Practical anatomy of the nerves and vessels supplying the head, neck and chest

Preface

Some apology may, perhaps, appear necessary from the author who has ventured to add one more to the long list of Manuals, Guides, and other anatomical works, which have been published from time to time, with a view of assisting the labors of the dissector.

I was long since impressed with the conviction, that a work like the present would form a useful companion to the practical anatomist ; and, as nothing which embraced my own views on the subject has hithero presented itself, I have at length been induced to make the attempt.

b

VI

•PREFACE.

The only recommendation which I can claim for this little book, is founded on its being the result of a tolerably active experience during some years in the dissecting room, and on the assurance that every part of it which may appear to deviate from ordinary anatomical precept, has been subjected to the careful and repeated test of the scalpel.

Every surgeon who has studied anatomy must retain -a lively impression of the difficulties, not to say vexations and disappointments which he encountered, whilst attempting to unravel the vessels and nerves of the head and neck : and as it has long been my daily occupation to assist the student in overcoming these difficulties, I have entertained the hope that I shall render myself still further useful, by presenting to him in a permanent form, that plan, order, and detail of dissection, which experience has taught me to be the most efficient, but which hitherto

PREFACE.

V1J lias been communicated to him, either by oral instruction, or by manual assistance.

In a part of the body so complicated as the head and neck, where the nerves and vessels cross and intersect each other in every direction, it will be found impossible to trace them by following the arrangement necessarily adopted in works of descriptive anatomy : because every description there laid down commences with the original trunks, and as they are all deeply buried beneath the sui'face, they are consequently the last parts to be laid bare by the knife of the dissector. Such a system is admirably adapted for a course of reading, as it admits of tabular classifications, and other methods of technical memory, well calculated to stamp the tedious detail on the wearied mind of the student : but, when he sits down to verify the knowledge thus acquired on the dead body itself, it becomes requisite that he should begin his dissection with the more superb 2

Vlll

PREFACE.

ficial parts, containing the smaller branches of the vessels and nerves; and, by tracing them, he is at length guided to the more deeply-seated structures, or the roots from which those branches emanate. He then discovers that the anatomical arrangement on the subject which he is dissecting, is the reverse of that system which he has so carefully studied in his book ; and, that in order to accommodate the one to the other, he must begin at the end of each chapter and read backwards.

With the intention of obviating these difficulties, I have followed up the dissection of the head, neck, and chest, by dividing it into regional portions, each forming a distinct section of the work, commencing with the subcutaneous structures, and proceeding to those which are more deeply seated.

In carrying out this plan, I have constantly held one main object in view; that of rendering the description of the vessels and

PREFACE.

IX nerves, as continuous, and as little disjointed, as was compatible with the possibility of bringing them all successively uuder inspection : and without entering into prolix description or minute anatomical detail, I have endeavoured to afford an easy and efficient plan of dissection, and to enable the student to employ his time and labour to the greatest advantage.

It may be asked why I have limited myself to the description of vessels and nerves, excluding the bones and muscles, a knowledge of which is equally important to the surgeon. I answer, that I was unwilling to increase the size, and consequently add to the expense of this work, by treating of subjects which have been so ably handled by other authors, as to leave little room for improvement either in arrangement or description. I have only attempted to fill up a deficiency where I conceived it to exist, and to supply what I considered to be a desi-

X

PREFACE.

deratum to the dissector. How far I have succeeded my readers must decide ; hut experience renders me confident in the expectation, that, by the method and order recommended in this work, the student will have the advantage of seeing every important part contained in the head, neck, and chest, during the dissection of a single subject; and, though he may sometimes feel disappointed, at leaving for a time a nerve or vessel which he has traced through a certain portion of its course, he will in the end be amply repaid by the economy thus insured in the materials of his labor, and the opportunity afforded of studying each part in its natural position, in relation to surrounding structures.

In conclusion, it will hardly be necessary to remind the student, that this volume can render him no service until he has made himself thoroughly acquainted with the bones and muscles of the different regions which

PREFACE.

