Columbia (Hnftttfitp intljeCttpofiJtogork College of ^(jpgtcians; anb burgeons JLibvavp 1 Dr. Clay Ray Murray MANUAL OF ANATOMY. MANUAL OF Practical Anatomy BY D. J. CUNNINGHAM, M D. (EDIN. RT DUBL.). D.SC, I.L.D. (ST. AND. ET GI.AS.), D.C.L. (OXON.), F.R.S., PROFESSOR OF ANATOMY IX THE UNIVERSITY OF EDINBURGH VOLUME SECOND THORAX; HEAD AND NECK FOURTH EDITION ILLUSTRATED WITH 236 EXGRAVIXGS, MANY IX COLORS NEW YORK WILLIAM WOOD AND COMPANY MDCCCCVII CI i All rights reserved PRINTED IX EDINBURGH, SCOTLAND J CONTENTS. THORAX. PAGE Introductory, ....... i Thoracic Wall, . . . 3 Thoracic Cavity, . 10 Mediastinal Space, 23 The Lungs, 25 The Pericardium, 35 The Heart, 40 The Aorta, 67 Trachea, .... 78 Bronchi, 79 Thoracic Duct, . ■ 87 Thoracic Wall, . 93 Thoracic Joints, . 97 HEAD AND NECK. Scalp, Removal of the Brain, . Dorsal Aspect of the Trunk. Side of i he Neck, Middle Line of the Neck, Dissection- of the Face, Temporal and Pterygo-Maxillary Regions, v 104 1 12 !32 17.S 205 243 279 VI I I »N1 ENTS MAXILLARY i Deep Dissection of the Neck, The Lateral Part of the Middle Craniai 1 »f the Orbit. Prevertebral Region, The Joints of the N Mouth and Pharynx. Carotid Canal. -ior Maxillary Nerve, Otic Ganglion. Nasal] SPHENO - PaLATIN E ( i ANGLION Artej . Intrapi rHE i altai Nerve and the tory Nerv; ..... The Lary: ...... Th- e, ..... and Internal • 295 ■ 306 . • 33° 353 362 382 383 386 39i Maxillary 401 404 408 431 THK BRAIN, General Appearance of the Brain. Membranes and Blood- Base of Brain, The Cerebrum, General Structure of jhe Cerebral Hemisphei Cerebral Lobes and Interlobar Fissures. . The Corpus Callosum. .... Lateral Ventricle, .... Septum Lucidum — Fornix — Velum Interposii lm. Optic Thalami and the Third Ventricli The Mesencephalon, .... Basal Ganglia of tt^e Cerebral Hemispheri Medulla Oblongata. Pons Varolii, Cerebellum, Cerebellar Peduncle- Fourth Ventricle, 439 441 454 461 463 465 4S2 487 497 502 507 514 521 533 533 540 54i CONTENTS VI 1 THE AUDITORY APPARATUS. PAGE The External Ear, ... . 547 The Tympanic Cavity, . 550 Membrana Tympani, 553 Auditory Ossicles, 555 Eustachian Tube, 558 Vestibule, .... 559 Semicircular Canals, 560 The Cochlea, 560 THE EYEBALL. General Structure, 564 The Sclerotic, 565 The Cornea, 566 The Vascular Tunic, 567 The Retina, 572 The Vitreous Body, 573 Crystalline Lens, 575 Chambers of the Eyeball, 576 INDEX, 579 vol. 11. — a 2 LIST OF ILLUSTRATIONS. FIG. PAGE 1. Cervical Domes of the Pleural Sacs, and parts in relation to them, ....... 2 2. Diagram of one of the Upper Intercostal Nerves, . . 5 3. Dissection of the Anterior Wall of the Thorax from behind, . 8 4. Lines along which the Sternum should be divided, . . 12 5. Diagrammatic representation of a cross section through the two Pleural Sacs, . . . . . .14 6. The Right Pleural Chamber opened up by the removal of its outer wall, . . . . . < .15 7. The Left Pleural Chamber opened up by the removal of its outer wall, ....... 17 8. Diagram to show the relation of the lungs and the pleural sacs to the anterior thoracic wall, . . . .18 9. Diagram to show the parts which lie in front of the pericardium and heart, ....... 19 10. Left Pleural Sac, ...... 20 11. Right Pleural Sac, . . . . . .21 12. Dissection to show the relations of the Pleural Sacs posteriorly, 22 13. The Trachea, Bronchi, and Lungs of a Child, . . .25 14. Cervical Domes of the Pleural .Sacs, and parts in relation to them, ....... 26 15. The Mediastinal Surface of a Right Lung, . . .27 16. Inner or Mediastinal Aspect of a Left Lung, . . .28 17. The two Pulmonary Roots transversely divided close to the hilum of each lung, ....... 33 18. The Pericardium and Great Vessels of the Heart, . . 36 19. To show position of the Heart in relation to the mesial plane, . 41 20. The relations of the Heart and of its Orifices to the Anterior Thoracic Wall. (Young and Robinson), . . .42 21. Anterior or Sternal Aspect of the Heart, . . .43 22. The Anterior Aspect of the Auricular Part of the Heart, . 44 23. Transverse section through the Auricular Part of the Heart of an Ox, ....... 45 24. Posterior or Basal Aspect of a Heart, . . .46 ix x LIST OF ILLUSTRATIONS FIG. PAGE 25. The Base of the Ventricular Part of the Heart, . . 47 26. The Coronary System of Veins on the Surface of the Heart. (Diagram), ....... 50 27. A portion of the Right Auricle of the Heart, . . .52 28. Sagittal section through the Right Auricle of the Heart and the Root of the Right Lung. . . . . -53 29. Interior of Right Auricle of Heart, . . . .54 30. Transverse section through the Ventricular Part of the Heart. (From Luschka), ...... 56 31. The Interior of the Right Ventricle, . . . -57 32. Diagram of the arrangement of the Cusps and Chordae Tendinese of the Tricuspid Valve, . . . . .58 33. Heart of a seven months' Foetus. (From Gegenbaur), . 59 34. Dissection of a Heart to show the Left Auricle and the Left Ventricle. (Stiles), . . . . .61 35. Section through the Ventricular Portion of the Heart, . . 62 36. Diagram of the arrangement of the Cusps and Chordse Tendineae of the Mitral Valve, ...... 63 37. The relations of the Heart and of its Orifices to the Anterior Thoracic Wall. (Young and Robinson), . . .66 38. Transverse section through the Superior Mediastinum, . . 68 39. Transverse section through the Mediastinal Space, . . 69 40. Transverse section through the Superior Mediastinum, . . 71 41. Dissection of the Heart of a Calf by Dr. Waterston to show the Auriculo-ventricular Bundle, . . . . -77 42. Diagram of the Base of the Ventricular Portion of the Heart, . 78 43. The Trachea and Bronchi, . . . . -79 44. Tracing of section through the Posterior Mediastinum, . 81 45. Tracing of a section through the lower part of the Posterior Mediastinum, ...... 82 46. Posterior Aspect of the Heart with the Descending Aorta, the Trachea and Bronchi, and the (Esophagus, . . .83 47. The Thoracic Duct and its Tributaries. . . .88 48. Schema of the Branching of the Two Bronchi. From Gegen- baur), ....... 91 49. Costo-vertebral Joints as seen from the front, . . .99 50. Posterior Common Ligament of the Vertebral Column, . 102 51. Section through the Scalp and Cranial Wall, . . . 105 52. Superficial Nerves on the Side of the Neck and Back of the Scalp. (Hirschfeld and Leveillej, . . . 108 53. Diagrammatic section through the Meninges of the Brain. (Schwalbe), . . . . . .113 54. Mesial section through the Frontal Bone and corresponding part of the Longitudinal Blood Sinus, . . . .115 55. Diagram of a coronal section through the middle portion of the cranial vault and subjacent brain to show the membranes of the brain and the Pacchionian bodies, . . .116 LIST OF ILLUSTRATIONS xi FIG. PAGE 56. The Dura Mater and the Superior Longitudinal Sinus, etc., . 117 57. Sagittal section through the Skull, . . . 11S 58. Coronal section through the Cranial Cavity, . . .123 59. Aperture between the Dorsum Sellre and the anterior con- cave free margin of the Tentorium. (Hirschfeld and Leveille), . . . . . . .124 60. Floor of the Cranium, ...... 125 61. Pituitary body. (Schwalbe), . . . . .131 62. Skin incisions for the dissection of the dorsal aspect of the trunk, 133 63. Superficial dissection of the Back of the Neck, . . . 135 64. Diagram to show the Connexions of the Lumbar Fascia, . 141 65. Dissection of the Ligamentum Nucha? and of the Vertebral Artery7 in the Neck, . . . . . .147 66. Dissection of the Sub-occipital Region, . . . 155 67. Membranes of the Spinal Cord, and the mode of origin of the Spinal Nerves, . . . . . .161 68. Lateral view of the Spinal Cord, Dura Mater, and Ligamentum Denticulatum. (Hirschfeld and Leveille), . . 164 69. Sagittal section through the lower part of the Vertebral Canal, 165 70. A segment of the spinal cord ; anterior aspect. (SCHWALBE, after Allen Thomson), . . . . .167 71. Sacral Canal opened up from behind. (After TESTUT), . 168 72. Transverse section through the upper part of the Cervical Region of the Cord, . . . . . .172 73. Transverse sections through the Cord in different regions, . 175 74. Transverse section through the upper cervical part of the Cord. 176 75. Skin incisions for dissection of the Triangles of the Neck, . 179 76. Superficial Nerves on the Side of the Neck and Back of the Scalp. (Hirschfeld and Leveille), . . . 1S3 jy. Diagrammatic representation of a transverse section through the neck. (Treves), . . . . . .184 78. Dissection of the Posterior Triangle of the Neck, . . 190 79. Diagram of the Brachial Plexus, .... 194 80. Diagram to show the Boundaries of the Triangles of the Neck, 199 81. Dissection of the Front of the Neck, .... 206 82. Sterno-clavicular and Costo-sternal Joints, . . .212 S3. Dissection of the Posterior Triangle <>f the Neck, . . 215 84. Muscle-Attachments to the Upper Surface of the First Rib, and the Outer Surface of the Second Rib, . . . 217 85. Diagram of the Subclavian Artery and its Branches. (TURNER), 218 86. Deep Dissection of the Root of the Neck on the Left Side, . 225 87. Diagram of the Cervical Plexus and the Ansa Hypoglossi, . 227 88. Transverse section through the Neck at the level of upper part of Thyroid Cartilage, . . • • 231 89. Transverse section through the Neck at the level of the Cricoid Cartilage, ....... 232 90. Diagram of the Fxternal Carotid Artery and its Branches, . 234 xii LIST OF ILLUSTRATIONS FIO. . PAGE 91. Dissection of the Front of the Neck, .... 241 92. Transverse section through the Thyroid Body, Trachea, and Gullet, at the level of the first Dorsal Vertebra, . . 242 93. Eyelid slightly everted to show the Conjunctiva, . . 244 94. Dissection of the Parotid, Submaxillary, and Sublingual Glands, 247 95. Transverse section through the Head at the level of the I lard Palate, ....... 24S 96. Dissection of the Parotid Region and the upper part of the Anterior Triangle of the Neck, .... 250 97. The Facial Muscles, ...... 255 98. Arrangement of the Fibres of the Buccinator Muscle at the Angles of the Mouth, ..... 257 99. Diagram of the Orbicularis Oris Muscle, . . . 258 100. Nerves of the Face, ...... 262 101. Arteries of the Face, ...... 267 102. The Pinna, ....... 269 103. Eyelid slightly everted to show the Conjunctiva. . . 273 104. Diagram of the Structure of the Eyelids, . . . 274 105. Dissection of the Right Eyelid, .... 275 106. Diagram of the Lachrymal Ducts and Sac, and of the Nasal Duct. (Gegenbaur), ..... 277 107. Cartilages of the Nose, . 279 108. Dissection of the Pterygo- maxillary Space, . . . 283 109. Section through Temporo-maxillary Joint, . . . 288 no. Diagram of the different positions occupied by the head of the mandible and the interarticular cartilage as the mouth is opened and closed, ...... 289 111. Diagram of the C.asserian Ganglion and the Inferior Maxillary Division of the Fifth or Trigeminal Nerve, . . 291 112. Dissection of Submaxillary Region, .... 297 113. Coronal section through the Tongue and Submaxillary Region in a plane behind the molar teeth, .... 29S 1 14. Dissection of the Parotid, Submaxillary, and Sublingual Glands, 299 115. Coronal section through the Closed Mouth in the plane of the second molar teeth ...... 300 116. Diagram of Carotid System of Vessels in the Neck with the Glosso- pharyngeal, Vagus, Spinal Accessory, and Hypo- glossal Nerves, ...... 308 117. Diagram of the relation of parts in the Jugular foramen, . 311 118. Section through the Head a little to the right of the .Mesial Plane, . . . . . . .312 119. Section through the Cavernous Sinus. (After MERKEL, somewhat modified), . . . . . • 324 j 20. Coronal section through the Cavernous Sinus to show the posi- tion of the Nerves on its wall, .... 325 121. Dissection of the Orbit and the Middle Cranial Fossa, . 326 122. The Ophthalmic Nerve of the Left Side, . . . 332 LIST OF ILLUSTRATIONS xiii FIf;- PAGE 125. Diagram of the Superior Oblique Muscle. (From Hermann Meyer), 335 124. Dissection of the Eyeball showing the Distribution of the Ciliary Nerves and Vessels, .... 339 125. Diagram of the Ophthalmic Artery and its Branches. (After Quain and Meyer, modified), .... 340 126. Diagram of the Orbital Cavity, . . . 342 127. Dissection of the Orbit and the Middle Cranial Fossa, . 344 128. Dissection of the Capsule of Tenon from the front, . . 346 129. Prevertebral Muscles of the Neck. (Paterson), . . 350 130. Dissection of the Ligamentum Nucha? and of the Vertebral Artery in the Neck, ..... 352 131. Coronal section through bodies of certain of the Cervical Vertebrae, ........ 354 132. The Ligamenta Subflava in the Lumbar Region of Spine, . 356 133. Mesial section through the Basilar Process of Occipital Bone, the Atlas, and the Axis. (From Luschka, slightly modified), ....... 358 134. Dissection from behind of Ligaments connecting the Occipital Bone, the Atlas, and the Axis with each other, . . 360 135. The Sublingual Region in the Interior of the Mouth, . . 364 136. Isthmus of the Fauces as seen through the widely opened Mouth, 365 137. Profile view of the Pharynx to show the Constrictor Muscles. (From Turner), ...... 369 138. Sagittal section through the Nasal Chamber, the Mouth, Larynx, and Pharynx, a little to the right of the mesial plane, ....... 372 139. Superior Aperture of Larynx exposed by laying open the pharynx from behind, ..... 375 140. Transverse section through the Neck at the level of upper part of Thyroid Cartilage, . . . . . 376 141. Diagram of the Superior Maxillary Nerve, 142. Antero- posterior section through the Nose, Mouth, and Pharynx, a little to the left of the mesial plane, . . 388 143. Coronal section through the Nasal Cavities opposite the Crista Galli of the Ethmoid Bone, .... 392 144. Outer Wall of the Left Nasal Fossa. (From SCHWALBE), . 394 145. Outer Wall of Nasal Chamber and Naso-pharynx, . . 396 146. Diagram of the Facial Nerve. (Thane, Quairis Anatomy), 406 147. Coronal section through Larynx to show Compartments, . 410 148. The Larynx as seen in the living person by means of the laryngoscope, . . . . . .411 149. Mesial section through Larynx to show the Outer Wall of the Right Half, ....... 412 150. Diagram of Rima Glottidis, ..... 413 151. The Crico-thyroid Muscle, ..... 4I0 152. Muscles on the Posterior Aspect of the Larynx, . . 417 j< XIV FIG. 153- 154- 155- 156. 157. 158. 159- 160. 161. 162. 163. 164. 165. 166. 167. 168. 169. 170. 171. 172. 173- 174. 175- 176. 177. 178. 179. 180. 181. 182. 183. 184. LIST OF ILLUSTRATIONS PAGE Muscles in the Lateral Wall of Larynx, . . . 419 Lateral part of Cricothyroid Membrane, . . .421 Cartilages and Ligaments of Larynx viewed from the front, . 426 Profile view of Cartilages and Ligaments of Larynx, . . 427 Cartilages and Ligaments of Larynx as viewed from behind, . 428 The Sublingual Region in the Interior of the Mouth, . . 433 Muscles of the Tongue. (From Gegenbaur), . . 435 Transverse section through the hinder part of the Tongue. (From Gegenbaur), ..... 436 Longitudinal section through the Tongue. (From Aeby), . 437 Transverse section through the Tongue. (From Aeby), . 438 The Base of the Brain with the Cranial Nerves attached, . 440 Diagrammatic section through the Meninges of the Brain. (Schwalbe), ...... 442 Diagram of a coronal section through the middle portion of the cranial vault and subjacent brain to show the mem- branes of the brain and the Pacchionian bodies, . . 443 Floor of the Cranium after the removal of the Brain and the Tentorium Cerebelli, ..... 446 Internal and Tentorial Surfaces of the left Cerebral Hemi- sphere. (Semi-diagrammatic), .... 448 Inferior Surface of the Cerebral Hemisphere, . . 450 Outer Surface of the Cerebral Hemisphere. (Semi-diagram- matic), . . • • • • • 451 Diagram of the Circle of Willis, . . . .453 The Base of the Brain with the Cranial Nerves attached, . 455 Front view of the Medulla, Pons, and Mesencephalon of a full-time Foetus, ...... 457 Section through the Head a little to the right of the Mesial Plane, ....... 459 Diagrammatic view of the manner in which the several parts of the Brain are connected with each other. (From Schwalbe), 460 Gyri and Sulci on the Outer Surface of the Cerebral Hemisphere, 464 The Gyri and Sulci on the Mesial Aspect of the Cerebral Hemisphere, ...... 468 Gyri and Sulci on the Tentorial and Orbital Surfaces of the Cerebral Hemispheres, . . . . .471 Posterior Part of Inner Surface of the Left Hemisphere, . 