior intercostal nodes. • Those draining the overlying skin excluding areola and nipple drain into:

■ Axillary nodes – from outer part ■ Supraclavicular nodes – from upper part ■ Parasternal nodes – from inner part ■ Subdiaphragmatic nodes – from inner part

Applied anatomy Carcinoma of the breast: The breast is common site of carcinoma. The important points to know about the carcinoma breast are • The cancer cells may infiltrate the suspensory ligaments (Cooper’s ligaments) and as a result the breast becomes fixed and immobile. • The contraction of the ligaments causes retraction or puckering of the skin. • The infiltration of the lactiferous duct and their consequent fibrosis leads to retraction of the nipple. • Secondary breast cancer are usually lodged in the liver, ovaries or the peritoneum making the prognosis worse. • The cancer cells may migrate transcelomically to ovary producing a secondary tumour called Krukenberg tumour. • The cancer cells can also spread to the vertebrae and the brain via venous route, through the communication between the veins draining the breast and the vertebral venous plexus. • Peau d’orange: In breast cancer, the skin over the breast presents an orange peel appearance. This occurs due to obstruction of cutaneous lymphatics leading to breast oedema and deepening of the mouths of sweat glands and hair follicles. ❖ Describe the development of the breast/mammary gland in brief.  AN9.3 • The mammary gland develops in the pectoral region from the milk line (Fig. 1.4). • The milk line is linear thickening of surface ectoderm that appears in the 4th week of intrauterine life. • The milk line extends from axilla to the inguinal region on the ventral aspect of the body wall of the embryo. • The fibrofatty stroma of the breast develops from the underlying mesoderm.

FIG. 1.4 Development of the mammary gland: A, mammary ridge (right side) and positions of accessory nipples (left side); B, stages of development of the mammary glands.

N.B. The full development of breast occurs at about 19 year of the age. ❖ Enumerate the congenital anomalies of the breast. • Polymastia: Supernumerary breasts • Amastia: Absence of breast (rare) • Athelia: Absence of nipple • Polythelia: Supernumerary nipples (commonly seen in axilla) ❖ Discuss the microscopic/histological structure of the mammary gland.  AN9.2 • The mammary gland is a modified sweat gland of apocrine variety. It is also called serous, tubuloalveolar gland according to nature of secretion and secretory units. • The histological structure of mammary gland differs according to its physiological status, i.e. (a) nonlactating and (b) lactating (Fig. 1.5). The differences are given in Table 1.1.

FIG. 1.5 Microscopic structure of the mammary gland. Source: (Source: Textbook of Histology: Atlas and Practical Guide, 3rd Edition: JP Gunasegaran, Fig. 1.5A: Box 15.7 H/P, Page 331; Fig. 1.5B: Box 15.8 H/P, Page 332, RELX India Private Limited, 2016.)

TABLE 1.1 Differences Between Nonlactating and Lactating Breast Nonlactating Breast Predominantly made of fibrofatty tissue and a little glandular tissue Lumina of duct and alveoli are not clearly visible and do not contain secretion (milk) Alveoli underdeveloped and represented by solid balls of cells

Lactating Breast Predominantly made of glandular tissue and a little fibrofatty tissue Lumina of ducts and alveoli are clearly visible and filled with secretion (milk) Alveoli are well developed with distended lumen filled with homogeneous vacuolated material – the milk; the alveoli are lined by simple cuboidal epithelium

Extensive branching of duct system

Ducts are few

❖ Enumerate the muscles of pectoral region. • Pectoralis major • Pectoralis minor • Subclavius ❖ Give the origin, insertion, nerve supply and actions of the pectoralis major muscle.  AN9.1

Origin (fig. 1.6) • Clavicular head: From the anterior surface of the medial 1/2 of clavicle. • Sternocostal head arises from: ■ Anterior surface of the sternum up to 6th costal cartilage. ■ Medial parts of 2nd to 6th costal cartilages. ■ Aponeurosis of the external oblique muscle.

FIG. 1.6 Origin and insertion of pectoralis major muscle. Figure in the Inset on the right shows the insertion of bilaminar tendon insertion of pectoralis major on the lateral lip. Anterior lamina is formed by clavicular and manubrium fibres while posterior lamina is formed by sternocostal (minus manubrial fibres) and aponeurotic fibres.

Insertion (fig. 1.6) By a bilaminar tendon on to the lateral lip of the bicipital groove in a ‘U-shaped manner’ with two laminae continuous with each other inferiorly.

Nerve supply Medial and lateral pectoral nerves.

Actions Adduction and medial rotation of the shoulder. ❖ Give the origin, insertion, nerve supply and actions of the pectoralis minor muscle.  AN9.1

Origin Arises from 3rd, 4th and 5th ribs anteriorly near their costal cartilages.

Insertion Medial border and upper surface of the coracoid process of the scapula.

Nerve supply Medial and lateral pectoral nerves (C6–C8).

Action • It draws the scapula forward across the chest wall along with serratus anterior. • It depresses the shoulder as in bringing the arm down from ‘above head position’.

❖ Give the origin, insertion, nerve supply and actions of the serratus anterior muscle.  AN10.11 Serratus anterior is a broad flat muscle of trunk in the medial wall of axilla. It lies between the ribs and scapula at the upper lateral part of the chest (Fig. 1.7).

FIG. 1.7 Origin and insertion of serratus anterior muscle.

Origin Arises by eight digitations from outer surfaces and upper borders of upper eight ribs. Each digitation arises from the corresponding rib but the 1st digitation arises from both 1st and 2nd ribs.

Insertion Into whole length of the medial border of costal surface of the scapula. The 1st digitation is inserted into a triangular area on the superior angle. The next two or three digitations are inserted in the whole length of the medial border. The lower four or five digitations are inserted into the large triangular area over the inferior angle.

Nerve supply By the nerve to serratus anterior (also called long thoracic nerve of Bell), which arises from C5, C6 and C7 roots of brachial plexus.

Actions • Rotation of the scapula which helps in the abduction of shoulder beyond 90°. • Chief muscle concerned with pushing and punching movements as in boxing. Hence, it is also called ‘boxer’s muscle’.

❖ Write a short note on clavipectoral fascia. The clavipectoral fascia is the strong fascial sheet deep to the pectoralis major muscle. It extends from clavicle above to the axillary fascia below.

Attachments (fig. 1.8) Medial: Medially, it fuses with anterior intercostal membrane of the upper two intercostal spaces and attaches to the 1st rib.

FIG. 1.8 Clavipectoral fascia, as seen in sagittal section of anterior axillary wall.

Lateral: Laterally, it becomes thick and dense and attaches to the coracoid process. Above: It splits to enclose subclavius and attaches to the lips of the subclavian groove of clavicle. Below: It splits to enclose pectoralis minor and thereafter it continues downward as suspensory ligament of axilla, which is attached to the convex dome of the axillary fascia.

Modifications • Costocoracoid ligament: Thickening of clavipectoral fascia between coracoid process and 1st rib. • Suspensory ligament of axilla (vide supra).

Functional significance Acts as a suspensory ligament of axilla to maintain its concavity.

Applied anatomy The cancer cells from breast may pass across the clavipectoral fascia to invade the Rotter’s lymph nodes lying in front of pectoralis minor muscles. Hence, the knowledge of clavipectoral fascia is of great surgical significance. ❖ Enumerate the structures piercing clavipectoral fascia (Fig. 1.9). Clavipectoral fascia is pierced by four structures: • Lateral pectoral nerve • Thoracoacromial artery • Cephalic vein • Lymphatics from infraclavicular nodes and deep part of breast to apical group of axillary lymph nodes

FIG. 1.9 Structures piercing clavipectoral fascia. PM, pectoralis major; Pm, pectoralis minor.

N.B. Structures passing inwards are cephalic vein and lymphatics while structures passing outwards are lateral pectoral nerve and thoracoacromial artery.

Axilla The axilla is a pyramid-shaped space between upper part of the arm and thorax. ❖ Describe the axilla under the following headings: (a) boundaries, (b) contents and (c) applied anatomy.  AN10.1

Boundaries (fig. 1.10) Anterior wall: It is formed by: • Pectoralis major • Subclavius muscle • Clavipectoral fascia • Pectoralis minor

FIG. 1.10 Boundaries and contents of axilla as seen in a horizontal section. AA, axillary artery; AV, axillary vein; L, lateral cord; M, medial cord; P, posterior cord.

Posterior wall: It is formed by: • Latissimus dorsi • Teres major • Subscapularis

Medial wall: It is formed by serratus anterior muscle, covering the upper part of lateral thoracic wall (upper 4–5 ribs). Lateral wall: It is narrow and formed by intertubercular sulcus of the shaft of humerus, which contains coracobrachialis and short head of biceps brachii. Apex (also called cervicoaxillary canal): It is triangular and directed upwards and medially towards the root of the neck. It is bounded: • Anteriorly, by the posterior border of clavicle • Medially, by the outer border of 1st rib • Posteriorly, by the upper border of scapula Base: It is formed by the axillary fascia extending between anterior and posterior axillary folds.

Contents (fig. 1.10) • Axillary artery and its branches • Axillary vein and its tributaries • Cords of brachial plexus • Axillary lymph nodes AN10.4 • Fibrofatty tissue • Long thoracic and intercostobrachial nerves • Axillary tail of breast (tail of Spence)

Applied anatomy Axillary abscess: It occurs due to infection and suppuration of axillary lymph nodes. Axillary abscess is drained by giving an incision midway between the anterior and posterior axillary folds. The direction of edge of knife should face towards the medial wall. AN10.7 Lymphadenopathy: Axillary lymph nodes are often infected and enlarged. They should be removed very carefully because of their relationship to major vessels. AN10.7 Boils: Due to the presence of abundant hair follicles in axilla, the infection of hair follicles and sebaceous glands is very common and gives rise to multiple boils in the axilla.

Axillary pulse: Can be felt against the lower part of the lateral wall of axilla. ❖ Describe the brachial plexus under the following headings: (a) formation, (b) components, (c) location, (d) branches and (e) applied anatomy.  AN10.3

Formation (fig. 1.11) It is formed by ventral primary rami of C5, C6, C7, C8 and T1.

FIG. 1.11 Brachial plexus and its branches. DS, dorsal scapular nerve; LS, lower subscapular nerve; NS, nerve to subclavius; SS, suprascapular nerve; T, thoracodorsal nerve; US, upper subscapular nerve.

Components (fig. 1.11) The brachial plexus consists of four components: • Roots • Trunks • Divisions • Cords

Location

• Roots and trunks lie in the root of neck. • Divisions lie behind the clavicle. • Cords lie in the axilla.

Branches (fig. 1.11) From roots • Dorsal scapular nerve (C5) for rhomboids. • Nerve to serratus anterior (C5, C6 and C7) for serratus anterior as the name implies. From trunk (only upper trunk gives branches) • Suprascapular nerve (C5 and C6) for supraspinatus and infraspinatus muscles. • Nerve to subclavius. From cords • Lateral cord ■ Lateral pectoral nerve (C5–C7) ■ Lateral root of median nerve (C5–C7) ■ Musculocutaneous nerve (C5–C7) Mnemonic: Laila Loved Majnu. • Medial cord ■ Medial pectoral nerve for pectoralis major and pectoralis minor ■ Medial cutaneous nerve of arm ■ Medial cutaneous nerve of forearm ■ Medial root of median nerve ■ Ulnar nerve • Posterior cord ■ Upper subscapular nerve for subscapularis muscle ■ Lower subscapular nerve for subscapularis and teres major muscles ■ Nerve to latissimus dorsi (thoracodorsal nerve) ■ Axillary nerve for deltoid and teres minor muscles ■ Radial nerve Mnemonic: ULNAR

Applied anatomy • Erb paralysis: It occurs due to injury of the upper trunk of brachial plexus at the Erb’s point. • Klumpke paralysis: It occurs due to injury of the lower trunk of brachial plexus (for details, see p. 15). • Horner syndrome: It occurs due to involvement of the sympathetic fibres (T1) (for

details, see p. 139). • Winging of scapula: It occurs due to injury of the nerve to serratus anterior. Erb paralysis (fig. 1.12) AN10.6 • Site of injury: Erb’s point (the region of upper trunk where six nerves meet, i.e. ventral rami of C5 and C6, anterior and posterior divisions of the upper trunk, and suprascapular nerve and nerve to subclavius) (Fig. 1.12A). • Cause: Undue (i.e. too much) separation of head from shoulder, e.g. (a) pulling of fetal head by forceps during delivery (birth injury) and (b) fall on shoulder. • Clinical features: ■ Arm hangs by the side. It is adducted and medially rotated, i.e. person is unable to abduct and laterally rotate the arm. ■ Forearm is extended and pronated, i.e. person is unable to flex and supinate the forearm. ■ Loss of sensations over a small area on the lower part of the deltoid.

FIG. 1.12 Erb–Duchenne paralysis: A, Erb’s point; B, policeman receiving a tip position of upper limb.

N.B. The deformity of upper limb produced in Erb paralysis is termed policeman tip taking position/Waiter’s tip taking position (Fig. 1.12B). Klumpke paralysis AN10.6 • Site of injury: Lower trunk of brachial plexus involving C8 and T1, mainly T1. • Causes: Undue abduction of arm from body, e.g. (a) birth injury (pulling of upper limb during delivery) (b) reflex catching of something with hand while falling from a height, i.e. branch of a tree while falling from a tree. • Clinical features:

■ Claw hand, due to paralysis of intrinsic muscles of the hand ■ Sensory loss along the medial border of forearm and hand ■ Horner syndrome due to involvement of sympathetic nerve to head and neck (for details, see p. 139) ❖ Describe the axillary artery in brief.  AN10.2

Source and extent (fig. 1.13) • It is a continuation of subclavian artery into axilla. • It extends from the outer border of 1st rib to the inferior border of teres major.

FIG. 1.13 Course and branches of axillary artery.

Parts It is divided into three parts by pectoralis minor: • First part: Proximal to the muscle • Second part: Deep/behind to the muscle • Third part: Distal to the muscle

Branches (fig. 1.13) They are six in number: • First part gives one branch: Superior thoracic artery.

• Second part gives two branches: (i) thoracoacromial artery and (ii) lateral thoracic artery. • Third part gives three branches: (i) subscapular artery, (ii) anterior circumflex humeral artery, and (iii) posterior circumflex humeral artery.

Applied anatomy The axillary artery can be effectively compressed against the upper part of shaft of humerus (lower part of the lateral wall of axilla). ❖ Describe the axillary vein in brief.  AN10.2

Source and extent (fig. 1.14) • It begins at the lower border of teres major by the union of basilic vein and venae comitantes of brachial artery. • It runs upwards and medially to continue as subclavian vein at the outer border of 1st rib.

FIG. 1.14 Axillary vein and axillary lymph nodes.

Tributaries • Veins corresponding to the branches of axillary artery, i.e. lateral thoracic, subscapular, etc. • Cephalic vein.

Applied anatomy Spontaneous thrombosis of axillary vein may occasionally occur following unaccustomed movements of the arm at shoulder joint. ❖ Describe the arterial anastomosis around scapula.  AN10.9 The arterial anastomosis around scapula is formed between the branches of the first part of subclavian artery and the branches of third part of the axillary artery (Fig. 1.15).

FIG. 1.15 Anastomosis around the scapula (scapular anastomosis).

The following branches from first part of the subclavian artery and third part of the axillary artery take part in this anastomosis:

Clinical importance This anastomosis around scapula provides collateral channels to ensure adequate circulation to the upper limb in case the subclavian artery or axillary artery is blocked anywhere between the first part of subclavian artery and third part of axillary artery. ❖ Describe the axillary lymph nodes in brief and discuss their applied importance.  AN10.4

Location In fibrofatty tissue of axilla.

Groups Axillary lymph nodes are 15–20 in number which are divided into five groups (Fig. 1.14): Anterior group • Lies along the inferior border of pectoralis minor/lateral thoracic vein. • It drains most of the lymph from the breast. Posterior (subscapular) group • It lies along the subscapular vein and drains lymph from axillary tail of the breast. Lateral group • It lies posteromedial to axillary vein along the upper part of humerus. • It drains lymph from entire upper limb. Central group • It lies in the upper part of axilla. • It receives lymph from other groups (vide supra). Apical group • It lies at the apex of axilla along the medial side of axillary vein. It receives lymph from central group, breast and thumb.

Applied anatomy • Axillary lymph nodes are involved and enlarged in breast cancer. • Axillary lymph nodes are also enlarged if infection occurs anywhere in areas of their drainage. They are routinely palpated by the clinicians while examining a patient.

2

Back of the body and scapular region Back of the body ❖ Give a brief account of posterior axio-appendicular muscles.  AN10.8 • These are the muscles that attach the scapula with the back of the trunk. • These are arranged into two layers: ■ Superficial layer – Trapezius – Latissimus dorsi ■ Deep layer – Levator scapulae – Rhomboideus minor – Rhomboideus major ❖ Give the origin, insertion, nerve supply and actions of trapezius muscle.  AN10.8

Origin (fig. 2.1) Trapezius muscle arises from: • Medial one-third of the superior nuchal line of occipital bone. • Ligamentum nuchae. • Spinous processes and supraspinous ligaments from C7 to T12.

FIG. 2.1 Origin and insertion of trapezius and latissimus dorsi muscles.

Insertion (fig. 2.1) It is inserted as follows: • Superior fibres, into lateral one-third of the posterior border of clavicle. • Middle fibres, into medial margin of the acromion and upper lip of the crest of spine of scapula. • Lower fibres, into deltoid tubercle of the spine of scapula.

Nerve supply • Spinal root of accessory nerve (CN XI) • Ventral rami of C3 and C4 spinal nerves

Actions • Shrugging of shoulder • Retraction of scapula • Rotation of scapula to help abduction of arm beyond 90°

❖ Give the origin, insertion, nerve supply and actions of latissimus dorsi muscle.  AN10.8

Origin (fig. 2.1) Latissimus dorsi muscle arises from: • Spinous processes and supraspinous ligaments from T7 to T12 • Posterior layer of thoracolumbar fascia (attached to spinous processes of lumbar and sacral spines) • Last four ribs • Inferior angle of scapula • Posterior one-third of iliac crest

Insertion Into the floor of bicipital groove of humerus after spiralling around the teres major muscle.

Nerve supply (fig. 2.1) Thoracodorsal nerve (C6, C7 and C8)

Actions • Extends, adducts and medially rotates the arm. • Costal attachment helps in deep inspiration and forced expiration. ❖ Write a short note on the triangle of auscultation.  AN10.9

Location Back of thorax near the inferior angle of scapula.

Boundaries Medial: Lateral border of trapezius muscle. Lateral: Medial border of scapula. Inferior: Upper border of latissimus dorsi muscle. Floor: Sixth and 7th intercostal spaces and rhomboideus major muscle.

Applied anatomy • Respiratory sounds from the apex of lower lobe of lung can be heard over this triangle. • Sounds of swallowed liquids may be auscultated over this triangle. ❖ Give the origin, insertion, nerve supply and actions of levator scapulae, rhomboideus minor and rhomboideus major muscles. These are given in Table 2.1. TABLE 2.1 Origin, Insertion, Nerve Supply and Actions of Levator Scapulae, Rhomboideus Minor and Rhomboideus Major Muscles

Scapular region ❖ Give the origin, insertion, nerve supply and actions of the deltoid muscle.  AN10.10 The deltoid is a three-in-one muscle (Fig. 2.2). It is strong triangular muscle covering the shoulder like a hood. It is responsible for the rounded contour of the shoulder.

FIG. 2.2 Origin and insertion of the deltoid muscle.

Origin Anterior unipennate part: From anterior border and upper surface of lateral one-third of clavicle. Intermediate multipennate part: From lateral border of acromion process of scapula. Posterior unipennate part: From lower lip of crest of spine of scapula.

N.B. Architecture of deltoid muscle. The acromial part is multipennate and strongest. The acromial fibres arise from four intramuscular tendinous septa and are attached on either side of three tendinous septa ascending from the insertion of the muscle on the deltoid tuberosity of humerus (Fig. 2.3).

FIG. 2.3 Architecture of the deltoid muscle.

Insertion In the V-shaped deltoid tuberosity on the lateral aspect of the shaft of humerus.

Nerve supply Axillary/circumflex nerve (C5, C6).

Actions • Lateral (acromial) fibres cause abduction of shoulder joint from 15° to 90°. • Anterior (clavicular) fibres cause medial rotation and flexion of the shoulder joint. • Posterior (spinous) fibres cause lateral rotation and extension of the shoulder joint (i.e. they draw the arm backwards and rotate the humerus laterally). ❖ Enumerate the structures under cover of deltoid muscle.  AN10.10 Following are the structures under cover of deltoid muscle (Fig. 2.4): • Axillary nerve • Insertion of all the muscles of rotator cuff (supraspinatus, infraspinatus, teres minor and subscapularis) • Circumflex humeral vessels • Surgical neck of humerus

FIG. 2.4 Structures under cover of deltoid muscle. C, capsule of shoulder joint; G, glenoid cavity.

❖ Give the origin and insertion of supraspinatus, infraspinatus, teres minor, subscapularis and teres major muscles.  AN10.10 The origin and insertion of these muscles are given in Table 2.2 and shown in Figs 2.5 and 2.6.

FIG. 2.5 Origin and insertion of supraspinatus, infraspinatus, teres minor and teres major muscles. TM, teres minor.

FIG. 2.6 Origin and insertion of subscapularis muscle.

TABLE 2.2 Origin and Insertion of Supraspinatus, Infraspinatus, Teres Minor, Subscapularis and Teres Major Muscles Muscle Origin Supraspinatus Medial two-third of the supraspinous fossa of the scapula Infraspinatus Medial two-third of the infraspinous fossa of the scapula and fibrous intermuscular septa Teres minor Upper two-third of the dorsal surface of the lateral border of the scapula Subscapularis Medial two-third of the subscapular fossa Teres major

Lower one-third of the dorsal surface of lateral border and inferior angle of the scapula

Insertion Upper facet on the greater tubercle of the humerus Middle facet on the greater tubercle of the humerus Inferior facet on the greater tubercle of the humerus Lesser tubercle of the humerus Medial lip of bicipital groove of the humerus

❖ Give nerve supply and actions of supraspinatus, infraspinatus, teres minor, subscapularis and teres major muscles. Muscle • Supraspinatus • Infraspinatus

Nerve Supply Suprascapular nerve (C5, C6) Suprascapular nerve (C5, C6) • Teres minor Axillary nerve (C5, C6) • Upper and lower Subscapularis subscapular nerves (C5, C6) • Teres major Lower subscapular nerve

Action Abduction of shoulder joint from 0° to 15°, i.e. it initiates the abduction of shoulder joint Lateral rotation of arm Lateral rotation of arm Adduction and medial rotation of arm

Adduction and medial rotation of arm

(C5, C6)

N.B. These muscles also help in holding the head of humerus into the glenoid cavity. ❖ Write a short note on musculotendinous cuff/rotator cuff of the shoulder joint.  AN10.10 The musculotendinous cuff (Fig. 2.7) is a fibrous sheath around the shoulder joint. It is formed by the flattened tendons of four muscles, which blend with the capsule of shoulder joint as follows: • Supraspinatus, superiorly • Infraspinatus and teres minor, posteriorly • Subscapularis, anteriorly

FIG. 2.7 Musculotendinous cuff.

N.B. The musculotendinous cuff provides strength to the capsule of shoulder joint all around except inferiorly. For this reason, dislocation of the shoulder joint commonly occurs inferiorly. ❖ Write briefly about the quadrangular space. The quadrangular space (Fig. 2.8) is one of the subscapular intermuscular spaces present in the region of axilla.

FIG. 2.8 Subscapular intermuscular spaces. Q, quadrangular space; U, upper triangular space; L, lower triangular space.

Boundaries Superior • Subscapularis in front • Teres minor behind • Capsule of the shoulder joint (in between subscapularis and teres minor) Inferior: Teres major Medial: Long head of the triceps brachii Lateral: Surgical neck of the humerus

Structures passing through the space • Axillary nerve • Posterior circumflex humeral vessels

Applied anatomy The fracture of surgical neck of humerus may damage the axillary nerve leading to paralysis of deltoid muscle. ❖ Write briefly about the upper triangular space.

The upper triangular space (Fig. 2.8) is one of the subscapular intermuscular spaces present in the region of axilla.

Boundaries Superomedial: Teres minor Lateral: Long head of the triceps brachii Inferior: Teres major

Structure passing through the space The circumflex scapular artery which interrupts the origin of the teres minor to reach the infraspinous fossa.

Applied anatomy The circumflex scapular artery anastomoses with the suprascapular and deep branch of the transverse cervical arteries to form an important arterial anastomosis around scapula. ❖ Write briefly about the lower triangular space. The lower triangular space (Fig. 2.8) is one of the subscapular intramuscular spaces.

Boundaries Medial: Long head of the triceps brachii Lateral: Shaft of humerus Superior: Teres major

Structures passing through this space • Radial nerve • Profunda brachii vessels

Applied anatomy The fracture of middle-third of humerus may damage radial nerve leading to wrist

drop.

3

Arm ❖ Enumerate the muscles on the front of arm and give their nerve supply.  AN11.1 The muscles on the front of arm are • Biceps brachii • Coracobrachialis • Brachialis All these muscles are supplied by the musculocutaneous nerve. ❖ Draw the transverse section of arm at the level of insertion of coracobrachialis to show the arrangement of various structures. The transverse section of arm is given in Fig. 3.1.

FIG. 3.1 Transverse section of arm at the insertion of coracobrachialis.

❖ Give the origin, insertion, nerve supply and actions of biceps brachii.  AN11.1

Origin Biceps brachii (Fig. 3.2) arises by two heads: • Long head arises from the supraglenoid tubercle of scapula (origin is intracapsular but extrasynovial). • Short head arises from the tip of coracoid process of scapula along with

coracobrachialis.

FIG. 3.2 Origin and insertion of biceps brachii.

Insertion By a tendon into the tuberosity of radius (posterior rough part).

Nerve supply Musculocutaneous nerve.

Actions • Flexor of elbow joint. • Supinator of forearm when elbow is flexed. • Long head keeps the head of humerus in position during abduction of shoulder joint. ❖ Name the joints at which biceps brachii acts and tell the movements that it produces at these joints.

• Biceps brachii acts at three joints: (a) shoulder joint, (b) elbow joint and (c) superior radioulnar joint. • Movements produced at these joints are (a) At shoulder joint: Flexion of arm (by short head) (b) At elbow joint: Flexion of forearm (c) At superior radioulnar joint: Supination of forearm when forearm is semiflexed in midprone position ❖ Give the origin, insertion, nerve supply and actions of coracobrachialis.  AN11.1

Origin From the tip of coracoid process of scapula along with the short head of biceps brachii.

Insertion In the middle of the medial border of the shaft of humerus.

Nerve supply Musculocutaneous nerve.

Actions Adducts the arm and flexes the shoulder joint. ❖ Give the origin, insertion, nerve supply and actions of brachialis.  AN11.1

Origin From lower half of the front of humerus and medial and lateral intermuscular septa.

Insertion Into coronoid process and tuberosity of ulna.

Nerve supply • Musculocutaneous nerve • Radial nerve (supplies only a small lateral part)

Action Flexor of elbow joint.

N.B. The brachialis is also termed workhorse of the elbow joint. ❖ Describe the musculocutaneous nerve in brief.  AN11.2

The musculocutaneous nerve, as its name implies, supplies the muscles of front of arm and skin on the lateral side of forearm (Fig. 3.3).

FIG. 3.3 Course and main branches of musculocutaneous nerve.

Origin From lateral cord of brachial plexus (C5, C6 and C7).

Course It arises obliquely from the lateral cord of brachial plexus behind pectoralis minor muscle. There it lies lateral to axillary artery. It pierces coracobrachialis muscle and reaches the lateral side of the arm. Then it runs laterally downwards between biceps brachii and brachialis muscles. At the crease of elbow, it pierces the deep fascia lateral to the tendon of biceps brachii from where it continues as lateral cutaneous nerve of forearm.

Branches Muscular: To coracobrachialis, biceps brachii and brachialis.

Cutaneous: Lateral cutaneous nerve of forearm to lateral side of forearm. Articular: To elbow joint.

Applied anatomy Isolated lesions of the musculocutaneous nerve are rare. ❖ Describe the brachial artery in brief and discuss its applied anatomy.  AN11.2

Origin The brachial artery is continuation of the axillary artery below the lower border of teres major muscle (Fig. 3.4).

FIG. 3.4 Brachial artery.

Course It runs downward to reach the cubital fossa where it terminates at the level of neck of

radius by dividing into radial and ulnar arteries.

N.B. It is superficial throughout its course.

Branches Apart from the muscular branches, the named branches of brachial artery are • Profunda brachii artery (largest branch) • Nutrient artery to humerus • Superior and inferior ulnar collateral arteries

Applied anatomy • Blood pressure is recorded by auscultating the pulsations of brachial artery in the cubital fossa medial to tendon of biceps brachii. • Brachial artery can be compressed digitally at midarm against the tendon of coracobrachialis on the medial side of the humerus. • Brachial artery may be ruptured in supracondylar fracture of humerus. ❖ Write a short note on profunda brachii artery.   AN11.2

Origin It is the largest (main) branch of brachial artery arising just below the lower border of teres major muscle.

Course The artery accompanies the radial nerve posteriorly in the radial groove, deep to triceps. In radial groove, it gives various branches.

Branches (fig. 3.5) Apart from muscular branches, the name of branches of profunda brachii artery are: 1. Nutrient artery to humerus near the deltoid tuberosity. 2. Ascending branch, ascends between long and lateral heads of triceps to anastomose with posterior circumflex humeral artery. 3. Radial collateral artery is the continuation of the profunda brachii artery and pierces the lateral intermuscular septum with the radial nerve, reaches the elbow and anastomoses with the radial recurrent artery. 4. Middle collateral artery, also called posterior descending branch, descends through the medial head of triceps, reaches the elbow and anastomoses with the interosseus recurrent artery.

FIG. 3.5 Profunda brachii artery.

Applied anatomy Branches of profunda brachii artery take part in the formation of arterial anastomosis around elbow. ❖ Enumerate the various anatomical events that occur at the level of insertion of coracobrachialis. The anatomical events occurring at the level of insertion of coracobrachialis are: • Circular shaft of humerus becomes triangular below this level. • Deltoid and coracobrachialis are inserted at this level. • Upper end of origin of brachialis extends up to this level. • Brachial artery passes from medial side of arm to its anterior aspect. • Basilic vein pierces the deep fascia at this level. • Median nerve crosses in front of brachial artery from lateral to medial side. • Radial nerve pierces lateral intermuscular septum to pass from the posterior compartment of arm to the anterior compartment of arm. • Ulnar nerve pierces medial intermuscular septum to go from the anterior compartment of arm to the posterior compartment of arm. • Medial cutaneous nerves of arm and forearm pierce the deep fascia at this level. • Nutrient artery pierces the humerus at this level. Therefore, the site of insertion of coracobrachialis is an important anatomical

landmark in the arm. ❖ Enumerate the contents of posterior compartment of the arm.  AN11.1 The contents of posterior compartment of arm are: • Triceps brachii muscle • Radial nerve • Profunda brachii artery ❖ Give the origin, insertion, nerve supply and actions of triceps brachii.  AN11.1

Origin Triceps brachii muscle (Fig. 3.6) arises by three heads – long, lateral and medial.

FIG. 3.6 Origin and insertion of triceps brachii.

Long head: From infraglenoid tubercle of scapula. Lateral head:

From oblique ridge above the spiral groove (i.e. lateral lip of the spiral groove). Medial head: From posterior surface of shaft of humerus below the level of spiral groove.

Insertion Into the posterior part of the superior surface of olecranon process of ulna.

Nerve supply Radial nerve (C7, C8). Note. Each head is supplied by a separate branch. The branch supplying long head arises in axilla, the branch supplying lateral head arises in spiral groove and the branch supplying medial head arises both in axilla and spiral groove.

Action Extensor of elbow. ❖ Write a short note on the arterial anastomosis around the elbow joint.  AN11.6 The arterial anastomosis around the elbow joint (Fig. 3.7) is formed between the branches of the following arteries: • Brachial artery • Radial artery • Ulnar artery

FIG. 3.7 Arterial anastomosis around elbow joint. L, lateral epicondyle; M, medial epicondyle.

(For details, see p. 31) ❖ Write a short note on cubital fossa.  AN11.5 Cubital fossa (Fig. 3.8) is a triangular hollow in front of the elbow joint.

FIG. 3.8 Boundaries and contents of cubital fossa.

Boundaries • Base is formed by an imaginary horizontal line, joining the medial and lateral epicondyles of the humerus. • Medial wall is formed by pronator teres. • Lateral wall is formed by brachioradialis. • Roof is formed by skin, superficial fascia, deep fascia, and bicipital aponeurosis. The superficial fascia contains median cubital vein, lateral cutaneous nerve of forearm and medial cutaneous nerve of forearm. • Floor is formed by brachialis muscle in the upper and medial part, and supinator muscle in the lower and lateral part. • Apex is a point where pronator teres disappears underneath the brachioradialis muscle.

Contents From medial to lateral side: • Median nerve • Brachial artery • Biceps tendon • Superficial branch of radial nerve Mnemonic: MBBS.

Applied anatomy • The brachial artery is auscultated in cubital fossa for recording the blood pressure. • The median cubital vein is used in the region of cubital fossa for venipuncture, as it lies superficial to bicipital aponeurosis and is the most fixed vein.

4

Forearm Front of forearm ❖ Describe the flexor retinaculum at wrist in brief.  AN12.3 The flexor retinaculum is a strong fibrous band formed by the thickening of deep fascia in front of carpal bones (anatomical wrist). It bridges the anterior concavity of carpus and converts it into an osseofibrous tunnel called carpal tunnel.

Attachments (fig. 4.1) It is rectangular in shape and attached as follows: • Medially, to pisiform bone and hook of Hamate • Laterally, to tubercle of scaphoid and crest of trapezium

FIG. 4.1 Attachments of flexor retinaculum on carpal bones/bones of carpus.

N.B. On either side, the retinaculum gives a slip: (a) A superficial slip on medial side (volar carpal ligament) is attached to the pisiform bone. The ulnar artery and nerve passes deep to this slip. (b) A deep slip on lateral side is attached to the medial lip of the groove on trapezium, converting this groove into a tunnel, which provides passage to the tendon of flexor carpi radialis.

Features • Converts the concavity of carpus into an osseofibrous tunnel – the carpal tunnel. • Proximally, it gives attachment to the tendon of palmaris longus. • Distally, it gives attachment to the apex of palmar aponeurosis.

Superficial relations These are (Fig. 4.2) • Ulnar artery and nerve • Palmar cutaneous branch of median nerve • Tendon of palmaris longus • Superficial palmar branch of radial artery

FIG. 4.2 Flexor retinaculum: A, formation at the level of proximal row of carpal bones (I) and formation at the level of distal row of carpal bones (II); B, structures passing deep to the flexor retinaculum (i.e. through carpal tunnel). FDP, flexor digitorum profundus; FDS, flexor digitorum superficialis.

❖ Enumerate the structures passing deep to the flexor retinaculum/carpal tunnel.  AN12.3 The structures passing deep to the flexor retinaculum are (Fig. 4.2) • Median nerve • Four tendons of the flexor digitorum superficialis • Four tendons of the flexor digitorum profundus • Tendon of the flexor pollicis longus • Ulnar bursa

• Radial bursa

N.B. The tendon of the flexor carpi radialis passes between the two slips of retinaculum through the groove of the trapezium. ❖ Enumerate the superficial muscles on the front of forearm.  AN12.1 They are five in number. From medial to lateral side, these are • Flexor carpi ulnaris • Palmaris longus • Flexor digitorum superficialis • Flexor carpi radialis • Pronator teres

N.B. All the superficial muscles on the front of forearm are supplied by the median nerve except flexor carpi ulnaris, which is supplied by the ulnar nerve. ❖ Give the origin, insertion, nerve supply and actions of pronator teres.  AN12.1

Origin It arises by two heads (Fig. 4.3).

FIG. 4.3 Origin and insertion of pronator teres.

Humeral head: From the lower part of the medial epicondyle of the humerus. Ulnar head: From the medial border of the coronoid process of ulna.

Insertion (fig. 4.3) Into the lateral surface of the radius at its maximum convexity (middle of the lateral border of the radial shaft).

Nerve supply Median nerve as it passes between its two heads of pronator teres.

Action Pronation of the forearm. ❖ Give the origin and insertion of superficial muscles of the forearm in a tabular form.   AN12.1 Muscle

Origin

Insertion

Pronator teres

Flexor carpi radialis Palmaris longus

Medial epicondyle of humerus and coronoid process of ulna Medial epicondyle of humerus Medial epicondyle of humerus

Flexor digitorum superficialis • Medial epicondyle (FDS) of humerus • Humeroulnar • Medial border of head coronoid process of • Radial head ulna • Anterior oblique line of shaft of radius Flexor carpi • Medial epicondyle ulnaris of humerus • Humeral head • Posterior border of • Ulnar head ulna

Middle of lateral aspect of shaft of radius

Bases of 2nd and 3rd metacarpal bones

Flexor retinaculum and apex of palmar aponeurosis

Muscle divides into four tendons; each tendon divides into two slips that are inserted onto the sides of middle phalanges of medial four fingers

Pisiform bone: Insertion is prolonged further to be attached to the hook of hamate and base of 5th metacarpal bone forming pisohamate and pisometacarpal ligaments

N.B. The five superficial muscles on the front of forearm have common origin from medial epicondyle of humerus, which is termed ‘common flexor origin’. ❖ Enumerate the deep muscles on the front of forearm.  AN12.1 These are three in number as follows: • Flexor pollicis longus (FPL) • Flexor digitorum profundus (FDP) • Pronator quadratus ❖ Give the origin and insertion of deep muscles on the front of forearm in a tabular form.  AN12.1 Muscle Origin Flexor • Upper threedigitorum fourth of the profundus anterior and (FDP) medial surfaces of the shaft of ulna • Upper threefourth of the

Insertion Muscle forms four tendons to be inserted into medial four fingers; opposite the proximal phalanx of the corresponding digit, each tendon perforates the tendon of the flexor digitorum superficialis before being inserted on the palmar surface of the base of the corresponding distal phalanx

posterior border of ulna • Medial surface of the olecranon and coronoid processes of ulna • Adjoining part of interosseous membrane Flexor • Upper threeInto the palmar surface of the distal phalanx of the thumb pollicis fourth of the longus anterior surface of (FPL) the shaft of radius below anterior oblique line • Adjoining part of interosseous membrane Pronator Lower oneLower one-fourth of the anterolateral aspect of the shaft of quadratus fourth of the radius above ulnar notch anteromedial aspect of the shaft of ulna

N.B. All the deep muscles on the front of forearm are supplied by anterior interosseous nerve (C8, T1) – a branch of median nerve except medial half of FDP, which is supplied by ulnar nerve. ❖ Enumerate the structures on the front of the wrist.  AN12.2 From lateral to medial side, these are (Fig. 4.4) • Radial artery • Tendon of flexor carpi radialis (FCR) • Median nerve • Tendon of palmaris longus • Tendon of flexor digitorum superficialis (FDS) • Ulnar artery • Ulnar nerve • Tendon of flexor carpi ulnaris

FIG. 4.4 Structures lying in front of the wrist.

Back of forearm ❖ Describe the extensor retinaculum at wrist in brief.  AN12.14 The extensor retinaculum is a strong fibrous band about 2 cm broad running obliquely downwards and medially on the back of the wrist. It is formed by the thickening of deep fascia. It holds the extensor tendons in place.

Attachments Laterally to: Lower 2 cm of anterior border of radius. Medially to: • Styloid process of ulna • Triquetral bone • Pisiform bone

Compartments Space deep to extensor retinaculum is divided into six osseo-fascial compartments by septa, extending from retinaculum to the ridges on the dorsal aspect of the lower ends of radius and ulna. The compartments are numbered I–VI from lateral to medial side. ❖ Enumerate the structures passing through various compartments underneath the extensor retinaculum.  AN12.14 The structures passing through various compartments underneath the extensor retinaculum are (Fig. 4.5):

Compartment I

Structure passing through • Abductor pollicis longus (APL)

II

• Extensor pollicis brevis (EPB) • Extensor carpi radialis longus (ECRL)

III

• Extensor carpi radialis brevis (ECRB) • Extensor pollicis longus (EPL)

V

• Extensor digitorum (ED) • Extensor indicis (EI) • Posterior interosseous nerve • Anterior interosseous artery • Extensor digiti minimi (EDM)

VI

• Extensor carpi ulnaris (ECU)

IV

FIG. 4.5 Transverse section of forearm just above the wrist showing structures passing deep to the extensor retinaculum.

❖ Enumerate the superficial muscles on the back of forearm.  AN12.11 They are seven in number as follows: • Anconeus • Brachioradialis • Extensor carpi radialis longus • Extensor carpi radialis brevis • Extensor digitorum • Extensor digiti minimi • Extensor carpi ulnaris ❖ Give the origin and insertion of superficial muscles on the back of forearm.  AN12.11 Muscle Anconeus Brachioradialis

Origin Posterior aspect of lateral epicondyle of humerus Upper two-third of lateral

Insertion Lateral surface of olecranon process of ulna Base of styloid process of radius

Extensor carpi radialis longus (ECRL) Extensor carpi radialis brevis (ECRB) Extensor digitorum (ED) Extensor digiti minimi (EDM) Extensor carpi ulnaris (ECU)

supracondylar ridge of humerus Lower one-third of lateral supracondylar ridge of humerus

Posterior surface of base of 2nd metacarpal bone

Anterior aspect of lateral epicondyle of humerus

Posterior surface of base of 3rd metacarpal bone

Anterior aspect of lateral epicondyle of humerus Anterior aspect of lateral epicondyle of humerus Anterior aspect of lateral epicondyle of humerus

By four tendons on bases of middle phalanges of 2nd to 5th digits Extensor expansion of little finger Base of 5th metacarpal bone

N.B. • All the superficial muscles on the back of forearm except anconeus and brachioradialis and ECRL arise by a common extensor tendon from the anterior aspect of lateral epicondyle of humerus. This is termed common extensor origin. • All the muscles on the back of forearm are supplied by deep branch of radial nerve (posterior interosseous nerve except anconeus, brachioradialis and ECRL, which are supplied by radial nerve directly). ❖ Give the origin, insertion, nerve supply and actions of the brachioradialis.  AN12.11

Origin Upper two-third of the lateral supracondylar ridge of the humerus (Fig. 4.6).

FIG. 4.6 Origin and insertion of brachioradialis.

Insertion Lateral aspect of lower end of radius just above its styloid process (Fig. 4.6).

Nerve supply Radial nerve (C5, C6).

Actions • Flexion of the elbow in the midprone position as required when carrying the apron over the shoulder. • Actively involved in alternate movements of flexion and extension of elbow, acting like a shunt muscle. • It also helps in both supination and pronation.

N.B. It is flexor of the elbow, although it is supplied by a nerve of extensor compartment of forearm.

❖ Enumerate the deep muscles on the back of forearm.  AN12.11 These are five in number and as follows: • Supinator • Abductor pollicis longus (APL) • Extensor pollicis brevis (EPB) • Extensor pollicis longus (EPL) • Extensor indicis ❖ Give the origin and insertion of deep muscles on the back of forearm in a tabular form.  AN12.11 Muscle Supinator

Abductor pollicis longus Extensor pollicis brevis Extensor pollicis longus Extensor indicis

Origin • Supinator crest and supinator fossa of ulna • Lateral epicondyle of humerus, annular ligament of superior radioulnar joint Posterior surface of shaft of radius (upper part) and shaft of ulna (middle one-third) Lower one-third of posterior surface of shaft of radius

Insertion Neck and upper one-third of shaft of radius (between anterior and posterior oblique lines)

Base of 1st metacarpal bone

Base of proximal phalanx of thumb

Middle one-third of posterior surface of shaft of ulna

Base of distal phalanx of thumb

Lower part of posterior surface of shaft of ulna

Extensor expansion of index finger

N.B. All the muscles on the back of forearm are supplied by posterior interosseous nerve (deep branch of radial nerve). ❖ Give the origin, insertion, nerve supply and action of the supinator muscle.  AN12.11

Origin (fig. 4.7) Deep part: From supinator crest of ulna and triangular area in front of it (supinator fossa).

FIG. 4.7 Origin and insertion of supinator muscle.

Superficial part: From lateral epicondyle of humerus, radial collateral ligament and annular ligament.

Insertion (fig. 4.7) Upper one-third of the lateral surface of the radius between anterior and posterior oblique lines.

Nerve supply Posterior interosseous nerve (i.e. deep branch of the radial nerve [C6, C7]).

Action Supination of the forearm. ❖ Describe the posterior interosseous nerve in brief.  AN12.12 It is the deep terminal branch of the radial nerve (Fig. 4.8).

FIG. 4.8 Branches of posterior interosseous nerve.

Origin It arises from radial nerve just above cubital fossa in front of lateral epicondyle.

Course The nerve winds around the lateral side of radius and passes through the supinator muscle (between its superficial and deep laminae) to appear on the back of forearm.

Termination On the back of wrist where it ends by forming a pseudoganglion.

Branches • In the cubital fossa, it supplies: • Extensor carpi radialis brevis • Supinator (as it passes through the muscle) • In the back of forearm, it supplies: • Abductor pollicis longus • Extensor pollicis brevis

• Extensor pollicis longus • Extensor digitorum • Extensor indicis • Extensor digiti minimi • Extensor carpi ulnaris

Applied anatomy The lesion of posterior interosseous nerve produces wrist drop due to unopposed action of the flexor muscles.

5

Hand Palm of the hand ❖ Describe the palmar aponeurosis briefly and discuss its applied anatomy. The palmar aponeurosis (Fig. 5.1) is the thick central part of the deep fascia of the palm. It is triangular in shape with its apex facing proximally and base facing distally. It overlies the superficial palmar arch, long flexor tendons, terminal part of the median nerve and superficial branch of the ulnar nerve.

FIG. 5.1 Palmar aponeurosis.

Attachments Apex: It is attached to the flexor retinaculum and provides insertion to the tendon of palmaris longus.

Base: Just proximal to the heads of metacarpals, divides into four longitudinal slips – one for each medial four digits. Each slip has a superficial and a deep set of fibres. The superficial fibres are attached to the skin of fingers at their roots. The deep fibres blend with the fibrous flexor sheaths and are also connected to deep transverse ligaments of palm.

Relations • Between the slips (in the web spaces of fingers), the digital nerve and vessels emerge to pass distally. • From the medial and lateral borders of palmar aponeurosis, medial and lateral intermuscular septa extend inwards and get attached to 5th and 1st metacarpals, respectively. These septa divide the palm into compartments.

Functions • Protects the underlying tendons, nerves and vessels • Helps to improve the grip of hand by fixing the skin of the palm

Applied anatomy The progressive contraction of medial part of palmar aponeurosis produces a deformity called Dupuytren’s contracture. The little and ring fingers are usually involved. The proximal and middle phalanges become flexed and cannot be straightened. The distal phalanges, however, remain unaffected or may become hyperextended (Fig. 5.2).

FIG. 5.2 Dupuytren’s contracture.

❖ Enumerate the intrinsic muscles of the hand.  AN12.5 These are given next. Subcutaneous muscle • Palmaris brevis Muscles of thenar eminence • Abductor pollicis brevis • Flexor pollicis brevis • Opponens pollicis Adductor of thumb • Adductor pollicis Muscles of hypothenar eminence • Abductor digiti minimi • Flexor digiti minimi • Opponens digiti minimi

Lumbricals • Four in number • Numbered from lateral to medial side (1, 2, 3 and 4) Interossei • Palmar interossei (four in number) • Dorsal interossei (four in number)

N.B. All the intrinsic muscles of the hand are supplied by ulnar nerve except muscles of thenar eminence and lateral two (i.e. 1st and 2nd) lumbricals, which are supplied by the median nerve. ❖ Write a short note on adductor pollicis.  AN12.5 It is a fan-shaped deeply placed muscle in the lateral part of hand (Fig. 5.3).

FIG. 5.3 Origin and insertion of adductor pollicis muscle. H, hamate; C, capitate; T, trapezoid; Tr, trapezium.

Origin (a) Oblique head: From capitate, and bases of 2nd and 3rd metacarpals. (b) Transverse head: From linear ridge on the middle of the palmar surface of 3rd metacarpal.

Insertion Two heads converge and meet to form a tendon, which is inserted into the medial side

of base of proximal phalanx of the thumb and often contains a sesamoid bone. Nerve supply: By deep branch of ulnar nerve (C8, T1). Action: Adduction of thumb towards other fingers as in power grip. ❖ Give the origin, insertion, nerve supply and actions of lumbrical muscles.  AN12.5 The origin and insertion of lumbrical muscles are presented in Table 5.1 and Fig. 5.4.

FIG. 5.4 Lumbrical muscles.

TABLE 5.1 Origin and Insertion of Lumbrical Muscles Origin From four tendons of FDP • First, from lateral side of tendon of 2nd digit • Second, from lateral side of tendon of 3rd digit • Third, from adjacent sides of tendons of 3rd and 4th digits • Fourth, from adjacent sides of tendons of 4th and 5th digits

Insertion Via extensor expansion on to the dorsum of bases of distal phalanges

N.B. First and 2nd lumbricals are unipennate, while 3rd and 4th lumbricals are bipennate.

Nerve supply First and 2nd lumbricals are supplied by median nerve, whereas 3rd and 4th lumbricals are supplied by deep branch of ulnar nerve.

Actions Flexion of metacarpophalangeal (MP) joints and extension of proximal and distal interphalangeal (PIP + DIP) joints. ❖ What are interossei muscles? Describe their origin, insertion, nerve supply and actions in brief.   AN12.5 The interossei are small muscles present between the metacarpals. They are divided into two groups: palmar interossei and dorsal interossei; each group consists of four muscles.

Origin and insertion The origin and insertion of interossei muscles are presented in Table 5.2 and Fig. 5.5.

FIG. 5.5 Interosseous muscles: A, palmar interossei; B, dorsal interossei.

TABLE 5.2 Origin and Insertion of Interossei Muscles Muscle Origin Palmar interossei • Arise from (unipennate, four in metacarpals number) • First from medial side of base of 1st metacarpal • Second from medial

Insertion • Inserted through dorsal digital expansion • First and 2nd on the medial side of the bases of proximal phalanges of thumb and index finger, respectively • Third and 4th on the lateral side of the bases of phalanges of ring and little finger, respectively

Dorsal interossei (bipennate, four in number)

side of 2nd metacarpal • Third from lateral side of 4th metacarpal • Fourth from lateral side of 5th metacarpal • First from adjacent Via extensor expansion into dorsum of bases of sides of 1st and 2nd proximal phalanges of 2nd, 3rd and 4th digits metacarpals • Second from adjacent sides of 2nd and 3rd metacarpals • Third from adjacent sides of 3rd and 4th metacarpals • Fourth from adjacent sides of 4th and 5th metacarpals

Nerve supply All the interossei are supplied by the deep branch of the ulnar nerve.