XI are described, together with the viscera of the thoracic cavity. When thus prepared, and not till then, he may proceed with confidence to the dissection of the nerves and vessels, as they are arranged in the following pages.

X

SYNOPSIS.

Section I

Description of the Superficial Nerves ramifying on the Head and Neck.

PART i

The superficial branches derived from the cervical plexus, and emerging from under the posterior edge of the sterno-cleido-mastoideus muscle. The accessory nerve coming through the muscle.

Situation of muscles r 1

Superficial cervical nerves 2

Ascending set ib.

Auricular branch , 3

Transverse cervical branch ib.

Small occipital branch 4

[Spinal accessory nerve] ib.

[External jugular vein] 5

Descending set ib.

Supra-clavicular branches 6

Supra-acromial branches ib.

Sub-clavicular branches „ ib.

XIV

SYNOPSIS.

Part II

The branches of the facial nerve, as they pierce the parotid gland, and ramify over the face and cranium, p. 8.

Main trunk of the facial nerve 9

Digastric and stylo-hyoideal -branches ib.

Branches of junction ib.

Posterior auricular branch ib.

Temporo-facial nerve 10

Temporal branches ib.

Superior facial branches ib.

Middle facial branches ib.

Cervico-facial nerve 11

Inferior facial branch * 12

Descending facial branch ib.

Part II

The common carotid artery, with the internal jugular vein and pneumo-gastric nerve. — The transverse portion of the lingual nerve with its descending branch.

Parts contained in the anterior triangular space of the

neck 1 81

[Situation of muscles] ib.

Descendens lingualis nerve 22

Transverse portion of lingual nerve 23

Accessory nerve 24

Carotid sheath and its contents ib.

Common carotid artery 25

i

Part III

The course of the external carotid artery, p. 27.

XVI

SYNOPSIS.

Part IV

The branches of the external carotid — The superior thyroideal, facial, sterno-mastoidean, posterior aural, and temporal branches, traced to their termination.— The lingual, occipital, and internal maxillary branches traced until they become concealed by muscles not yet removed.

Branches of the external carotid artery 29

Superior thyroideal artery 30

Hyoideal branch ib.

Laryngeal branch 31

Muscular branches ib.

Glandular branches ib.

Lingual artery — commencement of. ib.

Facial artery 32

[Facial vein] 34

Inferior palatine branch 35

Glandular branches , ib.

Submental branch ib.

[Mylo-hyoid nerve] 36

Labial branch ib.

Inferior coronary branch ib.

Superior coronary branch ib.

Lateral nasal branch . . 37

Angular branch ib.

Muscular branches '. 38

Sterno-mastoidean artery 39

Occipital artery — commencement of ib.

Meningeal branch 40

Posterior aural artery ib.

Ascending pharyngeal artery— origin of — 41

Internal maxillary artery— commencement of ib.

SYNOPSIS.

XVII

Temporal artery 41

Transverse facial branch .. 42

Small branches ib-

Temporo-frontal branch 43

Temporo-occipital branch ib.

Section III

Description of Vessels and Nerves ; brought into View by detaching some of the Muscles between the Os Hyoides and the Lower Jaw, and removing the Zygoma with the Ascending Ramus of the Inferior Maxillary Bone.

PART i

The course and distribution of the lingual artery, with the distribution of the lingual and gustatory nerves, p. 45.

Lingual nerve — distribution of 47

Gustatory nerve — distribution of ib.

Lingual artery — distribution of 43

Hyoideal branch ib.

Dorsal branches 49

Sublingual branch 'ib.

Ranine branch ib.

Part II

The course and distribution of the internal maxillary artery, together with the second and third division of the fifth pair of nerves, p. 50.

Internal maxillary artery 52

Spheno-spinal branch .. 54

Dental branch 55

SYNOPSIS.

Muscular branches 56

[Spheno-maxillary fossa] 57

Superior dental branch 58

Spheno-palatine branch 50

Pterygoid branch ib.

