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Pejitland s Sttidents Manuals,

MANUAL OF ANATOMY.

NUNQUAM ALIUD NATURA, ALIUD SAPIENTIA DIGIT.

MANUAL

PRACTitAL' Anatomy

BY

D. J. CUNNINGHAM,

M.D. (eDIN. ET DUDL.)i D.SC, LL.D., D.C.L. (oXON.). F.R.S.,
PROFESSOR OF ANATOMY AND CHIRURGERV, UNIVERSITY OF DUBLIN.

VOLUME SECOND.
THORAX; HEAD AND NECK.

SECOND EDITION.

ILLUSTRATED WITH ENGRAriXGS.

EDINBURGH AND LONDON:

YOUNG J. PENTLAND.
1896.

EDINBURGH : PRINTED FOR YOUNG J. PENTLAND, II TEVIOT PLACE, AND
38 WEST SMITHFIELD, LONDON, E.C., BY K. AND E. CLARK, LIMITED.

A II rights reserved.

PREFACE.

In carrying out the revision of the text for this edition the
author has availed himself of many valuable suggestions
from brother anatomists. More particularly is he indebted
iri this respect to Professor Birmingham, of the Catholic
University in Dublin ; Professor Wardrop Griffiths, of
University College, Leeds ; and to Professor Fawcett, of
University College, Bristol. He has also to express his
indebtedness to Mr. E. B. Knox, Student in the School
of Physic, for the great assistance he has rendered in con-
nection with the correction of the proof-sheets.

Trinity College, Dublin,
May 1896.

C O iN T E N T S.

THORAX.

Introductory, .

PAGE
I

Thoracic Wall,

Thoracic Cavity,

II

The Mediastinum,

21

The Lungs,

22

The Pericardium,

32

The Heart and its Vessels,

37

The Aorta,

62

Trachea and Bronchi,

74

Thoracic Duct,

83

Thoracic Wall,

S9

Thoracic Joints,

94

HEAD AND NECK.

Scalp, .

Removal of the Brain,

Dorsal Aspect of the Trunk,

Side of the Neck,

Middle Line of the Neck,

Root of the Neck,

Dissection of the Face,

Temporal and rTERYGO-^Lwii.LARY Regions,

lOI

no

184
217
228

257
297

CONTENTS.

Submaxillary Region, . . . .

Deep Dissection of the Neck,

Structures in the Lateral Part of the Middle

Cranial P'ossa, .....
The Orbit and Structures passing through the

Sphenoidal Fissure, ....

Prevertebral Region, ....

Vertebral and Cranio-Vertebral Articulations,
Mouth and Pharynx, ....

Carotid Canal and Superior Maxillarv Nerve, .
Otic Ganglion, .....

Nasal Foss^, ......

Spheno-Palatine Ganglion, ....

The Larynx, ......

The Tongue, ......

THE BRAIN.

General Appearance of the Brain,

Membranes and Blood-Vessels,

Base of Brain, .....

The Cerebrum, ....

The Cerebral Hemispheres,

Cerebral Lobes and Fissures,

Corpus Callosum, ....

Lateral Ventricle, ....

The Fornix, .....

The Velum Interpositum,

Optic Thalamus, ....

The Mesencephalon, ....

Basal Ganglia of the Cerebral Hemispheres,

Medulla Oblongata, ....

Pons Varolii, .....

The Cerebellum, ....

CONTENTS.

IX

Cereiiki-lar Pkouncles,
Fourth Ventricle,

PAGE
580

THE AUDITORY APPARATUS.

The External Ear, .

5S7

The Tympanic Cavity,

590

Memhrana Tympani, .

594

Auditory Ossicles,

596

Tympanic Muscles,

59S

The Eustachian Tube,

599

The Vestibule,

599

Semicircular Canals,

601

The Cochlea, .

602

THE EYEBALL.

General Structure, .

610

The Sclerotic,

611

The Cornea, ....

613

The Vascular Tunic,

614

The Retina, ....

619

The Vitreous Body, .

621

Cry.stalline Lens,

624

Chamuers of the Eyehall, .

625

Index,

629

LIST OF ILLUSTRATIONS.

Pi.ATF. II. The head of an adult female, 35 years of age, in
which the cerebrum is exposed in situ. Bars
of bone are left along the lines of the cranial
sutures, and also along the line of the temporal
ridge. (From a model), . . facing page 520

FIG. PAGE

167. Diagram of one of the upper intercostal nerves, . 6

168. Posterior aspect of the anterior wall of the thora.x and upper

part of the abdomen. (Luschka), ... 9

169. Horizontal section of the thorax of a man aged 57, looked

at from above. (Symington), . . . .12

170. Dissection to expose the anterior mediastinum, . . 14

171. Diagram of the two pleural sacs, . . . .16

172. Tracing from a transverse section through the frozen chest, 19

173. Diagram to illustrate the amount of outward deviation of

the left pleural sac. (Gegenbaur), . . .20

174. The lungs. (Gegenbaur), . . . .24

175. Sagittal section through the thoracic cavity, . 2S

1 76. Dissection to show the abdominal viscera which lie in rela-

tion to the under surface of the diaphragm. (Braune), . 33

177. The relation of the heart to the mesial plane. (Braune), . 38

178. Diagram to show the position of the heart in relation to the

anterior chest wall. (Braune), . . . -39

179. Anterior aspect (facies sternalis) of the heart. (Gegenbaur), 40
I So. Posterior surface (facies diaphragmatica) of the heart.

(Gegenbaur), . . . . . .41

181. Transverse section through the auricular part of the heart, 42

LIST OF ILLUSTRATIONS.

FIG.

182. Diagram to show the manner in which the right auricle

should be opened, .....

183. Diagram to show the manner in which the right ventricle

should be opened, ....

184. Transverse section through the ventricular part of the heart

(Luschka), .....

185. Interior of the right auricle and right ventricle. (Luschka)

186. Heart of a seven months' foetus. (Gegenbaur),

187. Section through the basal part of the heart,

188. Horizontal section of the thorax of a man aged 57 years

looked on from above. (Symington),

189. Diagram to show the manner in which the left auricle and

left ventricle should be opened, .

190. Section through the ventricular portion of the heart near

the apex, .....

191. Transverse section through the thorax at the level of the

fourth dorsal vertebra, ....

192. Section through the mediastinal sjDace at the level of the

fifth dorsal vertebra, ....

193. Transverse section through the superior mediastinum at the

level of the third dorsal vertebra,

194. Diagram of the base of the ventricular portion of the heart,

195. Tracing of a section through the posterior mediastinum at

the level of the eighth dorsal vertebra, .

196. Tracing of a section through the lower part of the posterior

mediastinum, where its anterior wall is formed by the
diaphragm, .....

197. Dissection of the roots of the lungs, the pericardium, the

pneumogastric nerves, etc., from behind,

198. Schema of the branching of the two bronchi. (Gegenbaur)

199. Diagram of the azygos and innominate veins,

200. Section through the scalp and cranial wall, .

201. Superficial nerves on the side of the neck and back of the

scalp. (Hirschfeld and Leveille),

202. Diagrammatic section through the meninges of the brain

(Schwalbe), .....

203. Diagrammatic section through an arachnoidal villus

(Schwalbe), .....

204. The dura mater and the superior longitudinal sinus, etc.,

205. The dura mater. (Luschka),

LIST OF II.LUSI'KAJIONS.

FIG.
206.

207.

20S.

209.
210.

213.
214.
215.

216.

217.
218.

219.
220.

221.
222.

223.
224.

225.

226.

227.

22S.

Diagramii\atic coronal section through the posterior part of

the cranium with the dura mater in position. (Luschka), 122
Aperture between the dorsum selhe and the anterior con-
cave free margin of the tentorium. (Ilirschfeld and
Leveiili'). • • • '23

The cranial nerves leaving the cranial cavity and the circle

of Willis, . . . . .124

The blood sinuses of the dura mater. (Ilenle), . . 129

(i) Pituitary body ; (2) in mesial section ; {3) in horizontal

section. (Schwalbc), ..... 132

Skin incisions for the dissection of the dorsal aspect of the

trunk, . . . . .134

Superficial dissection of the posterior aspect of the neck and

head. (Luschka), . . . . .136

Diagram to show the connections of the lumbar fascia, . 143
Ligamentum nucha\ (Cruveilhier), . . .150

Transverse section through the spinal cord and its mem-
branes. (Schwalbe), ..... 166

Lateral view of the spinal cord, dura mater, etc. (Ilirsch-
feld and Leveille), . . .168
Segment of spinal cord ; anterior aspect. (Schwalbe), . 171
Sacral canal opened up from behind to show the sacral nerve
roots and the membranes in relation to them. (Modified
from Testut), . . . . . .172

Segment of spinal cord ; lateral aspect. (Schwalbe), . 177

Cross section of the dorsal part of the spinal cord. (Gegen-

baur), ....... 179

Sections through difterent parts of the cord. (Schwalbe), . iSi
Transverse section through the upper cervical part of the
cord of a full-time fcetus treated by the Pal-Weigert
process, . . . . . . . 1S3

Skin incisions for dissection of the triangles of the neck, . 1S6
.Superficial nerves on the side of the neck and back of the

scalp. (Ilirschfeld and Leveille), . . . 1S9

Diagrammatic representation of a transverse section through
the neck at the level of the isthmus of the thyroid body.
(Treves), . . . . .192

Triangles of the neck. (Delepine), . . 196

Dissection of the lower part of the posterior triangle of the

neck, ....... 200

Diagram of the brachial plexus, .... 205

XIV

LIST OF ILLUSTRATIONS.

FIG. PAGE

229. Triangles of the neck. (Delepine), . . . 210

230. Deep aspect of carotid vessels, with the intercarotic body

and the nerves in relation to them. (Luschka), . . 214

231. Dissection of the middle line of the neck, . . . 219

232. Hyoid bone and larynx. (Gegenbaur), . . . 223

233. Diagram of the subclavian artery and its branches. (Turner), 231

234. Dissection of the neck. The sterno-mastoid and the inner

half of the clavicle have been removed. (Luschka), . 238

235. Diagram of the cervical plexus and the ansa hypoglossi, . 240

236. Transverse section through the neck, just below the upper

border of the thyroid cartilage and the bifurcation of the

common carotid artery, ..... 245

237. Transverse section through the neck at the level of the

cricoid cartilage, ...... 246

238. Diagram of the external carotid artery and its branches, . 248

239. Parotid gland. (Gegenbaur), .... 261

240. Transverse section through the head at the level of the hard

palate, ....... 262

241. Diagram of certain of the muscles of the face, . . 269

242. Diagram illustrating the arrangement of the fibres of the

buccinator muscle, . . . . .271

243. Diagram of the orbicularis oris muscle, . . . 272

244. Diagram of the facial nerve, .... 276

245. Diagram of the sensory branches of the trigeminal nerve to

the face, ....... 280

246. The pinna, ....... 285

247. Diagram of the structure of the eyelids, . . . 289

248. Dissection of the eyelids to show the septum orbitale and

the tendinous expansion of the levator palpebrse

superioris. (Testut), ..... 290

249. Lachrymal apparatus. (Gegenbaur), . . . 293

250. The inner wall of the orbit and the tensor tarsi muscle.

(Luschka), ...... 294

251. Cartilages of the nose, ..... 296

252. Dissection of the pterygo-maxillary space, . . . 301

253. Diagram of the different positions occupied by the head of

the mandible and the intei^articular cartilage as the mouth

is opened and closed. (After Merkel), . . . 307

254. Diagran of the inframaxillary division of the fifth cranial

nerve, ....... 309

255. Dissection of the submaxillary space, . . . 316

LIST OF ILLUSTRATIONS, XV

FIG. PAGE

256. Coronal section llirouyh llic mouth and suljniaxillary

regions, ....... 317

257. Coronal section tlirouyh the lore-part of the mouth and

submaxillary region, ..... 320

25S. Diagram of the relation of parts in the jugular foramen, . 331

259. Diagram of the tympanic nerve, .... 334

260. Section through the cavernous sinus. (Modi lied from

Merkel), ....... 346

261. Diagram of the ophthalmic division of the Idtli nerve.

(Prof. Thane, Qiiaiii's Aiia(oiiiy), . . . 355

262. Diagramof the superior oblique muscle. (Hermann Meyer), 358

263. Dissection of the eyeball showing the distribution of the

ciliary nerves and vessels, .... 361

264. Diagram of the ophthalmic artery and its branches. (After

Quain and Meyer, modified), .... 363

265. Diagram of the orbital cavity and of the origin ol the ocular

muscles, etc., ...... 366

266. Diagram of the third nerve and ciliary ganglion. (Prof.

Thane, Quam's Anatomy), .... 367

267. Dissection of the capsule of Tenon from the front, . . 370

268. Prevertebral region. (After Luschka, modified), . 375

269. The intertransverse muscles, .... 376

270. Coronal section through the bodies of two cervical vertebrce, 379

271. Mesial section through the basilar process of the occipital

bone, the atlas, and the axis. (Luschka), . . 3S3

272. Ligaments on the anterior wall of the spinal canal which

connect the occipital bone, the atlas, and axis, etc.
(Luschka, modified), ..... 385

273. Transverse section through the atlas and odontoid process.

(Cruveilhier, modified), ..... 387

274. Mesial section through the nose, mouth, pharyn.x, and

larynx. (Gegenbaur), ..... 390

275. Anterior part of the floor of the mouth, . 392

276. Isthmus of the fauces, ..... 393

277. Profile view of the phar)'nx to show the constrictor nuiscles.

(Turner), . . . . -397

278. Antero-posterior section through the nose, mouth, and

pharynx, a little to the left of the mesial plane, . . 401

279. Transverse section through the neck at the level of the

upper border of the thyroid cartilage, . . . 403

2S0. Diagram of the superior maxillary nerve. (Thane), . 412

XVI

LIST OF ILLUSTRATIONS.

FIG.

281. Antero-posterior section through the nose, mouth, and

pharynx, .......

282. Coronal section through the nasal cavities opposite the crista

Galli of the ethmoid bone ; viewed from behind,

283. Outer wall of the left nasal fossa. (Schwalbe),

284. Outer wall of nasal fossa. (Gegenbaur), .

285. Diagram of the facial nerve. (Thane),

286. Coronal section through the larynx to show the three sub

divisions of its cavity. (Luschka),

287. The larynx as seen in the living person by means of the

laryngoscope, .....

288. Transverse section through the larynx at the level of the

true vocal cords. (Luschka), ...

289. Outer aspect of larynx. (Gegenbaur),

290. Dissection of the larynx viewed from behind and the right

291. Diagram to show the connections of the crico-thyroid mem

brane. (Aeby), .....

292. Cartilages of larynx seen from the front. (Luschka),

293. Posterior view of the cricoid and arytenoid cartilages

(Luschka), .....

294. Muscles of the tongue. (Gegenbaur),

295. Transverse section through the hinder part of the tongue,

(Gegenbaur), .....

296. Longitudinal section through the tongue. (Aeby),

297. Transverse section through the tongue. (Aeby), .

298. The base of the brain, ....

299. Diagram of the meninges of the brain,

300. Diagram of the membranes of the brain and of the Pac

chionian bodies. (Roberts),

301. The circle of Willis and the distribution of the arteries on

the under surface of the cerebrum,

302. The vessels supplying the cortex on the inner surface of the

cerebrum, .....

303. The arteries distributed on the outer surface of the cerebral

hemisphere, .....

304. The cranial nerves leaving the cranial cavity and the circle

of Willis, .....

305. Base of the brain, showing the interpeduncular space,

(Gegenbaur), .....

306. Anterior aspect of the medulla and pons of a full-time

foetus, .......

416

LIST OF ILLUSTRATIONS.

xvil

FIG. I'AGE

307. Diagrammatic view of the iiianner in which the several parts

of the brain are connected with each other. (Schwalbe), 491

30S. Outer surface of the right cereljral hemisphere of a female

brain, ....... 49^

309. Mesial or inlernal surface of the riglU hemi.spliere of a

female brain, ...... 5°*^

310. The inferior surface of thj right cerebral hemisphere of a

female brain, ...... S^S

311. Diagram to show the correspondence between the priv-

central and intraparietal system of furrows, . . 5°^

312. Posterior part of inner surface of the left hemisphere, . 5''

313. Fissures and gyri on the surface of the insula. (Eber-

staller), ....... 5'5

314. Coronal section through the lower part of the left cerebral

hemisphere (chimpanzee), . . . .518

315. To show the relation of the infero-laleral and the supra-

ciliary borders of the cerebral liemisphere to the surface

of the cranium, ...... 520

316. Mesial section through the corpus callosum and the parts

subjacent to it. (Gegenbaur), .... 522

317. Anterior end of the corpus callosum and jts peduncles.

(Cruveilhier), ...... 523

31S. From a cast of the ventricular system of the brain.

(Schwalbe, after Welcker), . . . -525

319. Coronal section through the anterior part of the cerebrum, 526

320. Coronal section through the cerebrum a short distance

behind that depicted in Fig. 319, . . ■ 527

321. Coronal section tlirough the posterior horn of the right

lateral ventricle, ...... 529

322. The detached occipital and temporal lobes of the cerebrum,

etc. (Schwalbe), . . . . -532

323. Diagram of the fornix ; profile view, . 535

324. Dissection to show the velum interpositum and tlie lateral

ventricles, . . . . . -537

325. Diagrammatic coronal section through the optic thalami

and the parts in immediate relation to them, . . 53^

326. The medulla, mesencephalon, and thalamencephalon.

(Gegenbaur), ...... 54*^

327. Upper surface of the left thalamus, . . . .541

328. Mesial section through the brain, .... 543

XVlil LIST OF ILLUSTRATIONS.

FIG. PAGE

329. Diagrammatic outline of the third ventricle as viewed from

the side, ....... 544

330. Diagram of the roots of the optic tract, . . . ■ 547

331. The origin and relations of the optic tract. (Prof. Thane,

Quain^s Anatomy), ..... 549

332. Diagrammatic view of the cut surface of the mesencephalon

when transversely divided, .... 55*^

333. Horizontal section through the right side of the cerebrum.

(Gegenbaur), . . . . . -553

334. Coronal section through the cerebrum so as to divide the

head of the caudate nucleus in front of the lenticular
nucleus, ....... 554

335. Coronal section through the cerebrum a short distance

behind that depicted in Fig. 334, . . . 555

336. Coronal section through the cerebrum in a plane posterior to

the section exhibited in Fig. 335, . • • 55^

337. Diagrammatic representation of the radiation of the fibres

of the internal capsule. (After Testut, modified), . 55^

338. Horizontal section through the left optic thalamus.

(Schwalbe), 559

339. Anterior aspect of the medulla and pons of a full-time

foetus, ....... 561

340. Diagram of the decussation of the pyramids, . . 5^3

341. Lateral aspect of the medulla and pons of a full-time foetus, 5^4

342. Posterior aspect of the medulla, pons, and mesencephalon of

a'/uU-time fcstus, ...... 5^5

343. Transverse section through the closed part of the medulla

of a full-time foetus, ..... 569

344. Transverse section through lower end of the medulla of a

full-time foetus, ...... 57°

345. Transverse section through the medulla of new-born child

at the level of the lower part of the olivary eminence, . 57 1

346. Transverse section through the medulla at the level of the

mid-point of the olive, ..... 57^

347. Upper surface of the cerebellum. (Schwalbe), . . 575

348. Lower surface of the cerebellum. (Schwalbe), . . 578

349. Mesial section through the vermis of the cerebellum.

(Gegenbaur), ...... 579

350. Transverse section through the upper part of the pons.

(Schwalbe, after Stilling),. .... 586

351. Coronal section of the right temporal bone, . . S'&S

LIST OF ILLUSTRATIONS. XIX

FIG. PAOK

352. Schematic vertical section through the tympanum. (Tcstut), 591

353. Antero-e.\tcrnal view of the inner wall of the tympanic

cavity of the loft car of an eighth-month foetus. (Prof,

l-'awcelt), ...... 592

354. The tympanic membrane viewed from the inside. (Testut), 593

355. Schematic representation of the mcmhrana tympani and

the malleus. (Tcstut), ..... 594

356. The right mcmbrana tyinpani as seen from the outside.

(Morkol), 595

357. Left malleus and incus, (llclmholtz), . 596
35S. The right stapes. (Schwalbe), .... 597

359. A dissection of the labyrinth of the right ear of an eighth-

month fcetus, seen from the outer side. (Prof. Fawcett), 600

360. The inner wall of the right vestibule, . . 601

361. From a cast of the left bony labyrinth. (Ilenle), . . 602

362. Petrous portion of left temporal bone of child seen from

above and behind. (Prof. Fawcett), . . . 603

363. Diagram of the osseous and membranous labyrinth. (Modi-

fied from Testut), ..... 605

364. Coronal section of the right temporal bone, . 606

365. Vertical section of the left temporal bone, . . 607

366. Vertical section of the left temporal bone, . . . 608

367. Horizontal section through the left eyeball ; diagrammatic, 610

368. Posterior aspect of right eyeball. (Modified from Testut), 612

369. Dissection of the eyeball, showing the vascular tunic, etc., . 616

370. The ciliary processes of the eyeball, viewed from behind.

(Merkel), ...... 617

371. Diagram of the retina and retinal vessels as seen from the

front, . . . . . . .621

372. Diagrammatic representation of the ciliary region, as seen

in vertical section, ..... 623

Vv?'*' &<u^ " ■ ' ~ -^

fJSdj^^^ |yvOi.cAxCwL»^ ^*toLXAX

MANUAL OF ANATOMY.

MANUAL

OF

PRACTICAL ANATOMY.

THORAX.

'T'HE dissection of the thorax is commenced on the
-*■ eleventh day ^ after the subject has been placed in
the dissecting-room. By this time the upper Hmbs have
been detached from the trunk.

In form the thorax resembles a truncated cone. In
front and behind it is flattened ; but laterally it is full and
rounded. During life the movements of the thoracic walls
produce alterations in the capacity of the chest cavity, and
play an essential part in the function of respiration.

In front, the thoracic cavity is bounded by the sternum
and costal cartilages ; behind, it is bounded by the twelve
dorsal vertebrae and the intervening cartilaginous discs,
together with the portions of the ribs which extend out-
wards from the vertebral column as far as the angles ;
laterally, the shafts of the ribs from their angles behind to
their anterior extremities in front limit the thoracic cavity.
These parts constitute the framework of the thorax, and
can be studied on the skeleton.

' Saturdays and Sundays are not counted.
VOL. II. — 1

2 THORAX.

The anterior wall of the thorax is shorter than the
posterior wall. Thus, during expiration, the upper margin
of the manubrium sterni is placed opposite the disc be-
tween the second and third dorsal vertebrae, whilst the
lower end of the body of the sternum corresponds in level
with the middle point of the body of the ninth dorsal
vertebra. The bodies of the dorsal vertebrae project for-
wards into the cavity of the thorax, and greatly diminish its
antero-posterior diameter in the mesial plane ; but on either
side of the vertebral column, owing to the backward sweep
of the posterior portions of the ribs, a deep hollow is formed
for the reception of the most massive part of the lung.

The superior aperture, or inlet of the thorax, is a narrow
opening which is bounded by the first dorsal vertebra, the
first pair of costal arches, and the manubrium sterni. The
plane of this opening is very oblique ; it slopes from behind
forwards and downwards. Through the inlet of the thorax
enter the windpipe, gullet, the pneumogastric nerves, the
gangliated cords of the sympathetic, and the great veins
which carry blood towards the heart from the head and
neck and the superior extremities ; whilst through the same
opening egress is given to the thoracic duct and to the
arteries which convey blood to the neck, head, and upper
limbs.

The base or dependent part of the thorax is very wide,
and is sometimes called the outlet. In front it is bounded
by the ensiform cartilage, and behind by the twelfth dorsal
vertebra. Between these points the lower margin of the
thorax presents a curved outline. Starting from the ster-
num, it proceeds downwards, outwards, and backwards
along the cartilages of the seventh, eighth, ninth, and
tenth ribs. At the tip of the eleventh rib the direction
of the lower margin of the thorax changes, and it proceeds
upwards, backwards, and inwards along the twelfth rib to
the vertebral column.

Attached to the lower margin of the thorax is the dia-
phragm, a muscular partition which intervenes between the
cavity of the chest above and the cavity of the abdomen

THORACIC WAIL. 3

below. It is highly vaulted or dome shaped, and projects
upwards so as to form a convex floor for the thorax, and a
concave roof for the abdomen. The upward projection of
the diaphragm greatly diminishes the vertical de[)th of the
thoracic cavity.

But the diaphragm docs not form an unbroken parti-
tion. It presents three large openings, by means of which
structures pass to and from the thorax, viz. — (i) for the
aorta, thoracic duct, and vena azygos major; (2) for the
'oesophagus and pneumogastric nerves; (3) for the inferior
v"cria cava. Besides these there are other smaller apertures
which will be mentioned later on.

THORACIC WALL.

Two days at least should be devoted to the dissection of
the thoracic wall.

In addition to the osseous and cartilaginous framework,
the walls of the chest are built up partly by muscles, and
partly by membranes, and in connection with these there
are numerous nerves and blood-vessels.

r External intcrcostals,
. \ Inlcrnal inter

Muscles, . . ■', Inlcrnal inlercostals.

iTriangularis sterni.
Anterior intercostal membrane.
Membranes, . . \ I'oslerior intercostal mcmljranc.

Pleural meml)rane (parietal part).
■Intercostal nerves.

/-inie

I Aortic intercostal arteries.

I Superior mtercostal artery.

Nerves and Arteries,

itcrnal mammary artery

Disscclioii. — l\irtions of certain of the muscles of the upper limb and
of the abdominal wall will lie noticed attached to the thoracic wall.
I'roni before backwards the dissector will meet with the pcctotalis major,
\\\\i pcctoralis minor, and \.\\c scrraftis mas^^iixs, whilst towarils the lower
marj^in of the chest he will recognise the rectus aMomiiiis in front, and
the ol>h'(jiii(s t'.v/t';7///.f and /a/issimiis dorsi w^x\ its lateral as|iect. The
mundeil tendon of the su/uliwiits may also be observed taking origin
from the first costal arch, and posteriorly to this the suileniis postitns
extends downwards to its insertion into the second ril). With the single

4 THORAX.

exception of the scalenus posticus, these muscles should be removed so
as to lay bare the costal arches and the intercostal muscles. In detach-
ing the serratus magnus be careful not to injure the lateral cutaneous
nerves which make their appearance in the intervals between its digita-
tions. The aiiterior aitaneous nerves and perforatmg branches of the
internal mammary artery must also be preserved ; they pierce the origin
of the pectoralis major in the intervals between the costal cartilages,
and close to the margin of the sternum.

Intercostal Muscles. — These muscles occupy the eleven
intercostal spaces on each side of the thoracic wall. In
each space there are two strata of muscular fibres — a
superficial and a deep. The superficial layer of muscular
fibres is called the external intercostal muscle, and the deep
layer the internal intercostal muscle.

The external intercostal muscles (musculi intercostales
externi) are already exposed, and very little -cleaning is
necessary to bring out their connections. Observe that
entering into their constitution there is a large admixture
of tendinous fibres, and that these, as well as the muscular
fibres, are directed from above, obliquely downwards and
forwards from the lower border of the rib above to the
upper border of the rib below. They do not extend farther
forwards in the various spaces than a point corresponding
to the union of the bony with the cartilaginous parts of
the costal arches. In many cases, especially in the upper
spaces, they do not reach so far. Here the muscular fibres
stop short, but the tendinous fibres are prolonged onwards
to the sternum in the form of a membrane, which may
be called the anterior intercostal membrane. The external
intercostal muscles of the two lower spaces are exceptions
to this rule. They extend forwards to the extremities of
the spaces. Posteriorly the muscles pass backwards as far
as the tubercles of the ribs, but this is a point which can
only be satisfactorily demonstrated after the thorax has
been opened.

Dissection. — To bring the internal intercostal mtiscles into view it is
necessary to reflect the external intercostal muscles, and also the anterior
intercostal membranes. Divide them along the upper borders of the
ribs which bound the spaces inferiorly, and throw them upwards. This

THORACIC WALL. 5

(lisscclion sliould be performed in each intercostal space, and, in cflcct-
iii;^ it, care must he tai<en of the intercostal arteries which lie between
tlie two muscular strata.

The internal ijttercostql_jnuscles (musculi intcrcostalcs
intcrni) thus laid bare will be seen to be similar in their
constitution to the external muscles. The fibres, however,
run in the opposite direction — viz. from above, obliquely
downwards and backwards. Superiorly, they are attached
to the inner surface of the upper rib, immediately above
the subcostal groove ; inferiorly, they arc attached upon
the inner surface of the lower rib, close to the upper
margin. The internal intercostal muscles are prolonged
forwards to the sternum. Posteriorly they reach back-
wards to the angles of the ribs, from which to the spine
the muscles are replaced by a series of thin membranes —
the l^oskrior intercostal membranes — which will be seen after
the thorax has been opened. If the internal oblique
muscle of the abdomen has not been removed, the
dissector should note that the anterior fibres of the two
lowest internal intercostal muscles become continuous
with the fibres of that muscle.

Intercostal Nerves. — The intercostal nerves are alto-
gether out of sight in the present stage of the dissection.
They are hidden by the lower borders of the ribs which
bound the intercostal spaces superiorly. By gently pulling
upon their lateral cutaneous branches they can be drawn
downwards, and they are then seen to lie between the two
muscular strata as far forward as a point midway between
llie spine and sternum. Here they disappear from view
by_sinking into the substance of the internal intercostal
muscles, amidst the fibres of which they may be traced as
fiir as the anterior extremities of the bony ribs. They now
reach the deep surface of these muscles and are carried
inwrTrds, lirsTTipon the pleura, and then upon the triangu-
laris sterni muscle. Lastly, they cross the mTernal
mammary artery, and come forwards at the side of the
sternum as^the anterior cutaneous nerves of the pectoral
region. Eachlierve, TDeTore it reaches the surface, pierces

6 THORAX.

— {a) the internal intercostal muscle ; {f) the anterior
intercoslal membrane; {c) the origin of the pectoralis major;
and id) the deep fascia (Fig. 167).

But this description only holds good for the upper five
intercostal nerves. The loiver six nerves, on leaving the
anterior ends of the intercostal spaces, pass forwards into
the abdominal wall between the internal oblique and trans-
versalis muscles, where they have already been displayed by
the dissector of the abdomen.

TRIANQ. STERNl

Fig. 167. — Diagram of one of the upper
intercostal nerves.

The intercostal nerves, as they traverse the thoracic wall,
give off — (a) the lateral cutaneous branches, and (b) twigs
to the intercostal muscles and triangularis sterni. Their
terminal branches constitute the anterior cutaneous nerves.
The lateral cutaneous branches come off midway between
the spine and the sternum, and, piercing the external inter-
costal muscles, appear in the intervals between the digita-
tions of the serratus magnus.

IIIORACIC WAl.I.. 7

II is lint iK'ccss;!!)' It) make a clissc'clii)ii of ilic intercostal nerves in
more than 1\m> nr tliree o( tiic spaces.

Intercostal Vessels. — The intercostal arteries sliuuld be
dissected in those spaces in which the nerves have not been
traced, and in which, therefore, the internal intercostal
muscles are still entire. It is only in a well-injected subject
that a satisfactory view of these vessels can be obtained.
In each intercostal space one artery is found passing from
behind foncards, and two, the anterior intercostal arteries,
running from before backivards.

In the upper two spaces the vessels which run from
behind forwards are derived from the superior intetyostal
branch (truncus costo-cervicalis) of the subclavian artery ;
in the nine lower spaces they spring directly from the aorta,
and are called the iwrtkjjikixa^al arteries.

The anterior intercostal arteries of the upper six spaces
proceed directly from the Jnternal mammary, whilst in
the case of the lower spaces they come from the outer
of its two terminal branches — viz. the musculo-phrenic
artery. ~

The intercostal vessels are for the most part distributed
between the two muscular strata. From the angles of the
ribs onwards to a point midway between the spine and
sternum, the aortic intercostal arteries lie under shelter of
the lower margins of the ribs which bound the spaces
superiorly, and at a hjjilij^r level than the corresponding
nerves. Here each divides into two branches, and these
pass forwards in relation to the upper and lower margins of
the intercostal space. They give off small branches which
accompany the lateral cutaneous nerves. The si//>erior
intercostal arteries are disposed in a similar manner. The
anterior intercostal arteries are two in number for each
space. At their origin they lie under cover of the internal
intercostal muscles, and they run outwards in relation to the
upper and lower margins of the ribs bounding each space.
After a short course they pierce the internal intercostal
muscles, and end by anastomosing with the aortic and
superior intercostal arteries.

8 THORAX.

Dissection. — The dissector should next proceed to remove the inter-
costal muscles. This dissection must be carried out with more than
usual care, because immediately subjacent to the internal intercostal
muscles, over the greater extent of the chest wall, is the delicate pleural
membrane lining the inner surface of the costal arches. Upon no
account detach this membrane from the deep surface of the ribs, and take
the greatest care to preserve it intact during the dissection.

On the front of the chest, the internal -mammary artery and the
triangularis stenii muscle will be seen to intervene between the pleura
and the costal cartilages. The internal mammary artery, with its two
companion veins, will be seen descending in a vertical direction, about
half an inch from the outer margin of the sternum. Clean these vessels
carefully in the intervals between the costal cartilages, and note some
small lymphatic glands which lie along the course of the vessels. As a
rule, the artery ends by dividing into two terminal branches in the
interval between the sixth and seventh rib cartilages. Most likely this
space will be so narrow that a view of the bifurcation cannot be
obtained. If this be the case, pare away the edges of the cartilages over
the artery, or if necessary remove the inner part of the sixth cartilage
completely. The perforating branches of the internal mammary artery
which accompany the anterior cutaneous nerves should be preserved.

The muscle upon which the internal mammary artery lies is the
triangularis sterni. Endeavour to define its slips in the intervals
between the costal cartilages.

Towards the lower margin of the thorax the pleural sac is not pro-
longed downwards to the lowest limit of the recess between the diaphragm
and the costal arches. Indeed, in the axillary line, it will be found
to fall considerably short of this. Consequently, when the internal
intercostal muscles are removed from this portion of the chest wall, the
dissector will come down directly upon the diaphragm ; and, as the fibres
of the diaphragm correspond somewhat in their direction with those of
the internal intercostal muscles, it is no uncommon occurrence for the
student to remove them, and thus expose the peritoneum, under the
impression that he has simply laid bare the pleura. When the dissection
has been properly executed, a strong fascia will be observed to pass from
the surface of the diaphragm on to the surface of the costal pleura so as
to hold it in position. Preserve this for further examination.

The Internal Mammary Artery (arteria mammaria in-
terna) arises in the root of the neck from the first part of
the subclavian, and enters the thorax, by passing down-
wards behind the inner end of the clavicle and the cartilage
of the first rib. Accompanied by two veins, it descends
to the interval between the sixth and seventh costal
cartilages, where it ends by dividing into the superior

TllOKAClC HALL.

i/<ii^asfnc and the musculo-plircnic branches. It runs parallel
with the outer margin of the sternum, from which it is
separated by an interval of about half an inch.

I'lu. 168. — Posterior aspect of the anterior wall of the thorax
and upper part of the abdomen. (From Luschka. )

1. Manubrium stcrni.

2. Gladiolus.

3. Ensiform cartilage.

4. Internal intercostal muscle.

5. Triangularis slerni.

6. 'I'ransversalis abdominis.

7. Sternal origin of diaphragm.

8. Costal origin of diaphragm.

9. Internal mammary artcrj-.

10. Superior epigastric arter>'.

11. Musculo-phrenic arterj".

12. \\\ occasional branch of the internal

mammarj'.

Placed in front of the internal mammary artery are the
upper si.x costal cartilages, with the intervening intercostal

lo THORAX.

muscles and anterior intercostal membranes. It is crossed
by the series of intercostal nerves before they turn forwards
to gain the surface. In the upper part of its course the
artery is supported by the pleura", but lower down it rests
upon the triangularis sterni which intervenes between it
and the pleural sac.

In addition to its two terminal branches, a large
number of small collateral twigs proceed from the internal
mammary —

1. The anterior intercostal, .1

2. The perforating, . . / t° ^^e thoracic parietes.

3. The comes nervi phrenici, 1 • , • • r 1 ,

4. Mediastinal and thymic, . / *« P^^-^^ '" the mtenorof the thorax.

5. Superior epigastric, . 1 , . , ,
^ the termmal branches.

6. Musculo-phrenic,

:}'

The anterinr inte.rcostal arteries (rami intercostales) are
supplied to the upper six intercostal intervals, and have
already been dissected (p. 7). Two are given to each
space : frequently these arise by a common trunk.

HhQ perforating arteries (rami perforantes) accompany the
ariterior cutarieous nerves, .and reach the surface by piercing
the internal intercostal muscles, the anterior intercostal
membranes, and the pectoralis major muscle. One, or
perhaps two, are given off in each intercostal space. And
in the female two or three of the intermediate members of
tfie series (rami mammarii) attain a special importance,
inasmuch as they constitute the principal arteries of supply
to the mammary gland.

The superior epigastric artery (arteria epigastrica superior)
enters the sheath of the rectus muscle of the abdominal wall
by passing downwards behind the seventh costal cartilage.

The jnusculo-phrenic artery (arteria musculo-phrenica)
turns outwards and downwards along the costal origin of
the diaphragm and behind the rib-cartilages. Opposite the
eighth costal cartilage it pierces the diaphragm and enters
the abdomen. It gives off the anterior intercostal arteries
to the lower intercostal spaces (p. 7).

THORACIC CAVriY. ii

The Triangularis Stemi (luusculus iransvcrsus thoracis)
is a thill muscular layer l)la_ccd on the deep surface of the
sternum and costal cartilages. It is continuous below with
the transversalis muscle of the abdominal wall, and arises
fr^m the posterior surface of the ensiform cartilage, the lower
part of the body of the sternum, and from the inner ends of
tlie 5tTr, 6th, and 7th costal cartilages. From this origin
its fibres radiate in an upward and outward direction, and
separate into five slips, which are inserted into the deep
surfaces and lower borders of the 2nd, 3rd, 4th, 5th, and
6th costal cartilages, close to their junction with the ribs

(Fig: 168).

In many cases the muscle is feebly developed, and does not show
connections so wide as those which are described above. U[ion the
superficial aspect of llie triangularis slcrni are placed the internal
mammary artery and the series of intercostal nerves.

It is only a partial view of the muscle which is obtained in the present
dissection, i)ul it is not advisable to remove the costal cartilages to expose
it further, as this would very materially interfere witli the subsequent
display, in their proper relations, of other more important structures.

THORACIC CAVITY.

The arrangement of the two pleural sacs within the
thoracic cavity nmst now engage the attention of the
student ; but in order that the relations of these may be
understood, it is absolutely necessary that the dissector
should have some preliminary knowledge of the thoracic
viscera. The principal viscera of the chest are the lungs
and the heart. The two lungs occupy by far the greatest
part of the space, and lie one upon either side of the mesial
plane. The heart is placed between the lungs, and projects
more into the left than the right side of the cavity. It is
completely enveloped by a loose conical fibro-serous sac
called the pericardium^ which is attached by its base to the
upper surface of the dia[)hragm. Each lung is connected
with the base of the heart by several large vessels which

THORAX.

pierce the pericardium, and these, with the corresponding
division of the windpipe passing to the lung, constitute the
piiliuonary root or pedicle. The lungs are free within the
thorax except where they are attached by their roots.

Fig. 169. — Horizontal section of the thorax of a man aged 57,
looked at from above. (From Symington.)

9 D.V. Ninth dorsal vertebra, cut near
its upper surface.
S. Body of sternum.
4, 9. Fourth and ninth ribs ; between
these are the fifth, sixth,
seventh, and eighth ribs.
4'. Fourth costal cartilage.
N. Nipple.
R.V. Conus arteriosus of right ven-
tricle.

R.A. Right auricle.
L. A. Left auricle. "> Between these
L.V. Left ventricle. /the mitral valve.
Between L.V. and R.A. are portions of
two of the aortic semilunar valves.
D.A. Descending aorta ; to its right
side, the oesophagus.
f. Right phrenic nerve.
e. Left pleural cavity.

Pleural Sacs. — The pleural sacs are two in number, one
in each side of the chest cavity. They are serous sacs, and
therefore closed. Each pleural bag is so disposed that it
not only lines the recess in which the lung lies, but is also
reflected over the lung so as to give to it an external

THORACIC CAVITY. 13

covering, which is intimately connected with the puhnonary
substance. \\'o recognise, therefore, in connection with
each pleura a lining:; or parietal part., and an investing or
visceral part. It must be clearly understood, however, that
these terms arc merely applied to indicate different portions
of one continuous membrane.

The dissection which has already been made shows the
pleura lining the deep surface of the costal arches and
internal intercostal muscles. This portion is called the
pleura costalis. The manner in which the pleura of each
side is reflected backwards from the posterior aspect of the
sternum must now be investigated. This entails a some-
what complicated dissection.

Dissecfioii. — The sternum must be divided with the saw into four
portions by tiiree separate cuts, viz. (i) a transverse section through the
manubrium sterni, on a line with the lower margins of the first pair of
costal cartilages ; (2) a transverse cut through the lower part of the
body of the sternum, in the interval between they?/?// and sixth costal
cartilages; (3) an oblique section, beginning below at the inferior
transverse cut, close to the left margin of the sternum, and carried up-
wards to the middle of the superior transverse cut. By the last section
the central portion of the sternum is divided into two lateral pieces, to
each of which four costal arches are attached (Fig. 170).*

In making these sections through the sternum, the saw should only
be used until the thick periosteum on the back of the bone is reached.
This can then be divided cautiously with the knife. Of course the
internal mammary vessels must be preserved, and the greatest care must
be taken not to separate the parietal pleura at any point from the deep
surface of the thoracic wall.

Anterior Mediastinum. — The two lateral portions of the
central piece of the sternum should now be gently separated
from each other, and, on looking between them, the parietal
pleura of each side will be seen leaving the posterior surface
of the sternum, and passing backwards to reach the peri-
cardium. ]jut the pericardium is not in view, except
perhaps to a very small extent below, because the two
pleural membranes, where they make this reflection, are in
contact. Introduce the finger between the two pleural sacs,

' Tliis dissection was devised by Sir William 'I'urnor.

14 THORAX.

and pass it upwards and downwards through the loose
areolar tissue which holds them together. The pericardium
is in this way exposed, and a striking demonstration is
obtained of a space which is termed the anterior medias-
tinwn. In front this space is bounded by the posterior
surface of the body of the sternum, and usually also by the

Fig. 170. — Dissection to expose the anterior mediastinum.

inner ends of the fifth, sixth, and seventh costal cartilages
of the left side, clothed by the left triangularis sterni muscle ;
behind, by the pericardium ; and uJ)on each side, by the
pleura as it passes from the back of the sternum to the front
of the pericardium. In its upper part the space can hardly
be said to exist, seeing that the pleural sacs are in contact ;
but below, the left pleura falls somewhat short of the right

THORACIC CAVITY. 15

pleura, and an interval is apparent. The only contents to
be noticed in the anterior mediastinum are, in its lower
part, a few small lymphatic glands and some loose areolar
tissue, in which ramify lymphatic vessels and some minute
arterial twigs from the internal mammary artery.

Dissection. — Having now ascertained the relations of the pleura to
the chest wall, proceed to the study of its connections within the thorax.
For this purpose the parietal pleura must he separated from the rihs as
far forwards as the cartilages. This can hest be done by gently insinu-
ating the forefinger loetween each of the ribs and the ]ileura, and then
running it backwards and forwards. Upon no account detach the
pleura from the cartilages. Next divide with the knife the second, third,
fourth, fi fill, and sixth costal arches at the junction of the osseous with
the cartilaginous jiortions, and remove these ribs by snipping through
them with the bone jiliers as far back as possible. The sternum and
cartilages, to which the pleura is still adherent, must be left in position
until the arrangement of the membrane has been thorougldy investigated.

The greater ]iarl of the costal pleura now lies flaccid upon the surAice
of the lung. Make a vertical incision through it, midway between the
spine and sternum, from the level of the second costal arch down as far
as the .seventh rib. From each extremity of this vertical cut carry an
incision forwards for two or three inches.

Relations of the Pleura. — A considerable piece of the
parietal pleura can now be thrown forwards like a door,
and the interior of the pleural sac is exposed. The inner
surface of the membrane, if healthy, presents an appear-
ance which is characteristic of all serous membranes. It
is smooth, polished, and glistening, and is moistened by a
small amount of serous fluid. It is thus admirably adapted
to allow the movements of the lung during resjjiralion to
take place with the stnallest possible degree of friction.
When the surface of the membrane becomes roughened by
inflammatory exudation, the so-called " friction sounds " of
pleurisy become evident when the ear is applied to the
chest.

Introduce the hand into the pleural sac, and exi)lore its
extent and connections. l''irst carry it inwards behind the
costal cartilages. Its passage across the mesial plane of
the body is effectually barred by the reflection of the pleural
membrane from the back of the sternum to the front of

i6

THORAX.

the pericardium. Above the level of the pericardium it
passes right back to the vertebral column, and then proceeds
outwards on the ribs. Upon the lateral aspect of the
pericardium it can be traced backwards towards the spine,
and here it must be studied from two points of view, viz.
(i) at the level of the root of the lung, and (2) below the
root of the lung.

At the level of the pulmonary root, the pleura is carried
outwards, so as not only to envelop this, but also the
entire lung. The smooth glistening surface of the organ

p. Pericardium.
R. Root of lung.
L. Lung.

- parietal pleura.
visceral pleura.

Fig. 171. — Diagram of the two pleural sacs.

is due to the pleural investment which it thus acquires.
This, then, is the visceral pleura, and it should be noticed
that it is very much finer and thinner than the parietal
pleura. Further, it is inseparably attached to the pulmonary
substance. Behind the root of the lung the pleura is pro-
longed backwards upon the pericardium, and on the left
side over the descending thoracic aorta to the bodies of
the vertebrae. On the right side it passes directly from
the pericardium to the bodies of the vertebrse. This can
be seen by tilting forwards the thick posterior border of
the lung. From the vertebrae, the pleura passes outwards
upon the deep surfaces of the ribs.

I

rilORACIC CAVITY. 17

IJclow ihc level of the root of the lung, the pleura can
be traced backwards upon the pericardium to the si)ine,
from which it is conducted outwards upon ihe riljs. 15ut
it does not [)ass backwards uninlerrui)lcdly.

The same two layers which envelop the pulmonary root
are prolonged outwards from the pericardium in apposition
with each other. Meeting the inner surface of the lung,
they separate to enclose the low^er portion of this organ.
The fold of pleura which is thus formed is called the
ii):;a//i<:/Uum latum puhnonis^ and it can be brought into
view by enlarging the opening in the pleural sac, and draw-
ing the basal portion of the lung outwards and backwards.
It will then be seen in the form of a triangular fold of
pleural membrane, which extends from the lower border of
the pulmonary root along the inner surface of the lung to
the diaphragm.

The dissector has now traced the continuity of the
l)leural sac in the transverse direction. He has observed
that it lines the deep surface of the costal arches, and is
reflected backwards in the form of an intra-thoracic parti-
tion from the back of the sternum to the spine. This
partition is called the mediastinal pleura, and it is unin-
terrupted, except where it is pushed outwards over the
lung and lung-root in the form of an investment. But the
continuity of the membrane in a longitudinal direction
must also be established. This inquiry will render clear
its relations in the upper and lower parts of the thoracic
cavity.

In the upper part of the chest cavity, the pleura will be
observed to extend upwards through the thoracic inlet
into the root of the neck, and to form in this locality a
dome-shaped roof for each side of the chest (Fig. i 70).
This portion of the pleura is called the cervical pleura^
and it passes upwards above the level of the anterior part
of the first costal arch for a distance of from i to 2 inches.
The height to which it rises varies considerably in different
individuals. The subclavian artery arches over and lies in
a groove on the inner and anterior aspect of this cul-de-sac
VOL. II — 2

1 8 THORAX.

near its summit, and the scalenus anticus muscle _is in
relation to its outer surface. Further, the_ cervical pleura
is supported and strengthened by an aponeurotic expansion
{^Sibson^ s fascia) which is spread over it, and receives attach-
ment to the inner concave margin of the first rib. This
fascia is derived from a small muscular slip which takes
origin from the transverse process of the seventh cervical
vertebra. It may be regarded as a derivative from the
scalene group of muscles.

In-tbe-4ower part of the thorax the parietal pleura is
reflected from the inner surface of the chest wall on to the
upper surface of the diaphragm, and is carried inwards
upon this towards the pericardium. This portion of the
membrane is termed the diaphragjuatic pleura.

Tlie Lines of Pleural Eeflection. — The two pleural sacs
are not shaped alike. The right pleura is shorter and
wider than the left, and consequently the lines along which
the two membranes are reflected from the sternum and
costal cartilages backwards towards the pericardium, and
^Iso from the chest wall on to the diaphragm, differ some-
what on the two sides.

Behind the manubrium sterni the two pleural sacs are
separated from eacli other by an angular interval, but near
the upper end of the gladiolus they come together, and
proceed downwards in close contact, and slightly to the left
of the mesial plane, as far as the sternal end of the fourth
costal cartilage. Not only are they in contact, but in trans-
verse sections through the chest it will be seen that the
left pleural sac in this position slightly overlaps the right
pleural sac (Fig. 172). At the level of the attachment of
the fourth costal cartilage to the sternum the two sacs part
company. The left pleura deviates outwards, whilst the
right pleura is continued downwards in a straight .hne
behind the sternum to the back of the ensiform cartilage.
Here it turns sharply outwards, and running obliquely
downwards and backwards upon the deep surface of the
seventh costal cartilage, is reflected from this on to the
upper surface of the diaphragm. Following the line of

THORACIC CAVITY.

«9

dia[)liiagiuatic icllcclion un iho right side, it will be seen
to continue in a downward and backward direction across
tlic bony extremity of the eighth rib, across the ninth rib,
until it reaches in the axillary line the ninth intercostal
space, or, perhaps, the upper margin of the tenth rib.
Crossing the tenth rib, it runs inwards and backwards
along the eleventh rib, and reaches the spine at the level
of the vertebral end of the twelfth rib.

Trace now the line along which the left pleura is
reflected from the chest wall below the level of the sternal
end of the fourth costal cartilage. At this point it retires

Fig. 172. — Tracing from a transverse section througli
the frozen chest, at the level of the junction of the third
costal cartilages with the sternum.

S. .Sternum ; L.P. Left pleura ; K.P. Righl pleura.

in an outward direction from the right pleura, and descends
at a variable distance from it, so as to leave a small
triangular portion of the pericardium uncovered by pleura,
and in direct contact with the anterior chest wall. This
area is very variable in its extent, but the accompanying
diagram (Fig. 173) may be considered to represent the
maximum amount of outward deviation of the left pleural
sac in connection with this part of the chest wall. As a
rule, the area of the pericardium which is left bare is not
so extensive.

Proceeding downwards behind the fourth intercostal
space, the fifth costal cartilage, the fifth intercostal space.

THORAX.

and the sixth costal cartilage, close to the margin of the
sternum, the line of left pleural reflection will then be seen
to incline obliquely outwards and downwards behind the
seventh costal cartilage, and across the eighth, ninth, and
tenth ribs, until it reaches a point midway between the
spine and the sternum. The line of the diaphragmatic

Apex pulmonis.

Incisura cardiaca.

Fig. 173. — The pleural reflection on each side is repre-
sented by a solid black line. The outline of the lung is
indicated by a dotted line. (From Gegenbaur. )

reflection of the left pleura is placed at a slightly lower
level than the corresponding line on the right side. The
left pleura is therefore deeper than the right pleura, and, in
the axillary line, it reaches the lower margin of the tenth
rib. From this point, as on the opposite side, the lower
limit of the left pleura extends backwards along the eleventh
rib towards the spine, which it reaches at the level of the
vertebral extremity of the twelfth rib.

THORACIC CAvrrv. 21

On neither side docs the i)lcura reach to the lowest
limit of the recess between the diaphragm and the chest
wall. This has already been noted in the dissection of the
intercostal spaces, and a strong fascia has been observed to
pass from the uncovered part of the surface of the diaphragm
and from the costal cartilages to the surface of the costal
pleura, so as to hold it firmly in place. It may be compared
with Si7>so/i s fascia, which covers the cervical pleura, but is I
more strongly marked and more tendinous in character. It \
may be termed the phrenico-pleural fascia.

Mediastinum. — The fnediastini/m or mediastinal space is
the name whicii is given to the interval which is left between
the two pleural sacs. It is within this space that by far the
greater part of the dissection of the thorax has to be con-
ducted, and, consequently, it is important that the student
should acquire an accurate conception of its extent and
connections. We have noted that the mediastinal portion
of the pleura extends backwards from the front wall of the
thorax on either side of the mesial plane, in the form of an
intra-thoracic partition. This forms the lateral boundary of
the space, whilst in front it is bounded by the sternum, and
behind by the vertebral column. But it is customary to
subdivide in an arbitrary manner the mediastinal S[)ace into
four portions, termed respectively sujierior, anterior, middle,
and [)OSterior, according to the relations which they present
to the pericardium.

Superior Mediastinum. — This is the part of the general
mediastinal space which lies above the level of the peri-
cardium. \isJ>oundaries :ixc the following: — In front, the
manubrium sterni, to the posterior aspect of wTiicTi are
attached the lower ends of the sterno-hyoid and sterno-
thyroid muscles ; l>ehind^\.]iQ upper four dorsal vertebrre with
the longus colli muscles; bcjow^^yx imaginary and oblique
plane extending from the lower border of the manubrium
sterni backwards and ui)wards to the lower border of the
fourth dorsal vertebra ; and laterally, the mediastinal pleura
as it extends on each sidi- from the back of the sternum to
the vertebral column.

22 THORAX.

Figs. 191 and 193 (pp. 65 and 67) are reproduced from
tracings of two sections through the superior mediastinum
at different levels. Fig. 191 represents a section through
its upper part, and Fig. 193 a section through its lower part
at the level of the fourth dorsal vertebra. The boundaries,
form, and contents of the space are clearly seen.

Within the superior mediastinum are placed — (i) the
aortic arch, and the three great vessels which spring from it;
(2) the innominate veins and the superior vena cava in its
upper part; (3) the trachea, gullet, and thoracic duct; (4) the
vagus, phrenic, left recurrent laryngeal and cardiac nerves ;
(5) the_thymus gland. The relative positions of these can
be studied, in the meantime, in Figs. 191 and 193 ; after-
wards they will be displayed in the course of dissection.

The Middle Mediastinum is the wide middle part of the
space which contains the- pericardium, and lies below the
superior mediastinum. In addition to the pericardiuin_and
itj^ contents, the middle mediastinum contains the phrenic
nerves and their arteriae comites (Figs. 169 and 192).

Tlie Anterior Mediastinum is that portion of the inter-
pleural space which lies between the pericardium behind
and the body of the sternum in front. It has already been
examined (p. 14).

The Posterior Mediastinum is situated between the peri-
cardium and the bodies of the vertebra. It will be studied
later on.

Dissection. — The central portion of the sternum, with the attached
costal cartilages, may now be removed and laid aside until a suitable
opportunity arises for the study of the chondro-sternal joints. Carefully
strip the mediastinal pleura from the side of the pericardium. This will
bring into view the phrenic nei-ve and the slender arteria comes nei-vi
phrenici, a branch of the internal mammary artery which accompanies
the phrenic nerve upon the side of the pericardial sac. During this
dissection the minute inediastinal and thymic h-anches of the internal
mammary artery will be brought into view.

The Lungs (pulmones) are two soft, spongy organs placed
one on either side of the mediastinal space. When the
thorax is opened, they collapse to about one-third of their

THORACIC CAVITY. 23

original bulk, and it is difficult for the student to realise
their proper dimensions and shape.

With ihe consent of the dissector of the head and neck, the nozzle of
the bellows may he introduced into the cervical part of the trachea so as
to inflate the kings with air. A truer conception of these organs will
thus he ol)tained, and a demonstration will he aflorded of their high
ehisticity, and of their connection with the windpipe.

When healthy and sound, the lungs lie free within the
cavity of the chest, and are only attached by their roots and
by their ligamenta lata. It is rare, however, that a healthy
lung is seen in the dissecting-room. Adhesions between
the visceral and parietal portions of the pleura due to
pleurisy are generally present. It is accurately adapted to
the space in which it lies, and, in the natural state, it bears
on its surface impressions and elevations which arc an exact
counterpart of the inequalities of the parts with which its
surfoces are in contact.

In its natural condition, before the chest is opened, each
lung is conical in form, and presents for examination an
apex, a base, an outer and an inner surface, and an
anterior and a posterior border. The apex of ihe lung
(apex pulmonis) is blunt and rounded, and rises above the
level of the first costal arch, protruding upwards through
the thoracic inlet into the root of the neck. The sub-
clavian artery arches outwards upon the- inner and front
aspects of the apex of the lung, a short distance below its
summit, and a groove (sulcus subclavius) corresponding to
the vessel may be recognised upon it. The cervical pleura
intervenes between them. The base of ihe lung (basis
pulmonis) presents a semilunar outline, and is adapted to
the upper surface of the diaphragm. Consequently, it is
deeply hollowed out ; and as the right cupola of the
diaphragm ascends higher than the left, the basal con-
cavity of the right lung is deeper than that of the left
Itmg. Laterally, and behind, the base of each lung is
limited by a thin sharp margin, which passes downwards
in the narrow pleural recess [sinus plireniio-costalis) between
the diaphragm and chest wall. This margin extends

24

THORAX.

much lower down behind and at the outer side than in
front.

But the bases of the lungs establish important relations
with the viscera, which occupy the costal zone of the
abdominal cavity — the diaphragm alone intervening. Thus
the base of the right lung rests upon the right lobe of the
liver; whilst the base of the left lung is in relation to Ae
left lobe of the liver, the stomach, the spleen, and in
some cases to the splenic flexure of the colon (Fig. 176,

P- 33)-

The outer surface of the lung (fades costalis pulmonis)
is very extensive and is full and convex. It is in relation
to the parietal pleura, as it clothes the ribs and inter-
costal muscles, and it bears the impress of the costal
arches. T\\Q.Jmier surface (facies mediastinalis pulmonis)
presents a much smaller area than the outer surface,
and is deeply concave in adaptation to the pericardium
upon which it fits. As the heart projects more into the
left side of the chest, the_ concavity on the inner side

of the left lung is more
marked than it is in the
right lung. Upon this
surface is the hilijni, or the
place of attachment of the
root. It is situated some-
what nearer the apex than
the base, and also nearer
the posterior than the an-
terior border of the lung.
Through the hilum enter
the arteries, nerves, and
bronchus, whilst through
the same slit the veins and
lymphatics emerge.
The two borders of the lung stand in marked contrast
to each other. The anterior border is short, thin, and
sharp, and extends forwards and inwards in front of the
pericardium into the narrow pleural recess behind the

( From

Fig. 174. — The Lungs.
Gegenbaur. )

f, Superior lobe ; vt. Middle lobe ;
i, Inferior lobe.

THORACIC CAVITY. 25

Sternum and costal cartilages {sinus cosfo-mcdiasfitia/is).
The posterior border of tJie lung is thick, long, and rounded.
It forms the most bulky part of the organ, and occupies
the deep hollow of the thoracic cavity which is placed on
each side of the spine.

During respiration the two surfaces, the posterior bor<ler and the
lower surface of ihc hasc and the apex of the lung always remain in
close ajiposition with the wails of the cavity in which the organ lies.
I/The sharp margin around the hase rises and falls in the sinus ]ihrenico-
f CDStalis, hut it is dnul)tful if it ever, even in the decjiest insjiiration,
reaches tlie lowest limit of this recess. The anterior sliarji margins
of the Imigs ajiproach and retreat to a slight degree from each other in
front of the pericardium in the sinus costo-mediastinales. In full in-
si^iraliort, behind the u]i|ier two ]iieces of the gladiolus of llie sternum,
they are only sejiarated from each other hy the two layers of mediastinal
pleura, and as a general rule the left lung slightly overlaps in this
locality the right lung.

But there are some points in which the two lungs differ •.
from each other: (i) The right lung is slightly larger than
the left, in^the proportion of 1 1 to 10. (2) The right lung s^.
is sjiorter and wider than the left lung. This difference is :.:■,
due to the great bulk of the right lobe of the liver, which
elevates the right cupola of the diaphragm to a higher
level than the left cupola, and likewise to the heart and \
pericardiimi, projecting more to the left than the right,
and thus diminishing the width of the left lung. (3) The
anterior sharp margin of the right lung is more or less
straight ; the corresponding margin of the left lung presents,
in its lower part, a marked angular deficiency {incisura
cardiaca) for the reception of the apex of the heart and
the pericardium. (4) The right lung is subdivided into
three lobes, and the left lungTiito two.

Lobes of the Lungs. — The left /it/ig is divided into two
lobes by a long oblique deep fissure which penetrates its
substance to within a short distance of the root. This
Gssure begins above at the posterior border, about three
inches below the apex, and al.)otit the \v\\'\ of the vertebral
end of the third rib, and is continued in a somewhat spiral

W^

26 THORAX.

direction- downwards and forwards to the anterior end of
the base of the lung. The upper lobe of the lung (lobus
superior) lies above and in front of this cleft. It is conical
in form with an oblique base. The apex and the whole of
the anterior border belong to it. The lower lobe (lobus
inferior), somewhat quadrangular, lies below and behind
the fissure, and belonging to it we recognise the entire
base and the greater part of the thick posterior border.
It is therefore the more bulky of the two.

In the right limg a similar cleft is present, but in
addition to this a second fissure maps off from the lower
end of the upper lobe, a third or intermediate lobe. This
second cleft begins at the posterior border of the lung in
the oblique fissure, and proceeds horizontally forwards on
the outer surface to the anterior border. The middle or
intermediate lobe of the right lung (lobus medius) is
triangular or wedge-shaped in outline.

Root of the Lung (radix pulmonis). — This is the term
which is applied to a number of structures which enter the
lung at the hilum or slit upon its inner concave surface.
These structures are held together by an investment of
pleura, and constitute a pedicle which retains the lung in
its place when the thoracic cavity is opened.

The pleura should be carefully stripped from around the
root of the lung ; but, before undertaking the dissection of
the structures which compose the root, the relation which
it bears to neighbouring parts should be determined.

Injront there are — (i) A delicate plexus of nerves, the
anterior pulmonary plexus ; and (2) the phrenic nerve jwith
the arteria comes nervi phrenici. Behind, the pneumo-
gastric nerve breaks up into the posterior pulmonary
plexus ; whilst, inferiorly, there is the ligamentum latum
pulmonis. These are the relations which are common to
the root of the lung upon both sides of the body, but
there are others which are peculiar to each side.

On the right jide — (i) The^ vena azygos major, as it
passes forwards to join the superior vena cava, is in relation
to the upper border of the pulmonary root; (2) the superior

I

THORACIC CAVITY. 27

vena cava, in the lower part of its course, lies in front of
the pulmonary root.

On the left side, the aorta arches over the root of the lung,
and the descending thoracic aorta passes down behind it.

Dissecftoii. — Now proceed to dissect out ihe constituent parts of the
root of the lung. I

Constituent parts of the Pulmonary Root. — The most ,

important structures which enter into the formation of the
pulmonary root are — (i) \\\q. two pulmonary veins ; (2) the
pi/Inionary artery ; (3) the bronchus. But, in addition to '
these, there are one or two small bronchial arteries and
veins, the pulmonary nerves, and the pulmonary lymphatic
vessels. These are bound together by some loose areolar
tissue, and the whole is invested by pleura.

The pulmonary nerves are derived from the anterior and
[)Osterior pulmonary plexuses. The anterior pulmonary
plexus is composed of two or three delicate filaments, which
come from the pneumogastric nerve before it reaches the
posterior aspect of the pulmonary root. These join with
the sympathetic twigs on the wall of the pulmonary artery.
The deep cardiac plexus gives twigs to the anterior pul-
monary plexus on both sides of the body. But the plexus
of the left side is larger than that of the right side, because
it likew^c nsceivcs' a few filaments from the superficial
cardiac plexus. It is only under the most favourable
circumstances that a good dissection of these nerves can
be made.

Dissect ion. — 'Y\\z posterior pulmonary plexus is easily dissected. To
fjct at it, the lung must be thrown well forwards over the pericardium,
and the pleura stripped from the jwsterior surflice of the puhiionary
root. The pneumogastric nerve sliould then he secured and followed
downwards. On the left side it will he found crossing the aortic arch ;
on the right side it lies by the side of the trachea.

The posterior pulmonary plexus is formed by the entire
trunlT^of the pneumogastric neiye^ breaking up into a
flattened network immediately under cover of the pleura
upon the posterior aspect of the root of the lung. Several

28

THORAX.

minute twigs from the upper thoracic ganglia of the sym-
pathetic enter this plexus. The posterior pulmonary

innominate artery.

sterno-clavicular
joint.

left innominate vein.

vena azygos major.

^0 — right bronchus.

4i^^^ right pulmonary
^■^ artery.

sulcus terminalis.

crista terminalis.

ight pulmonary
veins.

auricular appendix.

hepatic vein,
vena cava inferior.

Fig. 175. — Sagittal section through the thoracic cavity a
short distance to the right of the mesial plane. The
cavity of the right auricle and the relations of the parts
forming the right pulmonary root are seen.

plexuses of opposite sides are connected by some strong
branches, which cross the mesial plane in front of and
behind the oesophagus (Fig. 197, p. 78). From both the

THORACIC CAVITY. 29

anterior and i)uslcrior pulmonary plexuses fine twigs are
|)rolongcd into the lung along the divisions of the bronchi.
The posterior branches, however, are much larger than the
anterior.

The broncldal arteries (arteri;e bronchiales), one or two in
number on each side, are the proper nutrient vessels of the
lung. They are placed on the posterior aspect of the root
of the lung, and have, no doubt, been exposed in the dis-
section of the posterior pulmonary plexus. As a general
rule they lie in close contact with the back of the corre-
sponding bronchus and follow it into the lung. , ^

Dissection. — 'Y\\c pulmonary vessels and the bronchus should now be
separated from each other with the handle of the knife, and their relative
positions in the root of the luni;; studied. This dissection should be made,
not only in front, but also behind, so that the parts may be thoroui^hly
isolated and rendered distinct. Hardened and blackened bronchial
glands sometimes make the dissection a difficult one. These must be
removed.

The pulmonary veins are placed most anteriorly and the
bronchus most posteriorly, whilst the pulmonary artery is
intermediate in position. When examined in respect to
their relations from above downwards, the right and left
pulmonary roots are seen to differ from each other. On
both sides the veins occupy thejowest level. On the ri^ht
side the bronchus is highest and the artery intermediate,
whereas on the left side the artery is highest and the bronchus
intermediate in position. The different position of the
bronchus in the roots of the lungs is not due to any differ-
ence in the direction of the main stems or trunks of the
tubes, but to the fact that on the right side a branch arises
from the bronchus close to its origin, and proceeds almost
horizontally outwards to the upper lobe of the lung. This
division, which is not represented on the left side, lies above
the level of the pulmonary artery, and in consequence
receives the name of the epartcrial bronchus. The other
branches of the right bronchus, and all the branches of the
left bronchus, lie below the level of the main trunk of the

/;■

30 THORAX.

corresponding pulmonary artery, and are termed hyparterial
bronchi.

The relation of parts in the roots of the two lungs may
be shortly expressed thus : —

From Before Backwards.

(Veins.
Artery.
Bronchus.

From Above Downwards.

(Artery.
Bronchus.
Veins.

{Bronchus.
Artery. , __
Veins.

Phrenic Nerve (nervus phrenicus). — This is a long nerve
which arises in the neck from the cervical plexus, and
traverses the entire length of the mediastinal space to
reach the diaphragm. It has already been exposed upon
the lateral aspect of the pericardium in front of the root
of the lung. Follow it upwards and downwards.

The phrenic nerve enters the chest cavity through the
thoracic inlet, and as it does so it passes behind the sub-
clavian vein, and crosses obliquely the internal rnammary
artery in a directionTrom without inwards. It now proceeds
downwards through the superior mediastinum into the
middle mediastinum. In the latter it is applied to the
side of the pericardium in front of the root of the lung,
and is covered by the mediastinal pleura. Finally reaching
the diaphragm, the nerve breaks up into several branches
which pierce its substance and spread out on its under
surface.

But the two phrenic nerves of opposite sides present
certain differences. They differ (i) in length; and (2) in
certain of their relations.

The left phrenic is the longer of the two nerves, and this
is due, partly, to the greater projection of the heart and
pericardium to the left side, and partly to the fact that the
left cupola of the diaphragm which it enters does not rise so

IllORACIC CAVIJY. 31

high as llic right cupula. The difilrcnccs in rclalioiisliip
arc the following : — (i) As they traverse the superior nicdias-
tiiuiin the left phrenic nerve crosses the aortic arch, whilst
the right phrenic nerve lies in relation to the rijjlit side of
the right innominate vein and the superior vena cava; (2)
one or more of the terminal branches of the right nerve
I)ass through the opening in the diapliragm for the inferior
vena cava.*

The branches of the phrenic are chiefly destined for the
supply of the diaphragm, but in its course through the
middle mediastinum it gives a few fine filaments to the
pericardium and the pleura.

The small branch of the internal mammary artery which
accompanies the phrenic nerve, the arteria comes nervi
phrenici, may be traced in a well-injected subject to the
forepart of the diaphragm. It takes origin high up in the
tliorax, and gives branches to the pericardium.

Superficial Cardiac Plexus. — The best plan to adopt in
making a dissection of these delicate nerve filaments is to
begin by securing the two cardiac nerves which enter the
plexus from above. These are — (i) the cardiac branch from
the superior cervical ganglion of the sympathetic of the
/e/t side ; (2) the inferior cervical cardiac branch of the hifi
pTieumogastric nerve. Look for both of these nerves upon
the aortic arch. They will be found crossing it to the left
of the phrenic nerve, between it and the pneumogastric
nerve. The cardiac branch from the left pneumogastric
nerve is the smaller of the two, and as a general rule it lies
nearer the phrenic nerve than the other.

The superficial cardiac plexus into which these nerves
may be traced lies in the concavity of the aortic arch, and
upon the bifurcation of the pulmonary artery. At the point
of junction of the nerves the minute ^^fig/io/i of IVrisberg
may be discovered. The manner in which this plexus is

' It is somc'limos stalctl that the right jihrcnic nerve lies deeiier in the
chest than the left phrenic. This is not the case, as any one may ascer-
tain for himself by the examination of a scries of transverse sections
through the frozen thoracic cavity (wV/t* Figs. 169, 191, 192, and 193).

32 THORAX.

distributed to the heart will be afterwards noted : in the
meantime observe that it gives some fine offsets to the left
anterior pulmonary plexus.

Dissection. — The pericardium should now be cleaned. In removing
the loose areolar tissue from its anterior surface two ligamentous bands
which connect it to the posterior aspect of the sternum will be observed.
Of these, one — the inferior sterno-pericardiac ligament — binds it to the
ensiform cartilage, whilst the other — the superior sterno-pericardiac
ligament — connects it with the manubrium sterni, and comes into rela-
tion with the pretracheal layer of the deep cervical fascia. The upper
surface of the diaphragm should be carefully cleaned at the same time,
in order that its relation to the pericardium may be studied.

The Pericardium is a fibro-serous sac which loosely en-
velops the heart. It is placed in the middle subdivision
of the mediastinal space, and presents a somewhat conical
form. By its base it rests chiefly upon the central tendinous
part of the diaphragm, but beyond the limits of this it
encroaches, to some extent, upon the muscular portion.
More especially is this the case on the left side. Except at
one point, no difficulty will be experienced in separating
the pericardium from the diaphragm. The two are simply
bound together by some intervening areolar tissue. To-
wards the middle line, however, it will be found over a small
area to be inseparably blended with the central tendon. It
is important to recognise the abdominal viscera which stand
in relation to the base of the pericardium. It is placed, for
the greater part of its extent, over the upper surface of the
liver, the diaphragm alone intervening; but in front, a
small part corresponding to the apex of the heart projects
beyond the area of the liver and comes to lie over the
stomach (Fig. 176). The upper narrow part of the peri-
cardium will be noticed to close upon certain of the great
vessels that issue from the base of the heart. Upon each
side the pericardium is adapted to the concave inner surface
of the lung. It is clothed by the mediastinal pleura, and
has in relation to it the phrenic nerve and the arteria comes
nervi phrenici. Li front, very important relations have to be
studied. It lies behind the sternum and costal cartilages.

T/fOKACrC CA17TV.

33

and is for the most part separated from these by the two
pleural sacs, and by the anterior thin margins of the lungs.
Below the level of the sternal end of the fourth costal
cartilage, however, owing to the left pleura retreating some-
what to the left, a small area of the anterior surface of the
pericardium, as a general rule, comes into direct relation
with the chest wall. The extent ^ of this area, as we have

Fig. 176. — Dissection to show the abdominal viscera
which lie in relation to the under surface of the diaphragm.
The dotted line marks off the part of the pericardium in
relation to the stomach. (From Braune. )

1. CEsophagus.

2. Aorta.

3. Vena cava inferior.

4. Liver.

5. Pericariliuni.

6. Stomach.

7. Lobus Spigelii of the liver.

8. Spleen.

already seen, is variable. Behind, the pericardium forms
the anterior wall of the posterior mediastinum, and is
in relation to the contents of this space. Its relation to
the oesophagus is especially intimate.

' The importance of recognising this bare area of the pericardium
will be understood when it is remembered that it is here that the
surgeon taps the cavity of the sac when distended with fluid.

VOL. II. — 3

34 THORAX.

When the pericardium is denuded of the loose areolar
tissue which surrounds it and binds it to adjacent structures,
the strong dense character of the fibrous membrane which
forms its oideji^layer will be seen. This fibrous layer is
pierced by the various vessels which pass to and from the
heart, and is prolonged upon the walls of these vessels in
the form of tubular investments which gradually become
lost upon their coats. The only vessel which fails to receive
such a prolongation is the inferior vena cava, and this is
due to the fact that this vein pierces the pericardium where
it rests on the diaphragm, and can, therefore, hardly be said
to have any intra-thoracic course outside the pericardium.

The entire length of the pulmonary artery and_of the
ascending aorta are enclosed within the fibrous sac of the
pericardium.

Dissection. — The pericardium may be opened by means of a crucial
incision, viz. — (i) a longitudinal incision along the middle line of the
body from the point where it blends with the sheath of the aorta
downM'ards to the diaphragm ; (2) a transverse cut, extending from the
middle of the root of one lung to a similar point on the opposite side.

The Internal Serous Layer of the Pericardium is now

i exposed. This layer, which forms a completely closed
(Sac, lines the entire inner surface of the fibrous pericardium,
land is reflected from this, upon the vessels which pierce
I ^he fibrous layer, on to the surface of the heart. It gives
k smooth, poHshed appearance to the heart and to the
interior of the pericardial sac. The lining part of the
serous . laY-ei. is termed the parietal poriion ; the investing
ptsrtion which covers the heart is called the visceral part
or the epicardium. The great vessels in connection with
the heart, as they lie within the fibrous pericardium, also
receive more or less complete coverings from the serous
layer. The two arteries, viz. the pulmonary artery and
the aorta, are completely surrounded by a single tubular
sheath. This investment only leaves uncovered the
surfaces of these vessels which are in apposition with each
other — a fact which can readily be demonstrated by

THORACIC CAVITY. 35

passing the forefinger behind them. The term mius
trausvcrsus pericardii is given to the passage through which
the finger goes. It intervenes between the two arteries
in front, and the auricular part of the heart behind.

In the case of the veins, the covering which they
receive from the serous pericardium is not so complete. ,_,,
They are covered in front and on each side, whilst (
posteriorly they are bare and in contact with the fibrous
layer of the sac. The superior vena cava, which lies
immediately to the right of the ascending part of the
aorta, is a good example of this. Its lower half is en-
closed within the fibrous sac, but only two-thirds of its
circumference has a serous covering. The inferior vena
cava, which pierces the base of the pericardium, and at
once opens into the right auricle of the heart, receives a
very small investment.

When the apex of the heart is drawn forwards and
upwards, a deep, blind recess of the serous pericardium
will be seen, passing upwards behind it, between the
pulmonary veins of opposite sides.

Lastly, separate the left pulmonary artery from the
upper of the two left pulmonary veins, as they lie within
the fibrous pericardium. Stretching across the interval
between them will be seen a prominent semilunar fold of
the serous pericardium. This is the '■'■ vestigial fold of
Marshall.''^ It contains between its two layers a minute
fibrous band (ligamentum cavDS sinistra?), the remnant of
the left superior vena cava of the embryo.

Remains of the Thymus. — The thymus gland, which
is a very conspicuous object in the superior mediastinum
of the fcetus and young child, is only represented in the
adult by some condensed tissue of a brownish colour,
placed above the level of the aortic arch, and in front of
the innominate and left common carotid arterfes as they
spring from the arch. A few thymic /'ranches from the
internal mammary artery enter the wasted remains of the
gland, and some small veins pass from it and join the
subjacent left innominate venous trunk.

36 THORAX.

Dissection. — Remove the thymus, and dissect out the two innominate
veins and the superior vena cava. The left innominate vein will be
seen crossing the superior mediastinum from left to right. The short
right innominate vein is placed in the upper and right part of the
superior mediastinum. The union of these two trunks forms the vena
cava superior. The tributaries which enter these veins must also be
secured. One, the left superior intercostal vein, ascends upon the
aortic arch to reach the left innominate.

Innominate Veins. — The innominate vein of each side
is formed behind the sternal end of tlie clavicle by the
union of the subclavian and internal jugular veins. Be-
hind the lower part of the junction of the first costal
cartilage of the right side with the sternum, they unite to
form the superior vena cava.

Xhe right ifinominate vein (vena anonyma dextra) is
short. It is not more than one inch in length, and it has
a nearly vertical course from above downwards. Its outer
surface is covered with pleura and is in relation to the
phrenic nerve. The upper part of the innominate artery
lies to its inner side.

The left imio^nifiate vein (vena anonyma sinistra) is
much longer than the right vein, and has an oblique course
from the left downwards and to the right. It is placed
behind the manubrium sterni and the remains of the
thymus gland, and crosses in front of the three great
arteries which spring from the aortic arch.

The innominate vein of each side receives the following
tributaries : —

1. The vertebral vein.

2. The inferior thyroid vein.

3. The vein which drains the blood from the first or highest

intercostal space.
4.' The internal mammary vein.

The left innominate vein in addition receives the left
superior intercostal vein, and some small venous twigs
from the thymus gland. The left superior i?itercostal vein is
formed by the union of the veins from the second and
third intercostal spaces. It crosses the arch of the aorta,

THORACIC CAVITY. yj

and is of interest in so far that its uijpcr part represents
the upper pervious portion of the occluded left superior
vena cava of the embryo.

The Vena Cava Superior should also be examined at
this stage. It is formed behind the first costo -sternal
junction of the right side by the union of the two in-
nominate veins. From this it proceeds downwards, and
it opens into the upper part of the right auricle of the
heart aL the level of the upper border or~the jhjrd costal
cartilage of the right side. It is three inches long, and
shows very different relations in its upper and lower parts.
In the upper half of its course it hes in the superior
mediastinum (I^g. 191, p. 65). On the right side it is^
clothed by the mediastinal pleura, and has the phrenic
nerve in contact with it ; on the left side it is in relation
to the innominate artery. In the loiver half oi its course
it is enclosed within the fibrous pericardium, and is placed
in the middle mediastinum. The serous pericardium
covers it in front and laterally, whilst immediately to its
left side is the ascending aorta. This portion of the
superior vena cava lies in front of the pulmonary artery
and the upper pulmonary vein of the right side (Fig. 192,
p. 66).

The vena azygos major is the only large tributary which
joins the superior vena cava. It comes forwards above
the right bronchus, and enters the vena cava immediately
above the point where it pierces the pericardium. Minute
pericardiac and fuediastinal veins also pour their blood into it.

The Inferior Vena Cava is a larger vessel than the
superior vein of the same name. It enters the thora.x by
piercing the central tendon of the diaphragm. It can
hardly be said to have any course within the thorax^ seeing
that it immediately passes through the base of the pericar-
dium, and opens into the lower and back part of the
right auricle of the heart.

The Heart and its Vessels. — The heart is a hollow
organ with muscular walls, somewhat conical in shape,
and about the size of the clenched fist. It is placed

38

THORAX.

obliquely within the middle mediastinum, so that its
basal portion (basis cordis) is directed upwards, backwards,
and to the right, while its pointed apex looks downwards,
forwards, and to the left. But it is also placed un-
symmetrically within the chest cavity. In other words, it
projects more to the left than to the right, and in cases
where the frozen body is divided accurately in the mesial
plane, it is found that about one-third of the organ is in

the right, and about two-
thirds in the left half of
the thoracic cavity (Fig.

177)-

The general relations

of the organ should now
be examined. The base
is placed in front of the
middle portion of the
dorsal segment of the
vertebral column. Four
dorsal vertebrae lie above
it, and four below it,
whilst the intermediate
four (viz. the 5th, 6th^
7 th, and 8th). lie behind
it. The g/g;^ approaches the anterior wall of J;he-iharax,
and in life will be felt beating in the fifth intercostal
space of the left side, one and a half inches below
the nipple, and three and a half inches from the middle
line. The posterior_surface (facies diaphragmatica), which is
flattened, and looks more downwards than backwards,
res^japon_the diap.liTagm — the floor of the pericardium
alone intervening. Immediately below the cardiac area
of the diaphragm is the upper surface of the liver, and in
front and to the left a small piece of the stomach (Fig.
176, p. 33). The anterior surface (facies sternalis) of the
heart looks upwards as well as forwards, and lies behind
the greater part of the gladiolus of the sternum and
certain of the costal cartilages. On both sides the third,

Fig. 177. — The vertical line drawn
through the heart represents the
mesial plane. (From Braune. )

THORACIC CAVITY

39

fuLirili, and I'llih costal caililagcs arc in IVunl ul the heart,
l)ut as the chief bulk of the organ is situated to the left of
the mesial plane, the left sixth costal cartilage is also in
front of it. Three costal cartilages on the right side,
therefore, and four on the left side are in relation to the
anterior surface of the heart. The pleural sacs and the
anterior thin margins of the limgs intervene between the

ffltP?;,.

Fig. 178. — Diagram to show the position of the heart in
relation to the anterior chest wall. (From Braunc. )

heart enclosed within the pericardium and the anterior
wall of the thorax. A small portion of the pericardium in
the lower part of the anterior mediastinum is_in^ direct
relation to the triangularis sterni muscle as it covers the
deep surface of the sternum, and the inner extremities of
the fifth and sixth costal cartilages of the left side. A
wider area at the same level, owing to the incisura cardiaca
in the anterior margin of the left lung, is uncovered by the
lung. This area may be mapped out on the chest wall by

40

THORAX.

drawing a vertical line along the middle line of the
sternum, from the level of the inner extremities of the
fourth costal cartilages to the lower end of the gladiolus,
and by carrying two other lines, from the extremities of
the first line, outwards so as to meet at a point over the
apex beat of the heart. On either side., the heart and
pericardium is supported by the mediastinal pleura and
the inner surface of the lung.

superior vena cava

obliterated ductus ar-
teiiosus.

— -pulmonary artery,
left auricular appendix.

apex of the
heart.

Fig. 179. — Anterior aspect [fades sternalis) of the heart.
( From Gegenbaur. )

Ventr. d. Right ventricle.
Ventr. s. Left ventricle.

Atir. Right auricular appendix.
A triuin d. Right atrium.

The heart lies free within the sac formed by the peri-
cardium, except where it is attached by the great vessels
which are connected with its basal portion. Its position
is influenced, to a .certain extent, by the position of the
body. I /-■ _

External Configuration of the Heart. — In studying the
form and appearance of the heart, the dissector will find it
advantageous to refer to an injected specimen. At the

THORACIC CAVriY.

4«

same lime lie shuultl remember Uuil such a specimen is apt
to convey an erroneous inii)ression, in so far that during Hfe
the auricular and the ventricular chambers are never fully
tlislendcd at the same time.

The interior of the heart is divided by an internal [)arti-
tion into a right and a left cavity. Further, each of these
is still further subdivided into an upper auricular and a
lower ventricular chamber^ which communicate freely with

aortic arcli.
loft puliiioiiary artery,
left pulmonary veins..

vena cava superior.

right pulmonary

artery,
right pulmonary

veins.

— vcn.n cava in-
ferior.

Fig. i8o.

-Posterior surface {fades diaphragmatica) of the
heart. (From Gegeiibaur. )

I'enlr. s. Left ventricle.
Ventr. d. Right ventricle.
Aur. Left auricular appendix.

Atr. Left atrium.
Atr. d. Right atrium.

each other through a wide auriculo-ventricular opening.
The right and the left cavities of the heart, however, are
completely shut off from each other.

On the exterior of the heart there are markings which
indicate this internal subdivision, and enable us to map
out with the greatest accuracy the walls of the four cham-
bers. Thus encircling the heart in transverse direction,
nearer the base than the ape.x, is a deep furrow which is

42

THORAX.

continuous all the way round, except in front, where it is
interrupted by the root of the pulmonary artery. This is
the atmculo-yentricidar groove (sulcus coronarius). It in-
tervenes between the aurides which lie above it and the
ventricles which are placed below it. In the undissected
heart, with the epicardium in position, the depth of this
furrow is somewhat obscured, from the fact that it lodges
some large blood-vessels and a certain amount of fat.

The Auricular Part of the heart stands in marked con-
trast with the firm ventricular portion. Its walls are thin
andjlaccid, and in the uninjected heart they are collapsed,
so that it is difficult to realise the shape of this portion of
the organ. It is crescentic in^ form. The chief bulk of it
is placed behind, but_it sends forwards two processes or
cornua, termed, the ^auricular appendices. A deep con-
cavity or hollow is thus produced, in which lie the two
great arterial trunks which spring from the ventricles, viz.
the pulmonary artery in front and the aorta behind. The ac-
companying diagram, which
represents a tranverse sec-
tion through the auricular
portion of the heart, will
serve to illustrate this point
(Fig. i8i).

On the posterior aspect
of the auricular part of
the heart a faintly marked
groove extends upwards in
a vertical direction from the
auriculo- ventricular furrow
(Figs. 1 80 and 181). This
groove passes over the top of
the auricular part, and then
downwards in front of it.
It corresponds to the in-
ternal attachment of the interauricular septum (septum
atriorum), which intervenes between the right and left
auricular cavities, and therefore it is termed the inter-

FiG. 181. — Transverse section
through the auricular part of
the heart.

R.A. Right auricle.
L.A. Left auricle.

P. Pulmonary artery.

A. Aorta.

THOKACIC CAVITY. 43

aurkulur furrmv. 'J'lie posterior capacious part of each
auricle is somewhat (juadrangular Tn shape, and is called
tTic tiTrium cordis : the prolongation forwards on cither side
of the great arterial trunks is termed the auricular appendix
(auricula cordis).

It should be noted that the left auriclg forms a greater
part of the _j30Sterior wall of the auricular portion of the
heart than the right auricle. In other words, whilst the
left auricle is placed almost completely behind, the right
auricle comes, to a certain extent, to the front of the
heart in connection with the right part of its base
(Fig. 179).

On the outer and posterior aspect of the right auricle
(when it is distended), a faint furrow descends from the
upper part of the base of the auricular appendix over the
back of the atrium towards the auriculo-ventricular groove.
This is the sulcus Icnninalis of His. It has an embryo-
logical significance (I'ig. 175, p. 28).

The Ventricular Part of the heart is firm to the touch
and possesses thick fleshy walls. It is very distinctly
conical in form. Its apex corresponds to the apex of the
heart ; whilst it^ base is connected above with the two
atria of the auricular part of the heart, and givesjorigin in
front of these, and in_tbe_ interval between the auricular
appendices, to the two great arteries which conduct the
blood from the ventricular chambers, viz. the pulmonary
artery in front and the aorta behind.

In addition to the base and apex, the ventricular part
of the heart presents two borders and two surfaces. The
right borjlcr is long and sharp, and is directed obliquely
from right to left, from the base to the apex. It is called
the wrtr^'o acutus. The left border or margo obtusus is short,
thick, and rounded.

The anterior surface (facies sternalis) of the ventricular
part of the heart is full and convex, and is traversed by a
groove which begins above at the auriculo-ventricular furrow
immediately to the left of the origin of the pulmonary artery,
and proceeds downwards towards the right sharp margin,

44 THORAX.

which it reaches a httle to the right of the apex. This
groove is the anterior interventricular furrow^ (sulcus longi-
tudinaUs anterio7)7and it is placed much nearer to the left
margin than to the right margin of the heart. The posterior
surface (facies diaphragmatica) is flattened and traversed by
a similar groove, the posterior interventriculur furrow (sulcus
longitudinalis posterior). This joins the anterior groove
below, round the right sharp margin of the heart, and is
placed nearer the right than the left margin. These grooves
are occupied by vessels and lodge a little fat. They
indicate on the surface the anterior and posterior attach-
ments of the interventricular septum, and therefore the
extent of the walls of the two cavities. Roughly speaking,
two-thirds of the anterior surface, the margo acutus, and
rather more than one-third of the posterior suFface, belong
to the right ventricle ; whilst one-third of the anterior sur-
face, the margo obtusus, the apex of the heart, and rather
less than two-thirds of the posterior surface, belong^ to_the
left ventricle. On the anterior surface of the heart_a
bulging_of_the wall of the right ventricle will be noticed in
its upper and front part. This is_ termed \ht infundibulum
or conus arteriosus. From its summit the pulmonary artery
takes origin.

Dissection. — The vessels and nerves which are distributed to the
substance of the heart may now be dissected. The main trunks occupy
the furrows, and can be exposed by removing the epicardium and the
soft fat which is generally placed around them. In a young subject,
where the fat is scanty and the vessels well injected, very little dissection
is required. The nerves are exceedingly delicate and are derived from
the cardiac plexus. It is seldom that they can be satisfactorily displayed
in an ordinary dissecting-room subject.

The Coronary Arteries are the nutrient vessels of the
heart. They are two in number, and spring from the root
of the ascending aorta. It is here, therefore, that they
must in the first instance be sought, by dissecting deeply
in the auriculo-ventricular furrow. The left coronary artery
(arteria coronaria sinistra) springs from the left posterior

TirORACIC CAVITY. 45

sinus of \'alsalva,' and proceeds outwards behind tlic
pulmonary artery. It winds round the left side of the
heart (ramus circumflcxus), and ends on its posterior
aspect. Throughout its entire course it lies in the auriculo-
ventricular furrow. It gives off numerous twigs to the left
auricle and left ventricle, and one large branch will be
observed to pass downwards in the anterior interventricular
groove towards the apex of the heart (ramus descendens).

The right coronary artery (arteria coronaria dextra) arises
from the anterior sinus of Valsalva, and winds round the
right margin of the heart in the auriculo-vcntricular groove
to reach its posterior aspect, where it ends near the termina-
tion of the artery of the left side. An arterial circle is
thus formed, which embraces the base of the heart. The
right coronary artery gives off two large branches. Of
these, one passes downwards upon the right sharp margin
of the heart, whilst the second and larger descends towards
the apex in the posterior interventricular groove (ramus
descendens). It also supplies numerous smaller twigs to
the right ventricle and right auricle.

Cardiac Veins (vense cordis). — Take hold of the heart
by the apex and pull it upwards, so as to bring into view
its posterior surface. In the groove between the left
ventricle and left auricle — the coronary sinus (sinus coron-
arius) — a short wide venous channel will be seen. Open
it with the scissors along its whole length. By one ex-
tremity it opens into the right auricle, whilst by its other
end it becomes continuous with the great cardiac vein, and
the point of junction is marked by a valve of two segments.
Several posterior cardiac veins from the posterior aspect of
the ventricles also open into this sinus, and each orifice
is guarded by a distinct valve. Of these, one much larger
than the others, and called the middle cardiac vein (vena
cordis media), ascends in the posterior interventricular
groove. The right or small cardiac vein (vena cordis parva)

' The three sinuses of Valsalva are three bulgings of the wall of the
aortic root. One is on the front, and the other two on the back of the
vessel.

46 THORAX.

likewise joins the coronary sinus close to its termination.
It occupies that part of the auriculo-ventricular furrow
which, on the posterior surface of the heart, intervenes
between the right auricle and right ventricle. Lastly, the
oblique vein of Marshall (vena obliqua atrii sinistra) from
the back of the left auricle opens into the sinus close to
the point where it joins the right auricle. The orifice of
this vein is devoid of a valve. The oblique vein is very
minute, and would not deserve special mention, were it
not that it represents the lower previous part of the
obliterated left superior vena cava of the embryo.

The great cardiac vein (vena cordis magna) begins upon
the anterior aspect of the heart at the apex. It ascends in
the anterior interventricular groove to the auriculo-ven-
tricular furrow, in which it turns rounds th£- left margin of
the heart toj^oin^the coronary sinus. On its way it is joined
by numerous veins from the surface of both the ventricular
and auricular parts of the heart.

The anterior cardiac veins will be seen on the front sur-
face of the right ventricle. They open directly into the
right auricle.

But, in addition to those veins which appear upon the
surface, there are minute vessels in the substance of the
heart — the vencz Thebesii or vence minimce cordce — the orifices
of which will be recognised, when the right auricle is
opened, as the foramina Thebesii.

The cardiac veins, therefore, which drain the blood from
the heart, do not correspond with the arteries. The follow-
ing table expresses the arrangement in a brief form :

' Great cardiac vein. > ■' ' i Opening into

Posterior cardiac veins. ■ J coronary

Upon the surface^ Right cardiac vein. j gj^^^g

of the heart. 1 Oblique vein. ^ ■ '

. ... r opening into

Anterior cardiac veins. \ . ,

^ l right auricle.

In the substance "j .. c Opening into

01 the heart. J ( right auricle.

It is only in a heart which has been specially injected that all these

THORACIC CAV/JV.

47

veins can he scon. The [general ananj^cnicnt, however, can usually he
studied in (he course of an ()r<linary dissection. In certain cases, where
the veins are emi)ty and the fat on the surface of the heart scanty, they
may be inflated with air Ijy introducing a hlow-pipe into some of the
larj^er members of the series.

Cardiac Nerves. — For the most i)art the fine nerves
which form the superficial cardiac plexus are prolonged
downwards, and re-
ceiving close to the c-
heart a considerable
reinforcement from
the deep cardiac
])le.\us, they form the
righf coronary plexus
which comes into
relation with the cor-
responding artery.
The left coronary
plexus which accom-
panies the artery of
the same name is
derived from the
deep cardiac plexus.
The nerves do not
slavishly follow the
arteries, they soon
leave the vessels,
and are ultimately
lost in the substance
of the heart. Here
and there ganglia are
developed in connec-
tion with them.

Fig. 182. — Diagram to show the manner in which
the right auricle should be opened. The draw-
ing is taken from an injected heart in the
Edinburgh University. The dotted lines give
the directions in which the two incisions
should be made, a, Superior vena cava ;
/', Left innominate vein ; c, Right innominate
vein ; d. Vena azygos major ; e. One of the
pulmonary veins ; fy Inferior vena cava ;
S, Aortic arch ; //, Pulmonary arterj-.

Dissection. — Thecham-
iiers of the heart should

now be opened in the order in which the blood flows through them.
Begin with the right auricle, and, to bring it fully into view, draw
the heart well over to the left side of the Ijody. I'"ig. 1 82 .shows the
ilirection in which the incisions through its walls must be made. Two

48 THORAX.

cuts are required — ( i ) A vertical incision from the point at which the
superior vena cava enters the auricle to the point of entrance of the
inferior vena cava. In making this incision, care must be taken not
to injure the Eustachian valve — a fold of endocardium placed in front
of the mouth of the inferior vena cava. (2) An oblique incision carried
from about the middle of the first cut to the tip of the auricular
appendix. The dark venous blood should be washed away from the
interior of the auricle with a sponge.

When the dissector has fully studied the interior of the right auricle,
he may slit open with the scissors the superior vena cava and the two
innominate veins. By this proceeding he may satisfy himself that no
valves are present in these vessels.

Right Auricle (atrium dextrum). — The internal surface
of the cavity presents a smooth glossy appearance, due to
its endocardial lining. In the auricular ap£e.ndix the wall
is raised into a series of closely applied parallel ridges,
called the niusculi pectinati^ from their resemblance to the
teeth of a comb. These ridges are alsq_pres£nt pn the
right wall of the auricle, and when followed backwards they
are seen to end jon a smooth vertical ridge, called the crista
terminalis (His). (Fig. 175, p. 28.) It represents in the
interior of the auricle the groove on the exterior already
described under the name of the sulcus terminalis. In the
intervals between the musculi pectinati the wall of the
auricle is very thin.

The blood enters the atrium of the auricle by the fol-
lowing openings: — (i) the opening of the superior vena
cava; (2) the opening of the inieiipr_yena_cava; (3) the
opening of the coiW]iary_sinus ; (4) the orifices of three or
four anterior cardiac veins from the surface of the right
ventricle; (5) the foramina Thebesii.

The bipod, flows out of the cavity, into the right ventricle,
tjirough the large auriculo-yentricular opening.

The orifice of the superior vena cava is situat^ed at the
upper part of the auricle. The inferior vena _ cava opens
into the lower part of the cavity. The dissector should
note that these tWo veins are so directed that the currents
of blood, which flow from them into the auricle, shall not
be opposed the one against the other. The blood of the

THORACIC CAVJTY. 49

superior vena cava is diroclcd towards the auriculo-vcnlri-
cular opening, whilst the stream of blood flowing from the
moulh of the inferior vena cava is directed so as to im[)inge
against the septum between the auricles.

The aunciilo-vcntricujar orifice is the large, oval opening
situated in the lower part or floor of the auricle. Through
this aperture three fingers can be readily passed into the
ventricle. If the student now looks between this opening
ajid the orifice of the in^ferior vena cava, he will discover
the mouth of the coronary sinus^ imperTectly guarded by a
fold of endocardium, which receives the name of the
coronary^ valve or valve of Thebesius. An attentive examina-
tion of the inner surface of the auricular wall will further
reveal several minute, round, irregularly scattered openings
called the foramina Thebesii. Some of these are simply
small ctecal pits in the substance of the heart, whilst
others are the mouths of minute veins — the venic Thebesii.

Examine, in the next place, the posterior wall of the
right auricle. It is formed by the partition which separates
the two auricles from each other {seftum atrioruni). Upon
this an oval depression, surrounded by a prominent ridge,
will be noticed a short distance above the mouth of the
inferior vena cava. The depression is called xXxc fossa ova/is.
Its floor is exceedingly thin, and it marks_jiie position of
the foramen ovale of the foetal heart. The ridge which
encircles it is deficient below. It is, therefore, crescentic
in form, and is called the anmilus ovalis (limbus fossa; ovalis).
In a few cases, a communication between the two auricles
may be found by slipping a probe under the upper and best-
marked part of the annulus. Stretching between the
anterior horn of the annulus ovalis and the anterior margin
of the mouth of the inferior vena cava is a crescentic fold of
endocardium, sometimes cribriform and often very feebly
marked, called the Eustacliian valve.

Disscilioii. — The riylil vcnlriclc may now l)e opened by the following
incisions, (i) A vertical incision through the anterior wall of the
ventricle about a quarter of an inch to the right of the anterior inter-
ventricular furrow. Knter the knife above at the conus arterit)sus, and
carry it downwards, parallel to the furrow, as far as the right margin of

VOL. II.— i

so

THORAX.

the heart. (2) A transverse incision, through the anterior wall of the
ventricle, from the upiaer end of the first incision to the right margin of
the heart. This cut should be made parallel to the auriculo-ventricular
groove, and about half an inch below it. Both incisions must be made
with care and deliberation, but more especially the second one. In this

case the auriculo-ventricular
valve is liable to injury, and
it is well to protect it by
introducing the forefinger of
the left hand through the
auriculo-ventricular opening
into the ventricle.

The anterior wall of the
right ventricle can, in this
way, be raised in the form of
a V-shaped flap and turned
to the right. Wash away
the blood and clots.

Right Ventricle (ven-
triculus dexter). — The
cavity of tlie righit
ventricle, now laid open
and exposed to view, is
of a somewhat triangular
form, the base being
directed upwards, and
the apex downwards to-
wards the apex of the
heart. It does not
reach the apex of the
heart, however, but cor-
responds to the junction
of the anterior and pos-
terior interventricular furrows around the right sharp margin
of the heart. On transverse section, the cavity of the
right ventricle is semilunar in outline, owing to the thick
fleshy interventricular septum which constitutes its inner
and posterior wall bulging into it (Fig. 184). The wall is
thickest at its upper part, and thins slightly towards the apex.
With the exception of the conus arteriosus, the interior

Fig. 183. — Diagram to show the manner in
which the right ventricle should be
opened. The dotted lines indicate the
direction of the incisions, a, Superior
vena cava ; h. Pulmonary artery ; c,
Aorta.

THORACIC CAVITY.

S'

of which is sinoulh and even, the inner surface of ihe walls
of the right ventricle is rendered extremely irregular by the
l)rojection of fleshy ridges called columiuc carncic (trabeculae
carne;c). It is customary to describe these as presenting
three different forms —

{ii) simple elongated
ridges; {b) fleshy slips or
lrabecuk\i free through-
out the greater part of
their extent, but fixed
to the wall by their two
e^ljljijpilics ; {c) conical
fleshy projections of
considerable size, which
project into the cavity,
and are attached by their
bases only. These last
are called nmsculi papil-
lares^ and are arranged
so as to form an anterior
and _a posterior set.

Fig. 184. — Transverse section through
the ventricular part of the heart.
(From Luschka. )

1. Cavity of right ventricle.

2. Cavity of left ventricle.

3. Ventricular septum.

4. Thick wall of left ventricle.

5. Thinner wall of right ventricle.

6. Posterior interventricular furrow
with middle cardiac vein and pos-
terior branch of right coronary
artery.

7. Anterior interventricular furrow,
with great cardiac vein and anterior
branch of left coronary artery.

The free end of each of
these papiTIary muscles
gi\-es origin to several
delicate thread-like ten-
dons— ths cIiordcR ten-
djjim- — and by these
they are brought into connection with the segments of the
auriculo^yentricular valve. A transverse fleshy band will
be noticed to spring from the base of the anterior papiflary
muscle, and stretch across the ventricular cavity to the
septum, to which it is attached. This is the moderator
band. By fixing the yielding anterior wall of the ventricle
to the more solid septum, it is said to prevent over-dis-
tension of the cavity.

There are t\vo openings in the right ventricle — (i) the
auriciih-vaitriailar, which gives admission to the stream of
blood; (2) the pulmonary, through which the blood passes

52 THORAX.

into the pulmonary artery. Both these openings are situated
at_the base o£ the ventricle. The large oval auriculo-
ventricular orifice lies to the right, close to the right margin
oFTEe heart, whilst tKe pulmonary_aperture is placed to the
left, in front of the oth errand at the summit of tTie conus
arteriosus. Both of these openings are guarded by valves,
which act so as to give the blood its proper direction
through the heart.

The vah^e which guards the mouth ofthe pulmonary^
artery is composed of three semilunar segments, and is
called the semihmar or ihQsi^moid valve. By looking upwards
into the lumen of the artery, a view of these segments
may be obtained, but it is better to defer their examination
until the vessel itself has been studied.

The RighlL_Auriculo-Ventricular or Tricuspid Valve
(valvula tricuspidalis) is composed of three triangular,
pointed, membranous segments, termed aisj>s, which hang
down into the cavity. These are united by their bases so as
to form an annular membrane, and, through the intermedia-
tion of this, they are fixed around the auriculo-ventricular
opening. In the intervals between these larger segments
three smaller cusps may frequently be detected.

Each cusp is composed of two layers of endocardium,
between which there is a certain amount of fibrous tissue.
This fibrous tissue is, for the most part, confined to the
central portion of the cusp, the margins of which are there-
fore thin and translucent. When the valve is in action, it
prevents regurgitation of blood into the auricle during the
contraction of the ventricular wall. Attached to the
ventricular surface and margin of each segment, as well as
into the circumference of the auriculo-ventricular opening,
are several of the chordae tendinese which have been seen to
take origin from the apices of the papillary muscles. In
consequence of this, the ventricular surface of the valve is
rough, whilst the auricular surface — that surface over which
the blood flows — is smooth.

It is necessary, however, to note the relative position of
these cusps. One, the largest of the three, is suspended so

THORACIC CAVITY.

53

as to intervene between the auriculo ventricular opening and
th^ejiuluiojiary; orifice. It lies in front and to the left of the
opening. T\\h i^.i\\c i>ifi/jiiii7>ii/ari-iisj>. Another is placed
posteriorly to the auriculo-ventricular opening, and lies
closely applied to the septum. This is the sepfal cusp.
The tliirdJs. situated to the right, near the margin of the

Fig. i8 =

-Interior of the right auricle and right ventricle.
(From Luschka.)

I.

Superior vena cava.

9-

Septal cusp.

2.

Inferior vena cava.

lO.

Marginal cusp.

3-

Fossa ovalis.

II.

.\nterior papillarj- muscle.

4-

Annulus ovalis.

12.

Small papillary muscle on the

5-

Foramina Thebesii.

septum.

6.

Eustachian v.ilve.

'3-

Posterior papillary muscle.

7-

Opening of coronarj' sinus.

M-

Pulmonarj' arterj-.

8.

Infundibular cusp of tricuspi

J valve.

15-

Aorta.

I. Right auricle ; II. Right ventricle ; III. Left ventricle.

heatt, and may be termed the viarghtal cusp, The chordae
tendineaj of the anterior papillary muscle are distributed in
tlie interval between the infundibular and marginal flaps ;
those from the posterior papillary mu.scle go to the interval
between the marginal and septal flaps ; whilst to the interval
between the infundibular and septal flaps pass a number of
short chorda; tendinere, some of which spring directly from
the septum, whilst others proceed from low, feeble musculi
papillares, also connected with the upper part of the septum.

54

THORAX.

pulmonary artery.

Pulmonary Artery (arteria pulmonalis). — This vessel is
a short wide trunk about two inches long. It has an oblique
direction upwards and backwards, so as to reach the lower
aspect of the aortic arch. It here divides"into a right and
a left branch. At first, it lies in front of the root of the
aorta, but, before it terminates, it is placed upon the left
side of the ascending aorta (Fig. 179, p. 40). In relation

to each side of the pul-
monary artery the dis-
^°'"'^- sector will notice the

ductus arteriosus. Corresponding coronary
artery and auricular
appendix. It is almost
completely enclosed
within the fibrous peri-
cardium, the serous
layer of which forms a
single tubular sheath
around it and the as-
cending aorta.

The righj. pdmon-
ary_ artery is somewhat
longer and larger than the left. It passes transversely out-
wards behind the ascending aorta and superior vena cava
to reach the root of the right lung, where it has already
been dissected (Fig. 192, p. 66). Th.& leftjmlmpnary artery
runs outwards in front of _the descending aorta and left
bjTonchus to gain the root of the left lung (Fig. 192, p. 66).
The blood is thus conducted from the right ventricle of the
heart to the two lungs.

The Ligamentum Arteriosum or Obliterated Ductus
Arteriosus is a strong fibrous cord which will be observed
connecting the upper surface of the root of the left
pulmonary artery with the under surface of the aortic arch.
The ligamentum arteriosum has the same direction as the
trunk of the pulmonary artery. During foetal life it is the
patent continuation of the pulmonary artery, and conducts
the blood into the aorta. At this period, the right and

Fig. 186. — Heart of a seven months
fcetus. (From Gegenbaur. )

77/i^A'.lC/C CAr/'fV.

55

left pulmonary arteries arc of a .small size, and convey a
very small part of the blood-stream to the lungs. In
dissecting the fibrous remains of the ductus arteriosus,
note that the left recurrent laryngeal branch of the pneu-
mogastric nerve hooks round it at its attachment to tlie
aorta.

Dissi-ifi'oii. — The iwlmoiiary artery may now be slit open, so as to
exixisc tlio valve wliich f^iiards its orifice. This incision must he made
carefully, and tlie knife carried upwards ihrout^h the wall of the vessel
in the interval lielween two of the three segments which enter into its
formation.

Pulmonary Valve. — Each semilunar i^^ment will he

pillnion.iiy ii|H:iiiiii;

left appenilix.

right auricle.

coronary
sinus.

Fk;. 187. — Section through the basal part of the heart.
The aorta and the pulmonary arteries arc severed im-
mediately above their orifices. Note the orifices of the
coronary arteries.

observed to be attached by its convex margin, whilst its
concave border is free. Three minute pouches are thus
formed around the mouth of the vessel, and the openings of
these pouches are directed upwards. A good idea of the
valve may be obtained by filling the pouches with cotton
wadding. 'I'hc segments consist of a double layer of endo-
cardium, strengthened by intermediate fibrous tissue, ami
if the free margin of one be taken between the finger and

56

THORAX.

thumb, a minute nodule of cartilage may be felt about its
middle. This is the corpus Arantii, In structure, these
little flaps are similar to the corresponding segments of the
aortic valve — only weaker. We shall defer their more par-

FiG. 188. — Horizontal section of the
years, looked at from above. (

8 D.V. Eighth dorsal vertebra, cut
across near its upper surface.
S. Body of sternum.
3, 4, 8. Ribs ; between 4 and 8 fifth,
sixth, and seventh ribs are seen ;
behind seventh rib, the scapula.
3'. Third costal cartilage.
P. Pulmonary orifice, the three
semilunar segments of its valve
are seen.
A. A. Ascending aorta. On its right
side, the superior vena cava and
right auricular appendix.

L.A.

L.

D.A,

thorax of a man aged 57
From Symington. )

Atrium of left auricle.
Left auricular appendix.
Descending aorta ; to its right

side, the oesophagus.
Pericardial cavity.
Left pleural cavity.
Right phrenic nerve. Left

phrenic is seen on left side of

left auricular appendix.
Right upper pulmonary vein.
Right pulmonary artery.
Right bronchus.

ticular description, therefore, until the aortic valve is under
consideration. Opposite each seg^ment, the wall of the
artery shows a slight dilatation or bulging, called \h&jimis
of Valsalva. The three segments of the pulmonary valve

THORACIC CAVITY. 57

arc so placed llint two arc in front and one hcliind the
opening (I'ig. 188).

Pulmonary Veins(vcnre pulmonales). — The blood is con-
veyed hack to I lie heart by the pulmonary veins. These
have already been studied in the roots of the lungs. Two
issue from each lung. The right veins are longer than the
left, and pass inwards behind the superior vena cava and
the right auricle. The (eft veins pass in front of the de-
scending aorta (Fig. 188). If the inferior vena cava be
now divided and the heart turned upwards, the pulmonary
veins will be seen opening into the left auricle upon its
posterior aspect.

Dissection. — To open the left auricle, the heart must be turned well
over to the right side of the bodj-, and its apex lilted forwards. Fig. 189
shows the incision which should he made through its wall in order to
display its interior. Enter the knife well back, and carry it obliquely
forwards into the auricular appendix. The cavity is usually more or
less distended with injection, and after this has been removed the walls
should be washed with warm water.

Left Auricle (atrium sinistrum). — The only part of the
left auricle which can be seen from the front is its appendix.
This is narrower and more elongated than the corresponding
portion of the right auricle. Its margin also is more
distinctly notched. When laid open it will be seen that
the miisculi pedinati are confined entirely to the appendix.
Everywhere else the inner surface of the wall of the
left auricle is smooth. Qn the posterior wall the four
openings of the pulmonary veins will be seen. In some
cases the two pulmonary veins of one or both sides unite
before opening into the left auricle. The number of
venous orifices is thus reduced. They are not provided
with valves. In the lower and fore part of the auricle is
the oval aiiriculo-ventricidar opening. It only admits the
passage of two fingers into the ventricle, and is therefore
smaller than the corresponding orifice of the right side.
The position of the fcetal forajnen ovale can also be
distinguished upon this side of the septum atriorum, but
ii is not so well marked as it is in the right auricle. It

58

THORAX.

presents the appearance of a faint depression bounded
below by a slightly marked crescentic border.

Dissection. — To open the left ventricle, the dissector should stand
upon the right side of the body and grasp the heart with the left hand^

Fig. 189. — Diagram to show the manner in which the
left auricle and left ventricle should be opened. The
dotted line gives the direction in which the incision through
the wall of the auricle should be made. a, coronary
sinus ; b, great cardiac vein ; c and d, the two left pulmon-
ary veins ; e, pulmonary artery ; f, aortic arch.

so that the forefinger rests upon the upper part of the posterior inter-
ventricular furrow, and the thumb upon the upper part of the anterior
interventricular furrow. The wall of the ventricle should then be trans-
fixed by a long knife (fig. 189). Enter the knife below the thumb, about
half an inch to the left of the anterior furrow, and push it through the
ventricular wall towards the forefinger, so that the point emerges below
this, and half an inch to the left of the posterior furrow. Now carry the
knife downwards towards the apex, but do not allow it to come nearer
to the furrows than it was when first entered. If necessary, the cut on
each side may be extended upwards towards the base of the ventricle
with a small knife.

%.

THORACIC CAVITY.

59

Left Ventricle (vcnlriculus sinister). — The cavity of the
loft vcnlriclc is~T()ngcr and narrower than that of the right
ventricle. It reaches down to the apex of the heart, and
is somewhat conical in shape — tapering towards its lower
end. In cross section it presents a circular or broadly oval
outline {Fig. 184, p. 51). The walls of the left ventricle
are very much thicker than those of the right ventricle.

W'lu'ii the injection ;ind blood have been washed away

right ventricle.

left ventricle.

septum ventri-
culorum.

Fig. 190. — Section through the ventricular portion of tlic heart near the
apex. It shows the greater depth of the left ventricle.

from the interior of the left ventricle with hot water, the
coliDiDhc. carnecc. will be observed to fonn dense reticulations
on the inner surface of its walls. This network is especially
complicated at the apex and on the posterior wall of the
cavity. The surface of the septum and the upper part of
the anterior wall are, comparatively speaking, smooth. The
nii/sculi paf>i//ares, with their attached chordai tendinea^,
are collected into two strongly marked groups. They
are much larger than the pai)illary muscles of the right
ventricle, but do not project so distinctly into the cavity.

The left ventricle has two opcuLngs — (i) tl^e auriculo-
ventricular opening, through which the blood enters from
the auricle; (2) the aortic orifice, through which the blood
flows into the aorta. These apertures are situated close
together at the base of the ventricle, the aunailo-vcntrUular

6o THORAX.

Opening lying behind and to the left, whilst the aortic orifice is
placed in front and to the right. Both openings are guarded
by valves — the auriculo-ventricular opening by the mitral ox
bicuspid valve, and the aortic opening by the aortic valver

Tlie Mitral Valve (valvula bicuspidalisj prevents regurgi-
tation of the blood into the left auricle during the contraction
or systole of the ventricle. It consists of two large pointed
cusps with two smaller portions intervening. These are
similar in structure to the cusps of the tricuspid valve, but
the segments are larger and much stronger and thicker.
The fibrous tissue between the two layers of endocardium
is more abundant, but it is arranged in precisely the same
manner. The chordae tendinese from each musculus papillaris
proceed to one of the two intervals between the cusps, and
are attached to the adjacent margins and to the ventricular
surfaces of the two cusps. The anterior cusp is the larger
of the two, and lies in front and_to_the_rjght of ihe ^opening,
being so placed as to intervene between the _auriculo-
ventricular and the aortic apertures. The posterior cusp lies
behind and to the left of the opening.

Aortic Opening. — The part of the ventricular cavity
immediately below the orifice of the aorta has been termed
the aortic vestibule (Sibson). Its walls are not muscular but
fibrous, and therefore it does not collapse during the diastole
of the ventricular part of the heart. This is of advantage in
so far that it affords space for the proper action of the aortic
valve.

Looking upwards into the circular mouth of the aorta,
the aortic valve will be seen. It is similar in all respects to
the pulmonary valve, only its segments are stronger and
thicker, and the sinuses of Valsalva at the root of the aorta
are more strongly marked. The aortic valve will be studied
more fully at a later stage of the dissection.

Septum Ventriculorum. — The septum between the two
ventricles is a thick fleshy partition, — the anterior and
posterior attachments of which are indicated on the surface
of the heart by the anterior and posterior interventricular
furrows. Now that both surfaces of the septum are exposed.

THORACIC CAVITY. 6 1

i_t will 1)0 seen to bo thickest near the apex of the heart, and
to thin slightly in_an upward direction. In its upper and
fore part a small portion may be noted which is completely
destitute of muscular tissue, and which consists merely of
the two layers of endocardium, with some intervening fibrous
tissue. This portion is_termed \.\\c^J>ars meinbramicea si'/>/i\
and it is of interest from the tact that it is at this point that
congenital deficiency of the septum is most liable to occur.
The pars membranacea septi forms a portion of the wall of
the aortic vestibule, and lies immediately below the con-
tiguous ends of the anterior and right posterior flaps of the
aortic valve. i-U

Action of the Heart. — The above details will be dry and meaning-
less unless they are looked at in connection with the action of the heait
during life. It is impossible to understand the construction of lie
heart unless we study at the same time its function. During life, the
blood is driven through and from the heart by means of successive
rhythmical contractions and dilatations of its walls. But the entire
heart does not contract simultaneously. First, the auricles contract
together, and this is succeeded by the contraction of the ventricles ; in
other words, the auricular contractions correspond to the ventricular
dilatations, and vice versd. But, again, there is a period immediately
preceding the auricular contraction, during which the entire heart is at
rest, and this is called the period of cardiac rest. These three conditions
of the walls of the heart, viz. — (a) the cardiac rest, {b) the auricular con-
traction, {c) the ventricular contraction — follow each other consecutively
and without intermission, the one after the other ; and they are collect-
ively termed "a cardiac revolution." Let us study what is going on
inside the heart during each of these three stages.

Dwi'mg \.\\c />erioci of caniiac n-st the auricles are filling. Blood is
flowing into the right auricle through the openings of the superior vena
cava, inferior vena cava, and the coronary sinus ; and into the left
auricle through the orifices of the four pulmonary veins. A portion of
this blood trickles down through the auriculo-ventricular openings into
the ventricles ; but the blood is passing into the auricles in greater
quantity than it is trickling into the ventricles, and the result is, dis-
tension of the auricles. The second stage of the cardiac revolution
now takes place — viz. f/tc auricular contraction. The auricles contract
sharply and suddenly, and the blood is forced through the auriculo-
ventricular orifices into the ventricles. But how is it that the blood,
during this contraction, does not regurgitate into the veins, the mouths
of which are devoid of valves ? l-or the simple reason that the con-
traction begins at the venous orifices and auricular appendices, and
travels towards the auriculo-ventricular openings. The ventricles are

62 THORAX.

now full, and the third stage of the cardiac revolution takes place — viz.
the ventricular contraction. The ventricles contract more slowly, and
more deliberately than the auricles, and the blood is discharged into the
pulmonary artery and into the aorta. Regurgitation of blood through
the auriculo-ventricular openings into the auricles is prevented by the
apposition of the segments of the tricuspid and bicuspid valves, and when
the ventricular contraction ceases, regurgitation from the arteries into
the ventricles is prevented by the semilunar valves being thrown across
the arterial orifices.

The segments of the auriculo-ventricular valves are retained in posi-
tion, and prevented from being forced upwards into the auricle during
the ventricular contraction by the musculi papillares and the chordee
tendincce. As the ventricular wall in its contraction to a certain extent
advances towards the auriculo-ventricular opening, the musculi papil-
lares, in their contraction, retreat from it, and keep the tendinous cords
tense— never allowing them to slacken. When the contraction of the
ventricle ceases, and the vis a tergo is removed from the blood, the
recoil of the expanded wall of the artery exerts a pressure upon the
column of blood. Its backward flow is prevented by the filling of the
pouches of the semilunar valve.

Topography of the Cardiac Orifices. — The position of the different
cardiac orifices, with reference to the anterior wall of the chest, is a
matter of some importance. The pulmonary aperture is the most super-
ficial, and lies behind the upper part of the junction of the third left
costal cartilage with the left margin of the sternum. The pulmonary
artery itself lies behind the anterior end of the second left intercostal
space. The aortic opening is placed more deeply and at a slightly lower
level. It is situated behind the left margin of the sternum opposite the
lower border of the junction between the third left costal cartilage and
the sternum. The 7-ight auriculo-ventricular orifice lies behind the
sternum, close to the extremity of the fourth intercostal space of the
right side. The left atiriculo-ventricular opening is very deeply placed.
It is situated behind the left margin of the sternum at the level of its
junction with the fourth left costal cartilage.

Dissection. — The aorta should now be examined, and the various
structures in relation to it must be carefully dissected out.

The Aorta. — The aorta is the great arterial trunk which
conveys blood from the left ventricle of the heart, and dis-
tributes it by means of its branches to every part of the body.
After leaving the heart it arches over the root of the left lung,
and proceeds downwards in front of the vertebral column.
It leaves the thoracic cavity by passing through a special
opening in the diaphragm, and it ends in the abdominal
cavity upon the left side of the body of the fourth lumbar

TJIORACIC CAl'lTY. 03

vertebra, by dividing into the two conuiion iliac arteries.
The part of this great vessel which is contained withiti the
chest is divided, for convenience in description, into three
portions : viz. the ascendini:; aorta, the arch of the aorta, and
the desiendini^ thoracic aorta.

The asceiidiii}^ aorta takes origin from the base of the left
ventricle of the heart, and proceeds oblicjuely upwards and
to the right behind the sternum. It also inclines, to some
extent, forwards, so as to approach more closely to the
anterior wall of the chest. Reaching the upper border of
the second costal cartihii^e of the ri^^ht side, it changes its direc-
tion, and i)asses into the aortic arch. In the first instance
the aortic arch bends upwards and to the left in front of the
trachea, and then turns suddenly backwards so as to gain
the lower border of the body of the fourth dorsal vertebra.
Here the vessel makes a bend in a downward direction,
and becomes continuous with the descending:; thoracic aorta.

The Ascending Aorta (aorta ascendens) extends from the
base of the left ventricle, in a curved direction, to the upper
border of the second right costal cartilage. For the most
part it lies behind the sternum, but it projects slightly beyond
the right margin of the bone at the level of the second inter-
costal space. Throughout almost its entire length it is
enclosed within the fibrous pericardium, whilst the same
sheath of serous pericardium surrounds it and the pulmonary
artery. It is therefore placed within the middle medias-
tinum (Figs. 188 and 192, pp. 56 and 66).

It does not possess a uniform diameter. At its root,
opposite'^tRe segments of the aortic valve, it presents the
three bulgings termed tlie sinuses of, Valsalva ; whilst higher
ii£^on cross section, it generally exhibits a transversely oval
and not a circular outline. This is due to the presence of
a^iffuse bulging of the right wall, which receives the name
of thg_g/'(g<?/ aortuL sinus. . Against the wall of this sinus the
blood is driven with great force as it leaves the ventricle, and
at first sight it might seem to be aneurismal in its origin,
but its presence in the fietus renders such a view untenable.
It is, however, a very favourite site for aneurismal dilatation.

64 ./-fN»'e»l THORAX.

The more immediate relations of the ascending aorta may
now be examined. It is intimately associated with.the pul-
monary artery throughout its entire length. At_ijts_Qiigin Jt
iijes, behind the root of the pulmonary artery; higher up, this
vessel is placed to the left of the ascending aorta. To its
right side is the superior vena cava, whilst behind, it is in
relation to the left auricle and the right pulmonary artery
(Fig. 192, p. 66). It is overlapped by the right pleura
and the anterior thin margin of the right lung, which
intervene between it and the chest wall.

The coronary arteries have already been seen to spring
from this portion of the aorta.

The Aortic Arch, (arcus aortse) extends from the upper
border of the second right costal cartilage to the left side of
the body of the fourth dorsal vertebra. It is placed -within
the superior mediastinum, and the left pleura is applied to
its left aspect throughout almost its entire extent (Fig. 191).
It lies behind the manubrium sterni, and is crossed, under
cover of the left mediastinal pleura, by the left phrenic nerve,
the inferior cardiac branch of the left pneumogastric nerve,
the left superior cardiac branch of the sympathetic, the left
pneumogastric nerve, and the left superior intercostal vein, in
that order from before backwards. At first the aortic arch lies
in front of the trachea; afterwards it is placed to the left of
the trachea, the oesophagus, thoracic duct, and the left recur-
rent laryngeal nerve (Fig. 191). The iipper border of this sub-
division of the aorta is in relation to the left vena innominata,
and from this aspect of the vessel three large arteries take
origin, viz. from right to left — (a) the innominate, {b) the left
common carotid, and {c) the left subclavian. Its lower
surface^ which forms the concavity of thearch, overhangs the
byurcationjif Jhe^uhnonary artery, and is connected wjth
the root of the left pulmonary artery by the fibrous liga-
mentum arteriosum. Hooking round this surface is the
recurrent' laryngeal branch of the left vagus nerve.

Dissection. — The three large branches which spring from the aortic arch
carry blood for the supply of the two upper limbs and the head and ijeck.
They should now be dissected. The left common carotid takes origin some-

THORACIC CAVITY.

65

what nearer tlie innominate artery than the left siiijclavian. They are
all contained within the superior mediastinum, and Fi^. 193, p. 67, which

Fig. 191. — Transverse section through the thorax at the
level of the fourth dorsal vertebra. Tliis figure and Fig.
8, Vol. I. p. 28, are taken from the same specimen.

1. Left pneumoK.istric nerve.

2. .Scconil rib.

3. Left phrenic nerve.

4. Left superior intercost.^l vein.

5. Transverse part of tlie aortic arch.

6. Internal ni.ininiary vessels.

7. Right phrenic nerve.

8. Superior vena cava.

9. Trachea.
VOL. n. 5

10. Right pneumogastric.

11. (Esophagus.

12. Upper aortic intercostal arteries.

13. Vena azygos major.

14. liody of fourth dorsal vertebra.

15. Sympathetic cord.

16. Vena azygos minor superior.

17. Thoracic duct.

66

THORAX.

is taken from a tracing of a transverse section through the upper part of
this space a short distance above the level of the aortic arch, shows their
more important relations.

The Innominate Artery (arteria anonyma). — The inno-
minate artery is the largest of the three branches which

internal mammary vessels.

left pleural cavity,

pericardium,
pulmonary artery.

left phrenic nerve,
left bronchus.

descending aorta,

fifth dorsal vsrte'
bra.

right pleural cavity.

right lung,
pericardium,
ascending aorta,
right phrenic nerve.

superior vena cava.

right pulmonary
artery.

.right bronchus.

ight pneumogas-
tric nerve,
bronchial artery,
vena azygos major.

intercostal artery,
sympathetic cord.

Fig. 192. — Section through the mediastinal space at the
level of the fifth dorsal vertebra.

spring from the aortic arch. It passes obUquely upwards
and to the right, and, gaining the posterior aspect of the
right sterno-clavicular articulation, ends behind the upper
margin of the clavicle, by dividing into the right common
carotid and right subclavian arteries, hi front of the vessel
is the manubrium sterni, to the posterior aspect of which

i

THORACIC CAVITY

67

arc attached the stcrno-hyoid and sterno-thyroid muscles.
Further, the artery is crossed superficially, and close to its
origin, by the left vena innominata. Behind is the trachea ;
hut as the vessel inclines to the right, it comes to lie, at a
higher level, upon the right side of the windpipe. To the
r/X'/// side of the artery, in its upper part, are the pleura, the
right innominate vein, and the right phrenic nerve.

With the exception of the two trunks into which it
divides, the innominate artery gives off no branches. The
thyroidea ima, an occasional artery, may be seen to spring
from it in some cases.

Left Common Carotid Artery (artcria carotis communis

cost. cnrt. I

sterno-thyroid.

-int. mammary
arterj'.

left innomin-
ate vein.

innominate
arterj-.

right innomin-
ate vein.

phrenic nerve.

trachea.

oesophagus.

Fig. 193. — Transverse section through the superior medias-
tinum at the level of the third dorsal vertebra.

sinistra). — This artery ascends to the posterior aspect of
the left sterno-clavicular articulation. At this point it
leaves the thorax and enters the neck. It lies deeply in
the thorax, at a greater distance from the manubrium
stcrni than the innominate artery. /// front of this vessel

68 THORAX.

are the remains of the thymus gland, and the left vena
innominata, which crosses it. Behind, it is in relation, in
the first instance, to the trachea, and higher up to the
oesophagus and thoracic duct. To its left side is the left
vagus nerve. Further, it is supported on the left side by
the left pleura and lung. It gives off no branches within
the thoracic cavity.

The Left Subclavian Artery (arteria subclavia sinistra),
which springs from the aortic arch, near its termination,
lies very deeply in the superior mediastinum. It takes a
vertical course upwards towards the thoracic inlet, through
which it passes by arching outwards over the cervical
pleura and apex of the left lung to gain the upper surface
of the first rib. In front is the left common carotid artery,
the left vena innominata, and the left pneumogastric nerve.
To its right side are the trachea and the left recurrent
laryngeal nerve, and higher up, the oesophagus and thoracic
duct. Behind and to its left side are the left mediastinal
pleura and the left lung. The artery lies in a groove on
the inner aspect of the apex of the left lung, and, before
the dissection of the mediastinum, if the apex of the lung
be pulled outwards, the injected artery will be seen to
bulge into the pleural cavity (Fig. 193).

Dissection. — The deep cardiac plexus should now be dissected.
Divide the aortic arch at its commencement and termination. Two
ligatures should be placed around the vessel at each of these points and
the section made between them. This is done to prevent the escape
of the injection with which the artery is filled. The superior vena cava
may also be severed immediately below the point where it is joined by
the vena azygos major. By cutting the fibrous ductus arteriosus the
aortic arch can be drawn aside so as to expose the trachea and the
cardiac nerves in relation to it.

Cardiac Plexus (plexus cardiacus). — There are three
large nerve plexuses, formed in front of the vertebral
column, in connection with the sympathetic system. One
of these, the cardiac plexus, is situated within the thorax ;
the other two, the solar and the hypogastric with its pelvic
prolongations, are placed within the abdomen.

THORACIC CAVITY. 69

The cardiac ^cxus is subdivided into a superficial and a
deep portion, but these are in direct connection with each
other, and are to be regarded merely as different parts of
one i)le.\us. The deej) cardiac plexus is further massed in
two portions — a right and a left — which are united across
the middle line by many communicating filaments.

The superficial cardiac plexus is small in comparison with
the deep plexus. It has already been examined, and has
been observed to lie in the concavity of the aortic arch in
front of the bifurcation of the pulmonary artery. The deep
cardiac plexus is situated behind the aortic arch upon the
lower L'lul of the trachea. It is therefore placed on a
deeper plane and at a slightly higher level than the super-
ficial plexus. The branches which enter the different
parts of the cardiac plexus are derived from the cervical
portions of the gangliated cor3s of the sympathetic^ from
the pneumogastric nerves, and from the recurrent laryngeal
nerves.

The sympathetic ^cardiac branches which arise in the neck
are three in number on each side — one from each cervical
ganglion — and they are termed respectively the upper^
middle., and loiver sympathetic cardiac branches. The upper
sympathetic cardiac branch of the_ left side has already
been traced across the aortic arch into the superficial
cardiac |)l_e:xus.

'riie middle and loK<er branches of .the left side |oin the
left })oriion of the deep cardiac plexus on the trachea.
The ///;■(•(■ sympathetic cardiac branches of the 7'ight side
join the right portion of the deep plexus. ^Vithin the
thorax they run oblicjucly downwards and inwards behind
the innominate artery to reach their destination on the
side of the trachea.

The cardiac branches of the pneumogastric nerves are
given off partly in the neck and partly in the thorax, 'i'he
cervical branches, with the exception of the lowest on each
side, as a rule, join the sympathetic cardiac branches, and
thus lose their identity. The lowest cervical cardiac branch
of the left pneumogastric has been previously traced over

v

70 THORAX.

the aortic arch into the su2erficial_ cardiac_4)lexus. The
corresponding branch on the right side.. proceeds down-
wards in relation to the innominate artery, and joiiis the
right portion of the deep cardiac plexus.

Thoracic cardiac^ l?ra?iches are only given off__from the
trunk of the right pneumogastric. They join the right
portion of the deep plexiis.^

The recurrent laryngeal branches of the pneumogastric
nerves also supply cardiac twigs to the deep plexus. On
the left side, where the recurrent laryngeal hooks round the
arch of the aorta, these branches are more numerous, and
replace the thoracic cardiac branches of the left pneumo-
gastric. The following table shows the arrangement of
the cardiac nerves with reference to the plexus : —

I" I. Superior cardiac branch of sym-

c c • 1 T 1 pathetic of left side,

buperfacial cardiac plexus, . .\ t ^ ■ 1 t i i

^ ' "^ Lowest cervical cardiac branch

of left pneumogastric.

Middle and lower cardiac

branches of the sympathetic

Left portion of the deep cardiac f tt . ' • 1 j-

, '- / 1. Upper two cervical cardiac

plexus \

' ■ " ■ ' branches of the pneumogastric.

Cardiac branches of the left
recurrent laryngeal.

Three cardiac branches of sym-
pathetic of right side.

Cervical cardiac branches of
the right pneumogastric.

Thoracic cardiac branches of
the right pneumogastric.

Cardiac branches of the right
recurrent laryngeal.

The manner in which the different offsets from the
cardiac plexus are distributed has, to a certain extent,
been examined. From^ the right portion of the _deep
pjexus proceed — (i) an offset to join the right anterior
pulmonary plexus; (2) an offset for the supply of filaments
to the right jmricle of the heart; and (3) a very consider-
able prolongation, which passes downwards in front of the

Right portion of the deep cardiac
plexus,

THORACIC CAVirV. 71

right i)ulinon;iry artery to join the suijcrlicial cardiac
l)lcxu.s, and form the /•/>/// coronary plexus (p^ 47).

From the left pgrtiqn of the deep cardiac i)lc.\u.s i)roceed
— (i) an offset to the left auricle ; (2) an offset to the left
a nterio r pii 1 m o n a ry~ple x us ; ~wh ils't (3)" thc'greater part of
it is prolonged downwards in relation to the left pulnionon

artery to form the lefi coronary plexus (p. 47). '**"'% r^t»-

" - *f"v«vr A»

Removal of the Heart from the Body. — To do this it is only qj ^ • '^
necessary lo divide liie pulmnnaiy artery and the pulmonary veins. ^M<A»*.^
The other vessels have alreatly been severed. The ascending aorta
which is attached to the heart should next be slit open, care being taken
lo carry the knife accurately between two of the segments of the valve
so as not to injure either.

The Aortic Valve may now be studied and compared
with the pulmonary valve which guards the mouth of the
[)ulmonary artery. The rnembranous valve segrnents,_ai:e:
three in number^ and are of semilunar form. Attached
around the opening by their convex margins, their free
concave edges project into the lumen of the vessel. Three
little pockets, open towards the interior of the artery, are
in this manner produced. In the case of the pulmonary
artery the segments are arranged so that two are in front
and one at the back of the orifice. In the aorta, however,
one lies at the front and two at the back of the opening,
and on looking into the sinuses of Valsalva, which corre-
spond to the segments, the orifices of the coronary arteries
will be seen (Fig. 187, p. 55). Note that tlie)|^ are placed,
as a rule, opposite the free edges^ of the corresponding
valve segments, and further, that the right artery springs
from the anterior sinus of Valsalva, and the left artery from
the left posterior sinus of Valsalva. There are no such
openings to be seen in the pulmonary artery.

The aortic valve segments are constructed upon a
stronger plan than the pulmonary segments, although in
both the structure is the same. In the aortic segments
the fibrous tissue which intervenes between the two layers
of endocardium is more abundant, and the corpora Arantii
more apparent. The fibrous tissue is not uniformly dis-

72 THORAX.

tributed throughout the valve segment, as may be seen by
placing one of them on the point of the finger. A firm
cord runs along the free edge, and also along the attached
border. In addition to this, the fibrous tissue is spread
out in the segment in a uniform layer, except in two
localities called the lunulcz. These are semilunar in out-
line and lie next the free margin — one on either side of
the corpus Arantii. These lunulce. are thin and trans-
parent, seeing that they are formed of little more than the
two opposed layers of endocardium. When the valve is in
action and opposing the return of blood into the heart
during diastole of the ventricles, the thin lunular portions
of the valve segments are closely applied, and afford mutual
support to each other. The full brunt of the blood-
pressure is borne by the stronger portions of the valve
segments.

Cardiac Wall. — The last step in the dissection of the
heart consists in the examination of the parts which enter
into the formation of the cardiac wall. On the outside, the
heart is clothed by epicardium or serous pericardium, and
on JheJxLsidfi- its cavities are lined by the thin smooth endo::
cardium which is continuous through the orifices with the
lining membrane of the veins and arteries, and takes a large
share in the construction of the valve-flaps. Between the
epicardium and the endocardium is placed the muscular
tissue of the heart, which isjermed the myocardium. The
muscular fibres of the heart are disposed in several layers,
in each of which the fibres take a special direction.

But in an ordinary dissecting-room heart very little information can
be obtained as to the arrangement of the muscular fibres. The con-
tinuity of the walls is destroyed by the openings which have been made
to obtain a view of the interior of the different chambers. It is better,
therefore, to obtain a fresh sheep's heart. After filling it with a thick
mixture of flour and water, it should be boiled for a quarter of an hour.
The boiling has the effect of expanding the paste, while at the same
time it dissolves the connective tissue, and hardens the muscular
fasciculi. When the boiling is completed, the heart should be placed
in cold water, and the dissection carried out. The epicardium and the
muscular fibres should be torn off without using the cutting edge of the
scalpel.

THORACIC CAMTY.

73

The filircs of llio auricles arc dilVicull to dissect ; luit in llie veiUricular
portion of the heart, tlie student should be aljle to make out — (l) that
the difl'erent layers of muscular fa.sciculi cross each other oblicjuely, and
are for the most jwrt attached to the fdirous rings which encircle the
auriculo- ventricular o])enings ; (2) that the superficial fasciculi arc
common to both ventricles ; (3) that the majority of the fasciculi of the
left ventricle bend inwards at the ventricular septum ; and (4) that
a remarkable spiral or whorled arrangement of fibres (vortex cordis)
occurs at the apex of the heart.

Construction of the Ventriculax Orifices. — The heart
which is obtained in the dissecting-room, however, must not
be cast aside, because several very essential and important
I points may be made out by
its further dissection. In the
first place, it is easy to de-
termine the relation of the
auricles and ventricles. By
separating the epicardium
from the base of the ventricles
and the adjacent part of the
auricles, and removing the fat
and vessels from the auriculo-
ventricular furrow, it will be
seen that the muscular tissue
which enters into the forma-
tion of the ventricular walls
is quite distinct from _that of
the auricular walls. The bond
of jinion between the auricles
and ventricles consists of two fibrous rings which surround
the auriculo-ventricular openings. By removing the auricles
with a pair of scissors these can be more fully displayed.
It is to these rings that the triangular auriculo-ventricular
valye_cusps- arc^ attached, and it is from them that they
derive the fibrous tissue which intervenes between the
two layers of endocardium which form them. Two fibrous
rings are also placed around the arterial openings, and
supply the strengthening fibrous tissue to the semilunar
valve segments.

Fig. 194. — Diagram of the base
of the ventricular portion of
the heart.

P. Pulmonarj' opening.
\. Aortic opening.
L. Left auriculo-ventricular opening.
R. Right auriculo-ventricular ofx:n-
ing.

74 THORAX.

When the auricles are removed from the ventricles, the
relative positions of the orifices at the base of the ventri-
cular portion of the heart can be studied. The auriculo-
ventricular openings lie posteriorly and side by side. The
aortic opening is placed in front and between them, whilst
the pulmonary orifice is situated in front of the aortic open-
ing. A wide interval intervenes between the apertures of
the right ventricle : the aortic and left auriculo-ventricular
orifices, however, lie close together, and their fibrous rings
for a short distance are confluent with each other. In the
triangular interval, between the aortic and two auriculo-
ventricular openings, there is a mass of fibro-cartilage which
stands in intimate connection with the fibrous rings.

Dissection. — To expose the trachea more fully, separate the right and
left pulmonary arteries with the knife, and throw each outwards towards
the lung with which it is connected. The aortic arch must be drawn
aside, and some bronchial glands which occupy the angle between the
bronchi removed.