Actions Palmar interossei adduct the digits while dorsal interossei abduct the digits. Mnemonic: PAD and DAB (D, dorsal; P, palmar; AD, adductor; AB, abductor) ❖ Write a short note on dorsal digital expansion.  AN12.9 Each tendon of extensor digitorum flattens to form an aponeurotic expansion over the dorsal aspect of MCP joint, which covers the dorsum and sides of the proximal phalanx like a hood. At the PIP joint, the aponeurotic expansion divides into three slips: a central slip and two collateral slips. The central slip is attached to the base of the middle phalanx and the two lateral slips join each other to form a single slip which is attached to the dorsal aspect of the base of distal phalanx. The margins of the extensor expansion are reinforced by intrinsic muscles of the hand – the interossei and lumbrical muscles (Fig. 5.6).

FIG. 5.6 Dorsal digital expansion of left middle finger and insertion of lumbricals and interossei into it.

Functional significance of the dorsal digital expansion The intrinsic muscles arising from the palmar aspect of the hand and inserting along the dorsal aspect of the fingers can have unique function in that they flex the metacarpophalangeal (MP) joints, and extend the proximal and distal interphalangeal (i.e. PIP and DIP) joints. ❖ What are fascial spaces of the hand?  AN12.10 A number of fascial spaces in the region of hand are formed due to arrangement of fasciae and fascial septa. These are as follows. Palmar spaces • Midpalmar space • Thenar space • Pulp space Dorsal spaces • Dorsal subcutaneous space • Dorsal subaponeurotic space Parona’s space • Fascial space in front of distal forearm ❖ Write a short note on midpalmar space.  AN12.10

It is a triangular space located under the inner half of the hollow of the palm.

Boundaries (fig. 5.7) Anterior: From superficial to deep, the structures forming anterior boundary are palmar aponeurosis, superficial palmar arch, ulnar bursa enclosing flexor tendons of middle, ring and little fingers, and 2nd, 3rd and 4th (medial three) lumbricals.

FIG. 5.7 Cross-section of hand showing palmar spaces and spaces on the dorsum of the hand.

Posterior: Fascia covering the interossei of the 3rd and 4th spaces. Lateral: Oblique intermediate palmar septum extending from palmar aponeurosis to 3rd metacarpal bone, which separates it from thenar space. Medial: Medial palmar septum extending from palmar aponeurosis to 5th metacarpal bone, which separates it from hypothenar muscles. Proximally: It is continuous with the Parona’s space situated deep to the flexor tendons and in front of pronator quadratus. Distally: It continues as extensions around lumbrical canals to web spaces of medial three fingers.

Applied anatomy This space is primarily infected by puncture wounds. It may be involved secondarily due to infection spreading from digital synovial sheaths of flexor tendons. From here, the infection may spread to Parona’s space. If this space is infected, then there is tenderness in the palm over the area of midpalmar space and painful flexion of little, ring and middle fingers. The pus from midpalmar space can be drained by an incision into 3rd or 4th web space, depending on where the pus points. ❖ Write a short note on thenar space.   AN12.10 It is a triangular space located under the outer half of the hollow of palm.

Boundaries (fig. 5.7) Anterior: Flexor tendons of index finger, 1st lumbrical and palmar aponeurosis. Posterior: Fascia covering transverse head of adductor pollicis and 1st dorsal interosseous muscle. Medial: Oblique intermediate palmar septum, which separates it from midpalmar space. Lateral: Lateral palmar septum extending from palmar aponeurosis to 1st metacarpal. Proximally: It is continuous with Parona’s space. Distally: Extends around the 1st lumbrical (1st lumbrical canal) to 1st web space.

Applied anatomy Primary infection to thenar space occurs through puncture wounds. Secondary infection may be due to infection spreading from digital synovial sheath of index finger. This space can be drained by an incision in the 1st web space or where the pus points. ❖ Write a short note on pulp space.  AN12.10 It is a closed subcutaneous space in front of distal phalanx of each digit (Fig. 5.8).

FIG. 5.8 Pulp space of finger.

Boundaries In front and sides: Skin. Behind: Distal two-third of distal phalanx.

Features The space is divided into many compartments by fibrous septa extending between the skin and the bone. The proximal one-fifth of the distal phalanx is outside the pulp space and corresponds to the epiphysis of the bone, which receives its blood supply from epiphyseal artery – a branch of digital artery that does not pass through pulp space. The distal four-fifth of distal phalanx lies within the space and receives its blood supply from digital artery, which runs through the space.

Applied anatomy The infection of the pulp space is called whitlow. It can produce necrosis of the distal four-fifth of the phalanx due to occlusion of digital artery. The complete regeneration is possible because the proximal epiphyseal portion of phalanx remains unaffected. ❖ Write a short note on Parona’s space.  AN12.10 It is a rectangular fascial space located in front of distal forearm.

Boundaries Proximally: It extends up to the origin of flexor digitorum superficialis from anterior oblique line of

radius. Distally: It is continuous with fascial spaces in palm. Superficially: Long flexor tendons. Deep: Pronator quadratus.

Applied anatomy Infection from palmar spaces may extend proximally into this space and form an hourglass swelling. ❖ Describe the ulnar and radial bursae in brief.  AN12.9

Ulnar bursa (fig. 5.9) • It is a large synovial sac that encloses the tendons of flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS). • Proximally, it extends up to 2.5 cm above the flexor retinaculum and distally up to proximal one-third of the metacarpal bones. • Distally, on the medial side, it is continuous with the digital synovial sheath of the little finger.

FIG. 5.9 Synovial sheaths of long flexor tendons of thumb and fingers.

Radial bursa (fig. 5.9) • It is synovial sheath around the tendon of flexor pollicis longus. • Proximally, it extends about 2.5 cm above the flexor retinaculum and distally continuous with the synovial sheath of the thumb.

N.B. Digital synovial sheaths enclose the long flexor tendons in front of digits and extend from the level of the neck of the metacarpal bones up to the insertion of these tendons into the base of distal phalanges.

Dorsum of the hand ❖ Write a short note on anatomical snuffbox. It is an elongated triangular depression seen on the dorsal aspect of 1st metacarpal when the thumb is hyperextended.

Boundaries (fig. 5.10) Medial: Tendon of extensor pollicis longus.

FIG. 5.10 Boundaries and contents of anatomical snuffbox.

Lateral

• Tendon of abductor pollicis longus • Tendon of extensor pollicis brevis Floor: Scaphoid, trapezium. Roof: Deep fascia stretching between the medial and lateral boundaries. Contents • Radial artery

Structures crossing the roof • Cephalic vein • Terminal branches of superficial radial nerve

Applied anatomy • Tenderness in the region of anatomical box indicates fracture of scaphoid. • Pulsations of radial artery can be felt at this site. ❖ What is dorsal subaponeurotic space? Give its applied importance.  AN12.10 The dorsal subaponeurotic space (Fig. 5.7) lies between the aponeurotic sheath and the dorsal surfaces of medial four metacarpals and the dorsal interossei. On the dorsum of hand, the extensor tendons of the fingers are bound to one another by oblique bands of deep fascia in such a manner as to form an aponeurotic sheath, which is attached to the borders of 2nd and 5th metacarpals on the lateral and medial sides, respectively.

Applied anatomy The primary infection of this space is due to wounds on the dorsum. The space may be involved secondarily due to infections spreading from midpalmar space via the lymphatics. ❖ Give sensory innervation of the palmar aspect of the hand.  AN12.7 • Lateral two-third of palm and lateral 3½ digits are supplied by the median nerve. • Medial one-third of palm and medial 1½ digits are supplied by the ulnar nerve. • It is shown in Fig. 5.11.

FIG. 5.11 Sensory innervation of palmar aspect of the hand.

❖ Give sensory innervation of the dorsal aspect of the hand.  AN12.7 • Lateral two-third of the dorsum of hand and lateral 3½ digits are innervated by the radial nerve. • Medial one-third of the dorsum of hand and medial 1½ digits are innervated by the ulnar nerve. It is shown in Fig. 5.12.

FIG. 5.12 Sensory innervation of dorsal aspect of the hand.

N.B. The skin on the dorsal aspect of distal phalanges of lateral 3½ digits is innervated by the median nerve, while that of medial 1½ digits by the ulnar nerve.

6

Vessels of the upper limb Arteries ❖ What is axis artery of upper limb? Enumerate the various arteries that represent the axis artery in the adult. • The axis artery is formed by the 7th cervical intersegmental artery. • In the adult, it persists in the form of the following arteries: ■ Axillary artery ■ Brachial artery ■ Anterior interosseous artery ■ Deep palmar arch ❖ Give a brief account of the axillary artery.  AN10.2 See p. 15. ❖ Give a brief account of the brachial artery.  AN11.2 See p. 30. ❖ Describe the radial artery in brief.  AN12.2

Origin It is the artery of lateral side of the forearm. It arises in the cubital fossa, 1 cm below the bend of the elbow, as a smaller terminal branch of the brachial artery.

Course and termination It runs downwards along the lateral side of the front of forearm to reach the distal end of radius. At the wrist, the radial artery winds dorsally passing deep to the tendons of abductor pollicis longus and extensor pollicis brevis to enter the anatomical snuffbox on dorsolateral part of the hand. It enters the palm by passing between the two heads of 1st dorsal interosseous muscle and terminates by forming the deep palmar arch.

Branches 1. Radial recurrent artery

2. Dorsal carpal branch 3. Palmar carpal branch 4. First dorsal metacarpal artery – on dorsum of hand 5. Superficial palmar branch. 6. Arteria princeps pollicis 7. Arteria radialis indicis

Applied anatomy The pulsations of radial artery can be felt at two sites: (a) laterally in front of the distal one-third of radius (radial pulse) and (b) in the anatomical snuffbox. ❖ Write a short note on ulnar artery.  AN12.2

Origin • Ulnar artery is the larger terminal branch of the brachial artery. • It arises in the cubital fossa at the level of neck of radius 1 cm below the bend of the elbow. • In the upper one-third, it runs obliquely, downwards and medially while in the lower two-third, it runs vertically downwards along the medial side of the front of forearm to the lateral side of pisiform bone. • It enters palm by passing superficial to flexor retinaculum. In the palm, it forms superficial palmar arch. ❖ Enumerate the branches of ulnar artery.  AN12.2 • Anterior ulnar recurrent artery • Posterior ulnar recurrent artery • Common interosseous artery • Posterior interosseous artery through common interosseous artery • Palmar carpal branch • Dorsal carpal branch ❖ Describe the superficial palmar arch in brief and discuss its applied anatomy.  AN12.7 The superficial palmar arch is an important anastomosis between ulnar and radial arteries in the palm of the hand.

Formation (fig. 6.1) It is formed by the superficial palmar branch of the ulnar artery (the main continuation of ulnar artery). The arch is completed on the lateral side by one of the following arteries (Fig. 6.1): • Superficial palmar branch of the radial artery (most common)

• Princeps pollicis artery • Radialis indices artery

FIG. 6.1 Superficial and deep palmar arterial arches.

Note: The princeps pollicis and radial indices arteries are not the branches of deep palmar arch.

Location and branches • The superficial palmar arch lies superficial to the long flexor tendons with convexity directed distally. • It lies at the level of distal border of the fully extended thumb. • It gives off four palmar digital arteries, which supply medial 3.5 digits.

Applied anatomy The superficial palmar arch is one of the important anastomotic arterial channels for efficient blood supply to the hand in case of blockage of the radial or ulnar artery. ❖ Describe the deep palmar arch in brief and discuss its applied anatomy.  AN12.7

Formation It is formed by the continuation of radial artery in the palm. The arch is completed on the medial side by the deep branch of the ulnar artery (Fig. 6.1).

Location and branches The arch lies deep to long flexor tendons with convexity directed distally. It lies about 1 cm proximal to the superficial palmar arch (at the level of proximal border of the fully

extended thumb). It gives off the following branches: • Three palmar metacarpal arteries (to second, third and fourth interosseous spaces) • Three perforating arteries • Recurrent branches

Applied anatomy The deeper palmar arch is one of the important anastomotic arterial channels between the radial and ulnar arteries for efficient blood supply to the hand in the event of blockage of the radial or ulnar artery. ❖ Give a brief account of arterial anastomosis around the scapula and discuss its applied anatomy.   AN10.9 See p. 17. ❖ Give a brief account of anastomosis around the elbow joint (Fig. 6.2).  AN11.6 It is an arterial anastomosis around the elbow between the branches of brachial artery with the branches from upper ends of ulnar and radial arteries. The anastomoses take place in front and behind the two epicondyles of the humerus (also see Fig. 3.7).

FIG. 6.2 Arterial anastomosis around elbow joint.

In front of lateral epicondyle: Between the anterior descending branch (radial collateral artery) of the profunda brachii

artery and the radial recurrent artery – a branch of the radial artery. Behind the lateral epicondyle: Between the posterior descending branch (middle collateral artery) of the profunda brachii artery and the interosseous recurrent branch of the posterior interosseous artery. In front of medial epicondyle: Between the inferior ulnar collateral branch of the brachial artery and the anterior ulnar recurrent branch of the ulnar artery. Behind the medial epicondyle: Between the superior ulnar collateral branch of the brachial artery and the posterior ulnar recurrent artery – a branch of the ulnar artery. ❖ Enumerate the sites in the upper limb where arterial pulsations can be felt.  AN13.7 • Pulsations of axillary artery can be felt against the lateral wall of the axilla. • Pulsations of brachial artery can be felt: (a) on the medial side of midarm where it lies on the tendon of insertion of coracobrachialis and (b) in the cubital fossa medial to the tendon of biceps brachii. • Pulsations of radial artery can be felt: ■ At the wrist in front of lower end of radius lateral to the tendon of flexor carpi radialis ■ In the anatomical snuff box • Pulsations of ulnar artery can be felt at the wrist just lateral to the pisiform bone.

Veins ❖ Enumerate the veins of the upper limb.  AN13.7

Deep veins • Venae comitantes of radial and ulnar arteries • Venae comitantes of brachial artery • Brachial vein • Axillary vein

Superficial veins • Cephalic vein • Basilic vein • Median vein of forearm

❖ Give a brief account of axillary vein.  AN10.2

Commencement It begins as the continuation of basilic vein at the lower border of teres major.

Course It passes upwards to reach the axilla where it lies medial to axillary artery. At the outer border of 1st rib, it continues as the subclavian vein.

Tributaries • Brachial veins (at its commencement) • Cephalic vein near its termination • Veins corresponding to branches of the axillary artery, i.e. lateral thoracic vein, subscapular vein, etc. ❖ Give a brief account of cephalic vein.  AN12.2 The cephalic vein is the superficial preaxial vein of the upper limb (Fig. 6.3).

FIG. 6.3 Superficial veins on the front of upper limb.

Commencement, course and termination

Begins from the lateral side of dorsal venous arch of hand. It passes upwards across the roof of anatomical snuffbox on the dorsum of hand; then it curves around the radius to reach the front of forearm. It ascends on the lateral part of the front of forearm. One inch below the elbow, it gives the median cubital vein which joins the basilic vein on the medial side. Then it ascends lateral to biceps, and pierces deep fascia at the lower border of pectoralis major to enter the deltopectoral groove to reach the infraclavicular fossa. Here it takes a sharp turn backwards to pierce the clavipectoral fascia and ends in the axillary vein. At elbow, the greater part of its blood is drained into basilic vein through median cubital vein.

Tributaries • Unnamed veins from front and back of lateral side of forearm • Median cephalic vein (if present)

Applied anatomy It is used for intravenous injection.

N.B. Occasionally, a persistent embryonic vein passes in front of the clavicle linking the cephalic vein to external jugular vein. ❖ Describe the basilic vein in brief and discuss its applied anatomy.  AN12.2 It is the superficial postaxial vein of the upper limb (Fig. 6.3).

Commencement, course and termination • Begins from the medial side of the dorsal venous arch of hand. • Ascends on the medial border of the forearm. Then it curves forwards a little below elbow, to ascend on the front of the elbow. • One inch above the elbow, it is joined by the median cubital vein. • Then, it ascends on the medial side of the biceps and pierces the deep fascia in the middle of the arm. • Thereafter, it ascends medial to the brachial artery; and at the lower border of teres major it continues into the axilla as axillary vein.

Tributaries • Unnamed veins from front and back of medial side of forearm • Median cubital vein

Applied anatomy It is used for:

• Giving intravenous injections • Performing cardiac catheterization ❖ Give a brief account of the median cubital vein and discuss its applied anatomy.   AN11.2, AN11.3 The median cubital vein (Fig. 6.3) is a large communicating venous channel on the front of the elbow joining the cephalic vein with the basilic vein. It begins from cephalic vein 2.5 cm below the bend of elbow and runs upward and medially to join the basilic vein 2.5 cm above the bend of elbow. It shunts the blood from cephalic vein to the basilic vein. It is the most superficial vein in the body.

N.B. The median cubital vein is separated from brachial artery and median nerve by bicipital aponeurosis.

Applied anatomy The median cubital vein is the most preferred site for intravenous injections because: • It is easy to access, as the vein is superficial and prominent. • It is well supported by the underlying bicipital aponeurosis when elbow is extended. • It is anchored by a perforating vein to the deep veins so that it does not slip during the venepuncture.

7

Nerves of the upper limb ❖ Enumerate five main nerves that supply the upper limb. These are • Axillary nerve • Musculocutaneous nerve • Radial nerve • Median nerve • Ulnar nerve ❖ Describe the axillary nerve in brief and discuss its applied anatomy.  AN10.3, AN10.13

Root value Ventral rami of C5 and C6 (Fig. 7.1).

FIG. 7.1 Axillary nerve and its main branches.

Course and relations The axillary (or circumflex) nerve arises from the posterior cord of brachial plexus

posterior to third part of axillary artery. It passes posteriorly through the quadrangular space. Here it lies below the capsule of the shoulder joint. As it is about to pass behind the surgical neck of humerus, it terminates by dividing into anterior and posterior branches. The anterior branch (along with posterior circumflex artery) runs deep to deltoid muscle and supplies deltoid muscle and skin over it. The posterior branch supplies posterior part of deltoid and teres minor muscles. It pierces deep fascia to become upper lateral cutaneous nerve of arm.

Branches Muscular: To deltoid and teres minor. Nerves to teres minor possesses pseudoganglion. Cutaneous • Upper lateral cutaneous nerve of arm • Sensory innervation of skin over the lower half of deltoid

Applied anatomy The damage of axillary nerve in inferior dislocation of the shoulder joint and fracture of surgical neck of humerus will result in: • Paralysis of deltoid leading to loss of power of abduction from 15° to 90° • Loss of rounded contour of shoulder • Prominence of greater tubercle of humerus • Loss of cutaneous sensations over lower half of deltoid ‘regimental badge area of sensory loss’ ❖ Give a brief account of musculocutaneous nerve. AN11.2 See p. 30. ❖ Describe the radial nerve under the following headings: (a) root value; (b) origin, course and relations, (c) branches and distribution and (d) applied anatomy. AN12.2 The radial nerve is the thickest and largest nerve of the upper limb (Fig. 7.2).

FIG. 7.2 Radial nerve and its main branches.

Root value Ventral rami of C5, C6, C7, C8 and T1.

Origin, course and relations • It arises from the posterior cord of brachial plexus in axilla behind the third part of the axillary artery. It is the thickest and largest branch of the brachial plexus. • It courses successively through three regions: axilla, radial groove on the back of arm and front of forearm. On the front of forearm, it ends by dividing into superficial and deep terminal branches. The course and relations of radial nerve in three regions traversed by it are as follows. Axilla: In the axilla, the radial nerve lies against the muscles forming the posterior wall of axilla, i.e. subscapularis, teres major and latissimus dorsi. Then it passes through the lower triangular space between teres major, long head of triceps brachii and shaft of humerus. In axilla, it gives two muscular branches to supply long and medial heads of triceps and one cutaneous branch (posterior cutaneous nerve of arm). Radial groove

The radial nerve from axilla enters the radial groove through the lower triangular space, where it lies between the long and medial heads of triceps brachii along with profunda brachii artery. It leaves the radial groove by piercing the lateral intermuscular septum. In the radial groove, it gives three muscular branches to supply long and medial heads of triceps and anconeus and two cutaneous branches, i.e. lower lateral cutaneous nerve of arm and posterior cutaneous nerve of forearm. Front of arm: The radial nerve enters the lower anterolateral part of the front of arm and lies between brachialis on the medial side and brachioradialis and extensor carpi radialis longus on the lateral side. It supplies all these muscles. Forearm: The radial nerve enters the cubital fossa where in front of lateral epicondyle it ends by dividing into two terminal branches: (a) superficial terminal branch (superficial radial nerve) and (b) deep terminal branch (posterior interosseous nerve). Deep terminal branch (posterior interosseous nerve): It lies in the lateral part of cubital fossa, where it supplies extensor carpi radialis brevis and supinator muscles. Then it enters the back of forearm by passing through supinator muscle. Here, it supplies abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor digitorum, extensor indicis, extensor digiti minimi and extensor carpi ulnaris. At the back of wrist, it ends in a pseudoganglion, branches of which supply the wrist and distal radioulnar joints. Superficial branch (superficial radial nerve): It is regarded as the downward continuation of the trunk of radial nerve. It runs on the lateral side of the front of forearm accompanied by the radial artery in the upper twothird of forearm with radial artery being on its medial side. About 7 cm above the wrist, it curves posteriorly deep to tendon of brachioradialis to reach the anatomical snuff box. Here, it divides into four or five digital branches, which supply the skin of lateral half of dorsum of hand and lateral 2½ digits till their distal interphalangeal joints.

Branches and distribution In axilla • Muscular branches: Long and medial heads of triceps brachii • Cutaneous branches: Posterior cutaneous nerve of arm In radial groove • Muscular ■ Lateral head of triceps brachii ■ Medial head of triceps brachii

■ Anconeus • Cutaneous ■ Lower lateral cutaneous nerve of arm ■ Posterior cutaneous nerve of forearm • Vascular ■ To profunda brachii artery In the arm • Muscular ■ Brachioradialis ■ Extensor carpi radialis longus ■ Lateral part of brachialis (proprioceptive) In the forearm • Superficial terminal branch: Digital branches to supply the skin of lateral half of dorsum and lateral 3½ digits up to distal interphalangeal (DIP) joints. • Deep terminal branch (posterior interosseous nerve): Muscular branches to all the muscles of back of forearm except anconeus, brachioradialis and extensor carpi radialis longus.

Applied anatomy The effects of injury to the radial nerve at different levels are given in Table 7.1. TABLE 7.1 Sites of Radial Nerve Injury and Their Effects

FIG. 7.3 Wrist drop resulting from radial nerve injury.

❖ Give the effects of injury to the posterior interosseous nerve. AN12.2 The posterior interosseous nerve supplies all the muscles on the back of forearm except anconeus, brachioradialis and extensor carpi radialis longus. The posterior interosseous nerve is commonly injured in fracture or dislocation of the head of radius.

Effects • Paralysis of all the muscles on the back of forearm except extensor carpi radialis longus, brachioradialis and anconeus (which are supplied by radial nerve directly). • There is no wrist drop because extensor carpi radialis longus being a powerful muscle keeps the wrist joint extended. ❖ Describe the median nerve under the following headings: (a) root value, (b) course and relations, (c) branches and distribution and (d) applied anatomy. AN10.3, AN12.2 The median nerve is so called because it runs in the median plane of the forearm.

Root value Ventral rami of C5 to C8 and T1 (Fig. 7.4).

FIG. 7.4 Median nerve and its main branches.

Course and relations The median nerve is formed in the axilla by two roots – lateral root from lateral cord of brachial plexus and medial root from medial cord of brachial plexus. Then it courses successively through four regions: axilla, arm, forearm and palm of the hand. The medial root crosses the axillary artery to join the lateral root. Axilla: In the axilla, the median nerve lies first anterior and then lateral to the axillary artery. Arm: In the arm, the median nerve continues to run on the lateral side of brachial artery till the midarm (i.e. insertion of coracobrachialis), where it crosses in front of the brachial artery to lie on its medial side, and then passes anterior to elbow joint to enter the forearm. Forearm: In the forearm, the median nerve passes through cubital fossa lying medial to the brachial artery. It leaves the fossa between the two heads of pronator teres before crossing superficial to the ulnar artery from medial to lateral side and giving its anterior interosseous branch below this.

Then it passes deep to fibrous arch of flexor digitorum superficialis. It adheres to deep surface of flexor digitorum superficialis, and leaves the muscle, along its lateral border. About 5 cm above the wrist, it lies between the tendons of palmaris longus and flexor carpi radialis. It enters the palm through carpal tunnel under the flexor retinaculum, but in front of common synovial sheath enclosing tendons of flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP). Palm: In the palm at the distal border of flexor retinaculum, it ends by dividing into lateral and medial terminal branches. Before dividing into terminal branches, the median nerve gives off a recurrent muscular branch from its lateral side.

Branches and distribution (fig. 7.4) In axilla: No branch In arm: Muscular branch to pronator teres In the cubital fossa • Muscular branches to: ■ Flexor carpi radialis ■ Palmaris longus ■ Flexor digitorum superficialis In the forearm • Anterior interosseous nerve, which supplies: ■ Lateral half of FDP ■ Flexor pollicis longus ■ Pronator quadratus • Palmar cutaneous branch to supply lateral two-third of palm In the palm • Recurrent muscular branch, which supplies muscles of thenar eminence, i.e., abductor pollicis brevis, flexor pollicis brevis and opponens pollicis • Lateral terminal branch, which gives off digital nerves to supply both the sides of thumb and radial side of index finger Note: The digital branch to lateral side of index finger also supplies 1st lumbrical muscle. • Medial terminal branch, which gives off digital nerves to supply the adjacent sides of index and middle fingers and adjacent sides of index and little fingers

Note: The digital nerve to adjacent side of middle and ring finger also supplies 2nd lumbrical muscle.

N.B. The median nerve in the palm supplies: (a) all thenar muscles, (b) 1st and 2nd lumbricals, (c) skin of the lateral half of palm, and (d) skin of the lateral 3½ fingers including dorsal aspects of their distal phalanges.

Applied anatomy The effects of lesion to the median nerve depend on the site of lesion (Table 7.2). TABLE 7.2 Effects of Lesions of the Median Nerve

N.B. In case of suicidal cut above wrist, there is sensory loss over the thenar eminence because palmar cutaneous nerve is given just above the flexor retinaculum; but in case of carpal tunnel syndrome there is no sensory loss over the thenar eminence for the same reason. ❖ Write a short note on carpal tunnel syndrome. AN12.4 It occurs due to compression of median nerve in the carpal tunnel. The carpal tunnel is an osseofibrous tunnel formed by the anterior concavity of the corpus bridged by the flexor retinaculum. This tunnel is tightly packed with long flexor tendons of the fingers with their surrounding synovial sheaths and the median nerve.

Clinical features • Painful paraesthesia (i.e. burning pain or pins and needles) along the distribution of the median nerve to the palm and lateral 3½ fingers. • Weakness and wasting of thenar muscles. • No paraesthesia over the skin of thenar eminence because this area of skin is supplied by the palmar cutaneous branch of median nerve, which arises in the forearm proximal to flexor retinaculum. • It is more frequent in women than in men. • Intermittent attacks of pain are more common at night.

N.B. The causes of compression of median nerve in carpal tunnel include tenosynovitis and thickening of synovial sheaths of the long flexor tendons, myxoedema, arthritic changes in the carpal bones, etc. ❖ Describe the ulnar nerve under the following headings: (a) root value, (b) course and relations, (c) branches and distribution and (d) applied anatomy. AN10.3, AN12.2 The ulnar nerve is so named because it runs along the ulnar side of the upper limb.

Root value Ventral rami of C8 and T1 (Fig. 7.5). It also gets contribution from ventral ramus of C7.

FIG. 7.5 Ulnar nerve and its main branches. DT, deep terminal branch; ST, superficial terminal branch.

Course and relations It is the continuation of the medial cord of brachial plexus in the axilla. It courses successively through four regions: axilla, arm, forearm and hand, where it terminates by dividing into superficial and deep branches. The course and relations of ulnar nerve in these regions are as follows. Axilla: In axilla, the ulnar nerve lies between the axillary vein and the axillary artery on a deeper plane, medial to 3rd part of axillary artery. Arm It enters the arm by running downwards on the medial side of the brachial artery in its proximal part. At the midarm (i.e. at the level of insertion of coracobrachialis), it pierces the medial intermuscular septum to enter the back of arm. Here it descends to run in a groove on the back of medial epicondyle of humerus, where it can be palpated. Forearm: The ulnar nerve enters the front of forearm by passing between two heads of flexor carpi

ulnaris. Here it lies on medial part of flexor digitorum profundus. It is accompanied by the ulnar artery on its lateral side in the lower two-third of forearm. Hand: The nerve enters the palm by passing superficial to the flexor retinaculum and medial to ulnar artery. At the distal border of flexor retinaculum, it ends by dividing into superficial and deep terminal branches.

Branches and distribution In axilla and arm: No branches In forearm • Muscular branches to supply: ■ Flexor carpi ulnaris ■ Flexor digitorum profundus (medial half) • Palmar cutaneous branch: It arises at about midforearm and provides cutaneous innervation to skin of the hypothenar eminence. • Dorsal cutaneous branch: It arises about 5 cm above the wrist and gives off dorsal digital nerves to supply sensory innervation to dorsal aspects of the medial 1½ digits excluding their distal phalanges. In hand • Superficial terminal branch, which supplies: ■ Palmaris brevis muscle ■ Cutaneous innervation to medial one-third of palm and medial 1½ fingers, including their nail beds • Deep terminal branch, which supplies: ■ Medial two lumbricals ■ Muscles of hypothenar eminence (abductor digiti minimi, flexor digiti minimi and opponens digiti minimi) ■ All the interossei (three palmar and four dorsal) ■ Adductor pollicis

Applied anatomy The effects of lesion to the ulnar nerve depend on the site of lesion. The details are given in Table 7.3. TABLE 7.3 Effects of the Ulnar Nerve Lesions

Site of Causes Lesion Elbow • Fracture dislocation of the elbow joint • Entrapment of nerve in the cubital tunnela

Wrist

aCubital

Effects

• Atrophy and flattening of hypothenar muscles • Loss of adduction of thumb • Loss of adduction and abduction of medial four digits • Ulnar claw hand • Loss of sensation on medial 1½ digits, on both the dorsum and the palm of hand • Loss of sensation on anterior and posterior surfaces of medial 1½ digits including their nail beds • Cut wounds Same effects as in lesion at elbow except that there will be no loss of • Compression by sensation on the medial side of dorsum of hand and posterior volar carpal surfaces of medial 1½ digits ligament • Compression in Guyon’s tunnel

tunnel: It is formed by a tendinous arch connecting the two heads of flexor carpi ulnaris.

8

Joints of the upper limb ❖ Enumerate the components of shoulder complex. AN10.12 The shoulder complex consists of the following five components: • Glenohumeral joint (shoulder joint proper) • Acromioclavicular joint • Sternoclavicular joint • Subacromial joint (between coracoacromial arch and subacromial bursa) • Scapulothoracic joint (linkage between scapula and thoracic wall) The last two components are functional joints. ❖ Describe the shoulder joint (glenohumeral joint) under the following headings: (a) classification, (b) articular surfaces, (c) ligaments, (d) relations, (e) nerve supply, (f) movements and (g) applied anatomy. AN10.12

Classification Synovial joint of ball and socket type.

Articular surfaces They are formed by the large hemispherical head of humerus and shallow glenoid cavity of scapula (Fig. 8.1).

FIG. 8.1 Coronal section of shoulder joint.

The glenoid articular surface is deepened by the glenoid labrum. Glenoid labrum • It is a rim of fibrocartilage attached to the peripheral margin of the glenoid cavity. • It is triangular in cross-section and deepens the shallow glenoid cavity.

Ligaments Capsular ligament • Attachments (Fig. 8.1) ■ Medially: To peripheral margin of glenoid cavity outside the glenoid labrum. The supraglenoid tubercle is intracapsular. ■ Laterally: To anatomical neck of humerus except on medial side where it descends about 2–3 cm on the shaft, up to the surgical neck of humerus. • Muscles strengthening the capsule: In general, the capsule is loose and lax, but it is strengthened by the musculotendinous (rotator) cuff formed by the following muscles:

• Openings in the capsule: The capsule presents two openings/deficiencies: ■ One in front, for communicating with subscapular bursa ■ One at the intertubercular sulcus to provide the passage for the tendon of long head of biceps brachii Transverse humeral ligament: This ligament bridges across the bicipital groove. Glenohumeral ligaments: These are thickenings in the anterior part of the capsule and are seen when the capsule is exposed from the behind. They are three in number and named superior, middle and inferior glenohumeral ligaments according to their location. Coracohumeral ligament: It is a wide, strong fibrous band on the superior surface of the joint, extending from the base of coracoid process to the anterior aspect of greater tubercle of humerus. Coracoacromial ligament: It extends between the lateral side of coracoid process and the medial border of acromion.

Relations (fig. 8.2) Superiorly • Coracoacromial arch • Subacromial bursa • Supraspinatus • Tendon of long head of biceps brachii (intracapsular) • Deltoid

FIG. 8.2 Relations of shoulder joint as seen in sagittal section. B, long head of biceps; G, glenoid cavity.

Anteriorly • Subscapularis • Coracobrachialis • Short head of biceps • Deltoid Posteriorly • Infraspinatus • Teres minor • Deltoid Inferiorly • Long head of triceps • Axillary nerve • Posterior circumflex humeral vessels

Nerve supply The nerves supplying the joint are • Suprascapular nerve • Axillary nerve • Musculocutaneous nerve

Movements The movements and muscles producing them, with their nerve supply, are given in Table 8.1. TABLE 8.1 Movements of Shoulder Joint and Muscles Producing Them with Their Nerve Supply Movements Muscles Flexion • Pectoralis major (clavicular fibres) • Deltoid (anterior fibres) • Coracobrachialis

Extension Abductiona

Nerve Supply • Lateral and medial pectoral nerves • Axillary (circumflex) nerve • Musculocutaneous nerve • Deltoid (posterior fibres) • Axillary nerve • Teres major • Lower subscapular nerve • Latissimus dorsi • Thoracodorsal nerve Initiated by supraspinatus up to 15°, and then by the Suprascapular and axillary acromial fibres of deltoid up to 90° nerves, respectively

Adduction

• Pectoralis major • Latissimus dorsi

Medial rotation

• Pectoralis major (sternal fibres) • Deltoid (anterior fibres) • Teres major • Latissimus dorsi • Infraspinatus • Deltoid (posterior fibres) • Teres minor

Lateral rotation

• Medial and lateral pectoral nerves • Thoracodorsal nerve • Lateral pectoral nerve • Axillary nerve • Lower subscapular nerve • Thoracodorsal nerve • Suprascapular nerve • Axillary nerve • Axillary nerve

aAbduction:

(a) 1°–15° by supraspinatus; (b) 15°–90° by middle fibres (acromial fibres) of deltoid; (c) 90°–120° by serratus anterior; and (d) 120°–180° by serratus anterior and trapezius.

Applied anatomy Dislocation of shoulder joint • The shoulder joint is the most commonly dislocated joint in the body due to (i) disproportionate size of articular surfaces – head of humerus and glenoid cavity of the scapula (the head of humerus is much larger to fit properly into smaller glenoid cavity of scapula [4:1 ratio]) and (ii) laxity of joint capsule. • Dislocation most commonly occurs inferiorly because the joint is least supported below. Frozen shoulder (adhesive capsulitis) It is a clinical condition characterized by painful and uniform restriction of all movements of shoulder joint. It occurs due to shrinkage of joint capsule leading to adhesion between rotator cuff and head of humerus. ❖ Enumerate the factors providing stability to shoulder joint. AN10.12 • Musculotendinous (rotator) cuff • Glenoid labrum • Long head of biceps brachii muscle • Coracoacromial arch ❖ Enumerate the synovial bursae related to the shoulder joint. AN10.12 • Subscapular bursa: Lies deep to subscapularis and communicates with joint cavity through a gap between superior and middle glenohumeral ligaments. • Subacromial bursa: Lies deep to acromion and upper part of deltoid. It is the largest synovial bursa in the body. • Between tendons of infraspinatus and teres major. • Between coracoid process and joint capsule. • Between teres major and long head of triceps brachii.

❖ Write a short note on coracoacromial arch. It is bony-fibrous arch lying above the shoulder joint formed by (a) coracoid process, (b) coracoacromial ligament and (c) acromial process. The coracoacromial ligament is a flat triangular ligament which extends from the medial border of acromion (narrow end) in front of acromioclavicular articulation to the lateral border of the coracoid process (broad end). Just below this arch, the supraspinatus muscle passes above the head of humerus on its way to greater tubercle of humerus for insertion. The coracoacromial arch is separated from this muscle by subacromial bursa to allow free movements of shoulder during contraction of supraspinatus (Fig. 8.3).

FIG. 8.3 Coracoacromial arch.

Applied Anatomy: The coracoacromial arch acts as a secondary socket of shoulder joint and prevents its superior dislocation. ❖ What are various types of sternoclavicular joint? AN8.2, AN13.4 The sternoclavicular joint is of following types: synovial, saddle, compound and complex. The details are as under: (a) Synovial, because it has synovial cavity filled with synovial fluid (b) Saddle, because articulating surfaces are concavo-convex in shape (c) Compound, because more than two bones are articulating, i.e. sternal end of clavicle, clavicular notch of manubrium sterni and upper surface of 1st costal cartilage (last two form a continuous concavo-convex surface) (d) Complex, because its articular surfaces are covered by fibrocartilage and its cavity is divided into two parts by an intra-articular fibrocartilaginous disc ❖ Write a short note on abduction at shoulder joint. AN10.12 • The abduction at shoulder joint is a complex movement.

• It is performed by conjoint action of both prime movers and synergists.

FIG. 8.4

Sternoclavicular joint.

• Prime movers are (a) Middle fibres of deltoid (b) Supraspinatus • Synergist muscles are (a) Subscapularis (b) Infraspinatus (c) Teres minor The sequence of events occurring during abduction at shoulder is as follows (Fig. 8.5): (a) Natural range of abduction at shoulder joint is only 60°. (b) When the humerus is rotated medially, range of movement of abduction is increased up to 90°. (c) When humerus moves in the plane of body of scapula, range of movement is increased up to 120°. (d) When humerus is rotated laterally by contraction of infraspinatus and teres minor, range of movement is increased up to 180°.

FIG. 8.5 Abduction at shoulder joint. CP, coracoid process; AC, acromion process; G, glenoid cavity; H, humerus.

N.B. • Out of total 180° elevation ■ Humerus moves 120° at shoulder joint ■ Scapula moves 60° at joint of shoulder girdle • In every 15° elevation ■ Shoulder joint contributes 10° ■ Girdle joint contributes 5° (i.e. in ratio of 2:1) ❖ Describe the elbow joint under the following headings: (a) classification, (b) articular surfaces, (c) ligaments, (d) relations, (e) nerve supply, (f) movements and (g) applied anatomy. AN13.3

Classification Synovial joint of hinge variety.

Articular surfaces It is a compound joint consisting of two articulations (Fig. 8.6). Humeroradial: Between capitulum of humerus and head of radius. Humeroulnar: Between trochlea of humerus and trochlear notch of ulna.

FIG. 8.6 Components of the elbow joint: A, schematic diagram; B, radiograph of normal elbow joint (anteroposterior view). Source: (Drake, Richard L; Vogl, Wayne; Mitchell, Adam WM. Gray’s Anatomy for Students. Philadelphia: Elsevier Inc., 2005.)

The elbow joint communicates with superior radioulnar joint.

Ligaments Capsular ligament • Attachments ■ In front • Superiorly, it is attached to the humerus above the coronoid and radial fossae. • Inferiorly, it is attached to the coronoid process of ulna and annular ligament of superior radioulnar joint. ■ Behind • Superiorly, it is attached to the margins of the olecranon fossa. • Interiorly, it is attached to the upper margins of olecranon process and annular ligament of superior radioulnar joint. • On either side: The capsule becomes continuous with medial and lateral collateral ligaments of the elbow joint. Medial (ulnar) collateral ligament: It is triangular in shape and consists of the following three parts: • Anterior part, which extends from front of medial epicondyle of humerus to the

medial margin of coronoid process of ulna • Posterior part, which extends from back of medial epicondyle of humerus to the medial margin of the olecranon process of ulna • Inferior part, which extends between lower ends of anterior and posterior parts and stretches between the olecranon and coronoid processes of ulna

N.B. Medial collateral ligament is crossed superficially by the ulnar nerve. Lateral (radial) collateral ligament: It extends from lateral epicondyle of humerus above to the annular ligament below.

Relations Anterior • Brachialis • Tendon of biceps brachii • Median nerve • Brachial artery Posterior • Tendon of triceps brachii • Anconeus Medial • Flexor carpi ulnaris • Ulnar nerve • Common flexor origin Lateral • Supinator • Common extensor origin

Nerve supply • Radial nerve • Musculocutaneous nerve • Median nerve • Ulnar nerve

Movements

The movements and muscles producing them with their nerve supply are given in Table 8.2. TABLE 8.2 Movements of the Elbow Joint and Muscles Producing Them with Their Nerve Supply Movements Flexion

Extension

Muscles • Brachialis • Biceps brachii • Brachioradialis • Triceps brachii • Anconeus • Supinator (humeral origin)

Nerve Supply • Musculocutaneous and radial nerves • Musculocutaneous nerve • Radial nerve • Radial nerve • Radial nerve • Posterior interosseous nerve

Applied anatomy Dislocation: The dislocation of elbow joint usually occurs posteriorly and is often associated with fracture of coronoid process. Effusion: The effusion of elbow joint causes distension on the posterior aspect of elbow because the joint capsule is weak posteriorly. Tennis elbow (lateral epicondylitis) It presents with pain and tenderness over lateral epicondyle of humerus. It occurs due to: • Sprain of lateral collateral ligament of the elbow joint • Tearing of fibres of extensor carpi radialis brevis (ECRB) • Inflammation of bursa underneath the ECRB • Tear of common extensor origin ❖ What is carrying angle? Give its clinical significance. • It is an angle formed between long axes of arm and forearm when the elbow is fully extended (Fig. 8.7). • This angle occurs because the medial flange of trochlea lies 6 mm lower than that of lateral flange of trochlea. • It varies from 10° to 15° in males and 15° to 30° in females.

FIG. 8.7 Carrying angle.

Functional significance • It helps in holding and carrying the objects. • It prevents rubbing of forearm with pelvis in females. • It helps to put food in mouth during eating.

Applied anatomy An increase in carrying angle causes cubitus valgus deformity of the elbow. ❖ Give a brief account of radioulnar joints and discuss the movements occurring at these joints. AN13.3 There are three radioulnar joints (Fig. 8.8), i.e. superior, middle and inferior.

FIG. 8.8 Interosseous membrane.

• Superior Radioulnar Joint: It is a pivot type of synovial joint between head of radius and radial notch of ulna. The annular ligament surrounds the head of radius and keeps it in contact with the radial notch of ulna. A fibrous band – the quadrate ligament extending from inferior border of radial notch of ulna to the neck of radius – closes the joint from below. • Intermediate Radioulnar Joint: It is a fibrous joint of syndesmosis type between the shafts of radius and ulna. Here radius and ulna are joined by an interosseous membrane whose fibres are directed downwards and medially. It binds the radius and ulna but allows some movement. • Inferior Radioulnar Joint: It is also a pivot type of synovial joint between head of ulna and ulnar notch of radius. A triangular articular disc of fibrocartilage extends from depression near the styloid process of ulna to the articular margins of ulnar notch of radius. It separates this joint from wrist joint. The synovial membrane of inferior radioulnar joint projects upwards to form a pouch in front of interosseous membrane – the recessus sacciformis.

Movements Movements occurring at radioulnar joints are

• Supination • Pronation ❖ Write a short note on interosseous membrane (Fig. 8.8). AN13.3 • It is a fibrous membrane which extends between interosseous borders of radius and ulna. • The direction of fibres in this membrane is downwards and medially towards ulna. • It forms intermediate (middle) radioulnar joint of syndesmosis type. • Superiorly the gap between oblique cord and upper border of membrane, provides passage to posterior interosseous artery to go into the posterior compartment. • Inferiorly interosseous membrane blends with capsule of inferior radioulnar joint. • An opening in the inferior part of membrane provides passage to anterior interosseous artery to enter the posterior compartment. • Membrane is related anteriorly to flexor pollicis longus (FPL), flexor digitorum profundus (FDP) and pronator quadratus (PQ). • Membrane is related posteriorly to supinator, abductor pollicis longus (APL), extensor pollicis longus (EPL), extensor pollicis brevis (EPB), extensor indicis and posterior interosseous nerve and vessels.

Functional significance Interosseous membrane: (a) helps in transmission of force from the radius (received from wrist joint) to the ulna for onward transmission to the humerus and (b) helps in supination and pronation. ❖ Give a brief account of movements of supination and pronation and discuss their functional significance. AN13.3

Movements • Supination: It is the movement of forearm in which the palm of hand is turned forwards/upwards. • Pronation: It is the movement of forearm in which the palm of hand is turned backwards/downwards. The details of movements of supination and pronation are given in Table 8.3 and shown in Fig. 8.9.

FIG. 8.9 Movements of supination and pronation.

TABLE 8.3 Movements of Supination and Pronation

N.B. • Movements of supination and pronation occur mainly at superior and inferior radioulnar joints. • Axis of movements of supination and pronation is an oblique axis that passes from the head of radius to the head of ulna. • During supination and pronation, ulna remains relatively stationary, while the radius moves.

• All the muscles producing supination and pronation are inserted into radius. • Movements of supination and pronation are homologous to the movements of inversion and eversion of the foot.

Functional significance • They help in picking up food and putting it into the mouth. • They are used in mechanical jobs, e.g. opening and tightening the screws with screw driver. ❖ Describe the wrist joint under the following headings: (a) classification, (b) articular surfaces, (c) ligaments, (d) relations, (e) nerve supply, (f) movements and (g) applied anatomy. AN13.3

Classification Structural: Synovial joint of ellipsoid variety. Functional: Diarthrosis.

Articular surfaces (fig. 8.10) Proximally • Inferior articular surface of the lower end of the radius • Inferior surface of the articular disc of the inferior radioulnar joint

FIG. 8.10 Coronal section through wrist region.

Distally • Scaphoid • Lunate • Triquetral

N.B. Ulna does not form the articular surface of the wrist joint; hence, wrist joint is also called radiocarpal joint.

Ligaments Capsule: It is attached above to the peripheral margins of the proximal and distal articular surfaces including the articular disc. Distally, it blends with the palmar and dorsal radiocarpal ligaments. Radial collateral ligament: It extends from the styloid process of radius to the lateral aspects of scaphoid and trapezium. Ulnar collateral ligament: It extends from the styloid process of ulna to the medial aspects of triquetral and pisiform bones. Palmar and dorsal radiocarpal ligaments: These are the thickenings on the palmar and dorsal aspects of the fibrous capsule.

Relations Anterior • Superficial: Tendons of flexor carpi radialis and palmaris longus • Intermediate: Radial artery median nerve and flexor digitorum superficialis • Deep: Tendons flexor pollicis longus and flexor digitorum profundus Posterior: Extensor tendons of the wrist and fingers with their synovial sheaths. Lateral: Radial artery.

Nerve supply

• Anterior interosseous nerve • Posterior interosseous nerve

Movements Movements and muscles producing them with their nerve supply are given in Table 8.4. TABLE 8.4 Movements of the Wrist Joint Movement Flexion Extension

Muscles Producing Them • Flexor carpi radialis • Flexor carpi ulnaris • Extensor carpi radialis longus • Extensor carpi radialis brevis • Extensor carpi ulnaris

Abduction

• Abductor pollicis longus • Extensor pollicis brevis

Adduction

• Flexor carpi ulnaris • Extensor carpi ulnaris

Nerve Supply • Median nerve • Ulnar nerve • Radial nerve • Posterior interosseous nerve • Posterior interosseous nerve • Posterior interosseous nerve • Posterior interosseous nerve • Ulnar nerve • Posterior interosseous nerve

Circumduction Combination of flexion, extension, abduction and adduction

Applied anatomy Colles fracture: It is fracture of distal end of radius due to fall on outstretched hand with distal fragment being displaced upwards and backwards. Smith fracture: It is reverse of Colles fracture due to fall on the back of the hand with distal fragment being displaced upwards and forwards (i.e. palm is flexed). ❖ Enumerate the range of movement at the wrist joint. AN13.3 • Flexion = 60°–85° • Extension = 50°–60° • Abduction = 15° • Adduction = 30°–45° ❖ Write a brief note on the 1st carpometacarpal joint. AN13.4

Classification Structural: Synovial joint of saddle variety Functional: Diarthrosis

Articular surfaces Proximally: Distal surface of trapezium Distally: Proximal surface of the base of 1st metacarpal (MC) bone

Ligaments Capsular ligament: It is a loose fibrous sac, which encloses the joint cavity. It is thickest dorsally and laterally. Lateral ligament: Broad fibrous band extending from the lateral surface of trapezium to the lateral surface of 1st MC. Anterior ligament: Extends obliquely from the palmar surface of trapezium to the ulnar side of base of 1st MC. Posterior ligament: Extends obliquely from the dorsal surface of trapezium to the ulnar side of 1st MC.

Relations Anterior: Muscles of thenar eminence Posterior: Long and short extensors of thumb Medial: First dorsal interosseous muscle Lateral: Abductor pollicis longus Posteromedial: Radial artery

Nerve supply Median nerve

Movements The movements and muscles producing them with their nerve supply are given in Table 8.5. TABLE 8.5 Movements of 1st Carpometacarpal Joint Movement 1. Flexion (occurs in the plane of palm) 2. Extension (occurs in the plane of

Muscles • Flexor pollicis brevis • Opponens pollicis • Extensor pollicis longus

Nerve Supply • Median nerve • Median nerve • Posterior

• Extensor pollicis brevis

palm)

3. Abduction (occurs at right angle to the plane of palm)

• Abductor pollicis longus • Abductor pollicis brevis

4. Adduction (occurs at right angle to the plane of palm) 5. Opposition 6. Circumduction

• Adductor pollicis • Opponens pollicis Combination of flexion, extension, abduction and adduction

interosseous nerve • Posterior interosseous nerve • Posterior interosseous nerve • Median nerve Ulnar nerve Median nerve

N.B. Movements of the medial and lateral rotation also occur at the 1st carpometacarpal (CM) joint. Movements at 1st CM joint are much more free than at any other corresponding carpometacarpal joints because it is the only CM joint which has a separate joint cavity (Fig. 8.11).

FIG. 8.11 First carpometacarpal joint. A, formation; B, showing various movements of thumb.