477 Fissures and Gyri on the Surface of the Insula. (Eber- staller), .....•• 479 The Corpus Callosum exposed from above and the Right Half dissected to show the course taken by the Fibres, . . 484 Mesial section through the Brain, .... 485 Anterior end of the Corpus Callosum and its Peduncles. (From Cruveilhier), ..... 486 Dissection to show the Lateral Ventricles, . . . 487 Cast of the Ventricles of the Brain. (From Retzius), . 488 LIST OF ILLUSTRATIONS xv FIG. 185. Dissection to show the Posterior and Descending Cornua of the Lateral Ventricle on the left side, . . . 489 186. Coronal section through the Cerebrum, . . . 490 187. Coronal section through the Posterior Horns of the Lateral Ventricles, ... .... 492 188. Dissection to show the Posterior and Descending Cornua of the Lateral Ventricle, ..... 494 189. Coronal section through the Cerebrum, Mid-brain, and Pons Varolii in the plane of the geniculate bodies, . . 495 190. Diagram of the Fornix ; profile view, . . • 499 191. Dissection to show Velum Interpositum and the parts in its vicinity, ....... 500 192. Diagrammatic coronal section through the Optic Thalami and the parts in immediate relation to them, . . .501 193. The two Optic Thalami and the Third Ventricle as seen from above, ....... 503 194. Mesial section through the Corpus Callosum, Third Ventricle, Mesencephalon, Pons, Cerebellum, and Medulla, . . 506 195. Diagrammatic outline of the Third Ventricle as viewed from the side, ....... 507 196. Diagram of the Roots of the Optic Tract, . . . 509 197. The Origin and Relations of the Optic Tract. (Professor Thane, from Quairfs Anatomy), . . . .510 198. Diagrammatic view of the Cut Surface of the Mesencephalon when transversely divided, . . . . .511 199. Transverse section through the Mesencephalon at the level of the inferior quadrigeminal body, . . . .512 200. Section through upper part of Mesencephalon at level of superior quadrigeminal body, . . . 5 1 3 201. Horizontal section through the Right Cerebral Hemisphere at the level of the widest part of the lenticular nucleus, . 515 202. Coronal section through the Frontal Lobes of the Cerebrum, . 516 203. Coronal section through the Cerebrum so as to cut through the anterior part (putamen) of the lenticular nucleus, . • 5J7 204. Coronal section through the Cerebrum in such a plane as to cut the three parts of the lenticular nucleus, . • 518 205. Front view of the Medulla, Pons, and Mesencephalon of a full- time Foetus, . . . . . .521 206. Diagram of the Decussation of the Pyramids. (Modified from Van Gehuchten), . . . 523 207. Lateral view of the Medulla. Pons, and Mesencephalon of a full-time Foetus, ...... 524 208. Back view of the Medulla, Pons, and Mesencephalon of a full- time Foetus, ...... 526 209. Section through the lower part of the Medulla of the Orang, . 529 210. Transverse section through the closed part of the Medulla of a full-time Foetus, ...... 530 xvi LIST OF ILLUSTRATIONS FIG. 211. Transverse section through lower end of the Medulla of a full- time Foetus, ...... 530 212. Transverse section through the Medulla of newd:>orn Child, . 531 213. Transverse section through the Medulla, . . . 532 214. Upper Surface of the Cerebellum, .... 536 215. Lower Surface of the Cerebellum, .... 537 216. Mesial section through the Vermis of the Cerebellum. (From Gegenbaur), ..... 538 217. Transverse section through the upper part of the Pons Varolii of the Orang, ....... 545 218. Coronal section of the Right Temporal Bone, . . . 548 219. Vertical transverse section through the Right Ear. (HOWDEN), ....... 549 220. Schematic vertical section through the Tympanum. (From Testut), . . . . . . -550 221. Section through the Left Temporal Bone showing the Inner Wall of the Tympanic Cavity. (Howdex), . 551 222. Left Membrana Tympani and Recessus Epitympanicus viewed from within. (Howdex), ..... 552 223. Left Membrana Tympani and Chain of Tympanic Ossicles seen from the inner aspect. (Howdex), . . . 553 224. Left Tympanic Membrane as viewed from the external auditory meatus during an otoscopic examination. (Howdex ), ....... 554 225. Left Malleus and Incus. (Helmholtz), . . . 555 226. The Left Malleus. (Howdex), .... 556 227. The Left Incus. (Howdex), ..... 556 228. Left Stapes. (Howdex), ..... 557 229. Interior of the Left Bony Labyrinth viewed from the outer aspect. (Howdex 1. ..... 559 230. Left Bony Labyrinth viewed from outer side. (Howdex ), . 560 231. Diagram of the Osseous and Membranous Labyrinth. (Modi- fied from Testut), ..... 562 232. Horizontal section through the Left Eyeball. (Diagrammatic), 564 255. Diagram of the posterior aspect of the Left Eyeball. (After Testut, modified), . .... 566 234. Dissection of the Eyeball showing the Vascular Tunic and the Distribution of the Ciliary Nerves and Vessels. . . 568 235. The Ciliary Processes of the Human Eyeball viewed from behind. (MERKEL), ..... 569 236. Diagrammatic representation of the Ciliary Region, as seen in vertical section, ...... 574 MANUAL OF ANATOMY. MANUAL OF PRACTICAL ANATOMY. THORAX. THE dissection of the thorax is commenced on the eleventh day1 after the subject has been placed in the dissecting- room. By this time the upper limbs 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 outwards 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. 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 between the 1 Saturdays and Sundays are not counted. VOL. II — 1 THORAX 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 forwards 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 tliorax, is a narrow opening which is bounded by the first dorsal vertebra, the subclavian artery Righl innominate vein Innominate artery Trachea Vagus nerve \ Right < Ksophagus Left subclavian artery Sulcus subclavius VagUS nerve Left common carotid Left nnominate vein FiG. i. — Cervical Domes of the Pleural Sacs, and parts in relation to them. fust 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 the apices of the lungs project upwards into the root of the neck, and between these the windpipe, gullet, the pneumo- gastric 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 enter the chest; 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 o( 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 sternum, THORACIC WALL 3 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 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 depth of the thoracic cavity. But the diaphragm does not form an unbroken partition. It presents three large openings, by means of which structures pass to and from the thorax, viz. — (1) for the aorta, thoracic duct, and vena azygos major; (2) for the oesophagus and pneumogastric nerves ; (3) for the inferior vena 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. ( External intercostals. \ Int Muscles, . . J Internal intercostals. I Triangularis sterni. [ Anterior intercostal membranes. Membranes, . . J Posterior intercostal membranes. I Pleural membrane (parietal part). /"Intercostal nerves. XT i a ♦ • Aortic intercostal arteries. iScrves and Arteries, e . , , j Superior intercostal artery. ternal mammary artery. Un Dissection. — Portions of certain of the muscles of the upper limb and of the abdominal wall will be noticed attached to the thoracic wall. From before backwards the dissector will meet with the pectoralis major, the pectoralis minor, and the serratns magnus, whilst towards the lower margin of the chest he will recognise the rectus abdominis in front, and the obliquus externus and laiissimns dorsi upon its lateral aspect. The rounded 11— 1 a 4 . THORAX tendon of the subclavins may also be observed taking origin from the first costal arch, and posteriorly to this the scalenus posticus extends downwards to its insertion into the second rib. With the single exception of the scalenus posticus, these muscles should be removed so as to lay bare the costal arches and the intercostal muscles. In detaching the serratus magnus be careful not to injure the lateral cutaneous nerves which make their appearance in the intervals between its digitations. The anterior cutaneous nerves and perforating 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 ninscles (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 mem- brane. 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 muscles 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 dissec- tion should" be performed in each intercostal space, and, in effecting it, care must be taken of the intercostal arteries which lie between the two muscular strata. The internal intercostal muscles (musculi intercostales interni) thus laid bare will be seen to be similar in their constitution THORACIC WALL TRIANG. STERNI 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 are 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 backwards to the angles of the ribs, from which to the spine the muscles are replaced by a series of thin membranes — the pos- terior intercostal mem- branes— 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 con- tinuous with the fibres of that muscle. Intercostal Nerves. — The intercostal nerves are altogether 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 the 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 far as the anterior extremities of the bony ribs. They now reach the deep surface of these muscles and are carried inwards, first upon the pleura, and then upon the triangularis sterni muscle. Lastly, they cross the internal mammary artery, and come Fig. 2. — Diagram of one of the Upper Intercostal Nerves. 6 THORAX forwards at the side of the sternum as the anterior cutaneous nerves of the pectoral region. Each nerve, before it reaches the surface, pierces — (a) the internal intercostal muscle ; (b) the anterior intercostal membrane ; (c) the origin of the pectoralis major; and (d) the deep fascia (Fig. 2). But this description only holds good for the upper five intercostal nerves. The lower six nerves, on leaving the anterior ends of the intercostal spaces, pass forwards into the abdominal wall between the internal oblique and transversalis muscles, where they have already been displayed by the dissector of the abdomen. The intercostal nerves, as they traverse the thoracic wall, give off — (a) the lateral cutaneous branches, (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 intercostal muscles, appear in the intervals between the digitations of the serratus magnus. The first intercostal nerve gives off no lateral and no anterior cutaneous branch ; the lateral cutaneous branch of the second intercostal nerve takes the form of the intercosto- humeral nerve. It is not necessary to make a dissection of the intercostal nerves in more than two or three of the spaces. Intercostal Vessels. — The intercostal arteries should 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 forwards ; and in each of the upper nine intercostal spaces, two, the anterior intercostal arteries, running from before backwards. In the upper two spaces the vessels which run from behind forwards are derived from the superior intercostal branch (truncus costo-cervicalis) of the subclavian artery ; in the nine lower spaces they spring directly from the aorta, and are called the aortic intercostal arteries. The anterior intercostal arteries of the upper six spaces proceed directly from the internal mammary, whilst in the THORACIC WALL 7 case of the seventh, eighth, and ninth 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 higher 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 lower two aortic intercostal arteries are carried onwards beyond the thoracic wall into the abdominal wall. The superior intercostal arteries are dis- posed in a manner similar to the aortic intercostal vessels. 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 inter- costal muscles, and end by anastomosing with the aortic and superior intercostal arteries. Dissection. — The dissector should next proceed to remove the intercostal 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 me??ibrane 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 triangu- laris sterni muscle will be seen to intervene between the pleura and the costal cartilages. The internal mammary artery, with its two companion veins, descends 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. 11— lb 8 THORAX Towards the lower margin of the thorax the pleural sac is not prolonged 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 Sternohyoid ~-4^^ rj- Sterno-thyroid ~^j£k jm ; Triangularis sterni Intercostal nerve and artery Internal mammary artery Sternal glands Triangularis terni Musculo- phrenic artery | Musculo- S^*J phrenic artery Fig. 3. — Dissection of the Anterior Wall of the Thorax from behind. 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. Internal Mammary Artery (arteria mammaria interna). — This vessel arises in the root of the neck from the first part of the subclavian, and enters the thorax, by passing downwards behind the inner end of the clavicle and the cartilage of the THORACIC WALL 9 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 epigastric and the musculo- phrenic bra?iches. It runs parallel with the outer margin of the sternum, from which it is separated by an interval of about half an inch. Placed in front of the internal mammary artery are the upper six costal cartilages, with the intervening intercostal 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 behind 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, . \ , thoracic narietes 2. The perforating, . J r ^. The conies nervi phrenici,! , .,,... c ,1 ,1 J ,, \. ,. , , X . ' J- to parts in the interior of the thorax. 4. Mediastinal and thymic, . J l 5. Superior epigastric, . j h terminal branches. 6. Musculo-phrenic, . . J The anterior intercostal arteries (rami intercostales) are supplied to the upper six intercostal intervals, and have already been dissected (p. 6). Two are given to each space : frequently these arise by a common trunk. The perforathig arteries (rami perforantes) accompany the anterior cutaneous 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 the 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 musculo-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 terminates io THORAX on its abdominal surface. It gives off the anterior intercostal arteries to the seventh, eighth, and ninth intercostal spaces (P- 7)- Triangularis Sterni (musculus transversus thoracis). — This is a thin muscular layer placed on the deep surface of the sternum and costal cartilages. It is continuous below with the transversalis muscle of the abdominal wall, and arises from the posterior surface of the ensiform cartilage, the lower part of the body of the sternum, and from the inner ends of the 5th, 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. 3). In many cases the muscle is feebly developed, and does not show connections so wide as those which are described above. Upon the superficial aspect of the triangularis sterni 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, but it is not advisable to remove the costal cartilages to expose it further, as this would materially interfere with the subsequent display, in their proper relations, of other more important structures. THORACIC CAVITY. The arrangement of the two pleural sacs must now engage the attention of the student ; but in order that the relations of these may be understood, it is necessary that the dissector should have some preliminary knowledge of the thoracic cavity and its contents. 