Trachea and Bronchi. — The thoracic portion of the
trachea, or windpipe, traverses the superior mediastinum.
It is a wide tube, which is kept constantly patent by a series
of cartilaginous rings which are embedded in its walls.
Posteriorly these rings are deficient, and in consequence
the tube is flattened behind. Its appearance in transverse
section may be seen in Fig. 191, p. 65. It^begns in the
neck opposite_the_sixth cervical vertebra, where it is con-
tinuous with the larynx, and it enters the chest cavity
through the thoracic inlet. Here it lies iri__the superior
juediastinal ^spacg,,, and ends by djviding into the two
bronchi opposite the intervertebral disc b_etwe£n jthe Jourth
and fifth dorsal^ vertebrae. Except at its lower end, which
is very slightly inclined to the right, it adheres rigorously
to the mesial plane.

The relations of the thoracic part of the trachea are as
follows: — In front — (i) the manubrium sterni, to the
posterior aspect of which the sterno-hyoid and sterno-
thyroid muscles are attached; (2) the remains of the thymus
body; (3) the left innominate vein ; (4) the aorti^_arch

THORACIC CAVITY. 75

and ihc ojijyiia_uLjJiy.i"'l''J"i''i'^'^<-' 'I'l^J '^"f^ common carcjlicl
arteries ; (5) the deep cardiac plexus. Jjehind, it rests upon
thetcsophagus, which lies somewhat to the IcTt side of the
mesial plane. On its rij;/if side arc the pleura and the right
pneumo^aalxic nT.Tve,^aiid afaTiigher level iKe innominate
artery ; and on its Af/ side arc the aortic arcB7 the left
recurrent laryiigeal nerve, and the left subclavian artery
(Figs. 191 andi93, pp. 65 and 67). v!t>

The two bronchi difTer considerably from each other.
The n'^/i/ bronchus is shorter and wider than the left, and
appears to be more directly in a line with the trachea. The
vena azygos major passes forwards in contact with its u[)per
surface. The suiicrior-vicna^cayaiind llie right pulmonary
artery lie in front of it (Fig. 192). The kJt_b^ronchus is
longer and narrower than the right. As it passes outwards
and downwards it crosses in front of the oesophagus and
the descending aorta, and behind the left pulmonary artery
(Fig. 192). From its postero- inferior aspect a slender
muscular slip may, in some cases, be observed to take
origin. This fasciculus connects it with the oesophagus,
and is therefore called the bro)icho-cesophageal muscle.

The relations of the bronchi in the roots of the lungs
have already been studied {vide p. 29).

Posterior Mediastinum. — This term is applied to that
part of the interpleural space which lies behind the peri-
cardium. It may be regarded as a continuation downwards
of the posterior part of the superior mediastinum, and many
of the structures in the one are prolonged downwards into
the other. The arbitrary upper limit of the posterior
mediastinum is the lower border of the fourth dorsal
vertebra. In front, it is bounded by the pericardium,
e.\cept in its very lowest portion, where the anterior wall is
formed by the posterior surface of the diaphragm (Fig. 196).
Behind, it is limited by the bodies of the dorsal vertebras
below the fourth, and on each side by the mediastinal pleura/
as it passes back from the pericardium to the spine. In
transverse section its outline is quadrilateral. Figs. 195
and 196 are taken from tracings of transverse sections

76

THORAX.

through the space. They serve to show the character of
the space and the relative positions of some of the more
important contents. The following is a list of the struc-
tures which it contains : —

1 . The descending thoracic aorta.

2. The oesophagus.

3. The pneumogastrlc nerves.

4. The thoracic duct.

5. The venajix^gosjiiajor.

Certain of the right aortic inter-
costal arteries. " """ '~
The vena azygos minor superior.
The vena azygos mintDr inferior.
The great__splanchnic nerves.

pericardium

thoracic aorta,

vena cava inferior.

cesophagus.

thoracic duct,
vena azygos major.

pleura

.pleura.

Fig.

195. — Tracing of section through the posterior medias-
tinum at the level of the eighth dorsal vertebra.

Dissection. — To open into the posterior mediastinal space it is neces-
sary to make a vertical incision through the pericardium, M^hich forms
its anterior wall. Carry the knife along the line of the oesophagus, and
throw the pericardium outwards. If this be done with care, a fleshy
band may, in some cases, be observed crossing the superficial aspect of
the thoracic aorta, and extending from the oesophagus to the pleura,
which forms the left lateral wall of the posterior mediastinal space.
This is the pletiro-xsophageal muscle. In the majority of cases, how-
ever, this muscle is only represented by a few slender muscular fasciculi,
which are difficult to isolate from the areolar tissue in which they lie.

Pneumogastrlc Nerves (nervi vagi). — The pneumogastrlc
nerves can now be followed throughout their entire course
within the thorax. They traverse both the superior and
posterior mediastinal spaces, but differ so much in their

THORACIC CAVITY.

77

relations on the two sides of the body that it is best to
examine each separately.

The lefl pneumozasiricjtierve enters the thorax in the in-
terval between the left common carotid and left subclavian
arteries, and behind the left innominate vein (Fig. 193,
p. 67). It has already been oi)servcd crossing the arch of
tjic aorta behind and to the left side of the phrenic nerve
and the two superficial cardiac nerves {V'vs,. 191, p. 65).
Here also it has been seen to gi\r <'IT iis iniirunt laryngeal

pericirdium.

diapliragni

thoracic duct.
"^ right pleura.
~v. azygos ni.ij.

Fic. 196. — Tracing of a section through the lower part
of the posterior mediastinum, where its anterior wall is
formed by the diaphragm.

braoclL. Leaving the aorta, it sjnks behind the root of
the left lung (Fig. 197), and at once breaks up into a
number of branches, which unite in a plexiform manner
to form the left posterior pulmonary plexus. It issues from
this plexus in the form of one or two cord^, which pass to
the anterior aspect of the cesophagus. Upon the oesophagus
another plexus — the p>lexus guLz — is formed. Both of the
pneumogastric nerves take part in the formation of this
plexus. From the plexus gulre the left pacumogastric
ejnerges_as onejtrunk^and passes out of the thorax by the
cesopliagoal opening of tlie diaphragm. AVithin the ab-
domen it breaks u[) into branches upon the anterior
surface of the stomach. "

78

THORAX.

"Y^jight pneumogastric nerve, in the upper part of the
superior mediastinum, lies deeper in the thorax than the
left nerve. It enters by passing between_J;h.e suhclaYJan
artery and the right innominate vein, and descends by the
side of the trachea (Figs. 191 and 193) to the posterior

left vagus.

left recurrent
laryngeal nerve.

posterior left pul-

monary plexus.

left bronchus. —-
left pulmonary vein.

right vagus nerve.

right recurrent
laryngeal nerve.

trachea,
cardiac nerves,
oesophagus.

— vena azygos major.

posterior right
pulmonary plexus.

^ right bronchus,
pericardium.

I ight pulmonarj'
vein.

I I sophagus.
plexus guise.

vena cava inferior.

diaphragm.

Fig. 197. — Dissection of the roots of the lungs, the peri-
cardium, the pneumogastric nerves, etc., from behind.
( Brooks. )

aspect of the root of the right lung (Figs. 197 and 192).
Here it breaks up into the n'g/i^ posterior pulmonciry plexus,
gjid; issuing from this in the form of two nervous cords, it
takes part in the formation of the plexus giilce. It leaves
this plexus upon the posterior aspect of the oesophagus.

THORACIC CAVITY. 79

and, entering the abdomen througli the ccsophagcal open-
ing of the diaphragm, it breaks up into branches on the
posterior aspect of the stomach, x

The pneumogastric nerves give off the following branches
within the thorax : —

1. l\ecurreiit laryngeal (left side).

2. Thoracic cardiac.

3. Pulmonary.

4. G^^sophageal.

5. Pericardial.

The left 7-ecinTent laryngeal tte^'ve (nervus laryngeus inferior
sinister) springs from the pneumogastric as it crosses the
arch of the aorta. It hooks round the aortic arch, or
rather the attachment of the ligamentum arteriosum to the
under surface of the arch, and reaching the trachea, ascends
by the side of this to the larynx. The right recurretit laryn-
geal f/erve (nerxus laryngeus inferior dexter) arises in the root
of the neck, and liooks round the subclavian artery.

The thmricic cardiac bratiches (rami cardiaci inferiores) of
the right side proceed in part from the pneumogastric and
in part from the recurrent laryngeal nerve of that side.
On the left side of the body they are derived from the left
recurrent laryngeal nerve as it turns round the aortic arch.

The pulmonary branches have already been studied in
connection with the root of the lung {vide p. 28).

The (esophageal branches (rami cesophagei) are dispensed
to the gullet in two sets — (i) a few delicate twigs are given
by the pneumogastric before it enters the pulmonary plexus
to that portion of the oesophagus which lies in the superior
mediastinum ; (2) numerous filaments are supplied by the
plexus guL-e to that part of the oesophagus which is placed
in the posterior mediastinum.

The pericardial branches are a few fine filaments which
come from the plexus gulx and, perhaps, from the posterior
pulmonary plexus and enter the back of the pericardium.

(Esophagus. — The thoracic portion of the oesophagus
should next be studied. It lies partly in the superior
mediastinum and partly in the posterior mediastinum. It

So THORAX.

is the narrowest, but at the same time the most muscular,
part of the alimentary canal. It descends in front of the
spine, following its antero-posterior curvature, and leaves
the thoracic cavity opposite the tenth dorsal vertebra by
passing through the oesophageal opening of the diaphragm.
The oesophagus, does not pursue a straight course through
the thorax : it Jfiters somewhat to the left of the middle
line ; but on tracing it downwards, it will be noticed-.Jto
incline inwards, so as to assume a mesial position ojjposite
the fifth dorsal vertebra. From this it again^deviates to the
left so as to gain the oesophageal opening in the diaphragm.
In the superior mediastinum the oesophagus lies imme-
diately behind the trachea (Figs. 191 and 193); below this
it is crossed by the left bronchus, with which it is sometimes
connected by the broncho-oesophageal muscle (Fig. 192).
From this point onwards through the posterior mediastinum
it is covered in front by the pericardium, which is applied
closely to it (Fig. 195). Just before entering the abdomen
it lies behind the posterior part of the diaphragm (Fig. 196).
From above downwards, therefore, the immediate anterior
relations of the oesophagus are: (i) trachea; (2) left
bronchus; (3) pericardium; (4) diaphragm. Behind^ the
gullet lies, except at its lower end, in front of the vertebral
column, but there are many structures which intervene
between them. Thus, in the superior mediastinum the
longus colli muscle separates the gullet .fLom the__spiine,
while in the posterior mediastinum it is placed in franl__of
the vena azygos major and the thoracic duct, and the vena
azygos minor inferior and the right intercostal arteries cross
behind it. In its lower part, the gullet inclines forwards
and to the left, so that it comes to rest directly upon the
anterior surface of the thoracic aorta. These relations are
seen in Figs. 195 and 196. Upon \.h.e. right side, during its
course through the posterior mediastinum, the oesophagus
is clothed by the mediastinal pleura, whilst on the /eft side
it is related in the posterior mediastinum to the thoracic
aorta, except where in its lower part it lies in front of that
vessel (Figs. 195 and 196). In the superior mediastinum

THORACIC CAVITY. 8i

the thoracic duct is closely ap[)licd to the left side of the
cesophagus, and the left pleura comes into partial relation-
shi[) with it (Fig. 193)- Below this, however, it is not
directly related to the pleura of the left side.

The pneumogastric nerves form the plexus gula; on the
walls of the gullet, as it traverses the posterior mediastinum,
and accompany it in the form of two nerve-trunks through
the ceso[)hageal opening — the right nerve being placed on its
posterior aspect, whilst the left nerve is placed in front of it.

The Descending Thoracic Aorta (aorta thoracica). — The
descending thoracic aorta is the direct continuation of the
aortic arch, and it traverses the posterior mediastinum. It
begins at the lower border of the fourth dorsal vertebra,
and ends opposite the last dorsal vertebra by entering the
abdomen through the aortic opening of the diaphragm, and
becoming the abdominal aorta. At its commencement it
lies somewhat to the left of the middle line, but as it pro-
ceeds downwards it inclines inwards, so that at its termina-
tion it^is mesial in position. It lies upon the bodies of the
vertebra;, and therefore it shows a curve corresponding to
that of the vertebral column in the dorsal region. In front.,
it is crossed by the root of the left lung. Below this, it is
covered by the pericardium and the posterior part of the
diaphragm. Behind., it rests upon the vertebral bodies and
the intervening intervertebral discs, whilst crossing behind
it the dissector will observe the vena azygos minor inferior,
and, in many cases, the vena azygos minor superior. To the
left side, and closely applied to the vessel, is that part of the
pleura which forms the left lateral wall of the posterior media-
stinum ; whilst on its right side will be noticed the thoracic
duct and the vena azygos major (Figs. 192, 195, and
196).

The oesophagus has a varying and important relationship
to the thoracic aorta. At first it lies to the right of the
aorta, but as it approaches the diaphragm it inclines to the
left, and comes to lie in front of the vessel ; and lastly,
before it passes through the oesophageal opening of the
diaphragm, it is somewhat to its left side.
VOL. II. — 6

82 THORAX.

The Branches of the Descending Thoracic Aorta may

be grouped under the heads of visceral and parietal.

Visceral.

/'Bronchial.
I Pericardiac.
I CEsopEageal.
\^Posterior mediastinal.
Parietal. Intercostal (nine on each side).

The bronchial arteries (arteriae bronchiales) are usually
three in number — two for the left lung and one for the right
lung. They are' very variable in their manner of origin.
The right bronchial artery often springs from the first aortic
intercostal artery. The left bronchial arteries generally
take origin from the aorta. They run upon the posterior
aspect of the corresponding bronchus, and they have already
been studied as constituent parts of the roots of the lungs.
In the substance of the lung, they follow the bronchi, and
show a similar mode of branching and distribution.

The bronchial veins are of small size. The left opens
into the vena azygos minor superior; the right joins the
vena azygos major. ' ^"'

The pericardial branches (rami pericardiaci) are some
minute twigs which are distributed to the posterior aspect
of the pericardium.

The oesophageal arteries (arterige oesophagese) are the
vessels of supply to the gullet. They are four or five in
number, and are irregularly placed. They spring from the
front or right side of the aorta, and form a chain of anas-
tomoses on the wall of the oesophagus. Above, this chain
communicates with branches of the inferior thyroid artery,
whilst below, it communicates with the ascending oesopha-
geal branches of the coronary artery of the stomach.

The posterior 7?iediastinal branches (rami mediastinales)
are very small, and are given to the areolar tissue and glands
in the posterior mediastinal space.

The intercostal branches (arterige intercostales) will be
observed arising in pairs from the posterior aspect of the
aorta. Defer their examination until the thoracic duct and
the sympathetic cords have been dissected.

rilORACIC CAVITY. 83

The Thoracic Duct (ductus thoracicus). — The thoracic
cUnl, altliough a vessel of small calibre, is one of high
importance. It receives all the lymphatic vessels of .the
body below the diaphragm (except those from part of the
upper surface of the liver), the lymphatics of the left side
of the chest (including the left lung and left side of the
heart), and the lymphatics of the left superior extremity
and left side of the head and neck. R will be found by
dissecting in the loose areolar tissue which Hes between the
aorta and the vena azygos major. Its diameter is not much
greater than whip-cord, and it will be recognised from its
position, and by the great elasticity which it exhibits when J

it is pulled by the forceps. Trace it downwards, and it will Ujp^'^
be found to enter the thorax upon the right side of the
aorta, and through the same opening in the diaphragm. It
commences within the abdomen upon the body of the
second lumbar vertebra in a dilatation, called the recepta-
culum chyli. As it is followed upwards it will be noticed
to incline gradually to the left. At the level of the
fourth dorsal vertebra it passes behind the aortic arch and
oesophagus (Fig. 191). It now ascends to the neck between
the oesophagus and left pleura, and ends by joining the
internal jugular vein at its point of union with the subclavian
vein. In the diagrams which are given of the posterior and
superior mediastinal spaces, the relations of the thoracic duct
may be studied (Figs. 191, 192, 193, 195, and 196). It
will be seen that in the posterior mediastinum it lies behind
the oesophagus, but in the superior mediastinum it is placed
upon the left side of the oesophagus. In the former situa-
tion, before the parts are disturbed by dissection, it can
readily be exposed by raising the right huig and dividing
the right mediastinal pleura ; in the latter situation the left
/u/igmust be raised and the left mediastinal pleura divided.
As it passes upwards through the thorax, the thoracic duct
pursues a somewhat wavy or flexuous course. It frecjuently
breaks up into two or more branches, which unite again to
form a single trunk. It is provided at intervals with valves
of two segments, and these, when the duct is injected, give

84 THORAX.

it a beaded or nodulated appearance. The valves are more
especially numerous in the upper part of the duct.

Thoracic Lymphatic Glands. — Throughout the dissection of the
thorax the dissector has, from time to time, met with groups of lymph-
atic glands. These are of considerable importance, seeing that their
enlargement in disease is not unfrequently the cause of serious thoracic
trouble. The following are the chief groups : — ( i ) Two chains of
minute glands, which are placed in relation to the anterior thoracic wall
and follow the course of the internal mammary vessels. They are
termed sternal glands (lymphoglandulje sternales), and are joined by
lymphatic vessels from the anterior thoracic wall, the mammary glands,
the front jDart of the diaphragm, and the upper part of the front wall of
the abdomen. (2) Two chains of glands on the posterior thoracic wall
— one on either side of the spine in relation to the vertebral extremities
of the ribs. They are very minute, and offsets from these chains ac-
company the intercostal vessels between the intercostal muscles. They
are therefore called the intercostal glands (lymphoglandulee intercostales),
and they receive the lymphatics of the posterior thoracic wall. (3)
Anterior mediastinal glands (lymphoglandulse mediastinales anteriores),
two or three in number, and receiving lymphatics from the diaphragm
and upper surface of the liver. They occupy the lower open part of the
anterior mediastinum. (4) Posterior mediastinal glands (lympho-
glanduloa mediastinales posteriores), following the course of the thoracic
aorta, and joined by lymphatics from the diaphragm, pericardium, and
oesophagus. (5) Superior mediastinal glands (lymphoglandulse medi-
astinales superiores), an important group, eight to ten in number,
and placed in relation to the aortic arch. The lymphatics of the heart,
pericardium, and thymus body enter them. (6) Bronchial glands
(lymphoglanduls bronchiales), continuous above with the preceding,
and massed chiefly in the interval between the two bronchi. They are
also prolonged into the roots of the lungs. The lymphatic vessels of
the lungs poiir their contents into them. In the adult, they are gener-
ally dark in colour, and sometimes as black as ink.

The lymphatics of the right side of the chest, the right lung, and the
right half of the heart join the right lymphatic duct (ductus lymphaticus
dexter), a minute and short vessel situated in the root of the neck. It
opens into the angle of union between the right internal jugular and
right subclavian veins.

Removal of the Lungs. — The lungs may now be removed by divid-
ing the trachea about an inch and a half above its bifurcation. The
bronchi and vessels should be traced into the lobes of the lungs, and
their manner of subdivision and distribution throughout its substance
studied.

Ramification of the BroncM and Vessels within the

THORACIC CAVITY. 85

Lungs. — The student has previously observed that the two
kings are not symmetrical. The right lung is subdivided
into three lobes, whilst the left lung is cleft into two lobes.
The bronchi exhibit a corresponding want of symmetry.
Each tube, as it approaches the pulmonary hilum, divides
into branches for the different lobes. The right bronchus
gives off two such branches for the upper and middle lobes
of the right lung respectively, whilst the main stem of the
tube sinks into the inferior lobe. The left bronchus sends
off a large branch to the upper lobe of the left lung, and
then enters the lower lobe. The first branch of the right
bronchus leaves the main stem about one inch from the
trachea. The first branch of the left bronchus, on the other
iiand, takes origin about twice that distance from the
trachea.

But^he relation of the pulmonary artery to the bronchial
subdivisions is different on the two sides. In both cases, it
lies in front of the undivided portion of the tube, but on the
right side it turns backwards, so as to reach the posterior
aspect of the bronchus below the first and above the secojid
division. It is due to this arrangement that the right
bronchus occupies the highest level in the right pulmonary
root. On the left side, the pulmonary artery turns back-
wards above the level of the first bronchial branch, and
therefore holds the highest place in the left pulmonary root.
On the rijght side, then, the first bronchial branch is placed
above the pulmonary artery, and it is termed the efaiicrial
bronchus ; all the others lie below it, and are termed hypar-
terial bronchi. On the left side there is no eparterial tube;
they are all hvparterial.

A consideration of these relations led Aeby to conclude that the epar-
terial bronchus, and the upper lobe of the right lung to which it goes,
arc not represented on the left side of the body. In other words, he
believed that the middle lobe of the right lung is the representative of
the upper lobe of the left lung.

When the main stem of the bronchus is followed into the
inferior lobe on either side, it will be observed to travel
downwards towards the back part of the base, and give off,

86

THORAX.

as it proceeds, a series of large ventral., and a series of
smaller dorsal branches. The first hyparterial division on
each side {i.e. the branch to the middle lobe of the right
side, and the branch to the upper lobe of the left side)

Fig. 198. — Schema of the branching of the two bronchi.
(From Gegenbaur. )

P. Pulmonary artery.

d. Dorsal divisions of the bronchi.

V. Ventral divisions of the bronchi.

The highest v on each side indicates the first hyparterial bronchus,
or, in other words, the branch to the upper lobe of the left side
and the middle lobe on the right side.

may be regarded as the first member of the ventral group
(Fig. 198).

It should be observed that when the bronchial tubes
enter the lung, they cease to be flattened posteriorly, and
become uniformly cylindrical. This is due to the cartilage

THORACIC CAVITY. 87

being disposed arouml the tulie on all its aspects, in the
form of irregular flakes, and imperfect rings. The farther
the tubes arc traced, the scarcer and finer become the
particles of cartilage.

The pulmonary vessels in the substance of the lungs run
with the bronchi. The veins still keep to the front of the
air-passages ; the arteries, however, as \vc have noted, turn
backwards to reach their posterior aspect, and this relation
they maintain in the lung substance.

Dissection. — The dissector should next turn his attention to the
thoracic portion of the sympathetic nervous system. In order to expose
it, he must strip the parietal pleura from the sides of the vertebrce and
the inner surflice of the ril)s.

Gangliated Cord of the Sympathetic (pars thoracicalis
ncrvi sympathici). — This extends downwards through the
thoracic cavity upon the heads of the ribs and the interven-
ing intercostal spaces, and has an appearance somewhat
similar to that of a knotted string. The thoracic ganglia
arc usually eleven in number. For the most part these
lie^on the heads of the ribSj but the first is placed over the
inner part of the first intercostal space. Towards the dia-
phragm the cord inclines forward, so that one or two of
the lower ganglia come to lie upon the bodies of the dorsal
vertebra;. The first ganglion is considerably larger than
those which succeed it. They are all linked together by
intervening nervous cords. Superiorly, the thoracic part of
the sympathetic is continuous with the cervical sympathetic;
whilst inferiorly it becomes continuous with the abdominal
l)ortion of the sympathetic by passing behind the liga-
mcntum arcuatum internum of the diaphragm.

The brandies which spring from the ganglia may be
divided into an external and an internal scries.

The external series ^re branches of connection between
the ganglia^ and the intercostal ncrye^s. Two run between
each nerve and the corrcsjionding ganglion. These differ
in the kind of fibres which compose them. One is chiefly
composed of white cerebro-s[)inal nerve-fibres ; the other is

88 THORAX.

mainly formed of gi£yL sympathetic nerve-fibres. Through
the agency of these two twigs, an interchange of fibres takes
place between the intercostal nerve and the sympathetic
cord.

The internal series are branches_oL-disixibution. From
the upper Joiir or five ganglia the internal branches go tojhe
thoracic viscera, whilst in the case of the lower six or seven
ganglia, the internal branches unite to form the splanchnic
nerves which are destined for the supply of abdominal
XJscera^ The thoraci^Jwigs of supply are very small, and
are given to the aorta, to the vertebra and their ligaments,
and to the lungs. The pulmonary branches proceed from
thF third and fourth ganglia, and they enter the posterior
pulmj3jiary-.-plexus. The splanchnic nerves are three in
number, and are distinguished by the terms, great^^mqll,
and smallest;^

The great splanchnic nerve (nervus splanchnicus major) is
formed by the union of five roots derived from the sixth,
seventh, eighth, ninth, and tenth ganglia. This description,
however, must be regarded as being somewhat arbitrary, as
there is a considerable amount of variability in the number
and manner of origin of the roots of this nerve. The great
splanchnic has more the appearance of a cerebro-spinal
rierveThan^a sympathetic nerve, owing to the large number
of spinal nerve fibres which it contains. It passes down-
wards upon the bodies of the vertebrae, and leaves the
thorax by piercing the crus of the diaphragm. Within the
abdomen it ends_by joining the upper part_of_thesemilunar
ganglion.

Upon the last dorsal vertebra, a ganglion called the splancJiJiic
ganglion will in all probability be found in connection with the great
splanchnic nerve. This ganglion is usually of small size, involving only
a very few of the anterior fibres of the nerve. Sometimes, however, it
forms a distinct oval bulging on the-^ nerve-trunk. A few slender fila-
ments are given by the ganglion to the coats of the aorta, and these in
some cases may be made out to communicate across the middle line of
the body with the corresponding branches of the ganglion of the
opposite side.

The small splanchnic nerve (nervus splanchnicus minor)

71I0RACIC CAVITY. 89

arises by two roots from the ninth and tenth or from tenth
and eleventh thoracic ganglia. It enters the abdomen by
piercing the cms of the diaphragm, and it ends by joining
the lower part of the semilunar ganglion.

The smallest splanchnic nerve (nervus splanchnicus imus)
is a minute twig which takes origin from the lowest thoracic
ganglion. It pierces the diaphragm, and ends in the renal
ple.xus. It is often absent, and then its place is taken by
one or more filaments from the small splanchnic nerve.

To obtain a proper view of this minute nerve, the diaphragm should
lie divided over its course, but this can only be done in cases where
the dissector of the abdomen has completed his examination of the
diaphragm.

Thoracic Wall. — The thoracic wall should now be
studied from within. Certain facts which have previously
been stated regarding it can now be verified {vide p. 4).
The internal intercostal muscle, in each space, will be seen to
extend backwards as far as the angles of the ribs. At this
point it stops abruptly, but the external intercostal muscle
is not exposed to view. It is covered on its deep aspect
by the posterior intercostal membrane, the connections of
which can now be ascertained.

The posterior intercostal mevibrane is a strong aponeurotic
layer which is continuous internally with the outer margin
of the superior costo-transverse ligamentj^ and extends
outwards upon the deep surface of the external intercostal
muscle. At the inner margin of the internal intercostal
muscle it passes between the two intercostal muscular
strata and is gradually lost. The intercostal vessels and
nerve extend outwards upon its anterior aspect under
cover of the pleura.

The subcostal muscjes ara also displayed. They are
small fleshy fasciculi placed upon the ribs, internal to
their^_angles. The muscular fibres which compose them
have the same direction as the internal intercostal muscles.
They extend ov;ei^ one ox^ in many cases, two intercostal
spaces.

90 THORAX.

Dissection. — Remove the posterior intercostal membrane from one
or two of the spaces, and the subjacent external intercostal muscles will
be brought into view. These muscles reach backwards as far as the
tubercles of the ribs.

Intercostal Arteries. — The aortic intercostal arteries have
already been seen taking origin from the thoracic aorta.
One is given to each of the._nin-e_,lo.W-er intexcostaLspaces
upon both sides of the body. As the aorta lies somewhat
to the left of the middle line, the right, aortic intercostal
arteries are loriger than those of the left side. In both
cases they run outwards over the' bodies of the vertebrae,
and under cover of the gangliated cord of the sympathetic.
On the right side, the arteries also pass under cover of the
oesophagus, the thoracic duct, and the vena azygos major.
As they leave the vertebral column to enter the intercostal
spaces, each of the vessels gives off a large dorsal branch
which passes backwards in the interval between the trans-
verse processes and is distributed to the muscles and skin
of the back. From this branch a spinal twig is supplied
through the intervertebral foramen to the spinal cord and
its membranes. In each space, the intercostal artery
proceeds outwards, first lying between the posterior inter-
costal membrane and the pleura, and afterwards between
the two muscular strata. Each artery is accompanied by
a nerve and a vein. The vein usually occupies the high^t
level, the nerve _ the lowest level, whilst the artery: is inter-
mediate. The distribution of these vessels in the thoracic
parietes has already been studied (vide p. 7).

The position of the intercostal artery in the intercostal
space is a matter of some surgical importance. At first it
crosses the intercostal space obliquely, so as to gain the
shelter of the subcostal groove of the rib which bounds
the space above. It attains this position near the angle
of the rib, and as it proceeds forwards the groove affords
it a very efficient protection against wounds from without.

The intercostal arteries which supply the two highest
intercostal spaces are _derived from the superior intercostal
branch of the subclavian artery. The superior intercostal

THORACIC CAVITY. 91

artery descends upon the necks of the first two ribs, and
external to the gangliatcd cord. It anastomoses with the
first aortic intercostal artery, and sends outwards, two
vessels for the two highest spaces. Each of these, in
turn, gives off a dorsal branch similar to the dorsal branches
of the aortic intercostal arteries.

The Intercostal Nerves pass outwards in company with
the arteries. The connecting twigs which pass between
these nerves and the sympathetic ganglia have already
been noted. Each nerve lies at a lower level than the
corresponding artery, and is at first placed between the
posterior intercostal membrane and the pleura, and then
between the two muscular strata. The further course of
these nerves is described at p. 5.

The first 'dorsal nerve will be found passing upwards
over the neck of the first rib to join the brachial plexus.
It gives a small branch to the first intercostal space, but
this nerve, although it is disposed after the manner of an
intercostal nerve, does not furnish, as a rule, a lateral
cutaneous branch. The second dorsal or ifitercostal fierve, as
a rule, sends a branch upwards over the neck of the
second rib to join that portion of the first dorsal nerve
which enters the brachial plexus. This communicating
twig is usually minute and insignificant, but sometimes _it
is a large nerve ; and, in these cases, the intercosto-
humeral nerve, or lateral cutaneous branch of the second
intercostal nerve, is very small or altogether absent.

Veins of the Thoracic Wall. — When the dissector has
traced the intercostal veins to their various destinations, he
will find that they differ in their arrangement upon the
two sides of the body. On the_^^v^j^^_they_tenninate
in three different ways : —

1. The intercostal vein of the first or highest stxicc joins the right

inuoiiiiiiate vein (sometimes the z'crlcbral vein).

2. The intercoatalyciiys of the second .ind ihinl spnces (and some-

times of the fourth space) unite into a common trunk, which
i^oins the upper part of the vena azvsros inajor. The common
trunk is termed the superior intercostal vein.

92 THORAX.

3. The intercostal veins of the eight lower spaces join 'Co^vmaJiSQlgos
major.

On the left side of the body four modes of termination
mayl5e recognised : —

1 . The intercostal vein of the first or highest space has the same

termination as the corresponding vein of the right side. It
joins the left innominate vein (sometimes the vertebral vein of
its own side).

2. The intercostal veins of the second and third spaces (and some-

times of the fourth space) cgnverg^ej and by their union form a
single trunk, termed the strperior intercostal vein, which crosses
the arch of the aorta and joins the left innominate vein inde-
pendently of the first intercostal vein.

3. The intercostal veins of the fourth, fifth, sixth, seventh, and

eighth spaces terminate in the ve^ia azygos minor superior.

4. The intercostal veins of the ninth, tenth, and eleventh spaces

join the vena azygos minor inferior.

The azygos veins which thus receive the blood of the
great majority of the intercostal veins should now be
studied.

Vena Azygos Major (vena azygos). — This vein takes
origin within the abdomen in iho. ascending lumbar vein {yex\2L
lumbalis ascendens), a vessel which links together certain
of the lumbar veins^ and sometimes presents a direct
communication with the common iliac vein. It enters
the thorax through the aortic opening of the diaphragm,
lying upon the right side of the thoracic duct and the
aoftai Irnhe~thorax it extends upwards upon the bodies
of the dorsal vertebra and over the right intercostal
arteries, until it reaches the level of the upper border of
the root of the right lung. At this point it hooks forwards
over the right bronchus^ and ends„Jby joimng the superior
vena cava. It is situated in the posterior mediastinum,
with the aorta and thoracic duct lying to the left (Figs.
195 and 196).

The tributaries of the vena azygos major are as follows :
— (i) the superior intercostal vein of the right side ; (2)
the intercostal veins of the eight lower spaces. o£ the righJL-
side; (3) thevena_azvgos minor sjip^iior ; (4) the vena

THORACIC CAVITY.

93

azygos minor inferior ; (5) ihc broncliiul vein from the
right lung ; (6) certain of the cesophageal veins ; (7) some
iiiimilc pericardiac veins.

The \cna azygos major communicates below_wilh some

INF THYROID
HT LYMPHATIC DUCT

INT. MAMMARY
INTERCOSTAL.!

OESOPHAGEAL

VENA AZYQOS MAJ

ASC9 LUMBAR

-INT. JUGULAR

THORACIC DUCT.

— SUBCLAVIAN
INTERCOSTAL I.
SUP.INTEHCOSTAL

VENA AZYOOS SUP.

VENA AZYQOS INF.

Fig. 199. — Diagram of the azygos and innominate veins.

of the lumbar veins — tributaries of the inferior vena cava ;
whilst above, it pours its blood into the superior vena

cava. In this way it forms a link by which the superior

vena cava is brought into connection with the inferior
vena cava.

94 THORAX.

Vena Azygos Minor Superior (vena hemiazygos acces-
soria). — The vein is formed on the left side of the body by„
the union of the intercostal veins of the fourth^^fifth, sixth,
seventh, and eighth spaces. It communicates above with
the left superior intercostal vein, which carries the blood
from the second and third intercostal spaces to the left
innominate vein. At the level of the eighth dorsal vertebra
it turns inwards behind the aorta and thoracic duct, and
crossing the middle line ends by joining the vena azygos
major. In many cases, however, it joins the vena azygos
minor inferior. In addition to the intercostal veins it
receives the left bronchial vein.

The Vena Azygos Minor Inferior (vena hemiazygos). —
This vein takes origin within the abdomen as the left
ascending lumbar vein, rt^^fftefs'the thorax by piercing
the left crus of the diaphragm, and is continued upwards
upon the vertebral column as far as the ninth dorsal
vertebra. At this point it turns to the right, and crossing
behind the aorta and the thoracic duct, ijt joins the vena
azygos ^major independently of the vena azygos minor
superior.

The tributaries of this vein are the intercostal veins of
the three lower spaces of the left side.

The veins of the thoracic parietes are extremely variable, and the
above description of them must be looked upon as merely representing
their more usual arrangement.

\y

THORACIC JOINTS.

The student should now complete the dissection of the
thorax by an examination of the various thoracic joints.

Dissection. — The portion of the sternum with the cartilages of the
ribs which was laid aside, together with the other joints in connection
with the anterior wall of the thorax, should now be dissected. Inter-
sternal, costo-sternal, and inter-chondral articulations require examina-
tion. Very little dissection is necessary. After the ligaments have
been defined, the dissector should remove a thin slice from the anterior

THORA CIC JOINTS. 95

aspect of c;ich iirticuliUion, in ortlor that tlic interior of the joint may
be displayed.

The Manubrio-gladiolar Articiilation between the manu-
brium and the gladiolus of the sternum partakes of the
nature of an amphiarthrosis. 'J'he opposing surfaces of
bone are covered by a layer of hyaline cartilage, and are
united by intermediate fibro-cartilage in which a synovial
cavity sometimes appears. The joint is supported by
some anterior and posterior longitudinal fibres which are
developed in connection with the strong and thick
periosteum. The posterior ligament is the stronger of
the two.

Stemo-costal Articulations. — Seven ribs articulate, by
means of their cartilages, directly with each side of the
sternum. The articulations of the first and the sixth are
peculiar, inasmuch as they articulate with single pieces of
the sternum, viz. with the manubrium and the lowest
piece of the gladiolus respectively, whereas the cartilages
of the other true ribs each articulates with two segments
of the sternum. The cartilage of the first rib is implanted
upon the side of the manubrium without any synovial
membrane, or other material, intervening. The second
costal cartilage is usually separated from the sternum by
two synovial membranes, between which an interarticular
ligament is developed. In the case of the other joints it
is more common to find a single synovial cavity and no
interarticular ligament. There is, however, considerable
variety in these articulations, and a synovial membrane is
very frequently wanting altogether in the costo-sternal
joint of the seventh costal cartilage.

With the exception of the first, and very frequently the
seventh, the sterno-costal joints belong to the diarthrodial
variety. They are provided with anterior and posterior
ligaments, and also in those cases where the joint presents
a double synovial cavity with an interarticular ligament.

The anterior and posterior ligaments (ligamenta sterno-
costalia radiata) are strong, flattened bands of fibres which
radiate from the extremities of the rib-cartilages, and blend

96 THORAX.

with the periosteum on the anterior and posterior surfaces
of the sternum. The interarticular ligaments are feeble
bands which pass from the tips of the rib-cartilages to the
sternum, and divide the articulations in which they exist
into an upper and a lower compartment, each lined by a
synovial membrane.

The Inter-cliondral Articulations are joints formed be-
tween the adjacent margins of the costal cartilages of some
of the lower ribs (generally from the fifth or sixth to the
ninth). They are protected by capsules formed by strong
oblique ligamentous fibres, and are lined by synovial
membranes.

Costo-vertebral Articulations. — With the exception of
the first and the last three ribs, the head of each rib arti-
culates with the bodies of two vertebrse and the intervening
intervertebral substance (articulatio capituli costae). The
costal head is wedge-shaped, and the socket formed for its
reception presents a corresponding form. From the inter-
vertebral disc taking part in the formation of the socket, a
certain amount of elasticity is communicated to the joint,
and shocks given to the thoracic wall are the more success-
fully counteracted. The heads of the first, tenth, eleventh,
and twelfth ribs are implanted directly upon the bodies of
the corresponding vertebrae, although in the case of the
first rib the intervertebral disc immediately above also
takes a considerable share in the formation of its socket.
The articulations between the heads of the ribs and the
bodies of the vertebra are termed the capitular joints
(articiilationes capitulorum).

But the vertebral extremities of the ribs present another
series of articulations. The upper ten ribs, by means of
their tubercles, rest upon and articulate with the extremities
of the transverse processes of the corresponding dorsal
vertebrae. These joints are termed the costo-transverse arti-
culations (articulationes costo-transversariae). The eleventh
and twelfth ribs have no tubercles, and do not articulate
with the transverse processes of the vertebrae with which
they are connected.

I

THORA CIC JOINTS. 97

Capitular Joints. — These joints belong to tlic diar-
throdial variety, and are provided with — (i),an anterior
capitular ligament ; (2) an interarticular ligament ; and (3V,
two synovial membranes. In the case of the four ribs,
however, which articulate with the body of one vertebra
alone (viz. the first, tcntli, eleventh, and twelfth), the joint
cavity is single.

The anterior capitular or stellate ligament (ligamentum
capituli costae radiatum) is placed in front of the joint. It
is composed of strong fibres, which radiate in a fan-shaped
manner from the head of the rib. Its vertebral attachment
is effected by three, more or less distinct, slips — (i) the
uppermost, which is the largest, passes upwards and inwards
to the body of the vertebra, which forms the upper part of
tKe socket for the head of the rib; (2) the middle slip is
attached to the intervertebral disc ; and (3) the lowest slip
goes to the body of the vertebra below the head of the rib.
The part of the joint uncovered by the stellate ligament is
surrounded by short fibres which form a capsule., enclosing
the synovial membranes.

In the four joints in which the head of the rib is in
contact with the body of one vertebra, the stellate liga-
ment is composed of only two slips. Of these, the loiver
is attached to the body of the vertebra which supports the
rib, whilst the upper passes upwards to the lower border of
the vertebral body immediately above.

Disseition. — The interarticular ligament may be exposed by removing
the stellate ligament from the front of the joint.

The interarticular ligament of the capitular joints is com-
posed of short strong fibres which are attached, on the one
hand, to the ridge between the two articular facets on the
head of the rib, and on the other hand to the intervertebral
disc. It divides the joint into two synovial cavities, and it
is absent in those cases in which the head of the rib
articulates with the body of one vertebra.

The synoz'ial membranes are two in number, except in
the capitular joints of the first and last three ribs. One
VOL. II. — 7

98 THORAX.

is placed above, and the other below the interarticular
ligament.

The Costo-transverse Articulations are provided with
capsular ligaments, and with superior, middle, and posterior
costo-transverse ligaments. Each joint cavity is lined by
a synovial membrane.

The superior costo-traftsverse liga7nent (ligamentum costo-
transversarium anterius) passes obliquely downwards and
inwards from the lower border of the transverse process to
the upper border of the neck of the rib next below it. Its
internal margin is thick and well defined, and its outer
border becomes continuous with the posterior intercostal
membrane.

The interosseous costo-transverse ligament (ligamentum
costo-transversarium posterius) consists of fibrous bands
which pass between the neck of the rib and the anterior
surface of the transverse process against which it rests.

The fibres of this ligament are so short that it is exceedingly difficult
to obtain a proper view of them. The best plan is to saw off, in a
horizontal direction, the upper parts of the neck of the rib and the
transverse process to which it is attached.

The posterior costo-trafisverse ligament (ligamentum tuber-
culi costse) is a strong flattened band which passes, on the
posterior aspect of the joint, from the tip of the transverse
process to the rough portion of the tubercle of the rib.

The posterior costo-transverse ligament, supplemxcnted
by a few fibres which surround the synovial membrane of
the joint, forms the capsular ligament. When the posterior
costo-transverse ligament is removed, the synovial membrane
is displayed.

Intervertebral Articulations. — The bodiesoiih& vertebrae
are held together by a series of a.mphiarthrodial joints, sup-
ported in front by an anterior common ligament, and behind
by a posterior common ligament. The neural arches, by
means of the articular processes, form a series of diarthro-
dial joints surrounded by capsular ligaments, and lined
by synovial membranes. Certain ligaments pass between
different portions of the neural arches and their processes,

THORA CIC /Of NTS. 99

viz. the Ijgamenta subflava between adjacent lamina;, the
mter-jransve^, the inter-splnous, and the supra-spinous

ijsamentj,

The laniiiiiv and the spinous processes of the vertehne have been
removed by the dissector of the head and neck in opening up the
spinal canal to display the spinal cord. Consequently, the liganienta
subdava, the inler-spinous and supra-spinous ligaments, cannot he seen
at present.

The anterior common ligament (ligamentum longitudinale
anterius) is situated in front of the bodies of the vertebrae,
and extends from the axis vertebra above to the first piece
of the sacrum below. It consists of stout glistening fibrous
bands, which are firmly attached to the margins of the
vertebral bodies and to the intervertebral discs. The most
superficial fibres are the longest, and extend from a given
vertebra to the fourth or fifth below it. The deeper fibres
have a shorter course, and pass between the borders of
two, three, or four adjacent vertebrae. The dissector can-
not fail to notice that the origin of the longus colli muscle
is inseparably connected with this ligament.

'Yht posterior common ligament (ligamentum longitudinale
posterius) is placed on the back of the vertebral bodies,
and therefore within the spinal canal. It is firmly con-
nected to the margins of the vertebral bodies, and to the
intervertebral discs, but is separated from the central parts
of the bodies by some loose connective tissue and by a
plexus of veins. It is constricted where it covers this
venous plexus, but widens out opposite the intervertebral
discs. It therefore presents a scalloped or denticulated
appearance.

The inten<ertebral siibstafice(f)hxo-cdiXi\\-:igo intervertebralis)
is disposed between the vertebrae in a series of flattened
discs of white fibro-cartilage which correspond in outline
to the vertebrae between which they are situated. The
peripheral part of each disc is tough and fibrous (annulus
fibrosus), the central portion soft and pulpy (nucleus
pulposus). In a transverse section the peripheral portion
appears concentrically laminated : in a vertical section the

loo HEAD AND NECK.

most peripheral laminae are seen to be bent with the con-
vexity turned away from the centre of the disc, the most
central laminae to be bent in the opposite direction, and
the intermediate laminae to be nearly straight. It will be
easily seen that this remarkable arrangement increases the
elasticity of the spine, and tends to restore it to its
natural curvature after it has been deflected by muscular
action.

The intervertebral discs constitute the main bond of
union between the bodies of the vertebrse, but, except in
old people, they are not directly attached to the bone. A
thin layer of encrusting hyaline cartilage coats the opposing
vertebral surfaces.

Vertical and transverse sections must be made through two or more
of the intervertebral discs, in order that their structure may be dis-
played.

The facets of the articular processes are coated by hyaline
cartilage. A capsular ligament lined by a synovial mem-
brane encloses each joint.

The intertransverse ligaments are feeble bands which pass
between the tips of the transverse processes. In the lower
part of the dorsal regions they are intimately blended with
the intertransverse muscles : in the middle and upper parts
of the dorsal region they entirely replace the muscles.

HEAD AND NECK.

The dissector of the Head and Neck begins work on the
same day that the subject is brought into the dissecting-
room. It is placed on a short table for this purpose, and
of the two days during which it remains in the lithotomy
position, the first should be devoted to the dissection of the
scalp, and the second to the removal of the brain.

SCALP.

SCALP.

Strictly speaking, the term " scalp " should be restricted
to the soft parts which cover the vault of the cranium
above the level of the temporal ridges and the superior
curved line of the occipital bone, but it is convenient to
dissect at the same time the superficial structures in the
temporal regions.

Above the level of the temporal ridges we meet with five
strata as we dissect from the surface to the bone, viz. —
(i) the skin; (2)
the superficial
fascia ; (3) the
occipito - frontalis
muscle, with its
extensive epicranial
aponeurosis ; (4) a
layer of loose areolar
tissue ; and (5) the
periosteum, which
is "here termed the
pericranium.

Below the level
of the temporal

ridges additional structures are observed coating the
cranium. As many as eight layers may be recognised,
viz. — (i) skin ; (2) superficial foscia ; (3) the small extrinsic
muscles of the ear ; (4) the thin lateral part of the epi-
cranial aponeurosis ; (5) a thin layer of fascia descending
from the temporal ridge to the pinna ; (6) the temporal
fascia; (7) the temporal muscle; (8) the periosteum.

The scalp is richly supplied with both nerves and blood-
vessels.

Dissection. — The dissector shoukl place a block under the head so
as to raise it to a convenient height, and proceed with the dissection.

Three incisions through the skin are required, viz. — (l) from the root
of the nose along the middle line of the cranium, lo a point a little
hcyond the external occipital protuberance ; (2) from the tip of the

Fig. 200. — Section through the scalp and
cranial wall, (Modified from Merkel.)

\\\

I02 HEAD AND NECK.

mastoid process on one side, over the summit of the head to a corre-
sponding point upon the opposite side ; (3) from a point on the latter
incision immediately above the pinna on each side downwards in front
of the auricle to the root of the zygoma. Four flaps of skin are thus
marked out, and these should be carefully raised from the subjacent
superficial fascia. This, however, is no easy matter, owing to the very
firm connection which exists between them. The roots of the hair
which pierce the integument obliquely, and are embedded in the
superficial fascia, add another difficulty to the proper reflection of the
integument.

Superficial Fascia. — On the summit of the cranium the
superficial fascia, although thin, is exceedingly dense and
tough, owing to strong septa of fibrous tissue which bind it
on the one hand to the integument, and on the other to
the subjacent epicranial aponeurosis. The meshes formed
by these fibrous processes are filled with small lobules of
fat, which give this layer a granular appearance. As the
fascia is traced forwards towards the forehead, and down-
wards on each side towards the ears, it loses in great part
its dense fibrous character, and becomes looser and less
fatty. It is in the superficial fascia that the cutaneous
vessels and nerves ramify before they enter the skin.

Dissection. — The superficial fascia may now be removed from the
surface of the occipito-frontalis. In doing this, the dissector must pro-
ceed very cautiously, so as not to injure the cutaneous nerves and
blood-vessels which ramify in its midst. It is impossible, owing to its
density, to raise it in one layer ; it must be taken away piecemeal.

The Occipito-frontalis (epicranius) is a quadricipital
muscle possessing two occipital and two frontal bellies.
The (?<;«)>//a/(5^///(?.r (musculi occipitales) — Fig. 201 (2) — are
quite distinct from each other, and are separated by
a marked interval. Each arises from the oiiter two-
thirds of J;he superior curved, line of the occipital Jbone,
and from a small portion of the adjoining part of the
mastoid process of the temporal bone immediately above
the insertion of the sterno-mastoid. From this the fibres
ascend for a distance of about two inches in the form of a
thin, dark-red, fleshy layer, which is inserted into the
epicranial aponeurosis.

SCALP. 103

The frontal bellies (imisciili fruntalcs) are composed of
pale fibres, and are not perfectly distinct from each other.
l''or a short distance above the root of the nose their inner
margins are blended along the middle line. Above this,
however, they diverge slightly, and are separated by a
narrow interval. They possess little or no direct attach-
ment to the bone. The greater number of the fibres
mingle with those of the orbicularis palpebrarum and the
corrugator supercilii muscles, and gain an attachment to
the integument and subcutaneous tissue over the eyebrow,
whilst a few of the innermost fibres proceed downwards
upon the nasal bone to form the pyramidalis nasi muscle.
Ascending upon the forehead, the frontal bellies are
inserted near the line of the coronal suture into the
epicranial aponeurosis.

The Epicranial Aponeurosis (galea aponeurotica), which
connects the occipital and frontal bellies of the occipito-
frontalis muscle, constitutes a continuous layer over the
summit and sides of the head. Posteriorly it can be traced
backwards in the interval between the two occipital bellies
of the muscle, when it will be observed to have an attach-
ment to the external occipital protuberance and the
superior curved line of the occipital bone. Laterally, it
presents no sharply defined margin, but, losing its apo-
neurotic character, it is prolonged downwards as a fine
expansi )n over the temporal fascia. In this locality it
gives origin to two of the small auricular muscles.

Disscclion. — Divide the epicranial aponeurosis by a mesial incision
nf about an inch and a half in length, and then carry across the middle
i)f this a second short transverse cut. On raising the corners thus
marked out, the aponeurosis will be seen to rest ujion a layer of loose
llocculent areolar tissue, containing no A\t — \\\q. fourth slralitiii of the
seal)). Owing to the great laxity of this tissue, the occipito-frontalis
muscle by its contractions can move the hairy scalp freely over the
jiericranium which invests the bone.

Extrinsic Muscles of the Ear. — In man these muscles
are very poorly developed, and the auricle possesses in

I04 HEAD AND NECK.

consequence only a very limited power of independent
movement. They are three in number, viz. : —

1. Attollens auriculam.

2. Attrahens auriculam.

3. Retrahens auriculam.

The first two of these are so thin that it requires an ex-
perienced and careful dissector to isolate them from the
superficial fascia.

Attollens auriculam (musculus auricularis superior) —
Fig. 201 (i). — To expose this muscle" the upper part of
the auricle must be dragged downwards, and then fixed in
this position by means of a hook. The muscular fibres
are thus rendered tense and stand out in relief When
cleaned it will be seen to be a fan-shaped muscle, placed
immediately above the ear. Above, it is broad, and arises
from the epicranial aponeurosis where it covers the
temporal fascia ; below, the fibres converge as they
approach the auricle and gain an insertion into the
upper part of the cranial surface of the pinna.

The attrahens auriculam (musculus auricularis anterior),
which is smaller than the preceding, is placed in front of
the ear, and the auricle must therefore be pulled backwards
in order that its fibres may be rendered tense. It arises
from the epicranial aponeurosis, and it is inserted into the
anterior aspect of the helix of the pinna.

The retrahens auriculam (musculus auricularis posterior)
— Fig. 201 (3) — consists of two or three short bundles of
muscular fibres which spring from the mastoid process of
the temporal bone, and are mserted into the posterior part
of the concha. It is readily exposed by drawing the ear
forwards.

The attrahens auriculam is supplied by a twig from the
temporal branches of the facial nerve ; the j-etrahens and
attollens by the posterior auricular branch of the facial
nerve.

Nerves of the Scalp. — Two nerves are given to the
frontal and parietal portions of the scalp by the frontal

Fig. 201.

-Superficial nerves on the side of the neck and back of the scalp.
(Hirschfeld and LevcilliS.)

Attollcns .iiiriculam
Poslerior belly of occipito-fron-
Reirahcns .uiricul.im [t.nlis

C.rc.it occipital nerve
llruat luriulir nerve
Splciiius muscle
SterciO'ina&toid muscle
Small occipital nerve (present
OS two branches)

9. Great auricular nerve

10. lixtenial ju^jular vein

11. Superficial cervical nerve

12. Spinal accessory nerve

13. Descendinj; branches of cer-

vical plexus

14. Ccr\'ical branches to trapezius

15. Trapezius muscle

16. Supra-clavicular branches

17. Supra-acromial branches

18. Auricular iwig^s of gnat auri-

19. farotid gland [culor nerve
30. Facial nerve

21. Masseler muscle

22. Infra-niandibiilar nerve

23. Anterior ju^^ular vein
34. Supra-siernal tiranchcs
25. riatysiiia inyuides

io6 HEAD AMD NECK.

branch of the ophthalmic division of the trigeminal nerve.
These are (a) the supra-trochlear, {h) the supra-orbital.

The supra-trochlear nerve (nervus supra-trochlearis) leaves
the orbit close to its inner angle and then turns upwards
under cover of the orbicularis palpebrarum. It becomes
superficial by piercing the frontal portion of the occipito-
frontalis, and, after a short course in the superficial fascia,
it ends in the integument of the forehead.

The supra-orbital nerve (nervus supra-orbitalis) is much
larger than the preceding, and quits the orbit by turning
upwards in the supra-orbital notch. The position of this
notch in the superior margin of the orbit can generally be
detected by the finger. The nerve now ascends under
cover of the orbicularis palpebrarum and the frontal belly
of the occipito-frontalis, and divides into an inner and an
outer division. There is a slight difference in the manner
in which these reach the surface. The inner division
becomes superficial by piercing the anterior belly of the
occipito-frontalis, whilst the outer division comes to the
surface a little farther back by piercing the epicranial
aponeurosis. Both ramify in the superficial fascia over
the parietal bone, and give numerous twigs to the skin.
The outer division can be traced as far back as the
lambdoidal suture.

In the temporal region^ nerves from three sources are to
be found, — {a) from the facial nerve ; il?) from the orbital
branch of the superior maxillary division of the trigeminal
nerve ; ic) from the auriculo-temporal branch of the inferior
maxillary division of the trigeminal nerve.

The temporal bra?iches of the facial nerve will be noticed
running upwards over the zygoma. They furnish twigs of
supply to the attrahens auriculam, frontal belly of the
occipito-frontalis, orbicularis palpebrarum, and corrugator
supercilii.

The temporal bratich of the orbital nerve (ramus zygo-
maticotemporalis) is a minute twig, which is somewhat
difficult to find. If the finger be carried downwards from
the external angular process of the frontal bone along the

SCALP. 107

posterior margin of the malar bone, a tubercle on the latter
will be felt. This is the guide to the temporal branch
of the orbital nerve ; it pierces the temporal fascia im-
mediately behind it. It therefore makes its appearance
about one inch above the anterior part of the zygoma, and
the dissector is frequently led to it by a communicating
twig from one of the facial branches. It is distributed to
a limited area of skin in this region.

The aitriculo-temporal nerve (nervus auriculotemporalis)
will be found immediately in front of the ear, in close
contact with the superficial temporal artery. It soon
divides into two branches, which diverge from each other
IS they ascend, and a careful dissector may be able to
:race twigs from these as far as the summit of the head,
[ts branches terminate in the skin of the scalp.

In the mastoid and occipital regions of the scalp, the*
dissector will meet with four nerves, each from a different
source ; ((/) the posterior auricular branch of the facial nerve
— Fig. 201 (3); il') the mastoid branch of the great auricular
nerve; (r) the small occipital nerve from the anterior primary
division of the second cervical nerve — Fig. 201 (8); and {d)
the great occipital nerve from the posterior primary division
of the second cervical nerve — Fig. 201 (4).

The posterior auricular (nervus auricularis posterior) is a
small nerve which ascends upon the front of the mastoid
process, immediately behind the ear. The guide to it is
the posterior auricular artery, which lies in contact with it.
After effecting a communication with the great auricular
nerve, it divides into an auricular and an occipital division.
The auricular division continues its upward course, and ends
by supplying the retrahens auriculam and attollens auriculam
muscles ; the occipital division inclines backwards along the
superior curved line of the occipital bone, and ends in the
occipital belly of the occipito-frontalis muscle.

In searching for the posterior auricular nerve, the dissector
will, in all probability, meet with the mastoid branch of the
great auricular nerve, which ascends upon the mastoid pro-
cess on a more superficial plane.

io8 HEAD AND NECK.

The small occipital nerve (nervus occipitalis minor) will be
discovered midway between the ear and the external
occipital protuberance. It supplies numerous branches to
the integument, and furnishes an auricular twig to the skin
over the upper part of the cranial aspect of the ear. It
communicates with the great auricular nerve on the one
hand, and with the great occipital nerve on the other.

The great occipital (nervus occipitalis major) is a large
nerve, and there will be little difficulty experienced in
finding it, as it lies close to the occipital artery, a short
distance external to the occipital protuberance. Its
branches spread out over the back of the head, and supply
a wide area of integument. It sends an auricular tivig to
the skin over the cranial aspect of the ear, and communi-
cates with the small occipital nerve.

Blood- Vessels of the Scalp. — Two small arteries, viz.
the frontal and the supra-orbital., both branches of the
ophthalmic, leave the orbit to supply the forehead. The
former is associated with the supra-trochlear nerve, and the
latter with the supra-orbital nerve. The veins correspond-
ing to these arteries unite at the inner margin of the orbit
to form the angular vein, which afterwards becomes the
facial vein.

The superficial temporal artery (arteria temporalis super-
ficialis) will be noticed ascending upon the temporal fascia,
immediately in front of the ear. At a variable point above
the zygoma it divides into its two terminal branches — viz.
the anterior and posterior superficial temporal arteries.

The anterior superficial temporal artery (ramus frontalis)
takes a tortuous course upwards and forwards to the fore-
head, and supplies numerous branches to the integument,
muscles, and pericranium. Further, it anastomoses with
the frontal and supra-orbital arteries, and with the corre-
sponding vessel of the opposite side.

The posterior superficial temporal artery (ramus parietalis)
inclines upwards and backwards, arching over the cranium
above the auricle. It gives off numerous twigs to the parts
in this region, and communicates with its fellow of the

SCALP. 109

opposite side, and with ihc posterior auricular and occipital
arteries.

The posterior auricular artery (artcria auricularis posterior)
ascends in the angle between the cartilage of the ear and
the mastoid process, and ends by dividing into two branches,
named respectively the auricular and the mastoid. The
auricular branch ascends under cover of the retrahens
auriculam muscle, and supplies several twigs to the pinna,
and, finally turning forwards above the auricle, it anasto-
moses with the posterior superficial temporal artery. The
mastoid branch inclines backwards towards the occiput,
where it communicates with the occipital artery.

The posterior auficular vein is a comparatively large
vessel. It joins the posterior division of the temporo-
niaxillary vein, near the angle of the lower jaw, to form the
external jugular vein.

The occipital artery (arteria occipitalis), which will be
found a short distance to the outer side of the occipital
protuberance, sends large tortuous branches over the back
of the head. These anastomose with the corresponding
vessels of the opposite side, and with the posterior auricular
and ])osterior temporal arteries.

Temporal Fascia (fascia temporalis). — If the epicranial
aponeurosis with the attached auricular muscles be now
raised in the temporal region, a thin but distinct sheet of
fascia will be observed proceeding from the upper temporal
line of the parietal bone, in close relation to the deep
surface of the attollens auriculam, to the pinna. \\'hen
this is removed the strong temporal fascia which covers the
temporal muscle is brought fully into view. Its connec-
tions will be studied at a later period.

Surgical Anatomy of the Scalp. — The close connection between
the llircc .sii[K-rricial la\crs of tlic scalp (viz. skin, superficial fascia, and
ejiicranial aiioneurosis), and the loose manner in which these are hound
hy areolar tissue to the jiericraniuni, are points of great interest from a
surgical point of view. When the scalp is wrenched from the head by
machiner)', or by any other means, the scjiaration is efi'ected in the
jilane of the areolar layer. The blood-vessels, however, lie for the
most part in the superficial fascia, and therefore large flaps of detached

no HEAD AND NECK.

scalp can be replaced upon the denuded periosteum, and yet retain
their vitality. It is a rare occurrence for a scalp flap to slough.

The scalp is richly supplied with blood-vessels. Incised wounds in
this region, therefore, bleed very profusely ; but, in addition to this, they
bleed with more than usual persistence. This is accounted for by the
dense character of the superficial fascia, and by the fact that the fibrous
septa of this stratum adhere to the coats of the vessels, and prevent them
from retracting freely when divided.

As will readily be understood, a collection of pus in the scalp will
produce very different results, according to the position it occupies. If
it is formed under the epicranial aponeurosis it spreads in all directions ;
indeed, it is only limited in front by the superciliary ridges of the
frontal bone, and behind by the superior curved line of the occipital
bone. If it is formed in the superficial fascia, it is confined to the point
at which it originates.

REMOVAL OF THE BRAIN.

On the second day after the subject has been placed on
the table, the two dissectors of the head and neck should,
in conjunction with each other, proceed to remove the
brain.

Dissection. — The head being supported upon a block, an incision is
made along the middle line of the head, through the epicranium, the
subjacent areolar tissue, and the pericranium, from the root of the nose
in front, to the external occipital protuberance behind. This must be
done boldly, so as to divide everything right down to the bone. With
a series of sharp strokes with the handle of the scalpel, the pericranium
on each side can easily be turned outwards, so as to leave the bone
perfectly bare. Observe, however, that although the pericranium is
loosely attached over the surface of the various bones of the vault, that
it is firmly attached along the lines of the cranial sutures by processes
that dip in between the bones, so as to separate their edges. On reach-
ing the temporal ridges, push the knife through the attachment of the
temporal fascia, so that the blade lies between the temporal muscle and
the bone. Then run the knife backwards and forwards, so as to
thoroughly divide the attachment of the fascia to the ridge. When this
is done on either side, the fascia and muscle can be easily raised
together from the temporal fossa, and thrown down over the ear with
the remains of the scalp.

The dissectors should next obtain a saw, a chisel, and a mallet,
and proceed to remove the calvaria. The line along which the saw
is to be used may be marked out on the skull by encircling it

REMOVAL OF THE BRAIN. in

with ;i piece of string, and tiicn marking ihc cranium with a pencil
along liie line of the string. In front the cut should be made
fully three-quarters of an inch above the margins of the orbits, behind
it should be carried round at the level of a point midway between the
lambda' and the external occipital protuberance. The saw should only
be used to divide the outer table of the skull. When the dijiloe is
reached, which will be observed by the sawdust becoming red and
moist, the saw should be abandoned. The hammer and chisel are now-
brought into requisition, and by these the inner table can readily be
split along the line in which the outer table of the cranium is divided.
By insinuating the hook at the end of the cross-bar of the chisel into the
fissure in front, the skull-cap can be forcibly wrenched ofl".

Dura Mater (dura mater encephali). — The brain is
clothed by three distinct membranes, which are termed

Fig. 202. — Diagrammatic section through the meninges of
the brain. (Schwalbe. )

d. Dura mater.
sd. Subdural space.

a. Arachnoid mater.
sa. Sub-arachnoid space and trabecula;.

7'. Veins.
/. Pia mater.
CO. Grey matter of cerebral convolutions.

the meninges. These are from without inwards — (i) the
dura mater; (2) the arachnoid mater; and (3) the pia
mater.

' The term " lambda'" signifies the ape.\ of the occipital bone, or the
point at which the sagittal and lambdoidal sutures meet.

HEAD AND NECK.

When the skull-cap is detached, the outer surface of
the dura mater, as it covers the upper surface of the
cerebral hemispheres, is exposed. It is rough, and dotted
over with bleeding points. If a portion were placed in

water, its roughness
would become still more
manifest, and be seen
to be due to a multi-
tude of fine fibrous and
vascular processes, by
which it is connected
with the deep surface
of the bones. These
have necessarily been
torn asunder in the
removal of the skull-
cap. The bleeding
points are most numer-
ous along the middle
line, or, in other words,
along the line of the
superior longitudinal
sinus ; and if the handle
of the knife be run from
before backwards, so as
to make pressure along
this line, a considerable
quantity of blood will
ooze out. This shows
that a number of small
veins from the cranial
bones have been rup-
tured. The degree of
adhesion between the
dura mater and the inner surface of the cranial bones varies
in different subjects and in different localities. In all cases
it is most adherent along the lines of the sutures ; and,
further, it is very much more firmly attached to the base

Fig. 203. — Diagrammatic section
through an arachnoidal villus.
(Schwalbe. )

J>a. Villus (Pacchionian body).

d. Dura mater (deep layer).

d' . Superficial layer of dura mater.
ds. Deep layer of dura around villus.

V. Lacuna lateralis or parasinoidal sinus
into which the villus projects.
sd. Subdural space.
sd . Subdural space around villus.

a. Arachnoid mater.
sa. Sub-arachnoid space and trabeculse.

/. Pia mater.

CO. Convolution of cerebrum.

REMOVAL OF THE BRAIN. it 3

than the vault of the cranium. In the child — indeed, as
long as the bones of the cranium are growing — it is more
adherent than in the adult ; and it is also more firmly
bound to the bone in old age.

The dissector should now w-ipe the outer surface of the
dura mater with a sponge. He will then recognise the
middle meningeal artery upon each side, ascending in the
substance of the membrane, and sending off its branches
in a widely arborescent manner. It stands out in bold
relief from the membrane in which it ramifies ; and if the
skull-cap be examined, its inner surface will be observed
to be deeply grooved by its ramifications. The meningeal
arteries, as the name might lead one to imagine, are not
intended for the supply of the membrane alone. They
also must be looked upon as the nutrient vessels of the
mner table and diploe of the cranial bones.

The Pacchionian bodies (granulationes arachnoidales),
which are almost invariably present, and which are as a
rule best marked in old subjects, will attract notice at this
stage. They are small granular bodies, ranged in clusters
on either side of the superior longitudinal sinus, into which
they not unfrequently protrude (Fig. 204). As a general
rule, they are most evident towards the hinder part of the
parietal region. At first sight these bodies appear to be
protrusions from the dura mater, but this is not the case.
They spring from the arachnoid mater, and are enlarge-
ments of the normal villi of this membrane.

The relation which the Pacchionian bodies present to the dura mater
is somewhat intricate. When they project into the superior longitudinal
sinus they push before them a thin covering continuous with the floor of
the sinus, so that in no sense can they be said to pierce its wall. On
either side of the superior longitudinal sinus there are a number of
"irregular spaces or intervals which communicate with the sinus either by_
a small ajierture or a narrow channel. These recesses are termed para-
sinoidal sinuses or lacttnic lateralis, and the independent meningeal veins,
and some of the diploic veins, pour their blood into them. J'acchionian
bodies push themselves into the parasinoidal sinuses from below in such
a manner that they receive a complete covering by the invagination of
the floor. Nor does the bone escape. As tiic I'accliionian bodies
enlarge, they cause absorption of the cranial wall, and small pits are

VOL. II. — 8

114 HEAD AND NECK.

hollowed out on its deep surface for their reception. The superficial
walls of the lacunae — very much thinned — line these depressions in the
calvaria.

Two Layers of the Dura Mater. — Having learned these
• preliminary details from an examination of the outer surface
of the dura mater, as it clothes the upper surface of the
cerebral hemispheres, the student is in a position to under-
stand that this membrane does not belong entirely to the
brain. It performs a double function: (i) it^cts as an
iiiternal periosteum to the bones forming the cranial cavity ;
and (2) it gives support to the different parts of the brain.
Consequently, it consists of two strata, which, in most
localities, are firmly adherent, but which nevertheless can
usually be easily demonstrated in the dissecting - room.
These strata may very appropriately be termed the endo-
cranial and the supporting layers. Along certain lines
these two layers separate from each other, and for two
distinct purposes. In some cases they separate for the
purpose of forming channels, termed blood sinuses (sinus
durae matris), for the conveyance of venous blood ; in
other cases they separate in order that the inner supporting
layer may form strong folds or partitions, which run in
between the various parts of the brain. By these latter
the^cranial cavity is divided into compartments com-
municating freely with each other, and each holding a
definite subdivision of the brain (Fig. 205).

Dissection. — These points must now be verified. Begin by tilting
the head forwards. Support it in this position, and make two incisions
through the dura mater in an antero-posterior direction — one on each
side of the superior longitudinal sinus, and along its whole length.
From the mid-point of each of these incisions another cut must be made
through each lateral portion of the dura mater downwards to the cut
margin of the skull immediately above the ear (Fig. 204). The dura
mater covering the upper aspect of the brain is thus divided into a
central strip containing the superior longitudinal sinus and four tri-
angular flaps. The flaps should now be turned downwards over the
cut margin of the skull, and in this position they preserve the brain
during its removal from laceration by the sharp bony edge.

The Subdural Space (cavum subdurale) is now opened

REMOVAL OF THE BRAIN.

"5

into. This is tlic term which is applied to the interval
between the dura mater and the arachnoid mater — Fig.
202 {sd\ p. III. It contains a very small quantity of
serous fluid which moistens the opposed surfaces of these
membranes. A striking contrast between the two surfaces
of the dura mater will be observed. The superficial sur-
face, as we have noted, is rough and flocculent. The

mouth of
cerebral
vein.

cerebral
vein.

Fig. 204. — 'I'hc ciuia mater and the superior longitudinal
sinus, etc. The lines along which the dura mater should
be incised in removing the brain are indicated by dotted
lines on the right side.

deep surface, which is turned towards the subdural space,
is smooth, polished, and glistening.

The Cerebral Veins returning the blood from the
surface of the cerebral hemispheres will be seen shining
through the arachnoid. They are lodged in the sulci
between the convolutions, and run upwards to the middle

ii6

HEAD AND NECK.

line. Reaching the superior longitudinal sinus they are
suddenly directed forwards, and lie against the wall of the
sinus for some distance before they open into it (Fig. 204).
Superior Longitudinal Sinus (sinus sagittalis superior).
— Open into this venous channel by running the knife
through its upper wall from behind forwards (Fig. 204).
It begins in front at the crista galli of the ethmoid bone,
where it not unfrequently communicates with the veins in

Fig. 205. — The dura mater. (Luschka. )

2. The oval aperture between anterior

border of tentorium and dorsum
sellse.

3. Falx cerebri.

4. Tentorium.

5. Anterior concave margin of tentorium.

6. Vein of Galen entering the straight

sinus.

the nasal cavity through the foramen caecum, and it extends
backwards, grooving the cranial vault in the middle line,
to the internal occipital protuberance (Figs. 204 and 206).
Its lumen, which is triangular in form, is very small in
front, but expands greatly as it is followed backwards.
The mouths of the superior cerebral veins are observed
opening into it (Fig. 204). These veins pour their blood
into it in a direction contrary to that in which the blood
flows within the channel. The terminal portions of the

REMOVAL OF THE BRAIN. 117

veins are directed from behind forwards, whilst the blood
in the sinus flows from before backwards. The channel is
crossed at its inferior angle by a number of minute bands.
These receive the name of chordtc Willisii.

Falx Cerebri (Figs. 205 and 206). — This is a sickle-
shaped reduplication of the supporting layer of the dura
mater, which descends in the mesial plane between the two
cerebral hemispheres. In order to expose it, the cerebral
veins, as they open into the superior longitudinal sinus,
must be divided, and the hemisphere gently pulled out-
wards. In front, the falx cerebri is narrow, and attached
to the crista galli of the ethmoid bone. As it is followed
backwards, it increases in breadth, and behind, it is
attached in the middle line to the upper surface of the
tentorium cerebelli, its two lamellce separating along the
Ime of junction so as to form with the tentorium a blood
sinus, termed the straight sinus — Fig. 206 (6), p. 122.
Along its superior convex border its two layers separate
and form, with the endocranial layer of the dura mater,
the superior longitudinal sinus — Fig. 206 (5), p. 122. Its
inferior concave margin is free, and overhangs the corpus
callosum, with which, however, it is not in contact, except,
perhaps, very slightly behind. Running backwards in this
margin is the i/iferior longitudinal sinus.

Removal of the Brain. — The dissectors should now
proceed to remove the brain. Having divided the attach-
ment of the falx cerebri to the crista galli, pull it backwards.
Next, removing the block upon which the head rests, and
supporting the occiput and posterior lobes of the brain with
the left hand, let the head drop well backwards. In all
probability, the frontal lobes will fall away by their own
weight from the anterior fossa of the base of the cranium,
and perhaps carry with them the olfactory bulbs. Should
they remain in position, however, gently raise them with
the fingers, and separate, at the same time, with the
handle of the knife the olfactory bulbs from the cribriform
plate of the ethmoid. In raising the olfactory bulbs, the
minute olfactory nerves which spring from them and perforate

Ii8 HEAD AND NECK.

the cribriform plate of the ethmoid bone are torn across.
The large round and white optic nerves (second pair of
cranial nerves) now come into view as they leave the
cranium through the optic foramina. When these are
divided, the internal carotid arteries will be exposed, and
between them, in the mesial plane, the infundibulum, a
hollow conical process which connects the pituitary body
with the tuber cinereum — a lamina of grey matter on the
base of the brain. It will be noticed that the infundibulum
lies slightly behind the internal carotid arteries.^ Sever in
turn each of these structures. We then come upon the
oculo-jfiotor nerves (third pair of cranial nerves), which must
be dealt with in like manner. Observe first, however, that
they lie behind, and external to the carotid trunks. The
dissector should now see upon either side the anterior
extremity of the inner free margin of the tentorium
cerebelli as it passes forward to be attached to the anterior
clinoid process. Pressing this outwards with the point of
the knife, the minute tfvchkar tiei've (fourth cranial nerve)
will be brought into view. It lies under shelter of the
free border of the tentorium, and should be divided at this
stage. The head must in the next place be turned forcibly
round, so that the face is directed over the left shoulder.
On raising the posterior part of the right cerebral hemi-
sphere with the fingers, it will be observed to rest upon the
tentorium cerebelli — a broad horizontal process of dura
mater, which intervenes between it and the cerebellum.
Divide the tentorium along its attached border, and take
care in doing this not to injure the subjacent cerebellum.
When the division is effected, push the tentorium back-
wards out of the way with the point of the knife. Now
. turn the head so as to bring its left side uppermost, and
treat the tentorium on this side in the same manner. The
two parts of the trigeminal nerve (fifth cranial nerve) per-
forating the dura mater near the apex of the petrous

^ In dividing the cranial nerves, 4t is well to cut them close to the
point where they pierce the dura mater on one side of the body, and
close to the brain on the other side.

REAfOV.iL OF THE BRA IN. 119

portion of the temporal bone ; the abducent nerve (sixth
cranial nerve) piercing the dura mater behind the dorsum
selloi of the sphenoid bone ; the portio dura ox facial nerve,
the pars intermedia, and the portio tnoi/is or auditory nerve
disappearing into the internal auditory meatus ; the ,(^losso-
pharyni^cal, the va,i^us, and the spinal accessory nerves leaving
the skull through the jugular foramen ; and the two slips
of the hypoglossal fierve piercing the dura mater over the
anterior condyloid foramen, will each in turn come into
view upon either side, and each must be divided in
succession. In the case of the three ner\-es passing out of
the cranium through the jugular foramen, the dissector
should endeavour to leave the spinal accessory of the right
side intact within the cranium, by dividing its roots of
origin from the medulla, whilst on the other side he should
remove it with the brain. This nerve will be readily
recognised from its ascending from the spinal canal into
the cranial cavity through the foramen magnum. It is
only necessary now for the dissector to thrust the knife
into the spinal canal, and divide the vertebral arteries as
they turn forwards upon the upper part of the spinal cord,
and then sever at a lower level the spinal cord, the spinal
accessory nerve of the left side, and the roots of the first
pair of spinal nerves. By letting the head fall well back-
wards, and gently dislodging the medulla and cerebellum,
the whole brain can be removed. The veins of Galen, as
they pass from the interior of the brain to enter the straight
sinus, are ruptured by this proceeding.

Preservation of the Brain. — In order that the brain may be studied
to best advantage, it is necessary that it should be subjected to some
hardening reagent. Methylated spirit, or a mixture of this with
Midler's fluid, gives good results. The dissector must obtain a vessel
large enough to hold the brain, and, at the same time, allow the harden-
ing reagent to surround and cover it completely. It must likewise be
provided with an accurately fitting lid to jirevent evajioration. A small
amount of cotton wadiling should be arranged at the bottom of the
vessel, in the form of a nest, so as to preserve, as far as possible, the
natural form of the brain. The brain should be placed upon this, with
its base or lower surface uppermost, and the meninges of the base should
be torn across, so as to give free admission to the fluid. It is well also

I20 HEAD AND NECK.

to raise the cerebellum slightly from the cerebrum by means of a small
pad of wadding, and it is advantageous to tear across the arachnoid at
the back of the corpus callosum.

If spirit be employed, it should, in the first instance, be diluted with
fully a third part of water. In three days the brain should be taken
out of the vessel, and the membranes stripped from its surface. Before
doing this, however, the dissector must study the manner in which the
arachnoid and pia mater is disposed, and the distribution of the blood-
vessels. A description of these will be found in the chapter referring
to the dissection of the brain. In moving the membranes from the
base of the brain, the very greatest care must be taken not to injure the
cranial nerves as they emerge from its substance.

The brain should now be immersed in pure spirit to complete the
hardening.

Mailer's fluid has the following composition, and it can readily be
prepared by the student : —

Bichromate of potash, .... 25 grms.

Sulphate of soda, . . . -. 10 grms.

Water, ■ . 1000 c.c.

To hasten the solution of the potassic bichromate, the water may be
slightly heated, but the fluid should not be applied to the brain until it
is quite cold. Methylated spirit should be added in the proportion of
one oi spirit to three of Miiller's fluid. To' prevent the separation of
the chromic salts, all light must be excluded. A relatively large quan-
tity of the fluid must be used, and it must be changed at least three
times — viz. at the end of '(h& first, fou7'th, and eighth days.

For ordinary dissection, spirit alone should be used ; but for a study
of the sectional anatomy of the organ, it is best to employ the Miiller's
fluid and spirit solution. It is true that it imparts to the brain a dark
colour, but this to some extent can be removed by steeping the organ,
after its removal from the hardening fluid, in a large quantity of water
(and frequently changing the water) for a period of twenty-four hours.
Six weeks are usually required to harden a brain in this solution ; and
it is not necessary to remove the membranes until the dissector is
prepared to study the organ, so great is the permeating power of the
fluid.

It is best to defer the study of the brain until the dissection of the
head and neck is completed.

Dura Mater at the Base of the Cranium. — The dissector
has observed that the dura mater^can, as a rule, be easily
separated from the under surface-of-the cranial vault. He
would find it impossible to raise it in hke manner from the
base of the cranium. It is closely adherent to the crista

REMOVAL OF THE BKAIN. 121

ga[H, to the posterior margins of the lesser wings of tiie
sphenoid, to the posteriorjclinoid processes, to the petrous
portions of the temporal bones, to tlie basilar j^rocess of the
occipital bone, and around the margin of the foramen
magnum. Another cause of its close adhesion in this
locality jsj that it gives sjieaths to the cranial nerves, and
passes out. of- tiie cranium through ihe basal foramina to
become continuous with the periosteum on the external
siirfiice of the skull. So close, indeed, is the union between
the dura mater and the base of the cranium, that it would
require maceration to effect a complete separation.

Partitions of Dura Mater. — The dura mater gives off, as
we have already seen, processesTvhich act as partial parti-
tions within the cranial cavity. These are four in number,
viz. : —

( I . )_The falx cerebri (whicli has already been studied),
( 2. ) Yh e tentorium cerebelli.
(3.) The falx cerebelli.
(4.) The diaphragma sellae.

Tentorium Cerebelli (Fig. 205 (4), and Fig. 206 (4),
p. I 22). — This is a large crescentic fold of dura mater which
cojistitutes a membranous roof for the posterior fossa of the
cranium, and at the same time forms a partition between
the posterior lobes of the cerebrum and the cerebellum. It
is not horizontal. It is accurately applied to the upper
surface of the cerebellum. Its highest point, therefore,, is
i_n front, in the mesial plane, and from this it gradually
slopes downwards to its attached border. A very imperfect
idea of its natural appearance can be obtained in the present
instance, seeing that its connections have been severed in
the removal of the brain. Before it is disturbed it is per-
fectly tense, and this tension is due to its connection with
the falx cerebri. These two processes of dura mater are
mutually dependent on each other in this respect — divide
one and both become relaxed.

'Y\\Q posterior border of the tentorium is convex. Behind^ it
is attached to the horizontal ridges which mark the deep sur-
face of the occipital bone, and beyond this, on each side, to

HEAD AND NECK.

the posterior inferior angle of the parietal bone; laterally., it is
firmly fixed to the upper border of the petrous portion of the
temporal bone. In the former situation it encloses between
i^two layers the lateral blood, sinuses — Fig. 206 (7), — and
in the latter the superior petrosal blood sinus on each side.
The anterior border is sharp, free, and concave (incisura
tentorii), and forms, with the dorsum sellae of the sphenoid,
an oval opening within which the mesencephalon is placed.

Beyond the apex of the
petrous portion of the
temporal bone the two
margins of the tentorium
cross each other like the
Umbs of the letter X ; the
free margin is carried for-
wards to be attached to
the ^anterior clinoid pro-
cess, whilst the attached
border is continued in-
wards to be fixed to the
posterior clinoid process
(Fig. 207).

Falx Cerebelli. — This
is a small falciform fold of
dura mater placed under
the tentorium, which ex-
tends forwards in the
mesial plane from the in-
ternal occipital crest. It
occupies the notch which separates the two lateral hemi-
spheres of the cerebellum posteriorly. Above, it is attached
to the posterior part of the under surface of the tentorium.
Its anterior border is free ; whilst inferiorly, it bifurcates into
two small diverging ridges, which gradually fade away as they
are traced forwards on either side of the foramen magnum.
The Diaphragma Sellse is a small circular fold of the inner
layer of the dura mater which forms a roof for the sella
turcica. A small opening is left in its centre for the trans-

FlG. 206. — Diagrammatic coronal
section through the posterior part
of the cranium with the dura
mater in position. (Luschka. )

1. Compartment for cerebellum, etc.

2. Compartments for occipital lobes

of the cerebrum.
Falx cerebri.
Tentorium.

Superior longitudinal sinus.
Straight sinus.
Lateral sinuses.

REMOVAL OF THE BRAIN.

'23

mission of the infiindibiilum. An almost complete case is
thus formed for the pituitary body.

Cranial Nerves. — The dissector should now turn his
attention to the cranial nerves, and study the manner in
which they leave the
cranial cavity. Each
nerve carries put with
it a _coyering__d£xij£ed
from, each of the^thzee
membranes of the brain.
In the case of the optic
nerve these remain dis-
tinct ; but in all the
others the sheath de-
rived from the arach-
noid very soon disap-
pears.

Begin by examining
the cribriform plate of
the ethmoid. From this
the olfactory bulb has
been displaced in the
removal of the brain.
About twenty minute
olfactory nerves (nervi
olfactorii) proceed from
the under surface of the
bulb and descend into
the nose through the
holes in the cribriform
plate. These have been
ruptured close to their
origin, but in all probability traces of them will be observed.

The seco?id ox optic nerve {ncrxvi^ opticus) — Fig. 207 (3) —
will be seen entering the orbit through the optic foramen.
It is accompanied by the ophthalmic artery, which lies
below it. The student should note the strong loose sheath
of dura mater which envelops the nerve.

Fig. 207. — Aperture between the dor-
sum sellce and the anterior con-
cave free margin of the tentorium.
(Hirschfeld and Leveill^. )

1. Optic foramen.

2. Olivary process of sphenoid.
Optic nerve.

Oculo-motor cranial nerve.
Trochlear cranial nerve.
Trigeminal cranial nerve.
Hypoglossal nerve.

8. The aperture in front of the tentorium.

9. .\nterior free edge of tentorium.

10. .Abducent cranial nerve.

11. Posterior clinoid process.

12. Anterior clinoid process.

124

HEAD AND NECK.

Th&-Jhird or oculo-motor nerve (nervus oculomotorius) —
Figs. 207(4) and 208 — is a firm cord-like nerve, which pierces
the dura mater in front of the posterior clinoid process, within
a triangular area indistinctly marked out by the intersection
of the margins of the tentorium, as they pass to be attached

antr. cerebral
artery.

internal carotid
artery.

middle cerebral /

artery.

postr. communicat
ing artery.

olfactory bulb.

vertebral artery.

hypoglossal nerve

Fig. 208. — The cranial nerves leaving the cranial cavity and the
circle of Willis.

to the clinoid_processes. The nerve enters the wall of the
cavernous sinus, in which it will be afterwards traced.

The minute thread-like fourth or trochlear nerve (nervus
trochlearis) — Figs. 207 (5) and 208 — also enters the wall of
the cavernous sinus, to gain which it perforates the dura
mater a short distance behind, and to the outer side of the
third nerve, but within the same triangular area. Its aperture
of exit lies under shelter of the free margin of the tentorium.

I

REMOVAL OF THE PyRAIN. 125

The fifth or trigeminal nerve (ncrvus trigeminus) — Figs.
207 (6) and 208 — is composed of two parts — viz. a large,
soft, sensory portion, consisting of loosely connected funi-
culi, and a small, firmer motor portion, which lies upon the
inner surface of the sensory part. They can generally be
easily distinguished, and both pierce the dura mater at the
apex of the petrous portion of the temporal bone, and
under the anterior extremity of the tentorium.

The sixth or abducent nerve (nervus abducens) — Figs. 207
(10) and 208 — is a small, round nerve, which disappears
through the dura mater at the lower and outer part of the
dorsum sellae, and enters the wall of the cavernous sinus.

The auditor}' nerve (nervus acusticus), the facial nerve
(nervus fLicialis) (Fig. 208), and the small pars intermedia
(nervus intermedius), all enter the auditory meatus, where
the pars intermedia joins the facial nerve. They are
accompanied by the auditory artery.

The glosso-pharyngeal (nervus glossopharyngeus) the
pneutnogastric (nervus vagus), and the spinal accessory (nervus
accessorius) pierce the dura mater over the internal jugular
foramen in the order in which they have been named, from
before backwards (Fig. 20S). The glosso-pharyngeal has a
separate aperture of exit in the dura mater, and therefore
receives a separate sheath of dura mater, whilst the vagus
and spinal accessory have a common aperture, and a
common sheath of both arachnoid and dura mater.
They all leave the skull through the middle compartment
of the jugular fossa. The spinal accessory has already
been noticed ascending from the spinal canal.

The hypoglossal tierve (nervus hypoglossus) pierces the
dura mater opposite the anterior condyloid foramen at two
separate points, in the form of two distinct slips (Fig. 208).
These unite in the foramen.

Venous Blood Sinuses (sinus durx matris). — The blood
sinuses which traverse the dura mater should next be
examined. Each should be opened in turn by running
the knife through the dura mater which forms its wall.
The following is a list of these sinuses : —

126 HEAD AND NECK.

1. Superior longitudinal.

2. Inferior longitudinal.

3. Straight.

4. Occipital.

5. Cavernous.

6. Spheno-parietal.

7. Circular.

8. Superior petrosal.

9. Inferior petrosal.
10. Basilar.

As already pointed out, the cranial blood sinuses are in
some cases formed by a separation of the two layers of the
dura mater ; in other cases they are formed in the redupli-
cations of the inner layer of the dura mater which constitute
the partitions. The channels thus constituted are lined by
a smooth membrane, which is continuous with the internal
coat of the veins.

Torcular Herophili (confluens sinuum). — The superior
longitudinal sinus has been already examined, except at the
point where it terminates. The dissector should notice that
as it descends upon the deep surface of the occipital bone,
it, as a rule, inclines slightly to one or other side of the
mesial plane, more usually to the right side, and in this way
it terminates upon one side of the internal occipital pro-
tuberance. Here it is somewhat dilated, and then turns
suddenly outwards, to form the lateral sinus of that side.
This expansion of the superior longitudinal sinus is termed
the torcular Herophili, and it communicates by means of a
transverse channel, which crosses the front of the internal
occipital protuberance, with the commencement of the
lateral sinus of the opposite side.

Inferior Longitudinal Sinus (sinus sagittalis inferior). —
Fig. 209 (&/). — This small sinus runs backwards in the
lower free border of the falx cerebri. It begins at a
variable point behind the crista galli, and ends posteriorly
at the anterior free edge of the tentorium, where it pours
its blood into the straight sinus.

The Straight Sinus (sinus rectus) extends backwards
and downwards in the mesial plane, from the anterior free
edge of the tentorium to the internal occipital protuberance.
Its course corresponds with the attachment of the posterior
broad end of the falx cerebri to the upper surface of the
tentorium. Indeed, it is formed by the opening out of

REMOVAL OF THE BKAIN. 127

the two layers of the falx on the upi)cr surface of the
tentorium. At its anterior extremity it receives the blood
from the inferior longitudinal sinus and the vena magna
C.aleni. The latter returns the blood from the interior of
the cerebrum, and its ruptured end may be noticed at the
point where it enters the straight sinus (Fig. 207, p. 123).
At the internal occipital protuberance, the straight sinus
bends suddenly outwards, in a direction opposite to that
taken by the superior longitudinal sinus, and it forms the
lateral sinus of that side. A few small cerebellar veins
pour their blood into the straight sinus.

Occipital Sinus (sinus occipitalis) — Fig. 209 {So).—
This is a minute blood-channel, which is placed between
the layers of the falx cerebelli. Above, it opens into the
tonular Herophili, whilst below, at the foramen magnum.
It bifurcates, and the two divisions not unfrequently run
forwards to join the lower end of the lateral sinus upon
either side. Sometimes the occipital sinus is double
throughout its whole course.

The Lateral Sinuses (sinus transversi)— Fig. 209 {Sir)
— are two in number — one on each side. They are
variable in their mode of origin, but, as we have noted,
the right lateral sinus is commonly formed by the superior
longitudinal sinus, whilst the left is formed by the straight
sinus. They commence one upon either side of the
internal occipital protuberance, and communicate with
each other by a transverse channel of variable width,
which passes in front of this bony prominence. The sinus
which represents the continuation of the superior longi-
tudinal sinus is generally considerably larger than the other.
From the occipital protuberance, each lateral sinus passes
at first outwards and upwards, and grooves the occipital
bone and the inferior angle of the parietal bone along the
attached border of the tentorium. Reaching the temjjoral
bone, It is joined by the superior petrosal sinus, and then
suddenly curves downwards and inwards, in the deep
furrow upon the mastoid portion of the temporal bone,
and ilie jugular process of the occipital bone. Lastly, it

128 HEAD AND NECK.

turns forwards and disappears into the posterior compart-
ment of the jugular foramen, where it terminates in the
bulb of the internal jugular vein. In this course the
lateral sinus describes an arch (Birmingham) with the
convexity upwards, the highest point of which, as a rule,
corresponds with the posterior inferior angle of the parietal
bone.

Venous tributaries which come from the cerebellum,
back part of the cerebrum, and from the diploe of the
cranial bones, may be noticed opening into the lateral
sinus.

Two large and important emissary veins connect it_ffiith
the veins of the scalp, and allow its blood, when it is over-
charged, to drain partly away in this direction. These are
the mastoidal vein (emissarium mastoideum), joining it
through the mastoid foramen, and the posterior condyloid
vein (emissarium condyloideum), which joins it through
the posterior condyloid foramen.

Cavernous Sinus (sinus cavernosus) — Fig. 209 (&). —
It is not advisable that the dissector should open the
cavernous sinus at this stage, on account of the various
nerves which pass forwards in its walls to the orbit, and
which are best studied with the parts in that cavity. He
should simply note, therefore, at present, that this sinus
lies upon the side of the body of the sphenoid bone.

The Circular Sinus (sinus circularis) — Fig. 209 {Sia) —
however, which surrounds the pituitary body, may be
examined. It consists of two transverse channels (the
anterior and the posterior intercavernous sinuses) which
connect the cavernous sinuses, and lie one in front and
the other behind the infundibulum of the pituitary body.

The Petrosal Sinuses — Fig. 209 I^Sps and Spi) — drain
the blood from the posterior end of the cavernous sinus.
They are two in number on each side — viz. superior and
inferior. The superior petrosal sinus (sinus petrosus superior)
runs along the superior border of the petrous portion of
the temporal bone, and joins the lateral sinus. The
inferior petrosal sinus (sinus petrosus inferior) is the larger

REMOVAL OF THE BRAIN.

Ssi Sss I

129

Sir So Sss

Fig. 209. — The blood sinuses of the dura mater. (Henle.)

Sss.

Ssi.

Sia.

Ssp.

Sip.

Sc.

Sps.

Spi.

Str'

Str.

Superior longitudinal sinus.
Inferior longitudinal sinus.
Anterior intercavernous sinus.
Sphcno-p.irietal sinus.
Posterior intercavernous sinus.
Cavernous sinus.
Superior petrosal sinus.
Inferior petrosal sinus.

\ Lateral sinus.

So. Occipital sinus.

Pb. Basilar sinus.

1. Falx cerebri.

2. Optic nerve.

3. Internal carotid artery.

4. Third cranial nerve.

5. r^orsum sella;.

6 Eighth cranial nerve.

VOL. II. — S

I30 HEAD AND NECK.

of the two, but has a shorter course. It passes backwards
and outwards in the groove between the basilar process
of the occipital bone and the inferior margin of the petrous
portion of the temporal bone. It leaves the cranial cavity
by passing through the anterior compartment of the
jugular foramen, and ends by joining the commencement
of the internal jugular vein.

The Basilar Sinus (plexus basilaris) — Fig. 209 i^Pb) —
is not a single channel, but a plexus of minute sinuses
which permeate the dura mater over the basilar process of
the occipital bone. It connects the two inferior petrosal
sinuses, and posteriorly communicates with the anterior
intraspinal veins.

The Spheno-Parietal Sinus (sinus alse parvse) — Fig. 209
(&/)^is a minute blood - channel which runs inwards
under shelter of the lesser wing of the sphenoid bone. .
Externally it commences in one of the small meningeal
veins, whilst internally it pours its blood into the fore-part
of the cavernous sinus. Owing to its position, this sinus
is somewhat difficult to demonstrate.

Arteries entering the Cranial Cavity. — The student
has now examined the various channels by means of which
the venous blood is drained out of the cranial cavity. He
should next examine the arteries which introduce the blood
into this cavity. These are —

^ I. The_vertebral arteries.

' 2. The internal carotid arteries.

'^ 3. The meningeal arteries.

The Vertebral and Internal Carotid Arteries carry blood
for the supply of the encephalon and the parts within the
orbit. The internal carotid artery will be observed piercing
the dura mater immediately behind, and to the inner side
of the anterior clinoid process. At this point it gives off
its ophthalmic branch which accompanies the optic nerve
through the optic foramen, and immediately beyond this
the internal carotid trunk has been severed in the removal
of the brain. The vertebral artery will be observed piercing

REMOVAL OF THE BRAIN. 131

the dura mater immediately below the foramen magnum.
It also has been divided close to its point of entrance.

Meningeal Arteries. — These are the nutrient arteries of
the dura mater, and the inner table and diploe of the cranial
bones. They are derived from a great number of different
sources, but the only one of any size is ihc ^niddk meningeal,
which comes from the internal ma.\illary artery. The others
are small twigs, and, except in a well-injected subject, will
not be easily made out. They are: — {i) anterior meningeal
from the anterior ethmoidal artery; (2) the small meningeal
from the internal maxillary arter}- ; (3) some small blanches
from the ascending pharyngeal, occipital, and vertebral
arteries.

The middle meningeal artery (arteria meningea media), a
branch of the internal maxillary artery, enters the cranium
through the foramen spinosum of the sphenoid, and divides
into two large terminal branches. Of these, the anterior
branch ascends upon the great wing of the sphenoid, and
the anterior inferior angle of the parietal bone, grooving
both deeply, whilst the posterior branch turns backwards
upon the squamous portion of the temporal bone. The
wide distribution of these vessels in the dura mater has
already been noticed.

Two veins accompany the middle meningeal artery.
Above, these vessels communicate with the superior longi-
tudinal sinus (Testut); whilst below, they unite in a common
trunk which joins the pter}-goid plexus.

The anterior mjningeal artery (arteria meningea anterior)
proceeds from the anterior ethmoidal artery as it lies on
the cribriform plate of the ethmoid bone, along with the
nasal nerve. It supplies a limited area of dura mater in
the anterior fossa of the cranium.

The small meningeal arten- (ramus meningeus accessorius)
is somewhat inconstant, and not unfrequently springs from
the middle meningeal. It enters the cranium tlirough the
foramen ovale, but it should not be looked for at the present
"stage, as it is best examined along with the Gasserian ganglion
and the three divisions of the trigeminal nerve.

.132

HEAD AND NECK.

The meningeal branches from the ascending pharyngeal
artery are the terminal twigs of this vessel, and enter the
cranium through the foramen lacerum medium, through
the jugular foramen, and through the anterior condyloid
foramen. The branch which passes through the jugular
foramen is the largest.

The meningeal branches of the occipital and vertebral
arteries are small. The former enters through the jugular
foramen, whilst the latter gains admittance to the cranium
through the foramen magnum, and is distributed in the
posterior cranial fossa.

Fig. 2IO. — I, Pituitary body ; 2, in mesial section ;
3, in horizontal section. (Schwalbe. )

a. Anterior lobe.

b. Posterior lobe.

cm. Corpus mammillare.

i. Tuber cinereum.

ch. Optic commissure in section.

7'o. Optic recess of the third ventricle.
o. Optic nerve.
a! . Infundibulum with projection from

anterior lobe upwards in front

of it.

Pituitary Body (hypophysis cerebri) — Fig. 210. — The
overhanging margin of the diaphragma sellee should be
freely cut in two or three places, and the pituitary body
carefully dislodged from the sella turcica of the sphenoid
bone. If this be done successfully, the body will be seen
to be an oval structure, slightly flattened from above down-
wards, and with its long axis directed transversely. Further,
it may be noticed to consist of a large anterior lobe, and a
smaller posterioiiJobe. The former of these is hollowed
out behind so as to form a concavity for the lodgment .of
the latter. If a horizontal section be made through the
body, the line of separation between the two lobes is very

DORSAL ASPECT OF THE TRUNK. 133

distinct. The infundibulum which connects the i)iluitaiy
body with the tuber cinereum of the brain is continued
into tlie posterior lobe, and is in no way structurally con-
tinuous with the larger anterior lobe. Thus, even in the
adult, we have a clue to the different modes of development
of the two lobes. The posterior lobe is derjved from Jhc
brain, whilst the anterior lobe is an off- shoot from the.
primitive buccal cavity.

The dissectors of the head and neck niiisl now prepare for the chang-
ing of the position of the subject. Some tow, or a sponge, soaked in a
mixture of methylated spirit and carboHc acid, should be introduced
into the cranial cavity. The skull-cap should then be replaced and
retained in position by bringing the scalp flaps over it, and stitching
them accurately together. It is a very common practice with students,
when the scalp has been dissected and the brain removed, to throw the
skull-cap aside. This proceeding cannot be too strongly condemned,
because the contour of the head is then lost, and in the subsequent
dissection false conceptions are apt to be formed.

DORSAL ASPECT OF THE TRUNK.

On the third day after the subject has been placed in
the dissecting-room its position is changed. It is now
laid on its face, with its chest and pelvis supported by
blocks. The head should be allowed to fall well over the
end of the table (Fig. 211). During the four days that the
body is allowed to lie in this position, the dissectors of the
head and neck have to dissect the dorsal aspect of the
cervical, thoracic, lumbar and sacral regions, and, in addition,
remove the spinal cord.

The dissectors of the upper limbs take part in this dissection. It is
their duty to dissect the superficial and deep fasciiv in the thoracic and
lumbar regions, and also those structures which connect the limb to the
trunk posteriorly. To them, therefore, belong the trapezius muscle
below the seventh cervical spine, the latissimus dorsi and the rhomboid
muscles, together with their vessels and nerves of sujiply. The levator
anguli scapula.' and the omo-hyoid are to be regarded as common pro-
perty. The dissectors of the upper limbs are allowed two days to
complete this work.

134

HEAD AND NECK.

During the first two days allowed for the dissection of the
back, the dissector of the head and neck has merely to
examine the superficial parts on the back of the neck, and
take part along with the dissector of the upper limb in the
dissection of those structures which are common to both.

The first day should be devoted to the reflection of the
skin, and the dissection of the superficial nerves and that
portion of the posterior triangle of the neck which can be
examined in the present position of the subject. On the
second day the trapezius may be reflected, and the following
structures examined — viz. the levator anguli scapulae and its

r^~-\r r'^^ii^

Fig. 211.

nerves, the posterior scapular artery, the superficial cervical
artery, the suprascapular artery and nerve, the transversalis
colli artery, and the origin of the omo-hyoid.

Surface Anatomy. — First make out the position of the
external occipital protuberance, and having traced the
superior curved line of the occipital bone as it passes out-
wards towards the mastoid process, press deeply into the
neck immediately below the occiput, and in the middle line;
here the bifid extremity of the massive spinous process of
the axis vertebra can be felt. Carrying the finger downwards,
the posterior edge of the ligamentum nuchas can be
distinguished, but the short spines of the third, fourth, and
fifth cervical vertebrae can hardly be detected. The spines

DOKSA/. ASPECT OF THE IKUNK. 135

of the sixth and seventh cervical vertebriu, however, arc
usually very prominent.

Reflection of Skin (Fig. 211). — Three incisions are recjuired — (i)
AIoiil; ilic niidtllo line, from the external occipital protuberance to the
prominent si)ine of the seventh cervical vertebra. (2) From the lower
enil of this mesial incision transversely outwards to the inner border
of the acromion process of the scapula. (3) From the u]iper end of the
primary incision transversely outwards over the occiput to the ear.

The cjuailrilateral flap of skin thus marked out must be raised from
the subjacent superficial fascia. On reaching the side of the neck, the
head nutst be held well over to the opposite side. Here, unless the
ilissector keep close to the skin, there is a danger of the knife slipping
in under llie posterior border of the sterno-mastoid muscle.

Superficial Nerves. — The nerves to be looked for in the
superficial fiiscia, which is now exposed, are derived partly
from the posterior primary divisions, and partly from the
anterior primary divisions of the cervical nerves. They
are : —

,, . r I. Great occipital.

rrom iiostenor I ^^ : — , / • r .u • . 11 u

' . . . •; 2. Terminal twigs ot the internal branches

' ■"'" a } 1 1\ IS o b. 1^ oT the third, lourtlT^and fifth nerves.

From anterior ( I. Small occipital.

primary divisions. ^ 2. Great auricular.

Dissection. — The main trunk of the great occipital nerve may be found
piercing the trapezius about an inch below the occipital protuberance,
and about half an inch external to the mesial plane. The fascia at this
spot is usually very dense, and the readiest method to adopt in exposing
the nerve is to carefully shave it off in slices until the plane of the
muscle is reached.

The g^reat occipital (nervus occipitalis magnus) — Fig. 201
(4) — is the internal branch of the posterior primary divisioii
of the second cervical nerve, and its branches of distribu-
tion have already been noticed, spreading out on the back
of the scalp (p. 108). As it becomes superficial, it joins
the occi|)ital artery, and both are directed upwards to supply
the scalp.

The kniiinal hvi^s of the internal branches_ of the posterior
divisions of the third., fourth^ and fifth cervical nerves enter
the superficial fascin rlnsi- fo th^^ mesial plane. andL-then
t urn transversely out wards to supply the skin of the neck.

136

HEAD AND NECK.

The third cervical brafichstnAs in addition a large twig
upwards to the integument over the occiput. This nerve
runs along the inner sid£_Q£-the— great-&cei-pitaUand.^s a
rule, communicates with it. From its distribution, it is
frequently termed the third acdMtal nermA'nS-r^v& occipitalis
tertius).

PW'^'

Fig. 212. — Superficial dissection of the posterior aspect of
the neck and head. (Luschka. )

1. Trapezius.

2. Sterno-raastoid.

3. Splenius capitis.

4. Complexus.

5. Occipital artery.

6. Posterior auricular vein.

7. Occipital vein.

8. Great occipital nerve,
g. Small occipital nerve.

Dissection. — The small occipital nerve will be found by dividing the
fascia along the posterior border of the sterno-mastoid muscle.

The_y;;;^// nr(.ipit(jJ npry^ (nervus occipitalis minor) — Fig.
201 (8)— springs fromJhe^nterm]L4iiiffiaTi[J[ivi^^^
secoad^cemcal nerve^and runs upwards to assist in the
supply of the integument over the occiput. Its terminal
twigs have aheady been dissected in the superficial fascia

DORSAL ASPECT OF THE TRUNK. 137

of the scalp (p. 108). Occasionally llie small occipital is
represented by two separate nerves.

Dissection. — The great auricular nerve can readily be exposed by
drawing the head well over to the opposite side and then dividing the
fascia over the outer surface of the sterno-niasloid muscle very ohlicpicly.
Begin the incision at the posterior margin of the muscle about the
middle of the neck, and carry it upwards and forwards towards the
lobule of the ear.

Gjxrt__aia-iciilar_nayc (nervus auricuUiris magnus) — Fig.
201 (9). — The great auricular nerve is a branch of the
cervical plexus, and takesorigin from the second and third
cervical nerves. Turning round the posterior border of fITe
sterno-mastoid muscle, it proceeds upwards and forwards F A A)
on the surface of that muscle towards the lobule of tlie
ear. Near this point it will be found to end by dividing
into three sets of branches — viz. facial, auricular, and
mastoid.

The facial branches will be traced afterwards in the dis-
section of the face. The others may be followed, however,
at the present stage. The auricular branches supply the
integument upon the cranial aspect of the auriclu. and if
they be carefully dissected, several of them will be noticed
to pierce the cartilage to reach the integument on its outer
surface. Communications may also be made out between
these twigs and the posterior auricular branch of the facial
nerve. The viastoid branch extends upwards upon the
mast^lki_process, where it is connected with the posterior
auricular and small occipital nerves.

Dissection. — Whilst the subject is lying upon its face we can only
obtain a ver)' meagre idea of the posterior triangle of the neck. It is
only its upper and least important part which can at present be exposed.
To bring the boundaries, floor and contents, of this portion into
view, the dissector should begin by cleaning the cervical part of the
trapezius. Occupying the interval between the trajiezius and sterno-
mastoid, two contiguous muscles, taking a somewhat oblique course, will
be observed. The higher of these is the sjilenius cajntis, and the lower
is the levator anguli scai)ul;e. These, together with the posterior border
of the sterno-mastoid, must be cleanefl. In carrying out this dissection
the dissector must jiroceed with some degree of caution ; and above all,

138 HEAD AND NECK.

he must be careful not to raise the sterno-mastoid nor disturb the
cervical nerves which lie under cover of it, because these can be studied
at much greater advantage when the subject is turned. In cleaning the
levator anguli scapulse the dissector must secure two small nerves which
issue from the cervical plexus for the supply of that muscle. They are
closely applied to its surface, and are apt to be removed with the fascia
covering the muscle, unless they are specially looked for. Further,
the sjDinal accessory nerve, and two or three cervical nerves crossing
from the posterior border of the sterno-mastoid to the trapezius, should
be dissected out.

The Posterior Triangle, of which the upper part is- thus
sbf^ displayed, is bounded ?>? /;w?/^bj^he £Osterior_border_of
\ the sterno-mastoid. and behin_d \pi the anterior border of
1 the trapezius. The apex., which is directed upwards, is
formed at the superior curved hne of the occipital bone by
the apposition of the occipital attachments of these two
muscles. The £oor of that portion of the space which is
exposed will be observed to be formed by the splenius
capitis and the levator anguli scapulae^ But it often
happens that the occipital attachments of the sterno-
mastoid and trapezius (more especially of the latter) are so
poorly developed that they fail to meet on the superior
curved line of the occipital bone. In this case a small
portion of the complexus (readily recognised by the vertical
direction of its fibres) will be noticed entering into the
formation of the floor of the space above the level of the
splenius. The contents of the space, in so far as they can
be seen in the present position of the body, are — (i) the
great auricular and small occipital nerves as they appear
at the posterior margin of the sterno-mastoid muscle; (2)
the spinal accessory nerve, the cervical nerves to the
trapezius, and two small nerves from the cervical plexus to
the levator anguli scapulae. An additional structure also
enters the space when the sterno-mastoid and trapezius do
not meet to form a distinct apex for the triangle, viz. the
occipital artery. In such a case a small portion of the
vessel will be noticed upon the complexus muscle, close to
the superior curved line of the occipital bone.

The Spinal Accessory Nerve (nervus accessorius) appears

DOKSAL ASPECT OF TIJK 77WNA'. 139

in the posterior triangle by emerging from the substance
of the sterno- mastoid muscle. It crosses the triangle
obli([ucIy, running from above downwards and backwards,
and finally disappears under the anterior border of the
trapezius.

The Cervical Branclies to the Trapezius, two or three
in number, spring from the third and fourth cervical nerves.
They enter the posterior triangle by leaving the shelter of
the ster'io-mastoid, and are carried downwards and back-
wards across the space parallel with, but at a lower level
than, the spinal accessory nerve. This, together with the
fact that they are somewhat smaller than the spinal acces-
sory, is sufficient to distinguish them from that nerve. They
finally disappear under the anterior border of the trapezius.

Dissection. — On the second day afler the subject has been placed
on its face, the trapezius may be reflected. This must be done in con-
junction with the dissector of the arm. First separate the muscle from
the occipital bone, and then divide it about half an inch from the spines
of the vertebni;. The muscle can now be raised and thrown outwarcfs
towards its insertion. On its deep surface the spinal accessory nerve,
the cervical nerves of supply, and the superficial cervical artery will be
noticed. It is the duty of the dissector of the upper limb to dissect
these, but the dissector of the head and neck should trace the superficial
cervical artery to its origin from the transversalis colli.

The attachments of the levator anguli scapula' must also be defined.
Two nerve-twigs from the cervical plexus, which lie on its surface and
finally enter its substance, have already been secured. Further, pass-
ing downwards under cover of this muscle, the ncn'c to the rlwiithoids
and the posterior scapular artery will be found. Almost invariably the
nerve to the rhomboids gives one or two twigs to the levator anguli
scapula:.

The Levator Anguli Scapulae (levator scapuhx;) arises l)y
four slips from the posterior tubercles of the transverse pro-
cesses of the upper four cervical vertebne. These unite to
form an elongated muscle which extends downwards and
backwards to be inserted into that portion of the vertebral
border of the .scapula which is placed above the root of the
spine. As already noted, the nerve-supply of the levator
anguli scapula; comes from the third and fourth cervical
nerves, and also from the nerve to the rhomboids.

I40 HEAD AND NECK.

The Transversalis Colli Artery will be seen terminating
near the outer margin of the levator anguli scapulae, by
dividing into the superficial cervical and posterior scapular
arteries. The former of these proceeds upon the superficial
aspect of the levator anguli scapulae, whilst the latter passes
under cover of that muscle. It is the duty of the dissector
of the upper limb to trace the further course of these
branches of the transversalis colli artery.

Dissection. — The posterior belly of the omo-hyoid muscle, and the
supra-scapular artery and nerve can now be displayed by dissecting
towards the upper margin of the scapula. This dissection must be
effected in conjunction with the dissector of the upper limb, and it is
well not to expose these structures at the present stage for more than
an inch from the upper border of the scapula.

The Posterior Belly of the Omo-hyoid Muscle is a slender
muscular band which arises from the upper border of the
scapula, immediately behind the suprascapular notch. It
also derives fibres from the ligament which bridges across
this notch. The further connections of the omo-hyoid will
be studied in the dissection of the triangles of the neck
after the body has been turned.

The Suprascapular Artery and Nerve. — The supra-
scapular artery will be noticed to enter the supraspinous
fossa of the scapula, by passing over the suprascapular
ligament. The suprascapular nerve., on the other hand, is
carried into the fossa under cover of the ligament.

The second dafs work is now completed, and on the same day the
dissector of the upper limb must finish his share of the dissection of the
back, so as to allow the dissector of the head and neck to begin the
examination of the deeper structures on the dorsal aspect of the trunk.

Two days are allowed for this dissection, and these may be disposed
of in the following manner : — On ^& first day, all the muscles, fascise,
nerves, and blood-vessels of the back, with the exception of those in
connection with the sub-occipital triangle, should be studied ; on the
second day, the sub-occipital space must be examined, and the spinal
cord displayed. Should the dissector find that the work is greater than
he can undertake in the allotted time, the sub-occipital space may be
left over until the head and neck is removed from the trunk.

Serrati Muscles. — These are two thin sheets of fleshy

DOKSAI. ASPECT OF THE TRUNK. 141

fibres, which arc placed upon the posterior aspect of the
tlioracic wall. The scrmtus posticus siij^crior (serratus
posterior superior) is much the smaller of the two ; it
arises by a thin aponeurotic tendon — (1) from the lower
part of the ligamentum nucha;; (2) from the spinous pro-
cess of the seventh cervical vertebra ; and (3) from the
spinous processes of the upper two or three dorsal vertebra;.
From this origin it proceeds obliquely downwards and out-
wards, and is inserted by distinct digitations into the outer
surfaces of four ribs — viz. the second, third, fourth, and
fifth — a short distance in front of their angles.
I 'YYi^ serratus posticus inferior {%&xx2i\M% posterior inferior)
will bebrought into view by raising and throwing inwards
that portion of the latissimus dorsi which the dissector of
the upper limb has left attached to the lumbar fascia. The
serratus posticus inferior will then be observed to take
origin from the spinous processes of the last two dorsal
and upper two lumbar vertebrag, as well as from the
supraspinous ligaments which stretch between these bony
prominences. The dissector will note, however, that
this is not an independent and distinct attachment, but
that it is effected through the medium of the vertebral
aponeurosis and posterior lamella of the lumbar fascia,
with both of which the aponeurotic tendon of the muscle
blends. The precise extent of the origin is thus rendered
somewhat obscure. The serratus posticus inferior is
directed upwards and outwards, and is inserted by four
digitations into the lower borders of the four lower ribs.

Vertebral Aponeurosis. — The connections of the ver-
tebral aponeurosis can be easily made out. It is the strong
but thin and transparent fascia which bridges across the
hollow between the spinous processes of the dorsal vertebra;
and the portions of the ribs which lie internal to their
angles. It confines in this hollow the proper muscles of
the spine and head. Make a transverse incision through
it about the middle of the dorsal region, and introduce
under it the handle of a knife. By carrying this first in an
inward and then in an outward direction, the attachment

142 HEAD AND NECK.

of the aponeurosis to the spines of the dorsal vertebra
and to the angles of the ribs will be rendered manifest.
In the next place, note that when it is followed in an up-
ward and downward direction the fascia presents a different
relation to the two serrati muscles. Superiorly, it proceeds
under cover of \h^t serratus posticus superior and the splenius
muscles, and is lost in the deep layers of fascia of the neckj_
inferiorly, it blends with the aponeurotic tendons of the
serratus posticus inferior and the latissimus dorsi, and with
these forms the posterior lamella of the lumbar fascia.

The Lumbar Fascia is an exceedingly dense aponeurotic
structure, which gives great support to the muscles of the
loins, and also serves as a means of origin for two of the
flat muscles of the abdominal wall — viz. the transversalis
abdominis and obliquus internus. It is attached internally
to the vertebral column by three distinct lamellse, which are
separated from each other by intervening muscular masses.
The posterior or superficial lamella is at present seen in the
form of a strong opaque aponeurotic sheet stretching out-
wards from the lumbar spines. It is formed, as we have
already observed, by a continuation downwards of the verte-
bral aponeurosis, and by a union of this with the aponeurotic
tendons of the latissimus dorsi and the serratus posticus
inferior. Divide this lamella in a longitudinal direction
about one inch external to the middle line, and raise it
from the subjacent erector spinse muscle.

Mesially it will be seen to have a strong attachment to
the tips of the lumbar spines and the intervening supra-
spinous ligaments, whilst inferiorly it is fixed to the back
part of the crest of the ilium, and to the subjacent tendon
of the erector spinae, where this lies upon the dorsum of
the sacrum.

The erector spinse should now be pushed inwards either
with the fingers or with the handle of a knife. This pro-
ceeding will bring into view the second or middle lamella
of the lumbar fascia. Further, the union of the posterior
and middle lamellae beyond the outer border of the erector
spinae, and the attachment of the middle lamella to the tips

DORSAL ASPECT OF THE T/amh'. ,43

of the transverse processes of the lumbar vertchrx may l)c
seen. Note, however, that whilst the main attachment of
this lamella is to the apices of the transverse processes, it
also extends inwards between them and is attached to their
contiguous margins. The next step consists in dividing the
middle lamella longitudinally close to its vertebral attach-
ment. The quadratus lumborum is then brought into view
and gently raising the middle lamella from the surface of
this muscle until its outer border is exposed, the whole

erector
s|)in.t.

quadratus
lumborum.

Fig. 213.— Diagram to show the connections of tlic himbar fascia.

muscle should be pushed inwards. This brings into view
the third or anterior lamella of the lumbar fascia, and its
junction on the one hand with the middle lamella, and on
the other with the bodies of the lumbar vertebrae close to
the roots of the transverse processes, can be made out.

The lumbar fascia, therefore, is formed at the outer
borders of the erector spinae and quadratus lumborum
muscles by the union of these three lamella. Superiorly,
It is attached to the last rib ; inferiorly, it is fixed to the

144 HEAD AND NECK.

crest of the ilium ; whilst externally it is continued into the
transversalis abdominis muscle, of which it may be con-
sidered to be the posterior aponeurosis. By its superficial
surface it gives origin to fibres of the internal oblique muscle
of the abdominal wall.

Dissection. — The serratus posticus superior must be di\-ided close to
its origin from the vertebral spines, and turned outwards in order that
the splenius muscle may be displayed.

Splenius Muscle. — The splenius has a continuous origin
from rather more than the lower half of the hgamentum
nuchse, and from the spines of the seventh cervical and
upper six dorsal vertebrse. From this the fibres pass
obliquely upwards and outwards in the form of a thick,
flat muscle, which soon divides into a cer\dcal and a
cranial portion. These are termed respectively the splenius
colli and the splenius capitis.

The splenius colli (splenius cervicis) turns forwards and
is inserted, behind the levator anguli scapulae, by tendinous
slips, into the posterior tubercles of the transverse processes
of the upper two or three cervical vertebrae.

The splenius capitis passes under cover of the upper part
of the sterno-mastoid muscle, and gains insertion into the
lower part of the mastoid process and into the outer
portion of the superior curved line of the occipital bone.
To obtain a view of this insertion, the sterno-mastoid
muscle may be divided along the superior curved line
of the occipital bone as far as the mastoid process.
Upon no account, however, detach it from the mastoid
process.

Dissection. — The erector spinae and complexus muscles must now be
dissected. Begin by reflecting the splenius muscle. Detach it from its
origin and throw it outwards and upwards towards its insertion. In
doing this preserve the cutaneous branches of the cer^^cal nerv'es which
pierce it.

\Vhen the splenius capitis is fully reflected, a small triangular space
will be noticed close to the superior curved line of the occipital bone.
In front, it is bounded by the trachelo-mastoid muscle ; behind, by the
outer border of the complexus ; and above, by the superior curved line

DORSAL ASPECT OF THE TRUNK. 145

i)f the uccipital boiic. Tlio lloor of lliis liule sjiacc is formcil by ihc
superior obliijuc muscle of the head, and it is traversed liy the occijnlal
artery, whicli in tliis part of its course gives off its arteriu princeps
cervicis branch.

Next remove tlie vertebral aponeurosis and turn the lalissimus dorsi,
the serratus posticus inferior, and the superficial lamella of the lumbar
fascia outwards.

Erector Spinse (sacro-spinalis). — Under this name \vc
include a series of muscular strands which stretch with a
greater or less degree of continuity along the entire length
of the dorsal aspect of the spinal column. In the lumbar
region it constitutes a bulky fleshy mass w'hich may bo
considered the starting-point. This bulky mass sends a
pointed process downwards on the back of the sacrum,
and has the following origin: — (i) from the spines of the
lower two dorsal, all the lumbar and all the sacral vertebrrc ;
(2) from the supraspinous ligaments which bind the lumbar
and dorsal spines together; (3) from the back of the sacrum
and from the posterior sacro-coccygeal ligament ; (4) from
the posterior fifth of the iliac crest. In great part the super-
ficial surface of this muscular mass is covered by a very
dense tendon, which in its lower part becomes blended, as
already noted, with the superficial lamella of the lumbar
fascia.

As the erector spinK is followed upwards it is seen to
divide into three columns. The outer column first separates
from the general mass, and to it the name of ilio-costalis is
given ; the middle column is termed the longissimiis ; and
the inner column, which only becomes quite distinct as we
approach the upper part of the dorsal region, is called the
spinalis dorsi.

Ilio-costalis (ilio-costalis lumborum). — The intermuscular
interval between this nmscle and the longissinius becomes
apparent about the level of the last rib. The separation
is rendered all the more distinct by the external branches
of the posterior primary divisions of the dorsal spinal nerves
which appear in the interval.

Turn the muscle outwards with the handle of the knife, and clean
VOL. II. — 10

146 HEAD AND NECK.

its slips of insertion. The nerves must at the same time be carefully
preserved.

The ilio-costalis will now be observed to end in six or
seven tendinous slips, which are inserted into the angles of
" the six or seven lower ribs. But wherever the ilio-costalis
drops one of these slips, another tendinous slip takes
origin from the upper border of the same rib. In this way
a second muscle is formed, which continues the outer
column of the erector spinse upwards. This muscle is
called the viusculus accesso7'ius.

The Musculus Accessorius (ilio-costalis dorsi), there-
fore, arises close to the inner side of the ilio-costalis by
six tendinous slips from the upper borders of the six lower
ribs. It terminates in tendons which are inserted into the
angles of the upper six ribs, and also into the transverse
process of the lowest cervical vertebra.

Cervicalis Ascendens (ilio-costalis cervicis). — This
muscle may be looked upon as the continuation of the
outer column upwards into the neck. It arises close to
the inner side of the accessorius by four slips from the
third, fourth, fifth, and sixth ribs, and is inserted into the
posterior tubercles of the transverse processes of the
fourth, fifth, and sixth cervical vertebrse.

Longissimus Dorsi. — The longissimus dorsi is the
largest of the three divisions into which the erector spinse
splits, and it extends upwards as high as the first dorsal
vertebra. It is inserted by two distinct rows of tendinous
and fleshy slips. The inner row consists of a series of
tendons attached in the dorsal region to the tips of the
transverse processes of all the dorsal vertebrae, and in the
loin to the accessory processes of the lumbar vertebrae ;
the outer row is composed of fleshy slips, which are inserted
in the dorsal region into the lower ten ribs, midway between
their tubercles and angles, and in the loin to the transverse
processes of the lumbar vertebrae and to the middle layer
of the lumbar fascia. But this muscular column does not
end in the dorsal region ; it is carried up into the neck,
and even reaches as high as the mastoid process of the

DORSAL ASPECT OF THE TRUXk'. ,47

skull l,y two muscular continuations termed respectively—
(I) the transversalis cervicis, and (2) the trachelo-masto d.
TransversaJis Cervicis (longissimus cervicis). -This
muscle takes or.gm in the upper dorsal region, by four or
lue -shps from the transverse processes of a co responding
number of the upi)er dorsal vertebra, and it gains insert on
.no the posterior tubercles of the transverse processe of
alUhecervcul vertebra., with the exception of the first and

The Trachelo-mastoid (longissimus capitis) is prolonged
upwarch. m the neck under cover of the splenius. ^Its
origm from the transverse processes of three or four of the
upper dorsal vertebrae is intimately associated with that of
he transversalis cervicis. In addition to its dorsal origin
however, it also draws three or four slips from the articul";
processes of a like number of the lower cervical ver ebr^
Ihe narrow fleshy band which results is inserted into the

capitis and sterno-mastoid muscles

Spinalis Dorsi—This, the innermost, shortest and
weakest of the three columns, is in some respects the most
di^cult to define. Below, it is" intimately bl nSd w tl U^
ongissimus dors,, but it may be regarded as taking oi^n

and t"wo';o 1""/'' ^^'^^^ ^' '''' ^^- "PPer lumb
and t^so lower dorsal vertebra. These, by their union
orm a small muscle, which is inserted by a'seri:! of 1^

t\Z\ ""'^'' "^^^-^^ °' '''' "Pi-^ ^---^J opines-
dorsi. ^ '"""''''"^ ''''^' '^'' ^"^j'-^^^^"^ semispinalis

have been dissected as they ran^lfy^i^' thf ^^T , xooT" The""'l
part of the vessel, which extends from unde hd ^r of I ^l

Occipital Artery (arteria occipitalis).-The second part

148 HEAD AND NECK.

of the occipital artery is now displayed. In the region of
the mastoid process it is very deeply placed ; indeed, no
less than five structures lie superficial to it. These are
(enumerating them in order from the vessel outwards) —
(i) the origin of the posterior belly of the digastric muscle ;
(2) the mastoid process; (3) the trachelo-mastoid ; (4) the
splenius capitis; and (5) the sterno-mastoid.^ As the
artery runs backwards, it very soon emerges from under
cover of the first three of these structures, and a little
farther on it leaves the shelter of the splenius; so__that
it is covered by the sterno-mastoid alone. . Issuing from
under cover of the posterior border of this muscle, the
artery crosses the apex of the posterior triangle, and
disappears under the trapezius, which it finally pierces near
the external occipital protuberance, to reach the scalp.
Two muscles constitute its deep relations — viz. the in-
sertion of the superior oblique and the complexus.

The following brafiches may be traced from this portion
of the occipital artery : —

1. Arteria princeps cervicis.

2. Mastoid.

3. Muscular.

The arteria princeps cervicis (ramus descendens) is a twig
of some size, which gives off a small branch to the deep
surface of the splenius, and then sinks under cover of the
complexus, where it will be subsequently dissected.

The small mastoid artery (ramus mastoideus) enters the
mastoid foramen to supply the diploe and the meninges of
the brain.

The muscular twigs go to the neighbouring muscles.

The veins corresponding to the occipital artery are two,
or perhaps three in number. They drain the blood from
the occipital portion of the scalp, and open into the large
ve7ia profunda cervicis. The outermost of the occipital veins

1 It is not uncommon to find the artery at this point of its course
nearer the surface. It may pass backwards between the splenius and
the trachelo-mastoid.

DORSAr. ASPECT OF THE TRUNK'. 149

effects, as a general rule, a communication (cmissarium
mastoideum) with the lateral sinus through the mastoid
foramen.

Dissti/ioii. — In cleaning the coniplcxus nuisclc, and in defining its
aUaohmcnts, care must l)e taken of tiie internal branches of the posterior
primary divisions of the second, third, fourth, and fifth cervical nerves.
The first of these — or, in other words, the great occipital — from its
great size, rims little risk of injury, hut the others are liable to be over-
looketl. They all emerge from the suiislance of the muscle close to the
mesial plane.

The Complexus Muscle, placed in the cervical and upper
dorsal regions, inclines obliquely upwards and inwards to
its insertion into the occi[)ut. It arises by seven tendinous
slii)s from the transverse processes of the last cervical and
upi)er six dorsal vertebrae, and by three slips from the
articular processes of the fourth, fifth, and sixth cervical
vertebrae. A thick fleshy muscle is thus formed, and this
is inserted into a large, somewhat oval impression between
the superior and inferior curved lines of the occi[)ital bone,
close to its crest. The muscle narrows somewhat as it
passes upwards, and is separated from its neighbour of the
opposite side by the ligamentum nuchae.

The inner portion of the muscle, w'hich is to a certain
extent distinct from the general mass, and is divided into
two bellies by an intermediate tendon, is frequently desig-
nated the biventer cervicis.

Dissection. — The complexus must now be reflected liy detaching it
from the occiput and throwing it outwards. This dissection requires
great care, not only on account of the nerves which have been seen to
perforate it to reach the surface, but also on account of the structures
which it covers. In its upper part it lies over the sub-occipital triangle
and the muscles bounding it, whilst below it covers the semispinalis
muscle. A thick dense fascia is placed over these subjacent parts, and
in this we find certain of the cervical nerves and the anastomosis be-
tween the arteria princeps cervicis antl arteria profuntla cervicis. The
dissector must specially look for a small twig from the sub-occipital
nerve which enters the deep surface of the upper part of the complexus,
and for a larger branch to the same muscle from the great occipital
nerve. The inner margin of the complexus will be seen to be in con-
tact with a mesial fibrous partition which separates it from the corre-
sponding muscle of the opposite side. This is the ligamentum nuchiv.

15°

HEAD AND NECK.

The Ligamentum Nuchse (Fig. 214) is a strong fibrous
partition placed in the mesial plane between the muscles
on the back of the neck. It represents a powerful elastic
structure in quadrupeds, which helps to sustain the weight

Vc I.

Fig. 214. — Ligamentum nuchas. (Cruveilhier. )

O. Occipital bone.
Vc I. First cervical vertebra.
Vc 7. Seventh cervical vertebra.

of the dependent head. In man, however, there is not
much elastic tissue developed in connection with it, and it
appears to be a continuation upwards of the supraspinous
ligament from the spine of the seventh cervical vertebra to
the external occipital protuberance. In shape it is some-

DORSAL ASPECT OF THE TRUNK. 151

what triangular. By its base it is attached to the crest of
the occipital lionc ; by its anterior border it is fixed by a
series of sHps to the posterior tul)ercle of the atlas, and to
the bifid spines of the cervical vertebra; in the intervals
between their tubercles. Its apex is formed by its attach-
ment to the spine of the seventh cervical vertebra, whilst
its posterior border is in a measure free and gives origin to
the trapezius, rhomboid, serratus posticus superior, and
splenius muscles.

Arteria Princeps Cervicis and Arteria Profunda Cervicis.
— The Jeep ccn'ical aitcry springs from the superior inter-
costal branch of the subclavian, and reaches the dorsum by
passing backwards between the transverse process of the
last cervical vertebra and the neck of the first rib. At the
present stage of the dissection it is seen ascending ui)on the
semispinalis colli muscle and anastomosing with the arteria
princeps cervicis. The latter artery, as we have seen, is a
branch of the occipital. Both vessels likewise anastomose
with twigs from the vertebral artery.

The arteria profunda cervicis is accompanied by a large
vein — the vena profunda cervicis. This vessel begins in the
sub-occipital region, where it is joined by the occipital veins,
and it ends in the vertebral vein close to its termination.
It reaches this point by turning forwards under the transverse
process of the last cervical vertebra.

Posterior Primary Divisions of the Spinal Nerves. — The ,C ^ ^
nerves of the back must now be examined. They are the u -^ -
posterior primary divisions of the spinal nerves. \\'\\\\ four (i.r<r<-A.
exceptions (viz. the first cervical, fourth and fifth sacral,
and the coccygeal nerves), each posterior division will be
found to divide into an external and an internal branch.

Examine ihese nerves successively in the cervical, dorsal, and Imnbar
regions. It is well, however, to defer the dissection of the sacral and
coccygeal nerves until the mullifulus spina: muscle has been studieil.

Cervical Region. — Here the posterior primary divisions
of the spinal nerves are eight in number. The posterior
division of thefrst or sub-occipital nerve, which, as we have

152 HEAD AND NECK.

seen, fails to divide into an external and an internal branch,
lies deeply in the sub-occipital triangle, and will be examined
when this space is dissected.

The posterior primary division of the second cervical nerve
is very large, and appears between the neural arches of the
atlas and axis vertebrse. The posterior primary divisions of
the succeeding six cervical nerves arise from the correspond-
ing spinal nerve-trunks in the intervertebral foramina a short
distance farther out, and, turning backwards under cover, of
the posterior intertransverse muscles, appear in the intervals
between the transverse processes.

The external branches are of small size, and are entirely
devoted to the supply of muscles. They give twigs to the
splenius colli and to the cervical and cranial prolongations
of the erector spinge.

The internal bra^iches are not all distributed alike, nor
indeed do they present the same relations. Those from the
second^ third, fourth, dind fifth nerves run inwards towards the
spinous processes, superficial to the semispinalis colli muscle,
and under cover of the complexus. When close to the mesial
plane they turn backwards, pierce the complexus, splenius,
and trapezius muscles and become superficial. In their
course to the surface they give numerous twigs to the
neighbouring muscles.

The internal branch of the second nerve is remarkable for
its large size. It receives the special name of great occipital.
It will be noticed turning round the lower border of the
inferior oblique muscle, to which it supplies some twigs.
In passing to the surface it pierces the complexus and
trapezius. To the former it gives several twigs. The
distribution of this nerve on the occiput has already been
noticed (p. .108).

The internal branch of the third nerve likewise sends an
offset to the occipital portion of the scalp (p. 136).

The internal branches of the lower three posterior divisions
of the cervical nerves resemble the preceding, in so far that
they take a course inwards towards the spinous processes.
They differ from them, however, in running under cover of

DORSAL ASPECT OF THE TRUNA'. 153

the semispinalis muscle, and in being, as a rule, entirely
expended in the supply of muscles.

Dorsal Region. — The posterior primary divisions of the
dorsal nerves make their appearance in the intervals between
the transverse processes. The external branches proceed
outwards under cover of the middle column of the erector
spinie muscle, and appear in the interval between the
longissimus dorsi on the one hand, and the ilio-costalis and
accessorius on the other. The upper six or seven of these
nerves are exhausted in the supply of the middle and outer
columns of the erector spince, and the levatores costarum ;
the Imver five or six, however, are considerably larger, and
contain both motor and sensory fibres. After giving up their
motor fibres to the same muscles, they become superficial,
by piercing the serratus posticus inferior, and the latissimus
dorsi, in a line with the angles of the ribs.^

The internal branches are also distributed differently in
the upper and lower portions of the dorsal region. The
lorverfive or six are \ery small, and end in the multifidus spinae
muscle. The upper six or seven pass inwards between the
multifidus and semispinalis, and after supplying the muscles
between which they are situated, they are directed back-
wards, and become superficial. In passing towards the
surface they pierce the splenius, rhomboideus, and trapezius
muscles.^

Lumbar Region. — The internal branches of the posterior
divisions of the five lumbar ner\-es are of small size, and,
like the corresponding twigs in the lower dorsal region, they
have a purely muscular distribution. They end in the
multifidus spinae muscle.

The external brancJus sink into the substance of the
erector spinae, and are concerned in the supply of that
muscle, and also of the lumbar intertransverse muscles.
The upper three of these ner\es are of large size, and
become cutaneous by piercing the superficial lamella of

' The cutaneous distribution of these nen'cs has already been examined
')■ the dissector of the upper limb.

154 HEAD AND NECK.

the lumbar fascia. They have already been traced by the
dissector of the lower limb to the skin of the gluteal region.
The lowest external branch communicates with the corre-
sponding branch of the first sacral nerve.

Blood-Vessels of the Back. — In the cervical region the
dissector has already noticed the arteria profunda cervicis,
the second part of the occipital artery, and its branch
termed the arteria princeps cervicis. Deep in the sub-
occipital region he will subsequently meet with a small
portion of the vertebral artery. In addition to these, how-
ever, minute twigs may be discovered, in a well-injected
subject, passing backwards from the vertebral artery in the
intervals between the transverse processes, and also in the
sub-occipital space. These supply the muscles, and anasto-
mose with the other arteries in this region.

In the dorsal region the dorsal branches of the aortic
intercostal arteries make their appearance between the
transverse processes. Each of these vessels reaches this
point by passing backwards in the interval between the
body of a vertebra and the superior costo-transverse liga-
ment. It is associated with the corresponding posterior
primary division of a spinal nerve, and with it is distributed
to the muscles and integument of the back.

In the lumbar region similar branches are derived from
the lumbar arteries. They are distributed in the same
manner.

In both dorsal and lumbar regions these vessels, before
reaching the back, furnish small spinal branches which
enter the spinal canal through the intervertebral foramina.
These will be traced at a later period.

The accompanying veins of the dorsal branches of the
lumbar and intercostal arteries pour their blood into the
lumbar and intercostal veins. These veins are of large
size, being joined by tributaries from the dorsal spinal
venous plexus, and also by others from the interior of the
spinal canal.

Transversus Spinalis. — Under this name are included a
system of muscles which occupy the vertebral groove from

DORSAL ASPECT OF THE TRUNK. 155

the back of the sacrum as high as the axis vertebra. When
this muscular mass is analysed, it is found to consist of three
strata, each of which is composed of a series of bundles or
slips pursuing a more or less ol)liquc course. As the term
given to the whole system implies, these slips for the most
part stretch from the transverse processes upwards and
inwards to be inserted into the spinous processes of the
vertebrc'B. The superficial slips pass over five or more
vertebroe and connect distant points on the column ; the
deeper slips are shorter, and the most deeply placed of all
merely pass between contiguous vertebra;.

The superficial layer is termed the semispinalis muscle ;
the intermediate layer is called the midtifidus spititB ; whilst
the deep stratum is composed of a series of short muscles,
termed the rotatons spina. In the dorsal and cervical
regions we find the three layers (Hughes) ; in the lumbar
and sacral regions the semispinalis is absent.

Dissection. — The semispinalis muscle is already in great part ex-
}X>sed. To display it fully, however, it is necessary to remove the
spinalis dorsi muscle.

The Semispinalis Muscle is described in two parts — the
semispinalis dorsi and semispinalis colli.

The semispinalis dorsi is composed of a series of muscular
slips, with long tendons at either end, which arise from the
transverse processes of five of the lower dorsal vertebraj
(viz. from the si.xth to the tenth). It is inserted into the
spines of the upper four dorsal and lower two cervical
vertebrce.

The semispinalis colli lies under cover of the complexus.
It springs from the transverse processes of the upper five
dorsal vertebra;, and is inserted into the spines of four
cervical vertebrne (viz. from the second to the fifth).

The slips composing the semispinalis muscle stretch
over five or more vertebra;.

Dissection. — The multifidus spinx is of great extent. Beginning in
the .sacral region, it jxisses upwards as far as the axis vertebra. It is
weakly dcveloixtl in the dorsal region, hut is strongly marked in the

156 HEAD AND NECK.

loin and in the neck — more especially in the former. To bring it
thoroughly into view, the semispinalis muscle must be detached from
the spines and thrown outwards : the erector spinae muscle must also
be separated from the lumbar and sacral spines and drawn aside — if,
indeed, this has not been already done in following out the nerves.

Multifidus Spinse (multifidus). — In the lumbar and sacral
regions the multifidus will be seen to constitute a thick
fleshy mass, which clings closely to the vertebral spines.
In this situation it has a very extensive origin — viz. (i)
from the deep surface of the aponeurotic origin of the
erector spinse ; (2) from the posterior surface of the sacrum
as low as the fourth aperture ; (3) from the posterior sacro-
ihac ligament ; (4) from the posterior superior spine of
the ilium; and (5) from the mammillary processes of the
lumbar vertebrae. In the dorsal region it takes origin from
the transverse processes of the vertebrse, and in the cervical
region from the articular processes of at least four of the
lower cervical vertebree. The bundles which compose the
nmltifidus pass over two, three, or four vertebree, and are
inserted into the whole length of the various spinous pro-
cesses of the movable vertebrse as high up as the axis.

The Eotatores Spinse (submultifidus) are a series of small
muscles which may be exposed by raising the multifidus.
In the dorsal region each muscle springs from the root of a
transverse process, and is inserted into the lamina of the
vertebra immediately above, close to the root of the spinous
process. Somewhat similar muscles have been described in
the cervical and lumbar regions, and also a series of longer
and more superficial slips which connect alternate vertebrae
with each other (Hughes).

Interspinales and Intertransversales. — The dissector
should next examine the minute interspinous and inter-
transverse muscles.

The interspinous muscles can hardly be said to exist in the
dorsal region, except in its upper and lower parts, where they
are present in a rudimentary condition. In the neck they
are arranged in pairs — two occupying each interspinous
interval, with the exception of that between the axis and

DOKSAL ASPECT OF THE TKUNA'. 157

atlas. In iho lumbar region they arc also well marked and
in pairs ; here they are attached to the whole length of the
spinous processes.

The inlcrtransi'ersc muscles (interlransversarii) are strongly
developed in the lumbar region, and occupy the entire
length of the intertransverse intervals. Additional rounded
fasciculi may be observed passing between the accessory
processes. These are termed the interaccessorii.

In the dorsal region intertransverse muscles — very weak
and poorly developed — are only found in the lower three
or four spaces.

In the cervical region the intertransversales are present
in pairs. They will be better examined at a subsequent
period.