❖ Give the classification of metacarpophalangeal (MP), proximal intraphalangeal (PIP) and distal interphalangeal (DIP) joints, and discuss the movements occurring at these joints. AN13.4 The classification and movements of MP, PIP and DIP joints are given in Table 8.6.

TABLE 8.6 Classification and Movement of MP, PIP and DIP joints Joints MP

Classification Synovial joint of ellipsoid variety

PIP DIP

Synovial joint of hinge variety Synovial joint of hinge variety

Movement • Flexion • Extension • Abduction • Adduction Flexion and extension Flexion and extension

❖ Write a short note on 1st metacarpophalangeal joint. AN13.4, AN12.6 • Type: Ellipsoid type of synovial joint (Fig. 8.12) • Articular surfaces: Convex articular head of 1st metacarpal and curved articular base of proximal phalanx • Ligaments: Capsular ligaments, palmar ligaments, and medial and lateral collateral ligaments ■ Capsular ligament: Thick in front and thin behind ■ Palmar ligament: Fibrocartilaginous plate which replaces deep transverse metacarpal ligaments ■ Medial and lateral collateral ligament: Oblique bands extending downwards and forwards from head of metacarpal to the base of proximal phalanx

FIG. 8.12 First right metacarpophalangeal joint.

Movements and muscle producing them • Flexion: Flexor pollicis brevis • Extension: Extensors of thumb • Abduction: Abductor pollicis brevis • Adduction: Adductor pollicis

❖ Enumerate the chief flexors of MP, PIP and DIP joints. AN13.4 MP joints: Lumbricals and interossei PIP joints: Flexor digitorum superficialis DIP joints: Flexor digitorum profundus ❖ Which movements of thumb are tested to confirm the integrity of radial, ulnar and median nerves? AN12.6 (a) To test integrity of radial nerve: Test extension of thumb, because this movement of thumb is lost if radial nerve is damaged. (b) To test integrity of ulnar nerve: Test adduction of thumb, because this movement of thumb is lost if ulnar nerve is damaged. (c) To test integrity of median nerve: Test abduction and opposition of thumb, because both these movements of thumb are lost if median nerve is damaged.

SECTION II

Head and Neck OUTLINE 9. Scalp, temple and face 10. Side, front and back of the neck 11. Parotid and submandibular regions 12. Deep structures of the neck and prevertebral region 13. Oral cavity 14. Pharynx and palate 15. Nose and paranasal air sinuses 16. Larynx 17. Infratemporal fossa, temporomandibular joint and pterygopalatine fossa 18. Ear and orbit 19. Dural folds, intracranial dural venous sinuses and pituitary gland 20. Cranial nerves 21. Meninges and cerebrospinal fluid 22. Spinal cord

9

Scalp, temple and face ❖ Describe the scalp under the following headings: (a) definition, (b) layers, (c) arterial supply, (d) venous drainage, (e) nerve supply and (f) applied anatomy.  AN27.1 The soft-tissue structures covering the vault of skull form the scalp. The boundaries of scalp are as follows. Anteriorly: Superciliary arches of the frontal bone. Posteriorly: Superior nuchal lines of the occipital bone. On each side: Superior temporal line.

Layers of scalp The scalp consists of five layers, which can be easily remembered by the initial letter of each layer, i.e. SCALP. From superficial to deep, these are (Fig. 9.1) • S: Skin • C: Connective tissue • A: Aponeurosis (epicranial aponeurosis) • L: Loose areolar tissue • P: Pericranium (outer periosteum)

FIG. 9.1 Layers of the scalp.

Mnemonic: SCALP

Arterial supply (fig. 9.2) Each lateral half of the scalp is supplied by five arteries:

FIG. 9.2 Arteries (right half) and sensory nerves (left half) supplying the scalp. ST, supratrochlear; SO, supraorbital; T, supraficial temporal; PA, posterior auricular; O, occipital; ZT, zygometicotemporal; AT, auriculotemporal; GA, great auricular; LO, lesser occipital; GO, greater occipital; TO, third occipital.

Venous drainage Each lateral half of the scalp is supplied by five veins: • Three in front of the auricle ■ Supratrochlear vein ■ Supraorbital vein ■ Superficial temporal vein • Two behind the auricle ■ Posterior auricular vein ■ Occipital vein

Nerve supply Sensory Each lateral half of the scalp is supplied by eight nerves: • Four in front of the auricle (i.e. anterior quadrant)

• Four behind the auricle (i.e. posterior quadrant) ■ Great auricular, GA (C2, C3) ■ Lesser occipital, LO (C2, C3) ■ Greater occipital, GO (C2) ■ Third occipital, TO (C3) Motor Each lateral half of the scalp is supplied by two nerves – one in front of the auricle and one behind the auricle. • In front of the auricle ■ Temporal branch of the facial nerve • Behind the auricle ■ Posterior auricular branch of the facial nerve

Applied anatomy • Wounds of the scalp bleed profusely because: ■ Walls of torn vessels fail to retract because they are adhered to the dense connective tissue. ■ It is profusely supplied with blood.

• Wounds of the scalp heal quickly because of profuse blood supply. • Scalp is the commonest site of sebaceous cysts because it contains maximum number of sebaceous glands as compared to anywhere else in the body. • Dangerous layer of the scalp: The layer of loose areolar tissue (i.e., fourth layer of the scalp) is called dangerous layer of the scalp because if the pus collects in this layer, the infection from here may travel through emissary veins into the intracranial dural venous sinuses causing their thrombosis and associated meningitis. • Black eye: If blood collects in the fourth layer of scalp due to trauma on head. It tracks anteriorly in the subcutaneous tissue of eyelids in a couple of days where it clots. As a result, the eyelids appear black (black eye). ❖ Give the origin, insertion, nerve supply and actions of occipitofrontalis muscle.  AN27.1 The occipitofrontalis muscle along with epicranial aponeurosis forms the third layer of the scalp. This muscle consists of four bellies: two occipital bellies and two frontal bellies (Fig. 9.2).

Origin (fig. 9.3)

FIG. 9.3 Occipitofrontalis muscle.

Occipital bellies: From lateral two-third of superior nuchal lines of the occipital bone. Frontal bellies: From subcutaneous tissue of eyebrows and root of the nose where it blends with orbicularis oculi muscle.

Insertion (fig. 9.3) Into epicranial aponeurosis (galea aponeurotica).

Nerve supply (fig. 9.3) Posterior auricular and temporal branches of the facial nerve.

Actions • Moves the scalp forward and backward by alternate contractions of frontal and occipital bellies. • Occipital bellies draw the epicranial aponeurosis backwards, allowing the frontal bellies to contract, and cause transverse wrinkles in the skin of forehead. ❖ Write a short note on superficial temporal artery. • It is the smaller terminal branch of the external carotid artery. It begins in the parotid gland behind the neck of mandible. • It runs vertically upwards across the root of zygoma in front tragus. About 5 cm above the zygoma, the artery divides into terminal anterior and posterior branches which supply temporal fossa and scalp.

Branches 1. Transverse facial artery arises within parotid gland and runs forwards over the masseter muscle. It supplies TMJ, parotid gland and masseter muscle. 2. Anterior auricular branch: It supplies lateral surface of auricle and part of external auditory meatus. 3. Middle (deep) temporal artery: It pierces temporal fascia to supply temporalis muscle. 4. Zygomatico-orbital branch runs towards orbit along the upper border of zygomatic arch. 5. Anterior terminal branch runs forwards towards the frontal tuberosity to supply soft tissues of the region. It often becomes noticeably tortuous in old age. 6. Posterior terminal branch runs upwards, backwards and towards the occipital region to supply the soft tissues in the region. ❖ Give the origin, insertion, nerve supply and actions of the platysma. AN28.1 The platysma is a thin, quadrilateral, broad sheet of muscle in the superficial fascia of the side of the neck (Fig. 9.4).

FIG. 9.4 Origin and insertion of the platysma.

Origin From skin and deep fascia covering pectoralis major and anterior part of deltoid.

Insertion Into lower border of mandible and angle of mouth.

Nerve supply By cervical branch of facial nerve.

Actions • Forms wrinkles in the skin of neck • Releases pressure of the skin on the underlying superficial veins of the neck to help in venous return • Draws the angle of mouth downward and laterally as seen clearly in the faces of marathon runners. ❖ Enumerate the characteristic features of the muscles of facial expression. AN28.1 • Lie in the superficial fascia • Develop from 2nd pharyngeal arch • Supplied by the facial nerve • Represent (morphologically) panniculus carnosus

❖ Give origin, insertion, nerve supply and actions of buccinator muscle. AN28.1

Origin (fig. 9.5) • Upper fibres, from alveolar process of maxilla, opposite upper molar teeth. • Lower fibres, from alveolar process of mandible, opposite lower molar teeth. • Middle fibres, from pterygomandibular raphe.

FIG. 9.5 Buccinator muscle: A, origin; B, location in face and insertion.

Insertion • Upper fibres pass straight to be inserted into the upper lip. • Lower fibres pass straight to be inserted into the lower lip. • Middle fibres decussate before passing to the respective lips.

Nerve supply By facial nerve.

Actions • Flattens cheek against gum and teeth. • Prevents accumulation of food into the vestibule of mouth. • Helps in blowing the cheek (hence is also called whistling muscle). ❖ Define temple (superficial temporal region) and enumerate the layers of soft tissue present in this region. AN27.1 Temple is an area on the side of skull between the superior temporal line and the zygomatic arch. Soft-tissue layers: There are six layers of soft tissue in this region. From superficial to deep, these are:

• Skin • Superficial fascia • Thin extension of epicranial aponeurosis • Temporal fascia • Temporalis muscle • Pericranium ❖ Describe the sensory innervation of the face in brief. AN28.2 The sensory innervation to the skin of whole face is derived from the branches of trigeminal nerve except the skin over the angle of lower jaw, which is innervated by the great auricular nerve, a branch of cervical plexus (C2 and C3; Fig. 9.6).

FIG. 9.6 Sensory innervation of the face.

The details are given in Table 9.1. TABLE 9.1 Sensory Innervation of the Head and Face Source Cutaneous Nerves Ophthalmic division of • Supratrochlear nerve trigeminal nerve (V1) • Supraorbital nerve • Lacrimal nerve • Infratrochlear nerve • External nasal nerve Maxillary division of • Infraorbital nerve trigeminal nerve (V2) • Zygomaticofacial nerve

Area of Distribution • Upper eyelid and forehead • Scalp up to vertex • Eyelids • Root, dorsum and tip of the nose • Lower eyelid, side of ala of nose and upper lip

• Zygomaticotemporal nerve Mandibular division of • Auriculotemporal nerve trigeminal nerve (V3) • Buccal nerve • Mental nerve

Cervical plexus

• Anterior division of great auricular nerve (C2 and C3) • Upper division of transverse (anterior) cervical nerve of neck (C2 and C3)

• Upper part of the cheek • Anterior part of temple • Upper two-third of the lateral side of auricle and temple • Lower part of the cheek • Chin and lower lip • Skin over angle of the jaw and over the parotid gland • Lower margin of the lower jaw

❖ Write a short note on dangerous area of face. Dangerous area of the face: This includes (Fig. 9.7): • Upper lip • Lower part of the nose including nasal septum • Adjoining parts of the cheek

FIG. 9.7 Dangerous area of the face.

This area is called dangerous because infective emboli from this area can reach the cavernous sinus and cause cavernous sinus thrombosis. As a result, cranial nerves present within the cavernous sinus are compressed leading to paralysis of the muscles of eyeball.

Route of spread: The venous blood from dangerous area of the face is drained into cavernous sinus as follows (Fig. 9.8): Deep facial vein → pterygoid venous plexus → emissary vein → cavernous sinus

FIG. 9.8 Venous drainage of the face.

❖ Write a short note on the lacrimal apparatus. AN31.4 The group of structures concerned with the formation and drainage of lacrimal fluid (tear fluid) constitutes the lacrimal apparatus.

Components Lacrimal apparatus consists of the following components (structures; Fig. 9.9): • Lacrimal gland and its ducts • Conjunctival sac • Lacrimal puncta and lacrimal canaliculi • Lacrimal sac • Nasolacrimal duct

FIG. 9.9 Lacrimal apparatus.

N.B. The opening of nasolacrimal duct in the inferior meatus of the nose is guarded by a fold of mucous membrane called valve of Hasner.

Route of drainage

Applied anatomy Dacryocystitis It is an inflammation of lacrimal sac and presents with pain, oedema and redness at the medial angle of the eye. Epiphora: The obstruction of lacrimal fluid pathway (i.e. at the level of puncta, canaliculi or nasolacrimal duct) causes overflow of tears on the cheek. It is called epiphora. ❖ Describe the development of the face in brief.  AN43.4

The face develops from five mesenchymal processes, which appear around the stomodeum (primitive mouth). These processes (facial primordia) are (Fig. 9.10) • Frontonasal process – unpaired • Maxillary processes – paired • Mandibular processes – paired

FIG. 9.10 Ventral aspect of a fetal head showing the five processes around the stomodeum.

Frontonasal process: It lies above the stomodeum and is formed by the proliferation of mesenchyme deep to the ectoderm in front of the forebrain. On either side of the frontonasal process, the ectoderm thickens to form olfactory placodes. As each olfactory placode depresses from the surface, the olfactory pit is formed. A horseshoe-shaped elevation is formed around each olfactory pit. The medial limb of horseshoe-shaped elevation is called medial nasal process, while its lateral limb is called lateral nasal process. Maxillary processes: These develop from the mesenchyme of the first arch. They are dorsolateral to lateral nasal processes and are separated from them on each side by the optic vesicle and a lineal furrow of ectoderm termed nasolacrimal groove. Ectodermal cells in the floor of this groove proliferate to form the solid ectodermal cord. The canalization of this cord gives rise to nasolacrimal duct. Mandibular processes: These are derived from the mesenchyme of the 1st pharyngeal arch. The various parts of the face derived from the above-mentioned processes are given in the box below. Facial primordia

Parts of face

Frontonasal processes give rise to Maxillary processes give rise to Mandibular processes give rise to

Forehead, external nose and philtrum of the upper lip Lateral parts of the upper lip and upper parts of the cheek Lower lip, lower parts of the cheek and chin

Applied anatomy • Cleft upper lip (Fig. 9.11) ■ Median cleft (or hare lip) occurs if the frontonasal process fails to form philtrum. ■ Lateral cleft develops if the frontonasal process fails to fuse with the maxillary process. It can be unilateral or bilateral. • Cleft lower lip occurs if two mandibular processes fail to fuse with each other. It is very rare (Fig. 9.11). • Oblique facial cleft occurs if the maxillary process fails to fuse with the lateral nasal process. The oblique cleft extends from the median angle of eye to the upper lip.

FIG. 9.11 Types of cleft lip: A, unilateral; B, bilateral; C, median cleft lip (hare lip); D, cleft lower lip.

10

Side, front and back of the neck ❖ Enumerate the structures present in the superficial fascia of the neck. The superficial fascia of the neck contains: • Platysma • Cutaneous nerves • Superficial veins • Superficial lymph vessels and lymph nodes

N.B. The cutaneous nerves and veins lie deep to platysma. ❖ Write a short note on platysma. See p. 92. ❖ Write a short note on external jugular vein. AN35.4

Formation The external jugular vein is formed on the sternocleidomastoid muscle below and behind the angle of mandible by the union of the posterior auricular vein and posterior division of the retromandibular vein. It has two valves – one before its termination and another an inch above the middle of clavicle (Fig. 10.1).

FIG. 10.1 External jugular vein. Other superficial veins of the neck are also shown.

Course It descends obliquely downwards and backwards across the sternocleidomastoid. It pierces the superficial lamina of investing layer of deep cervical fascia above clavicle in the region of the subclavian triangle. Here it crosses the third part of the subclavian artery and after piercing a deep lamina of investing layer of the deep cervical fascia ends in the subclavian vein deep to clavicle.

Tributaries These are • Anterior jugular vein • Transverse cervical vein • Suprascapular vein

Applied anatomy • Air embolism: If external jugular vein is cut an inch above the clavicle, its lumen is held open because its margins are adhered to the deep fascia. As a result, the air is sucked into the lumen of the external jugular vein during inspiration, leading to air embolism that may subsequently cause death. • External jugular vein is used by the clinicians to measure the external jugular venous pressure and/or pressure in the right atrium. ❖ Enumerate the various layers of the deep cervical fascia. AN35.1 The deep cervical fascia consists of the following three layers (Fig. 10.2):

• Investing layer • Pretracheal fascia/layer • Prevertebral fascia/layer

FIG. 10.2 Diagrammatic transverse section through neck at the level of the 6th cervical vertebra to show the horizontal disposition of the three layers of deep cervical fascia.

❖ Describe the investing layer of the deep cervical fascia in brief. AN35.1 It surrounds the neck like a collar (Fig. 10.2).

Attachments Superiorly • External occipital protuberance • Superior nuchal line • Mastoid process • Base of mandible Inferiorly • Spine of scapula • Acromion process of scapula • Clavicle • Manubrium sterni Anteriorly • Symphysis menti • Hyoid bone • Oblique line of thyroid cartilage Posteriorly

• Ligamentum nuchae • Spine of 7th cervical vertebra

Features • Splits to enclose: ■ Two muscles: Trapezius and sternocleidomastoid ■ Two salivary glands: Parotid and submandibular ■ Two spaces: Suprasternal and supraclavicular • Forms two pulleys/slings – one each for intermediate tendon of digastric and omohyoid • Thickens to form two structures: Stylomandibular ligament and parotidomasseteric fascia ❖ What is suprasternal space (of Burns)? Give its contents. AN35.1 It is a triangular space above the suprasternal notch enclosed between the two layers of investing layer of deep cervical fascia.

Contents • Sternal heads of sternocleidomastoid muscles • Jugular venous arch • Interclavicular (‘T’) ligament • Lymph node (sometimes) ❖ Write a short note on pretracheal fascia. AN35.1 The pretracheal fascia is so called because it is a layer of deep cervical fascia that lies in front of trachea (Fig. 10.2).

Attachments Superiorly • Hyoid bone in the median plane • Oblique line of thyroid cartilage • Cricoid cartilage Inferiorly: It splits to enclose thyroid gland, i.e. forms capsule of thyroid gland and finally blends with the arch of the aorta. On either side, it fuses with the front of the carotid sheath.

N.B. The posterior layer of thyroid capsule, on either side of midline thickens to form

suspensory ligament of thyroid gland (ligament of Berry).

Functions • Provides a slippery surface for the free movements of trachea during deglutition • Supports thyroid gland and does not allow it to sink into the mediastinum

Applied anatomy Thyroid swelling moves up and down during swallowing because it is enclosed in the pretracheal fascia, which is attached to laryngeal skeleton (i.e. cricoid and thyroid cartilages and hyoid bone). Since larynx moves up and down during swallowing, the thyroid gland also moves up and down during swallowing. ❖ Write a short note on prevertebral fascia. AN35.1 It is so called because it lies in front of the cervical part of vertebral column (Fig. 10.2).

Attachments Superiorly: Base of the skull. Inferiorly: Bodies of T3 and T4 vertebra. Laterally: Merges with posterior lamina of investing layer of the deep cervical fascia enclosing trapezius muscle.

Features to remember • Forms the fascial carpet of the floor of posterior triangle. • Cervical and brachial plexuses of nerves lie deep to it. • Forms axillary sheath, which extends into the axilla. (Note: The subclavian and axillary veins lie outside the sheath, so that they could dilate during increased venous return from the limb.) ❖ Write a short note on carotid sheath. AN35.1

Formation • It is formed by the condensation of fibroareolar tissue around common and internal carotid arteries and internal jugular vein (Fig. 10.3). • It extends from the base of the skull to the arch of the aorta. • Its anterior wall is connected to the pretracheal fascia while its posterior wall is

connected to the prevertebral fascia.

FIG. 10.3 Carotid sheath: A, surface view; B, sectional view.

Thickness It is thick around common and internal carotid arteries, and thin around internal jugular vein to allow the free expansion of vein during increased venous return.

Relations Anteriorly: Ansa cervicalis is embedded in the wall or sheath. Posteriorly: Sympathetic trunk is present behind the sheath.

Contents (fig. 10.3) • Common and internal carotid arteries • Internal jugular vein • Vagus nerve

Applied anatomy It is frequently exposed in block dissection of the neck during surgical removal of the deep cervical lymph nodes. ❖ Write a short note on cervical lymph nodes. AN28.5, AN35.5 The cervical lymph nodes are divided into two groups: (a) superficial and (b) deep (Fig. 10.4).

FIG. 10.4 A, Superficial cervical nodes; B, deep cervical nodes. SM1, submental; SM2, submandibular; RP, retropharyngeal; Pr.T, pretracheal; Pa.T, paratreacheal.

Superficial lymph nodes Following groups of superficial lymph nodes are present at the craniocervical junction. (a) Submental nodes (b) Submandibular lymph nodes (c) Preauricular (superficial parotid) nodes (d) Retroauricular nodes (e) Occipital nodes Others (a) Nodes lying along the facial vein (b) Node lying along the anterior jugular vein (c) Nodes lying along the external jugular vein

Deep lymph nodes Groups of lymph nodes lying along the internal jugular vein (a) Jugulo-digastric nodes (b) Jugulo-omohyoid nodes Others (a) Retropharyngeal (b) Prelaryngeal (c) Pretracheal and paratracheal

❖ Describe the sternocleidomastoid muscle in brief. AN29.1 The sternocleidomastoid muscle is a large superficial muscle of the neck. It lies obliquely on the side of the neck between anterior and posterior triangles (Fig. 10.5). It stands out prominently when head is turned to the opposite side.

FIG. 10.5 Origin and insertion of sternocleidomastoid muscle.

Origin It arises by two heads – sternal and clavicular. Sternal head: By a rounded tendon from the upper part of the anterior surface of the manubrium sterni. Clavicular head: By the musculoaponeurotic fibres from the superior border and anterior surface of medial one-third of clavicle.

Insertion By a strong tendon into the lateral surface of mastoid process and by thick aponeurosis into the lateral half of superior nuchal line of the occipital bone.

Nerve supply

• Spinal accessory nerve (motor) • Ventral rami of C2 and C3 (proprioceptive)

Actions • Tilts the head towards the shoulder on the same side and simultaneously rotates the head in such a way that the face is turned to the opposite side and upwards. • Both the muscles acting together draw the head forwards and downwards, as in lifting/elevating the head from the pillow when lying down on bed in supine position.

Applied anatomy Torticollis: It is a deformity of the neck in which the head is bent to one side and chin faces towards the opposite side. It occurs due to spasm or contracture of the sternocleidomastoid muscle. ❖ Describe the posterior triangle under the following headings: (a) boundaries, (b) contents and (c) applied anatomy. AN29.1–29.4 It is a triangle on the side of neck.

Boundaries (fig. 10.6)

FIG. 10.6 Posterior triangle: A, muscles forming the floor of the posterior triangle; B, subdivisions and main contents of posterior triangle.

Anterior: Posterior border of sternocleidomastoid. Posterior: Anterior border of trapezius. Inferior (or base): Middle one-third of clavicle. Apex: Meeting point of sternocleidomastoid and trapezius at superior nuchal line of the occipital bone. Floor: It is muscular and formed by the following muscles from above to downwards (Fig. 10.6): • Semispinalis capitis • Splenius capitis • Levator scapulae • Scalenus medius

N.B. Floor is covered by the prevertebral layer of the deep cervical fascia (fascial carpet). Roof

• Investing layer of the deep cervical fascia • Superficial fascia containing platysma

Contents The main contents are (Fig. 10.6) • Roots and trunks of the brachial plexus • Third part of the subclavian artery • Subclavian vein • Spinal accessory nerve • Occipital artery • Lymph nodes • Inferior belly of omohyoid

Applied anatomy • Pus from tubercular abscess of cervical spine may track into the posterior triangle, deep to prevertebral layer of the deep cervical fascia (i.e. underneath the fascial carpet of posterior triangle), and may produce swelling. • Left supraclavicular lymph nodes (Virchow lymph nodes) may be enlarged in malignancy of stomach and other abdominal organs. ❖ What are the subdivisions of the posterior triangle? AN29.1–29.4 The posterior triangle is divided into two parts by an inferior belly of omohyoid: • A larger upper part is called occipital triangle because it contains occipital artery. • A smaller lower part is called subclavian triangle because it contains subclavian artery. It is also called supraclavicular triangle. ❖ Enumerate the structures piercing the roof of the posterior triangle. AN29.1–29.4 The roof of the posterior triangle is pierced by the following structures.

Four cutaneous nerves • Lesser occipital nerve (C2) • Great auricular nerve (C2 and C3) • Transverse cervical nerve (C2 and C3) • Supraclavicular nerves (anterior, middle and posterior; C3 and C4)

One vein • External jugular vein

❖ Describe the digastric (submandibular) triangle in brief. AN32.2

Boundaries (fig. 10.7)

FIG. 10.7 Digastric (submandibular) triangle: boundaries and contents. SG, submandibular gland.

Anteroinferiorly: Anterior belly of digastric. Posteroinferiorly: Posterior belly of digastric and stylohyoid. Superiorly (base) • Base of mandible • Imaginary line, joining the angle of mandible to the mastoid process Floor: From anterior to posterior, it is formed by three muscles: • Mylohyoid • Hyoglossus • Middle constrictor of pharynx Roof: It is formed by:

• Investing layer of the deep fascia enclosing submandibular gland • Superficial fascia containing: ■ Cervical branch of the facial nerve ■ Cutaneous branch of great auricular nerve ■ Common facial vein

Contents These are: (a) In Anterior Part

(b) In Posterior Part

• Submandibular gland • Submandibular lymph nodes • Submental artery • Mylohyoid nerve and vessels • Facial artery • Facial vein

• Parotid gland • External carotid artery • Styloid process and muscles attached to it (styloglossus, stylopharyngeus and stylohyoid muscles) • Upper part of carotid sheath with its contents

❖ Describe the boundaries and contents of the carotid triangle. AN32.2

Boundaries (fig. 10.8)

FIG. 10.8 Carotid triangle: boundaries and contents.

Anterosuperiorly: Posterior belly of the digastric and the stylohyoid. Anteroinferiorly: Superior belly of the omohyoid. Posteriorly: Anterior border of the sternocleidomastoid.

Contents Arteries • Common carotid artery • Internal carotid artery • External carotid artery and its first five branches (superior thyroid, lingual, facial, ascending pharyngeal and occipital arteries) Veins • Internal jugular vein • Common facial vein • Pharyngeal vein • Lingual vein Nerves • Vagus nerve • Superior laryngeal branch of the vagus nerve, dividing into the external and internal laryngeal nerves • Spinal accessory nerve running obliquely backwards and downwards over the internal jugular vein • Hypoglossal nerve running horizontally forwards over the external carotid, internal carotid and lingual (loop) arteries • Ansa cervicalis • Sympathetic chain Lymph nodes Deep cervical lymph nodes Special structures • Carotid sinus • Carotid body

❖ Write a short note on the ansa cervicalis. AN35.1 The ansa cervicalis is a ‘U’-shaped nerve loop derived from ventral rami of C1, C2 and C3 nerves (Fig. 10.9).

FIG. 10.9 Formation and distribution of ansa cervicalis.

Location It lies on the anterior wall of the carotid sheath in the carotid triangle.

Roots • Superior root (limb) is formed by descendens hypoglossi (a branch of hypoglossal nerve), which contains the fibres of the ventral ramus of C1 nerve. • Inferior root (limb) is formed by descendens cervicalis, which contains the fibres of the ventral rami of C2 and C3 nerves.

Distribution Superior root → superior belly of omohyoid Inferior root → sternohyoid, sternothyroid and inferior belly of omohyoid ❖ Describe briefly carotid sinus and carotid body.

Carotid sinus It is a dilatation in the terminal part of common carotid artery and/or the beginning of

internal carotid artery. It is richly innervated by glossopharyngeal and sympathetic nerves. It functions as baroreceptor. The pressure on the carotid sinuses (in individuals with carotid sinus hypersensitivity) can lead to slowing of heart rate (bradycardia) and syncope (carotid sinus syndrome).

Carotid body It is a small, reddish-brown oval body that lies behind the bifurcation of common carotid artery. It is supplied by glossopharyngeal, vagus, and sympathetic nerves. It acts as chemoreceptor and responds to O2 and CO2 level, and pH of the blood. ❖ Describe the external carotid artery in brief. AN43.5, AN43.6, AN43.8, AN43.9

Origin and extent • It is one of the two terminal branches of the common carotid artery. • It extends from the level of upper border of thyroid cartilage to the back of the neck of mandible, where it terminates by dividing into superficial temporal and maxillary arteries.

Branches (fig. 10.10) They are eight in number which corresponds to the number of alphabets in the term ‘EXTERNAL’, i.e. 8.

FIG. 10.10 Branches of the external carotid artery.

From below to upwards, these are

❖ Write a short note on the facial artery. AN28.3

Origin and extent (fig. 10.11) It arises from the anterior aspect of external carotid artery in the carotid triangle of neck, just below the level of tip of greater cornu of the hyoid bone.

FIG. 10.11 Course and branches of the facial artery.

It extends from its site of origin in the neck to the medial angle of eye in the face, where it terminates by anastomosing with the dorsal nasal artery, a branch of the ophthalmic artery.

Branches In the neck • Ascending palatine artery • Glandular branches to the submandibular gland • Tonsillar artery • Submental artery In the face • Superior labial artery • Inferior labial artery • Lateral nasal branch • Unnamed muscular branches

N.B. Terminal part of the facial artery is called angular artery. The facial artery is tortuous to allow the movements of pharynx, mandible, lips and cheeks.

Applied anatomy The pulsations of the facial artery can be felt:

• On the base of mandible, at the anteroinferior angle of the masseter • 1.25 cm lateral to the angle of mouth, just lateral to modiolus with index finger put in the oral cavity and thumb placed on the outer aspect of the cheek ❖ Describe the boundaries and contents of the muscular triangle. AN32.2

Boundaries Anteriorly: Anterior median line of the neck. Posterosuperiorly: Superior belly of omohyoid. Posteroinferiorly: Anterior border of the sternocleidomastoid.

Contents Infrahyoid (ribbon) muscles:

N.B. All the infrahyoid muscles are supplied by the branches of ansa cervicalis except thyrohyoid, which is supplied by the nerve to thyrohyoid – a branch of the hypoglossal nerve containing C1 fibres. ❖ Describe the boundaries and contents of submental triangle. AN32.2

Boundaries Lateral (on each side): Anterior belly of digastric. Base: Body of hyoid bone. Apex: Symphysis menti. Floor:

Oral diaphragm (formed by mylohyoid muscles). Roof: Investing layer of deep cervical fascia.

Contents • Submental lymph nodes (three to four in number) • Submental veins, which unite to form anterior jugular veins ❖ Enumerate the structures in the anterior median line of the neck. From above to downwards, these are • Mylohyoid raphe (a fibrous raphe extending from the symphysis menti to the hyoid bone) • Body of hyoid bone • Median thyrohyoid ligament • Angle of thyroid cartilage (Adam’s apple in male) • Median cricothyroid ligament • Cricoid cartilage • First ring of the trachea • Isthmus of the thyroid gland lying on 2nd, 3rd and 4th tracheal rings • Infrahyoid veins and thyroidea ima artery (sometimes) • Jugular venous arch connecting two anterior jugular veins

N.B. The anterior median region of the neck includes 2- to 3-cm wide strip in the anterior midline of the neck, extending from the symphysis menti to the suprasternal notch. ❖ Describe the boundaries, contents and applied anatomy of the suboccipital triangle. AN42.2 The suboccipital triangle is an intermuscular triangular space situated deep in the suboccipital region (Fig. 10.12).

FIG. 10.12 Boundaries and contents of suboccipital triangle.

Boundaries Superomedially: Rectus capitis posterior major supplemented by the rectus capitis posterior minor. Superolaterally: Obliquus capitis superior. Inferiorly Obliquus capitis inferior. Floor • Posterior arch of atlas • Posterior atlanto-occipital membrane Roof • Medially ■ Dense fibrous tissue covered by semispinalis capitis • Laterally ■ Longissimus capitis ■ Splenius capitis

Contents • Third part of the vertebral artery • Dorsal ramus of the 1st cervical nerve (suboccipital nerve) • Greater occipital nerve (dorsal ramus of C2) • Suboccipital plexus of veins

Applied anatomy The suboccipital triangle is the • Site for cisternal puncture • Site through which neurosurgeons approach the posterior cranial fossa of cranial cavity

11

Parotid and submandibular regions Parotid region ❖ What are the boundaries of parotid region? AN28.9

Boundaries Anterior: Anterior border of masseter Posterior: Mastoid process Above: Zygomatic arch Below: Line joining the angle of mandible to the mastoid process ❖ What is parotid bed? AN28.9 It is the retromandibular space where the parotid gland lies.

Boundaries Anterior: Posterior border of ramus of mandible Posterior: Mastoid process Superior: External acoustic meatus Medial: Styloid process

N.B.

The parotid-bed is made soft by the muscles covering its anterior, posterior and medial bony boundaries (i.e. ramus of mandible is covered by masseter and medial pterygoid muscles; mastoid process is covered by sternocleidomastoid and posterior belly of digastric muscle; and styloid process is covered by styloglossus, stylohyoid and stylopharyngeus muscles). ❖ Describe the parotid gland under the following headings: (a) external features, (b) relations, (c) nerve supply and (d) applied anatomy. AN28.9

External features The parotid gland is the largest salivary gland (weight: 25 g) located in the parotid region. It resembles three-sided inverted pyramid and presents the following features (Figs 11.1 and 11.2).

FIG. 11.1 Main features of the parotid region.

Apex: Directed downwards Base: Directed upwards Three surfaces: • Superficial (largest) • Anteromedial • Posteromedial Three borders:

• Anterior • Posterior • Medial

Relations (figs 11.2 and 11.3) Apex: It is related to posterior belly of digastric.

FIG. 11.2 Horizontal section through parotid gland showing its relations and the structures passing through it. The figure in the inset shows borders and surfaces of the parotid gland. SG, styloglossus muscle; SH, stylohyoid muscle; SP, stylopharyngeus muscle.

FIG. 11.3 Structures emerging at the periphery of the parotid gland.

N.B. The cervical branch of the facial nerve and anterior and posterior divisions of the retromandibular vein emerge through the apex. Base: It is related to: • External acoustic meatus • Posterior aspect of the temporomandibular joint

N.B. The superficial temporal vessels and auriculotemporal nerve emerge through the base. Superficial surface: It is related to: • Skin • Superficial fascia containing platysma, branches of great auricular nerve and superficial parotid lymph nodes • Parotidomasseteric fascia

• Deep parotid lymph nodes embedded in the gland Anteromedial surface: It is related to: • Masseter • Posterior border of ramus of mandible • Medial pterygoid Posteromedial surface: It is related to: • Mastoid process and muscles covering it • Styloid process and muscles covering it

N.B. The facial nerve trunk and external carotid artery enter the gland through this surface. Anterior border: The following structures (from above to downwards) emerge underneath this border:

Posterior border: The following structures emerge from underneath this border: • Posterior auricular nerve • Posterior auricular vessels Medial border: It is related to the lateral wall of pharynx.

Nerve supply (fig. 11.4)

FIG. 11.4 Nerve supply of the parotid gland. ATN, auriculotemporal nerve.

Secretomotor (parasympathetic): • Preganglionic fibres arising from inferior salivatory nucleus and travel to otic ganglion as follows: Inferior salivatory nucleus → Glossopharyngeal nerve → Tympanic branch of glossopharyngeal nerve (Jacobson’s nerve) → Tympanic plexus → Lesser petrosal nerve → Relay in otic ganglion • Postganglionic fibres arise from otic ganglion and travel through auriculotemporal nerve to supply the parotid gland. Vasomotor (sympathetic): • Preganglionic fibres arise from T1 segment of spinal cord and relay in the superior cervical sympathetic ganglion. • Postganglionic fibres arise from superior cervical sympathetic ganglion, run along the arteries (e.g. external carotid artery) to supply the gland. Sensory: • Auriculotemporal nerve • Great auricular nerve

N.B. The sympathetic and sensory fibres pass through the otic ganglion but do not relay in it.

Applied anatomy Mumps (viral parotitis): It is the inflammation of parotid gland by mumps virus. Mumps characteristically do not suppurate. In adults, the mumps may cause complications like orchitis in male, oophoritis in female and pancreatitis in both sexes. Parotid swellings: These are very painful due to unyielding nature of parotid fascia, which encloses the gland. Parotid abscess: It is drained by a transverse incision in the parotidomasseteric fascia to avoid injuries to the facial nerve (Hilton’s method). Frey syndrome: It occurs due to the damage of branches of auriculotemporal and great auricular nerves by penetrating wounds in the parotid region. During regeneration, secretomotor fibres of auriculotemporal nerve join the fibres of great auricular nerve. As a result, the stimulation of parotid gland causes stimulation of great auricular nerve, which leads to sweating and redness (hyperaemia) in the area of distribution of great auricular nerve (e.g. parotid region).  AN28.10 ❖ Write a short note on the parotid capsule.  AN28.9 It is a facial capsule that encloses the parotid gland (Fig. 11.5). It is derived from investing layer of the deep cervical fascia. At the lower end of the gland, the fascia splits into superficial and deep laminae to enclose the gland. • The superficial lamina is extremely dense and tough, and is attached to the lower border of the zygomatic arch. It blends with the perimysium of masseter to form the parotidomasseteric fascia. • The deep lamina is relatively thin and is attached to the styloid process, tympanic plate and mandible. It also forms the stylomandibular ligament.

FIG. 11.5 Parotid capsule.

❖ Enumerate the structures present within the parotid gland. AN28.9 From superficial to deep, these are as follows (Fig. 11.2): • Deep parotid lymph nodes • Facial nerve • Retromandibular vein • External carotid artery

N.B. Sometimes deep parotid lymph nodes are also present within the parotid gland. ❖ Write a short note on the parotid duct (Stensen’s duct). AN28.9

General features • It is a 5-cm long and 3-mm wide tube. • It emerges from middle of the anterior border of the parotid gland and opens into the vestibule of mouth opposite the crown of 2nd upper molar tooth on the parotid papilla.

Course (fig. 11.6) • Runs forward over masseter muscle. • Turns medially (1st bend) at the anterior border of masseter and pierces buccal pad of fat, buccopharyngeal fascia and buccinator muscle in succession. • Runs forward (2nd bend) between the buccinator and mucous membrane for some distance. • Turns medially (3rd bend) to open on the summit of the parotid papilla to pour its secretions in the vestibule of mouth.

FIG. 11.6 Course of parotid duct, showing three bends marked as I, II and III.

Applied anatomy • The parotid duct can be palpated and rolled on the firm anterior edge of masseter. • Sinuous course of the parotid duct serves a valve-like mechanism to prevent the entry of infective agents in the duct from mouth during violent blowing. ❖ Describe the development of the parotid gland in brief. AN43.4 • It develops as a furrow/groove arising from ectodermal lining of stomodeum between the mandibular and maxillary arches at the site of future lateral angle of mouth. • The ectodermal groove is converted into a tube. • The anterior part of the tube forms the parotid duct. • The posterior part of the tube branches rapidly in the substance of cheek and forms the parenchyma, i.e. glandular substance. • Supporting tissue of gland develops from surrounding mesenchyme. ❖ Describe the histological features of the parotid gland in brief. AN43.2 It is a compound tubuloalveolar gland and presents the following histological features (Fig. 11.7).

FIG. 11.7 A, Histological features of parotid salivary gland; B, the figure in the inset shows detailed structure of a serous acinus. Source: (Source for Fig. 11.7A: Textbook of Histology: Atlas and Practical Guide, 3rd Edition: JP Gunasegaran, Box 3.1, Page 43, RELX India Private Limited, 2016.)

Connective tissue: The connective tissue (fibrous) septa divide the gland into lobes and lobules. Acini: • Presence of large number of serous acini. • Acini are round and shows biphasic stain with H&E stain, basophilic in basal part and eosinophilic in apical parts. They have with very small lumen. • Acini are lined by pyramidal cells with round nuclei placed near the centre. Ducts: • Intercalated ducts are lined by simple squamous epithelium. • Striated ducts are lined by simple columnar epithelium with basal striations. They are stained dark with eosin.

• Interlobular ducts are present in connective tissue septa between the lobules and are lined by stratified cuboidal/low columnar epithelium.

N.B. The intercalated and striated ducts together form intralobular ducts.

Submandibular region ❖ Write a short note on the digastric muscle. AN32.2 • This muscle lies above hyoid bone in the submandibular region. • It has two bellies – anterior and posterior.

Origin Anterior belly: It is unipennate and arises from the digastric fossa of mandible. Posterior belly: It is bipennate and arises from the mastoid notch of occipital bone.

Insertion The two bellies meet to form an intermediate tendon, which is anchored by a fibrous pulley to the hyoid bone.

Nerve supply Posterior belly: By facial nerve (nerve of second arch) Anterior belly: By mandibular nerve through nerve to mylohyoid (nerve of 1st arch)

Action It elevates the floor of mouth and hyoid bone during the second phase of deglutition. ❖ List the relations of posterior belly of the digastric muscle. AN32.2

Superficial relations • Skin • Superficial fascia • Deep fascia

• Mastoid process • Parotid gland

Deep relations (fig. 11.8) • Transverse process of atlas crossed superficially by spinal accessory nerve. • Both the internal and external carotid arteries. • Internal jugular vein. • Vagus nerve descending between the internal jugular vein and the internal carotid artery. • Hypoglossal nerve. • Along its upper border the posterior auricular branch of external carotid artery and along its lower border the occipital branch of external carotid artery pass upwards and laterally. • Lingual and facial arteries.

FIG 11.8 Deep relations of the posterior belly of digastric muscle.

❖ Describe the origin, insertion, nerve supply and actions of the hyoglossus muscle. AN39.1 It is the key muscle of the submandibular region.

Origin From greater cornu and lateral part of the body of hyoid bone.

Insertion

Fibres run upwards and forwards to be inserted into the side of tongue. The styloglossus muscle interlaces at its insertion.

Nerve supply Hypoglossal nerve (CN XII).

Action Depresses the tongue to make its dorsum convex. ❖ Enumerate the relations of the hyoglossus muscle. AN39.1

Superficial relations (fig. 11.9)

FIG. 11.9 Superficial relations of hyoglossus muscle.

From above to downwards, these are as follows: • Lingual nerve with the submandibular ganglion suspended from it. • Deep part of the submandibular gland and submandibular duct. • Hypoglossal nerve and its venae comitantes. • Loop of communication between the lingual and the hypoglossal nerves. • Styloglossus muscle.

Deep relations Two muscles: Middle constrictor and genioglossus An artery: Lingual artery and its dorsal linguae branches A nerve:

Glossopharyngeal nerve A ligament: Stylohyoid ligament ❖ Enumerate the structures passing deep to the posterior border of hyoglossus.  AN39.1 From above to downwards, these are as follows: • Glossopharyngeal nerve (CN IX) • Stylohyoid ligament • Lingual artery ❖ Describe the submandibular gland under the following headings: (a) location and parts, (b) external features, (c) relations, (d) nerve supply and (e) applied anatomy.  AN34.1

Location and parts The submandibular gland lies in the digastric triangle. It is divided into two parts: • Superficial • Deep The large, superficial part is located below the mylohyoid muscle and almost fills the digastric triangle. The small, deep part is located above the mylohyoid muscle. The two parts are continuous with each other around the free posterior margin of the mylohyoid muscle (Fig. 11.10).

FIG. 11.10 Horizontal section through submandibular region showing the location and parts of submandibular gland. The sublingual salivary gland is also seen.

The gland is enclosed between the two layers of investing layer of deep cervical fascia. The superficial layer covers the superficial surface of the gland and is attached to the base of the mandible. The deep layer covers the medial surface of the gland and is attached to the mylohyoid line of the mandible.

Superficial part of submandibular gland External features: It presents: • Two ends: Anterior and posterior • Three surfaces: Inferior, lateral and medial

Relations (figs 11.11 and 11.12)

FIG. 11.11 Relations of the superficial (inferior) surface of the submandibular salivary gland. The relations of anterior part of medial (deep) surface are also seen.

FIG. 11.12 Relations of the medial (deep) surface of submandibular gland.

Inferior surface is related to: • Skin • Superficial fascia • Platysma • Deep fascia • Common facial vein • Cervical branch of facial nerve • Submandibular lymph nodes Lateral surface is related to: • Submandibular fossa of mandible • Medial pterygoid muscle • Facial artery Medial surface: It is extensive and is divided into three parts: anterior, intermediate and posterior. • Anterior part is related to: ■ Mylohyoid muscle ■ Mylohyoid nerve and vessels ■ Submental artery (a branch of facial artery) • Intermediate part is related to: ■ Hyoglossus muscle

■ Lingual nerve ■ Submandibular ganglion ■ Hypoglossal nerve ■ Submandibular duct • Posterior part is related to: ■ Styloglossus muscle ■ Stylopharyngeus muscle ■ Middle constrictor of pharynx ■ Glossopharyngeal nerve ■ Lingual artery

Deep part of submandibular gland • It is small and lies on hyoglossus muscle. • Posteriorly, it is continuous with superficial part around the posterior border of the mylohyoid muscle (Fig. 11.10). • Submandibular duct emerges from its anterior end.

Nerve supply (fig. 11.13)

FIG. 11.13 Nerve supply of submandibular gland/submandibular ganglion and its connections.

Secretomotor (parasympathetic): • Preganglionic fibres arise from superior salivatory nucleus, pass successively through facial nerve, geniculate ganglion, chorda tympani and the lingual

nerves to reach and relay in the submandibular ganglion. • Postganglionic fibres arise from submandibular ganglion and enter the submandibular gland to supply it. Vasomotor (sympathetic): • Preganglionic fibres arises from T1 spinal segment and relay in the superior cervical sympathetic ganglion. • Postganglionic fibres arises from superior cervical sympathetic ganglion and run along the arteries to supply the gland. These fibres do not relay in the ganglion. Sensory: • Lingual nerve. • Sensory fibres also do not relay in the ganglion.

Applied anatomy • Formation of calculi is more common in submandibular gland than in parotid gland, because of (a) its secretion being more viscous and (b) tortuous upward course of its duct (i.e. drainage occurs against gravity). This leads to stasis of secretion which leads to formation of stone. AN34.2 • To excise submandibular gland, the skin incision is given at about 4 cm below the angle of mandible to avoid injury to the marginal mandibular nerve. • A stone in submandibular duct can be palpated bimanually in the floor of mouth and may even be seen if sufficiently large. • Submandibular gland swelling can be palpated bimanually as it lies on both the aspects of the oral diaphragm (i.e. mylohyoid muscle). ❖ Describe the histological features of the submandibular salivary gland in brief.  AN43.2 The important histological features of the submandibular salivary gland (Fig. 11.14): • Presence of both serous and mucous acini. • Mucous acini are made up of truncated columnar cells with flattened basal nuclei. They are stained light pink with H&E. • Serous acini are described on p. 120. They stain basophilic in the basal part and pink in the apical part. • Serous demilunes of Giannuzzi capping some of the mucous acini are seen. • Moderately developed duct system.

FIG. 11.14 Histological features of submandibular gland; The figure in the inset on the right side shows detailed structure of (A) mucous acinus and (B) mucous acinus with serous demilune. Source: (Source for left side Fig.: Textbook of Histology: Atlas and Practical Guide, 3rd Edition: JP Gunasegaran, Box 3.3, Page 44, RELX India Private Limited, 2016.)

❖ Write briefly about sublingual gland. AN34.1 • It is small, almond-shaped salivary gland located in the floor of mouth on the mylohyoid muscle underneath the oral mucosa. • It weighs about 3–4 g. • About 15–20 ducts emerge from the gland (ducts of Rivinus) and open directly into the floor of mouth on the sublingual fold. • Its nerve supply is similar to that of submandibular gland.

Applied anatomy The cystic degeneration of sublingual gland forms a swelling, which resembles the belly

of a frog; hence, it is called ranula. ❖ Write a short note on the submandibular ganglion. AN34.1 • The submandibular ganglion is a small parasympathetic ganglion lying on the hyoglossus muscle (see Fig. 11.13). • Topographically, it is connected to lingual nerve, whereas functionally it is connected to the facial nerve. (Note: The chorda tympani nerve is a branch of the facial nerve.)

Roots Parasympathetic root: • Preganglionic fibres arise from superior salivatory nucleus. These fibres then pass successively through nervus intermedius, facial nerve, chorda tympani and lingual nerves to relay in the ganglion. • Postganglionic fibres arise from ganglion and supply submandibular and sublingual salivary glands. Sympathetic root: • Preganglionic fibres arise from T1 spinal segment and relay in the superior cervical sympathetic ganglion. • Postganglionic fibres arise from the superior cervical sympathetic ganglion, form plexus around external carotid artery, pass through ganglion without relay, and supply the submandibular and sublingual glands. Sensory: • Lingual nerve. • Sensory fibres also do not relay in the ganglion. ❖ Describe the chorda tympani nerve in brief. AN28.4

Origin The chorda tympani nerve is a branch of facial nerve. It arises from facial nerve at about 6 mm above the stylomastoid foramen.

Functional components • General visceral efferent (GVE) fibres (i.e. postganglionic parasympathetic fibres), which provide secretomotor supply to the submandibular and sublingual salivary glands.

• Special visceral afferent (SVA) fibres, which carry taste sensations from anterior two-third of the tongue, except from vallate papillae.

Course (fig. 11.15) Arises from vertical part of the facial nerve → enters middle ear through posterior canaliculus → runs across the lateral wall of middle ear → enters anterior canaliculus → enters infratemporal fossa through petrotympanic fissure → crosses medial aspect of spine of sphenoid → joins lingual nerve.

FIG. 11.15 Chorda tympani nerve. SSN, superior salivatory nucleus; NTS, nucleus tractus solitarius; SG, submandibular ganglion.

Applied anatomy The lesions of chorda tympani nerve leads to: • Decrease in the production of saliva • Loss of taste sensations in the anterior two-third of tongue

12

Deep structures of the neck and prevertebral region Deep structures of the neck ❖ Describe the thyroid gland under the following headings: (a) gross anatomy, (b) parts and relations, (c) blood supply, (d) development and (e) applied anatomy.  AN35.2

Gross anatomy (fig. 12.1) • It is a large endocrine gland situated on the front (and side) of the lower part of the neck. • It consists of right and left lobes, joined by an isthmus. Sometimes, a third small pyramidal lobe may project upwards from isthmus.

FIG. 12.1 Location, parts and extent of the thyroid gland.