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 diaphragm. Each lung is connected with the base of the heart by several large vessels which pierce the pericardium, and these, with the corresponding division of the windpipe passing to the lung, constitute the pulmonary root or pedicle. Each lung is free within the thorax except where it is THORACIC CAVITY u attached by its root and by a fold of pleural membrane which will afterwards be described under the name of the liga??ientum latum pulmonis. The thoracic cavity is subdivided into two large lateral chambers which contain the lungs by a central vertical partition called the mediastinum thoracis. This partition extends from the anterior thoracic wall in front to the vertebral column behind, and from the fact that both sides of it, as well as the other walls of the lateral chambers, are lined by two serous membranes called the pleicrce, the chambers receive the name of the pletcral cavities. The mediastinal partition is built up of the several structures which lie in or close to the mesial plane. The more important of these are the heart enveloped in its pericardium, the thoracic aorta with the branches which spring from its arch, the pulmonary vessels and great veins in the neighbourhood of the heart, the trachea, the gullet, and the thoracic duct and the vagus and phrenic nerves. The mediastinum is not median in position. Owing to the marked pro- jection of the heart to the left side and to the position of the descending thoracic aorta on the left side of the bodies of the vertebrce, the left pleural chamber, although it is deeper than the right, is considerably reduced in width. The two pleural cavities, therefore, are not symmetrical in form. 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 chamber in which the lung lies, but is also reflected over the lung so as to give to it an external covering, which is intimately connected with the pulmonary substance. We 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 are 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 somewhat complicated dissection. Dissection. — The sternum must be divided with the saw into four portions by three 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 the fifth and s/.\//i costal cartilages ; an oblique section, beginning below at the inferior trai at, close to the left margin of the sternum, and carried upwards to the middle of 12 THORAX 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. 4). 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 care must be taken not to separate the parietal pleura at any point from the deep surface of the thoracic wall. Anterior Mediastinal Space. — 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 sur- face of the sternum, and passing backwards to reach the pericardium. But the pericardium is not in view, except perhaps to a small extent below, because the two pleural membranes, where they make this re- flection, are in contact. Introduce the finger be- tween the two pleural sacs, and pass it upwards and downwards through the loose areolar tissue which Fig. 4— Lines along which the Sternum holds them together. The should be divided. pericardium is in this way exposed, and a demonstra- tion is obtained of a space which is termed the anterior mediastinal space. In front this space is bounded by the posterior surface of the body of the sternum, and usually also by the 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 upon 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 pleura, and an interval is THORACIC CAVITY 13 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 other connections within the thorax. For this purpose the parietal pleura must be separated from the ribs as far forwards as the cartilages. This can best be done by gently insinuating the forefinger between each of the ribs and the pleura, 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, fifth, and sixth costal arches at the junction of the osseous with the cartilaginous portions, and remove these ribs by snipping through them with the bone pliers 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 thoroughly investigated. The greater part of the costal pleura now lies flaccid upon the surface 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 appearance 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 respiration to take place with the smallest 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 explore its extent and connections. First 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 corresponding side of the mediastinal partition. Above the level of the pericardium it passes right back upon the upper part of the mediastinal partition to the vertebral column, and then proceeds outwards on the ribs. Upon that part of the mediastinal partition which is formed by the lateral aspect of the pericardium it can be traced backwards towards the M THORAX 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 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 Parietal pleura Pleural cavity N Visceral pleura sms6 Parietal pleura Pleural cavity Visceral pleura Fig. 5. — Diagrammatic representation of a cross section through the two Pleural Sacs. the root of the lung the pleura is prolonged 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 from the pericardium over the oesophagus to the bodies of the vertebrae. 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. Below the level of the root of the lung, the pleura can be traced backwards upon the pericardium to the spine, from which it is conducted outwards upon the ribs. But it does not pass backwards uninterruptedly. The same two layers which envelop the pulmonary root THORACIC CAVITY 15 are prolonged outwards from the pericardium in apposition Thoracic sym- pathetic cord Intercostal vessels and nerve Vena azygos major Pulmonary !u*V artery Eparterial __J bronchus Hyparterial I bronchus Pulmonar veins Scalenus anticus Brachial nerves Right subclavian artery Right subclavian vein Right innominate vein Internal mammary artery Trachea K Right vagus nerve \ ■^fc- Left innominate vein (Esophagus Ligamentuni latum pul- monis (cut) Ascending aorta and pulmonary artery Superior vena cava Internal mam- mary artery Phrenic nerve and accom- Danying artery Pericardium and heart Diaphragm 1 i<,. 6. The Right Pleural Chamber opened up by the removal <>f its outer wall. The lung has been taken away so as to expose the mediastinal wall of the pleural chamber. Several of the structures in the medias- tinal septum are seen shining through the mediastinal pleura 1 6 THORAX with each other. Meeting the inner surface of the lung, they separate to enclose the lower portion of this organ. The fold of pleura which is thus formed is called the ligamentum latum pulmonis, and it can be brought into view by enlarging the opening in the pleural sac, and drawing the basal portion of the lung outwards and backwards. It will then be seen to be a fold which stretches between the pericardium and the lower part of the inner surface of the lung, and which presents a free border below. The dissector has now traced the continuity of the pleural sac in the transverse direction. He has observed that it lines the deep surface of the costal arches, and is reflected backwards upon the surface of the intra-thoracic mediastinal partition from the back of the sternum to the spine. This portion is called the mediastinal pleura, and it is uninterrupted, 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. n). This portion of the pleura is called the cervical pleura. Its summit or highest point reaches the level of the lower border of the neck of the first rib ; but owing to the obliquity of the first costal arch this point is placed from one to two inches above the anterior extremity of the first rib, and from a half to one and a half inches above the clavicle. The subclavian artery arches over and lies in a groove on the inner and anterior aspect of this cul-de-sac near its summit, whilst at a lower level the innominate and subclavian veins also lie upon its inner and anterior aspects. The cervical dome of pleura is supported on its outer side by the scalenus anticus and scalenus medius muscles, and is strengthened by an aponeurotic expansion (Si&son's fascia) which is spread over it, and receives attachment 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 the lower part of the thorax the parietal pleura is THORACIC CAVITY 17 reflected from the inner surface of the chest wall on to the Scalenus amicus Brachial nerves Left subclavian artery Left subclavian vein Left subclavian artery Left vagus nerve Left common / AA carotid artery / Left innominate vein ^J^t Internal mammary && artery Phrenic nerve and accompanying artery / Pulmonary / artery /■■ j Heart and pericardium tJC; Thoracic duct < Esophagus Recurrent laryngeal Aortic arch Left pulmon- ary artery Left bronchus Left pulmon- ary veins Cut edge of parietal pleura Descending thoracic aorta Ligamentum a turn pulmonis < Esophagus Diaphragm Fig 7. — The Left Pleural Chamber opened up by the removal 01 its outer wall. The lung has been taken away and a window has been made into the superior mediastinum by the removal of a portion of the medias- tinal pleura. Several of the Structures which form the mediastinal partition are ieen shining through the mediastinal pleura. VOL. II — 2 i8 THORAX upper surface of the diaphragm, and is carried inwards upon this towards the base of the pericardium, where it becomes continuous with the mediastinal pleura. The portion of the membrane which clothes the diaphragm is termed the diaphragmatic pleura. Lines of Pleural Reflection. — The two pleural sacs are not shaped alike. The chambers which they line are not symmetrical, and con- sequently the lines along which the two membranes are re- flected from the ster- num and costal carti- lages backwards to - wards the pericardium, and also from the chest wall on to the dia- phragm, differ some- what on the two sides. First consider the sternal line of reflection, or that along which the pleura leaves the an- terior thoracic, wall to become themediastinal pleura. Behind the manubrium sterni the two pleural sacs are separated from each Fig. 8. — Diagram to show the relation of the Other by an angular lungs and the pleural sacs to the anterior interval nnt near the thoracic wall. The lungs are depicted in , f , red, and the pleural sacs in blue. upper end Ot 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. At this level the two sacs part company. The left pleura deviates outwards, whilst the right pleura is continued downwards in a straight line 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. THORACIC CAVITY i9 Opposite the sternal end of the fourth costal cartilage the left pleura retires 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. Cervical dome of pleura Left subclavian artery Left common carotid artery Left innominate vein Internal mam- mary artery Anterior margin of right pleural sac Intercostal nerve ^* "V Pericardium y 1 Triangularis stern i Diaphragm Fig. 9. — Diagram to show the parts which lie in front of the pericardium and heart. The outline of the heart is indicated in red by a dotted line, and the anterior margins of the pleural sacs are represented by blue lines. This area is very variable in its extent, but the accompanying diagram (Fig. 8) may be considered to represent the average amount of outward deviation of the left pleural sac in con- nection with this part of the chest wall. Leaving the sternum, the reflection-line of the left pleura descends parallel and close to the left margin of the sternum behind the fourth intercostal space, the fifth costal cartilage, and the fifth intercostal space to the back of the sixth costal 20 THORAX cartilage. Here it turns outwards and downwards and passes into the diaphragmatic reflection-line. The diaphragmatic reflection-line is that along which the CEsophagus Left subclavian artery Left common carotid artery Left superior intercostal vein Left innominate vein _Cut edge of parietal pleura Aortic arch Cut edge of parietal pleura Pericardium Pulmonary artery Bronchus Lower pul- monary vein (Esophagus Diaphragmatic pleura Fig. to. — Left Pleural Sac in a subject hardened by formalin injection opened into by the removal of the costal pleura. The left lung has also been removed so as to display the mediastinal pleura. The line along which the pleura is reflected from the diaphragm on to the thoracic wall is exhibited. pleura leaves the thoracic wall and is reflected on to the upper surface of the diaphragm. This reflection takes place along a curved line which, except behind as it approaches the vertebral column, is placed a short distance above the lower THORACIC CAVITY 21 border of the thoracic wall. It differs slightly on the two sides of the body. On the left side the diaphragmatic line of reflection proceeds downwards and outwards behind the Cervical dome of pleura Cut edge of parietal pleura Trachea Vena azygos major Bronchus (eparterial) Pulmonary artery Bronchus (hyparterial) Pulmonary veins Inferior vena cava Cut edge of parietal pleura Right innominate vein Left innominate vein Superior vena cava Aorta and pul- monary artery within the pericardium Cut edge of parietal pleura Phrenic nerve Pericardium Diaphragmatic pleura Pl6> IT. — The Right Pleural Sac in a subject hardened by formalin injection opened into by the removal of the costal part of the parietal pleura. The right lung has also been removed so as to display the right mediastinal pleura. Note the line of diaphragmatic reflection of the pleura. ascending part of the sixth costal cartilage, crosses behind the anterior end of the sixth intercostal space and the descending part of the seventh costal cartilage. Still continuing to descend, it passes behind the eighth costal arch at the junction n— 2 a 22 THORAX between its cartilaginous and bony parts. This is a fairly constant relation on both sides of the body, and it should be noted that a vertical line drawn downwards from the nipple (mammillary line) intersects the line of pleural reflection close to the point where it presents this relation to the eighth costal arch. Beyond this point the line of diaphragmatic reflection Crus of diaphragm Crus of diaphragm Ligamentum arcuatum externum Diaphragm Spleen Intestine Ligamentum arcuatum externum Diaphragm Liver Ascending colon Fig. 12. — Dissection of a subject hardened by formalin injection to show the relations of the Pleural Sacs posteriorly ; more especially to the kidneys and last ribs. is carried downwards and outwards across the extremities of the bony portions of the ninth and tenth ribs. As it passes under cover of the tenth rib, or it may be as it proceeds across the tenth intercostal space, the line of pleural reflection reaches its lowest point, and it is important to observe that this point lies in the mid-lateral line (i.e., a vertical line drawn downwards on the side of the chest midway between spine and sternum). From this it curves slightly upwards as it proceeds backwards to the spine. Thus it cuts across the eleventh rib and reaches THORACIC CAVITY 23 the twelfth rib. The relation which it presents to the twelfth rib varies in accordance with the length of that bone. When the rib is not unusually short, the pleura clothes its inner half and the line of reflection falls below this portion of the rib so as to meet the spine midway between the head of the last rib and the transverse process of the first lumbar vertebra. Here therefore the line of diaphragmatic reflection falls below the lower border of the thoracic wall, and this is a point of high practical importance. In operations on the kidney the incision cannot be carried above the level of the transverse process of the first lumbar vertebra and the ligamentum arcuatum externum without the risk of wounding the pleura (Fig. 12). On the right side the line of diaphragmatic pleural reflection differs from that on the left side chiefly in front. Here it descends to a lower level. Thus it proceeds outwards behind the ascending part of the seventh costal cartilage, but it cuts the eighth costal arch, as a rule, at the same point as on the left side, viz., at the junction between its cartilaginous and bony portions. From this backwards to the spine the relations are so similar to those of the left side that a separate description is unnecessary. It is commonly stated that the left pleural sac reaches a lower level than the right. This is by no means the rule. In those cases where the two pleural sacs do not reach the same level at their lowest points it is some- times the right and sometimes the left pleura which oversteps the mark. In the dissection of the intercostal spaces a strong fascia has been observed to pass from the uncovered part of the diaphragm and from the costal cartilages to the surface of the costal pleura along the line of diaphragmatic reflection. It may be compared with Sidsori's fascia, which covers the cervical pleura, but is more strongly marked and more tendinous in character. It may be termed the phrenico-pleural fascia. Mediastinal Space. — The term mediastinal space is applied to the interval which is left between the two pleural sacs. It is within this space that by far the greater part of the dissec- tion of the thorax has to be conducted, and, consequently, it is important that the student should acquire an accurate conception of its extent and connexions. 