Infra-orbitar branch ib.

Palato-maxillary branch ib.

Second division of the fifth pair of nerves 60

Superior dental branch 61

Infra-orbitar branch.. .., ib.

Malar twig ib.

Branches of junction with Meckel’s ganglion ib.

Meckel’s ganglion 02

Spheno-palatine nerve ib.

Palato-maxillary nerve 63

Pterygoid nerve ib.

Inferior branch ib.

Superior branch 64

Third division of the fifth pair of nerves 65

Pterygoid branches GO

Temporal branches ib.

Masseteric branches ib.

Buccal branches ib.

Gustatory branch 67

Dental branch 68

Mylo hyoid twig ib.

Auricular branch ib-

SYNOPSIS.

XIX

Section IV

Description of Vessels and Nerves lying deeply seated upon the Cervical Vertebra;, immediately below the Base of the Skull, to the outer Side of the Pharynx ; and brought into mew by removing the Lower Jaw and Styloid Muscles.

PART i.

The ascending pharyngeal, and internal carotid arteries, passing upwards towards the base of the skull.

Ascending pharyngeal artery Internal carotid artery

PART II.

The glosso-pharyngeal, pneumo-gastric, spinal accessory, and lingual nerves, descending from the posterior lacerated and condyloid foramina, and connected with the first cervical ganglion.

Reference to foramina at the base of the skull 74

Internal jugular vein 75

Glosso-pharyngeal nerve 76

Glossal branch 7 7

Pharyngeal branches ib.

Carotid filaments 78

Pneumo-gastric nerve — cervical portion of ib.

Pharyngeal branch 79

Superior laryngeal branch ib.

Small filaments 80

Cardiac branches ib.

XX

SYNOPSIS.

Spinal accessory nerve 81

Pharyngeal branch ib.

Muscular branches 82

Lingual nerve ib.

Section V

Description of some of the Parts Internal to the Cranium ; viz. the Vessels of the Dura Mater — the Base of the Brain — the Arteries of the Brain — the Origin of the Cerebral Nerves.

PART i.

The dura mater as it appears on removing the calvarium — the vessels ramifying on its surface.

The dura mater 86

Meningeal arteries ib.

Longitudinal sinus 87

PART II.

The removal of the brain with the vessels and nerves necessarily divided in so doing.

Directions for removing the brain 88

Nerves and vessels connecting the brain to the base of

the skull ib.

First pair of nerves ib.

Second ditto 89

Carotid arteries ib.

Infundibulum ib.

Third pair of nerves ib.

Fourth ditto ib.

XXI

Fifth pair of nerves 69

Sixth ditto

Seventh and eighth ditto

Ninth and tenth ditto 'b-

Spinal-accessory nerves

Eleventh pair of nerves ib.

Vertebral arteries 'b.

PART III. Outline of the inferior surface of the brain

The base of the brain 91

Division of the cerebral lobes ib.

Cerebellum 92

Pons Varolii ib.

Crura cerebri ib.

Tractus opticus ib.

Commissure of the optic nerves ib.

Tuber cinereum ib.

Infundibulum -. ib.

Eminentise mammillares ib.

Substantia perforata ib.

Medulla oblongata ib.

Corpora pyramidalia 93

Corpora restiformia ib.

Corpora olivaria ib.

Tractus respiratorius ib.

Fourth ventricle ib.

Calamus scriptorius ib.

c xxii

SYNOPSIS.

Part IV

Course and distribution of the internal carotid and vertebral arteries within the cranium.

Internal carotid artery 95

Ophthalmic branch — commencement of ib.

Posterior communicating branch ib.

Anterior cerebral artery 96

Transverse communicating branch ib.

Middle cerebral artery ib.

Branch to choroid plexus 97

Vertebral artery ib.

Posterior spinal branch 98

Anterior spinal branch ib.

Inferior cerebellar artery 99

Basilar artery ib.

Auditory branch 100

Superior cerebellar artery ib.