Situation and extent (fig. 12.1)

• The thyroid gland is situated in front of C5 to C7 and T1 vertebrae. • Each lobe extends from the oblique line of the thyroid cartilage to 4th or 5th tracheal ring. • The isthmus extends from 2nd to 4th tracheal ring. Weight: 25 g (larger in females) Dimensions • Each lobe measures 5 × 2.5 × 2.5 cm • Isthmus measures 1.25 × 1.25 cm Capsules/coverings The thyroid gland is enclosed into two capsules: true and false. • True capsule: It is formed by the condensation of the connective tissue of the gland itself at its periphery. • False capsule: It is formed by the pretracheal layer of the deep cervical fascia. It is thin along the posterior border but thick on the medial surface of the gland, where it thickens to form a suspensory ligament of Berry connecting the gland to the cricoid cartilage.

N.B. A dense capillary plexus is present deep to the true capsule. Hence, to avoid haemorrhage during thyroidectomy, the thyroid gland is removed along with its true capsule.

Parts and relations (fig. 12.2)

FIG. 12.2 Transverse section of anterior part of the neck at the level of thyroid isthmus, showing relations of thyroid gland.

Thyroid lobe Each lobe is conical in shape and presents the following features: • Apex • Base • Three surfaces: lateral, medial and posterolateral ■ Lateral/superficial surface is covered from deep to superficial by: • Sternothyroid • Sternohyoid, and superior belly of omohyoid • Anterior border of sternocleidomastoid ■ Medial surface is related to: • Two tubes: Trachea and oesophagus • Two muscles: Inferior constrictor and cricothyroid • Two nerves: External laryngeal and internal laryngeal ■ Posterolateral/posterior surface is related to carotid sheath. • Two borders: Anterior and posterior ■ Anterior border is related to anterior branch of superior thyroid artery. ■ Posterior border is related to: • Longitudinal anastomosis between superior and inferior thyroid arteries • Superior and inferior parathyroid glands • Inferior thyroid artery • Thoracic duct (on left side only) Isthmus The isthmus presents: • Two surfaces: Anterior and posterior ■ Anterior surface is related to: • Right and left sternothyroid and sternohyoid muscles • Anterior jugular veins ■ Posterior surface is related to 2nd, 3rd and 4th tracheal rings. • Two borders: Superior and inferior ■ Upper border is related to anastomosis between the anterior branches of right and left superior thyroid arteries. ■ Inferior border is related to the inferior thyroid veins.

Blood supply Arterial supply (fig. 12.3)

• Superior thyroid artery is a branch of the external carotid artery. It supplies upper two-third of the thyroid lobe and upper half of the isthmus. Superior thyroid artery is accompanied by external laryngeal nerve which leaves it near the upper pole of the gland. • Inferior thyroid artery is a branch of the thyrocervical trunk. It supplies lower onethird of the thyroid lobe and lower half of the isthmus. Inferior thyroid artery is closely related to the recurrent laryngeal nerve near the lower pole of the thyroid gland. • Arteria thyroidea ima (if present) is a branch of brachiocephalic trunk or arch of aorta. It supplies the isthmus. • Small accessory arteries derived from the oesophageal and tracheal arteries.

FIG. 12.3 Arterial supply of the thyroid gland.

Venous drainage (fig. 12.4) • Superior thyroid vein: It emerges from the upper pole and drains into internal jugular vein. • Middle thyroid vein (a short wide venous trunk): It emerges from middle of the thyroid lobe and drains into internal jugular vein. • Inferior thyroid vein: It emerges from lower border of the isthmus and drains into left brachiocephalic vein. • A fourth vein (of Kocher), if present, emerges between middle and inferior thyroid veins and drains into internal jugular vein.

FIG. 12.4 Venous drainage of the thyroid gland.

Development (fig. 12.5) • The thyroid gland develops from a median endodermal diverticulum – the thyroglossal duct, which grows downwards in front of neck from the floor of primitive pharynx. • The distal end of thyroglossal duct bifurcates and then differentiates to form thyroid gland. The remaining part of the duct obliterates.

FIG. 12.5 Development of the thyroid gland; note the different stages in the development.

N.B.

The follicular cells develop from the thyroglossal duct, while the parafollicular (C cells) cells develop from the neural crest cells of ultimobranchial bodies.

Applied anatomy • Enlargement of the thyroid gland is called goitre. • During thyroidectomy (removal of thyroid gland), the superior thyroid artery should be ligated as near to the superior pole of gland as possible, while inferior thyroid artery should be ligated as away from the gland as possible to avoid injuries to external laryngeal and recurrent laryngeal nerves, respectively. • Swellings arising from thyroid gland moves up and down during swallowing because thyroid capsule is attached to the laryngeal skeleton. • Partial thyroidectomy is preferred to total thyroidectomy to avoid postoperative hypothyroidism due to inadvertent removal of parathyroid glands. • Compression of structures by large goitre leads to characteristic symptoms of: ■ Dyspnoea, due to compression of trachea. ■ Dysphagia, due to compression of oesophagus. ■ Dysphonia, due to compression of recurrent laryngeal nerves. Mnemonic: 3D • Thyroglossal cyst ■ It results from persistence of a portion of thyroglossal duct. ■ It is commonest congenital anomaly of thyroid gland. ■ It is usually located below the hyoid bone (subhyoid). ❖ Describe the histological features of the thyroid gland in brief. AN43.2 Microscopically, the thyroid gland consists of parenchyma and stroma (Fig. 12.6).

FIG. 12.6 Histological features of the thyroid gland.

Parenchyma • Presence of spheroidal thyroid follicles (about 0.9 mm in diameter). • Thyroid follicles are lined by simple cuboidal epithelium and filled with eosinophilic colloid material (thyroglobulin). • Simple cuboidal epithelium lining the thyroid follicles is made up of follicular cells. • Presence of parafollicular cells (C cells) in between the thyroid follicles in the connective tissue or sometimes within the follicles close to the basement membrane.

Stroma • It forms the connective tissue framework of the gland. • Stroma includes the capsule and sparse intralobular connective tissue rich in capillaries. ❖ Describe the parathyroid glands in brief. AN43.2

General features • These are two pairs (superior and inferior) of small endocrine glands. • The superior and inferior parathyroid glands are located on the posterior border of each thyroid lobe within the capsule of the thyroid gland. Each parathyroid gland is small, yellowish-brown, oval or lentiform body measuring 6 × 4 × 2 and weighing about 50 mg (about the size of a split pea). The superior and inferior parathyroid glands lie on the posterior aspect of the thyroid lobe along the anastomotic artery between the superior and inferior thyroid arteries, which is used as a guide to locate them during surgery.

Position/location Superior parathyroid It is more constant in position and usually lies at the middle of the posterior border of the lateral lobe of the thyroid gland at the level of cricoid cartilage. It usually lies between the true and false capsules of the thyroid gland and dorsal to the recurrent laryngeal nerve. Inferior parathyroid It is more variable in position. It may lie: • Within the thyroid capsule below the loop of inferior thyroid artery, near the lower pole of thyroid gland.

• Outside the thyroid capsule, immediately above the loop of inferior thyroid artery. • Within the substance of the thyroid gland near its posterior border.

Function The parathyroid glands secrete a hormone called parathormone, which plays an important role in calcium metabolism.

Development • Superior parathyroid develops from 4th pharyngeal pouch; hence, it is also called parathyroid IV. • Inferior parathyroid develops from 3rd pharyngeal pouch; hence, it is also called parathyroid III.

Applied anatomy • Hypoparathyroidism: It may occur due to inadvertent removal of the parathyroid glands during thyroidectomy. It leads to tetany due to low blood calcium level. Clinically, it presents as carpopedal spasm. • Hyperparathyroidism: It occurs due to tumours of the parathyroid glands. It leads to decalcification of bones and formation of renal stones due to high blood calcium level.

Prevertebral region ❖ What are scalene muscles? • These are deep muscles on the side of vertebral column of the neck (paravertebral region). • They extend from transverse processes of cervical vertebrae to the first two ribs. • They are usually three in number, i.e.: ■ Scalenus anterior (key muscle at the root of neck) ■ Scalenus medius (largest of the three scalene muscles) ■ Scalenus posterior ❖ Describe the origin, insertion, nerve supply, actions and relations of scalenus anterior muscle. AN29.4

Origin From anterior tubercles of transverse processes of C3 to C6 vertebrae (i.e. from all typical cervical vertebrae; Fig. 12.7).

FIG. 12.7 Attachments (origin and insertion) of scalenus anterior muscle.

Insertion Into scalene tubercle on the inner border of 1st rib.

Nerve supply By ventral rami of C4 to C6 spinal nerves.

Actions • Acting from below, it bends the neck forwards and laterally. • Acting from above, it elevates the 1st rib and thus acts as an accessory muscle of respiration.

Relations It is key muscle at the root of neck because many important structures are related to it. Anterior relations: • Two nerves: Phrenic nerve and descendens cervicalis • Two arteries: Transverse cervical and suprascapular • Two veins: Anterior jugular and subclavian • Two muscles: Inferior belly of omohyoid and sternocleidomastoid

Posterior relations: • Branchial plexus (lower trunk) • Subclavian artery (second part) • Cervical pleura • Suprapleural membrane Lateral: Trunks of brachial plexus Medial: Thyrocervical trunk

Applied anatomy • Scalene syndrome occurs if roots of brachial plexus and subclavian artery are compressed between scalenus anterior muscle and first rib. • Cervical rib syndrome occurs when cervical rib passing through a gap between scalenus anterior and scalenus medius muscles compressing lower trunk of brachial plexus and subclavian artery. Clinically these syndromes present as: • Tingling and numbness in the little finger and medial half of ring fingers due to involvement of T8 and T1. • Absence of radial pulse due to compression of subclavian artery. ❖ Describe the scalenus medius muscle in brief. AN29.4 It is the longest and largest scalene muscle (Fig. 12.8).

FIG. 12.8 Attachments (origin and insertion) of scalenus medius muscle.

Origin From the posterior tubercles of transverse processes of C2 to C6 vertebrae.

Insertion On the superior surface of 1st rib behind the groove for subclavian artery and in front of tubercle of 1st rib.

Nerve supply Ventral rami of C3 to C8 spinal nerves.

Actions Same as scalenus anterior (see p. 135). ❖ Describe the boundaries of scalene triangle in brief and enumerate the structures passing through it. AN29.4

Location Root of the neck (Fig. 12.9)

FIG. 12.9 Scalene triangle (yellow coloured area). Note the boundaries and structures passing through it.

Boundaries Anterior: Scalenus anterior Posterior: Scalenus medius Base: 1st rib Apex: Meeting point of the scalenus anterior and scalenus medius

Structures passing through this triangle • Subclavian artery • Brachial plexus (lower trunk)

Applied anatomy • Scalene syndrome: Occurs due to compression of the lower trunk of brachial

plexus and subclavian artery in scalene triangle due to (a) spasm of scalene muscles or (b) presence of cervical rib. • Clinically, it presents as: ■ Tingling and numbness in the area of distribution of C8 and T1. ■ Progressive wasting of intrinsic muscles of the hand due to involvement of C8 and T1. ■ Absence of radial pulse due to compression of the subclavian artery. ❖ Describe the boundaries and contents of scalenovertebral triangle (triangle of vertebral artery).  AN43.8, AN43.9

Location Deep, at the front of the root of neck.

Boundaries Medial: Longus colli Lateral: Scalenus anterior Apex: Transverse process of C6 vertebrae Base: First part of the subclavian artery

Contents • First part of the vertebral artery • Thyrocervical trunk and vertebral artery • Stellate (inferior cervical sympathetic) ganglion • Thoracic duct (left side only) • Ansa subclavia ❖ What are subclavian arteries? List their branches. AN35.3 The right subclavian artery is a branch of brachiocephalic trunk, whereas the left subclavian artery is a direct branch of arch of aorta. On each side, the subclavian artery extends up to the outer border of the 1st rib.

Branches Each subclavian artery is divided into three parts by scalenus anterior muscle:

• First part (medial to scalenus anterior) gives rise to: ■ Thyrocervical trunk ■ Vertebral artery ■ Internal mammary artery (internal thoracic artery) ■ Costocervical trunk (on the left side) • Second part (behind the scalenus anterior) gives rise to costocervical trunk on the right side. • Third part (lateral to scalenus anterior): Usually does not give any branch, but sometimes it may give origin to dorsal scapular artery. ❖ Describe the vertebral artery in brief. AN43.8, AN43.9 • It is the largest branch of subclavian artery and is one of the two main sources of blood supply to the brain. • It runs upwards to enter the foramen transversarium of C6 vertebra. It then passes successively through the corresponding foramina of other cervical vertebrae above to reach the upper surface of C1 vertebra. Here, it turns medially in the suboccipital triangle to finally enter the cranial cavity through foramen magnum. Here, it joins the vertebral artery of opposite side at the lower border of pons to form the basilar artery.

Parts The vertebral artery is divided into four parts: • First part: It lies in the triangle of vertebral artery. • Second part: It passes through the foramina transversaria of C6 to C1 vertebrae. • Third part: It lies in the suboccipital triangle. • Fourth part: It lies in the cranial cavity.

Branches • In the neck: ■ Spinal branches ■ Muscular branches • In the cranial cavity: ■ Meningeal branch ■ Anterior spinal branch ■ Posterior spinal branch ■ Posterior inferior cerebellar artery ■ Medullary branches ❖ Describe the origin, course and termination of internal carotid artery. List its parts and their branches. AN43.8, AN43.9

Origin, course and termination • It begins as one of the two terminal branches of common carotid artery at the upper border of the thyroid cartilage. • It enters the cranial cavity through the carotid canal and foramen lacerum. • In the cranial cavity, it traverses through the cavernous sinus and finally terminates at the base of brain by dividing into anterior and middle cerebral arteries.

Parts and branches • Cervical part: ■ No branch • Petrous part: ■ Caroticotympanic branches to the middle ear ■ Pterygoid branch, which enters the pterygoid canal • Cavernous part: ■ Cavernous branches to the wall of cavernous sinus and trigeminal ganglion ■ Hypophyseal branches to the hypophysis cerebri ■ Meningeal branches • Cerebral part

❖ Describe the cervical sympathetic chain in brief and discuss its applied anatomy. AN35.6

Location and extent • It is part of the sympathetic chain that lies in front of the transverse processes of the cervical vertebrae and neck of 1st rib. • It continues upwards into the carotid canal as internal carotid nerve and downwards as thoracic part of the sympathetic chain.

Ganglia The cervical sympathetic chain possesses three ganglia: 1. Superior cervical ganglion: It lies in front of the transverse processes of C2 and C3, and represents the fused C1 to C4 primitive ganglia. 2. Middle cervical ganglion: It lies in front of the transverse process of C6 and represents the fused C5 and C6 primitive ganglia. 3. Inferior cervical ganglion: It lies in front of the transverse process of C7 and neck of

1st rib, and represents the fused ganglia of C7 and C6 primitive ganglia. It often fuses with T1 ganglion to form stellate ganglion.

Applied anatomy Horner syndrome: It occurs due to the lesion of cervical sympathetic chain involving T1 fibres supplying head and neck.

Clinical features • Anhydrosis (loss of sweating) • Partial ptosis (partial drooping of the upper eyelid) • Myosis (constriction of pupil) • Enophthalmos (recession of the eyeball) • Absence of the ciliospinal reflex ❖ Write a short note on the cervical plexus.

Formation and location (fig. 12.10) It is formed by the vertebral rami of C1 to C4 nerves, and lies on levator scapulae and scalenus medius muscles deep to prevertebral layer of deep cervical fascia.

FIG. 12.10 Cervical plexus and its cutaneous branches.

Important named branches (fig. 12.10) • Lesser occipital • Great auricular • Transverse cervical • Supraclavicular

N.B. C1 and C2 also contribute to form the inferior root of ansa cervicalis while C3 and C4 contribute to from the phrenic nerve. ❖ Describe the phrenic nerve in brief and discuss its applied anatomy. AN24.4

Origin It is formed by ventral rami of C3 to C5, with chief contribution being from C4.

Course It first descends obliquely on the anterior surface of scalenus anterior. Then it runs vertically downwards on the cervical pleura to enter thoracic cavity behind the 1st costal cartilage.

Branches and distribution • Motor branches to diaphragm • Sensory branches to central part of the diaphragm, pleura, pericardium and peritoneum (subdiaphragmatic)

Applied anatomy • Damage of phrenic nerve in the neck leads to paralysis of corresponding half of the diaphragm. The paralysed half of diaphragm becomes relaxed and pushed up into thorax by the positive intra-abdominal pressure. This leads to collapse of the lower lobe of the lung. • The fibres of C5 instead of joining phrenic nerve at its commencement may join it at the thoracic inlet through a communication received from nerve to subclavius. This communication is referred to as accessory phrenic nerve. In phrenic avulsion, the accessory phrenic nerve if present should be cut, otherwise C5 fibres will escape and diaphragm may continue to function and defeat the whole purpose of phrenic crush. • In pleurisy, the pain from diaphragmatic pleura may be referred to shoulder region, which receives nerve supply from some spinal segments as that of phrenic nerve, i.e. C3 and C4. ❖ Describe the internal jugular vein in brief. AN35.4

Formation, course and termination The internal jugular vein begins as direct continuation of the sigmoid sinus at the jugular foramen of skull and terminates by uniting with the subclavian vein behind the sternoclavicular joint to form the brachiocephalic (innominate) vein.

Tributaries • Inferior petrosal sinus • Common facial vein • Pharyngeal veins • Lingual vein • Superior thyroid vein • Middle thyroid vein • Kocher’s vein (if present)

N.B. The internal jugular vein is the chief vein of the head and neck. The deep cervical lymph nodes lie on and along the internal jugular vein.

Applied anatomy • The internal jugular vein is easily accessible in the lesser supraclavicular fossa and is used for recording jugular venous pulse pressure. • In congestive heart failure (CHF), it is the most dilated vein. ❖ Describe the atlanto-occipital joints in brief (Fig. 12.11). AN43.1

FIG. 12.11 Atlanto-occipital and atlantoaxial joints.

These are a pair of joints between the superior articular facets of atlas and condyles of the occipital bone.

Classification

Synovial joint of ellipsoid variety.

Articular surfaces • Condyle of occipital bone, superiorly. • Superior articular facet on the lateral mass of atlas, inferiorly. • The articular surfaces are reciprocally curved.

Ligaments These are • Fibrous capsule. • Anterior and posterior atlanto-occipital membranes.

Movements Nodding movements, i.e. the flexion and extension of the head that occurs when indicating approval; hence, these movements are also called ‘yes movements’. ❖ Describe the atlantoaxial joints in brief (Fig. 12.11). AN43.1

Atlantoaxial joints These are three in number: median atlantoaxial joint and right and left lateral atlantoaxial joints. Classification: • Median atlantoaxial joint: Pivot type of synovial joint • Lateral atlantoaxial joint: Plane type of synovial joint

Articular surfaces and ligaments • Median Atlantoaxial Joint (Fig. 12.12): It is formed between the dens of axis and the anterior arch of the atlas. The articular facet on the anterior aspect of dens articulates with the facet on the posterior surface of the anterior arch of atlas. Posteriorly between the base of dens of axis and transverse ligament of atlas lies a synovial bursa. It is a pivot type of synovial joint. • Lateral Atlanto-axial Joints: It is formed between the superior articular facet of axis and inferior articular facet of atlas. It is a plane type of synovial joint.

FIG. 12.12 Median atlantoaxial joint.

Movements The atlanto-occipital joints are responsible for rotation of the head. They permit the head to be turned from side-to-side, e.g. when rotating the head to indicate disapproval. Hence, these movements are also called ‘no movements’.

N.B. • Excessive rotational movements of the head are prevented by alar ligaments. • During rotation of the head, the dens of axis is held in a collar formed by the anterior arch and transverse ligament of atlas.

13

Oral cavity ❖ Write a short note on oral cavity. AN36.1–36.5

Boundaries (fig. 13.1)

FIG. 13.1 Subdivisions of oral cavity as seen in its coronal section.

Roof: Hard palate Floor: Oral diaphragm On either side: Cheek

Communications Anteriorly: To exterior through oral fissure guarded by the upper and lower lips. Posteriorly: To oropharynx through oropharyngeal isthmus guarded on either side by the

palatoglossal arch.

Structures present within oral cavity • Teeth and gums • Tongue • Soft palate ❖ What are the parts of oral cavity? List their boundaries. The oral cavity (mouth) is divided into two parts (Fig. 13.1): (a) an outer smaller part called vestibule of mouth and (b) an inner larger part called oral cavity proper.

Boundaries of vestibule of mouth Externally: Lips and cheeks Internally: Teeth and gums

Boundaries of oral cavity proper Above (roof): Hard palate Below (floor): Oral diaphragm formed by two mylohyoid muscles On either side (lateral): Teeth and gums ❖ Enumerate the ducts that open in the oral cavity.

Parotid ducts One on either side, open in the vestibule of mouth opposite the crown of 2nd upper molar tooth.

Submandibular ducts One on either side, open in the floor of oral cavity proper on the summit of sublingual papilla.

Sublingual ducts About a dozen in number, on either side, open in oral cavity proper on the sublingual

fold in a row. ❖ Enumerate the layers of cheek. From superficial to deep, the layers of cheek are as follows: • Skin • Superficial fascia containing buccal pad of fat • Buccopharyngeal fascia • Buccinator muscle • Submucosa • Buccal mucosa ❖ Briefly describe the parts of a tooth.

Parts Each tooth consists of three parts: Crown: A part that projects above the gum Neck: A part between crown and root, and surrounded by gum Root: A part that is embedded in the alveolar process of jaw ❖ Write a short note on the structure of the tooth. Structurally, each tooth is made up of five components (Fig. 13.2): • Pulp – an inner core of soft tissue containing blood vessels and nerves. • Dentine – a calcified material surrounding the pulp/pulp cavity. • Enamel – a densely calcified material covering the crown. • Cementum – a thin bony covering over the dentine. • Periodontal membrane – a fibrous membrane (akin to periosteum), connecting root of tooth with the alveolar socket.

FIG. 13.2 Structure of the tooth.

❖ Write a short note on the development of a tooth. The tooth develops from two sources: (a) ectodermal epithelial lining the alveolar process of jaw and (b) underlying neural crest mesenchyme. The details are summarized as follows: • Ectodermal epithelium lining of alveolar process → Dental lamina → Tooth buds/enamel organs → Ameloblasts → Enamel.

The structural components of tooth derived from these two sources are given in Table 13.1 TABLE 13.1 Source of Development of Various Components of the Tooth Ectoderm • Enamel

Neural Crest Mesenchyme • Pulp • Dentine • Cementum • Periodontal membrane

❖ Briefly describe the stages of tooth development. The stages in the development of tooth are: • Dental lamina

• Enamel organs • Dental papilla • Dental sac ❖ Briefly describe the eruption and shedding of teeth. The human beings are diphyodont animals, i.e. they have two sets of teeth, which develop at different times of life. The two sets are (a) deciduous teeth, which develop first and shed off and (b) permanent teeth, which appears later after the shedding of deciduous teeth and do not shed off. The usual time of eruption and shedding of the teeth is given in Tables 13.2 and 13.3. TABLE 13.2 Eruption and Shedding of Deciduous Teeth Teeth Medial incisor Lateral incisor First molar Canine Second molar

Eruption Time 6–8 months 8–10 months 12–16 months 16–20 months 20–24 months

Shedding Time 6–7 years 7–8 years 8–9 years 10–12 years 10–12 years

TABLE 13.3 Eruption and Shedding of Permanent Teeth

❖ Define tongue and list its functions. AN39.1 The tongue is a mobile, muscular organ situated in the floor of the mouth. It performs the following functions: • Taste • Speech • Mastication • Deglutition ❖ Enumerate the external features of the tongue. AN39.1

• Tongue has apex, tip and body. • Body presents: (a) Dorsal surface (also called dorsum) (b) Ventral surface (c) Right lateral margin (d) Left lateral margin

Dorsum of tongue Anatomically and developmentally, the dorsum of tongue is divided into two parts: anterior two-third (oral part) and posterior one-third (pharyngeal part). The two parts are separated from each other by a V-shaped sulcus – the sulcus terminalis. A blind foramen at the apex of sulcus is called foramen caecum. The foramen caecum represents the site of development of endodermal thyroglossal duct which grows down into the neck during embryonic development. Features on the dorsal surface of tongue (fig. 13.3) • Posterior one-third presents: ■ A large number of lymphoid follicles, which together form lingual tonsil. ■ A large number of openings of mucous and serous glands. • Anterior two-third presents: ■ A median furrow. ■ A large number of papillae.

FIG. 13.3 Features on the dorsal surface of the tongue.

Ventral surface of tongue Features on the ventral surface of tongue (fig. 13.3) The ventral surface of tongue presents:

• Frenulum linguae: A median fold of mucous membrane extending between the tongue and floor of the mouth. • Plica fimbriata: Two, fringed corrugated folds of mucous membrane, one on either side of frenulum linguae converging towards the tip of the tongue. • Prominences of deep lingual veins: These are visible, one on either side, between frenulum linguae and plica fimbriata. ❖ Enumerate the features in the sublingual region. These are shown in Fig. 13.4.

FIG. 13.4 Features on the ventral (inferior) surface of the tongue and sublingual region.

Sublingual papillae Two rounded elevations – one on either side of the root of frenulum linguae for the opening of the submandibular gland duct.

Sublingual folds Two elongated elevations – one on either side of frenulum linguae on the floor of mouth produced by an underlying sublingual salivary gland. The sublingual ducts open on these folds. ❖ Enumerate the various types of papillae of tongue. AN39.1

Vallate papillae They are of large size (1–2 mm in diameter) and are located in front of sulcus terminalis. They are 8–12 in number and surrounded by a ditch (trench). The taste buds are found in the wall of the ditch.

Fungiform papillae They are numerous and located near the tip and margins of the tongue. They have a narrow pedicle and rounded head.

Filiform papillae These are the smallest and most numerous, and cover the dorsum of the anterior twothird of the tongue and give it a characteristic velvety appearance.

Foliate papillae These are transverse mucosal folds on the lateral margins of the tongue, in front of palatoglossal arch. The papillae of tongue are shown in Fig. 13.3. ❖ Describe the tongue under the following headings: (a) muscles of tongue, (b) nerve supply, (c) blood supply, (d) lymphatic drainage and (e) applied anatomy.  AN39.1

Muscles of tongue The muscles of tongue are paired and divided into two groups: intrinsic and extrinsic. Intrinsic Muscles (arise and are inserted within the tongue). These are as follows: • Superior longitudinal • Inferior longitudinal • Transverse • Vertical Extrinsic Muscles (arise outside the tongue but are inserted into the tongue). These are as follows: • Genioglossus • Hyoglossus • Styloglossus • Palatoglossus The origin, insertion and actions of extrinsic muscles are given in Table 13.4. TABLE 13.4 Origin, Insertion and Actions of Extrinsic Muscles of the Tongue

The origin and insertion of extrinsic muscles of the tongue are shown in Fig. 13.5.

FIG. 13.5 Extrinsic muscles of the tongue.

Nerve supply Motor Supply: All the intrinsic and extrinsic muscles of the tongue are supplied by the hypoglossal nerve, except palatoglossus which is supplied by the cranial root of accessory nerve via pharyngeal plexus. Sensory supply: Anterior two-third of the tongue

• General sensations • Taste sensations

• Lingual nerve • Chorda tympani nerve

Posterior one-third of the tongue Posteriormost part of the tongue

• General sensations • Taste sensations • General sensations • Taste sensations

• Glossopharyngeal nerve • Glossopharyngeal nerve • Internal laryngeal nerve • Internal laryngeal nerve

Blood supply • Lingual artery (chief artery of tongue), a branch of external carotid artery supplies the oral part of the tongue. • Tonsillar and ascending palatine arteries, branches of the facial artery supply the pharyngeal part of the tongue.

Lymphatic drainage (fig. 13.6) The lymph from the tongue is drained by the following three sets of lymph vessels: marginal, central and posterior. Marginal Vessels: • From tip, drains bilaterally into the submental lymph nodes. • From margins and lateral part of the dorsum of tongue, drains into the submandibular and jugulo-omohyoid lymph nodes. Central Vessels: From central region of the dorsum of anterior two-third of tongue descends between genioglossi muscles and drains bilaterally into the submandibular lymph nodes. Posterior Vessels:  From posterior one-third of tongue drains bilaterally into the deep cervical lymph nodes, principally into the jugulodigastric lymph node (also called lymph node of the tongue; Fig. 13.6).

FIG. 13.6 Lymphatic drainage of the tongue: showing course and direction of apical, marginal

and basal lymph vessels.

Applied anatomy • Injury of hypoglossal nerve causes paralysis of muscles of the tongue on the side of lesion; hence, protruded tongue deviates to the same side (i.e. the side of injury) due to unopposed action of muscles on the healthy side. • In unconscious patient, the tongue may fall backward into oropharynx and obstruct the air passage to cause choking. This can be prevented by turning the head to one side and pulling the mandible forwards. • Carcinoma of tongue most commonly occurs along the margin of tongue. Cancer in posterior one-third of tongue has bad prognosis because of bilateral lymphatic drainage. ❖ Describe the development of tongue in brief and correlate the nerve supply of tongue with its development. AN43.4 The tongue develops in the floor of primitive pharynx from 1st, 2nd, 3rd and 4th pharyngeal arches. The epithelium, muscles and connective tissue of tongue develop as follows.

Epithelium (table 13.5) The epithelium of tongue develops from four swellings (Fig. 13.7):

FIG. 13.7 Development of the tongue: A, four swellings forming tongue with subdivision of hypobranchial eminence into cranial and caudal parts; B, definitive tongue.

TABLE 13.5 Correlation of Nerve Supply of Tongue with Its Development

Structure • Muscles of tongue • Epithelium of tongue ■ Anterior twothird of the tongue ■ Posterior onethird of the tongue ■ Posteriormost part of the tongue

Source of Development Occipital myotomes

Nerve Supply Hypoglossal nerve

• 1st arch (lingual swellings)

• Lingual nerve supplemented by chorda tympani (pretrematic branch of nerve of 2nd arch, i.e. facial) • Glossopharyngeal nerve

• 3rd arch (cranial part of the hypobranchial eminence) • 4th arch (caudal part of the hypobranchial eminence)

• Internal laryngeal nerve (a branch of the vagus nerve)

The various parts of the tongue develops from above-mentioned four swellings as follows: • Epithelium of anterior two-third of the tongue develops from two lingual swellings and tuberculum impar derived from 1st arch. The contribution from tuberculum impar is insignificant. • Epithelium of posterior one-third of the tongue develops from cranial (anterior) part of the hypobranchial eminence, derived from 3rd arch. • Epithelium of posteriormost part develops from caudal (posterior) part of the hypobranchial eminence derived from 4th arch.

Muscles (table 13.5) The muscles of tongue develop from occipital myotomes (Fig. 13.8).

FIG. 13.8 Development of muscles of the tongue.

Connective tissue The connective tissue of tongue develops from local mesenchyme. ❖ Give the embryological basis of tongue-tie (Fig. 13.9). AN43.4

FIG. 13.9 Tongue-tie.

• The tongue-tie (ankyloglossia) occurs when frenulum linguae is overdeveloped and extend up to the tip of tongue. The overdevelopment of frenulum linguae occurs due to incomplete separation of tongue from floor of primitive mouth by alveololingual sulcus. • Clinically it presents as: (a) Disturbed speech, i.e. difficulty in speaking (b) Restriction of tongue movements specially one which prevents protrusion

14

Pharynx and palate ❖ Describe the pharynx under the following headings: (a) parts, (b) structure, (c) muscles and (d) nerve supply. AN36.1–36.5 The pharynx is funnel-shaped muscular tube situated behind the nose, mouth and larynx.

Parts of pharynx (fig. 14.1) The pharynx is subdivided into three parts: • Nasopharynx, lying behind the nose. • Oropharynx, lying behind the mouth. • Laryngopharynx, lying behind the larynx.

FIG. 14.1 Location and subdivisions of the pharynx.

Functions • The nasopharynx provides passage to air only. • The oropharynx provides passage to both air and food. • The laryngopharynx provides passage to air only.

Structure of pharynx The pharyngeal wall consists of four layers. From within to outwards these are as follows: • Mucosa • Pharyngobasilar fascia • Muscular coat • Buccopharyngeal fascia

Muscles of pharynx Three pairs of constrictors (forming outer circular layer of muscle coat): • Superior constrictor • Middle constrictor • Inferior constrictor Three pairs of longitudinal muscles (forming inner longitudinal layer of muscular coat): • Stylopharyngeus • Palatopharyngeus • Salpingopharyngeus

Nerve supply Motor: All the muscles of pharynx are supplied by cranial root of accessory nerve (CN XI) via pharyngeal plexus, except stylopharyngeus which is supplied by glossopharyngeal nerve (CN IX). Sensory: • Glossopharyngeal nerve • Internal laryngeal nerve ❖ Discuss the origin and insertion of the constrictors of the pharynx. AN36.1–36.5

Origin Superior Constrictor: It arises from the pterygoid hamulus, pterygomandibular raphe, posterior end of mylohyoid line and the side of the tongue. Middle Constrictor: It arises from the lower part of the stylohyoid ligament,

lesser and greater cornua of the hyoid bone. Inferior Constrictor: It consists of two parts – thyropharyngeus and cricopharyngeus. • Thyropharyngeus: From the oblique line of thyroid cartilage. • Cricopharyngeus: From the side of cricoid cartilage.

Insertion All the constrictors of pharynx are inserted into a median raphe, on the posterior wall of the pharynx. The upper end of this raphe is attached to the pharyngeal tubercle on the basilar part of the occipital bone. ❖ Write a short note on nasopharynx. AN36.1–36.5 Nasopharynx is the upper portion of pharynx lying behind the nasal cavities with which it communicates. Internally it is lined by mucous membrane.

Boundaries (fig. 14.2) Roof and lateral wall are formed by body of sphenoid which forms a continuous sloping surface, and the basilar part of the occipital bone.

FIG. 14.2 Nasopharynx. TE, tubal elevation; Spa, salpingopalatine fold; Sph, salpingopharyngeal fold.

Floor is formed by sloping upper surface of the soft palate.

Features • Presence of nasopharyngeal tonsil at the junction of roof and posterior wall, deep to the mucous membrane, more prominent in children. When enlarged it is called as adenoid. • Pharyngeal opening of pharyngotympanic tube which maintains equilibrium of air pressure on both sides of tympanic membrane. • Tubal tonsil is an aggregation of lymphoid tissue along the upper and posterior

margin of tubal opening deep to mucous membrane producing elevation called tubal elevation. • Salpingopharyngeal and salpingopalatine folds. Out of these two folds, one extends downwards towards the wall of pharynx enclosing salpingopharyngeus muscle and is called salpingopharyngeal fold, while other extends downwards and forward to the soft palate enclosing levator palati muscle and is called salpingopalatine fold. • Pharyngeal recess is a depression behind the tubal elevation. ❖ What is gag reflex? AN36.1–36.5 It is a protective reflex characterized by elevation of palate and contraction of pharyngeal muscles with associated retching and gagging in response to stimulation of mucosa of oropharynx. The afferent limb of this reflex is formed by the glossopharyngeal nerve, while its efferent limb is formed by the vagus nerve. ❖ Write a short note on Killian’s dehiscence and pharyngeal diverticulum. AN36.5 There is a small, triangular region in the lower part of the posterior wall of the pharynx (the junctional region between the thyropharyngeus and cricopharyngeus), which is not covered by muscles. This weak area is termed Killian’s dehiscence. The mucosa and submucosa of pharyngeal wall may bulge out through this weak area to form pharyngeal diverticulum/Zenker’s diverticulum (Fig. 14.3).

FIG. 14.3 Pharyngeal diverticulum.

This diverticulum occurs due to neuromuscular incoordination between propulsive thyropharyngeus muscle (supplied by external laryngeal nerve) and sphincteric cricopharyngeus muscle (supplied by recurrent laryngeal nerve).

❖ Write a short note on Waldeyer’s ring. AN36.2 It is a ring of submucous aggregations of lymphoid tissue, which surrounds the beginning of respiratory and digestive tracts.

Formation (fig. 14.4) The Waldeyer’s ring is formed as follows: • Above and behind, by pharyngeal tonsil • Below and in front, by lingual tonsil • On each side, by palatine tonsil • Superolaterally on each side, by tubal tonsil

FIG. 14.4 Waldeyer’s ring.

Applied anatomy The Waldeyer’s ring provides the first line of defence to respiratory and digestive tracts by preventing the spread of infection from nasal and oral cavities to these tracts. ❖ Describe tonsil under the following headings: (a) location, (b) external features, (c) tonsillar bed, (d) nerve supply, (e) arterial supply, (f) venous drainage and (g) applied anatomy.  AN36.1, AN36.4

Location The palatine tonsil is an almond-shaped mass of lymphoid tissue (dimension of about 2 cm) located in the tonsillar fossa on each side in the lateral wall of the oropharynx. The tonsillar fossa is a triangular recess that is bound in front by palatoglossal fold and behind by palatopharyngeal fold.

External features of tonsil (fig. 14.5)

The tonsils present the following features: • Two surfaces: medial and lateral • Two borders: anterior and posterior • Two ends: upper and lower

FIG. 14.5 Horizontal section through tonsillar fossa showing medial and lateral surfaces of the tonsil and tonsillar bed.

The lateral surface is covered by a sheath of condensed connective tissue called hemicapsule of tonsil (Fig. 14.5).

Tonsillar bed (fig. 14.5) From deep to superficial, it is formed by: • Pharyngobasilar fascia • Superior constrictor muscle supplemented by palatopharyngeus • Buccopharyngeal fascia

N.B. Loose areolar tissue between tonsillar capsule and tonsillar bed is called peritonsillar space. Structures deep to tonsillar bed are facial and ascending pharyngeal arteries, glossopharyngeal nerve, styloglossus muscle and submandibular salivary gland.

Nerve supply • Glossopharyngeal nerve • Lesser palatine nerves

Arterial supply of the tonsil (fig. 14.6)

The tonsil is supplied by the following five sets of arteries: • Tonsillar branch of the facial artery (principal artery) • Dorsal lingual branches of the lingual artery • Ascending pharyngeal artery – a branch of the external carotid artery • Ascending palatine artery – a branch of the facial artery • Greater/descending palatine artery – a branch of the maxillary artery

FIG. 14.6 Arteries supplying the tonsil.

Venous drainage By paratonsillar vein into pharyngeal venous plexus, which in turn drains into internal jugular vein.

Lymphatic drainage Lymph vessels from tonsil drain into jugulodigastric lymph nodes. These lymph nodes lie in the angle formed between posterior belly of digastric (inferior border) and internal jugular vein (anterior aspect) deep to the mandible.

Applied anatomy • Tonsillitis: It is an infection of tonsil, which is usually of viral origin. This leads to the enlargement of jugulodigastric lymph nodes.

• Quinsy (peritonsillar abscess): It is the name given to collection of pus in the peritonsillar space. • Referred pain: Pain of tonsil is referred to middle ear because both are supplied by the glossopharyngeal nerve. • Commonest source of bleeding after tonsillectomy. It is due to damage of the paratonsillar vein. • After tonsillectomy, all blood clots in the tonsillar fossa are removed to prevent bleeding as removal of these clots allows the retraction of blood vessels due to muscle contraction. The only other organ in the body where such removal of blood clots is done is uterus. ❖ Write a short note on the development of tonsil. AN43.4 The tonsil develops form 2nd pharyngeal pouch in the 4th week of intrauterine life. • The epithelial lining of the tonsil develops from endoderm of 2nd pharyngeal pouch. • The stroma of tonsil develops from local mesenchyme. • The lymphocytes of tonsil are derived from either local mesenchyme or from circulating lymphocytes. ❖ Discuss the histological features of a tonsil.  AN43.2 The histological features of tonsil are as follows (Fig. 14.7): • Surface is lined by stratified, squamous, nonkeratinized epithelium. • Surface epithelium dips at places into the substance of tonsil to form tonsillary crypts. • Presence of subendothelial lymph nodules underneath the stratified squamous epithelium, along the crypts. • Presence of mucous glands in the deeper part. • Fibrous capsule on outer side.

FIG. 14.7 Histological features of a palatine tonsil.

N.B. The invaginations of epithelium at places deep into the substance of tonsil form crypts. ❖ Briefly describe the pharyngotympanic tube/auditory tube/eustachian tube.  AN40.2

General description (fig. 14.8) • It is a funnel-shaped osseocartilaginous tube that connects the middle ear cavity (tympanum) with the nasopharynx. • It is about 4 cm (36 mm) long. • It is directed downwards, forwards and medially. • Its bony part forms lateral one-third of the tube, while its cartilaginous part forms medial two-third of the tube. • Its bony part (12 mm long) lies at the base of skull, lateral to carotid canal below the tympanic plate of temporal bone. • Its cartilaginous part (24 mm long) lies in sulcus tubae – a groove between the greater wing of sphenoid and apex of petrous temporal bone.

FIG. 14.8 Pharyngotympanic tube.

Function Maintains equilibrium of air pressure on either side of the tympanic membrane for its

proper vibration by the sound waves.

Applied anatomy This provides passage for infection to travel from the upper respiratory tract (URT) to middle ear causing otitis media. The otitis media is common in children because the auditory tube is much shorter (18 mm) and straight in them. ❖ Briefly discuss the hard palate. AN36.1 It is a bony partition between nasal and oral cavities.

Formation • Anterior two-third of hard palate is formed by palatine processes of the maxillae. • Posterior one-third of hard palate is formed by horizontal plates of the palatine bones.

Development • Small triangular part anteriorly (premaxilla) opposite to incisor teeth develops from frontonasal process. • Remaining part develops from palatine shelves of maxillary processes. ❖ Describe the soft palate in brief. AN36.1 It is movable, muscular flap suspended from the posterior border of hard palate. It separates nasopharynx from oropharynx.

Muscles of soft palate (fig. 14.9) Palate has five pair of muscles: • Tensor palati • Levator palati • Musculus uvulae • Palatoglossus • Palatopharyngeus

FIG. 14.9 Muscles of the soft palate.

Nerve supply All the muscles of palate are supplied by cranial root of accessory nerve (CN XI) via pharyngeal plexus, except tensor palati which is supplied by the mandibular nerve (through nerve to medial pterygoid).

Applied anatomy The paralysis of soft palate leads to: • Nasal regurgitation of food • Nasal twang of voice • Flattening of palatal arch on the side of lesion • Deviation of uvula opposite to the side of lesion ❖ Describe development and congenital anomalies of palate. AN43.4

Development The primary palate, the small triangular anterior part opposite incisor teeth (i.e. premaxilla), develops from frontonasal process (strictly speaking from intermaxillary segment formed by the fusion of medial nasal processes of frontonasal process). The secondary palate, the remaining large posterior part, develops from two shelf-like outgrowths, the palatine shelves, on each side from maxillary processes.

Congenital anomalies The congenital anomalies of palate are common due to failure of fusion of its primitive parts, viz. premaxilla and right and left palatine shelves. These are as follows: a) Complete cleft: It may be unilateral or bilateral (Fig. 14.10A and B). It is usually associated with cleft lip as the philtrum (the median triangular part) of upper lip also develops from’ frontonasal process. b) Incomplete cleft lip: It may present as bifid uvula or cleft of soft palate (involving only uvula or whole of soft palate.

FIG. 14.10 Complete cleft palate: A, unilateral; B, bilateral. The actual clinical photographs are also given below each type. Source: (Source for clinical photographs: The Developing Human: Clinically Oriented Embryology, 8th edition: Keith L. Moore and T.V.N. Persaud, ISBN: 9781416037064. Source for For Fig. A: Page 190, Fig. 9.39; Source for Fig. B: Page 192, Fig. 9.41 Copyright Elsevier, 2008.)

❖ Write a short note on pharyngeal apparatus. AN43.4 The pharyngeal apparatus consists of the following components (Fig. 14.11): a) Five pharyngeal arches b) Four pharyngeal pouches c) Four pharyngeal clefts d) Four pharyngeal membranes

FIG. 14.11 Components of pharyngeal apparatus.

All these components develop in the lateral wall of primitive pharynx caudal to the primitive mouth/stomodeum. ❖ Write a short note on pharyngeal arches. AN43.4 These are horseshoe-shaped cylindrical bars/elevations on either side in the anterolateral portion of wall of primitive pharynx. Each pharyngeal arch consists of four components (Fig. 14.12): 1. A core of mesoderm 2. A cartilaginous bar 3. A pharyngeal arch artery 4. A nerve

FIG. 14.12 Structure of pharyngeal arch.

❖ Enumerate the mesodermal derivatives of 1st and 2nd pharyngeal arches in tabular form.  AN43.4 These are as follows: Teeth First arch (mandibular arch)

Second arch (hyoid arch)

Skeletal Derivatives • Malleus

Muscle • Muscles of mastication

• Anterior ligament of malleus

• Anterior belly of digastric and mylohyoid • Tensor tympani • Tensor palati

• Incus • Sphenomandibular ligament • Remnants of Meckel’s cartilage • Maxilla • Mandible • Stapes • Styloid process • Stylohyoid ligament • Lesser cornua of hyoid bone • Superior part of body of hyoid bone

• Stapedius • Stylohyoid • Posterior belly of digastric • Muscle of facial expression • Auricular muscles • Occipitofrontalis • Platysma

❖ Discuss the embryological basis of branchial cyst/cervical cyst. AN43.4 • It is congenital cyst (lined by ectoderm) which appears on the side of neck along the anterior border of the sternocleidomastoid below and behind the angle of mandible (Fig. 14.13). • It appears when 2nd, 3rd and 4th pharyngeal clefts fail to obliterate (Fig. 14.13 inset).

FIG. 14.13 A cervical cyst. The figure in the inset on the right shows development of branchial/cervical cyst. 1, 2 and 3 = 1st, 2nd and 3rd pharyngeal clefts; I, II and III = 1st, 2nd and 3rd pharyngeal arches; SCM, sternocleidomastoid muscle.

N.B. If branchial cyst ruptures on the surface of neck, it is called external branchial fistula. On the other hand, if it opens into tonsillar sinus of pharynx, it is called internal branchial fistula.

15

Nose and paranasal air sinuses Nose ❖ What is nose? List its functions. AN37.1 The nose is a pyramidal-shaped projection in the midface. It presents tip (apex), alae, dorsum, root and nostrils or nares. Its cavity is divided into two halves by a median nasal septum. Each cavity (also called nasal cavity) communicates anteriorly to the exterior through nostril (anterior nare) and posteriorly with the nasopharynx through choana (posterior nare).

Functions • Is the organ of smell. • Plays a significant role in respiration. • Provides protection to the lower respiratory tract. • Performs air conditioning of inspired air. • Provides vocal resonance to voice. ❖ Enumerate the bones and cartilages forming the skeleton of external nose.  AN37.1

Bones (four in number) • Two nasal bones • Frontal processes of maxillae

Cartilages (five in number) • Two lateral nasal cartilages/superior nasal cartilages • A single, median septal cartilage • Two major alar cartilages/inferior nasal cartilages ❖ Describe the nasal septum under the following headings: (a) formation, (b) arterial supply, (c) nerve supply and (d) applied anatomy. AN37.1

Formation (fig. 15.1) The nasal septum is a median osseocartilaginous partition between two nasal cavities

covered on each side by the mucous membrane. • Bony part is formed by: ■ Vomer, below and behind ■ Perpendicular plate of ethmoid, above • Cartilaginous part is formed by: ■ Septal cartilage ■ Septal processes of major alar cartilages • Cuticular part is formed by: ■ Fibrofatty tissue

FIG. 15.1 Formation of nasal septum.

N.B. The median partition of soft tissue separating two nostrils is called columella.

Arterial supply • Anterosuperior part, by anterior ethmoidal artery • Posteroinferior part, by sphenopalatine artery • Anteroinferior part, by superior labial and greater palatine arteries • Posterosuperior part, by sphenopalatine artery

Nerve supply General sensory: • Anterosuperior part by internal nasal branches of the anterior ethmoidal nerve • Anteroinferior part by anterior superior alveolar nerve • Posterosuperior part by medial, posterior and superior nasal branches of pterygopalatine ganglion • Posteroinferior part by nasopalatine nerve – a branch of pterygopalatine ganglion

Special sensory by olfactory nerve.

Applied anatomy Deviated nasal septum (DNS): It may occur as a sequel to postnasal trauma (most common cause) or due to congenital malformation. Excessive deviation of nasal septum may cause nasal obstruction. It is treated by submucous resection (SMR) of septum. Epistaxis: It is nose bleeding that commonly occurs due to trauma of Kiesselbach’s plexus in the Little’s area (for details, see Little’s area, Fig. 15.2).

FIG. 15.2 Arterial supply of the nasal septum.

❖ What is Little’s area? Describe its clinical importance. AN37.1 It is an area in the anteroinferior part of the nasal septum where four arteries anastomose to form an arterial plexus called Kiesselbach’s plexus (Fig. 15.2). The arteries forming this plexus are as follows: • Septal branch of sphenopalatine • Septal branch of greater palatine • Septal branch of anterior ethmoidal artery • Septal branch of superior labial artery – a branch of facial artery

Clinical importance The Little’s area is the most common site of nose bleeding (i.e. epistaxis) in young adults, usually due to fingernail trauma (nose picking)/small ulcer. Septal branch of the sphenopalatine artery is largest, longest and tortuous. It is the main source of bleeding.

Hence, it is also termed artery of nose bleeding/rhinologist’s artery. ❖ Enumerate the characteristic features of lateral wall of the nose. AN37.1 The lateral wall of nose presents the following features (Fig. 15.3):

FIG. 15.3 Features of the lateral wall of the nasal cavity.

Three conchae/turbinates Superior concha: It is a curved bony projection from medial surface of the ethmoid bone. It is smallest concha. Middle concha: It is a curved bony projection from medial surface of the ethmoid bone. Inferior concha: It is an independent bone.

Three meatuses Three meatuses are passages beneath the overhanging conchae. Superior meatus: Lies below the superior concha. Middle meatus: Lies underneath the middle concha. It presents: • Ethmoidal bulla, a rounded elevation produced by underlying middle ethmoidal sinus. • Hiatus semilunaris, a deep semicircular sulcus below the bulla.

Inferior meatus (largest): Lies underneath the inferior concha.

Sphenoethmoidal recess It is a triangular recess situated just above and behind the superior concha.

Opening of paranasal air sinuses and nasolacrimal ducts The features of lateral wall of the nose are shown in Fig. 15.4.

FIG. 15.4 Lateral wall of the nose with conchae removed showing openings of various sinuses and nasolacrimal duct.