Levatores Costarum. — These constitute a series of
twelve fiin-shapcd muscles, which pass from the transverse
processes to the ribs. To bring them thoroughly into
view, the longissimus dorsi, ilio-costalis, and accessorius
muscles should be removed. The first muscle of the
series springs from the tip of the transverse process of the
last cervical vertebra, and, expanding as it proceeds down-
wards and outwards, is inserted into the outer border of the
first rib, immediately beyond the tubercle. Each of the
succeeding muscles takes origin from the tip of a dorsal
transverse process, and is inserted into the outer surface
of the rib immediately below, along a line extending from
the tubercle to the angle.

Posterior Primary Divisions of the Sacral Nerves. —
These are very small. The upper four will be found emerg-
ing from the posterior sacral foramina; the fifth appears at
the lower end of the sacral canal.

To expose the upper three the multifidus spinne muscle
covering the upper three sacral apertures must be carefully
removed. Each of these three nerves will be found to
divide in the usual manner into an internal and external
branch.

The internal branches are very fine, and end in the
multifidus spina;.

158 HEAD AND NECK.

The external branches are somewhat larger, and join
together so as to form a looped plexus upon the back of
the sacrum. This communicates above with the external
branch of the last lumbar nerve and below with the pos-
terior division of the fourth sacral nerve. Branches pro-
ceed from the loops thus formed to the surface of the great
sacro-sciatic ligament. Finally they become superficial by
piercing the gluteus maximus muscle, and they supply a
limited area of skin over the gluteal region. They have
already been examined by the dissector of the lower
limb.

The lowest two posterior primary divisions of the sacral
nerves do not exhibit the usual division into external and
internal branches. They are very small, and, after com-
municating with each other, and also with the coccygeal
nerve, they distribute filaments to the parts on the back of
the lower portion of the sacrum and on the dorsal aspect
of the coccyx.

Minute twigs from the lateral sacral artery accompany
the sacral nerves and anastomose with twigs from the
gluteal and sciatic arteries.

The Posterior Division of the Coccygeal Nerve is a
slender twig which emerges from the inferior opening of
the sacral canal, and, after being joined by a filament
from the last sacral nerve, is distributed on the back of
the coccyx.

Dorsal Spinal Venous Plexus. — A plexus of veins is
situated upon the superficial aspect of the neural arches of
the vertebrse, subjacent to the multifidus muscle. This
plexus collects blood from the integument and muscles of
the back, and in the dorsal and lumbar regions pours it
into the posterior tributaries of the intercostal and lumbar
veins. In the neck it is especially well marked, and its
blood is emptied into the vertebral veins. It is hardly to
be expected, however, that the dissector, in an ordinary
dissection, will make out much of,these venous channels.

Directions. — The last day upon which the body is allowed to remain
in its present position must be devoted to the dissection of the sub-

DORSAL ASPECT OF THE TRUNK. 159

occipital triangle, and to the display of the spinal cord, its membranes,
nerve-roots, and blood-vessels.

In the event of the dissector being [lUshed for lime, it is belter that
he should proceed at once to ex|X)se the spinal cord, and. defer the
dissection of the sub-occipital region until the head and neck has been
removed from the iiod)-.

The Sub -Occipital Space is a small triangular area,
exposed by the reflection of the complexus muscle. It
is bounded by three muscles — viz. (i) the rectus capitis
posticus major, which forms its upper and inner boundary ;
(2) the oblicjuus inferior, which limits it below ; and (3) the
obliquus superior, which bounds it above and to the outer
side. When dissected, its floor will be found to consist of
two structures — viz. the posterior arch of the atlas and
the thin posterior occipito-atlantal ligament. It contains
within its area a portion of the vertebral artery and the
posterior primary division of the sub-occipital or first
cervical nerve.

Dissection. — Before cleaning the muscles bounding the triangle, the
sub-occipital nerve must be secured. This can best be done by tracing
into the space the minute twig which it has been seen to give to the
deep surface of the complexus, or, if this has not been observed, by
endeavouring to find the twig which it gives to the rectus capitis posticus
major. The tissue in which the nerve lies is very dense, and the dissec-
tion in consequence is rendered somewhat difficult.

The Rectus Capitis Posticus Major springs by a pointed
origin from the spine of the axi.s, and, expanding as it passes
upwards and outwards, it is inserted into the occipital bone
along the outer portion of the inferior curved line and the
surface immediately below.

The Rectus Capitis Posticus Minor is a minute fan-
shaped muscle, placed to the inner side and upon a deeper
plane than the preceding muscle. It takes origin from the
tubercle on the posterior arch of the atlas, and is inserted
into the inner part of the inferior curved line of the
occipital bone and the surface between this and the fora-
men magiiiun.

The Obliquus Capitis Inferior stretches from the bifid
spine of the axis, from the extremity of which it takes

i6o HEAD AND NECK.

origin, to the posterior tubercle of the transverse process of
the atlas. The great occipital nerve will be seen hooking
round its lower border.

The OWiquus Capitus Superior springs from the trans-
verse process of the atlas, and is inserted into the occipital
bone in the interval between the curved lines.

The Posterior Division of the Sub-Occipital Nerve does
not divide into an external and internal branch. It enters
the sub-occipital triangle by passing backwards between the
posterior arch of the atlas and the vertebral artery ; so that
even in cases where all its branches have been divided,
the trunk is readily found in this position. The nerve
at once breaks up into branches which go to supply five
muscles — viz. the two recti, the two oblique muscles, and
the complexus. In addition to these muscular twigs it
gives a commuiticating, and sometimes a cutaneous filament.

The comnmnicating bratich generally proceeds from the
nerve to the obliquus capitis inferior, and joins the great
occipital nerve. The cutaneous branch when present accom-
panies the occipital artery to the integument over the
occiput.

Vertebral Artery (arteria vertebralis). — It is only a small
portion of this vessel which occupies the sub-occipital
triangle. Emerging from the foramen in the transverse
process of the atlas, it runs backwards and inwards in
the groove upon the posterior arch of the same bone.
In this course it crosses the sub-occipital nerve, and lies
immediately behind the lateral mass of the atlas. It leaves
the space and enters the cranial cavity through the foramen
magnum by turning forwards below the posterior occipito-
atlantal ligament and piercing the dura mater.

Small branches proceed from the vertebral artery in this
situation to supply the parts in its immediate neighbourhood,
and to anastomose with the arteria princeps cervicis and the
arteria profunda cervicis. / ;

Dissection to open the Spinal Canal. — The first step consists in
thoroughly cleaning the vertebral laminje and spinous processes upon
either side. The multifidus spinee must also be completely removed

DORSAL ASPECT OF Tllli TRUNK. i6i

from the back of llic .s;icruin. At the same lime tlie posterior primary
divisions must be relained, so that their continuity witli the various
spinal nerve-trunks may lie afterwards established. The posterior wall
of the spinal canal should now be removed in one piae by sawing
through the lamimv of the vertebnv on either side, and dividing the
ligamenta subtlava, from the third cervical vertebra down to the lower
opening of the canal on the back of the sacrum.

In making this dissection the student must atlenil to the following
points : — (i) the cut should be directed through the laminiv close to the
inner side of the articular processes ; (2) the saw must be used in an
oblicjue plane, so that the cut through the lamina; slants slightly inwards;
(j) in cutting ihrougii the cervical laminixi the head and neck should
hang over the end of the table, and be pressed as fer forwards as possible
whilst the saw is worked from below upwards ; (4) in the case of the
lumbar region, where, indeed, most difficulty will be met, a high block
must be placed under the abdomen of the subject, whilst the blocks
supporting the chest and pelvis are removed. It will probably be
necessary at this point to have recourse to the hammer and chisel.

The lamina: and spinous processes which are thus removed are con-
nected with each other liy the ligamenta subflava and the supraspinous
and interspinous ligaments. They should therefore be laid aside for
the present. A description of these ligaments w ill be found farther on.
When the specimen is fresh, however, the dissector should note the
high elasticity of the ligamenta subflava. This can be tested by stretch-
ing the specimen.

Between the dura mater and the walls of the spinal canal, the dis-
sector will notice a quantity of loose areolar tissue and soft fat. The
latter is especially plentiful in the sacral region, where it resembles
somewhat the marrow which occupies the medullary cavity of a long
bone. In the midst of this areolo-falty material, great numbers of large
veins and minute arteries are found ramifying upon the walls of the
canal.

Spinal Arteries. — A minute spinal artery in a well-injected
subject will be seen entering the spinal canal through each
intervertebral foramen. These arteries are derived from
different sources in the different regions of the spine. In
the cervical region they come from the vertebral artery ; in
the dorsal region from the dorsal branches of the intercostal
arteries ; in the lumbar region from the dorsal branches of
the lumbar arteries. They supply with blood the spinal
cord and its meninges, the bones, the periosteum, and the
ligaments ; and their arrangement is very much the same
in the three regions.

VOL. II. — 11

1 62 • HEAD AND NECK.

Each spinal artery may be looked upon as giving off three
main twigs : of these, one^ a very small branch, ramifies upon
the deep surface of the neural arches and ligamenta subflava ;
another can be followed to the dura mater, which it pierces
immediately above the point of exit of the corresponding
spinal nerve ; whilst the third is carried inwards in front of
the dura mater towards the posterior surface of the vertebral
bodies. The last -mentioned branch divides into an
ascending and descending twig. These anastomose with
the corresponding twigs of the arteries above and below,
and in this manner a continuous series of minute arterial
arcades is formed. From these arcades, branches pass
inwards upon the posterior aspect of the vertebral 'bodies,
and join a small median longitudinal artery which extends
along the anterior wall of the spinal canal.

In the cervical region small branches from the ascending
cervical artery also find their way into the spinal canal ;
whilst in the sacral portion of the canal the dissector will
find branches from the lateral sacral arteries.

Intraspinal Veins. — These are very large and very
complicated in their arrangement. They may be looked
upon as forming a posterior and an anterior intraspinal
plexus.

. The. posterior intraspinal venous plexus consists of two main
longitudinal vessels, united by many cross branches, which
run along the deep aspect of the neural arches and ligamenta
subflava. Above, they communicate with the occipital
sinus, whilst all the way down they are connected with the
dorsal spinal venous plexus hyWide channels which pierce the
ligamenta subflava. Laterally they send branches through
the intervertebral foramina to join the posterior branches
of the intercostal and lumbar veins.

The anterior intraspinal venous plexus cannot be dissected
whilst the spinal cord and its membranes are in situ, but it
will be more convenient to describe it at this stage. Indeed,
the dissection is one of considerable difficulty, even under
the most advantageous circumstances. Like the preceding,
it is composed of two longitudinal venous channels placed

DORSAL ASPECT OF THE TRUNIC. 163

one upon either side of the posterior common ligament of
the vertebral bodies, and joined by numerous transverse
branches which cross the mesial plane under cover of this
ligament. These transverse veins receive large tributaries
from the interior of the vertebral bodies. Superiorly each
of the main longitudinal channels communicates with the
occipital and basilar sinuses within the cranium, and gives
off a branch which emerges above the neural arch of the
atlas to form the commencement of the vertebral vein.
Opposite the various intervertebral discs they send off
branches which run towards the intervertebral foramina,
and, joining the corresponding branches of the posterior
intraspinal plexus, form a plexus around the corresponding
spinal nerve.

Meninges of the Spinal Cord — Fig. 2 1 5. — The spinal cord,
like the brain, with which it is continuous, is enveloped
by three membranes termed meninges. The most external
investment is a strong fibrous membrane called the dura
mater ; the second, in order from without inwards, is a
non-vascular tunic termed the arachnoid mater ; whilst the
third and most internal is the pia mater. These mem-
branes are directly continuous with the corresponding in-
vestments of the brain.

Dissection. — The outer surface of the dura mater must now be
cleaned. This is effected by removing from the spinal canal the loose
areolar tissue, soft fat, and posterior intraspinal veins. It is necessar)',
also, to carefully define the numerous lateral prolongations which the
membrane gives to the spinal nerves.

Dura Mater Spinalis — Fig. 2 1 5 {d). — In the spinal canal
the dura mater constitutes an exceedingly dense and tough
fibrous tube, which extends from the foramen magnum
above, to the level of the second or third piece of the sacrum
below. Even before this tube of membrane is laid open,
the dissector can readily satisfy himself that it is very loosely
adapted to the spinal cord and the nerve-roots which form
the Cauda equina ; in other words, it is very capacious in
comparison with the volume of its contents. Its calibre,
moreover, is by no means uniform ; in the cervical and

1 64 HEAD AND NECK.

lumbar regions it is considerably wider than in the dorsal
region, whilst in the sacral canal it rapidly contracts and
finally ends by blending with the filum terminale, a fibrous
thread which is prolonged downwards through the sacral
canal from the extremity of the spinal cord. Above, the
dura mater is firmly attached to the third cervical vertebra,
to the axis vertebra, and around the margin of the occipital
foramen ; belozv, the filum terminale, on which it terminates,
can be traced as far as the dorsal aspect of the coccyx,
where it is lost by blending with the periosteum investing
that bone.

If the student recall the characteristics of the cranial dura
mater, he cannot fail to observe certain striking points of
difference between it and the spinal dura mater. The rela-
tions which the latter presents to the walls of the spinal
canal are altogether different. Within the cranial cavity the
dura mater is closely adherent to the bones, and forms for
them an internal periosteum. As it is traced into the
spinal canal it splits at the foramen magnum into its two
constituent layers. The inner of these two laminae is carried
downwards as the long cylindrical tube which encloses the
spinal cord. The outer lamina, which is very much thinner,
becomes continuous, behind and on each side of the fora-
men magnum, with the periosteum on the exterior of the
cranium, whilst in front it is prolonged downwards into the
vertebral canal in connection with the ligaments and perio-
steum on the anterior wall of the canal. The spinal dura
mater corresponds, therefore, to the supporting layer of the
cranial dura mater and to it alone. It is separated from the
walls of the spinal canal and its lining periosteum by an
interval or space, which is filled by loose fat, areolar tissue,
and the intraspinal plexuses of veins. In connection with
the spinal dura mater there are no venous sinuses such as
are present in the cranial cavity, but it should be noted that
the intraspinal veins, placed between the periosteum of the
spinal canal and the tube of dura mater, occupy the same
morphological plane as the cranial sinuses. Another feature
which serves to distinguish the spinal dura mater from the

DORSAL ASPECT OF THE TRUNK. 165

rranial dura mater consists in the fact that it gives off from
its deep surface no partitions or septa.

The cylindrical tube of spinal dura mater docs not lie free
within the vertebral canal, although its attachments are of
such a nature that they do not in any way interfere with the
free movement of the vertebral column. On either side the
spinal ncr\-e roots, as they pierce the dura mater, carry with
them into the intervertebral foramina tubular sheaths of
the membrane, whilst in front loose fibrous prolongations —
more numerous above and below than in the dorsal region
— connect the tube of dura mater to the posterior common
ligament of the vertebral column. No connection of any
kind exists between the dura mater and the neural arches
of the vertebrae or ligamenta subflava.

Dissection. — The tube of dura mater may now lie opened with the
scissors. The incision should be carried through the membrane in the
mesial plane. Care, however, must be taken not to injure the delicate
arachnoid, which is subjacent.

Subdural Space (cavum subdurale). — The capillary
interval between the dura mater and the arachnoid mater
is termed the subdural space — Fig. 215 {sd). The deep
surface of the dura, which is turned towards this space, is
smooth, moist, and polished. Upon either side the dis-
sector will notice the series of apertures of exit for the roots
of the spinal nerves. These are ranged in pairs opposite
each intervertebral foramen, and the subdural space is pro-
longed outwards for a short distance upon each of the
nerve-roots.

Viewed from the inside of the tube of dura mater, each of the
two nerve-roots belonging to a spinal nerve is seen to carry with it a
s|x;cial and distinct sheath. WHien examined, however, on the outside
of the tube of dura mater, the appearance is such that the dissector
might be led to conclude that both roots are enveloped in one sheath.
This is due to the Hict that the two sheaths are closely held together on
the outside by intervening connective tissue, which can be renu)veil with
a little careful dissection. When this is done, the two tubular sheaths
will be observed to remain distinct as far as the gangli<in on the ]X)slerior
root of the nerve. At this point they blend with each other.

1 66

HEAD AND NECK.

Arachnoidea Spinalis — Fig. 215 {a). — The arachnoid
resembles the dura mater in forming a loose, wide invest-
ment for the spinal cord. Unlike the dura, however, it is
remarkable for its great delicacy and transparency. The
sac which it forms is most capacious towards its lower part,
where it envelops the extremity of the cord and the collec-
tion of long nerve-roots which constitute the canda equina.
Here it can be most easily demonstrated by making an
incision into it, and inserting the handle of the scalpel, or,
better still, by inflating the sac with air by means of a blow-

self- \ / sd

Fig. 215. — Transverse section through the spinal cord
and its membranes. (Schwalbe, after Key and Retzius. )

Id. Ligamentum denticulatum.
a. Arachnoid mater.
sd. Subdural space.
d. Dura mater.
sp. Septum posticum.
sa.p. Sub-arachnoid space behind.

7-j>. Posterior nerve-root.
ds. Sheath of dura mater.
as. Sheath of arachnoid mater.
7-a. Anterior nerve-root.
ins. Spinal cord.
sa.a. Sub-arachnoid space in front.

pipe. Above, the arachnoid mater becomes continuous at
the level of the foramen magnum with the corresponding
membrane which clothes the brain, whilst, laterally, it is pro-
longed outwards upon the various nerve-roots, thus contri-
buting to each a tubular sheath.

Sub-arachnoid Space (cavum subarachnoideale) — Fig.
215 (sa.p.). — This term is applied to the wide space between
the arachnoid and pia mater. It is occupied by a variable
amount of cerebro-spinal fluid, and is directly continuous
with the cranial sub-arachnoid space. Three incomplete

DORSAL ASPECT OF THE TRUNK'. 167

septa partially subdivide the spinal suh-arachnoid space
into compartments. One of these septa is a mesial parti-
tion calleil the septum posticum, which connects the pia
mater covering the posterior aspect of the cord with the
arachnoid mater. In the upper part of the cervical region
the septum posticum is very imperfect, and is simply repre-
sented by a number of strands passing between the two
membranes ; in the lower part of the cervical region and
in the dorsal region it becomes tolerably complete. The
other two septa are formed by the ligamenta denticulata.
These spread outwards from each side of the spinal cord,
and will be studied with the pia mater.

Dissection. — Clear away the arachnoid mater from a portion of the
cord, and proceed to the study of the pia mater.

Pia Mater Spinalis. — This is a firm vascular membrane,
which closely invests and is firmly adherent to the surface
of the spinal cord. In front, it sends a fold into the
antero-median fissure of the spinal cord, whilst behind a
septum continuous with its deep surface dips into the
postcro-median fissure. Anteriorly, in the mesial plane, it
is thickened in the form of a longitudinal glistening band,
which receives the name of the linea splendens. Of course
this can only be seen after the cord has been removed from
the spinal canal.

The Ligamentlun Denticulatum — Fig. 216 (3) — is a
remarkable band, which stretches outwards from either
side of the pia mater, so as to connect it with the
dura mater. Its pial or inner attachment extends in a
continuous line between the anterior and posterior nerve-
roots, from the level of foramen magnum above to the
level of the body of the first lumbar vertebra below. Its
outer marii^in is widely serrated or denticulated. From
twenty to twenty- two denticulations may be recognised,
riiey occur in the intervals between the spinal ner\-es, and,
[)ushing the arachnoid before them, they are attached by
their pointed extremities to the inner surface of the dura
mater.

1 68

HEAD AND NECK.

The ligamenta denticulata partially subdivide the sub-
arachnoid space into an an-
terior and a posterior com-
partment. In the anterior
compartment the anterior
nerve -roots pass outwards;
the posterior compartment
contains the posterior nerve-
roots, and is imperfectly
subdivided into two lateral
subdivisions by the septum
posticum.

By means of the ligamen-
tum denticulatum of either
side, the spinal cord is sus-
pended in the middle of the
sac of dura mater.

Spinal Cord (medulla
spinalis). — The spinal cord
itself may now be studied
in situ. It is a cylindrical
structure, slightly flattened
in front and behind, which
extends from the margin of
the foramen magnum, where
it is continuous with the
medulla oblongata of the
brain, to the lower border
of the body of the first or the
upper border of the body of
the second lumbar vertebra.
Its lower end rapidly tapers
to a point, and is termed the
conus inedullaris. From the
extremity of this, a slender
filament, termed the filum
terminale or central ligament,
is prolonged downwards.

Fig. 2 1 6. — Lateral view of the
spinal cord, dura mater, and
ligamentum denticulatum. —
(Hirschfeld and Leveille. )

I and 2. Fasciculi of origin of nerve-roots.

3. Ligamentum denticulatum.

4. Anterior nerve-root.

5. Posterior nerve-root.

6. Section through nerve-roots.

7. Spinal nerve with its sheath of dura

mater.

DORSAL ASPECT OF IIIF. TRUNK. 1O9

III llio female the average length of the spinal cord is
sixteen and a (juarter inches; in the male it is seventeen
and a half inches.

'rhroughout the greater part of the dorsal region the
spinal cord presents a uniform girth, but in the cervical
and lower dorsal regions it shows marked swellings, termed
respectively the cervical and lionbar enlargements. From
these expansions proceed the nerves which supply the ui)per
and lower limbs. The cervical swelling (intumescentia
cervicalis) is the more evident of the two. It begins at
the upper end of the cord and attains its greatest breadth
(13 to 14 mm.) opposite the fifth or sixth cervical vertebra.
Below it subsides opposite the second dorsal vertel)ra. The
lumbar swelling (intumescentia lumbalis) begins at the level
of the tenth dorsal vertebra, and attains its maximum trans-
verse diameter (i I to 13 mm.) opposite the last dorsal vertebra.
Below it rapidly tapers into the tapering conus medullaris.

Filum Terminale. — This delicate thread-like filament
lies amidst the numerous long nerve-roots which occupy the
lower part of the spinal canal, and it can readily be detected
from these (i) by its silvery glistening appearance, and (2)
l)y its continuity with the extremity of the comes medullaris.

Although the central canal of the spinal cord is prolonged
down in its interior for nearly half its length, and nervous
elements can be traced in its substance for a like distance,
the filum terminale is chiefly composed of pia mater
carried downwards from the conus medullaris. The linea
splendens and the lower ends of the ligamenta denticulata
may also be considered to be continued into it. At the level
of the second or third sacral vertebra it pierces the tapered
end of the tul)e of dura mater, and receives an investment
from it, and, finally, reaching the lower end of the sacral
canal, it terminates by blending with the periosteum on the
back of the coccyx or last piece of the sacrum.

In length the filum terminale measures about six inches.
The part within the tube of dura mater is termed ihc fill/ m
terminale internum, the portion outside is distinguished as
\.\\c filum terminale externum.

I70 HEAD AND NECK.

Spinal Nerves. — Thirty-one spinal nerves take origin
from each side of the spinal cord. These are classified
into five groups, according to the vertebrae with which they
are associated. The dorsal, lumbar, and sacral nerves cor-
respond in number with the number of vertebra in each of
these regions, — thus, there are twelve dorsal, five lumbar,
and five sacral nerves, each of which issues from the spinal
canal below the vertebra with which it numerically corre-
sponds. In the cervical region, however, there are eight
nerves, the first of which comes out between the occiput
and the atlas, and is therefore distinguished by the special
name of \hQ. sub-occipital neive. There is only one coccygeal
nerve on each side.

Spinal Nerve Roots — (Fig. 217). — Each spinal nerve
springs from the side of the spinal cord by two roots — an
anterior (radix anterior) and a posterior (radix posterior).
Except in the case of the sub-occipital nerve (where,
indeed, the posterior root is sometimes absent), the posterior
nerve-root is the larger of the two. In addition to this,
the posterior root is distinguished by possessing an oval
ganglion, termed the spinal jvot-ganglion (ganglion spinale).
There is, likewise, a wide physiological difference between
the two roots, — the posterior root is composed of sensory
fibres, the anterior root consists of motor fibres. Im-
mediately beyond the ganglion the two roots unite to form
the spinal ?ierve trunk, which, in consequence, contains a
mixture of both motor and sensory nerve-fibres.

The mode of attachment oi the two nerve-roots to the side
of the spinal cord is somewhat different in the two cases.
In each instance they are attached to the cord by several
separate fasciculi (fila radicularia). In the case of the
posterior root these enter the cord consecutively along a
continuous straight line and at the bottom of a slight
furrow. The fasciculi of the anterior root, on the other
hand, are not so regularly placed. They emerge from the
cord over an area of some breadth.

The size of the nerve -roots will be observed to differ
greatly. The lower lumbar and upper sacral nerve-roots

DORSAL ASPECT OF THE TRUNK.

171

arc much the largest, whilst the lower sacral and the
coccygeal roots are the smallest. In the cervical region
the roots increase in size from above downwards, but more
rapidly in the lower members of the group ; in the dorsal
region the roots of the first nerve are large, but those
which succeed it are small and of uniform size.

In relative length., and in the direction which they follow
in the spinal canal, the nerve-roots also show great differ-
ences. This is due to the spinal cord being so much
shorter than the canal in which it lies. In the upper part
of the cervical region the nerve-roots are short, and proceed
outwards in a more or less horizontal direction. Below

Fig. 217. — Segments of spinal cord ; anterior aspect.
(Schwalbe, after Allen Thomson.)

1. Anterior median fissure.

2. Posterior median fissure.

3 and 5. Fasciculiof anterior nerve-root.
4. Postero-lateral groove.

6. Posterior nerve-root.
6'. Spinal ganglion.

7. Anterior primary division.
7'. Posterior primaiy division.

this the nerve - roots gradually lengthen, and have to
descend in the spinal canal for a distance which is always
increasing the farther down we go. The arrangement of
the lower dorsal, the lumbar, sacral, and coccygeal nerve-
roots is particularly characteristic. They are exceedingly
long, and descend vertically from the lower portion of the
cord, in the form of a bunch or leash which, from its appear-
ance, has been termed the cauda equina.

Mode of Exit of Spinal Nerves from Spinal Canal. —
The six lower cervical nerves, the dorsal nerves, and the
lumbar nerves make their exit through the intervertebral

172

HEAD AND NECK.

foramina ; whilst the upper four sacral nerves find their
way out by the sacral foramina. The two upper cervical
nerves, the fifth sacral nerve, and the coccygeal nerve, how-
ever, follow a different course. The sub-occipital emerges
by passing over the neural arch of the atlas, and the

filum terminale.

teirainale

V sacral nerve

coccygeal nerve

Fig. 2 1 8. — Sacral canal opened up from behind to show
the sacral nerve roots (lower part of cauda equina) and the
membranes in relation to them. (After Testut. )

second cervical nerve by passing over the neural arch of
the axis. The fifth sacral and the coccygeal nerve leave
the sacral canal through its lower aperture (Fig. 218).

DORSAL ASPECT OF THE TRUNK. 173

Dissection. — Tlic ncrvc-rools of one or two spinal nerves in each
region shoulil be followed into the corresponding intervcrtel)rnl fora-
mina. This can be easily done by snipping away the articular processes
with the bone-pliers. The position of the ganglion on the posterior
root, the connections of the sheath of dura mater, the union of the two
roots to form the sjiinal nerve trunk, and the division of the latter into
the anterior anil posterior primary divisions, can thus be studied. An
attempt should also be made at the same time to discover the minute
siiiti-vcrtcbral noTC (ramus meningeus) of Luschka. This is a fine
twig which is formetl by the union of a small filament from the spinal
nerve trunk with a minute branch from the sympathetic cord. It takes
a recurrent course through the intervertebral foramen to end in the
bones and periosteum of the vertebral canal.

The Spinal Root-Ganglia. — These ganglia are oval
swellings developed upon the posterior nerve roots, just
before they unite with the anterior roots to form the
spinal nerve trunks. They are usually found upon the
posterior roots of all the nerves, although occasionally the
ganglion may be absent in the case c^f the sub-occipital
nerve.

Except in the case of the two upper cervical nerves,
and the sacral and coccygeal nerves, the spinal ganglia are
formed upon the posterior nerve roots as they lie in the
intervertebral foramina. The ganglia of the first two
cervical nerves lie upon the neural arches of the first and
second cervical vertebrae respectively ; the ganglia of the
sacral nerves are placed within the sacral canal, but out-
side the tube of dura mater. The ganglion on the posterior
root of the coccygeal nerve will be found inside the tube
of dura mater.

Spinal Nerve Trunks. — These are formed by the union
of the anterior and posterior nerve roots immediately
beyond the spinal ganglia, and from what has been said it
must be evident that this union takes place in the case of
the coccygeal and sacral nerves in the sacral canal ; in the
lumbar, dorsal, and lower six cervical nerves in the inter-
vertebral foramina ; and in the case of first two cervical
nerves on the neural arches of the atlas and axis.

The nerve - trunk is exceedingly short ; indeed, it is
almost no sooner formed than it divides into its a/i/crior and

174 HEAD AND NECK.

posterior primary divisions. In the case of the sacral and
coccygeal nerves, this subdivision takes place in the sacral
canal, and the spinal nerve trunks of these nerves are dis-
tinctly longer than in the case of the nerves which occupy
a higher level.

The distribution of the posterior primary divisions has
already been examined (p. 151).

Dissection. — At this stage the dissector may adopt one of two
methods in the further treatment of the cord and the nerves which
spring from it. If the cord is fresh and in such a condition that it may
be successfully hardened, it is best to transfer it at once to the pre-
servative fluid. If, on the other hand, it is soft and not fit for proper
preservation (and it must be admitted that this is generally the con-
dition in which the spinal cord is found in the dissecting-room), it
should be removed with all its membranes and nerve-roots, and placed
in a cork-lined tray filled with water. There is no method by which
the arachnoid, the pia mater, the ligamenta denticulata, and the nerve-
roots can be so well studied as this.

In removing the spinal cord, the spinal nerves should be divided as
they lie in the intervertebral foramina, and in such a manner that as
long a piece as possible of each nerve remains attached' to the dura
mater and the cord. Wlierever it is possible the ganglia should be
taken with the nerves. The same rule also applies to the sacral nerves.
The cord and its membranes should then be cut across at the highest
limit of the vertebral dissection. By pulling upon the dura mater the
whole specimen may now be lifted from the vertebral canal and trans-
ferred to the water-bath. The dura mater should then be slit down
the mesial plane over the front of the cord, and the edges of each
lateral piece drawn outwards. By fixing the dura mater to the cork at
the bottom of the tray with pins, the further dissection can be conducted
with great advantage.

Arteries of the Spinal Cord. — It is only in cases where
a paint or a starch injection has been used that the spinal
arteries can be made out satisfactorily.

A large number of small arteries are supplied to the
spinal cord. These are the anterior and posterior spinal
arteries which spring from the vertebral, and a series of
lateral spitial arteries which reach the side of the spinal
cord and are derived from different sources in each region.
In the 7ieck they come from the spinal branches of the
vertebral, ascending cervical, and deep cervical arteries;

DORSAL ASPECr OF THE TRUNK. 175

and in the dorsal and lumbar ixgions from the spinal twigs
of the dorsal branches of the intercostal and lumbar arteries.
By the anastomoses of these arterial twigs, five longitudinal
trunks are formed upon the surface of the spinal cord.
One of these occupies the mesial plane in front, and may
be termed the anfero-median artery. The other four arc
placed in relation to the sulci along which the posterior
nerve roots enter the cord. One runs downwards in front
of the line of entrance of these roots, and the other behind
it on each side of the cord. These slender arterial trunks
may therefore be termed the postero- lateral longitudinal
vessels.

The antero-Diedian vessel is formed in its upper part by the union
of the two anterior spinal branches of the vertebral arteries. One of
these is larger than the other, and takes a much greater share in the
formation of the median trunk. Below the level of the fifth pair of
cervical nerves the continuity of the median vessel depends upon the
reinforcements which it obtains from the lateral spinal vessels. The
number of lateral spinal arteries which join the median vessel is very
variable. The majority of these arteries end on the nerve-roots ; five
to ten only reach the median vessel. The antcro-median arien< runs
downwards, under cover of the linea splendens of the pia mater. Its
calibre is uniform throughout, and where the cord ends it proceeds
onwards for some distance upon the filum terminale.

The postero-lateral arteries on each side of the cord are formed in
the upper part of the cervical region by the bifurcation of the corre-
sponding posterior spinal branch of the vertebral arter}-. Lower down
their continuity is maintained by twigs which reach them on the ix)Sterior
roots of the spinal nerves from the lateral spinal arteries. It may be
regarded, as a rule, that where a lateral spinal arter)- gives a branch to
one of the postero-lateral arterial trunks, it does not furnish another
to the antcro-mcdian arterial trunk. In this way difl'erent lateral spinal
arteries are in connection with the longitudinal trunks on the anterior
and ix)sterior aspects of the cord. The postero-lateral vessels end at
the lower extremity of the cord.

From the five main arterial channels which thus extend along the
cord numerous anastomosing twigs ramify in the pia mater.

Veins of the Spinal Cord. — These veins are small and
numerous, and their disposition cannot be said to corre-
spond with that of the arteries. They are very tortuous,
and form a ple.xus with elongated meshes. Four more or

176

HEAD AND NECK.

less perfect longitudinal venous trunks may be noticed on
the surface of the cord in connection with this plexus.
Two of these are mesial, and are placed respectively on
the anterior and posterior aspects of the cord. The
anterior trunk runs upwards under cover of the antero-
median spinal artery. The other two are lateral, and are
situated one on either side of the cord in relation to the
anterior nerve roots.

Upon either side, the veins of the spinal cord effect
communications with the veins in the spinal canal by means
of small twigs which run outwards on the nerve-roots.

How to distinguish the anterior from the posterior surface of
the spinal cord.

Anterior Surface.

1. Linea splendens.

2. Single anterior spinal artery in

mesial plane.

3. Anterior nerve roots smaller

than posterior, and springing
by fasciculi which emerge from
the cord, not in a continuous
straight line, but irregularly
over an area of some width.

Posterior Surface.

The postero-lateral arteries in
relation to the posterior nerve
roots.

Fasciculi of origin of posterior
nerve-roots entering the cord
along a straight and continu-
ous line, and at the bottom of
a distinct sulcus.

Posterior nerve roots larger
than the anterior, and pro-
vided with ganglia.

Preservation of the Spinal Cord. — If the spinal cord be in a fit state
for preservation, the dissector should immerse it for a few weeks in methy-
lated spirit, or in a large quantity of a saturated solution of bichromate
of potash. When sufficiently firm, the dissector should endeavour to
learn something of its internal structure by making transverse sections
through it at different levels, and inspecting the cut surface closely with
the naked eye, or with the aid of a magnifying glass.

Internal Structure of the Spinal Cord. — A good deal
can be learned by a naked eye inspection of cross sections
of the cord made in different regions and at different
levels.

The spinal cord is then seen to be a bilateral structure.
It is partially subdivided into a right and a left half by two

/>()A'.v.// ,isr/:cT or the t/wnk.

177

median clefts, — one upon the anterior, and the other ui)on
tlie posterior aspect. These clefts are called the anlcro-
mcdian and the postcro-mcdian fissures^ and they extend
along the entire length of the cord.

At the same time, it must be noted that these two
median fissures present many points of difference. The
antero-median fissure is, for the greater part of its length,
much shallower than the postero-median fissure ; further, it
is wider and much more apparent,
and the pia mater dips down into
it to form a fold or reduplication
within it. The postero-median
cleft, in addition to its being
deeper and narrower, contains
only a single septum of pia mater
prolonged into it from the deep
surface of the enclosing mem-
brane.

The two halves of the cord
thus marked off from each other
are to all intents and purposes
symmetrical, and they are joined
by a more or less broad band or
commissure which intervenes be-
tween the two median fissures.

An inspection of the surface
of each lateral half of the cord
brings into view a groove or
furrow at some little distance from
the postero-median furrow. Along
the bottom of this groove the
fasciculi of the posterior nerve -roots enter the cord in
accurate linear order. It is called the postero-lateral sulcus.
There is no corresponding furrow on the fore-part of each
lateral half of the cord in connection with the emergence
of the fasciculi of the anterior nerve roots. As we have
already observed, these fascicles emerge over a broad
area, which corresponds in its width to the thickness
VOL. II. — 12

Fig. 219. — Segment of
spinal cord ; lateral
aspect. (Schwalbe,

after Allen Thomson. )

1. Anterior median fissure.

2. Posterior median fissure.

5. Fasciculiofanteriornerve

root.

6. Posterior nerve root.

6. Spinal ganglion.

7. Anterior primarj-divisioii.

178 HEAD AND NECK.

of the subjacent extremity of the anterior horn of grey
matter.

By means of the postero- lateral sulcus and line of
entrance of the fascicles of the posterior nerve roots on the
one hand, and the emergence of the fascicles of the anterior
nerve roots on the other hand, the surface of each lateral
half of the cord is subdivided into three columns, which are
respectively termed posterior, lateral, and anterior. The
posterior colu??in (funiculus posterior) is placed between the
postero-median fissure and the postero-lateral furrow ; the
lateral column (funiculus lateralis) lies between the postero-
lateral furrow and the outermost of the fascicles of the
anterior nerve roots as they emerge from the cord; the
anterior column (funiculus anterior) includes that district
which extends from the antero-median fissure to the emerg-
ence of the outermost of the anterior nerve-root fascicles.

The spinal cord is composed of an inside core of grey
matter which is surrounded on all sides by an external
coating of white matter.

G-rey Matter of the Spinal Cord. — The grey matter in
the interior of the spinal cord has the form of a fluted
column. When seen in transverse section, it presents the
shape of the letter H. In each lateral half of the spinal
cord there is a crescentic mass shaped somewhat like a
comma (j), the concavity of which is directed outwards,
and the convexity inwards. The two crescents of opposite
sides are connected across the middle line by a transverse
band, which is called the grey commissure. The postero-
median fissure cuts through the cord until it reaches the
grey commissure. The bottom of the antero-median
fissure is separated from it by an intervening strip of white
matter which is termed the anterior white commissure (com-
missura anterior alba). In the grey commissure may be
seen the central canal of the cord (canalis centralis). It is
just visible to the naked eye as a minute speck. This
canal tunnels the entire length of the cord, and opens
above (after having traversed the lower half of the medulla
oblongata) into the fourth ventricle of the brain. The

DOKS.tf. ASPECT OF TIIF. TRUNK.

'79

portion of llic grey comniissurc which hcs hcliiiul the rcntral
canal is callcil the posterior i^rcy cominismrc (conimissura
posterior) ; the portion in front receives the name of
(Vtfcrior grey commissure (conimissura grisca anterior).

In each crescentic mass of grey matter certain well-
defined parts may be recognised. The projecting portions
which extend behind and in front of the connecting trans-
\crse grey commissure are termed respectively \\\c posterior

postcro-median fissure,
posterior coriiu.

processus reticularis,
posterior s^ey commissure.

central can.il.
anterior grey commissure.

anterior white commissure.

lateral horn.

antero-meclian fissure.

Fig. 220. — Cross section of the dorsal p.nrt of the
spinal cord. (From Gegenbaur. )

h.s. Posterior column.
s.s. Lateral column.
r<.s. Anterior column.

H.W. Posterior nerve root.
V.W. Anterior nerve root.

and the anterior cornua of grey matter (columns grisca;).
These can be distinguished from each other at a glance.

The anterior cornu is short, thick, and very blunt at its
extremity. Further, its extremity falls short of the surf;ice
of the cord, and is separated from it by a tolerably thick

i8o HEAD AND NECK.

coating of white matter. Through this the fascicles of the
anterior nerve roots pass on their way to the surface. The
thickened end of the anterior cornu is termed the caput
cormi, whilst the slightly constricted part close to the grey
commissure is called the cervix cornu. The posterior cornu
is in most localities in the cord elongated and narrow.
Further, it is drawn out to a fine point which almost
reaches the bottom of the postero-lateral sulcus. This
pointed extremity receives the name of the apex cornu;
the slightly swollen part which succeeds it is the caput
cormi; whilst the slightly constricted part adjoining the
grey commissure goes under the name of the cervix cornu.

Covering the tip of the posterior cornu there is a
substance which differs in its composition from the
general mass of grey matter, and presents a semi-trans-
parent appearance. It is termed the substa7itia gelatinosa
of Rolando.

When we apply the terms cervical, dorsal, lumbar, sacral, etc., to
different portions of the cord, we refer to those parts of the cord to
which the different groups of nerves are attached.

The grey matter is not present in equal quantity through-
out the entire length of the cord. It may be regarded as a
general law that wherever there is an increase in the bulk
of the nerves attached to a particular part of the cord,
that there a corresponding increase of the grey matter may
be noticed. It follows from this that the districts in which
the grey matter bulks most largely are the lumbar and
cervical swellings. The great nerves which go to form the
limb plexuses enter and pass out from those portions of
the cord. In the intermediate dorsal region there is a
reduction in the quantity of grey matter in correspondence
with the smaller size of the dorsal nerves.

But the shape of the crescentic masses is not the same
in all regions. In the dorsal region both horns are
narrow, although the distinction between the anterior horn
and the still more attenuated posterior horn is still suffici-
ently manifest. In the cervical region the contrast between

DORSAL ASPECT OF THE TRUNK'. i8i

the cornua is most marked ; the anterior horn is very thick
in comparison with the much narrower posterior horn.
In tlie lumbar region, on the other hand, the difference in

Fig. 221. — Sections through different parts of the cord.
(From Schwalbe.)

A. B. C. Enlarged twice the size of nature.

D. E. F. Enlarged three times the size of nature.

a. Anterior nerve roots.
/. Posterior nerve roots.
.'\. Section through the middle of

the cervical enlargement.
B. Section through the middle of

the dorsal region.

Section through the middle of the
lumbar enlargement.

Section through the upper part of
the conus medullaris.

Section at the level uf the fifth
sacral nerve.

Section at the level of the coccy-
geal nerve.

i82 HEAD AND NECK.

the thickness of the two horns is not nearly so apparent
owing to a broadening out of the posterior horn. A
section taken from the centre of each of these regions can
very readily be recognised by these features.

In the dorsal region of the cord, more especially in the
upper part, there is another character which is very
distinctive. A pointed and prominent triangular projec-
tion juts out from the external aspect of the crescentic
mass of grey matter nearly opposite the grey commissure.
This is called the lateral kor?i (Figs. 220 and 221). Traced
upwards into the cervical region of the cord and down-
wards into the lumbar region, it is seen to blend with the
anterior horn, and it contributes in these districts to the
thickening of that cornu. Curiously enough it again
becomes evident in the sacral region of the cord.

The White Matter of the Spinal Cord. — The white
matter forms a thick coating on the outside of the fluted
column of grey matter. It is marked off into three
columns (funiculi medullas spinalis). The posterior column
is wedge-shaped in transverse section, and lies between the
postero-median fissure and the posterior cornu of grey
matter. The lateral column occupies the concavity of the
grey crescent. Behind, it is bounded by the posterior
grey cornu and the postero-lateral sulcus, whilst in front
it extends as far as the outermost fasciculi of the anterior
nerve roots as they pass out from the anterior grey horn.
The atiterior column includes the white matter between the
antero-median fissure and the anterior horn of grey matter,
and also the white matter which separates the thick
extremity of the anterior grey cornu from the surface of
the cord. This latter portion of the anterior column is
traversed by the emerging fascicles of the anterior nerve
roots.

In the cervical region a faint longitudinal groove runs
downwards on the surface of the posterior column of the
cord. This indicates the position of a septum which passes
into the column from the deep surface of the pia mater and
divides it incompletely into two unequal strands. The

DOA'S.I/. AsriiCT or THE TRUXK.

«S3

groove is termed the paramedian furro7v ; the smaller and
more internal of the two strands is called \\\c posfero-median
column or t/ie trad of Go//, whilst the outer and larger
strand receives the name of the postcro-externa/ co/iimn or
f/w tract of Burdac/i.

The white matter of the spinal cord increases steadily in
quantity from below upwards.

The tracts of Goll and Burdach, which form the posterior column of
the cord, are composed of fibres which enter the cord through the
fascicles of the posterior nerve roots. In the lower portion of the cord

poslero-median fissure
postero-lateral groove

crossed pyramidal,
tract.

I

direct pyramidal tract

tract of Goll.
tract of Burdach.

substantia gelatinosa
Rolanui.

direct cerebellar
tract.

fascicle of origin of
the spinal acces-
sory nerve.

antero-median furrow.

Fig. 222. — Transverse section through the upper cervical part of the
cord of a full-time foetus treated by the Pal-Weigert process.

the septum of pia mater which intervenes between these two strands
fails, so that it is only in the upper part of the cord that they are marked
off from each other.

In the lateral and anterior columns of the adult cord it is not possible
to distinguish the different strands of fibres ; and yet we know that such
exist, jxissessing both different functions and presenting different con-
nections. In the fcKtal cord, however, the medullary sheath is developed
at a later period around the fibres of certain tracts than in the case of
others, and if thin .sections of developing cords be subjected to the Pal-
Weigert staining process the tracts in which the medullary sheaths have
appeared are dyeil black and stand out in marked contrast to the non-
meduUated tracts which remain pale (I'ig. 222). In the present instance
it is only necessary to indicate the three best defined tracts in the antero-
lateral part of the cord. These are ( i ) the ascending direct cerebellar

1 84 HEAD AND NECK.

tract ; (2) the descending crossed pyramidal tract ; (3) the descending
direct pyramidal tract.

The direct cei-ebellar tract meduUates comparatively early. Con-
sequently in Fig. 222 it stands out conspicuously as a narrow area
placed close to the surface of the cord, in the posterior part of the
lateral column, immediately in front of the postero-lateral groove. It
ascends to the cerebellum, but, traced in the opposite direction, it is
found to disappear in the lower dorsal area of the cord. The crossed
pyramidal tract, when seen in transverse section, occupies a larger
district of the cord. Further, it medullates late, and the area which it
occupies appears pale in Fig. 222. It is placed in the lateral column
behind the posterior horn of grey matter and immediately internal to
the direct cerebellar tract. As the direct cerebellar tract fails in the
lower reaches of the cord the crossed pyramidal tract comes to the
surface and it can be traced as low as the fourth sacral nerve. The
direct pyramidal tract forms the narrow strip of the anterior column
which lies immediately adjacent to the antero-median furrow. Like
the crossed pyramidal tract it medullates late and therefore in Fig. 222
it appears pale. It only reaches down to about the middle of the dorsal
region of the cord and then disappears.

SIDE OF THE NECK.

Four days having now been devoted to the dissection of
the posterior aspect of the body, the subject is turned on its
back, and blocks being placed under the thorax and pelvis,
the dissection of the side of the neck is commenced. This
region may be said to present a somewhat quadrilateral
figure. In front, it is bounded by the middle line of the
neck ; behind, it is limited by a line corresponding to the
anterior margin of the trapezius muscle ; below, are the upper
margin of the manubrium sterni and the prominent clavicle ;
above, the base of the lower jaw, the mastoid process and
the occiput.

Surface Anatomy. — Certain important landmarks must
be recognised before the skin is reflected from the side of
the neck. The sterno-mastoid muscle, pursuing a diagonal
course through the space from its antero-inferior to its
postero-superior angle, is, perhaps, the most essential of
these. By drawing the head well over to the opposite side.

SIDE OF THE NECK. 185

it will be rendered evident. The region in front of the
sterno-niastoid corresponds to the anterior triangle of the
neck ; that behind it constitutes the posterior triangle.
Above the notch of the manubrium sterni, and between
the sternal tendons of the two sterno-mastoid muscles,
the deep supra-sternal fossa will be noted. Subjacent to
this fossa lies the trachea, but it is only in emaciated
individuals that the rings of this tube can be felt from the
surface. In its upper part the trachea is always obscured
by the isthmus of the thyroid body which crosses it.

The dissector should now run his finger upwards in the
middle line of the neck. Beyond the trachea the ring-like
cricoid cartilage will be felt. This is a highly important
landmark. \\'ith it as his guide the surgeon is able to mark
out the points at which the trachea or larynx may be opened,
and also the level at which the common carotid artery is
most favourably placed for the application of a ligature.
Above the cricoid cartilage the finger enters the narrow
interval between the cricoid and thyroid cartilages — a gap
which is occupied by the tense crico-thyroid membrane. In
this interval the operation of laryngotomy may be performed.
Ne.xt comes the thyroid cartilage with its prominent /f/;///;//
Adatni. Beyond the thyroid cartilage is an interval occu-
pied by the thyro-hyoid membrane, and bounded above by
the hyoid bone. The body and cornua of the hyoid can
be plainly felt from the surface. In the usual attitude of
the head the hyoid bone will be observed to be placed on
a level with the lower margin of the mandible. Above the
hyoid bone, between it and the symphysis of the lower jaw,
is the anterior part of the floor of the mouth.

Dissection. — In the first instance merely the structures superficial to
the deep cervical fascia should be dissected. A good-sized block being
pl.iced under the shoulders of the subject, the head is pulled backwards
and the chin dragged over to the opposite side. The jwrts will be put
still further on the stretch if the shoulder be depressed by drawing the
arm downwards and then fixing it in this position.

For the reflection of the skin three incisions are required, viz. —
(I) a vertical incision along the middle line of the neck, from the
chin above to the sternum below ; (2) a transverse cut from the lower

1 86 HEAD AND NECK.

end of the mesial incision outwards along the line of the clavicle to
the acromion process of the scapula ; (3) an oblique incision, beginning
above at the mastoid process behind the ear, and carried downwards and
forwards along the anterior border of the sterno-mastoid muscle, until
it meets the middle line of the neck at the top of the sternum.

Two triangular flaps of skin, corresponding in a measure to the two
triangular areas of the neck, are thus mapped out, and must now be
carefully raised. Throw the anterior flap upwards towards the lower
jaw, and turn the posterior flap backwards towards the trapezius muscle.

Superficial Fascia. — The superficial fascia in this region
contains in its midst the platysma myoides muscle — the
representative in the human subject of the panniculus

Fig. 223.

carnosus in the lower animals. In the male, the adipose
tissue which distinguishes the superficial fascia is generally
very sparse in this locality, so that the fleshy fibres of the
muscle are observed shining through it. In females and
children the fat is more abundant, giving a fuller and more
rounded appearance to^ the neck. In all cases the fatty
tissue is most plentiful between the chin and the hyoid bone,
forming in stout individuals the so-called " double-chin."

Dissection. — The fibres of the platysma myoides muscle, which run
upwards and forwards, must now be cleaned and its borders defined.
In clearing the fatty tissue from its surface, minute nervous filaments
will be observed piercing it to reach the skin. These are chiefly branches
of the superficial cervical nerve. As the muscle extends downwards on

SIDE OF THE NECK. 187

lu ihc front of the chest and upper part of the shoulder, it cannot lic
fully studied until the dissector of the arm hiis reflected the skin from
these rei^ions.

The Platysma Myoides is an exceedingly thin quadri-
lateral sheet of muscular fibres, which clothes the side and
front of the neck, and lies superficial to the deep fascia.
Below, it takes origin by scattered and sparse fibres from the
skin and subcutaneous fascia covering the upper portions of
the pectoralis major and deltoid muscles. From this it pro-
ceeds upwards and forwards over the clavicle and acromion,
but obtains little or no attachment to these bones. On
the side of the neck it decreases somewhat in width, and
its fibres being thus more closely aggregated, it becomes
thicker and more distinct. Finally, it reaches the lower
jaw into the outer surface of which the majority of the
fibres are inserted. The anterior fibres decussate below
the chin with the corresponding fibres of the opposite
muscle, whilst the posterior fibres proceed upwards into
the face, and curve forwards towards the angle of the mouth
where they blend with the facial muscles in this locality.

Reflection of the Platysma. — This must be done very carefully, so
as not to injure the structures which lie between it and the deep fascia.
These are ( i ) the external and anterior jugular veins ; (2) the descending
superficial branches of the cervical plexus, which are especially liable
to injury as they cross the clavicle and acromion process ; (3) the
superficial cervical nerve and cervical division of the facial nerve ; and
(4) the superficial lymphatic glands. The muscle should be raised from
below upwards, and left attached by its facial connections.

The External Jugular Vein (vena jugularis externa) —
Fig. 224 (10) — is usually a vein of some size. It will be
seen emerging from the substance of the parotid gland
immediately behind the angle of the lower jaw, where it is
formed by the junction of the i)u>Lciior auricular vein, and
posterior division of the lciii[ini(i luuxillary vein. From this
it descends in a nearly vertical direction upon the deci)
cervical fascia, taking a course which may be mapped out
on the surface with tolerable accuracy, by drawing a line
from a point behind the angle of the jaw to the middle of

1 88 HEAD AND NECK.

the clavicle. It crosses the sterno-mastoid obliquely, and,
reaching the posterior margin of this muscle, disappears
from view by dipping through the deep cervical fascia
immediately above the clavicle. It will subsequently be
traced to its termination in the subclavian vein.

Shortly after "its origin, it effects, as a general rule, a
communication with the internal jugular vein, and lower
down one or more superficial^ twigs may connect it with
the anterior jugular. Half-way down the neck it is joined
by a tributary of some size, which comes from the occipital
region and the back of the upper part of the neck ; this
vein is termed the posterior external jugular.

Superficial Cervical Glands.— These form a group of
small lymphatic glands which lie along the course of the ex-
ternal jugular vein. They vary from four to six in number.

The Anterior Jugular Vein (vena jugularis anterior) —
Fig. 224 (23)— is small in comparison with the preceding.
Sometimes, however, it exceeds it in calibre— the size of
the one very much depending upon that of the other. It
begins by the confluence of some small veins in the sub;_
maxillary region, and descends vertically at a short distance
from the mesial plane. Immediately above the inner end
of the clavicle it will be observed to dip through the deep
cervical fascia. It terminates by turning abruptly outwards
under cover of both heads of the sterno-mastoid muscle,
and opening into the external jugular or into the subclavian
vein. After it has pierced the fascia, a shart transverse
branch wKich crosses the mesial plane connects it with its
fellow of the opposite side.

Superficial Branches of the Cervical Plexus.— These all
take origin from the second, third, and fourth cervical nerves,
and emerging from under cover of the posterior margin of
the sterno-mastoid about its middle, pierce the deep fascia,
and arrange themselves into ascending, transverse, and
descending branches.

The ascending branches zxe two in number, and both have
already been examined in the superficial dissection of the
back of the neck (p. 136). They are {a) the small occipital

I'lG. 224.— Superficial nerves on the side of the neck and back of the scalp.
(Hirschfeld and Levoill<i.)

^ttoUcns

aiiriculam

li'lly of occipito-fron-
' nl.im lialis

nerve
I ucr\-o

' t' li muscle

i-i|il.il nerve (present

1 bnuichcs)

9. Great auricular ner

10. hxtcrnal jugular vein

11. Superlicial cervical nerve

12. Spinal accessory nerve

13. ncscentlinn brandies of cer-

vical plexus

14. Cervical branches to trapezius

15. Trapezius muscle

16. Supra-clavicular branches

17. Supra-acroniial branches

18. Auricular twi^s of trrcal auri-

19. Parutiil Kland [cular nervo
-'o. l''aci.il nerve

21. Mabseter nuiscle

33. Infra-niandibular nervo c
23. Anterior jujjnlar vein

34. Supra-sternal br.inclies

35. riatyswa myoiilcs

190 HEAD AND NECK.

— Fig. 224 (8), — springing from_the second cervical nerve,
and (l>) the great auricular — Fig. 224 (9), — which takes
origin from the second and third cervical nerves.

The transverse branches proceed from a single nerve called
the superficial cervical nerve (nervus cutaneus colli) — Fig.
224 (11). This arises from the second and third cervical
nerves, and winding round the posterior border of the
sterno-mastoid about its middle, proceeds transversely, for-
wards upon the deep fascia to reach the area over the
anterior triangle of the neck. Here it divides into two
branches, of which one inclines upwards and the other
downwards. The upper branch communicates freely with
the cervical division of the facial nerve and forms one or
more wide loops with it in the region between the hyoid
bone and the mandible (Fig. 224). Its branches pierce
the platysma and supply the skin as high as the base of the
lower jaw. The lower branch can be traced as low as the
sternum. Its branches also reach the skin by piercing the
platysma.

The descending branches take origin by a single large
trunk from the third and fourth cervical nerves. This
emerges from under the posterior border of the sterno-
mastoid, and soon breaks up into several twigs, which pierce
the deep fascia and spread out widely from each other as
they descend over the lower part of the posterior triangle,
•founder cover of the platysma. The ultimate distribution of
these twigs is to the integument over the upper part of the
front of the chest and over the shoulder. To gain this
destination they are carried downwards over the clavicle
and acromion process, and are classified into three groups
according to their position — viz. (i) supra-acromial ; (2)
supra-clavicular; {^supra-sternal — Fig. 224(17, 16, 24).

Cervical Division of Facial Nerve. — After emerging
from the parotid gland this nerve pierces the deep fascia. _
It will be found immediately below the angle of the lower
jaw. Its branches spread forwards and form a series of
loops which extend as low down as the hyoid bone. It is
the nerve of supply to the platysma muscle, and effects a

S/D^ OF THE XECK. 191

free communication with the upper branch of the superficial
cervical nerve — l''ig. 224 (22).

Deep Cervical Fascia (fascia colli) (Fig. 225). — The
cervical fascia should now be cleaned, and its connections
studied. It constitutes a continuous and strong aponeu-
rotic envelope for the neck, very much in the same manner
that the brachial aponeurosis invests the upper arm or the
fascia lata the thigh. As in the case of these fasciae also,
processes are given off from its deep surface which pene-
trate into the neck to form sheaths for the various structures
enclosed within the general investment. Certain of these
processes stretch across the mesial plane in the form of
partitions or septa, which subdivide the neck into fascial
compartments. Let us first examine the general envelope
as it is at present displayed, and then we shall be in a
position to study the more important septa and processes.

The envelope formed by the deep cervical fascia is not
equally developed in all subjects. In many cases, and
more especially in females, it is thin and inconspicuous.
Neither is it of equal strength at all points. As it stretches
over the triangles of the neck, it is distinctly stronger than
where it covers either the trapezius or sterno-mastoid.
Traced backwards, it splits at the anterior border of the
trapezius into two lamellK to enclose this muscle. The
superficial layer is very thin, and both blend posteriorly
with the ligamentum nuchse. When the investing apo-
neurosis is followed forwards it is found to split again at the
posterior border of the sterno-mastoid into the two lamella;,
which encase that muscle and reunite at its anterior
margin. Of these layers the superficial is so delicate that
the fleshy fasciculi of the muscle are distinctly seen
through it. From the sterno-mastoid the aponeurosis is
prolonged over the anterior triangle to the middle line,
and passes continuously over to the opposite side of the
neck. In its passage, however, from one side to the other,
it obtains a firm attachment to the hyoid bone.

Its connections at the upper and lower limits of the
neck may now be examined. Above^ it is attached along

192

HEAD AND NECK.

the whole length of the base of the lower jaw. Behind the
angle of the jaw it is carried upwards upon the surface of
the parotid gland, as the parotid fascia, to gain attachment
to the lower margin of the zygoma — a connection which
will be afterwards seen in the dissection of the face. Still
farther backwards, it is fixed to the mastoid process, and
to the superior curved line of the occipital bone.

Fig. 225. — Diagrammatic representation of a transverse
section through the neck at the level of the isthmus of the
thyroid body to show the arrangement of the cervical
fascia. (Treves. )

T. Trachea.

c. Depressor muscles of the larynx

and hyoid bone.
e. Prevertebral muscles.
g. Carotid artery and its sheath.
b. Sterno-mastoid.

f. Scalenus anticus.
d. Platysma.
h. External jugular vein.
a. Trapezius.
i. Deep muscles on back of neck.

Its connections below are no less definite. It is attached
to the anterior border of the clavicle, and to the top of the
sternum. The latter attachment, however, is of a some-
what intricate character. As the fascia is traced downwards
between the two sterno-mastoid muscles, it will be found

SIDE OF THE NECK. 193

to split a short distance above tlie stcrnuni into two layers.
Of lliese, the superficial layer is very weak., and is attached
to the anterior border of the nianubriuni sterni. 'I'lic deeper
layer lies innnediately in front of the sterno-hyoid and sterno-
thyroid muscles, and is fixed below to the posterior border
of the manubrium sterni and to the inter-clavicular ligament.
Upon either side the two layers unite beyond the sternal
Iiead of origin of the sterno-mastoid ; and the space between
ihem contains — (i) a little fiitty areolar tissue ; (2) the two
anterior jugular veins for a very short part of their course ;
(3) the cross branch of communication between the anterior
jugular veins of opposite sides when this exists; (4) some-
times a lymphatic gland ; and (5) the sternal heads of the
sterno-mastoid muscles. Open into the space by dividing
the anterior layer close to the sternum, and gauge its extent
by means of the handle of the knife.

The processes and partitio7is which proceed from the deep
surface of the cervical fascia cannot in every case be dis-
played at the present stage of the dissection, but it is
necessary that they should be described, in order that the
student may be able to recognise them and a[)preciate their
bearings as they are unfolded in the subsetjuent dissection
of the neck. Those requiring special notice are : —

1. The prevertebral fascia.

2. The pretracheal fascia.

3. The carotid shealh.

4. The slylo-maxillary ligament.

The prevertebral fascia is a strong partition which
stretches across the neck immediately in front of the
vertebral column and the prevertebral muscles. On either
side it extends outwards behind the carotid vessels and the
internal jugular vein, to obtain attachment to the layer of
the investing aponeurosis which lies on the deep surface of
the sterno-mastoid muscle. In an ui)ward direction it can
be traced to the base of the skull to which it is fixed,
whilst below it passes continuously downwards into the
thorax upon the longus colli muscles. The prevertebral
fascial sei)tum thus subdivides the investing tube of cervical

VOL. II.— 13

194 HEAD AND NECK.

fascia into — {a) a posterior compartment which contains the
vertebral column and the muscles which surround it ; and
ip) an anterior or visceral compariment, which contains the
pharynx, the larynx, the trachea, the gullet, the thyroid
body, and the depressor muscles of the larynx and hyoid
bone. It is important to note that there is no barrier
interposed between this visceral compartment and the
superior mediastinal space of the thoracic cavity.

The pretracheal fascia is a partition of no great strength,
which springs from the deep aspect of the lamella clothing
the deep surface of the sterno-mastoid. It passes right
across the visceral compartment of the neck in front of the
thyroid body and trachea, and behind the anterior belly of
the omo-hyoid, the sterno-thyroid, and sterno-hyoid muscles.
It gives off" processes which ensheathe the thyroid body and
the trachea, and is prolonged downwards into the thorax in
front of the great vessels at the root of the neck, to gain an
attachment to the fibrous layer of the pericardium.

The great vessels of the neck lie under cover of the
sterno-mastoid muscle, and are contained within the outer-
most part of the visceral compartment on either side of the
neck. They are enclosed within a special investment of
fascia which receives the name of the carotid sheath. Both
the prevertebral and the pretracheal septa take part in the
formation of this sheath, and in addition to the carotid
artery and the internal jugular vein there are included
within it the vagus and the descendens hypoglossi nerves.
Further, the gangliated cord of the sympathetic may be
considered to be embedded in its posterior wall.

The stylo-maxillary ligament is a strong process of the
cervical fascia in the upper part of the neck, which passes
from the angle and posterior margin of the lower jaw to
the styloid process. It is firmly attached to these bones,
and is so placed that it constitutes a firm fibrous partition
between the submaxillary and parotid glands. It can
readily be exposed at the present stage.

Dissection. — The sterno-mastoid muscle, as we have observed,
divides the side of the neck into two triangular spaces — an anterior

'l^N'/i

SIDE OF rfrC\NECR'. 195

triangle placed in front of it, and a ]X),stcrior triangle behind it. This
muscle, therefore, should he studied before proceeding further.
Carefully clean its superficial surface, and define its attachments. It
may also be raised in its lower two-thirds from the subjacent layer of
deep cervical fascia. In doing this, care must be taken not to injure
the sterno-mastoid branch of the superior thyroid artery which will be
seen entering its deep surface. In its upper third it should be left
undisturbed in the meantime.

Stemo-Mastoid (sternocleidomastoideus). — The sterno-
mastoid muscle takes its origin below by two heads — a
sternal and a clavicular. The sternal head is rounded, and
chiefly tendinous, and springs from the upper part of the
anterior face of the manubrium sterni. The clavicular head \'~,
broad and fleshy, with only a few tendinous fibres intermixed,
and it arises from the inner third of the upper surface of the
shaft of the clavicle. A narrow interval separates these
heads below, but at a higher level the sternal portion
overlaps the clavicular, whilst half-way up the neck they
both unite into a fleshy mass which ascends to the mastoid
process and occiput. Here the muscle expands somewhat.
In front, it is thick and tendinous, and is inserted into the
fore-part and outer surface of the mastoid process ; behind,
it is thin and aponeurotic, and is inserted into rather more
than the outer half of the superior curved Hne of the
occipital bone. In the dissection of the back, this latter
part of the muscle has been detached from the occiput.

Dissection. — The posterior triangle of the neck should be dissected
first. For this purpose the shoulder must be depressed and the head
pulled well over to the opposite side and supported upon a block. This
interferes, of course, with the dissection of the axilla. It is necessary,
therefore, that the dissectors of the head and neck, and of the upjier
limb, should arrange to work at different hours. Again, the lower part
of the posterior triangle, and the upper part of the axilla, constitute a
region of the highest importance to both dissectors, seeing that it is
here the great blood-vessels and nerves leave the root of the neck and
enter the arm. Arrangements, therefore, must be made for each to have
an opportunity of studying these structures. But in this a difficulty
arises. Four days are required to complete the dissection of the axilla,
whilst two days are amply sufficient for the dissection of the superficial
parts of the neck and the posterior triangle. It is not necessarj', how-
ever, that the dissector of the head and neck should stop work. After

196

HEAD AND NECK.

Fig. 226. — Triangles of the neck.

A. Occipital triangle.

B. Subclavian triangle.

C. Digastric triangle.

D. Carotid triangle.

E. Muscular triangle.

1. Superior constrictor.

2. Anterior belly of digastric.

3. Mylo-hyoid.

4. Stylo-glossus.

5. Hyo-glossus.

6. Stylo-hyoid.

7. Posterior belly of digastric.

8. Middle constrictor.

9. Hyoid-bone.

10. Thyro-hyoid.

11. Inferior constrictor.

12. Omo-hyoid.

13. Sterno-mastoid.

14. Sterno-hyoid.

15. Levator anguli scapulae.

16. Sterno-thyroid.

17. Trapezius.

18. Scalene muscles.

19. Omo-hyoid.

SIDE OF J HI: NECK. 197

he has liisplaycil iho [Kirls in the sikicc ;us far as he can without tlividing
the clavicle, he may proceed \s itli the dissection of the anterior triangle,
and on tlie fourtli day return to the posterior triangle and complete the
work with the co-operation of the dissector of the arm.

The upper part of the jxjsterior triangle has already been displayed
in the dissection of the ix)sterior aspect of the neck (p. 138), but the
space can only be studied in its entirety when the subject is placed
ujxjn its back. The trapezius which has been reflected should be
restored as far as possible to its natural iwsilion and retained by means
of a stitch.

When the investing cervical fascia which bridges over the lower pari
of the posterior triangle between the trapezius and the slerno-m;vstoid
muscles is removed, a variable amount of fatty areolar tissue is cx|X)sed
in the supraclavicular region. Embedded within this will be found the
Iransversalis colli and the suprascapular %'essels, with the posterior belly
of the omo-hyoid muscle and some lymphatic glands. The supra-
scapular artery emerges from under cover of the sterno-mastoid, and
losses outwards immediately subjacent to the clavicle ; the transversalis
colli artery also comes out from under cover of the sterno-mastoid, but
it lies at a higher level. The posterior belly of the omo-hyoid muscle
is a narrow muscular band which appears at the angle which is formed
by the anterior border of the trapezius muscle and the clavicle, and
proceeds forwards and upwards on the side of the neck to disappear
under cover of the sterno-mastoid. It should be noted that the posterior
belly of the omo-hyoid muscle is enveloped in a sheath of fascia which
is loosely disjxjsed around it, and is then prolonged downwards to obtain
an attachment to the clavicle. As the muscle disappears under cover of
the sterno-niasloid it gives place to a rounded tendon. Upon the under
surface of this, closely applied to it, and between the two layers of
fascia which invest it, will be found a minute nervous twig which
comes from the ansa hypoglossi, and ends in this portion of the omo-
hyoid. The lymphatic glands in this region belong to the group which
receive the name of inferior deep cei'vical glands. When the fatty
areolar tissue is removed from these structures, a strong layer of fascia
spread over the subclavian vessels and the brachial nerves will be
brought into view.

Deep Layer of Fascia in the Supraclavicular Region. —
This Is a strong sheet of fascia which is spread over the
brachial nerves and the subclavian vessels. When traced
inwards under cover of the sterno-mastoid it will be observed
to cover the scalenus anticus muscle and to become con-
tinuous with the prevertebral fiiscia and the posterior part
of the carotid sheath. In a downward direction it may be
followed into the a.xilla as the sheath of the axillary vessels

igS HEAD AND NECK.

and nerves, and here it establishes a connection with the
costo-coracoid membrane. A distinct space or interval
exists between this deep layer of fascia and the investing
fascia of the neck. This interval is filled with fatty areolar
tissue, and also contains the transversalis colli and supra-_
scapular vessels, the posterior belly of the omo-hyoid muscle,^
and some of the inferior deep cervical glands. Seeing that
the investing cervical fascia is attached to the clavicle, and
the deep layer of fascia is more or less intimately connected
with the costo-coracoid membrane, the intra -aponeurotic
space between them extends downwards for a short distance
behind the clavicle. An incision should now be made
through the deep layer of fascia as it lies over the great
brachial nerves. If the handle of the knife be introduced
into this and passed downwards along the course of the
nerves behind the fascia, it will be found to proceed with
the greatest freedom into the axilla.

Dissection. — The dissector should now proceed with the dissection of
the posterior triangle. The deep layer of fascia which is spread over the
great vessels and nerves must be removed. The brachial nerves will
then be seen emerging from between the scalenus anticus and the
scalenus medius muscles. At this stage in the dissection the minute
nerve of supply to the subclavius is apt to be injured. It passes verti-
cally downwards upon the superficial aspect of the brachial nerves, and
must be secured before they are touched. The brachial nerves are closely
matted together by dense connective tissue, which must be removed,
but care must be taken at the same time not to injure the branches
which spring from them. When the lowest trunk of the brachial plexus
is reached the subclavian artery will come into view. This vessel must
be thoroughly displayed, and the groove on the first rib on which it lies
may be rendered evident by scraping the bone with the handle of the
knife. By tracing the external jugular vein downwards, the subclavian
vein will be found lying very deeply behind the clavicle. The scalenus
anticus muscle, with the phrenic nerve passing downwards upon its
anterior surface, will also be observed. Both lie under cover of the
sterno-mastoid muscle.

Posterior Triangle. — This is a long, narrow, triangular
space placed between the posterior border of the sterno-
mastoid and the anterior border of the trapezius. It is
covered by the superficial and deep fasciae of the neck, and

SIDE OF THI: XECK. 199

also in its lower part by the platysma niyoidcs nnisclc.
Certain cutaneous nerves and the external jugular vein have
also been noticed in the superficial fascia which is spread
over this area. Near the occiput is the small occipital
nerve ; near the clavicle are the supraclavicular descending
branches of the cervical plexus, and a very short portion of
the external jugular vein.

Inf/v/if, the posterior triangle is bounded by the posterior
margin of the sterno-mastoid, and behind, by the anterior
margin of the trapezius. The base which is below is
formed by the middle third of the clavicle, whilst the apex
which is above is formed by the meeting of the sterno-
mastoid and trapezius on the superior curved line of the
occipital bone.

The posterior belly of the omo-hyoid, which crosses the
lower part of the posterior triangular space, subdivides it
into an upper portion called the occipital triangle, and a
lower part termed the supraclavicular or subclavian triangle.

The Occipital Triangle is much the larger subdivision.
lit is bounded in front by the sterno-mastoid ; behind by
pe trapezius ; whilst its base is formed by the omo-hyoid.

Within the limits of the occipital triangle we find the
following structures : —

1 . The occipital artery in a very small part of its course, and only

when the sterno-mastoid fails to meet the trapezius at the apex
of the triangle.

2. The spinal accessory nerve.

3. The branches from the third and fuurtli cervical nerves which

cross the space to supjily the trapezius muscle.

4. The superficial branches of the cervical plexus as they appear at

the posterior border of tlie sterno-mastoid previous to piercing
the deep fascia.

5. Branches of supply to the levator anguli scapui.e from the tiiird

and fourth cervical nerves.

6. The transversalis colli artery and vein, which cross the lower part

of the space.

7. The upper part of the bracliial plexus of nerves.

The contents of the occipital triangle have already in a
great measure been studied (p. 138).

HEAD AND NECK.

The Supraclavicular Triangle is a very small space.
It is bounded above by the omo-hyoid; below by the
clavicle ; and in front by the sterno-mastoid. The area
thus circumscribed is very variable in its extent in different
subjects. Indeed, in the natural position of parts, the
posterior belly of the omo-hyoid passes forwards so close
to the clavicle that a very small interval is left between
them, and it is only after the fascial connections of the

trapezius.

spinal accessor^'
nerve

levator anguli
scapulae.

branch from cer-
vical plexus to
trapezius.

transversalis colli
artery and vein.

suprascapular
nerve.

omo-hyoid.

descending cervi
cal nerves.

calenus medius.
brachial nerves.

ext. jugular
vein.

scalenus anticus.

sterno-mastoid.

subclavian
artery.

suprascapular
artery and /
vein. / ).

clavicle, y

Fig. 227.

-Dissection of the lower part of the posterior triangle
of the neck.

muscle have been divided that the triangle becomes well

marked.

Cases also occur in which the omo-hyoid takes partial or complete
origin from the clavicle, and thus the supraclavicular^ space is still
further reduced in size. Another condition which materially affects the
dimensions of the supraclavicular triangle is the muscular development
of the subject. The more powerful the neck, the more extensive are
the attachments of the trapezius and sterno-mastoid to the clavicle, and
the narrower in consequence is the triangle. In a few instances these
muscles will be observed to meet on the clavicle, and thus obliterate

SIDE OF THE NECK. 201

the s|iacc allugcthcr. This lallcr condiliun, however, is nol necessarily
associated with a specially hiyh development of ihe muscles.

In the supraclavicular space a great number of highly
important structures are collected together within a very
limited area. The great blood-vessels and nerves which
pass from the neck to the upper limb traverse this space.
Its contents are the following : —

{Subclavian.
Transversalis colli.
Suprascapular.
(External jugular.
Suprascapular.
Transversalis colli.
Subclavian.
Nerves — The trunks of the brachial ple.xus and their branches.
Lymphatic glands.

Subclavian Artery (arteria subclavia). — It is only the
thwJLparJ.o'i the subclavian artery which is included in the
supraclavicular triangle. This portion of the vessel extends
from the _outer margin of the scalenus anticus to the outer
border of the first rib. Here it enters the axilla and
becomes the_axillary artery. It takes a very oblique
course ; at first it lies at a variable distance above the
level of the clavicle, but as it runs from above downwards
and outwards, it finally comes to lie behind the clavicle
and the subclavius muscle.

It is this portion of the artery that the surgeon selects,
when the choice lies in his own hands, as the seat for
applying a ligature. Its relations, therefore, must be
studied with especial care.

In front of the \essel are the coverings of the space in
which it lies — viz. superficial fascia, platysma, superficial
descending supraclavicular branches of the cervical plexus^
and the deep cervical fascia. Towards its termination,
however, as we have seen, it passes behind the clavicle and
subclavius muscle, and here also it is crossed by the supra-
scapular artery. But perhaps the most important anterior
relation, and one which, in tying the vessel, may somewhat

202 A^^yJZ) AND NECK. B^;, ';> -^

embarrass the surgeon, is that estabHshed by the external
jugular vein and certain of its tributaries. This vein crosses
in front ofThe artery close to the scalenus anticus, and
whilst occupying this position^, two, or it may be three,
tributaries join it — viz. the transversalis colli, the supra-
scapular, and the anterior jugular veins. . Observe further
that the^ small nerve to the subclavius is carried vertically
downwards in front of the artery.

Below., the thi^d part of the subclavian artery rests upon
the first rib ; at a higher level, and also emerging from
under cover of the scalenus anticus, are the brachial nerves.
Behind., the vessel is in contact with the scalenus medius,
although the lowest brachial nerve -trunk may intervene
between the muscle and the artery. TJie subclavian vein
is placed at a lower level than the artery, and on a plane
slightly anterior to it.

Although, as a rule, no branch springs from this portion
of the subclavian, it is not uncommon to find the posterior
scapular artery taking direct origin from its upper surface.

Surgical Anatomy. — The dissector should again examine the rela-
tions of the subclavian artery, with the view of determining those which
would constitute the most trustworthy guides in cases where it is neces-
sary to apply a ligature to its third part. He should note that the
posterior belly of the omo-hyoid will give no information beyond that
of the depth at which the operator has arrived. The true guide is the
outer border of the scalenus anticus muscle. This, as a rule, lies imme-
diately subjacent to the posterior margin of the sterno-mastoid. By
passing the forefinger downwards along the outer margin of the scalenus
anticus, the scalene tubercle on the first rib will be reached. When the
finger-nail rests on this tubercle the finger-pulp is applied to the artery,
and in the living subject will feel its pulsations.

Suprascapular and Transversalis Colli Arteries. — Both
of these arteries will be observed emerging from under cover
of the outer border of the sterno-mastoid. Their origin from
the thyroid axis will be seen in a subsequent dissection.

The suprascapular artery (arteria transversa scapulse) pro-
ceeds outwards under shelter of the clavicle and across the
third part of the subclavian artery and the brachial nerv^Bfc
At the outer limit of the supraclavicular triangle it passes

SIDE 01- THE NECK. 20 j

under cover of the trapezius to reach the superior border
i)f the scapula where it has already been examined (p. 140).
Tiie transvcrsalis colli (arteria transversa colli) is placed at
a higher level, and is carried outwards across the posterior
triangle. It passes under cover of the posterior belly of the
omo-hyoid, and, as a rule, superficial to the brachial nerves.
It has already been observed to end under cover of the
anterior margin of the trapezius, by dividing into the
posterior scapular and the superficial cervical arteries
(p. 140).

Veins. — 'jlie arrangement of the veins has been noticed
in studying the relations of the subclavian artery. The
exterml jugular vein, as a rule, crosses the third part of this
_aLtcry and joins the subclavian vein. It is joined close to
its 'termination by the suprascapular and transversalis colli
veins, and perhaps by the anterior jugular as it emerges
from under cover of the sterno-mastoid. In many cases,
however, the anterior jugular joins the subclavian vein
directly.

Floor of the Posterior Triangle. — The floor of the
posterior triangular space is formed by a succession of
muscles, and at its very lowest part by a small portion of
the first rib. In the occipital subdivision the dissector will
observe that the floor is constituted from above downwards
by — (L)the splcnius capitis; (2) the levator anguli scapula;;
and (3) b^the scalenus medius and posticus. At the apex
of the triangle an additional factor may sometimes be
observed — viz. a small portion of the complexus.

In the supraclavicular triangle the floor lies very deeply.
It is formed by the scalenus medius and posticus, a portion
of the first rib, and a small part of the first digitation of the
serratus niagnus muscle.

Section of the Clavicle. — In order that a satisflictory view may he
ohtaincd of the nerves furmini; the hrachial plexus, it is necessary to
remove llie middle third of the clavicle. This, of course, can only be
done when the dissector of the upper limb has completed the dissection
of the axilla. Saw through tlie clavicle at two points — viz. at the
posterior margin of the sterno-mastoid, and the anterior margin of the
trapezius — anil remove the intermediate [>iece of bone, after having

204 HEAD AND NECK.

carefully detached it from the subclavius. The nerve to the subclavius
should now be traced to its distribution. Then divide the fibres of the
subclavius which still adhere to the acromial third of the clavicle, and
throw the muscle inwards. This will allow the shoulder to drop well
backwards.

Brachial Plexus. — This great nervous plexus is formed
by the anterior primary divisions of the four lower cervical
nerves and the greater part oi the large anterior primdry
division of the first dorsal nerve. Above, the plexus is
further reinforced by a very small twig of Communication
which passes from the fourth to the fifth cervical nerve,
whilst below, a similar connecting twig not infrequently
passes upwards in front of the neck of the second rib from
the second to the first dorsal nerve. The five brachial
nerves are brought into connection with the middle and
inferior ganglia of the cervical sympathetic by means of fine
rami communicantes.

The great brachial nerves emerge from the interval
between the scalenus anticus and scalenus medius, and
proceed downwards and outwards through the lower part of
the posterior triangle towards the axilla. The manner in
which they unite to form the plexus is upon the whole very
constant. The fifth and sixth nerves unite to form an
upper trunk ; the seventh nerve remains single and proceeds
downwards as a middle trunk ; and the eighth cervical
and first dorsal nerves join, whilst still under cover of the
scalenus anticus, to constitute a third or lower trunk.
Whilst still within the posterior triangle of the neck each
trunk splits into an anterior and a posterior division. Raise
the three anterior divisions on the handle of the knife, and
then it will be seen that the three posterior divisions unite
to form the posterior cord of the pjexus, and, further, that
the innermost of these divisions is much smaller than the
other two. Of the three anterior divisions the outer two
join to constitute the outer cord, whilst the innermost is
carried down by itself as the inner cord of the plexus.
From the three cords of the brachial plexus are given off
the branches which supply the upper limb.

STDE OF THE NECK.

205

Fig. 228. — Diagram of the brachial plexus.

CV, CVI, CVII, CVIII. The four anterior primarj- divisions of the cervical spinal
ner\'es which take part in its formation.

Dl and DII. The anterior primary'
divisions of the first two dorsal
ner\'es.
c.c. Communicating twig from the
fourth cervical nerve.
r. Nerve to rhomboids.
ss. Suprascapular nerve.
sc. Nerve to subclavius.
€.r. External respiratorj- ner\'C, or
nerve of Hell.
e.a.t. External anterior thoracic ner\'c.

i.a.t.
l.i.c.

i.e. ft.

Musculo-cutaneous nerve.
Median ner\'e.

Internal anterior thoracic nerve.
Lesser internal cutaneous nerve,

or the ner\'e of Wrisberg.
Intercosto-humera! nerve.
Internal cutaneous nerve.
Ulnar ner\'e.

The three suliscapular ner\-es.
Circumflex nerve.
Musculo-spiral nerve.

2o6

HEAD AND NECK.

From the above description it will be seen that the
plexus, from changes which are eifected in the arrangement
of its fibres, may be divided into four stages : —

1st Stage.

2nd vStage.

3rd Stage.

4th Stage.

5 separate
nerves (viz.

4 lower
cervical and
first dorsal).

3 nervous
trunks (viz.

an upper,

middle, and

lower).

3 anterior

divisions and

3 posterior

divisions.

3 nervous
cords (viz.
an outer,
innei", and
a posterior).

The first three of these stages are generally observed in the
lower part of the posterior triangle and in the upper part of
the axilla. It must be understood, however, that the points
at which division and union of the different parts of the
plexus takes place are subject to some variation.

Supraclavicular Branches of the Brachial plexus. — The
only branches of the brachial plexus which fall to the lot of
the dissector of the head and neck are those given off above
the level of the clavicle. These are for the most part
destined for the supply of muscles in the neighbourhood.
They are : —

Nerve to rhomboids, from the 5th cervical nerve.

Nerve to subclavius, 1 ^ , , , , , . ,

0 1 f from the i;th and oth cervical nerves. «"
Suprascapular, J -'

r T. 11 ' Krom the i^th, 6th, and 7th cervical nerves,

nerve of Bell, J j > j /

1 wigs to scalene j fj.Qj^^ various cervical nerves before they
muscles and longus \ ^^^^^ ^^e plexus.

colli,
]ommu
to phrenic nerve,

Communicating twig \^^^^ ^^ ^^^^j^^j^
2, i

The nerve to the rhomboids (nervus dorsalis scapulae) is a
long slender branch which springs, by a stem common to it
and the uppermost root of the nerve of Bell, from the fifth
cervical nerve as it lies upon the scalenus medius. Draw
the fifth cervical nerve forwards, and the branch in question

SIDE OF Tim NECK. 207

will he seen passing baekwards through the fibres of that
iiuiscle to reach the deep surface of the levator anguli
scaj^)ul;x;. It here meets the posterior scapular artery, and
proceeds with it downwards under cover of the rhomboid
muscles close to the base of the scapula. It supplies one
or two twigs to the levator anguli scapulte, and is finally
exhausted in the rhomboids.

The nerve to the subclavius (ncrvus subclavius) is a minute
twig which springs from the upper trunk of the plexus, and
then passes vertically downwards upon the plexus, and
across the subclavian artery to the subclavius muscle, which
it reaches by piercing the posterior lamina of its sheath.

A communicalion between the nerve to the subclavius and the phrenic
is by no means uncommon. This connecting filament may join the
phrenic in the neck or in the thorax. In all probability, it represents
that communicating twig (or at least a portion of it) which, on other
occasions, passes directly from the fifth cervical nerve to the phrenic.

The suprascapular nerve (nervus suprascapularis) is the
largest branch given off above the clavicle. It springs from
the upper trunk of the plexus, andjuns downwards, out-
wards, and backwards, at a higher level than the brachial
nerves, to the suprascapular notch of the scapula, through
which it enters the supraspinous fossa. As it approaches
the scapula, it passes under cover of the trapezius and
poigterior belly of the omo-hyoid, and comes into relation
with the artery of the same name.

The external respiratory nerve of Bell., also called the
posterior thoracic (nervus thoracicalis longus), is formed
by the union of three roots. The roots from the fifth
and sixth cervical nerves pass backwards through the
fibres of the scalenus medius, and unite into one stem
which gives branches to the upper part of the serratus
magnus. The third root from the seventh cervical nerve
does not pierce the scalenus medius. It is carried down-
wards on the surface of that muscle, and ultimately joins
the stem formed by the union of the upper two roots.
The posterior thoracic nerve enters the axilla behind the

208 HEAD AND NECK.

axillary vessels, and,is_entirely_devoted to the supply of the
serratus magnus muscle.

Dissection. — At this stage, the dissector of the upper limb removes
the arm from the trunk. The dissector of the head and neck mijst see
that the vessels and nerves are not cut too short. The outer border
of the first rib is the level at which they should be divided.

The dissector should now proceed with the dissection of the anterior
triangle. In this dissection the visceral compartment of the neck is opened
up, and its contents displayed. Let the head hang well over the end
of the table, and, raising the lower jaw as much as possible, fix it in this
position by means of hooks. Begin the dissection by throwing the super-
ficial cervical nerve and the cervical division of the facial nerve backwards,
and then carefully raise the cervical fascia from the area in front of the
sterno-mastoid. The anterior triangle is subdivided into three smaller
triangles by three muscles which traverse it in different directions. These
muscles are : — ( i ) the anterior belly of the omo-hyoid ; (2) the digastric ; .
and (3) the stylo-hyoid. It is well, therefore, at this stage to define
these muscles, and accurately determine the precise position and extent
of each subdivision of the space. ^\^^ anterior belly of the omo-hyoid
appears by emerging from under cover of the anterior border of the
sterno-mastoid, a short distance above its sternal origin. It crosses
the space very obliquely, running upwards and forwards to the body
of the hyoid bone. The digastric, as its name implies, is a two-bellied
muscle. The posterior belly comes out from under cover of the
sterno-mastoid, close to the mastoid process, and behind the lower
part of the parotid gland. It proceeds downwards and forwards to
the hyoid bone, and there the intermediate tendon is developed.
The anterior belly is directed upwards and forwards to the symphysis
of the lower jaw. The intermediate tendon of the digastric muscle
is bound down to the hyoid bone by a process of deep fascia, and in
cleaning the muscle, care must be taken not to detach this. The stylo-
hyoid muscle lies on a deeper plane than the posterior belly of the
digastric, and in relation to the upper border. It is pierced by the
digastric tendon at the hyoid bone. In the first instance, merely clean
the superficial surface of these muscles. In the case of the anterior
belly of the omo-hyoid, be careful not to injure the twigs from the
descendens hypoglossi nerve, which enter its upper border, and, whilst
dealing with the digastric muscle, bear in mind that the facial vein,
and the anterior division of the temporo-maxillary vein, usually descend
superficial to its posterior belly, and must be secured before the muscle
is touched. The filaments from the mylo-hyoid nerve, which enter the
upper border of its anterior belly, are not liable to injury if ordinary
caution be exercised.

Anterior Triangle of the Neck. — The anterior triangle

SIDE OI- J HE \EC/\. 209

differs from the posterior triangle in having its base above
and its apex l)elo\v. It js bounded /v///W by the anterior
margin of the slerno-mastoid, and itt^Jront_\yj the middle
Hne of the neclc. Its Inxsc is formed by the inferior margin
of the lower jaw, and a hne drawn from the angle of the
mandible to the sterno-mastoid muscle, whilst its dependent
apex is constituted by the meeting of its anterior and
l)osterior limits at the upper border of the sternum.

Spread over the anterior triangle there are the skin, the
superficial fascia with the platysma, and the deep cervical
fascia. In the interval between the platysma and the deep
fascia are placed the branches of the superficial cervical
nerve, the cervical branch of the facial nerve, and also the
anterior jugular vein.

Subdivisions of the Anterior Triangle. — Distinctive
terms are applied to the three subsidiary triangles which
are mapped out within the area of the anterior triangular
space by the anterior belly of the omo-hyoid muscle and
the two bellies of the digastric muscle. The lowest sub-
division is termed the Imver or muscular triangle; the
intermediate space receives the name of carotid triangle ;
whilst the highest subdivision is called the submaxillary
or digastric triangle (Fig. 229).

The muscular triangle is bounded in front by the middle
line of the neck, and behind by the sterno-mastoid. Its
base is above, and is formed by the anterior belly of the
omo-hyoid, whilst its apex is below at the upper margin of
the sternum.

The carotid triangle is limited above by the posterior
belly of the digastric, and below by the anterior belly of
the omo-hyoid. Its base is directed backwards, and is
formed by the sterno-mastoid, whilst its apex is at the
hyoid bone.

The digastric triangle is bounded belotv and behind by
the posterior belly of the digastric and the stylo-hyoid
muscle, and beloto and in fro)it by the anterior belly of
the digastric. Its base is above, and is constituted by the
body of the lower jaw, and a line drawn backwards from
VOL. II. — 11

HEAD AND NECK.

Fig. 229, — Triangles of the neck.

A. Occipital triangle.

B. Subclavian triangle.

C. Digastric triangle.

D. Carotid triangle.

E. Muscular triangle.

1. Superior constrictor.

2. Anterior belly of digastric.

3. Mylo-hyoid.

4. Stylo-glossus.

5. Hyo-glossus.

6. Stylo-hyoid.

7. Posterior belly of digastric.

8. Middle constrictor.

9. Hyoid-bone.

10. Thyro-hyoid.

11. Inferior constrictor.

12. Omo-hyoid.

13. Sterno-mastoid.

14. Sterno-hyoid.

15. Levator anguli scapula;.

16. Sterno-thyroid.

17. Trapezius.

18. Scalene muscles.

19. Omo-hyoid.

SIDE OF THE NECK. 211

the angle of the mandible to tlie stcrno-masloid nuiscle ; its
apex points downwards, and is formed by the intermediate
tendon of the digastric muscle.

Dissection. — Tlie numerous and diverse structures contained within
the anterior triangle must now be disi)layed. This is a dissection
which requires care and some jireliminary knowledge of the parts to he
exjwsed. The student is therefore advised to read the general account
which is given of the parts which are brought into view, as each sub-
division of the sjxice is opened up (p. 21 1 to p. 217), before undertaking
the work. The dissection should be carried out over the entire area at
once, and the structures found in one subdivision followed upwards or
downwards, as the case may be, into the other subdivisions of the space.
It is a common fault with dissectors to fail to ojien up the digastric
triangle until the two lower triangles have been fully dissected. Two
small nerves are especially liable to injury, and therefore should be
secured as early as possible. They are the thyro-hyoid branch of the
hypoglossal nerve and the external laryngeal nerve. The hypoglossal
nerve, which will be found crossing the carotid triangle at the lower
border of the posterior belly of the digastric, should be traced forwards ;
as it approaches the hyoid bone, its minute thyro-hyoid branch will be
discovered, leaving its lower border at an acute angle, and proceeding
downwards and forwards to reach the thyro-hyoid muscle. The external
laryngeal nerve is a long slender branch which occupies a deeper plane.
To expose it the carotid vessels should be pulled outwards from the
larynx, and the loose tissue in the interval thus opened up divided care-
fully in an oblique direction and along a line connecting the cricoid car-
tilage with the bifurcation of the common carotid artery. The nerve will
be found as it passes downwards and forwards to disappear under cover
of the depressor muscles of the larynx. It will be traced to its ultimate
distribution at a subsequent stage of the dissection.

Musctilar Triangle. — As this triangle is gradually opened
up, the following structures will come into view : —

1. The sterno-hyoid and sterno-thyroid muscles.

2. The branches from the ansa hypoglossi to these muscles,
j. The external laryngeal n^rve.

4. The superior thyroid artery.

5. The greater part of the larynx, the thyroid body, and the trachea.

6. The oesophagus on the left side.

7. The recurrent laryngeal nerve.

When the fascia is removed from this part of the anterior
triangle, the only structures which are seen within its limits
are the sterno-hyoid and sterno-thyroid muscles. It is for

212 HEAD AND NECK.

this reason that the term muscular is appUed to the space.
As the dissection is proceeded with, however, the large
nerve of supply for these muscles, which comes from the
ansa hypoglossi, will be found lying near the outer border
of the sterno-thyroid and breaking up into numerous twigs.
Towards the upper part of the space the superior thyroid
artery will be noticed passing downwards under cover of
the omo-hyoid, sterno-thyroid, and sterno-hyoid muscles to
reach the thyroid body. At a slightly higher level than
this artery, the external laryngeal nerve runs forwards to
end in the crico-thyroid muscle. Under cover of the
sterno-hyoid and sterno-thyroid muscles will be observed
the larynx, the isthmus and a considerable part of the
lateral lobe of the thyroid body, and the trachea. The
recurrent laryngeal nerve lies deeply. It will be found
in the interval between the gullet and trachea. As the
oesophagus inclines to the left behind the trachea, it follows
that it is only seen, when in its natural position, in the
left muscular triangle.

Carotid Triangle. — During the dissection of the carotid
triangle the following parts are displayed : —

Arteries-<

( I . Common carotid dividing into external and internal
carotid arteries.
Superior thyroid. ■v

Lingual. I

Facial. ^

Occipital. I

Veins

3-

4-
5-
6.

7-
8.

9-
^,io.

I.

2.

3-

4-
5-

Branches of the
external
carotid.

Ascending pharyngeal.
Hyoid. -.

Sterno-mastoid. j-

Superior laryngeal. -'
Sterno-mastoid branch of the occipital.

Internal jugular.

Facial. ^

Anterior temporo-maxillary.

Lingual.

Superior thyroid.

Middle thyroid.

Branches of the
superior thyroid.

Tributaries of the
internal jugular.

Nerves

SIDE or THE NECK. 213

1. Hypoglossal. \ ^."^^'"S the space in a

^^ ^ j transverse direction.

2. Descendens hypoglossi. •>

3. Nerve to thyro-hyoid. I Crossing

4. Internal laryngeal. > the space

5. External laryngeal. I obliquely.

6. Sninal accessory. '

6. Spinal accessory,

1
vertically.

7. \'agus. 1 Descending

lathetic. J

Intcrcarotic body.
Portion of the larynx and phaiynx.
Cireater cornii of the hyoid bone.
Lymphatic vessels and glands.

This subdivision of the anterior triangle, when opened
up, contains portions of each of the three carotid arteries.
It therefore receives the name of carotid triangle. It is
well, however, that the dissector should clearly understand
that it is only after the parts are relaxed by dissection that
these vessels come to lie within the space. When the
fascia and platysma are in position they are completely
overlapped by the sterno-mastoid muscle. The common
carotid artery is enveloped, along with the internal jugular
vein^and vagus nerve, in a common sheath of fascia. The
carotid sheath should be slit open, care being taken of the
descendens hypoglossi nerve, which also descends obliquely
witliin it. The intimate connection which this sheath pre-
sents with the prevertebral layer of fascia can now be made
out. The cpmnion oirotid usually bifurcates opposite the
upper border of the thyroid cartilage. Observe thjaJt the
internal carotid artery at first lies behind., a>id to the outer
side of the external carotid. Upon the coats of these
vessels numerous sympathetic twigs ramify (Fig. 230), and,
at the point of bifurcation of the common carotid, a small
oval body, termed the intercarotic body, will be found closely
applied to the deep surface of the vessel. Fig. 230 (25).
The branches of the external carotid which take origin in
the area of this triangle run for only a very short part of
their course within it. Three branches will be noticed
springing from the anterior aspect of the external carotid.
Named from below upwards these are : ( i ) the superior

V

214

HEAD AND NECK.

thyroid, which, after having given off its hyoid, superior

laryngeal, and sterno-mastoid
branches, disappears under
cover of the omo-hyoid
muscle, and enters the
muscular triangle ; (2) the
lingual, which leaves the
space by passing under
cover of the digastricTand
stylo-hyoid muscles ; and
(3) tiie/aqql, which ascends
under the same rnuscJes
to gain the digastric tri-

FiG. 230. — Deep aspect of carotid
vessels, with the intercarotic
body and the nerves in rela-
tion to them. (Luschka.)

1. Common carotid.

2. Internal carotid.

3. External carotid.

4. Superior thyroid.

5. Lingual.

6. Facial.

7. Occipital.

8. Superficial temporal.

9. Internal maxillary.

10. Vagus nerve.

11. Spinal accessory.

12. External portion of spinal accessory.

13. Internal part of spinal accessory

joining the vagus.

14. Glosso-pharyngeal.

15. Branches to carotid plexus.

16. Pharyngeal branch of vagus.

1 7. Superior laryngeal branch of vagus.

18. External laryngeal nerve.

20. Superior cervical ganglion.

21. Sympathetic cord.

22. Superior cardiac branch of sym-

pathetic.
23; Sympathetic twigs to carotid
plexus.

24. Carotid plexus.

25. Intercarotic body.

SIDE OF THE NECK. 215

angle. The oiri/>ifai artery coninionly springs from the
posterior aspect of the external carotid close to the
lower border of the digastric, and soon (juits the space
by running upwards and backwards under cover of the
sterno- mastoid muscle. Its sterno-viastoid branch conies
off as it leaves the triangle, and accompanies the spinal
accessory nerve. The ascending pluiryngeal artery will be
found by separating the external and internal carotid
arteries from each other, and dissecting between them.
It springs from the posterior aspect of the former about
half an inch above its origin, and then takes a vertical
course upwards on the prevertebral muscles.

The internal jugular vein lies close to the outer side of the
common carotid artery, and is included within the same
fascial sheath. Several tributaries join it as it passes through
this space. The most conspicuous of these is the coMUMn
facial vein, which is formed by the union of the facial vein
and the anterior division of the temporo-maxillary vein.

The nerves which are brought into view as the carotid
triangle is gradually opened up are very numerous, but they
can be classified according to the direction which they take
through the space. One large nerve, the hypoglossal^ takes
a more or less transverse course across the upper part of the
space. It forms a loop across this part of the neck im-
mediately beloNv the lower margin of the digastric muscle.
Two descend vertically — viz. the vagus and the gangliated
cqrcTorthe sympathetic. Th^ vagus lies in the posterior
part of the carotid sheath between the common carotid
artery and the internal jugular vein. The sym_pathetic cord
is embedded in the posterior wall of the carotid sheath.
The remaining five nerves traverse the triangle obliquely.
Kour run from above downwards and forwards, .,vi?^be
descendens hypoglossi, the thyro-hyoid, the internal and
external laryngeal nerves ; and one — the spinal accessory
— is directed from above downwards and backwards.

The descendens hypoglossi springs from_Lhe_ hypoglossal
nerve as it hooks round the occipital artery, and descends
within the carotid sheath. It is joined at the upper border

2l6

HEAD AND

NECK. %^.,,J^,/.^

of the omo-hyoid by one or two branches from the cervical
plexus, and in this manner the ansa hypoglossi is formed.
The thyro-hyoid is a minute nerve which arises from the
hypoglossal nerve before it disappears under cover of the
posterior belly of the digastric. The internal laryjigeal nerve
descends behind the carotid vessels. It will be readily
found, with the corresponding artery, in the interval
between the hyoid bone and upper border of the thyroid
cartilage. It enters the larynx by piercing the thyro-hyoid
membrane. The external laryngeal nerve, a branch of the
preceding, is a much smaller twig. It leaves the space by
passing under cover of the depressor muscles of the larynx
and hyoid bone. The spinal accessory nerve is placed
high up in the interval between the digastric and the
sterno-mastoid muscles. It soon disappears by sinking
into the substance of the sterno-mastoid. uL^-'

The Digastric Triangle may be divided very con-
veniently into an anterior and posterior part by the stylo-
maxjllary ligament and a line drawn downwards from it.
The portion in front has a distinct floor, composed, in
great part, by the mylo-hyoid muscle, and behind this by a
portion of the hyoglossus muscle.

The parts exposed during the dissection of the digastric
space may be classified according to the subdivision in
which they lie : —

Anterior Part.

Posterior Part,

1. Submaxillary gland.

2. Facial artery and vein.

3. Branches from ^ a. Ascending palatine.

facial artery \_h. Tonsillitic.
in this part | c. Submaxillary,
of its course. J d. Submental.

4. Hypoglossal nerve.

5. Mylo-hyoid nerve.

6. Mylo-hyoid artery.

7. Lymphatic glands.

1 . Portion of the parotid

gland.

2. External carotid ar-

tery.

3. Posterior auricular

artery.

SIDE OF THE NECK. 217

The most conspicuous object in the fore-part of the
digastric triangle is the submaxillary ^land. The facial
artery passes upwards and forwards in the midst of this
gland, whilst the facial vcifi lies superficial to it. But
whilst the facial artery runs througintie glanH, the dissector
should note that it can be separated from it without any
laceration of the gland lobules. The gland is, as it were,
wrapped round it, so that, although at first sight the artery
seems to pierce it, it is in reality merely contained in a deep
furrow in its substance. Before entering the gland, the
facial artery gives off its tonsillitic and ascending palatine
branches, whilst its submental and submaxillary branc/ies
arise within the gland. The submental artery runs for-
wards towards the chin. The mylo-hyoid nerve and artery
will be seen passing forwards and downwards upon the
mylo-hyoid muscle under cover of the submaxillary gland.
The twigs of the nerve to the muscle of the same name
and to the anterior belly of the digastric should be followed
out. Only a very small part of the hypoglossal nerve is sfeen
in this space. It lies upon the hyoglossus muscle immedi-
alcly above the hyoid bone, and disappears under cover of
the posterior border of the mylo-hyoid muscle. Numerous
small lymphatic glands lie under shelter of the base of the
lower jaw.

The external carotid artery enters the posterior part of
the digastric triangle. Here it lies under cover of the
lower part of the parotid gland, and gives off its posterior
auricular branch, which passes upwards and backwards
along the upper border of the posterior belly of the
digastric muscle. ^

Middle Line of the Neck. — Before the parts are further
disturbed the dissector should examine the structures
which occupy the middle line of the neck — a region, more
especially in its lower part, of the highest importance and
interest to the surgeon. The middle line of the neck may
be divided by means of the hyoid bone into an upjK'r
supra-liyoid and a lower infra-hyoid portion.

\\\ \.\\<i suprahyoid part -xxc found structures which are

2i8 HEAD AND NECK.

concerned in the construction of the floor of the mouth.
The student has already noticed that the fatty superficial
fascia is more fully developed here than elsewhere in the
neck, and that the anterior margins of the two platysma
muscles meet in the mesial plane about half an inch or so
below the chin. Above this point their fibres decussate.
In the present condition of parts the two anterior belUes of
the digastric muscles are observed attached to the mandible
on either side of the symphysis. From this they descend
towards the hyoid bone, and diverge slightly from each
other so as to leave a. narrow triangular space between
them (Fig. 231). The floor of this space is formed by the
anterior portions of the two mylo-hyoid muscles, whilst
bisecting the triangle in the mesial plane is the fibrous
raphe, into which these muscles are inserted. Not un-
frequently the inner margins of the digastric muscles send
decussating fibres across the interval between them.

The infra-hyoid part of the middle line of the neck
extends from the hyoid bone to the upper margin of the
manubrium sterni. Below the hyoid bone is the thyro-
hyoid membrane succeeded by the thyroid cartilage with
its prominent pomtim Adavii. Then comes the tense crico-
thyroid membrane and the cricoid cartilage. Except along
a narrow interval on either side of the mesial plane, these
structures are covered by two muscular strata, viz. a super-
ficial layer formed by the sterno-hyoid and omo-hyoid
which He on the same plane, and a deeper layer formed by
the sterno-thyroid and its continuation upwards, the thyro-
hyoid. In addition to these an elongated process of the
thyroid gland not unfrequently stretches upwards (usually
upon the left side), under cover of the sterno-hyoid. If
this be present, it will in all probability be observed to be
attached to the hyoid bone by a narrow muscular band
termed the levator glandules thyroidece. The divergent
inner margins of the two small crico-thyroid muscles, as
they extend upwards and outwards upon the cricoid car-
tilage towards the lower margin of the thyroid cartilage,
will also be seen. Upon the crico-thyroid membrane, as it

SIDE OF THE NECK.

219

appears between these muscles, the small crico-thyroid
artery runs transversely inwards.

Below the cricoid cartilage the dissector comes upon the
trachea, which extends downwards through the remaining
portion of the middle of the neck. As the tube descends
it gradually recedes from the surface, so that at the upper

eric. thyr. muscle.

middle thyroid
vein.

hyold hone.

thyro-hyoid

membrane,
thyroid cartilage.

crico-thyroid
membrane,
cricoid cartilage.

trachea.

isthmus of
thyroid body.

infr. thyr. artery,
oesophagus,
infr. thyroid vein.

recurrent laryn-
geal nerve.

Fig. 231. — Dissection of the middle line of the neck.

margin of the sternum it lies very deei)ly. The length of
this portion of the trachea varies with the position of the
head. When the chin is raised, and the head thrown as
far back as possible, about two inches and three-quarters of
the tube will be found between the cricoid cartilage and
the sternum ; when, on the other hand, the head is held in
its usual altitude, the length of the cervical part of the
trachea is diminished by fully three-quarters of an inch.

220 HEAD AND NECK.

These measurements must be regarded as merely expressing
the average condition. They vary considerably in different
individuals, and are much influenced by differences in the
length of the neck.

The dissector must study carefully the parts which lie
superficial to the trachea in this portion of its course. In
the first place, examine the structures which are in immediate
contact with it. These are ( i ) the isthmus of the thyrgid
body; (2) the inferior thyroid veins; (3) at the root of the
neck, the innominate artery and the left innominate vein ;
(4) the thymus body in young children; and (5) the occa- -
sional thyroidea ima artery. The isthmits of the thyroid is a
thin band of thyroid substance which crosses the mesial
plane upon the anterior aspect of the trachea. As a general
rule it covers the second, third, and fourth tracheal rings, so
that only one ring is left exposed between its upper margin
and the cricoid cartilage. Almost invariably a branch of
the superior thyroid artery runs along the upper margin of
the isthmus, whilst upon its anterior surface is placed a
plexiform arrangement of small veins. The inferior thyroid
veins are two in number, and of large size. They are formed
by several tributaries which issue from the lateral lobes, and
proceed downwards upon the front of the trachea, one upon
either side of the mesial plane. They are separated from
each other by a narrow interval, and immediately below the
isthmus they are connected by. a_plexus_oL_small veins_
which lies in front of the trachea. An additional median
veift, taking origin from the isthmus, _may_ also exist. Close
to the sternum the innominate artery will be observed lying
upon the trachea, and slightly below the level of the upper
border of the bone the left innominate vein crosses it. The
thymus body in children of two years or under is always
prolonged upwards for some distance into the neck in front
of the trachea. The thyroidea ima is an occasional branch
of the innominate artery. When present it passes vertically
upwards in front of the trachea to the isthmus of the thyroid
gland.

The_parts which separate the trachea, with the structures

I

SIDE OF THE NECK. 221

in imniodialo rclnlioti to its anterior as[)cct, from the surface
should now be studied. The two anterior jugular veins
as they run downwards in the superficial fascia, one upon
either side of the mesial plane, have been already noticed ;
also, thcjjvo- lay4^fs-©l— t4Tr-d«ep cervical fascia close to the
upper margin of the sternum, and in the interval between
these the cross-branch co^nnecting. the two anterior jugular
veins. Behind the fascial envelope of the neck come the
two muscular strata formed by the sterno-hyoid and the
sterno-thyroid muscles. The inner margins of the sterno-
hyoid muscles are almost contiguous above, and held
together by the fascial sheaths which enclose them ; helpw,
hawever, they diverge slightly from each other, so as to
expose, close to the sternum, the inner margins of the
sterno-thyroid muscles. The sterno-thyroid muscles, in
contact with each other below, gradually separate from
each other as they ascend. A narrow, lozenge-shaped
space is thus left between the inner borders of these
muscles. Over this area, the trachea is not covered by
any muscular structure.

Surgical Anatomy. — The principal operations which are performed
in the middle line of the neck are those of laryngotomy and tracheotomy.

In_laryrigaiQI>}Ii_an opening is made into the larynx. This can most
rcailiiy be done in the Jntcrval. between the thyroid and cricoid
cartilages. A vertical mesial incision through the integument is made
over this interval. The crico-thyroid membrane is thus exposed, and
is divided traiisz'crscly cXos^t to the upper margin of the cricoid cartilage.
It is a very simple proceeding, and one which is attended with little or
no danger if ordinary care be taken. The crico-thyroid membrane is
divided transversely, and in its lower part, for two reasons — viz. (l) to
avoid injury to the crico-thyroid artery, which, although, as a general
rule, of small size and of no surgical importance, is sometimes large
enough to give rise to awkward results if wounded ; and (2) to place
the opening as low down as possible.

Traclicolomy is a more serious operation. The opening into the
trachea may be made abovejir below_the_ isthtniis dL the thyroid body.
The high operation is ver)' properly preferred by the surgeon. Its
advantages are very apparent : here the trachea lies near the surface,
and no veins of any im|x)rtance are met with. The only drawback
consists in the small portion of trachea which intervenes between the
isthmus and the cricoid cartilage. Still, this can be increased by push-
ing down the isthmus, which, within certain limits, can be easily dis-

k

222 HEAD AND NECK.

lodged in a downward direction. Many surgeons, indeed, consider
that the wounding of the isthmus is a matter of comparatively slight
importance. The fact, however, that a large branch of the superior
thyroid artery is generally found in relation to its upper border, should
make the operator hesitate before having recourse, in all cases, to this
expedient for gaining additional space. In the child it is frequently
necessary to combine the high operation of tracheotomy with that of
laryngotomy — viz. by cutting through the cricoid cartilage.

The low operation is a formidable undertaking. It is true that there
is a greater length of tube to be operated upon ; but this is situated
very deeply, and the surgeon encounters many difficulties before it is
reached. If the dissector reflect upon the structures which intervene
between this part of the trachea and the surface, he will fully realise
this ; and he must bear in mind that these difficulties are greatly
intensified in the living subject by the engorged state of the veins, and
the convulsive movements of the windpipe as the patient struggles for
breath. In the child, the thymus body interposes an additional
obstacle ; and this, combined with the more limited space, the _small
calibre and great mobility of the trachea, renders the operation, in such
cases, a very serious responsibility. In the low operation, the trachea
must be opened in an upward direction, so as to avoid injury to the
innominate artery and left innominate vein, which are placed in front
of it at the upper margin of the sternum.

Infra-hyoid Mtiscles. — These are a series of flat, narrow,
band-like muscles which lie upon the trachea, thyroid body,
and larynx. They are disposed in two strata — viz. the
omo-hyoid and the sterno-hyoid constituting a superficial
layer ; and the sterno-thyroid and thyro-hyoid a deep layer.

The omo-Kyoid (musculus omohyoideus), as we have
noted, is a two-bellied muscle. The posterior belly springs
from the upper border of the scapula and the suprascapular
ligament. It crosses the posterior triangle of the neck, so
as to divide it into an occipital and supraclavicular portion,
and finally terminates in the intermediate tendon. This
tendon lies under cover of the sterno-mastoid muscle, and
is held in position by a strong process of fascia derived
from the cervical aponeurosis, and firmly attached below to
the sternum and the first costal cartilage. The anterior
belly emerges from under cover of the anterior border of
the sterno-mastoid, and takes an almost vertical course
through the anterior triangle. It is inserted irito the lower
border of the body of_the_hymd. bone^ cl_o_se_to the-outer

SIDE OF run XKCK.

223

side of the stcrno-hyoiH. In the anterior triangle of the
neck, the anterior belly of the omohyoid forms the
boundary between tlie carotid and the muscular sub-
divisions of this area.

The stcnio-hyoid (musculus sternohyoideus) arises from
the posterior aspect of the irmer end of the clavicle and
the posterior sterno-clavicular ligament. Its origin, how-
ever, is very variable; thus, it may be shifted either in-

boJy of the hyoid bone ~,

lliyrO-hyoid membrane

thyroid cartilage

crico-lhyroid membrane

cricoid cartilage

Fig. 232. — Hyoid bone and larynx. (Gcgenbaur. )

wards or outwards. In the former case, it springs from
the back of the manubrium sterni and the ligament ; in
the latter case, from the clavicle alone. It is inserted into
the lower border of Jhe body of the hyoid bone, between
the mesial plane and the insertion of the omo-hyoid. A
short distance above the sternum an oblique fibrous inter-
section frequently divides it into two portions.

' Wuc stcrno- thy raid {\w\\%zv\wi sternothyreoideus) lies under
cover of the preceding muscle, and is both broader and

224 HEAD AND NECK.

shorter. It springs, from the posterior aspect of the
rnanubrium sterni and from the cartilage of the .first rib.
Diverging slightly from its neighbour as it ascends, it is
inserted into the oblique line on the outer face of the ala
ofthe thyroid cartilage. An incomplete tendinous inter-
section may sometimes be noticed interrupting its muscular
fibres.

The thyro-hyoid (musculus thyreohyoideus) lies on the
same plane as the sterno - thyroid j indeed, it may be
regarded as its continuation upwards. It takes origin
from the oblique line on the thyroid ala, and is inserted
into the lower border of the body and a part of the great
cornu of the hyoid bone under cover of the sterno-hyoid
and omo-hyoid muscles.

Digastric Muscle (musculus digastricus). — This muscle
limits the submaxillary triangle inferiorly, and intervenes
between it and the carotid triangle.

The anterior belly of the digastric^ spririgs from aq im-
pression upon the deep aspect of the base of the mandible,
close to the symphysis, whilst the posterior belly takes origin
from the digastric fossa of the temporal bone under cover
of the mastoid process. Both bellies converge as they
proceed towards the upper border of hyoid bone, where
they are joined by a strong round mtermedtate tendgn. The
posterior belly is the longer of the two, and is fusiform in
shape ; the anterior belly is shorter and flatter, and descends
in a more vertical direction. The intermediate tendon is
bound down to the great cornu and the body of theJiyoid
bone by a strong aponeurotic band.

Stylo-Hyoid Muscle (musculus stylohyoideus). — The
stylo-hyoid muscle lies along the upper border of the
posterior belly of the digastric. It is a small muscular
band which .arises from the posterior aspect of the styloid
process of the temporal bone not far from its base. It is
generally inserted by two slips into the hyoid bone at the
point where the great cornu joins the body. The inter-
mediate tendon of the digastric passes forwards between
^^ the two slips of insertion of the stylo-hyoid.

:^i

SIDE OF THE NECK'. 225

Hypoglossal Nerve (norvus hypoglossus). — The portion
of the liy[)c)glossal nerve which traverses the anterior
triangle can be studied at this stage. It appears by
emerging from under cover of the posterior belly of the
digastricj and immediately turns forwards by hooking
round the occipital artery. Near the upper border of the
hyQid__boue it^dkappears from the present dissection by
passing under cover of the mylo-hyoid muscle. Informs
a loop on the side of the neck which lies upon the
external carotidTahd lingual arteries, and finally, above the
liy'Oid^'Bone, "upon the hyoglossus muscle. It is crossed by
the intermediate tendon of the digastric_and the two slips
of insertion of the stylo-hyoid-

Two l^anches will be seen to arise from this portion of
the hypoglossal nerve, viz. : —

1. The_ramus descgndens.

2. The thyro-hyoid.

The ramus descendens hypoglossi, as a rule, leaves the
hypoglossal iiefve at the point where it turns round the
occipital artery. It' proceeds downwards and inwards so
a^ to cross the common carotid artery very obliquely.
Reaching the upper border of the anterior belly of the
omo-hyoid, it ends by joining a slender branch which
advances towards it from the second and third cervical
nerves. This nerve is called the_ ramus ccnncalis descendens^
and by its union with the ramus descendens hypoglossi a
nerve-loop is formedjii front of the common carotid artery,
which is called the ansa hyJ)dgIossr{¥\g. 235).

From the convexity of this loop branches arc given off
which supply both bellies of the omo-hyoid, the sterno-
hyoid, and sterno-thyroid muscles.

~The branches for the anterior belly of the omo-hyoid
may proceed from the ramus descendens hypoglossi before
it reaches the ramus cervicalis descendens. The filament
for the posterior belly runs downwards and backwards
along the lower border of the intermediate tendon, and
between the two laminaj of the fascial sheath which retains

VOL. II. — 15

226 HEAD AND NECK.

the tendon in position. The branch for the sterno-hyoid
and sterno-thyroid muscles is a nerve which breaks up
along their outer margins into a number of twigs for their
supply. One small filament may sometimes be traced into
the thorax, where it communicates with the phrenic and
\ cardiac nerves.

Xbie.. thyro-hyoid ..nerve is a slender twig which comes off
from the hypoglossal as it approaches the hyoid bone. It
supplies the thyro-hyoid muscle.

Sterno-Clavicular Articulation (articulatio sterno-clavi-
cularis). — The dissector must now examine the sterno-
clavicular joint, as the next step consists in the disarticula-
tion of the clavicle and the reflection of the clavicular
origin of the sterno-mastoid muscle.

The structures which hold the two bones in position at
this joint are the following : —

( Anterior sterno-clavicular.
Ligaments proper. | Posterior sterno-clavicular.

Accessory ligaments. | ColTo-davkular or rhomboid.
Interarticular fibro-cartilage.

Dissection. — To expose these ligaments the origin of the pectoralis
major from the clavicle and the manubrium sterni must be removed.
The sternal origin of the sterno-mastoid is also, to a certain extent, in
the way, but it is not advisable to divide this.

Sterno-Clavicular Ligaments. — These are placed one in
front and the other behind the joint, but they are not
isolated sharply-defined bands. Above, they are united by
their margins with the interclavicular ligament, whilst below
they run into each other so as to constitute in this manner
a capsule for the joint (capsula articularis). The anterior
sterno-clavicular lig^ament ^springs from the front of the
inner end of the clavicle, and proceeds obliquely down-
wards and inwards _to gain attachment to the anterior
aspect of the manubrium sterni. The posterior sterno-
clavicular ligament has a corresponding position, and
presents similar attachments on the posterior aspect of
the joint.

SIDE OF THE XECK. 227

These ligaments limit the backward and forward move-
ments of the inner end of the clavicle, upon the sternal
facet.

The Interclavicular Ligament (ligamentum interclavi-
culare) is a strong band which c^niiects the inner ends
of the two clavicles. It is firmly fixed to the upper edge
of each bone, and as it passes across the middle line it
dips into the notch on the upper margin of the sternum,
and is attached to it also.

The Rhomboid. Ligament (ligamentum costoclaviculare)
is composed of short oblique fibres. It is placed behind
the subclavius muscle, the remains of which must therefore
be removed to expose its anterior surface ; at the same
time the clavicle must be tilted upwards as high as possible.
The rhomboid ligament is attached by its_LQ>yer border to
tl\e_ cartilage., of .tjie first _ rib. From this it is carried
obliquely upwards, backwards, and outwards, and is_ fixed
by its upper border to a rough depression upon the under
surface of the inner end of the clavicle.

The rhomboid ligament plays an important part in the
mechanism of the joint, and adds greatly to its security.
It checks excessive elevation of the shoulder, and restrains,
within certain limits, both forward and backward move-
ment of the clavicle.

Dissection. — The interarlicular fibro-cartilage is the most important
of all the agents concerned in maintaining the apposition of the inner
end of the clavicle with the sternum. To obtain a view of this
structure, the joint must be opened into ; indeed, it is well to remove
as far as possible all the ligaments. Begin by dividing the rhomboid
ligament. To effect this the clavicle must be raised and the knife
carried inwards between its inner end and the first costal cartilage.
Next remove the interclavicular and anterior and posterior sterno-
clavicular ligaments. It is difficult to get at the posterior sterno-
clavicular ligament in the present condition of parts, but with a little
care the sterno-hyoid muscle may be detached from its surface, and its
fibres divided. The clavicle should now be forcibly pulled outwards,
when the interarlicular fibro-cartilage will become apparent.

The-Interaxticular Fibrojj3artilage (discus articularis)

is n i'"'nrly '"■'•^nlnr moiiiscus or i)late interposed between

228 HEAD AND NECK.

the inner .end of -the clavicle and-the sterjaal_face.t. Its
surfaces are accurately moulded upon both. As a general
rule it is thicker around its circumference than in the
centre, where it is occasionally perforated. In removing
the capsule of the joint, the dissector will notice that by
its circumference it is closely attached to this, both in
front and behind. Above., it is firmly fixed to the upper
edge of the inner end of the clavicle ; below, its margin is
thinned and passes outwards under the clavicle to gain
attachment to the inner end of the cartilage of the first
rib.

The part which the interarticular meniscus plays is very
apparent. Its function is twofold ; (i) it acts as a cushion,
and thus lessens the shock of blows received upon the
shoulder; (2) it acts as a bond of union, and prevents the
clavicle from being driven upwards upon the top of the
sternum when force is applied to its outer end.

Synovial Membranes. — The sterno-clavicular joint is
provided with two synovial membranes, placed one upon
either side of the interarticular fibro-cartilage. These are
quite distinct from each other, except in cases where the
fibro-cartilage is deficient in its centre. In this case the
two synovial cavities communicate.

Dissection. — Complete the disarticulation of the clavicle by dividing
the attachment of the fibro-cartilage to the first costal arch. By this
step the meniscus is removed with the clavicle, and can therefore be
more fully examined. Further, the clavicular portion of the sterno-
mastoid can now be thrown forward, and the parts under cover of this
muscle dissected. The sternal origin of the sterno-mastoid should not
be interfered with until the subclavian and carotid vessels have been
studied.

Certain structures at the root of the neck must now be displayed.
These are : —

1. The scalene muscles.

2. The phrenic nerve.

3. The subclavian vessels and their branches.

4. The cervical pleura.

5. The thoracic duct on the left side, and the right lymphatic

duct on the right side.

6. The lower part of the internal jugular vein.

SIDE OF THE NEC A'. 229

7. The vagus nerve.

8. The lower part of the common carotid artery.

9. The lower part of the cervical symjiathelic.

As the dissection is proceeded with, a large number of important
structures will be observed grouped in relation to the scalenus anticus
muscle. Thus it is crossed in front and from below upwards by — ( i )
the subcla\nan vein, which lies upon its insertion into the first rib ; (2)
the suprascapular artery ; (3) the transversalis colli artery ; and (4) the
omo-hyoid muscle, with the nerve to its posterior belly. Under cover
of these, the phrenic nerve is carried downwards upon the anterior aspect
of the muscle, whilst the thoracic duct on the left side, and the right
lymphatic duct on the right side, lie for a short distance in front of the
scalenus amicus near its inner margin. Both of these ducts open into
the venous system at the angle of union between the internal jugular and
subclavian veins. Behind \.\\q scalenus anticus, the cervical pleura bulges
upwards for a short distance into the neck, and at a higher level the
subclavian artery and the brachial nerves are also in relation to its
posterior surface. Close to its inner margin are the thyroid axis, the
vertebral artery and vein, and, somewhat overlapping it, the large internal
jugular vein ; whilst ascending in the interval between the scalenus
anticus and the rectus capitis anticus major is the small ascending
cervical artery.

Between the scalenus anticus and the trachea will be found the
internal jugular vein, the vagus nerve, common carotid arter}-, the
first part of the subclavian artery with its branches, and the sympathetic
cord.

This is a tedious dissection, on account of the numerous twigs
which are given off by the sympathetic. Certain of these descend in
relation to the first part of the subclavian artery, and must be carefully
preserved. The middle cervical ganglion, as a general rule, rests upon
the inferior thyroid artery, whilst the lowest ganglion in the neck is
placed in the depression between the transverse process of the last
cervical vertebra and the neck of the first rib.

Scalene Muscles. — These muscles constitute the fleshy
mass which is seen extending from the transverse processes
of the cervical vertebras to the upper two costal arches.
They are three in number, and are named, from their relative
positions, anfici/s, /neJius, and />os//cus.

The scaliiius anticus (musculus scalenus anterior) is a
well-defined muscle which is separated from the scalenus,
niedius by^tlie bxachial nerves aad^ the subclavian artery.
It arises from the aiitcrior- tubercles of tlie transverse
processes of four cervical vertebroi^viz. the third, fourth,

230 HEAD AND NECK.

fifth, and sixth — and, tapering somewhat as it descends, is
inserted into the scalene tubercle on the inner margin of
the first rib, and also into the upper surface of the same
bone between the two subclavian grooves.

The scalenus mediiis (musculus scalenus medius) is a more
powerful muscle than the preceding. It springs from the
posterior tubercles of all the cervical transverse processes
(with the exception, in some cases, of the first), and it is
inserted into _a rough oval impression which marks the upper
surface of the first rib between the tubercle and the groove
for the subclavian artery.

The scaktiiis postiais (musculus scalenus posterior) is
generally inseparable at its origin from the scalenus medius.
It is the smallest of the three, and springs by two or three
slips from the transverse processes of a correspDn:ding
number of the lower cervical vertebrae in common with the
scalenus medius. It is inserted into the upper border of
the second rib, immediately in front of the insertion of the
levator costse.

Subclavian Artery (arteria subclavia). — The subclavian
artery is the first subdivision of the great vessel which
carries blood for the supply of the upper limb. It arises
differently on the two sides of the body. On the right side
it takes origin behind the sterno- clavicular articulation by
the bifurcation of the innominate artery. On the left side it
springs, within the cavity of the thorax, from the aortic arch.
In both cases it takes an arched course outwards across
the root of the neck, behind the scalenus anticus muscle
and above the pleura. At the outer border of the first rib
it enters the axilla and receives the name of axillary artery.

The relations of the subclavian artery are so numerous,
and of so varied a character, at different parts of its extent,
that it is found necessary to subdivide it into three portions.
The first part extends from the origin of the vessel to the
inner margin of the scalenus anticus; th.e second portion Vies
behind this muscle ; whilst the third part extends from the
outer border of the scalenus anticus to the outer border of
the first rib.

SIDE OF THE NECK,

23«

First part. — Qiiiiig to the difference of origin, the
relations presented by the first portion of the subclavian
artery are not tlie same on the twojides of the body. Let
us examine, in the first instance, the vessel of the right side,
and then comiiarc it with that of the left side. The first

Fig. 233. — Uiaj^ram of the subclavian artery and its
branches. (Turner. )

I.

Innominate arteiy.

1 1.

Deep cervical.

2.

Common carotid artery.

12.

Internal mammary.

3-

Vertebra! arterj'.

•3-

Posterior scapular.

4-

Thyroid a.\is.

14.

Ascending cervical.

5-

Inferior thyroid artery.

a.

First rib.

6.

Transversalis colli.

h.

Scalenus anticus.

7-

Superficial cervical.

c.

Thyroid body.

8.

Posterior scapular.

<i.

Phrenic nerve.

9-

Suprascapular.

e.

Vagus nerve.

lO.

Superior intercostal.

/■

Recurrent Inryngea

part of the right subclavian extends obliquely upwards and
outwards, and at its termination, at the inner margin of the
scalenus anticus, it has reached a point above the level of
the clavicle. It is placed very deeply. /// front, it is
cpvercd liy the skin, superficial fascia, plalysnia, deep fascia,
and three muscular strata — viz. the clavicular origin of the
sterno-mastoid, the sterno-hyoid, and the sterno-thyroid.

232 HEAD AND NECK.

Three veins and some nerves are also placed in front of it.
Thus, it is crossed by the internal jugular and vertebral_
veins, as these proceed from above downwards, whilst the
interior jugular vein, as it passes outwards under cover of
the sterno-mastoid, is separated from it by the sterno-hyoid
and sterno-thyroid muscles. The nerves which cross it are
the vagus, with one or two cardiac branches as they run
towards the thorax, and a loop from the sympathetic. As_
the vagus nerve leaves the artery it gives off its recurrent
branch.

The first part of the subclavian artery presents most
important relations to the pleura. The cervical dome of
this membrane bulges upwards behind it so that the vessel
rests upon its anterior surface a short distance from its
summit. The sympathetic cord passes downwards behind
the artery, and the recurrent laryngeal branch of the vagus
nerve hooks round it, and is thus related to it both below
and behind.

Immediately below the first part of the subclavian, and
upon a more anterior plane, the right innominate vein is
formed by the union of the internal jugular and subclavian
trunks.

On the left side, the first part of the subclavian ascends
almost vertically from its origin from the aortic arch, and
reaching the root of the neck, turns abruptly outwards upon
the pleura to gain the inner margin of the scalenus anticus.
It is only with that portion of the vessel which lies in the
root of the neck that we are concerned at present. Its
relations are somewhat different from those on the right
side. The same fascial and muscular layers, and the same
nerves and veins, lie in front of it. Owing to its different
direction, however, the latter are placed more or less parallel
to it. Three additional relations are established — viz. (i)
the phrenic nerve,^ which descends in front of it; (2) the
left innominate vein, which crosses it; and (3) the thoracic
duct, which first passes upwards in relation to its inner side,
and then arches over it to reach the angle of junction between
the subclavian and internal jugular veins.

SIDE OF THE NECK. 233

The recurrent laryngeal nerve, which on this side hooks
round the arch of the aorta, lies to the inner side of the
subclavian artery.

Second part. — The second portion of the subclavian
artery forms the highest part or summit of the arch. The
average height to which the subclavian artery rises in the
neck varies from half an inch to an inch above the level of
the clavicle. In some cases, however, it may reach higher,
whilst in others it is placed at a lower level — indeed, it may
not extend above the clavicle at all.

In this part of its course the vessel is not so deeply
placed. In front it is covered by — (i) skin ; (2) superficial
fascia and platysma ; (3) deep fascia ; (4) clavicular head
oftlie sterno-mastoid ; (5) scalenus anticus. The phrenic
rferve on the right side is also an anterior relation. It
passes downwards in front of the vessel, but separated from
it by the inner margin of the scalenus anticus. Behind and
below., the vessel is in contact with the pleura. The sub-
clavian vein lies at a lower level and in front of the artery.
It is separated from the artery by the scalenus anticus,
which intervenes between the two vessels.

The third pari of the subclavian artery has already been
examined (p. 201).

Branches of the Subclavian Artery. — Four branches
spring from the subclavian trunk (Fig. 233). In this respect,
however, the vessel is subject to considerable variation.
They all take origin, as a general rule, close together ; three
proceeding from the first part of the artery close to the
scalenus anticus, and one from the second part. They are —

r I . Vertebral.

,, ,, I I Inferior thyroiil.

rrom the tu ■ 1 • t ■• n-

fi f j^ f \~- ^ nyroid axis. -, Transvorsalis ^oUi.

■^ " ' \ i Sujirascapular.

^^. Internal maniniar)-.

P , _ ( I Superior intercostal

, . - i^uperior intercostal. -j proj>er.

" ■ \ (.Deep cervical.

In a great number of cases, a branch of considerable size will be
observed springing from the third part of the subclavian artery. This,

234 HEAD AND NECK.

in all probability, will be the posterior scapular artery arising directly
from the subclavian. It is so common an occurrence that the dissector
must always be prepared to meet it.

Verte'bral Artery (arteria vertebralis). — This is the first
branch which is given off by the subclavian. It springs
from the posterior aspect of the trunk about a quarter of
an inch from the inner margin of the scalenus anticus on
the right side, and from the point where the vessel reaches
the root of the neck on the left side. Only a small portion
of its extent is seen in the present dissection. It proceeds
upwards in the interval between the longus colli and the
scalenus anticus muscles, and disappears by entering the
foramen transversarium of the transverse process of the sixth
.cervical vertebra. It is placed very deeply, and is covered
in front by its companion vein and the internal jugular
vein. Numerous large sympathetic twigs accompany it.

The vertebral artery on the left side is crossed by the
thoracic duct.

The vertebral vein will be noticed issuing from the
aperture in the transverse process of the sixth cervical
vertebra. It passes downwards in front of its companion
artery, and behind the internal jugular vein, to open into
the posterior aspect of the commencement of the correspond-
ing innominate vein. Near its termination it crosses the
subclavian artery. It receives the deep cervical and the
ajiterior vertebral veins.

Thyroid Axis (truncus thyreocervicalis). — This is a short
wide trunk, which arises from the front of the subclavian
artery, close to the inner margin of the scalenus anticus,
and under cover of the internal jugular vein. It lies be-
tween the phrenic and pneumogastric nerves, and almost
immediately breaks up into its three terminal branches —
viz. the inferior thyroid, the suprascapular, and the trans-
versalis colli.

The Inferior Thyroid Artery (arteria thyreoidea inferior)

takes a sinuous course to reach the thyroid body. At first,

it ascends for a short distance upon the vertebral artery,

^ \ and under cover of the internal jugular vein ; then it turns

SIDE OF THE NECK. 235

suddenly downwards and inwards, and passes behind the
sympathetic and the common carotid artery j lastly, it bends
upwards, and ends in branches at the base of the lateral
lobe_QjLtlie thyroid body.

The following branches will be noticed arising from the
inferior thyroid artery : —

1. Ascending cervical.

2. Inferior laryngeal.
^. Tracheal.

4. GEsophageal.

5. Thyroid.

6. Muscular.

The ascending cervical artery (arteria cervicalis ascendens)
is a small but very constant vessel, which runs upwards in
the interval between the scalenus anticus and rectus capitis
anticus niajor^ and dispenses branches to the muscles in
front of the vertebral column. Other twigs from the as-
cending cervical, termed spinal branches^ enter the spinal
canal upon the spinal nerves, and anastomose with branches
from the vertebral artery. The ultimate distribution of the
spinal branches has already been noticed (pp. 161 and 1 74).

The inferior laryngeal artery (arteria laryngea inferior)
is a small vessel which accompanies the recurrent laryngeal
nerve to the larynx. The tracheal (rami tracheales) and
oesophageal (rami cesophagei) branches in like manner supply
the trachea and gullet. They are of small size, andjinasto-
mose with the bronchial and oesophageal branches of the
thoracic aorta. The thyroid or terminal branches (rami
glandulares) are usually two in number. One ascends upon
the posterior aspect of the lateral lobe of the thyroid body,
whilst the other is given to its base or lower end. Ihey
inosculate with the corresponding vessels of the opposite
side, and also with the branches of the superior thyroid
artery. The muscular branches are a series of irregular
twigs given to the various muscles in the neighbourhood.

The inferior thyroid vein does not run in company with
the artery of the same name. It is a large vessel which
comes from the lateral lobe of the thyroid body, and
descends upon the trachea under cover of the sterno-
thyroid muscle. The veins of both sides enter the thorax,

236 HEAD AND NECK.

and unite to form a short common steixi, which opens^iato
the left innominate trunk. In many cases, however, the
right vein will be observed to open separately into the
angle of union between the two innominate veins. Both
veins receive, as they proceed downwards, tributaries from
larynx, trachea, and oesophagus.

The anterior vertebral vein accompanies the ascending
cervical artery, and opens into the vertebral vein.
/ Tlie Suprascapular and Transversalis Colli Arteries have
already been examined in the greater part of their course
(p. 140). After taking origin from the thyroid axis, they
both pass outwards upon the scalenus anticus muscle, and
under cover of the clavicular head of the sterno-mast^oTd.
The suprascapular (arteria transversa scapulae) crosses the
anterior scalene muscle close to its insertion, immediately""
above the subclavian vein ; the transversalis colli (arteria
transversa colli) is placed at a slightly higher level. Both
vessels cross in front of the phrenic nerve. ' ~

The suprascapular and transversalis colli veins have
already been seen joining the subclayian or the external
jugular vein.

The Internal Mammary Artery (arteria mammaria
interna) springs from the lower aspect of the subclavian
opposite the thyroid axis. It proceeds downwards upon the
anterior surface of the pleura and behind the inner end of
the clavicle, to reach the thora^ic^cavjtx- In the cervical
part of its course it will be observed to pass behind the
subclavian vein, and to be cros_sed frorn without inwards.jby
* the phrenic nerve. In the neck, the internal mammary
I artery is not accompanied by a companion vein.

Superior Intercostal Artery (truncus costocervicalis). —
This branch takes origin from the posterior aspect of the
second portion of the subclavian artery, close to the inner
border of the scalenus anticus. On the left side, however,
it, as a rule, proceeds from the first part of the parent
trunk. To bring it into view, the subclavian artery must
be dislodged from its position. It is a short trunk which
passes backwards and slightly upwards, and almost _im-

SIDE OF THE NEC A'. 237

mediately divides into the deep cervical artery and the
superior intercosfararlery J^roJ^er.

Tlic t/eep ce/vica/ a r/erj' (artcna. cervicalis profunda) passes
backwards, and disappears from view between the transverse
process of the seventh cervical vertebra and the neck of the
fust rib. It has been already noticed in the dissection of
ihe back of the neck (p. 151). V'^'^ '

The superior intercostal artery (arteria intercostalis
suprcma) turns downwards over the neck of the first rib,
close to the outer side of the sympathetic cord, and ends
in the thorax by giving branches to the upper two inter-
costal spaces. ' "■ * • <-♦-- .« ^-^-^ ^-" '^.»-' *^ *"^-

The deep cervical veifi is a large vessel. It joins the
vertebral vein.

The Subclavian Vein (vena subclavia) is the continuation
of the axillary vein into the root of the neck. It begins,
therefore, at the outer border of the first rib, and arches
inwards in front of the scalenus anticus muscle close to its
insertion. At the inner margin of this muscle it joins the
internal jugular to form the innominate vein. In con-
nection wi'th the subclavian vein, note: (i) that the arch
which it forms is not so pronounced asjiLthe case of the
corresponding artery j (2) that throughout its whole course
it lies at a lower level, and upon a plane anterior to the
artery; and (3) that it is separated from the artery by the
scalenus anticus and the phrenic nerve.

I'he tributaries of the subclavian vein are (i) thee.xternal
jugular vein, and (2) in some cases the anterior jugular
velrT.^ These join it at the outer margin of the scalenus
anticus muscle (Fig. 234).

Thoracic and Right Lymphatic Ducts. — The thoracic duct
(ductus thoracicus) is the vessel by means of which the
lymph and chyle, derived from by far the greater part of
the body, is poured into the venous system on the left side.
Its terminal or cervical portion is displayed in the present
dissection. I^i? a small delicate vessel, frequently mistaken
for a vein, which enters the root of the neck upon the left
side of the oesophagus. It is here, therefore, that it should

HEAD AND NECK.

Fig. 234.— Dissection of the neck. The sterno-mastoid and the inner half of the
clavicle have been removed. (Luschka.)

a. External juiTular vein.

b. Temporal vein.

c. Posterior auricular vein.

d. Anterior teraporo-maxillary vein.

e. Facial vein.

/. Common facial vein.
g. Transversalis colli vein.
Ii. Anterior jugular vein.

i. Communicating branch between anterior
jugular and facial veins.

k. The part of the anterior jugular which
turns horizontally oiitwards under cover
of the sterno-mastoid.

/. Transverse communication between the two
anterior jugular veins.
m. Deep cervical vein.

n. Mastoid emissary vein.

o. Internal jugular vein.

p. Superior thyroid vein.

q. Middle thyroid vein,

r. Spinal accessory nerve.

.f. Ansa hypoglossi.

SIDE OF THE NECK. 239

be sought. When it roaches the level of the seventh, or
perhaps the sixth cervical vertebra, it changes its course
and arches outwards and forwards, and then downwards
upon the apex of the pleura, to gain the outer margin of
tlie internal jugular vein at its angle of union with the sub-
clavian, and into this it opens. As the thoracic duct
courses outwards, it is placed at a higher level than the
subclavian artery, and passes behind the internal jugular
vein. Further, as it approaches the point at which it
ends it crosses the first part of the subclavian artery.