Posterior cerebral artery ib.

Circle of Willis 101 part v.

Origin of the cerebral nerves, and the course which they take, until they leave the cavity of the cranium, or become concealed by passing between layers of the dura mater.

Origin of the cerebral nerves 102

1. — The olfactory ib.

2. — The optic 104

3. — The common oculo-muscular 105

4. — The inner oculo-muscular ib.

5. — The trigeminal 106

SYNOPSIS.

XX1U

6. — The outer oculo-muscular 106

7. — The auditory 107

8. — The facial ib.

9. — The glosso-pharyngeal 108

10. — The pneumo-gastric 109

[Tractus respiratorius] ib.

[Spinal accessory nerve] ib.

1 1 . — The lingual 110

Section VI

Description of the Third, Fourth, Fifth, and Sixth Pairs of Nerves, where they are enclosed between Layers of the Dura Mater, previous to their exit from the Cranium.

PART i. The semilunar ganglion of the fifth pair

Situation of the semilunar ganglion 113

First division ib.

Second division ib.

Third division ib.

Motor and sentient portions of the fifth 114

[Pterygoid branch from Meckel’s ganglion] 115

PART II. The cavernous sinus and its contents

Situation of cavernous sinus 115

Contents of cavernous sinus 116

Position of internal carotid artery ib.

Position of third, fourth, first division of fifth, and sixth pair of nerves 1 1 7

XXIV

SYNOPSIS.

Section VII

Description of the Nerves and Vessels situated within the Orbit.

PART I.

Distribution of the third, the fourth, the ophthalmic division of the fifth, and the sixth pair of nerves.

Contents of the orbit 120

Fourth pair of nerves 122

Ophthalmic division of the fifth pair ib.

Supra orbitar branch ib.

Trochlear twig 123

Lachrymal branch ib.

Nasal branch ib.

Lenticular twig . 124

Ciliary twigs ib.

Internal nasal twig ib.

External nasal twig ib.

Sixth pair of nerves 125

Lenticular twig ib.

Third pair of nerves 126

Superior branch ib.

Inferior branch ib.

PART II.

The lenticular ganglion and its branches.

Situation of lenticular ganglion 127

Ciliary nerves ib.

SYNOPSIS.

XXV

PART III. Course and distribution of the ophthalmic artery

Course of the ophthalmic artery 128

Lachrymal branch 129

Central artery of the retina ib.

Supra-orbitar branch 130

Short ciliary arteries ib.

Long ciliary arteries 131

Muscular branches 132

Anterior and posterior ethmoidal branches ib.

Superior and inferior palpebral branches ib.

Terminating branches 133

SECTION VIII. Description of the Cerebral Sinuses

General description of the sinuses 135

The great sinuses 136

Longitudinal sinus ib.

Straight sinus ib.

Torcular Herophili ib.

Lateral sinuses 137

The small sinuses ib.

Inferior longitudinal sinus ib.

Occipital sinus ib.

XXVI

SYNOPSIS.

Cavernous sinuses 138

Anterior and posterior clinoid sinuses ib.

Circular sinus of Ridley ib.

Superior and inferior petrosal sinuses ib.

Transverse sinus ib.

PART i

General remarks — the sub-occipital nerve —the seven cervical nerves, p. 140.

General arrangement of cervico-spinal nerves 141

The sub-occipital nerve ib.

Anterior branch ib.

Posterior branch 142

The seven cervical nerves — general description .... ib.

Part II

The three superior cervical nerves, forming the cervical plexus, by the union of their anterior branches.

First cervical nerve 144

Anterior branch ib.

Posterior branch ib.

Second cervical nerve 145

Anterior branch ib.

Posterior branch ib.

Third cervical nerve 146

Anterior branch ib.

Posterior branch ib.

[Phrenic nerve] ib.

SYNOPSIS.

XXVII

Part III

The four inferior cervical nerves, and the first dorsal, forming, by the union of their anterior branches, the axillary plexus.