❖ Enumerate the openings into the lateral wall of the nose. AN37.1 The following structures open in the lateral wall of the nose (Fig. 15.4): 1. Sphenoidal air sinus: Opens into the sphenoethmoidal recess. 2. Posterior ethmoidal air sinuses: Open into the superior meatus. 3. Middle ethmoidal air sinuses: Open on the bulla ethmoidalis in the middle meatus. 4. Maxillary air sinus: Opens into the posterior part of hiatus semilunaris at its posterior end in the middle meatus. 5. Anterior ethmoidal air sinuses: Open into the anterior part of hiatus semilunaris in the middle meatus. 6. Frontal air sinus: Opens into the infundibulum at the anterior end of hiatus semilunaris in the middle meatus. 7. Nasolacrimal duct: Opens into the anterior part of the inferior meatus. ❖ Enumerate the structures opening in the middle meatus of the nose. AN37.1 These are as follows (Fig. 15.4): 1. Middle ethmoid air sinus 2. Frontal sir sinus 3. Anterior ethmoidal air sinus 4. Maxillary air sinus

Paranasal air sinuses ❖ What are the paranasal air sinuses? Name them and enumerate their functions.  AN37.2 The paranasal air sinuses are air-filled cavities in the paranasal bones, such as frontal, ethmoid, sphenoid and maxilla. They are named according to the bones in which they are present, i.e.: • Frontal air sinuses are present in the frontal bone. • Ethmoidal air sinuses are present in the ethmoid bones. • Sphenoidal air sinuses are present in the body of sphenoid bone. • Maxillary air sinuses (largest air sinuses) are present in the body of maxillae.

Functions The functions of air sinuses are as follows: • Make the skull lighter. • Add resonance to the voice. • Humidify the air during inspiration. • Provide adult shape to the facial skeleton. ❖ Describe the maxillary air sinus under the following headings: (a) location, (b) boundaries, (c) drainage, (d) development and (e) applied anatomy. AN37.2, AN37.3

Location The maxillary air sinus is the largest paranasal air sinus located into the body of maxilla.

Boundaries It is pyramidal-shaped cavity in the body of maxilla. Its boundaries are as follows (Fig. 15.5):

FIG. 15.5 Location and relations of maxillary air sinus.

Apex: It is directed towards zygoma and often extends into the zygomatic bone. Base: It is formed by the lateral wall of the nasal cavity. Roof: It is formed by the floor of the orbit. Floor: It is narrow and formed by the alveolar process of the maxilla. It lies about 1 cm below the level of the floor of the nose.

N.B. The roots of maxillary teeth, particularly those of first two molars, often protrude into the floor of maxillary sinus and may even perforate it.

Drainage It drains in the middle meatus of nose in the posterior part of hiatus semilunaris. Note: The ostium for the maxillary air sinus is located near its roof – a disadvantageous location for a natural drainage.

Development It is the 1st paranasal air sinus to develop. It develops in the 4th month of IUL. It grows rapidly during 6–7 years of life and reaches the adult size after the eruption of permanent teeth.

Applied anatomy

Maxillary sinusitis (most common): The maxillary sinus is most commonly infected because its ostium is located near the roof, which hampers its drainage. The infection may reach the sinus either from nasal cavity or from caries of the upper molar teeth. Referred pain: Pain of the maxillary sinus may be referred to the upper teeth due to same nerve supply. ❖ Write briefly about frontal air sinuses. AN37.2 These are located in the frontal bone between its outer and inner tables behind superciliary arches. The right and left frontal air sinuses are rarely of equal size, and the septum separating them is rarely situated in the median plane. The frontal sinus drains through frontonasal duct inferiorly into a funnel-shaped infundibulum at the anterior end of hiatus semilunaris of middle meatus. The infection of frontal sinus (frontal sinusitis) usually causes severe and localized pain in the forehead (frontal headache). The frontal headache shows characteristic periodicity, i.e. it increases as the sun rises and decreases as the sun sets. The pain of frontal air sinus may extend up to vertex through supraorbital nerves which supply it. The frontal sinusitis can lead to brain abscess in the frontal lobe.

16

Larynx ❖ Define larynx and list its functions. AN38.1 The larynx is the first part of the lower respiratory tract (LRT). It is located on the front of neck opposite C3 to C6 vertebrae.

Functions • Phonation • Respiration • Protection • Deglutition ❖ Enumerate the cartilages forming the skeleton of larynx. List their types. AN38.1 The skeleton of larynx is formed by nine cartilages (three unpaired and three paired; Fig. 16.1): • Unpaired cartilages ■ Epiglottis ■ Thyroid ■ Cricoid • Paired cartilages ■ Arytenoid ■ Corniculate ■ Cuneiform

FIG. 16.1 Skeleton of the larynx: A, anterior view; B, posterior view.

Types • The thyroid, cricoid and most of arytenoid are made up of hyaline cartilage. • The epiglottis, corniculate, cuneiform and apices of arytenoids are made of yellow elastic cartilage. ❖ Name the safety muscle of larynx and give the reason why it is so named. The posterior cricoarytenoid is a safety muscle of larynx. It is so named because it is the only intrinsic muscle of larynx, which abducts the vocal cords to allow the entry of air into the LRT. All the other intrinsic muscles of larynx adduct the vocal cords and restrict the entry of air into the LRT. ❖ What are the boundaries of laryngeal inlet? • Anterior: Epiglottis • On each side: Aryepiglottic fold • Posterior: Interarytenoid fold ❖ List the subdivisions of laryngeal cavity. Mention the narrowest part of the laryngeal cavity. The laryngeal cavity is divided into three parts (Fig. 16.2): • Vestibule: Between laryngeal inlet and vestibular folds. • Ventricle (sinus): Between vestibular folds above and vocal folds below. • Infraglottic part: Below the vocal folds, and up to the lower border of cricoid cartilage.

FIG. 16.2 Coronal section of laryngeal cavity showing its subdivisions.

The glottis (i.e. space between the two vocal folds) is the narrowest part of the laryngeal cavity. ❖ Enumerate the intrinsic muscles of larynx. The intrinsic muscles of larynx are: • Cricoarytenoid • Posterior cricoarytenoid • Lateral cricoarytenoid • Transverse arytenoid • Oblique arytenoid • Aryepiglotticus • Thyroarytenoid • Thyroepiglotticus

N.B. • All the intrinsic muscles of larynx are paired except transverse arytenoid, which is unpaired. • Cricothyroid is the only intrinsic muscle that lies outside the larynx, i.e. on the external aspect of larynx. • All the intrinsic muscles of larynx are supplied by recurrent laryngeal nerve except cricothyroid, which is supplied by the external laryngeal nerve. ❖ List the origin, insertion, nerve supply, actions and applied anatomy of cricothyroid muscle.

Origin Anterolateral part of the arch of cricoid cartilage (Fig. 16.3).

FIG. 16.3 Action of cricothyroid muscle.

Insertion Inferior cornu and adjoining part of the lower border of thyroid cartilage.

Nerve supply External laryngeal nerve.

Actions It lengthens and tenses vocal cords by tilting the thyroid cartilage forwards. It also causes adduction of vocal cords.

Applied anatomy The cricothyroid muscle is an important muscle for pitch and tone of voice. Hence, its paralysis may alter the voice significantly, which is noticeable especially in singers. ❖ What is rima glottidis? Mention its boundaries. The rima glottidis is the narrowest part of the laryngeal cavity. It is an anteroposterior cleft, bounded in front by angle of thyroid cartilage, behind by interarytenoid fold and on each side by vocal fold (in anterior three-fifth) and by vocal process of arytenoid cartilage (in posterior two-fifth). ❖ Draw a labelled diagram to show structures seen in the laryngeal cavity during laryngoscopy. The structures seen in the laryngeal cavity during laryngoscopy are presented in Fig. 16.4.

FIG. 16.4 Laryngoscopic view of the laryngeal cavity during moderate respiration. Note the location of rima glottidis in the center.

❖ Write a short note on vocal cords. They are a pair of folds extending anteroposteriorly within the laryngeal cavity. The gap between the right and left vocal folds is called rima glottidis. Each vocal cord is made up of vocal ligament (medially) and vocalis muscle (laterally).

The vocal ligament extends from the tip of vocal process of arytenoid cartilage posteriorly to the inner aspect of thyroid cartilage anteriorly. The vocalis muscle (the detached medial part of thyroarytenoid muscle) also extends from inner aspect of thyroid cartilage (anteriorly) to the vocal process of the arytenoid cartilage (posteriorly). The posterior part of vocal folds is formed by arytenoid cartilages. Each vocal cord is covered by mucous membrane. ❖ Write a note on changes in size and shape of rima glottidis. Functionally rima glottidis consists of two parts: a. Intramembranous part (anteriorly three-fifth) between vocal cords b. Intracartilaginous part (posteriorly one-fifth) between arytenoid cartilage The changes in size and shape of rima glottidis takes place during respiration and speech. These are: • During quiet respiration, vocal cords lie only, at some distance. • During full respiration, vocal cords move apart. • During whispering, only intracartilaginous part widens. • During high-pitched voice, both intramembranous and intracartilaginous parts adduct and rima glottidis is reduced to a linear chink. ❖ Why vocal cords do not swell much in laryngitis? Explain its anatomical basis.  AN38.2 The laryngitis is the inflammation of the larynx. The vocal cords do not swell much in laryngitis due to the following reasons: • They are lined by stratified squamous epithelium (cf. rest of the laryngeal cavity is lined by pseudostratified ciliated columnar epithelium). • The mucous membrane of the vocal cords is firmly attached to the vocal ligaments. • There is no submucous tissue and glands in the vocal cords. ❖ What are vocal nodules/singer’s nodules? The vocal nodules are bilateral swellings in the vocal cords at the junction of their anterior one-third and posterior two-third (Fig. 16.5).

FIG. 16.5 Vocal nodules.

When the vocal cords vibrate during phonation, they come in maximum contact with each other at the junction of their anterior one-third and posterior two-third. The inflammatory swellings (inflammation due to friction) which appear at these sites are called vocal nodules. The size of vocal nodules varies from pin-head to split-pea and their colour varies from reddish (in early stage) to whitish (in later stage). ❖ Enumerate the effects of lesions of laryngeal nerves. AN38.3 The effects of lesions of laryngeal nerve are given in Table 16.1. TABLE 16.1 Effects of Lesions of Laryngeal Nerves

❖ Describe piriform fossa in brief and discuss its clinical importance. AN36.3 The piriform fossa is a deep recess in the lateral wall of the laryngopharynx, one on each side of laryngeal inlet (see Fig. 16.2; p. 170).

Boundaries Medially: Aryepiglottic fold

Laterally: Thyrohyoid membrane and thyroid cartilage

Clinical importance The foreign bodies like fish bones and safety pins may be lodged in piriform fossa. If care is not taken during the removal of these foreign bodies, the instrument used for the removal of foreign bodies may pierce the mucous membrane lining, the floor of fossa and damage the internal laryngeal nerve and vessels, which lies just beneath it.

N.B. Piriform fossa is also called smuggler’s fossa because in earlier bygone days it was artificially deepened by smugglers to smuggle out precious stones, diamonds, etc.

17

Infratemporal fossa, temporomandibular joint and pterygopalatine fossa Infratemporal fossa ❖ Define infratemporal fossa and enumerate its boundaries and contents. AN33.1 The infratemporal fossa is a large irregular space beneath the zygomatic arch between side wall of pharynx and ramus of mandible.

Boundaries Anterior: Posterior (infratemporal) surface of the body of maxilla. Posterior: Styloid process. Medial: Lateral pterygoid plate and pyramidal process of palatine bone. Lateral: Ramus of mandible. Roof: Infratemporal surface of the greater wing of sphenoid. Floor: Open and extends up to the base of mandible.

Contents Two muscles: Lateral and medial pterygoids. (Note: In addition to these muscles, the tendon of temporalis muscle also lies in this fossa.) Two nerves: Mandibular and chorda tympani. One artery: Maxillary artery. Two venous structures: Pterygoid venous plexus and maxillary vein. One ganglion: Otic ganglion. ❖ Enumerate the muscles of mastication. AN33.2 • Chief muscles of mastication (Fig. 17.1) ■ Masseter (most superficial) ■ Temporalis ■ Lateral pterygoid ■ Medial pterygoid • Accessory muscles of mastication (Fig. 17.1) ■ Buccinator muscle ■ Digastric muscle

FIG. 17.1 Muscles of mastication. Source: (The chief muscles of mastication are labelled in boldface.)

❖ Discuss the origin, insertion, nerve supply and action of masseter muscle.  AN33.2

Origin (fig. 17.2) Superficial part: From the anterior two-third of the lower border of zygomatic arch and adjoining part of zygomatic process of maxilla. Deep part: From the inner surface of zygomatic arch.

FIG. 17.2 Origin and insertion of masseter muscle.

Insertion (fig. 17.2) Into the outer surface of the ramus of mandible.

Nerve supply Masseteric nerve from the anterior division of the mandibular nerve.

Action Elevation of mandible to close the mouth (as required during biting). ❖ Discuss the origin, insertion nerve supply and actions of temporalis muscle.  AN33.2

Origin (fig. 17.3) From the floor of temporal fossa and deep surface of temporal fascia.

FIG. 17.3 Origin and insertion of temporalis muscle.

Insertion (fig. 17.3) Into the coronoid process (tip, inner surface and anterior border) of the ramus of mandible.

Nerve supply Two deep temporal nerves from the anterior division of the mandibular nerve.

Actions • Elevation of mandible • Retraction of mandible • Helps in side-to-side movement of the lower jaw during grinding ❖ Discuss the origin, insertion, nerve supply and actions of lateral pterygoid muscle.  AN33.2 The lateral pterygoid is the key muscle of infratemporal region.

Origin (fig. 17.4) By two heads: • Upper smaller head arises from the infratemporal crest and infratemporal surface of the greater wing of the sphenoid. • Lower larger head arises from the lateral surface of the lateral pterygoid plate.

FIG. 17.4 Origin and insertion of lateral pterygoid muscle.

Insertion (fig. 17.4) Into the pterygoid fovea present on the front of the neck of mandible. Some fibres are also inserted into the articular disc and capsule of the temporomandibular joint.

Nerve supply A branch from the anterior division of the mandibular nerve.

Actions • Depression of mandible to open the mouth; while doing so, muscle pulls the articular disc forwards. • Protrusion of mandible. • Along with ipsilateral medial pterygoid muscle, it pushes the chin to the opposite side. ❖ Discuss the origin, insertion, nerve supply and actions of medial pterygoid muscle.  AN33.2

Origin (fig. 17.5) By two heads: • Smaller superficial head arises from the tuberosity of maxilla. • Larger deep head from the medial surface of the lateral pterygoid plate.

FIG. 17.5 Origin and insertion of medial pterygoid muscle.

Insertion (fig. 17.5) Into the medial surface of the ramus of mandible, above the angle of mandible and below the mandibular foramen. Nerve supply Nerve to medial pterygoid, a branch from main trunk of the mandibular nerve.

Actions • Elevation of mandible • Helps in protrusion of mandible • Along with ipsilateral, lateral pterygoid pushes the chin to opposite side

N.B. • All the chief muscles of mastication are supplied by the mandibular nerve. • All the muscles of mastication close the mouth except lateral pterygoid, which opens the mouth. Thus, closing of mouth is much more powerful action than the opening. ❖ Why lateral pterygoid muscle is regarded as the key muscle of the infratemporal region? List its relations. AN33.2 The lateral pterygoid muscle is regarded as the key muscle of the infratemporal region because its relations provide the fair idea of the layout of the structures in the infratemporal fossa.

Relations (fig. 17.6) Superficial relations • Masseter • Ramus of mandible • Tendon of temporalis • Maxillary artery

FIG. 17.6 Relation of lateral pterygoid muscle.

Deep relations • Mandibular nerve • Middle meningeal artery • Sphenomandibular ligament • Deep head of medial pterygoid Structures emerging from the upper border • Deep temporal nerves • Masseteric nerve Structures emerging from its lower border • Lingual nerve • Inferior alveolar nerve • Middle meningeal artery (in fact passes upward deep to muscle) Structures passing between two heads • Maxillary artery (enters) • Buccal branch of mandibular nerve (comes out) ❖ Describe the mandibular nerve under the following headings: (a) origin, (b) course, (c) branches and (d) distribution. AN33.1

Origin and course (fig. 17.7) The mandibular nerve is the largest division of trigeminal nerve. It arises from the trigeminal ganglion and enters the infratemporal fossa through foramen ovale. In the foramen ovale, it is joined by the small motor root of the trigeminal nerve, and thus emerges from the skull as a mixed nerve. After emerging from foramen ovale, it divides almost immediately into the anterior and posterior divisions.

FIG. 17.7 Course and distribution of mandibular nerve. SM, submandibular ganglion.

Branches and distribution (fig. 17.7) From the trunk • Meningeal branch (nervus spinosus), which enters the skull through foramen spinosum and supplies the dura mater. • Nerve to medial pterygoid, it passes through otic ganglion and supplies the medial pterygoid muscle. In addition to it, it also supplies twigs to the tensor palati and tensor tympani muscles. From the anterior division • Muscular branches to the temporalis (deep temporal nerves), masseter (masseteric nerve) and nerve to the lateral pterygoid. • Buccal nerve (sensory to the skin and mucosa of the cheek). From the posterior division

• Auriculotemporal nerve (sensory to the auricle and temple). • Lingual nerve (sensory to the anterior two-third of tongue). • Inferior alveolar nerve: Gives the mylohyoid nerve and then enters into the mandibular canal to supply sensory fibres to the lower teeth and gums. It gives mental nerve, which supplies the skin of the chin, and skin and mucosa of the lower lip. Note: The nerve to mylohyoid supplies mylohyoid muscle and anterior belly of digastric.

N.B. • All the branches from the anterior division of mandibular nerve are motor except buccal nerve, which is sensory to skin and mucous membrane of the cheek. • All the branches from the posterior division of mandibular nerve are sensory except mylohyoid nerve, which is motor to mylohyoid and anterior belly of digastric. ❖ Describe the otic ganglion in brief under the following headings: (a) location, (b) roots and (c) distribution. AN33.1

Location It is a small parasympathetic ganglion of 2–3 mm in size (about the size of pin-head) and is located in the infratemporal fossa, just below the foramen ovale. It lies medial to mandibular nerve and lateral to tensor palati muscle.

Roots (fig. 17.8) Parasympathetic root: From lesser petrosal nerve. Sympathetic root: From sympathetic plexus around middle meningeal artery. Sensory root: From auriculotemporal nerve. Motor root: From nerve to medial pterygoid.

FIG. 17.8 Otic ganglion and its connections.

Distribution (fig. 17.8) Parasympathetic (secretomotor) fibres: Supply parotid gland through auriculotemporal nerve. Sympathetic (vasoconstrictor) fibres: Supply blood vessels of parotid gland through auriculotemporal nerve. Sensory fibres: Provide sensory innervation to parotid gland through auriculotemporal nerve. Motor fibres: Supply three muscles through nerve to medial pterygoid – medial pterygoid, tensor palati and tensor tympani. ❖ Draw a flowchart to show the secretomotor pathway to the parotid gland.  AN33.1, AN28.9 Below is the Flowchart 17.1, showing secretomotor pathway to the parotid gland.

FLOWCHART 17.1 The secretomotor pathway to the parotid gland.

❖ Write briefly about chorda tympani nerve. AN28.4 It is described in Chapter 11 (p. 127 and 128).

❖ Describe the maxillary artery under the following headings: (a) origin and extent, (b) parts, (c) branches and (d) applied anatomy. AN33.1

Origin and extent (fig. 17.9) The maxillary artery is the larger of two terminal branches of the external carotid artery. It extends from behind the neck of the mandible to the sphenopalatine foramen, where it continues as the sphenopalatine artery.

FIG. 17.9 Origin, extent and branches of the maxillary artery.

Parts (fig. 17.9) For descriptive purposes, the maxillary artery is divided into three parts by lateral pterygoid (inferior head). First part: It extends from the neck of the mandible to the point where it crosses the lower border of lateral pterygoid (inferior head). Second part: It lies superficial or deep to lateral pterygoid. Third part: It is beyond the upper border of lateral pterygoid. It passes between two heads of lateral pterygoid, passes through pterygomaxillary fissure to enter into pterygopalatine fossa, where it terminates by dividing into sphenopalatine and greater palatine arteries.

Branches (fig. 17.9) From first part: ■ Anterior tympanic artery ■ Deep auricular artery ■ Middle meningeal artery

■ Accessory meningeal artery ■ Inferior alveolar artery From second part: Muscular branches to supply temporalis (deep temporal arteries), pterygoids, masseter and buccinator (buccal branch) muscles. From third part: ■ Posterior superior alveolar arteries ■ Greater palatine artery ■ Infraorbital artery ■ Pharyngeal branch ■ Artery of pterygoid canal ■ Sphenopalatine artery (the continuation of maxillary artery)

Applied anatomy Middle meningeal artery: It often ruptures inside the cranial cavity following a trauma on the lateral aspect of the skull and leads to the formation of extradural haematoma. Inferior alveolar artery: Sometimes it may rupture during extraction of tooth of the lower jaw leading to osteomyelitis of the lower jaw. Sphenopalatine artery: Its septal branch (rhinologist’s artery) takes part in the formation of Kiesselbach’s plexus in Little’s area of nose. It is the most common source of nose bleeding. ❖ Write a short note on middle meningeal artery. AN33.1 The middle meningeal artery arises from first part of the maxillary artery in the infratemporal fossa deep to lateral pterygoid muscle. • The artery ascends upwards and enters into middle cranial fossa through foramen spinosum. • On entering the cranial cavity, it lies in the groove deep to corresponding vein and divides into anterior (frontal) and posterior (parietal) terminal branches. The larger anterior branch ascends crossing the greater wing of sphenoid in a groove just deep to the pterion of lateral wall of skull. Then it runs obliquely upwards and backwards parallel to and little in front of central sulcus, on precentral gyrus. • The smaller posterior branch runs backwards over the superior temporal sulcus of cerebrum about 4 cm above the zygomatic arch.

Branches Predominantly, middle meningeal artery is periosteal artery which supplies bone and red marrow within the dipole. Within the cranial cavity it gives rise to the following branches:

1. Anterior branch supplies dura mater and skull bones in the frontal region of skull. 2. Posterior branch supplies dura mater and skull bone in the parietal region. 3. Ganglionic branches to trigeminal ganglion. 4. Petrosal branch enters the hiatus of greater petrosal nerve to supply facial nerve. 5. Superior tympanic branch to supply tensor tympani muscle. 6. Temporal branches pass through foramina in the greater wing of sphenoid to enter in the temporal fossa. 7. Anastomotic branch which anastomoses with the recurrent meningeal branch of lacrimal artery.

Applied anatomy (fig. 17.10) Middle meningeal artery is the commonest source of extradural haemorrhage. Fractures on the lateral side of skull involving pterion tear the middle meningeal artery (anterior branch) producing extradural haematoma lying over premotor area of cerebral cortex. This leads to pressure symptoms, e.g. contralateral hemiplegia. Hence, extradural haematoma is an acute surgical emergency.

FIG. 17.10 Middle meningeal artery. A, course and termination; B, extradural haematoma. P, parietal bone; F, frontal bone; T, temporal bone; S, sphenoid bone.

Temporomandibular joint ❖ Describe the temporomandibular joint (TMJ) under the following headings: (a) classification, (b) articular surfaces, (c) ligaments, (d) relations, (e) nerve supply, (f) movements and (g) applied anatomy. AN33.3

Classification It is synovial joint of condylar variety. Special features of TMJ: • It is atypical synovial joint because its articular surfaces are covered by fibrocartilage instead of hyaline cartilage. • It is a complex synovial joint because its cavity contains an articular disc. • Two condyles of mandible articulate with a mechanically single bony component, the cranium; hence, two TMJs together function as single unit and form a single craniomandibular joint of bicondylar variety.

Articular surfaces (fig. 17.11) Above: Articular fossa and articular tubercle/eminence of temporal bone. It is concavoconvex from behind to forward and is covered by a fibrocartilage. Below: Head of mandible. It is elliptical and is also covered by a fibrocartilage.

FIG. 17.11 Articular surfaces of the temporomandibular joint.

The joint cavity is divided into two parts by an articular disc: (a) upper meniscotemporal compartment that permits gliding movements and (b) lower meniscomandibular compartment that permits rotational as well as gliding movements.

Ligaments (fig. 17.12) Main ligaments

• Capsular ligament: It is attached above to the articular tubercle, the circumference of mandibular fossa and squamotympanic fissure, and below to the neck of mandible. • Lateral ligament/temporomandibular ligament: It is a thick band of fibrous tissue that covers the lateral aspect of capsule and strengthens it. It extends from articular tubercle on root of zygoma above to the lateral aspect of the neck of mandible below. Its fibres run downwards and backwards.

FIG. 17.12 Ligaments of the temporomandibular joint: A, fibrous capsule and lateral ligament; B, accessory ligaments.

Accessory ligaments • Stylomandibular ligament: It extends from styloid process of temporal bone to the angle of mandible. It is formed due to thickening in the investing layer of deep cervical fascia. • Sphenomandibular ligament: It extends from spine of sphenoid to the lingula of mandible. It is derived from the first pharyngeal arch cartilage.

N.B. Lateral and accessory ligaments limit the range of movements of condyles and prevent them from coming in contact with tympanic plate behind and the articular tubercles in front.

Relations Lateral • Skin and fasciae • Parotid gland • Temporal branches of facial nerve Medial

• Tympanic plate of temporal bone • Spine of the sphenoid and sphenomandibular ligament • Auriculotemporal and chorda tympani nerves • Middle meningeal artery Anterior • Lateral pterygoid • Masseteric nerve and artery Posterior • Parotid gland, which separates the joint from the external auditory meatus • Superficial temporal vessels • Auriculotemporal nerve Superior • Middle cranial fossa • Middle meningeal vessels Inferior • Maxillary artery and vein

Nerve supply • Auriculotemporal nerve • Masseteric nerve

Movements The movements of the temporomandibular joints and muscles producing them are given in Table 17.1. TABLE 17.1 Movements of TMJ and Muscles Producing Them Movements Elevation (closing of mouth) Depression (opening of mouth)

Muscles • Medial pterygoid • Masseter, temporalis • Lateral pterygoid • Anterior belly of digastric • Geniohyoid • Mylohyoid

Protraction (i.e. protrusion of mandible) Retraction (backward movement of mandible) Side to side movements (chewing movements)

• Temporalis (posterior fibres) • Lateral and medial pterygoids of each side acting alternatively

N.B. Most movements occur simultaneously at the right and left temporomandibular joints.

Applied anatomy • Dislocation of temporomandibular joints (TMJs): The TMJs are mostly dislocated anteriorly. When the mouth is open, the mandibular condyles lie underneath the articular eminences of the temporal bone (the most unstable position of TMJ). In this position, if mouth is opened widely or even a severe muscular spasm (e.g. a convulsive yawn) it may displace the heads of mandible forward and upwards to be locked into the infratemporal fossa, leading to anterior dislocation of TMJ. As a result, there is inability to open mouth (Fig. 17.13). AN33.5 The reduction of joint can be easily achieved by pressing the molar teeth downwards with thumbs, and at the same time pushing the chin upward and backward. • Jaw clicking: The articular disc of TMJ may become partially detached from the capsule. As a result, movements of jaw becomes noisy and produces an audible click during movements of the TMJ.

FIG. 17.13 Dislocation of TMJs. A, normal; B, dislocation.

❖ Write briefly about articular disc of TMJ. AN33.3

General features • It is an oval plate of fibrocartilage, which divides the cavity TMJ into two

compartments: (a) an upper meniscotemporal compartment and (b) a lower meniscomandibular compartment. • It presents a thick peripheral margin and a thin central part. • It has concavoconvex superior surface and a concave inferior surface. • Its periphery is firmly attached to the fibrous capsule. • Morphologically, it represents the tendon of lateral pterygoid muscle.

Parts of articular disc In sagittal section, it presents five parts. From before to backwards these are (Fig. 17.14): • Anterior extension • Anterior thick band • Intermediate thin part • Posterior thick band • Posterior bilaminar extension

FIG. 17.14 Parts of articular disc of the temporomandibular joint as seen in sagittal section.

Pterygopalatine fossa AN33.1 The pterygopalatine fossa is a pyramidal-shaped space that lies in the depth of pterygomaxillary fissure. ❖ Define pterygopalatine fossa and enumerate its boundaries and contents. AN33.1

Boundaries Anterior: Posterolateral surface of maxilla. Posterior: Pterygoid process and greater wing of sphenoid. Medial: Perpendicular plate of palatine.

Lateral: Fossa presents pterygomaxillary fissure. Floor: Angle between the anterior and posterior walls of fossa. Roof: Body of sphenoid.

Contents • Maxillary nerve • Pterygopalatine ganglion • Maxillary artery (3rd part) ❖ Describe the maxillary nerve under the following headings: (a) origin, (b) course and (c) branches. AN33.1

Origin and course (fig. 17.15) The maxillary nerve arises from trigeminal ganglion in the middle cranial fossa. It passes forward and traverses foramen rotundum to reach the upper part of the pterygopalatine fossa. From fossa, it enters the orbit by passing through the inferior orbital fissure. As it enters the orbit, it is called infraorbital nerve. In the orbit it first runs in the infraorbital groove, and then passes through the infraorbital canal, to finally appear on the face by emerging through the infraorbital foramen.

FIG. 17.15 Origin, course and branches of the maxillary nerve.

Thus, the maxillary nerve traverses through four successive regions during its course: (a) middle cranial fossa, (b) pterygopalatine fossa, (c) orbit and (d) face. Note: The infraorbital nerve is considered as the continuation of maxillary nerve.

Branches (fig. 17.15) They are given in Table 17.2. TABLE 17.2

Branches of Maxillary Nerve Region Middle cranial fossa Pterygopalatine ganglion

Orbit Face

Branches • Meningeal branch • Ganglionic branches • Posterior superior alveolar nerves • Zygomatic nerve • Middle superior alveolar nerve • Anterior superior alveolar nerve • Three terminal branches (palpebral, nasal and labial)

❖ Describe the pterygopalatine ganglion (sphenopalatine ganglion) in brief under the following headings: (a) location, (b) roots, (c) branches, (d) distribution and (e) applied anatomy. AN33.1

Location The pterygopalatine ganglion is the largest peripheral parasympathetic ganglion. It is located in the pterygopalatine fossa.

N.B. Topographically, it is related to the maxillary nerve, but functionally it is related to the facial nerve.

Roots (fig. 17.16) It has following three roots: Parasympathetic root: From greater petrosal nerve. Sympathetic root: From sympathetic plexus around internal carotid artery through deep petrosal nerve. Sensory root: From maxillary nerve.

FIG. 17.16 Pterygopalatine ganglion, its roots and branches. PG, pterygopalatine ganglion.

Branches • Orbital branches • Palatine branches • Nasal branches

Distribution Parasympathetic (secretomotor) fibres: Supply the lacrimal, nasal and palatine glands. Sympathetic (vasomotor) fibres: Supply the mucous membrane of nose, paranasal air sinuses and nasopharynx. Sensory fibres: Provide sensory innervation to periosteum of orbit and mucous membrane of nose, palate and pharynx.

N.B. The distribution of different types of fibres from pterygopalatine ganglion takes place through its orbital, nasal, palatine and pharyngeal branches (vide supra).

Applied anatomy The allergic conditions such as hay fever or cold causes irritation of pterygopalatine ganglion, which leads to running of nose and eyes. For this reason, the pterygopalatine ganglion is also termed ganglion of hay fever. The alcohol injection is occasionally used to relieve/treat the intractable cases of allergic rhinitis.

18

Ear and orbit Ear ❖ What is ear? List its subdivisions. AN40.1 The ear is the organ of hearing and balance. It is subdivided into the following three parts (from lateral to medial): • External (outer) ear • Middle ear • Internal (inner) ear ❖ Discuss the sensory nerve supply of the auricle/pinna. AN40.1

Lateral (facial) surface • Lower one-third by great auricular nerve (C2, C3) • Upper two-third by auriculotemporal nerve

Medial (cranial) surface • Lower one-third by great auricular nerve (C2, C3) • Upper two-third by lesser occipital nerve (C2)

N.B. In addition to above, the concha on the lateral surface of pinna is supplied by an auricular branch of vagus nerve and eminentia conchae on the medial surface of pinna is supplied by a sensory twig of facial nerve. ❖ Write a short note on external auditory (acoustic) meatus. AN40.1 • The external acoustic meatus is an ‘S’-shaped osseocartilaginous tube, which extends from bottom of concha to the tympanic membrane. • It is about 24 mm long, of which medial two-third (16 mm) is bony and lateral one-third (8 mm) is cartilaginous. • It conducts sound waves from concha to the tympanic membrane. • It develops from first pharyngeal cleft.

❖ Write a short note on tympanic membrane. AN40.1, AN40.2

Introduction • The tympanic membrane or ear drum is a semitransparent oval membrane, which separates the external acoustic meatus from the middle ear cavity. • Its diameter measures about 9 × 10 mm and is placed obliquely at an angle of 55° with the floor of external acoustic meatus. It faces downwards, forwards and laterally. The circumference of membrane is made up of fibrocartilaginous ring. The sulcus is absent between anterior and posterior malleolar folds. The part of membrane enclosed between malleolar folds is called pars flaccida.

Structure It consists of three layers: • An outer cuticular layer (ectodermal in origin), continuous with the skin of external auditory meatus. • A middle fibrous layer (mesodermal in origin), consisting of superficial radiating fibres and deep circular fibres. • An inner mucous layer (endodermal in origin), lined by ciliated columnar epithelium, continuous with the mucosa of middle ear.

Features (fig. 18.1) • Most of tympanic membrane is tightly stretched and called pars tensa. A small upper part between two malleolar folds is loose and called pars flaccida (vide supra). The pars flaccida is crossed internally by the chorda tympani nerve. • The tympanic membrane has outer and inner surfaces. The outer surface is concave. The inner surface is convex and provides attachment to the handle of malleus, which extends up to its centre. The point of maximum convexity on the inner surface is called umbo. The cone of light is the reflection of light from the otoscope. • The handle of malleus is embedded in the middle fibrous layer.

FIG. 18.1 External surface of tympanic membrane as seen through otoscope: 1, posterosuperior quadrant; 2, anterosuperior quadrant; 3, posteroinferior quadrant; 4, anteroinferior quadrant.

Applied anatomy • The otoscopic examination may reveal the bulging, perforation or retraction of tympanic membrane. • The membrane is incised (myringotomy) to drain the pus present in the middle ear. The incision should be given in the posteroinferior quadrant of membrane to avoid injury to the chorda tympani nerve. • The rupture of tympanic membrane usually occurs in pars flaccida. ❖ Describe the middle ear under the following headings: (a) location, shape and dimension, (b) contents, (c) boundaries, (d) nerve supply and (e) applied anatomy.  AN40.2

Location The middle ear is narrow, slit-like, air-filled cavity in the petrous part of temporal bone. It communicates anteriorly with nasopharynx through auditory tube and posteriorly with mastoid antrum through aditus ad antrum.

Shape Biconcave hollow disc, resembling the red blood cell (RBC).

Dimension Vertical: 15 mm Transverse: ■ 6 mm: At roof ■ 2 mm: In the centre ■ 4 mm: At floor

Contents • Air • Two muscles: Tensor tympani and stapedius • Three ear ossicles: Malleus, incus and stapes • Two nerves: Chorda tympani nerve and tympanic plexus.

N.B. Air is actual content. The remaining structures are covered by the mucosa of the middle ear.

Boundaries (fig. 18.2) Roof or tegmental wall: Formed by tegmen tympani, a thin plate of bone that separates middle ear from middle cranial fossa.

FIG. 18.2 Schematic diagram showing the boundaries (and their relations) of the middle ear. The middle ear is akin to a six-sided box. Note its lateral side is opened out. O, oval window; P, pyramid; PC, processus cochleariformis; PM, promontory; R, round window; S, sinus tympani; TP, tympanic plexus.

Floor or jugular wall • Formed by jugular fossa of temporal bone. • Separates middle ear from superior bulb of internal jugular vein. Anterior wall or carotid wall

• Upper part presents: Canals for tensor tympani and auditory tube. • Lower part forms: Posterior wall of carotid canal.

N.B. The bony septum between canals for tensor tympani and auditory tube extends backward along the medial wall of tympanic cavity and upturns at its distal end to form a hook-like process. It is called processus cochleariformis. Medial or labyrinthine wall: It separates middle ear from internal ear and presents the following features: • Promontory: A rounded elevation produced by first turn of cochlea. • Oval window (fenestra vestibuli): An oval opening posterosuperior to the promontory that leads to vestibule of internal ear. It is occupied by the base of stapes. • Round window (fenestra cochleae): A round opening posteroinferior to the promontory that leads to scala tympani of cochlea and closed by secondary tympanic membrane. • Sinus tympani: A depression behind promontory. • Prominence of facial canal, just above the oval window. • Prominence of lateral semicircular canal, above the prominence of facial canal. Lateral or membranous wall • Separates middle ear from external ear. • It is formed: ■ Mainly by tympanic membrane. ■ Partly by squamous part of temporal bone in the region of epitympanic recess. Posterior wall or mastoid wall: It presents the following features. From above downwards these are: • Aditus to mastoid antrum (aditus ad antrum) • Fossa incudis: Depression for incus. • Pyramid: A conical bony projection. The apex of pyramid presents an opening for tendon of stapedius. • Posterior canaliculus for chorda tympani, lateral to pyramid.

Nerve supply • Tympanic branch of glossopharyngeal nerve. • Superior and inferior caroticotympanic nerves from sympathetic plexus around internal carotid artery.

Applied anatomy Otitis media: The throat infections commonly spread to the middle ear through auditory tube. It is more common in children because in children the tube is shorter, wider and horizontal. AN40.4 The longstanding otitis media often leads to collection of pus in the middle ear – a condition called chronic suppurative otitis media (CSOM). The pus from middle ear: • May be discharged in the external ear following the rupture of tympanic membrane. • May erode the roof leading to meningitis and temporal lobe abscess. • May erode the floor causing thrombosis of internal jugular vein. • May spread backward into mastoid antrum leading to mastoid abscess. Bleeding from ear: Fracture of middle cranial fossa can cause bleeding through the ear. ❖ Write a short note on mastoid antrum.  AN40.2 • The mastoid antrum is an air space in mastoid portion of temporal bone (Fig. 18.3). • It communicates anteriorly with the tympanic cavity through aditus ad antrum (entrance to the mastoid antrum).

FIG. 18.3 Mastoid antrum as seen in section along the long axis of petromastoid bone.

Boundaries Roof is formed by tegmen tympani. Lateral wall is formed by a plate of bone about 1.5 cm thick just deep to suprameatal triangle.

Posterior wall is formed by a thin plate of bone which separates it from sigmoid sinus.

Functions 1. Provides resonance to voice. 2. Acts as acoustic insulator and provides protection to middle ear from physical damage. 3. Acts as sound receptor.

Applied anatomy • Mastoid air cells are major contributor to the middle ear inflammatory disease. • Lateral wall of antrum is approached for surgery, through suprameatal triangle. ❖ Write a short note on ear ossicles. AN40.2 • There are three tiny bones present in the middle ear cavity. • From medial to lateral, these are malleus (hammer), incus (anvil) and stapes (stirrup) (Fig. 18.4). Malleus is the lateral ossicle. It has head, neck and three processes, i.e. handle, lateral process and anterior process. ■ Head articulates with incus ■ Handle passes downwards and is attached to the tympanic membrane. Medial aspect of handle receives insertion of tensor tympani. ■ Anterior process is attached to the spine of sphenoid by a ligament. ■ Lateral process is attached to the tympanic sulcus (bony) by anterior and posterior malleolar folds. Incus is the middle bone. It has body, short process and long process. ■ Body articulates with the head of malleus. ■ Short crus is attached to the floor of aditus by a ligament. ■ Long crus articulates with the head of stapes. Stapes is the most medial (innermost) ossicle. It has head, neck, anterior and posterior limbs and footplate. ■ Head articulates with the long process of the incus. ■ Footplate is held in fenestra vestibule (oval window) by annular ligament. ■ Neck of stapes receives an insertion of stapedius.

FIG. 18.4 Ear ossicles.

Applied anatomy The vibrations of sound waves are transmitted from tympanic membrane to the fluid (perilymph) of inner ear by the ossicular chain. • Paralysis of stapedius leads to hyperacusis. • Otosclerosis (abnormal ossification of annular ligament which anchors the footplate of stapes leads to conduction deafness). ❖ Briefly describe the internal ear. AN40.3 The internal ear is involved in both hearing and balance. It consists of two components: membranous labyrinth and bony (osseous) labyrinth.

Membranous labyrinth It consists of four membranous parts/structures: • Cochlear duct • Saccule • Utricle • Three semicircular ducts All these parts are interconnected to each other to form a labyrinth. Functions • The sensory receptor within the cochlear duct is spiral organ of Corti. It is concerned with hearing. • The sensory receptors present within saccule and utricle are maculae. They are concerned with static balance. • The sensory receptors within the semicircular ducts are cristae ampullaris. They are concerned with kinetic balance.

Bony labyrinth It consists of intercommunicating bony spaces in the petrous part of temporal bone. The bony labyrinth consists of three parts: • Cochlea • Vestibule • Three semicircular canals ❖ Write a short note on the spiral organ of Corti. AN40.3 It is an end organ of hearing, located on the basilar membrane of cochlear duct.

Components (fig.18.5) Microscopically, organ of Corti consists of five components: • Basilar membrane: A fibrous membrane that extends from osseous spiral lamina to the outer wall of cochlear duct. • Tunnel of Corti: Formed by inner and outer rod cells and contains corticolymph. • Hair cells are receptor cells of hearing located on the basilar membrane. These cells bear stereocilia and form the most important component of spiral organ of Corti. They are divided into inner and outer hair cells. The hair cells perform the following functions: ■ Detect movements of endolymph ■ Detect vibrations of basilar membrane ■ Transfer vibrations into nerve impulse to the cochlear nerve • Supporting cells: The inner hair cells are supported by phalangeal cells, while the outer supporting cells are called Henson’s cells. • Membrana tectoria: It is a gelatinous membrane that overlies the hair cells. The shearing force between the hair cells and tectorial membrane stimulates the hair cells.

FIG. 18.5 Spiral organ of Corti as seen in a section through the cochlear duct.

Innervation of organ of corti The hair cells are innervated by the peripheral processes of bipolar neurons of spiral ganglion located within the modiolus near the base of spiral lamina. There are two types of neurons: Type I neurons: They are myelinated and afferent. They innervate inner hair cells and responsible for auditory sensation. Type II neurons: They are unmyelinated and efferent from contralateral superior olivary nucleus. They innervate outer hair cells and are responsible for auditory discrimination.

Orbit ❖ Enumerate the structures present in the orbit. AN31.1, AN31.2 These are: • Eyeball • Extrinsic muscles of eyeball ■ Four recti ■ Superior rectus (SR) ■ Inferior rectus (IR) ■ Medial rectus (MR) ■ Lateral rectus (LR) ■ Two obliques ■ Superior oblique (SO) ■ Inferior oblique (IO) • Levator palpebrae superioris muscle • Nerves ■ Optic nerve ■ Three divisions of ophthalmic nerve: ■ Nasociliary ■ Lacrimal ■ Frontal ■ Three motor nerves: ■ Oculomotor (upper and lower divisions; CN III) ■ Trochlear (CN IV) ■ Abducent (CN VI) • Ciliary ganglion • Ophthalmic artery • Ophthalmic veins • Lacrimal gland

• Orbital pad of fat ❖ Write about the origin, insertion, nerve supply and actions of the extrinsic muscles of eyeball. AN31.1

Origin (fig. 18.6) Four recti: From common tendinous ring. Superior oblique: From the body of sphenoid superomedial to the optic canal. Inferior oblique: From rough impression in anteromedial part/angle of floor of orbit.

FIG. 18.6 Origin and nerve supply of extraocular muscles. NC, nasociliary nerve.

Insertion Four recti: Into sclera, a little posterior to the limbus (i.e. corneoscleral junction). Distance from cornea is as follows: SR = 7.7 mm; IR = 6.5 mm; MR = 5.5 mm; LR = 6.9 mm Superior oblique: Into sclera, behind the equator in the posterosuperior quadrant of eyeball between SR and LR. Inferior oblique: Into sclera, behind the equator in the posteroinferior quadrant of eyeball.

Nerve supply All the extrinsic muscles of the eyeball are supplied by CN III, except superior oblique, which is supplied by CN IV and lateral rectus which is supplied by CN VI. Mnemonic: LR6SO4 (LR, lateral rectus; SO, superior oblique)

Actions (fig. 18.7) These are given in Table 18.1.

FIG. 18.7 Schematic diagram Source: (modified after Starling) showing actions of various extraocular muscles. IO, inferior oblique; IR, inferior rectus; LR, lateral rectus; MR, medial rectus; SR, superior rectus; SO, superior oblique.

TABLE 18.1 Actions of Extrinsic Muscles of the Eyeball Muscle Superior oblique

Inferior oblique

Superior rectus

Inferior rectus

Medial rectus Lateral rectus

Actions • Depression • Abduction • Intorsion • Elevation • Abduction • Extorsion • Elevation • Adduction • Intorsion • Depression • Adduction • Extorsion • Adduction • Abduction

❖ Write about the origin, insertion, nerve supply and actions of the levator palpebrae superioris muscle. AN31.1

Origin

From undersurface of lesser wing of sphenoid near the apex of orbit.

Insertion • Upper major skeletal part, into the skin of upper eyelid. • Lower minor smooth part (also called Müller’s muscle), into the superior border of tarsal plate of upper eyelid.

Nerve supply • Larger part of skeletal muscle, by oculomotor nerve • Smaller part of smooth muscle, by sympathetic fibres derived from superior cervical sympathetic ganglion

Action Elevation of the upper eyelid to open the eye.

Eyeball AN41.1 Eyeball is the organ of sight (vision) located in the anterior two-third of the orbital cavity. ❖ Write a short note on Tenon’s capsule and mention its applied anatomy. AN41.1

General features • It is a membranous (fibrous) sac, which envelops the eyeball. It extends from the optic nerve to the corneoscleral junction. • It is separated from the eyeball by an episcleral space. • It forms a socket of the eyeball for its free movements.

Applied anatomy During enucleation of eyeball, the Tenon’s capsule is left intact to allow the movements of the implanted artificial eyeball. ❖ Enumerate the coats of eyeball. AN41.1 The eyeball consists of the following three coats from superficial to deep these are: • Outer fibrous coat called sclera in its posterior five-sixths and cornea in its anterior one-sixth • Middle vascular coat called uveal tract (consisting of choroid, ciliary body and iris) • Inner neural coat called retina

❖ Write a note on microscopic structure of retina. AN43.2 The cells of retina are arranged in the following four layers, from outside to inside: 1. Pigment cell layer 2. Layer of rods and cones 3. Layer of bipolar cells 4. Layer of ganglion cells

N.B. Axons from ganglion cells form the optic nerve. ❖ What are the compartments of eyeball? AN41.1 The interior of eyeball is divided into two compartments by the lens within the eyeball (Fig. 18.8).

FIG. 18.8 Compartments of the eyeball.

Anterior compartment It is small and lies in front of the lens. It is filled with aqueous humour. It is further subdivided into two parts: • A smaller anterior chamber, between iris and cornea. • A larger posterior chamber, between iris and lens.

These two portions of anterior chamber communicate with each other through a circular aperture in the iris, the pupil.

Posterior compartment It is large (four-fifth) and lies behind the lens. It is filled with colourless, transparent jelly-like material called vitreous humour/vitreous body. • The vitreous humour is enclosed in a delicate hyaloid membrane. • Anteriorly, the vitreous body presents a shallow depression (hyaloid fossa) to accommodate the lens. ❖ Enumerate the various refractive media of the eyeball. AN41.1 The four refractive media in the eyeball, from before backwards are as follows: • Cornea • Aqueous humour • Lens • Vitreous body ❖ What are eyelids? Enumerate the layers of the eyelid and discuss the related applied anatomy.  AN43.3 The eyelids are mobile curtains of soft tissue to close and open the eyes. They protect the eye from dust particles and help in its moistening.

The layers of eyelid From outside to inside, these are as follows: • Skin • Superficial fascia • Orbicularis oculi • Tarsal plate of palpebral fascia • Conjunctiva

Applied anatomy • Ptosis (drooping of upper eyelid): It occurs due to paralysis of levator palpebrae superioris muscle. • Stye (hordeolum): It is suppurative inflammation of glands of Zeis (i.e. sebaceous glands present in the eyelashes). • Chalazion: It is the inflammation of tarsal (meibomian) gland (a modified sebaceous gland in the tarsal plate). ❖ Enumerate the branches of ophthalmic artery. AN41.1 The ophthalmic artery is a branch of internal carotid artery. It gives rise to the following

branches within the orbit (Fig. 18.9): • Central artery of retina • Lacrimal artery • Posterior ciliary arteries • Supraorbital artery

FIG. 18.9 Branches of the ophthalmic artery.

❖ Write a short note on central retinal artery. AN41.2 It is the first and most important branch of ophthalmic artery. It pierces optic nerve 1.25 cm behind the eyeball and reaches the optic disc through the central part of the disc and divides into four branches, one for each quadrant. These branches are superior nasal, inferior nasal, superior temporal and inferior temporal. It supplies optic nerve and inner six or seven layers of retina.

Applied anatomy Any blockage of a central retinal artery leads to loss of vision. ❖ Write about the origin, course and distribution of ophthalmic nerve. AN41.1

The ophthalmic nerve is the first and smallest division of the trigeminal nerve. It arises from the trigeminal ganglion and enters the lateral wall of the cavernous sinus. Here it divides into three branches, nasociliary, frontal and lacrimal, which enter the orbit through superior orbital fissure (Fig. 18.10). • The nasociliary nerve runs forwards and medially crossing optic nerve obliquely from lateral to medial side, then runs along the medial wall of orbit to terminate by dividing into anterior ethmoidal and infratrochlear nerves. It gives rise to the following branches (Fig. 18.10): ■ Sensory root to the ciliary ganglion ■ Two or three long ciliary nerves ■ Posterior ethmoidal nerve ■ Anterior ethmoidal nerve ■ Infratrochlear nerve • The frontal nerve (largest branch) runs forward and terminates by dividing into supraorbital and supratrochlear nerves. • The lacrimal nerve (smallest branch) runs along the lateral wall of the orbit end and ends in the lacrimal gland. It gives rise to the following branches: ■ Branches to the lacrimal gland ■ Lateral palpebral branch to the skin of the lateral part of the upper eyelid

FIG. 18.10 Branches and distribution of the ophthalmic nerve.

❖ Write about the location, roots and distribution of the ciliary ganglion. AN41.1

Location It is a small peripheral parasympathetic ganglion of pin-head size (about 2 mm in diameter), located near the apex of orbit, between the optic nerve and lateral rectus muscle.

Roots (fig. 18.11) The roots are 3 in number as follows: • Parasympathetic root: It is derived from inferior division of oculomotor nerve. The preganglionic fibres arise from Edinger–Westphal nucleus, run in inferior division of oculomotor nerve and pass through the nerve to the inferior oblique to relay in the ciliary ganglion. The postganglionic parasympathetic fibres arise from ganglion and run through short ciliary nerves. • Sympathetic root: It is derived from sympathetic plexus around internal carotid artery. The preganglionic sympathetic fibres arise from T1 spinal segment and relay in the superior cervical sympathetic ganglion. The postganglionic fibres arise from this ganglion, form plexus around internal carotid artery and pass through the ciliary ganglion without relay to enter into short ciliary nerves. • Sensory root: It is derived from nasociliary nerve – a branch of ophthalmic nerve

passes through the ganglion without relay.