A valve composed of two segments guards its orifice
into the jugular vein. This allows its contents to flow
freely into the vein, but acts as a barrier to the passage of
venous blood into the duct.

The right lymphatic duct (ductus lymphaticus dexter) is
the corresponding vessel upon the right side. It is a very
insignificant duct, and draws its supply of lymph from a
much more restricted field. In length it rarely measures
more than half an inch. It will be foundNit^ the inner
margin of tlue scalenus anticus ojpcning into the angle of
union between the internal jugular and subclavian veins of
the right side. As in the case of the thoracic duct, its
orifice is guarded by a double valve.

Cervical Pleura. — The pleural sac of each side, with
the apex of the corresponding lung, projects upwards into
tlie root of the neck, and the dissector should now examine
the height to which it rises, and the connections "which it
establishes. Its height varies in different subjects. In
some cases it extends up for two inches above the sternal
end of the first rib ; in others for not more than one inch.
It forms a dome-like roof for each side of the thoracic
cavity, and is strengthened by a fascial expansion (frequently
termed Sibsofis fascia), which covers it completely, aod^is
attached on the one hand to the transverse process of the
seventh cervical vertebra and on the other to the inner
margin of the first rib. Observe, further, that the cervical
pleura is supported above by the scalene muscles, under
cover of which it ascejids into the neck, and that the sub-

240

HEAD AND NECK.

clavian artery arches outwards upon its anterior surface near
its apex.

Cervical Plexus (plexus cervicalis) (Fig. 235). — This

Fig. 235. — Diagram of the cervical plexus and the ansa
hypoglossi.

I, II, III, IV. — Anterior primary divisions of the upper four cervical nerves.

P. Phrenic.
C.C. Rami communicantes hypo-
glossi.
C.H. Communicating branch to hypo-
glossal.
H. Hypoglossal.
T.H. Thyro-hyoid nerve.
D.H. Descendens hypoglossi.
A.H. Ansa hypoglossi.

R. Branches to recti muscles.

G.A. Great auricular.

S.M. Branches to the sterno-mastoid.

S.O. Small occipital.

T.C. Superficial cervical.

L.A.S. Branches to levator anguli
scapulae.

D.T. Descending trunk.

C. Communicating to fifth cervical.

This diagram shows that the descendens hypoglossi, the branch
to the thyro-hyoid, and in all probability the branches to the genio-
hyoid, are composed of fibres given to the hypoglossal by the com-
municating twigs it receives from the first cervical nerve.

plexus is formed by the anterior primary divisions of the
upper four cervical nerves. These nerves are much smaller
than the lower cervical nerves which form the brachial

SIDE OF THE NECK.

241

plexus, and ihey have only a short course to run as in-
dependent trunks. With^ the exception of the first, each
divides into an ascending and a descending branch, and
ihese joining with each other, constitute the plexus, which,
tlierefore, consists of three loops. The descending branch
of the fourth nerve, which is very small, proceeds down-
wards to unite with the fifth nerve, and thus establish a
connection with the brachial plexus.

The cervical plexus thus formed has very definite rela-
tions. It lies under cover of the upper part of the sterno-
mastoid and in front of the scalenus medius and the levator
anguli scapulae muscles.

Its branches are very numerous, and may be classified in
the following manner : —

Superficial or
Cutaneous.

'Ascending.
Transverse.

^Descending.

/ .Small occipital.
\ Great auricular.

From 2nd.
'Vom 2nd iS; ud.

It

/ Muscular.

rFrom 3rd (.\; 4lh.

From 1st & 2nd.

From 2nd.

Deep.

.Superficial cervical
Supraclavicular.
Suprasternal.
.Supra-acromial.
('i. To rectus capitis'
anticus major.

2. To recUls capitis

anticus minor.

3. To rectus capitis

lateralis.

4. To slei-no-niastoid.

5. Ramus cervicalis

descendens (ram. ■ ,, , , ,

-lTom2ndiS; 3rd
comniunicantes 1 -^

hypoglossi). I

6. To levator anguli 1

scapula-. I ,. , ,. .

_ T, . , ,• , I'rom ;rd ov; 4ln

7. To scalenus medius. I -^

8. To trapezius. j

9. Phrenic to dia- \

phragm.
I. To hj-poglossal

'^1

'^Comiiuinicating.

t.jt;

To .sympalhelic.

j From 4tli \ 5lh.
From I si.

4, To spinal accessory. ■! o

J

/ From 1st, 2ncl,
\ 3rd, & 4lli-
From 2n(l, 3rd,

& 41I1.

vol. 11.^ — 10

242 HEAD AND NECK.

The superficial branches have already been examined, but
now that the plexus is fully dissected, the student should
again study their mode of origin.

Muscular Branches. — The atiterior recti muscles and the
rectus latej'alis receive twigs from the first loop of the plexus,
but as this is placed very high up in the neck, these branches
can only be satisfactorily displayed in the deep dissection
of the neck. The sterno-mastoid muscle draws one or more
twigs from the second cervical ^nerve, and by means of
these a communication is effected with the spinal accessory
nerve, which pierces, and at the same time supplies fila-,.
ments to the muscle. The levator anguli scapulce ohNd^j?,
receives two or three branches from the third and fourth
nerves, whilst the scalenus medius obtains its nerve-supply
from the same nerve-trunks before these have entered the
plexus. The branches to the trapezius come off in common
with the trunk which divides into the descending superficial
nerves, and are therefore derived from the third and fourth
nerves. Upon the under surface of the trapezius, these
branches unite with the spinal accessory, and form the
sub-trapezial plexus.

The ramus cervicalis descendens is formed by the union of
two long slender roots (rami communicantes hypoglossi)
which spring from the second and third nerves respectively.
It proceeds downwards and inwards under cover of the
sterno-mastoid, and either behind or in front of the internal
jugular vein, to join the ramus descendens hypoglossi and
form the ansa hypoglossi. In some cases the two roots 'of
the descendens cervicalis rem-ain separate throughout all
their course.

The phrenic nerve is the most important branch given off
by the cervical plexus. It springs from the fourth cervical
nerve, and as a rule obtains also a root from the fifth or the
third cervical nerve, or perhaps from both. If the root
from the fifth nerve fails, the phrenic will in all probability
be found to receive lower down a twig from the nerve_to
the subclavius. The course which the phrenic pursues in
the neck is so definite, that there should never be any

SIDE OF THE NECK. 243

ditticulty in recognising this nerve. It descends, inclining
at the same time inwards, in front of the scalenus anticus,
and leaves the neck to enter the thorax by passing under
cover of the subclavian vein, and crossing the internal
nianmiary artery from without inwards. As it proceeds
downwards on the scalenus anticus, it passes behind the
omo-hyoid, the transversalis colli artery, the suprascapular
artery, and on the left side the thoracic duct.

The phrenic nerve gives off no branches in the neck,
but before it enters the thorax it is usually joined by a
small sympathetic twig.

Communicating Branches. — (i) Ai the base of the skull,
the first loop of the cervical plexus is brought into close
connection, by means of connecting twigs, with the vagus
and hypoglossal nen'es. These cannot be displayed at
present, but will be examined in a subsequent dissection.
(2) Each of the four cervical nerves which form the plexus
is connected by , means of one or more communicating
filaments with the superior cervical ganglion of the sym-
pathetic. (3) Communications are effected indirectly in
two places by the second, third, and fourth nerves with the
spinal accessory, viz. in the substance of the sterno-mastoid
by the twig from the second nerve to this muscle, and
again on the under surface of the trapezius by the branches
which go to this muscle from the third and fourth nerves.

Common Carotid Artery (arteria carotis communis). —
The conmion carotid is the great artery of supply to the
head and the neck. Its origin is different on the two
sides of the body. On the right side, it springs with the
subclavian from the innominate artery behind the upper
part of the sterno-clavicular articulation ; on the left siile, it
arises within the thorax, from the aortic arch. In both
cases the common carotid ends opposite the fourth cer\-ical
vertebra, or at a level corresponding to the upper border of
the thyroid cartilage by dividing into the external and
internal carotid branches. The point at which this sub-
division takes place is subject to a considerable amount of
variation within certain limits, and it has been noticed that

244 HEAD AND NECK,

in short -necked individuals the common carotid artery
is relatively longer than in long -necked people. The
course which the common carotid arteries pursue in the
neck, and the relations which they exhibit, are so much
alike on the two sides that one description will suffice for
both.

The course of the common carotid is slightly oblique,
and may be marked on the surface by drawing a line from
the sterno-clavicular articulation to a point midway between
the lower jaw and the mastoid process. At the root of the
neck the two vessels are close together,^the trachea and
oesophagus alone intervening, but as they proceed upwards
they diverge slightly from each other, and where they end
they are separated by the entire width of the thyroid
cartilage and the pharynx.

Together with the internal jugular vein, the pneumo-
gastric nerve, and the descendens hypoglossi nerve, the
vessel is enveloped by a strongly-marked sheath derived
from the cervical fascia. This has been removed, but its
constitution, and the relation which its contents bear to
each other within it, have been already observed (pp. 194,

213)-

The_ common carotid artery is very differently circum-
stanced in regard to the surface in its lower and upper
parts. Opposite the cricoid cartilage it is crossed by the
anterior belly of the omo-hyoid, and below this it is placed
very deeply, being covered by the integument, platysma,
and deep fascia, and by three muscular strata, viz. the
sterno-mastoid, the sterno-hyoid, and the sterno-thyroid.

Above the level of the omo-hyoid muscle it lies, within
the limits of the carotid triangle, and is therefore placed
nearer the surface. Here it is merely overlapped by the
anterior margin of the sterno-mastoid muscle, and covered
by the platysma, fasciae, and integument. The vessels and
nerves in relation to its anterior surface are : —

1. Superior thyroid vein.

2. Middle thyroid vein.

3. Anterior jugular vein.

4. Sterno-mastoid artery.

5. Descendens hypoglossi nerve

and the ansa hypoglossi.

SIDE OF TTIR NECK.

245

The three veins cross the common carotid from within
outwards, and at different levels, viz. \.\\cs!//>enort/ijroid
riear its bifurcation, the middle thyroid bejow the level of
the cricoid cartilage, and Uie anterior Jugu/ar at the root of
the neck ; whilst, however, the thyroid veins are in iiii-
iiiediate relation to the vessel, the anterior jugular vein is
sejiarated from it by the sterno-hyoid and sterno-thyroid
muscles. The sferno-niastoid artery, a branch of tlic suiJcrior

THYRO.EPIOLOT.UC
GLOTTIS I STERNO.HYOID
ARr.EPIGLOT.FOlD\^J^==;. ^HVRO.HVOIO
COnNlCULA.l«BVKCIS,^ ^

SCAL.ANT

VERTEBRAL. A
LONG, COLLI

Fig. 236. — Transverse section tlirough the neck, just
below tlie upper border of the thyroid cartilage and the
bifurcation of tlie common carotid artery. The relations
of the common carotid at this level to the pharynx, to
surrounding nerves, muscles, etc. , are well seen.

thyroid, crosses the vessel obliquely as it lies within the
carotid triangle. Tht^ ramus descendens hypoglossi proceeds
downwards and inwards upon the vessel, and within its
sheath. The ansa hypoglossi is formed upon the anterior
aspect of the common carotid artery by the union of the
ramus descendens hypoglossi with the ramus descendens
cervicalis.

Behind^ the vessel is in apposition with the longus colli
and the scalenus anticus muscles. These intervene between
it and the transverse processes of the cervical vertebrx.
'i'he gangliated cord of the sympathetic, the recurrent

246

HEAD AND NECK.

laryngeal nerve, and the inferior thyroid artery are also
related to it posteriorly. The sympathetic cord descends
vertically in the substance of the carotid sheath, behind
the artery, and is interposed between the vessel and the
prevertebral muscles ; the recin-rejit laijfigeal nerve is carried
upwards and inwards behind the lower part of the vessel ;
the inferior thyroid artery crosses behind the carotid sheath
about the level of the sixth cervical vertebra.

To the outer side of the common carotid artery lie the
pneumogastric nerve and the internal jugular vein,^ whilst

sterno-
omo-hyoid. thyroid, sterno-hyold.

anterior jugular vein.

sup. thyr.
artery.

vertebral artery and longu
plexus of veins. colli.

re t ro-phary ngeal
space.

Fig. 237. — Transverse section through the neck at the level
of the cricoid cartilage.

internally., it is in contact with a succession of structures as
it proceeds upwards, viz. (i) the trachea and oesophagus,
with the recurrent laryngeal nerve in the groove between
them; (2) the lateral lobe of the thyroid body, which
overlaps the vessel; (3) the larynx and the pharynx.

1 On the left side, at the root of the neck, the internal jugular vein is
closely applied to the artery — so close is it, indeed, that it may be said to
overlap it. On the right side, however, the vein is separated from the
artery by a slight interval, through the middle of which the vagus nerve
passes down perpendicularly.

SIDE OF THE NECK. 247

As a general rule, the common carotid artery gives off
no collateral branches, and its calibre is of nearly equal
diameter throughout, except close to its bifurcation, where
a slight bulging or dilatation may usually be noticed.

Inter-carotic Body (Fig. 230, p. 214). — This is a little
oval reddish-brown body, placed upon the deep aspect of
the common carotid artery at the point where it bifurcates.
To expose it, therefore, the vessel must be twisted round
in such a manner that its posterior surface comes to look
forwards. It is closely connected with the sympathetic
filaments which twine around the carotid vessels, and for a
time was regarded as belonging to the sympathetic nervous
system. Itsstructure, however, shows it to be an arterial
gland similar in its nature to the minute coccygeal body
which rests upon the anterior aspect of the tip of the coccyx.
I'^ntering i^ are numerous minute arterial twigs, which take
origin from the termination of the common carotid and the
commencement of the external carotid. The function of
this remarkable little body is quite unknown. Most likely
it is a vestigial structure.

The External Carotid Artery (arteria carotis externa)
commences at the upper border of the thyroid cartilage,
and, taking an upward course, it ends in the substance of
the parotid gland, immediately behind the neck of the lower
jaw, by dividing into the superficial temporal and the internal
maxillary arteries. It is termed external^ not on account of
its position in relation to the internal carotid, but on
account of its being mainly distributed to parts on the
exterior of the skull. Indeed, at its^ origin its position in
relation to the internal carotid is the very reverse of that
which its name implies. It. lies in front of the internal
ca.rotid, and somewhat to its inner side. As it ascends,
however, it inclines slightly backwards, so that very shortly
it comes to lie directly over the internal carotid.

The external carotid artery may be divided very con-
veniently into three stages, corresponding to three marked
changes in the relations which it presents. The Jirst stage
is contained within the carotid triangle. It is therefore,

248

HEAD AND NECK.

comparatively speaking, superficial. Here it is overlapped
by the anterior border of the sterno-mastoid, covered by the
platysma, fasciae, and integument, and crossed by the
lingual and common facial veins as they run towards the
internal jugular vein. The second stage is more deeply
placed. It lies under cover^of the posterior belly of the

FACIAL A.
HYPOGLOSSAL N.

SUBMENTAL A,

HYOID BONE

HYOID BR.

SUP.LAR. A.
SUPR. THYR. A.
STERNO-HYOID M.
STERNO-MAST.A.

THYROID CART,

CRICOID CART.
COM OAR. A.

Fig. 238. — Diagram of the external carotid artery and
its branches.

digastric and the stylo-hyoid muscle, and is crossed by the
hypoglossal nerve. The third stage is in relation to the
parotid gland. Emerging from under cover of the digastric
and stylo-hyoid muscles, the artery ascends for a short
distance under cover of the lower part of the parotid gland,
and finally sinks into its substance. Whilst in the parotid
gland, the external carotid artery is crossed near its ter-
mination by the facial nerve, whilst the temporo-maxillary
vein passes downwards superficial to it.

SIDE OF THE NECK. 249

These relations cannot be seen at present, but they will
afterwards be exposed when the fitee is dissected. It should
be noted that while the artery is in tlie gland it lies much
nearer its deep than its superficial surface. Indeed, sections
til rough the parotid region of the frozen head show that
in reality only a very small part of the terminal portion
of the artery is enclosed within the gland. Below this
it merely lies in a groove on the deep surf^ice of the parotid
(Fig. 240, p. 262).

.AtitS-Conmiencement, the external carotid artery lies in
relation to the pharynx. Higher up it rests upon the stylo- /V^
pharyngeus muscle, the styloid process and the glosso-
pharyngeal nerve — three structures which intervene between
it and the internal carotid artery.

Branches of the External Carotid. — As the external
carotid ascends, it diminishes rapidly in calibre, owing to
the numerous large branches which it gives off.

It is customary to classify these, according to the direction
which they take, into the following groups : —

Superior tliyroid, . . \

Lingual, . . . | Directed forwards and

Facial, . . . . |" inwards.

Internal maxillary, . I

Occipital, . . . ^Directed backwards and

Posterior auricular, . | outwards.

Ascending pharyngeal, "^ Directed almost vertically

Superficial tenii)oral, . \ upwards.

But these are not the only branches which come off from
the external carotid. Small twigs are also given to the
parotid ghind, and to the jnasseter and internal pterygoid
muscles.

The Superior Thjnroid Artery (arteria thyreoidea superior)
arises within the carotid triangle, from the fore-part of the
external carotid close to its origin. From this it takes a
curved course downwards and forward.s, under cover of the
omo-hyoid, sterno-hyoid, and sterno-thyroid muscles, and
ends by breaking uj) into twigs, which enter the substance
of the thyroid body.

250 HEAD AND NECK.

The following branches proceed from it :-

1. Hyoid.

2. Superior laryngeal.

3. Sterno-mastoid.

4. Crico-thyroid.

5. Thyroid.

The hyoid (ramus hyoideus) is a minute twig, which
springs from the superior thyroid before it leaves the carotid
triangle, and runs transversely inwards under cover of the
thyro-hyoid muscle, and along the lower border of the hyoid
bone. It anastomoses with its fellow of the opposite side,
and with the hyoid branch of the lingual artery.

The superior laryngeal artery (arteria laryngea superior)
is a larger vessel. It springs from the superior thyroid as
it lies in the carotid triangle, and associating itself with
the internal laryngeal nerve, it enters the larynx by piercing
the thyro-hyoid membrane.

The sterno-mastoid artery (arteria sternocleidomastoidea)
is a small vessel which runs downwards and outwards across
the carotid sheath, to reach the deep surface of the sterno-
mastoid muscle, into which it sinks. It gives, in addition,
minute twigs to the depressor muscles of the larynx, and its
only claim to special description is the position it occupies
in relation to the common carotid artery.

The crico-thyroid artery (ramus cricothyreoideus) runs
inwards upon the crico-thyroid membrane, and anastomoses
with its fellow of the opposite side. It has already been
noticed in the dissection of the middle line of the neck
(p. 219).

The thyroid or termifial bra?iches (rami glandulares) of the
superior thyroid artery spring from the main trunk at the
apex of the lateral lobe of the thyroid body. Three main
branches may be recognised ; of these the largest is dis-
tributed on the posterior surface of the lateral lobe ; the
smallest ramifies on its outer surface ; whilst the third is
carried downwards upon the inner aspect of the lateral lobe,
and then along the upper border of the isthmus towards its
fellow of the opposite side. The anastomosis between the
thyroid arteries of the two sides is by no means free.

SIDE OF THE NEC A'. 251

The superior thyroid vein emerges from the upper part
of the thyroid body. It receives tributaries, which, in a
great measure, correspond with the branches of the artery,
and crosses the upper part of the common carotid to join
the internal jugular vein.

Lingual Artery (arteria lingualis). — Only a small portion
of this artery is seen in the present dissection. It springs
from the external carotid, a short distance above the superior
thyroid. In the first instance, it takes an upward course,
but very soon it changes its direction, and bends suddenly
downwards to reach the upper border of the hyoid bone.
Here it disappears from view by passing forwards under
cover of the hyoglossus muscle, and it will subsequently be
traced to its ultijnate distribution in the dissection of the
submaxillary region. Note in the meantime, however, that
the part under observation lies in the carotid triangle, and
that the loop which it forms is crossed by the hypoglossal
nerve. One small branch, termed the hyoid artc/y, springs
from this part of the vessel.

The hyoid branch (ramus hyoideus) arises from the lingual,
close to the posterior margin of the hyoglossus muscle, and
runs inwards along the upper margin of the hyoid bone to
anastomose with the corresponding vessel of the opposite
side, and also with the hyoid branch of the superior thyroid.

The Facial Artery (arteria maxillaris externa) can be
studied, at the present stage of the dissection, from its
origin up to the point where it mounts upon the base of
the mandible to reach the face. This is termed the cervical
part of the facial artery. It springs from the fore-part of
the external carotid, immediately above the lingual, and
then proceeds upwards and forwards. Finally, it enters the
region of the face at the anterior border of the masseter
muscle by passing over the base of the mandible. In its
course through the neck it presents stages very similar to
those already noticed in connection with the external carotid.
Thus it first lies in the carotid triangle, then it disappears
under cover of the posterior belly of the digastric, the stylo-
hyoid muscle and the hypoglossal nerve ; and finally it is

■K

252 HEAD AND NECK. ^

enclosed within the substance of the submaxillary gland.
With regard to this latter part of the artery, it is necessary
that the dissector should note: (i) that the vessel can be
disengaged from the submaxillary gland by dissection with-
out lacerating the gland structure ; it is placed, as it were,
in a deep furrow in the gland substance; (2) that in this
part of its course it is almost horizontal, and parallel with
the lower margin of the mandible; (3) that on emerging
from the gland it turns abruptly upwards to reach the face ;
and (4) that the facial vein passes backwards and down-
wards superficial to the submaxillary gland.

Four named branches spring from the facial artery in the
cervical part of its course : —

1. The inferior palatine. | i. vThe submaxillary.

2. The tonsillitic. | '2. The submental.

The inferior palatine artery (arteria palatina ascendens)
is given off for the supply of the soft palate, but it also gives
branches to the tonsil and Eustachian tube. Itjiscends
between the stylophaiyngeus and styloglossus muscles.
The tonsillitic artery (ramus tonsillaris) goes to the tonsil,
and at present is seen disappearing between the internal
pterygoid and styloglossus muscles. Both of these vessels
will be traced to their destination in the deep dissection of
the neck, and' in the dissection of the pharynx.

The submaxillary branches are given to the gland during
the sojourn of the facial artery in its midst.

The submental artery (arteria submentalis) is a branch
of some size. It springs from the facial, close to the
base of the mandible, and then runs forwards upon the
mylo-hyoid muscle towards the chin. Near the symphysis
it changes its direction, and is carried upwards over
the base of the lower jaw, to end 'in branches for the
muscles and integument of the chin and lower lip. In
the submaxillary region it gives numerous twigs to the
surrounding muscles, and anastomoses with the sublingual
artery by branches which pierce the mylo-hyoid muscle.
In the face it anastomoses with the inferior labial branch

SIDE OF THE NECK. 253

(5-

of the facial and the mental branch of the inferior
dental.

Facial Vein (\ena facialis anterior). — The cervical portion
of_the facial vein will be noticed passing backwards and
downwards, superficialto the submaxillary gland and facial
artery. After picking%p tributaries corresponding to the
branches of the similar part of the artery, it joins the
anterior division of the temporo-maxillary vein. The short
trunk thus formed is termed the common facial vein, and it
pours its blood into the internal jugular at the level of the
hyoid bone.

The Internal Maxillary Artery(arteria maxillaris interna)
will be displayed in the dissection of the pterygo-maxillary
space.

Occipital Artery (arteria occipitalis). — The occipital
artery springs from the posterior aspect of the external
carotid at the same level as the facial. It takes the lower
border of the posterior belly of the digastric muscle as its
guide, and\runs upwards and backwards to reach the
interval bet\vbcn the mastoid process and the transverse
process of the atlas. From this onwards it has been studied
in the dissection of the scalp and the back of the neck (pp.
109, 138, and 147). The first part of the vessel crosses
the internal carotid artery, the vagus nerve, the spinal
accessory nerve, and the internal jugular vein. The hypo-
glossal nerve hooks round it, and it is overlapped by the
lower border of the posterior Ifclly of the digastric muscle.

The only branches which spring from this portion of the
occipital are: — (i) muscular twigs; and (2) a meningeal
branch.

'i'he muscular twigs (rami musculares) are given to the
neighbouring muscles, and one of them, larger than the
others and very constant, is termed the sterno-mastoid branch,
because it associates itself with the spinal accessory nerve,
and sinks with it into the substance of the sterno-mastoid
muscle.

The menini:;cal branch (ramus nieningeus) associates itself
with the internal jugular vein, and can be followed upwards

254 HEAD AND NECK.

upon it to the jugular foramen, through which it passes into
the cranium.

The Posterior Auricular Artery (arteria auricularis
posterior) will be found above the level of the posterior
belly of the digastric, and, like the occipital, it takes origin
from the hinder aspect of the external carotid artery. In
the first part of its course it is placed deeply, and runs
upwards and backwards upon the styloid process of the
temporal bone to reach the interval between the mastoid
process and the back of the auricle. Here it joins the
posterior auricular nerve, and its further course has been
studied in the dissection of the scalp (p. 109). Before
gaining this point it lies under cover of the lower portion
of the parotid gland.

This portion of the posterior auricular artery gives off —
(i) muscular twigs; (2) a few branches to the parotid
gland ; and (3) the stylo-mast oid artery.

The stylo-niastoid^ artery (arteria stylomastoidea) is a
slender vessel which ^nters the stylo-mastoid foramen upon
the facial nerve. In the interior of the temporal bone it
has an extensive distribution. It supplies twigs to the
mastoid cells and to the tympanum, and is carried onwards
in the aqueduct of Fallopius to anastomose with the
petrosal branch of the middle meningeal.

The Ascending Pharyngeal Arteiy (arteria pharyngea
ascendens) is the smallest branch of the external carotid.
It takes origin a short distance from the commencement of
the parent trunk, and will be recognised by its proceeding
vertically upwards between the internal carotid artery and
the pharynx. It will be subsequently traced in the deep
dissection of the neck.

The Superficial Temporal Artery (arteria temporalis
superficialis) cannot be displayed at present. In the dis-
section of the face the student will have an opportunity of
studying it.

The Thyroid Body (glandula thyreoidea) may now be
examined. It is a highly vascular solid body, which clasps
the upper part of the trachea, and extends upwards for

SIDE OF THE NECK. 255

some distance upon each side of the larynx. In size it
varies greatly in difTerent individuals, and in females and
children it is always relatively larger than in adult males. It
consists of three well-marked subdivisions, viz. two lateral
lobes joined across the middle line by the isthmus. Each
lateral lobe is somewhat conical in form, its base extending
downwards as far as the fifth or the sixth tracheal ring,
whilst its apex rests upon the side of the thyroid cartilage.
Its superficial surface is full and rounded, and is clothed by
the pre -tracheal layer of cervical fascia, from which it
derives a sheath, and also by the sterno-thyroid, sterno-
hyoidj and omo-hyoid muscles. It is further overlapped
by the sterno-mastoid muscle (Fig. 237, p. 246). lis deep
surface is adapted to the parts upon which it lies, viz. to
the side of the trachea, the cricoid cartilage, and the thyroid
cartilage ; whilst its posteiior border extends backwards so
as to touch the oesophagus and pharynx, and overlap the
common carotid artery.

The isthmus of the thyroid body has already been
observed in the dissection of the middle line of the neck.
It_is a narrow band of varying width which lies in front of
the second, third, and fourth rings of the trachea, and
unites the bases or lower ends of the two lateral lobes:

A still further lobe is frequently found in connection
with the thyroid body. This is the pyramidal or the
middle lobe. When present it assumes the form of an
elongated slender process which springs from the isthmus
on one or other side of the mesial plane (more usually on
the left side), and extends upwards towards the hyoid bone.
To this it may be connected by fibrous tissue, or perhaps by a
narrow slip composed of muscular fibres, which receives the
name of levator glanduhe thyroideic. In some cases this
little muscle has an attachment to the thyroid body in-
dependently of the pyramidal process. The thyroid body
is firmly connected to the parts upon which it lies, and
therefore follows the larynx in all its movements.

The dissector will not fail to be struck with the i;real vascularity of
the thyroid body. Four large arteries, and occasionally a fifth smaller

256 HEAD AND NECK.

vessel, convey blood to its substance. The two superior thyroid
branches of the external carotid arteries divide at the apex of each
lateral lobe into three branches for its supply ; the two inferior thyroid
branches of the subclavian arteries distribute their terminal branches to
the basal portion and deep surface of each lateral lobe. The occasional
artery is the thyroidea i?na, a branch of the innominate (more rarely of
the common carotid or the aortic arch), which ascends upon the anterior
aspect of the trachea to reach the isthmus of the thyroid body. These
thyroid arteries anastomose with each other.

The veins which drain the blood away from the thyroid body are still
more numerous. They arise in part by tributaries which spring from a
venous network on the anterior face of the structure, but chiefly by
branches which emerge from its substance. They are three in number
on each side — viz. the superior thyroid, the middle thyroid, and the
inferior thyroid. The superior and middle thyroid veins cross the
common carotid artery and join the internal jugular ; the inferior
thyj-oid descends in front of the trachea. At the root of the neck it
usually joins its fellow of the opposite side to form a common stem
which opens into the left innominate.

The Trachea and the (Esophagus in the cervical portion
of their course may now be studied. Both begin at the
level of the cricoid cartilage, in front of the sixth cervical
vertebra. From this point they extend downwards in front
of the vertebral column to the thoracic cavity.

The trachea^ or ivindpipe, is a wide tube which is kept
constantly patent by the cartilaginous rings embedded in
its walls. These rings do not form complete circles ;
posteriorly they are deficient, and in consequence the
trachea is flattened behind. Above it is continuous with
the larynx, and throughout its whole course it is placed in
the mesial plane of the body. The anterior relations of the
trachea have already been fully discussed in connection
with the description of the parts occupying the middle line
of the neck (p. 220). Posteriorly^ it rests upon the„ gullet.
Upon either side is the common carotid artery ; whilst
closely applied to it in its upper part is the lateral lobe of
the thyroid body. The recurrent laryngeal nerve ascends
on each side in the angle between the trachea and oeso-
phagus.

The cesophagus or gullet is a narrow tube with thick
muscular walls, which extends from the pharynx to the

DISSECTION OF THE FACE. 257

stomach. In the cervical part of its course it lies between
the trachea and the prevertebral muscles, and as it descends
it inclines slightly to the left, so that it comes more closely
into relation with the lateral lobe of the thyroid l)ody and
the carotid sheath upon this side than with the same
structures on the opposite side.

DISSECTION OF THE FACE.

The deep parts of the neck cannot be displayed satis-
factorily until the pterygo - maxillary and submaxillary
regions have been opened up. It is necessary, therefore,
at this stage to leave the neck and proceed with the
dissection of the Hice.

Surface Anatomy of the Ocular Appendages. — Before
the skin is reflected from the face, the external anatomy of
the various appendages of the eye should be studied.
Under this head we examine : —

1. The eyebrows.

2. The eyelids.

3. The conjunctiva.

The eyebrows are two curved tegumentary projections
l)laced over the orbital arch of the frontal bone, so as to
intervene between the forehead above and the ocular
regions below. The short stiff hairs which spring from
these have an outward inclination. Whilst this is the
general arrangement, however, it will be seen that the
lower hairs at the same time incline upwards and the upper
hairs incline downwards.

The eyelids (palpebral) are two semilunar curtains pro-
vided for the protection of each eyeball. The upper lid
is the longer and much the more movable of the two.
When the eye is open the margins of the two lids are slightly
concave and the interval between them is elliptical in out-
line. This interval is termed the pn/l^elmTl^fissiin' (rima
palpebrarum). When the eye is closed and the margins of
VOL. 11. — 17

258 HEAD AND NECK.

the lids are in apposition with each other, the palpebral
fissure is reduced to a nearly horizontal line. Owing to
the greater length and freer mobility of the upper lid, the
fissure in this condition is placed below the level of the
cornea.

At the extremities of the palpebral fissure the eyelids
meet and form the palpebral commissures or canthi., and at
the inner canthus the fissure expands into a small triangular
space called the lams lachrymalis. If the dissector now
examine the free margins of the lids he will observe that to
the outer side of the lacus lachrymalis they are flat, and that
in each case the eyelashes project from the anterior border,
whilst the Meibomian follicles open along the posterior border,
— a distinct interval intervening between the cilia and the
gland-mouths. The small portion of the margin of each
eyelid, on the other hand, which bounds the lacus lachry-
malis is more horizontal in direction, somewhat rounded
and destitute both of eyelashes and Meibomian follicles.
At the very point where the eyelashes in each eyelid cease,
and the palpebral margin becomes rounded, a minute
eminence with a central perforation will be seen. The
eminence is the papilla lachrymalis^ whilst the perforation,
called tho. pimchmi lachry?7iale, is the mouth of the lachrymal
canal, the duct which conveys away the tears. Endeavour
to pass a bristle into each of the orifices. The upper canal
at first for a short distance ascends, whilst the lower one
descends, and then both run inwards to the lachrymal sac.

The conjunctiva is the membrane which lines the deep
surface of both the lids, and is reflected from them on to
the anterior aspect of the eyeball. At the margins of the
lids it is continuous with the skin, whilst through the
puncta lachrymalia and the lachrymal canals it becomes
continuous with the lining membrane of the lachrymal sac.
The line of reflection of the conjunctiva from the lids on to
the eyeball is termed the fornix conjunctivce. Owing to the
greater depth of the upper lid the conjunctival recess
between the upper lid and the eyeball is of greater extent
than that in connection with the lower hd. The connec-

DISSECTION OF THE FACE. 259

tion between the conjunctiva on the one hand, and the
eyelids and sclerotic coat of the eyeball on the other, is of
a loose character. Over the cornea, however, the mem-
brane becomes thinned down to a mere e[)ithelial covering,
which is closely adherent.

In connection with the conjunctiva the pliai semilunaris
and the carimcula lachrymalis must be examined. The
caruncula is the reddish fleshy -looking elevation which
occupies the centre of the lacus lachrymalis at the inner
canthus. From its surface a few minute hairs project.
The plica semilunaris is of interest because in the human
eye it is the rudimentary representative of the membrana
nictitans, or third eyelid, found in many animals. It is a
small vertical fold of conjunctiva, which is placed immediately
to the outer side of the caruncula and slightly overlaps at
this point the eyeball.

Dissection. — Tlie disscclion of the face is both difficult and tedious.
The ramificatiSns of the nerves are so intricate, and the fibres of the
facial muscles are so pale, and so closely surrounded by the soft sub-
cutaneous fat of the region, that great care and patience are required
on the part of the student to obtain a proper display of the various
structures. In cases where the dissection is undertaken for the first
time, it may be well to devote particular attention to the nerves and
muscles on the one side, and to the vessels and muscles on the opposite
side. At the same time it must be clearly understood that a good
dissector should be able to make a complete dissection upon both sides.

It will facilitate the dissection if the student introduce under the
eyelids, cheeks, and lips a small quantity of cotton-wadding or tow
soaked in spirit. The margins of the lips may then be stitched together.
In doing this it is necessary to employ a fine needle. Only one incision
is required for the reflection of the skin — viz. a vertical cut carried
upwards immediately in front of the ear until it meets the coronal
incision which was made in reflecting the integument from the scalp.
The skin may then be thrown forwards as far as the middle line of the
face and removed entirely.

In raising the skin the dissector must proceed with caution. Care-
fully preserve the fibres of the platysma, as they pass upwards upon the
lower jaw to blend with the fascia, to find insertion into the bone and
mix with the fibres of certain of the facial muscles (p. 1S7). The little
risoriiis muscle as it passes forwards from the masseteric region to the
angle of the mouth is apt to be injured, and must therefore be remem-
bered. In the case of the eyelids the skin is thin and is separated from

26o HEAD AND NECK.

the subjacent muscular fibres by a small amount of areolar tissue devoid
of fat. Some care therefore is required on the part of the dissector to
remove it successfully. Over the ala of the nose and the chin, the
integument is difficult to raise on account of its density and also from
its close connection with subjacent structures.

When the skin is completely reflected, and the attachments of the
platysma satisfactorily demonstrated, the latter may be turned up so as
to expose the facial artery passing upwards upon the jaw.

The Facial Brancli of the Great Auricular Nerve should
at the same time be traced forwards on the cheek. Several
small filaments from this will be seen to penetrate the
parotid gland, for the purpose of joining the facial nerve.
Others proceed forwards, and supply the skin over the
parotid, masseteric, and buccal regions.

Dissection. — The parotid gland should now be defined. In doing
this the greatest care must be taken not to injure the branches of the facial
nerve and the transverse facial artery, as they emerge from its substance,
along its upper and anterior borders. The duct also, which appears at
its anterior border, must be followed forwards upon the masseter muscle.
When the superficial relations of the parotid have been examined, the
gland-substance must be removed piecemeal, so as to bring into view
the various structures with which its deep surface is in contact, and at
the same time expose the blood-vessel and nerves which traverse it.
This can best be effected by tracing into it the branches of the facial
nerve, and the trunk of the transverse facial artery. Care must be taken
not to injure the auriculo-temporal nerve, which ascends under cover of
the upper part of its posterior border. The communicating twigs from
the auriculo-temporal and great auricular nerves to the facial nerve
must be preserved. By this dissection the termination of the external
carotid artery and the temporo-maxillary vein will be displayed.

The Parotid Gland (glandula parotis) is the largest of
the salivary glands. It is lodged in the niche between the
lower jaw and the ear, and being adapted to this recess, it
presents a very irregular figure. Above., it is limited by the
zygoma. Below., its lower border is in apposition with the
posterior belly of the digastric muscle, and is separated
from the submaxillary gland by that partition of the deep
cervical fascia which the student has already studied under
the name of the stylo-maxillary ligament. Behind, it abuts
against the auditory meatus, the mastoid process, and the
sterno-mastoid muscle. In front it will be seen to overlap

nissEcrioN of the i-ack.

261

the [)usicrior border of the niassetcr, and extend forwards
ii[)on it for some distance (Fig. 239). It is from the thin
anterior margin towards its u|)i)er part that the duct of the
gland emerges, and freciuently a small detached lobule of
gland substance will be observed lying ui)on the masseter in
relation to the upper aspect of the duct (Fig. 239). This
is termed \hs._Mciii^parotidis~ The superficial or external
surface of the parotid is slightly convex, and is covered by

Stenson's duct.

plalysma

Icrior belly of iligaslric.

Fig. 239. (From Gegcnbaur.)

the dense parotid fiiscia which the dissector has already
observed to be a prolongation upwards into the face of a
portion of the deep cervical fascia (p. 192). In relation to
this surface, and under cover of the fascia, there are usually
one or two small lymphatic glands.

The deep surface of the gland is in relation to many
important structures, and is moulded upon the various
parts with which it is in contact.

It rests upon the styloid process and the muscles which

262

HEAD AND NECK.

proceed from it, and is closely related to the internal jugular
vein and the vagus, spinal accessory and hypoglossal nerves.
A portion of the gland substance (sometimes called the
glenoid lobe) occupies the posterior or tympanic part of the
glenoid fossa, whilst in front, another portion extends for-

lev. lab. sup.

\ ^ antrum of Highmore.
zygomaticus major,
buccinator muscle.

mandibular vessels and
nerve.

pharynx,
stylo-pharyngeus.

stylo-glossus.
int. carotid.

sympathetic.

Fig. 240. — Transverse section through the head at the
level of the hard palate. It shows very well the relations
of the parotid gland, etc.

1. Temporo-maxillary vein.

2. Sterno-mastoid muscle.

3. Digastric (posterior belly).

4. Spinal accessory nerve.

5. Internal jugular vein.

6. Stylo-hyoid.

7. Glosso-pharyngeal nerve.

8. Vagus and hypoglossal nerves.

wards for a short distance under cover of the ramus of the
mandible and the internal pterygoid muscle.

T\it fascial connections of the parotid gland deserve some
attention. The recess in which it lies is Hned by a well-

DISSECTION OF THE FACE. 263

iiKukcd fascia, which separates it from subjacent structures,
ami we have noted the parotid fascia upon its superficial
aspect. The entire gland is enveloped, therefore, in a
strong envelope, which sends numerous strong septa into
its sut)stance, and accentuates its lobular appearance. The
parotid fascia presents very important connections. Above,
it is attached to the zygoma; behind^, jt is attached to the
meatus auditorius, and below that, it splits to enclose the
sterno-mastoid ; in front, it is continuous with the fascia
over the masseter, whilst below, it is continuous with the
deep cervical fascia.

Parotid Duct (ductus parotideus). — This is also called
Stciiso>i's duct. It issues from the anterior border of the
gland, and proceeds forwards upon the masseter muscle
about half an inch below the zygoma. In relation to it
above will be seen the socia parotidis and the transverse
facial artery, whilst accompanying it below, are some
branches of the facial nerve. At the anterior border of
the masseter, it dips inwards, and, piercing the buccinator,
runs forwards for a short distance between this muscle and
the mucous membrane. Finally, at a point corresponding
with the second molar tooth of the upper jaw, it opens
into the mouth by a minute orifice placed on the summit
of a small papilla. In length, the duct measures about
two inches, and its course may be marked out on the
surface of the cheek by drawing a line from the lower part
of the external auditory meatus of the auricle to a point
mid-way between the nostrils and the margin of the red
part of the lip. The dissector should now open the duct,
and pass a fine probe through it into the mouth. The
calibre of the tube will then be observed to be greatly
reduced at its opening upon the inner aspect of the cheek.
Evert the cheek, and examine this orifice.

Vessels and Nerves which traverse the Parotid. — By
the removal of the gland, the vessels and ncr\es which
traverse the gland are brought into view. These are : —

I. External carotid artery, ( Supcrlicial temporal.
~clivulirig Into . . \ Internal maxillary;

264 HEAD AND NECK.

2. Transverse facial artery.

3. Temporo-maxillary vein.

4. Facial nerve, or the seventh cranial nerve.

5. Communicating twigs from the great auricular and auriculo-
temporal nerves to the facial nerve.

The external carotid (arteria carotis externa), as it ascends
in the substance of the gland, lies nearer its deep than its
superficial surface. In fact, in the lower part of its parotid
sj:age the artery is not placed within the gland, but merely
in_a groove on its deep surface, a.nd slightly under shelter
of the posterior border of the ascending ramus of the
lower jaw. Note that the facial nerve crosses superficial
to it, and that opposite the neck of the lower jaw the vessel
divides into the superficial temporal and the internal
maxillary arteries.

The tejnpow-maxiUary vein is formed by the union of
the superficial temporal and internal maxillary veins behind
the neck of the lower jaw. It descends in the substance
of the parotid superficial to Jhe external carotid artery.
At the lower border of the gland it divides into an anterior
and posterior trunk. The former joins the facial vein,
whilst the latter unites with the posterior auricular vein to
form the external jugular.

The ititernal maxillary artery at once passes forwards
under cover of the neck of the jaw and disappears from
view. The superficial temporal artery may now be fully
followed out.

The Superficial Temporal Artery (arteria temporalis
superficialis) appears to be the direct continuation upwards
of the external carotid artery. At first in the substance of
the parotid, it soon emerges from this, and crossing the
root of the zygoma, ascends upon the temporal fascia for a
variable distance, and then divides into its two terminal
branches, the anterior (ramus frontalis) and posterior super-
ficial temporal (ramus parietalis) arteries. These are de-
scribed on p. 108. The superficial temporal artery is closely
accompanied by the auriculo-temporal nerve and the super-
ficial temporal vein.

DISSECTION 01' I HE FACE. 265

In addition to its terminal branches it gives off —

1. I'arotiil twills.

2. AiUerior auricular branches.

3. The transverse facial.

4. The miildle temporal.

5. The orbital.

The anterior auricular branches (rami auriculares ante-
riores) supply the anterior aspect of the external auricle
and anastomose with the posterior auricular artery. "^o ^

The transverse facial (arteria transversa faciei) is given
off in the substance of the parotid. It runs transversely
forwards, and, emerging from under cover of the anterior
border of the gland, proceeds onwards across the masseter
to end in twigs which anastomose with branches of the
facial, buccal and infra-orbital arteries. Whilst it lies on
the masseter muscle it is in relation to the upper border
of the parotid duct.

The middle temporal (arteria temporalis media) arises
immediately above the zygoma, and it pierces the temporal
fascia to reach the temporal muscle, and communicate
with the deep temporal branches of the internal maxillary
artery.

The orbital artery (arteria zygomatico-orbitalis) is an
inconstant branch which runs forwards above the zygoma
to supply the outer part of the orbicularis palpebrarum,
and the skin in this neighbourhood.

Muscles of the Face. — The muscles of the face are
arranged in groups around the different facial apertures.
There is thus a palpebral and superciliary group in relation
to each orbital opening ; an oral group around the mouth ;
and a nasal grou/> in connection with the nose. Each of
these groujis may be examined in turn. It is convenient
to l)egin with the palpebral and superciliary muscles. These
are three in number : —

1. Orbicularis iialjiebraruni.

2. Tv;nsor larsi (Horner's muscle).

3. Corrugator supercilii.

The ui)per eyelid has a special elevator, termed the lei<ator
palpebnc superioris, but this muscle is contained within the

266 HEAD AND NECK.

orbital cavity, and does not come under the notice of the dis-
sector at the present stage. The examination of the tensor
tarsi must also be deferred until the eyelids are dissected.

Internal Tarsal Ligament. — If the eyelids be drawn
outwards, a prominent cord-like ligament becomes apparent
on the inner side of the inner canthus. This extends out-
wards from the nasal process of the superior maxillary bone
to reach the eyelids, and is termed the internal tarsal
ligament. It will be afterwards more fully examined, but it
is necessary to notice it at present, seeing that it is closely
connected with the origin of the orbicularis palpebxarum.

The Orbicularis Palpebrarum (orbicularis oculi) is the
sphincter muscle of the palpebral fissure. It is a thin
sheet of muscular fibres, which occupies a very consider-
able area of the face. It is customary to regard it as
being composed of two parts, a palpebral and an orbital.
"DiQ. palpebral portion is the part which lies upon the eyelids.
It is thin and pale, and its. fibres arise from the margins
of the internal tarsal ligament. From these they sweep
outwards upon the two lids, describing a series of gentle
curves, and at the outer canthus they obtain attachment
to_ the external tarsal ligament. They form a continuous
layer of uniform thickness in both eyelids, except at their
free margins. Here, close to the bases of the eyelashes,
there is a more pronounced fasciculus, which is termed the
ciliary bundle.

The orbital portion is placed upon the margin of the
orbital opening; but it is not confined to this. It extends
for some distance beyond it, upwards on the forehead,
downwards on the cheek, and outwards so as to encroach
upon the temporal region. The.iasciculi which compose
this part of the muscle are of a darker and coarser type.
They all arise internally and sweep outwards around the
orbital margin in the form of a series of concentric loops.
The origin is a triple one — viz. (i) from the inner part
of the internal tarsal ligament, (2) from the internal angular
process of the frontal bone, and (3) from the ascending
process of the superior maxillary bone.

DISSECTION OF THE FACE. 267

Above and to the inner side, the fasciculi of the url^i-
cularis muscle are closely connected, and to a certain
extent interlaced with the fasciculi of the frontal i)art of
the occipito-frontalis, the corrugator sui)ercilii and the
pyraniidalis nasi, whilst from its lower margin a few
delicate fleshy bands are carried downwards through the
soft fat to gain insertion into the skin of the cheek.

Corrugator Supercilii. — This is a small but very distinct
band of dark-coloured muscular fibres which can be ex-
posed by raising the upper and inner part of the orbicularis,
with the frontalis muscle which is connected with it, from
the superciliary ridge. The corrugator supercilii will then
be seen arising from the inner extremity of this ridge. Its
fibres pass upwards and outwards, and the greater propor-
tion of them pass through the fasciculi of the orbicularis
and frontal belly of the occipito-frontalis to gain a direct
insertion into the skin of the eyebrow; one of its muscular
bundles, however, joins the orbicularis, whilst a few others
blend with the frontalis.

The Oral G-roup of Muscles. — The muscles of the lips
and mouth which are included in this group are the
following : —

1. Orbicularis oris.

,, . f major.

2. /yiromaticus -{ .-'

'° (^ minor.

3. Risorius.

4. Levator luhii supcrioris

aloeque nasi.

5. Levator labii supcrioris.

6. Levator anguli oris.

7. Depressor anguli oris.

S. Depressor labii inferioris.

9. Levator menti.

10. Buccinator.

The orbicularis oris is a sphincter muscle which sur-
rounds the oral aperture. The other muscles of this
group, with the exception of the levator menti, converge
towards it. From the nasal process of the superior maxilla,
and from the lower margin of the orbital opening, the
labial slip of the levator labii superioris ala:que nasi, and
the levator labii superioris descend into the upper lip.
Converging upon the angle of the mouth, the dissector
will have little difficulty in recognising the zygomaticus
major, the risorius, and the depressor anguli oris ; whilst

f^

268 HEAD AND NECK.

placed upon a deeper plane and extending towards the
same point are the levator anguli oris and the buccinator.
Entering the lower lip from below is the depressor labii
inferioris. The play of the lips is produced by the action
of these muscles antagonised to a certain extent by the
orbicularis. The levator menti has little connection with
the lips. It only acts indirectly on the lower lip, as will
be seen when its attachments are studied.

Dissection. — It is in dissecting these muscles that the chief difficulty
will be encountered in preserving the various nerves of the face. Several
large branches of the facial nerve will be found passing forwards under
cover of the zygomatic muscles to reach the under surface of the levator
labii superioris, where they form a complicated plexus with the infra-
orbital nerve. Other branches proceed forwards upon the buccinator
muscle, and enter into communication in front of the masseter with
the long buccal nerve. The mandibular division of the facial nerve
will also be noticed on the surface of the lower jaw. Its branches
disappear under cover of the depressor anguli oris. All these nerves
must be carefully followed out as the muscles are being exposed and
cleaned.

Zygomaticus Major, Risorius, and Depressor Anguli
Oris. — These three muscles may be grouped together,
seeing that they lie 'vs\ the same plane and run towards
the angle of the mouth. The platysma also occupies the
same plane, and many of its fibres blend with the depressor
anguli oris, whilst others ar6 carried forwards into the
risorius.

The zygomaticus major is a long fleshy band which
springs from the malar bone immediately in front of the
zygomatic suture. From this it proceeds downwards and
forwards, and at the angle of the mouth some of its fibres
are inserted into the skin, whilst others blend with the
orbicularis oris and with the depressor anguli oris.

■The risorius is sometimes regarded as a continuation
forwards on the face of the posterior fibres of the platysma ;
more frequently it takes independent origin from the fascia
covering the masseter, although some of its fibres come
directly from the platysma. It is composed of a few slender
fasciculi which pass transversely forwards in the fatty tissue

DISSECT/OAi OF rilK FACE.

269

of the check to the angle of the mouth, where they are
inserted into the skin.

The depressor angu/i oris is a flat triangular muscle
which presents a broad origin from the external oblique
line of the lower jaw. From this it proceeds upwards to
the angle of the mouth. Here its fibres, which are collected
in the form of a narrow bundle, are partly inserted into the
skin, and partly prolonged into the upper lip in the orbi-
cularis oris.

The mental hranch of the mandibular nerve and its

zygom.nticus
major.

platysni.i.

depressor anguli oris.
Fig. 241.

orbicularis.

mental nerve
and inf. labial
artery.

lev.ttor menti.

depressor labii
iiiferioris.

accompanying artery appear on the face under cover of
this muscle.

Levator Labii Superioris Alaeque Nasi.— rThis is a thin
fleshy band which lies along the side of the nose. It is
narrow al)Ove where it arises from the nasal process of the
superior maxillary bone, but it expands somewhat as it
jiroceeds downwards, and finally it divides into two slips —
a nasal and a labial. The inner and smaller nasal slip is
inserted into the wing of the nose, whilst the lahial slip is
|)rolonged into the upper lip, where some of its fibres blend

270 HEAD AND NECK.

with the orbicularis oris, and others obtain a direct attach-
ment to the skin.

The Levator Labii Superioris arises from the lower
margin of the orbital opening, immediately above the infra-
orbital foramen. It takes the form of a flat band which
proceeds downwards and slightly inwards, to end in the
skin of the upper lip. Under cover of this muscle the
large infra-orbital nerve emerges on the face, and joins with
branches of the facial nerve in the infra-orbital plexus.

The Zygomaticus Minor may be looked upon as a part
of the preceding muscle. It is also closely connected
with the orbicularis palpebrarum, from which some of its
fasciculi are often derived, and it lies on the same plane as
those slender slips which the orbicularis oris sends down-
wards from its lower margin to the skin of the cheek.

It is a slender fleshy bundle which arises from the malar
bone in front of the zygomaticus major, and passes down-
wards and forwards to join the^uter_margin of the levator
labii superioris.

Levator Anguli Oris (musculus caninus). — The origin of
this muscle is hidden by the levator labii superioris. It
springs from the upper part of the canine fossa, immediately
below the infra-orbital foramen, and proceeds downwards
and outwards to the angle of the mouth. Here some of its
fasciculi mingle with those of the orbicularis and enter the
lower lip, whilst others gain a direct insertion into the
skin.

It should be noticed that the bundle of fibres which is

given by the depressor anguli oris to the upper lip, and the

-"bundle which is contributed by the levator anguli oris to

the lower lip, decussate with each other at the angle of

the mouth (Fig. 243).

The Depressor Labii Inferioris (quadratus labii inferioris)
is a quadrate muscle partially hidden by the depressor
anguli oris which overlaps it (Fig. 241). It springs from
the lower jaw by a linear origin which extends from the
symphysis to a point a short distance beyond the mental
foramen, and passing upwards, with an inclination inwards,

DISSECTION OF THE FACE. 271

it joins the corresponding muscle of tlie opposite side, and
is inserted into the skin of the lower lip. Amongst the
fleshy fasciculi which compose this muscle there is a large
admixture of fat which renders it rather pale in colour.

Dissection. — The buccinator muscle must be cleaned with care,
because branches from the flicial nerve and the long buccal nerve form
a plexus upon its surface, and great numbers of nerves enter it, both for
the purjwse of supplying it, and also for the purpose of reaching the
mucous membrane of the mouth which lines its deep surface.

The Buccinator Mtiscle occupies the interval between
the upper and lower jaws. Above and belong its fibres take

Fig. 242.

origin from the outer surface of the alveolar margins of
both of these bones as far forwards as the first molar tooth.
Behind, its posterior border is attached to the pterygo-
maxillary ligament, which acts as the bpnd of union
between it and the superior constrictor muscle of the
pharynx. This attachment cannot be studied at present,
but will be afterwards examined in the dissection of the
pharyngeal wall. Anteriorly, it abuts against the angle of
the mouth, and its fibres blend with the orbicularis oris, a
large part of which it forms. But the manner in which
the fibres of this muscle enter the orbicularis must be
examined. The upper and lower fibres pass directly into
the corresponding lip ; the middle fibres, on the other
hand, decussate at the angle of the mouth, so that the
lower fibres of this series enter the upper lip, whilst the
higher fasciculi reach the lower lii).

272

HEAD AND NECK.

Orbicularis^ Oris. — The orbicularis oris is composed of
fleshy fasciculi which sweep round the oral aperture in the
interval between the skin and mucous membrane, and form
a considerable part of the substance of the two lips. Its
upper margin extends upwards as high as the nose, whilst

L.L.N.

LAO

DAO

Fig. 243. — Diagram of the orbicularis oris muscle. The
fibres which enter it from the buccinator are not repre-
sented.

L.L.N. Levator labii superioris

alaeque nasi.
L.L.S. Levator labii superioris.

L.A.O. Levator anguli oris.
D.A.O. Depressor anguli oris.
D.L.O. Depressor labii inferioris.

its lower margin corresponds to the groove on the face
which intervenes between the chin and the lower lip.

The fibres which compose the orbicularis oris are derived
from many different sources. The chief bulk of the muscle
iSL-formed by the continuation into the lips of fibres which
belong to the buccinator, the levator anguli oris, and the
depressor anguli oris of each side.

DISSECTION OF THE FACF. 273

The fasciculi of the buccinalor imiscle arrange themselves at the
angle of the mouth, in the manner already described, into two bundles,
and these are prolonged onwards into the two lips so as to encircle the
oral aperture, and become continuous with the corresjjonding fasciculi
of the opposite side. These fibres form the marginal part of the orbi-
cularis, and also the deeper peripheral part. The labial portions of the
levator anguli oris and the depressor anguli oris are arranged (juile
differently. The labial slip from the levator anguli oris passes into the
lower lip, and the corresponding slip from the depressor anguli oris
is continued into the upper lip. In neither case do the fibres reach the
opposite angle of the mouth ; they are inserted into the skin at the
middle of each lip. The fibres which come from these sources form
the superficial peripherjkl part of the orbicularis.

Jn addition to the fibres derived from these three muscles,
the orbicularis oris receives, certain slips which present
special attachments. Two are provided for each side of the
upper lip, viz. (i) the naso-labial band (w. miso-Iabialis\
and (2) the superior incisive band (w. incisivus superior);
and one, the inferior incisive band (w. incisivus iuferior), is
given to each side of the lower lip. The naso-labial band
is a rounded bundle which arises from the lower border of
the nasal septum, and turns outwards into the orbicularis
oris. The superior ituusive bundle takes origin from the
incisor fossa of the superior maxilla, and turns outwards in
the orbicularis ; whilst the inferior incisive bundle arises from
the corresponding fossa of the mandible, and presents
similar connections in the lower lip.

The incisive slips can be easily exposed by everting the lips, and
removing the mucous membrane from the neighbourhood of these fossie.
By this dissection two other small muscles will be displayed : (i) the
depressor ala; nasi to the inner side of the superior incisive slip ; and
(2) the levator menti to the inner side of the inferior incisive slip. The
concentric arrangement of the fibres of the orbicularis oris is well seen
when the mucous membrane is removed from the deep surface of the
lips. Numerous labial glands which lie between the muscle and the
mucous membrane are displayed by the same proceeding.

Levator Menti. — To expose this small muscle the lower
lip must be everted, and the mucous membrane removed
at the side of the frrenum of the lower lip. It is a short,
well-marked fleshy jDand, which springs from the incisor
fossa of the lower jaw, and proceeds downwards and slightly
VOL. II. — 18

274 HEAD AND NECK.

forward, to be inserted into the skin of the chin between
the two depressor muscles of the lower lip (Fig. 241).

Nasal G-roup of Muscles. — Under this head are com-
prised : —

1. Compressor naris.

2. Levator labii superioris

alceqiie nasi (already
examined).

3. Pyramidalis nasi,

4. Depressor alse nasi.

5. Dilatator naris posterior.

6. Dilatator naris anterior.

TheJjgmpressoxLlSlMis is a flat triangular muscle which
springs by a pointed fleshy origin from the superior maxillary
bone close to the margin of the anterior nasal aperture and
under cover of the levator labii superioris alaeque nasi.
From this it extends inwards and upwards, and expands
into an aponeurosis, which covers the cartilaginous part of
the nose, and in the mesial plane becomes continuous with
the corresponding aponeurosis of the opposite side.

The Pyramidalis Nasi is a narrow slip of muscular
fibres which springs from the aponeuxQsis_gJLthe ^ornpressqr
naris, and passes upwards upon the nasal bone. Some of
the fibres gain a direct insertion into the skin over the lower
part of the forehead ; others are continuous with the
fasciculi of the frontalis muscle.

The Depressor Alae Na,si is a minute muscle, the origin
of which has already been displayed by the removal of the
mucous membrane at the side of the frsenum of the upper
lip. It spjingsirom . the. incisor fossa of the superior maxilla
above and to the inner side of the superior incisive slip of
the orbicularis oris muscle. Its ojitet^margin_is usually
more or less blended with the compressor naris, and its
fibres arch upwards and forwards to become attached to the
lower and back part of both the ala and the septum of the
nose.

The Dilatator Muscles can rarely be satisfactorily dis-
played. The fibres which compose them are pale and
feeble, and they are embedded in the dense tissue at the
■lower and outer part of the nose immediately above the
aperture. An anterior slip (levator proprius alae nasi
anterior) is placed on the lower part of the side of the nose

DISSECTION OF THE FACE. 275

towards the lure -part of the nostril, and a posterior slip
(levator proprius aloe nasi posterior) at a short distance
behind this.

Nerves of the Face. — The nerves in this region may be
divided into two sets according as they supply the skin or
the muscles of the face. The motor nerve is the ncrvus
facialis. The sensory nerves come from various sources,
"and they reach the face either directly or indirectly through
the medium of filaments which join branches of the facial
nerve.

The following table shows the derivation of these
nerves : —

Nerves of the Face.

I. Motor. ^,

Facial nerve.

II. Sensory.

{a.) Appearing directly on the face.

1. Facial branches of the great auricular nerve.

2. Branches of the trigeminal nerve (5th cranial), viz. : —

/ Supra-orbilal.

T^ ., 1.1 1 • I Supra-trochlear.
rrom the ophlhulniic \ ■, ? 11

,. . . ' «i Inlra-lrochlear.

I Palpebral branch of the lachr)nia!.

\ Nasal.

„ , . ( Infra-orbilal.

rrom the superior I o 1 . 1

... 1- • • s bubcutaneus makv;.

maxillary division. | ~ , , , r ,. 1 •. .

■' ^^ Temporal branch of the orbital.

,. , . r . f Auriculo-temiwral.

rrom the inferior \ -, , ,

... ,• . . \ -Long buccal,

maxillary division. I ivr | 1

(^. ) Reaching the face indireclly.

1. Communicating branches from the great auricular nerve to ihe

facial nerve.

2. Communicating branches from the auriculo-temixjral nerve to

the facial nerve.

Whilst, therefore, the motor filaments come from one
source alone, the sensory nerves are derived partly from the
cervical plexus through the great auricular nerve, but chiefly
from the trigeminal nerve, each division of which furnishes
several branches to the face.

276

HEAD AND NECK.

Dissection. — The facial nerve is already, in a great measure, dis-
played. Its exit from the stylo-mastoid foramen can be rendered more
evident by chipping off the free projecting part of the mastoid process.
In doing this, first use the saw, and then complete the severance with
the chisel. Care must be taken not to injure the posterior auricular
branch of the facial nerve. By this proceeding a good view can be

Fig. 244. — Diagram of the facial nerve.

T.F. Temporo-facial division.
C.F. Cervico-facial division.
P.A. Posterior auricular.

D. Branch to the digastric muscle.
S.H. Branch to stylo-hyoid muscle.

T. Temporal branches.

M. Malar branch.
I.O. Infra-orbital branches.

B. Buccal branch.
S.M. Mandibular branch.
I.M. Cervical branch.

obtained of the origin of the posterior belly of the digastric, of the
stylo-mastoid branch of the posterior auricular artery, entering the fora-
men of the same name upon the facial nerve, and also of the occipital
artery in the deepest part of its course.

Facial Nerve (nervus facialis). — The trunk of the facial

DISSECTION OF THE FACE. 277

nerve eni£rgcs from the stylo-mastoid foramen and proceeds
forwards in the substance of the parotid gland. Near the
posterior margin of the ascending ramus of the lower jaw,
it ends by dividing into two branches, termed respectively
the fe mporo-facial a.r\d the ccrvico-facial divisions. From this
part of the nerve three branches^arise, viz. : — the posterior
auricular nerve, the nerve to the posterior belly of the
digastric muscle, and the nerve to the stylo-hyoid muscle.
The posterior auricular nerve has already been followed
out in its distribution to the retrahens auriculam, attoUens
auriculam, and posterior belly of the occipito - frontalis
(p. 107). Its origin is now exposed, and it will be seen
to arise from the facial trunk immediately after this issues
from the stylo-mastoid foramen.

At this stage it may be possible to make out a communication between
the auricular branch of the pneumogastric (Arnold's nerve) and the
posterior auricular branch of the facial. Arnold's nerve emerges from
the interval between the mastoid process and the auditor}' meatus, and
after sending a branch to join the posterior auricular nerve, it ends in
fdaments for the integument on the posterior aspect of the ear.

The nerve to the posterior belly of t/ie digastric (ramus
digastricus) is a stout, short branch which inclines down-
wards and forwards and soon divides into several filaments
which enter the upper surface of this muscle. One of these
twigs usually passes through the muscle to effect a com-
munication with the glosso-pharyngeal.

The nerve to the sfylo-hyoid (ramus stylohyoideus) is a
longer and more slender filament, which generally arises in
common with the preceding, and sinks into the posterior
aspect of this muscle.

' The Temporo-facial Division of the facial nerve is pro-
longed forwards through the parotid gland, and at once
divides into numerous branches which radiate widely from
each other, and stretch over an area extending from the ear
behind to the margin of the upper lip below. Whilst within
the substance of the parotid gland the temporo-facial nerve
crosses the external carotid artery near its termination, and
also the temporo-maxillary vein. It receives two, or it may

278 HEAD AND NECK.

be three, stout branches of communication from the auriculo-
temporal nerve, and forms a plexiform arrangement with the
branches of the cervico-facial division in the midst of the
parotid gland. This receives the name of the pes anserinus
or plexus parotideiis.

The branches into which this portion .of the facial trunk
divides are classified according to the direction which they
take into —

1 . Temporal.

2. JVLalar.

3. Infra-orbital.

The temporal branches, three or four in number, emerge
from the upper border of the parotid, and are carried up-
wards over the zygomatic arch to the temporal region.
Here they supply the attrahens auriculam, the frontal belly
of the occipito-frontalis, the orbicularis palpebrarum, and the
corrugator supercilii. They communicate with several
branches of the trigeminal or fifth cranial nerve, more
especially with the auriculo-temporal, the temporal branch
of the orbital, and the supra-orbital.

The malar branches run forwards upon the malar bone,
and end in filaments, which enter the outer and lower part
of the orbicularis palpebrarum muscle. Some of the twigs
may be traced to the upper and lower eyelids. On the
malar bone they communicate with the malar branch of the
orbital nerve, and in the eyelids they are connected with
the various branches of the trigeminal nerve which are
distributed to these structures.

The infra-orbital branches are larger than either of the
preceding, and they run horizontally forwards along the
lower border of the malar bone, and under cover of the
zygomaticus major to the infra-orbital region. Here they
supply twigs to the muscles in this neighbourhood as well
as to the muscles of the nose. They likewise communicate
with the infra-orbital, nasal, and infra-trochlear nerves.
With the infra-orbital nerve they form a complicated plexus
(the i?ifra-07-bital plexus), under cover of the levator labii
superioris.

nrssF.cTw.v of tiif. face. 279

The Cervico-facial Division of the Hicial trunk is smaller
than the temporo-facial division. It proceeds forwards, with
a slight inclination downwards, and breaks up in the sub-
stance of the parotid into three main branches, which arc
termed from the course which they take —

1. Buccal.

2. iV[anc1ihular. ^S^\, rKw^AO-

3. Cervical. !^.. p Vv^q^^

In the parotid gland the cervico-facial division crosses
the external carotid artery and receives several communicat-
ing twigs from the great auricular nerve.

The buccal branches run forwards upon the buccinator
mu-scle to the angle of the mouth, where they end in fila-
ments for the orbicularis oris. They supply the buccinator
mu.scle, and form, with the long buccal bi-anch q{ \\\c. inferior
maxillary division of the fifth nerve, a plexus around the
facial vein.

The mandibular branch proceeds forwards upon the lower
jaw to reach the muscles in connection with the lower lip.
Under cover of the depressor anguli oris it communicates
with the mental branch of the inferior dental nerve.

The cot'ical branch has already been examined in the
dissection of the neck (p. 190).

Sensory Branches to the Face from the Trigeminal
Nerve. — The branches which come froni^the flphihalmk
division of tJie Irigeniinal nove may first be studied. Of
these, hvo go to the skin of the forehead and scalp — viz. the
supra-orbital and the supra-trochlear ; tivo to the eyelids —
viz. the palpebral l)ranch of the lachrymal and the infra-
trochlear ; and one, the nasal, to the skin of the nose.

The supra-orbital and the supra-trochlear have already
been dissected in the scalp (p. 106). They should now be
followed downwards to the point where they turn round the
orbital arch of the frontal bone. This can be done by
cutting through the frontal belly of the occi[)ito-frontalis
and the orbicularis palpebrarum under cover of which they
pass upwards. The supra-orbital (juits the orbit by the

28o

HEAD AND NECK.

supra-orbital notch or foramen, and the supra-trochlear at
a point internal to this. Both nerves give twigs downwards
to the skin and conjunctiva of the upper eyelid.

The palpebral or terminal branch of the lachrymal di'^^'^das,

Fig. 245. — Diagram of the sensory branches of the
trigeminal nerve to the face. The branches from each of
the three divisions of the trigeminal nerve may be
recognised from the different shading which has been
employed to distinguish them.

A.T. Auriculo-temporal.
B. Buccal.
M. Mental.
T.O. Temporal branch of the orbital.
I.F. Infra-orbital.

S.O. Supra-orbital.

S.T. Supra-trochlear.

I.T. Infra-trochlear.

L. Palpebral branch of lachrymal.

N. Nasal.

in the upper eyelid above the outer canthus, where it pierces
the superior palpebral ligament, and gives filaments to the
skin and conjunctiva.

DISSECTION OF THE FACE. 281

The infra-trflchh'ixr fien'e will be found above the internal
tarsal ligament and the inner canthus. The twigs into
which it divides communicate with the facial and supply the
lachrymal sac, the conjunctiva and the skin of the eyelids,
and the root of the nose.

The fiasal iien'e (ramus nasalis externus) reaches the face
on the side of the movable part of the nose. To expose it,
divide the compressor naris, and it will be found appearing
between the lower margin of the nasal bone and the upper
lateral cartilage. It gives branches to the integument of
the nose and communicates with the facial nerve. It can
be traced downwards under cover of the compressor muscle
to the tip of the nose.

The branches of the suJ>enor maxillar)' division of the
trigeminal nerve which appear on the face are three in
number — viz. the temporal branch of the orbital nerve,
which has been already studied (p. 106); the malar branch
of the orbital nerve ; and the infra-orbital.

The fna/ar nerve (ramus zygomatico-facialis) is an ex-
ceedingly minute twig which ernerges on the face through
a minute foramen on the outer surface of the malar bone,
a short distance behind the external margin of the orbit.
To expose it the orbicularis palpebrarum must be carefully
raised from the bone in an upward direction.

The infra-orbital Jierve (nervus infra-orbitalis) is the ter-
minal part of the superior maxillary division of the trigeminal
nerve. It is a large branch which issues from the infra-orbital
foramen under cover of the levator labii superioris. It
forms, with the facial nerve, a dense plexus, and distributes
palpebral, nasal, and labial branches. The palpebral t^vigs
turn upwards to supply the skin and conjunctiva of the
lower eyelid; the 7iasal branches incline inwards upon the
side of the nose ; and the labial branches run downwards to
end in the skin and mucous membrane of the upper lip.

From the inferior maxillary division of the trigeminal
three nerves are furnished to the face, viz. the auriculo-
temporal, which has been described in p. 107 ; the long
buccal nerve ; and the mental nerve.

282 HEAD AND NECK.

The lo7ig buccal nerve (n. buccinatorius) will be found
coming out from under cover of the anterior border of the
masseter muscle. Its branches communicate freely with
the facial nerve around the facial vein, and supply the skin
and the mucous membrane of the cheek. The latter pierce
the buccinator muscle.

The mental nerve (nervus mentalis) is a large branch of
the mandibular nerve which appears through the mental
foramen of the lower jaw under cover of the depressor
anguli oris. It communicates with the facial, and supplies
the mucous membrane of the lower lip, and the integument
of the chin and lower lip. The mental foramen through
which the nerve emerges, lies directly below the interval
between the two bicuspid teeth. ^ "^

Arteries of the Face. — There are two main channels
concerned in conveying blood to the face, viz. (i) the traiis-
verse facial artery, a branch of the superficial temporal, and
already examined (p. 265); (2) the facial artery, a branch
of the external carotid. In addition to these a great
number of smaller vessels appear on the face with the
sensory branches of the trigeminal nerve. Those which
accompany the branches of the ophthalmic division are
derived from the ophthalmic artery, whilst those associated
with the branches of the superior and inferior maxillary
divisions proceed from the internal maxillary artery.

Facial Artery (arteria maxillaris externa). — The facial
artery will frequently be found smaller than usual. In such
cases its deficiency is compensated for by an increase in
the size of the transverse facial, or of some of the other
vessels which appear on the face.

The course of the facial artery in the neck has already
been noted (p. 251). It enters the face by passing on to
the mandible immediately in front of the masseter muscle.

1 If a line be drawn from the supra-orbital notch to the interval
between the two lower bicuspid teeth, and from that onwards to the
base of the lower jaw, it will pass over or close to the infra-orbital
and mental foramina. This line therefore can be used as a guide in
searching for these nerves.

D/SSECTION OF THE FACE. 2S3

It then takes a very tortuous course forwards and upwards
to a i)oint a short distance behind the angle of the mouth ;
from this it ascends to the inner canthus of the eye, and
much reduced in size by the numerous branches it has
given off, it^ terminates by anastomosing with the nasal
branch of the pphthahnic artery. Throughout its whole
length it is comparatively superficial. It is true that it is
placed somewhat' deeply in the fat of the cheek, but the
only muscles which cover it are, from below upwards : the
platysma, the risorius, and the zygomaticus major. Its
terminal part is usually embedded in the midst of the fibres
of the levator labii superioris al^ecjue nasi. The parts upon
which it rests as it extends through the face w'ill be seen
to be — (i) the lower jaw; (2) .the buccinator; (3) the
levator anguli oris ; (4) the levator labii superioris. The
facial vein does not accompany it closely in the face,
but lies, above the level of the lower jaw, at some
distance behind it. Several branches of the facial nerve
cross it.

Branches of the Facial Artery. — The branches which
arise from the facial artery are very numerous. Some of
inconsiderable size pass backwards. They are distributed
to parts in the buccal, masseteric and malar regions,
and anastomose with the transverse facial, the buccal, and
the infra-orbital arteries. Others proceed fonvards, and
being of larger size, they receive special, designations.
They are : —

1. Inferior labial. I 3. Superior coronary.

2. Inferior coronary. | 4. Lateral nasal.

5. Angular.

The inferior labial arises immediately above the base of
tiie lower jaw, and is carried forwards under cover of the
depressor anguli oris to supi)ly the parts in connection with
the chin and lower lip. It anastomoses with the mental,
the terminal branch of the submental, and the inferior
coronary arteries.

The inferior coronary takes origin opposite the angle of

284 HEAD AND NECK.

the mouth, and runs inwards in the lower Up near its free
margin between the mucous membrane and the orbicularis
oris. In a well -injected subject it will be seen shining
through the mucous membrane when the lip is everted. It
anastomoses with its fellow of the opposite side and with
the inferior labial.

The superior coronary arises under cover of the zygo-
maticus major, and is related to the upper lip in the same
manner that the inferior coronary is related to the lower
lip. It is generally of larger size. It gives off a branch
called the septal artery, which runs along the lower border
of the nasal septum and distributes twigs as far as the tip
of the nose.

The lateral nasal artery is a branch which is given to the
side of the nose, and as a rule passes forwards under cover
of the levator labii superioris alaeque nasi.

The angular artery is the name that .is applied to the
terminal part of the facial artery. It anastomoses with the
nasal branch of the ophthalmic artery.

Facial Vein (vena facialis anterior). — The facial vein
begins at the inner canthus of the eye, in a well-marked
venous trunk called the angular vein, which is formed by
tributaries coming from the forehead, the upper eyelid and
the root of the nose (p. io8). The course which the facial
vein takes is not nearly so tortuous as that of the corre-
sponding artery ; it lies behind the artery and is separated
from it by a considerable interval. Below the malar bone
it proceeds in a nearly verticab direction along the anterior
border of the masseter muscle, and at the base of the
lower jaw the two vessels come together.

NumeJ^QuS-Jjributariea join the facial vein as it courses
through the face, and a large branch called the deep facial
connects it with the pterygoid plexus of veins.

Tlie Auricle or Pinna. — Before dissecting the auricle, it
is well to learn the names of its various parts, and note the
position which they hold in relation to each other. The
concha is the wide and deep fossa which leads into the
external meatus ; the antihelix is the prominence which

DISSECTION OF THE FACE.

285

bounds this posteriorly ; the hi:lix is the folded or incurved
margin of the pinna ; and the lobule is its soft dei)endent
part. The concha is i)artially subdivided into an upper and
a lower part by the commencement of the helix, which
curves upwards and forwards on its floor to become con-
tinuous with the anterior border of the pinna. This portion
of the helix is called the ckks helicis. A small prominence
in front of the meatus, and projecting backwards so as to
overshadow it, is termed the fmgits, whilst a similar eminence
behind and below the meatus receives the name of the afiti-
tmgiis. The notch between these two prominences is

cms anlihelicis.
Darwin's tubercle.

fossa scaphoidia.
helix.

fossa triangularis,
crus antibelicis.
concha.

crus helicis.

tragus.

incisura iiUer-tragica.

Fig. 246. — The pinna.

termed the incisura inter-tragica. But it will be noted that
llie upper end of the antihelix bifurcates, and in this way
two fossae are marked off from each other ; one — the fossa
of the helix, or scaphoid fossa — is placed between the helix
and the antihelix, and the other — the fossa of the antihelix,
or triangular fossa — is situated between the two diverging
terminal limbs of the antihelix.

The pinna may now be dissected. It consists of a ihin plate of yellow
(ibro-cartjlage^ covered Ijy integument. It is fixed in position by certain
liyaments, and possess_c5_iwo sets of feeble muscles — viz. one group
termed the extrinsic muscles, passing to the cartilage from the aponeur-
osis of the occipito-fcunlalis and the mastoid process, and a sect)nil
group, in connection with the cartilage alone, antl therefore called the
intrinsic muscles.

Ligaments,

jAnterio
\ Posteric

iXXOT.

.'osterior.

\ Intrinsic muscles,

286 HEAD AND NECK.

(Attrahens. "|
AttoUens. I Already examined, p. 103.
Retrahens. J

Musculus helicis major, "l

Musculus helicis minor. I Upon the outer face of
Musculus tragicus. | the cartilage.

Musculus anti-tragicus. I

Musculus transversus. ^ Upon the cranial face of
L Musculus obhquus. j j^e cartilage.

The skin should be carefully removed from the entire extent of the
external auricle. Particular care must be taken in the regions where
the intrinsic muscles are placed.

The auricular cartilage extends throughout the entire pinna, with
the exception of the lobule and the portion between the tragus and the
helix. These portions are composed merely of integument, fatty tissue,
and condensed connective tissue. The shape of the cartilage corre-
sponds with that of the pinna itself. It shows the same elevations and
depressions, and by its elasticity it serves to maintain the form of the
auricle. But it also enters into the formation of the cartilaginous or
outer portion of the external auditory meatus. By its inner margin this
part of the cartilage is firmly fixed by fibrous tissue to the rough outer
edge of the auditory process of the temporal bone, and it is deficient
above and in front. Here the tube of the meatus is completed by tough
fibrous membrane, which stretches between the tragus and the com-
mencement of the helix.

In a successful dissection of the cartilage of the pinna, two other
points will attract the attention of the student. The first is a deep slit,
which passes upwards so as to separate the lower part of the cartilage of
the helix, termed the processus helicis catidatus, from the cartilage of the
anti-tragus ; the second is a sharp spur of cartilage which projects
forward from the helix at the level of the upper margin of the zygoma.
This is termed the spina helicis.

The ligaments of the auricle are two in number. The anterior
auricular ligament stretches from the spine of the helix to the root of
the zygomatic process. The posterior auricular ligament will be found
under cover of the retrahens auriculam. It is stronger than the pre-
ceding, and extends from a slight depression on the cranial aspect of the
concha to the mastoid process.

The intrinsic muscles of the pinna must be sought for with care.
The two muscles of the helix, the tragicus and the anti-tragicus, are
placed upon the outer face of the cartilage. The transversus and the
obliquus lie upon the cranial surface of the pinna.

The musculus anti-tragictis is the best-marked member of the outer
group. It lies upon the outer surface of the anti-tragus, and its fibres
pass obliquely upwards and backwards. Some fasciculi can be traced
to the processus helicis caudatus.

DISSECTION OF THE FACE. 287

The inusciilus Iragiais is a inimilc buntlli; of short vertical fihrcs
situated ii]H)ii llie outer surface of the tragus. Wlieii well (ieveiiji)eii a
slentler fasciculus may soinetinies be observed to jxiss upwards from it
to the fore-part of the helix, where it gains insertion into the spine of
the helix.

Tile iiiusathts hdicis major is a well-marked band, which springs
from the spina helicis, and extends upwards upon the fore-part of the
helix, to be inserted into the skin which covers it.

The musiulits helicis iiiiitor is a minute bundle of fleshy fibres which
is ]ilaced upon the crus helicis as it crosses the bottom of the concha.

The niKSiuliis /raiisz^crsiis auricuhc is found upon the cranial aspect
of the pinna. It is generally the most strongly developed muscle of the
scries, and it consists of fibres bridging across the hollow which, on this
aspect of the auricle, corresponds to the antihelix.

The iiiuscultts obliquus aKriciihe is composed of some vertical fasciculi
bridging across the depression which corresixjnds to the eminence of
the lower limb of the antihelix.

Eyelids. — The following strata will be exposed in each
eyelid as the student dissects from the surface towards the
conjunctiva lining its deep aspect : —

Upper Lid. i LowiiK Lid.

1. Integument.

2. PalpeTjral part of the orbicu-

laris palpebrarum.

3. The tarsus, the palpebral liga-

.ment, and the expanded ten-
don of the levator palpebriv
superioris.

4. Conjunctiva.

1. Integument.

2. Palpebral part of the orbicu-

laris palpebrarum.

3. The tarsus and the palpebral

ligament.

4. Conjunctiva.

In addition to these structures, two ligaments named the
internal and external tarsal ligaments will be noticed. They
attach the tarsal plates to the inner and outer margins of
the orbit.

The dissection should be carried on in both eyelids at the same lime.

Integument and Orbicnlaxis. — These strata have already
been examined, and the skin has been reflected. The
l>alpcbral part of the orbicularis muscle in each lid forms

288 HEAD AND NECK.

a thin layer of arching muscular fibres loosely connected
with the integument by some lax areolar tissue, h. fasciculus,
somewhat thicker than the others, lies along the free margin
of each lid, close to the bases of the eyelashes.

Dissection. — The entire orbicularis muscle may now be thrown
inwards. This will show very clearly the origin of its muscular fibres
at the inner margin of the orbit (p. 266). In raising the palpebral part
great care must be taken to preserve the palpebral vessels and nerves,
and at the same time to avoid injury to the palpebral ligament.

The Tarsi. — The removal of the palpebral part of the
orbicularis brings into view the palpebral ligaments and the
tarsal plates. These lie in the same morphological plane,
and they constitute the ground-work of the eyelids.

The tarsi are two thin plates of condensed connective
tissue placed one in each eyelid, so as to occupy an area
immediately adjoining its free margin. They differ very
materially from each other. The superior tarsal plate
is much the larger of the two, and presents the figure
of a half oval. Its deep surface is intimately connected
with the subjacent conjunctiva, whilst its superficial surface
is clothed by the orbicularis, and is in relation to the roots
of the eyelashes. Its superior border is thin, convex, and
continuous with the tendinous expansion of the levator
palpebrse superioris. The inferior border of the tarsal
plate is thickened and straight, and the integument adheres
firmly to it.

The inferior tarsal plate is a narrow strip which is similarly
placed in the lower lid.

Meibomian Follicles (glandulse tarsales). — At this stage
the attention of the student cannot fail to be attracted by
the Meibo7?iian follicles. To the naked eye they appear as
closely -placed, parallel, yellow, granular- looking streaks,
which run at right angles to the free margins of the lids.
They are more numerous and of greater length in the upper
lid, and, being lodged in furrows on the deep surface of
the tarsal plates, they are distinctly visible upon both
aspects of these, even while the conjunctiva is in position.
The ducts open upon the free margin of each lid behind the

DISSECTION OF THE FACE.

289

eyelashes, and by the aid of a magnifying-glass they can be
seen as round orifices placed in a single row.

The mouths of these glands can be well demonstrated by
squeezing the eyelid between the finger and thumb, when
the greasy secretion of the glands will be pressed out.

The Palpebral Ligaments are two broad membranous
sheets which extend into the basal portions of the eyelids
from the upper and lower margins of the orbital opening.
They form an incomplete membranous diaphragm around

frontal bone.

orbicularis palpebrarum.

superior palpebral ligament

superior conjunctival fornix
superior tarsal plate

conjunctival recess

inferior conjunctival fornix
inferior palpebral ligament.

Fig. 247. — Diagram of the structure of the eyelids.

the circumferential part of the orbital opening, termed the
septum orbitak. The superior ligament blends along the
orbital arch with the pericranium, clothing the frontal bone,
and with the periosteum lining the roof of the orbit, whilst
inferiorly it blends with the expanded tendon of the levator
palpebral superioris. The inferior ligament is continuous
on the one hand with the lower margin and anterior aspect
of the lower tarsal plate, and on the other with the periosteum
of the face and the floor of the orbit. Towards the inner
canthus, where the eyelids are supported by the internal

VOL. II. — 19

ago

HEAD AND NECK.

tarsal ligament, the palpebral ligaments become thin and
delicate.

The Tarsal Ligaments should in the next place be
examined. The palpebral ligaments fix the tarsi to the
upper and lower margins of the orbit ; the tarsal ligaments
attach the tarsi to the outer and inner orbital margins.

The external tarsal ligament is a narrow band of no great
strength, which springs from the malar bone where this
forms the outer margin of the orbit and proceeds inwards.

supra-orbital nerve.

superior palpe-
bral ligament.

palpebral branch
of lachrymal
nerve,
superior tarsus.

external tarsal
ligament.

inferior tarsus.

inferior palpebral
ligament.

infra-orbital
nerve.

supra-trochlear
nerve.

infra-trochlear
nerve.

Fig. 248. — Dissection of the eyelids to show the septum
orbitale and the tendinous expansion of the levator palpe-
bras superioris. (From Testut, modified.)

At the outer canthus, it divides into two pieces, an upper
and a lower, which are attached to the tarsal plates. This
ligament is merely a thickening of the palpebral ligaments
where they are continuous with each other at the outer
margin of the orbit.

T\\.Q. internal tarsal liga77ient is a much more important
structure. It has a double function to perform, viz. (i) to
serve as a tendon of origin for the orbicularis muscle, and
(2) to fix the tarsi to the inner margin of the orbit. To
obtain a satisfactory view of it, the muscular fibres which

DISSECTION OF THE FACE. 291

spring from its upper and lower margins must be com-
pletely removed.

The internal tarsal ligament is a strong fibrous band
which springs from the nasal process of the superior maxil-
lary bone immediately in front of the lachrymal groove. It
passes outwards and divides at the inner canthus into two
diverging portions which are attached one to each tarsal
plate.

The superficial surface of the internal tarsal ligament is
covered by the integument ; the deep surface crosses the
lachrymal sac a short distance above its centre and gives to
it a fibrous expansion, which is attached behind to the
posterior margin of the lachrymal groove.

Dissection. — The dissection of the lower lid is now completed, but in
the case of the upper eyelid the dissector must proceed to detach care-
fully the superior palpebral ligament from the margin of the orbit, and
throw it downwards towards the tarsal plate. This will expose the ex-
panded tendon of the levator palpebrze superioris.

Levator Palpebrse Superioris. — This muscle arises within
the cavity of the orbit. Its tendon spreads out into a wide
expansion which enters the basal part of the upper eyelid.
It is impossible in the course of an ordinary dissection to
make out all the very intricate connections of this tendon.
Its splits into three laminae. Of these the superficial layer
blends with the superior palpebral ligament, and is carried
forwards above the tarsal plate to the deep surface of the
palpebral part of the orbicularis muscle. The intermediate
stratum, largely composed of involuntary muscular fibres,^ is
inserted into the upper border of the tarsal plate ; whilst
the deepest lamina is attached to the fornix conjunctivae

(Fig- 247)-

Vessels ajid Nerves of the Eyelids. — At the inner
canthus two arteries — the palpebral branches of the oph-
thalmic artery — appear and run outwards in the upper and
lower lids. At the outer margin of the orbit, one or
more branches of the lachrymal artery pierce the palpebral
ligament, and anastomose with the palpebral arteries. An
arterial arch (arcus tarseus) is thus formed close to the

292 HEAD AND NECK.

margin of each eyelid, between the orbicularis muscle and
the tarsal plate.

The veins run inwards towards the root of the nose, and
open into the frontal and angular veins.
' The nerves are more numerous, and come from a number
of different sources. The motor filaments for the palpebral
part of the orbicularis proceed from the facial nerve, and
enter the lids at the outer margin of the orbit. The_sen-
soryjtwigs for the upper lid come from the lachrymal, supra-
orbital, supra-irochlear, and infra-trochlear nerves, whilst the
lower lid is supplied' by branches from the infra-orbital
nerve.

Lachrymal Apparatus. — The following structures are
included under this heading : —

1. The lachrymal gland and its ducts.

2. The lachrymal canals.

3. The lachrymal sac and the nasal duct.

4. The tensor tarsi muscle.

The Lachrymal Gland lies within the orbit, in the hollow
on the roof of this cavity, at the inner side of the external
angular process of the frontal bone. The fore-part of the
gland projects slightly beyond the orbital margin, and rests
upon the conjunctiva of the upper eyelid, as it is reflected
from the lid on to the eyeball. If the gland be now raised
gently and the point of the knife carried carefully up and
down through the connective tissue under it, several ex-
ceedingly delicate ducts, like fine threads, will be seen pro-
ceeding from the gland. These vary greatly in number,
and they open upon the under surface of the conjunctiva of
the upper lid, in the neighbourhood of the fornix or the re-
flection of this membrane upon the anterior surface of the
globe of the eye.

The tears secreted by the lachrymal gland thus reach the
under surface of the upper lid, and by the involuntary
closure of the fids in winking they are washed over the
exposed part of the eyeball and at the same time directed
inwards towards the inner canthus. From the lacus lachry-
malis they are drained away by the lachrymal canals.

DISSECTION OF THE FACE.

293

The Lacluymal Canals (ductus lacrimalcs) have in a
measure been already examined. The dissector has noted
ihc /^lonfa lachrymalia^ or the mouths of these minute canals,
upon the margins of the eyelids at the inner canthus, and
he has endeavoured to determine the course pursued by
each, by the introduction of a bristle. The upper canal at

lachrymal lachrymal
canal. sac.

nasal duct
opening into the inferior meatus

inferior turbinated bone
nasal septum

I'lo. 249. (From Gegenbaur. )

first ascends for a short distance, whilst the lower one
descends, and then changing their direction suddenly,_they
both run inwards in relation to the upper and lower margin?
of the internal tarsal ligament. They open close together
into the outer and anterior aspect of the lachrymal sac at a
point slightly above its centre. The upper canal is the
smaller and longer of the two, and it inclines downwards as
well as inwards to reach the lachrymal sac ; the lower canal
is nearly horizontal in direction.

294

HEAD AND NECK.

i

The Lachrymal Sac (saccus lacrimalis) is the blind upper
and somewhat expanded part of the passage which conducts
the tears to the nasal cavity. It is lodged in the deep
lachrymal groove in the fore-part of the inner wall of the
orbit, and it is crossed in front, a short distance above its

Fig. 250. — The inner wall of the orbit. (From Luschka. )

I.

Frontal bone.

6.

Tendo oculi or internal tarsal liga-

2.

Superior maxilla.

ment.

3-

Os planum of the ethmoid.

7-

The upper and (8) the lower origin

4-

Lachrymal bone.

of the orbicularis.

5-

The lachrymal sac covered by its

9-

Tensor tarsi.

fibrous lamella.

10.

Origin of the obliquus inferior oculi.

middle, by the internal tarsal ligament, from the deep
surface of which it receives a fibrous expansion. The
lachrymal canals open into it under cover of this ligament.
The nasal duct is the term which is applied to the
lower part of the same passage. It descends in the bony
nasal canal, and opens into the fore-part of the infeiioL-.
meatus of the nose. In length it measures about half an
inch.

'/

•(

a

DISSECTION OF THE FACE. 295

Dissection. — In cases where the dissector is dealing with undissccted
eyelids, the tensor tarsi muscle can be well exposed from the deep
aspect of the lids by dividing them vertically through the middle, and
turning the inner portions upwards and downwards. The removal of
the conjunctiva at the inner canthus will bring it into view.

The Tensor Tarsi Muscle is a little muscular slip which
can now be seen arising from the crest of the lachrymal
bone behind the lachrymal sai. '" l^isiimg outwards ana
forwards towards the tarsi, it divides into two slips which
blend with the ciliary muscles.

The lachrymal sac, therefore, lies between the internal
tarsal ligament and the tensor tarsi, and although anatomists
are not quite agreed as to the exact mode of action of this
muscle, there can be little doubt that it must be looked
upon as a dependency of the lachrymal apparatus. By its
contraction it either aids the propulsion of the fluid through
the lachrymal sac, or, by pulling on the tarsal plates, it places
the puncta in a more favourable position for the entrance of
the tears.

Dissection. — The cartilaginous part of the nose should now be ex-
amined by stripping off the compressor naris muscle and the remains
of the integument.

The Nasal Cartilages. — In addition to the septal
cartilage, which will be more appropriately studied in the
dissection of the nasal chambers, two cartilaginous plates
will be found upon each side. These are : —

1. The upper lateral cartilage.

2. The cartilage of the aperture.

The lifter lateral cariilage is a triangular plate which by
its posterior margin is attached to the lower border of the
nasal bone and the upper part of the sharp margin of the
nasal notch of the superior maxillary bone. In the mesial
plane this cartilage becomes continuous with its fellow of
the opposite side, and also with the subjacent anterior
border of the septal cartilage of the nose. Below, there is a
slight interval between the 'two lateral cartilages, in which is
seen the margin of the nasal septal cartilage. The inferior

296 HEAD AND NECK.

border of the lateral cartilage is connected with the outer
part of the cartilage of the aperture by some dense fibrous
tissue.

The cartilage of the aperture is bent upon itself and folded
round the orifice of the nostril in front and laterally, —
posteriorly it is deficient. The outer part is of an oval form,
and does not reach down to the margin of the nostril, nor
backwards as far as the nasal notch of the superior maxilla.

Fig. 251. — Cartilages of the nose.

N.N. Nasal nerve. 1 S.C. Sesamoid cartilages.

L.C. Lateral cartilage. I C. A. Cartilage of the aperture.

The interval between it and the bone is filled in by
fibrous tissue in which one or two small islands of cartilage
(cartilagines minores vel sesamoidese) appear. Li front, the
bent part of cartilage comes into contact with its neighbour
and forms the point of the nose. Internally, the inner part
of the cartilage is in the form of a narrow strip which lies
upon the lower part of the septal cartilage, and projects
slightly below it so as to support the margin of the nostril
upon this side. Its extremity is turned slightly outwards.

TEMPORAL AND PTERVGO-M AXILLARY REGIONS. 297

THF. TEMPORAL AND PTERYGO-MAXILLARY

RECIIONS.

Under this heading are grouped the parts which are
dissected in the temporal and zygomatic fossre of the skull.

Dissectioti. — The structures which cover and lie superficial to the
temporal fascia have already been examined in the dissection of the
scalp (p. 103).

Throw the temporal part of the orbicularis palpebrarum forwards ;
preserve the middle temporal artery, and the temporal branch of the
temporo-malar nerve, both of which pierce the temporal fascia ; turn
downwards the other vessels and nerves which lie on the temporal
fascia, and remove what remains of the temporal ]iart of the epicranial
aponeurosis and of the two upper ear muscles. Tlie temj^ral fascia is
in this manner laid bare.

The Temporal Fascia (fascia temporalis) is a strong
glistening aponeurosis which is stretched over the temporal
fossa, and binds down the muscle of the same name. Its
upper margin is attached to the upper of the two rough
lines which constitute the temporal ridge on the lateral
aspect of the skull, and in front to the temporal crest of
the frontal bone. As it approaches the zygomatic arch, it
splits into two lamina;, which are separated from each other
by a narrow interval filled with fat. These are attached to
the outer and inner margins of the upper border of the
zygomatic arch, and to the posterior border of the malar
bone. They can readily be demonstrated by dividing the
superficial layer close to its attachment, and throwing it
upwards ; by the handle of the knife the attachment of
the deep layer can then be made out. In the upper part
of its extent, the temporal fascia is comparatively thin, and
the fibres of the subjacent muscle may be seen shining
through it ; below it is thicker, and owing to the fat which is
interposed between its laminre, it becomes perfectly opaque.

Dissection. — The masseter muscle must now be thoroughly cleaned.
To do this effectually, it will be necessary to divide the trunk of the
facial tteti'c immediately beyond the point where it gives off the
branches to the digastric and stylo -hyoid muscles, and throw it
forwards, with the various branches which spring from it, towards the

298 HEAD AND NECK.

buccal region. The transverse facial artery must be also turned back-
wards. The dissector will recollect that he has previously removed from
the surface of the masseter a forward prolongation of the parotid gland,
the socia parotidis, Stenson's duct, twigs from the great auricular nerve,
scattered fibres of the platysma, and the origin of the risorius muscle.

The Masseter is a massive quadrate muscle which lies
upon the ascending ramus of the lower jaw. Its fibres are
arranged in two sets — a superficial and a deep. The super-
ficial part of the muscle arises from anterior two-thirds of
the lower border of the zygomatic arch, and its fasciculi are
directed downwards and backwards. The deep part springs
from the whole length of the inner aspect of the zygomatic
arch, and also from the posterior third of its lower border.
Its fibres proceed downwards and forwards. The ohly
portion of the deep part which appears on the surface is a
small piece at the upper and back part of the muscle. The
masseter is insetted into the outer surface of the ascending
ramus of the mandible, over an area which extends down-
wards to the angle, and upwards so as to include the outer
aspect of the coronoid process.

Dissection. — A dissection must now be undertaken to display the
temporal muscle, and at the same time expose the nerve and artery of
supply to the masseter. Begin by dividing the temporal fascia along
the upper border of the zygomatic arch. It may then be thrown
upwards and completely removed. The middle temporal artery and
the temporal branch of the temporo-malar nerve which pierce it must
be disengaged from it and preserved. The zygomatic arch with the
attached masseter must next be thrown down by dividing the bony arch
in front and behind the origin of the muscle. First make use of the
saw, and then complete the division by means of the bone-pliers. The
posterior cut should be made immediately in front of the glenoid fossa,
and the head of the lower jaw ; the anterior cut must extend obliquely
through the malar bone, from the extreme anterior end of the upper
margin of the arch, downwards and forwards to the point where the
lower margin meets the malar process of the superior maxillary bone.
In this way the whole of the masseteric origin is included between the
incisions, and the arch with the attached muscle may be readily thrown
downwards towards the angle of the lower jaw. The fleshy origin of
the deep portion of the masseter from the inner surface of the zygomatic
arch can now be seen, and frequently the dissection is complicated by
a number of fibres from the temporal muscle joining this part of the
masseter. In turning the masseter down, great care must be taken not

TEMPORAL AND PTERYGO-MAXILLARY REGIONS. 299

to injure its nerve and artery of supply. These pass outwards through
the sigmoid notch, between the neck of the lower jaw and the jxistcrior
margin of the temporal muscle. When they are exposed and cleaned,
they must be divided in order that the muscle may be fully reflected.
On no account detach the massetcr from the angle of the jaw. The
temporal muscle may now be cleaned.

The Temporal Muscle (musculus temporalis) is fan-
shaped. It arises from the entire extent of the temporal
fossa by an origin reaching upwards as high as the lower
of the two lines which constitute the temporal ridge, and
downwards as low as the zygomatic crest of the great wing
of the sphenoid. It also receives additional fibres from
the deep surface of the temporal fascia which covers it.
From this broad origin the fasciculi of the temporal muscle
converge towards the coronoid process of the lower jaw.
The anterior fibres descend vertically, the posterior fibres
at first pursue a nearly horizontal course, whilst the inter-
mediate fasciculi proceed with varying degrees of obliquity.
As it approaches its insertion, a tendon is developed upon
its superficial aspect, and this Is inserted into the summit
arTd anterior edge of the coronoid process of the mandible.
The deep part of the muscle remains fleshy, and gains
attachment to the inner surface of the same bony promi-
nence by an insertion which reaches as low down as the
point where the anterior margin of the ramus merges into
the body of the mandible.

Dissection. — The next step in the dissection of this region consists
in separating the coronoid process from the mandible, and turning it
upwards with the attached temporal muscle. A very oblique cut is
required ; it should extend from the centre of the sigmoid notch above,
downwards and forwards, to the point where the anterior margin of
the ascending ramus meets the Vjody of the mandible. First use the
saw, and then complete the division with the bone-pliers. The long
buccal uerve and its companion artery are in a position of great danger
during this dissection, and must be carefully guarded. They proceed
downwards and forwards under cover of the lower part of the temporal
muscle, and not unfrequently the nerve will be found traversing its
substance. The coronoid process and the temporal muscle should be
thrown well upwards, and the muscular fibres separated by the handle
of the knife from the bone forming the lower part of the tem]X)ral fossa.
This w ill bring into view the deep temporal iienes and arteries as they

300 HEAD AND NECK.

ascend between the cranial wall and the muscle. This is the time also
to follow the middle temporal artery. It will be noticed to give
branches to the muscle and extend upwards upon the squamous part
of the temporal bone. The temporal branch of the temporo-malar nerve
should likewise be traced to the point where it emerges from the minute
aperture on the temporal surface of the malar bone. At this point it
lies under cover of the temporal muscle.

The pterygoid region may now be fully opened up by removing a
portion of the ascending ramus of the mandible. Two horizontal cuts
must be made — one through the neck of the mandible, and the other
immediately above the level of the inferior dental foramen. To find
the level of the latter, the handle of the forceps should be thrust for-
wards between the ramus and the subjacent soft 'parts, and carried
downwards. Its progress will soon be arrested by the entrance of the
inferior dental vessels and nerve into the foramen, and the lower border
of the instrument will correspond with the line along which the bone
should be cut. Both incisions should be made with the saw, until the
outer table of the bone is cut through, and then the bone-pliers may be
employed to complete the division.

Parts displayed by the above Dissection. — When the
fat and areolar tissue are removed, the pterygoid muscles
will come into view. The external pterygoid will be
recognised from its extending horizontally backwards to
the neck of the mandible. The internal pterygoid., embrac-
ing the anterior part of the external pterygoid muscle
between its two heads of origin, proceeds downwards and
backwards upon the deep surface of the ramus of the
mandible. It bears very much the sarne relation to the
inner aspect of the ascending ramus that the masseter
presents to its outer surface. The great blood-vessel
of the space — the ifiternal maxillary artery — proceeds for-
wards upon the external pterygoid muscle. The nerves
will also be observed to be placed in close relationship to
the same muscle. Thus, emerging from between its upper
border and the cranial wall at the level of the infra-
temporal crest are the masseteric and the two deep temporal
nerves; appearing from under cover of its lower border
are the mandibular and the lingual nerves ; whilst the
auriculo-temporal net ve is related to it behind, and the long
buccal nerve in front. The former passes backwards under
cover of its insertion, and appears behind the temporo-

TEMPORAL AND rTERYGO-MAXILLARY REGIONS. 301

maxillary joint, and the long buccal either pierces it or
emerges from between its two heads of origin. The
internal lateral ligament of the lower jaw will likewise be
seen. It is the thin strip of membrane upon which the
inferior dental or mandibular nerve rests.

The External Pterygoid Muscle (musculus pterygoideus
externus) arises in the zygomatic fossa by two heads, an
upper and a lower. The upper head s^nngs from the infra-

superficial tem-
poral artery.

auriculo-temporal

middle meningeal
arterj'.

internal maxillary

artery.

inf. dental nerve and

artery.

ext. carotid artery.

niylo-hyoid nerve and

arterj'.

ingual nerve.

Fig. 252. — Dissection of the pterygo-niaxillary space.
.\nt. deep temporal nerve and artery. I 3. Post, deep temporal nerve and arlcrj-.

2. Long buccal nerve and artery.

4. Masseteric nerve.

temporal ridge and the zygomatic surf^ice of the great
wing of the sphenoid ; the Icmer head takes origin from
the outer surface of the external pterygoid plate. As the
muscle passes backwards it diminishes somewhat in width,
and is inserted into the fore -part of the neck of the

302 HEAD AND NECK.

mandible, and also into the anterior margin of the inter-
articular fibro-cartilage of the temporo-maxillary articulation.

Tlie Internal Pterygoid Muscle (musculus pterygoideus
internus) is also bicipital at its origin. Its two heads em-
brace the origin of the lower head of the external pterygoid.
The superficial and smaller head of the internal pterygoid
springs from the lower and back part of the tuberosity of
the superior maxilla and also from the outer surface of the
tuberosity of the palate bone ; the deep head, hidden by the
external pterygoid, arises in the pterygoid fossa from the
inner surface of the external pterygoid plate, and from the
surface of the tuberosity of the palate bone, which appears
between the two pterygoid plates. The two heads of the
muscle unite at the lower margin of the fore-part of the
external pterygoid, and its fibres proceed downwards with
an inclination backwards and outwards. They gain inser-
tion into the angle of the lower jaw, and into the lower
and back part of the inner aspect of the ascending ramus
as high as the mandibular foramen.

The Internal Maxillary Artery (arteria maxillaris interna)
is the larger of the two terminal branches of the external
carotid artery, and takes origin within the substance of the
parotid gland, immediately behind the neck of the mandible.
From this it proceeds forwards to the fore-part of the zygo-
matic fossa, where it disappears from view, by dipping
between the two heads of origin of the external pterygoid
muscle, and entering the spheno-maxillary fossa. It is cus-
tomary to divide it into three parts for convenience in descrip-
tion. The. first pari runs horizontally forwards u_nder cover
of the neck of thejnandible, and upon the internal lateral
ligament. It lies along the lower border of the posterior
part of the external pterygoid muscle, and usually crosses
the inferior dental nerve. The second part extends obliquely
upwards and forwards upon the surface of the external
pterygoid muscle, and under cover of the insertion of the
temporal muscle into the coronoid process of the mandible.
The third part dips between the two heads of the external
pterygoid, and is contained in the spheno-maxillary fossa.

TEMPORAL AND PTERYGOMAXFLLARY REGIONS. 303

Whilst this is the most frequent arrangement, it is by no
means uncommon to find the second part of the artery
lying in a deeper plane, viz. between the interjial and ex-
ternal pterygoid muscles. In this case the vessel makes a
bend outwards between the heads of the external pterygoid
muscle, and appears on its surface before entering the
spheno-maxillary fossa.

The branches of the internal maxillary artery are classified
into three groups according to the portion of the vessel
from which they spring. One branch only of the third
part, viz. the posterior dental or the superior posterior
alveolar artery., can be studied in this dissection. Those
arising from the first and second parts are : —

From the First Part.

From the Second Part.

1. The deep auricular.

2. Tympanic.

3. Middle meningeal.

4. Small meningeal.

5. Inferior dental.

1. Masseteric.

2. Pterygoid.

3. Anterior and posterior deep

temporal.

4. Buccal.

The deep auricular artery (arteria auricularis profunda)
is a small vessel which pierces the anterior wall of the
external auditory meatus to supply the skin which lines it
and also the superficial part of the tympanic membrane.

The meningeal and tympanic branches proceed upwards
under cover of the external pterygoid muscle, and therefore
cannot be fully studied until this muscle is reflected.

The inferior dental artery' (arteria alveolaris inferior) arises
opposite the middle meningeal, and runs downwards upon
the internal lateral ligament to enter the mandibular foramen
of the lower jaw. It is generally accompanied by two venae
comites, which lie one upon cither side of it, and it is
placed behind the inferior dental nerve. ]n?'\. before enter-
ing die canal, the inferior dental artery gives off the slender
niylo-hyoid branchy which is carried downwards and forwards

304 HEAD AND NECK.

with the corresponding nerve, upon the deep aspect of the
mandible, to the digastric triangle of the neck.

The branches frorn. the second part are given oiFfor the
supply of the neighbouring muscles. The masseteric (arteria
masseterica) passes outwards behind "^the temporal muscle
with the nerve of the same name, and has been seen
entering the masseter muscle. H\\& pterygoid branches {xdsca
pterygoidei) are a few irregular twigs, which are given to
the pterygoid muscles. The deep temporal arteries (arterise
terriporales profundse) are twonn~number — anterior and
posterior — and pass upwards in the fore and hinder part
of the temporal fossa, between the bony wall of the cranium
and the temporal muscle. They end in twigs for the supply
of the temporal muscle, and anastomose with the middle
temporal artery. The buccal artery (arteria buccinatoria)
accompanies the long buccar'nerTS, and is distributed to
the buccinator muscle and the mucous membrane of the
cheek. It anastomoses with the facial artery.

The posterior dental branch (arteria alveolaris superior
posterior), from the third part of the internal maxillary
artery, descends upon the posterior aspect of the superior
raaxilla, and sends branches through the posterior dental
fojamina for the supply of the upper molar and bicuspid
t.eeth (Fig. 252). Some small twigs also go to the gum,
whilst others find their way to the lining membrane of the
antrum of Highmore.

Pterygoid and Internal Maxillary Veins. — The veins in

this region are very numerous, but they cannot be studied

satisfactorily in an ordinary dissection. They are well seen,

however, when injected, in horizontal sections of the frozen

head made at the level of the external pterygoid muscle.

They constitute a dense plexus, termed the pterygoid plexj^s^

: around the external pterygoid muscle. Tributaries corre-

f ^ponding to the branches of the internal maxillary artery

! dpen into this network, whilst the blood is led away from

ilis back part by a short wide trunk, called the internal

niaxillary vein. This vessel accompanies the first part of

the internal maxillary artery into the parotid gland, and

TEMPORAL AND PTERYGO- MAXILLARY REGIONS. 305

joins the superficial temporal vein behind the neck of the
jaw, to form the temporo-maxillary trunk.

The pterygoid venous plexus also establishes by various
offsets, certain highly important connections. From its
fore-part the deep facial vein proceeds ; this extends forwards
under cover of the lower jaw and the masseter, and unites
^with the facial vein. Entering its upper part are one or ^
"more minute emissary veins from the cavernous sinus. \
These gain the exterior of the cranium by passing through
the foramen ovale. It likewise communicates with the
•cphthalmic vein through the sphcno-maxillary fissure.

Temporo-Maxillaxy Artictilation (articulatio mandibu-
laris). — This joint must next be studied, in order that the
external pterygoid muscle may be thrown forwards. In
connection with it we find —

Lir.AMENTs Proper.

1. The external lateral.

2. The capsular.

Accessory Ligaments.

An interarticular fibro-cartilage.

Internal lateral.
2. .Stylo-niaxillary.

The external lateral ligament is a strong band which is
attached above to the outer surface of the posterior part of
the zygomatic arch and to the tubercle at the root of the
zygoma. It is composed of short parallel fibres, which
proceed obliquely downwards and backwards to be inserted
into the outer and hinder part of the neck of the lower
jaw.

The capsule of the joint consists of a few scattered fibres,
which support the synovial membranes upon the inner,
anterior, and posterior aspects of the articulation.

The internal lateral ligament is a long membranous band
which sprinfTS ^r(^^ fjie spinous process Qf the sphenoid.
and is attached below to the lingula and to the sharp inner
margin of the mandibular foramen. It is not in direct
relationship with the joint. Above, it lies under cover of
VOL. II. — 20

3o6 HEAD AND NECK.

the external pterygoid muscle ; lower down, the internal
maxillary artery intervenes between it and the neck of the
mandible ; whilst, still lower, the inferior dental vessels and
nerve are interposed between it and the ramus of the
mandible.

The stylo -7naxillary ligaine?it has already been noticed.
It is an aponeurotic band, derived from the deep cervical
fascia, which is attached on the one hand to the styloid
process, and on the other to the angle and posterior border
of the ramus of the jaw between the internal pterygoid and
masseter muscles.

An examination of these ligaments will show that very
little is added to the strength of the joint by their presence..
The security of the joint depends not so much upon its
ligaments as upon the strong muscles of mastication, which
keep the head of the mandible in its place.

The interariicular fibro-cartilage is an oval plate, with its
long axis directed transversely. It is interposed between
the condyle of the manc^ible and the glenoid cavity, and
divides the joint cavity into an upper and lower portion,
each of which is provided with a separate synovial mem-
brane. To expose the cartilage, the external lateral liga-
ment must be removed. It will then be seen to be adapted
to the two bony surfaces between which it lie^. Above, it
is concavo-convex in correspondence with the emineritia—
articularis and the glenoid fossa of the temporal bone ;
whilst, below, it is concave, and fits upon the upper aspect
of the condyle of the mandible. In the centre it is thin,
and in some cases may be seen to be perforated. Its
circumference, more especially posteriorly, is thick. It
should also be noted that it is but loosely attached by its
periphery to the external lateral ligament, and that anteriorly
the external pterygoid muscle is partly inserted into it.

The synovial membrane which lines the upper cavity of
the joint is of greater extent and looser than that which
lines the lower compartment. This is owing to the articular
surface of the temporal bone being of larger size than the
condylar surface.

TEMPORAL AND PTERYGO-MAXILLARY REGIONS. 307

Movements. — The movements which the mandible can perform at
the temporo-maxillar)' joint are the following: — (i) depression; (2)
elevation ; (3) protraction ; (4) retraction ; (5) lateral or chewing
movements. When the lower jaw is depressed the interarticular fibro-
cartilagc with the condyle of the mandible moves forwards in the
glenoid fossa, and the latter finally takes up a position on the eminentia
articularis. This forward gliding of cartilage and condyle in the upper
compartment of the joint is accompanied by another movement in the
lower compartment of the joint, which consists in a rotation of the
condyle of the mandible on the lower surface of the interarticular fibro-
cartilage. Elevation of the mandible or closure of the mouth is brought
about by a reverse series of changes in both compartments of the joint.
Whilst these movements are going on, the mandible rotates around a

Fig. 253. — Diagram of the different positions occupied
by the head of the mandible and the interarticular car-
tilage as the mouth is opened and closed.

transverse axis which traverses the bone in the neighbourhood of the
mandibular foramen. This is the point, therefore, of least movement,
and consequently in opening and shutting the mouth the inferior dental
vessels and nerves are not unduly stretched. In protraction and re-
traction the movement is chiefly confined to the upper compartment of
the joint. The condyle of the mandible with the interarticular fibro-
cartilage glides forwards and backwards upon the temporal articular
surface. In the lateral movements of the jaw the mandible is carried
alternately from side to side, as in the process of chewing.

The muscles on each side which are chiefly engaged in producing
these movements are the following : — ( i ) depressors — the platysma, the
mylo-hyoid, and the anterior belly of the oTgastric ; (2) elevators — the
masseter, internal pterygoid, temporal ; (3) protractors — the external
pterj'goid, and to some extent the internal pter)'goid and the super-

3o8 HEAD AND NECK.

ficial fibres of the masseter ; (4) retractor — the posterior fibres of the
temporal ; (5) lateral movement is produced by certain of the muscles
of opposite sides acting alternately.

Reflection of External Pterygoid. — The head of the lower jaw
should now be disarticulated and thrown forwards with the attached
external pterygoid muscle. It is well to detach the interarticular fibro-
cartilage with the head of the bone, in order that it may be more
thoroughly examined. Great care must be taken not to injure the
auriculo-temporal nerve, which passes backwards in close proximity to
the deep aspect of the joint. When the disarticulation is complete, the
muscle may be turned forwards by gently insinuating the head of the
jaw under the internal maxillary artery.

The reflection of the external pterygoid muscle brings into view,
after a little dissection, the inframaxillary division of the trigetniual
nerve, emerging from the foramen ovale, and breaking up into its
branches of distribution. The slender chorda tympatti will likewise be'
found proceeding downwards and forwards to join the lingual nerve,
and the i/iiddle meningeal, tympanic, and small meningeal arteries may
be traced to the points where they leave the space.

Middle and Small Meningeal and Tympanic Arteries.

— The middle meningeal artery (arteria meningea media) has
aheady been seen arising from the first part of the internal
maxillary artery. It proceeds upwards under cover of the
external pterygoid muscle, and disappears from view by
entering the foramen spinosum, and thus gaining the
cranial cavity (p. 131). It will generally be observed to
be embraced by the two heads of origin of the auriculo-
temporal nerve.

The small meni?igeal (ramus meningeus accessorius) and
tympanic (arteria tympanica) arteries arise more frequently
from the preceding vessel than frOm the trunk of the
internal maxillary. The small meningeal inclines forwards
and upwards, and enters the cranial cavity by passing
through the foramen ovale ; the tympanic runs upwards
and slightly backwards, and reaches the tympanum by
passing through the Glaserian fissure. In the tympanic
cavity it anastomoses with the stylo-mastoid branch of the

I posterior auricular artery.

' Inferior Maxillary Division of the Trigeminal Nerve

(nervus mandibularis). — The inferior maxillary nerve arises-

TEMPORAL AND PTERYGO-MAXILI.ARY REGIONS. 309

witliin the cranium from the Gasserian ganglion, and enters
the pterygo-maxillary region through the foramen ovale. It
is composed oi sensory fibres, but it is accompanied through
the foramen by the small motor root of the trigeminal nerve,

« - I

Fig. 254. — Diagram of tlic inframaxillary division of the
fifth cranial nerve.

a. Sensory root entering the Gasserian

ganglion.
6. Motor root.
c. Ophthalmic division.
(/. Superior ma.villary division.
e. Inferior maxillary division passing

through the foramen ovale.
y. Nerve to the internal pterygoid.
g: .Vnterior division.

//. Recurrent branch.
;. Middle meningeal artery.
A. Foramen spinosum.
A .\uriculo-temporal nerve.
///. Chorda tympani.
«. Posterior division.
<'. Lingual nerve.
/. Mylo-hyoid nerve.
r. Inferior dental nerve.

and, a junction being effected between the two immediately
after they gain the exterior of the cranium, a mixed /lerve-
triink is the result. This nerve-trunk lies under cover of
the external pterygoid muscle, and after a very short course
(not exceeding two or three lines) it ends by dividing into

3IO HEAD AND NECK. ■

two parts, named respectively the anterior and posterior
divisions of the inferior maxillary nerve (Fig. 2 54).

Before it divides, the trunk of the inferior maxillary nerve
gives off two branches, viz. (i) the recurrent nerve (nervus
spinosus) {h\ and (2) the nerve to the internal pterygoid
muscle (/).

The recurrent nerve is a very slender twig which enters
the cranium by accompanying the middle meningeal artery
through the foramen spinosum. It is distributed to the
lining membrane of the mastoid cells and to the great wing
of the sphenoid bone.

The internal pterygoid nerve will be found passing und§r
cover of the posterior border of the internal pterygoid
muscle close to its origin. In close relation to the root of
this nerve is the otic ganglion.

From the two terminal divisions of the inferior maxillary
trunk the chief branches of distribution arise. The small
anterior division is much the smaller of the two, and is
composed almost entirely of motor fibres derived from the
motor root of the trigeminal nerve. The only sensory
fibres which it contains are those which form the long
buccal nerve. It gives off the following branches : —

1. Masseteric. I 3. External pterygoid.

2. Two deep temporal. | 4. Long buccal.

The large posterior division is chiefly sensory. It contains
only a very few fibres from the motor ro9t, and these are
prolonged into its inferior dental branch, and afterwards
come off in the form of the mylo-hyoid n&rve. The branches
of the posterior division are : —

1. Auriculo-temporal.

2. Inferior dental.

3. Lingual (or gustatory).

The masseteric nerve (nervus massetericus) is directed
outwards above the external pterygoid muscle, and, passing
through the sigmoid notch behind the posterior border of
the temporal muscle, it enters the hinder and upper part
of the deep surface of the masseter. In the substance of

TEMPORAL AND PTERYGOMAXILLARY REGIONS. 311

this muscle it may be traced with the companion artery
downwards and forwards to its lower and fore part. Before
reaching the masseter, it gives one or two twigs to the
temporo-maxillary joint.

The deep temporal nerves (nervi temporales profundi) are
usually two in number, and are termed anterior o.r\d posterior
according to the position they occupy in the temporal fossa.
The posterior nerve is the smaller of the two, and frequently
arises by a common root with the masseteric. Both deep
temporal nerves pass outwards above the external pterygoid
and then turn upwards upon the bony wall of the cranium.
After a short course they end in twigs which penetrate the
substance of the temporal muscle.

The Long Buccal Nerve (nervus buccinatorius) is the
largest of the branches proceeding from the anterior
dlvTsion of the inferior maxillary nerve. It proceeds out-
wards between the two heads of the external pterygoid
muscle and then runs downwards and forwards under
cover of the temporal muscle, and also of the anterior
border of the masseter, to reach the outer surface of the
buccinator muscle. Here it has been seen to form with
branches of the facial nerve t/ie buccal plexus, and to be
distributed to the mucous membrane- and skin of the
cheek (p. 2 88).

The long buccal is a sensory nerve, and all the sensory
fibres in the anterior division of the inferior maxillary nerve
enter into its composition. A few motor fibres, however,
are also prolonged into it ; these come off from it in two
branches, viz. (i) in the nerve to the extertial pterygoid^
which as a rule arises in common with the long buccal
and at once sinks into the deep surface of this muscle ; and
(2) in a third twig of supply to the temporal muscle. This
temporal branch springs from the long buccal after it has
reached the outer surface of the external pterygoid, and
proceeds upwards to supply the fore-part of the temporal
muscle (Fig. 252). In some cases the long buccal nerve
may be observed to pierce the temporal muscle instead of
passing under cover of it.

312 HEAD AND NECK.

The Auriculo- Temporal Nerve (nervus auriculo-tem-
poralis), "composed of sensory fibres, springs from the
posterior divTslon'^of tlie inferior maxillary b}^_two . rofits.
Xbiese pass backwards under cover of the external pterygoid
muscle and embrace the middle meningeal artery. Beyond
this vessel they unite, and the nerve is continued backwards
under cover of the neck of the lower jaw, immediately
below the temporo-maxillary joint. Gaining the interval
between the ear and jaw it turns upwards in relation to
the deep surface of the parotid gland, and crosses the
zygoma in company with the superficial temporal artery.
Its further course has already been examined (p. 107).

The following branches _proceed from it : — (i) one or two
strong branches of communication to the temporo-facial
nervej (2) a few slender filaments which enter the posterior
aspect of the temporo-maxillary joint ; (3) some twigs to the
parotid gland ; (4) terminal filaments to the skin over the_
temporal region and summit of the head (p. 107) ; (5) auri-
cular branches.

The auricular branches are usually two to the skin lining
the interior of the external auditory meatus and two to the
integument over the upper and fore part of the pinna. The
former gain the interior of the meatus by passing between
the osseous and cartilaginous portions of the canal.

The Inferior Dental Nerve (nervus alveolaris inferior)
is the largest branch of the inferior maxillary. Emerging
from under cover of the external pterygoid muscle it
passes downwards upon the internal lateral ligament of
the lower jaw and enters the mandibular foramen. The
inferior dental artery runs downwards behind it, whilst
the lingual nerve is in front of it and upon a somewhat
deeper plane. The inferior dental is a'sensory nerve, but
a few motor fibres from the motor root are prolonged
downwards within its sheath as far as the mandibular
foramen. At this point they come off as the slender
mylo-hyoid nerve.

The mylo-hyoid nerve, accompanied by the artery of the
same name, pierces the internal lateral ligament and pro-

TEMPORAL AND PTERYGOMAXILLARY REGIONS. 313

ceeds downwards and forwards in a groove upon the deep
surface of the lower jaw to the digastric triangle. A
narrow prolongation of the internal lateral ligament bridges
over the groove and holds the nerve and vessel in
position. In the digastric triangle the niylo-hyoid nerve
has already been dissected. It appears upon the surface of
the mylo-hyoid muscle, and, issuing from under cover of
the superficial part of the submaxillary gland, it breaks up
into numerous branches for the supply of two muscles,
viz. (i) the mylo-hyoid, and (2) the anterior belly of the
digastric.

Lingual Nerve. — This nerve is entirely sensory, and
is covered in the first part of its course, like the other
branches of the inframaxillary nerve, by the external
pterygoid muscle. Appearing at the lower border of this
muscle, it proceeds downwards and forwards between the
internal pterygoid muscle and the mandible and enters
the submaxillary region, where it will afterwards be traced
to the tongue. It is placed in front of and on a slightly
deeper plane than the inferior dental nerve. In this region
it gives off no branches, but, under cover of the external
pterygoid, it is joined at an acute angle by the chorda
tympayii branch of the facial nerve. Very frequently, also,
a communicating twig passes between it and the inferior
dental nerve.

The Chorda Tympani is a slender nerve which arises
from the facial in the aqueduct of Fallopius. It gains the
pterygo-maxillary region by traversing the tympanic cavity
and appearing through the inner part of the Glaserian
fissure. It will now be seen to run downwards and forwards
under cover of the internal lateral ligament of the lower
jaw, and unite with the lingual nerve near its origin. It is
joined by a slender filament from the otic ganglion.

Otic Ganglion. — As this ganglion lies under cover of the
inferior maxillary trunk, it cannot be satisfactorily studied
at this stage. It is true that it may be exposed by tracing
the nerve to the internal pterygoid muscle upwards, when
it will be seen to be developed in connection with the root

rJ 314^ HEAD AND NECK.

of this branch. Its connections, however, can only be
made out by dissecting from the inside, and it is well to
defer its examination until this can be done.

Dissection. — The student should now endeavour, by means of a Hey's
saw, a chisel, and the bone-pliers, to remove the outer table of the lower
jaw, and thus open up the mandibular canal.

Structures within the Mandibular Canal. — This canal
is traversed by the inferior dental vessels and Jierve. These
give off twigs which enter the fangs of the molar and
bicuspid teeth, and they each terminate by dividing into
a mental and incisor branch.

The menial artery and ?ierve appear on the face through
the mental foramen, and have already been examined ;
the incisor artery and nerve are carried forwards to the
symphysis and send up twigs to the canine and incisor
teeth. The vessel anastomoses in the bone with the corre-
sponding artery of the opposite side.

SUBMAXILLARY REGION.

The superficial area of the submaxillary region has
already been dissected, under the name of the anterior
part of the digastric or submaxillary triangle (p. 216). It
is now necessary to carry the dissection to a deeper plane,
in order to expose a number of parts in connection with
the tongue and floor of the mouth. The structures thus
displayed are : —

1. Mylo-hyoid muscle.

2. Submaxillary gland and its duct.

3. Sublingual gland.

4. Side of the tongue, and the mucous membrane of the mouth.

iHyoglossus.
Stylo-glossus.
Genio-hyoid.
Genio-hyoglossus.
( Hypoglossal.
6. Nerves. X Lingual.

(^ Glosso-pharyngeal.

SUBMAXILLARY REGION. 315

7. Submaxillary gantjlioii.

8. Lingual artery and veins.

9. Stylo-hyoid ligament.

Disscclioit. — To prepare the part for dissection, it is necessary to
throw back the head to its full extent, and turn it slightly to the opposite
side. If the stuffing in the mouth has not been previously removed
in the dissection of the pterygo-maxillary region, it should be taken out
now, and then the lip of the tongue should be seized with the forceps,
and drawn forcibly forwards between the teeth, and retained in this
position by stitching it to the nose.

In dissecting towards the mesial plane, three muscular strata arc
encountered, viz. the mylo-hyoid, the hyoglossus, the genio-hyo-
glossus. In the intervals between these, certain important structures
will be exposed. Begin with the first muscular stratum.

The mylo-hyoid inusi/e forms the fore -part of the floor of the
digastric triangle. To bring it fully into view, certain of the contents
of this space must be displaced. Divide the facial artery at the point
where it gains the lower jaw, and, disengaging it from the submaxillary
gland, throw it downwards, along with its submental branch and the
facial vein. Next, detach the anterior belly of the digastric from the
mandible, and deal with it in the same manner. The mylo-hyoid nerve
must also be cut, and the superficial part of the submaxillary gland
turned backwards. The superficial surface of the mylo-hyoid is in this
way completely exposed, and its fibres may be cleaned and its attach-
ments made out.

The Mylo-hyoid (musculus mylohyoideus) is a thin sheet
of muscular fibres, which arises from the mylo-hyoid ridge
upon the deep surface of the body of the mandible by an
origin which extends from the last molar tooth behind to
the symphysis in front. Its fibres are directed downwards,
inwards, and backwards, and present two different modes
of insertion. The posterior fibres are inserted into the body
of the hyoid bone ; these, however, form a comparatively
small part of the muscle. The greater number of the fibres
are inserted into a median raphe, which extends between
the symphysis of the lower jaw and the body of the hyoid
bone. 'I'he two mylo-hyoid muscles, therefore, in front of
the hyoid bone stretch across from one side of the body of
the mandible to the other, and constitute a floor for the
anterior part of the mouth. This floor is frequently termed
the diaphrai^ma oris. The mylohyoid muscle is supplied
by the mylo-hyoid brajich of the inferior dental nerve.

3i6

HEAD AND NECK.

Dissection. — The mylo-hyoid muscle must now be reflected, in order
that the parts subjacent to it may be brought into view. As these parts
lie in a great measure under shelter of the mandible, it is advantageous
to make at the same time a section of this bone, in order that it may be
turned upwards.

Carefully divide the fibres of the mylo-hyoid muscle close to the ridge
from which it arises. A very small piece may be left attached to the

■ STYLOID PROCESS

stylo-liyoid ligt.

glosso-phar.
nerve.

submaxillary
ganglion.

deep part of
submax. gland.

hypoglossal
nerve.

lingual artery.

middle constric-,
tor of pharynx.

Fig. 255. — Dissection of the submaxillary space.

mandible to serve as a landmark in the future dissection. This must be
done very cautiously, else the mucous membrane of the mouth will be
injured. When detached from the jaw, the muscle must next be
separated from the median raphe, and then it can be thrown down over
the hyoid bone. The lower jaw should next be divided, by means of
the saw and bone-pliers, a quarter of an inch to the outer side of
the symphysis. When the section is completed, the lower margin of
the mandible should be gently tilted upwards, and some means taken
to retain the loose piece of the bone in this position. Under no pretence
whatever should it be removed, and great care must be taken to preserve

SUBMAXILLARY REGION.

317

I

intact the mucous membrane passing from the floor of the mouth to the
deep surface of the gum.

Parts Exposed by the Reflection of the Mylo-hyoid (Fig.
255). — The side of the tongue is now hrought into view,
with a ntimber of structures in connection with it. First
note Uie mucous membrane stretching from the tongue to

:xt. pterj'
gold.

>maxillar>'
;land.

*p part of.
e submax-
vy gland.

yoglossus.

vpoglossal
lerve.

temporal
muscle.

ext. ptery-
goid.

pterygoid
process.

int. ptery-
goid.

lingual

nerve,
mylo-hyoid

muscle.

facial artery.

deep part of
submaxillary
gland.

hyoglossus.

hypoglossal
nerve.

Fig. 256. — Coronal section through the mouth and sub-
ma.xillary regions.

the gum of the lower jaw ; then identify the various muscles.
The hyogIflssus]\ portion of which was previously visible
behind the mylo-hyoid, is fully exposed. It is a square
sheet of fleshy fibres which extends from the hyoid bone to
the side of the tongue. Mark its position, because all the
structures in this region have a more or less intimate
relationship to it. Thus, behind it will be recognised the
sfylo-ghssus muscle^ and in front of it, the genio-hyoglossus
and the genio-hyoid. The gcnio-hyoid muscle occupies the
fore-part of the region, whilst the anterior part of the genio-
hyoglossus is seen in the interval between it and the hyo-

3i8 HEAD AND NECK.

glossus. Upon the surface of the hyoglossus, the lingual
and hypoglossal nerves, the deep portion of the submaxillary
gland with Wharton's duct, and the submaxillary ganglion
are to be dissected. T\i&_lingual jierve occupies the highest
level, and passes forward upon the muscle near its insertion
into the tongue. T\iQ_hypoglossal nerve, accompanied by
the ranine vein, crosses it close to the hyoid bone, whilst
the deep part of the suhnaxillary gland and Wharton's duct
occupy an intermediate place. Although the submaxillary
gafiglion is very minute, its relations are so precise that it
is very easily found. By seizing hold of the lingual nerve
and dissecting carefully with the point of the knife in the
interval between it and the deep part of the submaxillary
gland, the ganglion will be exposed and its roots and
branches of distribution made out. Upon the genio-hyo-
glossus, in front of the hyoglossus the dissector will note
the sublingual gland with its artery of supply. Certain
structures will also be seen passing under cover of the
posterior margin of the hyoglossus muscle ; these are : —
(i) the glosso- pharyngeal nerve immediately below the
stylo-glossus muscle; (2) the stylo-hyoid ligament, a little
lower down ; and (3) the Ungual artery, close to the hyoid
bone.

The Hyoglossus is a quadrate flat muscle which arises
from the whole length of the greater cornu, and also from
the body of the hyoid bone. Its fibres pass upwards to the
posterior part of the side of the tongue where they ascend
under cover of the stylo-glossus. The hyoglossus is
supplied by the hypoglossal nerve.

The Stylo-glossus is an elongated fleshy slip which takes
origin from the anterior aspect of the styloid process near
its tip and also to a slight extent from the upper end of the
stylo-hyoid ligament. Passing downwards and forwards its
fibres may be traced upon the side of the tongue as far as.
the tip. They decussate with the fasciculi of the preced-
ing muscle. The nerve of supply to the stylo-glossus comes
from the hypoglossal.

The G-enio-hyoid (musculus geniohyoideus) is placed

SUBMAXILLARY REGION. 319

close to the mesial plane, in contact with its fellow of the
opposite side. It is a short muscle which arises from the
lower of the two genial tubercles upon the posterior surface
of the symphysis of the mandible, and extends downwards
and backwards to gain insertion into the fore aspect of the
body of the hyoid bone. The hypoglossal gives the nerve
of supply to the genio-hyoid.

Submaxillary Gland (glandula submaxillaris). — The sub-
maxillary gland consists of a superficial and a deep portion ;
the superficial or main part has already been noted as the
most conspicuous object in the digastric triangle. In size
and shape it may be compared to a walnut, and it presents
very definite relations. It is covered by skin, superficial
fascia, platysma, and deep fascia, and lies under shelter of
the body of the mandible — a distinct depression in the
bone corresponding to its upper and outer surface. Behind,
it is shut off from the parotid gland by the stylo-maxillary
Jigament, whilst in front it is limited by the anterior belly
of the digastric muscle. It rests upon the mylo-hyoid,
and lodged in a deep groove in its substance is the facial
artery. The deep part of the gland is a slender prolonga-
tion, which is tucked round the posterior margin of the
mylo-hyoid. It lies between the mylo-hyoid and the hyo-
glossus muscles (Fig. 256).

Wharton's Duct (ductus submaxillaris). — The duct of
the submaxillary gland is termed ]]'7ia?io>i's duct. It
emerges from the main part of the gland, and with the
deep part of the gland it proceeds forwards upon the hyo-
glossus muscle between the lingual nerve above and the
hypoglossal nerve below. Reaching the surface of the
genio-hyoglossus muscle, it inclines slightly upwards and is
crossed by the lingual nerve. Fmajlj^ it passes under cover
of the sublingual gland, and gains the floor of the mouth.
Here it opens by a small orifice placed on the summit
of a papilla which lies close to the side of the fra^num
linguae.

The wall of Wharton's duct is much thinner than that
of the parotid duct. If a small opening be made in it, the

320 HEAD AND NECK.

dissector will experience little difficulty in passing a fine
probe or bristle along it into the mouth.

Sublingual Gland (glandula sublingualis).— The sub-
Hngual gland is the smallest of the three salivary glands.
It has an elongated shape, and in length it measures about
one inch and a half. Its relations are very defimte. Above,
it is related to the fore-part of the floor of the mouth, being
separated from the cavity by the mucous membrane alone

_ molar tootl

genio-glossus. genio:hyoid.

Fig. 257.— Coronal section through the fore-part of the mouth
and submaxillary region.

(Fig. 257). Internally it rests upon the genio-hyoglossus_
muscle, whilst externally it is lodged in a fossa on the deep
aspect of the mandible, immediately external to the sym-
physis. Below, it is supported by the mylo-hyoid muscle.
Its anterior extremity reaches the mesial plane above the
anterior border of the genio-hyoglossus and is in contact
with its fellow of the opposite side. The duct of Wharton
and the Ungual nerve are prolonged forwards under cover
of the sublingual gland.

Numerous small ducts (the number varying from eight

SUBMAXILLARY REGION. 321

to twenty) proceed from tlie sublingual gland. These arc
called the ducts of Riviiii^ and they have two modes of ter-
mination. Sorne open into Wharton's duct ; others open
directly into the mouth by piercing the mucous membrane
which overlies the gland. One of the latter, larger than
the others, receives the special name of the duct of Bartholin,
and this opens into the mouth close to the orifice of the
duct of AMiarton.

Lingual Nerve (nervus lingualis). — In the dissection of
the pterygo-maxillary region, the lingual nerve has been seen
passing downwards between the ranius^of the mandible and
th^ internal pterygoid muscle. It now inclines forwards to
reach the side of the tongue, and, passing over the superior
constrictor muscle of the pharynx, it lies below the last
molar tooth between the mucous membrane and^the body
of the mandible. At this point it is in danger of being
hurt by the clumsy extraction of one of the lower molars,
and here also it may be divided by the surgeon, from the
inside of the mouth. In its further course the nerve keeps
close to the side of the tongue, crossing the upper part of
the hyoglossus, and, beyond this, the duct of Wharton. It
is placed immediately under the mucous membrane of the
mouth, and it can be traced as far as the tip of the tongue.

The branches which proceed from the lingual nerve in
this region are of two kinds — (i) twigs of communication ;
(2) branches of distribution.

j I. Two or more to the submaxillary ganglion.

Twigs of I 2. One or two which descend along the anterior

Communication, j border of the hyoglossus muscle to unite

(^ with the hypoglossal nerve.

P , I I. Slender filaments to the mucous membrane of

' J. " J the mouth and gums.

T>.. , ., .. I 2. A few twigs to the sublingual rland.
Distribution. I „ , — f „ .

\l. liranches to the tongue.

The lingual branches pierce the substance of the tongue,
and then incline upwards to supply the mucous membrane
with the conical and fungiform papilla; over the anterior
two-thirds of this organ.
VOL. II. — 21

322 HEAD AND NECK.

Submaxillary G-anglion. — This is a minute gEinglion
which will be found lying upon the upper part of the hyo-
glossus muscle in the interval between the lingual nerve
and the deep part of the submaxillary gland, under cover
of the mylo-hyoid muscle. In size it is not larger than the
head of a large pin, and, when freed from the connective
tissue surrounding both it and its branches, it will be seen
to be suspended from the lingual nerve by two short
branches, which enter its upper border, and are separated
by a distinct interval. Of these, the posterior connecting
twig is frequently in the form of two or three filaments,
which convey to the ganglion its sensory and secretory
roots, whilst the anterior connecting branch must be looked
upon as a twig given by the ganglion to the lingual nerve.

In common with the other ganglia developed in con-
nection with the branches of the fifth cranial nerve, this
ganglion has three roots — viz. (i) ^^ sensory root from the
lingual nerve ; (2) 2. secretory root from the chorda tympani ;
and (3) a sympathetic root from the plexus around the facial
artery.

" From its lower border several minute twigs proceed, and
these are distributed — (i) to the submaxillary gland; (2)
to Wharton's duct ; and (3) to the mucous membrane of
the mouth.

The Hypoglossal Nerve (nervus hypoglossus) has been
traced in the dissection of the anterior triangle to the point
where it disappears under cover of the mylo-hyoid muscle
(p. 225). It is now seen passing forwards upon the hyo-
glossus muscle above the hyoid bone, and below the level
of the deep part of the submaxillary gland. At the anterior
border of the hyoglossus it gains the surface of the genio-
hyoglossus muscle, into the substance of which it sinks,
and finally breaks up into branches which supply the
nmscular substance of the tongue. Upon the hyoglossus
muscle it is accompanied by one of the Hngual veins,
frequently termed the ranhie vein.

The branches which spring from the hypoglossal nerve in
this region are very numerous, and are entirely distributed

SUBMAXII.I.A R I ' REGION. 323

to muscles. It supplies — (i) the stylo -glossus ; (2) the
hyoglossus ; (3) the gcnio -hyoglossus ; (4) the genio-
hyoid; and (5) the intrinsic muscles of the tongue.