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, on the surface of the intra-thoracic mediastinal partition. This forms the lateral boundary of the space, whilst in front II— 2 b 24 THORAX it is bounded by the sternum, and behind by the vertebral column. But it is customary to subdivide in an arbitrary manner the mediastinal space into four portions, termed respectively superior, anterior, middle, and posterior, 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 pericardium. Its boundaries are the following : — In front, the manubrium sterni, to the posterior aspect of which are attached the lower ends of the sterno-hyoid and sterno-thyroid muscles ; behind, the upper four dorsal vertebrae with the longus colli muscles ; below, an imaginary and oblique plane extending from the lower border of the manubrium sterni backwards and upwards to the lower border of the fourth dorsal vertebra ; and laterally, the mediastinal pleura as it extends on each side from the back of the sternum to the vertebral column. Figs. 38 and 40 (pp. 68 and 71) are reproduced from tracings of two sections through the superior mediastinum at different levels. Fig. 40 represents a section through its upper part, and Fig. 38 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 — (1) the aortic arch, and the three great vessels which spring from it ; (2) the innominate veins and the upper part of the superior vena cava; (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 structures can be studied, in the meantime, in Figs. 38 and 40 ; afterwards they will be displayed in the course of dissection. Middle Mediastinum. — This is the wide middle part of the space which contains the pericardium, and lies below the superior mediastinum. In addition to the pericardium and its contents, the middle mediastinum contains the phrenic nerves and their arteriae comites. Anterior Mediastinum. — The 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. 12). Posterior Mediastinum. — This is situated between the pericardium and the bodies of the vertebrae. It will be studied later on. THORACIC CAVITY 25 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 nerve and the slender arteria comes nervi phrenici, a branch of the internal mammary artery which accompar 'es_ the phrenic nerve upon the side of the pericardial sac. During this dissection the minute mediastinal and thymic branches of the internal mammary artery will be brought into view. Lungs (pulmones). — The lungs are two soft, spongy organs placed one on either side of the mediastinal space. When Subclavian sulcus Groove for innominate vein ^^ Subclavian sulcus Groove for innominate vein Lower lobe Cardiac notch Fig. 13. — The Trachea, Bronchi, and Lungs of a Child, hardened by formalin injection. the thorax is opened (unless they have been hardened in situ) they collapse to about one-third of their original bulk, and it is difficult for the student to realise their proper dimensions and shape. In the event of the lungs not having been hardened in situ by formalin injection, the dissector of the thorax may {with the consent of the dissector of the head and neck) introduce the nozzle of the bellows into the cervical part of the trachea so as to inflate the lungs with air. A truer conception of these organs will thus be obtained, and a demonstration will be afforded of their high elasticity, and of their connection with the windpipe. When healthy and sound, the lungs lie free within the 26 THORAX 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. Each lung is accurately adapted to the space in which it lies, and, in the natural state, it bears on its surface impressions and elevations which are an exact counterpart of the inequalities of the parts with which its surfaces 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 Vagus nerve Trachea (Esophagus Right subclavian artery Right s innominate vein Innominate artery Left subclavian artery Sulcus subclavius Vagus nerve Left _ common carotid Left .innominate vein Fig. 14. — Cervical Domes of the Pleural Sacs, and parts in relation to them. posterior border. The apex of the lung (apex pulmonis) is blunt and rounded, and rises above the level of the oblique first costal arch to the full height of the cervical dome of the pleura. It therefore protrudes upwards into the root of the neck. The subclavian artery arches outwards on its inner and anterior aspects a short distance below its summit, and a groove (sulcus subclavius) corresponding to the vessel is apparent upon it. At a lower level on the apex pulmonis a shallower and wider groove upon its inner and anterior aspects marks the position of the innominate and subclavian veins. Although these vessels impress the lung, they are separated from it by the cervical pleura. The base of the 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 THORACIC CAVITY 27 ascends higher than the left, the basal concavity of the right lung is deeper than that of the left lung. Laterally, and behind, the base of each lung is limited by a thin sharp margin, which passes downwards in the narrow pleural recess (sinus phrenico-costalis) between the diaphragm and chest wall. This margin extends much lower down behind and at the outer side than in front, but it falls considerably short of the bottom of the phrenico-costal sinus of pleura. Groove for innominate artery Groove for vena azygos major Groove for superior vena cava Bronchial gland Pulmonary artery Bronchus Cardiac surface Pulmonary Surface for oesophagus Ligamentum latum.pulmonis FIG. 15.— The Mediastinal Surface of a Right Lung hardened in situ. 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 the left lobe of the liver, the stomach, the spleen, and in some cases to the splenic flexure of the colon. The outer surface of the lung (facies costalis pulmonis) is very extensive and is full and convex. It is in relation to the parietal pleura, as it clothes the ribs and intercostal muscles, and it bears the impress of the costal arches. The inner or 28 THORAX mediastinal surface (facies mediastinalis pulmonis) presents a smaller area than the outer surface. It is applied to the mediastinal partition, and presents markings which are the exact counterpart of the inequalities upon this septum. Thus it is deeply hollowed out in adaptation to the pericardium upon which it fits. This pericardial concavity comprises the greater part of the mediastinal surface, and, owing to the Sulcus subclavius Groove for aortic arch Fissure in lung Bronchial gland Groove for descending aorta Groove for innominate vein >. /Pulmonary artery \ ^'Bronchus %\^- Pulmonary veins Cardiac depression Surface in apposition with oesophagus Ligamentum latum pulmonis Fig. 16. — Inner or Mediastinal Aspect of a Left Lung hardened in situ. greater projection of the heart to the left side, it is much deeper and more extensive in the left lung than in the right lung. Above and behind the pericardial hollow is the hilum of the lung. This is a wedge-shaped depressed area, within which the vessels, nerves, lymphatics, together with the bronchus, enter and leave the organ. The hilum is surrounded by the reflection of the pleura from the surface of the lung on to the pulmonary root. Behind the hilum and the peri- cardial area there is a narrow strip of the inner surface of the lung which is in relation to the lateral wall of the posterior mediastinum. On the right lu?ig this part of the surface is THORACIC CAVITY 29 depressed and corresponds to the oesophagus ; on the left lung it presents a broad longitudinal groove which is produced by the contact of the lung with the descending thoracic aorta, and also, close to the base, a small triangular flattened area in front of this which is applied to the oesophagus where it pierces the diaphragm. The portion of the inner surface of the lung which lies above the hilum and pericardial hollow is applied to the lateral aspect of the superior mediastinum, and the markings are accordingly different on the two sides. On the left lung a broad deep groove produced by the aortic arch curves over the hilum and becomes continuous with the aortic groove on the posterior mediastinal surface. From this a narrower, deeper, and much more sharply cut groove ascends and turns outwards over the apex pulmonis a short distance from the summit. This is the sulcus subclavius, and it contains the left subclavian artery when the lung is in its place. In front of this a shallow wide groove, also leading up to the front of the apex, corresponds to the left innominate vein. In the right lung the hilum is circumscribed above by a narrow curved groove which lodges the vena azygos major as it turns forward to join the superior vena cava. From the anterior end of the azygos sulcus a wide shallow groove leads upwards to the lower part of the apex pulmonis. This is produced by the vena cava superior and the right innominate vein. Close to the summit of the apex there is also, on its inner aspect, a sulcus for the upper part of the innominate artery. The two borders of the lung offer a 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 sternum and costal cartilages {sinus costo-mediastinalis). It begins abruptly above, immediately below the groove on the apex for the innominate vein, and extends down to the base, where it becomes con- tinuous with the sharp basal border. The posterior border of the 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. Differences between the two Lungs. — There are some points, besides those already mentioned, in which the two lungs differ from each other: — (1) The right lung is slightly larger than the left, in the proportion of 1 1 to 10. (2) The 3o THORAX right lung is shorter 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 pericardium, 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 cardiacd) for the reception of the apex of the heart and the pericardium. (4) The right lung is subdivided into three lobes, and the left lung into two. Lobes of the Lungs. — The left lung is divided into two lobes by a long oblique deep fissure which penetrates its substance to within a short distance of the hilum. This fissure begins above at the posterior border, about two and a half inches below the apex, and about the level of the vertebral end of the third rib, and is continued on the outer surface in a somewhat spiral 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 lung there are two fissures subdividing it into three lobes. One of these fissures is very similar in its posi- tion and relations to the fissure in the left lung. It is, however, more vertical in its direction, and ends below some- what farther outwards. It separates the lower lobe from the upper and middle lobes. The second cleft begins in the main fissure at the posterior border of the lung, and proceeds horizontally forwards on the outer surface to end at the anterior border of the lung at the level of the fourth costal cartilage. The middle or intermediate lobe is 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 mediastinal surface. These structures are held together by an investment of pleura, THORACIC CAVITY 31 and constitute a pedicle which attaches the lung to the mediastinal wall of the pleural cavity. 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. In front there are — (1) a delicate plexus of nerves, the anterior pulmonary plexus; and (2) the phrenic nerve with the arteria comes nervi phrenici. Behind, the pneumogastric 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 side — (1) The vena azygos major, as it curves forwards over the right bronchus to join the superior vena cava, is in relation to the upper border of the pulmonary root; (2) the superior 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. Dissection.— Now proceed to dissect out the constituent parts of the root of the lung. Constituent parts of the Pulmonary Root. — The most important structures which enter into the formation of the pulmonary root are — (1) the two pulmonary veins; (2) the pulmonary artery; (3) the bronchus. But, in addition to these, there are one or more small bronchial arteries and veins, the pulmonary nerves, the puh?wnary ly??iphatic vessels, and some bronchial glands. These are bound together by some loose areolar tissue, and the whole pedicle so constituted is invested by pleura. The pulmonary nerves are derived from the anterior and posterior 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, and the plexus of the left side likewise receives a few filaments from the super- 32 THORAX ficial cardiac plexus. It is only under the most favourable circumstances that a good view of these nerves can be obtained. Dissection. — The posterior pulmonary plexus is easily dissected. To get at it, the lung must be thrown well forwards over the pericardium, and the pleura stripped from the posterior surface of the pulmonary root. The pneumogastric nerve should then be secured and followed downwards. On the left side it will be 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 trunk of the pneumogastric nerve breaking up into a flattened network immediately under cover of the pleura upon the posterior aspect of the root of the lung. Several minute twigs from the upper thoracic ganglia of the sym- pathetic enter this plexus. The posterior pulmonary plexuses of opposite sides are connected by some strong branches, which cross the mesial plane in front of and behind the oesophagus. From both the anterior and posterior pulmonary plexuses fine twigs are prolonged into the lung along the divisions of the bronchi. The posterior branches, however, are much larger than the anterior. The bronchial arteries (arterise bronchiales), one to three 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. Part of the blood conveyed to the lungs by the bronchial arteries is returned by the pulmonary veins ; the remainder is returned by special bronchial veins, which open on the right side into the vena azygos major, and on the left side into the vena azygos minor superior. Dissection. — The 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 lung studied. This dissection should be made, not only in front, but also behind, so that the parts may be thoroughly isolated and rendered distinct. Hardened and blackened bronchial glands sometimes make the dissection a difficult one. These must be removed. The bronchus lies in the posterior part of the root of the lung behind both the pulmonary artery and the higher of the two pulmonary veins. The pulmonary artery holds an THORACIC CAVITY 33 intermediate position, whilst the higher of the two pulmonary veins is placed in front of the artery. 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 the lowest level — the lower vein being situated in the very lowest part of the hilum of the lung. On the right 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 EPARTERIAL BRONCHUS Reflection pleura Pulmonary veins Fig. 17. Ligamentum latum pulmonis -The two Pulmonary Roots transversely divided close to the hilum of each kins:. is due to the fact that on the right side a branch which is topo- graphically not represented on the left side arises from the bronchus a short distance from its origin, and proceeds almost horizontally outwards to the upper lobe of the lung. This division lies above the level of the pulmonary artery, and in consequence receives the name of the eparterlal 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 corresponding pulmonary artery, and are termed hyp- arterial bronchi. 