The four lower cervical nerves 147

Anterior branches ib.

[Axillary plexus] 148

[External respiratory nerve] ib.

Posterior branches 149

First dorsal nerve ib.'

Section X

Description of Parts brought into view by raising the Sternum. — The Arch of the Aorta, and its relative posi- ' tion with regard to the Vessels, Nerves, and other structures, situated above the Pericardium and between the two Pleural Cavities.

PART i. The arch of the aorta

Arch of the aorta 151

Relative position of the arch 152

Part II

The three great vessels given off by the arch of the aorta.

Arteria innominata 155

Left common carotid 156

Left subclavian 157

XXV111

SYNOPSIS.

Section XI

Description of the Course of the Subclavian Artery and Vein.

PART i.

Preliminary remarks.

Subclavian artery divided into three portions 159

PART II.

The first portions of the right and left subclavian artery ; together with the passage of the pneumo-gastric and phrenic nerves into the chest.

First portion of the subclavian * 160

Right side ib.

[Pneumo-gastric nerve] . 162

[Right side] •. ib.

[Recurrent laryngeal branch] ib.

[Phrenic nerve] .. 1G4

PART i

The branches arising from the first portion of the subclavian artery — the Vertebral — the Thyroid Axis — the Internal Mammary — the Superior Intercostal,

Vertebral artery 170

Branches of the vertebral 171

Thyroid axis 172

Inferior thyroideal branch ib.

Ascending cervical branch 173

Transverse cervical branch ib.

Superficial cervical ib.

Posterior scapular ib.

Supra-scapular branch 174

Internal mammary artery 175

Intercostal branches 176

Comes nervi phrenici ib.

Mediastinal branches 177

Intercosto-phrenic branch ib.

Abdominal branch ib.

Superior intercostal artery ib .

XXX

SYNOPSIS.

Part II

The single branch given off from the second or third portion of the subclavian trunk ; viz. The Deep Cervical Artery, p. 178.

Section XIII

The Course of the Phrenic and Pneumo-gastric Nerves as they pass through the Chest, and their ultimate Distribution.

PART i.

The phrenic nerve, p. 180.

PART II.

The pneumo-gastric nerve.

Course of pneumo-gastric nerve 181

CEsophageal plexus 182

Bronchial plexus 183

Section XIV

Description of the Dorso -spinal Nerves, their Origin, Course, and Distribution.

Dorso- spinal nerves — general description 185

Posterior branches 186

Anterior branches : ib.

SYNOPSIS.

xxxi

Section XV

Description of that Portion of the Sympathetic or Ganglionic System of Nerves belonging to the Head, Neck, and Chest.

PART i.

General outline of the sympathetic nerve, p. 191,

PART II.

Ganglia situated about the cranium and face. p. 194.

Ganglion of Meckel 195

Lenticular ganglion ib.

Ganglion of Cloquet ib.

Otic ganglion 196

Section XVI

Description of the Descending Thoracic Aorta, and the Branches which it gives off.

[Situation of the primitive vessels at the base of the

heart] 211

Descending thoracic aorta 213

Bronchial branches 214

(Esophageal branches 215

Intercostal branches ib.

SYNOPSIS.

XXX111

Section XVII

Description of the Vena Azygos, and Vena Azygos Minor .

Vena azygos 219

Vena azygos minor 220

Superior intercostal vein — right side ib-

Superior intercostal vein — left side 221

Intercostal veins ib.

[Thoracic duct] ib.

Section XVIII

Description of the Vessels and Nerves supplying the Posterior Regions of the Head, Neck, and Trunk.

PART i

The vessels and nerves brought into view during the dissection and removal of the two first layers of muscles.

Cutaneous nerves of the back 224

Occipital nerve .- 225

Occipital artery ib.

Accessory nerve ib.

Superficial cervical artery ib.

Posterior scapular artery 226

XXXIV

SYNOPSIS.

Part II

The vessels and nerves which are deeply seated among the muscles of the back.