In addition, it communicates freely with the lingual
nerve. The more apparent of these connections take place
in the form of one or more loops in relation to the anterior
border of the hyoglossus. Other communications with the
same nerve are effected in the substance of the tongue, ^-f-^

Reflection of the Hyoglossus. — The hyoglossus should now be
carefully delaclioil from the hyoid bone, and thrown upwards towards
the tongue. In doing this there is no need to divide the structures
which lie upon its surface. By the reflection of this muscle the follow-
ing structures will be fully displayed — (i) the second and third stage of
the lingual arter)', with its dorsalis lingua; branch and the veins which
accompany it ; (2) the posterior jmrt of the genio-hyoglossus ; (3) the
origin of the middle constrictor of the pharynx ; and (4) the attachment
of tlie styli^-hyoid ligament.

The Genio-hyoglossus (musculus genio-glossus) is a flat
triangular muscle, the inner surface of which is in contact
in the mesial plane with its fellow of the opposite side. It
arises by a short pointed tendon from the upper of the two
genial tubercles which project from the posterior aspect of
the symphysis of the mandible, and from this its fleshy
fasciculi spread out in a fan-shaped manner. By far the
greater part of the muscle is inserted into the tongue by
an insertion which extends from the tip backwards through-
out the whole length of the organ j below the tongue,
a few fibres reach the side of the pharynx, whilst the
remainder are inserted into the body of the hyoid bone.
As we have already noted, the genio-hyoglossus is supplied
by twigs from the hypoglossal nerve.

Lingual Artery (arteria lingualis). — As the lingual artery
is now fully exposed, it can be conveniently studied at this
stage. It springs from the fore-part of the external carotid,
and it is customary to describe it in three parts — viz. (i).a
part extending from its origin to_ the posterior border of
the hyoglossus muscle ; (2) a part lying in relation to the
upper border of the Iiyoid bone ; (3) a portion ascending

324 HEAD AND NECK.

under cover of the anterior border of the hyoglossus
muscle to the under surface of the tongue, where it ends
in a terminal branch called the ranine artery (Fig. 255).

The j^rst part has been fully examined in a previous
dissection. It lies in the carotid triangle of the neck, and
is therefore comparatively superficial. It is crossed by the
hypoglossal nerve, the tendon of the digastric and the
stylo -hyoid muscle. The second ___part proceeds forwards
along the upper border of the great cornu of the hyoid
bone, and is covered by the hyoglossus muscle which
intervenes between it and the hypoglossal nerve. The
nerve, however, is placed at a slightly higher level. The
deep or internal relations of the artery in this stage of its
course are the middle constrictor of the pharynx and the
genio-hyoglossus. The third part ascends almost vertically
upon the genio-hyoglossus. It is overlapped by the an-
terior border of the hyoglossus, and ends when it reaches
the under surface of the tongue by turning forwards into
its terminal or ranine branch.

The branches of the lingual artery are : —

1. Hyoid from \)a.& first part (p. 251).

2. Dorsalis linguae from the second part.

3. Sublingual from the third part.

4. The ranine or terminal branch.

The dorsalis Imguce. is generally represented by two or
more well-marked branches (rami dorsales linguae) which
pass upwards under cover of the hyoglossus muscle to end
in twigs to the mucous membrane covering the back part
of the dorsum of the tongue. Some twigs are also suppUed
to the muscular substance of the organ, and a few may be
traced backwards into the tonsil.

The sublingual artery (arteria sublingualis) emerges from
under cover of the anterior border of the hyoglossus, and
then ascends upon the genio-hyoglossus to reach the sub-
lingual gland which it supplies. It also gives branches to
the surrounding muscles and anastomoses with its fellow of
the opposite side and with the submental branch of the
facial artery.

DEEP DISSECTION OF THE NECK. 325

'\\\SLmninc arkry {^xii^n-x i)rofunda linguai) runs forwards
ui)on the inferior aspect of the tongue as far as the tip.
It can easily be exposed by dividing the mucous membrane
along its course, when it will be seen to lie close to the
attachment of the fra;num of the tongue, and to be con-
tinued forwards in the interval between the genio-hyo-
glossus and the inferior lingualis muscle. Its course is
tortuous to allow of the protrusion or elongation of the
organ, and it gives off numerous branches.

Lingual Veins. — 'Hie lingual artery is accompanied by
two small vena2 comites which lie with it under cover of
the hyoglossus ; but the main vein of the tongue, termed
the ra/ii/ie, accompanies the hypoglossal nerve upon the
siTperficial surface of the hyoglossus muscle. These veins
receive tributaries corresponding more or less closely with
the branches of the artery, and they open into the common
facial vein, or perhaps directly into the internal jugular
vein.

The Stylo-hyoid Ligament is the last structure to be
examined in this dissection. It is a fibrous cord which
springs from the tip of the styloid process and passes down-
wards and forwards to be attached under cover of the hyo-
glossus muscle to the lesser cornu of the hyoid bone. It is
not uncommon to find it partially ossified ; in other cases
it may assume a ruddy hue and contain muscular fibres.

DEEP DISSECTION OF THE NECK.

In the deep dissection of the neck the following structures
are displayed : —

1. The styloid process, with the three muscles wliicli take urijjin

from it.

2. The interiLil carotid artery.

3. The ascending i)haryngeai artery.

4. The tonsilhtic and ;i.scenihng palatine branches of the facial artery.

5. The internal jugular vein.

6. Glosso-pharynyeal nerve.

7. Vagus nerve.

326 HEAD AND NECK.

8, Spinal accessory nerve.

9. Hypoglossal nerve.

10. The cervical part of the sympathetic cord.

11. The first loop of the cervical plexus.

12. The rectus lateralis muscle.

Dissection. — Before the dissection is commenced, the skull-cap,
which, up to the present time, has been retained in position by the flaps
of scalp stitched over it, should be removed. The floor of the cranium
should then be cleansed by sponging it with spirit and carbolic solution.
To expose the styloid process and its muscles, it is necessary to turn aside
the posterior belly of the digastric, and the external carotid artery.
Detach the former from its origin, and throw it downwards and forwards
towards the hyoid bone. Its nerve of supply from the facial must also
be cut, and if the filament which connects this branch with the glosso-
pharyngeal nerve has not been previously seen it should now be sought
for. The external carotid artery may be divided immediately below the
point where it divides into its two terminal branches. After cutting the
occipital and jDosterior auricular arteries, it can be turned forwards out
of the way.

Of the parts in connection with the styloid process, the stylo-hyoid
and stylo-glossus muscles and the stylo-hyoid ligament have been already
fully examined; the stylo - pharyngeus muscle alone remains to be
described. In cleaning the fibres of this muscle, be careful not to injure
the glosso - pharyngeal nerve which appears at its lower border, and
gives to it its nerve of supply.

The Stylo-pharyngeus is the longest of the three slender
muscles which spring from the styloid process. It arises
from its deep or inner surface close to its root, and extends
downw^ards and forwards to gain the side of the pharynx.
Here it disappears under cover of the upper border of the
middle constrictor muscle, and its fibres spread out, to be
inserted for the most part into the upper and hinder borders
of the thyroid cartilage ; a certain proportion, however, are
lost in the wall of the pharynx. The stylo-pharyngeus
muscle is supplied by a branch from the glosso-pharyngeal
nerve.

Dissection. — Snip through the base of the styloid process with the
bone -pliers, and throw it and its attached muscles downwards and
forwards. The internal carotid and ascending pharyngeal arteries may
now be followed up to the base of the skull. The glosso-pharyngeal,
vagus, spiftal accessory, and hypoglossal nerves, and the superior cervical
ganglion, with their various connections and branches, must at the same

DEEP DISSECTION OF THE NECK. 327

lime l)c dissected. Tills is an exceedingly dillicuil dissection. A dense
and toui;h fascia envelops these structures, and a j^reat auKJunl of
patience is recjuired to trace the branches of the nerves through it. One
nerve — the pharyui:;cal brattch of the vastus — which jiroceeds downwards
and forwards ujion the superficial or outer aspect of the internal carotid,
is es|)ecially liable to injury, and must therefore be borne in mind from
the very outset of the dissection. The internal la)y)ii:;eal and the
external laryngeal neii'es have been previously displayed in the anterior
triangle of the neck. These, if traceil upwartls, will lead to the superior
laryns^eal braneli of the vagus, which is carried downwards upon the
deep aspect of the internal carotid artery. At the base of the skull, all
the nerve-trunks will ho. found making their appearance close together
in the interval between the internal jugular vein and the internal carotid
artery ; whilst behind the vein, the rectus lateralis muscle and {\\q first
loop of the ceri'ical plexus will be seen.

The Internal Carotid, Artery (arteria carotis interna) is
one of the two terminal branches of the common carotid,
and commences at the level of the upper border of the
thyroid cartilage. From this point it proceeds upwards in
the neck in a vertical direction, until it reaches the base of
the skull ; here it disappears from view by entering the
carotid canal of the petrous portion of the temporal bone,
through which it reaches the interior of the cranium. The
internal carotid artery can therefore be very appropriately
divided into three parts — viz. (i) a cervical; (2) a petrous;
and (3) an intracranial. The cervical part alone comes
under the notice of the student in the present dissection.

In the first instance, the internal carotid artery is placed
within the carotid triangle, and is therefore comparatively
superficial. It is covered by the integument, platysma, and
fascia, and is overlapped by the sterno-mastoid muscle. As
it proceeds upwards, it gradually sinks deeply, until it comes
to lie under cover of the entire mass of the parotid gland,
the styloid process, the stylo-pharyngeus muscle, the stylo-
hyoid muscle, and the posterior belly of the digastric,
T/iree nerves and f7V0 arteries will also be noticed to cross
the vessel superficially, viz. : —

1. The hypoglossal nerve. ] i. The occipital artery.

2. The glossopharyngeal nerve. 2. The posterior auricular artery.
J. The pharyngeal branch of the

vagus nerve. |

328

HEAD AND NECK.

The relationship of the external carotid artery to the
internal carotid is a varying one. At first the external
carotid lies in front of it, but soon, owing to its inclination
backwards, it comes to lie directly superficial to the internal
carotid. The following" structures intervene between the two
vessels : —

1. Styloid process.

2. Stylo-pharyngeus muscle.

3. Glosso-pharyngeal nerve.

4. Pharyngeal branch of vagus.

5. A portion of the parotid gland.

Behind., the internal carotid rests upon the rectus capitis
anticus major muscle, and is in contact with the vagus
nerve and the superior cervical ganglion of the sympathetic.
To its outer side is the internal jugular vein. A prolongation
upwards of the carotid sheath encloses the two vessels
together with the vagus nerve. On its inner aspect the
internal carotid is related to the pharynx and the tonsil. At
the same time it should be noted that the relationship to the
tonsil is not so close as has generally been supposed. This
may be seen in Fig. 240, p. 262, which represents a section
through the frozen head at the level of the upper part of the
tonsil.

Before leaving this vessel, note that at the base of the
skull four nerves appear in the interval between it and the
internal jugular vein \ these are the glosso-pharyngeal, the
vagus, the spinal accessory, and the hypoglossal.

Ascending Pharyngeal Artery (arteria pharyngea ascen-
dens). — The origin of this vessel from the external carotid
has already been observed (p. 254). It proceeds vertically
upwards to the base of the skull, where it ends by dividing
into minute meningeal twigs. Its relations are very simple.
It is placed between the internal carotid artery and the wall
of the pharynx, and this position it holds throughout its
entire course.

The following branches will be recognised as springing
from the ascending pharyngeal : —

1. Pharyngeal.

2. Prevertebral.

3. Meningeal.

DEEP DISSECTION OF THE NECK. 329

The pharyngeal branches (rami pharyiigci) supply the
l)harynx, and the lower members of the series anastomose
with the superior thyroid artery. Higher up, a larger />«/«-
tine branch distributes twigs to the Eustachian tube, the
soft palate, and the tonsil.

The prevertebral branches are small twigs which are
given to the pervertebral muscles, and anastomose with the
ascending cervical artery.

The meningeal tivigs enter the cranium through three
openings, viz. the foramen lacerum medium, the jugular
foramen, and the anterior condyloid foramen.

Inferior Palatine and Tonsillitic Arteries. — At this stage
the dissector should again examine these vessels — the first
branches which are given off by the facial artery. They
have already been described (p. 252), but their relations as
they ascend in the neck can now be more satisfactorily
studied. The size of the inferior palatine is very variable,
and depends very much upon that of the palatine branch
of the ascending pharyngeal.

Interial Jugular Vein (vena jugularis interna). — The
internal jugular vein is the largest venous channel of the
neck. It is directly continuous with the lateral sinus of the
cranial cavity, and it enters the neck through the posterior
compartment of the jugular foramen. From this it pro-
ceeds downwards, until it reaches the posterior aspect of
the inner end of the clavicle, where it joins the sub-
clavian vein to form the innominate or brachio-cephalic
vein. Its commencement in the jugular foramen shows
a slight dilatation, termed the bulby the lumen of which
remains at all times patent owing to the connection of its
walFs to the margms of the foramen. By passing a probe
from the lateral sinus into the internal jugular vein the
continuity of the two channels can be easily demonstrated.

The relations which the internal jugular vein presents
in the neck can be summed up in a very few words. At
the base of the skull it lies behind the internal carotid
artery, and rests upon the rectus lateralis muscle. Very
soon, however, it changes its relationship to the internal

330

HEAD AND NECK.

carotid, and comes to lie upon its outer side. This
position it maintains until it reaches the upper border of
the thyroid cartilage. Below this level it is continued
downwards upon the outer side of the common carotid
artery.

Throughout its whole length it is included within a
sheath of fascia common to it, the two arteries along which
it lies and the vagus nerve. Lastly, at the root of the
neck, its terminal part crosses the first portion of the
subclavian artery.

But there are some slight differences to be noted
between the two veins of opposite sides. The right vein
is usually considerably the larger of the two, and as they
approach the root of the neck both veins incline slightly to
the right. From this it follows that the left vein is closely
applied to the lower portion of the common carotid artery
of that side, whilst the right vein is separated from its
companion artery by a narrow interval which presents a
triangular figure. The base of this triangle is formed by
the first part of the subclavian artery, and it is bisected by
the vagus nerve.

The tributaries which join the internal jugular vein
have for the most part been previously studied. They

are

Inferior petrosal sinus (p. 128).
Pharyngeal veins.
Lingual veins (p. 325).
Common facial vein (p. 253).
Superior thyroid vein (p. 251).

6. Middle thyroid vein (p. 256),

7. Thoracic duct on the left side
and the right lympathic duct
on the right side (p. 237).

I.

2.
3-

4-
5-

T^e inferior petrosal sinus leaves the cranial cavity by the
anterior compartment of the jugular foramen, and joins the
fore-part of the internal jugular vein close to the base of
the skull. By passing a probe from the interior of the
skull through the sinus its connection with the vein can
readily be made out.

The pharyngeal tributaries join the internal jugular
about the level of the hyoid bone. They come from a
venous plexus which lies upon the side of the pharynx,

DEEP DISSECTION OF THE NECK.

331

and presents free communications above with the i)terygoid
plexus.

Dissection. — The internal juyular vein should now be slit ojxrn. A
short distance above its termination a single or a double flapped valve
will be discovered. The vein should then be divided about two inches
below its commencement and its upper part thrown upwards. This is
done to enable the dissector to obtain a better view of the hypoglossal
nerve as it issues from the anterior condyloid foramen.

The Glosso-pharyngeal, the Vagus or Pneumogastric,
and the Spinal Accessory Nerves. — These nerves have, on

sliealh of dura mater

around vagus and spinal

accessory nerves.

ganglion of trunk.
internal jugular vein.

superior laryngeal ner\'e.
spinal accessory nerve.

^fl-

sheath of dura mater around
glosso-pharj-ngeal nerve.

inferior petrosal sinus,
internal carotid arterj-.

glosso-pharj'ngeal nerve.

pharyngeal branch of
vagus.

internal laryngeal nerve,
external laryngeal nerve.

I"'1G. 258. — Diagram of the relation of parts in the
jugular foramen.

a previous occasion, been seen leaving the cranial cavity
through the middle compartment of the jugular fossa, in
the interval between the commencement of the internal
jugular vein behind and the inferior petrosal sinus in front
(p. 125 and Fig. 209, p. 129). It is well that the dis-
sector should again examine the interior of the cranial
cavity and refresh his memory as to the manner in which
they enter the foramen. The ghsso-p/iaryngcal occupies
the foremost position, and it is cut off from the others by
possessing a special and separate tube-like sheath of dura
mater. The spinal accessory is placed behind the vagus.

332 HEAD AND NECK.

and both are included within the same sheath of dura mater.
They therefore traverse the foramen in close contact with
each other. Reaching the exterior of the skull, the three
nerves at first lie together with the hypoglossal nerve in
the interval between the internal jugular vein and the
internal carotid artery, but soon they choose different
routes. The spinal accessory inclines backwards oyer or
behind the internal jugular vein ; the glosso -pharyngeal
inclines forwards over the internal carotid ; whilst the
vagus proceeds vertically downwards between these vessels
(Fig. 258).

In an ordinary dissection it is impossible to follow out many of the
minute twigs which take origin from these nerves in the region of the
basis cranii. To do so it is necessary to possess a perfectly fresh part,
which has been specially prepared by having the soft parts toughened
with spirit and the bone softened by immersion in a weak solution of
acid. Even then the dissection is a difficult one, although it should
certainly be undertaken by the advanced student in the event of his
being able to obtain a part for the purpose.

In the following description of these nerves the account
of the branches which can in all cases be traced is printed
in large type, whilst that of those requiring special dissec-
tion is printed in small type.

Glosso-pharyngeal Nerve (nervus glosso-pharyngeus). —
The glosso -pharyngeal nerve inclines downwards and
forwards and crosses the internal carotid artery super-
ficially. It passes under cover of the styloid process arid
the stylo-pharyngeus muscle, and at the lower border of
the latter it hooks round the muscle and then curves
forwards upon its superficial surface to gain the base of
the tongue. In the dissection of the submaxillary region,
its terminal part has been seen disappearing under cover
of the posterior border of the hyoglossus muscle ; here it
ends in lingual branches.

In the present dissection the following branches should
be made out : —

1. Communicating branch from

the facial.

2. Nerve to the stylo-pharyngeus.

3. Pharyngeal.

4. Tonsillitic.

5. Lingual.

DEEP DISSECTION OF THE NECK'. 333

The conimunicatiitg branch fro/n the facial is a small but
important twig. It springs from the nerve to the posterior
belly of the digastric, and, as a rule, emerges from midst
the fibres of this muscle to join the glosso-pharyngeal close
to the lower part of the jugular foramen. This branch is
considered to convey to the glosso-pharyngeal the motor
fibres which it supplies to the stylo-pharyngeus muscle.

The stylo-pharyngcal nerve is a small twig which enters
the muscle of the same name. The greater part of its
fibres, however, are continued through the muscle to the
mucous membrane of the pharynx.

The pharyngeal branches consist — (i) of one or two
small twigs which perforate the superior constrictor to
reach the mucous membrane of the pharynx: and {2) a
larger nerve which comes off higher up and joins the
pharyngeal branch of the vagus to form the pharyngeal
plexus. It frequently divides into two or more branches.

The tonsillitic branches proceed from the glosso-pharyn-
geal near the base of the tongue. They form a plexus
oveT the tonsil, termed the circulus tonsillaris, and give
twigs to the mucous membrane of the isthmus faucium
and the soft palate.

The terminal or lingual branches will be followed in the
dissection of the tongue.

There are still other points in connection \vilh the glosso-pharyngeal
nerve which require mention. At the lower part of the jugular foramen
two minute ganglia are formed upon its trunk, and from the lower of
these certain minute branches are given off. The upper ganglion is
called the jugular ganglion ; the .lower one is termed the petrous
ganglion.

T\\Q jugular ganglion is a minute ganglionic swelling, which only
involves a portion of the fibres of the nerve-trunk, and is placed in the
upper part of the bony groove in which the nerve lies as it proceeds
through the jugular foramen.

The /<e(rous ganglion \?, 7i\^xgcr swelling, which involves the entire
nerve-trunk, and lies at the opening of the jugular foramen between the
"Tnferior petrosal sinus (which intervenes between it anil the anterior
border of the foramen) anil the vagus nerve invested by its fibrous
sheath derived from the dura mater. Its length is not more than two
or three lines. Three branches of communicuion enter or pnxreed
li in it. These connect it with — (l) the superior cervical sympathetic

334

HEAD AND NECK.

ganglion; (2) the auricular branch of the vagus; and (3) the roqt;_
ganglion of the vagus.

In addition to these twigs the tympanic neive or the nerve of Jacobson
takes origin from the petrous ganglion.

Tympanic Nerve. — The ultimate destination of this nerve may be
regarded as being the otic ganglion, but it takes a very circuitous route
to gain this structure. It enters a minute foramen on the ridge which
separates the jugular fossa from the carotid foramen on the under

Fig. 259. — Diagram of the tympanic nerve,
from Henle. )

(Modified

a. Inferior maxillary division of trigem-

inal nerve.

b. Small superficial petrosal nerve.

c. Great superficial petrosal nerve.

d. Facial nerve.

e. Tympanic nerve in the tympanic

cavity.

f. Branch to Eustachian tube.

g. Small deep petrosal nerve.

h.- Carotico-tympanic nerve.
k. Communicating twig to vagus.
/. Petrous ganglion of the glosso-
pharyngeal.
m. Communicating twig to facial nerve.
11. Tympanic nerve before it enters the

petrous bone.
o and/, branches to the mastoid cells.
r. Branch to tympanic plexus.

surface of the petrous bone, and it is conducted by a narrow canal to
the tympanic cavity. It traverses the inner wall of this chamber,
grooving the promontory. Having gained the anterior part of the
tympanum, it enters the bone a second time, and runs in a minute
canal, which tunnels the petrous bone below the upper end of the
channel in which is lodged the tensor tympani muscle. In this part of
its course the tympanic nerve is joined by a branch from the geniculate
ganglion of the facial nerve, and, after the junction is effected, it is
termed the small superficial petrosal nerve.

The canal in which the small superficial petrosal nerve is lodged
opens into the cranial cavity upon the anterior face of the jDetrous bone.

DEEP DISSECTION OE THE NECK. 335

immediately external to the hiatus Fallopii. Through this the nerve
emerges, and soon leaves the interior of the cranium by passing (lf)\vn-
wards in the interval between the great wing of the sphenoid and the
petrous bone. Outside the skull it ends by joining the otic ganglion.

In the tympanic cavity the tyiitpauic nerve gives branches of supjjly
— (l) to the mucous membrane of the tympanum; (2) to the lining
membrane of the mastoid cells (Fig. 259, /, 0) ; and (3) to the mucous
membrane of the Eustachian lube (Fig. 259, /). It also gives off a fine
branch termed the small deep petrosal nerve (n. petrosus profundus
minor). This enters a canal in the processus cochleariformis which
conducts it to the foramen lacerum medium, where it effects a junction
with the carotid plexus. The tympanic nerve likewise receives a
minute twig from the carotid plexus which is called the ncrviis carotico-
tympanicus.

Vagus or Pneumogastric Nerve. — The vagus passes
through the middle compartment of the jugular foramen in
company with the spinal accessory — both being included
within the' same sheath of dura mater. In the neck it
pursues a vertical course, lying, in the first instance,
between the internal jugular vein and the internal carotid
artery, and afterwards between the same vein and the
common carotid artery. Further, as has been already
observed, it is enclosed within the sheath which envelops
these vessels, and it lies upon a plane posterior to them.
At the root of the neck it enters the thorax, and shows
different relations on the two sides. On the right side it
crosses the first part of the subclavian artery ; on the left
side it proceeds downwards between the common carotid
and left subclavian arteries, and passes under cover of the
left innominate vein.

As in the case of the glosso-pharyngeal, the vagus shows
two ganglia in connection with its upper part. These are
\.hc^(Uig/jon of the root {gang/ion fuguhxre) and the ganglion
of the trynk {ganglion nodosum).

The Ganglion of the Root is situated within the jugular foramen.
It is a rouiukil swelling which is connected by connnunicating twigs with
several of the nerves in the neighbourhood, and which gives olV two
branches of distribution.

336 HEAD AND NECK.

Branches of Communication.

Branches of Distribution.

1. With the facial nerve.

2. With the petrous ganglion

of the glosso-pharyngeal.

3. With the spinal accessory.

4. With the superior ganglion

of the sympathetic.

1. Recurrent nerve.

2. Auricular nerve.

The reairrent branch is a minute twig which runs backwards through
the jugular foramen, and, dividing into two branches, is distributed to
the dura mater in the posterior cranial fossa.

The auricular tterve (Arnold's nerve) obtains a filament of com-
munication from the petrous ganglion of the glosso-pharyngeal, and
proceeds backwards upon the outer surface of the bulb of the internal
jugular vein to enter a minute aperture on the posterior part of the outer
wall of the jugular foramen. A narrow canal now conducts it through
the substance of the temporal bone, and, on its way, it crosses internal
to the Fallopian canal a short distance above the stylo-mastoid foramen.
It is thus brought into close relation with the facial nerve, and is con-
nected with it by an ascending and a descending branch of communi-
cation. Finally, it appears on the surface of the skull in the interval
between the mastoid process and the external auditory meatus. Its
further course is described on p. 277.

Ganglion of the Trunk. — After emerging from the
jugular foramen, the vagus nerve is joined by the accessory
portmi of the spinal accessory nerve, and swells out into the
ganglion of the trunk.

The ganglion of the trunk is an elongated reddish-
coloured swelling of about three-quarters of an inch in
length, which is developed upon the stem of the vagus
nerve half an inch below the base of the cranium. Strong
branches of communication pass between this ganglion,
the first loop of the cervical plexus, and the superior
cervical ganglion of the sympathetic. Further, the hypo-
glossal nerve is generally closely bound to it by fibrous
attachment, in the midst of which some interchange of
nerve filaments takes place.

The Branches of Distribution which arise from the

DEEP DISSECTION OF THE NECK. 337

vagus nerve in the neck may now be studied. These
are :—

1. rharynj^cal.

2. Superior laryngeal.

3. Inferior or recurrent laryngeal.

4. Cardiac.

The Pharjmgeal Branch (ramus pharyngeus) springs
from the upper part of the ganglion of the trunk, and runs
downwards and forwards, superficial to the internal carotid
artery, to end in the f /laryngeal plexus. Very frequently
it is replaced by two branches, of which the upper is the
larger.

The Superior Laryngeal Nerve (nervus laryngcus
superior) is a much larger branch, which takes origin from
the middle of the same ganglion. It passes downwards
and forwards, but differs from the preceding nerve by
passing under cover of the internal carotid artery. In this
situation it ends by dividing into the internal laryngeal and
external laryngeal nerves ; both of these have been previously
seen in the dissection of the anterior triangle (pp. 212 and
216). Before it divides, the superior laryngeal effects
communications by means of fine twigs with the superior
cervical ganglion of the sympathetic, and it also receives
one or two filaments from the pharyngeal plexus.

The internal laryngeal nerve runs forwards to the interval
between the hyoid bone and the thyroid cartilage, and, dis-
appearing under cover of the posterior border of the thyro-
hyoid muscle, it pierces the membrane of the same name,
and enters the larynx.

The external laryngeal nerve is a very slender branch,
which inclines downwards and forwards to reach the crico-
thyroid muscle in which it ends. It supplies a few fila-
ments to the inferior constrictor of the pharynx and a fine
twig to the superior cardiac branch of the sympathetic^
whilst it receives a communicating branch from the superior
cervical ganglion of the sympathetic.

The Recurrent Laryngeal Nerve (nervus laryngeus
inferior) arises differently on the two sides. On the right

vol.. II. — 22

338 HEAD AND NECK.

side, it springs from the vagus as it crosses the first-'-pftrt
of the subclavian artery, and it adopts its recurrent course
by hooking round this vessel. On the left side, it arises
in the thorax, and hooks round the aortic arch (or, more .
correctly speaking, around the termination of the obliterated
ductus arteriosus). In the neck each nerve ascends in the
groove between the trachea and oesophagus, and passing
b^eliind or in front of the inferior thyroid artery, or it may
be between the two terminal branches of this artery, it
disappears under cover of the lower border of the inferior
constrictor muscle, to enter the larynx.

Before the recurrent laryngeal nerve reaches the larynx
it gives off several branches — viz. (i) cardiac branches;
(2) twigs to the trachea and oesophagus; and (3) a few
filaments to the inferior constrictor as it passes under
cover of its lower margin.

The Cardiac Branches. — One or two cardiac branches
arise from the vagus in the upper part of the neck (rami
cardiaci superiores). These join the cardiac branches of
the sympathetic. One branch (ramus cardiacus inferior)
springs from the vagus in the lower part of the neck. On
tlie left side this terminates in the superficial cardiac plexus ;
on the right side it ends in the deep cardiac plexus.

Spinal Accessory Nerve (nervus accessorius). — This
nerve consists of two parts — an accessory and a spinal. In
the foramen jugulare \h.& accessory portion \^ zonn^zV^di by
one or two fine twigs with the root-ganglion of the vagus,
and below the basis cranii it leaves the spinal part and
joins the vagus.

The_accessory part of the spinal accessory nerve contributes to the
vagus the greater proportion of its motor fibres. They pass over the
surface of the trunk-ganghon, and are continued into the pharyngeal
and into the superior laryngeal nerves. Some of the fibres are likewise
carried down the stem of the vagus into the cardiac branches and also
into the recurrent laryngeal nerve.

The sj)inal part of the spinal accessory is directed back-
wards under the transverse process of the atlas. It crosses
the internal jugular vein, and disappears into the substance

DEEP DISSECrrON OF THE NECK. 339

of llic slcrno-masloid muscle. Its further course bus Ijcen
already studied (pp. 138 and 216). It is distributed to two
nuisclcs — viz. the sterno-mastoid and the trapezius.

Pharyngeal Plexus (plexus pharyngeus). — This is a
nicshwork of line nerve filaments, which is formed upon
the lateral wall of the pharynx at the level of the middle
constrictor muscle. The pharyngeal branches of the vagus,
glosso-pharyngeal, and superior cervical ganglion of the sym-
pathetic enter into its construction, and one or more minute
ganglia are developed in connection with it. Its terminal
twigs are given to the muscles and mucous membrane of
the pharynx, and one branch (the ramus lirigualis vagi)
connects the plexus with the hypoglossal nerve.

The Hypoglossal Nerve (nervus hypoglossus) makes its
exit from the cranium, through the anterior condyloid
foramen. It i)ierces the dura mater in two separate
parts, which unite into one stem at the entrance of the
bony foramen. As^ it issues from the anterior condyloid
foramen it lies deeply under cover of the internal jugular
vein and the internal carotid artery, but it almost imme-
diately inclines outwards, and, taking a half spiral turn
around the trunk-ganglion of the vagus, it appears between
the two vessels, and is continued downwards and forwards.
Its close connection with the ganglion of the trunk of the
vagus has already been noted. The two nerves at this
point are almost inseparably united by dense connective
tissue, and in the midst of this an interchange of nerve
fibres takes place. Gaining the lower border of the
posterior belly of the digastric muscle, the hypoglossal
nerve hooks round the occipital artery, and enters the
anterior triangle of the neck. From this point' to the
under surface of the tongue it has already been traced.

Branches of communication. — Near the base of the skull
the hypoglossal is brought into connection with (i) the
superior cervical ganglion; (2) the vagus; and (3) the first
cervical nerve. Further, as it turns round the occipital
artery it receives the ramus /ingua/is vagi from the pharyn-
geal plexus.

340 HEAD AND NECK.

The importance of the connection between the hypo
glossal and the first cervical nerve has already been alluded
to (p. 240 V. Fig. 235).

Branches of distributmi. — With the exception of the
minute recurrent and vascular twigs, which come off within
the condyloid foramen, the branches of distribution which
proceed from the hypoglossal nerve have been described
(pp. 225 and 322).

The recurrent branch arises in the upper part of the anterior condy-
loid foramen, and, regaining the interior of the cranium, it is distributed
to the dura mater around the foramen magnum.

The vascidar twigs are some fine filaments, which are said to be
supplied to the deep aspect of the internal jugular vein.

Dissection. — In the dissection of the neck the greater part of the
cervical sympathetic, with the branches which proceed from it, has
been displayed. The inferior ganglion, which lies deeply in the hollow
between the transverse process of the seventh cervical vertebra and the
neck of the first rib, is still to a certain extent concealed, and must now
be displayed. Dislodge the subclavian artery from its place on the first
rib behind the scalenus anticus muscle, and turn it well inwards. To
do this efficiently, it will be necessary to cut the superior intercostal
artery at its origin ; this vessel runs downwards upon the outer side of
the sympathetic. Great care must be taken to preserve uninjured the
fine nerves which proceed downwards in front of the first part of the
subclavian artery. If more space for the dissection is required, the fore-
part of the first rib may be removed by the bone-pliers, but, as a general
rule, this will not be found to be necessary.

Sympathetic Cord in the Neck. — The number of ganglia
which are developed upon the sympathetic cord in the neck
is reduced to three ; but inasmuch as the superior cervical
ganglion is brought into connection with the four upper
cervical nerves, there is good reason to suppose that it is
formed by the coalescence of four ganglia. Upon similar
grounds, we may argue that the middle and inferior cervical
ganglia are each formed by the amalgamation of two primi-
tive ganglia.

The sympathetic cord takes a vertical course through
the neck in front of the roots of the transverse processes
of the vertebrae. It lies upon the rectus capitis anticus
major and the longus colli muscles, and is embedded in

DEEP DISSECTION OF THE NECK. 341

the posterior wall of the carotid sheath. Alxwc, it is pro-
longed u|)\vards in the form of a sto.ut, ascending nerve-
trunk, which accompanies the internal carotid artery into
the carotid canal.; l>e/(nv, \\. becomes continuous over the
neck of the first rib and behind the subclavian artery with
the thoracic portion. of the sympathetic. The branches
take origin from the ganglia ; occasionally, however, one
or more may be observed to arise from the connecting
cords.

The Superior Cervical Ganglion (ganglion cervicale
superius) is_ the largest of the thrcf ganglia. It is an
elongated fusiform body which varies somewhat in size.
It is placed upon the upper part of the rectus capitis
anticus major, opposite the second and third vertebras,
and behind the internal carotid artery. From its u[iper
end the stout branch proceeds which enters the carotid
canal, whilst its lower end tapers into the downward con-
tinuation of the cord. Numerous branches issue from it ;
of these some connect it with neighbouring nerves, whilst
others are distributed in various ways.

The connecting branches are: — (i) slender filaments
which connect it with the upper four cervical nerves; (2)
twigs to both ganglia of the vagus; (3) to the petrous gan-
glion of the glosso-pharyngeal ; and (4) to the hypoglossal.
It is not connected with the spinal accessory.

The branches of distribution are : —

1. Rami vasculares.

2. Pharyngecit.

3. Superior cardiac.

The 7-a»ii vasculares (nervi carotici externi) are soft deli-
cate filaments which run towards the external carotid artery,
and form a loose interlacement around it and its branches.
I""rpm this plexus a branch is given to the intercarotid body ;
further, the part continued upon the facial artery supplies,
as we have already noted, the sympathetic root to the sub-
maxillary ganglion, whilst the subdivision upon tlie middle
meningeal artery furnishes the corresponding root to the

342 HEAD AND NECK.

Otic ganglioiii as well as the external superficial petrosal nerve
which runs to the geniculate ganglion of the facial nerve.

The pharyngeal branches course inwards between the two
-y carotid arteries to join the pharyngeal plexus.

The superior cardiac nerve (nervus cardiacus superior) is
a long slender branch which springs by several roots from
the ganglion and then proceeds downwards behind the
carotid artery. At different stages of its course it is joined
by other branches of the sympathetic, by a branch from the
vagus, and also by filaments from the external laryngeal and
recurrent laryngeal nerves. The right superior cardiac nerve
is continued into the thorax by passing behind or in front
of the subclavian artery, and it ends in the deep cardiac
plexus. The left superior cardiac nerve follows the left
common carotid artery in the thorax, and, crossing the
arch of the aorta, ends in the superficial cardiac plexus.

The MMdle^ Cervical Gangli»n (ganglion eervicale
medium) is the smallest of the three ganglia of the neck.
It is placed opposite the sixth cervical vertebra in close
proximity to the inferior thyroid artery, upon which, indeed,
it not unfrequently rests. It presents the following
branches : —

1. Twigs_ which connect it with \hQ fifth and sixth spinal nerves, and

which pass between the contiguous margins of the scalenus
anticus and longus colU muscles.

2. Thyroid branches which run to the thyroid body along the inferior

thyroid artery, and which form connections with the external
and recurrent larnygeal nerves.

3. The middle cardiac nerve.

On both sides the middle cardiac nerve (nervus cardiacus
medius) enters the thorax and is lost in the deep cardiac
plexus. In the neck it is connected with the superior
cardiac nerve, and with the recurrent laryngeal nerve. On
the right side it passes behind or in front of the subclavian
artery ; on the left side it is continued downwards between
the common carotid and subclavian arteries.

The Inferior Cervical G-anglion (ganglion cervicale in-
ferius) is lodged in the interval between the transverse

DEEP DISSECTION OF THE NECK. 343

l)roccs.s of the seventh cervical vertebra and the neck of the
first ril). In this position it lies behind the vertebral
artery. It is by no means uncommon to find it more or
less completely fused over the neck of the first rib with the
first thoracic ganglion. Again, the connection between it
and the middle ganglion is generally in the form of two or
more slender nerve cords, of which one passes in front of
the subclavian artery. The loop which is thus formed is
termed the ansa Vieussenii (ansa subclavia).

The branches of the inferior cervical ganglion are : —

1. Connecting twigs with the seventh and eighth cervical nerves.

2. Rami vascuiares.

3. Inferior cardiac nerve.

The rami vascuiares are fine branches which form a
plexus around the subclavian artery and its branches.
Others, remarkable for their large size, join the vertebral
j\rtery.

The loiver cardiac nerdc (ncrvus cardiacus inferior) on Ijoth
sides enters the deep cardiac plexus.

Dissection. — The liule muscle termed the rectus capitis lateralis
should now be cleaned, and its attachments defined. It lies in the
interval between the transverse process of the atlas and the occiput,
behind the commencement of the internal jugular vein. The anterior
division of the first cervical nerve will be seen emerging from under
cover of its inner margin.

Rectus Capitis Lateralis. — The rectus lateralis arises
from the fore-part of the up[)er surface of the extremity of
the transverse process of the atlas, and is inserted into the
under surface of the jugular eminence of the occipital bone.
It is supplied by a branch from the anterior division of the
first cervical nerve.

, First Loop of the Cervical Plexus. — The anterior
primary division of the first cervical or suboccipital nerve
may next be examined. It will be noticed emerging from
under cover of the inner surface of the rectus lateralis
muscle. It at once turns downwards in front of the trans-
verse process of the atlas, and, joining the ascending branch

344 HEAD AND NECK.

of the second cervical nerve, forms the first loop of the
cervical plexus. From this loop branches are given to two
muscles — viz. the rectus capitis anticus major and minor.
It is likewise brought into connection by means of com-
municating twigs with — (i) the superior cervical ganglion;
(2) the vagus ; (3) the hypoglossal. ^^

If the rectus lateralis muscle be detached from the transverse process
of the atlas and turned upwards, a twig from the anterior division of the
first cervical nerve will be found entering its deep surface ; furthers ..by
cutting through the origin of the superior oblique muscle of the head,
this nerve-division may be traced to the upper surface of the neural
arch of the atlas, where it takes origin from the first spinal nerve-trunk
(suboccipital nerve).

The entire length of the anterior primary division of the
first cervical nerve may now be studied. It turns round
the superior articular process of the atlas, under cover of
the vertebral artery and the rectus capitis lateralis, and,
gaining the anterior aspect of the atlas, it enters into the
formation of the first loop of the cervical plexus. As it lies
in relation to the vertebral artery, it is joined by a filament
from the sympathetic plexus which surrounds that vessel.

Removal of the Head and Neck from the Trunk. — By the time
that the dissectors of the head and neck have arrived at this stage of
their work, the dissectors of the thorax have in all probability finished
their dissection. If this be the case, the head and neck may be removed
from the trunk by cutting thr-ough the vertebral column at the level of
the intervertebral disc between the third and fourth dorsal vertebrae.
By this proceeding the three upper dorsal vertebras, with the attached
portions of the first, second, and third pairs of ribs, are removed with
the neck. The scalene muscles and the longus colli are therefore pre-
served intact.

THE LATERAL PART OF THE MIDDLE
CRANIAL FOSSA.

The structures contained within the middle cranial fossa
may now be examined, and, in carrying out this dissection,
the head should be supported on a block so that the floor

C// / 'ERNO US SINUS. 345

of the cranial cavity looks u[)\vards. The following arc the
structures which must be displayed : —

1 . Cavernous venous sinus.

2. Internal carotid artery.

3. Middle meningeal artery.

4. Small meningeal artery.

5. The two roots of the trigeminal nerve, with the Gasserian

ganglion and the three main divisions of the trigeminal
nerve.

6. Oculo-molor nerve (3rd cranial).

7. Trochlear nerve (4lh cranial).

8. Abducent nerve (6th cranial).

9. Cavernous plexus of the sympathetic.

10. Great sujierficial petrosal nerve.

11. Small sujK'rficial petrosal nerve.

Disscctioti. — To expose these structures, the dura mater must be
stripped from tlie inner part of the lateral portion of the middle cranial
fossa. Enter the knife at the anterior clinoid process, and carry it
•backwards to the apex of the petrous bone. This incision must go no
deeper than is necessary to divide the dura mater, and must be made
immediately to the outer side of the openings in the membrane through
which the oculo-motor, the trochlear, and trigeminal nerves pass. It is
very important to preserve these apertures intact, so that the proximal
ends of these nerves may be held in position during the dissection.
The incision through the dura mater may now be carried along the
upper border of the petrous bone in the line of the superior petrosal
sinus, and also outwards along the posterior margin of the lesser wing
of the sphenoid. The dura mater may now be raised, and the greatest
care must be t.iken in doing so, because it is intimately connected with
the nerves which lie subjacent to it. Thus, where it forms the outer
wall of the cavernous sinus, it is closely applied to the oculo-motor and
trochlear nerves, and firmly att.ached to the ophthalmic division of the
trigeminal nerve, whilst over the petrous bone it is united to the surface
of the Gasserian ganglicjn. The edge of the knife, therefore, must be
kept close to the membrane, and a small portion of it may be left upon
the nerves. This can afterwards be removed as the nerves are defined.

Cavernous Sinus (sinus cavernosus). — Fig. 209 {Si\
p. 129). The cavernous sinus has been opened by the
above dissection. It is a short, wide venous channel,
which extends upon the side of the body of the sphenoid
bone, from the lower and inner end of the sphenoidal
fissure backwards to the ape.x of the petrous portion of the

346

HEAD AND NECK.

temporal bone. In front, blood is conducted into^jt by
the ophthalmic veins and the sphenoparietal venous sinus,
whilst behind, the blood is drained away by the superior
and inferior petrosal venous sinuses. But it has still other
connections ; thus, it receives some of the inferior cerebral
veins, and internally it is brought into communication with
the corresponding sinus of the opposite side by means of
the anterior and posterior intercavernous sinuses (p. 130).
Lastly, one or more emissary veins leave its under aspect.

NT CAROTID INFUNDIBULU)

OC ULO
TRO C H

OPHTHAL

SUPRAMAXILLAR

INFRAMAXILLARY N-

Fig. 260. — Section through the cavernous sinus.
Merkel, somewhat modified. )

(After

and, passing out of the cranium by the foramen ovale, ^
connect it with the pterygoid venous plexus.

The cavernous sinus is formed in the same manner as
the other venous sinuses. The two layers of the dura mater
are separated from each other, and the interval is lined by
a delicate membrane. A complicated network of interlacing
trabeculae occupies the lumen of the channel, and it is on
this account that the term " cavernous " is applied to it.
But, as we have already indicated, this sinus has an unusual
importance to the anatomist, on account of its being
traversed by the internal carotid artery, the cavernous

^ Or it may be through the foramen Vesalii when such exists in the
sphenoid bone.

THE TRIGEMINAL OR EIFTII CRANIAL NERVE. 347

plexus, and the oculo-motor, trochlear, and abducent nerves,
with the oi)hthalniic division of the trigeminal nerve. The
precise relation which these structures bear to its walls will
be described later on ; in the meantime, it is only necessary
to state that two, viz, the internal carotid artery and the
abducent ner\-e, are contained in the interval between the
two layers of the dura mater. These are shut out from the
blood-channel by the delicate lining membrane of the sinus.
The oculo-motor and trochlear nerves, with the ophthalmic
division of the trigeminal nerve, are embedded in the outer
wall of the sinus.

The Trigeminal or Fifth Cranial Nerve (nervus
trigeminus). — The two roots of this nerve have already
been seen piercing the dura mater at the apex of the
petrous portion of the temporal bone under the anterior
extremity of the tentorium. Now that the dura mater has
been raised from the lateral part of the middle cranial
fossa, the further relations of these nerve-roots within the
cranium may be studied. It will be noticed that the
loosely connected and parallel funiculi of the large setisory
root (portio major) at once begin to divide and join with
each other so as to form a dense plexiform arrangement,
whilst, at the same time, the nerve-root increases somewhat
in breadth. The interlacement thus brought about occupies
the smooth depression which marks the anterior aspect of
the apex of the petrous portion of the temporal bone, and
it sinks into the Gasserian ganglion.

The Gasserian ganglion (ganglion semilunare) is some-
what crescentic in form, and lies upon the sutural junction
between the apex of the petrous bone and the great wing
of the sphenoid bone. Here it is enclosed within a recess
or space formed by a separation of the two layers of the
dura mater, and called the caviim Mecke/ii. The concavity
of the ganglion is directed inwards, and it is upon this
aspect that it receives the interlacing fibres of the sensory
root of the trigeminal nerve ; the convexity of the ganglion
is directed outwards, and from it emerge the three main
divisions of the trigeminal nerve. These are, from before

;.

348 HEAD AND NECK.

backwards — (i) the first, or ophthalmic division; (2) the
second, or superior maxillary division; and (3) the third,
or inferior maxillary division. The outer surface of the
Gasserian ganglion has already been observed to be closely
attached to the deep surface of the supporting or inner
layer of the dura mater. By its inner part it is connected
with the sympathetic by some fine filaments which come
from the carotid plexus.

The niotor root (portio minor) of the fifth nerve should
now be followed. Before the nerve pierces the dura mater
the motor root lies along the inner side of the large sensory
root, but it soon changes its position and comes to lie upon
the under surface of the sensory part. To display this
relationship, draw the cut ends of the two roots through
the aperture in the dura mater which leads into the cavum
Meckelii, and, gently dislodging the Gasserian ganglion
from its place, turn it forwards and outwards so as to
expose its deep surface. The small firm motor root can
readily be recognised lying in a groove upon the deep
surface of the ganglion, and if it be raised from this, it will
be seen to have no connection with the ganglion, but to
be continued onwards towards the foramen ovale. It
ultimately joins the inferior maxillary division of the
trigeminal nerve. This junction may take place within
the cranium, in the foramen ovale, or immediately after it
gains the exterior of the skull.

The three principal divisions of the trigeminal nerve may
next be examined. Begin with the inferior maxillary divisioti,
which is the largest. This proceeds directly downwards,
and almost immediately leaves the cranial cavity through
the foramen ovale.

In isolating this large nerve-trunk and defining the bony aperture
through which it makes its exit, look carefully for the small meningeal
artery which enters the cranium through the same foramen. If the
injection has been forced into this vessel it can easily be detected.
Through the foramen ovale the minute emissary veins which connect
the cavernous sinus with the pterygoid venous plexus also pass.

The superior maxillary division, which is composed entirely

THE THIRD, FOURTH, AND SIXTH NERVES. 349

of sensory fibres, is prolonged forwards, and, after a short
course within the cranium, makes its exit through the
foramen rotundum. Near its origin it gives off a fine
recurrent branch to the dura mater.

The nxurreiii branch of the supra-maxillaris lakes origin by several fine
roots, and runs outwards to the anterior Ijranch of the middle meningeal
arter)'. It communicates with the fine filaments of the recurrent branch
of the infra-maxillary division of the fifth nerve (p. 310).

The ophthalmic division is the smallest of the three parts
of the trigeminal nerve, and, like the supra-maxillary, it is
entirely composed of sensory fibres. It proceeds forwards
in the outer wall of the cavernous sinus, and ends close
to the sphenoidal fissure by dividing into three terminal
branches. As it traverses the sinus it is accompanied by
the oculo-motor and trochlear nerves, both of which occupy a
higher level. Like the other two divisions of the trigeminal
nerve, the ophthalmic nerve gives off a recurrent branch to
the dura mater.

The recurrent branch springs from the ophthalmic nerve close to its
origin, and runs backwards for a short distance in the sheath of the
fourth nerve. After leaving this nerve it breaks up into fine terminal
filaments, which are distributed between the two layers of the dura
mater in the neighbourhood of the superior petrosal sinus.

The terminal branches of the ophthalmic division of the
trigeminal nerve are the nasal, the lachrymal, and the
frontal. The nasal, as a rule, takes origin first ; soon after,
the lachrymal is given off, and then the stem of the nerve
is continued onwards as ihe frontal. These three nerves
enter the orbit through the sphenoidal fissure.

The Third or Oculo-motor, Fourth or Trochlear, and
Sixth or Abducent Nerves. — The oculo-motor and trochlear
nemes, as the dissector has previously noted, pierce the
dura mater within the small triangular area, which is formed
by the divergence of the attached and free margins of the
tentorium. They now proceed forwards in the outer wall
of the cavernous sinus. The third or oculo-motor nerve
occupies the highest level, then comes the fourth or troch-

350 HEAD AND NECK.

lear nerve, and immediately below this is the ophthalmic
division of the fifth or trigeminal nerve. They therefore_
present a numerical order from above downwards. The
'sixth or abducent nerve^ which pierces the dura mater at the
lower and outer part of the dorsum selte, will be observed
to wind round the outer side of the internal carotid artery,
and then to proceed forwards more directly within the
cavernous sinus than the others and at a lower level.

The oculo-motor, trochlear, and abducent nerves give off
no branches during their course in relation to the cavernous
sinus. They all enter the orbit by passing through the
sphenoidal fissure. Before doing so, the oculo-motor nerve
divides into an upper and a lower division. During their
passage through the sphenoidal fissure the various nerves
undergo a change in their relative positions. This, how-
ever, will be studied in the dissection of the orbit when
that fissure is opened up.

Internal Carotid Artery (arteria carotis interna). — The
intracranial portion of the internal carotid artery may now
be examined. It lies upon the lateral aspect of the body
of the sphenoid, and for the greater part of its course it
traverses the cavernous sinus. It enters the cranium by
emerging from the carotid canal at the apex of the petrous
bone, and it first ascends vertically until it reaches the
root of the posterior clinoid process ; here it makes a bend
and is prolonged forwards to the inner aspect of the
anterior clinoid process, where it abruptly turns upwards
and pierces the dura mater immediately behind the
entrance of the optic nerve into the optic foramen. At
this point it has been severed in^Jhe removal of thej)rain,
but it will be afterwards seen to end at the commencement
of the Sylvian fissure of the brain, by dividing into the^
anterior and middle cerebral arteries. Throughout its
whole course it is surrounded by sympathetic filaments,
and soon after its entrance into the cranium, the abducent
nerve winds round its outer side.

The intracranial portion of the internal carotid artery
gives off the following branches : —

GREA T SUPERFICIA L PR TKOSAL NER VE. 351

1. Branclios to iho piluilary l)o(ly, 'j These arc minute Iwigs

2. Branches to ihe ("lasserian gangliun, \ which arise in Ihc

3. Branches to ihc dwra mater, J cavernous sinus.

4. Upiitlialmic, .

5. Posterior communicating, These will be studied at a later

6. Anterior cerebral, 1 terminal r stage.

7. Middle cerebral, J branches. J

The Cavernous Plexus (plexus cavernosus). — The sym-
pathetic filaments which form this plexus can only be
satisfactorily dissected in a subject which has not been
injected, and even then, the dissection is an exceedingly
difficult one. The cavernous plexus is placed in the
cavernous sinus and is chiefly massed upon the lower and
inner aspect of the internal carotid artery, at the point
where it makes its final bend upwards. It supplies fila-
ments to the pituitary body, to the third and fourth nerves,
and to the ophthalmic division of the fifth or trigeminal
nerve, and likewise the sympathetic root to the lenticular
or ophthalmic ganglion. ^ ""^

Great Superficial Petrosal Nerve. — This minute nerve,
along with a small arterial twig from the middle meningeal
artery, can readily be exposed in the groove on the anterior
face of the petrous bone which leads outwards to the hiatus
Fallopii. It is placed under cover of the Gasserian
ganglion, which must therefore be turned forwards and
outwards. Entering the hiatus Fallopii, the great super-
ficial petrosal nerve is conducted to the aqueduct of
Fallopius, where it joins the geniculate ganglion of the
facial nerve. If traced in the opposite direction, it will be
found at the posterior aspect of the body of the sphenoid
bone to join the hirge deep petrosal nen'e from the carotid
plexus. The trunk formed by the union of these two
filaments is the Vidian ticrve.

The Small Superficial Petrosal Nerve appears ujwn the anterior
face of llic pctrt)us bone ihroui^li an aperture which is placed imme-
diately external to the hiatus Fallopii. It leaves the cranial cavity by
passing downwards between the great wing of the sphenoiil, antl the
petrous part of the temporal bone to reach the otic ganglion. This
minute nerve, as has already been mentioned (p. 334), is formed by the

352 READ AND NECK. '^' ^■

union of the tympanic branch of the glossopharyngeal with a branch
from the geniculate ganglion of the facial.

External Superficial Petrosal Nerve. — It is convenient at this
stage to take note of a third petrosal nerve — the external supe^-Jicial
petrosal. It takes origin from the sympathetic plexus, which accom-
panies the middle meningeal artery, and entering the petrous bone, is
conducted to the geniculate ganglion of the facial nerve.

Middle and Small Meningeal Arteries. — The entrance
of the viiddle meningeal arlery. through the foramen spinosum
should now be examined. It gives minute twigs to Ih^
Gasserian ganglion, and one — the petrosal artery — which
accompanies the great superficial petrosal nerve into the
hiatus Fallopii. The farther course of the middle meningeal
artery has already been described (pp. 131 and 308). The
small recurrent branch of the inferior maxillary division of
the fifth nerve also enters the cranium through the fora,men
spinosum (p. 310).

The sma/l meningeal artery enters the cranium through
the foramen ovale, and is chiefly distributed to the Gasserian
ganglion.

DISSECTION OF THE ORBIT AND OF THE
STRUCTURES PASSING THROUGH THE
SPHENOIDAL FISSURE.

Within the orbital cavity we find grouped around the
eyeball and the optic nerve the following structures : —

'Rectus superior.

Rectus inferior.

Rectus externus.
Muscles, . \ Rectus internus.

Obliquus superior.

Obliquus inferior.
^Levator palpebrse superior.

(Ophthalmic artery and its branches.
Ophthalmic veins (superior and inferior) with their tribu-
taries.

PERIOSTKUM. 353

, Oculo-niolor (jrd cranial).
Trochlear (4lh cranial).
Abducent (6lh cranial).

Nerves -i '*'''^"^'*'' I from ophlhahnic division of ihe Irij^eminal

•' • Lachrymal ' .,r f.fih cranial nerve.

Nasal, J

Orbital branch of the .siii)erior nia.xillary divisicjn of the

trigeminal or fifth cranial nerve.
Lenticular ganglion.
Lachrymal gland.
The capsule of Tenon.

Disscitioii. — The roof of the orbit must be removed. The greater
part of this dissection should be done with a sharp chisel. Begin by
removing the thick cranial wall above the orbital opening, leaving
only a thin portion corresponding to the superior orbital arch. Whilst
this is being done, care should be taken to preserve the soft parts of
the forehead and the upper eyelid. It is of great advantage to retain
throughout the whole examination of the orbital cavity the bony ring
which constitutes its opening on the face. The thin roof of the orbit
may next be removed with the chisel. The lesser wing of the sphenoid,
where it forms the upper boundary of the sphenoidal fissure, should be
taken away by the bone-pliers, but the dissector should carefully jire-
scrve intact the ring of bone around the optic foramen. The sphenoidal
fissure is now fully opened up, and the various nerves, as they enter the
orbit from the cavernous sinus, may be followed out. Lastly, the
anterior clinoid process may be taken away with advantage.

Periosteum. — If the above dissection has been success-
fully carried out, the periosteum clothing the under surface
of the orbital roof will be exposed uninjured. The peri-
osteum of the orbit forms a funnel-shaped" sheath, which
encloses all the contents of the cavity, and is but loosely
attached to its bony walls. Behind, it will Ijc observed to
be directly continuous through the sphenoidal fissure with
the dura mater/ Expanding with the cavity, it becomes
continuous in front around the orbital opening witli the
periosteum, which clothes the exterior of the skull. Here
also it presents important connections with the palpebral
ligaments (p. 289).

Reflection of the Periosteum and the Subsequent Dissection. —
The periosteum should be divided along the middle line of the orbit,
and also transversely as far forwarils as possible. It can now be thrown
inwards and outwards. When this is done, the lachrymal gland will be
ex[)osed in the fore and outer part of the cavity resting upon the upper
vol,. II. — -23

354 HEAD AND NECK.

and outer aspect of the eyeball. Further, the large frontal nerve, lying
upon the upper surface of the levator palpebrse superioris, will be seen
stretching forwards in the middle line of the orbit ; as it apjDroaches the
fore-part of the cavity, it is joined by the supra-orbital artery. The
other superficial structures are usually more or less obscured by the soft
pliable fat, which everywhere fills up the interstices between the different
orbital contents. On carefully separating this, along the inner wall of
the orbit, the superior oblique muscle will be more fully displayed, and
lying upon and entering the hinder part of this muscle the small troch-
lear or fourth cranial nerve will be discovered. As a general rule the
dissector fails to find this nerve, because he looks for it too far forwards.
Lastly, the lachrymal nerve and artery will be found running along the
outer wall of the orbit, above the level of the upper margin of the
external rectus muscle.

These structures must be thoroughly cleaned and isolated by the
removal of the fat from around them. In tracing the superior oblique
muscle forwards, it will be found to end in a slender tendon, which
passes through a ring-like pulley, attached to the frontal bone at the
inner angle of the orbit. This pulley must be defined, and the tendon
of the muscle followed onwards to its insertion into the eyeball. It will
be observed that the levator palpebrte superioris lies upon the upper
surface of the superior rectus, and if it be raised, a nerve twig will be
noticed emerging from the substance of the rectus superior for the
supply of the levator palpebrae muscle. This is a branch of the superior
division of the third nerve.

The dissection of the above parts will be facilitated by grasping the
front of the eyeball with the forceps, and drawing it forwards. It may
be retained in this position by running a fine needle and thread through
the ocular conjunctiva and stitching it to the nose. In doing this, how-
ever, take care that the needle does not penetrate the cornea, because
this might render the subsequent inflation of the eyeball impossible.

Frontal Nerve (nervus frontalis). — The frontal nerve is
the continuation of the stem of the ophthalmic division of
the trigeminal or fifth nerve, after it has given off its
lachrymal and nasal branches. It enters through the
sphenoidal fissure above the muscles, and proceeds for-
wards upon the upper surface of the levator palpebrae
superioris immediately subjacent to the periosteal lining of
the orbital cavity. At a variable distance from the orbital
opening, it ends by dividing into the supra -orbital and
supra-trochlear nerves.

The supra-trochlear nerve is the inner and smaller of the
two terminal branches of the frontal. It runs towards the

THE LACHRYMAL NERVE.

355

pulley of the superior oblique muscle, above which it leaves
the orbit, by turning round the orbital arch to reach the fore-
head. Its further course has already been described (pp.
1 06 and 279). In the orbit it gives off one small twig close to
the pulley of the superior oblique muscle. This passes down-
wards to join the infra-trochlear branch of the nasal nerve.
The supra-orbital nerve is continued forward in the line
of the parent stem, and, passing through the supra-orbital
notch or foramen, it turns upwards on the forehead (pp.
106 and 279). In the dissection of the scalp this nerve

otiio '

KiG. 261. — Diagram of the ophthalmic division of the fifth nerve.
(Prof. Thane, Quain s Anatomy.)

has been seen to divide into an outer and inner division.
Sometimes this division takes place within the orbit, and in
that case tlie (W/cvlargerpart occupies the supra-orbital notch.

The Lachrymal Nerve (nervus lacrimalis) is the smallest #.
of the terminal branches of the ophthalmic division of the
fifth. It enters the orbit through the sphenoidal fissure
above the level of the muscles, and proceeds forwards along
the outer wall of the cavity, and above the upper margin
of the external rectus muscle. At the fore-part of the
orbit it continues its course under cover of the lachrymal #
gland until it reaches the outer part of the upper eyelid, in
which it ends (p. 280). Within the orbital cavity it gives

356 HEAD AND NECK.

numerous twigs to the deep surface of the lachrymal gland,
and sends downwards a filament which connects it with
the orbital branch of the superior maxillary nerve.

Fourth Cranial Nerve (nervus trochlearis). — This small
nerve is destined entirely for the supply of the superior
oblique muscle. Entering the orbit through the sphenoidal
fissure above the muscles, it is continued forwards and
inwards under the periosteum. It finally sinks into the-
upper or orbital surface of the superior oblique muscle not
far from its origin.

Lachrymal Gland. — The lachrymal gland is a small
flattened body of an oval form, and distinctly lobular
structure, which is placed obhquely in the fore and outer
part of the orbital cavity. It consists of two parts or groups
of lobules — an orbital and a palpebral — imperfectly sepa-
rated from each other. The orbital part (glandula lacrimalis
superior) constitutes the main mass of the gland. Its outer
surface is convex, and is lodged in a hollow upon the inner
aspect of the external angular process of the frontal bone.
It is bound to the outer part of the orbital arch by short
fibrous bands which proceed from the periosteum. The
deep or inner surface is slightly concave, and is directed
inwards and downwards towards the eyeball. The small
palpebral lobe (glandula lacrimalis inferior) is placed in front
of the orbital part, from which it is partially separated by
the expanded tendon of the levator palpebrge superioris.
It projects into the back part of the upper eyelid, and rests
upon the conjunctiva which lines the under aspect of the
lid. This portion of the gland has been already examined
in the dissection of the eyelids (p. 292); but even in the
undissected subject it can be seen through the conjunctiva
if the upper eyelid be fully everted.

The lachrymal gland secretes the tears, and its ducts
(three to five from the orbital part and three to nine from
the palpebral part) open upon the under surface of the
upper eyelid in the neighbourhood of the fornix (p. 292).

The Levator Palpebrae Superioris rests upon the upper
surface of the rectus superior. Behind, it is narrow and

RECTUS SUPERIOR. 357

pointed, hut it expands as it passes forwards above the
eyeball to reach the upj)er eyelid. It arises from the under
surface of the roof of the orbit immediately in front of the
optic foramen, and in the fore-part of the orbital cavity it
widens out into a broad membranous expansion, the con-
nections of which have already been described (p. 291).
The outer and inner margins of this expansion are fixed to
the rim of the orbital oi)ening, in close proximity to the
external and internal tarsal ligaments. By these attach-
ments excessive action of the muscle upon the upper eyelid
is jn a measure^ checked.

Dissection. — The frontal nerve should he divided, and the ends thrown
forwards and backwards. The levator palpebra; superioris may also be
cut midway between its origin and insertion. On raising the posterior
portion a minute nervous twig will be observed entering its deep or
ocular surface. This comes from the superior division of the third or
oculo-motor nerve.

The eyeball should now be inflated. This may be done from the
front or from behind. If the latter method is selected gently separate
the fat under cover of the superior rectus muscle, and, pushing aside
the ciliary nerves and vessels from the optic nerve, place a ligature
around it close to the eyeball. A minute aperture should next be
made in the sheath of the nerve behind the ligature, and, introducing
a blow-pipe into this, thrust it forciljly forwards into the interior of the
eyeball. The pipe should be provided with a stylette so as to keep
the aperture free. \Vhen the globe of the eye is fully inflated, the
ligature may be tightened as the blow-pipe is withdrawn. A very
much better plan, however, is to inflate the eyeball from the front.
For this purpose an oblique valvular aperture is made in an inward
direction through the sclcro-corneal junction with the point of a sharp
narrow-bladed knife. Through this the blow-pipe may be introduced,
and on its withdrawal after the inflation of the eyeball the valvular
character of the opening is sufficient to prevent the escape of the air.

At the back of the eyeball the dissector will notice a quantity of
loose bursal-like tissue. This is the Capsule of Tenon. Seize the
upper part of this with the forceps, and remove a small portion with
a ])air of scissors. An aperture is thus made into the capsule, and
the handle of the knife can be introduced into the space between it
and the eyeball. In favourable cases the extent of the capsule can be
gaugeil, and perhaps even the prolongations or sheaths which it gives
to the tendons of the ocular muscles made out. The description of
the cajisule of Tenon is given on p. 368.

Rectus Superior. — The rectus superior, which lies under

358

HEAD AND NECK.

cover of the levator palpebrse superioris, is now fully ex-
posed. It arises from the upper margin of the optic
foramen, and, passing forwards above the optic nerve,
ends upon the upper aspect of the eyeball in a thin,
delicate tendon, which expands somewhat to be inserted
into the sclerotic coat about three or four lines behind
the sclero-corneal junction. It is supplied by a branch
from the superior division of the oculo-motor nerve.

The Superior Oblique Muscle (musculusobliquus superior)

arises from the roof of
the orbit immediately in
front of the upper and
inner part of the optic
foramen, and extends
forwards along the inner
wall of the cavity above
the internal rectus. At
the fore-part of the orbit
it ends in a slender
tendon, which enters the
pulley 2cci& at once changes
its direction. It now
proceeds outwards and

Fig 262. -Diagram of the superior slightly backwards upon
oblique muscle. (From Hermann , r r t

the upper surface of the
eyeball, and under cover
of the superior rectus.
Beyond the outer edge of the latter muscle the tendon
expands somewhat, and is inserted into the sclerotic coat
midway between the entrance of the optic nerve and the
cornea.

The pulley through which the tendon passes is a small
fibro-cartilaginous ring, which is attached by fibrous tissue
to the trochlear fossa — a depression in the frontal bone
close to the internal angular process. The pulley is lined
by a small synovial sheath which facilitates the movement
of the tendon within it, and from its outer margin it gives
a fibrous investment to the tendon.

(From Hermann
Meyer. )

a. Pulley and synovial sheath.

NASA/. NF.RVK. 359

Dissi'ctioii. — The superior rectus nuisclc should now he divided
midway between its orifjin and its insertion, and the cut ends thrown
l)ackwar<Is and forwards. On raising the posterior part of the muscle
the su]-)erior division of the third nerve is brouijhl into view, and will
he seen to sink into its deep or ocular surface, and at the same time send
a twi;:; to the levator palpehnx; superioris. The removal of some fat
will bring the q\>\\z nerve more fully into view. At the hack part of
the orbit three structures will be observed crossing the optic nerve —
viz. (I) the nasal nerve; (2) the ophthalmic artery; and (3) the
su]icrior ophthalmic vein. These should be carefully cleaned and
their branches followed out. From the nasal nerve, one or two
delicate thread-like branches — the loiif; ciliary nerves — will be found
passing forwards along the optic nerve to reach the eyeball. The
short ciliary nerves, much more numerous, accompany the long ciliary
branches, and can readily be disengaged from the fat which surrounds
the optic nerve. A strong member of this group should be selected
and followed backwards ; it will lead the dissector to the lenticular or
ophthtilmic !;anglion. This is a minute body which is situated upon
the outer side of the optic nerve far back in the orbit. With a little
patience and care the roots which the nasal nerve and inferior division
of the oculo-motor or third nerve give to this ganglion can be isolated,
and perhaps even the sympathetic root from the cavernous jilexus may
be found.

Optic Nerve (ncrvus opticus). — The optic nerve enters
the orbit through the optic foramen. It carries with it a
strong loose sheath of dura mater, and also a more delicate
investment from the arachnoid. The ophthalmic artery
which accompanies it lies in relation to its outer and lower
aspect. Within the orbit the nerve inclines forwards and
outwards, and at the same time somewhat downwards, and,
gaining the back of the eyeball, it pierces the sclerotic coat
a short distance to the inner side of its centre. As the
dissector has already observed, i^s upper surface is crossed
by the ophthalmic artery and vein and the nasal nerve, and
it is closely accompanied by the delicate ciliary nerves and
vessels. The optic nerve is slightly longer than the distance
which it has to run from the optic foramen to the globe of
the eye, so that the movements of the eyeball may not be
interfered with. Within the eyeball the optic nerve spreads
out in the retina.

Nasal Nerve (nervus naso-ciliaris). — The nasal nerve
arises in the fore-part of the cavernous sinus from the

36o HEAD AND NECK.

ophthalmic division of the trigeminal. It passes through
the sphenoidal fissure and enters the orbital cavity between
the two heads of the external rectus muscle, and between
the two divisions of the third nerve. It now inclines
forwards and inwards, and, crossing the optic nerve
obliquely, it runs between the internal rectus and superior
oblique muscles. Here it reaches the inner wall of the
orbit, and ends by dividing into two terminal branches — r
viz. the infra-trochlear and the nasal proper. In addition
to these it gives off in the orbit the following branches : —

1. Long root to the lenticular ganglion.

2. Long ciliary nerves.

The long ganglmiic root (radix longa ganglii ciliaris) is a
very slender filament which springs from the nasal as it
enters the orbit between the heads of the external rectus. It
proceeds forwards on the outer side of the optic nerve, and
enters the upper and back part of the lenticular ganglion.

The lofig ciliary nerves (nervi ciliares longi) — usually two
in number — spring from the nasal as it crosses the optic
nerve. They proceed forwards upon the inner side of the
optic nerve to reach the globe of the eye, where they pierce
the sclerotic. One of the long ciliary nerves very constantly
unites with one of the short ciliary filaments.

The infra-trochlear nerve runs forwards along the inner
wall of the orbit under cover of the superior oblique.
Passing under the trochlea of that muscle, it emerges from
the orbit and appears upon the face, where it has already
been dissected (p. 281). Near the pulley it receives a com-
municating twig from the supra-trochlear nerve.

The nasal proper vs, the larger of the two terminal branches
of the nasal nerve. It leaves the orbit by the anterior in-
ternal orbital canal, and is conducted to the interior of the
cranium, in which it appears at the outer margin of the
cribriform plate of the ethmoid. The canal in which it
runs can readily be opened up by the bone-pliers and the
nerve exposed within it. Upon the cribriform plate it turns
forwards under the dura mater, and almost immediately

LENTICULAR GANGLION.

■\(>\

disappears througli a slit-likc aperture at the side of the
crista galh, to reach tlic nasal cavity. Here it gives branches
to the mucous membrane, and is continued downwards
upon the posterior aspect of the nasal bone. Finally, it
emerges upon the face by passing between the lower margin
of the nasal bone and the upper lateral cartilage of the
nose. Its terminal filaments have already been described
(p. 281).

The nasal tierce proper., therefore, takes a most circuitous

vena vorticosa

long postcrioi
ciliary artery.

long posterior
ciliary- artery.

Fig. 263. — Dissection of the eyeball showing the
distribution of the ciliary nerves and vessels.

route, being found — (i) in the orbit; (2) in the cranium;
(3) in the nasal fossa; and (4) in the face.

Lenticular Ganglion (ganglion ciliare) — (Fig. 266). —

The lenticular ganglion is a minute (juadrangular body,

not much larger than the head of a large pin ; but its size

varies considerably in different subjects. It is placed in

the back part of the orbit between the optic nerve and the

external rectus muscle, and very commonly on the outer

^ side of the ophthalmic artery. By its posterior border it

, receives its three roots; whilst from its anterior border the

1^ short ciliary nerves are given off.

362 HEAD AND NECK.

The sensory root comes from the nasal, and is called the
long root. It enters the upper and hinder angle of the
ganglion. The short or motor root is a short, stout trunk ;
it comes from the branch of the oculo-motor nerve, which
goes to the inferior obhque muscle, and it enters the lower
and hinder angle of the ganglion. The sympathetic root
comes from the cavernous plexus, and joins the posterior
border of the ganglion, close to the entrance of the long
root from the nasal nerve. In some cases it joins the long
root before it reaches the ganglion.

The short ciliary nerves (nervi ciliares breves) are from
four to six in number, and they come off in two groups, of
which one emerges from the upper and fore angle of the
ganglion, whilst the other springs from its lower and fore
angle. The lower group is generally more numerous than
the upper. As these fine nerves proceed along the optic
nerve they divide, and thus increase in number ; at the
back of the eyeball from twelve to eighteen may be counted.
Finally they pierce the sclerotic by a series of apertures
which are placed around the entrance of the optic nerve.

The Ophthalmic Artery (arteria ophthalmica) is a branch
of the internal carotid, and it accompanies the optic nerve
into the orbit through the optic foramen. At first it lies
below the optic nerve, but it soon winds round the outer
side of the nerve, and crossing it superficially proceeds
forwards along the inner wall of the orbit, under cover of
the superior oblique muscle. At the inner angle of the
orbit it ends by dividing into two terminal branches — viz.
the frontal and the nasal (Fig. 264).

The bratiches of the ophthalmic artery are very numerous,
and they can seldom be satisfactorily displayed, unless a
special injection has been made, or a cold injection used.
They are : —

I.

The lachrymal.

6.

Ethmoidal.

2.

Muscular.

7-

Palpebral.

3-

Arteria retinae centralis.

8.

Nasal.

4-

Ciliary.

9-

Frontal.

5-

Supra-orbital.

THE OrilTIIALMlC ARTERY.

363

The lachrymal artery (artcria lacrimalis) accompanies the
lachrymal nerve, and supplies the gland of that name and
the conjunctiva. Two branches, named external palpebral
(arterias palpebrales laterales), form an arch (arcus tarseus)
in each eyelid, near the free margin, with the internal
palpebral arteries.

The muscular tii'igs (rami musculares) come off at vari-
able points, not only from the main artery, but also from

NASAI
FRONTAL-

POST eTMM

MA14L NCRvE-

SUP EXT MUSC

Fig. 264. — Diagfram of the ophthalmic artery and its branches.
(After Qiiain and Meyer, modified.)

certain of its branches. They supply the muscles contained
in the orbital cavity.

The artcria retincc centralis is a minute but important
artery. It pierces the optic nerve about half an inch
» behind the eyeball, and is conducted in its substance to
the interior of the globe of the eye.

The ciliary arteries are very numerous. Two groups are
recognised — viz. a posterior and an anterior. l^\\c posterior
ciliary arteries run with the ciliary nerves. They ari.se by

364 • HEAD AND NECK.

two trunks which spring from the ophthalmic whilst it lies
below the optic nerve. These divide into several slender
branches, which pierce the sclerotic around the entrance of
the optic nerve. Two members of this group of vessels
enter the eyeball on either side of the optic nerve, somewhat
apart from the others. They are termed the long ciliary
' flr/^?7'i?^ (arterise ciliares posteriores longse) (Fig. 263). The
miterior ciliary arteries (arterise ciliares anteriores) come off

* in the fore -part of the orbit from the lachrymal and
muscular branches. They vary in number from six to

* eight, and run to the anterior part of the eyeball, where
they form an arterial circle under the conjunctiva. Finally,
they pierce the sclerotic immediately behind the cornea.

The sup7-a-oi'bital artery (arteria supraorbitalis) accom-
panies the supra-orbital nerve, and thus gains the forehead,
where it has been dissected at a previous stage (p. 108).

The ethmoidal arteries are two in number — anterior and
posterior — and they run to the anterior and posterior in-
ternal orbital foramina on the inner wall of the orbit. The
posterior eth??ioidal artery (arteria ethmoidalis posterior) sup-

* plies the mucous lining of the posterior ethmoidal cells, and
sends twigs to the upper part of the nose. The anterior
ethmoidal artery (arteria ethmoidalis anterior) is a larger
branch. It runs in company with the nasal nerve proper,
and gives off minute twigs at each stage of its course.
Thus in the anterior internal orbital canal it gives branches
to the mucous lining of the anterior ethmoidal cells and

""^ the frontal sinus ; during its short sojourn in the cranial

* cavity it supplies the small anterior meningeal artery (arteria
meningea anterior) (p. 131); in the nasal cavity it gives

" twigs to the mucous membrane ; whilst its terminal branch
appears on the face to supply parts on the side of the
nose.

The internal palpebral branches (arteria palpebrales medi-
ales) come off near the orbital opening, and are two in
number — one for the upper and the other for the lower
eyelid (p. 291).

The 7iasal bratich (arteria dorsalis nasi) is distributed at

r

THE RECTI MUSCLES. 365

the root of the nose, and anastomoses with the angular
branch of the facial artery.

The frontal arkry (arteria frontalis) accomi)anies the
supra-trochlear nerve to the forehead, where it has already
been dissected (p. loS).

The Ophthalmic Veins. — As a general rule these are two
in number — superior and inferior. The superior ophthalmic
vein is the larger of the two, and it accompanies the artery
across the optic nerve. It takes origin at the root of the
nose, where it communicates by a wide radicle with the
angular vein. The inferior ophthalmic vein lies deeper,
below the level of the optic nerve, and it is brought into
^communication with the pterygoid venous plexus by an
offset which passes through the spheno- maxillary fissure.
The two ophthalmic veins receive numerous tributaries
during their course through the orbit, and finally they pass
between the two heads of the external rectus muscle, and
through the sphenoidal fissure to open into the cavernous
sinus, either separately or by a common trunk.

The Recti Muscles. — The four straight muscles of the
eyeball converge to the apex of the orbit, and together form
the sides of a four-sided or pyramidal space, in which are
enclosed the optic nerve and the greater part of the globe of
the eye. The rectus superior, which has been reflected, has
already been studied. The rectus internus springs from the
inner side of the optic foramen, and the rectus inferior
takes origin from a fibrous band which bounds the inner
extremity of the sphenoidal fissure (Fig. 265). The rectus
externus is distinguished from the others by arising from a
fibrous arch, the extremities of which are termed its two
heads of origin. The lotver head arises in common with
the rectus inferior from the body of the sphenoid, where
this bounds the inner end of the sphenoidal fissure ; the
upper head is attached above the sphenoidal fissure upon
the outer side of the optic foramen, where its origin becomes
continuous with that of the superior rectus. Through the
archway which intervenes between the two heads of the
external rectus pass the two divisions of the oculo-motor

366

V o\"" HEAD AND NECK.

V» *^ r \,T.

,^^ nerve, the nasal nerve, the abducent nerve, and the oph-
thalmic veins (Fig. 265).

When the ocular surfaces {i.e. the surfaces turned towards the optic
foramen) of these muscles are examined, they will be seen to arise in a
great measure from two common tendons which, from their position and
connections, may be termed the superior and inferior common tendons
of the recti muscles. The superior coinnion tendon (Lockwood) springs
from the upper and outer margin of the optic foramen, and gives origin
to the superior rectus, the internal rectus, and the upper head of the
external rectus. The inferior common tendon, more usually known as

OPHTHAL. VEIN

LEV. PALP. SUP.
NASAL NERVE | SUP. REOT.

SPHEN. FIS.

LACHRYMAL. N.
FRONTAL. N.

TROCHLEAR. N.

N. ril. INF. DIV.

Fig. 265. — Diagram of the orbital cavity and of the
origin of the ocular muscles in relation to the optic fora-
men and the sphenoidal fissure.

the " Ligament of Zinn," arises from a distinct depression upon the lower
and outer aspect of the margin of the optic foramen, and divides into
three slips, which go to the internal rectus, the inferior rectus, and the
lower head of the external rectus. The slips from the two common
tendons which go to the external rectus become continuous' with each
other, forming in this way the tendinous arch referred to.

A better view of these attachments may be obtained by dividing the
optic nerve close to the optic foramen and turning forwards the eyeball.

The manner in which the recti muscles are inserted into
the eyeball should next be studied. Each ends in a delicate
membranous tendon, which is inserted into the sclerotic

NEK VES IN SPHENOIDAL FISSURE. 367

coat, about a quarter of an inch behind the sclcro-corneal
junction.

The Third Nerve (nervus oculomotorius). — The two
divisions of this nerve enter the orbit through the sphen-
oidal fissure, between the two heads of the external rectus.
The su^;£na£-dhjLsLo.n has been traced to the rgctus superior
and the levator palpebrce superioris. The inferior division
is much the larger of the two, and almost immediately
divides into three branches for the supply of the rectus
internus, the rectus inferior, and the obliquus inferior. The
nerves to the two recti enter the ocular surfaces of these
muscles ; the nerve to the inferior oblique is a long branch,
which is prolonged forwards in the interval, between the

Fig. 266. — Diagram of the third nerve and ciliary ganglion.
(Prof. Thane, Quain s Anatomy.)

S.R. Sympathetic root of ganglion. | L.R. Long root of the ganglion.

rectus inferior and rectus e.xternus, and enters the hinder
border of the inferior oblique muscle. Soon after its origin
this branch gives the slwrt 7notor root to the lenticular
ganglion, and likewise supplies two or three additional
filaments to the inferior rectus muscle.

The Sixth Nerve (nervus abducens) will be found closely
applied to the ocular surface of the external rectus, and it
enters the orbit by passing through the narrow interval
between the heads of this muscle. It is destined entirely
for the sui)ply of the rectus externus.

Arrangement of the Nerves in the Sphenoidal Fissure. —
Now that the orbit is dissected, and the various nerves
which were met in the dissection of the cavernous sinus
traced into the cavity, the dissector will observe that the

368 HEAD AND NECK.

arrangement of these nerves in the sphenoidal fissure is
somewhat different from that in the sinus.

The lachrymal, frontal, and trochlear or fourth nerves
enter the orbit above the muscles on very much the same
plane (Fig. 265). The other nerves enter between the heads
of the external rectus. Of these the superior division of
the oculo-motor nerve is the highest, next comes the nasal
nerve, then the inferior division of the oculo-motor nerve,
whilst the abducent nerve occupies the lowest level.

Dissection. — The inferior oblique muscle is placed very differently
from the other muscles of the orbit. It is situated below the eyeball,
and turns round its inferior and outer surface. It must be dissected
from the front. It is necessary, therefore, to restore the eyeball to its
natural place. Next, evert the lower eyelid and remove the conjunctiva
from its deep surface as it is reflected on to the globe of the eye. A
little dissection in the floor of the fore-part of the orbit and the removal
of some fat will reveal the inferior oblique muscle.

The Inferior Oblique Muscle (musculus obliquus inferior)
arises from a small depression on the orbital plate _iif the
superior maxillary bone immediately to the outer side of
the opening of the nasal duct. It passes outwards below
the inferior rectus muscle, and, inclining slightly backwards,
ends in a thin membranous tendon, which gains insertion
^into the outer aspect of the sclerotic coat of the eyeball
under cover of the rectus externus. This insertion is not
far from that of the superior oblique, but is placed farther
back. A branch of the inferior division of the third nerve
has been traced to the posterior margin of the inferior
oblique muscle.

The Capsule of Tenon (fascia bulbi) is a firm, loose
membrane in relation to the globe of the eye. Its connec-
tions are somewhat complicated, and they cannot in every
detail be satisfactorily displayed in an ordinary dissection.
It may be studied from a three-fold point of view — (i) in
its connection with the eyeball; (2) in its connections with
the muscles inserted into the globe of the eye; and (3) in
its connections with the walls of the orbit.

The relation which the capsule of Tenon exhibits to the

THE CAPSrr.R OF TEA'OX. 369

eyeball is very simple. TJie membrane is spread over the
posterior five-sixths of the globe — the cornea alone being
free from it. In front it lies under the ocular conjunctiva,
with which it is intimately connected, and it ends by
blending with the conjunctiva close to the margin of the
cornea. Behind it fuses with the sheath of the optic ner\-e,
where the latter pierces the sclerotic. The anterior surface
of the membrane {i.e. the surface towards the globe of the
eye) is smooth, and is connected to the eyeball by some
soft yielding and humid areolar tissue, the interval between
them in fact constituting an extensive lymph space. Its
posterior surface is in contact with the orbital fat, to which
it is loosely adherent, while farther forwards, as we have
noted, this surface is firmly attached to the ocular con-
junctiva. It is apparent, therefore, that by this membrane
a socket is formed for the eyeball, in which it can glide
with the greatest freedom.

The tendons of the various ocular muscles are inserted
into the eyeball within this capsule, and they gain its interior
by piercing the membrane opposite the equator of the globe
(Fig. 267). The lips of the openings through which the
four recti muscles pass are prolonged backwards upon the
muscles, in the form of sheaths, very much in the same
manner that the infundibuliform fascia is prolonged upon
the spermatic cord from the internal abdominal ring. These
sheaths gradually become more and more attenuated, until
at last they blend with the perimysium of the muscular
bellies. In the case of the superior oblique muscle the
corresponding prolongation is only related to its reflected
portion ; it reaches the pulley and there it ends by becom-
ing attached to its margin. The sheath of the inferior
obliiiue may be traced upon the muscle as far as the floor
of the orbit. The inner or ocular edge of each of the four
apertures through which the recti muscles pass is strength-
ened by a slip of fibrous tissue (Lockwood). The import-
ance of these slips will be understood wheri we remember
that the capsule of Tenon is at various points firmly bound
to the bony wall of the orbit. They therefore act as pulleys,

VOL. II. — 24

370

HEAD AND NECK.

and protect the globe of the eye from pressure during con-
traction of the muscles. The__ajperture for the superior
oblique is not furnished with such a slip, and it is doubtful
if the opening for the inferior oblique muscle possesses one.

Dissection. — An admirable view of the relations which the capsule
of Tenon presents to the eyeball and the tendons of the ocular muscles
can be obtained by the following dissection : — Divide the outer canthus
of the eyelids as far out as the margin of the orbital opening. Pull
the e3'elids widely apart, so as to expose as much as possible of the

tendon of superior oblique,
tendon of superior rectus,
tendon of external rectus.

- cut edge of capsule of Tenon
and conjunctiva.

tendon of inferior rectus.

tendon of internal capsule of Tenon thrown
rectus. back from eyeball.

Fig. 267. — Dissection of the capsule of Tenon from the front.

anterior face of the eyeball. Next divide the conjunctiva by a circular
incision just outside the cornea. At this point the capsule of Tenon
is so intimately connected with the conjunctiva that it is divided at the
same time. Now raise carefully both conjunctiva and Tenon's capsule
from the surface of the eyeball, and spread them out round the orbital
opening, as is depicted in Fig. 267. The openings in the capsule of
Tenon for the tendons of the ocular muscles and the thickened margins
of these apertures are well seen. Note also the sheaths which are
given to the muscles.

Check and Suspensory Ligaments. — The connections of
the capsule of Tenon to the walls of the orbital cavity are
somewhat complicated. The stispensory ligament (Lock-

THE TEMPORO- MALAR NERVE. 371

wood) is perhaps the most important of these. It stretches
across the fore-part of the ort)it, after the fashion of a
hammock, and gives support to the eyeball. Its two
extremities arc narrow, and are attached respectively to
the jnalaL iliid lachrymal bones. Be]pw the eyeball it
widens out and blends with the capsule of Tenon. The
external and internal clieck ligavietits also constitute bonds
of union between the capsule of Tenon and the orbital
wall. They arc strong bands which pass from the sheaths
around the external and internal recti muscles to obtain
attachment -to the malar and lachrymal bones respectively \
here they are brought into association with the extremities
of the suspensory ligament. The function of the check
ligaments is easily understood. They limit the contrac-
tion of the external and internal recti muscles, and thus
prevent excessive rotation of the eyeball in an outward or
inward direction. There is a similar but less direct pro-
visTon By means of which the action of the superior and
inferior recti muscles is limited. Tjie action of the
former muscle is checked through its intimate connection
with the levator palpebrre superioris in the fore-part of the
orbit ; the action of the inferior rectus is checked through
its connection with the suspensory ligament.^

Dissection. — In order that the temporo-malar, or orbital branch of
the superior maxillar)' division of the trigeminal nerve, may be displayed
in its course through the orbit, the orbital contents must be removed.
It will then be found in the midst of a little soft fat in the angle between
the floor and outer wall of the orbit.

The Temporo-Malar Nerve (nervus zygomaticus) arises
in the sphcno-maxillary fossa, from the superior maxillary
division of the trigeminal nerve, and it enters_the orbit by

' For further information regarding the capsule of Tenon the student
is referred to the admirable account wliich is given of its connections by
Mr. Lockwood in Journal of Anatomy and Physiology, vol. xx. , 1885.
He points out how important it is for the surgeon in the ojicration for
the removal of the upper jaw to carefully preserve the attachments of
the suspensory ligament. If these be destroyed, there is a danger of
the eyeball sinking downwards to such an extent that it may afterwards
be necessary to remove it.

i-

372 HEAD AND NECK.

passing through the spheno-maxillary fissure. It almost
immediately divides into two terminal branches — viz. the
temporal and the malar.

The temporal branch (ramus zygomaticotemporalis) runs
forwards and upwards upon the outer wall of the orbit,
under cover of the periosteum, and, after receiving a com-
municating twig from the lachrymal nerve, it enters the
temporal canal of the malar bone. This conducts it to the
fore-part of the temporal region, where it has already been
examined (pp. 106 and 281).

The malar branch (ramus zygomaticofacialis) continues
forward in the angle between the floor and outer wall of
the orbit, and is finally conducted to the face by a minute
canal which perforates the malar bone. Here it has been
displayed in the dissection of the face (p. 281).

PREVERTEBRAL REGION.

The following are the structures to be displayed in this
dissection : — ■

Prevertebral muscles.
Intertransverse muscles.
Cervical nerves.
Vertebral artery.

Vertebral vein.
Vertebral and cranio -verte-
bral articulations.

Dissection. — In order that we may obtain a proper view of the
pharynx and the prevertebral muscles, it is necessary to make a some-
what complicated dissection. The fore-part of the skull bearing the
pharynx must be separated from the back part of the skull and the
cervical portion of the vertebral column. Place the preparation upside
down, so that the cut margin of the skull rests upon the table, and,
having divided the common carotid artery, the internal jugular vein,
the vagus nerve, and the sympathetic cord on each side at level of the
neck of the first rib, draw the trachea and oesophagus, together with
the great blood-vessels and nerves, forwards from the anterior surface
of the vertebral column. This separation must be effected right up to
the base of the skull. At this point great caution must be observed,
otherwise the pharyngeal wall or the insertions of the prevertebral
muscles will be damaged. The base of the skull having been reached,
the point of the knife should be carried across the basilar process of the

rilE LONGUS COLLI. yji

Dicipital bone between llie pharynx and vertebral muscles, so as to
divitle the tliick investiiij^ perioslemn.

The basilar process nuist now be divided by means of a chisel.
Still retainintj the part upside down, place the skull so that its floor
rests upon the end of a wooden block. Then apply the edge of the
chisel to the under surface of the basilar process, adjust it accurately in
the interval between the pharyngeal wall and the prevertebral muscles,
and with a wooden mallet drive it through the base of the skull,
inclining it, at the same time, slightly backwards.

The next step in the dissection consists in making two saw-cuts
through the cranial wall. The head having been placed upon its side,
the saw must be applied to the outer a.spect of the skull half an inch
behind the mastoid process, and carried obliquely forwards and inwards
to reach a point immediately behind the jugular foramen. The same
saw-cut must be repeated upon the opposite side of the head.

To complete the dissection the dissector must again have recourse to
the chisel. Placing the preparation so that the floor of the cranium
looks upwards, divide the base of the skull, on each side, in the
interval between the petrous portion of the temporal bone and the
basilar portion of the occipital bone. In front, this cut should reach
the outer extremity of the incision already made through the basilar
process ; whilst behind, it should be carried backwards upon the inner
side of the jugular foramen to reach the inner end of the saw-cut.
When this has been done upon both sides of the basilar process, the
fore-part of the skull carrying the jiharynx and the great blood-vessels
and nerves can be separated from the back part of the skull and
cervical portion of the vertebral column. The only large nerve which
will be divided is the hypoglossal, but, as it is cut close to the basis
cranii, and below this it is firmly connected w ilh the trunk ganglion of
the vagus, it retains its position.

The i^harynx and anterior portion of the skull should now be covered
with a piece of cloth soaked in the spirit and carbolic solution, and the
whole enveloped in an oil-cloth wrapper. It can then be laid aside
until the dissection of the j)revertebral region and the ligaments of the
cervical vertebnv and the occiput have been studied.

Returning to the posterior part of the skull and the cervical portion
of the spine, the dissector should jjroceed to define the attachments of
the muscles which lie in front of the transverse processes and the bodies
of the vertebra". These are three in number on each side, viz. : —

1. The longus colli.

2. The rectus cajiilis anticus major.

3. The rectus capitis amicus minor.

The Longus Colli is the most powerful of tlie preverte-
bral muscles, and il lies nearest to the mesial i^lane. Its
connections are somewhat intricate, but when it has been

374 HEAD AND NECK.

thoroughly cleaned it will be seen to consist of three portions
— viz. an upper and lower oblique part, and an intermediate
vertical part.

The lower oblique^di\y'\%\on of the longus colli (Fig. 268, (5)
arises from the lateral aspect of the bodies of thejap^er^two
or three dorsal vertebrse. It extends upwards and slightly
outwards, and ends in two tendinous slips which are
inserted into the anterior tubercles of the transverse
processes of the fifth and sixth cervical vertebrae. In the

interval between this portion of the longus coUi and the

-b' ^ scalenus anticus, the vertebral artery will be observed.

y ^ Q^|f p';,^The upper oblique part of the longus colli (Fig. 268, c)

arises by three tendinous slips from the .anterior tubercles

„ -Q of the transverse processes of the third, fourth, and fifth

'. ^,t> cervical vertebrae, and tapers somewhat as it proceeds up-
wards and inwards, to obtain a pointed and tendinous
insertion into the anterior tubercle of the atlas. The
vertical part of the muscle (Fig. 268, a) is much the largest
of the three divisions, and it lies along the inner side of
the oblique portions, with both of which it is more or less
intimately connected. Thus below, it arises in common
with the inferior obUque part by two or three slips from the
sides of the bodies of the upper t\vo or three dorsal
vertebrae ; above this it derives additional slips of origin
froim the bodies of the lower two cervical vertebrae ; lastly,
its outer border is reinforced by slips from the transverse
processes of the lower three or four cervical vertebras. It
stretches vertically upwards and is inserted upon the inner
side of the upper oblique part of the muscle, by three
tendinous processes, which obtain attachment to the bodies
of the second, third, and fourth cervical vertebrae.

The Rectus Capitis Anticus Major (Fig. 268, i) is an
elongated muscle which arises by four tendinous slips from
the anterior tubercles of the transverse processes of the

\ / ' third, fourth, fifth, and sixth cervical vertebrae, and is

~ inserted in front of the foramen magnum, upon the under

^ '' aspect of the basilar process of the occipital bone. To

reach this insertion the muscle inclines slightly inwards as

THE RECTUS CATTTIS ANTICUS MAJOR. 375

it ascends upon tlic front of tlie vcrtcl)ral column. It

Fig. 268. —Prcvcrlcbral region. (From I.uschka. )

Rectus capitis amicus in:ijur.

Rectus capitis amicus minor.

Rectus lateralis.

(a. Vertical part.

I.ongus colli -I ^. Lower oblique part.
\c. Upper oblique part.

A supernumerary muscle frequently
present, and calleJ by I.uschka
musculus transver?alis ccrvicis
amicus.

Scalenus amicus.
.Scalenus mcdius.
Scalenus posticus.
Phrenic nerve.
Brachial nerves.
Subclavian artery.
Intertransverse nmsties

376

HEAD AND NECK.

is supplied by twigs from the first loop of the cervical

plexus.

Tlie Rectus Capitis Anticus Minor (Figs. 268, 2, and

269, 2) is a small muscle. It is in great part con-
cealed by the upper part of
the preceding muscle, which
should be detached from' its
insertion, and turned down-
wards so as to bring it fully into
view. It arises from the anterior
aspect of the root of the trans-
verse process of the atlas, and
proceeding upwards and in-
wards is inserted into the under
surface of the basilar process of
the occipital bone behind the
rectus capitis anticus major.
It is supplied by a filament from
the first loop of the cervical
plexus.

Before proceeding farther, the
dissector should again examine the
attachments of the scalene muscles
[v. p. 229).

Intertransverse Muscles

(musculi intertransversarii). —
To obtain a proper display of
the intertransverse muscles it
will be necessary to remove
the prevertebral and scalene
muscles. The intertransverse
muscles consist of seven pairs
of small fleshy slips, on each side, Avhich connect the bifid
extremities of the cervical transverse processes (Fig.
269, 3). The anterior slip of each muscle is attached to
the anterior tubercles of two adjacent transverse processes ;
whilst the posterior slip extends between the posterior
tubercles. The highest pair of muscular slips lies between

Fig. 269. — The intertrans-
verse muscles.

1. Rectus lateralis.

2. Rectus capitis anticus minor.

3. Intertransverse muscles.

4. Anterior primary divisions of

cervical nerves.

y

THE VEKTEBk'AI. ARTERY. 377

the atlas and the axis; the lowest pair connects tlie trans-
verse process of the seventh cervical vertebra with the
transverse process of the first dorsal vertebra.

The Cervical Nerves will be observed to have a very
definite relation to the intertransverse muscles. The
anterior primary branches of the lower six cervical nerves
make their appearance by passing outwards between the two
slips of the corresponding muscles. The posterior primary
divisions of the same nerves turn backwards l>c/ii/id the
posterior muscular slips.

The upper two cervical nerves emerge from the spinal
canal, as we have already noticed, differently from the
others. They pass backwards over the neural arches of the
atlas and axis respectively. The firsl or suboccipital nerve
has been sutlficiently examined at a previous stage of the
dissection (p. 343); but the dissector is now in a position
to observe that the anterior pritnary division of the second
cervical tierve turns forwards under cover of the posterior
slip of the first intertransverse muscle, and winds round the
outer side of the vertebral artery, to appear in front of the
anterior slip of the same muscle.

Dissci/iiui. — The vertebral artery as it traverses the succession of
foramina in the transverse processes of the cervical vertebra; should now
be exposed. Remove the intertransverse muscles as well as the muscles
still attached to the transverse process of the atlas — viz. the rectus
lateralis, the inferior oblique, and the superior oblique. The anterior
tubercles and the costal portions of the transverse processes of the third,
fourth, fifth, and sixth cervical vertebra: shoulii then be snippud oft by
the bone-pliers.

The Vertebral Artery (a ricria vertebralis) has previously
been traced to the point where it disappears through the
foramen in the transverse process of the sixth cervical
vertebra ; it is now seen to proceed vertically upwards
through the succession of foramina transversaria until it
reaches the foramen in the transverse process of the axis.
In this it is directed outwards in order that it may gain
the more outwardly placed foramen of the atlas. Upon
the u[)per surface of the atlas it again changes its direction
and proceeds backwards, behind the lateral mass, in a

378 HEAD AND NECK.

groove on the upper surface of the posterior arch of that
bone. Finally, it turns forwards under the posterior
occipito-atlantal ligament, pierces the dura mater, and
enters the cranium through the foramen magnum.

The vertebral artery is accompanied by a sympathetic
plexus of nerves derived from the inferior cervical ganglion,
whilst the vertebral vein breaks up in a plexiform manner
around it. The anterior divisions of the lower six cervical
nerves pass outwards behind it ; the corresponding division
of the first cervical nerve passes forwards internal to it,
whilst that of the second nerve turns forward upon its
outer aspect ; lastly, the posterior primary division of the
first cervical nerve enters the suboccipital triangle of the
neck by passing backwards between the artery and the
neural arch of the atlas.

The branches which are given off by the vertebral artery
in the neck are of small size. They are {a) muscular ; {b)
lateral spinal.

The muscular tivigs go to the muscles in the neighbour-
hood. The lateral spinal branches enter the spinal canal
upon the cervical nerves, and have been described on p.
174.

The Vertebral Vein does not take origin within the
cranium. It merely accompanies the vertebral artery in
the cervical part of its course, and forms a close venous
plexus around it as it proceeds through the succession of
bony foramina in the transverse processes of the cervical
vertebrae. Its radicles arise in the suboccipital region,
where they anastomose with the tributaries of the occipital
and deep cervical veins. Before it enters the transverse
process of the atlas it receives a large offset from the intra-
spinal venous plexus. Inferiorly, the vertebral vein opens
into the innominate vein (p. 234).

Dissection. — The muscles must now be completely removed in
order that the vertebral and cranio- vertebral joints, and the ligaments
in connection with the cervical portion of the spine may be examined.
The axis, atlas, and occipital bone present a series of articulations in
which the uniting apparatus is very different from that of the vertebrae
below.

LOWER FIVE CERVICAL ]-ERIEBR.-Ji.

379

Articiilations of the Lower Five Cervical Vertebrae. —

The lower five ccr\ieal vcitchrx arc united togclhfr very
much upon the same plan as the vertebrae in other regions
of the vertebral column. Both the bodies and the neural
arches are connected by distinct articulations and special
ligaments.

Three separate joints may be said to exist between the
opposed surfaces of the bodies of two adjacent vertebra; —
viz. a central amphiarthrodial joint and two small lateral
diarthrodial joints.

The amphiarthrodial joint (Fig. 270) occupies by far the

KiG. 270. — Coronal section through the bodies of two
cervical vertebra;.

(a <i) The two lateral diarthrodial joints between the bodies of two vertebrsc

greatest part of the space which exists between the vertebral
bodies, and it presents the usual characters of such an
articulation. The opposed bony surfaces are coated by a
thin layer of hyaline or encrusting cartilage, and are brought
into direct union by an interposed disc of fibro-cartilage.
The intervertebral discs are distinctly deeper in front than
behind, and upon this the cervical curvature of the column
in great measure depends.

The two diarthrodial joints are placed one on each side,
where the disc of fibro-cartilage fails. They are of small
extent, and are confined entirely to the intervals between
the projecting lateral lips of the upper surface of the

38o HEAD AND NECK.

centrum, and the bevelled off lateral margins of the lower
surface of the vertebral body immediately above. Here
the bony surfaces are coated with encrusting cartilage, and
are separated by a synovial cavity protected on the outer
side by a feeble capsular ligament (Fig. 270, a, a).

The ligaments which bind the bodies of the five lower
cervical vertebrae together are the direct continuation up-
wards of the anterior and the posterior common ligaments
of the spine. In the removal of the spinal cord, the
laminae of the vertebrae below the axis have been taken
away so that very little dissection will be required to make
out the connections of both of these ligaments. The
anterior commo?i liga7nent is a strong band placed in front of
the vertebral bodies. It is more firmly fixed to the inter-
vening intervertebral discs than to the bones. The posterior
common ligament which lies on the posterior aspect of the
vertebral bodies constitutes the anterior boundary of the
spinal canal. In the cervical region it completely covers
the bodies of the vertebrae, and does not present the
denticulated appearance which is so characteristic of it
lower down. It is chiefly attached to the cartilaginous
discs and the adjacent margins of the bones.

The neural arches of the lower five cervical vertebrae are
bound together by ia) the articulations between the articular
processes ; {f) ligamenta subflava ; ic) by interspinous liga-
ments ; and {(T) intertransverse hgaments.

TlvQ joitits between the opposing articular processes are
of the diarthrodial variety. The surfaces of bone are coated
with encrusting cartilage ; there is a joint cavity lined by
synovial membrane, and surrounded by a distinct capsular
ligament. This ligament is more laxly arranged in the
neck than in the lower regions of the spine.

The ligamenta subflava may be examined on the lamince which
were removed for the display of the spinal cord, and which the dis-
sector was directed to retain. In this specimen they may be studied
in the cervical, dorsal, and lumbar regions of the spine. They fill up
the gaps between the laminse of the vertebra, and can be best seen
when the fore aspect of the specimen is viewed.

AX/S, ATLAS, AND OCCIPITAL BONE. 381

Tlic ligamenta subjlava (liganicnta flava) arc composed
of yellow elastic tissue, and each ligament is attached
superiorly to the anterior surface and inferior margin of
the lamina of the vertebra above, whilst inferiorly it is
fixed to the posterior surface and superior margin of the
lamina of the vertebra next below. In this way they form
with the lamina: a smooth, even posterior wall for the
spinal canal. Each ligament extends from the posterior
part of the articular processes to the mesial plane, where
it is in contact by a free thickened inner border with its
neighbour of the opposite side. The mesial slit between
them in each interneural space is filled by some lax con-
nective tissue, and it allows the egress from the spinal
canal of some small veins. The width of the ligaments in
the different regions of the spine depends upon the size of
the spinal canal. Thus they are widest in the neck and
in the lumbar part of the column. The ligamenta sub-
flava, by virtue of their great strength and elasticity, are
powerful agents in maintaining the curvatures of the spine ;
they also give valuable aid to the muscles in restoring the
spine to its original position after it has been bent in a
forward direction.

The interspinous ligaments are most strongly developed in
the lumbar regions, where they fill up the intervals between
the adjacent margins of contiguous spinous processes. In
the dorsal region, and more especially in the neck, they are
very weak.

The supraspinous ligaments are thickened bands which
connect the summits of the spinous processes. In the neck
they are replaced by the ligamentum nuchas (p. 150).

The intertransverse ligaments are feebly marked in the
cervical region, and extend chiefly between the anterior
bars of the transverse processes.

Articulations of the Axis, Atlas, and Occipital Bone. —
The articulations which exist between these three bones all
belong to the diarthrodial class. Between the atlas and
axis there are three such joints — viz. a pair between the
opposed articular processes, and a third between the

Ligaments connecting atlas

382 HEAD AND NECK.

anterior face of the odontoid process and the posterior face
of the anterior arch of the atlas. Between the atlas and
occipital bone there are a pair of joints — viz. between the
occipital condyles above and the elliptical cavities upon
the upper aspect of the lateral masses of the atlas.

The ligaments connecting these three bones together
may be divided into three main groups as follows : —

/"Anterior atlanto-axial.
Posterior atlanto-axial.
Capsular.
'^"'.'^^""^- """ '"""""^ """"-^ Transverse portion of the cruciform

ligament.
Accessory ligaments of the atlanto-
^ axial joints.

Ligaments connecting occi- f Anterior occipito-atlantal
pital bone with atlas, . Postenor occipito-atlantal.
I, Capsular.

/'Posterior occipito-axial.
I^igaments connecting Appendices superior and inferior of the
occipital bone with-j cruciform ligament,

axis, . . . Alar odontoid or check.

'^Suspensory.

The ligaments which are placed in relation to the
exterior of the vertebrae should first be examined. These
are the anterior and posterior atlanto-axial, and the anterior
and posterior atlanto-occipital. The four capsular ligaments
may also be more or less satisfactorily studied at the same
time.

The Anterior Atlanto-axial Ligament (Fig. 271) may
be regarded as being a continuation upwards of the
anterior common ligament of the spine. Below it is
attached to the fore aspect of the body of the axis, whilst
above it is fixed to the anterior arch of the atlas. It is
thick and strong in the middle, but thins off towards the sides.

The Posterior Atlanto-axial Ligament fills up the
interval between the laminae of the axis vertebra and the
posterior arch of the atlas, to the contiguous margins of
which it is attached. It is broad and membranous, and is
the representative, as its attachments show, of the ligamenta
subflava. It is pierced on each side by the second cervical

.■iNTF.R/OK ATI.AXTO-OCCiriT.M. riGAMKNT. 383

nerve as this passes backwards over the neural arch of the
axis.

The Atlanto-axial Capsular Ligaments can he examined
from the outside. They are somewhat h\x, and on remov-
ing the outer part of each, the joint cavities will be opened
into (Fig. 272).

I'asilar process of occipital bone.

Ilura ni.iter

Vertebral artery anil
first cervii.al nerve

Posterior occipito-
axial ligament.

Vnterioratlanto-occipital ligament.

Two parts of the suspensory
odi>ntoicl ligament.

— Appendix superior.

—Anterior arch of atlas.

Transverse ligament.

.•\nterior atlantoaxial ligament.
.\ppendix inferior.

Lenticular disc of cartilage \x-
tween the body of the axis
and the odontoid process.

Fig. 271. — Mesial section ihrougli the basilar process of
occipital bone, the atlas and the axis. (I'rom Luschka,
slightly modified. )

Between the posterior occipito-axial ligament and the tr.insverse ligament a small
synovial bursa may be seen.

The Anterior Atlanto- Occipital Ligament (I'ig. 271)
extends from the upper border of the anterior arch of the
atlas to the under surface of the basilar process of the
occipital bone in front of the foramen magnum. On each
side of the mesial ])lane it is thin and membranous, and
stretches outwards so as to abut against the capsular liga-
ment. In the middle line there is an exceedingly strong

384 HEAD AND NECK.

cord-like band, which stands out in strong relief from the
rest of the ligament, and is carried downwards to the
anterior tubercle of the atlas. Part of its fibres are
attached to this, but a certain proportion become con-
tinuous with the central thickening of the anterior atlanto-
axial ligament, and through this, with the anterior common
ligament of the spine.

The Posterior Atlanto-Occipital Ligament is a thin and
weak membrane which occupies the wide gap between the
posterior arch of the atlas and the posterior border of the_
foramen magnum, to both of which it is attached. It is
very firmly connected with the dura mater, and on each
side it reaches the capsular ligament. Over each of the
grooves on the posterior arch of the atlas for the vertebral
arteries it is deficient ; here its lower border forms an arch,
under which the vessel and the first cervical nerve pass.
It is not uncommon to find this fibrous arch ossified.

The Atlanto-Occipital Capsular Ligaments (Fig. 272)
connect the occipital condyles with the lateral masses of the
atlas. They completely surround the joints, and are con-
nected in front with the anterior atlanto-occipital ligament,
and behind with the posterior atlanto-occipital ligament.

The occipital bone, therefore, round the foramen magnum ■
is attached by special ligaments to each of the four portions
of the atlas — viz. to the anterior arch, to the two lateral
masses, and to the posterior arch.

Dissection. — The remaining ligaments are placed within the spinal
canal in connection with its anterior wall. For their proper display it
is therefore necessary to remove with the bone-pliers the laminae of the
axis, and the posterior arch of the atlas. The tabular part of the occi-
pital bone must likewise be taken away by sawing it through, on each
side, immediately behind the jugular eminence and the condyle, and
carrying the saw into the foramen magnum. The upper part of the
tube of dura mater which still remains in the spinal canal must next be
carefully detached. A broad membranous band stretching upwards
over the posterior aspect of the body and odontoid process of the axis is
displayed. This is the posterior occipito-axial ligament.

The Posterior Occipito-axial Ligament (membrana
tectoria) (Fig. 271; and Fig. 272, 4 and 5) is a broad

CRANIO- VERTEBRAL JOINTS.

385

ligamentous sheet which is attached below to the posterior
aspect of the body of the axis vertebra, where it is con-
tinuous with the posterior common ligament of the spine.
It extends upwards, covering completely the odontoid pro-
cess and the anterior margin of the foramen magnum, and

Fig. 272. — Ligaments on the anterior wall of the spinal
canal which connect the occipital bone, the atlas, and axis.
The posterior occipito- axial ligament and the superior
apijendix of the cruciform ligament have been partially
removed, their attached extremities being alone left in
position. (From Luschka, slightly modified.)

1 . Portion of the atlanto-occipital capsular

ligament.

2. Appendix superior of the cruciform

ligament cut across.

3. Appendix inferior of the cruciform

ligament.

4. Lower part of posterior occipito-axial

ligament thrown downwards.

5. Upper part of the posterior occipito-

axial ligament thrown upwards.
VOL. IL — 25

Upper attachment of appendix

superior.
Hypoglossal nerve.
Two parts of the suspensory odon-
toid ligament.
Alar or check ligament.
. Odontoid process.
, Transverse ligament.
. Accessory atlanto-axial ligament.

386 HEAD AND NECK.

is attached above to the posterior grooved surface of the
basilar process of the occipital bone.

Dissection. — Detach this ligament from the axis and throw it up-
wards upon the basilar process. By this proceeding the accessory liga-
ments of the atlanto-axial joints and the cruciform ligament are brought
into view, and very little further dissection is required to define them.

The Accessory Atlanto-axial Ligaments (Fig. 272, 12)
are two strong bands which take origin from the posterior
aspect of the body of the axis vertebra close to the base of
the odontoid process. Each band passes upwards and out-
wards, and is attached to the inner and hinder part of the
lateral mass of the atlas. To a certain extent they assist
the odontoid check ligaments in limiting the rotary move-
ments of the atlas upon the axis.

The Cruciform Ligament (ligamentum cruciatum) (Fig.
272) is composed of a transverse and a vertical part. The
transverse ligament (ligamentum transversum atlantis) is by
far the most important constituent of this apparatus (Fig.
271; Fig. 272, 11; and Fig. 273, 4). It is a strong
band which stretches from the tubercle on the inner
aspect of the lateral mass of the atlas to the corresponding
tubercle on the opposite side. With the anterior arch of
the atlas it forms a ring which encloses the odontoid pro-
cess— the pivot' around which the atlas bearing the head
turns. It is separated from the posterior aspect of the
odontoid process by a loose synovial membrane which
extends forward on each side until it almost reaches the
synovial membrane in connection with the mesial joint
between the odontoid process and the anterior arch of the
atlas (Fig. 273, 2 and 3). Indeed in some cases a com-
munication exists between the two synovial cavities.

The vertical part of the cruciform ligament consists of an
upper and a lower limb, which are termed the appendices or
crura. Both are attached to the dorsal surface of the trans-
verse ligament. The crus superius is the longer and flatter
of the two, and extends upwards on the posterior aspect of
the head of the odontoid process to be attached to the

CRANIO- VERTEBRAL JOINTS.

387

posterior aspect of the basilar process immediately beyond
the anterior margin of the foramen magnum (Fig. 271;
and Fig. 272, 2 and 6). The cms i?i/enus, very much shorter,
extends downwards, and is fixed to the posterior aspect of
the body of the axis vertebra (Fig. 271 ; and Fig. 272, 3).

Disscc/ion. — Detach the appendix superior from the basilar process,
and throw it downwards. The suspensory Hgamcnl is thus displayed,
and a better view of the alar or check ligaments obtained.

Fig. 273. — Transverse section through the atlas and odontoid
process. (From Cruvcilhier, slightly modified. )

1. Odontoid process.

2. Synovial cavity between the odontoid

process and anterior arch of atlas.

3. Synovial cavity between the odontoid

process and the transverse ligament.

4. Transverse ligament.

5. Posterior occipito-axial ligament.

6. Vertebral vein.

7. Vertebral artery-

8. Tube of dura mater.

The Suspensory Ligament (ligamentum apicis dentis)
(Fig. 271 ; and Fig. 272, 8) of the odontoid consists of
two parts — an anterior and a posterior. The posterior
part is a rounded cord-like ligament which is attached
below to the summit of the odontoid process, and above to
the fore margin of the foramen magnum. This ligament,
inasmuch as it is developed around the continuation of
the chorda dorsalis from the odontoid to the basis cranii,

388 HEAD AND NECK.

is a structure of considerable morphological interest. The
anterior part of the suspensory ligament is a flat and weak
band which is attached above to the anterior margin of
the foramen magnum at the same point as the posterior
portion. Below, the two portions are separated by an
interval filled with cellular tissue, and the anterior part is
attached to the odontoid process immediately above its
articular facet for the anterior arch of the atlas.

The Alar or Check Ligaments (ligamenta alaria) (Fig.
272, 9) are very powerful bands which spring, one from
each side of the summit of the odontoid process, and
proceed outwards and slightly upwards to be attached to
the inner aspect of the condyloid eminences of the occipital
bone. They limit rotation of the head, and in this they
are aided by the accessory atlanto-axial ligaments.

Movements. — Nodding movements of the head are permitted at the
occipito-atlantal articulations. Rotatory movements of the head and.
atlas around the odontoid process, which acts as a pivot, take place at
the atlanto-axial joints. Excessive rotation is checked by the alar or
check ligaments.

MOUTH AND PHARYNX.

The dissector must now return to the anterior part of the
skull which had been laid aside while the dissection of the
prevertebral region was going on. The mouth and pharynx
should, in the first instance, engage his attention.

Mouth. — The mouth is the entrance to or the vestibule
of the alimentary canal. It is placed below the nasal
chambers, in the lower part of the face, and its cavity is
controlled by muscles which are under the influence of the
will. The mouth consists of two subdivisions, viz. a
smaller anterior part which is bounded in front by the
lips and cheeks, and behind by the teeth and gums, and a
large part, the mouth proper, which is placed within the
teeth. The mucous lining of the mouth should be
thoroughly cleansed, and the two subdivisions of the cavity
examined from the front through the oral fissure.

MO U TH A ND PH. I R ) '.V.V. 389

The anterior part of the mouth whicli passes round the
teeth and gums is a mere fissure except when the cheeks
are inflated with air. It is into this subdivision of the
mouth that the parotid duct opens (p. 263). Above and
belotv it is bounded by the refiection of the mucous mem-
brane from the lips and cheeks on to the alveolar margins
of the maxillary and mandibular bones. In front it opens
upon the face by means of the oral fissure, whilst posteriorly,
behind the last molar tooth, it communicates on each side
by means of a distinct aperture with the cavity of the
mouth proper. When all the teeth are in place the exist-
ence of this communication is of importance in cases of
spasmodic closure of the jaws, because through it fluids
may be introduced into the posterior part of the buccal
cavity or mouth proper.

The mouth proper is that part of the buccal cavity which
is placed within the teeth. It is bounded in front and
laterally by the gums and teeth, whilst behind it communi-
cates by means of the isthmus faudiim with the pharynx
(Fig. 274). T\\Q floor is formed by the tongue and the
mucous membrane which stretches to this from the inner
aspect of the mandible ; the roof is vaulted, and is com-
posed of the hard and the soft palate (Fig. 274). Into
this part of the buccal cavity the ducts of the sub-maxillary
glands (Wharton's ducts) and some of the ducts of the
sublingual glands (ducts of Rivini) open (pp. 320 and
321). When the mouth is closed the dorsum of the
tongue is applied to the palate, and the cavity is almost
completely obliterated.

The various parts which bound the oral cavity may now
be examined in turn.

Lips, — The structure of the lips has in a great measure
been already examined in the dissection of the face (p.
272). Each lip may be regarded as being composed of
I four layers. From before backwards these are — ( i ) cutane-
lous; (2) muscular; (3) glandular ; and (4) mucous. The
skin and mucous membrane become continuous with each
other at the free margin of the lip. From the deep aspect

390

HEAD AND NECK.

of each lip the mucous membrane is reflected on to the
alveolar margin of the corresponding jaw, and in the
mesial plane it is raised in the form of a free fold. These
folds are termed Xho. frcenula ; in the dissection of the face
they have been more or less destroyed. The muscular

Eustachian tube

palatum molle,
isthmus faucium

epiglottis
adil us
laryng is

basis ossis
hyoidei. —

cricoid
cart.

trachea.

Fig. 274.' — Mesial section through the nose, mouth,
pharynx, and larynx. (From Gegenbaur. )

layer constitutes the, chief bulk of the lips. It is formed
by the orbicularis oris and the various muscles which
converge upon the mouth. The labial glands are very
numerous and lie between the mucous membrane and the
muscular fibres. In each lip there is an arterial arch
formed by the corresponding coronary arteries (p. 284).

MOUTH AND PHARYNX. 391

The Cheeks have five layers entering into their construc-
tion, all of which have been examined in the dissection of
the face. They are — (i) skm ; (2) a fatty layer traversed
by some of the facial muscles and the facial artery ; (3) the
buccal aponeurosis; (4) the buccinator muscle; (5) the
mucousmembrane. The buccal glands are numerous and
are situated between the buccinator muscle and the buccal
aponeurosis. Their ducts pierce the muscle and open
upon the inner aspect of the mucous membrane. The
buccal aponeurosis is a dense fascia which covers the
buccinator muscle. Above and below it is attached to
the alveolar portions of the maxillary and mandibular
bones, whilst behind it is continued backwards upon the
side of the pharynx. The muscles which traverse the
fatty layer are chiefly the zygomaticus major, the risorius,
and the posterior fibres of the platysma. The parotid
duct pierces the three inner layers of the cheek, and opens
into the mouth opposite the second molar tooth of the
upper jaw.

Gums and Teeth. — The mucous membrane of the gums
is smuoth, vascular, and firmly bound down to the sub-
jacent [)eriosteum of the alveolar portions of the jaws by a
stratum of dense connective tissue. It is continuous on
the one hand with the mucous membrane of the lips and
cheeks, and on the other with the mucous membrane of
the floor of the mouth. The gum embraces closely the
neck of each tooth.

In the adult the teeth in each jaw number sixteen.
From the middle line backwards, on each side, they are
the two incisors, the canine, the two bicuspids, the three
molars.

Floor of the Mouth. — The mucous membrane is reflected
from tiie inner as[)ect of the lower jaw, on to the side of. the
tongue, but in the fore-part of the mouth the tongue lies free
in the buccal cavity. Here the mucous membrane stretches
across the floor from one side of the lower jaw to the other.
On each side of this region the projection formed by the
sublingual gland can be distinguished. Further, if the

392

HEAD AND NECK.

tongue be pulled upwards, a mesial fold of mucous mem-
brane will be seen to connect its under surface to the floor
1 his IS \h^fr^iuni lingucB. The dissector must also look
for the openings of Wharton's ducts. Each terminates in
a papillary orifice placed close to the side of the fr^num.
J^arther back, between the side of the tongue and the jaw
are the openings of the ducts of Rivini

.fraenum linguas.

opening of Whar-
ton's duct.

elevation corre-
sponding to sub-
lingual gland.

Fig. 275.— Anterior part of the floor of the mouth.

Roof Of the Mouth.— The hard and the soft palate
lorm the continuous concave and vaulted roof of the mouth
(1-ig. 274). Projecting from the middle of the posterior
free margin of the soft palate, and resting upon the dorsum
ot the tongue, will be seen the uvula (Fig 27^) The
palate both hard and soft is traversed by a median ridge
or raphe which terminates in front, opposite the anterior
palatine foramen, in a slight elevation or papilla. In the
anterior part of the hard palate the mucous membrane on
each side of the raphe is thrown into three or four transverse

MOUril AND rilARYNX.

>93

hard rorru!;alions or ridges ; bchiiul lliis il is comparatively
smoolli.

Isthmus Faucium. — This is the name wliich is given to
the communication between the buccal cavity and the
pharynx (Fig. 276). To obtain a good view of it from the
front, the mouth must be well opened and the tongue de-

uvula.

posterior pillar

anterior pillar.

posterior wall of.
oral pharynx.

tongue.

Fig. 276. — Istiimus of the fauces as seen through the
widely opened mouth. The tonsils in the individual from
which this drawing was taken were soipewhat enlarged.

' The isthmus faucium and the parts which bound it can best be
examined in the living subject (Fig. 276).

• pressed.' It is bounded above by the soft palate, below \
by the dorsum of the tongue, and on each side by two
curved folds of mucous membrane, termed respectively the
anterior and the posterior pillars of the fauces.

The pillars of the fauces spring from the base of the
uvula, and arch outwards and then downwards. The
anterior pillar (arcus glossopalatinus) as it descends in-

394 HEAD AND NECK.

clines forwards, and ends upon the side of the posterior
part of the tongue ; the posterior pillar (arcus pharyngo-
palatinus), more strongly marked, indines backwards,
and is lost upon the side of the pharynx. The former
encloses the palato-glossus muscle, the latter the palato-
pharyngeus muscle.

In the triangular interval which is formed by the diver-
gence of these two folds will be observed the tonsil.

Pharynx. — The pharynx is a wide musculo-aponeurotic
canal \\ inches long, which extends from the base of the
cranium to the level of the body of the sixth cervical
vertebra. Here at the lower border of the cricoid cartilage
it becomes continuous with the oesophagus. Placed behind
the nasal cavities, the mouth and the larynx, it serves as
the passage which conducts air to and from the larynx, as
well as the food from the mouth to the oesophagus.

To obtain a proper idea of the connections of the pharynx, the dis-
sector should moderately distend its walls by stuffing it with tow. This
may be introduced either from above, through the mouth, or from below,
through the oesophagus.

The pharynx will now present a somewhat ovoid form.
It is widest opposite the hyoid bone ; from this upwards it
narrows slightly as it ascends to the basis cranii. When
traced in an opposite direction its width diminishes rapidly
and uniformly, until it gives place to the oesophagus. Pos-
teriorly its wall is complete, and when in position rests
upon the upper five cervical vertebra, the prevertebral
muscles, and the prevertebral fascia. To these it is bound_
by some lax connective tissue which offers no barrier to
the movements of the canal during the process of degluti-
tion. Laterally^ the pharynx is related to the great vessels
and nerves of the neck as well as to the styloid process
and the muscles which take origin from it. Upon this
aspect of the pharynx also is placed the pharyngeal plexus
of nerves, which supplies its walls with motor and sensory
twigs. In front the pharyngeal wall is interrupted by the
openings of the nasal chambers, mouth, and larynx, and it

MOUTH AND rilARYMX. 395

is to the structures wliich lie in proximity to these apertures
that it derives its principal attachment. Thus from above
downwards it is fixed — (a) to the internal pterygoid plate ;
{b) to tlie pterygo-maxillary ligament ; (c) to the side of the
tongue ; {d) to the inner aspect of the mandible; {e) to the
hyoid bone ; {/) to the thyroid cartilage ; {g) to the cricoid
cartilage. Abot'c it is attached to the basis cranii. These
various attachments will be studied more fully when we
dissect the constituents which enter into the construction
of its wall.

It should be noted that a false idea of the natural form
of the pharynx is obtained when it is examined in its
present stuffed condition and apart from the vertebral
column against which it rests. When seen in transverse
sections of the frozen body it will be observed that with
the exception of its upper or nasal part, which remains
patent under all conditions, the anterior wall is more or
less nearly approximated to the posterior wall, and below the
opening of the larynx it presents the appearance of a simple
trans\-crsc slit.

Pharyngeal Wall. — The wall of the pharynx may be said
to consist of three well-marked strata — viz. an external
muscular, an intermediate aponeurotic, and an internal
mucous. The muscular layer, which is composed of the"
three constrictor muscles, with the stylo-pharyngeus and
palato-pharyngeus on each side, should first be dissected.

For this purpose, place the preparation so that the chin rests upon a
block, and the pharynx hangs downwards with its posterior surface
towards the dissector. The constrictor nuisclcs should now be carefully
cleaned in the direction of the muscular fibres, by removing the bucco-
pharyngeal fescia which covers them.

Bucco-pharyngeal Fascia. — This coating is sometimes
spoken of tuulcr the name of the tunica pharyngis externa^
more frequently, however, it is called the bucco-pharyiigt'al
fascia^ seeing that it is continuous in front with the buccal
aponeurosis. This fascial investment must not be con-
founded with the i)revertebral layer of cervical fascia which
forms a distinct lamina behind it. The bucco-pharyngeal

396 HEAD AND NECK.

and the prevertebral layers of fascia are separated from
each other by an interval occupied by lax connective
tissue, and which, from the ease with which fluids can
travel within it, is called the retro-pharyngeal space. Both
layers of fascia are connected laterally with the carotid
sheath.

Pharyngeal Veins. — Upon the posterior and lateral walls
of the pharynx the dissector will not fail to notice numerous
veins joined together in a plexiform manner. These con-
stitute the pharyngeal venous plexus, which collects blood
from the pharynx, soft palate, and prevertebral region, and
communicates with the pterygoid plexus. Two or more
channels lead the blood from it to the internal jugular vein
(p. 330). This venous plexus, together with the pharyngeal
plexus of nerves, will require to be removed in order to
display the muscles properly.

Constrictor Muscles. — The constrictor muscles are three
flat sheets of muscular fibres which are so arranged that
they overlap each other from below upwards ; thus the
inferior constrictor overlaps the lower part of the middle
constrictor, whilst the middle constrictor in turn overlaps the
lower part of the superior constrictor. The three muscles
are inserted in the mesial plane into the median raphe, which
descends from the basilar process of the occipital bone along
the posterior aspect of the pharynx.

The inferior constrictor (musculus constrictor pharyngis
inferior) (Fig. 277,/) is narrow in front at its origin, but
it spreads out as it passes backwards towards its insertion.
It arises by two heads ; of these the loiver springs from the
posterior part of the side of the cricoid cartilage, whilst the
upper and larger head takes origin from the inferior cornu,
the oblique line of the ala, and the uj)per border of Jhe
thyroid cartilage. The muscle curves backwards round
the pharyngeal wall to meet its fellow of the opposite side
in the median raphe. The lower fibres take a horizontal
direction, but the remainder ascend with increasing degrees
of obliquity, until the highest fibres reach the raphe at a
point a short distance below the basis cranii. The lower

MOUTH AND F/IARYNX.

397

margin of the inferior constrictor overlaps the commence-
ment of the cesophagus, and passing upwards under cover
of it, so as to reach the larynx, will be seen the recurrent

Buccinator.

Tensor palati.

Levator palati.

Superior constrictor.

Miiklle constrictor

Inferior constrictor.

Thyro-hyoid.

Hyoglossus.

Stylo-hyoid.

Mylo-hyoid.

Crico-thyroid.

Slylo-pharyngeus.

Stylo-glossus.

Stylo-hyoid ligament.

Pterj'go-niaxillary liga-
ment.

Glosso-pharyngeal nerve.

Superior larj'ngeal artery.

Superior laryngeal nerve.

External laryngeal nerve.

Inferior laryngeal nerve
and artery.

Fig. 277. — Profile view of the pharynx to show the constrictor
muscles. (From Turner.)

laryngeal nerve and the laryngeal branch of the inferior
tliyroid artery (Fig. 277, 5),

The middle constrictor (nuisculus constrictor pharyngis
medius) (I'ig. 277, <?) is a fan-shaped muscle. Narrow, and
pointed in front, it ajuses from the great and small cornua
of the hyoid bone as well as from the stylo-hyoid hgament.

398 HEAD AND NECK.

From this its fibres radiate widely, and pass round the
pharyngeal wall, to be inserted with the corresponding
fibres of the opposite side into the median raphe. The
lower portion of this muscle is overlapped by the inferior
constrictor, and in the interval which separates the margins
of the muscles in front, the internal laryngeal nerve and
the laryngeal branch of the superior thyroid artery will be
seen piercing the thyro-hyoid membrane to gain the interior
of the larynx (Fig. 277, 2 and 3).

^Dissection. — The superior constrictor possesses a somewhat compli-
cated origin, and to bring this fiilly into view, it will be necessary to cut
through the internal pterygoid muscle about its middle, and turn the
upper and lower portions aside. In doing this, be careful of the small
tensor palati muscle which lies immediately subjacent to the internal
pterygoid.

The superior constrictor (musculus constrictor pharyngis
superior) (Fig. 277, d) has a weak but continuous line of
origin from the following parts — viz. {a) the lower third of
the posterior border of the internal pterygoid plate^ arid Ae
hamular process ; {b^ the pterygo-maxillary ligament which
is common to it, and the buccinator muscle ; (c) the
ggsterior_end of the mylo-hyoid ridge on the inner aspect
of the mandible ; {d) the mucous membrane of thejnouth,
and side of the tongue. From this somewhat extensive
origin, the fibres curve backwards to reach the mesial
raphe, whilst, as a rule, some of the highest gain a distinct
insertion into the pharyngeal tubercle, on the under surface
of the basi-occipital bone.

The lower part of the superior constrictor is overlapped
by the middle constrictor, and in the interval between the
two muscles will be seen the stylo-pharyngeus as it passes
downwards under cover of the middle constrictor (Fig.
277, n\ In the same interval will be seen the glosso-
pharyngeal nerve. The upper border of the muscle is free
and crescentic, and it falls short of the basis cranii.

The PterygO:muxniaryJL!igameiit (Fig. 277, q) can now
be studied. It is a strong, narrow, tendinous band, which
e2ctendsJVQmJ;heJiainu]ar pr^ the internal pterygoid

MOUTH A XD rilARYXX. 399

plate, to the posterior part of the niy^lo-hjoid ridge of the
mandible. It acts as a tendinous bond of union between
the buccinator and superior constrictor muscles, and its
connections can be best appreciated by introducing the
finger into the mouth and pressing outwards along its
course.

Sinus of Morgagni. — This is the name which is applied
to the semilunar space wliich intervenes between the upper
crescentic margin_ofj:hc superior constrictor and the basis
cranii. The deficiency in the muscular wall of the pharynx
at this point is compensated for by the increased strength
of the pharyngeal aponeurosis. In contact with the outer
surface of the aponeurosis, a little dissection will display
two muscles belonging to the soft palate — viz. the levator
palati and the tensor J>alati{^\g. 277, rand b\ The levator
is rounded and fleshy, and lies behind the tensor, which is
flatter and more tendinous. The latter can readily be
recognised, from its position in relation to the deep surface
of the internal pterygoid muscle, and from its tendon wind-
ing inwards under the hamular process. In the upper part
of the space, close to the basis cranii, and in intimate
relationship to the origin of the two muscles, will be seen
the Eustachian tube.

Pliax3nigeal Aponeurosis. — The pharyngeal aponeurosis
is strongly marked in its upper part, and maintains the
integrity of the wall of the pharynx where the muscular
fibres are absent. As it is traced downwards it gradually
becomes weaker, until it is ultimately lost as a distinct
layer. It lies between the muscles and mucous membrane,
and only comes to the surface where the muscles are
absent. It is the principal means by which the pharynx is
attached to the base of the skull. Thus it isjixedjp the
basilar process-OL-UiC occipital bone, to the apex of the
petrous bone, and also to the cartilage which intervenes
between these boriesl

Dissection. — The pharynx should now be ojiencd by a vertical and
mesial incision through the entire lenijth of the posterior wall. At the
up|x'r extremity of this cut, the knife should he carried transversely

400 HEAD AND NECK.

outwards, close to the basis cranii, so as to divide the attachment of the
posterior wall to the basi- occipital bone. The stuffing should be
removed and the mucous surface of the pharynx cleansed.

Interior of the Pharynx (cavum pharyngis). — The roof
of the pharynx will be seen to be formed by the basilar
process of the occipital bone, covered by a dense periosteum,
and a thick coating of mucous membrane. It is im-
portant to note that the posterior wall and the roof of the
pharynx can be explored by the finger introduced through
the mouth.

The mucotis membrane, or innermost stratum which enters
into the construction of the pharyngeal wall, is now exposed,
and the dissector will note that it is continuous through the
various apertures with the mucous membrane of the nasal
fossae, of the Eustachian tubes, of the buccal cavity, of the
larynx, and of the oesophagus.

The glands in connection with the mucous membrane of
the pharynx are of two kinds — viz. racemose and follicular.
The racemose glands will be noticed to form a thick layer on
the lateral and posterior aspects of the upper part of the
pharyngeal wall. They gradually diminish in number as
they are followed downwards, and opposite the isthmus
faucium they are separated from each other by consider-
able intervals. 'Y\iq follicular glands are similar in character
to those which are observed on the root of the tongue, and
to those which constitute the tonsils. In some localities
they occur in an isolated condition, in others they are
collected together in masses of different sizes. Qjoe
aggregatiojaof considerable size is placed upon the upper
part of the posterior wall of the pharynx, where this joins
the roof. It is termed the pliaryngeal tonsil (Luschka), and
is of some cUnical importance. It is oval in form, and
about half an inch in length (Fig. 278).

The soft palate which hangs like a curtain over the
isthmus faucium may be regarded as dividing the pharynx
into an upper and a lower part. The iipper portion or naso-
pharynx (cavum pharyngo-nasale) is placed behind the nasal
fossse and remains always patent (Fig. 278). It presents

MOUTH AND PHARYNX.

401

four apertures through which it is brought into connection
with the nasal chambers and the tymi)anic cavities — viz.
the two choanal or posterior nares, and the mouths of the
two Eustachian tubes.

The posterior nares or choatue are two large oval openings,
placed immediately below the base of the skull, which look
directly backwards into the naso-pharynx. They constitute

frontal sinus.

.■sphenoidal air sinus.

right choana.
Eustachian opening.

pharj-ngeal recess,
arj'ngeal tonsil.

atlas.

oft palate.

transverse ligament,
axis vertebra.

epiglottis,
hyoiil bone.

F'lG. 278. — .Anlcro-posterior section through the nose, mouth, and
pharyn.x, a little to the left of the mesial plane.

the comnumication between the nasal fossae and the

l)harynx, and are separated from each other by the thin

posterior border of the vomer bone. The vertical diameter

of each opening measures about one inch, whilst the

transverse diameter at the widest part is about half an inch.

By looking through the posterior nares the dissector obtains

a partial view of the two lower meatuses of the nose, and of

VOL. II. — -JO

0^

sublingual glanJ

manilibl

402 HEAD AND NECK.

the posterior extremities of the middle and inferior turbi-
nated bones.

The orifices of the Eustachian tubes are placed one on
each lateral wall of the naso-pharynx, behind the lower part
of the posterior nares. The level at which these apertures
lie may be said to correspond closely with that of the
posterior extremities of the inferior turbinated bones. The
orifice of the Eustachian tube is bounded above and on the
posterior side by a high rounded prominent margin, which
is altogether deficient below and in front — a condition of
affairs which favours very materially the passage of the
Eustachian catheter.^ In the natural condition of parts
there is a narrow deep recess or slit on the lateral wall of
the naso-pharynx behind the prominent posterior lip of the
Eustachian orifice. This is termed the recessus infundi-
buliforviis or recessus phary?igis, and it possesses considerable
interest from a developmental point of view (Fig. 278).

When the naso-pharynx is illuminated by a mirror introduced
through the mouth, a view of the four orifices which open into this
part of the pharynx may be obtained. Owing to the mirror being
placed obliquely and below the level of the hard palate, only the
hinder parts of the inferior turbinated bones are visible through the
choanse, and the inferior meatus of the nose is altogether out of sight.
The middle and superior meatus of the nose, and the middle and
superior turbinated bones, however, can be brought into view and their
condition ascertained. The lateral wall of the naso-pharynx and the
Eustachian orifice can also be fully inspected.

Below the soft palate there are three mesial openings into_the
pharynx — viz. the opening of the fauces, the opening of the
larynx, and the opening into the oesophagus. The part of the
pharynx which lies behind the cavity of the mouth is some-
times called the oral pharynx (cavum pharyngo-orale), whilst
that part which is placed behind the hyoid bone and larynx
is termed the laryngo-pharynx (cavum pharyngo-laryngeum).

The isthmus faucium has already been studied from the

^ An Eustachian catheter can be very readily improvised by bending
the extremity of an ordinary blowpipe. The dissector is recommended
to practise the passage of this instrument into the Eustachian tube through
the nose.

MOUTH AND PHARYNX.

403

front, and its boundaries have been described. It should
now be carefully examined from behind, and the dissector
should notice how greatly the size of the aperture varies
with differences in the position of the soft palate. The
lumen of the portion of the pharynx which lies behind
the isthmus faucium (oral pharynx) is greatly influenced by
the position of the tongue.

The laryngeal oJ>eni>i£ is placed below the isthmus
faucium. It is a large obliquely placed aperture, which
slopes from above downwards and backwards. Somewhat

THYRO.EPICLOT.LIC
510TTIS I STEHMO.KTOID
ARr.EPICLOT.FOlA^^^-L^^::^ tmyrq.hyoio
CORNICULA.l«liVHCIS^

PLATYSMA

SUP.THYHJV

/ DESCENDENS

HYPOGLOSSI

SCAUANT
VERTEBRAL.A
LONG. COLLI

Fig. 279. — Transverse section through the neck at the
level of the upper border of the thyroid cartilage.

triangular in form, it is broadest in front, where it is
baundcd by the uprightly placed eJ^[glottis. Behind it is
narroNv, and ends in the interval between the two aryicnoid
cartilages ; on_^ither side stretches a sharp fold of mucous
membrane, called the aryteno-epiglottidea?i fold.

On either side of The posterior part of the laryngeal
opening, between the arytenoid cartilage and the posterior
part of the ala of the thyroid cartilage, there is a small
downwardly directed recess, which presents a wide entrance
but rapidly narrows towards the bottom (Fig. 279). It i^

404 HEAD AND NECK.

called the sinus_ J)ynformis, and it is important to the
surgeon TSecause it is in this little pocket that foreign bodies
introduced into the pharynx are raost liable to be caught.
Below the opening of the larynx, the anterior and posterior
walls of the pharynx are always closely applied to each
other, except during the passage of food.

The oesophageal opening is placed opposite the lower
border of the cricoid cartilage. This is the narrowest part
of the pharynx.