FIG. 18.11 Roots and distribution of the ciliary ganglion. TG, trigeminal ganglion.

Distribution (fig. 18.11) The distribution of its branches is as follows: • Parasympathetic fibres: They supply sphincter pupillae and ciliary muscles through short ciliary nerves. • Sympathetic fibres: They supply dilator pupillae and blood vessels of the eyeball through short ciliary nerves. • Sensory fibres: They provide sensory innervation to whole eyeball, except conjunctiva, through short ciliary nerves. The sensory supply of conjunctiva is derived from frontal, lacrimal and infraorbital nerves.

19

Dural folds, intracranial dural venous sinuses and pituitary gland ❖ Enumerate the dural folds (folds of dura mater). AN30.3 The dural folds are generally formed by folding of the meningeal layer of cranial dura, which projects into the cranial cavity to divide it into various compartments, which lodge the different lobes/parts of the brain (Fig. 19.1).

FIG. 19.1 Dural folds and dural venous sinuses enclosed within them, viewed from superolateral aspect.

The folds of dura mater are as follows: • Falx cerebri • Tentorium cerebelli • Falx cerebelli • Diaphragma sellae ❖ Briefly describe falx cerebri. AN30.3 Falx cerebri is a large, sickle-shaped fold of dura mater that lies in the median longitudinal fissure between the two cerebral hemispheres.

Features (fig. 19.1) It presents two ends – anterior and posterior; two margins – upper and lower; and two surfaces – right and left.

Anterior end: It is narrow and attached to the frontal crest of the frontal bone and crista galli of the ethmoid bone. Posterior end: It is broad and attached along the median plane to the upper surface of the tentorium cerebelli. Upper attached margin: It is convex and attached to the lips of the sagittal sulcus on the inner aspect of the cranial vault as far back as the internal occipital protuberance. Lower free margin: It is concave, free and lies close to the corpus callosum. Right and left surfaces: Each of these surfaces is related to the medial surface of the corresponding cerebral hemisphere.

Venous sinus enclosed in the falx cerebri (fig. 19.1) • Superior sagittal sinus along the upper margin • Inferior sagittal sinus along the lower margin • Straight sinus along the line of attachment of the falx cerebri to the tentorium cerebelli

Applied anatomy Thrombosis of superior sagittal sinus may occur due to spread of infection into it from nose, scalp and diploic veins. It interferes with the absorption of CSF, leading to increased intracranial pressure. ❖ Briefly describe tentorium cerebelli. AN30.3 Tentorium cerebelli is a tent-shaped fold of dura mater, which forms the roof of the posterior cranial fossa. It separates the cerebellum from the occipital lobes of the cerebrum.

Features (fig. 19.1) It has two margins and two surfaces. Margins • The inner free margin is U-shaped and encloses the tentorial notch for the passage of the midbrain. The anterior ends of concave free margin are attached to the anterior clinoid processes. • The outer attached margin is convex and attached on each side (from anterior to posterior) to the posterior clinoid process, superior border of petrous temporal bone, posteroinferior angle of parietal bone and lips of transverse sulcus on occipital bone.

N.B. The free and attached margins of tentorium cerebelli cross each other near the apex of the petrous temporal bone to enclose a triangular hollow, which is pierced by oculomotor nerve.

Surfaces • The convex upper surface slopes on either side from the median plane. In the median plane, it provides attachment to falx cerebri. • The concave inferior surface provides attachment to the falx cerebelli in its posterior part.

Venous sinus enclosed in tentorium cerebelli (fig. 19.1) • Superior petrosal sinus within the anterolateral part of the attached margin. • Transverse sinus within the posterior part of the attached margin. • Straight sinus along the line of attachment between falx cerebri and tentorium cerebelli. ❖ Define intracranial dural venous sinuses. Discuss their characteristic features and applied anatomy.  AN30.3, AN30.4

Definition The intracranial dural venous sinuses are endothelial-lined venous channels lying between the two layers of dura mater.

N.B. All the intracranial dural venous sinuses are present between endosteal and meningeal layers of dura mater except inferior sagittal sinus and straight sinus, which lie between two meningeal layers of dura mater.

Characteristic features • Are devoid of smooth muscle in their wall. • Are devoid of valves in their lumen. • Are lined by endothelium. • Drain CSF through arachnoid villi and granulations. • Receive emissary veins. • Communicate with extracranial veins through emissary veins. • Communicate with vertebral venous plexus through basilar venous plexus. • Receive veins from brain and diploic veins from cranial bones. • Noncompressive in nature (i.e. always kept patent) and equalize pressure within and outside the skull.

Applied anatomy The infection from extracranial sources can spread to the dural venous sinuses and then to the brain. ❖ Write about the classification of intracranial dural venous sinuses. AN30.3

The intracranial dural venous sinuses are classified into two types – paired and unpaired. The details are given in Table 19.1. TABLE 19.1 Classification of Intracranial Dural Venous Sinuses Paired • Cavernous • Superior petrosal • Inferior petrosal • Transverse • Sigmoid • Sphenoparietal • Petrosquamous • Middle meningeal vein

Unpaired • Superior sagittal • Inferior sagittal • Straight • Occipital • Anterior intercavernous • Posterior intercavernous • Basilar venous plexus

❖ Describe the cavernous sinus under the following headings: (a) formation and location, (b) relations, (c) contents, (d) tributaries and communications and (e) applied anatomy. AN30.3

Formation and location (fig. 19.2) The two cavernous sinuses are situated one on either side of the pituitary fossa and body of sphenoid. Each cavernous is large venous space (2 cm long and 1 cm wide) formed by the separation of endosteal and meningeal layers of dura mater, lined by endothelium. Its floor is formed by endosteal layer, whereas its lateral wall, roof and medial wall are formed by meningeal layer of the dura mater.

FIG. 19.2 Formation, location, relations and contents of cavernous sinuses.

Relations (fig. 19.2)

Superior: Optic chiasma, internal carotid artery and anterior perforated substance. Inferior: Foramen lacerum and greater wing of sphenoid. Medial: Hypophysis cerebri and sphenoidal air sinus. Lateral: Temporal lobe of the brain (uncus) and cavum trigeminale with trigeminal ganglion within it.

Contents (fig. 19.2) Structures present in the lateral wall: From anterior to posterior, these are • Oculomotor nerve (CN III) • Trochlear nerve (CN IV) • Ophthalmic nerve (CN V1) • Maxillary nerve (CN V2)

N.B. In section anterior looks superior and posterior looks inferior. Structures passing through the sinus • Internal carotid artery with sympathetic plexus around it • Abducent nerve – below and lateral to the internal carotid artery

Tributaries (fig. 19.3) • Superior and inferior ophthalmic veins from orbit • Central vein of retina • Sphenoparietal sinus • Anterior (frontal) trunk of middle meningeal vein • Superficial middle cerebral vein • Inferior cerebral veins (some)

• From eyeball • From meninges • From cranial wall • From brain

FIG. 19.3 Tributaries and communications of cavernous sinus. A, anterior intercavernous sinus; E, emissary vein; P, posterior intercavernous sinus.

Communications (fig. 19.3) • Superior petrosal sinus connects it with the transverse sinus. • Inferior petrosal sinus connects it with the internal jugular vein. • Emissary veins connect it with the pterygoid venous plexus. • Ophthalmic vein connects it with the facial vein. • Anterior and posterior intercavernous sinuses connect it with the opposite cavernous sinus.

N.B. All these communications are valveless and blood can flow in either direction.

Applied anatomy • Thrombosis of Cavernous Sinus: It may be caused by spread from septic infection in the dangerous area of face. The clinical features of cavernous sinus thrombosis are as follows: ■ Severe pain in the eye due to involvement of ophthalmic nerve. ■ Ophthalmoplegia due to involvement of CN III, IV and VI. ■ Oedema of eyelids due to congestion of orbital veins.

■ Exophthalmos due to congestion of orbital veins. • Arteriovenous Fistula: It is caused by rupture of the internal carotid artery into the cavernous sinus. It results into: ■ Unilateral pulsating exophthalmos ■ Loud systolic thrill/murmur over eye ❖ Define emissary veins. Enumerate the important emissary veins and discuss their functional and clinical importance. AN27.2 The emissary veins are thin-walled venous channels that connect the extracranial veins to the intracranial dural venous sinuses. Following are the important emissary veins: • Parietal emissary vein • Mastoid emissary vein • An emissary vein passing through the foramen ovale or emissary sphenoidal foramen • Small emissary veins passing through the foramen lacerum and connecting the cavernous sinus to the pterygoid plexus of veins • An emissary vein passing through the posterior condylar canal and connecting the sigmoid sinus to the suboccipital plexus of veins • Ophthalmic veins can also act as emissary veins

Functions The emissary veins help to maintain the constant intracranial pressure because blood passing through them can flow in either direction according to the state of intracranial pressure.

Clinical importance They can carry infection from outside the skull to inside the skull (i.e. the cranial cavity). ❖ Describe pituitary gland under the following headings: (a) definition and location, (b) gross features, (c) relations, (d) microscopic structure, (e) blood supply, (f) nerve supply, (g) development and (h) applied anatomy. AN30.1, AN30.5, AN43.2, AN43.4

Definition and location The pituitary gland/hypophysis cerebri is a small neuroendocrine gland located in the hypophyseal fossa (sella turcica) of the body of sphenoid (Fig. 19.4).

FIG. 19.4 Location of the pituitary gland.

Shape and measurements Shape Size

= =

Weight

=

Oval Anteroposterior: 8 mm Transverse: 12 mm 500 mg

Gross features (fig. 19.5) The pituitary gland consists of two parts, which are embryologically, morphologically and functionally different from each other: • Adenohypophysis (anterior pituitary) • Neurohypophysis (posterior pituitary)

FIG. 19.5 Subdivisions of the pituitary gland.

Adenohypophysis (anterior pituitary): It is highly cellular and presents an intraglandular cleft. It is further subdivided into three parts/lobes: • Anterior lobe (pars distalis): It is the major part of the adenohypophysis. • Intermediate lobe (pars intermedia): It is a thin strip of the glandular tissue between the intraglandular cleft in front and neurohypophysis behind. • Tuberal lobe (pars tuberalis): It is an upward extension of the anterior lobe that surrounds the part of the infundibulum. Neurohypophysis (posterior pituitary): It is continuous above with the infundibulum, which extends downward and forward from the floor of 3rd ventricle and enters the hypophyseal fossa after piercing the diaphragma sellae. It is subdivided into three parts: • Posterior lobe (pars posterior): It is smaller than the anterior lobe and lies in the posterior concavity of the larger anterior lobe. • Infundibulum (neural stalk): It contains the neural connections of the neurohypophysis. • Median eminence of the tuber cinereum: It is continuous with the infundibular stem.

Relations

Anterior: ■ Anterior intercavernous sinus Posterior: ■ Posterior intercavernous sinus ■ Dorsum sellae ■ Basilar artery ■ Pons Superior: ■ Diaphragma sellae ■ Optic chiasma ■ Tuber cinereum ■ Infundibular recess of the 3rd ventricle Inferior: ■ Hypophyseal fossa ■ Body of the sphenoid ■ Sphenoidal air sinuses Lateral (on each side): ■ Cavernous sinus with its contents

Microscopic structure (fig. 19.6) AN43.2 Anterior lobe (pars anterior/distalis): It forms three-fourth of the gland. It consists of two types of glandular cells arranged in irregular cords or clumps: • Chromophilic cells (50%) having affinity to colours, i.e. staining ■ Acidophils/alpha cells (about 43% of cells): Secrete GH, ACTH and prolactin ■ Basophils/beta cells (about 7% of cells): Secrete TSH, LH, FSH and MSH • Chromophobic cells (50%), which do not take the colour of stain: Resting cells, no secretion

FIG. 19.6 Structure of pituitary gland (highly schematic diagram).

Intermediate lobe (pars intermedia): It is made up of numerous basophilic and chromophobic cells. The cells are arranged in the form of small follicles containing colloid material. Posterior lobe (pars posterior/nervosa): It consists of: • Large number of nonmyelinated nerve fibres. • Modified neuroglial cells called pituicytes. • Presence of Herring bodies, the small, spherical masses that stain deeply with chrome–alum haematoxylin.

Blood supply Arterial supply: Venous drainage: Small short veins emerge from the surface of gland and drains into neighbouring dural venous sinuses.

Nerve supply By hypothalamo-hypophyseal tract, which arises from preoptic and paraventricular nuclei of hypothalamus.

Development AN43.4 The pituitary gland develops from two distinct sources:

• Adenohypophysis develops from Rathke’s pouch – an ectodermal diverticulum (outpocketing) from the roof of stomodeum that grows cranially in front of buccopharyngeal membrane. • Neurohypophysis develops from infundibulum – a downgrowth from the floor of 3rd ventricle.

Applied anatomy The pituitary gland produces number of hormones that control the secretions of other endocrine glands of the body. • Pituitary adenoma: It is not uncommon. It compresses the central part of optic chiasma leading to bitemporal hemianopia (tunnel vision). (For details, see Textbook of Anatomy: Head, Neck and Brain, Volume III, 3rd edition, p. 329 by Vishram Singh.) AN30.5 • Gigantism and acromegaly: The gigantism occurs due to excessive secretion of growth hormone (GH) before adolescence; hence, the person becomes very tall (8–9 feet) due to excessive length of the bone. The acromegaly occurs due to excessive secretion of GH in adults leading to coarse facial features with protrusion of jaw (prognathism). • Pituitary dwarfism: Occurs due to hyposecretion of GH causing shortening of limbs.

20

Cranial nerves ❖ Enumerate the various cranial nerves. AN30.2, AN62.1 There are 12 pairs of cranial nerves. They are serially numbered from 1 to 12 in craniocaudal order of their attachment on the surface of the brain and designated by Roman numerals as follows: • Olfactory (I) • Optic (II) • Oculomotor (III) • Trochlear (IV) • Trigeminal (V) • Abducent (VI) • Facial (VII) • Vestibulocochlear (VIII) • Glossopharyngeal (IX) • Vagus (X) • Accessory (XI) • Hypoglossal (XII) ❖ Describe the olfactory nerve in brief. The olfactory nerve consists of about a dozen filaments, which represent the central processes of the bipolar neurons present in the olfactory epithelium. It is a sensory nerve and carries sense of smell.

Functional component • Special somatic afferent fibres

Origin and course The cell bodies of the olfactory nerves are located in the olfactory epithelium of nasal mucosa. The olfactory nerve begins as a dozen of filaments representing axons of bipolar neurons from the olfactory mucosa of the nasal cavity. These filaments pass through the cribriform plate of ethmoid to synapse within olfactory bulb in the anterior cranial fossa.

N.B. Olfactory pathway: The olfactory bulb leads posteriorly to the olfactory tract, which lies on inferior

surface of the frontal lobe of cerebral hemisphere and conveys fibres to the prepyriform cortex, anterior perforating substance and septal area.

Applied anatomy The lesions of olfactory nerve result in loss of smell, which is called anosmia. The sense of smell is also responsible for the finer appreciation of taste of the food. ❖ Describe the optic nerve in brief and mention its unique features. The optic nerve is the nerve of sight, i.e. vision.

Functional components • Special somatic afferent fibres for the special sense of sight.

Origin and course The optic nerve extends from eyeball to the optic chiasma, which lies above the pituitary fossa containing pituitary gland. Its fibres arise from the retina and leave the eyeball at the optic disc. The fibres arising from nasal half of retina decussate in optic chiasma with that of the opposite side and then course along the optic tract of the opposite side, whereas those arising from temporal half of retina do not decussate in the optic chiasma and thus run in the optic tract of the same side. The fibres of the optic tract relay in the lateral geniculate body.

Unique features of optic nerve • It is not a true peripheral nerve, rather it is a tract of the forebrain. • It is surrounded by meninges, i.e. dura mater, arachnoid mater and pia mater, and thus by a subarachnoid space containing CSF. • Its fibres are myelinated by oligodendrocytes and not by Schwann cells. (cf. The fibres of peripheral nerves are myelinated by the Schwann cells.) • It cannot regenerate if damaged.

Applied anatomy The damage of optic nerve leads to complete blindness on the side of lesion. ❖ Describe the oculomotor nerve under the following headings: (a) functional components, (b) origin, course and distribution and (c) applied anatomy. AN31.5, AN30.2 The oculomotor nerve is purely motor and responsible for the movements (largely) and accommodation of the eye.

Functional components (fig. 20.1)

• General somatic efferent (GSE) fibres, to supply the extrinsic muscles of eyeball. They arise from large somatic component of oculomotor nucleus. • General visceral efferent (GVE) fibres, to supply the intrinsic muscles of eyeball (ciliaris and sphincter pupillae). They arise from small parasympathetic component of oculomotor nucleus (Edinger–Westphal nucleus). • General somatic afferent (GSA) fibres, to carry proprioceptive sensations from the muscles (vide supra).

FIG. 20.1 A, Nuclei and functional components of oculomotor nerve. B, Distribution of oculomotor nerve.

Origin, course and distribution (fig. 20.1) The oculomotor nerve arises from oculomotor nucleus, located in the upper part of the midbrain. The nerve emerges from midbrain in the interpeduncular fossa, then runs between the posterior cerebral and superior cerebellar arteries, and passes on to the lateral side of the posterior communicating artery. Now it runs forwards and upwards piercing the dura mater near the posterior clinoid process and travels forwards in the lateral wall of the cavernous sinus. After emerging from cavernous sinus, it divides into upper and lower divisions which enter the orbit through superior orbital fissure where: • The upper division supplies superior rectus of the eyeball and levator palpebrae superioris. • The lower division supplies medial rectus, inferior rectus, and inferior oblique of the eyeball. The nerve to inferior oblique gives a motor root to the ciliary ganglion.

N.B. The preganglionic parasympathetic fibres (GVE fibres) arise from Edinger–Westphal nucleus, and run successively through the undivided trunk, lower division of oculomotor nerve and nerve to inferior oblique to relay in the ciliary ganglion. The postganglionic parasympathetic fibres from ganglion run through short ciliary nerves to supply ciliary and sphincter pupillae muscles of the eyeball.

Applied anatomy

The lesion of oculomotor nerve (infranuclear lesion) leads to: • Ptosis, due to paralysis of levator palpebrae superioris • Loss of accommodation, due to involvement of ciliaris muscle • Lateral squint, due to paralysis of medial rectus muscle and unopposed action of healthy lateral rectus • Diplopia, due to paralysis of medial rectus muscle • Dilatation of pupil, loss of pupillary reflex, due to paralysis of sphincter pupillae Note: In paralysis of oculomotor nerve, the person cannot look upwards, downwards and medially. ❖ Describe trochlear nerve in brief. AN31.5, AN30.2 Trochlear nerve is the smallest cranial nerve.

Functional components • General somatic efferent (GSE) fibres to supply superior oblique muscle of the eyeball. • General somatic afferent (GSA) fibres to carry proprioceptive fibres from superior oblique to mesencephalic nucleus of CN V.

Origin, course and distribution The trochlear nerve arises from 4th nerve nucleus located in the lower part of the midbrain. Before emerging on the dorsal aspect of midbrain, its fibres decussate with the fibres of nerve of opposite side. After emerging, it passes forward in the subarachnoid space and pierces the dura mater to run in the lateral wall of the cavernous sinus. The nerve enters the orbit through superior orbital fissure and supplies the superior oblique muscle of the eyeball.

Applied anatomy The damage of trochlear nerve causes diplopia on looking downwards and laterally. ❖ Describe trigeminal nerve under the following headings: (a) functional components, (b) origin and course, (c) distribution and (d) applied anatomy.  AN30.2, AN33.1 Trigeminal nerve is a mixed nerve but mainly sensory.

Functional components • Special visceral efferent (SVE) fibres to muscles of mastication. • General somatic afferent (GSA) fibres to carry: ■ Pain and temperature sensations from the head and face

■ Proprioceptive sensations from the muscles of mastication

Origin and course It arises by two roots: • The large sensory root arises from sensory nuclei of the trigeminal nerve located in the brainstem and upper part of the spinal cord. • The small motor root arises from motor nucleus of the trigeminal nerve located in the pons. The sensory and motor roots emerge from the anterior surface of the pons, the motor root lying medial to the sensory root. After emerging from brainstem, the nerve passes upwards, forward and laterally in the posterior cranial fossa. On reaching the depression on the apex of petrous temporal bone in the middle cranial fossa, it expands to form the trigeminal ganglion. (Remember motor root passes deep to the ganglion, whereas sensory root forms the ganglion.) The anterior border of the trigeminal ganglion gives rise to three divisions of the trigeminal nerve: • Ophthalmic division: It is purely sensory and enters the orbit through superior orbital fissure. • Maxillary division: It is purely sensory and enters the pterygopalatine fossa through foramen rotundum. • Mandibular division: It enters the infratemporal fossa through foramen ovale. It is joined by the motor root (which also passes through foramen ovale) just below this foramen. Hence, it is both sensory and motor.

Distribution Sensory distribution: ■ Most of the skin of the head and face ■ Mucous membrane of nasal cavities, oral cavity and paranasal air sinuses ■ Teeth of both the jaws ■ Cornea and conjunctiva of the eye Motor distribution: Muscles of the mastication

Applied anatomy Trigeminal neuralgia (tic douloureux): A clinical condition characterized by intermittent attacks of severe lancinating pain in the region of sensory distribution of one or more divisions of trigeminal nerve in face, usually the 2nd and 3rd divisions (Fig. 20.2).

FIG. 20.2 Sensory distribution of trigeminal nerve on face.

The pain is so intense that it makes the patient to screw up his/her face. ❖ Describe the origin, course and distribution of the mandibular nerve. AN30.2, AN33.1 It is described on p. 177 and 178. ❖ Describe the origin, course and distribution of the maxillary nerve. AN30.2, AN33.1 It is described on p. 186 and 187. ❖ Describe the origin, course and distribution of the ophthalmic nerve. AN30.2, AN33.1 It is described on p. 200 and 201. ❖ Write a short note on nuclei of trigeminal nerve. AN58.3, AN59.3, AN62.1 The trigeminal nerve has the following four nuclei: 1. Principal sensory nucleus lies in the dorsolateral region of the tegmentum of upper part of the pons lateral to the motor nucleus of trigeminal nerve. It receives all sensory fibres of trigeminal nerve. 2. Mesencephalic nucleus lies in the midbrain above the main sensory nucleus. It receives proprioceptive impulses from muscle of mastication, TMJ and teeth.

3. Spinal nucleus lies in the spinal cord below main sensory nucleus. It receives pain and temperature sensations from face. 4. Motor nucleus lies in the upper part of bones. It gives motor fibres to muscles of mastication. ❖ Describe the abducent nerve under the following headings: (a) functional components, (b) origin, course and distribution and (c) applied anatomy. AN31.5, AN62.1 The abducent is CN VI. It is purely a motor nerve and supplies only one muscle – the lateral rectus of the eyeball.

Functional components • General somatic efferent (GSE) fibres to supply lateral rectus. They arise from abducent nucleus in the lower part of the pons. • General somatic afferent (GSA) fibres, which carry proprioceptive sensation from lateral rectus to the mesencephalic nucleus of the trigeminal nerve.

Origin, course and distribution (fig. 20.3) The abducent nerve arises from abducent nucleus in the lower part of the pons, and emerges from anterior surface of brainstem at the junction of the pons and medulla oblongata. After emerging from brain, it runs at first upwards, forwards and laterally in the posterior cranial fossa and pierces the dura mater over the clivus. It then turns sharply forwards, crossing the sharp superior border of the petrous temporal bone before entering the cavernous sinus. It traverses the cavernous sinus, lying at first lateral and then inferolateral to the internal carotid artery. The nerve enters the orbital cavity through the superior orbital fissure and supplies the lateral rectus muscle.

FIG. 20.3 Origin, course and distribution of abducent nerve.

Applied anatomy The abducent nerve is a thin motor nerve that takes the longest intracranial course, and hence it is often damaged in increased intracranial pressure associated with coning of the brainstem. The paralysis of abducent nerve results in: • Medial squint • Diplopia ❖ Describe the facial nerve under the following headings: (a) functional components, (b) origin and course, (c) branches and distribution and (d) applied anatomy. AN62.1, AN28.4, AN28.7 The facial nerve is the CN VII. It is a mixed cranial nerve (i.e. motor and sensory) but predominantly motor.

Functional components • Special visceral efferent (SVE) fibres to supply the muscles of facial expression, etc. • General visceral efferent (GVE) fibres to supply the lacrimal, submandibular and sublingual salivary glands. • Special visceral afferent (SVA) fibres, which carry taste sensations from anterior two-third of the tongue, except those from vallate papillae. • General somatic afferent (GSA) fibres, which carry general sensation from concha of the external ear.

Origin and course (fig. 20.4) The facial nerve has two roots: (a) a large medial motor root and (b) a small lateral, sensory root – the nervus intermedius.

FIG. 20.4 Origin, course and distribution of facial nerve. T, temporal; Z, zygomatic; UB, upper buccal; LB, lower buccal; M, mandibular; C, cervical.

The motor root arises from motor nucleus of facial nerve in the pons. The sensory root (nervus intermedius) arises from nucleus tractus solitarius, and superior salivatory and lacrimatory nuclei in the pons. The two roots of facial nerve emerge on the anterior surface of the brainstem at the lower border of the pons. They pass forwards and laterally in the posterior cranial fossa along with vestibulocochlear nerve and enter the internal acoustic meatus. At the distal end of internal acoustic meatus, the two roots join to form a single nerve. At the bottom of meatus, the nerve enters the facial canal. Now, it takes a dubious course in the facial canal through temporal bone and comes out of skull through stylomastoid foramen. Now it winds around the lateral aspect of styloid process to enter the parotid gland, where it divides into five terminal branches.

Branches and distribution (fig. 20.4) In the facial canal: ■ Greater petrosal nerve, which joins the deep petrosal nerve to form the nerve of pterygoid canal (Vidian’s nerve). This nerve carries parasympathetic secretomotor fibres to the lacrimal, nasal and palatine glands. ■ Nerve to stapedius. ■ Chorda tympani nerve: It arises about 5 cm above the stylomastoid foramen and joins the lingual nerve in the infratemporal fossa. The chorda tympani

nerve serves the following functions: ■ Carries taste sensations from the anterior two-third of the tongue, except from vallate papillae. ■ Supplies secretomotor fibres to the submandibular and sublingual salivary glands. At the stylomastoid foramen (after emerging from facial canal): ■ Nerve to posterior belly of digastric ■ Nerve to stylohyoid ■ Posterior auricular nerve to supply occipital belly of occipitofrontalis In the parotid gland, it gives rise to five terminal branches to supply muscles of facial expression: ■ Temporal ■ Zygomatic ■ Buccal (upper and lower buccal) ■ Mandibular ■ Cervical

Applied anatomy • Facial nerve paralysis: The effects of paralysis of CN VII depend on the site of lesion. The complete paralysis of facial nerve manifests as follows: 1. Loss of lacrimation due to involvement of lacrimal nerve and inability to close the eye to paralysis of orbicularis oculi. This leads to: a. Inability to close the eye on affected side due to paralysis of orbicularis oculi. b. Exposing cornea to the air and loss of lacrimation due to involvement of secretomotor fibres to this gland, which leads to corneal dryness and keratitis. 2. Angle of mouth goes down and dribbling of saliva due to paralysis of orbicularis oris. 3. Accumulation of food bolus in the vestibule of the mouth on the affected side due to paralysis of buccinator muscle. 4. Speech becomes defective due to paralysis of lip muscles. 5. Hyperacusis as a result of loss of control of movements of stapes following paralysis of stapedius. 6. Loss of taste sensations in the anterior two-third of tongue, due to paralysis of chorda tympani nerve. • Bell palsy: It is lower motor neuron type of facial palsy, which occurs due to compression of facial nerve into the facial canal just above the stylomastoid foramen following its inflammation and swelling, probably due to viral infection.

Clinical features (fig. 20.5)

■ Facial asymmetry, i.e. face of the paralysed side is pulled to the opposite/healthy side ■ Loss of wrinkles on the forehead ■ Inability to close the eye causing wide palpebral fissure ■ Inability of angle of mouth to move up during laughing ■ Loss of nasolabial furrow ■ Accumulation of food in the vestibule mouth ■ Dribbling of saliva from the angle of mouth ■ Inability to inflate/blow the cheek properly

FIG. 20.5 Bell palsy.

❖ Briefly describe vestibulocochlear nerve. It is nerve of hearing and balance (i.e. special sense). It consists of two parts: vestibular and cochlear. Both are purely sensory. The vestibular nerve helps in maintaining the balance, whereas cochlear nerve carries sense of hearing. The cochlear nerve carries sensations from spiral organ of Corti within the cochlear duct of internal ear. It is formed by the central processes of nerve cells of spiral ganglion of the cochlea. It comes out of temporal bone through the internal acoustic meatus, and reaches the lower border of the pons. Here, it enters the pons to end in ventral and dorsal cochlear nuclei situated on the ventral and dorsal aspects of the inferior cerebellar peduncle, respectively. The vestibular nerve carries sensations from maculae of utricle and saccule, and cristae ampullaris of semicircular ducts of the internal ear. It is formed by the central processes of nerve cells of vestibular ganglion in the distal part of the external acoustic meatus. It passes into the cranial cavity through internal acoustic meatus, and reaches

the lower border of the pons, where it enters the pons to end in the vestibular nuclei located in the floor of 4th ventricle.

N.B. On the surface of brain, the vestibulocochlear nerve emerges at the lower border of pons in the region of cerebellopontine angle and traverses the subarachnoid space to enter the internal acoustic meatus. ❖ Describe the glossopharyngeal nerve under the following headings: (a) functional components, (b) origin and course, (c) branches and distribution and (d) applied anatomy. AN35.7 The glossopharyngeal nerve is CN IX. It is a mixed nerve (motor and sensory) but predominantly sensory.

Functional components • Special visceral efferent (SVE) fibres to supply the stylopharyngeus muscle. • General visceral efferent (GVE) fibres, which supply the secretomotor fibres to the parotid gland. • Special visceral afferent (SVA) fibres, which carry taste sensations from posterior one-third of the tongue including vallate papillae. • General visceral afferent (GVA) fibres, which carry general sensations from skin of the auricle.

Origin and course (fig. 20.6) The glossopharyngeal nerve arises from its nuclei in the brainstem and emerges on surface from the lateral aspect of the medulla in the groove between olive and inferior cerebellar peduncle and enters the jugular foramen. After emerging from jugular foramen, it descends vertically between the internal jugular vein and internal carotid artery for some distance, then curves around the lateral surface of the stylopharyngeus, and passes forward into the tongue.

N.B. In the jugular foramen, it has two small sensory ganglia (superior and interior).

FIG. 20.6 Course and distribution of glossopharyngeal nerve.

Branches and distribution (fig. 20.6) • Tympanic nerve (Jacobson’s nerve), carrying secretomotor fibres to the parotid gland • Nerve to stylopharyngeus • Pharyngeal branch to the pharyngeal plexus • Sinus nerve to carotid sinus and carotid body • Terminal branches to the posterior one-third of the tongue including vallate papillae, tonsil, soft palate and epiglottis

Applied anatomy The paralysis of glossopharyngeal nerve leads to loss of gag reflex and loss of general and taste sensations in the posterior one-third of the tongue. The glossopharyngeal nerve is tested clinically by: • Eliciting gag reflex: The tickling of posterior wall of oropharynx/soft palate/tonsillar region causes reflex contraction of pharyngeal muscles leading to gagging and retching. ■ Note: The afferent limb of gag reflex is formed by the glossopharyngeal nerve, while its efferent limb is formed by the vagus nerve. • Testing sensations (general and taste) in the posterior one-third of the tongue

including vallate papillae. ❖ Describe the origin, course and branches of the vagus nerve in the neck. AN35.7 The vagus nerve is CN X. It is the longest cranial nerve and has a vague course.

Origin and course The vagus nerve arises from nuclei within the brainstem and emerges on surface from the lateral aspect of medulla in the groove between olive and inferior cerebellar peduncle, and comes out of cranial cavity through jugular foramen. After emerging from cranial cavity, it descends vertically between internal jugular vein and internal carotid artery. At the root of neck, the nerve enters the thorax. The right vagus nerve enters the thorax by crossing in front of right subclavian artery, while the left vagus nerve does so by passing between left common carotid and left subclavian arteries.

Branches of vagus nerve in the neck • Meningeal branch to dura mater of posterior cranial fossa • Auricular branch (Aldermen’s nerve/Arnold’s nerve) to the skin of external acoustic meatus • Pharyngeal branch to pharyngeal plexus • Superior laryngeal nerve • Recurrent laryngeal nerve (on the right side only) • Cardiac branches (cervical) ❖ Describe the origin, course, distribution and applied anatomy of the accessory nerve. AN35.7 The accessory nerve is the CN XI. It is purely a motor nerve and consists of two roots – cranial and spinal.

Origin and course • The cranial root arises from nucleus ambiguus in the medulla oblongata. It emerges on the surface of medulla between olive and inferior cerebellar peduncle. • The spinal root arises from the upper five cervical spinal segments. • The spinal root ascends to enter the cranial cavity through foramen magnum. It then turns laterally to join the cranial root. The united roots leave the skull through the jugular foramen, but just outside the foramen they separate again.

Distribution The spinal root descends in the neck to supply the sternocleidomastoid and trapezius muscles. The cranial root joins the vagus and is distributed through its branches. The distribution of cranial root of accessory nerve is as follows:

• It supplies all the muscles of palate through pharyngeal plexus except tensor tympani, which is supplied by mandibular nerve. • It supplies all the muscles of pharynx through pharyngeal plexus except stylopharyngeus, which is supplied by glossopharyngeal nerve. • It supplies all the intrinsic muscles of larynx through superior and recurrent laryngeal nerves (branches of vagus nerve).

Applied anatomy The lesion of accessory nerve leads to paralysis of sternocleidomastoid and trapezius. It is tested clinically: • By asking the patient to shrug his/her shoulder (trapezius) against the resistance. • By asking the patient to turn his/her face to the opposite side (sternocleidomastoid) against the resistance. ❖ Describe the hypoglossal nerve under the following headings: (a) functional components, (b) course and relations, (c) branches and distribution and (d) applied anatomy.   AN35.7, AN39.2 The hypoglossal nerve is CN XII. It is purely a motor nerve.

Functional components • General somatic efferent (GSE) fibres to supply the muscles of the tongue.

Course and relations (fig. 20.7) The hypoglossal nerve arises from hypoglossal nucleus located in the upper part of the medulla oblongata. It emerges from the anterior surface of the medulla between the olive and pyramid as 10–15 rootlets. The fibres run anterolaterally and leave the posterior cranial fossa through the hypoglossal canal (anterior condylar canal). After emerging from skull, it runs vertically downwards between the internal jugular vein and internal carotid artery.

FIG. 20.7 Course and distribution of hypoglossal nerve.

At the lower border of digastric (i.e. at the level of angle of mandible), the nerve curves forward horizontally, crossing in front of internal and external carotid arteries, hooking round the origin of occipital artery, crossing in front of loop of lingual artery, and then runs on the superficial surface of hyoglossus. At the anterior border of hyoglossus muscle, it enters the genioglossus and breaks up into terminal branches.

Branches and distribution (fig. 20.7) • Branches of the hypoglossal nerve proper: They supply all the muscles of tongue (intrinsic and extrinsic) except palatoglossus, which is supplied by the cranial root of accessory via pharyngeal plexus. • Branches of hypoglossal nerve containing C1 fibres: ■ The ventral ramus of 1st cervical nerve, C1 joins the hypoglossal nerve below the skull. The fibres of C1 are distributed through the following branches of hypoglossal nerve as follows: ■ Meningeal branchn ■ Descendens hypoglossi/superior root of ansa cervicalisn ■ Nerve to thyrohyoidn ■ Nerve to geniohyoid

Applied anatomy The lesion of hypoglossal nerve leads to paralysis of all the muscles of tongue on the side of the lesion. This leads to deviation of tongue on the side of lesion on protruding the tongue. Clinical Testing: The hypoglossal nerve is tested clinically by asking the patient to protrude his/her tongue. In the lesion of hypoglossal nerve, the protruded tongue deviates to the same side, i.e.

side of lesion. Thus, the deviated position of protruded tongue indicates the side of lesion.

21

Meninges and cerebrospinal fluid ❖ Give a brief account of the meninges. AN56.1 The brain and spinal cord are enclosed in three protective membranes called meninges. From outwards to inwards these are (i) dura mater, (ii) arachnoid mater and (iii) pia mater. The dura mater is mesodermal in origin, while arachnoid and pia mater are ectodermal in origin.

Dura mater The dura mater is the thick outermost covering of the brain and spinal cord. The part enclosing the brain is called cranial/cerebral dura, while the part enclosing the spinal cord is called spinal dura. It is very tough, opaque, inelastic membrane of fibrous tissue (Greek, dura = tough, mater = mother). It is also called pachymeninx (pachy = thick).

Arachnoid mater The arachnoid mater (Greek, arachnoid = cobweb like, mater = mother) is a delicate avascular membrane deep to dura mater. Many thread-like trabeculae extend from its inner aspect to the pia mater.

Pia mater The pia mater (Greek, pia = tender, mater = mother) is a thin, transparent, vascular membrane, closely adherent to the surface of the brain and spinal cord. The arachnoid mater and pia mater together are termed leptomeninges (lepto = thin). ❖ Describe subarachnoid cisterns in brief. AN56.2 The subarachnoid space is the space between the arachnoid mater and pia mater. It surrounds the CNS. The subarachnoid space around the brain is continuous with the subarachnoid space around the spinal cord. In the region of brain, it communicates with the ventricular system of brain.

Subarachnoid cisterns In certain situations, the subarachnoid space around the brain enlarges to form pools of cerebrospinal fluid (CSF) called subarachnoid cisterns. The principal subarachnoid cisterns are (Figs 21.1 and 21.2): Cerebellomedullary cistern: It is largest cistern (also called cisterna magna) and lies in triangle formed by cerebellum, medulla oblongata and occipital bone. It

receives the CSF from 4th ventricle through a foramen Magendie and foramina of Luschka. Pontine cistern: It lies on the ventral aspect of the pons and contains basilar artery. Interpeduncular cistern (basal cistern): It lies in the region of interpeduncular fossa and contains circle of Willis. Cistern of lateral sulcus (Sylvian cistern): It occupies the lateral sulcus and contains middle cerebral artery. Cistern of great cerebral vein (cisterna ambiens): It occupies the interval between splenium of corpus callosum and superior surface of cerebellum.

FIG. 21.1 Sagittal section of the brain showing location of principal subarachnoid cisterns.

FIG. 21.2 Circulation of cerebrospinal fluid from its sites of formation in the choroid plexuses of lateral ventricle to its sites of absorption into the superior sagittal sinus. Note the location of various cisterns.

❖ Describe the cerebrospinal fluid under the following headings: (a) formation, (b) circulation, (c) absorption, (d) functions and (e) applied anatomy. AN56.2 The cerebrospinal fluid (CSF) is a modified tissue fluid similar to blood plasma and interstitial tissue fluid. It is present in the ventricles of brain and subarachnoid space around the brain and spinal cord.

Formation (fig. 21.2) • The bulk of the CSF (80%–90%) is formed by choroid plexuses of lateral ventricles. • The small amount is formed by choroid plexuses of 3rd and 4th ventricles. • In an adult, the total quantity of CSF is about 150 mL, out of which only 30 mL lies in the ventricular system.

Circulation (fig. 21.2) It is given in the form of flowchart given below:

Absorption (fig. 21.2) The CSF is chiefly absorbed through the arachnoid villi and arachnoid granulations into the superior sagittal sinus. It is also absorbed partly by the perineural lymphatics around the cranial and spinal nerves and also via pial veins.

Functions • Provides protection to the CNS. • Provides nutrition to the CNS. • Removes waste products from the CNS.

Applied anatomy • Withdrawal of CSF: The CSF can be obtained by lumbar puncture, cisternal puncture and ventricular puncture for diagnostic and therapeutic purposes. • Hydrocephalus: The excessive accumulation of CSF within the skull due to either obstruction to the flow of CSF in the ventricular system or impairment of its absorption into the intracranial dural venous sinuses through arachnoid granulations, leads to hydrocephalus in children and raised intracranial pressure in adults. The characteristic clinical features of hydrocephalus are (Fig. 21.3) as follows: ■ Abnormally large head ■ Bossing of forehead ■ Wide, tense anterior fontanelle ■ ‘Setting-sun appearance’ of the eyes ■ Thin scalp with dilated scalp veinsn ■ Cracked-pot sound on skull percussionn ■ Dementia

FIG. 21.3 Clinical features of hydrocephalus in infants and young children.

22

Spinal cord ❖ What is spinal cord? List its functions. AN57.2 The spinal cord is a long lower cylindrical part of the central nervous system. It is about 45 cm long and lies in the upper two-third of the vertebral canal. It extends from the lower border of medulla oblongata to the lower border of L1 vertebra. It encloses the central canal of spinal cord which cntains CSF. It gives off 31 pairs of the spinal nerves.

Functions • Transmission of sensory information from most of the body to the brain • Transmission of motor information from the brain to the body • Execution of simple reflexes ❖ Enumerate the main ascending and descending tracts present within the spinal cord. AN57.4 In each half of the spinal cord, the white matter is divided into three regions called white columns. The important ascending and descending tracts in each white column of spinal cord are given in Table 22.1. TABLE 22.1 Ascending and Descending Tracts in White Columns

The main ascending and descending tracts as seen in the transverse section of the spinal cord are shown in Fig. 22.1.

FIG. 22.1 Transverse section of the spinal cord at mid-cervical region showing main descending (motor) tracts in the left half and ascending (sensory) tracts in the right half of the spinal cord.

❖ Enumerate the arteries supplying the spinal cord. AN57.1 The spinal cord is supplied by the following arteries.

Anterior spinal artery It is the artery formed by union of anterior spinal branches of the vertebral arteries. It descends on the front of the spinal cord in the anterior median fissure.

Posterior spinal arteries These are two posterior spinal arteries, one on each side. They are the branches of

vertebral arteries. Each posterior spinal artery divides into two branches, which descend one on either side of the dorsal nerve roots of corresponding side in the posterolateral sulcus.

Radicular arteries (segmental arteries) They run along the spinal nerve roots to reach the spinal cord. Their sources of origin vary in the different regions. From above downwards, they are branches of the deep cervical and ascending cervical in cervical region, posterior intercostals in thoracic region and subcostal and upper lumbar arteries.

N.B. The anterior spinal artery supplies the anterior two-third of the spinal cord, while the posterior spinal arteries supply the posterior one-third of the spinal cord. The segmental/radicular arteries at the level of T1 and T11 spinal segments are very large and are termed arteria radicularis magna. ❖ Write a short note on cauda equina. AN57.1 It is a leash of nerve roots of lumbar (except L1), sacral and coccygeal nerves around the filum terminale (Fig. 22.2). It is called cauda equina because of its fancied resemblance to the tail of a horse (cauda = tail, equina = horse).

FIG. 22.2 Lower end of the spinal cord with filum terminale and lumbar, sacral and coccygeal nerve roots. The spinal nerve roots forming the cauda equina are encircled.

N.B. The filum terminale is a silvery white, glistening, thin, thread-like prolongation of pia mater extending from the tip of lower conical end of the spinal cord (tip of conus medullaris) to the dorsal aspect of first piece of the coccyx. ❖ Write a short note on the lateral spinothalamic tract. AN57.4 It is a part of spinothalamo-cortical pathway. It carries pain and temperature sensations from the opposite side of the body to the brain (Fig. 22.3). • First-order neurons are found in the dorsal root ganglia. Their central processes (axons) enter the spinal cord through the lateral division of the dorsal root of spinal nerve and relay in the posterior horn of spinal cord. • Second-order neurons are found in the posterior horn. Their axons cross to the opposite side in the anterior white commissure and ascend in the contralateral white column (lateral spinothalamic tract). These axons terminate in the thalamus (ventral posterolateral [VPL] nucleus). • Third-order neurons are found in the VPL nucleus of thalamus. They project through the posterior limb of internal capsule to the primary somatosensory cortex (Brodmann areas 3, 1 and 2).

FIG. 22.3 Lateral and anterior spinothalamic tracts.

Applied anatomy The damage of the lateral spinothalamic tract results in contralateral loss of pain, touch (simple/crude) and temperature sensations. ❖ Write a short note on the ventral spinothalamic tract. AN57.4 The ventral spinothalamic tract carries light/simple touch (crude touch), pressure and itching sensations from the opposite half of the body. The course of this tract is same as that of lateral spinothalamic tract, except that the second-order neurons after crossing to the opposite side ascend in the contralateral ventral white column of the spinal cord (Fig. 22.3).

Applied anatomy The damage of ventral spinothalamic tract leads to loss of light touch (crude touch) and pressure on the opposite side of the body below the level of lesion.

N.B. The discriminative touch (fine touch) will still be present because it is carried by fasciculus gracilis and fasciculus cuneatus – the tracts in the posterior white column of the spinal cord. ❖ Write a short note on the dorsal column–medial lemniscal pathway. AN57.4 The dorsal column–medial lemniscal pathway carries proprioceptive sensations (e.g. muscle and joint sense, fine touch, vibration sensations) from the opposite side of the body. • First-order neurons are located in the dorsal root ganglia. Their axons enter the spinal cord through medial root of the spinal nerves, ascend in the ipsilateral dorsal white column as fasciculus gracilis and fasciculus cuneatus, and terminate in gracile and cuneate nuclei, respectively, located in the caudal part of medulla. • Second-order neurons are located in the gracile and cuneate nuclei of medulla. Their axons (internal arcuate fibres) decussate with those of opposite side in the midline. After decussation, they form a compact fibre bundle (medial lemniscus), which ascends in the contralateral half of brainstem and terminate in the ventral posterolateral (VPL) nucleus of thalamus. • Third-order neurons are located in the VPL nucleus of thalamus. Their axons project to the primary somatosensory cortex (areas 3, 1 and 2; Fig. 22.4).

FIG. 22.4 Posterior column–medial lemniscal pathway.

Applied anatomy The damage of dorsal column–medial lemniscal pathway above the sensory decussation causes contralateral loss of proprioceptive sensations, while below the sensory decussation it causes ipsilateral loss of proprioceptive sensations. ❖ Describe the corticospinal (pyramidal) tract in brief and discuss its applied anatomy. AN57.4 The pyramidal tract is a motor tract consisting of both corticospinal and corticonuclear tracts. However, conventionally it refers to only corticospinal tract.

Origin, course and termination • Most of the fibres of pyramidal tract arise from pyramidal cells of motor and premotor areas (areas 4 and 6) of the cerebral cortex. • These fibres descend and traverse the following parts of the CNS in succession, viz. corona radiata, internal capsule (anterior two-third of the posterior limb and genu), crus cerebri (middle three-fifth), basilar part of pons and pyramid of medulla. Note that after emerging from pons, they condense to form pyramid-shaped bundles in the upper part of the medulla oblongata. In the lower part of medulla oblongata, about 70%–80% fibres of pyramidal tract cross to the opposite side and then descend in the lateral white column of the spinal

cord on opposite side as lateral corticospinal/crossed pyramidal tract and terminate on the anterior horn cells. About 20%–30% fibres of pyramidal tract do not cross to the opposite side and descend in as uncrossed pyramidal tract/anterior corticospinal tract in the anterior white column of the spinal cord of same side. These fibres finally also cross to the opposite side and terminate on the anterior horn cells (Fig. 22.5).

FIG. 22.5 Course and termination of the fibres of corticospinal tract. The inset on the right side shows an abbreviated form of motor pathway. INN, internuncial neuron; LMN, lower motor neuron; UMN, upper motor neuron.

Function The pyramidal tract is concerned with voluntary movements of the body.

Applied anatomy • Lesion of pyramidal tract: It produces upper motor neuron (UMN) type of paralysis. If the lesion is above the level of motor decussation, it causes spastic paralysis on the opposite side of body, i.e. contralateral hemiplegia; while if the lesion is below the level of motor decussation, it leads to ipsilateral hemiplegia.

• Effects of upper and lower motor neuron type of paralysis: The lesions of upper motor neurons (UMNs) leads to: (a) Spasticitic paralysis (b) Increased muscle tone (c) Exaggeration of tendon reflexes (d) No wasting of muscles except disuse atrophy. The above signs and symptoms occur due to hyperactivity of LMNs, as the control of UMNs on LMNs is lost. The lesions of lower motor neurons (LMNs) leads to:

(a) Flaccid paralysis (b) Decreased muscle tone (c) Loss of tendon reflexes (d) Wasting of muscle i.e. muscle atrophy All these signs and symptoms occur due to loss of nerve supply of the muscle.

N.B. UMNs don’t supply muscles directly but through LMNs.

SECTION III

Brain OUTLINE 23. 24. 25. 26. 27. 28.

Overview of brain and brainstem Cerebellum and fourth ventricle Overview of cerebrum and functional areas Cerebrum Basal nuclei, limbic system and lateral ventricle Diencephalon and third ventricle

23

Overview of brain and brainstem Overview of brain ❖ Define brain and enumerate its major parts. The brain is that part of the CNS, which lies within the cranial cavity (hence it is also called cranial cargo). The brain weighs about 1400 g in males and 1200 g in females. The brain is the highest centre for various sensory and motor functions of the body. It is also the seat of intelligence, cognizance, memory, emotions, etc.

Major parts of the brain The brain consists of six major parts (Fig. 23.1): • Cerebrum consisting of two cerebral hemispheres. • Diencephalon consisting of thalamus, hypothalamus, metathalamus, subthalamus and epithalamus • Midbrain • Pons • Medulla oblongata • Cerebellum (Fig. 23.1)

FIG. 23.1 Parts of central nervous system. Note 6 major parts of brain (labelled in bold).

Brainstem ❖ What is brainstem? Discuss its functions. The brainstem is the stem-like lower part of brain consisting of three parts – midbrain, pons and medulla oblongata.

Functions • Provides passages to various ascending and descending tracts. • Contains vital (autonomic) centres – cardiac centre, vasomotor centre and respiratory centre. • Contains reticular formation responsible for consciousness and sleep. • Provides attachments to last 10 cranial nerves and contains their nuclei.

Medulla oblongata ❖ Enumerate the main structures seen in the transverse section of medulla oblongata at the level of pyramidal decussation. AN58.2 The main structures seen in the transverse section of medulla oblongata at the level of pyramidal decussation are (Fig. 23.2) as follows: • Decussation of pyramidal tracts • Appearance of nucleus gracilis and nucleus cuneatus

• Formation of nucleus of spinal tract of trigeminal nerve • Appearance of reticular formation • Detachment of anterior horns due to decussation of pyramidal tracts

FIG. 23.2 Transverse section through the lower closed part of the medulla oblongata at the level of pyramidal decussation.