Occipital artery 272

Posterior divisions of the cervical nerves 228

Occipital nerve ib-

Vertebral artery 229

Posterior division of the sub-occipital nerve ib.

Posterior divisions of the dorsal and lumbar nerves . . ib. Posterior branches of the intercostal and lumbar arteries ib.

Appendix

In 'which is described the Best Method of tracing those Nerves and Vessels, the Dissection of which was not completed in the previous part of the Work. p. 233.

PART i.

The dissection of the laryngeal nerves, p. 234.

PART II.

Dissection of the terminating branches of the internal maxillary artery, — the second division of the fifth pair of nerves, and the branches from Meckel’s ganglion, as they pass through the different canals and foramina which communicate with the spheno-maxillary fossa, p. 23d.

SYNOPSIS.

XXXV

Part I

The superficial branches derived from the cervical plexus, and emerging from under the posterior edge of the sterno-cleido-mastoideus muscle. The accessory nerve coming through the muscle.

According to the plan laid down in the table of situation of contents, we shall first examine the superficial m,lsUescervical nerves ; and before the student commences his dissection, he should consider the relation of the cervical region to the head and chest.

He should likewise recall to his memory the coverings of these parts, and trace the outline of the muscles beneath ; directing his attention more

B

Superficial nerves.

Ascending

set.

particularly to the position of the sterno-cleido-mastoideus as it crosses the neck obliquely, and divides that region into two triangular spaces which are respectively terminated, in front by the median line from the chin to the sternum, and behind by the edge of the trapezius muscle.

The superficial nerves of the neck are derived from the cervical plexus, which is formed by the junction of the three first cervico-spinal nerves*, and lies under the sterno-mastoid muscle : they are seen emerging from beneath the posterior edge of the sterno-mastoideus, and may be divided into an ascending and descending set ; the former turning over the edge of the muscle to gain its superficial surface, and taking their course under the platysma towards the head and face ; the latter passing downwards towards the chest and shoulder.

The ascending set are principally derived from the second cervical nerve, and may be found by cutting down on to the posterior edge of the sterno-mastoideus about its middle, where they

* In speaking of the cervical nerves, we shall consider them as seven in number, exclusive of the sub-occipital : the first cervical nerve leaving the spinal canal between the atlas and dentata, the seventh between the last cervical and first dorsal vertebra.

OF TIIE HEAD AND NECK.

will be seen turning round the muscle to gain its superficial surface. We distinguish three branches by name ; and the common trunk, from which they are derived, may, by turning up the edge of the muscle, be traced upwards to its root. Of these three branches, one is found to pass directly upwards to the ear, another upwards and forwards towards the chin, while the third takes a direction •

upwards and backwards to the occiput.

The first and most considerable is the auricular, Auricular which ascends vertically between the platysma and sterno-mastoid muscle, till it reaches the parotid gland where it divides into several branches. Some of these sink into the gland, and join with the facial ; other larger ones pass to be distributed to the auricle of the ear, while one or two smaller twigs supply the skin over the mastoid process and immediately behind the auricle.

The second nerve is called the transverse cer- Transverse vical, which turns over the edge of the sterno- branch.1 mastoid, and, dividing into several branches, ramifies over the side of the neck, principally taking a direction upwards and inwards, some of the twigs passing on to the face. It is situated under the platysma, which, together with the skin, it supplies, and forms junctions with the descend^- ing facial. We sometimes find it accompanied by f

Small occipital branch.

Spinal-ac-

cessory

nerve.

two or three smaller filaments which are distribilled in a similar manner.

The third and last branch to be described, is the small occipital. This, the smallest of the three, passes obliquely upwards and backwards along the posterior edge of the sterno-mastoid, and on reaching the head, divides into twigs which supply the origin of the occipito-frontalis, and ramify on the lateral part of the occiput.