Soft Palate (velum palatinum). The soft palate is a
movable curtain, which injervenes betweeri the buccal
cavity and the pharynx. During deglutition, however^t is
raised so as to shut off Jhe upper nasal part^ of the pharynx
from the portion below, and at the same time open up the
isthmus faucium. In front it is attached to the posterior
margin of the hard palate ; laterally., it is connected with
the sides of the pharynx; ^nY^^ posteriorly it presents a
free Uorder. From the centre of this free margin the
conical elevation termed the uvula projects. The upper
surface of the soft palate is convex and continuous with
the floor of the nasal fossse ; the inferior surface is con-
cave and continuous with the vaulted roof of the mouth.
Upon the latter surface may be seen a slightly marked
mesial ridge or raphe.

The soft palate is composed of a fold of mucous mem-
ibrane, between the two layers of which are interposed
muscular, aponeurotic, and glandular structures, together
with blood-vessels and nerves.

{The two levatores palati.
The two tensores palati.
The two palato-glossi.
The two palato-pharyngei.
The azygos uvulse. . ,

Palatal aponeurosis. Qj

Palatal glands.

( Ascending palatine from facial.

\ Palatine branch from ascendina: pharyngeal.
Arteries s • ^ o jt ^ o

' ■ \ Twigs from the descending palatine branch of the

' internal maxillary.

MOUTH AND PHARYNX. 405

r Small or posterior palatine, f from the spheno-pala-
crvcs, . ^ External palatine, . . \ tine ganglion.

Dissection. — The dissection of the soft palate is difiicult, and it is only
in a fresh part that the precise relations of the diflerent muscular layers
can be made out. Begin by rendering it tense by means of a hook, and
then remove carefully the mucous membrane from its upper and lower
surfaces, and also from the anterior and posterior pillars of the fauces.
The latter proceeding will expose the palato-glossus and the palato-
pharyngeus muscles on each side. The palatine glands will be chiefly
found on the upper surface of the soft palate, and around the UNtila.

The Palato-^ssus (musculus glosso-palatinus) is a
delicate mu^fular slip, which aiises . from the_ side of the
posterior part of the tongue, and curves upwards and
inwards to reach the under surface of the soft palate. Here
its fibres spread out, and become continuous with the
corresponding fasciculi of the opposite side. It forms the
lowest muscular stratum of the soft palate.

The Palato-pharyngeus (musculus pharyngo-palatinus)
forms two muscular strata in the soft palate which enclose
between them the azygos uvulse and the levator palati
muscles. The upper layer is very weak, and confined to
the posterior part of the velum. It constitutes the most
superficial muscular stratum on this aspect of the palate,
and becomes continuous with the corresponding portion
of the muscle of the opposite side. The deeper layer takes
origin from the posterior margin of the palate bone and
from the palatal aponeurosis, while some of its fibres mingle
with those of the corresponding muscle of the opposite side.
Outside the soft palate the two strata come together, and are
joined by one or two delicate muscular slips which spring
from the lower border of the cartilage of the Eustachian
tube. These slips are sometimes described as the salpingo-
pharyngeus muscle. The palato-pharyngeus thus formed
arches downwards and backwards in the posterior pillar of
the fiiuces to reach the stylo-pharyngeus with which it is
inserted into the superior and posterior borders of the
thyroid cartilage. Some of its fibres, however, incline back-
wards, and are inserted into the [)haryngeal aponeurosis.

\

406 HEAD AND NECK.

Azygos Uvulae (musculus uvulae). — This delicate muscle
is placed on the upper aspect of the soft palate, and
posteriorly it is covered by the superficial fibres of the
palato-pharyngeus. These must be removed to expose it
fully. It consists of two minute slips which, as a rule, arise
from the posterior nasal spine of the hard palate, and lie
one on either side of the mesial plane. As they proceed
backwards into the uvula they unite into a single rounded
muscular belly.

Dissection. — The levator palati muscle has already been seen on the
outer aspect of the pharynx in the sinus of Morgagni. To display it
fully it is necessary to remove the wall of the pharynx between the
Eustachian tube above, and the upper border of the superior constrictor
below, and then follow its fibres into the soft palate. In a well-injected
subject the dLssector will observe the ascending palatine artery in relation
to this muscle.

The Levator Palati (musculus levator veli palatini) is a
rounded fleshy muscle which arises from the lower and
inner border of the cartilage of the Eustachian tube, and
from the rough surface on the under aspect of the apex of
the petrous bone in front of the carotid canal. It passes
downwards and forwards, crosses the upper border of the
superior constrictor, and piercing the pharyngeal apo-
neurosis enters the soft palate. Here its fibres spread
out below the azygos uvulae and above the anterior or
deep portion of the palato-pharyngeus. In front, some
of the fibres are inserted into the palatal aponeurosis, but
behind this, the larger proportion of the fibres become
continuous with the corresponding fasciculi of the opposite
side.

Tensor Palati (musculus tensor veli palatini). — This
little muscle lies in front of the levator palati. It is flat
and band-like, and closely applied to the deep surface of
the internal pterygoid muscle. It arises from the scaphoid
fossa at the root of the internal . pterygoid plate, from the
spine of the sphenoid and from the outer aspect of \\^e
Kustachian tiibe. It descends perpendicularly and ends
in a tendon which turns horizontally inwards under the

MOUTH AND PHARYNX. 407

hanuilar process. A synovial bursa facilitates the play of
the tendon upon the bone. In the soft palate the tendon
expands below the deep part of the palato-pharyngeus, and
is inserted partly into the transverse ridge on the under
surface of the horizontal plate of the palate bone, and
partly into the palatal aponeurosis with which it blends.

Palatal Aponeurosis. — The palatal aponeurosis extends
backwards from the posterior margin of the hard palate to
give strength and support to the soft palate. At first it is
strongly marked, but becomes gradually weaker as it ap-
proaches the free border of the soft palate. A portion of
the deep fibres of the palato-pharyngeus, some of the fibres
of the levator palati, and the tendon of the tensor palati
obtain attachment to it.

Vessel and Nerves of the Soft Palate. — The inferior
or ascenditii^ palatine branch of the facial is, as a rule, the
principal artery of supply to the soft palate. It has already
been traced to the outer wall of the pharynx (pp. 252 and
329). Here it is seen in the sinus of Morgagni, in relation
to the levator palati muscle which it accompanies into the
soft palate. The palatine branch of the ascending pharyn-
geal artery may also be traced into the soft palate. In
cases where the preceding artery is small, this twig will be
found enlarged so as to take its place (p. 329). The
descending palatine branch of the internal maxillary artery
likewise sends small twigs to the soft palate and tonsil.

Two nerves enter the soft palate from Meckel's ganglion — viz. the
external ■iLwA \}nc. posterior palatine nerves. It would appear, however,
that they do not supply the muscles, but are distributee! to the mucous
membrane. The levator palati. theazygos uvulre, the palato-glo5SU?,
and the palato-pharyngeus are supplied by twigs from the phar)-ngeal
branches of ihc vagus, which convey to them fibres which are originally
derived from the accessory part of the spinal accessory (z\ p. 339)
(VV. Aldren Turner). The tensor iialati is probably supplied by the
branch which it receives from the otic ganglion, and which leads to
it fibres which originally come from the motor part of the trigeminal
nerve.

The Tonsils (tonsillar palatina;) arc two prominent
rounded bodies, placed one on each side of the faucus

4o8 HEAD AND NECK.

immediately above the base of the tongue and between
the two pillars of the soft palate. The buccal or internal
surface of the tonsil is perforated by a number of orifices
which lead into crypts or recesses in its substance : its
external surface rests upon the superior constrictor muscle.

The tonsils have a rich blood- supply. They derive
arterial twigs from the tonsillar and inferior palatine
branches of the facial, the descending palatine branch of
the internal maxillary, the ascending pharyngeal, and the
dorsalis linguse.

Eustachian Tube (tuba auditiva). — This is the canal
which conveys air from the pharynx to the tympanic
cavity. It is divided into two portions, according to the
parts which enter into the construction of its walls. Thus,
in the outer part of its course as it nears the tympanum,
its walls are bony, and it runs in the interval between the
squamous and petrous portions of the temporal bone.
The inner part is placed on the base of the skull, and is
lodged in the gutter or groove between the apex of the
petrous part of the temporal bone and the great wing of
the sphenoid. This is the subdivision of the tube which
comes under the notice of the dissector at the present
stage, and he should first note its direction and then study
its relations and the construction of its walls.

The direction of the canal can be readily ascertained
by passing a probe into it through its pharyngeal orifice.
It will be seen to run backwards and outwards with a
slight inclination upwards. At the same time it will he
noticed to pass between the origin of the levator palafi.
which lies upon its inner side, and the origin of the tensnr
palati, which is placed upon its outer side. This relation-
ship is best seen in coronal sections through the frozen
head. The dissector should now proceed to remove the
mucous membrane from around the pharyngeal orifice
of the tube. This will reveal the fact that its wall is
strengthened by a triangular plate of cartilage, which is
folded upon itself so as to protect the tube on its upper
and inner aspects. The cartilage is deficient below and

CAROTID CANAL. 409

externally, its place being taken by dense fibrous tissue,
which connects the margins of the cartilage and completes
the wall of the canal. This explains the characteristic
form which its pharyngeal orifice presents (p. 402). A
muscular slip, which descends from the outer margin of
the cartilage in relation to the outer unprotected side of
the tube, has been termed the dilatator tubcc (Rudinger).
It joins the tensor palati. The interior of the tube is
lined by mucous membrane continuous with that of the
pharynx, and it will be noticed that, as the tube is traced
towards the pharynx, it gradually increases in calibre.
Hence it is frequently described as trumpet-shaped.

CAROTID CANAL AND SUPERIOR
MAXILLARY NERVE.

Dissection. — The carotid canal, which traverses the fore-part of the
petrous bone, may now be opened up by removing its inferior wail
with the bone-pliers. In doing this, it is not necessary to interfere
with the Eustachian tube, which lies in close proximity. It is well to
preserve this structure until we undertake the dissection of the otic
ganglion.

Carotid Canal. — The carotid canal contains the internal
carotid artery and the stout ascending branch of the superior
cervical ganglion of the symi)athetic.

The internal carotid artery in this part of its course is
about three-fourths of an inch long. At first it ascends
vertically ; then, bending suddenly, it runs horizontally
forwards and inwards. It emerges from the canal at the
apex of the petrous bone. From this point onwards the
internal carotid artery has been already examined (p. 350).
Whilst within the carotid canal it lies in front of the
internal ear.

Ascending branch of the cervical sympathetic. — The dis-
sector has already noted a large branch proceeding from
the upper end of the superior cervical ganglion and
entering the carotid canal with the internal carotid artery.

4IO HEAD AND NECK.

This almostJxQJnediately divides into two parts, which
place themselves one _on either side "of the artery, and
supply branches to its coats. The further dissection of
these branches is a matter of great difificulty, and can
only be satisfactorily effected under specially favourable
circumstances. The external branchy breaics^ up_Jnto the
carotid plexus ; the internal bra?ich is continued into the
cavernous plexus. From these primary offshoots secondary
plexuses are prolonged upon the various branches which
spring from the internal carotid artery.

The carotid plexus, which lies upon the outer aspect of the internal
carotid artery, gives off the following branches — ( i ) one or two filaments
to the abducent or sixth nerve as it turns round the internal carotid
arfey"; "(2) one~or two twigs which join the inner part of the Gasserian
ganglion ; (3) the large deep petrosal nerve ; (4) the small carotico-
tympanic nerve.

The large deep petrosal nei-ve runs to the posterior aspect of the
body of the sphenoid, and at ttie entrance to the Vidian canal it
joins the gtecit superftctal petrosal nerve and lorms the Vidian nei've

V?- 351)- . .

The carotico-tympanic branch of the carotid plexus joins the tympanic
branch of the glosso-pharyngeal as it traverses the tympanum (p. 334,
and Fig. 259).

The carotid plexus alsd receives the small deep petrosal 7ierve from
the tympanic branch of the glosso-pharyngeal.

The cavernous plexus has already been sufficiently described on

P- 351-

Dissection to expose the Superior Maxillary Nerve. — As the

superior maxillary nerve proceeds forwards to reach the face, it traverses
the upper part of the spheno-maxillary fossa and the infra-orbital canal.
The dissector should therefore proceed to expose the nerve in these
localities. Remove the temporal muscle and the upper head of the
external pterygoid muscle, and, placing the saw upon the cut margin
of the skull at a point immediately above the external auditory meatus,
carry it obliquely downwards and forwards through the squamous part
of the temporal bone and the great wing of the sphenoid towards the
inner end of the sphenoidal fissure. This saw-cut should enter the
sphenoidal fissure immediately to the outer side of the foramen
rotundum. A second saw-cut should then be made from the cut
margin of the cranial wall, immediately above the anterior margin of
the great wing of the sphenoid bone downwards into the sphenoidal
fissure to meet the first saw-cut. The piece of bone included between
these cuts can now be removed. Additional space may be obtained
and the spheno-maxillary fossa more fully opened up by removing

SUrEFTOR MAX 11. 1.AR Y NER VE. 411

what remains of the great wing of the sphenoid upon the outer side
of the foramen rotundum, but the circumference of this aperture must
be carefully preserved. Proceed, in the next place, to open up the
infra-orbital canal. In its posterior part its up|K'r wall is usually so
thin that it can easily be removed by one of the blades of a pair of
forceps, but in front it sinks tleeply under the rim of the orbital open-
ing, and here the chisel must be employed. The superior maxillary
nerve can now be defined and its branches displayed. The infra-
orbital artery and vein, which accompany the nerve, will be exposed
at the same time.

Superior Maxillary Nerve (nervus maxillaris). — The
superior maxillary nerve springs from the Gosserian ganglion
within the cranial cavity (p. 347). It is composed entirely
of sensory fibres, and proceeds forwards under the dura
mater to the foramen rotundum through which it passes
into the spheno-maxillary fossa. The nerve is now carried
across the upper part of this fossa and enters the infra-
orbital canal, where it receives the name of infra-orbital.
Finally it emerges upon the face through the infra-orbital
foramen, and breaks up, under cover of the levator labii
superioris, into numerous branches, which form a dense
plexus with twigs from the facial nerve. Its terminal
filaments are distributed to the lower eyelid, the nose, and
the upper lip. From its origin within the cranium to its
termination on the face, the superior maxillary nerve
pursues a nearly straight course, and in each stage it gives
off one or more branches. These are : —

1. Within the cranium, -{ Recurrent (already described p. 349).

/OrbiJal or temporo-malar (already de-

2. In the spheno-maxil-J scribed, p. 371).

lary fossa, . . I Spheno-palatine.

I Posterior superior dental.

3. In the infra-orbital J Middle superior dental.

canal, . . I Anterior superior dental.

(Palpebral,
Nasal, V already described, p. 2S1.

Labial,

The temporo-malar nerve, which has already been dis-
sected in the orbit, can now be traced back to its origin

412

HEAD AND NECK.

from the superior maxillary nerve in the spheno-maxillary
fossa. The spheno-palatine branches are two stout twigs
which arise from the under aspect of the superior maxillary
nerve, and proceed vertically downwards in the spheno-
maxillary fossa to Meckel's ganglion, of which they con-
stitute the sensory roots.

Superior Dental Nerves (nervi alveolares superiores). —
These are usually three in number, and are distinguished
as posterior, middle, and anterior. The middle superior
dental nerve is sometimes absent as a separate trunk, in

Fig. 280. — Diagram of the superior maxillary nerve.
Thane, Quain's Anatomy.)

(Professor

which case it arises in common with the anterior superior
dental.

The posterior superior dental nerve takes origin in the
spheno-maxillary fossa, and almost immediately divides into
two branches, which proceed downwards upon the posterior
aspect of the body of the superior maxillary bone. They
contribute a few fine filaments to the mucous membrane of
the cheek and to the gum, and then disappear into the
minute posterior dental foramina to supply the three
molar teeth and the lining membrane of the antrum of
Highmore.

THE INFRA-ORBITAL ARTERY. 413

The middle superior dental tieix'c sui)plics the two bi-
cuspid teeth. It arises from the infra-orbital nerve, a short
distance in front of the spheno-maxillary fossa, and can be
easily detected (when present) by gently raising the parent
trunk from the fioor of the canal. It descends in a
minute canal which traverses the outer wall of the antrum
of Highmore.

The anterior superior dental newe, much the largest ot
the three dental branches, springs from the infra-orbital as
it approaches the fore -part of the canal. It can be
brought into view by raising the parent trunk from the
floor of the canal, and it will then be seen to enter a
special bony tunnel which traverses the upper jaw in front
of the antrum of Highmore. The dissector should en-
deavour to open up this canal with the chisel. After
supplying a branch to the mucous membrane of the lower
and fore-part of the nasal fossa, the anterior superior
dental nerve divides into branches for the incisor and the
canine teeth.

While traversing the upper jaw, the three superior dental branches
communicate with each other, and form two nerve-loops. Numerous
twigs proceed from these, and join in a fine plexus. It is from this
plexus that the terminal filaments to the teeth and gum take origin.

The Infra-orbital Artery (arteria infra-orbitalis) is a
branch of the internal maxillary. It arises in the spheno-
maxillary fossa, and accompanies the infra-orbital nerve.
In the face its terminal twigs anastomose with branches of
the facial, transverse facial, and l)uccal arteries ; in the
infra-orbital canal it gives some fine branches to the
contents of the orbital cavity, and also the anterior dental
artery (arteria alveolaris superior anterior), which accom-
panies the nerve of that name, and supplies the incisor
and canine teeth, and the lining membrane of the antrum.

The infra-orbital vein joins the pterygoid plexus.

414 HEAD AND NECK.

OTIC GANGLION— NASAL FOSS^— MECKEL'S
GANGLION— INTRAPETROUS PORTION OF
THE FACIAL NERVE.

Dissection. — The portion of the lower jaw which still remains,
together with the tongue and larynx, must now be removed from the
upper part of the skull. From the angle of the mouth on each side
carry the knife backwards through the buccinator and mucous membrane
of the cheek, the pterygo-maxillary ligament, and the lateral wall of the
pharynx. The internal pterygoid muscle has already been divided, but
it will be necessary to cut the internal carotid artery with the vessels
and nerves which still connect the pharynx with the skull. The larynx
and tongue may be laid aside for future dissection.

The fore-part of the skull should next be divided into two lateral
parts by sawing it through in the sagittal direction close to one side of
the nasal septum. As a general rule the nasal septum is not vertical,
but deviates more or less to one or other side of the mesial plane.
This deviation is more frequently directed to the right than to the left
side. Endeavour to determine the direction which it takes in the skull
under observation by passing a probe into the nasal fossae through the
posterior nares. The section through the skull should be made close
to the concave side of the septum. Begin in front by introducing a
knife into the nostril of that side, and carry it upwards through the
cartilaginous part of the nose to the nasal bone. Then place the
specimen so that the face rests upon the table, and divide the soft
palate from before backwards in the same plane. The section may
now be completed by sawing from behind forwards through the hard
palate and bony roof of the nasal fossa. The dissector should make
every effort to preserve the septum of the nose intact. As a general
rule the upper turbinated bone is partially injured. This is not a very
serious matter, as the outer aspect of the nasal fossa can be studied
upon the opposite side when the septum of the nose has been removed.

If the part has been well preserved, the dissector should be able at
this stage to expose the otic ganglion, and perhaps also some of its
more important connections. Turn the specimen so that its inner
surface looks upwards, and carefully detaching the levator palati from
its origin throw it downwards. Then remove the cartilaginous part of
the Eustachian tube. In doing this, the dissector must proceed with
the greatest caution, because the ganglion lies immediately subjacent.
By following the nerve to the internal pterygoid muscle upwards and
backwards to its origin the otic ganglion will be discovered.

The otic Ganglion (ganglion oticum) is a minute oval
body about 4 mm. in length. It is placed immediately

NASAL SEPTUM. 415

below the foramen ovale, between the deep surface of the
inferior maxillary nerve and the cartilaginous part of the
Eustachian tube. The middle meningeal artery lies behind
it. Two connecting filaments bind it to the inferior
maxillary nerve, and it either covers or surrounds the
origin of the nerve to the internal pterygoid muscle.

The ulic ganglion is usu.illy described as receiving motor, sensory,
and sympalholic roots. The motor and sensory roots are, in all prob-
ability, both supplied by the nerve to the internal pterygoid muscle ;
the sympathetic ;v<7/ comes from the plexus around the middle meningeal
artery. In addition to these, the small superficial petrosal iiei-i'e enters
the posterior border of the ganglion, and conveys to it sensory fibres
from the glosso-pharyngeal nerve, and probably also motor fibres from
the Aicial nerve (p. 334, Fig. 259).

The following are the branches which proceed from the otic
ganglion : —

I A twig which passes downwards and forwards to the
Branches of ) tensor palati.

distribution. \ A twig which proceeds upwards and backwards to
\ supply the tensor tympani.

I One or more fine filaments to one or both of the roots
Connecting 1 of the auriculo-temporal nerve,
branches, j A minute communicating filament to the chorda
' tympani.

Nasal Septum (septum nasi). — The nasal septum
divides the cavity of the nose into two narrow chambers —
the right and left nasal fossa;. It is not placed accurately
in the mesial plane, but almost invariably shows a bulging
or deviation to one or other side, so as to reduce the
width of one fossa, and increase the capacity of the other.
Immediately above the anterior aperture of the nasal fossa
the septum shows a slight depression, which corresponds
to the vestibule of the nose, and forms the inner wall of this
subdivision of the chamber. The vestibular part of the
partition is clothed by skin, continuous with the external
integument; from this a number of stiff hairs, termed
vibrissic^ project. Over the rest of its extent the septum
nasi is covered with mucous membrane, which is divided
into two districts, viz. a lower or respiratory area, and a
much smaller upper or olfactory area, comprising not more

4i6

HEAD AND NECK.

than the upper third of the septum in which the branches
of the olfactory nerve spread out. The respiratory mucous
membrane is very thick and spongy. It is highly vascular,
and contains numerous racemose glands. The minute
orifices of the gland ducts can be detected by the naked
eye. Over the olfactory district of the septum, the
mucous membrane is softer and more delicate, and not so

' frontal sinus.

nasal bone.

septal cartilage.

mesethmoid.

vestibule of/^
nasal chamber.

opening of.
Jacobson's organ.

sublingual gland,
mandible.

sphenoidal air sinus,

.right choana.
Eustachian opening.

■pharyngeal recess,
pharyngeal tonsil.

atlas.

soft palate,
transverse ligament,
axis vertebra.

•epiglottis,
byoid bone.

Fig. 281. — Antero-posterior section through the nose, mouth, and
pharynx, a little to the left of the mesial plane.

thick. In the fresh state it presents a yellowish colour,
and the glands are smaller.

In favourable cases a minute orifice may be detected in the mucous
membrane on the lower and fore part of the nasal septum immediately
behind the vestibular area. It is placed above the anterior end of a
well-marked elongated projection which passes obliquely backwards and
upwards, and corresponds to the thickened lower margin of the septal

CONSTRUCTION OT THE NASAL SETTUM. 417

cartilage. This apcrlurc varies in dianiclcr from A mm. to I \ mm.
(Schwall)e). It leads into a narrow canal, which passes backwards for
a short tlislance, and then ends blindly. It is of interest because it
represents in the human subject the rudiment of the origan of Jacobson,
a tubular structure which is highly developed in some of the lower
animals.

Construction of the Nasal Septum. — Strip tlic mucous
membrane from the exposed surface of the septum nasi.
By this proceeding the intimate connection which exists
between the mucous membrane and the subjacent peri-
osteum and perichondrium will become apparent, and the
parts forming the septum will be rendered visible. The
bulk of the partition is composed of the perpendicular
plate of the ethmoid and the vomer posteriorly, and of the
septal ^cartilage in front. Small portions of otKer bones
take a minor part in its construction. Thus, above and
behind there are the crest and rostrum of the sphenoid ;
above and in front is the nasal spine of the frontal bone \
whilst below there is the crest of bone formed by the
apposition of the palatal processes of the palate and
superior maxillary bonjis of opposite sides.

The septal cartilage (cartilago septi nasi) fills u^j tjie wide
angular gaj3_which intervcnes_bet\veen the perpendicular
plate of the ethmoid and the vomer, and it projects forwards
towards the point of the nose. It is a broad irregularly
quadrilateral cartilaginous plate. Its upper and posterior
border is in apposition with the fore border of the mes-
ethmoid ; its loiver and posterior border^ much thickened, is
received into the groove in the fore border of the vomer
and the incisor crest of the maxillary bones. The angle
between these two borders is prolonged backwards for a
varying distance in the form of a tongue-shaped cartilaginous
process, which occupies the interval between the two
plates of the vomer. The upper and anterior border of the
septal cartilage is in contact above with the suture between
the two nasal bones ; below this it is related to the two
lateral cartilages of the nose, whilst still lower down it is
seen in the interval between the two cartilages of the nasal
VOL. II. — 27

41 8 HEAD AND NECK.

aperture. Its connection with the lateral cartilage of each
side is a verj^ intimate one, indeed, below the nasal bones
the three cartilages may be considered to be directly con-
tinuous, but lower down they are separated by a fissure
which runs upwards for some distance on each side. The
lower and anterior border is very short; it is free, and
extends backwards to the anterior nasal spine. The
a.nterior angle of the septal cartilage is blunt and rounded,
and does not reach to the point of the nose, which is thus
formed by the cartilages of the aperture (p. 296).

The deviation of the septum nasi from the mesial plane
will now (in all probability) be seen to be due to a bulging
to one side of the vomer and mes-ethmoid along their line
of union. It is not developed until after the seventh year
of life (Zuckerkandl).

Dissection. — The septal cartilage and thin bony laminse must now be
removed piecemeal. This must be done very carefully, as it is necessary
to preserve intact the mucous membrane which clothes the opposite side
of the septum. It is in tMs that the nerves and blood-vessels must be
examined.

Vessels and Nerves of the Septum Nasi. — The following
is a list of the nerves : —

Nerves of Smell, . Olfactory.

j' I. Naso-palatine, or nerve of Cotunnius,

Nerves of Common J 2. Septal branch of the nasal nerve proper.

I Sensation, . . ] 3. Nasal branches from Meckel's gan-

V glion and the Vidian nerve.

The inner group of olfactory nerves which are distributed
in the mucous membrane of the upper part of the nasal
septum are barely distinguishable, except in a fresh part ;
further, they are so soft that it is hardly possible to isolate
them. They enter the nasal fossa through the inner series
of apertures in the cribriform plate of the ethmoid, and
proceed downwards in grooves on the surface of the per-
pendicular plate of the same bone.

The naso-palatine nerve (nervus naso-palatinus) is a long
slender twig which can easily be detected upon the deep
surface of the mucous lining of the septum. It springs

VESSELS AND NERVES OF THE SEPTUM NASI. 419

from Meckel's ganglion, and enters the nasal fossa through
the spheno-palatine foramen. In the first part of its course
it runs horizontally inwards upon the under surface of the
body of the sphenoid. Having gained the nasal septum,
ij changes- its dire_ction and proceeds downwards and
forwards in a shallow groove on the surface of the vomer
under cover of the mucous lining. Finally it enters the
foramen of Scarpa, and where the two foramina of Scarpa
opeiLJiTto. the_common anterior palatine canal, the nerves
of opposite sides unite in a plexus from which branches
are given to the mucous membrane covering the fore-part
of the hard palate. The naso-palatine nerve is accompanied
by the corresponding artery, and as it lies on the surface of
the vomer, it supplies some small twigs to the mucous
membrane of the septum nasi.

A few nasal Mzw/z^^Jfrom Meckel's ganglion, and also
from the Vidian nerve, reach the mucous membrane over
the upper and back part of the septum. They are very
minute, and it is very questionable if the dissector will be
able to discover any trace of them.

The septal branch of the nasal nerve proper will be found
descending over the fore-part of the nasal septum. It runs
between the mucous membrane and the septal cartilage,
and its terminal twigs may be traced as far as the vesti-
bule.

The arteries which convey blood to the septum nasi are :
(i) the iiaso-palatine, which accompanies the nerve of the
same name ; (2) a branch of the anterior edimoidal accom-
panying the septal branch of the nasal nerve ; (3) some
minute twigs to the upper part of the septum from the
posterior ethmoidal artery ; (4) the septal branch of the
superior coronary artery, which is distributed upon the
columna nasi.

Dissection. — Tlie mucous membrane of the septum may now be
divided by the scissors alonjj the roof of the nasal cavity. Before doing
this, disengage from its surface the naso-palatine nerve antl the septal
branch of the nasal nerve proper, in order that they may be afterwards
traced to their origins. When the layer of mucous membrane thus

420

HEAD AND NECK.

detached from the roof of the nose is thrown inwards the nasal fossa
is exposed.

The Nasal tossse (cavum nasi) are two chambers ^placed
one on each side of the septum nasi. They are extremely

4 5

Fig. 282. — Coronal section through the nasal cavities
opposite the crista Galli of the ethmoid bone ; viewed from
behind.

1. Anterior ethmoidal cell.

2. Infundlbulum.

3. Posterior angle of septal carti-

lage between vomer and per-
pendicular plate of ethmoid.

4. Inferior turbinated bone.

5. Inferior meatus.

6. Antrum of Highmore.

7. Middle turbinated bone.

8. Middle meatus.

The upper arrow passes through the opening of the anterior
ethmoidal cell into the infundlbulum. The lower arrow passes
from the antrum of Highmore into the infundlbulum.

rilE NASA I. rOSS.E. 421

narrow, but the vertical depth and antero-postcrior length
of each fossa is very considerable. The width increases
somewhat from above downwards ; thus, in the upper part,
the superior turbinated bone is only separated from the
septum by an interval of 2 mm., whilst lower down we
find a space of 4 or 5 mm. intervening between the inferior
turbinated bone and the septum. Each nasal fossa presents
an inner wall formed by the septum, an outer wall, a roof,
a floor, and an anterior and a posterior aperture.

The anterior apertures of the nasaTTossse or nostrils are
two oval orifices which open upon the face and look down-
wards. The posterior apertures or choancp, open into the
upper part of the pharynx and look directly backwards.

The narrow roof of the nasal fossa consists of an iuter-
tnediate horizontal portion formed by the cribriform plate
of the ethmoid bone, and of an anterior and a posterior
sloping part. The anterior part inclines downwards and
forwards, and is formed by the narrow grooved nasal surface
of the spine of the frontal bone, the nasal bone, and the
angle between the lateral cartilage and the septal cartilage.
"^VhQ posterior part of the roof, which slopes downwards and
backwards, is composed of the fore and under surfaces of
the body of the sphenoid, as well as the spread-out ala of
the vomer and the sphenoidal process of the palate bone,
both of which are applied to the under surface of the
sphenoidal body.

The. Jloor o{ the nasal fossa is wider than the roof It is
formed by the palatal processes of the superior maxillary
and palate bones, and is concave from side to side.
Further, it presents a gentle slope from before backwards, so
that it is slightly higher in front than behind. On the
anterior part of the floor, and close to the septum nasi, the
dissector may observe a minute funnel-shaped depression
of the mucous membrane into the incisor foramen. This
is of interest from a developmental point of view ; it is a
vestige of the extensive communication which existed in
the embryo between the cavities of the nose and the
mouth.

422 HEAD AND NECK.

Outer Wall of the Nasal Fossa. — The outer -wall of the
nasal ca-sity is rendered uneven and complicated by the
projection of the three turbinated bones.

The part which the difierent bones take in the formation of the outer
wall of the cavit)^ of the nose must- in the first place be studied in a
sagittal section through the macerated skull, and the dissector should
constantly refer to such a preparation during the dissection. In front,
the outer wall of the nasal ca\-ity is formed by the lateral cartilage, the
cartilage of the aperture, the nasal bone, and the ascending process of
the superior maxillary bone. Behind these, the lachr}-mal, the ethmoid,
and the inferior turbinated bones, with a small portion of the bodj' of
the superior maxillar}- bone, enter into its construction ; whilst, still
farther back, are the vertical plate of the palate bone and the internal
pter}-goid plate of the sphenoid. Placed in relation to the outer aspect
of this wall are the ethmoidal air-cells, which interv"ene between the
upper part of the nasal ca^-ity and the orbit, whilst, at a lower level,
the great air sinus of the superior maxillary bone, termed the antrum of
Highmore, is situated immediately to the outer side of the nasal fossa
(Fig. 282).

Turning now to the recent specimen, the dissector will
observe that the outer wall may very readily be subdivided
into three areas or districts. These are — (i) the vestibule,
(2) the atrium meatus medii, (3) the region of the turbinated
bones and inter\-ening meatuses.

Vestibulum Nasi. — The vestibular tart (Fig. 283, 6', 6)
of the outer wall is_ a depression of a somewhat oval form
placed immediately above the aperture of the nos^l. It is
partially divided into an upper and lower portion by a
short ridge w^hich projects forwards from its posterior
boundary, and it is clothed throughout by integument con-
tinuous with the skin. From this a number of stout, stiff
hairs, termed vibrisscB, project (Fig. 283, 5). The vibrissse
which spring from the anterior part of the region incline
backwards, whilst those which are implanted- into the
posterior part are directed forwards ; in this manner a
sieve-like arrangement is provided at the anterior aperture
of the nose. The vestibular part of the outer wall is
placed opposite the corresponding area on the septum nasi,
and the two together constitute an ampuUated entrance to
the nasal fossa. The capacity and shape of this section of

THE A TRIUM ME A TUS MEDIf.

423

the cavity is influenced to a certain extent by the contrac-
tion of the nasal muscles.

The Atrium Meatus Medii (Fig. 283, 8) is placed above,
and slighTTy behind the vestibular district, and it receives its
name from the fact that it leads directly backwards into the
nijildJc^nieiLUus. of the nose. It is slightly hollowed out and
concave, and on its upper part, near the nasal bone, a feeble

Fig. 283. — Outer wall of the left nasal fossa. (From Schwalbc. )

Frontal air sinus.

Free border of the n.isal bone.

Cribriform plate of ethmoid.

Sphenoidal air sinus.

Vibrissa;.

6. Two parts of the vestibular area.

Elevation intervening between the

vestibular district and the atrium.
Atrium meatus medii.
Agger nasi, or rudiment of an anterior

turbinal.
Upper part of the superior turbinated

bone (concha suprcnia).
Recessus sphcno-ethmoidalis.

18.
19.
20.

21.

Superior turbinated bone.

Superior meatus.

Middle turbinated bone.

Inferior turbinated bone.

Plica naso-pharj-ngea.

District intermediate between nose
and pharj-nx, and termed the region
of the ductus n.isopharj'ngeus.

Orifice of Eustachian tube.

Prominent inner lip of this orifice.

Wall of pharj'nx.

Anterior palatine canal.

, c. Free Ixjrder of the middle tur-
binated bone.

424 HEAD AND NECK.

elevation termed the agger nasi may be noticed, which begins
close to the fore-part of the attached margin of the middle
turbinated bone, and proceeds obliquely downwards and
forwards (Fig. 283, 9). This has been termed by Schwalbe
the " rudiment _of_tlie, anterior turbinal," and he considers
that it is the representative of the naso-turbinal which is
present in some mammals. A slight depression above the
agger nasi leads backwards to the olfactory district of the
outer wall of the nasal fossa, and receives the name of
sulcus olfactorius.

Turbinated Bones. — Behind the vestibule and the atrium
are the turbinated bones with the intervening meatuses.
The superior turbinated bone (concha superior) (Fig. 283, 12),
which projects from the lateral mass of the ethmoid bone,
is very short, and is placed on the upper and bac'ir~part of
the outer wall of the fossa. Its free borde^begins a short
distance below the centre _of the, cribriform plate, and
proceeds obliquely downwards and backwards to a point
immediately below the body of the sphenoid, where it ends.
The 7niddle turbinated bone (concha media) (Fig. 283, 14) ij.
also aTpartof the ethmoid. Its free border begins a short
distance below the fore-part of the cribriform plate, and
at first takes a vertical course downwards {a to b^ ; then,
bending suddenly, it proceeds backwards, and ends midway
between the body of the sphenoid and the posterior border
of the hard palate (c). The inferior turbinated bone (concha
inferior) (Fig. 283, 15) is an independent bone, and stretches
backwards upon the outer wall of the nasal fossa, midway
between the middle turbinated bone and the floor of the
nose. Its lower free margin is somewhat convex from before
backwards.

Meatuses of the Nose (meatus nasi). — The superior
meatus (Fig. 283, 13) is a short narrow fissure between the
superior and middle turbinated bones. The posterior
ethmoidal cells open into its upper and fore part by one,
or, in some cases, by several apertures.

To bring these orifices into view, the superior spongy bone should
be turned aside by introducing the blade of a pair of forceps under its

MEATUSES OF THE NOSE. 4^5

entire length, and forcing it upwards. Oire should be taken not to
injure the mucous membrane more than is absolutely necessar)-.

The middle meatus is a much more roomy passage which
lies between the middle and inferior turbinated bones, and
is continued directly forwards into the atrium.

The middle spongy bone should be forcibly tilled upwards and back-
wards.

The upper and fore part of the middle jiieatus leads
into a funnel-shaped passage which passes upwards into
the corresponding frontal sinus. This passage is called the
infioidibulum, and constitutes the channel of communica-
tion between the frontal sinus and the nasal chamber.

Upon the lateral >va]JLsf the nji^iilc iTaeaitus a deep curved
groove or gutter, which takes origin at the infundibulum
and runs from above downwards and backwards, will be
observed. In this groove, which is termed the hiatus semi-
lunaris (Fig. 284), are the ppenjngs^fjthe anterior ethmoidal
cells, and thejLUtrum _of_.Hig]imQre. The upper boundary
of the hiatus semilunaris is high and prominent. It is
termed the bulla ethmoidalis. At a higher level than the
bulla the aperture of the middle ethmoidal cells will usually
be seen (Fig. 284). The slit-like opening of the antrum
of Highmore will be noticed in the hinder part of the
hiatus semilunaris.

The dissector should now proceed to open up the antrum of High-
more by removing its outer wall. This may ])e done by sawing upwards
through the root of the zygomatic process of the superior maxillary bone.

The orifice by means of which this great air sinus com-
municates with the middle meatus will be noticed to be
placed on the inner wall of the cavity much nearer the roof
than the floor — a position highly unfavourable for the escape
of fluids which may collect within it. Sometimes, however,
a second orifice, circular in outline, will be found. This is
situated lower down, and opens into the middle meatus
inunediatcly above the middle point of the attached margin
of the inferior turbinated bone.

426

HEAD AND NECK.

The inferior meatus is the horizontal passage which
extends backwards between the inferior turbinated bone
and the floor of the nasal fossa. It is placed behind the
vestibule, and the free border of the projection, which
corresponds to the inferior turbinated bone, turns down-

opening of middle
ethmoidal cells.

mfundibulum.

superior meatus.

opening of antrum. --

orifice of Eustach
tube.

orifice of nasal duct.

Fig. 284.^ — Outer wall of nasal fossa. (From Gegen-
baur. ) The middle and inferior turbinated bones have been
taken away.

wards in front so as to limit it anteriorly (Fig. 283). This
condition, together with the backward slope of the floor,
renders the inferior meatus more accessible to the current
of expired air than to the current of inspired air (Schwalbe).
In the fore-part of this meatus will be found the opening
of the nasal duct — the canal which conveys the tears to the
nasal fossa (Fig. 284).

To bring the aperture of the nasal duct into view, remove a small
portion of the anterior part of the inferior turbinated bone with the
scissors.

MUCOUS MEMBRANE OE OUTER IVAIJ. OE NOSE. 427

The orifice of the nasal duct varies in form, according
to the manner in which the mucous membrane is arranged
around it. Sometimes it is wide, patent, and circular ; at
other times the mucous membrane is prolonged inwards
beyond the bony opening, so as to reduce the size of the
aperture and even give it a slit-like character. In some
cases indeed the orifice may be so minute that it is a
difficult matter to find it. Its continuity with the lachrymal
sac should in all cases be established by passing a probe
from above downwards through the nasal duct.

A fourth meatus is generally present on the outer wall
of the nose. It is not at all uncommon to find the superior
turbinated bone partially subdivided into an upper and
lower part by a short groove, which proceeds forwards from
the anterior aspect of the body of the sphenoid. This
additional meatus is termed the recessus spheuo-ethtnoidalis
(Meyer), and into its back part opens the aperture of the
sphenoidal air sinus (Fig. 283, 11). This orifice may be
circular or slit-like, according to the manner in which the
mucous membrane is disposed around it.^ The upper
portion of the superior turbinated bone which is placed
above this additional meatus is called the concha suprema
(Fig. 283, 10).

Mucous Membrane of the Outer Wall of the Nose. — The
vestibule, as we have noted, js lined by integument. The
remainder of the outer wall, as well as the roof and floor of
the nasal fossa, is lined by mucous membraiie,_which is
continuous through the nasal duct with the ocular con-
junctiva, through the various apertures with the delicate
lining membrane of the air-cells which open into the nose,
and through the posterior nares with the pharyngeal mucous
membrane. On the outer wall, as on the septum, the
mucous membrane is mapped out into an upper olfactory
and a lower respiratory portion. This subdivision cannot
be appreciated by the naked eye, as the one district passes

^ When the recessus sphcno-ctbmoidalis is absent, the sphenoid.nl air
sinus opens into the interval between the roof of the nasal fossa and the
superior turbinated bone.

428 HEAD AND NECK.

without any sharp line of demarcation into the other. The
olfactory region (regio olfactoria) comprises merely the upp^r
turbinated bone, the respiratory regio?i (regio respiratoria)
includes the middle, and inferior turbinated-Jajones, the
middle meatus, the lower meatus, and the— atrium. In
the lower part of the outer wall the mucous membrane is
thick and spongy. This is particularly noticeable over the
lower borders and posterior extremities of the middle and
inferior turbinated bones, where the membrane presents an
irregular surface and forms soft bulging cushions. This
condition is largely due to the presence of a .rich_ver30us
plexus, the vessels of which run for the most part in an
antero-posterior direction. In the case of the lower spongy
bone, the veins are so numerous that the mucous membrane
assumes the character of cavernous tissue, and is sometimes
spoken of as the " erectile body." When turgid with blood,
it swells out so as to obliterate the interval between the
turbinal bone and the septum. The mucous membrane of
the floor, meatuses, and the atrium, is smoother and not
so thick as that over the turbinated bones. Everywhere
numerous racemose glands are embedded in its midst, and
the minute . punctiform orifices of the ducts are visible to
the naked eye. In the olfactory region the lining mem-
brane of the nose in the fresh state is of a yellowish colour,
and is softer and more delicate than in the respiratory part.

The great vascularity of the mucous membrane of the
nose is doubtless for the purpose of moistening and raising
the temperature of the inspired air.

Nerves and Vessels on the Outer Wall of the Nasal
Fossa : —

Nerves of Smell, . Olfactory nerves.

'^ ri. External branch of nasal proper.

I 2. Nasal branch of anterior superior dental.

Nerves of CommonJ 3. Superior nasal branches from Meckel's gan-
"Sensation, '. . j glion and the Vidian nerve.

I 4. Two inferior nasal branches from the anterior

1^ palatine nerve.

The olfactory nerves are from twelve to twenty in number.

NERVES AND VESSELS OF THE NASAL LOSS A. 429

Tlicy arc fine filaments which s[)ritig from the under surface
and the extremity of the olfactory bulb, and passing through
the apertures in the cribriform plate of the ethmoid into
the nose, they separate into an outer and an inner group.
To each nerve an investment from the cerebral membranes
is given. The I'/i/ier or septal nerves have been already de-
scribed (p. 418). The outer nerves descend between the
mucous membrane and the periosteum on the outer wall of
the nose. At first lodged in shallow grooves or minute
bony canals, they soon divide into bunches of branches
which spread out over the up[)cr turbinated bone and the
back part of the sulcus olfiictorius. The dissection of these
nerves is exceedingly difficult even in the fresh subject, but
in a well-preserved part they can generally be partially
displayed.

The superior nasal branches which come from the spheno-
palatine ganglion and from the Vidian nerve are very minute
filaments, but the dissector should not be deterred on this
account from endeavouring to trace them to their distribu-
tion upon the outer wall. They enter the nose through the
spheno-palatine foramen, which is situated at the back part
of the superior meatus.

The best plan lo adopt for their display is to trace the naso-palatine
nerve, which has already been exposed on the nasal septum, outwards
across the roof of the nose. This will lead to the foramen, and by
carefully dissecting the mucous membrane in its neighbourhood, the
superior nasal nerves may be detected entering the nasal fossa.

They are distributed to the mucous membrane over the
ui)per and middle turbinated bones ; and some filaments
are prolonged to the septum.

The inferior nasal tierves are two in number, and they
both arise from the great or anterior palatine nerve.

Carefully raise the mucous membrane from the posterior part of the
outer wall of the nasal fossa. Make a vertical incision, 'through the
membrane over the internal pterygoid processs, and turn it cautiously
over from behind forwanls.

The upper of the. two inferior nasal nerves will be found

430 HEAD AND NECK.

emerging through a small aperture in the vertical plate of
the palate bone, at a point between the posterior extremities
of the middle and inferior turbinated bones. It divides into
an ascending and descending branch. The former runs
forwards on the middle spongy bone ; the latter extends
forwards upon the inferior spongy bone. The lower of the
two inferior nasal nerves appears through a foramen in the
vertical plate of the palate bone immediately behind the
posterior end of the inferior turbinated bone, upon the outer
surface of which it proceeds in a forward direction.

The nasal nerve proper should be exposed as it descends
in the groove upon the deep surface of the' nasal bone
(p. 360). It gives, as we have noted, a branch inwards to
the septum 3 an external twig may also be traced to the
mucous membrane over the fore-part of the outer wall and
to the fore-parts of the middle and inferior turbinated bones.

The main artery of supply to the nasal mucous membrane
is the spheno-palatlne, a branch of the internal maxillary. It
gains entrance to the nasal fossa through the spheno-palatine
foramen in company with the superior nasal and naso-
palatine nerves. One branch of this vessel — the naso-
palatine— accompanies the latter nerve, whilst others are
distributed upon the outer wall of the cavity. Several twigs
are also given by the descending palatine branch of the
internal maxillary and the hvo ethmoidal arteries, but these
are small and will only be seen in cases where the injection
of the subject has been unusually successful.

SPHENO-PALATINE GANGLION OR THE
GANGLION OF MECKEL.

Dissection. — Meckel's ganglion is placed on the outer side of the
spheno-palatine foramen, and can best be exposed at this stage by dis-
secting from the inside. The mucous membrane has already been
removed from the posterior part of the outer wall of the nasal fossa, and
the inferior nasal branches of the great palatine nerve have been found
piercing the vertical plate of the palate bone. The dissector cannot fail
to notice the course taken by the trunk from which these filaments arise.

THE SrilENO-PAI.ATINE GANGLION. 431

The lamina of bone wliich forms ihc inner wall of the jjostcrior palatine
canal is S(j thin that the nerve can he distinctly seen through it. By
carefully opening up this canal with a chisel, and following the great
palatine nerve upwards, the dissector will be led to the ganglion in the
spheno-maxillary fossa. The naso-palatine nerve should at the same
time be traced to its origin. The ganglion is so hemmed in by the bony
walls of the fossa that it is very difficult to display it thoroughly, but by
removing the orbital process of the palate bone, and a portion of the
body of the sphenoid with the bone-forceps, it may be more or less
satisfactorily exposed. In the same restricted space will be found the
terminal portion of the internal maxillar)' artery, from which numerous
branches are given off.

TheSpheno-palatineGanglion(gangliQnsphenopalatinum)
is a small triangular llatlcncd body, which is lodged in the
<;phpnn-maxillary fossa. It is embedded in soft fat, and"sur-
roundod by the terminal branches of the internal maxillary
artery. The two stout spheno-palatine branches which de-
scend from the superior maxillary nerve join it Irom above,
Ij^t only a certainjjroportion of their fibres are involved in
the ganglion ; the remainder are continued directly into the
nasal and palatine nerves which proceed from the ganglion.
The spheno-palatine nerves may be regarded as constitut-
ing the sensory roots of the ganglion.

From the spheno-palatine ganglion branches are given
off which radiate in four directions — viz. inwards to the
nose, downwards to the palate, backwards to establish con-
ncctions with the facial nerve and carotid plexus^ as well
as to supply the mucous membrane of tlie pharynx, and
upwards to the orbit.

, , , r Superior nasal.

Internal branches, ■ ^^-^^so-ixilatine.

( Great or anterior palatine.
Descending branches, •( Posterior palatine.

( External palatine.
,, . , , fX'idian.

Posterior branches, . ^ Pharj-ngeal.

Ascending branches, . Orbital.

From the internal maxillary artery twigs arc given off
which accompany these nerves.

The superior nasal and the naso-palatine nerves have been

432 HEAD AND NECK.

already described (pp. 429 and 418). They arise from the
inner aspect of the ganglion, but in some cases the naso-
palatine may be seen to take origin from the commence-
ment of the common palatine trunk, or even from one of
the spheno-palatine branches of the superior maxillary nerve
(Henle).

T^xQ^ palatine nerves (nervi palatini) are three in number,
and are distinguished as anterior., posterior., and external. As
a rule these spring by a common trunk from the lower
aspect of the ganglion. This descends in the posterior
palatine canal, which has already been opened up, but to
expose the nerves a dense fibrous investment must be re-
moved. The nerve-trunk will then be observed to break
up into its three constituents.

Dissection. — Trace, in the first instance, the two smaller nerves —
viz. the posterior and the external palatine branches. These leave the
main canal, and enter smaller tunnels, which conduct them through
the tuberosity of the palate bone. Before opening these up it is well to
secure the nerves as they emerge from the lower openings of the canals.
This can very readily be done by dissecting behind the hamular pro-
cess, and gently separating the soft parts from the under aspect of the
tuberosity of the palate bone. As the dissection is being made from the
inside, the small, or posterior palatine nerve, will be first encountered,
and it will be seen to pass backwards into the soft palate, under cover of
the tendinous expansion of the tensor palati. ^ This must be divided, in
order that the'posterior palatine nerve may be followed to its distribution.
The external palatine 7ierve will be found issuing from its canal a short
distance to the outer side of the preceding nerve. It is distributed to
the soft palate in the neighbourhood of the tonsil. It is smaller than
the posterior palatine nerve, and is sometimes absent. The great or
anterior palatine nerve should now be followed onwards to the hard
palate. To do this the lower part of the posterior palatine canal must
be opened up by removing a small portion of the posterior and outer
part of the horizontal plate of the palate bone.

The anterior palatine nerve (nervus palatinus anterior), as
it emerges from the posterior palatine foramen, turns
forwards, and divides into branches, which lie in grooves

1 The present is a good opportunity to observe the corrugated or
wrinkled appearance of the tendon of the tensor palati, as it passes under
the hamular process.

PALATINE NERVES. 433

on the under aspect of the hard palate. It siipph'es the
gum, the mucous membrane, and glands of the vault of
the mouth, and in the neighbourhood of the anterior
palatine foramen it effects a communication with the
naso-palatine nerve. During its passage through the
posterior palatine canal this nerve has already been ob-
served to su[)i)ly hvo inferior nasal branches (p. 429).

In tracing the anterior palatine nerve forwards in the
palate, the dissector should note the numerous glands
which are placed under the mucous membrane of the
vault of the mouth, and the manner in which these indent
the bone.^

Dissection. — Very considerable difficulty will be experienced in ex-
ix)sing the piiaryngeal and Vidian nerves. They proceed backwards
from the posterior part of the ganglion in canals which are verj*
inaccessible.

To open up the pterygo-palatine canal the sphenoidal process of the
palate bone must be cautiously removed by the bone-forceps, and then
the dissector should proceed to open up the Vidian canal, which traverses
the root of the pterygoid process. As the bone is very hard and brittle
at this point, the dissection must be effected very carefully.

The pharyngeal nerve occupies the pterygo-palatine canal,
and is distributed to the mucous membrane of the upper
part of the pharynx.

The Vidian nerve (nervus canalis pterygoidei) has
previously been seen to be formed by a junction between
the great superficial petrosal branch of the facial and the
great deep petrosal branch of the ca^rotid plexus (p. 351).
It traverses the Vidian canal, and jojng the posterior
aspect of the ganglion, of which it may be considered to
represent both the motor and sympathetic root. In the
canal it is invested by a strong fibrous envelope, and
when this is removed it may sometimes be noticed to
break up into a fine plexus which surrounds the accom-

^ An equally good method of tracing the posterior palatine nerve
forwards is to remove the palatal processes of the palate and superior
maxillary bones with the bone- pliers, and then to display the nerve and
artery on the upper surface of the mucous membrane and glands.

VOL. II. — 28

434 HEAD AND NECK.

panying artery. It has already been observed to give some
fine filaments to the mucous membrane of the nose.

The orbital branches (rami orbitales) of the ganglion are
exceedingly minute, and ascend through the spheno-
maxillary fissure to supply the periosteum of the orbit.

Termination of Internal Maxillary Artery. — The
internal maxillary artery breaks up into its terminal
branches in the spheno-maxillary fossa. These have
already been traced. They are —

1. The posterior dental (arteria alveolaris superior

posterior) (p. 304).

2. The infra-orbital (p. 413).

3. The descending palatine.

4. The Vidian.

5. The pterygo-palatine.

6. The spheno-palatine.

The descending palatine (arteria palatina descendens)
accompanies the anterior palatine nerve. During its passage
through the posterior palatine canal, it gives off twigs
which accompany the posterior and external palatine
nerves and the two inferior nasal branches of the great
palatine nerve. On the hard palate it dispenses branches
to the gum, mucous membrane, and glands, and sends a
small branch upwards through the incisor foramen to
anastomose with the naso-palatine artery.

The Vidian artery (arteria canalis pterygoidei) runs
backwards in the Vidian canal to supply the mucous
membrane of the upper part of the pharynx and of the
Eustachian tube.

The pterygo-palatine artery traverses the canal of the
same name, and has a corresponding distribution.

The sphenopalatine (arteria sphenopalatina) enters the
nasal fossa through the spheno-palatine foramen, and has
already been followed to its distribution (p. 430),

Dissection. — The facial and auditory nerves, together with the pars
intermedia, have already been traced into the internal auditory meatus
(p. 125). The dissector should now open up this meatus and follow the
facial nerve in its course through the petrous portion of the temporal

INTERNAL MAXILLA K Y AK TEK V. 435

bone. The canal which it occupies is termed the aqueduct of Fallopius.
This begins at the bottcjm of the internal auditory meatus, and opens on
the exterior of the skull at the stylo-mastoid foramen. Between these
points it pursues a complicated course, and this, combined with the
density of the bone, renders the dissection very difficult. I'erhaps the
easiest method of opening up the aqueduct is, in the first instance, to
decalcify the bone in a weak solution of acid, but, at the same time, it
should be clearly understood that, with a little care, there is nothing to
hinder the dissector carr)-ing out the dissection on the hard bone by
means of the saw and the chisel.

Sejxirate the temporal bone from the other cranial bones which still
adhere to it, and, having fixed it in its natural position (in a vice if
possible), remove the squamous portion by a horizontal saw-cut at the
level of the superior border of the petrous bone. A second horizontal
saw-cut should then be made through the pars petrosa immediately
above the roof of the internal auditory meatus. If this is successfully
carried out, the vestibule, the upper part of the tympanum, and the
mastoidal cells are opened. Upon the upper part of the inner wall of
the tympanum above the stapes and the foramen ovale, a prominent
ridge will be noticed running from before backwards. This is the
aqueduct of Fallopius. Extend the opening into the tympanum by
removing the remainder of its roof, and then, with the chisel, open up
the aqueduct as seen in this part of its course. The facial nerve is now
exposed in what may be said to be its intermediate or tympanic part.
To display its first stage within the bone, open up the internal auditory
meatus by removing what remains of its roof, and follow the facial
nerve forwards and outwards by means of the chisel. This will lead to
the geniculate ganglion — the swelling which marks the point at which
the nerve bends backwards to enter the tympanic part of the aqueduct.
Be careful at this point to secure the branches which proceed from the
gangliform enlargement. The terminal part of the aqueduct of Fallopius
is vertical, and its course can be indicated by pushing a fine pin upwards
through the stylo-mastoid foramen. To open it, the mastoid process
must be removed by a coronal (vertical-transverse) saw-cut on a plane
immediately behind the stylo-mastoid foramen. When this has
penetrated the bone as far as that foramen, a second saw-cut should be
made in the sagittal (antero-posterior and vertical) direction, to meet
the extremity of the first. The piece of bone thus marked out may
now be detached, and a little work with the chisel will display the
facial nerve in this part of the canal. Three branches are given off
from it here — viz. the nerve to the stapedius, the chorda tympani, and
the communicating branch or branches to the auricular nerve from the
vagus. The last of these is probably destroyed by the dissection, but
the other two can be brought into view by gently raising the nerve from
the anterior wall of the canal. By using the chisel in front, and to the
inner side of the geniculate ganglion, the cochlea will be exjx)sed.

436

HEAD AND NECK.

Intrapetrous Portion of the Facial Nerve. — As the facial
nerve traverses the petrous bone, it may be divided into
four stages, which differ from each other in the relations

PORTIO INTERMEDIA
.'',GENICULATE GANGLION

LARGE .SUPERFICIAL PETROSAL

SMALL SUPERFICIAL PETROSAL
SMALL DEEP PETROSAL
LARGE DEEP PETROSAL
VIDIAN

^5° SUP. MAXILLARY
SPHENO- PALATINE

DIGASTRIC---
STYLO-HYOID

P0STERI0B^4 ,
AURICULAR /fV

FROM AURICULO-TEMPORAL
TEMPORO- FACIAL

CERVIOO- FACIAL

Fig. 285. — Diagram of the facial nerve.
Qttain's Anatomy. )

(Professor Thane,

Ch. Ty. Chorda tympani ; its middle part
is removed.
Ty. Tympanic branch of the glosso-
pharyngeal.

Sy. Sympathetic on the internal
carotid artery.
Car. Ty. Carotico-tympanic nerve.

they present and in the direction which they take. They

are : —

1. A part within the internal auditory meatus.

2. A very short part which extends from the bottom of the internal

auditory foramen to the geniculate ganglion.

3. A part which occupies that portion of the aqueduct of Fallopius

which runs along the inner wall of the tympanum.

4. A part which extends vertically downwards to the stylo-mastoid

foramen.

First stage. — In the internal auditory meatus, the facial
nerve runs almost directly outwards in company with the

mrRAPETKOUS PORTION OF FACIAL NERVF. 437

auditory nerve and the pars intermedia. In this stage of
its course it lies in relation to the uj)per and fore part of
the auditory nerve, and is joined by the pars intermedia.
At the bottom of the auditory meatus it enters the aqueduct
of Fallopius.

Second stage. — The second part of the facial nerve is very
short. It runs outwards with a slight inclination forwards
between the vestibule and cochlea, and very soon ends in
the swelling termed the geniculate ganglion.

Third stage. — At the geniculate ganglion, the facial nerve
bends suddenly and then proceeds backwards and slightly
downwards in that portion of the aqueduct which runs
along the upper part of the inner wall of the tympanum,
immediately above the foramen ovale.

The first three portions of the facial nerve are nearly
horizontal, and pursue a somewhat V-shaped course. The
apex of the V is directed forwards, and corresponds to the
geniculate ganglion.

The. foufth stage is vertical, and arches downwards behind
the pyramid to gain the stylo-mastoid foramen.

The branches which spring from the facial nerve during
its passage through the temporal bone are : —

1. The great superficial petrosal nerve, "i

2. Communicating twig to tympanic branch of the 'from geniculate

glosso-pharyngeal, ( ganglion.

3. External superficial petrosal nerve, ./

4. Nerve to stapedius.

5. Chorda tympani.

6. Communicating twigs to the auricular branch of vagus.

The great superficial petrosal nerve has already been
examined (p. 351). Its origin from the geniculate ganglion
of the facial can now be established by breaking through
the roof of the hiatus Fallopii with the chisel.

The communicating branch to the tympanic nerve arises
from the geniculate ganglion, and its union with the
tympanic forms the small superficial petrosal nerve (p. 334,

l^'ig- 259)-

The external superficial petrosal nerve is not always

438 HEAD AND NECK.

present. It joins the sympathetic plexus which accom-
panies the middle meningeal artery (p. 252).

The tierve to the stapedius muscle arises from the facial as
it arches downwards behind the pyramid. It enters the
base of the pyramid and thus reaches the stapedius muscle.

The communicatitig tivigs to the auricular branch of the
vagus arise a short distance above the stylo-mastoid foramen

(P- ZZ^)-

The Chorda Tympani, which is the pars intermedia set
free from the facial nerve, is the largest branch which is
given off by the facial during its passage through the
aqueduct of Fallopius. It takes origin a short distance
above the stylo-mastoid foramen, and arching upwards and
forwards in a narrow canal in the petrous portion of the
temporal bone (iter chordae posterius) it appears in the
tympanum below the base of the pyramid, and close to the
posterior margin of membrana tympani. The bony tunnel
which it occupies can easily be opened up in a decalcified
bone, but is somewhat difficult to expose in the hard bone.
The chorda tympani now runs forwards upon the upper
part of the membrana tympani under cover of the mucous
layer. It crosses the handle of the malleus near its root.
To display it in this part of its course, the incus bone
should be removed. Finally, reaching the anterior end of
the tympanic cavity it crosses the processus gracilis of the
malleus, and near the inner end of the Glaserian fissure, it
enters a canal (canal of Huguier) which conducts it to the
exterior of the skull. With a little care the canal of
Huguier can be opened up by the chisel and bone-pliers.
From this point to its junction with the lingual nerve the
chorda tympani has already been traced (p. 313).

The Auditory Nerve. — In the internal auditory meatus
the auditory nerve lies at a lower level than the facial, and
at the bottom of the -passage it splits into two parts. Of
these, one is directed forwards to the cochlea, and the other
proceeds outwards to the vestibule.

THE LARYNX. 439

THE LARYNX.

The lateral portions of the lower jaw which are still
attached by mucous membrane to the sides of the tongue
should be removed, and the dissection of the lar)-nx com-
menced.

General Construction and Position. — The lar}-nx con-
stitutes the upper expanded portion of the air-passage,
specially modified for the production of the voice. Its walls
are composed of cartilages, muscles, ligaments, and an in-
ternal lining of mucous membrane. Before proceeding
with the dissection the student should study the form and
connections of the nine laryngeal cartilages in a permanent
specimen {v. p. 455).

The larynx is placed in the upper and fore part of the
neck, where it forms a marked projection. It lies below
the hyoid bone and tongue, whilst inferiorly it is directly
continuous with the trachea. In^fronf it is covered by
the integument and deep cerxical fascia, and on either side
of the mesial plane by two thin strata of muscles, \\z. the
sterno-hyoid, the omo-hyoid, the sterno- thyroid and the
thyro-hyoid. As a general rule a narrow process of the
thyroid body, termed the central lobe, is also continued up-
wards on its anterior surface. On each side the lateral lobe
of^ the thyroid body is prolonged upwards upon it, and it is
related to the great vessels of the neck. Posteriorly it is in
relation to the pharynx ; by this it is separated from the
prevertebral muscles. If we consider the tip of the epi-
glottis to represent its upper limit, the larynx in the adult
may be regarded as being placed in front of the bodies of
the third, fourth, fifth, and sixth cervical vertebrae ; but its
position alters somewhat with the movements of the head
and also during deglutition.

Interior of the Larynx. — The cavity of the larynx is
smaller than might be expected from an inspection of its
exterior. On looking into its interior from above it will be
seen to be subdivided into three portions by two elevated

440

HEAD AND NECK.

folds of mucous membrane which extend from before
backwards, and project inwards from each side of the

cavity. The upper pair
of folds are termed the
false vocal cords ; the lower
pair receive the name of
the tT^e vocal cords, because
they are the chief agents
in the production of the
voice. The entire larynx
is in a great measure con-
structed with the view of
bringing about changes in
the relative position and in
the degree of tension of
the true vocal cords.

The Upper Subdivision
of the laryngeal cavity (Fig.
286, A) extends from the
superior aperture of the
larynx down to the upper
or false vocal cords. It is
called the vestibule (vesti-
bulum laryngis). It is
bounded in front by the

Fig. 286. — Coronal section through epiglottis and the upper

the larynx to show the three sub- part of the angular dcprcs-

divisions of its cavity, viz. A, B, ■ , ° , -, r

andc. (FromLuschka.) sion between the al« of

the thyroid cartilage, be-
hind by the arytenoid
cartilages and the mucous
membrane which stretches
across the mesial plane
between them, and on each
side by the aryteno-epiglot-
tidean folds. The width
of this portion of the laryngeal cavity diminishes from
above downwards, and its depth diminishes in a marked

1. Hyoid bone.

2. Thyroid cartilage.

3. Cricoid cartilage.

4. First tracheal ring.

5. Thyro-hyoid membrane.

6. Epiglottis.

7. Cushion or tubercle of epiglottis.

8. False vocal cord.
g. True vocal cord.

THE LARYNX. 441

degree from before backwards. Above, it communicates
with the pharynx by the superior aperture of the larynx,
whilst below it is continuous with the middle subdivision
of the cavity through the interval between the false vocal
cords.

The superior aperture of the larynx has already been
examined in the dissection of the pharynx (p. 403). The
parts which bound it should again be carefully studied.

The t7>/X''/6'///.yj3roiects upwards behind the root of the
tongue. Its lingual or anterior surface is only free in the

FR/ENUM
EPIGLOTTIDI

EPIGLOTTIS

C ORN. LAR.

Fig. 287. — The larynx as seen in the living person by
means of the laryngoscope.

upper part of its extent, and 4s a_tta_ched^to the back part
of the tongue.by_a prominent mesial fold of mucous mem-
brane, termed the tniddle glosso-epiglottidean fold ox fnDium
oQlie epiglottis. Two lateral folds are also present which
connect its margins with the tongue ; these are called the
lateral glosso-epiglotiidean folds. Between the two layers of
mucous membrane which constitute each of these three
fra^nula, there is a small amount of elastic tissue. The
depression on each side between the tongue and the
epiglottis which is bounded by the median and lateral
glosso-epiglottidean folds is termed the vallecula (Fig. 287).
The posterior free surface of the epiglottisTforms, as we have

442 HEAD AND NECK.

noted, the greater part of the anterior boundary of the
i vestibule of the larynx. Owing to the tip of the epiglottis
jbeing curled forwards, the upper portion of this surface
is convex ; this is followed by a slight concavity, and below
this it swells out into a marked convexity, called the cushion
br tubercle of the epiglottis. In laryngoscopic examinations
the tubercle appears as a conspicuous object.

The aryteno-epiglottidean folds of mucous membrane en-
close between their two layers some connective tissue, the
aryteno-epiglottidean muscles, and posteriorly the cuneiform
cartilages, and the cornicula laryngis which surmount the
arytenoid cartilages. When the larynx is examined by the
laryngoscope these cartilages are visible on either side in
the form of two small rounded elevations or tubercles.

Between the outer aspect of the aryteno-epiglottidean
fold and posterior part of the ala of the thyroid cartilage,
there is a deep depression of mucous membrane on each
side, termed the sinus pyriforniis.

The Middle Subdivision of the laryngeal cavity (Fig. 286,
B) is the smallest of the three. Above it is bounded by
the false vocal cords, below by the true vocal cords, whilst
it communicates by the intervals between these folds with
the vestibule on the one hand, and the inferior compart-
ment of the larynx on the other.

The false vocal cords are two prominent mucous folds
which extend from before backwards on the side walls of
the laryngeal cavity. They are soft and somewhat flaccid,
and present a free border which is slightly arched — the
concavity looking downwards. The interval between the
false vocal cords is sometimes termed the false glottis^ and
is considerably wider than that between the true vocal cords.
It follows from this, that when the cavity of the larynx is
examined from above, the four cords are distinctively visible,
but when examined from below the true cords alone can
be seen.

The true vocal cords are placed immediately below the
false cords, and are sharp and prominent. The mucous
membrane which is stretched over them is so thin that the

THE LARYNX.

443

ycllowisli colour of the clastic ligaments which support ihcm
can readily be discerned. In section each true vocal cord
is somewhat prismatic in form, and the free border looks
upwards and inwards.

The true vocal cords are the agents by means of which
the voice is produced. The false vocal cords are of little
importance in this respect; indeed, they can in great part
be destroyed, and no
appreciable difference in
the voice result.

The rima glottidis is
the elongated fissure by
means of which the
middle compartment of
the larynx communicates
with the lower subdivi-
sion. It is placed some-
what below the middle
of the laryngeal cavity,
of which it constitutes
the narrowest part. In
front it corresponds to
the interval between the
true vocal cords ; behind
it corresponds to the in-
terval between the bases
and vocal processes of
the arytenoid cartilages
(Fig. 288). It is composed, therefore, of two very distinct
[)arts — (i) a narrow anterior portion, between the true
vocal cords, involving less than two-thirds of its length,
and called the glottis vocalis ; (2) a broader, shorter por-
tion between the arytenoid cartilages, and termed the glottis
respiratoria. The form of the rima glottidis undergoes
frecjuent alterations during life, but during ordinary
quiet respiration it is lanceolate in outline. The glottis
vocalis presents the form of an elongated triangle with
the base directed backwards, whilst the glottis respira-

FiG. 288.— Transverse section through
the larynx at the level of the true
vocal cords. ( From Lusclika. )

1. Ala; of thyroid cartilage.

2. Median lamina of thyroid cartilage.

3. Upper border of posterior lamina of

cricoid cartilage.

4. Arytenoid cartilage.

5. Processus muscularis.

6. Processus vocalis.

7. True vocal cord.

8. Thyro-arj'tenoideus.

444 HEAD AND NECK.

toria is somewhat quadrangular. The length of the entire
fissure differs considerably in the two sexes, as will be seen
from the following figures which are given by Krause : —

Length of rima glottidis in male, . . 19 to 25 m.m.

,, ,, in female, . . 14 to 17 m.m.

The side wall of the larynx in the interval between the
true and the false vocal cords shows a depression or recess
which is termed the laryngeal sinus. The dissector should
endeavour to gauge the extent of this, by means of a probe
bent at the extremity. The recess passes upwards, so as
to undermine somewhat the false vocal cord, and its mouth
or orifice is narrower than its cavity. Under cover of the
fore-part of the false vocal cord, an elongated aperture will
be detected. This leads into the laryngeal pouch or sac —
a small mucous diverticulum, which ascends between the
false vocal cord and the ala of the thyroid cartilage. This
sac is of variable extent, but as a rule it ends blindly at
the level of the upper border of the thyroid cartilage.

Distend the sinus, and if possible the sac, with cotton wadding.
This will greatly facilitate the subsequent dissection.

The Lower Subdivision of the Laryngeal Cavity (Fig.
286, C) leads directly downwards into the trachea. Above,
it is narrow and laterally compressed, but it gradually widens
out until in its lowest part it is circular. It is bounded by
the lower part of the thyroid cartilage, the crico-thyroid
membrane, and the cricoid cartilage. It is through the
anterior wall of this compartment that the opening is made
in the operation of laryngotomy.

The Mucous Membrane of the larynx is continuous above
with that lining the pharynx, and below with the mucous
lining of the trachea. Over the epiglottis it is very tightly
bound down, and it is plentifully supplied with glands.
The mucous membrane which covers the true vocal cords
is so thin that the yellowish colour of the subjacent liga-
ments can be seen through it ; here also, as well as in the
immediate vicinity, the glands are absent.

THE LARYNX.

445

Dissection. — Place the lar)'nx upon a block so that its anterior surface
looks upwards, and fix it in this position with pins. The Ijranches
which the external laryngeal nerve gives to the crico-thyroid muscle
should in the first place be followed out, and carefully preserving the
superior and inferior laryngeal vessels and the internal and recurrent
lar)-ngeal nerves, the dissector should in the next place proceed to
remove the thyroid body, and the omo-hyoid, sterno-hyoid, sterno-
thyroid, and thyro-hyoid muscles. The fibres of origin of the inferior
constrictor muscle should likewise be cleared away from the thyroid

thyro-hyoid membrane

thyroid cartilage

middle p.irt of crico-
thyroid membrane

cricoid cartilage

Fig.

(From Gegenbaur. )

and cricoid cartilages. The broad thyro-hyoid membrane, the central
l>ortion of the crico-thyroid membrane, and the crico-thyroid muscles
are now exposed, and their attachments may be defined.

The Thyro-hyoid Membrane is a broad membranous
sheet, which occupies tlie interval between the hyoid bone
and the thyroid cartilage. It is not equally strong through-
out, but shows a central thick portion and a cord-like right
and left margin, whilst in the intervals between these it is
thin and weak. The central thickened part {/iga/ncrifum
thyro-hyoideum medium) is largely composed of elastic fibres.

446 HEAD AND NECK.

Above, it is attached to the posterior aspect of the upper
margin of the body of the hyoid bone, whilst below, it is
fixed to the sides of the deep median notch, which interrupts
the superior border of the thyroid cartilage. The upper
part of its anterior surface is therefore placed behind the
posterior hollowed out surface of the body of the hyoid
bone ; a synovial bursa is interposed between them, and in
certain movements of the head and larynx the upper border
of the thyroid cartilage is allowed to slip upwards behind the
hyoid bone. On each side of the strong central part the
thyro-hyoid membrane is thin and loose. It is attached
below to the upper margin of the ala of the thyroid cartilage,
and above to the posterior aspect of the great cornu of the
hyoid bone. It is pierced by the internal laryngeal nerve
and superior laryngeal vessels. The posterior border of the
membrane on each side is thickened, rounded, and cord-like
{ligainenhim thyro-hyoideimi laterale), and is chiefly com-
posed of elastic fibres. It extends from the tip of the great
cornu of the hyoid bone to the extremity of superior cornu
of the thyroid cartilage. In this ligament there is usually
developed a small oval cartilaginous or bony nodule, which
is termed the cartilago triticea.

The Crico-thyroid Muscle is placed on the side of the
cricoid cartilage, and bridges over the lateral portion of the
crico-thyroid interval. Taking origin from the lower border
and outer surface of the anterior arch of the cricoid cartilage,
its fibres spread out in an upward and backward direction,
and are inserted into the inner aspect of the lower margin
of the thyroid cartilage, and also into the anterior border
of its inferior cornu. As a general rule, it is divided into
two parts. The anterior or oblique part is composed of those
fibres which are attached to the ala of the thyroid cartilage ;
the posterior or horizontal part is formed of those fibres
which are inserted into the inferior cornu of the thyroid
cartilage. It is closely associated with the inferior con-
strictor muscle. The crico-thyroid muscle is supplied by
the external laryngeal branch of the superior laryngeal
nerve.

THE LARYNX. 447

The Middle Portion of the Crico-thyroid Membrane can

be sludicil in the inlcrval between the two crico-tliyroid
muscles. It is a tense elastic and strong membrane, which
is attached below- to the median part of the upper border of
the anterior arch of the cricoid cartilage, and above to the
lower margin of the middle portion of the thyroid cartilage.
It is pierced by minute apertures, and is crossed superficially
by the crico-thyroid branch of the superior thyroid artery.
On each side, under cover of the crico-thyroid muscle, the
lateral part of the crico-thyroid membrane presents very
different connections, It is not attached to the lower
border of the thyroid cartilage, but stretches upwards into
the interior of the larynx, and takes part in the formation
of the true vocal cord. At a later stage of the dissection
it will be fully exposed.

Dissection. — The position of the larj'nx must now be reversed.
Fix it upon the block in such a manner that its posterior aspect is
directed upwards. The oesophagus should then be slit open by a
mesial incision through its posterior wall. Next remove with great
care the mucous membrane which covers the posterior aspect of the
cricoid and arytenoid cartilages. In doing this, bear in mind that the
inferior laryngeal artery, and the recurrent laryngeal nerve, pass upwards
between the thyroid and cricoid cartilages, and must be preserved.

Upon the posterior aspect of the broad lamina of the cricoid cartilage
the dissector will now note the two posterior crico-arytenoid muscles,
and the attachment of the anterior band of longitudinal muscular fibres,
which belongs to the resophageal wall. This takes origin from the
prominent mesial ridge on the back aspect of the cricoid cartilage. On
the posterior surface of the arytenoid cartilages, and bridging across
the interval between them, the dissector will observe the arytenoid
muscle. Especial care must be taken in cleaning this muscle in order
that the connections of the superficial decussating fibres may be fully
ascertained.

The outer layer of the right aryteno-epiglottidean fold of mucous
membrane should now be cautiously removed. This will expose the
aryteno-e])iglottidean muscle, the cuneiform cartilage, and the cartilage
of Santorini of that side. This is perhaps the most difficult part of the
dissection, because the dissector has to establish the continuity of the
sparse fibres which compose the pale aryteno-epiglottidean muscle with
the decussating fibres of the arytenoid muscle, and he has also to make
out a delicate ligament which extends downwards from the tip of the
cartilage of Santorini to the cricoid cartilage — viz. the ligamentum
jugale.

448

HEAD AND NECK.

The Posterior Crico-arjrtenoid Muscle is somewhat fan-
shaped (Fig. 290). It springs by a broad origin from the
depression which marks the posterior surface of the cricoid
cartilage on each side of the mesial ridge, and its fibres
converge to be inserted into the posterior surface and outer
angle of the processus muscularis of the arytenoid cartilage.^
In pursuing this upward and outward course, the fibres run

superior laryngeal
nerve.

epiglottis.

cuneiform cartilage.

cartilage of San-
torini.

thyro- epiglottidean

muscle,
aryteno-epiglotti-

dean muscle,
arytenoid muscle,
thyro-arytenoid

muscle,
crico-arytenoideus

lateralis muscle,
external laryngeal

nerve,
crico-arytenoideus

posticus muscle,
crico-thyroid

muscle.

recurrent laryngeal
nerve.

Fig. 290. — Dissection of the larynx viewed from behind
and the right.

with different degrees of obliquity. The uppermost fibres
are short and nearly horizontal ; the intermediate fibres are
the longest, and are very oblique ; whilst the lowest fibres
are almost vertical in their direction.

The Arytenoid Muscle consists of two portions, — a

The projecting outer angle of the base of the arytenoid cartilage.

THE LARYNX. 449

superficial part, termed the arytenoidcus obliquus, and a
deeper layer, called the arytenoidcus transversus.

The arytenoideiis obliquus is composed of two bundles of
muscular fibres, each of which springs from the posterior
aspect of the outer angle of the base of the corresponding
arytenoid cartilage (Fig. 290). From these points the two
fleshy slips proceed upwards and inwards, and cross each
other in the mesial plane like the limbs of the letter X.
Reaching the summit of the arytenoid cartilage on each
side, some of the fibres are inserted into it, but the greater
proportion are prolonged round the base of the cartilage of
Santorini into the aryteno-epiglottidean fold. Here they
receive the name of the aryteno-epiglottidean ?nusc/e, and as
they approach the epiglottis they are joined by the fibres
of the thyro-epiglottidean muscle. The oblique arytenoid
muscles may therefore be considered as constituting a weak
sphincter muscle for the superior aperture of the larynx.
Each bundle starting from the base of one of the arytenoid
cartilages is prolonged into the aryteno-epiglottidean fold
of the opposite side, and along this to the margin of the
epiglottis.

The arytenoideus transversus is an unpaired muscle. It is
composed of transverse fibres which bridge across the interval
between the two arytenoid cartilages, and are attached to
the posterior concave surfaces of both of these cartilages.

Dissection. — The further dissection of the laryngeal muscles should
be confined to the right side of the lar)-nx. The left side should be
reserved for the study of the nerves and vessels. Place the lar}'nx on
its left side, and, having fixed it in this position, remove the right
crico-thyroid muscle. The right lateral thyro-hyoid ligament should
next be divided, and the right inferior cornu of the thyroid cartilage
disarticulated from its facet on the side of the cricoid cartilage. An
incision should now be made through the right ala of the thyroid
cartilage a short distance to the outer side of the mesial plane, and the
detached piece carefully removed. Three muscles are now exposed,
and must be carefully cleaned and defined. They are named from
below upwards : —

1. The lateral crico-arytenoid.

2. The thyro-ar)'tenoid.

3. The thyro-epiglottidean.
VOL. II. — 29

4SO HEAD AND NECK.

The Lateral Crico-arytenoid Muscle is triangular in
form, and smaller than the crico-arytenoideus posticus. It
springs from the upper border of the lateral part of the
cricoid cartilage as far back as the facet which supports
the base of the arytenoid cartilage ; a few of its fibres like-
wise take origin from the crico-thyroid membrane. From
this attachment its fibres run backwards and upwards, and
converge to be inserted into the anterior surface and lower
border of the processus muscularis or outer projecting angle
of the base of the arytenoid cartilage. The superficial or
outer surface of this muscle is covered by the ala of the
thyroid cartilage and the upper part of the crico-thyroid
muscle ; its deep surface is applied to the lateral part of
the crico-thyroid membrane.

Thyro- arytenoid Muscle. — This is a muscular sheet
which is placed above the crico-arytenoideus lateralis. The
contiguous margins of these muscles are sometimes found
so intimately blended that it is impossible to effect a natural
separation.

The thyro -arytenoid muscle is usually described as
consisting of a superficial and a deep portion, termed
respectively the thyro-arytenoideus externus and internus.
Whilst we adopt this subdivision for convenience in de-
scription, it is necessary to state that it is not a natural
one, seeing that the two parts are as a general rule in-
separably united, and can only be isolated from each other
by artificial means.

The thyro-arytenoideus externus is a broad muscular layer
which lies immediately subjacent to the ala of the thyroid
cartilage. Its lower border is in contact with the lateral
crico-arytenoid muscle, whilst its upper border is placed at
a higher level than the true vocal cord. Its upper part,
therefore, is in relation to the wall of the laryngeal sinus.
The thyro-arytenoideus externus arises in front from the
lower half of the inner surface of the ala of the thyroid
cartilage, close to the angle, and also from the crico-
thyroid membrane. Its fibres pass backwards and are
inserted into the outer border and muscular process of the

THE LARYNX. 451

arytenoid cartilage. A certain proportion of its uppermost
fibres curve upwards and backwards to reach the epiglottis.
These constitute the thyro-cpiglottidean iniisde.

The thyro-arytenoideus internus is a slender three-sided
muscular band which is closely applied to the outer side of
the true vocal cord, and receives its prismatic form from
this adaptation. It arises in front from the angular de-
pression between the two alee of the thyroid cartilage, and
is inserted behind into the outer aspect of the processus
vocalis, and also into the adjoining part of the antero-
external surface of the arytenoid cartilage.

The thyro-arytenoideus internus is thicker behind than
in front. This is due to the fact that whilst all the fibres
which compose it are attached to the arytenoid cartil-
age, only a certain proportion obtain attachment to the
thyroid cartilage. A large number of the deeper fibres are
directly attached at different points to the outer side of the
true vocal cord. These constitute the ary-vocalis muscle
(Ludwig).

A muscle termed the thyro-arytenoideus superior is frequently present.
It is a slender band which arises from the inner aspect of the ala of the
thyroid cartilage close to the notch, and passes backwards and down-
wards to find insertion into the lateral border of the arytenoid cartilage
immediately above the processus muscularis.

The Thyro-ary-epiglottidean Muscle is composed of fibres
derived from the arytcnoideus obliquus and the thyro-
arytenoideus externus. The two parts of the muscle meet
in the upper part of the aryteno-epiglottidean fold of mucous
membrane, and are inserted into the margin of the epiglottis.

Dissection. — The lateral crico-arytenoid muscle should now be care-
fully removed, and at the same time the dissector should endeavour
to disengage the fibres of the thyro-ar)'tenoideus externus from the
deeper thyro-ar)'tenoideus internus, in order that its relation to the true
vocal cord may be studied. Finally remove the entire thyro-ar)-tenoid
muscle. This will display the outer surface of the lateral part of the
crico-thyroid membrane, the true vocal cord or inferior thyro-arytenoid
ligament, and the wall of the lar)-ngeal sinus. By carefully dissecting
between the two layers of mucous membrane which clothe the false vocal
cord, the weak superior thyro-arytenoid ligament which gives it support

452 HEAD AND NECK.

may be discovered, as well as a number of racemose glands which lie in
relation to it.

Lateral part of the Crico-tliyroid Membrane. — The

central part of the crico-thyroid membrane, as we have noted,
closes in front the interval between the cricoid and thyroid
cartilages. On each side, however, the lateral part of the
same membrane is not attached to the lower border of the
thyroid cartilage, but slopes upwards and inwards, and

very materially diminishes
the transverse width of the
lower subdivision of the laryn-
geal cavity in its upper part.
The attachments which it
effects are very definite.
Below it is fixed to the upper
border of the cricoid cartil-
FiG. 291.— Diagram to show the age, immediately subjacent
connections of the crico - thyroid to the mucous membrane ;

membrane. (From Aeby.) ^^ jr^^^^f j^. ^g attached tO the

a. Cricoid cartilage. lowcr half of the inner surface

b. U. The two arytenoid cartilages. ^f ^j^g ^|g^ ^f j.j^g thyroid Cartil-

c. Thyroid cartilage. The right ala has ■'

been removed. agc, closc to the angle j and

d. Crico-thyroid membrane. The exten- behind tO the lOWCr bordCr of

sion upwards of its two lateral parts ^^^ proceSSUS VOCalis of the
to form the true vocal cords is seen. tr

arytenoid cartilage. Above
it is directly continuous with the inferior thyro-aryienoid
ligament or true vocal cord. The latter, indeed, may be
looked upon as constituting its upper, thickened, free
border. In contact with its outer surface are the lateral
crico-arytenoid and the thyro-arytenoid muscles, whilst
its inner surface is clothed by the fining mucous mem-
brane of the larynx.

The Inferior Thyro-arytenoid Ligament or true vocal
cord is formed in connection with the upper free border of
the lateral part of the crico-thyroid membrane. It is
attached in front, close to its fellow of the opposite side, to
the middle of the angular depression between the two alse
of the thyroid cartilage. From this it stretches backwards,

THE LARYNX. 453

and is fixed behind to the tip and upper border of the
processus vocaHs, which projects forwards from the base of
tlie arytenoid cartilage. The inferior thyro-arytenoid hga-
nient is composed of yellow elastic fibres, and measures
from its anterior attachment to the point of the processus
vocalis from 14 to 16 mm. in the male, and from 9 to
1 1 mm. in the female (Krause). Its inner border is sharp
and free, and is clothed by mucous membrane, which in
this position is thin and firmly bound down to the ligament.
Embedded in its anterior extremity there is a minute
nodule of condensed elastic tissue.

By removing the mucous membrane which lines the
bottom of the laryngeal sinus the dissector will obtain a
good view of the parts which bound the rima glottidis — viz.
in front, the angle of the thyroid cartilage ; behind, the
arytenoideus transversus muscle ; on each side, the inferior
thyro-arytenoid ligament, the processus vocalis, and the
inner surface of the arytenoid cartilage (p. 459). These
parts are clothed by the lining mucous membrane of the
larynx.

The Superior Thyro-arytenoid Ligament supports the
false vocal cord. It is weak and indefinite, but somewhat
longer than the preceding ligament. In front it is attached
to the angular depression between the two alaj of the thyroid
cartilage, above the true vocal cords, and inmiediately below
the attachment of the thyro-epiglottidean ligament, and
extends backwards to be fixed to a tubercle on the antero-
external surface of the arytenoid cartilage above the pro-
cessus vocalis. It is composed of connective tissue and
clastic fibres, which are continuous with the fibrous tissue
in the aryteno-epiglottidean fold.

Dissection. — Remove the remains of the aryteno-epiglollidean fold,
the vocal cords, and the lateral jiart of the crico-thyroid membrane on
the right side of the larynx, hut he careful not to injure tlie arytenoid
cartilage and the cartilage of Santorini. SIkjuUI the cuneiform cartihxge
he present in the aryteno-epiglollidean fold it should he detached and
preserved. By this ilisseclion a closer view of the side wall of the
laryngeal cavity can he ohtained. The umlissected vocal cords of the
left side should again be e.\amined, the laryngeal sinus and pouch

454 HEAD AND NECK.

explored, and their precise connections and extent determined. When
the student has satisfied himself upon these points he can proceed to
display the vessels and nerves of the larynx. The superior laryngeal
artery and the internal laryngeal nerve reach the larynx by piercing the
outer thin part of the thyro-hyoid membrane. By applying traction to
the nerve, and at the same time dividing the mucous membrane upon
the inner surface of the thyro-hyoid ligament, they can easily be dis-
covered. In following the branches into which they divide, the mucous
membrane must be gradually removed from the inner wall of the larynx.
The inferior laryngeal artery and nerve enter from below, and proceed
upwards, under cover of the ala of the thyroid cartilage. They can only
be satisfactorily displayed by the removal of this piece of cartilage, but
the dissector is not recommended to adopt this method unless another
larynx is available for the examination of the cartilages and joints. By
drawing the thyroid cartilage well outwards the more iiiiportant branches
can be studied.

The Internal Laryngeal Nerve. — In the dissection of the
neck this nerve has been observed to arise from the superior
laryngeal branch of the vagus. It is a sensory nerve, and
its branches are chiefly distributed to the mucous membrane
of the larynx. Piercing the lateral part of the thyro-hyoid
ligament it divides into three branches. The uppermost of
these sends filaments to the aryteno-epiglottidean fold, to
the mucous membrane which covers the epiglottis, and to
the glosso-epiglottidean folds. The twigs which go to the
epiglottis ramify on its posterior surface, but many of them
pierce the cartilage to reach the mucous membrane on its
anterior surface. The intermediate branch of the internal
laryngeal nerve breaks up into filaments, which are given to
the mucous membrane lining the side wall of the larynx.
The lowest branch descends and gives filaments to the
mucous membrane which covers the outer and back aspects
of the arytenoid and cricoid cartilages. A well-marked twig
proceeds from this branch and runs downwards upon the
posterior aspect of the cricoid cartilage to join the recurrent
laryngeal nerve.

The Recurrent Laryngeal Nerve has previously been seen
to arise from the vagus, and it has been traced in the neck
up to the point where it disappears under cover of the lower
border of the inferior constrictor muscle. It now is observed

THE LARYNX. 455

to ascend upon the outer aspect of the cricoid cartilage, im-
mediately behind the crico-thyroid joint. Here it is joined
by the communicating twig from the internal laryngeal nerve,
and almost immediately afterwards it divides into two
branches. The larger of these proceeds upwards, under
cover of the ala of the thyroid cartilage, and breaks up into
filaments which supply the lateral crico-arytenoid, the thyro-
arytenoid, and the thyro-ary-epiglottidean muscles ; the
smaller ox posterior branch inclines upwards and backwards
upon the posterior aspect of the cricoid cartilage, and under
cover of the posterior crico-arytenoid muscle. It supplies
twigs to this muscle, and is then continued onwards to end
in the arytenoid muscle.

The recurrent laryngeal nerve is therefore the motor
nerve of the larynx. It supplies all the muscles with the
exception of the crico-thyroid, which draws its nerve-supply
from the external laryngeal. The recurrent laryngeal
nerve, however, is usually considered to contain a few
sensory fibres. These it gives to the mucous membrane of
the larynx below the rima glottidis.

Laryngeal Arteries. — The superior laryngeal arter\\ a
branch of the superior thyroid, accompanies the internal
laryngeal nerve ; the inferior laryngeal artery which springs
from the inferior thyroid accompanies the recurrent laryngeal
nerve. These two vessels ramify in the laryngeal wall and
supply the mucous membrane, glands and muscles.

Laryngeal Cartilages and Joints. — The cartilages which
constitute the skeleton of the larynx and give support to its
wall are the following : —

4. Arytenoid,

1. Thyroid, "j 5. Coniicvda iaryi

2. Cricoid, > single. or cartilages of]-paircil.

3. EpigloUis, J Sanlorini,

6. Cuneiform, -'

They are held together by certain ligaments and joints.

Dissection. — The mucous membrane and muscles must be carefully
removed from the cartilages, and the epiglotlidean, crico-thyroiil, and
crico-arytenoid ligaments defined. Great caution must Jje exercised in
cleaning the arytenoid cartilages and the cartilages of Santorini, in order

yngis

:s of;- pa;

456 HEAD AND NECK.

that the slender ligaments which attach the latter to the upper border of
the cricoid cartilage may be preserved (Fig. 293, p. 459).

The Epiglottis is a thin leaf-like lamina of yellow fibro-
cartilage placed behind the root of the tongue and in front
of the superior opening of the larynx. When divested of
the mucous membrane which covers it, it will be seen to
present a somewhat heart-shaped form, and to be indented
by deep pits and numerous perforations in which glands are
lodged. Its broad end is directed upwards and is free ; its
margins are almost completely enclosed within the aryteno-
epiglottidean folds. The anterior surface is only free in its
upper part; below, it is in relation to the thyro-hyoid
ligament, from which, however, it is separated by adipose
tissue and some mucous glands. The posterior surface is free
in all its extent and bounds the vestibule of the larynx in front.

Epiglottidean Ligaments. — The epiglottis is bound by
ligaments to the root of the tongue, to the hyoid bone, and
to the thyroid cartilage. The ihxQQ glosso-epiglottidean folds
have already been studied. In each there is a small
quantity of elastic tissue. The hyo-epiglottidean liga77ient is
a short, broad elastic band which connects the anterior face
of the epiglottis to the upper border of the body of the
hyoid bone. The thyro- epiglottidean ligaDient is strong,
elastic and thick. It proceeds downwards from the lower
pointed extremity of the epiglottis, and is attached to the
angular depression between the two alse of the thyroid
cartilage, below and behind the median notch.

The Thyroid (cartilago thyroidea) is the largest of the
laryngeal cartilages. It is composed of two broad some-
what quadrilateral plates, termed the alee., which meet in front
at an acute angle and constitute the projection in the neck
known as lYie po?num Adami. This is more prominent in
its upper part than below, and is always more marked in
the male than in the female. From the pomum Adami
the two alee diverge backwards and outwards, like the limbs
of the letter V, so as to enclose between them the posterior
lamina of the cricoid cartilage and the arytenoid cartilages.
The zipper border of each ala is somewhat convex, but in

THE LARYNX.

457

front it is cut away or bevelled off, so that with the corre-
sponding part of the opposite ala a deep median notch is
formed. This is called the incisura thyroidea. The Imver
border is nearly straight,
but is subdivided by a
slight tubercle into an
anterior and a posterior
concave part. T\\t posterior
border is thick and rounded
and gives attachment to
the fibres of the stylo -
pharyngeus and palato-
pharyngeus muscles. Above
and below this border pro-
jects in the form of pro-
minent processes. These
are termed the coniua.
The superior com u is longer
than the inferior cornu, and
gives attachment to the
lateral thyro-hyoid liga-
ment. The shorter, stronger

inferior cornu c\ix\Q?>s\\s\\i[y ' , ,

. J r\ ^-u ■ Fig. 292.— Cartilages of larynx seen

mwards. On the mner f_.,r.K„ f.„„, ^Pr^n. T.„<=rhL-n \
aspect of its tip there is a
facet which articulates with
the side of the cricoid car-
tilage

of the ala is flat. Immedi- ^
ately below the posterior
part of the upper border
and in front of the root
of the superior cornu there is a distinct tubercle. From
this an oblique ridge descends towards the tubercle on the
lower border of the ala. This ridge gives attachment to
the sterno-thyroid and thyro-hyoid muscles, and divides the
outer surface of the ala into an anterior and a posterior
part. To the latter, which is much the smaller of the two,

from the front. (From Luschka.)

Trachea.
Cricoid cartilage.

Central part of crico-tliyroid membrane.
The outer surface 4- Ate of thyroid cartilage^

- Intermediate lamina This is a part of
the cartilage which is more or less dis-
tinct from the ala: and connects them at
the pomum Adami. It is not described
in the text.

458 HEAD AND NECK.

is attached the inferior constrictor muscle of the pharynx.
The inner surface of the ala is smooth and shghtly concave.
To the angular depression between the two alge are attached
the thyro-epiglottidean ligament, the superior thyro-arytenoid
ligaments, and the inferior thyro-arytenoid ligaments.

The Crico-thyroid Joint, or the articulation on each side
between the tip of the inferior cornu of the thyroid
cartilage and the side of the cricoid cartilage, belongs
to the diarthrodial variety. The opposed surfaces are sur-
rounded by a capsular ligament which is lined by a
synovial membrane. The movements which take place at
these joints are of a twofold character — viz. (i) gliding;
(2) rotatory. In the case of the former the two opposed
surfaces glide upon each other in different directions. The
rotatory movement is one around a transverse axis which
passes through the centre of each joint. The capsular
ligament is strengthened by a stout band on the posterior
aspect of the joint.

The thyroid cartilage should now be removed by dividing the
hgaments which surround the crico-thyroid joint.

The Cricoid Cartilage (cartilago cricoidea) is shaped
like a signet ring. The hxod.di posterior lamina is somewhat
quadrilateral in form. Its superior border presents a faintly-
marked mesial notch, and on each side of this there is an
oval convex facet which articulates with the base of the
arytenoid cartilage. The posterior surface of the lamina is
divided by an elevated median ridge, into two slightly
hollowed out areas which give attachment to the posterior
crico- arytenoid muscles. The mesial ridge itself gives
origin to the fibres which form the anterior longitudinal
muscular band of the oesophagus. In front of the
posterior lamina, the ring of the cricoid cartilage is com-
pleted by an anterior arch. The lower border of this is
horizontal, and is connected to the first tracheal ring by
membrane. The arch is narrow in front, and is attached
to the lower border of the thyroid cartilage by the middle
portion of the crico-thyroid membrane. Behind this the
upper border rapidly ascends. Upon the posterior part of

THE LARYNX.

459

the lateral surface of the cricoid cartilage there is a circular,
slightly elevated, convex facet, which looks outwards and
upwards for articulation with the inferior cornu of the
thyroid cartilage. Internally the cricoid cartilage is lined
by mucous membrane. Inferiorly the lumen is circular,
but above it is elliptical.

Cartilage of Santorini (cartilago corniculata). — Before
proceeding to the study of the arytenoid cartilages the
dissector should examine the cartilages of Santorini and
the manner in which they are held in position. They are
two minute pyramidal nodules
of yellow elastic cartilage
which are placed on the
summits of the arytenoid
cartilages, and are directed
backwards and inwards. Each
cartilage of Santorini is en-
closed within the correspond-
ing aryteno-epiglottidean fold
of mucous membrane, and
is joined to the apex of the
arytenoid cartilage by a joint F'g- 293.— Posterior view of the

which may either partake of "''''^'^ ,3:'"^ arytenoid canil-

-' . ^ . ages. (From Luschka.)

the nature of diarthrosis or ^ .

, , . ,,,, . - I. Posterior lamina of cricoid cartilage,

synchondrosis. I he tips of ^_ Ar>-tenoid cirt.lage.
the two COrnicula laryngis are 3- Cartilage of Santorini.

connected to the upper border ^- Sesamoid cartilage.

. , . . S- L'gamentum jugale.

of the posterior lamina of

the cricoid cartilage by a delicate Y-shaped ligament,

termed the ligamentiim jugale.

Arytenoid Cartilage (cartilago arytaenoidea). — In deal-
ing with the arytenoid cartilages it is well to remove one
in order that its external form may be studied ; the other
should be retained in position for the purpose of afterwards
examining the crico-arytenoid joint, and the movements
which can be performed at this articulation.

The arytenoid cartilages are pyramidal in form, and sur-
mount the upper border of the posterior lamina of the

Vv^t^a*"

46o HEAD AND NECK.

cricoid cartilage. The apex of each is directed upwards,
and at the same time curved backwards and inwards. It
supports the cartilage of Santorini. Of the three surfaces,
one looks directly inwards towards the corresponding sur-
face of the opposite cartilage, from which it is separated by
a narrow interval ; another looks backwards ; whilst the
third is directed outwards and forwards. The ititernal
surface is narrow, vertical and even, and is clothed by
mucous membrane. The posterior surface is concave ; it
lodges and gives attachment to the arytenoideus transversus
muscle. The antero-external surface is the most extensive
of the three, and is uneven for muscular and ligamentous
attachments. Upon this aspect of the arytenoid cartilage
the thyro-arytenoid muscle is inserted, whilst a small
tubercle placed a short distance above the base gives
attachment to the superior thyro-arytenoid ligament — the
supporting ligament of the false vocal cord. The surfaces
of the arytenoid cartilage are separated by three borders,
viz. an anterior, a posterior, and an external. The external
border is the longest, and at the base of the cartilage it is
prolonged outwards and backwards in the form of a stout
prominent angle or process, termed the processus viuscularis.
Into the front of this the crico-arytenoideus lateralis muscle
is inserted ; into its posterior aspect the crico-arytenoideus
posticus muscle is inserted. Near the apex of the arytenoid
cartilage a small nodule of yellow elastic cartilage is fre-
quently placed upon the external border, and is held in this
position by the investing perichondrium. It is termed the
sesamoid cartilage. The anterior border of the arytenoid
cartilage is prolonged into the projecting anterior angle of
the base. This is called \}i\% processus vocalis. It is sharp
and pointed, is directed horizontally forwards, and gives
attachment to the inferior thyro-arytenoid ligament or true
vocal cord. The base of the arytenoid cartilage presents
an elongated concave facet on its under aspect for articula-
tion with the upper border of the posterior lamina of the
cricoid cartilage.

The Crico-arytenoid Articulation is of the diarthrodial

THE LARYNX. 461

variety. There is a distinct joint cavity surrounded by a
capsular ligament which is lined by a synovial membrane.
The cricoid articular surface is convex, that of the arytenoid
concave ; both are elongated in form, but they are placed
in relation to each other, so that the long axis of the one
intersects or crosses that of the other, and in no position
of the joint do the two surfaces accurately coincide ; a
portion of the cricoid surface is always left uncovered. The
movements allowed at this joint, as the dissector can
readily determine, are of a twofold kind — (i) gliding, by
which the arytenoid is carried inwards or outwards, or, in
other words, a movement by which the arytenoid advances
towards or retreats from its fellow; (2) rotatory, by which
the arytenoid cartilage revolves round a vertical axis. By
this movement the vocal process is swung outwards or
inwards, so as to open or close the rima glottidis.

The dissector should note that the capsule of this joint
is strengthened behind by a strong band which plays a
most important part in the mechanism of the articulation.
It acts in such a manner that it arrests forward movement
of the arytenoid cartilage.

The Cuneiform Cartilages are two little conical nodules
of yellow elastic cartilage, which are placed one in each
aryteno-epiglottidean fold near its back part. They are not
always present.

Action of the Laryngeal Muscles. — The dissector should now
consider the manner in uliich the muscles of ihe larj-nx operate upon
the true vocal cords in the production of the voice. Tension of the
vocal cords is produced by the contraction of the crico-lhyroid 7nuscles.
In this action the thyroid cartilage is more or less fixed. The oblique
parts of the muscles raise the anterior arch of the cricoid cartilage,
which causes the upper border of its posterior lamina with the ar)'tenoid
cartilages to pass backwards and downwards. At the same time the
posterior horizontal parts of the muscles tend through their insertion
into the inferior cornua to draw the cricoid cartilage backwards. When
the crico-thyroid muscles cease to contract, the relaxation of the cords
is brought about by the elasticity of the ligaments. The tliyro-arytctioid
muscles must be regarded as antagonistic to the crico-thyroid muscles.
When they contract, they draw forward the arj-tenoid cartilages and
posterior lamina of the cricoid cartilage, and still further relax the

462 HEAD AND NECK. \

cords, and when they cease to act, the elastic ligaments again bring
about a state of equilibrium. The ary-vocales muscles, by the insertion
of their fibres into the true vocal cords, may tighten portions of the
cords, and, at the same time, relax the parts behind. /

The width of the rima glottidis is regulated by the arytepoideus, which
approximates the arytenoid cartilages and by the cfico - arytenoidei
laterales and postici. The crico-arytenoidei postici, by drawing the
muscular processes of the arytenoid cartilages outwards and backwards,
swing the processus vocales and the vocal cord outwards, and thus
open the rima. The crico-arytenoidei laterales are antagonistic muscles,
and by drawing the muscular processes in an opposite direction, close
the rima.

But the muscles of the larynx have another function to perform
besides that of vocalisation. It was formerly thought that the superior
aperture of the larynx was closed during deglutition by the folding back
of the epiglottis ; that in fact the epiglottis, during the passage of the
bolus of food, was applied like a lid over the entrance to the vestibule
of the larynx. This view is now known to be erroneous. The in-
vestigations of Prof. Anderson Stuart have shown that the superior
aperture of the larynx is closed during swallowing by the close applica-
tion and the forward folding of the two arytenoid cartilages, so that
their apices become closely applied to the cushion of the epiglottis.
The muscles chiefly concerned in this movement are the external thyro-
arytenoid muscles and the transverse arytenoid muscle. These muscles
form a true sphincter vestibuli. The thyro-ary-epiglottidean muscle
also assists in the closure.

THE TONGUE.

The tongue is a muscular organ placed on the floor of
the mouth. It has important duties to perform in connec-
tion with the functions of mastication, deglutition, and
articulation. Moreover, the mucous membrane which
covers it is specially modified in certain localities in con-
nection with the peripheral terminations of the nerves of
taste. The root, or broad posterior extremity of the
tongue, is attached to the hyoid bone ; in front, the
pointed extremity is free. The dorsal aspect of its base
forms the lower boundary of the isthmus faucium, and is
surmounted on each side by the tonsil.

Mucous Membrane. — The lingual mucous membrane is
a part of the general mucous lining of the buccal cavity,

THE TONGUE. 463

and it envelops the dorsum, sides, tip, and under surface
of the tongue. It presents different appearances in different
localities. Thus over the posterior part of the dorsum, in
the region which is bounded behind by the epiglottis, and
on either side by the tonsil, the mucous membrane is
smooth, and presents no papilla; which are visible to the
unaided eye. It is from this district that the three glosso-
epiglottidean folds take origin, and every here and there
the surface is studded with low projections which are
produced by lymphoid follicles, placed subjacent to the
mucous membrane. About an inch or so in front of the
epiglottis, a median depression, termed \\\t foramen ccecum,
may be noticed, and in front of this the mucous membrane
which covers the dorsum, sides, and tip of the tongue is
beset with papillae of different kinds. As these are in-
dividually visible to the naked eye, the mucous membrane
presents a very characteristic appearance. Further, a
mesial groove or sulcus called the rap/ie extends back-
wards from the tip of the tongue to the foramen caecum,
and divides the anterior two-thirds of the dorsum into two
lateral parts.

On the under surface of the tongue the mucous mem-
brane is smooth and comparatively thin. In the mesial
plane it forms the f?-cEtiufn lingi/ce, which has been studied
at an earlier stage. "Dn either side of the median line the
lingual vein may be noticed in the living subject stretching
forwards towards the tip. To the outer side of this, and,
therefore, somewhat nearer the border of the tongue, is a
delicate and feebly marked fold of mucous membrane, from
the free border of which a row of fringe-like processes or
fimbriae project. It is termed the ^ca fimbriata.^ and as it
extends forwards towards the tip of the tongue, it inclines
towards the mesial plane and its neighbour of the opjiosite
side. On the side of the tongue, immediately in front of
the lingual attachment of the anterior pillar of the fauces,
five short vertical fissures in the mucous membrane
separated by intervening folds may be noticed. This
arrangement is termed ^o. papilla Joliata. It is the repre-

464 HEAD AND NECK.

sentative of a leaf-like condition of the mucous membrane,
which is much more highly developed in certain of the
lower animals (hare and rabbit), and which is specially
concerned in receiving the impressions of taste.

The Lingual Papillae (papillge linguales) are of three
kinds, and differ in size, shape, and in the position they
occupy on the surface of the tongue. They are termed the
circumvallate, the fungiform, and the conical.

The circumvallate papillce (papillse vallatae), seven to
twelve in number, are the largest, and are placed on the
posterior part of the dorsum in two rows, which diverge
from each other in an outward and forward direction, like
the two limbs of the letter V. The foramen csecum lies
immediately behind the median circumvallate papilla, which
forms the apex of the V. In form a circumvallate papilla
is broad and somewhat cylindrical, slightly narrower at its
attached than at its free extremity, and sunk in a pit. It
is surrounded by a deep trench, the walls of which are
slightly raised beyond the general surface of the mucous
membrane. The free extremity of each papilla is there-
fore encircled by an annular elevation, which is termed the
vallum.

The fungiform papillce (papillae fungiformes) are much
smaller, but are present in much greater numbers. They
are chiefly found on the tip and sides of the tongue, but
they are also scattered at irregular intervals over the
dorsum. They are very characteristic in form. Each
papilla presents a large, full, rounded knob-like extremity,
while it is greatly constricted at the point where it springs
from the mucous surface. In the living tongue the
fungiform papillae are distinguished by their bright red
colour.

The jW2^^/_^a^iZi2^ (papillce conicae) are present in very
large numbers. They are smaller than the fungiform
variety, and although they are quite visible to the naked
eye, they can be more conveniently studied by the aid of
an ordinary pocket lens. They are minute conical pro-
jections from the mucous membrane which taper towards

riJE TONGUE.

465

their free extremities, and occupy the dorsum and sides of
the tongue in front of the foramen CKCum. They are
arranged in parallel rows which are placed close together,
aricl'm Ihe back part of the tongue these diverge from the
mesial raphe in a forward ana outward direction. To-
wards the tip of the tongue the rows of conical papilLne
become more or less transverse in direction, and on the
sides of the tongue they are arranged perpendicularly.
Muscles of the Tongue. — The tongue is almost entirely

stylo-hyoid

posterior belly of
digastric.

aiucri'jr belly of diijabUic. myfj-hyoid. genio-hyoid.
Fig. 294. — Muscles of the tongue. (From Gegenbaur. )

composed of muscular fibres, with some adipose tissue
intermixed. It is divided into two lateral halves by a
mesial septum, and the muscles in connection with each
of these consist of an intrinsic and an extrinsic group.
They are as follows : —

Extrinsic M

r I. Gei

2. Ily

usclcs, A 2. Ch(

I. Genio-hyo-glossus.

o-glossus.

Chondro-glossus.

4. .Styln-glossus
^ 5. Palato-glossus.

VOL. 11. — ;;o

466

HEAD AND NECK.

Intrinsic Muscles,

1. Superficial lingual.

2. Inferior lingual.

3. Vertical.

4. Transverse.

The extrinsic muscles take origin from parts outside the
tongue, and thus are not only capable of giving rise to
changes in the form of the organ, but also of producing
changes in its position. The intrinsic muscles, which are
placed entirely within the substance of the tongue, are, for
the most part, only capable of giving rise to alterations in
its form.

palato-glossus.

stylo-glossus.
septum linguae,
lingualis inferior,
hyo-glossus.

genio-glossus.

Fig. 295. — Transverse section through the hinder part
of the tongue. (From Gegenbaur. )

With the exception of the chondro-glossus, the extrinsic muscles
have already been studied, but the dissector should take this op-
portunity of examining more fully their insertions, and the manner in
which their fibres are related to each other, and to those of the intrinsic
muscles. For this purpose carefully reflect the mucous membrane
from the right half of the tongue, and follow the muscles into that side
of the organ. At the same time the lingual nerves and the ranine
artery should be preserved. On the under surface of the tongue near
the tip, the removal of the mucous membrane will expose a group of
glands aggregated together, so as to form a small oval mass on each
side of the mesial plane (glands of Blandin).

The stylo-glossus will be observed to run along the side
of the tongue to the tip where the two muscles become
to a certain extent continuous. The hyo-glossus extends
upwards to the side of the tongue, and its fibres pass for
the most part under cover of those of the stylo-glossus to
reach the dorsum, over the posterior part of which they
spread out beneath the mucous membrane. The genio-hyo-

THE TONGUE.

4C7

glossus sends its fibres vertically upwards into the tongue on
each side of the mesial septum, and its insertion stretches
from the tip to the base. The fibres of the palato-glossus
become continuous with those which form tlic stratum
transversum.

The choitdro-glossus is not always present. It is separated
from the deep surfiice of the hyo -glossus by the lingual
vessels, and by the pharyngeal slip of the genio-hyo-glossus.
It is a slender muscular band which takes origin from the
inner aspect of the root of the lesser cornu, and the adjoin-
ing part of the body of the hyoid bone. Its fibres ascend

Fig. 296.

-Longitudinal section through the tongue.
( From Aeby. )

c. Lingualis superior.
/. Lingualis inferior.

d. Lamellae of stratum transversum.

g. Gcnio-hyoid.

a. Genio-hyo-glossus.

c. Hyoid bone.

to enter the tongue, and finally spread out on the dorsum
under cover of the lingualis superior.

The superficial lingual muscle (musculus longitudinalis
superior) is a continuous layer of longitudinal fibres which
covers the entire dorsum lingua;, from the root to the tip,
immediately beneath the mucous membrane. Towards the
base of the tongue it is thinner than in front, and here it is
overlapped by the transverse fibres of the hyo-glossus, and
is intermixed with the fibres of the chondro-glossus.

The inferior lingual muscle (musculus longitudinalis in-
ferior) is a rounded fleshy belly which is placed upon

HEAD AND NECK.

the inferior aspect of the tongue. Behind, it lies in the
interval between the hyo-glossus and the genio-hyo-glossus
and shows an attachment to the hyoid bone ; in front, it is
prolonged to the apex of the tongue between the inner
border of the stylo-glossus and the genio-hyo-glossus ; with
the former it is more or less blended.

The transverse muscular fibres (musculus transversus
linguae) lie under the lingualis superior, and constitute a
thick layer which extends outwards from the lateral face

of the septum linguae, to
reach the dorsum and
side of the tongue. The
fibres of the genio-hyo
glossus ascend through
the stratum transversum
and break it up into
numerous lamellae (Fig.
296, d\ It is joined by
the fibres of the palato-
glossus (Henle) (Fig.

295)-

The vertical muscular
fibres (musculus verticalis
Hnguae) extend in a
curved direction from the
dorsum to the under
aspect of the tongue, and
decussate with the fibres
of the stratum transversum.

Nerves and Vessels of the Tongue. — The nerves of the
tongue are — (i) the glosso- pharyngeal; (2) the lingual;
(3) the hypoglossal; and (4) a few twigs from the internal
laryngeal. These should be traced on the left side of the
tongue, where the mucous membrane is still in position.

The glosso-pharyngeal nerve has been traced up to the
point where it disappears under cover of the hyo-glossus
muscle. Here it divides into two branches. The smaller
of these extends forwards upon the side of the tongue, and

Fig. 297. — Transverse section through
the tongue. (FromAeby. )

a. Genio-glossus.

b. Hyo-glossus.

c. Stylo-glossus.

d. Stratum transversum.

e. Lingualis superior.
/. Lingualis infei'ior.
g^. Genio-hyoid.

/3. Hyoid bone.

THE BRAIN. 469

may be traced as far as a point midway l)et\veen the root
and the tip. The larger branch turns upwards and is dis-
tributed to the mucous membrane which invests the pos-
terior third of the dorsum linguae. It gives twigs to the
circumvallate papillre, and some fine filaments may be
followed to the anterior surfixce of the epiglottis. The
glosso-pharyngoal nerve is the principal nerve of taste.

The lingual and hypoglossal nerves are described in pages
321 and 322, and their terminal branches should now be
traced as far as it is possible to do so.

The internal laryngeal nerve gives a few delicate fila-
ments to the glosso-epiglottidean folds and the mucous
membrane of the root of the tongue.

The ranine artery should be followed to the tip of the
tongue, where it forms a small loop of anastomosis with its
fellow of the opposite side (p. 325).

Septum Linguae. — The septum of the tongue can best
be seen by making a transverse section through the organ.
This will also in a measure demonstrate the transverse and
perpendicular muscular fibres. The septum is a mesially
placed fibrous partition. It is strongest behind, where it
is attached to the hyoid bone.

THE BRAIN.

Directions. — In the first instance the brain should be placed on a
dissecting-room platter, with its superior surface uppermost. As it has
in all probability been removed from strong spirit, it is necessary to
keep it moist during the whole dissection, by means of a cloth dipped
in water. Unless this be done the membranes are apt to become dry,
and then they are exceedingly difficult to remove.

General Appearance of the Brain. — ^^'hen viewed from

above, the brain presents an ovoid figure, its broad end
being directed backwards. Its greatest transverse diameter
is in the neighbourhood of the parietal eminences. The

470

THE BRAIN.

only parts which are visible when the brain is in this posi-
tion are the two convoluted cerebral hemispheres. These
are separated from each other by a deep mesial cleft, called
the great longitudinal fissure, which extends from the front
to the back of the brain.

Fig. 2c

-The base of the brain.

I. The great longitudinal fissure.
I. Olfactory tract and bulb.
11. lies on anterior perforated spot,
and points to the optic nerve.
III. is placed on the crus cerebri, im-
mediately to the outer side of the
oculo-motor nerve.
IV. Trochlear nerve.
V. Trigeminal nerve.

VI. is placed on the pons Varolii, im-
mediately in front of the abducent
nerve.
VII. is placed on the middle peduncle
of the cerebellum, in front of the
facial and auditory nerves.
XL Spinal accessory nerve.
XII. Hypoglossal nerve.
C.I. First cervical nerve.
6. Medulla oblongata.

GENERAL Al'PEARANCE. 471

The position of ihc brain sliould now be reversed. Turn it so that
it rests on its sujicrior surface.

The inferior aspect of the brain is usually termed the
" base." It presents an uneven and irregular surface, which
is more or less accurately adapted to the inequalities on the
floor of tlie cranium. From this point of view some of the
main subdivisions of the organ may be recognised. Thus,
behind is seen the short cylindrical portion, called the
medulla oblongata or bulb^ through which, at the foramen
magnum, the brain becomes continuous with the spinal
cord. The bulb rests on the under surface of the cere-
bellum, being received into the vallecula or hollow which
intervenes between the two cerebellar hemispheres. The
cerebellum is a mass of considerable size which lies under
the hinder portions of the cerebral hemispheres. It can
lie easily recognised on account of the closely-set, curved
and parallel fissures which traverse its surface. Above the
medulla, and in direct connection with it, is a prominent
white elevation called the pons Varolii. The basilar artery
extends upwards in a mesial groove on its surface. Im-
mediately in front of the pons Varolii there is a deep hollow
or recess. This is bounded behind by the pons, on either
side by the projecting temporal lobes of the cerebrum, and
in front by the orbital portions of the frontal lobes of the
cerebrum. At the present stage of the examination of the
brain, the bottom of this hollow is hidden from view by the
arachnoid mater, which stretches over it like a veil ; but if
the pituitary body has been removed with the brain it will
be seen within its limits. Passing out from either side of
the fore-part of this recess will be seen the deep Sylvian
fissure, which intervenes between the pointed and projecting
extremity of the temporal lobe and the frontal lobe of the
cerebrum, whilst in the middle line in front the great longi-
tudinal fissure will be observed to separate the frontal
portions of the cerebral hemispheres. On either side of
the great longitudinal fissure, and separated from it by a
narrow gyrus, the olfactory peduncle and bulb may be re-
cognised.

472 THE BRAIN.

MEMBRANES AND BLOOD-VESSELS OF
THE BRAIN.

Arachnoid Mater (arachnoidea encephali). — This forms
the intermediate covering of the brain. Placed between
the dura mater and the pia mater it is directly continuous
with the arachnoidea of the spinal cord. It is an exceed-
ingly thin and delicate membrane, which can best be seen
on the base of the brain, as in this locality it is not so
closely applied to the pia mater as elsewhere. Unlike the
pia mater, it does not (except in the case of the great
longitudinal and the Sylvian fissures) dip into the sulci on
the surface of the cerebrum and cerebellum. It bridges
over the inequalities on the surface of the brain. It is
consequently spread out in the form of a very distinct
sheet over the medulla, the pons Varolii, and the hollow
on the base of the brain which lies in front of the pons.
The cut ends of several of the cranial nerves will be
observed projecting through this sheet; whilst in front,
immediately to the outer side of the optic nerve, the in-
ternal carotid artery may be noticed piercing it.

Subaraclinoid Space (cavum subarachnoidale). — The
interval between the arachnoidea and the pia mater
receives the name of the subarachnoid space. It contains
the subarachnoid fluid, and is broken up by a mesh work
of fine filaments and trabeculse, which connects the two
bounding membranes (viz. the arachnoidea and the pia
mater) in the most intimate manner, and forms a delicate
sponge-like interlacement between them. Where the
arachnoidea passes over the summit of a cerebral convolu-
tion, and is consequently closely applied to the subjacent
pia mater, the meshwork is so close and the trabeculse so
short that the two membranes cannot be separated from
each other. To the dissector they appear to form a single
lamina. In the intervals between the rounded margins of
adjacent convolutions, distinct angular spaces exist between
the arachnoidea and the pia mater. In these the sub-

MEMBRANES AND ni.OOD-]-ESSEI.S.

473

arachnoid tissue can be studied, and it will be seen that
by these intervals on the surface of the cerebrum, numerous
communicating channels are formed which serve for the
free passage of the subarachnoid fluid from one part of the
brain to another. The larger branches of the arteries and
veins of the brain traverse the subarachnoid space; their
walls are directly connected with the subarachnoid
trabecular, and are bathed by the subarachnoid fluid.

Cisternse Subarachnoidales. — In certain situations the
arachnoidea is separated from the pia mater by intervals of

Fig. 299. — Diagram of tlie meninges of the brain.

considerable depth and extent. These expansions of the
sut)arachn()id space are termed cisternse subarachnoidales.
In these the subarachnoid tissue is reduced to a minimum.
'I'here is no longer a close meshwork ; the trabecule con-
necting the two bounding membranes take the form of long
filamentous intersecting threads, which traverse the spaces.
A beautiful demonstration of these may be obtained by
dividing in the mesial plane, with the scissors, the sheet of
arachnoidea which is spread over the medulla and pons,
and turning the two pieces gently outwards.

Certain of the cistcrna." require sjiecial mention. The largest and

474 THE BRAIN.

most conspicuous is called the cisterna magna. It is a direct continua-
tion of the posterior part of the subarachnoid space of the spinal cord
upwards into the hinder part of the cranium. It is formed by the
arachnoid membrane bridging over the wide interval between the back
part of the under surface of the cerebellum and the medulla oblongata.

The cisterna poiit is is the name given to another of these recesses. It
is the continuation upwards on the floor of the cranium of the anterior
part of the subarachnoid space of the cord. In the region of the
medulla it is continuous on either side with the cisterna magna, so that
this subdivision of the brain is completely surrounded by a wide sub-
arachnoid space.

In front of the pons Varolii the arachnoid membrane bridges across
between the projecting temporal lobes, and covers in the deep hollow in
this region of the base of the brain. This space is called the cisterna

Pacchionian body
I Stnics laitrahs
Parietal lone.

Arachnoid
tnatcr
Subarachnoid-
space
Pia mate

Cerebt al-
co7ivolntioJi

Fig. 300. — Diagram of the membranes of the brain and
of the Pacchionian bodies. (Roberts.)

basalis, and within it are placed the large arteries which take part in
the formation of the circle of Willis. Leading out from the cisterna
basalis there are certain wide subarachnoid channels. Two of these
are prolonged into the Sylvian fissures, and in these are accommodated
the middle cerebral arteries and some of their branches. In front the
basal cistern passes into a space in front of the optic chiasma, and from
this it is continued into the great longitudinal fissure above the corpus
callosum. In this subarachnoid passage are lodged the anterior cerebral
arteries.

All the subarachnoid cisterns communicate in the freest manner with
each other, and also with the narrow intervals on the surface of the
cerebrum. The subarachnoid space does not communicate in any way
with the subdural space. In certain localities, however, it communicates
with the ventricular system of the brain. Three such apertures are
described in connection with the fourth ventricle, whilst another slit is
said to lead from the cisterna basalis into the lower end of the descend-
ing horn of the lateral ventricle.

M/^M/i NANUS AND B/.OOD-VESSEf.S. 475

Pacchionian Bodies. — The connection of the Pacchionian
l)odics with the arachnoid mater has already been referred
to (p. I i.O-

Pia Mater Encephali. — The pia mater forms the im-
mediate^ investment of the brain. It is finer and more
delicate than the corresponding membrane of the spinal
cord, and it follows closely all the inequalities on the sur-
face of the brain. Thus, in the case of the cerebrum, it
dips down so as to line both sides of every sulcus and
form a fold within it. On the cerebellum jhe relation is
not so intimate ; it is only the larger fissures of the cere-
bellum which contains folds of pia mater.

ThcJaigeJLhlQad=vcssels of the brain, as we have noted,
run in the subarachnoid space. The finer twigs enter the
pia mater and ramify in it before proceeding into the
substance of the brain. As they enter they carry with
them sheaths derived from the pia mater. Consequently,
if the dissector raises a portion of this membrane from the
surface of the cerebrum, a number of fine processes will be
seen to be withdrawn from the cerebral substance. These
are the blood-vessels, and they give the deep surface of the
membrane a rough and flocculent appearance.

The pia mater is not confined to the exterior of the brain.
A fold is carried into its interior. Tjiis will be exposed in
the dissection of the brain, and described under the name
of the velum interpositum or the tela choroidea superior.

Disscifiott. — The blood-vessels of the brain should now be followed
out as far as it is possible to do so without laceration of the brain sub-
stance. Begin by stripping the arachnoidea from the base of the brain.
This will bring into view the main trunks. In describing the vessels
of the brain it is unfortunately necessary to speak of many parts which
have not yet come under the notice of the dissector.

Arteries which supply Blood to the Brain. — I*"our main
arterial trunks carry blood into the cranium for the supply
of the brain — viz. the two internal carotid arteries and the
two vertebral arteries. The vertebral arteries enter through
the foramen magnum, whilst the internal carotid arteries
gain admittance through the carotid canals. These vessels

476 THE BRAIN.

have been divided in the removal of the brain. The cut
end of the internal carotid will be seen on the base of the
brain immediately to the outer side of the optic nerve ; the
vertebral lies on the side of the medulla oblongata. A very
remarkable and complete anastomosis takes place on the
base of the brain by the inosculation of branches which
spring from the carotid and vertebral arterial systems. This
is termed the circle of Willis. The branches which take
part in this anastomosis are placed in that large expansion
I of the subarachnoid space which we have termed the
cisterna basalis.

Two systems of branches, both going to the cerebrum, but
differing greatly in their mode of distribution, proceed from
the vessels forming the circle of Willis. One system consists
of very numerous slender twigs, which, as a rule, come off in
groups in certain localities, and at once pierce the substance
of the cerebrum so as to gain its interior. These are the
central or basal branches. The other system is composed of
branches which ramify over the surface of the cerebrum, and
are termed the cortical branches. The central parts of the
brain, including the basal ganglia, receive their blood-supply
from the basal system, and the vessels which constitute this
group do not anastomose with each other. The cortical
vessels supply the cerebral cortex, and the finer branches
which ramify in the pia mater anastomose with each other.
It so happens, therefore, that neighbouring vascular districts
of the cerebral cortex are not sharply cut off from each
other.

Vertebral Artery (arteria vertebralis). — The vertebral
artery enters the subarachnoid space in the upper part of
the vertebral canal by piercing the dura mater and the
arachnoid mater. Gaining the interior of the cranium
through the foramen magnum, it is continued upwards on
the side of the medulla oblongata. Soon it inclines forwards
towards the front of the medulla, and, meeting its fellow of
the opposite, side in the mesial plane, it unites with it at
the lower border of the pons Varolii to form the basilar
artery.

MEMBRANES AND BLOOD-VESSELS. 477

During this part of its course the vertebral artery gives
off the following branches: —

1. Posterior meningeal.

2. Posterior spinal.

3. Posterior inferior cerebellar.

4. Anterior spinal.

5. Bulbar.

T\\Q posterior meningeal branch (ramus meningeus) springs
from the vertebral artery before it pierces the dura mater,
and is distributed in the posterior cranial fossa (p. 132).

T]\e posterior spinal {ax\.Qn:x spinalis posterior) is the first
branch that is given off after the vertebral artery pierces the
dura mater. It passes downwards on the spinal cord in
relation to the posterior nerve-roots (p. 174).

The posterior inferior cerebellar (arteria cerebelli inferior
posterior) is the largest branch of the vertebral artery, and
it takes origin immediately above the posterior spinal artery.
It pursues a tortuous course backwards on the side of the
upper part of the medulla, between the nerve-roots of the
hypoglossal, and then between the roots of the vagus.
Finally, turning round the restiform body, it gains the
vallecula of the cerebellum, where it ends by dividing into
two terminal branches. Of these, one turns backwards in
the sulcus, between the inferior vermiform process and the
lateral hemisphere of the cerebellum, whilst the other
ramifies on the posterior part of the inferior surface of the
cerebellum.

The afiterior spinal artery (arteria spinalis anterior) arises
near the lower border of the pons Varolii. It is rare to
find the vessels of the two sides of equal size. They con-
verge on the anterior surface of the medulla, and unite to
form the commencement of the median vessel which extends
downwards on the ventral face of the cord.

The bulbar arteries are minute vessels which enter the
substance of the medulla, and spring both from the vertebral
artery itself and also from its branches.

The Basilar Artery (arteria basilaris), which is formed by
the union of tiie two vertebral arteries, is a short trunk which
extends in the mesial plane from the lower to the upper

478 THE BRAIN.

border of the pons Varolii. At the latter point it ends by
dividing into the two posterior cerebral arteries. The basilar
artery lies in the middle part of the cisterna pontis, and
occupies the median groove on the ventral or anterior surface
of the pons Varolii. In front, it is supported by the basilar
process of the occipital bone and the dorsum sellse of the
sphenoid.

The branches which spring from the basilar artery, for the
most part, proceed outwards from either side of the vessel.
They are : —

1 . Transverse.

2. Internal auditory.

3. Anterior inferior cerebellar.

4. Superior cerebellar.

5. Posterior cerebral.

The transverse arteries (rami ad pontem) are numerous
slender twigs which run outwards on the surface of the pons
and enter its substance. The auditory artery (arteria audi-
tiva interna) will be seen amongst these. It follows the
auditory nerve into the internal auditory meatus, and is
distributed to the internal ear.

The atiterior inferior cerebellar (arteria cerebelli inferior
anterior) inclines outwards and backwards to reach the
anterior part of the inferior surface of the cerebellum.

The superior cerebellar artery (arteria cerebelli superior)
is a large vessel which springs from the basilar close to its
termination. It winds outwards and backwards along the
upper border of the pons Varolii to reach the upper surface
of the cerebellum, upon which it spreads out in a number of
large branches which, for the most part, take a backward
course.

Tlie Posterior Cerebral Artery (arteria cerebri posterior).
— Immediately beyond the origin of the two superior cere-
bellar arteries, the basilar trunk bifurcates into the two
posterior cerebral arteries. These diverge from each other,
and, curving outwards, they encircle the mesencephalon, and
are carried backwards towards the under surface of the
splenium of the corpus callosum. In this course the pos-
terior cerebral artery lies deeply in the interval between the

MEMBRANES AND BLOOD-VESSELS.

479

corresponding cms cerebri and the hippocampal gyrus, and,
finally passing on to the tentorial surfiice of the cerebral hemi-
sphere, it disappears from view by sinking into the anterior
extremity of the calcarine lissure. In this fissure the artery
ends by dividing into two terminal branches, viz. the cal-
carine and the parieto-occipital (Figs. 301 and 302).

INT^ CAROTID -t'-J'/^ X\

MID CEREB-\;/p^ CIRCLE
1 OF

POST'COMMUNIC^ ^l WILLIS

SUP'CEREBELL

POST'CEREB

Fig. 301. — Diagram of the circle of Willis and the distribution
of the arteries on the under surface of the cerebrum.

The third or oculo-motor nerve passes forwards in the
interval between the posterior cerebral and the superior
cerebellar arteries, close to the place where they arise from
the basilar; and the small fourth or trochlear nerve is related
to the posterior cerebral artery as it winds round the crus
cerebri.

48o THE BRAIN.

The following branches spring from the posterior cerebral artery

r Postero-mesial.
Central or basal I Postero-lateral.

(_ Posterior choroidal.

( Temporal.
Cortical I Calcarine.

(_ Parieto-occipital.

The postero-mesial central arteries arise close to the origiir of the
parent trunk. They proceed upwards in the interval between the crura
cerebri, and piercing the locus perforatus posticus, they supply the optic
thalamus and the inner part of the crus cerebri.

The postero-lateral cetitral arteries are a group of small slender twigs
which arise on the outer surface of the crus cerebri, and go to the corpora
quadrigemina and the optic thalamus.

The posterior choroidal ai'te?y, somewhat larger, goes to the velum
interpositum and the choroid plexus of the lateral ventricle (Figs. 301
and 302).

The temporal branches, two or three in number, turn outwards over
the hippocampal gyrus, and ramify on the under surface of the temporal
lobe of the cerebrum (Fig. 301).

The calcarine branch (arteria occipitalis) follows the calcarine fissure
to the occipital pole of the cerebral hemisphere, round which it turns
to reach the outer surface of the occipital lobe. It is the chief artery
of supply to the cuneus and the lingual convolution, and is therefore
specially concerned in the nutrition of the visual centres in the cerebral
cortex (Fig. 302).

The parieto-occipital artery is the smaller of the two terminal branches
of the posterior cerebral. It runs upwards in the parieto-occipital
fissure, and reaching the upper margin of the cerebrum, it turns round
this to reach the outer surface of the occipital lobe. It supplies branches
to the cuneus and praecuneus (Fig. 302).

Internal Carotid Artery (arteria carotis interna). — The
terminal part of this great vessel lies on the outer side of
the optic chiasma, in the angle between the optic nerve
and the optic tract. At the anterior perforated spot, close
to the commencement of the Sylvian fissure, it ends by
dividing into the anterior and middle cerebral arteries
(Fig. 301). The middle cerebral artery is the larger of the
two terminal branches, and, as it enters the Sylvian fissure,
it appears to be the continuation of the parent trunk. The
anterior cerebral artety, on the other hand, proceeds inwards
from the internal carotid at almost a right angle. This
explains how it is that emboli pass more frequently into
the middle cerebral than into the anterior cerebral artery.

MEA/BRANES AND BLOOD-VESSELS.

From the internal carotid artery, after it has emerged from
the cavernous sinus (p. 350), the following branches arise : —

1. Ophlhiilmic (already studied,

p. 362).

2. Posterior communicalinc:.

3. Anterior choroidal.

4. Middle cerebral.

5. Anterior cerebral.

The posterior commufiicating artery (arteria communicans
posterior) is as a rule a slender branch which proceeds
backwards to join the posterior cerebral between its postero-
mesial and postero-lateral groups of basal twigs.

The (inferior choroidal artery (arteria choroidea) enters

^CtNTRALBR

ORBITAL BBS
T- CFHEBHAL A

f] MIDDLE

CEREBRAL DISTRICT

Cai-CARlNE SR

POST" CEREBWLA

Fig. 302. — Diagram of the vessels supplying the cortex on the
inner surface of the cerebrum.

the descending cornu of the lateral ventricle, and passes
into the choroid plexus in that cavity (Fig. 301).

The anterior cerebral artery (arteria cerebri anterior) in
the first instance takes a horizontal course inwards and for-
wards (Fig. 301). It passes above the optic nerve and in
front of the optic chiasma, and finally reaches the hinder end
of that part of the great longitudinal fissure which separates
the frontal lobes of the cerebrum. Here it lies close to its
fellow of the opposite side, and the two vessels are con-
nected by a short transverse trunk of communication, termed
the anterior communicating artery (arteria communicans

VOL. II. — 31

482

THE BRAIN.

anterior). The anterior cerebral artery now enters the great
longitudinal fissure, and is carried forwards and upwards on
the inner surface of the frontal lobe towards the genu or
anterior extremity of the corpus callosum (Fig. 302). Round
this it turns, and it is then continued backwards on the upper

EXr ORBITAL
INF FRONTAL

TEMf'oRAL BRANCHES

Fig. 303. — Diagram of the arteries distributed on the outer surface
of the cerebral hemisphere.

surface of the corpus callosum. Very much reduced in size,
it gives off its terminal branch (termed the artery of the
corpus callosum), which may be traced as far as the splenium
or posterior end of the corpus callosum.

Numerous branches proceed from the anterior cerebral artery : —

Basal or central <[ Antero-mesial.

/ Inferior internal frontal (or internal orbital).
P ,. 1 J Anterior internal frontal.

J Middle internal frontal (or paracentral).
V Posterior internal frontal (or praecuneal).

The antero-mesial group of arteries pierce the inner part of the locus
perforatus anticus, and supply the enlarged anterior end of the caudate
nucleus.

The inferior internal frontal branches (internal orbital) are two or
three in number, and turn round the inner margin of the great longi-
tudinal fissure to reach the inner part of the orbital surface of the frontal
lobe. They supply the gyrus rectus, the olfactory peduncle and bulb,
and the internal orbital convolution (Figs. 301 and 302).

The anterior internal frontal artery ramifies upon the fore-part of

A/EMnKA.VES .LV/) /U.OOn-rKSSE/.S. 4S3

the inner surface of the frontal lol)e, anil its terminal twigs turn round
the u]-)per margin of the cerebral hcmisjihere, and supply the outer
surface of the frontal lohe as fiir down as tlie sulcus frontalis medius
(Fig. 302).

The middle iiitcnial frontal arlciy (paracentral) ramifies on the inner
surface of the frontal lobe behind the preceding branch. Its terminal
part passes over the paracentral convolution, and reaches the adjacent
portion of the outer surface of the cerebral hemisphere (Fig. 302).

T\\c posterior internal frontal artoy [YxxQxmQf^xX) ramifies on the inner
surface of the pnvcuneus, and its terminal twigs turn round the upper
margin of the cerebral hemisphere to gain its outer surface.

The Middle Cerebral Artery (arteria cerebri media)
passes outwards and upwards in the Sylvian fissure, and soon
breaks up into a number of large terminal branches, which
spread out on the surface of the island of Reil. Before the
posterior limb of the Sylvian fissure is opened up so as to
expose the island of Reil, these branches are observed
streaming out from between its two lips (Fig. 303). They
then diverge so as to supply a wide area of cortex on the
outer surface of the cerebral hemisphere.

The branches wliich spring from the middle cerebral artery may be
classified thus : —

Central or basal 1a. , , ,
, \ Antero-latcral.

branches. J

, ( External orbita

r^rontal \ F^xternal inferior frontal.

Cortical brancln.

orbital.
> i^.^u^.i.iii inferior n
t^ Ascending frontal.

Parietal -\ Ascending parietal.

Parieto-temporal.
Temporal.

The antero-lateral group of basal arteries are very numerous. They
pierce the outer part of the anterior perforated spot and supply the
lenticular nucleus, the internal and the external capsule, the caudate
nucleus and a portion of the optic thalamus.

T\^c frontal and parietal bramhes turn round the upper lip of the
posterior limb of the Sylvian fissure and ascend on the outer surface of
cerebrum. The frontal brandies are: (i) an external orbital lo {he
outer part of the orbital surface of the frontal lobe; (2) an inferior
external frontal to the inferior frontal convolution ; (3) an aseendinj
frontal which runs upwards in relation to the ascending frontal convolu-
tion.

The ascending parietal branch extends in an upward and backward

484 THE BRAIN.

direction in relation to the ascending parietal convolution, and its
terminal twigs supply the greater part of the cortex of the superior
parietal convolution.

The parieto-temporai branch is a very large artery which issues from
the hinder part of the posterior limb of the fissure of Sylvius and sends
branches upwards to the inferior parietal convolution and others which

postr. communicat
ing artery.

vertebral artery

hypoglossal nerve

olfactory bulb. '

internal carotid
artery.

vagus nerve.

spinal accessory
nerve.

Fig.

304-

-The cranial nerves leaving the cranial cavity and the
circle of Willis.

incline downwards over the hinder part of the temporal lobe. Its twigs,
as a rule, do not encroach upon the outer surface of the occipital lobe.

The temporal branches, two or three in number, issue from the
posterior limb of the Sylvian fissure, and turning downwards and back-
wards over its lower lip {i.e. the first temporal convolution), they ramify
upon the outer surface of the temporal lobe.

Circle of Willis (circulus arteriosus Willisii). This
remarkable anastomosis is placed on the base of the brain
in the deep hollow in front of the pons Varohi. It takes

BASE OF BKA/N. 4S5

the form of a hcptagonal or hexagonal ring, and the vessels
which compose it lie in the large basal subarachnoid space.
In front it is closed by the anterior communicating artery
which links together the two anterior cerebral arteries. On
either side is the posterior communicating artery connecting
the internal carotid (from which the anterior cerebral springs)
with the posterior cerebral. Behind, the arterial ring is
completed by the bifurcation of the basilar artery into the
two posterior cerebral vessels (Fig. 301). As a rule the
circle of Willis is not symmetrical. The right posterior
communicating artery- is almost invariably larger than its
fellow of the opposite side.