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 vol. 11 — 3 34 THORAX 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 mammary artery in a direction from 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 high as the right cupola. The differences in relationship are the following : — (1) As they traverse the superior media- stinum the left phrenic nerve crosses the vagus nerve and the aortic arch, whilst the right phrenic nerve lies in relation to the right side of the right innominate vein and the superior vena cava; (2) one or more of the terminal branches of the right nerve pass through the opening in the diaphragm 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 fore-part of the diaphragm. It takes origin high up in the thorax, 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 — (1) the cardiac branch from THORACIC CAVITY 35 the superior cervical ganglion of the sympathetic of the left side; (2) the inferior cervical cardiac branch of the left pneumogastric 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 ganglion of Wrisberg may be discovered. The manner in which this plexus is distri- buted 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 stemo-pericardiac ligament — binds it to the ensi- form cartilage, whilst the other — the superior sterno-pericardiac ligament — connects it with the manubrium sterni, and comes into relation 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. Pericardium. — The pericardium is a fibro-serous sac which loosely envelops the heart. It is placed in the middle sub- division 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. Towards 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 cor- responding to the apex of the heart projects beyond the area of the liver and comes to lie over the stomach. The upper 3^ THORAX narrow part of the pericardium will be noticed to close upon certain of the great vessels that issue from the base of the heart. Upo?i each side the pericardium is adapted to the concave part of the mediastinal surface of the lung. It is clothed by the mediastinal pleura, and has in relation to it Common carotid artery Subclavian Mouth of superior vena cava Right pulmonary veins Common carotid artery Internal jugular vein Recurrent laryngeal nerve Subclavian artery Subclavian vein Left innominate vein Vagus nerve Phrenic nerve Left pulmonary artery Left bronchus Right pulmonary artery Left pulmonary veins Interior of pericardium Phrenic nerve Fig. i 8. — The Pericardium and Great Vessels of the Heart. The thoracic organs were hardened in situ by formalin injection. The pericardium having been opened by the removal of its anterior wall, the great vessels were divided and the heart removed. the phrenic nerve and the arteria comes nervi phrenici. In front, very important relations have to be studied. It lies behind the sternum and costal cartilages, 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 THORACIC CAVITY 37 the left pleura retreating somewhat 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 x of this area, as we have 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. Fibrous Pericardium. — 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 outer 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 peri- cardium. The entire length of the pulmonary artery and of the ascending aorta are enclosed within the fibrous sac of the pericardium. Portions also of the superior vena cava and the four pulmonary veins are contained within the fibrous pericardium. Dissection. — The pericardium may be opened by means of a crucial incision, viz. — (1) a longitudinal incision along the middle line of the body from the point where it blends with the sheath of the aorta down- wards 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. Serous Layer of the Pericardium. — The internal serous layer is now exposed. This layer, which forms a completely closed sac, lines the entire inner surface of the fibrous peri- cardium, and is reflected from this, upon the vessels which pierce the fibrous layer, on to the surface of the heart. It gives a smooth, polished appearance to the heart and to the interior of the pericardial sac. The lining part of the serous layer is termed the parietal portion ; the investing portion which covers the heart is called the visceral part or the epi- 1 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 it is distended with fluid. 38 THORAX cardium. 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 com- pletely surrounded by a single tubular sheath which is common to both. 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 passing the forefinger behind them. The term sinus trans- versus 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. The lower half of this vein is enclosed 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 peri- cardium, 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 up- wards, a deep, blind recess of the serous pericardium will be seen, passing upwards behind it, between the openings of the pulmonary veins of opposite sides into the back of the left auricle. This recess lies between the posterior or auricular surface of the heart and the posterior wall of the fibrous peri- cardium, and is called the oblique sinus. 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 peri- cardium. This is the "vestigial fold of Mars hall.'''' It contains between its two layers a minute fibrous band (ligamentum cavae sinistra^), the remnant of the left superior vena cava of the embryo. Remains of the Thymus. — The thymus gland, which is a large and conspicuous object in the superior and middle portions of the mediastinum of the foetus and young child, is only represented in the adult by two slender elongated THORACIC CAVITY 39 bodies placed in the fore part of the superior mediastinum in front of the aortic arch and the left innominate vein. A few thymic branches 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. 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 the clavicle by the union of the subclavian and internal jugular veins. Behind 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. The right innominate vein (vena anonym a dextra) is short. It is not more than one inch in length, and it has a nearly vertical course from above downwards. It is covered on its outer and anterior aspects by the right mediastinal pleura, and the phrenic nerve is applied to its outer side. The upper part of the innominate artery lies to its inner or left side. The left innominate vein (vena anonym a 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 and also in front of the left vagus and left phrenic nerves. In' the greater part of its extent it is covered by the left mediastinal pleura. 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 inter- costal 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 intercostal veifi is formed 40 THORAX by the union of the veins from the second and third inter- costal spaces. It crosses the arch of the aorta, and is of interest in so far that its upper part represents the upper pervious portion of the occluded left superior vena cava of the embryo. Vena Cava Superior. — This great vein is formed behind the first costo-sternal junction of the right side by the union of the two innominate veins. From this it proceeds down- wards, and it opens into the upper and back part of the right auricle of the heart at the level of the upper border of the third 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 lies in the superior mediastinum (Fig. 38, p. 68). On the right side it is clothed by the mediastinal pleura, and has the phrenic nerve in con- tact with it j on the left side it is in relation to the innominate artery. In the lower half 'of its course it is enclosed within the fibrous pericardium, and is placed in the middle media- stinum. 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 right bronchus, the right pulmonary artery, and the upper right pulmonary vein (Fig. 39, p. 69). The ve?ia azygos ??iajor 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 peri- cardiac and mediastinal veins also pour their blood into it. Inferior Vena Cava. — This is a larger vessel than the superior vein of the same name. It enters the thorax 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 pericardium, and opens into the lower and back part of the right auricle of the heart. Heart. — The heart is a hollow organ with muscular walls and somewhat conical in shape. It is placed obliquely within the middle mediastinum, so that its basal portion (basis cordis) is directed backwards, and slightly to the right, while its pointed apex looks downwards, forwards, and to the left. But it is also placed unsymmetrically within the chest cavity. In other words, it projects more to the left THORACIC CAVITY 4i 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. 19). General Relations of the Heart. — The base or posterior surface of the heart 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, 7th, and 8th) lie behind it. The apex approaches the anterior wall of the thorax, 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 inferior surface (facies diaphragm atica), which is flattened, and f looks downwards, rests upon the diaphragm — the floor of the pericardium alone inter- vening. Immediately below the cardiac area of the dia- phragm is the upper surface of the liver, and in front and to the- left a small piece of the stomach. The antero- superior surface (facies ster- nalis) of the heart looks upwards as well as forwards, and lies behind the greater part of the gladiolus of the sternum and the third, fourth, fifth, and sixth cartilages of both sides. Owing to the greater projection of the organ to the left, only a small portion of the inner ends of these cartilages lies in front of the heart on the right side. A much larger area of the antero-superior cardiac surface lies behind the left costal carti- lages. Indeed, behind the fourth and fifth costal cartilages the left margin of the heart approaches closely to the junction be- tween the osseous and cartilaginous portions of these costal arches. The pleural sacs and the anterior thin margins of the lungs intervene between the heart enclosed within the peri- cardium 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 Fig. 19. — The vertical line drawn through the heart represents the mesial plane. (From Braune. ) 42 THORAX 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 (Fig. 8, p. 18). This area may be mapped out on the chest wall by drawing a Fig. 20. — The relations of the Heart and of its Orifices to the Anterior Thoracic Wall. (Young and Robinson.) Af. Mitral orifice. P. Pulmonary orifice. RA. Right auricle. RV. Right ventricle. SVc. Superior vena cava. T. Tricuspid orifice. 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 its extremities, outwards so as to meet at a point over the apex beat of the heart. On either side, the heart I to VII. Costal cartilages A. Aortic orifice. Ao. Aorta. C. Clavicle. LA. Left auricle. LV. Left ventricle. THORACIC CAVITY 43 and pericardium is supported by the mediastinal pleura and the inner surface of the lung. 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. Right innominate vein Innominate artery Superior vena cava Serous pericardium Right appendix Auriculo- ventricular furrow Marginal branch of right coronar artery Right ventricle Left common carotid Left subclavian Left innominate vein Aortic arch Ligamentum arteriosum Left pulmonary artery Pulmonary artery Left appendix Infundibulum Anterior interven- tricular furrow with corresponding branch of left coro- nary artery Left ventricle Apex of heart Fig. 2i.— Anterior or Sternal Aspect of the Heart. External Configuration of the Heart. — In studying the form and appearance of the heart, the dissector will find it advantageous to refer to a specimen which has been hardened in situ by formalin injection. The interior of the heart is divided by an internal, obliquely placed partition into a right and a left cavity. Further, each of these is still further subdivided into an upper auricular and a lower ve?iiricular cha?nber, which com- 44 THORAX municate freely with each other through a wide auricula- ventricular ope?ii?ig. 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 chambers. Thus encircling the heart nearer the base than the apex, Right auriculo ventricular opening Superior vena cava Reflection of serous pericardium Right appendix Interauricular furrow Left auricle appendix Crista terminally Fossa ovalis Eustachian valve Inferior vena cava eft auriculo- ventricular opening Coronary sinus Fig. 22. — The Anterior Aspect ot the Auricular Part of the Heart. The auricles have been removed from the ventricles. The ventricular portion of the same heart is depicted in Fig. 25. The specimen was hardened in situ. and in a direction transverse to its long axis, is a deep furrow which is continuous all the way round, except in front, where it is interrupted by the root of the pulmonary artery. This is the auriculo-ventricular groove (sulcus coronarius). It intervenes between the auricles which lie behind it and the ventricles which are placed in front and, to some extent, below it. In the undissected heart, with the epicardium in position, the depth of this furrow is greatly obscured, from THORACIC CAVITY 45 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 and flaccid, and, in the heart which has not been hardened by formalin, 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 upwards and forwards two processes or cornua, termed the auricular appendices. A deep concavity 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. These great vessels are, as it were, clasped between the auricular appendices. On referring to the hardened organ it will be seen that the whole of the posterior surface or base of the heart is formed by the auricles. The surface thus constituted is somewhat quad- rangular in outline. Above, it is in intimate relation to the two pulmonary arteries as they run to the right and to the left to enter the pulmonary roots ; be- low, it is limited by that part of the auriculo-ventricular groove which is occupied by the coronary sinus. A groove which runs downwards on the right auricle from the front of the opening of the superior vena cava to the right of the opening of the inferior vena cava may be taken as bounding the posterior auricular surface on the right. This furrow is termed the sulcus termi?ialis, and it has an interesting embryological significance. The entrance of the two left pulmonary veins into the left auricle form the left limit of the posterior auricular surface of the heart. By far the greater part of this posterior surface is formed by the left auricle, and the exact proportions which the two auricular chambers contribute to this surface are indicated on the hardened organ by a faint groove termed the interauricular Fig. 23. — Transverse section through the Auricular Part of the Heart of an Ox. R.A. Right auricle. L.A. Left auricle. P. Pulmonary artery. A. Aorta. 