In the early part of this dissection, the spinal-accessory nerve will probably have become exposed where it emerges from the sterno-mastoid muscle, and is freely connected with the cervical nerves ; more particularly with the small occipital, which, crossing over it, forms so intimate a union as to give the appearance of being one of its branches. As the accessory comes from the cavity of the cranium, a more particular description of it must be given at a future period ; as regards its situation in the region which we are now exploring, it will merely be necessary to observe, that it emerges from the edge of the stemo-cleido-mastoideus about one-third below the insertion of that muscle, and passes obliquely downwards and backwards, until it becomes lost to view under the edge of the trapezius, to the substance of which it is finally distributed.

OF THE HEAD AND NECK.

Whilst we are tracing the ascending set of External

.1 , i jugular vein.

nerves, we can hardly fail to notice the external jugular vein descending along the side of the neck and crossing the sterno-mastoid muscle.

It will be seen to emerge above, from the parotid gland where it is formed by the junction of the temporal, internal maxillary, and posterior aural veins. Just below the angle of the jaw it is generally connected by a pretty considerable branch to the deep-seated or internal jugular. It then passes downwards and rather outwards, between the platysma and sterno-cleido-mastoideus, and, having reached the clavicle, sinks beneath it just at the outer edge of the last-mentioned muscle, and enters the subclavian vein. The origin of the vessel is subject to many deviations ; its size varies in different persons, and it sometimes terminates by dividing into two trunks, which separately enter the subclavian. The external jugular not unfrequently takes its course along the inner margin of the sterno-mastoid muscle, instead of crossing it, and occasionally a vein is found in each situation.

We shall now proceed to the dissection of the Descending descending superficial cervical nerves, or those 3etofuerveswhich, emerging from the posterior edge of the sterno-mastoideus, pass downwards andbackwards and occupy the triangular space formed by that

Supra- clavicular branches.

Supra-

acromial

branches.

Sub-clavicular filaments.

muscle, the trapezius and the clavicle. They are brought into view hy dissecting along the posterior edge of the stemo-mastoid, and clearing away the lymphatic glands, fat, and dense cellular membrane in which their filaments are involved. They will then he found coming from under the muscle, just below that point where the transverse cervical and auricular, formerly mentioned, are seen mounting upon its surface. They consist of from two to four branches derived chiefly from the third cervical nerve, and receive a filament or two from the second. They almost immediately divide into a number of branches which pass downwards with different degrees of obliquity.

The most internal, the supra-clavicular, will be seen descending over the middle of the clavicle, and passing along the origin of the stemo-cleido-mastoideus ; others bearing the same name, cross the bone nearer to its scapular extremity ; while the more external or supra- acromial pass over the anterior portion of the trapezius to reach the acromion. They are finally distributed to the skin of the shoulder and upper region of the chest, being therefore superjacent to the deltoid and pectoralis major muscles. Derived from this set of nerves, some smaller and more deeply-seated filaments can he traced, running under the clavicle

OF THE HEAD AND NECK.

and terminating in the omo-hyoideus, serratus anticus and subclavius muscles. These may he termed subclavicular branches.

The dissection of these nerves through the triangular space, is rendered excessively tedious and difficult by their innumerable connections and the quantity of glands, fascia, and cellular membrane with which they are surrounded. At the lower part, they are involved with the superficial branches of the subclavian artery, and the termination of the external jugular vein. The student is recommended to trace their origins as far as possible underneath the sterno-mastoid, and to clear the edge of that muscle, which will facilitate its removal hereafter, in order to display the original trunks of the cervical nerves, and the remaining branches they give off. In doing this, he will come down upon the ascending cervical artery sent off by the subclavian*.

* Although forming a deviation from the plan laid down in the table of contents, the student is recommended to examine the parts contained in the small triangular space, bounded by the clavicle with the omo-hyoideus and sterno-mastoideus muscles, before he proceeds to the nerves of the face. He will thus embrace the most favourable opportunity of dissecting the terminating portion of the subclavian artery, and judging of its relative position with the sealenic muscles, the accompanying vein, and the lower cervical nerves, before the upper extremity is removed