Dissection. — The brain being placed with its base uppermost, the
dissector should proceed to remove the blood-vessels and membranes
from its surface. This must be done with the forceps and a pair of
scissors. It is a dissection which requires very delicate manipulation,
because the cranial nerves at their points of attachment to the brain
are so intimately connected with the pia mater that any undue traction
applied to the membranes will tear the nerves away altogether. Indeed,
in the case of the medulla oblongata, the dissector is advised to leave the
pia mater in position until the nerve roots have been studied. The
relation of the pia mater to the fourth ventricle likewise renders this
desirable. In so far as the other nerves are concerned, the pia mater
may Ije divided carefully around their roots with the scissors.

In removing the arachnoidea and pia mater from the outer surface of
the cerebrum, it is well to raise it in the first instance from the margins
of the hemisphere, and then work towards the fissure of Sylvius. By so
doing, the membranes and vessels within this great fissure and in relation
to the island of Reil can be withdrawn without damage to the brain
substance. Of course, at the present stage, the membranes cannot be
removed from every jxirt of the brain, but as the dissection proceeds,
opportunities for completing the process will arise.

BASE OF BRAIN.

Interpedtmciilar Space. — When the membranes are
removed from the base of the brain, the crura cerebri, two
large rope-like strands, will be seen issuing from the upper
aspect of the pons Varolii. Placed close together as they
emerge from the pons, they diverge as they proceed upwards

486 THE BRAIN.

and forwards, and finally each crus disappears into the
corresponding side of the cerebrum. Turning round the
outer aspect of each crus where it passes into the cerebrum
will be seen a flattened band, called the o0ic tract. These
bands converge as they pass forwards, and are finally
joined together by a short transverse commissural portion.

olfactory bulb,
olfactory tract.

optic nerve.

optic chiasma.

anterior perforated spot.

optic tract.

infundibulum.

corpora mammillaria.

oculo-motor nerve.

posterior perforated spot

trochlear nerve

trigeminal nerve

abducent nerve

auditory and facial nerves.

glosso-pharyngeal nerve.

vagus nerve

spinal accessory nerve,

hypoglossal nerve

first cervical nerve

Fig. 305. — Base of the brain, showing the interpeduncular
space. (Gegenbaur. )

termed the ofitkjhiasma. This chiasma is placed below the
hinder end of that portion of the great longitudinal fissure
which intervenes between the frontal lobes of the cerebrum,
and when the brain is in position it rests upon the olivary
eminence of the sphenoid bone. The optic nerve is continued
forwards and outwards from the chiasma and the tract.

\

BASE OF BRAIN. 487

The crura cerebri, the optic tracts, and the optic chiasma
enclose a deep rhomboidal or lozenge-shaped interval on
the base of the brain, which is termed the interpeduncular
space. Within the limits of this area the following parts may
be seen as we pass from behind forwards: — (i) the locus
perforatus posticus ; (2) the corpora mammillaria ; (3) the
tuber cinereum, attached to which is the infundibulum of
the pituitary body. These structures form the floor of the
third ventricle of the brain.

The oculo-niotor nerves issue from the brain within the
interpeduncular space. Each nerve emerges from the inner
side of the corresponding crus cerebri.

Locus Perforatus Posticus. — At its posterior angle, im-
mediately in front of the pons Varolii, the interpeduncular
space is very deep, and is floored by a layer of grey matter
which is perforated by numerous small apertures. This is
\\\Q. locus perforatus posticus. From the apertures which are
dotted over its surface the postero-mesial basal branches of
the posterior cerebral artery have been withdrawn.

The Corpora Mammillaria are two small white pea-like
eminences placed side by side in front of the locus perforatus
posticus. At a later stage of the dissection their connection
with the anterior {)illars of the fornix will be brought out.

The Tuber Cinereum is a slightly raised field of grey
matter which occui)ies the interval between the anterior
portions of the optic tracts in front of the corpora
mammillaria. Springing from the fore-part of the tuber
cinereum, immediately behind the optic chiasma, is the
infundibulum or stalk of the pituitary body. In the
removal of the brain its connection with that body has
been severed.

The Locus Perforatus Anticus is a small triangular
district of grey matter on each side, which is bounded
behind by the uncinate extremity of the hippocampal
gyrus, in front by the diverging roots of the olfactory
peduncle, and internally by the optic tract. It leads in
an outward direction into the Sylvian fissure, and is
perforated by the antero-mesial and the antero-lateral

488 THE BRAIN.

groups of basal arteries. The grey matter in this area
is continuous above with the grey matter of the lenticular
nucleus.

Lamina Cinerea.- — If the optic chiasma be now gently
raised with the forceps, a thin lamina will be noticed passing
upwards from it into the great longitudinal fissure, to become
connected with the rostrum of the corpus callosum. This
is the lamifia cinerea. It closes the third ventricle in front,
and is continuous on either side with the grey matter of the
locus perforatus anticus.

Superficial Origins of the Cranial Nerves. — Twelve
cranial nerves are enumerated as arising from the brain on
either side of the mesial plane. These are the olfactory, or
first ; the optic, or second ; the oculo-motor, or third ; the
trochlear, or fourth ; the trigeminal, or fifth ; the abducent,
or sixth ; the facial, or seventh ; the auditory, or eighth ; the
glosso-pharyngeal, or ninth ; the vagus, or tenth ; the spinal
accessory, or eleventh ; and the hypoglossal, or twelfth.

Each of these nerves is said to have a " superficial " and a
" deep " origin. By the term " superficial origin " we refer
to the point where its fibres enter or leave the brain surface;
by the term " deep origin " we indicate the connections
which are established by the fibres of the different nerves
within the substance of the brain. It is the former only
which comes under our notice at the present time.

No fewer than eight of the cranial nerves have super-
ficial attachment to the medulla oblongata and the pons
Varolii.

Hypoglossal Nerve. — Upon the lateral aspect of the
medulla, in its upper half, a very conspicuous oval pro-
minence called the ojivary eminence may be distinguished.
A distinct sulcus or groove, which passes downwards in
front of this body, separates it from an elongated strand,
termed the anterior pyramid of the medulla. From the
bottom of this sulcus a continuous series of nerve fascicles
will be seen to issue along the whole length of the medulla.
These nerve fascicles belong to two different nerves. J^hose
which issue from the lower part of the groove, below the

BASE OF DRAIN.

4S9

level of the olivary eminence, belong to the anterior root of
i\\cjrrsrc€rvkat nerve ; those which emerge from the upper
part of the groove, in the~intcrval between the olivary body
and the pyramid, form the /lypog/ossa/ fwn'e.

Glosso-pharyngeal, Vagus and Spinal Accessory Nerves.
— Behind the olivary eminence, hclwecn it and a pro-

corpora mainmillaria.

Crus cerebri.

pons. 1

middle cerebell.ir
peduncle.

olive.

•interior pyramid.

superficial arcuate fibres.

dcciiss;ition of pyraniid.s.

lateral area.

abducent nerve.

trigeminal nerve.

nicial and auditory
nerves.

glosso-pharyngeal
nerve.

v.igus nerve.

hypoglossal nerve,
spinal accessory nerve.

Fig. 306. — -Xiilcrior as|)ect of the medulla and pons of a
full-time foetus.

minence called the rcstiforni body, there is another con-
tinuous row of nerve fascicles connected with the medulla.
These extend downwards beyond the level of the olivary
eminence, and are attached to the whole length of the
medulla in linear order. They belong to three nerves, but
it is impossible at present (seeing that the nerve-trunks
that they build up are divided) to determine precisely the
number of roots which belong to each. From below up-
wards the nerves which they form are the s/>///(i/ <i(ress(>ry,
the vagi/s, and the g/osso-/>/iaryngca/. The vagus and the
glosso-pharyngeal, which issue from the interval between
the olivary eminence and the restiform body, have their

490 THE BRAIN.

fascicles of origin much more closely crowded together
than the spinal accessory.

The medullary roots of the spinal accessory constitute
only one part of that nerve. The spijtal part springs from
the spinal cord, as low down as the sixth cervical nerve,
by a series of roots which issue from the lateral column
behind the attachment of the ligamentum denticulatum.

The Auditory and Facial Nerves issue close together_at
tjie lower border of the pons Varolii, and immediately above
the restiform body. The auditory tierve is the larger of the
two, and lies to the outer side of the facial. Its two roots
embrace the restiform body.

The facial nerve issues from the pons close to its lower
border, and immediately to the inner side of the auditory
nerve. Between these two nerves a slender filament will
be observed. This is the pars intermedia of Wrisberg. It
joins the facial in the internal auditory meatus.

The Abducent is a small nerve, which emerges from the
front of the medulla in the groove between tne loAver border
of the pons Varolii and the outer part of the anterior
pyramid.

The Trigeminal or Fifth is the largest of all the cranial
nervesT It appears on the side of the pons Varolii, nearer
its upper than its lower border, and in a line with the facial
and auditory nerves. It consists of two roots — a large
sensory root composed of a great number of fasciculi loosely
held together, and a small more compact motor root which
emerges in front and slightly to the inner side of the point
at which the sensory root enters the pons.

Trochlear Nerve. — The superficial origin of the trochlear
or fourth nerve cannot be seen at present. It erperges from
the valve of Vieussens. It is a delicate little nerve which
has a long intracranial course, and may be observed winding
round the outer side of the crus cerebri, between the cere-
brum and cerebellum.

The Oculo-motor Nerve may be seen within the inter-
peduncular space. It issues by several fascicles f^:om the
sulcus oculomotorius on the inner face of the crus cerebri.

BASE OF nix A IN.

491

The Optic is a large round nerve which proceeds out-
wards and forwards from the optic tract and optic chiasma.
The origin of the optic tract will be studied at a later
stage.

The Olfactory Nerves arise from the olfactory bulb or
lobe, and enter the nasal chamber through the foramina in
the cribriform i)late of the ethmoid bone.

General Connections of the Several Parts of the Brain.

A. Cerebrum.
/>. Cerebellum.
D. Medull.-x.
C. Pons Varolii.
h, a. Mesencephalon.

Fig. 307. — Diagrammatic view of the manner in whicii
the several parts of the brain arc connected with each
other. (I''roni Schwalbe. )

— Before proceeding to the more particular study of the
different parts of the brain, it is well that the student
should acquire a general conception of the manner in
which these are connected with each other. In the
posterior cranial fossa, below the tentorium, are placed the
medulla oblongata, the pons Varolii, and the cerebellum.
These structures surround a cavity which is called the
fourth ventricle of the brain, and all stand in intimate
connection with each other. The medulla oblongata is

492 THE BRAIN.

for the most part carried upwards into the pons Varolii,
but at the same time two large strands on its posterior or
dorsal aspect, termed the restiform bodies, are prolonged
into the cerebellum, and constitute its hife?'-ior peduncles., or
the bonds of union between the medulla and the cere-
bellum (Fig. 307, d). The transverse fibres of the pons
Varolii are gathered together on either side in the form of
a large rope-like strand. This disappears into the corre-
sponding hemisphere of the cerebellum and constitutes its
middle pedtmcle (Fig. 307, <:).

The great mass of the brain is termed the cerebrum.
This occupies the anterior and middle cranial fossae, and
extends backwards into the occipital region above the
tentorium and the cerebellum. The greater part of the
cerebrum is formed by the cerebral hemispheres, which are
separated from each other in the mesial plane by the great
longitudinal fissure. At the bottom of this fissure may be
seen the corpus callosum, a broad commissural band which
connects the two cerebral hemispheres with each other.
Each hemisphere is hollow — the cavity in its interior being
termed the lateral ventricle of the brain. Between and
below the cerebral hemispheres, and almost completely con-
cealed by them, is the inter-brain or the thalamencephalon.
The principal parts forming this portion of the brain are
the two optic thalami, between which is the third ventricle
of the brain — a deep, narrow cavity occupying the mesial
plane. The third ventricle communicates with the lateral
ventricles through two small apertures, termed X\\q. foramina
of Monro.

The cerebrum is connected with the parts in the
posterior cranial cavity (pons Varolii, cerebellum, and
medulla oblongata) by a narrow stalk called the isthmus
encephali, the mid-brain, or the mesencephalon. The mid-
brain is built up of the crura cerebri, passing from the
pons Varolii to the cerebrum (Fig. 307, a), the corpora
quadrigemina forming its dorsal part (Fig. 307, b), the
superior cerebellar peduncles proceeding from the cere-
bellum to the cerebrum, etc. It is tunnelled by a narrow

THE CEREBRUM. 493

passage — the (K/iicdiid of Sylvius — which extends between
the fourth and the third ventricles.

THE CEREBRUM.

The Cerebral Hemispheres. — Each cerebral hemisphere
presents an external, an internal, and an inferior surface,
separated from each other by more or less distinctly marked
borders. The external surface is convex, and is adapted
to the concavity of the cranial vault. The internal surface
is flat and perpendicular, and is more or less completely
separated from the corresponding surface of the opposite
side by the falx cerebri, which occupies the great longi-
tudinal fissure. The inferior surface is irregular, and is
adapted to the anterior and middle cranial fossae, and also
to the upper surface of the tentorium cerebelli. Travers-
ing this surface in a transverse direction, nearer the anterior
end of the hemisphere than the posterior end, is the stem
of the Sylvian fissure (Fig. 307, e). This deep cleft divides
the inferior surface into a front or orbital area, which rests
upon the orbital plate of the frontal bone, and is conse-
quently concave from side to side, and a more extensive
posterior area which lies on the floor of the lateral part of
the middle cranial fossa and the upper surface of the
tentorium cerebelli. This portion of the inferior surface
is fretjuently termed the tentorial surface.

The borders which separate these surfaces from each
other are the supero-mesial, the superciliary, the infero-
lateral, and the internal occipital. The supero-mesial border,
convex from before backwards, intervenes between the
internal and external surfaces. The superciliary border is
highly arched, and separates the orbital surface from the
external surface. The infero-lateral border marks off the
tentorial surface from the external surface. The internal
occipital border is not very distinct, except in cases where
the brain has been hardened /// situ. It extends from the
posterior extremity of the hemisphere to the hinder end of

494 THE BRAIN.

the corpus callosum, and intervenes between the mesial
and tentorial surfaces.

The most projecting part of the anterior end of the
cerebral hemisphere is usually called the frontal pole,
whilst the most projecting part of the hinder end is termed
the occipital pole. Again, on the under surface of the hemi-
sphere, the prominent point of cerebral substance, which
extends forwards below the Sylvian fissure, receives the
name of the temporal pole. In a well-hardened brain a
broad groove is usually present on the inner aspect of the
occipital pole of the right hemisphere. This corresponds
to the commencement of the right lateral venous sinus.

G-reat Longitudinal Fissure (incisura pallii). — This great
mesial cleft is occupied by the fold of dura mater termed
the falx cerebri. In front and behind, it completely
separates the cerebral hemispheres from each other, but in
its middle part it is floored by the corpus callosum — the
commissural band which passes between the hemispheres
and connects them together. The upper surface of the
corpus callosum can be displayed by gently drawing
asunder the two sides of the incisura longitudinalis.

Dissection. — If two brains are available, the dissector is advised at
this stage to separate in one of these the cerebrum from the cerebellum,
pons and medulla, by cutting transversely through the mid-brain or
isthmus encephali. The cerebrum may then be split in the mesial
plane by placing a long knife in the longitudinal fissure, and dividing
with one sweep the various parts which connect the two sides to each
other. By this proceeding, the three surfaces of each cerebral hemi-
sphere are exposed, and the gyri and sulci can be fully and satisfactorily
studied. If only one brain is at the disposal of the student, he should
not make this dissection, but endeavour to follow out the gyri and
sulci with the various parts of the brain in position. No doubt he
studies the hemispheres in this way at a disadvantage, but as the dissec-
tion goes on opportunities will occur which will enable him to examine
those districts of the surface which he can only see very imperfectly at
present.

Cerebral Gyri and Sulci. — The surface of the cerebral
hemispheres is rendered highly irregular by the presence
of convolutions or gyri, separated from each other by

THE CEREBRUM. 495

intervening furrows, termed sulci or fissures. The surf:\ce
pattern, which is presented by these gyri and sulci, is in
its general features the same in all human brains ; but
when the comparison is pushed into the more minute
details of the arrangement many differences become
manifest, not only in the brains of different individuals,
but also in the two cerebral hemispheres of one individual.

Of the furrows we have to recognise two varieties, viz.
complete and incomplete. The complete fissures are few in
number, and they consist of inwardly directed folds which
involve the whole thickness of the cerebral wall. They
consequently show in the interior of the cerebral cavity or
lateral ventricle in the form of internal elevations on its
wall. In this category we include (i) the dentate or hippo-
campal fissure ; (2) the anterior portion of the calcarine
fissure ; and (3) a portion of the collateral fissure. The
incomplete sulci are merely surface furrows of very varying
depth which do not produce any effect on the inner surface
of the ventricular wall.

General Structure of the Cerebral Hemispheres. — Each
cerebral hemisphere is composed of an outside coating of
grey matter spread in a continuous and uninterrupted layer
over its entire surface (except where the corpus callosum
enters), and an internal core of white matter. The grey
coating is termed the cerebral cortex, whilst the white in-
ternal part is called the medullary centre. But in addition
to the grey matter on the outside, there are certain large
deposits of grey matter embedded in the substance of
each hemisphere in its basal part. These constitute the
cerebral nuclei, and although to a certain extent isolated
from the grey matter on the surface, it will be observed
later on that at certain points they are directly continuous
with it.

Each convolution shows a corresponding structure. It
has an external covering of grey matter supported upon a
core of white medullary matter.

By means of the convolutions and sulci the grey matter
on the surface of the hemisphere is enormously increased,

496

THE BRAIN.

without unduly adding to the bulk of the organ, and the
vascular pia mater, which dips into every fissure, is in-
creased in extent to a like degree. Opportunity is therefore
afforded to the cortical vessels of breaking up into twigs
of exceeding fineness before entering the substance of the

Fig. 308. — Outer surface of the right cerebral hemi-
sphere of a female brain, in which the arrangement of the
gyri and sulci is very simple.

S. Stem of the fissure of Sylvius.
Si. Anterior horizontal limb of Sylvian
fissure.

52. Ascending limb of Sylvian fissure.

53. Posterior horizontal limb of Sylvian
fissure.

R. Fissure of Rolando.

O.P. Parieto-occipital fissure.

C.A. Ascending frontal convolution.

C.P. Ascending parietal convolution.
p.c.i. Inferior praecentral sulcus.
p.c.s. Superior praecentral sulcus.
p.c.in. Medial praecentral sulcus.
yi &y2. Superior and inferior frontal

sulci.
f.m. Middle frontal sulcus.
p.m.s. Paramedial sulcus.

Fi, Fz, & F3. Superior middle and in-
ferior frontal gyri.

F2S. Upper part of middle frontal gyrus.

F2I. Inferior part of middle frontal

gyrus.
d. Sulcus diagonalis.

A. Pars basilaris of inferior frontal

gyrus.

B. Pars triangularis of inferior frontal

gyrus.

C. Pars orbitalis of inferior frontal gyrus.
C.7JI. Calloso-niarginal fissure.

/i, p2, /3, /4. Four parts of the intra-

parietal sulcus.
s.t. Sulcus occipitalis transversus.
occ. lat. Sulcus occipitalis lateralis.
t-L and tT.. Superior and inferior tem-
poral sulci.
Ti, T2, T3. The three temporal gyri.
The upturned ends of the
posterior limb of Sylvian
fissure and the two temporal
sulci.

s. asc.
ti asc.-
to. asc.

THE CEREBRUM. 497

hemisplicrc. The distribution of the blood to the grey
cortex is in tliis way equahsed.

Cerebral Lobes and Interlobar Fissures. — Certain of the
fissures which traverse tiie surface of the cerebrum are
arbitrarily chosen for the purpose of subdividing the surface
into districts, termed lobes. These fissures, which receive
the name oi interlobar, are the following — (i) the fissure of
Syh-ius ; (2) the fissure of Rolando; (3) the parieto-
occipital; (4) the calloso-marginal ; (5) the collateral ; and
(6) the limiting sulcus of Reil.

The lobes which are mapped out by these fissures are —
(i) the frontal; (2) the parietal; (3) the occipital; (4) the
temporal; (5) the central or island of Reil; (6) the falci-
form or limbic. To these may be added a seventh lobe,
in no way related to the interlobar fissures, viz. the olfactory
lobe.

The Fissure of Sylvius is the most conspicuous fissure
on the surface of the cerebrum. It is composed of a short
main stem from the outer extremity, of which three branches
radiate. The stem of the Sylvian fissure is placed on the
inferior surface of the cerebrum (Fig. 308, S). It begins at
the locus perforatus anticus in a deep depression called the
vallecula Sylvii. From this it passes horizontally outwards,
forming a deep cleft between the temporal pole and the
orbital surface of the frontal lobe. Appearing on the outer
surface of the cerebrum, the Sylvian fissure immediately
divides into three radiating branches. These are — (i) the
ramus horizontalis posterior; (2) the ramus horizontalis
anterior ; and (3) the ramus ascendens anterior.

'W\ii. posterior horizontal limb (Fig. 308, S^) is the longest
and the most conspicuous of the three. It extends backwards
with a slight inclination uinvards for a distance of two inches
or more between the frontal and parietal lobes which lie
above it, and the temporal lobe which is placed below it.
Finally, it comes to an end by turning upwards into the
parietal lobe in the form of an ascending terminal piece
(Fig. 308, s. asc.)

The anterior horizontal limb (Fig. 308, S^) extends horizon-
VOL. II. — 32

498 THE BRAIN.

tally forwards in the frontal lobe for a distance of about three-
quarters of an inch immediately above and parallel to the
posterior part of the superciliary margin of the hemisphere.

The ascending Imib (Fig. 308, S^) proceeds upwards with a
slight inclination forwards into the lower part of the outer
surface of the frontal lobe for a distance of about an inch or
less. In many cases the two anterior limbs spring from a
common stem of greater or less length (Fig. 308).

Limiting Sulcus of Reil (sulcus circularis Reilii). — If the
lips of the Sylvian fissure be now gently but widely pulled
asunder, the island of Reil or the central lobe will be seen
at the bottom. This is surrounded by a limiting sulcus, of
which we recognise three parts, viz. an upper part bounding
it above, a lower part marking it off below, and an anterior
part limiting it in front. The insula thus mapped out is
somewhat triangular in form.

Opercula Insulse. — The present is a good time to study
the manner in which the insula or island of Reil is shut off
from the surface of the hemisphere. When the fissure of
Sylvius is held widely open, it will be observed that the
insula is overlaid by portions of cerebral cortex which
appear as if they were undermined. These by the ap-
proximation of their margins or lips form the three limbs
of the fissure of Sylvius, and are termed the opercula itisulce.
It will be noticed that the limbs of the Sylvian fissure cut
right through between the different opercula, and extend
from the surface of the hemisphere to the surface of the
island of Reil. The opercula are four in number, and are
named — (i) temporal, (2) fronto-parietal, (3) frontal, and
(4) orbital. They are easily distinguished.

The temporaLoperaihim Qxten^s upwards over the insula
from the temporal lobe ; it forms the lower lip of the
posterior horizontal limb of the Sylvian fissure.

The fronto-parietal operculum is carried downwards over
the insula to meet the temporal operculum. Its margin
forms the upper lip of the posterior horizontal limb of the
fissure of Sylvius.

The frontal operculum (Fig. 308, B) is the small triangular

THE CEREBRUM. 499

piece of cerebral cortex between the ascending and anterior
horizontal limbs of the Sylvian fissure. It is sometimes
termed the pars triangularis.

The orbital opercuium (Fig. 308, C) is for the most part on
the under surface of the hemisphere. It lies below and to
the inner side of the anterior horizontal limb of the fissure
of Sylvius, and proceeds backwards from the orbital aspect
of tiie frontal lobe over the fore-part of the insula.

Fissure of Eolando (sulcus centralis). — The fissure of
Rolando takes an oblique course across the outer convex
surface of the cerebral hemisphere (Fig. 308, R). Its upper
end cuts the supero-mesial border of the hemisphere a short
distance behind the mid-point between the frontal and occi-
pital poles, whilst its lower end terminates above the middle
of the posterior horizontal limb of the fissure of Sylvius. Its
superior extremity, as a rule, turns round the supero-mesial
border of the hemisphere, and is then continued backwards
for a short distance on its mesial surface (Fig. 309, R).
Although in its general direction the fissure of Rolando is
oblitjue, it is far from being straight. It takes a sinuous
course across the hemisphere, and makes two bends, which
are termed its genua. The superior genu is placed between
its upper and middle thirds, and its concavity looks forwards.
The inferior genu is situated in front of the superior bend
and a short distance lower down. Its convexity is directed
ftxwards. The short portion of the fissure between the two
genua is fre(iuently very nearly horizontal in direction.

Paxieto-occipital Fissure. — A very small part of this
fissure^appears on the outer face of the cerebral hemisphere
(Fig. 308, O.P.). It is situated, for the most part, oil the
internal surface (Fig. 309, P.O.). It is customary, there-
fore, to describe an external parieto-occipital and an internal
parietooccipital fissure. At the same time, it must be
clearly understood that they are directly continuous with
each other around the supero-mesial margin of the hemi-
sphere.

'ilie external parieto-occipital fissure cuts the supero-mesial
border of the hemisphere in a transverse direction from one

Soo

THE BRAIN.

and a half to two inches in front of the occipital pole. IHs
usually not more than half an inch in length, and it is brought
to an abrupt termination by an arching convolution which
winds round its extremity, and receives the convenient
name of anus J)arieto-ocdpitalis (Fig. 308).

The internal parieto-occipital fissure (Fig. t,o(), par.-occ.) is
carried downwards in a nearly vertical direction as a con-

5-.,..^.m.

Fig. 309. — Mesial or internal surface of the right hemi-
sphere of a female brain on which the convolutions are very
simply arranged.

The names of the convolutions are printed in capitals, whilst the
names of the fissures are printed in small type.

ro. Rostral sulcus.
cal.-marg. Calloso-marginal sulcus.
p.c.in. Sulcus prsecentralis medialis.
R. Upper end of fissure of Rolando.
P.O. Parieto-occipital fi.ssure.
par.-occ. Internal parieto-occipital fis-
sure.

calc. ant. Anterior portion of the cal-

carine fissure.
calc. post. Posterior part of the calcarine

fissure.
hip. Hippocampal fissure.
HIP. Hippocampal gyrus.
UNC. Uncus.
hic. temp. Incisura temporalis.

spicuous and deep cleft, which, by its lower end, runs into
the calcarine fissure.

Collateral Fissure (Fig. 309). — The sulcus coUateralis is
a strongly marked fissure on the tentorial part of the inferior
surface of the cerebral hemisphere. It begins near the

THE CEREBRUM. 5°^

occipital pole, and extends forwards towards the temporal
pole. In its posterior part it is placed below and parallel
to the calcarine fissure, whilst in front it is separated from
the hippocanipal or dentate fissure by the hippocampal
convolution, i.e. the innermost convolution on the tentorial
surface of the hemisphere (Fig. 309, HIP.).

In front of the anterior end of the collateral fissure a
shallow sulcus will be seen turning round \hs. anterior end of
the temporal lobe so as to intervene between the temporal
pole and the uncinate or hook-like extremity of the hippo-
campal gyrus. This is the incisura temporalis., and it may
be regarded as a forward prolongation of the collateral
fissure ; at the same time, it must be admitted that the two
are seldom continuous with each other.

The Calloso-marginal Fissure (Fig. 309, cal.-marg.) is a
strongly marked sulcus on the fore-part of the mesial surface
of the hemisphere. It divides the front portion of the
mesial surface into an upper marginal and a lower cajlosal
convolution, and forms on this aspect the lower limit of the
frontal lobe. Beginning below^ the fore end of the corpus
callosum, close to the locus perforatus anticus, the calloso-
marginal fissure curves round the genu of the corpus
callosum, and then extends backwards to a point a short
distance behind the middle of the supero-mesial surface.
It then turns upwards and cuts the supero-mesial margin of
the hemisphere immediately behind the upper end of the
fissure of Rolando (Fig. 308, cm.). The relation presented
by the two extremities of these fissures is such that they can
both be readily recognised, either when examined on the
outer or the mesial aspect of the cerebrum.

Boundaries of the Frontal Lobe. — The frontal is the
largest of the cerebral lobes. On the outer surface of the
hemisphere it is bounded behind by the fissure of Rolando,
and below, by the posterior horizontal limb of the fissure of
Sylvius. On the mesial face it is limited by the calloso-
marginal fissure, whilst on the inferior surface of the hemi-
sphere the stem of the fissure of Sylvius forms its posterior
boundary.

502

THE BRAIN.

External Surface of the Frontal Lobe. — On the outer
surface of the frontal lobe the following sulci and gyri may be
recognised : —

Sulci-<;

^Sulcus prcccentralis in-
ferior.

Sulcus prjecentralis su-
perior.

Sulcus paramedialis.

Sulcus frontalis superior.

Sulcus frontalis medius.

Sulcus frontalis inferior.

Sulcus diagonalis.
^Sulcus fronto-marginalis.

Gyri-<

■Gyrus frontalis ascendens (or

gyrus centralis anterior).
Gyrus front- 1 Pars superior,
alls superior J Pars inferior.
Gyrus front- 1 Pars superior,
alis medius j Pars inferior.

{Pars basilaris.
Pars triangu-
laris.
Pars orbitalis.

The inferior J?rcEceniral furraiv (sulcus prsecentralis in-
ferior) (Fig. 308,/.!;./.) consists of a vertical and a horizontal
part, and, when present in a well-marked form, it presents
a figure like the letter T or F- The vertical portion lies in
front of the lower part of the fissure of Rolando, whilst the
horizontal portion extends obliquely forwards and upwards
into the middle frontal convolution.

'T\\Q.^supe2J^__^racentra]_furr£]SL (sulcus prsecentralis sup-
erior) (Fig. 308, p.c.s^ is a short vertical sulcus which lies
at a higher level than the inferior praecentral furrow, in
front of the upper part of the fissure of Rolando. It is
almost invariably connected with the hinder end of the
superior frontal sulcus.

The ascending frontal convolution (gyrus centralis anterior)
is a long continuous gyrus which is limited in front by the
two praecentral furrows, and behind, by the fissure of
Rolando. It extends obliquely across the hemisphere, from
the supero-mesial margin above to the posterior horizontal
limb of the Sylvian fissure below (Fig. 308, C.A.).

The superior fj'ontal sulcus (sulcus frontalis superior. Fig.
308, f^) extends forwards in a more or less horizontal
direction from the sulcus prsecentralis superior.

The superior frontal gyrus (gyrus frontalis superior) (Fig.
308, F^) is the narrow convolution between the supero-
mesial border of the hemisphere and the superior frontal

THE CEREBRUM. 503

sulcus. It takes a horizontal course forwards to the frontal
pole.

The inferior frontal sulcus (sulcus frontalis inferior) (Fig.
308,/-) occupies a lower level than the superior furrow
of the same name. Its hinder end is placed in the angle
between the vertical and horizontal parts of the inferior
prKcentral sulcus, and is not infrequently confluent with
one or other of these. It proceeds forwards towards the
superciliary margin of the hemisphere, and ends a short
distance from this in a terminal bifurcation.

The middle frontal gyrus (gyrus frontalis medius) (Fig.
308, F-) is the broad convolution which lies between the
superior and inferior frontal furrows.

The inferior frontal gyrus (gyrus frontalis inferior) (Fig.
308, F^) is that portion of the outer surface of the frontal
lobe which is placed in front of the inferior prrecentral
sulcus and below the inferior frontal sulcus.

The sulcus ^aratfiedialis (Fig. 308, />.?n.s.) is the term
applied to a series of short irregular furrows arranged
longitudinally, close to the supero-mesial border of the
hemisphere. These rudimentary sulci partially subdivide
the superior frontal convolution into an upper and lower
division, and are of interest in so far that they are best
marked in high types of brain.

The middle frontal sulcus (sulcus frontalis medius of
Eberstaller) (Fig. 308, ////.) proceeds horizontally forwards
in the fore-part of the middle frontal convolution, so as to
divide it into an upper and a lower part (Fig. 308, F-'S and
F-I). When it reaches the superciliary margin of the hemi-
sphere it bifurcates, and its terminal branches spread out
widely from each other, and together constitute a transverse
furrow called the sulcus fronto-marginalis (Wernicke).

Owing to the subdivision of the superior and middle
frontal convolutions in the manner indicated, the typical
arrangement of the convolutions in the anterior part of the
outer surface of the frontal lobe is in five horizontal tiers,
and not in three tiers as previously descril)ed.

The inferior frontal convolution (gyrus frontalis inferior)

S04 THE BRAIN.

possesses a very special interest and importance, on account
of the localisation within it, on the left side, of the speech-
centre. It is cut up into three parts by the two anterior
limbs of the fissure of Sylvius. These are termed the pars
basilaris, the pars triangularis, and the pars orbitalis.

The pars basilaris (Fig. 308, A) is that part which lies
between the vertical limb of the inferior prgecentral sulcus
and the ascending limb of the Sylvian fissure. It forms the
anterior portion of the fronto-parietal operculum, and it is
traversed in an oblique direction by a shallow but constant
furrow, termed the sulcus diagonalis (Fig. 308, d).

The pars triangularis (Fig. 308, B) is simply another
name for the frontal operculum. It is triangular in form,
and lies between the ascending and anterior horizontal
limbs of the Sylvian fissure.

The pars orbitalis (Fig. 308, C) is placed below the
anterior horizontal limb of the fissure of Sylvius.

Mesial Surface of the Frontal Lobe. — On this aspect
of the frontal lobe there is an elongated, more or less con-
tinuous, convolution called the gyrus marginalis. It lies
between the supero-mesial border of the hemisphere and
the calloso-marginal fissure (Fig. 309). In the fore-part of
this gyrus one or two curved sulci are usually present.
These are termed the sulci rostrales (Fig. 309, ro).

Further, the posterior part of the marginal convolution is
more or less completely cut off from the portion which lies
in front. This part is called the paracentral lobule, and
into it the upper end of the fissure of Rolando is prolonged,
as it turns over the supero-mesial border of the hemi-
sphere (Fig. 309).

Orbital Surface of the Frontal Lobe. — On this aspect of
the frontal lobe there are two sulci — viz. the olfactory and
the orbital.

The olfactory sulcus (Fig. 310, olf) is a straight furrow
which runs parallel to the mesial border of the hemisphere.
It is occupied by the olfactory tract and bulb, and it cuts
off a narrow strip of the orbital surface close to the mesial
border which receives the name oi gyrus rectus (Fig. 310).

rilE CEREBRUM.

SOS

The flj'hital sulcus (tri-radiatc sulcus of Turner) is a com-
pound furrow which assumes many different forms. Most
frequently it takes the shape of the letter H, and we then
recognise three component parts — viz. an external limb,
an internal limb, and a transverse limb.

e. External part of the orbital sulcus.
tr. Transverse part of the orbital sulcus.
ol/. Olfactory sulcus.
O. Orbital part of the inferior frontal

gj'rus.
P. Posterior orbital convolution.
M. Anterior orbital convolution.
I. Internal orbital convolution.
T3. Inferior or third temporal convolution.
OCC. TEMP. Occipito - temporal convolu-
tion.
inc. temp. Incisura temporalis.
calc. Calcarine fissure.
HIP. Hippocampal convolution.
UNC. Uncus.

The names of the gyri are printed in capitals,
wliilst small type is used to indicate the
fissures.

Fig. 310. — The inferior surface of the right cerebral hemi-
sphere of a female brain.

The external limb (sulcus orbitalis externus) curves round
the orbital part of the inferior frontal gyrus, so as to limit
it internally (Fig. 310, e). The iiitcnml limb (sulcus
orbitalis internus) marks off a convolution between itself
and the olfactory sulcus which receives the name of
gyrus orbitalis internus {Y\g. 310, I). The transverse limb

5o6 THE BRAIN.

(sulcus orbitalis transversus) (Fig. 310, tr) takes a curved
course with the concavity directed backwards. It divides
the district between the external and internal limbs into
an anterior part, or gyrus orbitalis anterior (Fig. 310, M),
and a posterior part, or gyrus orbitalis posterior (Fig. 310,
P). The latter corresponds with the greater part of the
orbital operculum.

Boundaries of the Parietal Lol)e. — The parietal lobe
forms a considerable part of the external face of the cerebral
hemisphere, and it also appears on the mesial face in the
form of the prsecuneus or quadrate lobule. In front., it is
bounded by the fissure of Rolando, which separates.it from
the frontal lobe. Below., it is bounded in its fore-part by
the posterior horizontal limb of the Sylvian fissure. Behind
the upturned end of this fissure it is quite continuous
inferiorly with the temporal lobe, and an arbitrary line
drawn backwards on the surface of the brain in continuation
of the horizontal part of the posterior limb of the fissure of
Sylvius is taken as its inferior limit (Fig. 308). Posteriorly.,
it is separated from the occipital lobe at the supero-mesial
border of the hemisphere by the external parieto-occipital
fissure,. Below this it is more or less directly continuous
with the occipital lobe, and an arbitrary line drawn across
the outer surface of the hemisphere from the extremity of
the external parieto-occipital fissure to an indentation on
the infero-lateral border of the hemisphere, termed the
prceoccipital notch, may be regarded as furnishing a posterior
limitation. The prgeoccipital notch is, as a rule, only
visible in brains that have been hardened in situ. It is
produced by a slight wrinkle or fold of the dura mater on
the deep aspect of the parieto-mastoid suture, and in
relation to the portion of the lateral venous sinus which
lies in this locality. --The notch is placed on the infero-
lateral border of the hemisphere, about one inch and a
half in front of the occipital pole.

Mesial Surface of the Parietal Lobe — Prsecuneus. — On
the mesial surface of the hemisphere the parietal lobe is
represented by the prcBCtmeus ox_^ucidi:ate_Jobule^ This

■JIIR CEREBRUM.

507

district, which is somewhat cjuadrilatcral in form, lies
between the upturned hinder end of the calloso-marginal
fissure and the internal parieto-occipita.1 fissure. Below, it
is imperfectly separated from the limbic lobe by a some-
what \ariable sulcus called the post-limbic sulcus (Fig. 309).
External Surface of the Parietal Lobe. — The gyri and
sulci on the outer surface of the parietal lobe are the
following: : —

Gyri J

Ascending pariclal r)r

1")ostcentral.
Superior parietal lobule.
Inferior ( Supra-marginal,
parietal .' Angular,
lobule. [I'ostparietal.

Sulci--

'Sulcus postcentralis

Intra-

inferior.

parietal

Sulcus postcentralis

of ■

superior.

Turner.

Ramus horizontalis.

.Ramus occipitalis.

Upturned ends of —

{a.) Sylvian.

(/'.) Parallel.

(c ) Second temporal.

The Intraparietal Sulcus of Turner.— This is a composite
sulcus built up out of four originally distinct factors. Two
of these, termed the sulcus postcentralis inferior and the
sulcus postcentralis superior, take a more or less vertical
course across the hemisphere, and are most frequently
continuous with each other. The other two factors are
placed horizontally one behind the other, and they are
called the ramus horizontalis and the ramus occipitalis.

The sulcus postcentralis inferior (Fig. 311, p^) lies behind
the lower part of the fissure of Rolando, whilst the sulcus
postcentralis superior (Fig. 311, /"'") occupies a similar
position in relation to the upper part of that fissure. When
confluent with each other they form a long continuous
furrow, which stretches across the hemisphere behind the
fissure of Rolando and parallel to it (Fig. 308,/^ and/-).

The ramus horizontalis (Fig. 311, f") is continuous with
the upper end of the sulcus postcentralis inferior, and ex-
tends backwards, with a slight inclination upwards, between
the superior parietal lobule, which lies above it, and the
inferior parietal lobule, which lies below it. With the two

5o8

THE BRAIN.

confluent postcentral sulci it presents a figure like the letter
— I placed on its side.

The ramus occipitalis (Figs. 308 and 311,/*) is a curved
sulcus which bounds externally the arcus parieto-occipitalis,
or, in other words, the arching convolution which surrounds
the external parieto-occipital fissure. Sometimes the ramus
occipitalis is linked on to the ramus horizontals — more

Fig. 311. — Diagram to show the correspondence between the
prsecentral and intraparietal systems of furrows.

r. Fissure of Rolando.
p.c.s. Sulcus prascentralis superior.
p.c.i. Sulcus prEecentralis inferior.

h. Ramus horizontalis of sulcus prse-
centralis inferior.
f.m. Sulcus frontalis medius.
w. Fronto-marginal sulcus.

/i. Sulcus postcentralis inferior.
pi. Sulcus postcentralis superior.
p2,- Ramus horizontalis of intraparietal

sulcus.
pi,. Ramus occipitalis.
s.t. Sulcus occipitalis transversus.
p.o. E.xternal parieto-occipital fissure.

frequently it is separate. Its posterior end runs into the
occipital lobe, and behind the arcus parieto-occipitalis it
bifurcates into two widely spread-out branches. These
form a short transverse fissure in the occipital lobe, termed
the sulcus occipitalis transversus (Ecker) (Figs. 308 and
311, jr./.).

The upturned ends of the posterior horizontal limb of
the fissure of Sylvius (Fig. 308, s. asc), of the parallel or

THE CEREBRUM. 509

first temporal fissure (Fig. 308, /'. asc.\ and of the second
temporal sulcus (Fig. 308, /"-. asc.') extend for a short
distance, one behind the other, into the inferior parietal
lol)ulc.

Gyri on the External Surface of the Parietal Lobe. —
The intraparietal sulcus mai)s out three districts or areas on
the outer surface of the parietal lobe. These are the
ascending parietal convolution and the superior and inferior
parietal lobules.

The ascending parietal convolution or gyrus centralis
posterior (Fig. 308, CP.) is a long gyrus which extends
obliquely across the hemisphere from the supero- mesial
border above to the posterior limb of the Sylvian fissure
below. In front it is bounded by the fissure of Rolando,
and behind by the superior and inferior postcentral furrows.

The superior parietal lobule is the area of cerebral cortex
which lies between the ramus horizontalis below and the
supero-mesial border of the hemisphere above. In front it
is bounded by the superior postcentral sulcus, whilst behind
it is connected with the occipital lobe by the arcus parieto-
occipitalis. It is continuous around the supero-mesial
border of the hemisphere with the precuneus.

The inferior parietal lobule lies below the ramus horizon-
talis and the ramus occipitalis, and behind the inferior
postcentral furrow. It is more or less directly continuous
with the occipital lobe behind and the temporal lobe below.
From before backwards it presents three arching convolu-
tions, viz. the supra-marginal, the angular, and the post-
parietal.

The supra-marginal convolution (Fig. 30S) is folded round
the upturned end of the posterior limb of the fissure of
Sylvius, and stands in continuity with the first temporal
convolution. The angular gyrus (Fig. 308) arches over
the upturned end of the parallel or first temporal sulcus,
and is continuous with the second temporal convolution.
The post-parietal convolution (Fig. 308) winds round the
upturned end of the second temporal sulcus, and runs into
the third temporal gyrus.

Sio THE BRAIN.

boundaries of the Occipital Lobe. — The occipital lobe
forms the hinder pyramidal part of the cerebral hemisphere,
and it may be defined as being that portion of the hemi-
sphere which encloses the posterior horn of the lateral
ventricle. On the surface it is very imperfectly mapped off
from the parietal and temporal lobes which lie in front of it.
Being pyramidal in form, it presents thrjee-smfaces and -an
apex or occipital pole. On the mesial aspect of. thg h.emi-
sphere it is separated from the parietal lobe {i.e. the
pfaecuneus) by_the internal parieto- occipital fissure. On
the tentorial or inferior surface it is not marked off in any
way from the temporal lobe and the hippocampal part of
the limbic lobe which lie in front of it. It is necessary,
therefore, on this aspect, to employ an arbitrary line of
demarcation ; one which extends from the prseoccipital
notch on the infero-lateral border of the hemisphere to the
isthmus of the limbic lobe {i.e. the narrow part of the
limbic lobe immediately below the hinder end of the corpus
callosum) will serve the purpose. On the external^ surface
the external pa.rie to-occipital fissure and an arbitrary line
from this to the prseoccipital notch may be regarded _as
separating the occipital from the parietal and temporal
lobes. As a general rule, the upturned end of the second
temporal sulcus lies in the course of this line, and may in
these cases be considered as a bounding furrow.

Mesial Aspect of the Occipital Lohe. — On this surface
we find (i) the calcarine fissure; (2) the cuneusj and (;^
the gyrus lingualis.

The calcari?ie fissure begins on the occipital pole by a
bifurcated extremity which lies in the groove which is
formed on this part of the brain by the lateral sinus.
From this it pursues a slightly arched course forwards, and
ends by cutting into the limbic lobe immediately below the
thickened posterior extremity (splenium) of the corpus
callosum. The calcarine fissure is joined by the internal
parieto -occipital fissure at a point somewhat nearer its
anterior than its posterior extremity. Together the two
fissures present a -<-shaped figure.

TllK CKRKIIKUM.

5"

If the calcarinc and internal parieto-occipilal fissures be fully openeil
uj), su ius to expose the bottom in each case, two well-marked deep or
submerged gyri will be displayed (Fig. 312). One of these, the .i^'rw^
cuHci, marks tilT the parieto-occipital fissure from the calcarinc fissure ;
the other iiiterru])ls the calcarinc fissure immediately behind its junction
with the ]iarieto-occipital. It is called the anterior cuuco-liitgual deep
gyrus, and it divides the calcarinc fissure into an anterior and a posterior
part. The anterior calearine fissjire corresponds very nearly to the
stein of the K-shajied fissural arrangement. It is very deep, and being
a complete fissure, it gives rise to an elevation on the inner wall of the
posterior horn of the lateral ventricle, called the calcar avis or the
hippocampus minor. Tiie posterior ealearine fissure is much shallower.

internal p.irieto-
occipital fissure.

anterior ciineo-
lingual deep gj'rus.

posterior cuneo-
lingual deep gyrus.,-

callosal gyrus,
corpus callosum.
optic thalamus.
L;yrus cunei.

gyrus lingualis.

anterior part of the
calearine fissure.

Kig. 312. — Posterior part of inner surface of the left
hemisphere. The calearine and the internal parieto-occipital
fissures are widely opened up so as to show the deep gyri
within them.

The ciiiicus (Fig. 309) is the wcdgc-shapccl or tiiaiigular
district on the mesial aspect of the occipital lobe which
lies between the internal j)arieto-occipital and calearine
fissures.

The gyrus lingualis (Fig. 3ot^) is a well-marked con-
volution between the calcarinc fissure above and the
posterior part of the collateral fissure below, which stretches
forwards from the occipital pole. Anteriorly it becomes
very narrow, and joins the hippocampal part of the limbic
lobe. It lies partly on the mesial and partly on the
tentorial surface of the occipital lobe.

512 THE BRAIN.

Tentorial Surface of the Occipital Lobe. — On this aspect
there is only one convolution, viz. the posterior part of the
occipito-temporal gyrus (Y'lg. 310). It proceeds continuously
forwards into the temporal lobe on the outer side of the
collateral fissure, and it is bounded externally by the
occipito-te7nporal sulcus — a furrow which is rarely continuous,
but is usually represented by a series of detached pieces.

The External Surface of the Occipital Lobe. — There are
two well-marked sulci on this face of the occipital lobe —
viz. the sulcus occipitalis transversus and the sulcus occipi-
talis lateralis.

The sulcus occipitalis transversus (Fig. 308, s.t^j extends
transversely across the upper part of the lobe behind the
arcus parieto-occipitalis. It has already been described as
the terminal bifurcation of the ramus occipitalis of the
intraparietal sulcus of Turner.

The sulcus occipitalis lateralis (Fig. 308, occ. lat.) is a short
horizontal furrow which divides the outer surface of the
lobe into an upper and a lower area of very nearly equal
extent. These areas are connected by means of superficial
annectant gyri with the parietal and temporal lobes.

The Boundaries of the Temporal Lobe. — The temporal
lobe lies behind the stem and below the posterior horizontal
Hmb of the fissure of Sylvius. It is somewhat pyramidal
in form, and presents an upper, an outer, and a tentorial
surface, with a free projecting apex or pole. Above, it is
bounded by the posterior horizontal limb of the fissure of
Sylvius, together with the artificial line which is drawn
backwards from this. On the tentorial surface it is separ-
ated from the hippocampal part of the limbic lobe by the
collateral fissure, whilst behind, it is marked off from the
occipital lobe by the arbitrary lines already described
(p. 506). The apex or temporal pole projects forwards on
the under surface of the brain beyond the stem of the
Sylvian fissure. It should be noticed that the recurved
extremity of the hippocampal part of the limbic lobe
(uncus) which lies to the inner side of the temporal pole
does not project so far forwards as the latter, and is separ-

THE CEREBRUM. 513

ated from the pole by the incisura temporalis. This sulcus
may be regarded as the connecting link between the
anterior ends of the collateral fissure and the inferior
limiting sulcus of Reil.^

Upper or Opercular Surface of the Temporal Lobe. — This
is the surf:ace of the temporal operculum which is opposed
to the island of Reil and the fron to-parietal operculum.
The fissure of Sylvius must therefore be widely opened up
to expose it. For the most part the surface is smooth, but
towards its back part there are a few shallow transverse
furrows, called the sulci of Heschl^ whilst in front, on the
deep aspect of the temporal pole, two or three furrows are
also evident.

Outer Surface of the Temporal Lobe. — On this aspect
of the lobe there are two horizontal sulci, called respectively
the first temporal, or parallel, and the second temporal
sulcus.

T\\Q parallel sulcus (Fig. 307, t^) is a long continuous and
deep fissure which begins near the temporal pole, and
proceeds backwards below the posterior limb of the Sylvian
fissure. Its hinder end turns upwards into the parietal lobe,
and is surrounded by the angular gyrus.

The second temporal sulcus is placed midway between the
parallel sulcus and the infero-lateral border of the hemi-
sphere. It is very rare to find it in the form of a continuous
cleft. Usually it is broken up into several isolated pieces,
placed one behind the other. Its hinder part, which turns
upwards into the parietal lobe (Fig. 308, /- asc.\ and is
surrounded by the post-parietal gyrus, lies close to the
artificial line of demarcation between the occipital and
parietal lobes.

By the two temporal sulci the outer surface of the
temporal lobe is mapped out into three tiers of horizontal
convolutions, which are termed the first^ second^ and third
temporal gyri {¥'\g. 308, T\ T-, and T^).

' The importance of this connection is evident when we remember that,
strictly speaking, the inferior hmiting sulcus of Rcil is the true upper limit
of the temporal lol>e.

VOL. II. — 33

514 THE BRAIN.

Tentorial Surface of the Temporal Lobe. — On this
surface there is one fissure, termed the occipito-temporal

sulcus. ..._ ,.

The occipito-temporal sulcus (Fig. -^lo^ occ. te?np.) lies to
the outer side of the collateral fissure and close. _to the
infero- lateral border of the hemisphere. It runs in an
antero -posterior direction, and is not confined to the
temporal lobe, but extends backwards towards the occipital
pole. It is usually broken up into two or more separate
pieces.

The occipito-temporal convolutioti (Fig. 310) is situated
between the collateral fissure and the occipito-temporal
sulcus. It extends from the occipital pole behind to the
temporal pole in front.

The narrow strip of surface on the outer side of the
occipito-temporal sulcus is continuous round the infero-
lateral margin of the hemisphere with the third temporal
convolution on the outer surface of the cerebrum, and may
be reckoned as a part of it.

The three temporal convolutions and the occipito-
temporal convolution run into each other at the temporal
pole.

The Island of Reil or Insula. — The insula, ig a triangular
field,^ cerebral cortex which lies on a deeper plane than
the general surface of the hemisphere, and is hidden from
view by the four opercula which overlap it (p. 498). It is
bounded -by a distinct limiting sulcus (sulcus circularis
Reilii), which has already been described, and its dependent
apical part, which looks downwards, is in close relation to
the Sylvian vallecula and the anterior perforated spot on
the base of the brain.

The insula is divided into several diverging convolutions
by ^series of radiating sulci. Of the latter, one, which
presents the same directjon^and , lies iruthja-saJiLe-plaHfi..^.?
the fissure of Rolando, receives the naxne of the sulcus
centralis insula. It divides the insijja into an— ant£rior
frontal part and a posterior pari^to-ljvibif, pad!i,nn, -

Olfactory Lobe. — The olfactory lobe is small and rudi-

THE CEREBRUM.

5>5

mentary in the human brain. It is described by His as
consisting of a fyosterior lobule^ which inay be said to
correspond with that part of the cerebral cortex whicli is
named the locus perforatus anticus, and •xnanlcrior lobule
composed of (i) the olfactory bulb and tract, with the two

S.K.-v.

/.CL«. ..s,«.

S.R.rt. -'

Fig. 313.

-Fissures and gyri on the surface of the insula.
(Eberstaller. )

I, 2, and 3. Three short gyri on the

frontal part of the insula.
4 and 5. Two gj'ri on parieto-limbic part.
S.R.rt. Anterior limiting sulcus.
S.R.J. Superior limiting sulcus.
S.R./. Inferior limiting sulcus.
L. Limen insula;.
P. Pole of the insula.
F. Orbital operculum (for the most part

removed).

T. Temporal pole.
Ti. First temporal g>Tus.
Tz. Second temporal gjTus.
x.y. Gyri of Heschl.
s.i. Sulcus centralis insulae.
s.a. Sulcus praccentralis insuls.
III. G>Ti on deep surface of temporal
pole.

rnnt;j of th.^ Intt.T • (2) the trigonum olfactorium; and (3)

Tlii; n/f.irforv trc^t is a narrow white prismatic band,
which .■vprinrU .n ntt;n(,)rly into a swollen bulbous extremity
termed the olfactofx bulb. Both the tract and the bulb lie

Si6 THE BRAIN.

upon the olfactory sulcus on the orbital surface of the
TrbntalTobe, whilst the inferior surface of the bulb rests on
the cribriform plate of the ethmoid bone, and receives the
numerous olfactory nerves which reach it through the
foramina in that part of the cranial floor.

Posteriorlv. the olfactory tract will be seen to divide into
tjvn diverging rnntc: of afj-achmenL The mesial root curves
abruptly inwards, and may be followed into the extremity of
the callosal ^yrus {i.e. the anterior end of the limbic lobe).
The lateral root runs backwards and outwards over the
outer part of the locus perforatus anticus, and gradually
disappears from view. . In animals, in which the olfactory
apparatus is better developed than in man, it may be traced
into the uncinate extremity of the hippocampal convolution
{i.e. posterior end of the limbic lobe).

The tri^onu?n olfactorium is the little triangular field of
grey matter which occupies the interval between the roots
rif the olfactory tract at the point where they begm'to
diverge.

The area of Broca lies in front of the curved mesiaLmot
of the olfactory tract, and is continuous with the commence-

rqfpl- nf tVie rannc;a1 gyruS.

Limbic or Falciform Lobe. — This lobe is seen on the
mesial surface of the hemisphere, in the form of an elongated
ring -like convolution, the extremities of which approach
closely to each other at the locus perforatus anticus. These
extremities have been .qpt^n to be connected bv the roots
of the olfactory tract, and in this manner the limbic ring
rnay be considered to be closed.

The upper part of the limbir. Inbe is placed in intimate
relation to the extremities and upper surface of the corpus
callosum, and receives the name of raU/xial rmvpnlution or
p^lru f £nri^.r.atus. The lower portion of the lobe is termed
the hippocampal convolution and forms the inner part of the
tentorial face of the hemisphere. The continuity between
the hippocampal gyrus and the collosal convolution is
estabhshed below the hinder end of the corpus callosum
posteriorly by a narrow portion of the limbic lobe called

THE CEREPRUM. 5«7

tlie isthmus. From this i)oint the hippocampal gyrus
extends forwards towards the tcnii)oral pole. Einally, on
the side of the crus cerebri, tlxe J^ippocampal convolution
is folded back on itself, and ends in a recurved hook-like,
extremity, termed the uncus. The uncus does not reach
so far forwards as the temporal pole.

The callosal convolution begins below the anterior end of
the corpus callosuni at the locus perforatus anticus, and
winding round the genu of the callosum, it is continued
backwards on its upper surface to the hinder thickened
extremity or splenium. Finally, curving round this it
becomes greatly narrowed through the calcarine fissure
cutting into it. This narrow part is termed the isthmus.,
and constitutes the link of connection between the callosal
gyrus and the hippocampal gyrus.

The callosal gyrus is separated from the marginal con-
volution by the calloso-marginal fissure. Behind this it is
imperfectly marked off from the precuneus by the post-
limbic sulcus. From the corpus callosum it is separated
by the callosal sukus.

The hippocampal convolution is bounded on the outer
side by the anterior part of the collateral sulcus, and in ^
front of '^hi'^ ^'V '^*''ii inrijura temporalis, which separates its
hooked extremity, or uncus, from the temporal pole. On
its inner side it is Ijniited by the hippornmpal or dentate

fissure, whilst posteriorly, \\ '< rUvJH.Tl intn Xwcs pnrf<^ hy

the anterior extremity of -the -calcarine fissure. Of these,
the -upj3er- i^s■ the isthmus. ■which-CQnDj.:'"t-s it willi tlie

callosal gvrUS. whilst iK.- l(^vvr>r pnrtj^^p liripjT-i_H; itUo

direct continuity with the gyrus_Jingualis or infracalcarine
convolution.

If the dentate fissure wliich lies along the inner side of the liippo-
canipal convolution be now opened up, the i^yrus dcntalus and the
fiinbria lying side by siile will be brought into view.

The Fimbria (Fig. 314) is simply a portion of the
posterior pillar of the fornix prolonged into this region.
It is a conspicuous band of white matter, which presents a

5i8

THE BRAIN.

prominent free border. In front it runs into the recurved
extremity of the uncus, whilst, if it be traced backwards, it
will be seen to curve upwards behind the posterior end of
the optic thalamus and become continuous with the
posterior pillar of the fornix below the hinder part of the
corpus callosum.

If the handle of a scalpel be passed_ deeply into the brain

posterior part of lenticular
nucleus.

/ tail of caudate nucleus in the roof of
the descending horn of the lateral
ventricle.

taenia semicircularis.

fascia dentata at
the bottom of
the dentate
fissure.

fimbria.

descending cornu oi
lateral ventricle.

choroid plexus.

hippocampus major,
collateral fissure.

Fig. 314.— Coronal section through the lower part of the
left cerebral hemisphere (chimpanzee). The section passes
through the hippocampal convolution and the dentate
fissure. The pia mater is represented by a dotted line, and
it is seen to pass in towards the choroid plexus through the
lower part of the great transverse fissure of the cerebrum.

a|^mze„t}^p fimbria, it passcs directly into the descending
horn of the lateral ventricle. The gap through which it is
introduced is a part of the great transverse fissure of the
brain.

The Gyrus Dentatus (dentate fascia) is a fine free edge
of grey matter, which is placed between the fimbria and the

THE CEREBRUM. 519

dcc]) part of the upper surface of the hippocampal convolu-
tion. It is slightly notched along the margin, whilst iTs
surface is scored by numerous parallel and closely-placed
transverse grooves. It begins behind in the region of the
splcnium (the thickened posterior end of the corpus
callosum), and it is carried forwards into the cleft of_the
tincus.

Dentate Fissure. — This is a complete fissure, and the
elevation on the vcntriculnr wnll, >vhirh corresponds to Jt,
is called the hippocampus major (Fig. 3 1 4). It begins
behind the splenium of the corpus callosum, where it
is continuous with a shallow part of the callosal fissure,
and it proceeds forwards between the gyrus dentatus and
the hippocampal convolution. Its anterior end is enclosed
within the uncus.

Dissection. — A dissection should now be made with the view of
exposing the upper surface of the corpus callosum — the commissural
band which stretches across between the cerebral hemisphere at the
bottom of the great longitudinal fissure. With a long knife slice off
the top of the right hemisphere at the level of the calloso-marginal
fissure. The white medullary centre of the cerebral hemisphere, en-
closed on all hands by the grey cortex, is brought very conspicuously
into view, and the appearance receives the name of ceutruni ovale
minus. From the central white mass medullary prolongations proceed
into all the convolutions.

A transverse incision may next be made through the middle of the
callosal convolution, and insinuating the fingers gently under it, the
dissector should proceed to tear it away from the hemisphere in an out-
ward direction. If this be carried out successfully, the manner in
which the fibres of the corpus callosum enter the hemisphere will be
seen. In cases where the student is dissecting the brain for ihe second
lime, the knife should not be used at all in carrying out this dissection.
The top of the hemisphere down to the level of the calloso-marginal
fissure should, in the first instance, be torn oft", and then the callosal
convolutions may be treated in the same way. By this expedient the
fibres of the callosum may be traced into the convolutions.

The two figures which follow this paragraph show the relation of
the infero- lateral and the supraciliary borders of the cerebral hemisphere
to the surface of the cranium. In A. a profile view of the skull is given ;
in B. the skull is turned so that it is viewed from the front as well as
from the side. The outline of the cerebrum was obtainetl by perforating
the cranium from the inside along the border of the hemisphere with a

520

THE BRAIN.

fine drill. The manner in which the infero-lateral border of the fore-
part of the temporal lobe is depicted in both figures is perhaps somewhat
misleading. It is very difficult to say at this point what is the infero-
lateral border of the hemisphere : the outer surface passes insensibly
into the inferior or basal surface. It must be clearly understood, there-

E.O. P. External occipital pro-
tuberance.
S.M. Supraciliary margin of
the cerebrum.
I. L. M. Infero -lateral margin of
the cerebrum.
L.S. Position of the highest
part of the arch of the
lateral sinus.
R. Fissure of Rolando.
Si. Anterior horizontal limb

of Sylvian fissure.
82. Anterior ascending limb

of Sylvian fi.ssure.
S3. Posterior horizontal limb
of Sylvian fis.sure.
P.B. Pars basilaris of the in-
ferior frontal convolu-
tion.
P.T. Pars triangularis of the
inferior frontal convolu-
tion.
P.O. Pars orbitalis of the in-
ferior frontal convolution.

B.
Fig. 315. — To show the relation of the infero-lateral and
the supraciliary borders of the cerebral hemisphere to the
surface of the cranium.

PLATE II

The head of an adult female, 35 years of age, in which the brain is
exposed in situ. Bars of Ixinc are left along the lines of the cranial
sutures, and also along the line of the temporal ridge.

Frontal lobe,
Parietal lobe,

blue,
pink.

Occipital lobe,
TemporaJ lobe.

brown,
yellow.

THE CEREBRUM. 521

fore, that the line immediately above the zygomatic arch does not
indicate the deepest part of this portion of the temporal lobe. The
extremity of the lobe curves downwards and inwards, and attains a
depth considerably below the level of the upper border of the zygo-
matic arch.

The Cingulum. — If the deep surface^f die callosal con;
yolution which has been torn away be examined, a large
bundle of longitudinally directed fibres will be noticed
embedded in its substance. This is the cingulum. It can
be easily dislodged, and a very slight degree of traction is
all that is required to lift it out of its bed. In tront it

beg^ins a^the locus perforatus anticus, whilst — behind it

turns round the hinder end of the callosum, and enters
the hippocampal convolution. It belongs, therefore, to
the limbic lobe^

Dissection. —The g)Ti and sulci on the mesial surface of the left
hemisphere may now be studied, and then the dissection, which has
been carried out with the view of exposing the corpus callosum, may
be repeated on the left side. In doing this, however, take care not to
injure the mesial surface of the left hemisphere further back than the
parieto-occipital fissure. Indeed, an effort should be made to preserve
that fissure intact, so that it and the cuneus may be afterwards studied
on this side in connection with the gyri and sulci on the under surface
of the hemisphere.

The upper surface of the corpus callosum is now exposed, and it will
be seen that, stretching between the two hemispheres, it unites into one
mass the two medullary centres of the two hemispheres. The continu-
ous white field, consisting of the corpus callosum and the medullary
centre of each hemisphere, receives the name of centrum ovale majus.

Corpus Ca.nosiim. — This is the great transverse commis-
sure of the cerebrum. It is placed nearer the anterior than
the posterior end of the brain, and it unites the inner sur-
faces of the two cerebral hemispheres throughout very nearly
a half of their antero-posterior length. Looked at as a whole,
it is highly arched from before backwards, and presents a
convex upper surface and a concave lower surface.

The uf>(^cr surface of tlie corpus callosum foiuis thi' bottom
of the great longitudinal fissure, and on each mJc-oLlhis it
is covered by the callosal convulutijjn. Only in its posterior
part is it touched bv ^he filv r.-nbri ; in front, this process

522

THE BRAIN.

of dura mater falls considerably short of it. The upper
surface of the callosum is streaked in the transverse direction
—an indication that this structure is for the most part com-
posed of transversely directed bundles of nerve-fibres passing
from one hemisphere to the other. Certain longitudinal
markings are also evident in casesjwhere the brain has been
carefully preserved. In the mesial plane there is a shallow
lonp;itudinal groove, termed the raphe^ On either side of

foramen of Monro, anterior pillar of fornix.

anterior
commissure.

optic chiasma.

6 lamina quadri-
gemina.

Fig. 316. — Mesial section through the corpus callosum
and the parts subjacent to it. (From Gegenbaur. )

1. Infundibulum.

2. Corpus mammillare.

3. Grey commissure.

4. Ta;nia fornicis.

5. Pineal body.

5. Aqueduct of Sylvius.

this there is a low-lying but distinct ridge, formed by a
slender white tract of nerve fibres, called the <;ffia Jmi.ntijjii-
nalis medialis. Again, to the outer side of__this, and under
cover of the callosal gyrus, there are other feebly-marked
longitudinal ridges, termed the stricz Iniii^itudinaJe.!^ lateraks.
The two extremities of the corpus callosum (Fig. 316) are
greatly thickened, whilst the intermediate part, often' called
i/iehody, is considerably tTiinner. The massive posterior
end, which is full and rounded, "lies over the mesencephalon^

THE CEREBRUM.

523

a II d extends l)ack\vards as far as the highest goint of the
cerebdluni. It is called the splenium. The anterior end,
which is not quite so massive, is folded downwards and
backwards upon itself, and is called the.t.'tv//<'. The recurved
lower portion of the genu is separated from the part of the
corpus callosum which lies above by an interval ; it rapidly
thins as it passes backwards, and is termed the rostrum.

Gen. c

Lo- frc

N. olf.

Chiasma

Fig. 317. — Anterior end of the corpus callosum and its
peduncles, as seen from l>elo\v when the hemispheres are
slightly separated from each other. {From Cruveilhier. )

Gen. c. cal. Genu of the corpus callosum.
Lo. fro. Frontal lobe.
Chia.sma. Optic chiasma.

Pe. c. cal. Peduncle of corpus callosum.
R. gr. opt. Lamina cinerea.
N. olf. Olfactory tract.

The fine terminal edge of the rostrum has already been
seen to be connected with the lamina cinerea.

Both t h^" l.itt-rnl and the mesial longitudinal s t rise^jv-jii^i
tr.ir.>H backwards, are seen to turn round the splenium, and
run into the corresponding gyrus dentatus. In front, the
mesial sy^ art' carried round the {j'-"", ■Tit'I thrn backwards
on the under surface of the rostrum. Finally^ diverging;
from each other, tlu-v receive the name of the (^tdiincks oj'
t/ie corf>us callosum. Each of these proceeds backwards

524 THE BRAIN.

and outwards along the posterior limit of the anterior per-
forated spot to the anterior extremity of the temporal lobe.

To some extent the direction which is taken by the fibres of the
corpus callosum, as they radiate outwards into each cerebral hemisphere
to reach the convohitions, is seen in the present dissection. Two sets of
fibres are more conspicuous than the others. One of these, the forceps
minor, proceeding from the genu, curves forwards into the fore-part of
the frontal lobe ; the other, called the forceps major, issues from the
under part of the splenium, and takes a bold sweep backwards into the
occipital lobe. The term tapettim is given to a layer of fibres which
comes from the body of the corpus callosum, and curves outwards and
downwards so as to roof over and form the outer walls of the descend-
ing and posterior cornua of the lateral ventricle.

Dissection. — The lateral ventricle in the interior of the cerebral hemi-
sphere should now be opened up on each side. The corpus callosum,
which forms the roof, the body, and anterior horn of this cavity, must
therefore be partially removed. Make a longitudinal incision through
this structure about half an inch or less from the mesial plane on each
side. The central portion of the corpus callosum which lies between
these incisions is to be kept in position. The lateral portions must
be turned outwards and detached completely. As this is being done, it
will become evident that the lower part of the splenium which is pro-
longed into the forceps major is in reality a portion folded forwards in
close apposition with the under surface of the hinder end of the corpus
callosum. Be careful to leave the forceps major in its place.

The body and the anterior horn of the ventricle are now exposed ; but
the cavity of the ventricle is carried backwards into the occipital lobe in
the form of a posterior horn, and downwards and forwards into the
temporal lobe in the form of the descending horn. The posterior horn
can only at present be opened on the right side. Carry the knife back-
wards through the medullary substance which forms its roof, and remove
a sufficient amount of this to give a complete view of the interior of jthis
part of the cavity. Greater difficulty will be experienced in opening up
the descending horn. Place the point of the knife in the upper part of
the horn where it joins the body of the ventricle, and carry the blade
in a downward and forward direction through the outer part of the tem-
poral lobe towards the temporal pole, following the course of the cavity.
This corresponds very nearly with the course of the parallel fissure.
The outer wall of the descending horn is thus incised, and a sufficient
amount of the outer part of the temporal lobe must be removed to give
a view of the cavity. In doing this, the temporal operculum will be
taken away, but the surface of the insula should be preserved from
injury.

Lateral Ventricle. — The dissector will now perceive

THE CEREBRUM.

525

that each cerebral hemisphere is hollow. The cavity, in
the interior is called the lateral ventricle, and is lined by a
tiiin dark-coloured layer, which is termed the ependynia.
Ill health the walls of the cavity are in most localities more
or less closely applied to each other, and within the space
there is only a small amount of cerebrospinal fluid. The

Fig. 318. — :\ drawing taken from a cast of tlie ven-
tricular .svsteni of the brain. (From Schwalbe, after
W'elcker. )'

///. Third ventricle.
//'. Fourth ventricle.
F.M. Foramen of Monro.
a. Aqueduct of Sylvius.
r.l. Lateral recess of the fourth
ventricle.

c.a. Anterior horn of lati;ral ventricle.
c.i. Descending horn.
c.p. Posterior horn.
//. Depression corresponding to pro-
minence of hippocampus major.

lateral ventricle communicates with the third ventricle of
tTTe brain by means of a small foramen, just large (.'iiough
to admit a crow-quill, which is termed t he Joraimnjjf^Alonro.

526

THE BRAIN.

This aperture is placed in front of the fore end of the optic
thalamus, and behind the anterior pillar of the fornix.

The shape of the lateral ventricle is very irregular, and
can be best understood by the study of a plaster cast of its
interior (Fig. 318). It is divided into a body and three
horns, viz. an anterior, a posterior, and a descending horn.
The description of an anterior horn is highly artificial.
The anterior horn is that part of the cavity which lies in
front of the foramen of Monro. The body is the portion

■great longitudinal
fissure.

genu of corpus
callosum.

extremity of the
anterior horn of
lateral ventricle.

■great longitudinal
fissure.

Fig. 319. — Coronal section through the anterior part
of the cerebrum.

of the ventricle which extends from the foramen of Monro
to the splenium of the corpus callosum. At this point the
posterior and descending horns diverge from the hinder
end of the body. The posterior horn curves backwards and
inwards into the occipital lobe. It is very variable in its
length and capacity. The descending horn proceeds with a
bold sweep round the hinder end of the optic thalamus, and
then tunnels in a forward and inward direction through the
temporal lobe towards the temporal pole.

Anterior Horn of the Lateral Ventricle. — The anterior
horn forms the foremost part of the cavity, and extends in

THE CEREBRUM.

5^7

a forward and outward dircctionjn the frontal lobe. When
seen in coronal section it presents a triangular outliriC: — the
floor sloping upwards and outwards, to meet the roof at an
acute angle (Fig. 320). 1^ is bounded in front by the
posterior surface of the genu of the corpus callosum, whilst
the roof is formed by the fore-part of the same structure.
The inner wall^ which is vertical, is formed by the septum
lucidum. — a thin mesial partition between the lateral
ventricles of opposite sides. The sloping ^qr presents

Fig. 320. — Coronal section through the cerebrum a short
distance behind that depicted in Fig. 319.

1. Caudate nucleus.

2. Internal capsule.

3. Lenticular nucleus.

4. Claustrum.

5. Great longitudinal fissure.

6. Corpus callosum.

7. Septum lucidum.

8. Anterior horn of lateral ventricle.

a marked elevation or bulging, viz. the smooth rounded
and enlarged anterior extremity of the pear-shaped caudate
nucleus.

The Body of the Lateral Ventricle isjikewise roofed by
the cojpus callosum. On the inner or mesial side it is
bounded by the hinder part of the septum lucidum, and
behind this by the attachment of the forni.x to the under
surface of the corpus callosum. On the outer side it is

528 THE BRAIN.

closed, as in the case of the anterior horn, by the meeting
of the roof and the floor of the cavity.

On t]\& ^oor a number of important objects may be
recognised. From without inwards, and, at the same time,
to some extent from before baclcwards, these arejj-(i) the
caudate nucleus ; (2) a groove which extends obliquely from
before backwards and outwards between the caudate nucleus
and the optic thalamus, and in which are placed the vein
of the corpus striatum and a white band called the tsenia
semicircularis ; (3) a portion of the upper surface of the
optic thalamus ; (4) the choroid plexus ; (5) the thin sharp
lateral edge of the fornix.

The caudate nucleus as it proceeds backwards on the
outer part°~of the floor of the body of the lateral ventricle
narrows very rapidly.

The vein of the corpus striatian is exposed in the groove
between the caudate nucleus and the optic thalamus, if the
ependyma which covers it be scraped away. It joins the
vein of Galen at the foramen of Monro. In the same
groove is placed the tceyiia semicircularis — a narrow band of
white matter, which when traced forwards \fi\\ be found to
pass for the most part into the anterior pillar of the fornix.

The portion of the upper surface of the optic thalamus,
which appears in the floor of the lateral ventricle, is in
great part covered by the choroid plexus (plexus choroideus
lateralis). The latter is a rich vascular fringe which appears
from under cover of the sharp lateral edge of the fornix.
In front, it is continuous, behind the foramina of Monro,
with the corresponding choroid plexus of the opposite side,
whilst behind it is carried into the descending horn of the
ventricle. Although the choroid plexus has all the appear-
ance of lying free within the ventricle, it must be borne in
mind that it is invested by an epithehal layer which excludes
it from the cavity, and which is connected on the one hand
to the sharp margin of the fornix, and on the other to the
upper surface of the optic thalamus.

Posterior Horn of the Lateral Ventricle, — The posterior
horn is a diverticulum carried backwards into the occipital

THE CEREBRUM.

529

lobe from the hinder end of the body of the ventricle. It
tapers to a point and describes a gentle curve, the con-
vexity of which is directed outwards. The roof and oukr
wail o{ this portion of the ventricular cavity i^ formed by
the tapetum of the corpus callosum.

Upon the imier walliyso elongated curved elevations
may be observed. The uppermost of these is termed the
bu/d of the cornii (bulbus cornu posterioris) and is produced

splcnium of corpus
callosum.

bulb of the cornu.

posterior cornu

of the lateral

ventricle.

~~j hippocampus minor.

calcarine fissure.

Fig. 321. — Coronal section through the posterior horn
of the right lateral ventricle.

by the fibres of the forceps major as they curve abruptly
backwards from the lower part of the splenium of the
corpus callosum into the occipital lobe. Below this is the
elevation known as the hippocampus minor or the calcar avis.
It varies greatly in size in different brains, and is caused
by an infolding of the ventricular wall in correspondence
with the anterior calcarine fissure on the exterior of the
hemisphere.

On i\\c floor of the posterior horn, close to the hippo-
campus minor, a third elongated elevation may be visible.

VOL. II. — 31

530 THE BRAIN.

This is produced by a bundle of longitudinal fibres, termed
the. fasciculus longitudinalis inferior^ which passes from the
occipital into the temporal lobe.

Dissection. — The dissector should now gently insinuate his fingers
underneath the fronto-parietal operculum of the insula and tear this
portion of the cortex away in an upward direction. The frontal
operculum (pars triangularis) and the orbital operculum should Be
dealt with in the same manner. The greater part of the temporal
operculum has already been removed in opening up the descending
horn of the ventricle. The insula or island of Reil is therefore fully
exposed to view, and its relation to the parts in the interior of the
ventricle can be seen.

Descending Horn of the Lateral Ventricle. — The

descending horn must be regarded as the direct continuation
of the main ventricular cavity, into the temporal lobe. The
posterior horn is merely a diverticulum carried backwards
from the main cavity. At first directed backwards and out-
wards, the posterior horn suddenly sinks downwards behind
the optic thalamus into the temporal lobe, in which it takes
a curved course forwards and inwards to a point about an
inch behind the extremity of the temporal pole.

The roof of the descending horn is formed for the most
part by the tapetum of the corpus callosum. At the
extremity of the horn, the roof presents a slight bulging into
the ventricular cavity. This is the amygdaloid tubercle and
it is produced by a superjacent collection of grey matter,
termed the amygdaloid nucleus. The tcenia semicircularis
and the greatly attenuated tail of the caudate nucleus are both
prolonged into the descending horn, and are carried forwards
in its roof to the amygdaloid nucleus in which they both
end.

On the floor of the descending horn the dissector will
observe the following parts : (i) the hippocampus major ;
(2) the choroid plexus; (3) the fimbria; (4) the trigonum
ventriculi ; and (5) the eminentia collateralis.

The Hippocampus Major (cornu ammonis) is for the
most part covered by the choroid plexus. It is a prominent
elevation on the floor of the descending horn of the lateral

THE CEREBRUM. 531

ventricle, and is strongly curved in conformity with the
course taken by the horn in which it lies. It therefore
presents an internal concave border and an external con-
vex margin. Narrow behind, it enlarges as it is traced
forwards, and it ends below the amygdaloid tubercle in a
thickened extremity which presents some faint grooves or
notches on its surface. In consequence of this, the anterior
end of the hippocampus major receives the name of the
pes hippoawipi. The hippocampus major is the internal
elevation which corresponds to the dentate or hippocampal
fissure on the exterior of the cerebrum.

Tlie Fimbria (taenia hippocampi) is a narrow but very
distinct band of white matter which is attached by its outer
margin along the concave inner border of the hippocampus
major. The white matter composing it is continuous with
the thin white layer (alveus) which is spread over the sur-
face of the hippocampus major, and it presents two free
surfaces and a sharp free inner border. The fimbria has
already been examined in connection with the hippocampal
fissure and the gyrus dentatus, and the relations which it
presents to the posterior pillar of the fornix and the uncus
have been pointed out (p. 517).

Inferior Fissure of the Cerebrum. — \\^hen the pia mater
in the region of the hippocampal fissure is removed from
the surface of the brain, the choroid plexus in the interior
of the descending horn of the lateral ventricle is usually
withdrawn with it, and a fissure appears between the fimbria
and the roof of the ventricular horn. This is termed the
inferior fissure of the cerebrum or the lower part of the greixt
transverse fissure. By the withdrawal of the choroid plexus,
it is converted into a gap which leads directly from the
exterior of the brain into the interior of the descending
horn of tlie lateral ventricle (Fig. 314).

The Choroid Plexus is a convoluted system of blood-
vessels in connection with a fold of pia mater which is
prolonged into the descending horn of the lateral ventricle
through the inferior fissure of the cerebrum. It lies on the
surface of the hijjpocampus major, and is continuous

532

THE BRAIN.

behind the posterior border of the optic thalamus with
the choroid plexus in the body of the lateral ventricle.
But it must not be supposed that the choroid plexus lies
free in the ventricular cavity. It is clothed in the most

hippocampus major,

emmentia _
collaterali;

tngonum -
ventriculi.

incisura temporalis.

amygdaloid tubercle.

- hippocampal convolution.

- gyrus dentatus.

posterior pillar of
the fornix cut
across.

splenium of the
corpus callosum cut
across.

sf bulbus cornu posterioris.

posterior horn.

hippocampus minor.

Fig. 322. — The detached occipital and temporal lobes
of the cerebrum, with the descending and posterior horns
of the lateral ventricle opened from above. (From
Schwalbe. )

intimate manner by an epithelial layer, which represents
the inner or mesial wall of the descending horn pushed
into the cavity by the choroid plexus. The ventricle,
therefore, only opens on the surface through the inferior

THE CEREBRUM. 533

cerebral fissuri.' when this thin epithelial layer is lorn away
by the withdrawal of the choroid plexus.

The Trigonum Ventriculi (Fig. 322, //-.?•.) is a smooth
triangular surface on the floor of the ventricle at the junction
of the posterior and descending horns. The hippocampus
minor and the hippocampus major as they diverge from each
other — the former curving backwards into the posterior horn
and the latter curving forwards into the descending horn —
bound the trigonum ventriculi in front and behind.

The Eminentia Collateralis is not always present. It
may be recognised on the floor of the descending horn on
the outer side of the hippocampus major as an elevation of
very varying dimensions. It corresponds to the middle
part of the collateral fissure on the inferior surface of the
hemisphere.

Dissci'lioii. — The remains of tlie right temporal lohe and of the right
occipital lobe should now be detached from the cerebrum by cutting
through the fimbria where it passes into the posterior pillar of the
fornix and the forceps major of the splenium of the corpus callosum.
The knife should then be carried forwards from the anterior extremity
of the descending horn above the level of the uncus through the temporal
pole. The temporal lobe, with the hippocampal convolution along its
inner side, can then be separated from the remainder of the brain, along
the line of the inferior fissure of the cerebrum. In the detached part
of the cerebrum (Fig. 322) a good view is obtained of the floor of the
descending horn and of the parts in relation to it. Further, by replacing
it in position, the inferior cerebral fissure can be better understood, and
by turning the brain upside down a view of the roof of the descending
horn and the structures in relation to it is gained. In this way the tail
of the caudate nucleus and the tivnia semicircularis can be traced into
the amygdaloid nucleus.

The cut edge of the central part of the corpus callosum, which is still
in position, should now be still further pared away, so as to bring more
fully into view the subjacent septum lucidum and the fornix.

Septum Lucidum (septum pellucidum). — This is a thin
vertical partition which intervenes between the anterior
cornua and the fore-parts of the bodies of the two lateral
ventricles (Fig. 316). It is triangular in shape, and
posteriorly it is prolonged backwards in the narrow
interval between the body of the corpus callosum and

534 THE BRAIN.

the fornix, to both of which it is attached by its upper
and lower edges. In front it occupies the gap behind the
genu of the corpus callosum ; whilst below, in the narrow
interval between the rostrum of the corpus callosum and
the fornix, it is prolonged downwards to the base of the
brain as \he. peduncle of the septum lucidum.

The septum lucidum is composed of two thin laminse in
apposition with each other in the mesial plane. The mesial
cleft between the layers is termed the fifth ventricle (Figs. 320
and 324).

Dissection. — The narrow middle strip of the corpus callosum, behind
the bend of the genu, should now be removed. Cut it transversely
across behind the genu, and, gently raising it, separate the upper edge
of the septum lucidum from its lower surface. Further back, behind
the septum lucidum, it will be found to lie upon and to be anatomically
connected with the upper surface of the fornix. This connection must
also be severed. The left forceps major should be preserved, so that
its connection with the occipital lobe may be more fully made out at a
later stage. By snipping off the upper edge of the septum lucidum with
the scissors, the two laminae, with the interposed cleft or fifth ventricle
will be exposed.

Fifth Ventricle. — This is the name which is applied to
the mesial cleft between the two laminse of the septum
lucidum. It varies greatly in extent in different brains
and contains a little fluid. It is completely isolated and
presents no communication with the other ventricles or
with the surface. Indeed, the term " ventricle " is somewhat
inappropriate, because its developmental history shows that
it has nothing in common with the general ventricular
system of the brain. Each of its bounding laminse consists
of three thin strata, viz. an internal grey layer, an inter-
mediate white layer, and a layer of ependyma, continuous
with the lining ependyma of the lateral ventricle.

_Foriii.x. — The fornix is an arched bilateral structure,
composed of longitudinally directed fibres. In its inter-
mediate part, its two lateral halves are joined together in
tHe mesial plane, and form what is called the body of the
fornix, but in front and behind they are quite separate, and
constitute the anterior and posterior pillars of the fornix.

THE CEREBRUM. 535

The body of the fornix is triangular in shape. In front,
where it is continuous with the anterior pillars, it is narrow,
whilst behind it broadens out, becomes flattened, and is
prolonged into the posterior pillars. The upper surface of
the body of the fornix is in contact wiUi the under surface
of the cQrpus callosum^and in the mesial plane is adherent
to^iuand also^ to the posterior part of the lower edge of the
^fipiuui lucidum. Its lateral edges are free, and extend
outwards in the floor of the lateral ventricles. TThe lower
surface of the body of the fornix rests upon the velum
[nj^^rpositiim, a fold of pia yg^j^

mater whi£li_s£jiarate§._it from po.
the i"oof of .the third ventricle .^,.'
and till- ii[)per surfaces of the .„^. ,
two ()[)iir thalami. jo»

The autcrior pillars of the

fornix (columnre fornicis) are

two rounded strands which

c ,.\ ,. • ^ Fig. ■xQ.-i. — Diagram of the

_enierge^ from the anterior part ^^^3 /. ^^^^^^ ^^ ^.^^^.^

of the body of the fornix, and

then diverge very slightly from each other as they curve

downwards in front of the foramen of Monro. Sinking into

the grey matter on the lateral wall of the third ventricle,

ea^h__ani£rior— hoFn—proceeds downwards to the base of

the_brain^ where it protrudes in the form of the corpus

mammillare. ^l^his appears to be a twisted loop of the

anterior pillar, in which the pillar turns upon, itself, and is

then continued upwards and backwards into the anterior

tubercle of the optic thalamus. As there is good reason

to Uelieve that the strand which ascends from the corpus

mammillare is composed of fibres which are not directly

continuous with those of the anterior pillar of the fornix,

it receives the special name of \^J>undle of Mcq d\4zyr.

The conneclioiis which have just been described cannot lie made out
at present, Init at a later period the dissector will experience little
difficulty in tracini; the anterior pillar of the fornix to the corpus mam-
millare, and in displayini^ the connection of this with the bundle of Vicij
d'A/yr.

536 THE BRAIN.

The posterior pillars of the fornix are flattened bands
which diverge widely from the body of the fornix. At
first they are adherent to the under surface of the corpus
callosum, but soon they sweep downwards round the
posterior ends of the optic thalami, and enter the posterior
horns of the lateral ventricles. Here each posterior pillar
comes into relation with the corresponding hippocampus
major, and a portion of its fibres become spread out on the
surface of this prominence, forming the alveus, whilst the
remainder constitute the fimbria or taenia hippocampi, which
has already been described (pp. 517 and 531).

Dissection. — The body of the fornix should now be divided trans-
versely across its middle. Its posterior and anterior portions may then
be gently raised from the velum interpositum, and thrown forwards and
backwards. Had it been possible to raise the corpus callosum and
fornix together, the diverging posterior pillars of the latter would have
been seen to limit a triangular space on the under surface of the corpus
callosum in front of the posterior margin of the splenium. This interval
is termed the lyra, and is traversed by a series of oblique and longi-
tudinal markings. These markings indicate the presence of fibres,
which pass across from one pillar of the fornix to the other, so as to
form a white lamina. This lamina is not united to the under surface
of the corpus callosum, and the interval between them is sometimes
termed Vergds ventricle.

The Velum Interpositum is a double layer or fold of pia
mater which intervenes between the body of the fornix, which
is placed above it, and the roof of the third ventricle and the
two optic thalami, which lie below it. Between the two layers
are blood-vessels and some subarachnoidal trabecular tissue.
In shape the velum interpositum is triangular, and the narrow
anterior end or apex reaches as far forwards as the foramina
of Monro. The base Hes under the splenium of the corpus
callosum, and here the two layers of pia mater which form
the velum become continuous with the investing pia mater
on the surface of the brain.

Along each lateral margin the velum interpositutn is
bordered by the choroid plexus of the body of the lateral
ventricle, which projects into the ventricular cavity from
under cover of the lateral free edge of the fornix. Posteriorly

THE CEREBRUM.

537

this choroid plexus is continuous with the similar structure
in the descending horn of the ventricle, whilst in front it
narrows greatly and becomes continuous, across the mesial
plane, with the corresponding plexus of the opposite side,
behind the epithelium which lines the foramina of Monro.
From this median junction two much smaller choroid

genu of corpus
callosum.

septum lucidum
and fifih ventricle.

<terior pilla
of fornix

splenium of
corpus callosum '

anterior horn oi
lateral ventricle.

caudate nucleus.

ta-nia semi-
circularis.

])tic thalamus.

bulb of the comu.

hippocampus
minor.

vena magna CJaleni.

Fig. 324. — Dissection to show the velum inlerposiluni and
the lateral ventricles. The body of the corpus callosum and
the body of the fornix have been removed : the descending
horn of the right ventricle has also been opened up.

plexuses run backwards on the under surface of the
velum interpositum, and project downwards into the third
ventricle. These are the cJioroid pkxuscs of the third
ventricle (Fig. 325).

The most conspicuous blood-vessels in the velum inter-
positum are the iwo veifis of Gakfi, which run backwards —

538

THE BRAIN.

one on either side of the mesial plane. In front, each is
formed at the apex of the fold by the union of the vein of
the corpus striatum with a large vein issuing from the
choroid plexus ; behind, they unite to form the vena magna
Galeni, and this pours its blood into the anterior end of the
straight sinus (Fig. 205).

Great Transverse Fissure. — This name is given to the

VELUM
INTERPOSITUM

CHOROID PLEXUS'

OF

VENT. Ill

Fig. 325. — Diagrammatic coronal section through the
optic thalami and the parts in immediate relation to them.
The intermediate part of the great transverse fissure hold-
ing the velum interpositum is seen, and also the manner in
which this fissure is shut out from the lateral ventricles by
the epithelium which covers the choroid plexus on each side.

continuous cleft through which the velum interpositum and
the choroid plexuses of the two descending horns of the
lateral ventricles are introduced into the interior of the
brain. It consists of an upper or intermediate part and
two lateral parts. The former passes forwards between
the splenium of the corpus callosum and the body of the
fornix above, and the roof of the third ventricle and the
optic thalami below. It is limited by the epithelial cover-

THE CEREBRUM. 539

ing of the choroid plexuses, which shuts out these structures
from the cavity of the lateral ventricles.

The lateral part of the transverse fissure is termed the
inferior cerebral fissure or the choroidal fissure. It is con-
tinuous with the intermediate part, and has already been
studied in connection with the descending horn of the
lateral ventricle {p. 531).

Dissection. — The vein of the corpus striatum should now be divided
on each side as it passes into the vein of Galen. The apex of the
velum interpositum should then be seized with the forceps, and the
whole structure pulled backwards. The entire ujiper surface of the optic
thalamus on each side is thus exposed, and between these bodies is seen
the mesially placed third ventricle. The roof of this ventricle which is
epithelial and invaginated into the cavity by the choroid plexuses on
the under surface of the velum interpositum is torn away with that
stnicture. The basal part of the velum interpositum is intimately con-
nected with the pineal body which lies on the mesencephalon behind
the third ventricle. Care therefore must be taken to extricate this body
from the pia mater, otherwise it is sure to be pulled away.

Optic Thalamus. — The optic thalami are two large oval
masses of grey matter, placed close together on either side
of a deep mesial cleft which receives the name of the third
ventricle of the brain. Each of these bodies presents an
anterior and a posterior extremity, and an upper, lower,
inner, and outer surface. Th_c inferior and external surfaces
are in apposition, and indeed, directly connected with ad-
jacent parts, and on this account it is only possible to
study til em by means of sections through the brain. The
superior and internal surfaces are free, and may be examined
in ilic present dissection.

The external or lateral surface of the optic thalamus is
api)lied to a mass of white matter, termed i\^Jnternal cafsule,
which is largely composed of fibres derived from the crusta
or ventral part of the crus cerebri. The inferior or ventral
surface oCtlie thalamus, xcsla chiefly upon the subthalamic
region_ox \.\\k: proJDngation upwards of the dorsal tegmental
part of the crus cerebri. The relation, therefore, which
this body presents to the upward continuation of the crus
cerel)ri is very intimate.

540

THE BRAIN.

The superior or dorsal surface of the thalamus is free.
On the outer side it is bounded by the groove aheady
noticed on the floor of the lateral ventricle which intervenes

anterior cornu of lateral ventricle

septum lucidum

anterior pillars of fornix
foramen of Monro

Vent. III.
tsenia semicircularis

middle commissure

Vent. III.

posterior commissure

stria fornicis //^liM

pineal body

pulvinar

mesencephalon
trochlear neive

lingula

superior cerebellar peduncle

middle cerebellar peduncle -

restiform body
medulla

Fig. 326. — The medulla, mesencephalon, and thalamencephalon.

between the thalamus and the caudate nucleus — a groove
which contains the vein of the corpus striatum and the taenia
semicircularis. On the inner side the superior surface of
the thalamus is separated in its anterior half from the internal

THE CEREBRUM.

541

or mesial surface by a sharp edge, or rather by a somewhat
prominent ledge, produced by a small white strand, termed
\}ciQ jtria Joniicis or the stria pinealis. Posteriorly, this
stria leads to the pineal body, whilst anteriorly it runs into
the anterior pillar of the fornix.

The superior surface of the thalamus is slightly bulging
or convex, and is of a whitish colour owing to the presence
of a thin superficial coating of nerve fibres (stratum zonale).
It is divided into two areas by
a faint oblique groove which
begins in front a short dis-
tance behind the anterior ex-
tremity of the thalamus, and
extends obliquely outwards and
backwards. This sulcus cor-
responds to the free edge of
the fornix. The two areas
thus mapped out are very
differently related to the ven-
tricles of the brain. The outer
area includes the anterior ex-
tremity of the thalamus, and
forms a part of the floor of the
lateral ventricle ; it is covered
with ependyma, and overlapped
by the choroid plexus (Fig.

325). The Z/;;/^/' rrrm intervenes between the lateral and
third ventricles of the brain, and takes no part in the
formation of the walls of either. It is covered by the
velum interpositum, above which is the fornix. It includes
the posterior extremity of the thalamus.

Xhe anterior extremity of the thalamus, called the anterior
tubercle (tuberculum anterius), is_ rounded and prominent.
It projects into the lateral ventricle, lies behind and to
the outer side of the free portion of the anterior pillar of
tlie fornix, and bounds the foramen of Monro behind.

The posterior extremity of the thalamus is very pro-
minent, and projects backwards so as to overhang a portion

Fig. 327. — Upper surface of
the left thalamus.

542 THE BRAIN.

of the mesencephalon (viz. the brachia of the quadri-
geminal bodies) (Fig. 326). This projecting part is called
the pidvinar. But the hinder end of the thalamus shows
another prominence. This is situated below and behind
the pulvinar. It is oval in form, and receives the name of
the corpus geniciilatu?7i externujn.

The mesial surfaces of the two thalami are covered
with the lining ependyma of the third ventricle, and are
placed very close together. Indeed, at one spot they are
actually joined by a band of grey matter which forms
the grey or soft commissure of the brain (commissura
mollis).

Trigonum Habenulae. — This term is applied to a small,
depressed, triangular area which occupies the interval
between the pulvinar and the peduncle of the pineal body.

The Pineal Body (conarium or epiphysis cerebri) is a
little structure of a darkish colour, and about the size of
a cherry - stone, which is placed between the hinder
extremities of the two thalami on the dorsal aspect of the
mesencephalon (Fig. 326). It occupies the groove between
the two superior quadrigeminal bodies, and is shaped like
a fir-cone. Its base, which is directed upwards, is attached
by means of a hollow stalk or peduncle. This stalk is
separated into a dorsal and a ventral part by a continua-
tion backwards into it of a pointed recess of the cavity of
the third ventricle. The dorsal part of the stalk is carried
forAvards on each optic thalamus as the stria fornicis ; the
ventral part is folded round a narrow but conspicuous
cord-like band of white fibres, which crosses the mesial
plane immediately above the base of the pineal body, and
receives the name of the posterior commissure of the
cerebrum.

Anterior Commissure of the Cerebrum. — In the anterior
part of the cleft between the two optic thalami, and
immediately in front of the anterior pillars of the fornix, a
round bundle of white fibres will be seen crossing the
mesial plane. This is the anterior commissure. It is
very much larger than the posterior commissure, and will

'J- HE CEREBRUM.

543

be afterwards followed towards the temporal lobe in which
the greater part of it ends.

Third Ventricle. — This name is given to the deep
narrow cleft between the two optic thalami. Broadly
speaking, it may be said to extend from the posterior

I'"lG. 328. — Mesial section through the brain.

1. Fornix.

2. Velum inlerposituiii.

3. Pine.il body.

4. \"ena m.igna Galcni.

5. Splenium of corpus callosum.

6. Corpora quadri};eniina.

7. Valve of Vicussens.

8. .Aqueduct of Sylvius.

9. Oculo-motor nerve.

10. Corpus mammillarc.

11. Iiifuiidibulum.

12. Optic commissure.

13. Lamina cinerca.

14. .Anterior commissure.

15. For.imen of Monro.

16. Genu of corpus callosum.

17. Septum lucidum.

commissure behind to the anterior commissure in front.
Its floor is formed by the parts already studied within the
interpeduncular space on the base of the brain, viz. the
tuber cinereum, the corpora mammillaria, and the grey
matter of the locus perforatus posticus, and also to some
extent behind these by the tegmenta of the crura cerebri.

544 THE BRAIN.

In front it is bounded by the lamina cinerea and the
anterior commissure j whilst its lateral walls are formed by
the mesial surfaces of the two optic thalami. A little in
front of the middle of the ventricle the cavity is crossed
by the middle or soft com^tiissi^re, which connects the thalami
with each other, and in front of this the anterior pillar of
the fornix is seen descending in the lateral wall. At first
this is distinct and prominent, but it gradually becomes
more and more sunk in the grey matter on the side of the
ventricle as it approaches the corresponding corpus
mammillare.

The roof of the third ventricle is formed by a thin

FORAMEN OF MONRO.

yREOESSUS

OPTIC CH/ASMA-.^^;!^^^ _(S'SUPRAPINEALlS

RECESSUS PINEALIS

POSTR. COM.
AQUEDUCT OF SVLVIUS

Fig. 329. — Diagrammatic outline of the third ventricle
as viewed from the side.

epithelial layer continuous with the epithelial lining of the
cavity, which stretches across the mesial plane from the
one stria fornicis to the other. It is appUed to the under
surface of the velum interpositum which overlies the
ventricle, and is invaginated into the cavity by the choroid
plexuses which hang down from the under surface of this
fold of pia mater. In the removal of the velum inter-
positum this thin epithelial roof has been torn away.

The third ventricle communicates freely with the lateral
ventricles, and also with the fourth ventricle. The aqueduct
of Sylvms, a narrow channel which tunnels the mesen-
cephalon, brings it into communication with the fourth
ventricle. The opening of this aqueduct will be seen at
the posterior part of the floor of the ventricle, immediately

THE MESENCEPHALON. 545

below the posterior commissure. '\\\q foramina of Monro
bring it into communication with the two lateral ventricles.
The latter apertures are placed at the upper and fore
parts of the lateral walls, and lead outwards and slightly
upwards between the most prominent parts of the anterior
pillars of the fornix, and the anterior tubercles of the
optic thalami. They are just large enough to admit a
crow-quill, and through these passages the epithelial lining
of the three ventricles becomes continuous.

The outline of the third ventricle, when viewed from the side in a
mesial section through the brain (Fig. 329), or as it is exhibited in a
plaster cast of the ventricular system of the brain, is seen to be very
irregular. It presents several diverticula or recesses. Thus, in the
fore-part of the floor there is a deep funnel-shaped pit or recess leading
down through the tuber cinereum into the infundibulum of the pituitary
body. Another recess leads forwards immediately in front of this,
above the optic chiasma. Posteriorly two additional recesses are
present. One, the recesstis pinealis, passes backwards, above the
posterior commissure and the entrance of the aqueduct of Sylvius, for
a short distance into the stalk of the pineal body. The second is
placed above this and is carried backwards for a greater distance. Its
walls are epithelial, and therefore it cannot be seen in an ordinary
dissection. It is termed the rcwssies siiprapincalis.

Dissection. — The further study of the cerebrum should be postponed
until after the examination of the mid-brain or mesencephalon. The
membranes should be removed from the upper surface of the cerebellum,
and the prominent anterior part of this organ may then be gently
pulled backwards to expose as far as possible the corpora quadrigemina,
i.e. the four rounded eminences on the dorsal aspect of the mesen-
cephalon. In doing this, care should be taken to secure and preserve
the slender trochlear nerve which winds forwards round the outer side
of the crus cerebri, and which issues from a lamina called the valve of
\'ieussens, immediately below the inferior pair of quadrigeminal bodi^.

THE MESENCEPHALON.

Mesencephalon. — The mesencephalon or isthmus en-

cephali is the stalk which occupies the opening of the

tentorium cerebelli, and connects the cerebrum with the

parts in the posterior cranial fossa. It is about three-

VOL. II. — 35

546 THE BRAIN.

quarters of an inch long, and it consists of a dorsal part
composed of the corpora quadrigemina, and a much larger
ventral part which is formed by the two large crura cerebri.
In the undissected brain the corpora quadrigemina are
completely hidden from view by the splenium of the
corpus callosum, which projects backwards over them, and
also by the superimposed cerebral hemispheres. The
crura cerebri, however, can to some extent be seen on the
base of the brain, where they bound the posterior part of
the interpeduncular space. The mesencephalon is tunnelled
from below upwards by a narrow passage called the aqueduct
of Sylvius. This channel lies much nearer its dorsal than
its ventral surface.

Corpora Quadrigemina (optic lobes). — The four rounded
eminences on the dorsal aspect of the mesencephalon to
which this name is appHed are for the most part composed
of grey matter, although each has a superficial coating of
white fibres. The superior pair are larger and broader than
the inferior pair, but they are not so well defined nor yet
so prominent.

A longitudinal and a transverse groove separate the
quadrigeminal bodies from each other. The longitudinal
groove occupies the mesial plane, and extends upwards as
far as the posterior commissure. From its lower end a
short but well-defined narrow band of white fibres, the
fr<znulum veli, passes to the valve of Vieussens — a lamina
placed immediately below the inferior pair of quadrigeminal
prominences. The upper part of the longitudinal groove
is occupied by the pineal body. The transverse groove
curves round behind each of the superior pair of quadri-
geminal bodies, and separates them from the inferior pair.

Brachia of the Corpora Quadrigemina. — The corpora
quadrigemina are not marked off from the side of the
mesencephalon, but each body has in connection with it
on this aspect a prominent white strand, which is prolonged
upwards and forwards under the projecting pulvinar and
corpus geniculatum externum on the hinder end of the
optic thalamus. These strands are called the brachia of

THE MESENCEniA I. ON.

547

CORP:GEN EXT:

LATERAL BOOT

10 TRACT

the corpora quadrigeniina, and they are separated from each
other by a continuation on the side of the mesencephalon
of the transverse groove which intervenes between the two
pairs of bodies.

Corpus Geniculatum Internum. — Closely connected with
the brachia of the corpora quadrigemina will be seen the
corpus geniculatum internum. It is a little oval eminence,
very sharply defined, which lies on the side of the upper
part of the mesencephalon under shelter of the pulvinar of
the optic thalamus.

Connections of the Brachia and the Origin of the Optic
Tract. — It will now be seen that the brachia are intimately
connected with the optic
tract. 1 he lujerior bracluum
proceeding upwards from the
lower quadrigeminal body
advances towards the corpus
geniculatum internum, and
disappears from view under
cover of this prominence.
Upon the opposite side of
this same geniculate body,
the mesial root of origin of
the optic tract is observed to
arise, and the appearance is such that the dissector might
very naturally conclude that the inferior brachium and this
root of the optic tract are continuous. It is very doubtful,
however, if this is the case. The superior brachium is
carried upwards and forwards between the overhanging
pulvinar and the corpus geniculatum internum. It partly
enters the corpus geniculatum externum, but a portion of
it can easily be observed to be directly continuous with the
lateral root of the optic tract.

~-CORP:GEN INT:
^SUPR. BRACHIUM.
INFR. BRACHIUM.
^SUPR. QUAOBODY:
INFR. QUAD:BODY.

Fig. 330. — Diagram of the roots
of the optic tract.

Tlic optic tract, therefore, arises by two roots — a mesial and a lateral.
The mesial root emerges from under the inner geniculate Ixidy. The
lateral root is continuous with the superior brachium, and through it
with the superior quadrigeminal body. It also is closely connected
with, and derives fibres from, the corpus geniculatum externum and the

548 THE BRAIN.

pulvinar. The optic tract thus formed curves round the outer side of
the upper part of the crus cerebri to reach the optic chiasma.

Crura Cerebri. — The crura cerebri constitute the chief
bulk of the mesencephalon. When viewed from below,
they appear as two large rope-like strands, which emerge
close together from the upper aspect of the pons Varolii,
and diverge as they proceed upwards to enter the cerebrum.
At the point where each crus disappears into the corre-
sponding side of the hemisphere, it is embraced on its
outer side by the optic tract.

The crus cerebri of each side consists of two parts, viz.
a dorsal tegmentum, which is prolonged upwards to the
region below the thalamus ; and a ventral criista ox pes which
is carried upwards into the internal capsule on the outer
side of the thalamus. When the base of the brain is
examined, it is the crusta which is seen, and it is observed
to be white in colour and streaked in the longitudinal
direction. On the exterior of the mesencephalon, the
separation between the two parts of the crus cerebri {i.e.
the tegmentum and the crusta) is indicated by an inner
and an outer groove or sulcus. The inner or mesial sulcus
is the deeper and more distinct. It looks into the inter-
peduncular space, and from it emerge the fascicles of the
oculo-motor nerve. It consequently receives the name of
the sulcus oculomotor ius. The outer sulcus is termed the
stilcus lateralis.

Dissection. — The mesencephalon should now be divided transversely
by one sweep of the knife at the level of the lower borders of the
superior pair of corpora quadrigemina. By this proceeding, the cere-
brum is separated from the parts below. A number of very important
points can be made out on the cut surface of the mesencephalon.

Cut Surface of the Mesencephalon (Fig. 332). — Much
nearer the dorsal than the ventral surface of the mesen-
cephalon the transversely divided aqueduct of Sylvius may be
seen. As already stated, this narrow passage leads from the
fourth ventricle below, upwards through the mesencephalon
to the third ventricle above. It is surrounded by a thick

THE MESENCEPIIA I. OX.

549

layer of grey matter, called the Sylvimi g;rcy maifer, or the
central grey matter of the aqueduct. In a fresh brain this is
always very consj)icuous, and in its midst are situated the
nuclei of the oculo-motor and trochlear nerves, and the
upper nucleus of the trigeminal nerve, although of course

corpus gciiiculatum iiuornuni.
pulvinar,

irpiis gcniculatiini
extcniiini.

suji. bracliium.
inf. brachiuin.

sup. (Iliad, body.

inf. quad. body.

A,|. .S.

opt. tract
antr. perf. spot. —

_ post. perf. spot.
_ corpus albicantltim.

— tuber cinereuin.

— optic commissure.

optic nerve.

Fig. 331. — The origin and relations of the optic tract.
(Professor Thane, from Quain's Anatomy.)

these cannot lie detected by the naked eye. Below, this
grey matter of the aqueduct is continuous with the grey
matter spread out on the floor of the fourth ventricle, whilst
above, it is continuous with the grey matter on the floor
and sides of the third ventricle.

The division between the tegmentum and the crusta is
rendered very evident by a conspicuous mass of dark
pigmented matter which intervenes between them. This is
termed the substantia uiii^ra.

Substantia Nigra. — As seen in transverse section the sub-
stantia nigra presents a somewhat crescentic outline, and is
largely composed of pigmented nerve cells. It is in reality
a thick band which begins below at the upper border of the
pons Varolii, and extends upwards in the midst of the crus
cerebri, as high as the corpora mannnillaria. The margins

550

THE BRAIN.

of this band of dark-coloured substance come to the surface
at the oculo-motor and lateral sulci, and its inner part is
traversed by the emerging nerve fibres of the oculo-motor
nerve. The surface turned towards the tegmentum is
concave and uniform ; the opposite surface is convex, and
rendered highly irregular by the presence of numerous
slender prolongations of the substance into the crusta.

The Crusta. — The crusta is somewhat crescentic when
seen in section, and stands quite apart from its fellow of
the opposite side. It is composed of a compact mass of

GREY MATTER

AQUEDUCT OF SYLVIUS,

SULCUS LATERALIS

SULCUS OCULOMOTORIUS

Fig. 332. — Diagrammatic view of the cut surface of the
mesencephalon when transversely divided.

longitudinally directed nerve fibres which are carried upwards
into the internal capsule. The middle third of each crusta
is composed of the important pyramidal tract, but this is
quite indistinguishable from the portions of the crusta which
lie on either side of it.

The Tegmentum. — Unlike the crustse, the tegmenta are
directly continuous with each other in the mesial plane, a
faint line, termed the median raphe, alone indicating their
bilateral character. Towards the dorsum of the mesen-
cephalon they are also fused with the bases of the corpora
quadrigemina. Their la,teral surfaces therefore are alone
free.

THE MESENCEPHALON. 551

The togniontum is comiwscd of an atlniixturc of grey and while
matter, constituting wliat is termed the foniiatio 7r(iiii/aris. The
white matter is composed of fibres running l)otli transversely and
longituilinally. Certain of tlie longitudinal fdjres arc grouped together
and form well-marked tracts, which, in a section through the mesen-
cephalon of a fresh brain, can be detected by the naked eye. These
tracts are: (i) tlie__posterior longitudinal bundles; (2) the superior
cerebellar pedunclesorTHc l^rachia conjunctiva ; (3) the fillet.

'T\\c pos/cn'or hii^i^i/iiifiual bundle (Fig. 332) is a siiiall compact tract
which is placed upon the outer aspect of the lower portion of the central
grey matter of the aqueduct.

The superior cerebellar feduiidesja.xQ two large strands which are
ccintlmieilZupwatda from the cerebellum into the mesencephalon. By
pulling back the margin of the cercljellum where it overlaps the lower
(juadrigeminal bodies, these peduncles will be seen on the surface as
they converge in an upward direction. Stretching across iJie interval
between them, and bringing them into continuity with each other, js a
thin lamina called the valve of \'ieussens. When the peduncles under
consideration reach the bases of the inferior quadrigeminal bodies, they
sink into the substance of the mesencephalon, and in a transverse section
through the lower part of this portion of the brain they may be seen as
two white strands, semilunar in outline, and placed one on either side of
the grey matter of the aqueduct. As they ascend, they gradually
assume a deeper (i.e. a more ventral) position in the tegmental part of
the mesencephalon, and finally they decussate with each other across
the mesial plane and proceed upwards.

The Jillel is a very complicated tract, and very little can be learnt of
its connections in the course of an ordinary dissection. One part of it,
however, termed the lower or lateral Jillcl, can be readily detected on
the outer free surface of the lower part of the tegmentum in the form of
some curved and usually conspicuous fibres which extend upwards aiul
backwiirds tajrcadi theinferic^r cp^drigeminal body and its braclijuni.

Within the tegmentum there is a collection of nuclear matter which
i.<» termed the reii legmeitlal nucleus from its ruddy appearance when
seen in section. It is rod-like in form, and extends upwards into the
tegmental region below the optic thalamus. In transverse section it
jiresents a circular outline, and it is closely associated with the upward
prolongation of the fii)res of the superior cerebellar peduncle. The
su]KTior cerebellar peduncle is an efferent tract from the lateral hemi-
sl)here of the cerebellum, and its fibres end in the red nucleus and the
pulvinur of ihe optic thalamus of the opposite siile (.\drcn Turner).

552 THE BRAIN.

BASAL GANGLIA OF THE CEREBRAL
HEMISPHERES.

The basal ganglia of the cerebral hemispheres still
require to be examined. These are the caudate and
lenticular nuclei, which together form the corpus striatum ;
the claustrum ; and the amygdaloid nucleus. With these
it is necessary also to study the composition of the optic
thalamus and the external and internal capsules.

Dissection. — The right and left portions of what remains of the cere-
brum should be separated from each other by a mesial incision. On the
left portion the sulci, and convolutions on the under or tentorial surface
of the hemisphere, may be examined if this has not been done already
on another specimen.

A series of sections should, in the next place, be made through both
the right and left portions of the cerebrum, with the view of displaying
the basal ganglia. On the right side remove a succession of thin slices
by carrying a long knife in a horizontal direction through the parts
which form and lie before the floor of the body of the lateral ventricle.
It is not advisable to proceed further than the level of the anterior
commissure.

On the left side of the brain a series of vertical-transverse or coronal
sections should be made through the remaining portion of the cerebrum.
Begin by cutting off the portion in front of the head of the caudate
nucleus, and then proceed steadily backwards until the hinder part of
the optic thalamus is reached. One of the sections should be planned
to pass through the anterior commissure.

The Caudate Nucleus has already been partly examined
in connection with the lateral ventricle, into the cavity of
which it bulges. It is a pyriform highly arched mass of
grey matter, which presents a thick swollen head or anterior
extremity, and a long attenuated tail. The head projects
into the anterior horn of the lateral ventricle, whilst its
narrower part is prolonged outwards and backwards on the
floor of the body of the ventricle, where it is separated from
the optic thalamus by the taenia semicircularis. Finally, its
tail turns downwards and then forwards into the descending
horn of the lateral ventricle, on the roof of which it is pro-
longed until it finally joins the amygdaloid nucleus. The

Till-: CAUDATE NUCLEUS.

553

caudate nucleus, therefore, presents a free ventricular surface
covered with cpendyma, and a deep surface embedded in

genu of the corpus callosum.

anterior liorn of lateral ventricle.

head of caudate nucleus,
septum luciihun.

anterior pillar of fornix
external capsule

iiUcrnal c.Tpsule

claustruni

optic thalamus

nucleus lenticularis
splenium of the corpus callosum

tail of caudate nucleu-

posterior horn of lateral ventricK

I'iG. 333. — Horizontal section through right side of tin-
cerebrum — a little above the level of the anterior com-
missure. ( From Gegenbaur. )

a, b, c. The three nuclei of the I i. I'utamen.

optic thalamus. I 2. Globus pallidus.

the substance of the cerel)runi, and for the most part
related to the internal capsule.

554

THE BRAIN.

Owing to its arched form, it follows that in horizontal
sections below a particular level it is cut at two points,
and both the head and the tail must be looked for in the
field of section (Fig. 333). In coronal sections behind
the amygdaloid nucleus it is also divided at two places.

Fig. 334. — Coronal section through the cerebrum so as
to divide the head of the caudate nucleus in front of the
lenticular nucleus. It is the anterior surface of the section
that is fisfured.

1. Anterior horn of lateral ventricle.

2. Head of caudate nucleus bulging into

anterior horn of lateral ventricle.

3. Head of the caudate nucleus in

section.

4. Great longitudinal fissure.

5. Genu of corpus callosum.

6. Island of Reil.

7. Genu of corpus callosum (lower part).

8. Great longitudinal fissure.

The Lenticular Nucleus lies on the outer side of the
caudate nucleus and the optic thalamus, and is for the most
part completely embedded within the white medullary sub-
stance of the cerebral hemisphere. It does not occupy
so much ground as the nucleus caudatus. Indeed, it pre-
sents a very close correspondence in point of extent with
the island of Reil on the surface.

When seen in horizontal section (Fig. ZZZ) it presents a

THE LENTICULAR NUCLEUS.

555

shape similar to that of a biconvex lens. Its inner surface
bulges more than the outer surface, and its point of highest
convexity is placed opposite the taenia scmicircularis or
the interval between the caudate nucleus and the anterior
end of the optic thalamus.

When seen in coronal section, the appearance presented
by the lenticular nucleus differs very much in the different
planes of section. Figure 335 represents a section through
its anterior portion. Here it is semilunar or crescentic in

Fig. 335. — Coronal sccliun Uuouyh the cerebrum a short
distance behind that depicted in Fig. 334.

I. Caudate nucleus.
3. Internal capsule.

3. Lenticul.ir nucleus.

4. Claustrum.

5. Great longitudinal fissure.

6. Corpus callosum.

7. Septum lucidum.

8. .Anterior horn of lateral ventricle.

outline. Further, it is intimately connected with the head
of the caudate nucleus by bands of grey matter which pass
between the two nuclei and break up the fore-part of the
internal capsule. It is due to the ribbed or barred appear-
ance which is presented by such a section as this that the
term corf>us striatum is given to the two nuclei.

When the section is made in a plane farther back, the
divided lenticular nucleus assumes an altogether diflerent

556

THE BRAIN.

shape, and is seen to be completely cut off from the
caudate nucleus by the internal capsule (Fig. 336). It
is now triangular or wedge-shaped. Its base is turned
towards the external capsule, the claustrum, and the island
of Reil ; its internal surface is applied to the internal

Fig. 336. — Coronal section through the cerebrum in a plane
posterior to the section exhibited in Fig. 335.

I.

Caudate nucleus.

12.

Lateral ventricle.

2.

Claustrum.

13-

Septum lucidum.

3-

Internal capsule.

14.

Fornix.

4-

Putamen.

IS-

Island of Reil.

5-

External capsule.

16.

Anterior pillar of fornix

6.

Globus pallidus I.

17-

Anterior pillar of fornix.

7-

Globus pallidus II.

18.

Anterior commissure.

8.

Anterior commissure.

19.

Ventricle III.

9-

Amygdaloid tubercle.

20.

Optic tract.

10.

Extremity of descending horn of

21.

Tuber cinereum.

lateral ventricle.

22.

Pituitary body.

II.

Corpus callosum.

capsule ; whilst its inferior surface is directed downwards
towards the base of the brain. But, further, two white
laminae are now evident, the external and the internal
medullary lamince, which traverse its substance and divide
it into three zones. The outer, basal, and larger zone is

INTERNAL CAPSULE. 557

termed \.\\c piitamen (Fig. 336, 4). It is darker in colour
than the other two zones, and is traversed by fine radiating
white streaks. The two inner zones are of a faint yellowish
tint, and they together form what is termed the globus
pallidus (Fig. i^T^d, 6 and 7). The putamen has a greater
antero-posterior length than the globus pallidus. It follows
from this that it alone is connected with the head of the
caudate nucleus by the intervening bands of grey matter

(Fig- 335)-

The nucleus lenticularis comes to the surface at the
anterior perforated spot, and a continuity between the grey
matter forming it and the grey cortex of the brain is thus
established.

The Claustrum is a thin plate of grey substance em-
bedded in the white matter which intervenes between the
lenticular nucleus and the grey cortex of the island of Reil
(Figs. 335 and 336). Followed in an upward direction it
becomes gradually thinner until it ultimately appears, when
seen in section, as an exceedingly delicate grey streak. As
it is traced downwards, however, it thickens considerably,
and at the base of the brain it comes to the surface at the
anterior perforated spot, and becomes continuous with the
grey matter of the cerebral cortex. Its extent corresponds
very nearly with the area occupied by the island of Reil,
and its surface towards this portion of the cerebral cortex
shows ridges and depressions corresponding to the insular
gyri and sulci.

Internal Capsule. — This term is applied to the broad
band of white matter which intervenes between the len-
ticular nucleus on the outside, and the optic thalamus, tcenia
semicircularis, and caudate nucleus on the inner side. In
front it is much broken up by the connecting bands of grey
matter which pass between the head of the caudate nucleus
and the fore-part of the putamen of the lenticular nucleus
(Fig. 335); but behind this it forms a solid white mass of
nerve fibres. When seen in horizontal section, the internal
capsule is observed to be bent upon itself opposite the
taenia semicircularis, or the interval between the caudate

558

THE BRAIN.

nucleus and the thalamus (Fig. ZZZ)- This bend, which
points inwards, is called the genu. About one-third of the
internal capsule lies in front of the genu, and this part is
called the anterior limb ; the remaining two-thirds, which
lie behind the genu, constitute the posterior limb.

Connections of tlie Internal Capsule. — The internal
capsule is directly continuous below with the crusta of the
cerebral peduncle. The dissector can easily satisfy him-
self in the specimens before him of this continuity, but it
is more especially apparent in the more posterior of the

coronal sections which
he has made through
the left portion of the
cerebrum.

It has already been men-
tioned that the fibres which
occupy the middle third of the
crusta of the cerebral peduncle
belong to the motor pyramidal
tract. In the internal capsule
these occupy the anterior half
of the posterior limb, being
thus placed immediately be-
hind the genu. The fibres
which constitute the inner third
of the crusta are carried up-
wards into the anterior limb of
the internal capsule ; whilst
the fibres which form the outer third of the crusta enter the posterior
half of the posterior limb.

When the fibres of the internal capsule are traced upwards, they are
found to spread out in a radiating or fan-like manner so as to reach the
various convolutions of the cerebral hemispheres. This arrangement is
termed the corotia radiata. Now, it has been observed that the internal
capsule may be, broadly speaking, divided into thirds, each of which
corresponds with a portion of the crusta. The fibres of the anterior
third, or, in other words, of the anterior limb of the internal capsule,
pass upwards into the prefrontal region of the cerebral hemisphere ;
those of the middle third (the pyramidal fibres) go to the convolutions
of the Rolandic or motor area of the hemisphere ; whilst those of the
posterior third proceed into the occipital and temporal lobes.

Nuclei of the Optic Thalamus. — When a horizontal

Fig.

337. — Diagrammatic representa-
tion of the radiation of the fibres
of the internal capsule. (After
Testut, modified. )

EXTERNAL CAPSULE.

559

section is made ihruiigh the optic thalamus in a fresh brain,
or in one which has been preserved by means of a chromic
salt, the grey matter composing it is seen to be broken up
into an external, internal, and an anterior nucleus (Fig.
33S) by thin internal medullary laminx.

External Capsule. — This term is applied to the narrow
band of white matter which
intervenes between the len- \ ,$t.t. ^^j.

ticular nucleus and the ^'^"^ / ' '

claustrum (Figs. 333, 335j ^^^^^ :■.-
and zzd).

i

X-

/./r

7.77?. 7, -

irli.

Dissection. — The bundle of
Vicq d'Azyr and the anlerior
commissure should now be
followed as far as this is possible
in what remains of the right half
of the cerebrum. In neither case
is the dissection a difficult one.

By removing the remains of
the lenticular nucleus the anterior
commissure will be exposed in
its course towards the temporal
lobe. In the first instance, it
passes transversely outwards
through the lower part of the
globus pallidus and below the
putamen. It then bends suddenly
backwards to reach the medullary
centre of the temporal lobe, above
the descending horn of the lateral
ventricle. If the dissection be
successfully accomplished, the
anterior commissure will be seen
to present a twisted or rope-like
appearance.

The Immilc of Vicq iPAzyr may be traced from the corpus mam-
millare upwards into the anterior nucleus of the optic thalamus by
scraping away the grey matter on the side of the third ventricle. The
continuity between the anterior pillar of the fornix and the corpus
mammillare should at the same time be established. Within the corpus
mammillare there is a small nucleus of grey matter.

Fig. 338. — Horizontal section
through the left optic thala-
mus. (Schwalbe. )

call and cau i. Head and tail of the

caudate nucleus.

t'.X'. Anterior nucleus "v , .

\ of the

i.k. Inner nucleus r l i

, _ , f thalamus.
a.k. Outer nucleus J

st.t. Ta:nia semicircuiaris.

/.///./. Internal medullary laminx

r. External medullary lamina.

tr.h. Trigonum habcnulx.

56o THE BRAIN.

THE PARTS OF THE BRAIN WHICH LIE IN
THE POSTERIOR CRANIAL FOSSA.

The parts which lie below the tentorium cerebelli in
the posterior cranial fossa are the medulla oblongata, the
pons Varolii, and the cerebelbim. These are grouped around
the fourth ventricle of the brain — a cavity which communi-
cates below with the central canal of the spinal cord, and
above with the aqueduct of Sylvius. Through the latter it
establishes a connection with the third ventricle of the
brain.

Medulla Oblongata. — This is the continuation of the
spinal cord into the brain. It is not more than one inch
in length, and may be reckoned as beginning at the level
of the foramen magnum. From this it proceeds upwards
in a very nearly vertical direction, and ends at the lower
border of the pons Varolii. At first its girth is similar to
that of the cord, but it rapidly expands as it approaches
the pons, and consequently it presents a more or less
conical appearance. Its anterior surface lies behind the
groove on the basilar portion of the occipital bone, whilst
its posterior aspect is sunk into the vallecula of the cere-
bellum.

The medulla oblongata is a bilateral structure, and this
is evident even by an inspection of its exterior. The
antero-median and postero-median grooves on the surface
of the spinal cord are prolonged upwards on the anterior
and posterior faces of the medulla.

The antero-median groove, as it passes from the cord on
to the medulla, is interrupted at the level of the foramen
magnum by several strands of fibres which cross the mesial
plane from one side to the other. This inter-crossing is
termed the decussation of the pyramids. Above this level
the furrow is carried upwards without interruption to the
lower border of the pons. Here it expands slightly, and
ends in a blind pit, termed the foramen ccECum of Vicq
d'Azyr.

MEDULLA OBLOXGA T.I.

561

T\\c />osffro->iiedian Jissure is only carried up for half the
length of the niedulla. At this point the central canal of
the cord opens on the dorsal aspect of the medulla, and
the lips of the postero-median fissure are thrust widely
apart from each other, so as to constitute the limits of a
triangular area, which forms on the posterior surface of the
medulla, the lower part of the fossa rJiomboidalis, or the
floor of the fourth ventricle. The dissector is now in a

corpora mammillaria.

cms cerebri.

pons.

middle cerebellar

peduncle. X

olive.
anterior pyramid. — ■ —

superficial arcuate fibres. —

decussation of pyramids. —

lateral arex •''

abducent nerve.

trigeminal ner\e.

facial and auditory
nerves.

glosso-pharj-ngeal
nerve.

vagus ner\e.

hypoglossal nerve,
spinal accessory nerve.

Fig. 339. — Anterior aspect of the medulla and pons of a
full-time foetus.

position to understand the terms " closed " and " open "
as applied to different portions of the medulla. The lower
half of the medulla, containing as it does the central canal
in its interior, is the closed part ; the upper half, above the
opening of the central canal, which by its dorsnl surface
forms the lower part of the floor of the fourth ventricle, is
the open part of the medulla.

The surface of each lateral half of the medulla should
now be studied. It is well, however, to defer for a little
vol.. II. — 36

562 THE BRAIN.

the examination of the medullary part of the floor of the
fourth ventricle. The dissector has already noticed two
linear rows of nerve fascicles issuing from and entering the
medulla on each side. The anterior row consists of the
roots of the hypoglossal and the uppermost part of the
anterior root of the first cervical nerve. They continue
upwards on the medulla in the line of the anterior nerve
roots of the spinal cord, and they emerge along the bottom
of a more or less distinct groove. The posterior row is
formed of the nerve fascicles of the spinal accessory, vagus,
and glosso-pharyngeal nerves, and they lie in series with
the posterior roots of the spinal nerves.

By these two rows of nerve fascicles, each side of the
medulla is divided into three districts, viz. an anterior, a
lateral, and a posterior, similar to the surface areas of the
three columns on the side of the cord. At first sight,
indeed, they appear to be a direct continuation upwards of
these portions of the cord ; it is easily demonstrated, how-
ever, that this is not the case, and that the fibres in the
three columns of the cord undergo a rearrangement as
they are traced into the medulla.

Anterior Area of the Medulla — Anterior Pyramid. —
The district between the antero- median furrow and the
row of hypoglossal nerve fascicles issuing from the medulla
receives the name of the anterior pyramid. An inspection
of the surface is almost sufficient to show that this is
formed by a compact mass of longitudinally directed fibres.
It expands somewhat, and assumes a more prominent
appearance as it passes upwards, and finally reaching the
lower border of the pons Varolii, it becomes slightly con-
stricted and disappears from view by plunging into that
structure. The pyramids are the great motor strands of
the medulla.

Although the anterior pyramid at first sight appears to
be the continuation upwards of the anterior column of the
cord, it contains within itself only a very small proportion
of fibres derived from that source. This will be at once
manifest if the decussation of the pyramids be examined.

LATKNAI. .1/k/C.I Or THE MF.Dl'I.l.A.

S'iJ

crossed

pyramidal

tract.

For this i)iir[)osc iiitiodiicc the l)a(k of the kMiff-l)la(lc into
the aiitcro-mcdian furrow below the decussation, and on
one side push forcibly towards the anterior column of the
cord. The i)yraniid will then be seen to divide at this
level into two portions, viz. a small strand termed the
direct pyramidal tract, which
proceeds downwards into the
anterior column of the cord,
and takes up a position, close
to the antero-median furrow,
and a much larger strand
called the crossed pyramidal
tract, which at this level is
broken up into three or
more coarse bundles which
sink backwards, and, at the
same time, cross the mesial
plane to take u[) a position
in the opposite lateral
column of the cord, close
to the posterior horn of grey
matter. It is the intercross-
ing of the corresponding

bundles of the crossed pyramidal tracts of opposite sides
which produces this characteristic decussation.

But if only the direct pyramidal tract in the anterior cohimn of the
cord is prolonged upwards into the corresponding district of the
medulla, it may he asked : What becomes of the larger lateral part of
the anterior column of the spinal cord in the medulla ? It is thrust
aside by the decussating bundles of the crossed pyramidal tract, and
thus comes to occupy a deep position in the medulla.

Lateral Area of the Medulla. — This is the district on
the surface of the medulla which is included between the
two rows of nerve-roots, viz. the hypoglossal roots in front,
and the root fascicles of the spinal accessory, vagus, and
glosso- pharyngeal behind. It presents a very different
appearance in its upper and lower parts. In its lower
portion it appears to the eye as a continuation upwards of

Fig. 340. — Diagi-am of the decus-
sation of the pyramids.

564

THE BRAIN.

the lateral area of the cord ; in its upper part is seen the
striking oval prominence, which receives the name of the
olivary eminence.

The lower part of this district, however, is very far from
being an exact counterpart of the lateral column of the
cord. As we have already observed, the large crossed
pyramidal tract, which in the cord lies in the lateral
column, is no longer present in this district of the medulla ;
it has been transferred at the decussation of the pyramids

trigeminal nerve.

facial and auditory nerves.

middle peduncle of the
cerebellum.

ligula crossing the
restiform body.

clava.

funiculus cuneatus.

olive,

superficial arcuate fibres,
funiculus Rolandi.

anterior pyramid,
lateral column of cord.

Fig. 341. — Lateral aspect of the medulla and pons of a
full-time foetus.

to the pyramidal tract of the opposite side. Another
small strand of fibres, the direct cerebellar tract, prolonged
upwards in the lateral column of the cord, gradually leaves
this portion of the medulla. This tract of fibres Ues on
the surface, and it is often visible to the naked eye as a white
streak inclining obliquely backwards into the posterior
district of the medulla to join its upper part, i.e. the
restiform body. The great majority of the remainder of
the fibres which are prolonged upwards from the lateral
column of the cord disappear from the surface at the lower
border of the olivary eminence, by dipping into the sub-_

THE POSTERIOR AREA OF THE MEDULLA.

565

stance of the medulla under cover of that projection. A
narrow band, however, may be noticed to be carried up-
wards to the pons in the interval which exists between the
posterior border of the olive and the roots of the vagus
and glosso-pharyngeal nerves.

The olivary eminence is a smooth oval projection, whicli
occupies the upper part of the lateral area of the medulla.
Its long axis, which is vertical, is about half an inch long,
and its upper end is separated from the lower border of the
pons by a natural interval or groove.

fovea superior.^

acustic tubercle.^,
fovea inferior

trigonum vagi. '

corpora quadrigemina.

valve of Vieussens.
superior peduncle of the
cerebellum.

eminentia teres.

trigonum hypoglossi.

ligula.

restiform body.

clava.

cuneate tubercle.

Rolandic tubercle.

funiculus gracilis.

funiculus cuneatus.

Fig. 342. — Posterior aspect of the medulla, pons, and
mesencephalon of a full-time fo;tus.

The Posterior Area of the Medulla. — In its lower half
this district is bounded behind l)y the postero-median
fissure, and in its upper half by the lateral margin of the
medullary portion of the floor of the fourth ventricle. In
front it is separated from the lateral area by the row of
root-fascicles belonging to the spinal accessory, vagus, and
glosso-pharyngeal nerves. As in the lateral area we re-
cognise a lower portion and an upper portion or restiform
body, which are quite distinct from each other.

The lower part of the posterior area corresponds more

S66 THE BRAIN.

or less closely with the posterior columns of the cord. It
will be remembered that in the cervical part of the cord
the posterior columns are divided by a distinct septum of
pia mater into an inner postero-median strand (column of
Goll) and an outer postero- external strand (column of
Burdach). These are prolonged upwards into the medulla,
and in the lower part of the posterior area they stand out
distinctly, and are separated from each other by a con-
tinuation upwards from the cord of the paramedian groove.
In the medulla these strands receive different names.
The inner one is called the funiculus gracilis, whilst the
outer one is designated the funiculus cuneatus. Each of
these strands, when it reaches the lower part of the floor
of the fourth ventricle, ends in a slightly expanded pro-
minence. The swollen extremity of the funiculus gracilis
is called the clava ; it is thrust aside from its neighbour of the
opposite side by the opening up of the medulla to form
the floor of the fourth ventricle, and the central canal of
the cord opens on the surface in the angle between the
two clavce. The thickened end of the cuneate funiculus
receives the name of the cuneate tubercle, but it is only in
the young brain that it is well marked.

In sections through this region of the medulla, it is seen
that the prominences produced by these two strands and
of their enlarged extremities are in a great measure due to
the presence of two rod-shaped nuclei or collections of grey
matter which lie subjacent to them, and which gradually
increase as they are traced upwards. These are termed
respectively the gracile and the cuneate nuclei, and it can be
easily shown that as the grey matter increases in quantity
the fibres of the two corresponding strands diminish in
number. Indeed, it is doubtful if any of their fibres are
prolonged upwards beyond the level of the nuclei.

But a third longitudinal elevation is also apparent in
the lower part of the posterior area of the medulla. This
is placed on the outer side of the funiculus cuneatus —
between it and the posterior row of nerve-roots — and it
has no counterpart in the posterior column of the cord.

suPKRi'iciAi. ARCUAri-: I'inNr.s. 567

li is called ihc Junictiliis of Rolando^ because it is pro-
duced by the substantia gelatinosa Rolandi approaching
the surface along this line. Extremely narrow below, the
funiculus of Rolando widens somewhat as it is traced
u|)wards, and finally ends in an expanded extremity called
the tubercle of Rolando.

The restifonn body forms the upper part of the posterior
area. It lies between the lower part of the floor of the
fourth ventricle and the roots of the vagus and glosso-
pharyngeal nerves, and is thrust outwards by the opening
up of the medulla. It is a large rope-like strand, which
inclines ui)wards and outwards, and then finally takes a
turn backwards, and enters the cerebellum, of which it
constitutes///^ inferior peduncle. The restiform body, there-
fore, is to be regarded as the main connection between the
cerebellum above and the medulla and spinal cord below.
At the same time, it must be understood that it is not
formed of fibres which are prolonged into it from the
funiculus gracilis and funiculus cuneatus of its own side.
It is true that a surface inspection of the medulla might
very naturally lead to this supposition, because there is no
sharp line of demarcation marking it off from the tubercles
of these strands. [^

The fibres which huilil up the restiform bodies come from several
(lilTercnt sources. It will be sufficient to indicate the more important
of these — (i) from the lateral column of the spinal cord through the
direct ccrcbcltar tract ; (2) from the convoluted nucleus of the olivary
body of the opposite side ; (3) from the gracile antl cuneate nuclei of
the opposite side ; {4) from the gracile and cuneate nuclei of the same
side.

Superficial Arcuate Fibres. — On the surface of the
medulla, mure particularly in the neighbourhood of the
lower border of the olive, a number of curved bundles of
fibres, termed the superficial arcuate fibres., may be noticed.
They vary very greatly in number and in distinctness, and
they are sometimes so numerous as to cover over almost
entirely the olivary eminence. An attentive examination
will show that they come to the surface in the antero-

568 THE BRAIN.

median groove between the pyramids, and frequently in
the groove between the pyramid and the ohve. But at
whatever point they reach the surface, the majority have
one destination, viz. the restiform body — a considerable
part of which they form.

Dissection. — The anterior pyramid of one side should now be care-
fully raised. When dislodged from its bed it should be gently pulled
upwards towards the pons Varolii. In this way its entrance into the
pons is brought very clearly into view, and further, numerous arcuate
fibres will be seen running forwards across the mesial surface of the
opposite pyramid to reach the surface.

Very little of the structure of the medulla can be learnt from
specimens obtained in the dissecting-room. Further, it is not advis-
able to cut into the medulla at present, because the student has still to
study that portion of its dorsal surface which forms the lower part of
the floor of the fourth ventricle, and this cannot advantageously be
done until the cerebellum has been examined. Still, it is convenient
to say what little has to be said on the structure of the medulla at this
stage.

Structure of the Medulla. — ^When transverse sections are made
through the medulla at different levels, a faint line called the median
raphe, and occupying the mesial plane, is seen to divide it into two
exactly similar lateral portions. The raphe is formed by the close
intersection of fibres running in different directions.

Each half of the medulla is composed of {a) strands of white matter;
(5) grey matter, which is present both in the form of direct continua-
tions into the medulla of portions of the grey matter of the cord, and
also in the form of isolated clumps, which are not represented in the
cord ; and (c) the formatio reticularis, a substance which is composed
of grey matter coarsely broken up by fibres which traverse it in different
directions. The white matter, as in the cord, is for the most part dis-
posed on the surface and the grey matter in the interior, but in the
open part of the medulla the grey matter comes to the surface on
its dorsal aspect, and is spread out over that area which forms the
medullary portion of the floor of the fourth ventricle.

When the grey matter of the cord is traced up into the medulla,
many striking changes in its arrangement become apparent. Owing
to the increase in size of the large wedge-shaped gracile and cuneate
funiculi, the posterior horns of grey matter become folded outwards, so
that they soon assume a position at right angles to the mesial plane,
and lie very nearly in the same transverse line. At the same time, the
cuneate and gracile nuclear columns of grey matter which grow out
from the basal portion of this horn and underlie the strands of the
same name, begin to make their appearance. From the deep aspect

STRUCTURE OF THE MEDULLA.

569

of those nuclei, fibres, which take origin within iheni, stream forwards
anil inwards through the cervical portion of the jiosterior horn, so as lo
reacii the rapiie. The caput cornu is in lliis way completely cut off
from the basal jxirtion. The latter remains in close relation to the
central canal, whilst the caput or substantia gclalinosa Kolandi is
placed close to the surface, enlarges as it is traced u|iwards, and forms
the prominence on the surface which has already been described as the
funiculus and tubercle of Rolando. The fibres which have thus broken
up the cervical part of the posterior horn, and which come from the

funiculus
gracilis.

funiculus
cuncatus.

iscending root of
fiflh nerve.

direct cerebell.-ir
tract.

^racile nucleus.

^^cuncatc nucleus.

-7| — substantia
VI gelatinosa
;/ Kolandi.

decussation of
the fillet.

—internal
accessory
olivary- nucleus,
fascicles of the
hypoglossal

pyramid.

Fig. 343. — Transverse section through the closed part of
the medulla of a full-time foetus above the decussation of
the pyramid treated by the Pal-Weigert method. The grey
matter is white and the meduUated strands of nerve fibres
are rendered black.

cuneate and gracile nuclei, are termed the internal or iiccp arcuate
fibres. They reach the raphe on the deep or dorsal aspect of the
pyramids, and, crossing the mesial plane, they form a very con>|)letc
decussation with the corresponding fibres of the opposite side, which
is termed the decussation of the fillet or the sensory decussation, in
contradistinction to the term motor decussation, which is sometimes
applied to the cro.ssing of the pyramids. As soon as they reach the
op|)osite side of the medulla, these internal ox dee/> arcuate fibres turn
upwards and form a longitudinal tract, placed close to the ra|ihe and
on the dorsal aspect of the corresponding pyramid, which receives the
name of ihc filet or lemniscus.

570

THE BRAIN.

The anterior horn of grey matter shares a like fate in the medulla at
the hands of the crossed pyramidal tract. This great bundle, in passing
from the pyramid into the lateral column of the cord of the opposite
side, traverses the anterior horn so as to completely break up its inter-
mediate part and separate its head from its basal portion. The further
history of the detached head we need not trace, but it is well to observe
that the basal part of the anterior horn of grey matter remains in position
on the ventral and lateral aspect of the central canal.