46 THORAX furrow, which pursues a vertical course immediately to the left of the openings of the two venae cavae. This furrow indicates the posterior attachment of the interauricular septum. Each auricle is composed of a roomy capacious posterior Left common carotid Aorta Ligamentum arteriosum Left pulmonary artery Reflection of serous pericardium Left pulmonary veins Left auricle Oblique vein Margo obtusus Auriculo- ventricular groove'""|| Coronary sinus. Inferior surface ventricular part of heart Innominate artery Right innominate vein Vena azygos major Superior vena cava Right pulmonary artery Right pulmonary Sulcus terminalis Right pulmonary vein Interauricular sulcus Right auricle Inferior vena cava Fig. 24. — Posterior or Basal Aspect of a Heart hardened in situ by formalin injection. part into which the veins open and into which the blood flows, termed the atrium, and a more or less pointed pro- jection which springs from the upper and fore part of the atrium. This prolongation is the auricular appendix. The superior vena cava will be seen to open into the upper part of the atrium of the right auricle ; the inferior vena cava opens into the lower part of the same atrium. THORACIC CAVITY 47 Between these two openings, and immediately to the left of the interauricular furrow, the two right pulmonary veins pierce the posterior wall of the atrium of the left auricle ; the left pulmonary veins open into the same atrium at the left limit of the posterior surface of the heart. The Ventricular Part of the heart is firm to the touch and possesses thick fleshy walls. It is conical in form. Its Left pulmonary artery Pulmonary artery Anterior inter- ventricular branch Left posterior sinus of Valsal Left coronary artery Aortic cusp of mitral valve Posterior cusp-~J Ligamentum arteriosum Pulmonary artery -Aorta —Right pulmonary artery Infundibulum Right coronary artery Right posterior sinus of Valsalva \^\lu\ Infundibular cusp JliK of tricuspid valve Marginal cusp Septal cusp Marginal branch Inferior interventricular branch Fig. 25. — The Base of the Ventricular Part of the Heart from which the Auricles have been removed. The detached auricles are depicted in Fig. 22. The specimen was hardened in situ. apex corresponds to the apex of the heart ; whilst its base is connected behind with the two atria of the auricular part of the heart, and gives origin above and in front of these, and in the interval between the auricular appendices, to the two great arteries which conduct the blood from the ventri- cular chambers, viz., the pulmonary artery in front, and the aorta behind. In addition to the base and apex, the ventricular part 48 THORAX of the heart presents two borders and two surfaces. One border is long and sharp, and runs from right to Jeft, from the base to the apex. It occupies that part of the basal portion of the pericardium which lies in the narrow interval between the diaphragm and the anterior wall of the chest ; it is called the a?iterior border or the margo acutus. The left border or margo obtusus is short, thick, and rounded. The antero-superior 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 forwards and downwards towards the sharp margin, which it reaches a little to the right of the apex. This groove is the anterior interventricular furrow (sulcus longitudinalis anterior), and it is placed much nearer to the left margin than to the sharp anterior margin of the heart (Fig. 21, p. 43). The i?iferior surface (facies diaphragmatica) is flattened and traversed by a similar groove (Fig. 24, p. 46), the inferior interventricular furrow (sulcus longi- tudinalis posterior). This joins the anterior groove below, round the anterior sharp margin of the heart. These grooves are occupied by vessels and lodge a little fat. They indicate on the surface the attachments of the inter- ventricular septum, and therefore the extent of the walls of the two cavities. Roughly speaking, two-thirds of the antero-superior surface, the margo acutus, and rather more than one-third of the inferior surface, belong to the right ventricle ; whilst one-third of the antero-superior surface, the margo obtusus, the apex of the heart, and rather less than two-thirds of the inferior surface, belong to the left ventricle. On the antero-superior 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 the infundibulum or conus arteriosus (Fig. 21, p. 43). 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 ronoving 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. THORACIC CAVITY 49 Coronary Arteries (Fig. 25, p. 47). — These 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 sinus of Valsalva,1 and proceeds outwards behind the pulmonary artery. It winds round the left side of the left auriculo-ventricular opening (ramus circumflexus), and ends on the inferior aspect of the heart. 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 side of the right auriculo-ventricular opening in the auriculo- ventricular groove to reach the inferior aspect of the heart, where it ends near the termination of the artery of the left side. An arterial circle is thus formed, which embraces the heart in the auriculo-ventricular groove. The right coronary artery gives off two large branches. Of these, one passes towards the apex upon the sharp margin of the heart, whilst the second and larger proceeds towards the apex in the inferior interventricular groove (ramus descendens). It also supplies numerous smaller twigs to the right ventricle and right auricle. Cardiac Veins (vena? cordis). — Take hold of the heart by the apex and pull it upwards, so as to bring into view its inferior surface. In the groove between the left ventricle and left auricle — the coronary sinus (sinus coronarius) — a short wide venous channel will be seen (Fig. 24, p. 46). Open it with the scissors along its whole length. By one extremity 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 inferior aspect of the ventricles also open into this 1 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. VOL, ll 1 5° THORAX 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), occupies the inferior inter- ventricular groove. The right or small cardiac vein (vena cordis parva) 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 veifi of Marshall (vena obliqua atrii sinistra) from the back of the left auricle opens into the sinus close to the point where it joins Oblique vein of .Marshall Fig. 26. — The Coronary System of Veins on the Surface of the Heart. (Diagram. ) 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 pervious part of the obliterated left superior vena cava of the embryo. The great cardiac vein (vena cordis magna) begins upon the antero-superior aspect of the heart at the apex. It ascends in the anterior interventricular groove to the auriculo-ventricular furrow, in which it turns round the left margin of the heart to join 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. THORACIC CAVITY 51 The anterior cardiac veins will be seen on the front surface 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 vena Thebesii or vena i?iini??icz cordis — 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 following table expresses the arrangement in a brief form : f Great cardiac vein. I opening into Posterior cardiac veins. J coronary Upon the surface] Right cardiac vein. I sinus of the heart. Oblique vein. I . . , . . f Opening into Anterior cardiac veins. j right auricle# In the substance / Ven^ Thebesii. / Opening into of the heart. ^ I ngnt auricle. It is only in a heart which has been specially injected that all these veins can be seen. The general arrangement, however, can usually be studied in the course of an ordinary dissection. In certain cases, where the veins are empty and the fat on the surface of the heart scanty, they may be inflated with air by introducing a blow -pipe into some of the larger members of the series. Cardiac Nerves. — For the most part the fine nerves which form the superficial cardiac plexus are prolonged downwards upon the pulmonary artery, and being joined by a considerable reinforcement from the deep cardiac plexus, they form the right coronary plexus which is distributed in the course of the right coronary artery. The left coronary plexus which accompanies 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 connection with them. Dissection. — The chambers 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 body. Two cuts are required — (1) 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 II — 4 a 52 THORAX Right Auricle (atrium dextrum). Superior vena cava Auricular appendix- 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. The internal surface of the cavity presents a polished glossy ap- pearance, due to its endocardial lining. In the auricular appendix the wall is raised into a series of closely applied parallel mus- cular ridges, called the musculi pectinati, from their resemblance to the teeth of a comb. These ridges are also present on the right wall of the auricle, and when followed back- wards they are seen to end on a smooth verti- cal ridge, called the crista terminalis (Figs. 27 and 28). It re- presents in the interior of the auricle the groove on the exterior already described under the name of the sulcus terminalis. In the in- tervals between the musculi pectinati the wall of the auricle is very thin. To the left of the crista terminalis the walls of the auricle are smooth from the absence of musculi pectinati, and it is into this part that the veins open. The blood enters the atrium of the auricle by the following openings: — (1) the opening of the superior vena cava; (2) Atrium Musculi pectinati Crista terminalis Cut lferior vena Fig. 27. — A portion of the Right Auricle from same specimen as that depicted in Fig. 22. The auricular part of the heart has been divided in the line of the two caval veins, the anterior wall of the right auricle removed, and then the specimen turned slightly over to the right so as to give a view of the interior of the appendix, etc. The specimen was hardened in situ. THORACIC CAVITY 53 the opening of the inferior vena cava ; (3) the opening of the coronary sinus; (4) the orifices of three or four anterior cardiac veins from the surface of the right ventricle ; (5) the foramina Thebesii. The blood flows out of the cavity, into the right ventricle, through the large auriculo-ventricular opening. Vena azygos ^^pl major Pericardium Right bronchus Superior vena cava Musculi pectinati Crista terminalis Diaphragm Atrium of right auricle Inferior vena cava Hepatic vein Fig. 28. — Sagittal section through the Right Auricle of the Heart and the Root of the Right Lung. The orifice of the superior vena cava is situated at the upper and back part of the auricle. It should be noted that this aperture is devoid of a valve, and that the upper end of the crista terminalis is continuous with the sharply defined anterior border of the opening. The inferior vena cava opens into the lower part of the cavity, and has the rudi- mentary Eustachian valve in relation to its orifice. The dis- 54 THORAX (Fig- 22. penor vena cava dix of superior sector 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 auriculo-ventricular orifice is the large, oval opening situated in the anterior wall of the atrium of the auricle 44). Through this aperture three fingers can be readily passed in to the ventricle. If the student now looks between this opening and the ori- fice of the inferior vena cava, he will discover the mouth of the coronary sinus, imperfectlyguarded by a fold of endo- cardium, which re- ceives the name of the coronary valve or valve of Thebesius. An attentive ex- amination of the inner surface of the auricular wall will further reveal several minute, round, irregularly scattered openings called the j vram 1 n \a Fig. 29.— Interior of Right Auricle as seen by the . , .. onrnp nf removal of the anterior wall, or that wall op- J- muesli, ounic ui posed to the base of the Ventricles. This these are simply is a part of the same specimen that is depicted small ca^cal pits in in Fig- 22" the substance of the heart, whilst others are the mouths of minute veins — the venaz Thebesii. Examine, in the next place, the partition which separates the two auricles from each other {septum atriorum). 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 the fossa ovalis. Its floor is exceedingly thin, and it marks the position of the Crista terminalis Tubercle of Lower Annulus ovalis Fossa ovalis Left auriculo- ventricular orifice Opening of coronary sinus Thebesian valve ^—Eustachian valve Cut edge of auricular wall vena cava THORACIC CAVITY 55 foramen ovale of the foetal heart. The ridge which encircles it is deficient below. It is, therefore, crescentic in form, and is called the annulus ova/is (limbus fossse 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 Eustachian valve. The interauricular septum in the interval between the fossa ovalis and the mouth of the superior vena cava exhibits a slight promi- nence. This is termed the tubercle of Lower. Dissection. — The right ventricle may now be opened by the following incisions:— ( i) An incision through the wall of the ventricle extending from a short distance below the auriculo - ventricular groove along the sharp margin of the heart to the lower end of the anterior interventricular furrow. (2) A transverse incision, through the anterior wall of the ventricle, from the upper end of the first incision to the upper end of the anterior interventricular furrow. This cut should be made parallel to the auriculo-ventricular groove, and about half an inch below it. Both in- cisions 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 left. Wash away the blood and clots. Right Ventricle (ventriculus dexter). — The cavity of the right ventricle, now laid open and exposed to view, is of a somewhat triangular form, the base being directed backwards, and the apex forwards and downwards towards the apex of the heart. It does not reach the apex of the heart, however, but corresponds to the junction of the anterior and inferior interventricular furrows around the 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 wall bulging into it (Fig. 30). The wall is thickest at its upper part, and thins slightly towards the apex. With the exception of the conus arteriosus or infundi- bulum, from the summit of which the pulmonary artery arises, and the interior of which is smooth and even, the inner surface of the walls of the right ventricle is lendered extremely irregular by the projection of a lace-work of fleshy II — 1 A 56 THORAX ridges called colu??ince. carnece. (trabecular carneae). It is customary to describe these as presenting three different forms — (a) simple elongated ridges ; (b) fleshy slips or trabe- cular free throughout the greater part of their extent, but fixed to the wall by their two extremities ; (c) conical fleshy projections of considerable size, which project into the cavity, and are attached by their bases only. These last are called musculi papillares, and are arranged so as to form an anterior and a posterior set. The free end of each of these papillary muscles gives origin to several delicate thread-like tendon s — the chordaz tendinece — and by these they are brought into connection with the segments of the auriculo- ventricular valve. A trans- verse fleshy band will be noticed to spring from the base of the anterior papillary muscle, and stretch across the ventricular cavity to the septum, to which it is at- tached. 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- distension of the cavity. There are two openings in the right ventricle — (i) the aiiriculo-ventricular, which gives admission to the stream of blood; (2) the pulmonary, through which the blood passes into the pulmonary artery. Both these openings are situated at the base of the ventricle. The large oval auriculo-ventri- cular orifice lies to the right and behind, whilst the pulmonary aperture is placed to the left, above and in front of the other, and at the summit of the 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 valve which guards the mouth of the pulmonary artery is composed of three semilunar segments, and is called Fig. 30. — -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. Inferior interventricular furrow with middle cardiac vein and in- ferior hranch of right coronary artery. 7. Anterior interventricular furrow, with great cardiac vein and anterior branch of left coronary artery. THORACIC CAVITY 57 the semilunar or the sigmoid 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. Right Auriculo- Ventricular or Tricuspid Valve (valvula tricuspidalis). — This valve is composed of three triangular, Innominate artery Left subclavian artery Left common carotid artery Aortic arch - Serous pericardium "Ascending aorta Pulmonary artery -Right auricular appendix Sinus of Valsalva Pulmonary valve Superior vena cava Infundibulum Infundibular segment Septal segment Anterior papillary muscle Moderator band Inferior vena cava Marginal segment FlG. 31. — The Interior of the Right Ventricle. pointed, membranous segments, termed cusps, which project forwards into the cavity. These are united by their bases so as to form an annular membrane, and, through the inter- mediation of this, they are fixed around the auriculo-ventri- cular opening. In the intervals between these larger segments three smaller cusps may frequently be detected. Bach 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- 53 THORAX 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 ventri- cular surface and margin of each segment, as well as into the circumference of the auriculo-ventricular opening, are several of the chordae tendineae 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 eptal musculi papillares nfundibular cusp -Septal cusp Marginal cusp Anterior papillary muscle Posterior papillary muscle Fig. 32. — Diagram of the arrangement of the Cusps and Chordae Tendineae of the Tricuspid Valve. 