❖ Enumerate the main structures seen in the transverse section of medulla oblongata at the level of sensory decussation. AN58.2 The main structures seen in the transverse section of medulla oblongata at the level of sensory decussation are (Fig. 23.3) as follows: • Sensory decussation (decussation of arcuate fibres) • Formation of medial lemnisci • Formation of nucleus gracilis and nucleus cuneatus • Formation of nucleus of spinal tract of trigeminal nerve • Appearance of accessory cuneate nucleus • Formation of central grey matter and nuclei within it (e.g. hypoglossal nucleus, dorsal nucleus of vagus and nucleus tractus solitarius) • Appearance of inferior olivary nucleus

FIG. 23.3 Transverse section of medulla oblongata at the level of sensory decussation.

❖ Enumerate the main structures seen in the transverse section of medulla oblongata at the level of upper part of olives. AN58.2 The main structures seen in the transverse section of medulla oblongata at the level of upper part of olives are (Fig. 23.4) as follows:

• Fully developed inferior olivary nucleus. • Appearance of medial and dorsal accessory olivary nuclei. • Appearance of hypoglossal nucleus, dorsal nucleus of vagus and vestibular nuclei underneath the floor of 4th ventricle. • Appearance of nucleus ambiguus. • Appearance of nucleus tractus solitarius.

FIG. 23.4 Transverse section of medulla at the level of upper parts of olives. 1, Medial longitudinal fasciculus; 2, tectospinal tract; 3, medial lemniscus. NA, nucleus ambiguus.

❖ Write a short note on lateral medullary syndrome (posterior inferior cerebellar artery syndrome of Wallenberg). AN58.4

Cause Ischaemia of posterolateral part of medulla due to occlusion of posterior inferior cerebellar artery (Fig. 23.5).

FIG. 23.5 Transverse section of the upper part of the medulla. The red shaded areas indicate the sites of lesions. 1, Dorsal nucleus of vagus; 2, nucleus of tractus solitarius; 3, vestibular nuclei; 4, inferior cerebellar peduncle; 5, spinal tract of trigeminal nerve; 6, spinal nucleus of trigeminal nerve; 7, descending sympathetic tract; 8, nucleus ambiguus; 9, lateral spinothalamic tract; 10, inferior olivary nucleus; 11, hypoglossal nerve; 12, pyramidal tract; 13, arcuate nucleus. M, medial lemniscus.

Clinical features • Contralateral loss of pain and temperature in the body due to involvement of spinothalamic tract. • Ipsilateral loss of pain and temperature on the face due to involvement of spinal nucleus and tract of CN V. • Ipsilateral paralysis of palatal, pharyngeal and laryngeal muscles due to involvement of nucleus ambiguus. • Ipsilateral ataxia due to involvement of inferior cerebellar peduncle. • Nausea and vertigo due to involvement of vestibular nuclei. ❖ Write a short note on medial medullary syndrome. AN58.4

Cause Ischaemia of medial region of medulla due to thrombosis of anterior spinal artery (Fig. 23.5).

Clinical features • Contralateral hemiplegia (UMN type of paralysis) due to involvement of pyramid (pyramidal tract)

• Ipsilateral paralysis of tongue due to involvement of hypoglossal nerve (LMN type of paralysis) • Contralateral loss of proprioceptive sensations due to involvement of medical meniscus

Pons ❖ Enumerate the main structures seen in the transverse section of pons at the level of facial colliculi. AN59.2 The main structures seen in the transverse section of pons at the level of facial colliculi are (Fig. 23.6) as follows: • Abducent nucleus • Motor nucleus of facial nerve • Internal genu of facial nerve • Dorsal and ventral cochlear nuclei • Trapezoid body

FIG. 23.6 Transverse section through the lower part of the pons. M, medial longitudinal bundle; R, rubrospinal tract; T, tectospinal tract.

❖ Enumerate the main structures seen in the transverse section through the upper part of the pons. AN59.2 The main structures seen in the transverse section through the upper part of the pons are (Fig. 23.7) as follows: • Chief (main) sensory nucleus of trigeminal nerve • Motor nucleus of trigeminal nerve • Mesencephalic root of trigeminal nerve • Trigeminal lemniscus • Lateral lemniscus

FIG. 23.7 Transverse section through the upper part of the pons. M, medial longitudinal bundle; R, rubrospinal tract; T, tectospinal tract.

❖ Write a short note on pontocerebellar angle syndrome.

Cause Involvement of lateral region of caudal part of pons near pontocerebellar angle by Schwannoma of CN VIII.

Clinical features • Ipsilateral deafness due to involvement of cochlear nerve. • Ipsilateral imbalance and asynergia due to involvement of vestibular nerve. • Ipsilateral lower motor neuron type of facial palsy due to involvement of facial nerve. • Ipsilateral loss of pain and temperature on face due to involvement of spinal nucleus and tract of CN V.

Midbrain ❖ Enumerate the main structures seen in the transverse section of midbrain at the level of inferior colliculus. AN61.2 The main structures seen in the transverse section of midbrain at the level of inferior colliculus are (Fig. 23.8) as follows: • Decussation of superior cerebellar peduncles • Trochlear nerve nucleus • Mesencephalic nucleus of trigeminal nerve • Termination of lateral lemniscus • Nucleus of inferior colliculus

FIG. 23.8 Transverse section of the midbrain at the level of inferior colliculi. M, medial longitudinal fasciculus; R, rubrospinal tract; T, tectospinal tract.

❖ Enumerate the main structures seen in the transverse section of midbrain at the level of superior colliculus. AN61.2 The main structures seen in the transverse section of midbrain at the level of superior colliculus are (Fig. 23.9) as follows: • Oculomotor nucleus • Red nucleus • Nucleus of superior colliculus • Dorsal tegmental decussation (of Meynert) • Ventral tegmental decussation (of Forel)

FIG. 23.9 Transverse section of the midbrain at the level of superior colliculi.

❖ Write a short note on medial longitudinal fasciculus/medial longitudinal bundle. AN61.2

The medial longitudinal fasciculus (MLF) also called medial longitudinal bundle (MLB) is an important association tract one on either side of median plane in the brainstem. It extends cranially to the interstitial nucleus of Cajal (accessory oculomotor nucleus) and caudally it becomes continuous with the intersegmental fasciculus of the spinal cord. • It connects the nuclei of the cranial nerves that move the eyeballs and in this way it coordinates the movements of both eyeballs. • It connects the nuclei of the cranial nerves responsible for articulation, and in this way it associates together the movements of the organs responsible for articulation. • It connects both the vestibular and cochlear nuclei with the nuclei of the nerves of the eyeball and with the anterior horn cells of the spinal nerves; and in this way, it associates movements of eyes and those of the body in response to movements of the head or in response to the sound.

Functions • Coordination of the conjugate movements of the eyeball. • Coordination of the movements of head and neck in response to audiovisual reflexes.

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Cerebellum and fourth ventricle ❖ Define cerebellum and list its functions. The cerebellum (Latin, cerebellum = little brain) is the largest part of the hindbrain and second-largest part of the brain as a whole. It weighs about 150 g and is located in the posterior cranial fossa underneath the tentorium cerebelli, behind the pons and medulla oblongata.

Functions The functions of cerebellum include: • Maintenance of equilibrium • Maintenance of muscle tone • Maintenance of posture

N.B. It was regarded as the head ganglion of the proprioceptive system by Sherrington. ❖ What are the parts of cerebellum? AN60.1 The cerebellum consists of three parts: • Two large lateral hemispherical parts called cerebellar hemispheres. • A narrow median worm-like part which unites two cerebellar hemispheres called vermis. ❖ What are the anatomical lobes of the cerebellum? AN60.1 Anatomically, the cerebellum is divided into three lobes (Fig. 24.1): • Flocculonodular lobe: It is the smallest lobe that comprises two flocculi and their peduncles and the nodule. Together with the lingula of vermis, it forms the vestibular part of the cerebellum (archicerebellum). • Anterior lobe: It lies on the superior surface of cerebellum anterior to the fissura prima excluding the lingula; together with the pyramid and uvula of vermis, it forms the spinal part of the cerebellum (paleocerebellum). • Middle (posterior) lobe: It is the largest lobe and lies between fissura prima on the superior surface and posterolateral fissure on the inferior surface excluding the pyramid and uvula of vermis. It forms the cerebral part of the cerebellum (neocerebellum).

FIG. 24.1 Anatomical functional and morphological subdivisions of the cerebellum. The organ is being opened out (schematically) to show both superior and inferior surfaces together. The parts seen above the horizontal fissure form the superior surface and those below the fissure, inferior surface of the cerebellum. AL, ala; BL, biventral lobule; C, central lobule; CL, culmen; D, declive; F, folium; ISL, inferior semilunar lobule; LS, lobulus simplex; P, pyramid; QL, quadrate lobule; SSL, superior semilunar lobule; T, tuber; U, uvula.

❖ Enumerate the intracerebellar nuclei and discuss their connections. AN60.2 There are four intracerebellar nuclei on either side of the midline. From lateral to medial side these are (Fig. 24.2) as follows: • Dentate nucleus • Nucleus emboliformis • Nucleus fastigii • Nucleus globosus Dentate nucleus: It is the largest and has the shape of a crumpled bag (crenated crescent) with its hilum facing anteromedially. It receives afferents from the neocerebellum and sends efferents through the superior cerebellar peduncle to the red nucleus of the opposite side, which in turn projects the spinal cord. Nucleus emboliformis and nucleus globosus: The nucleus emboliformis is oval in shape, whereas nucleus globosus is round in shape. They receive afferents from the paleocerebellum and send efferents through the superior cerebellar peduncle to the red nucleus of the opposite side. These two nuclei together represent ‘nucleus interpositus’ of lower mammals, e.g. monkey. Nucleus fastigius: It lies near the midline in the region of vermis. It receives afferents from the archicerebellum and sends efferents through inferior cerebellar peduncle to the vestibular nuclei and the reticular formation of the medulla oblongata.

FIG. 24.2 Intracerebellar nuclei (also called central nuclei of the cerebellum).

❖ What are cerebellar peduncles? Enumerate their constituent fibres. AN60.2 The cerebellar peduncles are large bundles of afferent and efferent fibres that connect the cerebellum with other parts of the brain. They are three in number: Superior cerebellar peduncle is the most medial and connects the cerebellum with the midbrain. Middle cerebellar peduncle is the largest and connects the cerebellum with the pons. Inferior cerebellar peduncle connects the cerebellum with the medulla oblongata. The constituent fibres of three cerebellar peduncles are given in Table 24.1.

FIG. 24.3 Components of the inferior cerebellar peduncle. Afferent components are not shown. RF, reticular formation; VN, vestibular nucleus.

TABLE 24.1 Main Constituent Fibres of Cerebellar Peduncles Peduncle Superior cerebellar peduncle

Middle cerebellar peduncle Inferior cerebellar peduncle (Fig. 24.3)

Afferent Fibres • Anterior spinocerebellar fibres • Tectocerebellar fibres • Pontocerebellar fibres • Posterior spinocerebellar fibres • Olivocerebellar fibres • Parolivocerebellar fibres • Cuneocerebellar fibres • Vestibulocerebellar fibres • Reticulocerebellar fibres

Efferent Fibres • Dentatorubral fibres • Dentatothalamic fibres • Dento-olivary fibres •No efferent fibres • Cerebellovestibular fibres • Cerebello-olivary fibres • Cerebelloreticular fibres

❖ Enumerate the important signs and symptoms seen in the cerebellar lesions.  AN60.3 • Asthenia: Muscular hypotonia due to loss of muscle tone. • Asynergia: Jerky movements due to incoordination of muscles. ■ Ataxia: Staggering gait and inability to walk in a straight line due to

incoordination of different muscle groups in the lower limb. ■ Adiadokokinesis (disdiadokokinesis): Inability to perform alternate movements in rapid succession such as pronation and supination. ■ Dysmetria: Loss of ability to measure the distance for reaching the intended goal. ■ Dysarthria (or scanning speech): Loss of incoordination of muscles concerned with speech. ■ Rebound phenomenon: Inability to check the action of agonist muscles by the corresponding antagonist muscles. • Intention tremor: Due to dysmetria. The tremors are evident during purposeful movements, and are diminished or absent at rest. ❖ Define 4th ventricle and discuss its boundaries, communications and recesses.  AN63.1 The 4th ventricle is a tent-like cavity of hindbrain lined with ependyma. It lies behind the pons and medulla and in front of the cerebellum.

Boundaries (fig. 24.4) Lateral (on each side): • Superolaterally by the superior cerebellar peduncle • Inferolaterally by the inferior cerebellar peduncle Floor: It is formed by the posterior surfaces of pons and upper part of the medulla oblongata. It is rhomboidal in shape; hence, it is often called ‘rhomboid fossa’. Roof: It is formed by • Superior medullary velum, in the upper part • Inferior medullary velum, in the lower part

FIG. 24.4 Rhomboid fossa or floor of the 4th ventricle. Note important features of fossa are marked in bold.

Communications It communicates above with 3rd ventricle through cerebral aqueduct (aqueduct of Sylvius) and below with the central canal of the spinal cord. Posterolaterally, it communicates with the subarachnoid space through three foramina in its roof (foramen of Magendie and foramina of Luschka).

Recesses They are five in number: • Two lateral recesses • Median dorsal recess • Two lateral dorsal recesses ❖ Discuss the features of rhomboid fossa in brief. AN63.1 The features of rhomboid fossa are as follows (Fig. 24.4): • It is rhomboidal in shape and has four angles: rostral, caudal and two lateral. • The floor is divided into two equal halves by a median sulcus. Each half of the floor is further divided into two parts (pontine and medullary) by fibres of stria medullaris, which run from the median sulcus to the lateral boundary.

Features above the medullary striae (i.e. in the pontine part)

■ Presence of facial colliculus, on either side of median sulcus. It is an oval elevation produced by the fibres of the motor nucleus of facial nerve hooking around the abducent nucleus (internal genu of facial nerve). ■ A depression at the upper end of sulcus limitans called superior fovea. ■ A bluish-grey area (locus coeruleus), above superior fovea. The bluish colour is imparted by the underlying group of nerve cells containing melanin pigment.

Features below the stria medullaris (i.e. in the medullary part) ■ Inferior fovea, a triangular depression ■ Hypoglossal triangle, medial to inferior fovea ■ Vestibular triangle, lateral to inferior fovea ■ Vagal triangle, inferior to inferior fovea ■ Funiculus separans, a fine translucent ridge crossing the vagal triangle ■ Area postrema, a small area below the funiculus separans

25

Overview of cerebrum and functional areas ❖ Define cerebrum and discuss the surfaces of cerebral hemisphere. AN62.2 The cerebrum is the largest part of the brain. It is divided into two equal halves by a median longitudinal cerebral fissure. Each half is called cerebral hemisphere. The cerebrum is highly evolved in human beings.

Surfaces of cerebral hemisphere Each cerebral hemisphere has three surfaces. Superolateral surface: It is convex in conformity with the shape of the skull cap. It is most convex and most extensive of the three surfaces. Medial surface: It is flat and vertical. It is separated from its fellow of the opposite side by the falx cerebri lying in the median longitudinal fissure, but below the falx cerebri the two hemispheres are joined together by a large bundle of white fibres – the commissure called corpus callosum. In a separated cerebral hemisphere, the corpus callosum is seen as a C-shaped mass of white fibres. Inferior surface: It is uneven to adopt the floors of anterior and middle cranial fossae. It is divided by a deep horizontal fissure (the stem of the lateral sulcus) into an anterior orbital part (related to the floor of the anterior cranial fossa) and a posterior tentorial part (related to the floor of the middle cranial fossa and to the upper surface of the tentorium cerebelli). ❖ Name the sulci which help in demarcating the superolateral surface of cerebral hemisphere into four lobes. Discuss central sulcus in detail. AN62.2 The sulci which help in demarcating the superolateral surface of cerebral hemisphere into four lobes: a. Central sulcus b. Lateral sulcus (posterior ramus) c. Parieto occipital sulcus (terminal portion)

Central sulcus (of rolando) Features a. Presents on the superolateral surface of cerebral hemisphere

b. Begins at superomedial border of the cerebral hemisphere about 1 cm behind its midpoint c. Runs vertically downwards and slightly forwards and ends just above the lateral sulcus Significance a. Gyri lying in front and behind it are called precentral gyrus and postcentral gyrus, respectively. b. Precentral gyrus is motor in function and most of fibres of pyramidal tract arise in this gyrus to supply opposite half of the body (i.e. contralateral half of the body). c. Postcentral gyrus is sensory in function and receives sensory impulses from opposite half of the body (i.e. contralateral half of the body). d. Frontal branch of middle meningeal artery ascends parallel and in front of central sulcus, just deep to the pterion. The bone is thin here, and fracture at this site causes haemorrhage from artery and presses upon the precentral gyrus leading to pressure symptoms like hemiplegia. ❖ Discuss the demarcation of lobes of cerebral hemisphere on its superolateral surface. AN62.2 The superolateral surface of cerebral hemisphere is demarcated into four lobes as follows (Fig. 25.1): Frontal lobe: It lies anterior to central sulcus and above the lateral sulcus. It is so named because it is related to the frontal bone of skull. Parietal lobe: It lies posterior to central sulcus, above the lateral sulcus, and in front of an imaginary vertical line connecting parieto-occipital sulcus with the preoccipital notch. It is so named because it is related to the parietal bone of skull. Temporal lobe: It lies below the lateral sulcus and in front of imaginary vertical line extending from parieto-occipital sulcus to the preoccipital notch. It is so called because it is related to the temporal bone of skull. Occipital lobe: It lies behind the imaginary vertical line connecting parietooccipital sulcus with the preoccipital notch. It is so named because it is related to the occipital bone of skull.

FIG. 25.1 Division of superolateral surface of the left cerebral hemisphere into four lobes.

❖ Write a short note on insula. AN62.2 The insula is a submerged portion of cerebral cortex in the floor of lateral sulcus. It is hidden from surface view by overgrown adjacent areas of frontal, parietal and temporal lobes called opercula/lids. • It is triangular in shape and surrounded by a circular sulcus. • It is divided by central sulcus into anterior region having small gyri (gyri brevia) and posterior region bearing long gyri (gyri longa). • It is believed to be involved in consciousness and linked to emotion. ❖ Draw a labelled diagram to show the functional areas on the superolateral surface of cerebral hemisphere. AN62.2 Functional areas on the superolateral surface of the cerebral hemisphere are shown in Fig. 25.2, see p. 249.

FIG. 25.2 The functional areas on the superolateral surface of the left cerebral hemisphere.

❖ Draw a labelled diagram to show the functional areas on the inferomedial surface of cerebral hemisphere. AN62.2 Functional areas on the inferomedial surface of the cerebral hemisphere are shown in Fig. 25.3, see p. 249.

FIG. 25.3 The functional areas on the inferomedial surface of the right cerebral hemisphere.

❖ Write a short note on the primary motor area. AN62.2

Location The primary motor area (Brodmann area 4) is located in (see Fig. 25.2): • Precentral gyrus • Anterior wall of central sulcus • Anterior part of paracentral lobule

Representation of body The body is represented upside down (inverted homunculus) in the primary motor area. The sequence of representation of body parts from above to downward is leg, thigh, trunk, upper limb, face, larynx, lips, jaws, tongue and pharynx. The area of cortex representing a part of the body is not proportional to the size of that part, but to the skill of movements performed by that part. Thus, movements of the hands, lips, tongue and larynx are represented by relatively large areas of the cortex.

Functions • It controls the voluntary movements of the opposite side of the body. • It also controls the acts of micturition and defecation.

Applied anatomy A lesion in this area gives rise to upper motor neuron (UMN) type of paralysis on the opposite side of the body. ❖ Define paracentral lobule and mention its functions. AN62.2

The paracentral lobule is the area on the medial surface of cerebral hemisphere around the central sulcus. It is bounded above by superomedial border of the cerebral hemisphere, below by cingulate sulcus, posteriorly by upturned posterior end of cingulate sulcus and anteriorly by upturned ramus of cingulate sulcus (see Fig. 25.3).

Functions • It acts as cortical centre for micturition and defecation. • It is responsible for movements of the contralateral foot. ❖ Write a short note on motor speech area. AN62.2

Location The motor speech area (Brodmann areas 45 and 44) is located in the pars triangularis (area 45) and pars posterior (area 44) in the inferior frontal gyrus of frontal lobe in the dominant hemisphere (i.e. left hemisphere in right-handed persons; Fig. 25.2).

Function The motor speech area is essential for the production of expressive speech.

Applied anatomy If the motor speech area is damaged, the individual will suffer from motor aphasia. In this condition, there is inability to articulate properly, though there is no paralysis of muscles of lips, tongue, palate and vocal cords. The speech of person becomes nonfluent, dysarthric, telegraphic and incomprehensive.

N.B. The person can understand both written and spoken speech (i.e. he/she has good comprehension). ❖ Write a short note on primary sensory area. AN62.2

Location The primary sensory area (Brodmann areas 3, 1 and 2) is located in the postcentral gyrus and posterior wall of the central sulcus (Fig. 25.2).

Representation of body The body is represented upside down in primary sensory area similar to that in primary motor area (see p. 249).

Functions The primary sensory area is concerned with perception of exteroceptive (pain, light touch and temperature) and proprioceptive (muscle and joint sense) sensations from opposite

half of the body.

Applied anatomy The lesions of primary sensory area lead to loss of appreciation of exteroceptive and proprioceptive sensations in the opposite half of the body. ❖ Write a short note on sensory speech area (Wernicke’s area). AN62.2

Location The sensory speech area (Brodmann areas 22, 39 and 40) is located in: • Posterior part of the superior temporal gyrus (Brodmann area 22) of the dominant cerebral hemisphere (Fig. 25.2). • Parts of the inferior parietal lobule, including the supramarginal and angular gyri corresponding to Brodmann areas 40 and 39, respectively.

Functions • Understanding the written and spoken languages, i.e. it is concerned with the understanding and interpretation of language through visual and auditory input. • Essential for constant availability of learned word patterns. • Essential for the process of learning such as reading, writing and computing.

Applied anatomy If the sensory speech area is damaged, the affected individual will suffer from receptive or sensory aphasia. In this condition, the affected individual cannot understand spoken words though his hearing is normal; consequently, he/she is unaware of meaning of the words he/she uses. As a result, he/she uses incorrect words or even nonexistent words. To others his/her speech sounds like an incomprehensive foreign language. Other defects seen in sensory aphasia are as follows: • Alexia: Disability in reading. • Agraphia: Disability in writing. • Acalculia: Disability in computing. • Anomia: Inability in recognition of names of objects. ❖ Write a short note on visual cortex. AN62.2 The visual cortex is present over the occipital lobe. • It is located along the lips and floor of posterior part of calcarine sulcus (also called postcalcarine sulcus). • Anteriorly, it extends up to parieto-occipital sulcus and posteriorly it extends on the outer surface of the occipital pole and is limited by the lunate sulcus.

• It includes cuneus and lingual gyrus.

N.B. The visual cortex is granular type of cortex and is thinner than the cerebral cortex elsewhere. The inner granular layer of cerebral cortex presents a prominent band of horizontally arranged fibres called visual stria (or white line of Gennari). The visual cortex is highly sensitive to light, hence also called koniocortex. ❖ Write a short note on visual areas. AN62.2

Location (fig. 25.3) • The primary visual area (Brodmann area 17) is located in the walls and floor of postcalcarine sulcus. • The secondary visual areas (Brodmann areas 18/peristriate area and 19/parastriate area) surround the primary visual area and occupy most of the remaining visual cortex.

Functions • The primary visual area is concerned with reception and perception of isolated visual impressions such as colour, size and form. • The secondary visual areas relate the isolated visual impressions received by the primary visual area with past experience, thus enabling the individual to recognize and interpret what he/she is seeing.

Applied anatomy • Lesions of the primary visual area result in loss of vision in the opposite visual field (crossed homonymous hemianopia). • Lesions of the secondary visual areas result in loss of ability to recognize the objects (visual agnosia). ❖ Describe cerebral dominance in brief. AN62.2 The term cerebral dominance refers to that cerebral hemisphere, which is concerned with the perception and production of language/speech. In 90% of people, the left cerebral hemisphere subserves these functions; hence, it is termed dominant hemisphere. There is an important relationship between cerebral dominance and handedness. If the left cerebral hemisphere is dominant, the individual will be right-handed and if the right cerebral hemisphere is dominant, the individual will be left-handed. ❖ Enumerate the main functions of left and right cerebral hemispheres. AN62.2 The main functions of left and right cerebral hemispheres are shown in Fig. 25.4.

FIG. 25.4 Lateralization of functions in the dominant and nondominant hemispheres.

26

Cerebrum Blood supply of cerebrum ❖ Write a short note on the blood supply of the brain. The proper blood supply of the brain is the most essential because consciousness is lost within 10 seconds of the cessation of the blood supply and if this state continues, an irreversible brain damage starts at 4 minutes and is completed within 10 minutes. ❖ Write a short note on circle of Willis. AN62.6

Formation and location (fig. 26.1) The brain is supplied by two pairs of major arteries: (a) a pair of vertebral arteries and (b) a pair of internal carotid arteries. The branches of these arteries anastomose in the region of interpeduncular fossa at the base of brain to form somewhat circular anastomosis called circle of Willis. The two vertebral arteries unite at the lower border of pons to form the basilar artery, which divides at the upper border of the pons into right and left posterior cerebral arteries. The internal carotid artery of each side terminates in the region of anterior perforated substance by dividing into a smaller anterior cerebral artery and a larger middle cerebral artery. The posterior communicating artery (a branch of internal carotid artery) on each side communicates with the posterior cerebral artery. A single short anterior communicating artery connects the two anterior cerebral arteries.

FIG. 26.1 Circle of Willis and the branches of arteries supplying the brain. The central branches of cerebral arteries are shown by abbreviations: AL, anterolateral group; AM, anteromedial group; PL, posterolateral group; PM, posteromedial group.

The circle of Willis (circulus arteriosus) is thus formed by the anterior communicating artery and the anterior cerebral arteries anteriorly, the termination of the internal carotid artery and the posterior communicating artery on each side, and bifurcation of basilar artery including posterior cerebral arteries posteriorly (Fig. 26.1).

Function Provides various alternate routes for collateral circulation.

Applied anatomy The sites where two arteries unite to form circle of Willis may dilate to form berryshaped dilatations called berry aneurysms. The rupture of these aneurysms leads to subarachnoid haemorrhage at the base of brain in the region of interpeduncular fossa.

N.B. The most common cause of subarachnoid haemorrhage is the rupture of berry aneurysms. ❖ Write a short note on basilar artery. Give its branches.

Formation and termination • It is formed by the two vertebral arteries at the lower border of the pons. • It runs upwards and forwards in the midline groove on the ventral aspect of pons.

• On reaching the upper border of pons, it divides into right and left terminal branches – the posterior cerebral arteries.

Branches The branches of basilar artery are (Fig. 26.1): • Anterior inferior cerebellar arteries • Labyrinthine arteries • Pontine branches • Superior cerebellar arteries • Posterior cerebral arteries (terminal branches) ❖ Enumerate the branches of cerebral part of internal carotid artery.

❖ Describe briefly arterial supply of the superolateral surface of the cerebral hemisphere. AN62.2 • The narrow strip of about an inch breadth along its superomedial border as far as the parieto-occipital sulcus is supplied by the anterior cerebral artery. • The occipital lobe and narrow strip along the lower border of temporal lobe excluding the temporal pole (the inferior temporal gyrus) is supplied by the posterior cerebral artery. • The rest of the superolateral surface is supplied by the middle cerebral artery.

N.B. Most of the superolateral surface is supplied by the middle cerebral artery. The arterial supply of the superolateral surface of the cerebral hemisphere is shown in Fig. 26.2.

FIG. 26.2 Arterial supply of the superolateral surface of the cerebral hemisphere.

❖ Describe briefly arterial supply of the inferomedial surface of the cerebral hemisphere. AN62.2 • Medial surfaces of the frontal and parietal lobes are supplied by the anterior cerebral artery. • Medial surfaces of the occipital and most of the temporal lobes (except temporal pole) are supplied by the posterior cerebral artery. • Medial surface of the temporal pole is supplied by the middle cerebral artery. • Medial part (one-third) of the orbital surface (of inferior surface) is supplied by the anterior cerebral artery. The lateral part (two-third) of the orbital surface as well as the temporal pole on inferior surface is supplied by the middle cerebral artery. • Rest of the tentorial surface (of inferior surface) is supplied by the posterior cerebral artery.

N.B. Most of the medial surface is supplied by the anterior cerebral artery. ❖ Write a short note on great cerebral vein of Galen. The great cerebral vein of Galen is formed by the union of two internal cerebral veins below the splenium of the corpus callosum (Fig. 26.3). It joins the inferior sagittal sinus to form the straight sinus. The tributaries of great cerebral vein are as follows: • Internal cerebral veins • Basal veins

FIG. 26.3 Formation, course and tributaries of the internal cerebral veins and the great cerebral vein of Galen.

❖ Enumerate the deep cerebral veins. The deep cerebral veins are (Fig. 26.3): • Thalamostriate veins • Choroid veins • Septal veins

N.B. These veins one from each side unite in the region of interventricular foramen of Monro to form the internal cerebral vein (vide supra).

White matter of cerebrum ❖ Define white matter and discuss its various types. AN62.3 The white matter of cerebrum is made up of myelinated nerve fibres, which connect various parts of cerebral cortex on the same side, with opposite side and also with the other parts of the CNS.

Types of white fibres There are three types of white fibres in the cerebrum: association fibres, commissural fibres and projection fibres.

Association fibres (intrahemispheric): These fibres connect different areas of cerebral cortex of the same hemisphere. They are further classified into two types: (a) short association fibres, which connect the adjacent gyri and (b) long association fibres, which connect the distant gyri. Commissural fibres: These fibres connect the cortical areas of one cerebral hemisphere with the corresponding cortical areas of the opposite hemisphere. The bundles of such fibres are called commissures. The important commissures in the brain are (a) corpus callosum, (b) anterior commissure and (c) posterior commissure. Projection fibres: These fibres connect the cortical areas with the subcortical centres such as corpus striatum, thalamus, hypothalamus, brainstem and spinal cord. They include both motor and sensory fibres of long tracts. The most important bundles of projection fibres are (a) internal capsule and (b) fornix. ❖ Enumerate the various commissures of the brain. AN62.3 The important commissures of the brain: • Corpus callosum • Anterior commissure • Posterior commissure • Hippocampal commissure • Habenular commissure ❖ Describe the corpus callosum under the following headings: (a) definition, (b) parts, (c) course of fibres, (d) functions and (e) applied anatomy. AN62.3

Definition The corpus callosum is the largest commissure of the brain. It is 10 cm long, which is nearly half of the anteroposterior length of the cerebrum. It consists of 300 million fibres. The corpus callosum connects all the parts of neocortex, except for the lower and anterior parts of temporal lobes, which are connected by the anterior commissure.

Parts In sagittal section, the corpus callosum is divided into four parts, from before to backwards (Fig. 26.4): • Rostrum • Genu • Body/trunk • Splenium

FIG. 26.4 Median sagittal section of the cerebrum showing shape and parts of corpus callosum.

The corpus callosum begins at the anterior commissure in the upper part of lamina terminalis, which passes upwards and forwards as the rostrum, then bends sharply upwards and backwards to form the genu and finally it extends backwards as the body and ends posteriorly as a thick massive extremity called splenium. Its inferior surface is connected in the midline with the upper surface of the fornix by septum pellucidum, which lies between two lateral ventricles. Its superior surface is related to indusium griseum and medial and lateral longitudinal striae.

Course of fibres of corpus callosum (fig. 26.5) • The fibres of the genu curve forwards on each side towards the frontal cortex forming the forceps minor. • The fibres of the body spread out laterally on each side to form the roof of the central part of the lateral ventricle. These fibres are intersected by the vertically running fibres of the corona radiata. • The fibres of the splenium curve backwards on each side towards the occipital cortex forming the forceps major. Its fibres form the upper part of the medial wall of the posterior horn of the lateral ventricle. • The fibres of the posterior part of the body together with some fibres from the splenium extend laterally to form the roof of the posterior horn of the lateral ventricle and then turn downwards to form the lateral wall of both the posterior and inferior horns.

FIG. 26.5 Median sagittal section of the cerebrum showing course of fibres from different parts of corpus callosum.

N.B. The tapetum is a thin lamina of white fibres, which forms the roof and lateral wall of the posterior horn, and lateral wall of the inferior horn of the lateral ventricle. It is formed by those fibres of body and splenium of corpus callosum, which are not intersected by the fibres of corona radiata.

Functions • Interhemispheric transfer of learned/visual memory. • Interhemispheric transfer of speech function. • Coordination of activities of two cerebral hemispheres for proper bilateral coordination and responses.

Applied anatomy • Patients with lesion of corpus callosum respond as if they have two separate brains – a condition called Split-brain effect/syndrome. • A surgical section of corpus callosum has been attempted in the past to prevent spread of seizures. ❖ Write a short note on anterior commissure. AN62.3 The anterior commissure is a small, round bundle of commissural fibres that crosses the

midline in the upper part of the lamina terminalis. It consists of two components: • A large, posterior neocortical component, which interconnects the cortical areas of the lower and anterior parts of the temporal poles. • A smaller, anterior paleocortical component, which interconnects the olfactory regions, such as olfactory bulbs and olfactory tubercles, of two sides. ❖ Describe the internal capsule under the following headings: (a) definition and location, (b) gross anatomy, (c) fibres, (d) arterial supply and (e) applied anatomy.  AN62.3

Definition and location The internal capsule is a compact bundle of projection fibres lying in the inferomedial part of the cerebral hemisphere. Hence, it lies in a narrow space between the lentiform nucleus laterally, and the caudate nucleus and thalamus medially. The internal capsule connects the cerebral cortex to the brainstem and spinal cord. It contains important fibres belonging to pyramidal tract and sensory fibres from the opposite half of the body.

Gross anatomy (fig. 26.6) Shape: In horizontal section, it appears as a ‘V’-shaped mass of white fibres. Parts: It consists of five parts: ■ Anterior limb: Lies between the lentiform nucleus and the caudate nucleus. ■ Genu (bend of internal capsule): Lies in the angle between the caudate nucleus, thalamus and lentiform nucleus. ■ Posterior limb: Lies between the lentiform nucleus and the thalamus. ■ Retrolentiform part: Lies behind the lentiform nucleus. ■ Sublentiform part: Lies deep to the lentiform nucleus.

FIG. 26.6 Location, shape, boundaries and parts of the internal capsule. The sublentiform part is not seen.

N.B. The internal capsule continues above as corona radiata and below as cerebral peduncle.

Fibres (fig. 26.7) The constituent fibres in the different parts of the internal capsule are given in Table 26.1.

FIG. 26.7 Parts of the internal capsule and fibres/tracts passing through them.

TABLE 26.1 Constituent Fibres in the Different Parts of the Internal Capsule Part Anterior limb Genu Posterior limb

Retrolentiform part Sublentiform part

Descending Fibres • Frontopontine fibres • Corticonuclear and corticospinal fibres for head and neck • Corticospinal fibres for upper limb, trunk and lower limb • Corticorubral fibres • Occipitopontine fibres • Temporopontine fibres

Ascending Fibres • Anterior thalamic radiation • Anterior part of superior thalamic radiation • Superior thalamic radiation

• Posterior thalamic radiation (optic radiation) • Inferior thalamic radiation (auditory radiation)

Arterial supply The arterial supply of different parts of the internal capsule is as follows: • Anterior limb is supplied by the middle and anterior cerebral arteries. • Genu is supplied by the middle cerebral artery and recurrent artery of Heubner.

• Posterior limb is supplied by Charcot’s artery of cerebral haemorrhage and anterior choroidal artery. • Sublentiform part is supplied by the anterior choroidal artery. • Retrolentiform part is supplied by the posterior cerebral artery.

Applied anatomy • A small lesion in the internal capsule results in widespread paralysis and sensory loss because huge number of motor and sensory fibres are packed densely in the internal capsule. • The commonest lesion in the internal capsule occurs due to cerebral haemorrhage or cerebral thrombosis. It causes complete hemiplegia on the opposite side (i.e. contralateral hemiplegia). • The most common cause of cerebral haemorrhage is the rupture of Charcot’s artery of cerebral haemorrhage and it usually involves posterior limb of internal capsule leading to contralateral hemiplegia. ❖ Write a short note on thalamic radiation. AN62.5 With few exceptions, all the afferent fibres to brain relay in the thalamus. From thalamus, the thalamocortical fibres radiate in different directions to reach the widespread area of the cerebral cortex (thalamic radiation). The important thalamocortical fibres (or thalamic radiations) are as follows: • Sensory radiation from the thalamus to the sensory cortex in the postcentral gyrus. • Auditory radiation from the medial geniculate body to the auditory cortex in the temporal lobe. • Optic radiation from the lateral geniculate body to the visual cortex in the occipital lobe.

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Basal nuclei, limbic system and lateral ventricle Basal nuclei ❖ What are basal nuclei? List their functions. AN62.4 The basal nuclei are large masses of grey matter located in the basal part of the cerebral hemisphere. They include corpus striatum, claustrum and amygdaloid body.

N.B. Functionally, the term basal nuclei also include substantia nigra, red nucleus and subthalamus.

Functions • To control the automatic associated movements like swinging of arms during walking. • To help in smoothening the voluntary motor activities of the body. • To prevent the occurrence of involuntary movements. ❖ Write a short note on corpus striatum. AN62.4 The corpus striatum is situated lateral to the thalamus. Topographically, it is almost completely divided into two parts: the caudate and lentiform nuclei by a band of fibres of the internal capsule. However, anteroinferiorly the two parts are connected with each other by a thin band of grey matter across the anterior limb of internal capsule (Fig. 27.1).

FIG. 27.1 Corpus striatum: A, lateral aspect of the left corpus striatum; B, relationship of the corpus striatum to the internal capsule.

Caudate nucleus The caudate nucleus (Fig. 27.2) is large, comma-shaped mass of grey matter that surrounds the thalamus and is itself surrounded by the lateral ventricle. It is divided into three parts – head, body and tail. • The head is large and rounded, and lies in the floor and lateral wall of the anterior horn of the lateral ventricle. Its lower part is connected with the putamen by thin bands of grey matter. • The body is long and narrow. It lies in the lateral part of the central part of the lateral ventricle. • The tail is long and slender. It runs forward in the roof of inferior horn of the lateral ventricle and merges with the amygdaloid nucleus.

FIG. 27.2 Relationship of caudate nucleus with the cavity of the lateral ventricle and thalamus. Note that the stria terminalis, the main efferent tract of amygdaloid body projects to the septal area, anterior perforated substance and anterior hypothalamus.

Lentiform nucleus The lentiform nucleus is a large, lens-shaped (biconvex lens) nucleus. In the horizontal section of cerebrum, it appears wedge shaped. It has three surfaces: lateral, medial and inferior. Its lateral surface is highly convex. It is related to the external capsule, which separates it from the claustrum. Its medial surface is also highly convex. It is related to the internal capsule, which separates it from the head of the caudate nucleus and the thalamus. Its inferior surface is related to the sublentiform part of the internal capsule and lies close to the anterior perforated substance.

N.B. The lentiform nucleus is divided by a thin, white lamina into two parts: the larger lateral part called putamen, while the smaller, medial part called the globus pallidus. The putamen has densely packed smaller cells and is darker in colour. The globus pallidus consists of loosely packed larger cells and is paler in colour. ❖ Enumerate the disorders that may occur due to the lesions of basal nuclei.  AN62.4 The lesions of basal nuclei lead to various forms of involuntary movements such as: • Parkinsonism (see below). • Chorea, choreiform movements as in break dancing. • Athetosis, athetoid movements, i.e. slow, sinuous and writhing movements. • Ballismus, violent burst of irregular movements in trunk, girdles and limbs. ❖ Write a short note on parkinsonism. AN62.4 The parkinsonism is a degenerative disease involving substantia nigra and/or nigrostriatal fibres causing deficiency of dopamine in the striatum. The disease usually occurs after 50 years of age. The clinical signs of parkinsonism include (Fig. 27.3): • Bradykinesia • Stooped posture • Shuffling gait • Cog-wheel rigidity • Pill-rolling tremors • Masked facies • Resting tremors

FIG. 27.3 Clinical features of a patient suffering from parkinsonism.

N.B. The treatment of parkinsonism includes: (a) Administration of L-dopa – a precursor of dopamine. (b) Stereotactic surgery by placing small lesions in globus pallidus. (c) Striatal implants of dopamine-containing neurons of fetal origin.

Limbic system ❖ What are the components of hippocampal formation? AN62.4 This hippocampal formation consists of: • Hippocampus • Dentate gyrus • Indusium griseum • Medial and lateral longitudinal striae ❖ Write a short note on hippocampus. AN62.4 • Hippocampus is the area of cerebral cortex that has rolled on itself in the floor of inferior horn of the lateral ventricle during fetal life.

It is so named because of its resemblance to ‘sea horse’ in coronal section (Fig. 27.4). • Histologically, it consists of three layers (Fig. 27.4): ■ Superficial polymorphic layer ■ Middle pyramidal cell layer ■ Deep molecular cell layer

FIG. 27.4 Coronal section of the hippocampus and related structures.

The ventricular surface of hippocampus is covered by thin layer of white fibres called alveus. Near the medial border, the fibres of alveus converge to form the fimbria of hippocampus.

Function It plays an important role in recent memory.

Applied anatomy The lesions of hippocampus lead to loss of recent memory (amnesia). ❖ Describe the fornix in brief. AN62.4 The fornix is a large bundle of projection fibres (mainly) that connect the hippocampus with the mammillary body. On the medial surface of cerebral hemisphere, it is seen as an arched bundle of white fibres beneath the corpus callosum.

Parts (fig. 27.5) It consists of: • Fimbriae • Crura

• Body • Columns (anterior columns)

FIG. 27.5 Main parts of the fornix.

Types of fibres present in the fornix • Projection fibres, which project from hippocampus to mammillary body. • Commissural fibres, which connect the two hippocampi. • Association fibres, which connect the hippocampus with cingulate gyrus of the same side.

N.B. The fornix is the only fibre bundle in brain which contains all the three types of white fibres of the cerebrum – projection fibres, commissural fibres and association fibres.

Lateral ventricle ❖ Write a short note on lateral ventricle. AN63.1 • It is a c-shaped cavity within the cerebral hemisphere. • There are two lateral ventricles, one in each cerebral hemisphere of the cerebrum. • It is C-shaped and wraps itself around the thalamus, lentiform nucleus and caudate nucleus. • Each lateral ventricle is situated lateral to septum pellucidum and below the corpus callosum. • It is lined by an ependyma and is filled with CSF. • It has a capacity of about 7–10 mL. • It communicates with the 3rd ventricle through interventricular foramen (of

Monro).

Parts Each lateral ventricle is divided into four parts (Fig. 27.6): • Central part/body • Anterior horn • Posterior horn • Inferior horn

FIG. 27.6 Ventricular system of the brain; lateral view. Note the different parts of the lateral ventricle (labelled in bold letters).

Applied anatomy The blockage of interventricular foramina leads to excessive accumulation of CSF in the lateral ventricles causing a clinical condition called hydrocephalus. ❖ Discuss the boundaries of central part of the lateral ventricle. AN63.1

Boundaries (fig. 27.7) It is triangular in shape in coronal section and presents roof, floor and medial wall. Roof: It is formed by the inferior surface of the corpus callosum. Floor: From lateral to medial side, it is formed by: ■ Body of caudate nucleus ■ Stria terminalis

■ Thalamostriate vein ■ Lateral part of the upper surface of thalamus ■ Choroid plexus ■ Body of fornix (upper surface) Medial wall: The medial wall is formed by septum pellucidum.

FIG. 27.7 Boundaries of central part of the lateral ventricle.

❖ Discuss the boundaries of anterior horn of the lateral ventricle. AN63.1

Boundaries It is roughly triangular in coronal section and presents roof, floor, anterior wall, medial wall and lateral wall (Fig. 27.8). Roof: It is formed by the anterior part of the body of corpus callosum. Floor: It is formed by the upper surface of the rostrum of corpus callosum. Anterior wall: It is formed by genu of the corpus callosum. Medial wall: It is formed by the septum pellucidum. Lateral wall: It is formed by the head of corpus callosum.

FIG. 27.8 Boundaries of anterior horn of the lateral ventricle.

❖ Discuss the boundaries of posterior horn of the lateral ventricle. AN63.1

Boundaries It is quadrangular or diamond shaped in coronal section and presents roof, lateral wall, floor and medial wall (Fig. 27.9). Roof, lateral wall and floor: These are formed by tapetum. Medial wall: It is formed: ■ In the upper part by bulb of the posterior horn (an elevation/raised area formed by the forceps major). ■ In the lower part by calcar avis (a raised area formed by the anterior part of calcarine sulcus).

FIG. 27.9 Boundaries of posterior horn of the lateral ventricle.

❖ Discuss the boundaries of inferior horn of the lateral ventricle. AN63.1

Boundaries It appears on a transverse slit in coronal section and presents roof and floor (Fig. 27.10). Roof: It is formed by: ■ Tapetum, covered on its superficial surface by optic radiation and inferior longitudinal fasciculus ■ Tail of caudate nucleus ■ Stria terminalis ■ Amygdaloid body (sometimes) Floor: From lateral to medial side, it is formed by: ■ Collateral eminence, formed by collateral sulcus ■ Hippocampus covered by thin layer of its white matter called alveus ■ Fimbria, formed by alveus ■ Choroid plexus

FIG. 27.10 Boundaries of inferior horn of the lateral ventricle.

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Diencephalon and third ventricle ❖ What is diencephalon? List its subdivisions. AN62.5 The diencephalon is the part of brain that lies between brainstem and cerebrum. The cavity within it is called 3rd ventricle.

Subdivisions The major subdivisions of diencephalon are as follows: • Thalamus • Metathalamus, consisting of medial and lateral geniculate bodies • Epithalamus, consisting of pineal body and habenular nuclei • Hypothalamus ❖ What is thalamus? Enumerate its major nuclei. AN62.5 Anatomically, the thalamus is a large, egg-shaped mass of grey matter lying above the brainstem, from which it is separated by a small amount of neural tissue called subthalamus. Functionally, the thalamus is the great sensory relay station (gateway) to the cerebral cortex. It receives sensory impulses from the opposite half of the body and transmits them to the sensory cortex. There are two thalami situated one on each side of a slit-like cavity called 3rd ventricle. Thus, medial surface of each thalamus forms the side wall of the 3rd ventricle. The anterior end of thalamus is narrow and forms the tubercle of the thalamus. Its posterior end is expanded and free, which is called pulvinar.

N.B. All the sensory pathways relay in the thalamus, except olfactory pathways.

Major nuclei of thalamus The major nuclei of thalamus are (Fig. 28.1) as follows: • Anterior nucleus • Mediodorsal (dorsomedial) nucleus • Pulvinar • Ventral tier of nuclei: ■ Ventral anterior nucleus (VA) ■ Ventral lateral nucleus (VL) ■ Ventral posterior nucleus (VP) • Ventral posterolateral nucleus (VPL)

• Ventral posteromedial nucleus (VPM)

FIG. 28.1 Horizontal section of the thalamus (schematic) showing the location of various thalamic nuclei. The inset is the coronal section of thalamus passing in front of pulvinar showing ventral posteromedial (VPM), ventral posterolateral (VPL) nuclei and centromedian nucleus. LD, lateral dorsal nucleus; LP, lateral posterior nucleus; MN, mediodorsal nucleus; P, pulvinar; VA, ventral anterior nucleus; VL, ventral lateral nucleus.

N.B. • The VPL nucleus receives spinothalamic tract and medial lemniscus. • The VPM nucleus receives trigeminothalamic tract (trigeminal lemniscus). ❖ Write a short note on metathalamus. AN62.5 The metathalamus consists of medial and lateral geniculate bodies, which are rounded elevations on the inferior aspect of the pulvinar.

Lateral geniculate body The lateral geniculate body (LGB) is a small ovoid swelling that projects downwards and laterally form the pulvinar of the thalamus. It is visible at the terminal end of each optic tract. It is the thalamic visual nucleus. It receives fibres from the optic tract and gives fibres (optic radiation) to the visual cortex of the occipital lobe (areas 17, 18 and 19). It is the last relay station on the visual pathway. Structurally, the LGB consists of six laminae, numbered 1–6 from ventral to dorsal side. Laminae 1, 4 and 6 receive fibres from contralateral retina and laminae 2, 3, and 5 from the ipsilateral retina.

Medial geniculate body The medial geniculate body is a small oval swelling on the inferior surface of the pulvinar and more prominent than the LGB. It is the thalamic auditory nucleus. It receives the fibres from the lateral lemniscus through the inferior colliculus and inferior brachium, and gives fibres (auditory radiation) to the auditory cortex in the temporal lobe

(area 41 and 42). It is the last relay station on the auditory pathway. ❖ Write a short note on pineal gland. AN62.5 The pineal gland is a small cone-shaped body (only 3 × 5 mm in size) projecting downwards in the midline from the posterior wall of the 3rd ventricle. It is located in the groove between the superior colliculi below the splenium of corpus callosum. Its stalk divides into two laminae – ventral and dorsal. The ventral lamina is continuous with posterior commissure, while the dorsal lamina is continuous with the habenular commissure.

Functions • Produces melatonin – a hormone that inhibits the secretion of gonadotrophins (GnRH) from the hypothalamus. The melatonin probably holds back the development of reproductive organ till a suitable age (i.e. puberty). In other words, the melatonin is believed to regulate the onset of the puberty. • Acts as a biological clock and is responsible for circadian rhythm. • Regulates the secretion of all other endocrine glands.

N.B. Morphologically, the pineal gland represents parietal (3rd) eye that has disappeared during evolution.

Applied anatomy • Tumours of pineal gland cause precocious puberty. • Calcification of pineal gland: The calcareous concretions appear in the pineal gland after 17 years of age and form aggregations called brain sand or corpora arenacea. The calcification of pineal gland is seen as a radiopaque shadow in 50% of individuals in midline and provides a useful landmark to detect any shift of brain due to tumour, etc. ❖ Describe the hypothalamus under the following headings: (a) introduction, (b) boundaries, (c) regions/parts and nuclei, (d) functions and (e) applied anatomy.  AN62.5

Introduction The hypothalamus is a small part of diencephalon that lies below the thalamus. It forms the floor and lower part of the lateral walls of 3rd ventricle. The hypothalamus controls the various autonomic activities of the body. The sympathetic activities are controlled by its posterior part, while parasympathetic activities are controlled by its anterior part. Hence, it is also called head ganglion of the autonomic nervous system.