As we proceed up the closed part of the medulla, the central canal,
surrounded by the basal portions of the two horns of grey matter,

gracile nucleus

cuneate nucleus

grey matter
round canal.

central canal. -4^^J

funiculus
gracilis.

funiculus
cuneatus.

ascending root
of fifth nerve.;

substantia
gelatinosa
Rolandi.

direct cerebellar
tract.

detached head o

anterior corni

of grey mattei

lateral part of

anterior column

pushed aside

by decussation.

antero-median furrow.

Fig. 344. — Transverse section through lower end of the
medulla of a full-time foetus, treated by the Pal-Weigert
method. The grey matter is therefore bleached white ;
whilst the medullated tracts are black.

gradually inclines towards the dorsal aspect, until it finally opens on
the surface. The grey matter which surrounds it is now spread out on
the floor of the fourth ventricle, and in such a manner that the portion
which corresponds to the basal part of the anterior horn of the cord is
situated close to the mesial plane, whilst the part which represents the
base of the posterior horn occupies a more lateral position. This is
important, because the nucleus of origin of the hypoglossal nerve is
placed in the mesial part of the floor, whilst the nuclei of origin of the
vagus and glosso-pharyngeal nerves lie in the lateral part of the floor.

The most conspicuous of the isolated clumps of grey matter in the
medulla are the olivary nucleus and the two accessory olivary nuclei.
The olivary muleiis lies subjacent to the olivary eminence, and is a

STRUCTURE OF THE MEDULLA.

571

very conspicuous uhjccl in transverse sections through this region. In
such cases it presents the appearance of a thick wavy or undulating line
of grey matter folded upon itself so as to enclose a space fd led with
white matter and open towards the mesial plane. It is in reality a
lamina arranged in a purse-like manner with its open mouth directed
towards the raphe. The fibres which enter through its mouth con-
stitute the olivaiy pediuiclc.

The accessory olivary nuclei are two band -like laminiv of grey
matter, which are respectively placed on the dorsal and mesial aspects
of the main nucleus. When seen in transverse section each of these
nuclei presents a rod-like appearance (Fig. 346).

funiculus
gracilis.

funiculus

cuneatus.

ascending root of
the trigeminal
nerve.

Fig. 345.— Transverse section through the medulla of
new-born child at the level of the lower part of the olivary
eminence, stained by the Pal-Weigert method.

Behind, or deeper than, the olive on the one hand, and the pyramid
on the other, is {hcfonnado reticularis of the medulla. It forms a large
part of its substance, and is divided into a lateral and a mesial field by
the nerve fascicles of the hypoglossal as they traverse the substance of
the medulla to reach the surface. In the lateral portion, which lies
behind the olive, there is a considerable quantity of grey matter, con-
tinuous with that of the cord, present in the reticular formation ; it is
therefore called ihcformatiogrisea. In the mesial part, however, which
lies behind the pyramid, the grey matter is extremely scanty, and the
reticular matter here is termed \\\g form alio alba.

The nerve fibres which traverse the formatio reticularis run both in

572

THE BRAIN.

the transverse and in the longitudinal direction. The transverse fibres
are the deep or internal arcuate fibres. The longitudinal fibres are
derived from different sources in the two fields. In the lateral part of
the formation they represent the fibres of the lateral column (after the
removal of the direct cerebellar and the crossed pyramidal tracts) which
are continued up under cover of the olive. In the anterior part, or
formatio alba, the longitudinal fibres are largely derived from that
portion of the anterior column of the cord which lies on the outer side

mesial

accessory

olivary

nucleus.

Fig. 346. — Transverse section through the medulla at the level
of the mid-point of the olive ( Pal-Weigert stain).

of the direct pyramidal tract (ground-bundle), and which is thrust into
the substance of the medulla by the crossing of the pyramids.

In this position also two longitudinal strands take origin, viz. the
fillet and the posterior longitudinal bundle. Both lie close to the
raphe. The fillet is placed immediately behind the pyramid, and is
formed, as described, by the decussating internal arcuate fibres. The
posterior longitudinal bundle takes form in the upper part of the
medulla, immediately subjacent to the grey matter of the floor of the
fourth ventricle. It is formed by longitudinal fibres of the formatio alba
which come from the ground-bundle of the anterior column of the cord.

CEREBRI. I UM. 573

Pons Varolii. — The pons X'aiolii is the nKukud pro-
niitiencc on tlic base of the brain which is interposed
between the medulla nnd the crura cerebri, and which lies
in front of the cerebellum. It is convex from side to side,
as well as from before backwards, and the transverse streaks
on its surfiace show that superficially it is composed of
transverse bundles of nerve fibres. On either side, these
transverse fibres collect themselves together so as to form a
large compact strand which sinks in a backward and outward
direction into the white matter of the corresponding hemi-
sphere of the cerebellum. This strand is termed the middle
cerd'cllar pcdioiclc.

The ventral surface of the pons is in relation to the basilar
process of the occipital bone and the dorsum sellae of the
sphenoid bone. It presents a mesial groove which gradually
widens as it is traced upwards (Fig. 339, p. 561). In this
lies the basilar artery, but the groove is not caused by this
vessel, but is due to the prominence which is produced on
either side by the passage upwards through the pons of the
pyramidal bundles of the medulla. Where the pons Varolii
becomes the cerebellar peduncle the large trigeminal nerve
will be seen emerging from its ventral surface, nearer its
upper than its lower border.

\Vith the exception of the restiform bodies, the whole of
the medulla enters the lower aspect of the pons, and its con-
stituent parts are carried upwards within it. The crura
cerebri emerge from its upper aspect. The dorsal surface
of the pons cannot be studied at present. It is turned
towards the cerebellum, which hides it from view. It forms
the upper part of the fioor of the fourth ventricle.

Cerebellum. — The cerebellum is distinguished by the
numerous parallel and more or less curved sulci which
traverse its surface and give it a foliated appearance. As
in the case of the cerebral hemispheres, the grey matter is
spread over the entire surface, whilst the white matter forms
in the interior a central core.

In the cerebellum we recognise a median portion termed
the vermis, and two lateral and much larger portions, called

574 THE BRAIN.

the lateral hemispheres. The distinction between these main
subdivisions of the organ is not very evident from every point
of view. In front and behind there is a marked deficiency
or notch (Fig. 347). T^i^o. posterior notch., termed the incisura
marstipialis, is smaller and narrower than the anterior notch.
It is bounded laterally by the hinder parts of the cerebellar
hemispheres, whilst its bottom is formed by the median lobe
or vermis. It is occupied by the falx cerebelli. The an-
terior notch, also termed the incisura semilunaris, is shallower
but much wider than the marsupial notch. When viewed
from above, it is seen to be occupied by the inferior pair of
quadrigeminal bodies and the superior cerebellar peduncles.
As in the case of the incisura marsupialis, the sides are formed
by the lateral hemispheres and the bottom by the vermis.

On the superior surface of the cerebellum, there is little
distinction to be noted between the median lobe and the
upper surface of each lateral hemisphere. The median lobe
or superior vermis forms a median elevation, from which the
surface slopes gradually downwards on each side to the
margin of the hemisphere. The vermiform elevation is
highest in front, immediately behind the semilunar notch,
and from this it gradually inclines downwards towards the
marsupial notch. It receives the name of the monticulus
cerebelli. The folia on the surface of the vermis superior
will be seen to be thicker and fewer in number than those
on the upper surface of the lateral hemisphere. It is this
that gives it the worm-like appearance from which its name
is derived.

On the inferior surface of the cerebellum, the distinction
between the three constituent parts of the organ is much
better marked. On this aspect the lateral hemispheres,
which are full, prominent, and convex, are separated by a
deep, mesial hollow, which is continued forwards from the
marsupial notch. This hollow is termed the vallecula
cerebelli, and in its fore-part is lodged the medulla oblongata.
When the medulla is raised, and the lateral hemispheres
pulled apart so as to expose the bottom of the vallecula, it
will be seen that this is formed by the vermis inferior, and.

HORIZONTAL FISSURE OF CFREHEI.LUM.

575

further, that the latter is separated on each side from the
corresponding lateral hemisphere by a distinct furrow,
termed the sulcus vallccuhr.

U'hen the margin of the cerebellum, where it forms the
bottom of the semilunar notch on the superior aspect of the
organ, is gently pushed backwards, and the mesencephalon
l)ulled forwards, two strands lying upon the dorsal aspect
of the pons Varolii will be seen. These are the superior
cerebellar peduncles. Emerging from the white matter of
the cerebellum, they converge as they proceed upwards, and

Incisura sciiiilunaris

Lohulus centralis

'/'' ^^Wr*^ Cut men vionticuli

Incisura viarsupialis

Tuber valvulae

Clivus monticuli
J'olium cacutiiinis

Fig. 347. — Upper surface of the cerebellum.
(From Schwalbe.)

finally they disappear under the inferior quadrigeminal
bodies. The thin lamina which is stretched across between
them is the valve of Vieussens, or the superior medullary velum.
It is continuous below with the white core of the cere-
bellum, and it forms the roof of the upper part of the fourth
ventricle. From its dorsal surface, close to the inferior
(|uadrigeminal body, the small trochlear nerves emerge.

Certain of the fissures which traverse the surface of the
cerebellum, deeper and longer than the others, map out
districts which are termed lobes. The most conspicuous
of all these clefts is the i^reat horizontal fissure.

Great Horizontal Fissure of the Cerebellum. — The great

576 THE BRAIN.

horizontal fissure begins in front, and passes round the
circumference of the cerebellum, cutting deeply into its
outer and posterior margins. In front, its lips diverge from
each other so as to enclose the large middle peduncle,
where it passes into the interior of the cerebellum. This
fissure divides the organ into an upper and a lower part,
which may be studied separately.

Lobes on the Upper Surface of the Cerebellum. — When
examined from before backwards, the vermis superior
presents the following subdivisions: — (i) the hngula ; (2)
the central lobule ; (3) the culmen monticuli ; (4) the clivus
monticuli ; (5) the foHum cacuminis. With the exception
of the lingula, each of these is continuous on either side
with a corresponding district on the upper surface of the
hemisphere, thereby forming a cerebellar lobe. Thus, the
central lobule is prolonged outwards on each side in an
expansion called the ala ; the culmen constitutes a central
connecting piece between the two anterior crescentic lobules
of the hemispheres ; the clivus stands in the same relation
to the posterior crescentic lobules ; and the folium cacuminis
is the connecting band between the poster o-superior lobules
of the hemispheres.

The Lingula. — The lingula can only be seen when the
bottom of the semilunar notch is pushed backwards. It
consists of four or five small folia continuous with the
grey matter of the vermis superior, and prolonged forwards
on the surface of the valve of Vieussens or superior
medullary velum in the interval between the superior
cerebellar peduncles.

Lobus Centralis with its Alse. — The central lobule lies
at the bottom of the semilunar notch, and is only seen to a
very small extent on the upper surface of the organ. It is
a little central mass which is prolonged outwards for a short
distance round the semilunar notch in the form of two
expansions, termed the alee.

Lobus Culminis. — The culmen monticuli constitutes the
summit or highest part of the monticulus of the vermis
superior. It is prolonged outwards on either side into the

LOBES ON UNDER SURFACE 01- CEREBELLUM. 577

corresponding hemisphere as the anterior crcscciitk lobule.
This is the most anterior subdivision on the upper surface
of the hemisphere. The two anterior crescentic lobules,
with the culmcn monticuli, form the lobus culminis cerebelli.

LobusClivi. — The cliviis )iion(iculi\v^'f> Ijchind the culmen,
from which it is separated by a distinct fissure, and it forms
tlie sloping part or descent of the monticulus of the vermis
su[)erior. On each side it is continuous with the posterior
crescentic lobule of the lateral hemisphere, and the three
parts are included under the one name of lobus clivi.

The two .crescentic lobules on the upper surface of the
hemisphere are frecjuently described together as the quadrate
lobule.

Lobus Cacuminis. — Hhefoliuvi cacuminis forms the most
posterior part of the vermis superior, and it bounds the
great horizontal fissure superiorly at the posterior or mar-
supial notch. It is a single folium, the surface of which may
be smooth or beset with rudimentary secondary folia. It is
the connecting link between the \.\\q postero-superior lobules
of the hemispheres — the three parts constituting the lobus
cacuminis. As the folium cclcuminis is traced outwards into
the postero-superior lobule of the hemisphere, it is found
to expand greatly. The result of this is that the postero-
superior lobule on each side forms an extensive foliated
district bounding the hinder part of the great horizontal
fissure above.

Lobes on the under surface of the Cerebellum. — The
connection between the several parts of the vermis inferior
and the corresponding districts on the under surface of the
two hemispheres is not nearly so distinct as in the case of
the vermis superior and the lobules on the upper surface of
the heniisi)heres. A groove, the sulcus vallecuhc, intervenes
between the vermis inferior and the hemisphere on each
side.

From l)ehind forwards the following subdivisions of the
vermis inferior may l)e recognised — (i) the tuber valvula:,
(2) the pyramid, (3) the uvula, and (4) the nodule.

On the under surface of the hemisi)here there are five
VOL. II. — 37

578

THE BRAIN.

lobules mapped out by intervening fissures. These are —
(i) th.e flocculus, a little lobule lying on the middle peduncle
of the cerebellum; (2) the biventral lobule, which lies im-
mediately behind the flocculus, and is partially divided into
two parts by a fissure which traverses its surface; (3) the
tonsil or amygdala, a rounded lobule, which bounds the
vallecula on the inner side of the biventral lobule ; (4) the
slender lobule (lobulus gracilis), a narrow crescentic strip of
cerebellar surface which is situated behind the biventral
lobule; (5) ihe J)ostero-inferior lobule placed behind the

Sup: med: vel:

Lobtdiis centralis

Sup. peduncle

Middle peduncle
Flocculus

Fig. 348. — Lower surface of the cerebellum.

(From Schwalbe. )

N. Nodule. U. Uvula. P. Pyramid.

slender lobule, and bounding the great horizontal fissure
below.

These lobules of the hemispheres, with the corresponding
portions of the vermis inferior, constitute the lobes on the
under aspect of the cerebellum.

Lobus Noduli. — The lobus noduli comprises the nodule
and the flocculus with an exceedingly delicate connecting
lamina of white matter, termed the inferior medullary velum.

The velum cannot be properly seen at present, but it will be exposed
at a later stage of the dissection.

Lobus Uvulse. — The uvula is a triangular elevation placed

LOB us TUBER IS.

579

between the two tonsils. It is connected across the sulcus
valleculai with each tonsil by a low-lying ridge of grey matter
scored by a few shallow furrows, and in consecjuence termed
the furroivcd band. The two tonsils and the uvula form
the lobus uvuhii.

To sec llie furrowed hand it will be necessary to remove the tonsil
on one side.

Lobus Pyramidis. — The pyramid is connected with the
bivenlral lobule on each side by a faint ridge which crosses
the sulcus vallecula;. The term lobus pyramidis is given to
the three lobules which are thus associated with each other.

culinen central lobule

clivus

luber valvuUc"^'^'

lingula on the
superior medul-
lary velum.

Fig. 349. — Mesial section through the vermis of the
cerebellum. (From Gegenbaur. )

Lobus Tuberis. — The tuber valvu/ce, which forms the
most posterior part of the vermis inferior, is composed of
several folia, which run directly into the postero- inferior
lobule. The slender lobule is not directly connected with
the tuber valvuh\i, but it is included with it and the postero-
inferior lobule in the /obus tuberis.

Disscclioii. — .\ mesial section should now be made through the
vermis of the cerebellum and the two medullary vela into the cavity of
the fourth ventricle. When the two parts of the cerebellum are drawn
slightly asunder, a view of the fourth ventricle is obtained ; further, the
connections of the two medullary vela and the arrangement of the
peduncles of the cerebellum can be more clearly understood.

S8o THE BRAIN.

Arbor Vitse Cerebelli. — The cut surface of the cerebellum
presents a very characteristic appearance. The grey matter
on the surface stands out distinctly from the white matter in
the interior. Further, the complete manner in which the
surface is cut up by the fissures and sulci into secondary
and tertiary folia is seen. The central mass of white matter
is termed the corpus trapezoides. From this, main prolonga-
tions pass into the various lobules, and these give off
branches so as to supply each folium with a central white
stem or core. The term arbor vitce is applied to the appear-
ance which consequently results when a section is made
through the cerebellum.

Cerebellar Peduncles. — These are three in number on
each side — viz. the middle, the superior, and the inferior.
They are all directly connected with the white medullary
centre of the cerebellum, and are composed of fibres which
emerge from or enter the white central substance of the
organ.

The middle peduncle is much the largest of the three. It
is formed by the transverse fibres of the pons, and it enters
the cerebellar hemisphere on the outer side of the other
two. The lips of the anterior part of the great horizontal
fissure are separated widely from each other to give it
admission. Within the cerebellar hemisphere its fibres are
distributed in two great bundles. Of these, one composed
of the upper transverse fibres of the pons, radiates out in
the lower part of the hemisphere ; whilst the other, con-
sisting of the lower transverse fibres of the pons, spreads
out in the upper part of the hemisphere.

The inferior peduncle is simply the restiform body of the
medulla. It emerges from the white matter of the cere-
bellar hemisphere between the other two peduncles. At
first directed forwards, it then turns sharply downwards so
as to form the upper part of the posterior area of the
medulla {i.e. the restiform body).

The superior peduncles are composed of fibres which for
the most part come from the corpus dentatum of the
cerebellar hemisphere. As they issue from the cerebellum,

MEDULLARY VELA. 5S1

eachpeduncle lies close to the inncrsidc of the corresponding
middle peduncle. They then proceed upwards towards the
inferior pair of quadrigeminal bodies. At first they form
the lateral boundaries of the upper part of the fourth
ventricle, but they converge as they ascend on the dorsal
aspect of the pons Varolii, so that ultimately they come to
overhang that cavity and enter into the formation of its
roof. They disappear under cover of the quadrigeminal
bodies, and their course in the mesencephalon has already
been described.

Medullary Vela. — The medullary vela are closely associ-
ated with the peduncles. They consist of two thin lamince
of white matter which are projected out from the white
central core of the cerebellum. The superior medullary
velum., or valve of Fieussef/s, stretches across the interval
between the two superior cerebellar peduncles, with the
inner margins of which it is directly continuous. It is
triangular in form, and when traced downwards it is seen to
be carried with the superior peduncles into the white matter
of the cerebellum. Spread out on its dorsal surface is the
tongue-shaped prolongation of grey matter from the cortex
of the cerebellum, which is termed the lifigula, and issuing
from its substance close to the inferior quadrigeminal bodies
are the two trochlear nerves.

The inferior medullary velum is somewhat more compli-
cated in its connections. It presents the same relation to
tlie nodule that the superior velum presents to the lingula.
It is a wide thin lamina of white matter — so thin that it is
translucent — which is prolonged out from the white centre
of the cerebellum above the nodule. From the nodule it
stretches outwards to the flocculus, thereby bringing these
two small portions of the cerebellum into association with
each other. Where it issues from the white matter of the
cerebellum, it might almost be said to be in contact with
the superior medullary velum, but as the two laminie are
traced forwards they diverge from each other : the superior
velum is carried upwards between the superior peduncles
of the cerebellum, whilst the inferior medullary velum turns

582 THE BRAIN.

downwards round the nodule, and ends in a slightly
thickened free crescentic edge. The cavity of the fourth
ventricle is carried backwards between the two vela, which
from a tent-like roof for it.

Fourth. Ventricle. — This cavity is somewhat rhomboidal
in form. Below, it tapers to a point and becomes con-
tinuous with the central canal of the cord; above, it
narrows in a similar manner and is continued into the
aqueduct of Sylvius. The posterior wall is called the roof.
The anterior wall is termed the floor., and is formed by the
dorsal surface of the medulla and pons. On either side a
narrow pointed prolongation of the ventricular cavity is
carried outwards from its widest part round the upper part
of the corresponding restiform body. This is termed the
lateral recess (Fig. 318, p. 525). Looking into the cavity
between the two portions of the mesially divided cerebellum
the lateral recess is very apparent.

Floor of the Fourth Ventricle. — In its lower part the
floor of the fourth ventricle is formed by the dorsal surface
of the open part of the medulla, whilst in its upper part
it is formed by the dorsal surface of the pons Varolii. The
area thus constituted is distinctly lozenge-shaped, its widest
part being opposite the middle peduncles of the cerebellum.
Further, it is circumscribed by definite lateral boundaries.
Thus below, it is bounded on either side by the clava, the
cuneate tubercle, and the restiform body ; whilst above, the
lateral limit is formed by the superior cerebellar peduncle.

The floor of the fourth ventricle is divided into two
symmetrical and lateral portions by a median groove. At
the lower narrow end, between the two clav^, it receives
the name of the calamus scriptorius., from its fancied
resemblance to the point of a pen. Crossing each half of
the floor at its widest part are several transverse bundles of
fibres termed the strice acusticce. They appear to emerge
from the mesial groove, and they are carried outwards over
the restiform body. Their connections are somewhat
obscure, but the majority of the fibres are beheved to pass
on to the flocculus. The strise acusticae divide each lateral

FLOOR OF THE FOURTH VENTRICLE. 5S3

half of tlio ventricular floor into an upper and a lower
portion, which very nearly correspond to the subdivisions
of this area formed by the medulla and the pons. On the
lower medullary district a small triangular depression, placed
immediately below the stria; acustica;, catches the eye. This
is termed the/<wtv? inferior. It is shaped somewhat like an
arrow-head. The apex or point looks towards the striae,
whilst the lateral angles of the base are prolonged down-
wards in the form of diverging grooves. Of these, the
inner groove runs towards the opening of the central canal
at the calamus scriptorius, whilst the outer groove runs
towards the lateral boundary of the floor. In this manner
the portion of the floor which lies below the strije acusticae
is mapped out into three triangular areas. The mesial
subdivision is slightly elevated, and is termed the trigonum
/lypogiossi, because subjacent to this area is the nucleus of
origin of the hypoglossal nerve. The intermediate area
between the diverging grooves which proceed from the
base of the fovea inferior is the trigonum vagi, so called
because the vagus and glosso -pharyngeal nuclei lie sub-
jacent to it. The external area is the trigonum acustici.
The base of this area is directed upwards and runs con-
tinuously into an eminence, the acustic tubercle, over which
the striae acusticre pass. Subjacent to this region of the
floor of the ventricle the principal part of the auditory
nerve takes origin.

On the part of the floor of the ventricle which lits above
the striae acusticas, and which corresponds to the dorsal
surface of the pons, there is also a slight depression. This
is termed \.\\<i. fovea superior. Between it and the median
groove there is a marked prominence, termed the eminentia
teres. Inferiorly, this elevation passes downwards and be-
comes continuous with the trigonum hypoglossi, whilst
above it is carried upwards towards the opening of the
aqueduct of Sylvius. In both directions it becomes gradu-
ally less prominent, but still it forms a distinct elongated
elevation which stretches along the whole length of the
median groove. It is termed the fasciculus teres. Pro-

S84 THE BRAIN.

ceeding upwards from the fovea superior to the opening of
the Sylvian aqueduct there is a shallow depression, termed
the locus cceridens. When the ependyma is scraped away
from the surface of this part of the floor, some dark pig-
mented substance, termed the substantia ferruginea, will be
exposed.

Roof of the Fourth Ventricle. — In its upper part the
roof of the fourth ventricle is formed by the superior
medullary velum as it stretches across between the two
superior cerebellar peduncles, and also to some extent by
the approximation of these peduncles themselves as they
approach the mesencephalon.

In its lower part the roof of the ventricle is exceedingly
thin, and is not all formed of nervous matter. The inferior
medullary velum enters into its formation, and where this
fails the epithelial lining of the cavity, supported by pia
mater, is carried downwards towards the lower lateral bound-
aries of the ventricle. At the lowest part of the calamus
scriptorius, and also along each lateral boundary, a thin
lamina of white matter is carried for a short distance over
the epithelial roof. The small lamina at the calamus scrip-
torius overhangs the opening of the central canal, and is
termed the obex. The lamina in relation to the lateral
boundary of the ventricle is more extensive, and is called
the ligula. It begins on the clava, and passes upwards
along the cuneate tubercle to the restiform body.. On the
surface of this it turns outwards so as to bound the lateral
recess below, and in some cases it may be seen to become
continuous round the extremity of the lateral recess with
the inferior medullary velum.

A short distance above the calamus scriptorius there is
an aperture in the epithelial roof of the fourth ventricle, by
means of which the cavity of the ventricle communicates
with the subarachnoid space. This opening is termed the
foramen of Magendie. There is also an aperture of a similar
character in the epithelial roof of each lateral recess.

Two choroid plexuses, one on either side of the mesial
plane, invaginate the roof of the fourth ventricle in such a

JNyEKA'.lL STRUCTURE OF TOXS VAROLII. 5S5

way that they ai)pcar to he within the cavity. Offshoots
from those likewise protrude into the lateral recesses.

Dissectiott. — The dissector should now introduce liis fingers into the
great horizontal fissure of the right half of the cerebellum, and gently
tear the upper jiart of this siile of the organ away from the lower part.
By this proceeding the manner in which the peduncles enter the white
medullary centre, and also to some extent the general distribution of
their fibres, will be seen.

Both portions of the cerebellum should, in ihe next place, be removed
by cutting through the peduncles at the i)oints where they enter the
central white matter. A horizontal section may then be made through
the left half of the organ, rather nearer its upper sur(;\ce than its lower
surface. This will reveal the corpus denlatum.

Corpus Dentatum of the Cerebellum. — This is a collection
of grey matter, embedded in the white medullary centre of
the lateral hemisphere of the cerebellum, which presents an
appearance very similar to that of the olivary nucleus of the
medulla. It is a thin lamina of grey matter, which appears
on section as a wavy line folded upon itself, so as to form
a crumpled grey capsule with an open mouth towards the
mesial plane. The greater number of the fibres which build
up the superior cerebellar peduncle issue from its mouth.

There are other smaller isolated nuclei of grey matter in the white
medullary centre of the cerebellum, but these cannot, as a rule, be
demonstrated in a specimen obtained in the dissecting-room. They lie
nearer the mesial plane.

Dissection. — A series of transverse sections should now be made
through the pons \'arolii and the medulla, in order thai something of
their internal structure may be learned. The structure of the medulla
is briefly described at p. 568.

Internal Structure of the Pons Varolii. — When transverse sections
are made through liic |ions, ii is sllii Io consist of \.\\q well-defineil jiarts,
viz. a ventral and a dorsal. Broadly s]ieaking, the ventral |iart corre-
sponds with the pyramiilal parts of the medulla, and the jiedal ]iarts of
the crura cerebri ; whilst the dorsal part corresponds with the formatio
reticularis of the medulla and the tegmental ]iart of the crura cerebri.

'J'hc ventral part of the pons is the larger of the two subdivisions. It
is comjiosed of a large number (jf transverse bundles of fibres, through
the midst of which the longitudinal bundles of the pyramids are
carried upwards, to ultimately enter the crustiv of the crura cerebri.
Scattered amongst these fibres we have a certain amount of grey mailer

586

THE BRAIN.

termed the miclei pontis. In the lower part of the pons the pyramids
are seen in the form of one soUd bundle on each side ; almost immedi-
ately, however, these are broken up by intersecting transverse bundles
of fibres, so that they spread out and come to occupy a much wider area
as they proceed upwards. Of the transverse fibres two distinct sets may
be recognized, viz. the superficial transverse fibres, through the midst
of which the pyramidal bundles are prolonged, and a deeper set termed
the trapezium. The superficial transverse fibres on each side pass into
the corresponding middle peduncle of the cerebellum. The trapezial
fibres lie behind the pyramidal bundles, and are only seen in the lower

Fig. 350. — Transverse section through the upper part
of the pons. (Schwalbe, after Stilling. )

/. transverse fibres of the pons ; py. pyramidal bundles ; a. boundary-
line between the ventral and dorsal parts of the pons ; h. oblique
fibres of the lateral fillet ; /. lateral fillet ; /2. mesial fillet ; f.r. formatio
reticularis ; p.l. posterior longitudinal bundle ; s.c.p. superior cerebellar
peduncle; v.in.a. superior medullary velum ; /. grey matter of lingula ;
v.IV. fourth ventricle ; V.d. descending root of the fifth nerve ; s.f. sub-
stantia ferruginea ; g.c. nucleus of the aqueduct ; V. trigeminal nerve ;
r. raphe ; t. transverse fibres of the ventral part of the pons.

part of the pons. They are connected with the accessory auditory
nucleus.

The dorsal or tegmental part of the pons is for the most part formed
of a prolongation upwards of the formatio reticularis of the medulla.
Superiorly it is carried into the tegmental parts of the crura cerebri.

THE A UDITOR 1 ' APPA RA TUS. 587

It is divided into two liilcral parts hy a mesial iai)lic continuous liclow
witli tlic raplio of liic medulla and ahove with the raphe of the tegmental
part of the mesenceplialon, whilst over its dorsal surface is spread a
thick layer of grey matter which belongs to the upper part of the floor
of the fourth ventricle. In transverse sections through the pons a dark
spot in the outer part <>f this indicates the position of the substantia
ferniginca.

Three strands of longitudinal fibres are seen on each side in transverse
sections through the dorsal ]iart of the pons. These arc ( i ) the fdlet,
(2) the posterior longituilinal l>undle, and (3) the superior cerebellar
peduncle.

The Jilh-t has now assumed a ribbon-shaped form. It is placed
between the ventral part of the pons and the formatio reticularis of the
dorsal part. The fibres which form its lateral portion as they pass up-
wards will be seen in successive sections to curve outwards so as to gain
the surface.

The /posterior longitudinal bundle is much more distinct than it is
lower down in the medulla. It has separated itself more completely
from the longitudinal filires of the formatio reticularis, and it is now seen
close to the mesial plane immediately subjacent to the grey matter of
the floor of the fourth ventricle.

The superior ee rebel hi r peduncle in transverse sections presents a semi-
lunar outline. It occupies a lateral position in the dorsal part of the
pons, and gradually sinks deeply into its substance, although it does not
become completely submerged until it reaches the mesencephalon.

The superior olive is a small isolated clump of grey matter which is
embedded in the dorsal part of the pons immediately behind the lateral
part of the corpus trapezoides. It possesses considerable morphological
interest, but it is not likely that the dissector will be able to obtain a
view of it in a dissecting-room specimen.

ue^

THE AUDITORY APPARATUS.

The organ of hearing admits of a very naltual subdivision
into three parts, viz. the external, the middle, and the
internal ear. The external ear consists of the pinna and
the external auditory meatus. The pinna collects the waves
of sound, and is, comparatively speaking, of subsidiary im-
portance in man, although it is highly develoi)cd and of

S88 THE A UDITOR Y APPARA TUS.

considerable service in some of the lower animals. The
external auditory meatus is a passage which leads inwards
to the membrana tympani from the bottom of the concha.
The middle ear is a narrow chamber termed the tympanum
or drum of the ear. It is interposed between the external
auditory passage and the internal ear or labyrinth, and its
outer wall is formed by the membrana tympani. Stretch-

mastoidal antrum. aqueduct of Fallopius.

groove foi

membrana

tympani.

canal for Jacobson's nerve.

Fig. 351. — Coronal section of the right temporal bone
passing through the external and the internal auditory
meatuses.

ing across the cavity of the tympanum, from its outer to
its inner wall, there is a chain of three minute bones called
the auditory ossicles. The internal ear or labyrinth is the
essential part of the organ. It consists of a complicated
system of cavities in the densest part of the petrous portion
of the temporal bone. These cavities contain fluid called
perilymph, and also a membranous counterpart of the bony

MEATUS AUDI TORI US EXTERNUS. 589

cliambers called the membranous lahyrinlh. ^Vilhin the
latter there is fluid termed cndolyini)h.

Dissection. — In a leniporal bone to which the pinna is still allachcd
llic squamous portion should be removed by a horizontal saw-cut at the
level of the posterior root of the zyt;oma. Willi the chisel and bone
forceps the rt)of and anterior wall of the auditory passage should then
be taken away piecemeal, until a good view is obtained of the outer
surface of the membrana tympani.

Meatus Auditorius Externus. — The i)inna has already
been described (p. 284). The meatus is directed inwards
and slightly forwards, and describes a gentle curve, the
convexity of which is directed upwards. It is about one
inch and a half in length, and in its outer part (about half
an inch in length) its walls are composed of cartilage and
fibrous tissue, whilst in its inner part its walls are bony.
The passage is narrower in the inner bony portion than in
the outer cartilaginous part. The skin lining the carti-
laginous portion is abundantly furnished with ceruminous
glands, and is also provided with outwardly-directed hairs,
which tend to prevent the entrance of dust. The cutaneous
lining of the inner half, which is thin and tightly adherent
to the subjacent periosteum, is destitute of hairs, and glands
are for the most part absent. A small patch of glands,
however, is found at the upper and back part of the osseous
meatus, at its junction with the cartilaginous portion. The
cutaneous lining of the meatus is continued in the form of
an exceedingly delicate layer over the outer surface of the
membrana tympani.

If the subject is slightly decomixjsed the cuticular lining of the meatus
may be drawn out entire, like the finger of a glove, and the epidermal
covering of the mend)rana tympani is thus demonstrated.

Dissection. — The tympanic cavity can be most conveniently openeil
for inspection by the removal of its roof. The roof is formed by a
thin scale of bone (tegmen tymi)ani) which extends beyond the limits of
the tympanum and covers in the canal for the tensor tymjiani in front
and the masloidal antrum behind. An ojK-ning should be made ihnjugh
the legmen tympani, immediately external to the elevation fornuil by
the superior semicircular canal, and about three-eighths of an inch in
front of the superior border of the petrous bone. This will open into the

590 THE A UDITOR V APPA RA TUS.

mastoidal antrum. The opening can then be cautiously enlarged with
chisel and bone forceps until the whole of the tegmen tympani is picked
away piecemeal. The roof of the internal auditory meatus should also
be carefully removed with mallet and chisel. The mastoidal antrum,
the tympanum with its contents, the osseous portion of the Eustachian
tube, the tensor tympani muscle, and the auditory and facial nerves
are now displayed.

The Mastoidal Antrum is a large recess or air-chamber
placed behind the tympanum, and communicating by a
relatively large opening with the upper part of that cavity.
It is lined with mucous membrane, which is continuous
with the lining membrane of the tympanum. The mastoid
process is also occupied by the mastoid cells. The greater
number of these communicate with the mastoidal antrum,
are lined with mucous membrane, and contain air. Still it
is well to bear in mind that, as a general rule, a certain
proportion of the cells situated in the lower and back part
of the process are filled with marrow.

The Tympanic Cavity or Middle Ear is a small chamber
filled with air, which is placed between the bottom of the
meatus externus and the internal ear or labyrinth. Behind
it communicates by a relatively large orifice with the mas-
toidal antrum and air-cells, whilst in front the Eustachian
tube opens into it and brings it into connection with the
cavity of the pharynx. It contains the chain of auditory
ossicles which cross from its outer to its inner wall, and it
is lined by delicate mucous membrane.

The vertical depth and the antero-posterior length of the
tympanic cavity is about half an inch in each case. Its
width, however, from side to side, is not more than a sixth
of an inch, and as both its outer and inner walls bulge into
the cavity, its width in the centre is thereby still further
reduced. It presents for examination a roof and a floor
with four walls, viz. anterior, posterior, external, and
internal.

The roof\% composed of a very thin plate of bone termed
the tegmen tympani. This separates it from the cranial
cavity. In chronic inflammatory conditions of the middle

THE TYMPANIC CAVITY OR MIDDLE EAR. 591

car an extension of the inflammatory process to the
meninges of the brain is always to be apprehended.

T\\Q. floor is narrow and is also formed by a thin osseous
lamina, which is interposed between the tympanum and
the jugular fossa, which lodges the internal jugular vein.
An extension of an inflammatory condition of the middle
ear in this direction, therefore, might lead to thrombosis.

T\\Q. posterior ivall y^xQ.'aO.nX.?,, in its upper part, the open-
ing into the mastoidal antrum, and below this, close to the
inner wall, a small hollow coni-
cal projection termed the pyra-
mid. This is perforated on its
summit, and the aperture leads
into a canal which curves back-
wards and then downwards until
it finally opens into the lower
part of the last stage of the
Fallopian aqueduct. This
curved canal lodges the stapedius
muscle, the delicate tendon of
which enters the tympanic cavity
through the aperture on the
summit of the pyramid. On
the outer side of tlie pyramid is
the aperture on the posterior wall through which the
chorda tympani nerve enters the tympanum.

The anterior ivall is narrow, because the inner and outer
walls become somewhat approximated to each other as
they are traced forwards. In its upper part it is deficient,
as here the tympanic cavity is directly continued into the
osseous part of the Eustachian tube. Above this is the
canal, in which is lodged the tensor tympani muscle. In
its lower part, below the orifice of the Eustachian tube, the
anterior wall is formed by an exceedingly thin plate of
bone which intervenes between the tympanic cavity and
the ascending part of the carotid canal. This anatomical
relation explains the throbbings in the ear, synchronous with
the pulsations of the heart, from which certain patients suffer.

Fig. 352.
section
panum.

— Sclieniatic vertical
througli the tym-
(From Testut. )

External meatus.
Tympanic cavity.
Promontory or inner wall.
Membrana tympani.

592

THE AUDITORY APPARATUS.

The imier wall which intervenes between the tympanum
and the labyrinth presents certain important points for
study. The greater part of this wall bulges outwards into
the cavity in the form of a very evident elevation termed
the promontory. Above the hinder part of the promontory
there is an oval foramen, the long axis of which is directed
from before backwards. This is the fenestra ovalis, an

M.A.

c.c.

F.R.
P.R. F.O. S.F.

Fig. 353. — Antero - external view of the inner wall of the tympanic
cavity of the left ear of an eighth-month fretus. (Professor Fawcett. )

The promontory has been partially scraped away, showing the cochlea.

The osseous Eustachian tube has been removed and part of the wall of
the carotid canal has been removed to show more of the first turn of the
cochlea.

C.T. Canal for tensor tympani.

P.C. Processus cochleariformis.

A.C. Apex of cochlea lying under the
processus cochleariformis and the
canal for the tensor tympani.

P.R. Promontory caused by first turn
of cochlea.

C.C. Carotid canal.

CI. First turn of cochlea forming pro-
montory.

F.R. Fenestra rotunda.
F.O. Fenestra ovalis.
A.F. Aqueductus Fallopii.

P. Pyramid.
S. F. Stylo-mastoid foramen.
E.C. External horizontal semicircular

canal (ampulla of anterior limb) lying

above aqueductus Fallopii.
M.A. Mastoid antrum.

opening into the vestibular part of the labyrinth, which is
closed in the recent state by the foot-piece of the stapes,
the innermost of the auditory ossicles. The pyramid on

THE TYMPANIC CAVITY OR MIDDLE EAR.

593

the posterior wall will be seen to lie immediately behind
the fenestra ovalis. Above the fenestra ovalis, in the angle
formed by the meeting of the roof and inner wall of the
tympanum, a ridge, arching from before backwards, will be
seen. This is produced by the aqueduct of Fallopius

Fig. 354. — The tympanic
inside. The head of the
(From Testut. )

1. Membrana tympani.

2. Umbo.

3. Handle of the malleus.

4. Processus brevis of the malleus.

5. Plica anterior.

6. Plica posterior.

7. Membrane of Shrapnell.

8 and 9. Two slight fossa: (termed the
/osscr of TroelLsch).

VOL. II. — 38

membrane viewed from the
malleus has been remos'ed.

10. Rim of bone which gives att.ichment

to the membrana tympani.

1 1 . Fissure of Glascr.

12. Eustachian tube.

15. Orifice of entrance for the chorda
tympani nerve.

14. Orifice of e.xit of the same nerve.

15. Point of attachment on the f>osterior

wall of tympanum for the short
process of the incus.

594

THE AUDITORY APPARATUS.

bulging into the tympanum. Its wall is very thin, and
allows the white colour of the facial nerve which is con-
tained within the canal to be readily seen. In front of
this ridge, in the upper part of the inner wall of the tym-
panum, is '&i& processtcs cochkariformis supporting the tensor

ty7npmii muscle. The pro-
cessus cochleariformis forms
a trough or gutter of bone
which runs backwards towards
the anterior end of the fen-
estra ovalis, immediately above
which it terminates. Here
it makes a sharp bend, which
almost surrounds the tendon
of the tensor tympani, and
forms a pulley upon which
the tendon plays. Below the
hinder end of the promon-
tory is the fenestra rotunda.,
an aperture which, in the
macerated bone, leads into
the cavity of the cochlea,
but which in the recent state
is closed by a membrane
which is stretched across it,
and receives the name of the
secondary membrane of the tym-
panum.

The outer wall of the
tympanic cavity is formed for the most part by the mem-
brana tympani.

Membrana Tympani. — The membrana tympani is an
elliptical disc of membrane which is stretched across the
bottom of the meatus auditoris externus, so as to form the
greater part of the outer wall of the tympanum. It is
placed very obliquely ; its lower and its fore borders both
incline inwards.

Its mode of attachment around the bottom of the

Fig. 355- — Schematic representa-
tion of the membrana tympani and
the malleus. (From Testut. )

1. Processus brevis of malleus.

2. Attachment of membrana tympani.
Umbo.

External meatus.
Its superior wall.
Its inferior wall.
Handle of the malleus.
Tympanic cavity.

AlEMBRANA TYMPANI.

595

meatus is deserving of some alleiition. Here, there is a
ring-like ridge of bone very distinctly grooved which forms
us it were a frame in which the membrane is set. But this
ridge is deficient above, and at this point there is a deep
notch (the notch of Rivinus) between the extremities of
the bony ridge. This notch is occupied by a portion of
the membrane which is not so dense in its texture (see-
ing that the fibrous layer is absent), and not so tightly
stretched ; consequently it receives the name of the tnem-
bnxna flaccidix (Shrapnell's membrane).

The membrana tympani is composed of tlirce layers —

plica posterior, processus brevis mallei.

membrana flaccida.

Fig. 356. — The right mcmbran:i tj'mpani as seen from
the outside. (From Merkel. ) The plica anterior and
the plica posterior are the folds which limit the membrana
flaccida in front and behind. The handle of the malleus
is seen shinin£r throutih the membrane.

viz. an outside cuticular layer, an intermediate fibrous
lamina, and an inside mucous layer. The handle of the
malleus is intimately connected with the fibrous layer, and
is covered over by the mucous layer. It draws the mem-
brane inwards towards the tympanic cavity so that the
outer surface is deeply concave. The deepest point of this
concavity corresponds with the flattened extremity of the
handle of the malleus, and is termed the umbo or umhilicus.

In examining the living ear with a sixrculum, tlie .surface of the
membrane appears highly ixilished, and a cone of light extends down-

596

THE A UDITOR Y A PPA RA TUS.

wards and forwards from the tip of the handle of the malleus. A pair
of stride (Prussak's strise), called the anterior and posterior folds, extend
from the processus brevis to the margins of the notch of Rivinus, and
thus map out Shrapnell's membrane. The long process of the incus
can be faintly seen through the membrana tympani, parallel to and
behind the handle of the malleus.

Tympanic Mucous Membrane. — The tympanum is lined
throughout with mucous membrane which is continuous

with the mucous membrane
of the pharynx. As aheady
mentioned, it forms the inner-
most layer of the membrana
tympani, and is prolonged
backwards into the mastoidal
antrum and air-cells. It also
covers the ossicles and invests
the tendons of the stapedius
and tensor tympani muscles.

Auditory Ossicles. — These
are termed the malleus, the
incus, and the stapes.

The malleus presents a
head, a neck, a manubrium
or handle, and two processes
termed respectively the pro-
cessus brevis and the processus
gracilis. The head is large

Fig. 357. — Left malleus and incus.
(After Helmholtz. )

I. Tendon of tensor tympani.

3. Long process of the incus.

4. Short process of the incus.
6. Processus gracilis of the malleus.

The straight line a.b.c. connects

the extremities of the two processes and-roundcd. It is directed
of the incus with the extremity of upwards, and lics abovc the

the manubrium of the malleus. i i r j.t_ t_ a.

level or the membrana tym-
pani, close to the roof of the tympanum. On its posterior
aspect there is a notch-like articular surface directed back-
wards for articulation with the body of the incus. The
manubrium is attached to the fibrous layer of the mem-
brana tympani. The processus brevis is a stunted pro-
jection which springs from the root of the manubrium.
It is directed outwards, and abuts against the membrana
tympani immediately below the membrana flaccida. The
processus gracilis is a slender spicule of bone which is

AUDITORY OSSICLES. 597

dircclcd forwards, and enters the (ilaserian fissure. It

almost invariably breaks in detaching the malleus from the

adult skull, but it can be easily preserved in the skull of

an infant.

The incus is shaped somewhat like a bicuspid tooth in

which the fixngs are very divergent. It presents a body with

a long and a short process. The body

is provided with an articular surface

which looks forwards and articulates

with the head of the malleus. The

short process is directed backwards, and

its extremity is attached by ligaments

to the posterior wall of the tympanum

near the opening into the mastoidal

antrum. The long; process proceeds Fig. 358. — I he right
, , , . "^ ■', . %. . stapes, (bchwalbe. )

downwards and inwards in a direction

nearly parallel to that of the manu- '• '^^^ foot-pi^ce.

^ • r \ 11 1 • 1 2. Anterior crus.

bnum of the malleus, but internal, 3. posterior crus.
and on a plane posterior to that pro- 4- He.id or capUuium.
cess. From the inner side of its ^' ^'^.'^ " . ,.

6. Sulcus stapedis.

inferior extremity a small knob of

bone (os orbiculare) projects. This articulates with the

head of the stapes.

The malleus and incus move together on an axis which is formed by
the processus gracilis of the malleus and the short process of the incus.
The articular surfaces of the two bones are provided with peculiar catch-
teeth which interlock when the bones are performing their ordinary
movements. When, however, force is applied to the inner surface of
the membrana tympani, as, for instance, when the tympanum is inflated
through the Eustachian tube, the malleo-incudal joint gapes and the
malleus moves by itself. Traction upon the attachments of the stapes,
through the incus, is thus obviated.

The stapes is shaped like a stirrup and presents a head or
outer extremity separated by a slightly constricted neck
from two limbs or crura which join an internal plate or
foot-piece. The head is excavated by an articular cup for
the OS orbiculare of the incus. The crura are grooved
longitudinally on their concave sides (sulcus stapedis).

598 ' THE AUDITORY APPARATUS.

The posterior crus is more sharply curved than the anterior
crus. The foot-piece fits into the fenestra ovahs and
corresponds in its outKne with this aperture. Its lower
border is straight whilst its upper border is curved.

Ligaments of the Auditory Ossicles. — In addition to the
delicate capsular ligaments which surround the joints between
the auditory ossicles, there are certain bands which connect
the bones to the walls of the tympanum and serve to
restrain their movements.

In connection with the malleus there are ( i ) an anterior ligament
which passes from its fore-part at the root of the processus gracilis to
the anterior wall of the tympanum in the neighbourhood of the Glaserian
fissure ; (2) an external ligament which extends from its short process to
the margin of the notch of Rivinus ; and (3) a superior ligament which
connects the head with the roof of the -tympanum.

The ligament of the incus binds the extremity of its short process to
the posterior wall of the tympanum, whilst the annular ligament of the
stapes connects the margin of its foot-piece to the circumference of the
foramen ovale.

Tympanic Muscles. — These are two in number, viz. the
stapedius inserted into the neck of the stapes, and the tensor
tympani inserted into the malleus.

The stapedius occupies the interior of the pyramid
and the canal which curves downwards from it. The
delicate tendon of the stapedius enters the tympanum
through the aperture on the summit of the pyramid, and
is inserted into the posterior aspect of the neck of the
stapes.

The tensor tympani arises from the upper part of the
cartilage of the Eustachian tube and from the contiguous
part of the great wing of the sphenoid. From this it passes
backwards and outwards upon the processus cochleariformis
and above the osseous part of the Eustachian tube. In the
tympanic cavity the tendon turns sharply round the extremity
of the processus cochleariformis and proceeds directly out-
wards, from the inner towards the outer wall of the tympanum
to its insertion into the upper part of the manubrium of the
malleus on its internal aspect.

VESTIBULE. 599

The Chorda Tsrmpani Nerve wliidi iravcrscs the lynipanic
cavity in close relation to the upper part of the membrana
tympani is described on p. 313.

The Tympanic Plexus has also been previously described
on p. 334.

The Eustachian Tube is the passage which brings the
tym[)anic cavity into communication with the pharynx and
through which air reaches the tympanic cavity and the
mastoidal cells. It consists of an osseous and a cartilaginous
portion. 'J'he osseous portion is about half an inch in length.
It is widest at its entrance into the tympanum, and narrowest
at its other end. The cartilaginous portio?t is about an inch
in length, and has been already described on p. 408.

Disscc/ioti. — A good deal of the anatomy of the internal ear may
l)e learned by chiselling away the surrounding hone from the harder
walls of the different cavities which form the osseous labyrinth. When
this is being done the bone must beheld in a vice. The dissection can
best be carried out in the petrous bones of an eighth-month or a full-time
fielus.

Various sections should also be made through the macerated bone.
Some of the more essential of these will be described later on.

Internal Ear or Labyrinth.— The labyrinth consists of an
intricate system of cavities in the petrous part of the temporal
l)one. They contain hollow membranous structures in con-
nection with which the filaments of the auditory nerve end.
We therefore recognise an osseous and a membranous
labyrinth.

The osseous iabyrintJi is composed of an intermediate
chamber termed the vestibule, behind which are placed the
three semicircular canals, whilst in front is the cochlea. All
these cavities communicate with each other. The corre-
sponding membranous parts do not completely occupy the
osseous chambers and the intervening space is filled with
a fluid termed the perilymph. The membranous labyrinth
also contains a fluid which receives the name of endolymph.

Vestibule. — The vestibule is a small ovoidal bony
chamber, the antero-posterior diameter of which is about
the sixth of an inch in lensilh. It is situated between the

6oo

THE A UDITOR Y APPARA TUS.

inner wall of the tympanum and the bottom of the internal
auditory meatus. /

Into the back part of the vestibule the three semicircular
canals open by five round apertures ; whilst in its lower and
fore part is the opening of the scala vestibuli of the cochlea.

ASC

i

P.O.E.C

S.T. O.S.L.

Fig. 359. — A dissection of the labyrinth of the right ear of an
eighth -month fcetus, seen from the outer side. The vestibule
and cochlea have been opened up ; the last turn and a half of
the cochlea have been torn out. (Professor Fawcett. )

A.S.C. Anterior opening of superior
vertical semicircular canal.

E.C. External semicircular canal ; the
line is on the anterior limb.

P.O.E.C. Posterior external canal.

P.V.C. Posterior vertical canal.

A.O.S.P. Anterior opening of posterior
vertical canal.

C.S. Stem formed by union of posterior
limbs of superior and posterior ver-
tical canals.

CO. Opening of common stem into
vestibule.

F.HL. Fovea hemi-elliptica.

C. V. Crista vestibuli.

F.HS. Fovea hemispherica.

A.V. Aqueductus vestibuli.

F.R. Fenestra rotunda.

.9. T. Scala t3'mpani of cochlea, ending
to left at fenestra rotunda, and cut
off from cavity of vestibule by

O.S.L. The osseous spiral lamina.

6". V. Scala vestibuli communicating with
vestibule directly ; it is smaller than
scala tympani.

R.M. A foramen caused by pulling out
the core of the modiolus. The ring
round it is the festooned shell of the
modiolus which, on rising, becomes
the osseous spiral lamina. Both
correspond with the lower part of
the floor of the internal auditorj'
meatus.

SEMICIRCULAR CANALS.

60 1

On llic outer wall is llic fL-ncstra oralis, wiiicli is closed
in the recent slate hy the delicate i)eriosleal lining of the
chamber and the footpiece of the stapes. ^Vhcn these parts
are removed, the vestibule conmiunicatcs directly through
this aperture with the tympanum. On the anterior part of
the inner wall o{ the vestibule there is a circular depression,
termed \\\q fovea hemispherica, which is bounded behind by
a vertical ridge, called the crista vestibuli. The bottom of
the fovea hemispherica is perforated by some minute holes
which give admission to filaments from the vestibular part

1. Superior semicircular canal.

2. Common opening of superior

and posterior semicircular
canals.

3. Orifice of aqueduct of the

vestibule.

4. Crista vestibuli.

5. Fovea hemispherica.

6. Orifice of scala vestibuli.

7. Orifice of posterior semi-

circular canal.

8. Orifice of the external .semi-

circular canal,
g. E.\ternal semicircular canal.

KiG. 360. — The inner wall of the liglit vestibule.

of the auditory nerve. On the roof oi the vestibule another
depression, named ^\q fovea henii-elliptica, may be seen. It
is placed behind the crista vestibuli.

A small aperture placed on the posterior i)art of the inner
wall likewise deserves mention. It is the mouth of the
aquediictiis vestibuli — a small canal which leads backwards to
the posterior surface of the jietrous bone, where it opens
under the dura maler.

Semicircular Canals. — These are three bony canals or
tubes i)laced behind the vestibule. They are bent upon
themselves, so that each forms considerably more than half
a circle, and they occupy planes at right angles to each other

6o2

THE AUDITORY APPARATUS.

like three faces of a cube. They a.re termed superior, pos-
terior, and external, and they open into the back part of the
vestibule by five round orifices, the number of openings
being thus reduced through the adjoining extremities of the
superior and posterior canals becoming fused together so as
to present a common orifice. One extremity of each canal
where it joins the vestibule becomes expanded into what
is termed its ampulla. There are thus three ampuUated
ends.

The superior semicircular canal forms the highest part of
the labyrinth, and gives rise to a smooth elevation on the

vestibule. superior semicircular canal.

cochlea.

foramen ovale.

posterior semicircular
canal.

foramen rotundum.

external semicircular canal.

Fig. 361.

-From a cast of the left bony labyrinth.
(From Henle. )

anterior surface of the petrous bone, immediately in front
of its superior border. It is vertical, and placed somewhat
transversely to the long axis of the petrous bone. The
posterior set7iicircular canal, which is the longest of the three
tubes, is also vertical, and lies in a plane parallel to the
posterior surface of the petrous bone. The external semi-
circular canal is the shortest of the tubes, and occupies a
horizontal plane.

The Cochlea is a tapering tube which is coiled spirally
for two turns and a half around a central pillar, termed the
modiolus. The appearance produced is somewhat similar
to that of a spiral shell. The cochlea lies in front of the
vestibule, with its base directed towards the bottom of the
internal auditory meatus ; whilst its apex looks forwards

THE COCIir.EA.

6oj

and outwards, and coniL% into close relation with the canal
for the tensor tympani muscle.

The cochlear tube rapidly diminishes in diameter as il
is traced towards the apex of the cochlea, and its closed
extremity is termed the cupola. The first turn which it
takes around the modiolus produces the bulging of the

S.I!.—

M.S. I.A.iM.

Fig. 362. — Petrous portion of left temporal bone of ehild seen
from above and behind, showing the cochlea from above. (Pro-
fessor Fawcett.)

A.S. Anterior surface of petrous bone.

S.D. Superior border.

C. Cochlea exposed from above.

C. T. Canal for tensor tympani.

F.y. Facial nerve lying in aiiueductus

l'"allopii, which bounds e.\ternally

the cochlea.
A. l.M. Internal auditory meatus.
-•/./'. Acpieductus vestibuli.

U.S. H iatus subarcuatus bounded above
by

J'.r.i'. The posterior vertical .semi-
circular canal.

/•.".C. The e.\ternal horizontal semi-
circular canal.

The floccular fossa is the shallow fossa
leading into the hiatus subarcuatus.

inner wall of the tympanum, which has been described
under the name of the promontory.

The 7nodiolus is thick at the base, but rai)idly tapers
towards the a[)e.x. Its base abuts against the bottom of
the internal auditory meatus. It forms the inner wall of
the cochlear lube, and winding spirally round il like the

6o4 THE A UDITOR V APPA RA TUS.

thread of a screw is a thin lamina of bone, which partially
subdivides the tube into two compartments. This is
termed the lamina spiralis.

Numerous minute canals traverse the modiolus, and one more con-
spicuous than the others, the central canal of the modiolus, extends
along its centre. The spiral lamina is also tunnelled by small canals
in communication with those in the modiolus, whilst one, the spiral
canal of the inodioltts, winds spirally around the central pillar in the
attached margin of the spiral lamina. All these channels convey
filaments from the cochlear division of the auditory nerve to the
membranous cochlea.

The membranous cochlear tube is placed between the free
margin of the spiral lamina and the opposite side of the
wall of the cochlear tube. The two compartments of the
bony cochlea are thus separated from each other, and they
are respectively termed the scala tympani and the scala
vestibuli. The scala tympani is the larger of the two. It
begins at the foramen rotundum, where the secondary
membrane of the tympanum shuts it off from the tympanic
cavity. At the apex of the cochlea it communicates by
means of an aperture, termed the helicotrema, with the
scala vestibuli. At the base* of the cochlea the scala
vestibuli communicates with the lower and fore part of the
vestibule. The perilymph therefore, in the semicircular
canals and vestibule, is directly continuous with that in
the scala vestibuli and scala tympani.

It can now be easily understood how vibrations of the membrana
tympani are communicated to the perilymph within the osseous laby-
rinth. The chain of auditory ossicles throixgh the footpiece of the
stapes affects the perilymph in the vestibule. The vibrations of the
perilymph passing along the scala vestibuli into the scala tympani in
turn affect the secondary membrane of the tympanum which is stretched
across the foramen rotundum. With every inward movement of the
membrana tympani and of the footpiece of the stapes, there is an out-
ward movement of the membrane of the foramen rotundum and vice
versa. The vibrations of the perilymph affect the endolymph in the
membranous labyrinth, and thus excite the terminations of the auditory
nerve.

Membranous Labyrinth. — In the vestibule there are two mem-
branous sacs termed the utricle and the saccule. The utricle occupies
the fovea hemi-elliptica on the wall of the vestibule, and lies above

SECTJOA'S THROUGH THE TEMPORAL BONE. C05

and licliind tlie saccule. Into il open the ineinl>ianou.s .semicircular
canals.

The saccule is sliijhtiy smaller, and occupies ihe fovea hemisphcrica
on the fore-part of the inner wall of the vestibule. It communicates
hy means of a short narrow tube, termed the caitalis rcunictts^ with
the ductus cochlearis or membranous cochlear tube.

The saccule and the utricle are only indirectly brought into com-
munication with each other.

A slender lube termed the ductus eudolytiiphaticus occupies the
aqueductus vestibuli, and divides into two branches which pass rcsix;c-
tively into the saccule and the utricle (Fig. 363).

Ductus eiutolyvtphaticxts

Du'r'O.

Vestil/ule

Osseous -
cochlea

Osseous semicirc:
canal

Mcvibranous
•einicir: can:

^Stapes
Fenestra jvtunifa
Aqueductus cochleae

Jlodi'oli's

Fig. 363. — Diagram of the osseous and membranous labyrinth.
(Modified from Testut.)

U. Utricle.

^. .Saccule.

D.C. Ductus cochlearis.

The duel us cochlearis, or scala media, as we have already noted, lies
between the two scalce of the cochlear tube. It ends blindly at each
extremity, but close to its basal end it is brought into communication
with the saccule by the canalis reuniens.

Sections through the Temporal Bone. — Having now
learned something of the parts which form the auditory
apparatus, the student is recommended to extend his
knowledge as opportunity arises, by making the following
three sections through the macerated bone.

6o6

THE AUDITORY APPARATUS.

(i) A coronal section passing through the internal and external
auditory meatuses, nearer to their anterior than to their posterior walls
(Fig. 364). (2) A vertical section nearly parallel to the superior border
of the petrous bone, passing through the hiatus Fallopii, and the highest
part of the eminence which is produced by the superior semicircular
canal (Fig. 365). (3) A vertical section parallel to the superior border
of the petrous portion of the temporal bone, and about an eighth of an
inch external to that border (Fig. 366).

Section I. — The points which are exhibited by the first of these

mastoidal antrum. aqueduct of Fallopius.

groove for

membrana

tynipani.

canal for Jacobson's nerve.

Fig. 364. — Coronal section of the right temporal bone
passing through the internal and external auditory
meatuses.

sections are depicted in Fig. 364. At the inner extremity of the
external auditory meatus is the grooved ridge for the membrana
tympani. Passing through the floor of the tympanum is the canal for
Jacobson's nerve ; its internal opening is just below the promontory.
The promontory is seen in section. The posterior wall shows the iter
chordae posterius, the pyramid, and the opening into the mastoid
antrum. The mastoid antrum is roofed over by a thin plate of bone
termed the tegmen tympani. The acute bend in the aqueduct of

SECTIONS THROUGH THE TEMPORAL BONE. 607

Kallopius, which corrc.s])on(ls lo tlic geniculate gani^lion fif the facial
nerve, has been cut across, showing the canal divided in two places.
On the cut surAice of the opposite jiart of the bone (not figured) several
turns of the cochlea will be found lo be cut across, and the communica-
tion of the bend of the aqueduct of Fallopius with the hiatus l-'allopii
will be seen. On the same piece of bone the student should also note
the canal for the tensor tympani, which is situated immediately above
the processus cochleariformis, and the Eustachian tube which lies below
that thin bony lamella, lie should pass a pin through the CUaserian

1 234

carotid canal.
Eustachian tube.

promontorj'.
;iilar fossa.

fenestra rotunda.

ridge for membrana tympani

Fig. 365. — Vertical scclion of the left teniporal bone
passing through the hiatus I'allopii, and nearly parallel to
the superior liorder of the petrous bone.

1. Hiatus Fallopii.

2. At|ucdnct of Fallopius.

3. Superior semicircular canal.

4. Kxternal semicircular canal.

fissure, and in this way ascertain its internal opening. Immediately
external to that opening he will find the continuation of the ridge for
the membrana tymjiani.

Section II. — The parts in this .section are exhibited in Kig. 365.
The superior and external semicircular canals are divided, and their
ampulKv arc .shown. The middle portion of the aqueduct of Fallopius
is laid open, and the two bends of that canal are .seen. Just in front of
the posterior bend is the opening of the pyramid. The pyramid is ct)n-
nected to the promontory by a little spicule of bone, wliich hxs been
compared to a Hying buttress (Holden). The promontory forms a Ix^UI
eminence on the inner wall of the tyniixinum. Above it is placed the

6o8

THE A UDITOR Y APPARA TUS.

fenestra ovalis, below and behind it is the fenestra rotunda. The latter
opening is somewhat under the shadow of the promontory.

Section III. — In the section from which Fig. 366 is taken, the saw
has passed through the cochlea and the vestibule, the superior and ex-
opening of superior and posterior semi-
circular canals into vestibule.

carotid
canal.

fovea hemispherica.

Fig. 366. — Vertical section of the left temporal
parallel to the superior border of the petrous bone,
about one-eighth of an inch anterior to that border.

bone
and

ternal semicircular canals, and the first and third parts of the aqueduct
of Fallopius. The modiolus or axis of the cochlea is cut transversely
near its base. If the specimen be held up to the light and examined
with a pocket-lens, the modiolus will be seen to be pierced by a number
of fine holes (lamina cribrosa). At the end of the lowest turn of the
cochlea, close to the fenestra rotunda, is the inner opening of the
aqueductus cochlese, a canal which transmits a small vein to the com-
mencement of the internal jugular vein. Within the cavity of the
vestibule the following objects may be seen : — the fovea hemispherica
for the saccule, the fovea hemi-elliptica for the utricle, the common
opening of the posterior and superior semicircular canals, the ampulla
of the posterior semicircular canal, and the internal opening of the
aqueductus vestibuli. The latter canal transmits minute veins to the
inferior petrosal sinus, and lodges a process of the membranous labyrinth
(ductus endolymphaticus).

THE EYEBALL. 6 )

THE EYEBALL.

The eyeball is not perfectly spherical ; it may be said to
be composed of the segments of two spheres. The anterior
or corneal segment, forming only about one-sixth of the
entire eyeball, possesses a shorter radius than the hinder
or sclerotic segment. The anterior clear corneal part of
the eyeball forms, therefore, a dome-like bulging or promi-
nence on the front of the globe of the eye. The terms
anterior and posterior pole are respectively applied to the
central points of the anterior and posterior curvatures of
the eyeball. The imaginary line which joins these poles
receives the name of the sagittal axis, whilst another line
drawn in a coronal direction around the globe of the eye
midway between the two poles so as to divide the eyeball
into two hemispheres is termed the ecpiator. Imaginary
meridional lines are also drawn between the two poles so as
to cut the equatorial line at right angles. In studying the
structure of the eyeball it is necessary to have a proper
understanding of these terms.

Dissection of the Eyeball. ^\ satisfactory dissection of the globe of
the eye can only be made when the eyeball is fresh ; and in the dissect-
ing-room it is impossible to obtain suitable specimens. This does not
in reality matter very much because it is always easy to procure eye-
balls of the pig, sheep, or ox, which suit the purpose admirably. It is
essential, however, that the dissector should always complete his study
of the organ by the examination of a fresh human eyeball obtaine<l from
\\\Q. post-mortcnt room. In point of si/e and also in other particulars the
eyeball of the pig more closely resembles the human eyeball, but it is
perhaps better that the stuilent should begin with the eyeball of the ox,
seeing that the dissection can be more easily carried out.

We shall supjiose then that the dissector has ])rovided himself with
six eyeballs obtained from oxen. His first duty is to remove from
these the conjunctiva, capsule of Tenon, ocular muscles, and fat, which
adhere to them. Pinching up with the forceps the conjunctiva and
capsule of Tenon close to the corneal margin, he should snip through
these layers with the scissors and divide them completely round the
edge of the cornea. It is now easy to strip all the soft parts from the
surface of the sclerotic coal, working steadily Iwickwards towards the
entrance of the optic nerve. A little behind the equator of the eyekill

VOL. 11. — .•39

6io

THE EYEBALL.

the vense vorticosse will be noticed issuing from the sclerotic coat at wide
intervals from each other, and on approaching the posterior aspect
of the eyeball the posterior ciliary arteries and the ciliary nerves will be
seen piercing the same coat around the entrance of the optic nerve.

Before beginning the actual dissection of the eyeball, it is important
that the student should obtain a general conception of the parts which
compose it. This can best be done by selecting two of the specimens
and making sections through them in two different planes. One speci-
men may be divided at the equator into an anterior and a posterior
portion, whilst the other may be divided in an antero-posterior direction

suspensory ligament of lens,
ciliary muscle.

canal of Petit.

posterior chamber,
canal of Schlem.m.
conjunctiva,
ciliary process.

canal of Stilling.

optic nerve.

sheath of dura mater.

macula.

Fig. 367. — Horizontal section through the left eyeball.
Diagrammatic.

into a mesial and a lateral half. These sections cannot be made with
the knife. The eyeballs must first be frozen perfectly solid, and then
the division can be made by a fine saw. The freezing of the specimens
is a very simi^le matter. They should be placed in a small tin box,
and the box surrounded by a mixture of ice and salt. Two, or at most
three, hours is sufficient to complete the process. When the sections
are made, they should be placed under water in a cork-lined tray, and
preserved for reference as the study of the eyeball is proceeded with.

General Structure of the Eyeball. — The eyeball consists
of three concentrically arranged coats enclosing a cavity in
which are placed three refracting media.

SCLEROTIC COAT. 6ii

The tunics arc: (i)an external fibrous envelope com-
posed of a posterior opaque part, called the sclerotic coat,
and an anterior clear transparent portion called Xhc cornea ;
(2) an intermediate vascular envelope, in which we recognise
three subdivisions, viz. a hinder part called the choroid coat,
a front portion termed the ;m, which lies behind the
cornea, and an intermediate ciliary zone ; (3) the nervous
inner tunic or retina in which the fibres of the optic nerve
spread out.

The refracting media are: (i) behind the cornea a
watery fluid, called the aqueous humour, contained in a
space partially subdivided by the iris into the ttvo chambers
of the eye; (2) the crystalline lens behind this; and (3) the
vitreous body, occupying the posterior part of the interior of
the eyeball.

Dissection. — The superficial surface of the sclerotic coat and the
cornea should now be examined, but to complete the study of the
external tunic, a further dissection is required. Selecting an eyeball
for this i^urpose, an incision should be made with a sharp knife through
the sclerotic at the equator. This must be done carefully, and the
moment that the subjacent black choroid coat ap]iears the knife should
be laid aside. The cut edge of the sclerotic should now be seized with
the forceps, and the incision carried completely round the eyeball with
the scissors along the line of the equator. The outer fibrous tunic is
thus divided into an anterior and a posterior portion. These must now
be raised from the subjacent parts. As the anterior portion is turned
forwards, some resistance will be met close to the margin of the cornea
from the attachment of the ciliar)' muscle to the deep surface of the
sclerotic. This can easily be broken through with the blunt point of
the closed forceps ; as soon as this is done the aqueous humour escapes.
In the case of the posterior part of the sclerotic, its complete separation
can be eflected by dividing the fibres of the optic nerve close to the
[loint where they appear through the sclerotic.

WTien the above dissection is successfully carried out, the outer
fibrous tunic is isolated in two portions, whilst a continuous view of the
intermediate vascular coat is obtained. The eyeball, denuded of its
external tunic, should now be jilaced in a .shallow vessel filled with
water.

Sclerotic Coat. — The sclerotic is what is commonly
known as the white of the eye. It is a dense, resistant
tunic, opaque-while in colour, which envelops the posterior

6l2

THE EYEBALL.

five-sixths of the globe of the eye. It is thickest behind,
and becomes thinner as it is traced forwards. Near the
cornea, however, it again becomes thicker owing to the
accession of fibres which it receives from the tendons of
the ocular muscles. Except at the optic entrance and
close to the margin of the cornea, where it adheres to the
surface of the subjacent ciliary muscle, the deep surface of
the sclerotic is very loosely attached to the choroid coat.
Some pigmented flocculent connective tissue passes be-
tween the two coats and traverses what is in reality an
extensive lymph space.

short ciliary

arteries and

ciliary nerves.

optic entrance.

long posterior
ciliary arteries.

vena vorticosa

Fig. 368. — Diagram of ^, ior aspect of right eyeball. The ex-
centric position of the optic entrance is somewhat exaggerated. (After
Testut, modified.)

The point at which the optic nerve pierces the back part
of the sclerotic does not correspond with the posterior pole
of the eyeball. The optic e^itrance, as it is termed, is situated
about 3 mm. to the inner or nasal side of the posterior pole
and very slightly above it. Here the outer fibrous sheath
of the optic nerve, which is derived from the dura mater,
blends with the sclerotic coat, whilst the bundles of nerve-
fibres are carried forwards through a series of small aper-
tures. This perforated portion of the sclerotic is called the
la77iina cribrosa.

The sclerotic coat is also pierced by numerous blood-vessels and

THE CORNEA. 613

nerves. Thus the lonj^ aiul short posterior ciliary arteries willi the
ciliary nerves perforate the sclerotic around the ojjtic entrance ; four or
five ven;v vorticos.e issue from the interior of the eyeball by piercing the
sclerotic a little way behind the equator at wide intervals from each
other ; whilst the anterior ciliary arteries pierce the same coat near the
corneal margin.

In front the sclerotic coat is not only contiguous with,
hut is directly and structurally continuous with, the cornea,
'i'his is termed the conieo-scleral junction., and the faint
groove on the surface which corresponds with it receives
the name of the scleral sulcus. At this junction the sclerotic
tissue slightly overlaps the corneal tissue so that the line of
union when seen in section is oblique. Close to this a
minute canal in the substance of the sclerotic, termed the
canal (>/ Sch/'c nun, encircles the margin of the cornea.

The Cornea forms the anterior sixth of the outer fibrous
tunic of the globe of the eye. It is transparent and glass-
like, and it forms the window through which the rays of
light gain admittance into the eyeball. The curvature of
the cornea is more accentuated than that of the sclerotic,
and thus it constitutes the segment of a smaller sphere.
When viewed from behind it appears circular, but when
looked at from the front it is seen to be slightly wider in
the transverse direction. This is due to the fact that the
sclerotic overlaps it to a greater extent above and below
than it does at the sides. This is particularly noticeable
in the eyeball of the ox. The posterior concave surface of
the cornea forms the front- boundary of the anterior
chamber of the eyeball, and is separated by the aqueous
humour from the anterior surface of the iris.

The anterior convex surface of the cornea is clothed by
the conjunctiva which is here reduced to its epithelial layer.
On its posterior aspect there is an elastic glassy stratum,
termed the elastic membrane of Desccmet. \Vhen the cornea
is relaxed this membrane becomes wrinkled, and it can be
torn away in shreds from the proper corneal tissue. When
dealt with in thie way the portions removed show a tendency
to curl up.

6i4 THE EYEBALL.

Ligamentum Pectinatum Iridis. — At the margin of the
cornea the membrane of Descemet becomes fibrillar, and
some of its fibres are continued into the iris forming the
pillars of the iris or the ligamentum pectinatum iridis, whilst
others are prolonged backwards into the choroid and the
sclerotic. The ligamentum pectinatum iridis bridges across
the angle between the cornea and the iris, and the bundles
of fibres into which the membrane of Descemet breaks up
in this region constitute an annular meshwork or sponge-
like series of minute spaces termed the spaces of Fontana.
These communicate with the anterior chamber of the eye-
ball, and are filled with lymph or aqueous humour.

Intermediate Vascular Tunic. — The intermediate or
vascular tunic is exposed in its entire extent in the eyeball,
from which the sclerotic coat and the cornea have been
removed. As previously mentioned, the vascular tunic con-
sists of three portions, viz. a choroid coat, a ciliary zone,
and the iris. The choroid coat is the dark-coloured portion
which lies behind the ciliary muscle. The ciliary zone con-
sists of a superficial ciliary muscle and the subjacent ciliary
processes. The ciliary muscle presents the appearance of a
conspicuous white, ring-like band, which encircles the fore-
part of the eyeball immediately behind the corneo-scleral
junction. The ciliary processes are directly continuous
behind, under the ciHary muscle, with the choroid coat,
and also in front with the iris. The iris is a circular
curtain with a central aperture which lies behind the
cornea.

The Choroid Coat is pierced behind by the optic nerve,
and is somewhat thicker behind than it is in front. Its
superficial surface is connected with the deep surface of the
sclerotic by some lax connective tissue and also by blood-
vessels and nerves which pass from the one into the other.
The deep surface of the choroid is moulded upon the retina
and connected with a layer of deeply-pigmented cells, which
usually adheres to the choroid when this tunic is removed,
although in reality it must be regarded as a portion of the
retina.

CILIARY MUSCLE. 615

In ihe eyes of many mammals, but not in man, the posterior |)art of
the clioroid when viewcti from the front presents an extensive brightly-
coloured area, which exliibits a metallic lustre. This appearance is due
to the presence of an additional layer in the choroid termed the lapetiiin.
In the horse, elephant, ox, the tapetum is composed of fibres (tapctum
fibrosum) ; in carnivora, it is formed of cells (tapctum cellulosum). In
the ox, it is a brilliant green colour with a golden lustre ; in the dog,
it is white with a bluish border ; in the horse, it is blue with a silvery
lustre.

The chief bulk of the choroid coat is composed of blood-
vessels. These are arranged in two well-marked layers,
viz. a deep, closely-meshed capillary layer called the iu/tica
cJiorio-capillaris or the tunica Ruyschiana, and a more super-
ficial venous layer composed of the vasa vorticosa. The short
posterior ciliary arteries proceed forwards between these
vascular layers.

The eyeball in which the outer surface of the choroid is exposed
should be immersed in water and the pigment washed out of it by
means of a camel-hair brush. The vasa vorticosa will then appear as
white curved lines converging towards four or five points, from which
the larger venx vorticosaj take origin (Fig. 369).

Ciliary Muscle. — This is composed of involuntary mus-
cular tissue, but the arrangement of its fibres can only be
seen when thin sections of the eyeball are examined under
the microscope. The fibres are then observed to be dis-
posed in two groups, viz. a radiating and a circular.

The radiating fibres arise from the deep aspect of the
sclerotic coat close to the margin of the cornea. From this
they radiate backwards in a meridional direction, and gain
insertion into the choroid coat in the region of the ciliary
processes.

The circular fibres consist of two or three bundles placed
upon the deep aspect of the radiating portion of the musclo.
They form a muscular ring around the circumference of the
iris.

Dissection. — To oljtain a view of the ciliary processes, a coronal section
should be made with the scissors through an eyelxxll a short distance in
front of the equator. The portion of the vitreous body which occupies
the anterior segment of the eyeball should be carefully removeil. When

6i6

THE EYEBALL.

this is clone, the deep aspect of the ciliary processes will be seen as they
radiate backwards from the circumference of the crystalline lens. By
washing out the pigment from this part of the vascular tunic, the
arrangement of the processes will be more fully displayed.

A second dissection may be made in another eyeball with the object
of exposing the ciliary processes from the front. In this case remove
the cornea with the scissors by cutting round the corneo-scleral junction.
The iris is now brought conspicuously into view, and may, with advan-
tage, be studied at this stage. Several cuts in the meridional direction,
and at equal intervals from each other, should in the next place be made

anterior ciliary
artery.

sclerotic coat.

vena vorticosa

long posterior
ciliary artery.

vena vorticosa.

long posterior
ciliary artery.

Fig. 369. — Dissection of the eyeball showing the vascu-
lar tunic and the distribution of the ciliary nerves and
vessels.

through the anterior part of the sclerotic coat. The strips of sclerotic
should then be separated from the ciliary muscle, and pinned backwards
in a cork-lined tray filled with water. The last step in the dissection
consists in the removal of the iris.

Ciliary Processes. — When the choroid coat is traced
forwards under the ciliary muscle, it is seen to form a series
of elongated prominent thickenings, which radiate back-
wards from the margin of the crystalline lens like the folds
of a goffered frill. These thickenings are the ciliary
processes. They vary slightly in their degree of prominence,

THE IKIS.

617

and alsu in Icnglh, bul they are very constant in number.
In the human eye seventy ciliary processes, as a rule, may
be counted. As each process proceeds forwards, it becomes
gradually more and more prominent until ultimately it
ends in a thickened projection, which occupies the space
between the margin of the iris and the circumferential part
of the anterior surface of the crystalline lens. In this
position the ciliary processes bound peripherally the pos-
terior chamber of the eyeball (Fig. 367).

The ciliary processes rest upon the subjacent zonule of
Zinn, i.e. the membrane, which covers the fore-part of the

Fig. 370. — The ciliary processes of ihe human eyeball,
viewed from behind. (From Merkel.)

vitreous body. This membrane is adapted in the most
intimate manner to the ciliary processes. It is folded or
wrinkled in such a way that the folds occupy the sulci or
valleys between the processes.

The Iris lies in front of the crystalline lens, and it is
separated from the cornea by the anterior chamber filled
with aqueous humour. By^ its circumference it is con-
tinuous with the choroid coat, and it is at the same^tme
connected by the ligamentum pectinatum iridis with the
margin of the cornea.

The iris is circular in form, and is perforated in the centre
by a round opening which is termed the//////. Its anterior
surface is faintly striated in a radial direction. It is
coloured differently in different individuals. Its posterior
surface is deeply pigmented. The pupil presents a very

y

6i8 THE EYEBALL.

nearly circular outline,^ and during life it constantly varies
in its dimensions so as to control the amount of light
which is admitted into the interior of the eyebell. These
changes in the size of the pupil are produced by the con-
tractile properties of two groups of involuntary muscular
fibres which are present in its substance. One group is
composed of muscular fibres, arranged circularly around the
pupil in the form of a sphincter ; the second group consists
of fibres, which have a radial direction, and pass from the
sphincter towards the circumference of the iris, so as to
constitute a dilatator muscle. By many anatomists these
radial fibres are considered to be elastic and not muscular.

Ciliary Nerves. — The ciliary nerves which arise from
the lenticular ganglion and the nasal nerve, after piercing
the sclerotic at the back of the eyeball around the optic
entrance, extend forwards between this coat and the
choroid. They will be seen in the specimen in which the
sclerotic has been turned backwards in separate flaps in
the form of delicate white filaments (Fig. 369). In the
posterior part of the eyeball they occupy grooves on the
deep surface of the sclerotic, and can only be separated from
it with difficulty. Reaching the ciliary zone the ciliary
nerves break into branches, which join in aplexiform manner
and send twigs to the ciliary muscle, the iris, and the cornea.

Ciliary Arteries. — Of these we recognise three groups,
viz. : — (i) the short posterior ciliary arteries; (2) the long
posterior ciliary arteries ; and (3) the anterior ciliary arteries.

The short posterior ciliary arteries, branches of the oph-
thalmic, pierce the sclerotic around the optic entrance, and
are distributed in the choroid coat between the vasa vorti-
cosse and the membrana chorio-capillaris.

The long posterior ciliary arteries, also branches of the
ophthalmic, are only two in number. They perforate the
sclerotic on either side of the optic nerve(Figs. 368 and 369),
a short distance beyond the short cihary arteries, and are

^ It may be as well to mention here that the pupil in the ox and the
sheep is greatly elongated in the transverse direction. In the pig, how-
ever, it is approximately circular.

THE RETINA. 619

then carried forwards between the sclerotic coat and the
choroid. When they gain the ciliary zone each artery
divides into an ascending and a descending branch, and
these, with the anterior ciliary arteries, form an arterial
ring termed the circulus iridis major. From this branches
are given to the ciliary muscle, the ciliary processes, and
the iris.

The circulus iridis minor is the name applied to a second arterial
ring in the iris at the outer border of the sphincter pupilK^.

The anterior ciliary arteries are very small twigs, which
arise from the branches of supply to the recti muscles.
They pierce the sclerotic close to the margin of the cornea,
take part in the formation of the circulus iridis major, and
send twigs to the ciliary processes.

Venae Vorticosae. — From each venous vortex in the
choroid a large vein arises, which makes its exit from the
eyeball by piercing the sclerotic obliquely a short distance
beliind the equator. They are four or five in number.

Disseclion. — The vitreous body and retina in the hinder part of the
eyeball, which was cut into two for the purpose of exposing the ciliary
processes from behind, should now be dislodged. By raising the choroid
coat from the deep surface of the sclerotic, under a flow of water from
the tap, the vemu vortico&T; entering the deep surface of the sclerotic
will be brought into view. When these are divided, and the separation
of the two coats is carried back towards the optic entrance, the
posterior short ciliar)- arteries as they emerge from the sclerotic and
enter the back part of the choroid will be seen.

In the eyeball from which the sclerotic and cornea have been
removed, the iris, ciliary processes, and the choroid should be care-
fully stripped off piecemeal under water. This will expose the retina.

The Eetina is composed of two strata — viz. a thin
pigmentary layer, which adheres to the deep surface of the
choroid coat, and has been removed with it, and a delicate
nen'oiis layer, which is moulded on the surface of the
vitreous body, but presents no attachment to it except at
the optic entrance. The latter extends forwards beyond
the equator of the eyeball, and a short distance from the
ciliary zone it_appears to end in a well-defined wavy or

620 THE EYEBALL.

festooned border termed the ora serrata. This appearance,
however, is somewhat deceptive. The nervous elements,
it is true, come to an end along this line, but a lamina in
continuity with the retina is in reality prolonged forwards
as far as the margin of the pupil. The part in relation
to the ciliary processes is exceedingly thin, and cannot
be detected by the naked eye. . It fs termed the pars
dliaris retincz. The portion on the deep surface of the
iris forms its posterior uveal pigmentary layer (pars iridica
retinae).

During life the retina proper is transparent, but after
death it soon assumes a dull greyish tint and becomes
opaque. Posteriorly it is tied down at the optic entrance.
When viewed from the front this appears as a conspicuous
circular disc termed iho. porus opticus or optic disc. From
this spot the optic nerve fibres radiate out so as to form
the deep layer of the retina. The optic disc, in corre-
spondence with the entrance of the optic nerve, lies to the
inner or nasal side of the antero-posterior axis of the eye-
ball. Exactly in the centre of the human retina, and
therefore in the axis of the globe of the eye, there is a
small yellowish spot termed the macula lutea.^ It is some-
what oval in outline, and in its centre it is depressed,
thereby forming what is called the. fovea centralis.

Retinal Arteries and Veins. — In a fresh eyeball the
arteria retince centralis (Fig. 371) will be seen entering the
retina at the optic disc. It immediately divides into an
ascending and a descending branch, and each of these
breaks up into a large outer or temporal division, and a
smaller inner or nasal division. These ramify in the retina
as far as the ora serrata ; but the resultant branches do
not anastomose with each other nor with any of the other
vessels in the eyeball.

The retinal veins converge upon the optic disc, and dis-
appear into the substance of the optic nerve in the form of
two small trunks which soon unite.

^ There is no macula lutea in the eyeball of the ox or sheep.

THE VITREOUS BODY.

621

The retinal vessels, the optic disc, and the macula can all he examined
ill the living eye by means of the ophthalmoscope. The red reflex
olitaincd from the fundus of the eyeball is produced by the blood in the
membrana chorio-capillaris.

Dissection. — For the study of the vitreous body and the crystal-
line lens, which together may be termed the " eye-kernel," it is better
to take an eyeball which is not perfectly fresh (Anderson Stuart). The
eyeball selected for this purpose should be allowed to stand untouched

Fig. 371. — Diagram of the left retina and retinal vessels
as seen from the front. The veins are represented black,
whilst the arteries are drawn in outline.

from one to three days according to the season. The coats of the eye
should then be divided round the equator, and on gently separating the
cut edges, and turning the coats forwards and backwards, the "eye-
kernel ■' will slip out. It should be allowed to drop into a vessel fdled
with clean water. The examination of the jxirts forming the eye-
kernel will be greatly facilitated by placing it en masse in strong picro-
carmine solution for a few minutes. When removed from the staining
fluid, it should be well washed in water. In this way the hyaloid
membrane enclosing the vitreous body, the capsule of the lens, and the
zonule of Zinn, are stained red, and their connections become ver)-
apparent (.\nderson Stuart).

The_SitreoilS-Bady isji soft, yielding, perfectly trans-
parent jelly-like body, which occupies the posfenor 'four-

622 THE EYEBALL.

fifths of the interior of the eyeball. The retina is spread
over its surface as far forwards as the ora serrata, but is in
no way attached to it, except at the optic disc. In front
of the ora serrata, the ciliary processes are applied to the
vitreous body and indent its surface. Anteriorly, the
vitreous body is hollowed out, and presents a deep con-
cavity, the. fossa patellaris, for the reception of the posterior
convex surface of the crystalline lens.

The substance of the vitreous body is enclosed within a
delicate transparent membrane, which completely envelops
it, and receives the name of the hyaloid membrane. Extend-
ing forwards through the midst of the vitreous mass from
the region of the optic disc to the back of the crystalline
lens is a minute canal, lined by a tube-like prolongation of
the hyaloid membrane, and containing a watery fluid.
This is termed the hyaloid canal., or the canal of Stilling.,
and it represents the path which was taken by a branch of
the arteria retinae centralis, which in the fcetus extends
forwards for the supply of the capsule of the lens, but
afterwards disappears.

The canal of Stilling, as a rule, cannot be seen in an ordinary dis-
section of the eyeball ; but if the eye-kernel be shaken up in the
picro - carmine solution as recommended by Anderson Stuart, it may
sometimes be rendered evident through the staining fluid entering it.

Zonula of Zinn and tlie Suspensory Ligament of the
Lens. — In the ciliary region the hyaloid membrane of the
vitreous body becomes thickened and strengthened, and
forms what is termed the zonula of Zinn. As this
approaches the margin of the crystalline lens, it splits into
two parts, viz. an exceedingly delicate deep lamina, which
lines the fossa patellaris (Anderson Stuart), and a more
.superficial stronger part, which becomes attached to the
capsule of the crystalline lens.

The- zonula of Zinn lies subjacent to the ciliary processes,
and is radially plaited or wrinkled in correspondence with
these.' " Thus the elevations or wrinkles of the zonule extend
inTo "the intervals between the ciliary processes whilst the

ZONULA OF ZINN.

623

ciliary processes in their turn lie in llie depressions between
the wrinkles of the zonula. When the eye is fresh, these
opposing parts are closely adherent.

The zonula of Zinn is strengthened by radially directed
meridional elastic fibres, and after the delicate membrane
which lines the fossa patellaris is given off from its deep
surface, it extends forwards as a distinct layer, and is
attached to the anterior surface of the capsule of the lens
a short distance beyond the margin of that body. In this
manner the suspensory ligament of the lens is formed. But

retina.

sclerotic.

suprachoroid space.

ciliary muscle (radiating fibres).

muscle (circular fibres).

of Schlemni.

paces of Fontana.
iarj' process,
canal of Petit.

pensory ligament.

Fig. 372. — Diagrammatic representation of the ciliary region,
as seen in vertical section.

this is not the only attachment of the suspensory ligament.
Some scattered fibres are attached to the circumference or
equator of the lens (equatorial fibres), whilst others are fixed
to its posterior surface close to its margin (post-equatorial
fibres).

In this way the crystalline lens is firmly held in its place
in the fossa patellaris. Further, the degree of tension of its
suspensory ligament is influenced by the radiating fibres of
the ciliary muscle, which by their contraction pull upon the
ciliary processes, and produce relaxation of the zonule of Zinn.

624 THE EYEBALL.

Canal of Petit. — This is a circular lymph space, which
surrounds the circumference of the lens. It is bounded in
front by the suspensory ligament, and behind by the hyaloid
membrane, enclosing the vitreous body. It is filled with a
watery fluid.

By introducing the point of a fine blow-pipe into the canal of Petit
through the suspensory ligament, it can be partially, or, perhaps com-
pletely, mflated with air. It then presents a sacculated appearance.

Dissectio7i.~T\i& crystalline lens may be removed by snipping
through the suspensory ligament with scissors.

Crystalline Lens.— The crystalline lens is a biconvex,
solid, and transparent structure, which lies behind the iris,'
and in front of the vitreous body It is enclosed within a
glassy, elastic capsule, to which the different parts of the
suspensory ligament are firmly cemented, and it presents
for study an anterior surface, a posterior surface, and a
circumference or equator.

The anterior surface is not so highly curved as the
posterior surface. Its central part which corresponds with
the pupillary aperture of the iris looks forward into the
anterior chamber of the eye. Around this part the margin
of the pupillary orifice of the iris is in contact with the
lens, whilst nearer the equator the anterior surface of the
lens is separated from the iris by the fluid in the posterior
chamber of the eyeball. The posterior surface of the lens
presents a higher degree of curvature than the anterior
surface, and is received into the fossa patellaris of the
vitreous body. The equator or circiimference is rounded.
It forms one of the boundaries of the canal of Petit, and
the manner in which the suspensory ligament is attached
to the capsule in this vicinity has already been described.

Faint radiating lines may be seen on both surfaces of
the lens. ^ These give a clue to the structure of the lens.
They indicate the planes along which the extremities of
the lens-fibres come into apposition with each other.

The capsule of the lens is a resistant glassy membrane,
which is considerably thicker in front than behind.

CHAMBERS OF THE EYEBALL. 625

The anterior wall of the capsule may now be divided with a sharp
knife. A little pressure will cause the body of the lens to escape
through the opening. The stained capsule, whilst floating in water,
can be very advantageously studied.

If the lens body be compressed between the finger and thumb, it
will be observed that the outer portion or cortical part is soft, whilst
the central part or nucleus is distinctly firmer. When the lens is
hardened in alcohol it can easily be proved that it is composed of
numerous concentrically arranged lamins;.

Chambers of the Eyeball. — The anterior chamber of the
eyeball is the space between the cornea in front, and the
iris and central part of the lens behind. At the irido-
corneal angle, it is bounded by the ligamentum pectinatum,
and here the aqueous humour which fills this chamber finds
access to the spaces of Fontana.

The fosferior chamber is a circular space or interval which
is bounded in front by the posterior surface of the iris, and
behind by the circumferential part of the anterior face of
the lens. Externally, this space is closed by the thick
anterior projecting ends of the ciliary processes. It is also
filled with aqueous humour.

VOL. II. — 40

INDEX.

INDEX.

Abducent Nerve, 119, 125,350,490

Acoustic Tubercle, . • 5^3

Action of Heart, . . .61

,, Laryngeal Muscles, 461

Alar Ligament, . . • 3^^

Amygdaloid Tubercle, . . 53°

Angular Artery, . . • 284

,, Gyrus, . . ■ $09

Annulus Ovalis, . . • 49

Ansa Ilypoglossi, . . 216, 225

Anterior Cerebral Artei7, 4S0, 481

,, Common Ligament,

99. 380
,, Cutaneous Nerves, . 5
,, Intercostal Arteries, 7

Jugular Vein, . 188, 245
,, Mediastinum, . 13. 22

,, I'yramid, . • S^~

,, Triangle of Neck, . 208
,, Vertebral Vein, 234, 236
Antero-median Spinal Artery, 177

Aorta, 62

Aortic Arch, . • -64

,, Intercostal Arteries, . 7
,, Opening, ... 60
,, Orifice, . • • 59

,, Valve, . . 60, 71

Aponeuroses —

Buccal, . • • -39'
ICpicranial, • • '03

Palatal, -407

Aponeuroses — coiitiuued.

Pharyngeal, . • -399
Vertebral, . • .141

Aqueduct of Sylvius, . 544> 54^
Aqueductus Veslibuli, . • 601
Arachnoid Mater, in, 163, 472
Arachnoidal Villi, . .112

Arachnoidea Spinalis, . . 166
Arbor Vitre Cerebelli, . . 580
Arcuate Fibres, . .567. 572
Arnold's Nerve, . • • 33^
Arteries—

Angular, . . . • 284

Anterior Intercostal, . . 7> 1°

,, Spinal, . ■ 477

Antero-median Spinal, . 177

Aorta, . . . • 62

,, Arch of, . . . 64

,, Ascending, . . 63

,, Descending Thoracic, 81

Aortic Intercostal, . ■ 7. 9°

Arteria PrincepsCervicis, 148, 151

,, Ketinai Centralis, 363, 620

Ascending Cervical, . . 235

Pharyngeal, 132, 215,

254, 328

Hasilar, . . ■ • 477

Bronchial, . • 29, 82

Carotid, Common, 67. 213, 217,

243

External, . 217, 247

630

INDEX.

Arteries — continued.

Arteries — continued.

Carotid, Internal, 118,

I30> 327,

Posterior Dental,

• 303

350,

409, 480

,, Scapular,

140, 202

Cerebral, Anterior, .

480, 481

Postero-lateral, .

• 177

Middle, .

480, 483

Pterygoid,

• 304

,, Posterior, .

. 478

Pterygo-palatine,

• 434

Ciliary,

363, 618

Pulmonary,

54, 71

Circle of Willis,

■ 484

Ranine,

• 325

Comes Nervi Phrenici,

31

Septal,

. 284

Coronary, .

44, 64

Spheno-palatine,

430, 434

Crico-thyroid, .

■ 250

Spinal,

161, 174

Deep Cervical, .

151, 237

Sterno-mastoid,

214, 250

,, TemiDoral,

• 304

Stylo-mastoid, .

• 254

Descending Palatine, .

430, 434

Subclavian, . 68, 201, 230

Dorsalis Linguae,

• 324

,, Branches of, . 233

Ethmoidal,

364, 430

Sublingual,

• 324

Facial, . 214, 217,

251, 282

Submaxillary, .

• 252

,, Branches of, .

. 283

Submental,

• 252

Frontal, .

108, 365

Superficial Temporal

, 108, 254,

Hyoid,

214, 250

264

Inferior Coronary,

. 283

Superior Coronary,

. 284

Dental, .

303, 314

,, Epigastric,

10

,, Labial, .

. 283

,, Intercostal,

7, 90, 236

,, Palatine,

252, 329

,, Laryngeal,

214, 250

Innominate,

66, 220

,, Thyroid,

214, 249

Intercostal,

. 7, 90

Supra-orbital,

108, 364

Internal Mammary, .

9. 236

,, -scapular, . 140, 202, 236

„ Maxillary, 253, 264, 302,

Thyroidea Ima,

67, 220

434

Tonsillitic, ; .

252, 329

Laryngeal,

• 455

Tracheal, .

• 235

Lateral Nasal, .

. 284

Transverse Facial,

265, 282

Left Common Carotid,

■ 67

Tympanitic,

• 303

Left Subclavian,

. 68

Vertebral, 130, 160,

234, 377,

Lingual, . . 214

251, 323

477

Masseteric,

• 304

Vidian,

• 434

Mastoid, .

109, 148

Articulations—

Meningeal, Anterior,

• 131

of Thorax .

• 95

,, Middle, 131

, 308, 352

Atlas, Axis, and Occipital

,, Small, 131,

308, 352

Bone,

. 381

Musculo-phrenic,

■ 9, 10

Capitular, .

• 97

Naso-palatine, .

• 430

Costo-transverse,

96, 98

Occipital, 109, 147,

215, 253

Costo-vertebral,

• 96

OEsophageal,

82, 235

Crico-arytenoid,

. 460

Ophthalmic,

• 362

Crico-thyroid, .

. 461

Orbital, .

. 265

Inter-chondral, .

. 96

Perforating,

10

Iniervertebral, .

• 98

Pericardiac,

. 82

Manubrio-gladiolar,

95

Pharyngeal,

• 329

Sterno-clavicular,

. 226

Posterior Auricular, log

,217,254

Sterno-costal,

95

,, Communicating, . 481

Temporo-maxillary,

• 305

INDEX.

631

I-ACE

PAGB

Ary teno - epiglollidcan Kolils,

403,

Buccal Plexus,

3"

442

Buccinator, .

271.

391

Arytenoid Cartilajjcs, . 403,

459

Bucco-pharyngeal Fascia,

395

Muscle,

449

Ary-vocalis Muscle,

451

Calamus Scriptorius,

582

Ascending Aorta, .

63

Calcarine Fissure, .

510

,, Cervical Artery, .

235

Callosal Convolution, .

517

,, Frontal Convolution

502

,, Sulcus,

5'7

,, Lumbar Vein,

92

Calloso-marginal Fissure,

501

I'arietal,

509

Capitular Articulations,

96

riiaryngeal Artery,

132,

Capsule of Lens, .

624

215, 254,

328

,, Tenon,

357,

368

Atlanto-axial Ligaments,

382

Cardiac Orifices, Topography of, 62

,, -occipital ,,

383

,, Plexus,

68

Atrium Meatus Medii, .

423

Veins,

45

Auditory Apparatus,

587

,, Walls,

72

Nerve, 119, 125, 438,

490

Carotid Arteries, 67, 118,

130,

213,

Ossicles, .

596

217, 243,

247.

327.

,, Ligaments of.

598

350.

409

480

Auricle, Left,

57

,, Canal,

409

„ Right, .

48

., Plexus,

410

,, Ligaments of, .

286

,, Sheath,

194

Auricular Cartilage,

286

,, Triangle,

209

212

Auriculo-temporal js^erve, 107

312

Cartilago Triticea,

446

-ventricular Groove, .

42

Caruncula Lachrymalis,

259

,, -ventricular Orifice. .

49

Caudate Nucleus, .

528

552

Azygos Uvulce,

405

Cavernous Sinus, .

128

345

Cerebellum, . .471

560

573

Bartholin, Duct of,

321

,, Great Horizontal

Basal Ganglia of Cerebral

Fissure of.

575

Hemispheres,

552

Lobes on Upper

Basilar Artery,

477

Surface of.

576

., Sinus,

130

., Under .

Sur-

Bell, Nerve of, .

207

face

of.

577

Biventer Cervicis, .

149

,, Peduncles of.

573,

580,

Biventral Lobule, .

5>8

587

Blood-Vessels of Hack, .

>54

Cerebral Arteries, 47S

480

483

,, ,, Scalp, .

108

,, Hemispheres, .

493

Brain, Base of, . . 470

485

,, Gyri

and

(Jeneral Apjiearance of.

469

Sulc

of,

494

Preservation of, .

119

,, ,, General

Removal of, no

"7

Structure of

495

Broca, Area of.

5'6

Lobes,

497

Bronchi, ... 74, 84

,, Nuclei, .

495

Bronchial Arteries, . 29, 82

,, Veins,

"5

,, Veins, .

82

Cerebrum, .

493

Broncho-cKsophageal Muscle,

75

,, Inferior Fissure

of,

531

Buccal Aponeurosis,

391

Cervical Glands, Deep, .

•97

Glands.

39'

., Superficial, .

1 88

.. Nerve,

282

Nerves,

'5>

377

632

INDEX.

3i3>

401,
438,

Cervical Pleura,

,, Plexus, . 188, 240

,, Region, Nerves of, .

,, Sympathetic, .

,, Vertebrae, Articula-
tions of,
Cervicalis Ascendens Muscle,
Cervico - facial Division of

Facial Nerve,
Chambers of Eye, .
Cheeks, ....

Choanse,

Chorda Tympani,
Chordse Tendinese,

,, Willisii,
Choroid Coat,

,, Plexus,
Choroidal Fissure
Ciliary Arteries,
,, Muscle,
,, Nerves,
,, Processes,
Cingulum,
Circle of Willis,
Circular Sinus,
Circumvallate Papillse, .
CisternEe Subarachnoidales,
Claustrum, .
Clava, ....
Clavicle, Section of.
Coccygeal Nerve, .
Cochlea,

Collateral Fissure,
Columnse Carnese,
Comes Nervi Phrenici, .
Commissures of Spinal Cord,
Complexus Muscle,
Compressor Naris,
Concha Suprema, .
Conical Papillze, .
Conjunctiva, .
Connections of Several Parts

of the Brain, . . -491
Conus Arteriosus, ... 44
,, Medullaris, . . .168
Cornea, . . . .613

Cornua of Spinal Cord, . .179

Coronary Arteries, . 44, 64

,, Sinus, . . 45, 49

,, Valve, ... 49

239
343
151
409

379
146

279
625

391
421

599

• 51
. 117

611, 614
528, 531, 584

• 539

• 363
614, 615

. 362, 618
614, 616
521
484
128

473
557
566
203
158
602
500
59
31
178
149
274
427
464
258

Corpora Mammillaria . . 487
,, Quadrigemina, . 546

Corpus Arantii, ... 56
,, Callosum, . . 492, 521
, , Dentatum of Cerebellum, 585
,, Geniculatum Externum, 542
,, ,, Internum, 547

,, Striatum, .

Corrugator Supercilii, .

Costo-transverse Articulation,
,, -vertebral ,

Cotunnius, Nerve of.

Cranial Blood Sinuses,

Cricoid Cartilage, .

Crico-arytenoid Joints,
,, ,, Muscles

Crico-thyroid Artery,
,, ,, Joint,
,, ,, Muscle,

Cruciform Ligament,

Crusta, .

Crystalline Lens, .

Cuneate Tubercle,

Cuneiform Cartilages,

Deep Auricular Artery,
,, Cervical Artery,
,, ,, Glands,

,, ,, Vein,

,, Temporal Artery,
,, ,, _ Nerve,

Dentate Fascia,

,, Fissure, .
Depressor Alee Nasi,
,, Anguli Oris,
,, Labii Inferioris,
Descendens Hypoglossi.

418,

555

267

96

96

431
. 125

• 458
. 460

• 448

• 250

• 458
446, 450

. 386

• 550
611, 624

. 566
. 461

i5i>

303
237
197

237
304
3"
518
519
274
268
270
215, 225

Descending Thoracic Aorta, . 81

Diaphragma Oris, . . -315

,, Sellse, . . 122

Digastric Muscle, . . 209, 224

,, ,, Nerve to

Posterior Belly, 277
,, Triangle, . 209, 216

Direct Cerebellar Tract, . 567

Dissection of —

Anterior Mediastinum, . 13

,, Triangleof Neck, 208,211

Back of Head, . . -137

Base of Brain, . . . 552

INDEX.

633

Dissection ov— continued.

Hloocl-\'esseIs of lirain, . 475
Cardiac Plexus, ... 655
Carotid Canal, . . . 409
Cerebellum, . . 579, 5S5
Cerebral Hemispheres, 494, 519,
524
Dorsal Aspect of Trunk,

135. 137, 139, 144, 155
Ear, .... 589, 599
Eyeball, 609, 611, 615, 619, 621
Eyelids, . . 2S8, 291, 295
Face, 257, 259, 268, 271, 276
Heart, . . 49, 57, 58, 71
Lar)-nx, 445, 447, 449, 451, 453,

455
Lateral Ventricles of l>rain,

524, 530, 533
Lung, . . . . 27, 84
Meckel's Ganglion, 430, 432, 433
Medulla Oblongata, . . 568
Meninges,. . . 114, 133
Mesencejihalon, . 545, 548

Middle Cranial Fossa, 345, 348
Nasal Cavity, 41S, 419, 422, 424,

425

Neck, Side of, . . 185, 186

„ Deep, 325, 326, 331, 340,

343
,, Posterior Aspect of,

.137, 147, 149
,, ,, Triangle,

195
Nerves of Face,
Nose, ....

Orbit, 352, 353, 357, 368,

198
276
297
370,
371
414

32

Otic Ganglion, .
Pericardium,
Pharynx, 394, 395, 398, 399, 404
Pinna, .... 284
Pleura, . . . -15

Posterior Mediastinum, . 76
,, Pulmonary Plexus, 27
Prevertebral Region, 372, 377,
3S4, 386, 387
Removal of Brain, . no, 117
Scalp, . . 101, 102, 103
Spinal Canal, 160, 163, 165, 174
Sternoclavicular Joint, 226, 227

Dissection of — coutiuu«l.

Sul)maxillar)' Region, 315, 316
Sub-occipital Space, . . 160
Superior Maxillary Nerve, . 410
Temporal and Pterygo-

maxillary Region, 297, 298,

299

Thoracic Cavity, 13, 23, 27, 29

,, Portion of Sym-

pathetic,

87

Wall, 3,4,8, 13, 22, 90

Thorax, . . . . i

Tongue, .... 466

Dorsal Aspect of Trunk, . 133

,, Region, Nerves of, 91, I53

,, Spinal Venous Plexus, 158

Dorsalis Linguce, . . . 324

Ductus Arteriosus, . . 54

Dura Mater, . Ill, 114, 120, 121

,, Spinalis, . . 163

Ear, Extrinsic Muscles of, . 103

,, Internal . . 588, 599

,, Middle, . . . 5S8, 590

Kminentia Collateralis, . . 533

Teres, . . .583

Eparterial Bronchus, . . 85

Ependynia, .... 525

Epicardium, . . . 34, 72

Epicranial Aponeurosis, . 103

Epiglottis, . . 403, 441, 456

l^rector .Spina;, . . .145

I'.thmoidal Arteries, . 364, 430

luistachian Tubes, 399, 402, 408,

599

,, \ alve, . . 49

External Auditory Meatus, . 5S9

,, Capsule, . . . 559

,, Laryngeal Nerve, 210, 337

Eyeball, . . . 609, 610

Eyelids, . . 257, 287, 291

Face, Dissection of, 257, 259, 26S,
271, 276

Facial Artery, 214, 217, 251, 2S2
,, Nerve, 119, 125, 190

,, ,, Temporal Branch, 106

,, Vein, . . 220, 253, 284

Falciform Lobe, . . . 516

l-allopius. Aqueduct of, . . 435

634

INDEX.

PAGE

Falx Cerebelli,

122

,, Cerebri,

• "7

Fasciculus Teres, .

• 583

Fascia —

Bucco-pharyngeal,

• 395

Deep Cervical, .

. 191

Lumbar, .

. 142

Phrenico-pleural,

21

Pretracheal,

• 194

Prevertebral,

• 193

of Supra-clavicular Region, 197

Sibson's, . . 18, 21, 239

Superficial, of Scalp, . . 102

Temporal, . . . 109, 297

Fauces, .... 393

Fenestra Ovalis, . . 592, 598

,, Rotunda, . . 594

Fifth Cranial Nerve, 118, 125, 347

,, Ventricle, . . -534

Fillet, .... 551, 569

Filum Terminale, . . 168, 169

Fimbria, . . . 517, S3 1

Fissure of Rolando, . . 499

,, Sylvius, . . 497

Folium Cacuminis, . . 577

Follicular Glands, . . . 400

Foramen Ovale, . . 49, 58

,, of Magendie, . . 584

Foramina of Munro, 492, 525, 545

Fornix, _ . . . -534

Fossa Ovalis, ... 49

,, Patellaris, . . . 622

Fourth Cranial Nerve, 118, 124, 349,

356

,, Ventricle, . 560, 582, 584

Fovea Inferior, . . . 583

,, Superior, . . .583

Framework of Thorax, . . i

Frontal Artery, . . 108, 365

,, Lobe, . . 501, 504

,, Nerve, . . -354

Fungiform Papillse, . 464

Funiculus Cuneatus, . 566

,, Gracilis, . . 566

Galen, Veins of, . . . 537
Gangliated Cord of Sympathetic,

2, 87, 246
Ganglia of Spinal Nerve Roots, 173
Ganglion of Root, . 173,336

Ganglion of Meckel, . . 430

,, Trunk, . . 336

,, Wrisberg, . . 31

Gasserian Ganglion, . . 347

Genio-hyoid Muscle, . . 318

,, -hyoglossus, . 323, 467

Globus Pallidus, . . -557
Glosso-epiglottidean Folds, . 441

,, -pharyngeal Nerve, 119, 125,
331, 332, 468, 489
Great Auricular Nerve, 137

,, Cardiac Vein,

,, Horizontal Fissure,

,, Longitudinal Fissure, .

,, Occipital Nerve, . 108,

,, Transverse Fissure, 51
Grey Matter of Spinal Cord,
Gums and Teeth, .
Gyri and Sulci
Gyrus Dentatus, .

,, Fornicatus,

,, Frontalis, Inferior,

,, ,, Medius,

,, Marginalis,

Head and Neck, . . . 100
Heart, 37

,, Action of, . . . 61

,, Dissection of, 49, 57, 58, 71

,, Form of, . . . 40

,, Relations of, . . 37

HeschI, Sulci of, . . -513

Highmore, Antrum of, . . 525

Hippocampal Convolution, . 516

Hippocampi, . . . 5^9

Horner's Muscle, . ,271

Hyaloid Canal, . . . 622

,, Membrane, . . 622

Hyoglossus Muscle, . 318, 466

Hyoid Artery, . .214, 250

Hyparterial Bronchus, . 30, 85

Hypogastric Plexus, . . 68

Hypoglossal Nerve, 119, 125, 215,

225, 322, 339, 469, 488

260
46
575
494
i35>
152
538
178

391
494
518
516
502
502
504

Ilio-costalis Muscle,
Incisura Cardiaca,
,, Marsupialis,
,, Semilunaris,

145

25

574
574

INDEX.

635

I'Ar.E

PAGE

Incisura Temporalis, . 501, 513

Intertransverse Muscle,

156

376

,, Tliyioiilcn, . . 457

Interventricular .Septum,

60

Incus, 597

Intervertebral Articulations, .

98

Inferior Cervical Ganglion, . 342

,, Discs,

99

Dental Nerve, . -312

Iris, ....

617

Frontal Convolution, 502

Island of Reil,

514

,, ,, Sulcus, . 503

Isthmus of Fauces,

393

402

,, Laryngeal Artery, . 235

,, Thyroid,

220

,, Longitudinal Sinus, 1 17, 126

,, Maxillary Division of

Jacobson, Nerve of,

334

Fifth Nerve, . 2S1

,, Organ of.

417

,, Ohlique Muscle, . 368

Joints of Thorax, .

94

,, Palatine Artery, 252, 329

Jugular Ganglion, .

III

,, Petrosal Sinus, . 330

,, Thyroid Axis, . . 234

Labial Glands,

390

,, ,, Veins, 220, 235,256

Lacus Lachrymalis,

258

Infra-mandibular Nerve, . 279

Lachrymal Canals,

293

,, -orbital Artery, . .413

„ Gland,

292

356

,, ,, Nerve, . .281

,, Nerves,

355

Plexus, . . 278

,, Sac,

294

,, -trochlear Nerve, . . 281

Lamina Cinerea, .

488

Infundibuluni, . . 44, 118

,, Cribrosa, .

612

Inlet of Thorax, ... 2

,, F'usca,

612

Innominate Artery, . 66, 220

,, Spiralis, .

604

,, Veins, . 36, 220

Laryngeal Cartilages,

455

Interarticular Fibro-cartilage, 227,

,, Muscles,

461

306

,, Opening,

403

Interauricular Furrow, . . 43

,, Sinus, .

444

Intercarotic Body, . 213, 247

Laryngotomy,

221

Interchondral Articulations, . 96

Larynx,

439

Interclavicular Ligament, . 227

Lateral Nasal Artery,

284

Intercostal Arteries, . . 7, 90

,, Occipital Sulcus,

512

,, Membranes, 5, 6, 89

,, Sinus,

127

,, Nerves, . 3, 5, 91

,, Ventricle, .

524

Interlobar I-'is.sures, . . 497

Left Auricle, .

57

Intermediate Vascular Tissue, 614

,, \'entricle,

59

Internal Ca]isule, . . . 557

Lenticular Ganglion,

361

,, Carotid Arteries, 118, 130,

,, Nucleus,

554

330. 327, 350. 409, 480

Levator Anguli Oris,

270

Ear, . . 588, 599

,, ,, Scapukt,

139

,, Jugular \'ein, . 215, 329

,, Glandukv: Thyroid

ere.

,, Laryngeal Nerve, 216, 337,

218

255

454

,, Labii Supcrioris,

270

,, Mammary Artery, . 8

,, ,, AUvque Nas

>> ■

269

,, Maxillary Artery, 253, 264,

,, Menti,

273

302, 434

Levator Palati,

399

406

,, ,, Vein, . 304

Levatores Costarum,

•57

,, Tarsal Ligaments, 266, 290

Ligamentum Arteriosum,

54

Interpeduncular Space, . . 485

,, Denticulatum

167

Interspinales, . .156

,, Latum Pulmonis,

17

<JjU

PAGE

^ii,yv.

PAGE

Ligamentum Pectinatum Irid

is, 614

Lips, ....

■ 389

Ligaments—

Lobus Cacuminis,

• 577

Accessory Atlanto-axial,

. 386

,, Centralis,

• 576

Alar,

. 388

,, Clivi, .

• 577

Atlanto-axial, .

. 382

,, Culminis,

• 576

,, -capsular,

• 383

,, Noduli,

. 578

,, -occipital,

■ 383

,, Pyramidis,

• 579

Capitular, .

• 97

,, Tuberis,

• 579

Check and Suspensory, o

f

,, Uvulae,

• 578

Capsule of Tenon, .

• 370

Locus Coeruleus,

• 584

Common, . . . c

9, 380

,, Perforatus Anticus,

• 487

Costo-transverse,

. 98

,, ,, Posticus,

. 487

Cruciform,

. 386

Long Buccal Nerve, . 282,311

Epiglottidean, . . .

• 456

Longissimus Dorsi,

. 146

Interarticular, .

97

Longus Colli Muscle, .

• 373

Interclavicular, .

. 227

Lumbar Fascia,

. 142

Internal Tarsal, . 26

6, 290

,, Region, Nerves of.

• 153

Interspinous,

381

Lungs, ....

22

Intertransverse, .

381

,, Borders of.

24, 25

Lateral Tarsal, .

288

,, Lobes of, .

• 25

Ligamenta Subflava, .

380

,, Roots of, .

26, 27

Ligamentum Denticulatum

, 167

,, Topography of, .

23, 26

,, Nuchee, .

150

of Pinna, .

284

Macula Lutea,

. 620

Palpebral, .

289

Magendie, Foramen of.

• 584

Pterygo-maxillary,

398

Malar Nerve,

. 281

Rhomboid,

227

Malleus,

• 596

Stellate, .

97

Mandible, Movements of.

• 307

Sterno-clavicular,

226

Mandibular Canal,

314

,, -costal, .

95

Marshall, Vein of,

46

,, -pericardiac.

32

,, Vestigial Fold of.

35

Stylo-hyoid,

325

Masseter Muscle,

298

,, -maxillary, . 19

4, 306

Masseteric Artery,

304

Supra-spinous, .

381

,, Nerve,

299

Suspensory of Odontoid,

387

Mastoidal Antrum,

590

,, of the Lens,

622

,, Vein, .

128

Tarsal, . . . .

290

Meatus Auditorius Externus,

589

Temporo-maxillary, .

305

Meckel's Ganglion, . 41

4, 430

Thyro-ary tenoid ,

452

Median Vein,

220

Ligament of Zinn,

366

Mediastinum,

21

Limbic Lobe,

516

,, Anterior, .

14, 22

Linea Splendens, .

169

Middle, .

22

Lines of Pleural Reflection, .

18

, , Posterior,

22, 75

Lingual Artery, . . 25

i> 323

,, Superior, .

21

,, Nerve,

321

Medulla Oblongata,

560

,, Papillae, .

464

Medullary Vela, .

581

,, Veins,

325

Meibomian Follicles, . 25

8, 288

Lingualis Inferior,

467

Membrana Tympani,

594

,, Superior,

467

Membranous Labyrinth,

604

Lingula, . . . .

576

Meningeal Arteries,

131, 30

8>352

/A^/>^A'.

637

PAGH

I'AGE

Meninges of Brain,

III

M u sci.ES—co//n'/ttu\/.

,, Spinal Coril,

«63

Infrahyoid,

222

Mental Nerve,

282

3H

Intercostals,

•4,89

Mesencephalon,

492

545

Internal Pterygoid,

302

Middle Cerei)ral Artery,

480

483

Interspinales,

156

,, Cervical Ganglion,

342

Intertransverse,

156

376

„ Ear, .

588

590

Intrinsic, of Auricle, .

285

,, Mediastinum,

22

Levator Anguli Oris, .

270

,, Mcninijeal Artery,

131,

308,

,, Glanduk-e ThyroideK,

352

218,

255

M'>nro, Foramina of, 492

525

545

,, ,, Scapulre

, .

139

Morgagni, Sinus of,

399

Lahii Superioris

, .

270

Mouth and Pharynx,

3S8

,, Aliv:que Nasi,

269

,, Floor of, .

391

Menti, .

273

,, Roof of,

392

Palati, .

399,

406

Miiller's Fluid,

120

,, Palpebral Superioris,

Multifidus Spina% .

155

156

265,

291,

356

Muscles—

Levatores Costarum, .

157

Arytenoid,

449

Lingualis Inferior,

467

Ary-vocalis,

451

,, Superior,

467

Attollens Auriculam, .

104

Longissimus Dorsi, .

146

Altrahens,

104

Longus Colli,

373

Azygos UvuIk, .

405

Masseter, .

298

Broncho-cesophageal,

75

Multifidus Spina-,

»55>

156

Buccinator,

271

Musculi Papillares, .

5"

> 59

Cervicalis Ascendens,

146

Musculus Accessorius,

146

Chondro-glossus,

467

Mylo-hyoid,

3«S

Ciliary,

614

Nasal Group,

274

Complexus,

149

Obliquus Capitis Inferioi

, .

159

Compressor Naris,

274

,, ,, Superior,

160

Constrictors of Pharynx

396

Occipito-frontalis,

102

Corrugator Supercilii,

267

Omo-hyoid, . 140,

208,

222

Crico-arytenoid,

448

Orbicularis Oiis,

272

,, -thyroid, .

446

,, Palpel)rarum

,266

,287

Depressor Ala: Nasi, .

274

Palato-glossus, .

405,

467

,, Anguli Oris,

268

,, -pharyngcus.

405

,, Lahii Inferioris, .

270

Pleuro-rcsophageal, .

76

Diaphragm,

2

Pyramidalis Nasi,

274

Digastric, . . 209,

224

288

Rectus Capitis Anticus A

ajor

374

Dilatator, .

274

„ ,, M

inor

376

Dilator Tubiv, .

409

,, ,, ,, Lateralis,

343

Erector Spin;v, .

•45

,, ,, Posticus

External Pterygoid, .

301

,, Maj

or.

159

Extrinsic, of Auricle, .

103

285

,, ,, Minor,

159

Face, Muscles of.

265

,, Superior,

357,

365

Genio-hyoglossus,

3-j

467

Retrahcns Auriculam,

104

,, -hyoid,

318

Risorius, .

259,

268

I lyoglossus.

3i"iJ

466

Rotatorcs Spina-,

155,

156

Ilio-costalis,

145

Scaleni,

229

Inferior Oblique,

368

Scmi-spinalis Dorsi, .

15s

638

INDEX.

Muscles — continued.

Serrati, .... 140

Spinalis Dorsi, . . 145, 147

Splenius Capitis, . . 144

,, Colli, . . . 144

Stapedius, . . . 598

Sterno-hyoid, . . . 223

,, -mastoid, . -195

,, -thyroid, . . . 223

Stratum Transver.sum, . 467

,, Perpendiculare, . 467

Stylo-glossus, . . 318, 466

,, -hyoid, . . . 224

,, -pharyngeus, . . 326

Subcostal, .... 89

Superior Oblique, . . 358

Temporal, . . . 299

Tensor Palati, . . 399, 406

,, Tarsi, . . 266, 295

,, Tympani, . 594, 598

Thyro-ary-epiglottidean, . 451

,, -arytenoid, . . 450

,, -epiglottidean, . -451

Trachelo-mastoid, . . 147

Transversalis Cervicis, . 147

Triangularis Sterni, . . 8, 11

Tympana, .... 598

Zygomatici, . . . 268

Muscular Triangle, . 209,211

Nasal Cartilages, . . . 295
Duct, .... 294
Fossae, . 414, 420, 428

Group of Muscles, . 274
Nerve, . 281, 360, 428

Septum, . . -415
Naso-pharynx, . . . 400
Neck, Deep Dissection of, . 325
Middle Line of, . . 217
Posterior Aspect of, . 137
,, Triangle of, 198, 199
Side of, . . .184
Surgical Anatomy of, . 221
Nerves —

Abducent, 119, 125, 349, 490
Ansa Hypoglossi, . 216, 225
Anterior Palatine, . . 432
Arnold's Nerve, . . 336

Auditory, . 119, 125, 438, 490
Auriculo-temporal, . 107, 312

Nerves — continued.

Bell, Nerve of, . . . 207
Brachial Plexus, . . 204

Cardiac, . • 31^ 47> 68, 338
Cervical, . . . 151, 377
,, Plexus, 188, 240, 343
Chorda Tympani, 313, 438, 599
Ciliary, . . . 362, 618

Coccygeal, . . . 158

Coronary Plexus, . . 71
Cranial Nerves, Superficial

Origin of, . . . 488
Deep Temporal, . ■ 3 1 1

Descendens Hypoglossi, 215, 225
Descending Cervical, . . 242
Dorsal, ... 91, 153
External Laryngeal, . 216, 337
Facial, 119, 125, 190, 276, 436,
490
Fifth Cranial, . 118, 125, 347
Frontal, . . . -354
Gangliated Cord of Sympa-
thetic, . . . 87, 246
Ganglion of Root, . 173,336
Great Auricular, . 137, 260

,, Occipital, 108, 135, 152
Hypogastric Plexus, . . 68
Hypoglossal, 119, 125, 215, 225,
_ 322, 339, 469, 488
Inferior Cervical Ganglion, 342
,, Dental, . . . 312
, , Maxillary Division

of Trigeminal, 281, 308,
348
Intercostal, . . 3, 5, 91

Internal Laryngeal, 216, 337, 454,
469
Jacobson, Nerve of, . . 334
Lachrymal, . . . 355
Lenticular Ganglion, . .361
Lingual, . . 313

Long Buccal,

Lumbar
Malar, ' .
Masseteric,
Mental,

Middle Cervical
Mylo-hyoid,
Nasal,
Naso-palatine,

321, 469
282, 311

• 153
. 281

• 310

282, 314

Ganglion, 342

217, 312

281, 359, 430

• 418, 431

INDEX.

639

Nervks — con tinned.

Nerves of 15ack of 1 lead ami

Neck, . . IJ5

of Coivical l\egioii, 151
of Dorsal Ket^ioii, . 153
of Lunihar Region, 153
of Nasal Sepluni, . 418
of Palate, . 407, 430
of Scalp, . 104, 135

Nerve to Rhomboids, I42, 206
Subclavian, . . 207
Oculo-niotor, 118, 124, 349, 487,
490
CEsophageal, ... 79
Olfactory, 117, 123, 418, 491

Ophthalmic Division of Tri-
geminal,

Optic,

Orbital Branch of Facial,

• 349

118, 123, 359, 491

106

313.

ihl

414
280
333
339
30, 242

,; !^
li^-i 335

107, 277
78

Otic Ganglion,
Palpebral, .
Pharyngeal,

,, Plexus, .

Phrenic,
Plexus Gulx',
Pneumogaslric, 77, 125
Posterior Auricular, .
Pulmonary Plexus,
Recurrent Laryngeal, 79, 21 1, 246,

337, 454
Sacral, Posterior Primary

Division, . . -157

Small Occipital, . 108, 136

Solar Plexus, ... 68

Spheno-jialatine Ganglion, 430

Spinal Accessory, 119, 125, 138,

216, 11], 338, 4S9

,, ,, Portion of, 336

Splanchnic, ... 88

Stylo-pharyngeal, . . 333

Sub-occipital, . 151, 159, 377

Superficial Cervical, . . 190

,, Petrosal, Great, 351,

4«o, 437

,, ,, External,

352, 437
Small, 334,

Superior Cervical Ganglion, 341
,, Dental, . .412

Nkkvks — < on finned.
.Superior Laryngeal, .

,, Maxillary Division
of Trigeminus, 349,

106,

106,

279,
140,

279,
371,

216,

118, 125, 347,
118, 124,

Supra-orbital
,, -scapular, .
,, -trochlear,
Temporo-malar,
Thoracic Cardiac,
Tiiyro-hyoid,
Toiisillitic,
Trigeminal,
Trochlear, .
Tympanic,
Vagus, 76, 215, 331, 335,
Nose, Dilator Muscles of,
,, Meatuses of,
,, Mucous Membrane of,
Oblicjuus Capitis Inferior,

,, ,, Superior,

Obliterated Ductus Arteriosus,
Occipital Artery, 109, 147, 215,
,, Lobe,

,, Nerves, . 107,

Sinus,
Sulcus, .
Triangle,
Occipilo-frontalis Muscle,

,, -temporal Convolution,
Oculo-motor Nerve, 118, 124,

Oesophageal Arteries, .
,, Nerves,

,, Opening, .

Qisophagus, ... 79,
Olfactory Lobe,

Nerves, 117, 123,418,
Sulcus, .
Tract, .
Olivary Eminence,
Omo-hyoid Muscle,
Ophthalmic Artery,
Vein, .
Optic Chiasma,
,. Disc, .
.. Nerve,.

Thalanuis,
., Tract, .
Oral Muscles,
., Pharynx,

140, 208,

118, 123, 359,
• 528, 539,

337

411

355
207

354
411

79
226

333
490
490

334
489
274
424
427
159
160

54
253
510
135
127

512
199
102
514
349,
487
82

79
404
256
514
491
504

515
565

J62

365
486
620
4S6
55S
486
267
402

640

INDEX.

Orbicularis Oris, . . . 272

,, Palpebrarum, 266, 287

Orbit, Periosteum of, . . 353

Orbital Artery, . . . 265

,, Nerve, . . . 106

,, Sulcus, . . -505

Otic Ganglion, . . 313, 414

Outlet of Thorax ... 2

405

Pacchionian Bodies, . 113
Palate, Vessels and Nerves of.
Plica Fimbriata, .
Palato-glossus,

,, -pharyngeus,
Palpebral Fissure,

,, Ligaments, .
Papilla Foliata,
Paracentral Lobule,
Parallel Sulcus,
Paramedial Sulcus,
Parasinoidal Sinuses,
Parietal Lobe,

,, Lobules, .
Parieto-occipital Fissure,
Parotid Duct,

,, Gland,
Pars Basilaris,
,, Intermedia, .
,, Membranacea Septi,
,, Orbitalis,
,, Triangularis, .
Perforating Arteries,
Pericardium, .

,, Dissection of,

,, Relations of,

Pes Anserinus
Petit, Canal of,
Petrosal Sinus,
Petrous Ganglion, .
Pharyngeal Aponeurosis,
,, Arteries,

, , Nerves,

,, Plexus,

,, Tonsil,

,, Veins,

Wall, .
Pharynx,

,, Constrictor Muscles of, 396

,, Interior of, . . 400

Phrenic Nerve, . . 30, 242

475
407

463
467

405
257
289

463
504
513
503
"3
506

509
499
263
260

504
490

61
504
504

10

> 32

32

34

278

624

128

333

399

330

333

337, 339

400

396
395
394

• 23
163, 475
167

544

132
187
13
7, 239

13
18
18
15

334

n, 78

218, 456

560, 573

. 119

. 119

Phrenico-Costal Sinus,
Pia Mater, .

,, Spinalis,
Pineal Body,
Pinna, .
Pituitary Body,
Platysma Myoides,
Pleura, .

Cervical,
Costalis,
Diaphragmatic,
Reflections of,
Relations of,
Pleural Sacs,
Plexus Circulus Tonsillaris;

,, Guise,
Pomum Adami, . 185,
Pons Varolii, . 471,

Portio Dura,
,, Mollis,
Posterior Auricular Artery

109, 217, 254
,, ,, Nerve, 108, 277

,, Cerebral Artery, . 478
, , Communicating

Artery, . . 481

,, Common Ligament, 99
;, Condyloid Vein, . 128
,, Cranial Fossa, . . 560
,, Dental Artery, . . 303
,, Mediastinum, . 22, 75

,, ,, Dissec-

tion of, 76
,, Nares, . . . 401
,, Scapular Artery, 140, 202
,, Triangle of Neck,

_ 138, 198, 203
Postero-lateral Arteries, . 177

Post-parietal Convolution, . 509
Prsecentral Furrows, . .510
Preservation of Brain, . . 119
,, of Cord, . . 179

Prevertebral Region, . . 372
Promontory, . . . 592

Pterygoid Arteries, . . 304

,, Muscles, . . 301
Punctum Lachrymale, . . 25S
Putamen, .... 557
Pyramid, . . . -591

Pyramidalis Nasi, . . .274

INDEX.

641

Racemose Glands, . 400

Ranino Artery, . . 325

Raphe of Tongue, . 463

Recti Muscles, . . . 365
Rectus Capitis Anticus Major, 374
,, ,, ,, Minor, 376

,, Posticus Major

and Minor, . 159
,, Superior, . . 357, 365
Recurrent Laryngeal Nerve,

79, 211, 246, 337
Reflection of External Ptery-
goid, . . 308
,, of Hyoglossus, . 323
,, of Platysma, . . 187
Reil, Island of, . . -514
,, Sulcus of, . . . 498
Removal of Brain, . no, 117

,, of Head and Neck, 344
,, of Lungs, . . 84

Restiform Body, . . 567

Retina, . . .611, 619

Retinal Arteries and Veins, . 620
Rhomboid Ligament, . . 227
Rhomboids, Nerve to, . . 206
Right Auricle, ... 48
,, Auriculo - ventricular

Valve, . . -52

,, Lung, .... 26

,, Lymphatic Duct,. 84, 237

,, Ventricle, ... 50

Rima Glottidis, . 443

Risorius, . . . 259, 268

Rivini, Ducts of, . •321

Rolando, Fissure of, . . 499

,, Funiculus of, . . 567

,, Substantia Gelatinosa

of, . . . 180

,, Tubercle of, . . 567

Rotatores Spince, . . -155

Sacral Nerves, Posterior Primary
Divisions, . . -157

Santorini, Cartilages of, 459

Scalp, loi

,, Dissection of, .101

,, Nerves of, . .104

,, Surgical Anatomy of, . 109
,, Vessels of, . . 108

Scalene Tubercle, . . . 202

VOL. II. — 41

Scaleni Muscles, .

229

Schlemm, Canal of,

613

Sclerotic Coat,

611

Semicircular Canals,

601

Semilunar Valve, .

52

Semispinalis,

155

Septal Artery,

284

,, Cartilage, .

417

Septum Lucidum, .

533

,, Posticum,

167

,, Ventriculorum,

60

Serous Layer of Pericardium,

34

Serrati Muscles, .

140

Shrapnell's Membrane,

595

Sibson's Fascia,

18, 21

239

Sinus Pyriformis, .

403

442

,, Transversus Pericardii,

35

Sinuses of Valsalva,

45. 57

,, Venous Blood,

125

.Sixth Cranial Nerve,

118

125

Small Occipital Nerve,

108

136

Socia Parotidis,

261

Soft Palate, .

404

Solar Plexus,

68

Sphenoidal Fissure,

367

.Spheno-parietal Sinus,

130

Spinal Accessory Nerv(

J, ii9>

I25>

138, 216, 3:

}i, 338

489

,, Arteries, .

161

174

,, Cord,

168

Splanchnic Nerves,

88

Splenius Capitis, .

144

Stapes,

597

Stenson's Duct,

263

Sterno-clavicular Joint,

226

,, -costal Joints,

95

,, -hyoid Muscle,

223

,, -mastoid Artery,

214,

250

,, ,, Muscle,

195

,, -pericardiac Ligan

nents,

32

Stilling, Canal of, .

622

.Straight .Sinus,

117,

126

Stria Fornicis,

541

StriK Longitudinaks,

522

Stylo-glossus Muscle,

318,

466

,, -hyoid Ligament, .

325

,, ,, Muscle,

224

,, -mastoid Artery, .

254

,, -maxillary Ligamen

I.

194

,, -pharyngeal Nerve,

333

642

INDEX.

PAGE

PAGE

Stylo -pharyngeus Muscle, . 326

Surface Anatomy —

Subarachnoid Space, . 166, 472

of Cardiac Orifices, .

62

Subclavian Artery, 68, 201, 230

of Lungs, .

24

,, ,, Surgical

of Side of Neck,

184

Anatomy of, 202

of Trunk, .

134

Vein, . . .237

Sylvius, Aqueduct of, .

544,

548

Subdural Space, . . 114, 165

,, Fissure of.

497

Sublingual Artery, . . 324

,, Grey Matter of.

549

,, Gland, . . 320

S)mipathetic Cord in Neck

,2^5

340

Submaxillary Artery, . . 252

,, Gangliated Cord

,, Ganglion, . 322

of, 2, 87,

246

,, Gland, . 217, 319

Synovial Membranes, 97,

228,

306

Suboccipital Nerve, 151, 159, 377

Space, . .159

Tjenia Semicircularis, .

528,

530

Substantia Ferruginea, .

584

Tarsi, ....

288

,, Nigra, .

549

Teeth, ....

391

Subtrapezial Plexus,

242

Tegmentum,

550

Sulci Rostrales,

504

Temporal Artery, Superficial,

108,

Sulcus Coronarius,

42

254,

264

„ ofReil,

49S

,, Bone, Sections of.

605

,, Vallecula, .

575

,, Fascia, .

109,

297

Superficial Arcuate Fibres,

567

, , Lobe of Cerebrum, •

512

,, Cardiac Plexus,

31

,, Muscle,

299

,, Temporal Artery, 108,

Temporo-facial Nerve, .

277

254, 264

,, -maxillary Articula-

Superior Cervical Ganglion, . 341

tion,

305

,, Dental Nerve, . 412

Tenon, Capsule of.

357,

368

,, Epigastric Artery, . 10

Tensor Palati,

399,

406

,, Frontal Gyrus, . 502

,, Tarsi,

266,

295

,, ,, Sulcus, . 502

,, Tympani, .

598

,, Laryngeal Artery, 214, 250

Tentorium Cerebelli,

121

Nerve, . 337

Thalamencephalon,

492

,, Longitudinal Sinus, 116,

Thebesius, Foramina of.

49

117, 126

,, Valve of,

49

,, Mediastinum, . . 21

Third Occipital Nerve, .

136

,, Medullary Velum, 575, 581

,, Ventricle, .

543

,, Oblique Muscle, . 358

Thorax,

I

,, Thyroid Artery, 214, 249

„ Boundaries of, .

I

Vein, 251, 256

,, Frame vv^ork of, .

I

,, Vena Cava, . . 37

,, Inlet of, .

2

Supra-clavicular Triangle, 200, 203

,, Joints of, .

94

,, -mandibular Nerve, . 279

„ Outlet of, .

2

,, -marginal Convolution, 509

„ Wall of, .

■ 3,89

,, -orbital Artery, . 108, 364

Thoracic Cardiac Nerves,

79

Nerve, 106, 279, 355

,, Cavity .

II

,, -scapular Artery, 140, 202,

,, Duct,

83,

237

236

,, Joints,

94

„ ,, Nerve, . 140, 207

,, Lymphatic Glands,

84

,, ,, Veins, . . 236

Wall, .

• 3,89

,, -trochlear Nerve, 106, 2;

^9, 354

Thymus Gland,

35,

220

INDEX.

643

PAGE

PAGE

Thyro-arytenoid Ligaments,

• 452

Vagus, . 76, 119. 331. 335

489

,, ,, Muscle,

• 450

Vallecula,

441

497

., -hyoid Membrane,

• 445

Valsalva, Sinuses of,

45. 57

,, Nerve,

21

6, 226

Valves—

Thyroid Arteries, .

234, 250

Eustachian,

49

,, Axis, .

• 234

Mitral,

60

Body,

• 254

Pulmonary,

55

,, Cartilage,

• 456

Sigmoid, .

52

Thyroidea Ima,

67, 220

Tricuspid, .

52

Tongue,

. 462

Veins

,, Muscles of,

465

of Galen, .

537

Tonsils,

394. 407

of Scalp, .

108

Tonsillitic Arteries,

25

2, 329

of Spinal Cord, .

175

,, Nerves,

333

Angular, .

108

284

Topography of Cardiac

Ori

Anterior Jugular,

118

245

fices.

62

,, Vertebral,

236

, , of Lungs, .

^l

Ascending Lumbar,

92

Torcular Herophili,

126

Bronchial,

82

Trachea,

74, 256

Cardiac, .

45

Tracheal Arteries,

235

,, Great, .

46

Trachelo-mastoid Muscle,

147

Cavernous Sinus,

128,

345

Tracheotomy,

221

Cerebral, .

.

115

Transversalis Cervicis Muscle

, 147

Deep Cervical, .

237

,, Colli Artery

140, 202,

Dorsal Spinal Ple.xus,

158

236

Emissary, .

128

,, Veins,

236

External Jugular, ib

7, 203,

264

Transverse Facial Artery,

265, 282

Facial, , .21

7> 253,

284

,, Occipital Sulcus,

512

Inferior Petrosal Sinu

330

Triangularis Sterni,

8, II

,, Thyroid, 22

0, 235,

256

Trigeminal Nerve, Ii8,

125, 347,

Innominate

36,

220

490

Internal Jugular,

2I5>

329

Trigonum Habenulas, .

542

,, Maxillar)',

304

Hypoglossi, .

583

Intra-spinal,

162

,, Olfactorium, .

516

Lingual, .

325

Vagi,

583

Marshall's {See Cardia

c), '.

46

,, Ventriculi,

533

Mastoidal,

128

Trunks of Spinal Nerves,

173

Median, .

220

Tuber Cinereum, .

487

Pharyngeal,

396

Turbinated Bones,

424

Posterior Auricular, .

109

Turner, Intraparietal Sulcus c

A, 507

,, Condyloid, .

128

,, Tri-radiate Sulcus of,

505

Pterygoid ,

304

Tympanic Artery, .

303

Pulmonar)',

57

Cavity, .

590

Rachidian,

166

,, Mucous Membrane

. 596

Retinal, .

620

,, Muscles,

598

Subclavian,

237

,, Plexus, .

599

Superior Longiuidinal

Sinus,
116,

117

,, Thyroid,

251,

256

Umlio, ....

595

Tcmporo-maxillary, .

264

Uvula, ....

392

VenK Azygos Major, .

92

644

INDEX.

Veins — continued.

Vense Azygos Minor, . 94

,, Cava Superior, . 37

,, ,, Inferior, . . 37

,, Thebesii, ... 46

,, Vorticosse, . .619

Vertebral, . . . 234, 378

Velum Interpositum, . . 536

Venous Blood Sinuses, . .125

Verga's Ventricle, . . 536

Vermis of Cerebellum, . . 573

Vertebral Aponeurosis, . . 141

Arteiy, 130,160, 234, 377,

477
Vestibule, .... 599
Vestibulum Nasi, . . . 422
Vestigial Fold of Marshall, . 35

Vibrissce,

Vicq d'Azyr, Bundle of,

415, 422
535> 559

Vicq d'Azyr, Foramen caecum

of, .... 560

Vidian Artery, . . . 434
,, Nerve, . . 410, 433
Vieussens, Valve of, . 575, 581
Vitreous Body, . . 611, 621
Vocal Cords, . . . 442

Wall, Thoracic, . . • 3, 89

,, ,, Veins of, . 91

Wharton's Duct, . . -319
White Matter of Spinal Cord, 182

Willis, Cords of, . . -117

,, Circle of, . . . 484

Wrisberg, Ganglion of, . . 31

Zinn, Ligament of, . . 366

,, Zonula of, . . . 622

Zygomaticus Major Muscle, . 268

,, Minor „ . 270

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