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 as to intervene between the auriculo-ventricular opening and the pulmonary orifice. It lies in front and to the left of the opening. This is the infundibular cusp. Another is placed posteriorly to the auriculo-ventricular opening, and lies closely applied to the septum. This is the septal cusp. The third is situated to the right, near the anterior sharp margin of the heart, and may be termed the marginal cusp. The chordae tendineae of the anterior papillary muscle are distributed in the interval between the infundibular and marginal flaps ; those from the posterior papillary muscle go to the interval between THORACIC CAVITY 59 Pulmonary artery the marginal and septal flaps ; whilst to the interval between the infundibular and septal flaps pass a number of short chordae tendineas, 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. 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, as it ascends, it takes a spiral turn round the ascending aorta, so that before it terminates it is placed upon the left side of that vessel (Fig. 21, p. 43). In relation to each side of the pulmonary artery the dissector will notice the corresponding coronary artery and auricular appendix. The vessel is completely en- closed within the fibrous peri- cardium, the serous layer of which forms a single tubular sheath around it and the as- cending aorta. The right pulmonary artery is somewhat longer and larger than the left. It passes trans- versely outwards behind the ascending aorta and superior vena cava to reach the root of the right lung, where it has already been dissected (Fig. 24, p. 46). The left pulmonary artery runs outwards in front of the descending aorta and left bronchus to gain the root of the left lung (Fig. 39, p. 69). The blood is thus conducted from the right ventricle of the heart to the two lungs. Ligamentum Arteriosum or Obliterated Ductus Arteri- osus.— This 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 liga- mentum 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 left pulmonary Fig. 33. — Heart of a seven months Foetus. ( From Gegenbaur. ) 60 THORAX arteries are 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 pneumogastric nerve hooks round it at its attachment to the aorta. Dissection. — The pulmonary artery may now be slit open, so as to expose the valve which guards its orifice. This incision must be made carefully, and the knife carried upwards through the wall of the vessel in the interval between two of the three segments which enter into its formation. Pulmonary Valve. — Each semilunar segment will be ob- served 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. The segments consist of a double layer of endocardium, strengthened by intermediate fibrous tissue ; and if the free margin of one be taken between the finger and 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 particular description, therefore, until the aortic valve is under consideration. Opposite each segment, the wall of the artery shows a slight dilatation or bulging, called the sinus of Valsalva. The three segments of the pulmonary valve are so placed that two are in front and one behind the opening (Fig. 31). Pulmonary Veins (venae pulmonales). — The blood is con- veyed back to the 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 left veins pass in front of the descending aorta (Fig. 39). 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 body, and its apex tilted forwards. 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. THORACIC CAVITY 61 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 pecti?iati are confined entirely to the appendix. Everywhere else the inner surface of the wall of the left auricle is smooth. On the posterior wall the four openings of the pulmonary veins A. Aorta. P. A. The right and left pul- monary arteries. P.V. Right and left pulmon- ary veins. L.A.A. Left auricular appendix. M.V. Mitral orifice. L.V. Left ventricle. R.V. Right ventricle. R.A. Right auricle. L.A. Left auricle. S.V.C. Superior vena cava. Fig. 34. — Dissection of a Heart hardened in situ to show the Left Auricle and the Left Ventricle. The ascending aorta, the anterior cusp of the mitral valve, the trunk of the pulmonary artery, and the inter- auricular septum and portion of the interventricular septum have been removed. (Stiles.) 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. When the interior of the left auricle of a formalin-hardened heart is examined from the front a projecting crescentic ridge is observed to pass downwards on the left wall in front of the orifices of the two left pulmonary veins so as to hide them from view. In the fore-part of the auricle is the oval auriculo-ventricular opening. It only admits the passage of two fingers into the 62 THORAX ventricle, and is therefore smaller than the corresponding orifice of the right side. The position of the fcetal foramen ovale can also be distinguished upon this side of the septum atriorum, but it is not so well marked as it is in the right auricle. It presents the appearance of a faint depression bounded below by a slightly marked crescentic border. Foramina Thebesii and the small orifices of venae minimi cordis are also present on the walls of the left auricle. 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, so that the forefinger rests upon the upper part of the inferior interventricular furrow, and the thumb upon the upper part of the anterior interventricular furrow. The wall of the ventricle should then be transfixed by a long Right ventricle Left ventricle — \ Septum ventriculorum Fig. 35. — Section through the Ventricular Portion of the Heart near the apex. It shows the greater depth of the left ventricle. knife. 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 inferior 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. Left Ventricle (ventriculus sinister). — The cavity of the left ventricle is longer 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. 35). The walls of the left ventricle are very much thicker than those of the right ventricle. When the injection and blood have been washed away from the interior of the left ventricle with hot water, the THORACIC CAVITY 63 columnce carnece will be observed to form dense muscular reticulations on the inner surface of its walls. This network is especially complicated at the apex and on the inferior wall of the cavity. The surface of the septum and the upper part of the anterior wall are, comparatively speaking, smooth. The muscitli fiapillares, with their attached chordae tendineae, are collected into two strongly marked groups. They are much larger than the papillary muscles of the right ventricle, but do not project so distinctly into the cavity. The left ventricle has two openings — (1) the auriculo- ventricular opening, through which the blood enters from Aortic or anterior cusp Posterior cusp Anterior papillary muscle Posterior papillary muscle Fig. 36. — Diagram of the arrangement of the Cusps and Chordae Tendinea? of the Mitral Valve. 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 auriculo-ventricular 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 or bicuspid valve, and the aortic opening by the aortic valve. Mitral Valve (valvula bicuspidalis). — The mitral valve prevents regurgitation of the blood into the left auricle during the contraction or systole of the ventricles. 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 64 THORAX thicker. The fibrous tissue between the two layers of endocardium is more abundant, but it is arranged in pre- cisely the same manner. The chordae tendineae from each papillary muscle 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 or aortic cusp is the larger of the two, and lies in front and to the right of the auriculo-ventricular opening, being so placed as to inter- vene between the latter and the aortic aperture. The posterior or marginal 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. 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 inferior attachments of which are indicated on the surface of the heart by the anterior and inferior interventricular furrows. Now that both surfaces of the septum are exposed, it will be seen to be thickest near the apex of the heart, and to thin slightly in an upward direction. In its basal 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 the pars membranacea septi, and it is of interest from the fact 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. Action of the Heart. — The above details will be dry and meaningless unless they are looked at in connexion with the action of the heart during life. It is impossible to understand the construction of the heart unless we THORACIC CAVITY 65 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 simul- taneously. 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 versa. 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 contraction, (c) the ventricular contraction — follow each other consecutively and without intermission, the one after the other ; and they are collectively termed "a cardiac revolution." Let us study what is going on inside the heart during each of these three stages. During the period of cardiac rest 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 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, distension of the auricles. The second stage of the cardiac revolution now takes place — viz. , the auriadar 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 ? For the simple reason that the contraction begins at the venous orifices and auricular appendices, and travels towards the auriculo-ventricular openings. The ventricles are now full, and the third stage of the cardiac revolution takes place — viz., the ventrictdar 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 position, and prevented from being forced upwards into the auricle during the ventricular contraction, by the musculi papillares and the chorda? tendinese. As the ventricular wall in its contraction to a certain extent advances towards the auriculo-ventricular opening, the musculi papillares, 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 elastic 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 Heart. — The outline of the heart may be delineated on the anterior surface of the chest as follows: — (1) draw a curved line convex outwards from the sternal end of the third right costal cartilage to the sternal end of the sixth right costal cartilage ; this line should attain its point of maximum convexity as it crosses the fourth intercostal space, and this point should be \\ inches from the middle line; the line thus drawn will correspond to the right outline of the right auricle ; (2) connect by a straight line the sternal end of the sixth right costal cartilage with VOL. II — 5 66 THORAX the point on the chest wall which corresponds to the apex of the heart ; this gives the lower limit of the heart, and for the most part it corresponds with the margo acutus ; (3) from the apex of the heart draw a third line slightly curved outwards to the sternal end of the second left costal cartilage ; this line follows on the surface the outline of the margo obtusus and the appendix of the left auricle. FlG. 37. — The relations of the Heart and of its Orifices to the Anterior Thoracic Wall. (Young and Robinson. ) I to VII. Costal cartilages. A. Aortic orifice. Ao. Aorta. C. Clavicle. LA. Left auricle. LV. Left ventricle. M. Mitral orifice. P. Pulmonary orifice. RA. Right auricle. RV. Right ventricle. SVc. Superior vena cava. T. Triscuspid orifice. An oblique line extending across the front of the sternum from the middle line at the level of the third costal cartilage to the sternal end of the sixth right costal cartilage indicates on the surface the position of the auriculo -ventricular groove. The pulmonary aperture is the most superficial of the cardiac orifices, 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 and THORACIC CAVITY 67 the second left costo-sternal articulation. 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 right aurictdo- ventricular orifice lies behind the sternum, opposite the extremity of the fourth intercostal space of the right side. The left auriculo-ventriadar 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. Aorta. — The aorta is the great arterial trunk which con- veys blood from the left ventricle of the heart, and distributes 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 open- ing in the diaphragm, and it ends in the abdominal cavity upon the left side of the body of the fourth lumbar vertebra, by dividing into the two common iliac arteries. The part of this great vessel which is contained within the chest is divided, for convenience in description, into three portions : viz., the ascending aorta, the arch of the aorta, and the descending thoracic aorta. The ascending aorta takes origin from the base of the left ventricle of the heart, and proceeds obliquely 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 level of the upper border of the second costal cartilage of the right side, it changes its direction, and passes 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 left side of 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. Ascending Aorta (aorta ascendens). — The ascending aorta takes origin from the base of the left ventricle behind the left margin of the sternum opposite the lower border of the third costal cartilage. From this it passes upwards, and to the right, and ends in the aortic arch behind the right margin of the sternum at the level of the upper border of the second costal cartilage. Throughout its entire length it is enclosed within the fibrous pericardium, whilst the same sheath of 68 THORAX serous pericardium surrounds it and the pulmonary artery. It is therefore placed within the middle mediastinum (Figs. 31 and 39, PP- 57 and 69). It does not possess a uniform diameter. At its root, opposite the segments of the aortic valve, it presents the Internal g^ mammary ,v -nyi;,-.: ;;-;..•.•.";.' / ^2^=^^, ^ vessels Superior vena cava Phrenic nerve Aortic arch Vagus nerve-g Recurrent laryngeal nerve Left superior intercostal vein GEsophagus-^S| Thoracic duct-^HK. Sympathetic-* Phrenic nerve Mediastinal pleura Trachea Vagus nerve Intercostal "VB arteries f^j Vena azygos BR major ^-* .| Sympathetic Fig. 38. — Transverse section through the Superior Mediastinum at the level of the fourth dorsal vertebra. three bulgings termed the sinuses of Valsalva ; whilst higher up, on cross section, it generally exhibits a transversely oval and not a circular outline. This is due to the presence of a diffuse bulging of the right wall, which receives the name of the great aortic sinus. Against the wall of this sinus the blood is driven with great force as it leaves the ventricle, and THORACIC CAVITY 69 at first sight it might seem to be aneurismal in its origin, but its presence in the foetus renders such a view untenable. It is, however, a favourite site for aneurismal dilatation. The more immediate relations of the ascending aorta may now be examined. It is intimately associated with the pulmonary artery throughout its entire length. At its origin Left phrenic nerve Pulmonary artery Left pulmonary artery ( K>ophagus Left vagus nerve Thoracic duct- Descending aorta Vena azygos minor superior Internal -nammary vessels Pericardium Ascending aorta Right phrenic nerve Superior vena cava Right pulmon- ary artery Bifurcation of trachea Right vagus nerve Bronchial artery Vena azygos major Intercostal artery Sym pathetic cord PlG. 39. — Transverse section through the Mediastinal Space at the level of the fifth dorsal vertebra. it lies behind the root of the pulmonary artery; higher up, this vessel is placed to the left of the ascending aorta. To its right side, and partly behind it, is the superior vena cava ; whilst behind, it is in relation to the anterior wall of the right auricle and the right pulmonary artery (Fig. 24, p. 46). It is overlapped by the right pleura and the anterior thin margin of the right lung, which intervene between it and the chest wall. 7o THORAX The coronary arteries have already been seen to spring from this portion of the aorta. Aortic Arch (arcus aortae). — The arch of the aorta extends from the termination of the ascending aorta 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. 