Boundaries The hypothalamus is bounded: • Anteriorly by the lamina terminalis • Posteriorly by the subthalamus • Laterally by the internal capsule • Medially by the cavity of 3rd ventricle • Superiorly by the thalamus • Inferiorly by the structures in the floor of the 3rd ventricle, i.e. tuber cinereum, stalk of infundibulum and mammillary bodies (these are actually parts of hypothalamus)

Regions/parts and nuclei (fig. 28.2) The various regions of hypothalamus and nuclei present in them are as follows: • Preoptic region adjoining the lamina terminalis: It contains preoptic nucleus. • Supraoptic region (above the optic chiasma). It contains: ■ Supraoptic nucleus ■ Anterior nucleus ■ Paraventricular nucleus • Tuberal region includes tuber cinereum, infundibulum and area around it. It contains: ■ Arcuate (infundibular) nucleus ■ Ventromedial nucleus ■ Dorsomedial nucleus • Mammillary region (includes mammillary bodies and area around it). It contains: ■ Posterior nucleus ■ Mammillary nuclei

FIG. 28.2 Different nuclei of hypothalamus in sagittal section. The lateral nucleus of the hypothalamus is not shown.

N.B. The whole of hypothalamus is a derivative of diencephalon except its preoptic region, which is a derivative of the telencephalon.

Functions • Autonomic control: The anterior part controls the parasympathetic nervous system, while the posterior part controls the sympathetic nervous system. • Endocrine control: By producing releasing hormones or release-inhibiting hormones, it controls the functions of endocrine glands of the body. • Neurosecretion: The oxytocin and antidiuretic hormone (ADH)/vasopressin are synthesized in the supraoptic and paraventricular nuclei, respectively, and are transported to the posterior pituitary via hypothalamo-hypophyseal tract. • Regulation of food and water intake: The medial zone is responsible for hunger, thirst and drinking, while lateral zone acts as a ‘satiety centre’. • Temperature regulation: The anterior portion prevents rise in temperature, while the posterior portion promotes heat production and conservation. • Control of sexual behaviour and reproduction: By influencing the secretion of gonadotrophin (GnRH) by the pituitary gland. • Control of emotional behaviour like laughing, crying, sweating and flushing. • Acts as biological clock, i.e. regulates the cyclic activities of the body (sleep and wake cycle called circadian rhythm).

N.B. The important subcortical centres for autonomic system are (a) vasomotor centre, (b) cardiovascular centre and (c) respiratory centre. These are present in the brainstem.

Applied anatomy The impaired secretion of ADH/vasopressin leads to diabetes insipidus characterized by polyuria and polydipsia. The absence of glycosuria differentiates it from diabetes mellitus. ❖ Describe the 3rd ventricle under the following headings: (a) gross anatomy, (b) boundaries, (c) recesses and (d) applied anatomy. AN63.1 The 3rd ventricle is a midline slit-like cavity of diencephalon, which extends from lamina terminalis anteriorly to the upper end of cerebral aqueduct posteriorly. The 3rd ventricle communicates with the lateral ventricles through interventricular foramina (of Monro) and with 4th ventricle through cerebral aqueduct (of Sylvius).

Boundaries (fig. 28.3) The 3rd ventricle presents anterior wall, posterior wall, floor, roof and lateral walls. • Anterior wall is formed from above downwards by: ■ Anterior column of fornix ■ Anterior commissure ■ Lamina terminalis • Posterior wall is formed from above downwards by: ■ Pineal gland ■ Posterior commissure ■ Commencement of cerebral aqueduct • Floor is formed from before backwards by: ■ Optic chiasma ■ Tuber cinereum ■ Infundibulum (stalk of pituitary gland) ■ Mammillary bodies ■ Posterior perforated substance ■ Tegmentum of midbrain • Roof is formed by the ependyma stretching across the upper limits of the two thalami. • Lateral wall is formed by: ■ Medial surface of the anterior two-third of thalamus (forms the lateral wall above the hypothalamic sulcus) ■ Medial surface of the hypothalamus (forms the lower part of the lateral wall below the hypothalamic sulcus)

FIG. 28.3 Boundaries and recesses of 3rd ventricle as seen in sagittal section. 1, Infundibular recess; 2, optic recess; 3, anterior recess; 4, suprapineal recess; 5, pineal recess. HS, hypothalamic sulcus; I, interthalamic adhesion.

Recesses (fig. 28.3) These are extensions (pocket-like protrusions) of the cavity of 3rd ventricle into the surrounding structures: • Suprapineal recess: Above the stalk of pineal gland • Pineal recess: Between the superior and inferior laminae of the stalk of pineal gland • Infundibular recess: Into the stalk of pituitary gland • Anterior recess (also called vulva of the ventricle): Between the diverging anterior columns of fornix in front of the interventricular foramen and behind the anterior commissure

Applied anatomy • The obstruction of 3rd ventricle leads to accumulation of excessive CSF in it and two lateral ventricles, which causes increase in intracranial pressure in adults and hydrocephalus in infants. • The ventriculography is often done to visualize the obstruction/dilatation of 3rd ventricle.

SECTION IV

General Anatomy OUTLINE 29. 30. 31. 32. 33. 34. 35. 36.

Introduction and anatomical terminology Skin, superficial fascia and deep fascia Skeletal system Joints Muscles Cardiovascular system Lymphatic system Nervous system

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Introduction and anatomical terminology ❖ What is anatomy? The anatomy is the science which deals with the structure of the body from submicroscopic to the macroscopic level. The term anatomy is derived from a Greek word ‘anatome’ meaning to ‘cut up’ (ana = apart, tomy = cut). The term dissection is the Latin equivalent of the Greek term ‘anatome’. ❖ Enumerate the major subdivisions of the anatomy. AN1.1 The major subdivisions of the anatomy are as follows: • Gross anatomy, which includes cadaveric anatomy, living anatomy/surface anatomy, endoscopic and radiological anatomy. • Histology/microscopic anatomy • Embryology • Genetics • Imaging/radiological anatomy ❖ Who is the father of anatomy? Briefly describe his life and achievements. Herophilus (325–280 BC) (Fig. 29.1) is considered as the father of anatomy.

FIG. 29.1 Herophilus.

He was a Greek physician and was regarded as the founder of school of medicine at Alexandria, the then capital of Egypt. He taught anatomy in this medical school through vivisections (dissections of living humans) and dissections of human cadavers. Herophilus provided great descriptions of the skull, eye, various visceral organs and their relationships. He also described functional relationship of the spinal cord to the brain. Herophilus regarded the brain as the seat of intelligence and described many of its structures such as cerebrum, cerebellum and the 4th ventricle. He was the first to identify that nerves are either sensory or motor. He is also credited with the discovery of the ovum. Two monumental works of Herophilus were titled On Anatomy and On the Eyes. ❖ Who is the father of modern anatomy? Briefly describe his life and achievements. Andreas Vesalius (1514–1564) (Fig. 29.2) is considered as the father of modern anatomy. He was born in Brussels to a family of physicians. He studied anatomy and medicine for 3 years in the University of Paris. He became Professor of Anatomy and Surgery at the age of 23 years at the University of Padua in Italy. He performed human dissections and initiated the use of live models to determine the surface landmarks for internal structures. His masterpiece anatomical treatise De humani corporis fabrica (On the Workings of the Human Body) written in seven volumes at the age of 28 years revolutionized the teaching of anatomy and remained an authoritative text for two centuries. The various body systems and individual organs were beautifully illustrated and described in the fabrica. In his book, he boldly challenged hundreds of Galen’s erroneous concepts that were taught as facts. Bitter controversies ensued between

Vesalius and Galenic anatomists. Vesalius became so incensed by the relentless attacks that he destroyed much of his unpublished work and stopped doing dissections. However, by freeing anatomy from many of the Galen’s errors, Vesalius laid the foundation on which many subsequent advances in medicine and surgery could take place.

FIG. 29.2 Andreas Vesalius.

He started the era of anatomical basis of surgery. Another credit of Vesalius is that, unlike other anatomists of his time (Sylvius, Fallopius, Eustachius, etc.), he chose not to have his name attached to the parts of the body that he described. He remained a bachelor and a teacher of anatomy throughout his life. Vesalius was the greatest anatomist of his time and is now regarded as the Father of Modern Anatomy. He is also called ‘reformer of anatomy’. ❖ Enumerate the characteristic features of humans. The characteristic features of humans are as follows: • Bipedal locomotion • Well-developed cerebrum (brain) • Skilled hand with opposable thumb • Well-developed articulated speech • Prominent chin

• Stereoscopic vision ❖ What are the parts/regions of the human body? For descriptive purposes, the human body is divided into following six parts/regions: • Head1 • Neck • Thorax • Abdomen • Upper limb • Lower limb

Anatomical terminology Anatomical language is one of the fundamental languages of medicine. The medical doctors throughout the world use a common language of special anatomical terms while referring to the structures of the body in any position to avoid any ambiguity. The anatomical terms are mostly Greek or Latin in origin. ❖ Define the anatomical position and give its significance.  AN1.1 In anatomical position, it is presumed that the body is standing erect, the upper limbs hanging by the sides of body with palms of the hands facing forwards, the feet parallel to each other, digits facing forwards and eyes directed forwards (Fig. 29.3).

FIG. 29.3 Anatomical position.

Significance Since the interrelationship of various parts of the body keep changing with various positions of the body (supine, prone, hanging upside down, etc.), all descriptions in the human body are expressed in relation to the anatomical position. ❖ Define the fundamental position. The fundamental position is same as the anatomical position, except that the person stands erect with upper limbs hanging by the side of the body and palms of the hands face medially towards the sides of the body. ❖ Briefly discuss fundamental planes of the body and give their significance.  AN1.1 There are four fundamental planes of the body: • Midsagittal (median) plane: It is an imaginary vertical plane that passes through the central axis of the body and divides the body into right and left halves. It corresponds to the sagittal suture of skull, hence the name midsagittal plane. • Sagittal plane: Any vertical plane parallel to the median plane is called sagittal plane. It may be present on right or left side of the median plane. It divides the body into two unequal halves. • Coronal plane: It is vertical plane that passes at right angle to the median plane and divides the body into anterior and posterior parts. It corresponds to the coronal suture of the skull, hence the name coronal plane. • Transverse/horizontal plane: It passes horizontally and divides the body into upper and lower parts. This plane passes at right angle to both sagittal and coronal planes and is perpendicular to the long axis of the body or limbs. Note: The radiologists refer to transverse plane as transaxial. Convention dictates that the axial anatomy is viewed as though looking from feet towards the head.

N.B. Any plane passing through the body or any of its parts other than the above-mentioned planes is termed oblique plane. ❖ Briefly describe the following movements: (a) circumduction, (b) supination and pronation, (c) inversion and eversion and (d) opposition. AN1.1

Circumduction • This movement is a combination of flexon, extension, abduction and adduction in a sequence.

• It is a cone-like circular movement in which the distal portion of moving part moves in a circle. For example, during bowling of a cricket ball, there is circumduction of upper limb at the shoulder joint, while hand, holding the cricket ball moves in a circle. Such movements are possible at shoulder, hip joints, etc.

Supination and pronation In supination, the forearm and hands are rotated laterally around their longitudinal axes from midprone position so that palm of the hand faces anteriorly/upwards. In pronation, the forearm and hand are rotated medially around their longitudinal axes from the midprone position so that the palm of the hand faces posteriorly/downward. The movements of supination and pronation occur at the superior and inferior radioulnar joints. For details, see p. 80.

Inversion and eversion In inversion, the medial border of foot is raised, so that the sole of foot faces inwards/medially, while in eversion, the lateral border of foot is raised so that the sole of foot faces outwards/laterally. These movements occur at talo-calcaneo-navicular and subtalar joints.

Opposition In this movement, the tip of thumb touches the tips of other digits, e.g. when one does count on fingers. This movement occurs at 1st carpometacarpal joint. 1

The head includes skull, face and brain.

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Skin, superficial fascia and deep fascia Skin ❖ What is skin? List its functions. AN4.1 The skin (integument) is the outer covering of the body with a total area of about 20 square feet. It is the largest organ (area wise) of the body constituting about 16% of the body weight.

N.B. The skin is considered as an organ because it consists of several different types of tissues (e.g. epithelial tissue, adipose tissue, glandular tissue, blood vessels and nerves) that are structurally arranged to function together.

Functions • Protection of the body from heat, cold, ultraviolet rays, etc. • Prevention of loss of the body fluids and absorption of water within the body. • Regulation of the body temperature. • Acts as a sensory organ. • Synthesis of vitamin D with the help of ultraviolet rays. • Absorption of lipid-soluble materials, e.g. vitamins like A, D, E and K; solvents like acetone; and heavy metals like arsenic, lead and mercury. ❖ What are the layers of the skin? AN4.1 The skin consists of two layers: • Epidermis: It is the superficial layer. It consists of stratified squamous epithelium and is derived from ectoderm. It is avascular. • Dermis: It is the deep layer. It is made up of connective tissue and is derived from mesoderm. It is highly vascular and contains glands, nerve endings and hair follicles. ❖ Enumerate the layers of epidermis. AN4.1 The thick skin presents the following five layers, from deep to superficial (Fig. 30.1): • Stratum basale/stratum germinatum/basal layer • Stratum spinosum/spiny layer

• Stratum granulosum/granular layer • Stratum lucidum/clear layer • Stratum corneum/cornified layer

FIG. 30.1 Layers of the epidermis. The dermis is also seen.

❖ What are the differences between thin and thick skin? AN4.2 The differences between thin and thick skin are given in Table 30.1. TABLE 30.1 Differences Between Thin and Thick Skin

Epidermis

Epidermal ridges Hair follicles Sebaceous glands Sweat glands Sensory nerve endings Distribution

Thin skin • Thin (0.10–0.15 mm) • Stratum corneum thin • Stratum lucidum absent • Absent • Present • Present • Few • Few • All parts of the body, except palms and soles

❖ What are the layers of dermis? The dermis consists of two layers:

Thick skin • Thick (0.6–4.5 mm) • Stratum corneum thick • Stratum lucidum present • Present • Absent • Absent • Numerous • Numerous • Palms and soles

• Papillary layer: It is superficial and forms one-fifth of the total thickness of dermis. It sends finger-like projections (called dermal papillae) towards epidermis. • Reticular layer: It is a deep layer and contains course bundles of collagen fibres. It also contains blood vessels and nerves. ❖ What are cleavage lines/Langer’s lines? Mention their clinical significance.  AN4.2 These are lines on the surface of the skin. They are produced by the pull of collagen fibres present within the dermis, and radiate in definite directions. They correspond to the natural orientation of collagen fibres in dermis. In general, the Langer’s lines tend to run longitudinally in the limbs and circumferentially in the neck and the trunk (Fig. 30.2).

FIG. 30.2 Tension lines/Langer’s lines of the skin: A, front; B, back.

Clinical significance The knowledge of orientation of these lines is of special interest to surgeons as: • Incisions made parallel to these lines heal rapidly and produce hair-line scar (due to formation of less scar tissue). • Incisions made across these lines heal poorly and produce wide scar (due to

formation of more scar tissue). ❖ What are the appendages of the skin? AN4.2 Appendages of the skin: • Hair • Sweat glands • Sebaceous glands • Nails

Superficial fascia ❖ What is superficial fascia? • It is a layer of loose connective tissue located deep to skin. It connects the skin to the underlying deep fascia. The superficial fascia contains subcutaneous fat, nerves and vessels. It is mostly heavily infiltrated with fat in females and children, which is the main factor responsible for smooth external contours of the body in females and children. AN4.3 • It allows mobility of the skin on the underlying structures. • It acts as a distributary layer in which blood vessels, lymphatics and nerves can travel before entering the dermis. • It forms a kind of insulating layer over the body surface and accounts for the increased resistance of the females to cold in comparison with the males. • It is extremely thin and devoid of fat in the eyelids, the external ear, penis and scrotum. • In palms, soles, back of neck and scalp, it is made up of dense connective tissue, which firmly bind it to the underlying structures. ❖ Enumerate the sites of subcutaneous injections. The sites of subcutaneous injectionare: • Posterior aspect of arm • Anterior aspect of forearm • Anterior abdominal wall • Anterior aspect of thigh ❖ What is panniculus carnosus? Enumerate the muscles that represent panniculus carnosus in humans. The panniculus carnosus is a thin sheet of striated muscle present in the superficial fascia of lower animals. Its fibres are inserted into the skin. The following muscles in the human body represent the panniculus carnosus: • Muscles of the scalp

• Muscles of the facial expression • Platysma (in neck) • Subareolar muscle (of breast) • Palmaris brevis (in hand) • Dartos muscle (of scrotum) • Corrugator cutis ani (around the anal orifice)

Deep fascia ❖ What is deep fascia? Mention its clinical significance. AN4.4 • It is a dense, inelastic fibrous membrane that separates the superficial fascia from the underlying structures. It is made up of regularly arranged collagen fibres. • It sends septa between muscles from its deep aspect forming intermuscular septa (Fig. 30.3). • It ensheaths the muscles, vessels and nerves. The sheath around the muscles forms tunnels within which muscles can slide independent of the adjacent muscles. • It forms thickened bands – the retinacula – at certain sites, such as wrist and ankle, which hold the tendons in place and prevent their bow stringing during the movements of the hand and feet at these sites.

FIG. 30.3 Transverse section through the middle of the right thigh to show the three intermuscular septa and three osteofascial compartments as seen from above.

Clinical significance The deep fascia forms fascial planes that are of special interest to surgeons because: • They can operate along the fascial planes easily with minimal injury to adjoining structures. • Deep fascia provide better understanding of the location and the routes of spread of pus as pus tracks along the fascial planes (i.e. paths of least resistance). ❖ Enumerate the modifications of deep fascia. AN4.4 • Intermuscular septa, in limbs to form fascial compartments • Retinacula, i.e. extensor and flexor retinacula around wrist and ankle • Fibrous flexor sheaths in digits of hand and feet • Aponeurosis, i.e. palmar aponeurosis in palm and plantar aponeurosis in sole • Ligaments to connect the bones at joints • Fascial sheath around certain muscles • Interosseous membranes in forearm and leg

N.B. In true sense, aponeurosis is a thick, wide sheet of fibrous tissue that provides attachments to the muscles.

31

Skeletal system The skeletal system is made up of bones and cartilages. It provides strong and flexible framework to the body.

Bones ❖ What is bone? The bone is a specialized connective tissue with mineralized matrix by calcium salts, e.g. calcium hydroxyapatite crystals. It provides hardness to the human skeleton. ❖ Classify bones according to their shape.

Classification Long bones: They consist of a shaft and two ends. The elongated tubular shaft or body is called diaphysis. It contains medullary cavity within it. The expanded ends are called epiphyses. Examples: Long bones of limbs such as femur, tibia and fibula in the lower limb and humerus, radius and ulna in the upper limb. Short long bones (also called miniature long bones): They have shaft and only one epiphysis. Examples: Metatarsals, metacarpals and phalanges. Short bones: They are smaller in size and usually cube shaped. Examples: Carpal and tarsal bones. Flat bones: They are flat (plate like) and consist of two layers (plates) of compact bone with spongy bone, filled with bone marrow between them. Examples: Bones forming the skull cap such as frontal, parietal and occipital. The ribs, sternum and scapula are also classified as flat bones. Irregular bones: They have irregular shape. Examples: Bones of the face and base of the skull; vertebrae and hip bones. Pneumatic bones: They contain cavities within them, which are filled with air. These bones are confined to the skull. Examples: Paranasal bones such as maxilla, ethmoid, sphenoid and frontal bones. Accessory bones: They are sometimes present in the limbs and skull. Examples: Os trigonum (os vesalianum), os cubiti in the limbs and wormian bones in the skull. Sesamoid bones: They develop in the tendons of muscles and are devoid of periosteum. Examples: Patella and fabella. ❖ What are the functions of the bones?

Functions • Form skeletal framework of the body, thus providing shape to the body. • Protect vital organs such as brain, spinal cord, heart and lungs. • Provide surface for attachments to the skeletal muscles. • Act as a storehouse for mineral salts, e.g. calcium and phosphorus. • Act as levers for the body movements by the muscles. • Produce blood cells. ❖ Enumerate the structural components of a long bone.

Structural components • Mineralized matrix • Specialized cells, e.g. osteoblasts, osteocytes and osteoclasts • Periosteum • Endosteum • Medullary cavity • Bone marrow ❖ What are the sites where red bone marrow is present in adults? AN1.2 The sites where red bone marrow is present in adults: • Proximal ends of femur and humerus • Ribs • Sternum • Skull • Vertebrae • Hip bone ❖ What are the parts of a long bone? AN2.1 The long bone consists of the following parts: • Epiphyses: Ends of a long bone that ossifies from secondary centres. • Diaphysis: Shaft of a long bone that ossifies from a primary centre. It consists of an outer cortex of compact bone and inner medullary cavity filled with bone marrow. ❖ Write a short note on periosteum. AN2.1 The periosteum forms the outer fibrous covering of the bone. It covers whole of the bone surface, except where bone is covered by articular cartilage. The periosteum is attached to the bone tissue by Sharpey’s fibres. It consists of two layers: • An outer fibrous layer, which becomes continuous at the ends of the bone with the fibrous capsule of a joint. It protects the bone.

• An inner cellular layer containing osteoprogenitor cells (osteogenic cellular layer), which ends at the epiphyseal line. This layer is responsible for deposition of bone on the surface of the shaft and thus adds to the growth of bone in girth. It is also essential for fracture repair.

Functions • Protects the bone, as it covers the outer surface of bone. • Helps in bone formation, helping bone growth in young age and repair of fracture in adults, as it contains bone-forming cells. • Helps to provide nutrition to bone, as it is richly supplied with blood vessels. • Makes bone sensitive to pain as it is supplied with sensory nerves. • Provides medium for attachment of ligaments, tendons and muscles to the bone.

N.B. All the bones in the body are covered by periosteum, except sesamoid bones and ear ossicles. ❖ What are Sharpey’s fibres? The periosteum is anchored to the outer part of bone tissue by Sharpey’s fibres. From the inner layer of periosteum, coarse collagen fibres extend inwards to enter the bone matrix. These are called Sharpey’s fibres (perforating fibres). The Sharpey’s fibres enter the bone matrix like spikes of a shoe and thus anchoring the periosteum to the bone. ❖ Classify bones according to their structure. Structurally, the bones are classified into two types: compact bone and cancellous bone. The differences between these two types are given in Table 31.1. TABLE 31.1 Differences Between Compact and Cancellous Bones Compact Bone • Dense like an ivory • No spaces are visible on naked eye examination • Located superficial to cancellous bone • Consists of haversian systems • Lamellae are arranged in regular

Cancellous Bone • Porous like a sponge • Spaces are visible on naked eye examination

• Located deep to compact bone • No haversian system. Consists of meshwork of bony spicules (small rods and curved plates) with spaces between spicules filled with bone marrow; no Haversian system • Lamellae are arranged in irregular fashion

fashion

❖ Enumerate the parts of a growing/developing long bone. AN2.1 The parts of growing long bone (Fig. 31.1): • Epiphysis: It is the end of long bones that ossifies from secondary centre. • Diaphysis: It is the shaft/body of long bone that ossifies from secondary centre. • Metaphysis: It is part of diaphysis near the epiphysis. It is a zone of active bone growth. • Epiphyseal plate: It is a plate of hyaline cartilage between epiphysis and diaphysis. The epiphysial cartilage is responsible for growth of bone in length. Hence, it is also called growth plate.

FIG. 31.1 Parts of a growing long bone.

❖ Write a short note on the arterial supply of a growing long bone.  AN2.1 The growing long bone is supplied by the following arteries (Fig. 31.2): • Nutrient artery: It is tortuous and enters the middle of shaft through the nutrient foramen. It runs obliquely through cortex into medullary cavity, where it divides into ascending and descending branches. Each branch in turn divides and redivides into parallel vessels, which run in metaphysis, where they terminate by forming hairpin bends. The ascending and descending branches also ramify in the endosteum and give twigs to adjoining canals.

It supplies medullary cavity and inner two-thirds of cortex. The nutrient foramen is directed opposite to growing end of long bone. It anastomoses with periosteal and metaphyseal arteries. • Juxta-epiphysial (metaphyseal) arteries: These are derived from arterial anastomosis around the joint. They pierce the metaphysis along the line of attachment of joint capsule. • Epiphysial arteries: These are derived from periarticular vascular arcades, found on nonarticular bony surface and enter the bone distal to epiphyseal cartilage. • Periosteal arteries: These ramify beneath the periosteum and supply the outer two-third of the cortex. The removal of periosteum may cause necrosis of underlying bone.

FIG. 31.2 Blood supply to a growing long bone.

N.B. Nutrient arteries are the most source of blood supply to the bone. ❖ Metaphysis is the common site for osteomyelitis in children – mention its anatomical basis. AN2.1 This is because the metaphysis is a zone of active growth. It is profusely supplied with blood by end arteries, which form ‘hairpin bends’. The bacteria and emboli are easily

trapped in these hairpin bends leading to infarction and subsequently to osteomyelitis. ❖ Describe sesamoid bones briefly. AN2.3 The sesamoid bones are seed-like bony nodules found embedded in the tendons of muscles (in Arabic: Sesame = seed).

Characteristic features • Develop in tendons of the muscles after birth. • Are devoid of periosteum. • Are devoid of Haversian systems. • Ossify by multiple secondary centres.

Functions • Alter the direction of pull of muscle tendon. • Minimize the friction of tendon against bone. • Modify and sustain pressure. • Provide additional articular surface to a joint. • Protect the tendons from wear and tear. • Act as pulleys for muscular contraction.

Sites • Tendon of quadriceps femoris (patella) • Lateral head of gastrocnemius muscle (fabella) • Tendon of flexor carpi ulnaris (pisiform) • Two bony nodules (sesamoid bones) beneath the head of 1st metatarsal in the tendon of flexor pollicis brevis • Bony nodule in the tendon of adductor hallucis • Bony nodule in the tendon of peroneus longus where it winds around the cuboid bone ❖ Define ossification and ossification centres. AN2.2

Ossification It is the process of bone formation.

Ossification centre The ossification centres are sites where bone formation begins. There are two types of ossification centres: (a) primary and (b) secondary. Primary centre: It appears before birth in the centre of shaft or body of bone which it forms.

Secondary centre: It appears later, usually after birth at each end of bone which it forms. ❖ Write a short note on endochondral/cartilaginous ossification. AN2.2 It is the process of formation of bone from the preformed cartilaginous model (premature long bone) (Fig. 31.3). • The process of bone formation begins in the centre of the shaft of long bone. This site where bone formation begins is called primary ossification centre. This centre forms the diaphysis. • Later, centres of ossification appear at different interval at each end of cartilaginous model. These are called secondary ossification centres. These centres form the epiphyses. • The plate of hyaline cartilage separating the epiphysis and diaphysis is called epiphyseal plate/growth plate. It is essential for growth of bone in length. • When the epiphysis unites with the diaphysis, the epiphyseal plate is replaced by a linear scar called epiphyseal line.

FIG. 31.3 Cartilaginous ossification of a long bone.

(For details, see Chapter 8, p. 84 of Textbook of Clinical Embryology, 1st ed. by Vishram Singh.) ❖ Define membranous ossification. AN2.2 It is a process of bone formation from mesenchymal model. (For details, see Chapter 8, p. 84 of Textbook of Clinical Embryology, 1st ed. by Vishram Singh.) ❖ What are the different types of epiphyses? AN2.1 There are four types of epiphyses: Pressure epiphyses: They are present at the ends of long bone. They are, therefore,

articular in nature and take part in the transmission of weight, e.g. head of femur, lower end of radius and medial end of clavicle. Traction epiphyses: They are nonarticular in nature and are not involved in transmission of weight. They provide attachment to one or more muscle tendons, which exert traction on it, e.g. greater and lesser trochanters of femur, greater and lesser tubercles of humerus. Atavistic epiphyses: Phylogenetically, they represent a separate bone, which in man has become fused secondarily to another bone, e.g. coracoid process of scapula, posterior tubercle of talus (os trigonum). Aberrant epiphyses: They are not always present but appear sometimes, e.g. epiphysis at the head of 1st metacarpal.

Cartilage ❖ What is cartilage? AN2.4 The cartilage is a specialized connective tissue, with rubbery matrix (gel-like matrix) due to deposition of proteoglycans which provides firmness along with elasticity to the skeletal framework of the body. Phylogenetically, it is older than the bone tissue. • It is made up of dense network of collagen or elastic fibres, which provide tensile strength to it. • Its fibres are embedded in a firm, jelly-like amorphous substance made up of mucopolysaccharides, which allows the cartilage to bear weight without bending. • It is firm in consistency and has elasticity. • It is an avascular tissue. The invasion of cartilage by blood vessels results in its calcification and death. • It has no lymphatics. • It is well adapted to coat the articular ends of the bone. ❖ What are the different types of cartilages? AN2.4 The cartilages are classified into three types: (a) hyaline cartilage, (b) yellow elastic cartilage and (c) fibrocartilage. For details see Chapter 39, p. 333.

32

Joints ❖ Define joints and describe their classification. AN2.5 The joints are the junctions/meeting points between two or more bones. However, they can also be formed between bone and cartilage or between bone and tooth.

Classification Joints are classified in two ways: • On the basis of type of tissue (fibres or cartilage) binding the articulating bones or presence or absence of synovial cavity between the articular bones (structural classification). • On the basis of range and type of movement they permit (i.e. functional classification). Structural classification • Fibrous joint: It lacks the joint cavity and the articular bones are joined by the fibrous tissue. These joints are immovable or permit only slight movement. • Cartilaginous joint: It also lacks the joint cavity and the articular bones are joined by the cartilage. These joints are immovable or permit only slight movement. • Synovial joint: It has a joint cavity. The articular surfaces of the bones are covered by the articular (hyaline) cartilage. The articular bones are enclosed by a fibrous capsule. The joint cavity between the articular surfaces contains viscous synovial fluid. These joints are freely movable and permit maximum degree of movement. Functional classification • Immovable joint (synarthrosis), e.g. fibrous joints (vide supra) • Slightly movable joints (amphiarthrosis), e.g. cartilaginous joints (vide supra) • Movable joints (diarthrosis), e.g. synovial joints (vide supra) ❖ What are the different types of fibrous joints? AN2.5 • Sutures: These joints are found in the skull and are immovable (i.e. synarthrosis). The articulating bones are connected by sutural ligaments or thin membranes of fibrous tissue.

• Syndesmosis: The articulating bones are connected to each other by interosseous ligaments, and bones involved lie at some distance apart, e.g. inferior (distal) tibiofibular joint (Fig. 32.1). Slight movement is permitted at these joints; hence, functionally it is classified as amphiarthrosis. • Gomphosis/peg and socket joint (dentoalveolar joint): Here, the cone-shaped root of the tooth fits into the alveolar socket of the jaw. The tooth is attached to the alveolar socket by the fibrous tissue (periodontal ligaments) (Fig. 32.2).

FIG. 32.1 Syndesmosis: inferior tibiofibular joint representing syndesmosis.

FIG. 32.2 The gomphosis (peg and socket joint): tooth in alveolar socket representing gomphosis.

This type of joint is immovable, hence functionally classified as synarthrosis. ❖ Define a synovial joint and mention the characteristic features of a typical synovial joint.  AN2.5 A synovial joint is a joint with cavity between the two or more articulating bones. The cavity is lined by synovial membrane and is filled with a synovial fluid. The synovial joints permit a free movement, hence functionally classified as diarthrosis.

Characteristic features The characteristic features of a typical synovial joint (Fig. 32.3): • Articular surfaces are covered with hyaline (articular) cartilage, which provides smooth, slippery surface to reduce friction between the articular surfaces of the bones during movement. • Articular ends of bones are enclosed by a fibrous capsule; hence, it has joint cavity. • Inner surface of capsule and all intra-articular structures, except articular cartilages, are covered by a synovial membrane, which secretes synovial fluid. • They are freely movable joints, hence functionally classified as diarthroses. • Joint cavity is filled with synovial fluid.

FIG. 32.3 Diagrammatic representation of a typical synovial joint.

❖ What are the differences between atypical, complex and compound synovial joints?  AN2.5 • If the articular surfaces of a synovial joint are covered by a fibrocartilage, it is termed atypical synovial joint, e.g. temporomandibular joint. • If the cavity of a synovial joint is divided completely or incompletely into two compartments by an intra-articular disc, it is called complex synovial joint, e.g. temporomandibular joint and sternoclavicular joint. • If more than two articular surfaces are enclosed in a single fibrous capsule, it is called compound synovial joint, e.g. elbow joint. ❖ Classify various types of synovial joints. AN2.5 • Plane joints: These are the joints in which the articular surfaces are flat and in contact. Only gliding movements are possible at these joints. Examples: Intercarpal joints and intertarsal joints. • Hinge joints: These are the joints in which one articular surface is convex and the other is reciprocally concave. The movements take place around a transverse axis. Examples: Humeroulnar joint, interphalangeal joints, knee joints and ankle joints. • Pivot joints: These are joints in which a bony pivot-like process rotates within an osseofibrous ring or an osseofibrous ring rotates around the bony pivot. Thus, the movements are possible only around longitudinal axis through centre of pivot. Examples: Superior radioulnar joint, inferior radioulnar joint and median atlantoaxial joint. • Condylar joints: In such joints, the convex condyle or condyles (articular

surfaces) of one bone articulate with concave articular surface or surfaces of other bone. Movements occur not only mainly in transverse axis but also partly in vertical axis (rotation). Examples: Knee joint and temporomandibular joint. • Ellipsoid joints: These joints are formed by an oval convex surface of one bone and an elliptical concave surface of the other bone. Examples: Radiocarpal joint (wrist joint) and metacarpophalangeal joints. Movements that are possible at such joints are flexion, extension, abduction, adduction and circumduction. No rotation occurs around central axis. • Saddle joints: In such joints, the articular surfaces are reciprocally concavoconvex (saddle shaped). Movements permitted at these joints are same as in condylar type with some rotational movement. Examples: Carpometacarpal joint of thumb, sternoclavicular joint, calcaneocuboid joint and incudomalleolar joint. • Ball and socket joints: In such joints, the rounded articular surface of one bone (the ball) fits into a cup-shaped cavity (the socket) of other bone. In these joints, the movements are possible in every direction around a common centre. Examples: Hip joint and shoulder joint. ❖ What are the types of cartilaginous joints? AN2.5 There are two types of cartilaginous joints: primary and secondary. • Primary cartilaginous joints (synchondroses): The bones forming these joints are united by a hyaline cartilage. They are immovable (synarthroses). After certain age, the hyaline cartilage is slowly replaced by bone (synostosis). Examples: Joints between epiphysis and diaphysis of a growing long bone, costochondral joints, spheno-occipital joint (joint between basiocciput and basisphenoid at the base of skull) and 1st costosternal joint. These are temporary joints.

N.B. The primary cartilaginous joint between basiocciput and basisphenoid is converted into synostosis at about 25 years of age. • Secondary cartilaginous joints (symphyses): These joints occur in the median plane of the body. The articular surfaces are covered by a plate of hyaline cartilage, which are then connected by a broad, flat fibrocartilaginous disc. Examples: Manubriosternal joint, pubic symphysis and intervertebral discs. These are permanent joints and do not disappear with age. Slight movement is possible (amphiarthrosis) at these joints. ❖ Compare and contrast the primary and secondary cartilaginous joints. AN2.5 Primary Cartilaginous Joint • Articular surfaces are united by a hyaline cartilage

Secondary Cartilaginous Joint • Articular surfaces are united by a fibrocartilage

• Immovable • Temporary, as they ossify with age • May or may not lie in midline • Examples are joints between epiphysis and diaphysis, and between basiocciput and basisphenoid

• Partially movable • Permanent, as they do not ossify with age • Always lie in midline • Examples are symphysis pubis, intervertebral discs, manubriosternal joint

❖ What are the closed-packed and loose-packed positions of a joint? AN2.5

Closed-packed position It is the position of a joint in which fibrous capsule and ligaments are taut and articular surfaces are fully congruent, i.e. have maximum area of contact with each other. This is the most stable position of joint and therefore dislocations are rare in this position.

Loose-packed position It is the position of a joint in which articular surfaces are not congruent. The capsule and ligaments are lax. This is an unstable position of joint; therefore, dislocations commonly occur in this position. ❖ Enumerate the intra-articular structures found within the synovial joint. AN2.5 • Cartilaginous structures: ■ Articular discs of temporomandibular and sternoclavicular joints ■ Articular menisci (semilunar cartilages) of the knee joint ■ Labrum: Glenoid labrum of the shoulder joint and the acetabular labrum of the hip joint • Ligament-traversing joint: They bind articular surfaces, e.g. ligamentum teres of the hip joint and cruciate ligaments of the knee joint • Tendons traversing the joint cavity: These arise inside capsule of joint and transverse the joint cavity, e.g. tendon of long head of biceps traversing the cavity of shoulder joint and tendon of popliteus traversing the cavity of the knee joint ❖ List the nerve supply of a synovial joint. AN2.6 The synovial joint is supplied by three types of nerves: • Sensory nerves carrying pain from articular fibrous capsule, ligaments and synovial membrane. • Sensory nerves carrying proprioceptive sensations from articular fibrous capsule and ligaments. • Autonomic nerves supplying blood vessels. They regulate the flow of blood in an articular fibrous capsule. ❖ What is Hilton’s law? AN2.6

This law enunciates that the nerves supplying sensory fibres to the capsule of the joint also supply the muscles crossing the joint and skin over the joint. Therefore, when the joint is diseased, the irritation of these nerves cause (a) reflex spasm of muscles to bring the joint in the position of maximum comfort and (b) the pain of joint is referred to the overlying skin. ❖ What are the types of movements that commonly occur in the synovial joints?  AN2.5 Four types of movements commonly occur in the synovial joints: • Gliding • Angular • Circumduction • Rotation ❖ Write a short note on adjunct and conjunct rotation. The rotation around a longitudinal axis is called rotation proper. It may be adjunct or conjunct. The adjunct rotation takes place actively by some muscles, while the conjunct rotation takes place passively due to configuration of the articular surfaces or tension of some ligaments. The differences between the adjunct and conjunct rotation are summarized in the following table: Adjunct Rotation • Active movement • Takes place by some muscles

Conjunct Rotation • Passive movement • Takes place due to configuration of articular surfaces or tension of some ligaments • Examples are rotation of hip, shoulder • Examples are rotation of knee joint during locking and atlantoaxial joints and unlocking

❖ Enumerate the factors maintaining stability of the joints. • Configuration of articular surfaces • Ligaments • Muscles • Atmospheric pressure

33

Muscles ❖ What is the muscle? AN3.1 The muscle is a contractile tissue (the muscle cells contain contractile proteins in their cytoplasm) that brings about the movements of the body. During contraction, the muscles shorten and convert the chemical energy into mechanical energy. ❖ What are the different types of muscles? AN3.1 There are three types of muscles: • Skeletal muscle • Cardiac muscle • Smooth muscle ❖ What are the properties of the muscles? AN3.1 The properties of muscles are as follows: • Irritability, i.e. they are sensitive to stimuli. • Contractility, i.e. they contract in response to stimuli. • Extensibility, i.e. they can stretch. • Elasticity, i.e. they can assume a desired shape after being stretched. ❖ Compare and contrast three types of muscles – skeletal, cardiac and smooth.  AN3.1 This is given in Table 33.1. TABLE 33.1 Comparison and Contrast Between Skeletal, Cardiac and Smooth Muscles

❖ Classify the various types of muscles according to their shape and direction of

their muscle fibres.  AN3.2 • When the direction of muscle fibres is parallel to each other, i.e. in line of pull ■ Strap muscles: These muscles are like long ribbons. Examples: Sternohyoid, sternothyroid and sartorius. ■ Fusiform muscles: These muscles are spindle shaped. Examples: Biceps femoris and biceps brachii. ■ Quadrilateral/quadrate muscles: These muscles are square shaped. Examples: Pronator quadratus and thyrohyoid. ■ Flat muscles: These muscles are in the form of thin sheets of fleshy fibres. Examples: Muscles of anterior abdominal wall such as external oblique, internal oblique, and transversus abdominis. • When the direction of muscle fibres is oblique to line of pull ■ Triangular, e.g. temporalis and adductor longus. ■ Pennate (feather-like): ■ Unipennate, e.g. extensor digitorum longus, flexor pollicis longus, palmar and plantar interossei. ■ Bipennate, e.g. rectus femoris, dorsal interossei and flexor hallucis longus. ■ Multipennate, e.g. deltoid (acromial part) and subscapularis. ■ Circumpennate, e.g. tibialis anterior. • When the direction of muscle fibres is circular, i.e. they are arranged circularly around the orifice, e.g. orbicularis oris and orbicularis oculi. • When the muscle fibres are arranged in a twisted manner, e.g. trapezius, pectoralis major and latissimus dorsi. • When the muscle fibres are arranged in two planes in different directions and cross, these are called cruciate muscles, e.g. masseter, sternocleidomastoid and adductor magnus. ❖ Enumerate the parts of a typical skeletal muscle. AN3.2 These are given in the following flowchart:

❖ What is the difference between the fleshy and tendinous parts of a muscle.  AN3.1 The differences are given in Table 33.2.

TABLE 33.2 Differences Between Fleshy and Tendinous Parts of a Muscle Fleshy Part • Highly specialized • Contractile • Vascular • Cannot withstand friction

Tendinous Part • Unspecialized • Noncontractile • Avascular • Can withstand friction

❖ Write a short note on a tendon. AN3.1 • The tendon is silvery white, fibrous, cord-like part of the muscle, which connects the muscle to the bone. It is made up of parallel, dense, collagen fibres. The tendon transmits forces of muscular contraction to the bone. It is attached to the periosteum and through it to the cortical bone through Sharpey’s fibres. • The fibres of tendon are twisted or plaited so that the force of muscle pull is distributed to all the points at the site of insertion. • The tendon is extremely powerful; for example, a tendon with cross-sectional area of 1 square inch can support a weight up to 9700–18,000 pounds. When tendon is subjected to sudden accidental traction at its insertional end, it may cause avulsion/fracture of the bone without being ruptured itself. This shows tremendous power of the tendon. ❖ What is ‘aponeurosis’? AN3.2 The aponeurosis is a silvery white, flat fibrous sheet that connects the muscle to the bone or deep fascia. It is made up of densely arranged collagen fibres. The aponeurosis provides a wider area of muscular attachment. ❖ Classify muscles according to the force of their action. AN3.3

Classification • Spurt muscles • Shunt muscles When muscle contracts, its force of contraction at the site of insertion is resolved into two components: (a) swing and (b) shunt. Swing component produces movement at the joint, while shunt component pulls the distal bone towards the joint. If the site of insertion is close to the joint and the site of origin is away from the joint, when the muscle contracts, its swing becomes more powerful than shunt. These muscles are called spurt muscles, e.g. brachialis. On the contrary, if the site of insertion is away from the joint and the site of origin is close to the joint, then shunt becomes more powerful than swing. Such muscles are called shunt muscles, e.g. brachioradialis.

❖ What are the types of muscles according to their action? AN3.2 A single muscle or a group of muscles alone cannot produce a desired movement at a particular joint. Any particular movement of a joint is brought about by a group of muscles, while the whole range of any movement is brought about by the smooth coordinated actions of different groups of muscles. These groups of muscles are as follows: • Prime movers (agonists): These are the muscles that initiate and bring about a desired movement. They are responsible for the specific movements. Examples: Biceps brachii and brachialis are prime movers to cause flexion at elbow joint. • Antagonists: These are the muscles that have opposite action to that of prime movers, i.e. they oppose prime movers or initiate and maintain a movement converse to that produced by agonists. Examples: Triceps brachii, which acts as antagonist during flexion of the elbow joint but helps in smooth flexion of the elbow joint by gradually relaxing itself. • Fixators: These are the muscles that stabilize the proximal joint/joints of a limb to provide a fixed base for the agonist muscle (prime mover) to act on a distal joint to bring about a desired movement. • Synergists: These muscles help the prime movers in bringing out the desired movement. They eliminate the undesired actions at proximal joint when the prime movers cross two or more joints. Examples: While making a tight fist, extensors of the wrist act as synergists to long flexor tendons. ❖ Write a short note on the nerve supply of a skeletal muscle. AN3.1 The nerves supplying skeletal muscles are somatic nerves and consist of three functional components. Motor fibres: They enter the individual muscle fibres at a point called motor end plate/neuromuscular junction. The nerve fibres are of following two types: ■ Alpha motor fibres arising from alpha motor neurons of anterior horn cells and supply the extrafusal muscle fibres. ■ Gamma motor fibres arising from gamma motor neurons of anterior horn cells and supply the intrafusal muscle fibres of muscle spindle (sensory end organ of skeletal muscle). Sensory fibres: ■ Myelinated fibres: They are distributed to muscle spindles, tendon and fascia of the muscle and carry exteroceptive and proprioceptive sensations. The fibres carrying pain sensations are free nerve endings around the muscle fibres, while the fibres carrying sensation of tension and degree of contraction, end in special sense organs called Golgi tendon organs. ■ Nonmyelinated fibres: Distribution of these fibres is not known as yet. Autonomic fibres: These fibres innervate the smooth muscle of the blood vessels present within the muscle. These fibres thus regulate the amount of blood flow

in the muscle. ❖ Write a short note on motor unit. AN3.1 It is a functional unit of muscle. It consists of a single alpha motor neuron and all the muscle fibres which it innervates (Fig. 33.1).

FIG. 33.1 Motor unit.

About 150 muscle fibres are innervated by a single alpha motor neuron (Fig. 33.1). The motor units are of two types: large and small. The large motor units supply large number of muscle fibres, i.e. 2000–3000. These units supply muscles responsible for coarse but powerful actions, e.g. gluteus maximus, gastrocnemius and deltoid. The small motor units supply small number of muscle fibres, i.e. 10–20. These units supply muscles responsible for fine and precise movements, e.g. muscles causing eye movements, finger movements and vocal cord movements. ❖ Write a short note on neuromuscular junction (or motor end plate). AN3.1 It is a junction between the nerve terminal and cell membrane (sarcolemma) of a muscle fibre. At neuromuscular junction, the axon loses its myelin sheath and breaks up into number of branches to supply the individual muscle fibres. Each branch becomes distended to form synaptic knob which contains large number of vesicles containing acetylcholine. The muscle fibre at this site also becomes specialized into a sole plate (Fig. 33.2). Here the muscle membrane, i.e. sarcolemma, is thrown into folds and contain receptors for acetylcholine.

FIG. 33.2 Neuromuscular junction.

The narrow space between the two plates – the synaptic cleft – is filled by a chemical substance called acetylcholine (a neurotransmitter). At the time of passage of impulse, the acetylcholine is broken down by an enzyme called acetylcholinesterase.

N.B. At neuromuscular junction, the impulse is transmitted from nerve to the muscle. ❖ Define a synovial bursa and mention its types. The synovial bursa (bursa = purse) is a closed sac of synovial membrane filled with a capillary film of a synovial fluid. The bursae are supported by an irregular connective tissue. They reduce friction between two mobile units to permit free movements.

Types According to the location, the synovial bursae are classified into the following types: • Subcutaneous, between skin and bone, e.g. prepatellar bursa and subcutaneous infrapatellar bursa. • Submuscular, between muscle and bone, e.g. bursa deep to medial head of gastrocnemius. • Subtendinous, between tendon and bone, e.g. trochanteric bursa of gluteus medius. • Subfascial, between fascia and bone. • Interligamentous, between ligaments. ❖ What are adventitious bursae? The adventitious bursae develop in the subcutaneous tissue over bony prominences where the skin is subjected to pressure and friction. Examples:

• Tailor’s ankle: A bursa develops over lateral malleolus in tailors who sit in cross-legged position while at work, thus bringing lateral malleolus in contact with the table leading to pressure and friction. • Weaver’s bottom: A bursa develops between gluteus maximus and gluteal tuberosity in weavers who sit for prolonged periods for weaving the cloth. • Porter’s shoulder: A bursa develops over clavicle in porters who hang heavy luggage on their shoulders.

34

Cardiovascular system ❖ Define cardiovascular system and mention its functions. AN5.1 The cardiovascular system consists of heart and blood vessels.

Functions • Distribution of nutrients and oxygen to all body cells • Distribution of hormones to target tissues • Thermoregulation • Removal of metabolic waste products and CO2 from all body cells ❖ Classify blood vessels. AN5.3 The blood vessels are classified into the following types: • Arteries • Arterioles • Capillaries and sinusoids • Venules • Veins ❖ What are the differences between the arteries and veins? AN5.3 The differences between the arteries and veins are shown in Table 34.1 and Fig. 34.1. TABLE 34.1 Differences Between Arteries and Veins Features Thickness of wall Valves Lumen Fibromuscular tissue Elasticity Internal elastic lamina Tunica media Thickest coat

Arteries Thick walled Absent Narrow (always patent) More More Well defined Thicker than tunica adventitia Tunica media

Veins Thin walled Present Larger (may be collapsed) Less Less Not seen Thinner than tunica adventitia Tunica adventitia

FIG. 34.1 Microscopic structure of a medium-sized artery and vein as seen in a cross-section: A, artery; B, vein. Note the lumen is surrounded by three concentric coats: tunica intima, tunica media and tunica adventitia.

❖ What are types of circulation? Describe each type in brief. AN5.2 There are two types of circulation: • Pulmonary • Systemic

Pulmonary circulation In pulmonary circulation, the blood is pumped by the heart into the lungs through pulmonary trunk for oxygenation and then the oxygenated blood is returned to the heart via pulmonary veins.

Systemic circulation In systemic circulation, the oxygenated blood is pumped by the heart to the entire body through arteries and then the deoxygenated blood is returned to the heart via veins. ❖ Discuss the portal circulation in brief. AN5.5 The portal circulation begins and ends with capillaries, i.e. blood passes through two sets of capillaries before it is drained into a systemic vein. The vessels connecting two sets of capillaries are called portal vessels. The portal circulation is seen in the liver, hypophysis cerebri, kidney and suprarenal gland, where it is termed hepatic portal circulation, hypothalamo-hypophyseal portal circulation, renal portal circulation and suprarenal portal circulation, respectively. ❖ Write a short note on hepatic portal circulation.  AN5.5 In hepatic portal circulation, the venous blood from capillary bed of GIT (also from spleen and pancreas) passes to the hepatic sinusoids (capillary bed) through the portal vein before it is drained into a systemic vein – the inferior vena cava (Fig. 34.2).

FIG. 34.2 Hepatic portal circulation.

❖ What are the various types of arteries? AN5.4 The arteries are of three types: • Elastic/conducting arteries, e.g. aorta, pulmonary trunk, common carotids, brachiocephalic trunk and subclavian arteries. • Muscular/distributing arteries (most common), e.g. branches of carotids, axillary, brachial, femoral and popliteal arteries. • Arterioles (smallest type of muscular arteries with diameter