38). It lies behind the manubrium sterni, and as it turns backwards it is crossed, under cover of the left media- stinal pleura, by the left phrenic nerve, the inferior cardiac branch of the left pneumogastric nerve, the left superior cardiac branch of the sympathetic, and the left pneumogastric nerve. The left superior intercostal vein ascends upon this surface of the great vessel in the interval between the vagus and phrenic nerves. 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 recurrent laryngeal nerve (Fig. 38). The upper border of this subdivision 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, (p) the left common carotid, and (c) the left subclavian. Its lower surface, which forms the concavity of the arch, overhangs the bifurcation of the pulmonary artery, and is connected with the root of the left pulmonary artery by the fibrous ligamentum 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 neck. They should now be dissected. The left common carotid takes origin some- what nearer the innominate artery than the left subclavian. They are all contained within the superior mediastinum, ar.d Fig. 40, p. 71, which 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. Innominate Artery (arteria anonyma). — The innominate artery is the largest of the three branches which spring from the aortic arch. It passes obliquely upwards and to the right in the superior mediastinum, 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. In 1 front of the vessel are the remains of the thymus gland and the manubrium THORACIC CAVITY 71 sterni, to the posterior aspect of which are attached the sterno-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 ; but as the vessel inclines to the right, it comes to lie, at a higher level, upon the right side of the windpipe. To the right side of the artery, in its upper part, are the pleura, the right innominate vein, the superior vena cava, and the right phrenic nerve. Left innomi- nate vein Innominate Phrenic nerve Left common carotid Vagus nerve Left subclavian Recurrent laryngeal nerve Mediastinal pleura Thoracic duct Cartilage of first rib Internal mam- mary vessels ^^ Right innomi- nate vein Phrenic nerve Trachea Vagus Oesophagus Mediastinal pleura -->*«^gr: Fig. 40. — Transverse section through the Superior Mediastinum at level of the third dorsal vertebra. 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 (arteria carotis communis sinistra). — This artery ascends in the superior mediastinum 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 sterni than the innominate artery. In fro?it of 72 THORAX the left common carotid artery 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 are the left phrenic and vagus nerves. Further, it is supported on the left side by the left pleura and lung. It gives off no branches within the thoracic cavity. Left Subclavian Artery (arteria subclavia sinistra). — This vessel springs from the aortic arch, near its termination, and 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 innomi- nata, 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. 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 connexion 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. The cardiac plexus is subdivided into a superficial and a deep portion, but these are in direct connexion with each other, and are to be regarded merely as different parts of one plexus. The deep 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 THORACIC CAVITY 73 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 end of the trachea. It is therefore placed on a deeper plane and at a slightly higher level than the superficial plexus. The branches which enter the different parts of the cardiac plexus are derived from the cervical portions of the gangliated cords of the sympathetic, from the pneumogastric nerves, and from the recurrent daryngeal 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 tipper, middle, and lower sympathetic cardiac branches. The upper sympathetic cardiac branch of the left side has already been traced across the aortic arch into the superficial cardiac plexus. The middle and lower branches of the left side join the left portion of the deep cardiac plexus on the trachea. The three sympathetic cardiac branches of the right side join the right portion of the deep plexus. Within the thorax they run obliquely 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. The cervical branches are two in number, viz., superior and inferior. The inferior cervical cardiac branch of the left pneumogastric has been previously traced over the aortic arch into the super- ficial cardiac plexus. Both branches on the right side proceed downwards behind the subclavian artery, and then along the trachea to join the right portion of the deep cardiac plexus. The upper branch of the left side joins the left part of the deep cardiac plexus. Thoracic cardiac branches are only given off from the trunk of the right pneumogastric. They join the right portion of the deep plexus. 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 pneumogastric. The following table shows the arrangement of the cardiac nerves with reference to the plexus : — 74 THORAX c c • i i- i pathetic of left side Superficial cardiac plexus, . • - T • i \ V rwiTf^r ceruiM rare (i. Superior cardiac branch of sym- I2' left pneumogastric. Lower cervical cardiac branch of Left portion of the deep cardiac plexus, Right portion of the deep cardiac plexus, .... f I. Middle and lower cardiac branches of the sympathetic of left side. Upper cervical cardiac branch of the pneumogastric. Cardiac branches of the left recur- rent laryngeal, 'i. Three cardiac branches of sym- pathetic of right side. Both cervical cardiac branches of the right pneumogastric. Thoracic cardiac branches of the right pneumogastric. Cardiac branches of the right re- current 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 plexus proceed — (i) an offset to join the right anterior pulmonary plexus; (2) an offset for the supply of filaments to the right auricle of the heart ; and (3) a very considerable prolongation, which passes downwards in front of the right pulmonary artery to join the superficial cardiac plexus, and form the right coronary plexus (p- 51). From the left portion of the deep cardiac plexus proceed — (1) an offset to the left auricle; (2) an offset to the left anterior pulmonary plexus; whilst (3) the greater part of it is prolonged downwards in relation to the left pulmonary artery to form the left coronary plexus (p. 51). Removal of the Heart from the Body. — To do this it is only necessary to divide the pulmonary artery and the pulmonary veins. The other vessels have already been severed. The ascending aorta which is attached to the heart should next be slit open, care being taken to carry the knife accurately between two of the segments of the valve so as not to injure either. Aortic Valve. — This valve may now be studied and com- pared with the pulmonary valve which guards the mouth of the pulmonary artery. The membranous valve segments are three in number, and are of semilunar form. Attached around the opening by their convex margins, their free con- cave 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 THORACIC CAVITY 75 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 correspond to the segments, the orifices of the coronary arteries will be seen (Fig. 25, p. 47). Note that they 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 distributed 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 lunula. These are semi- lunar in outline and lie next the free margin — one on either side of the corpus Arantii. These lunula 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 the inside its cavities are lined by the thin smooth endocardium 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 epi- cardium and the endocardium is placed the muscular tissue of the heart, which is termed the myocardium. The muscular fibres of the heart are disposed in several layers, in each of which the fibres take a special direction. 76 THORAX But in an ordinary dissecting-room heart very little information can be obtained as to the arrangement of the muscular fibres. The continuity 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. The fibres of the auricles are difficult to dissect ; but in the ventricular portion of the heart, the student should be able to make out — (i) that the different layers of muscular fasciculi cross each other obliquely, and are for the most part attached to the fibrous rings which encircle the auriculo- ventricular openings ; (2) that the superficial fasciculi are 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 Ventricular Orifices. — The heart which is obtained in the dissecting-room, however, must not be cast aside, because several very essential and important points may be made out by its further dissection. In the first place, it is easy to determine 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 re- moving the fat and vessels from the auriculo-ventricular furrow, it will be seen that the muscular tissue which enters into the formation of the ventricular walls is quite distinct from that of the auricular walls. At only one place is there a direct continuity between the muscular tissue of the auricles and that of the ventricles. This connecting bridge is a small slip, termed the auriculo-ventricular bundle, which passes from the septum between the auricles to the septum between the ventricles. It therefore cannot be seen from the outside of the heart. To expose the auriculo-ventricular bundle the right auricle and right ventricle should be opened from the front, and the anterior half of the right auriculo-ventricular ring removed. The septal cusp of the valve having been detached, a little dissection immediately below the pars membranacea septi will bring the bundle into view as it passes from the septum of the auricles on to the septum of the ventricles. It is easily distinguished on account of its pale colour. At the lower border of the pars membranacea septi it divides into two parts. One part is carried down on the right face of the ventricular septum and the other upon its left face. The bond of union between the auricles and ventricles THORACIC CAVITY 77 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 valve cusps are attached, and it is from them that they derive the Portion of bundle which goes to the left face of the inter- ventricular septum Auriculo-ven- ;v tricular bundle^ -" / Right auricle Aorta Right or y marginal flap I Portion of sep tal flap of tri cuspid valve Posterior papillary ^v*W muscle Pulmonary artery Os cordis _lnfundibulum Portion of auricula- ventricular bundle w-which is related to the right face of the inter- ventricular septum Interventricular septum Moderator band on which fibres from the ~auriculo-ven tricular bundle are spread- ins out FlG. 41. — Dissection of the Heart of a Calf by Dr. Waterston to show the Auriculo-ventricular Bundle. This band is regarded as the pathway by which the wave of auricular contraction passes from the auricular to the ventricular wall. 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. When the auricles are removed from the ventricles, the relative positions of the orifices at the base of the ventricular portion of the heart can be studied (Fig. 25, p. 47). The 7 THORAX auriculo- ventricular openings lie side by side below and posteriorly. The aortic opening is placed in front and between them, whilst the pulmonary orifice is situated in front of the aortic opening. 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 connexion 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 oc- cupy the angle between the bronchi removed. Trachea. — The thoracic por- tion of the trachea, or wind- pipe, 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. 38, p. 68. It begins in the neck opposite the sixth cervical vertebra, where it is continuous with the larynx, and it enters the chest cavity through the thoracic inlet. Here it lies in the superior mediastinal space, and ends by dividing into the two bronchi opposite the intervertebral disc between the fourth and fifth dorsal vertebras. A short dis- tance above the bifurcation an impression, sometimes strongly marked, is usually seen on the left side of the trachea. This is due to the close contact of the aortic arch as it passes backwards against this part of the tube. Except at its lower end, which is very slightly inclined to the right, the trachea adheres rigorously to the mesial plane. The relations of the thoracic part of the trachea are as Fig. 42. — Diagram of the Base of the Ventricular Portion of the Heart. P. Pulmonary opening. A. Aortic opening. L. Left auriculo-ventricular opening. R. Right auriculo-ventricular open- ing. THORACIC CAVITY 79 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 aortic arch and the origins of the innominate and left common carotid arteries ; (5) the deep cardiac plexus. Behind, it rests upon the oesophagus, which lies somewhat to the left side of the mesial plane. On its right side are the pleura and the right pneumogastric nerve, and at a higher level the innominate artery ; and on its left side are the aortic arch, the left recurrent laryngeal nerve, and the left sub- clavian artery (Figs. 38 and 40). Bronchi. — The two bronchi proceed down- wards and outwards from the termination of the trachea — each towards the hilum of the corresponding lung. Like the trachea, they are kept permanently patent by the pres- ence of cartilaginous rings in their walls. These rings are de- ficient posteriorly, so that each bronchus exhibits a flattened posterior surface similar to that of the trachea. The two bronchi differ from each other in length, width, and in the direction which they pursue, as well as in the relations which they present. The first collateral branch arises from the right bronchus Thyroid cartilage Cricothyroid membrane Cricoid cartilage Part of trachea covered by isthmus of thyroid body Common carotid artery Left subclavian artery Aortic arch Left bronchus Left pulmonary artery / Hyparterial bronchus Fig. 13 ■ Gullet hparterial bronchus Hyparterial bronchus Right pulmonary artery The Trachea and Bronchi. The dotted line gives the outline of the thyroid body. 8c THORAX much nearer the trachea than in the case of the left bronchus. Taking the origin of this branch as indicating the terminal limit of each of these tubes, the left bronchus is at least twice as long as the right bronchus. On the other hand, the right bronchus is wider than the left, and this is clearly due to the greater size of the right lung. In so far as the direction which they pursue is concerned, it will be noticed that the right bronchus takes a more vertical course than the left bronchus. It therefore lies more in a line with the trachea, and it is owing to this, as well as its greater width, that when foreign bodies are introduced into the trachea there is a greater tendency for them to enter the right bronchus. The more horizontal course of the left bronchus is due to the marked projection of the heart to the left side of the mesial plane. Arching forwards over the right bro?ichus is the vena azygos major, whilst the vena cava superior passes downwards in front of it. Arching over the left bronchus is the aortic arch, whilst passing down behind it are the oesophagus and the descending thoracic aorta. On each side, as the pulmonary artery passes outwards, it crosses in front of the correspond- ing bronchus : on the right side it is placed below the first collateral branch (eparterial bronchus), on the left side it lies above the first collateral branch (first hyparterial bronchus). On the posterior aspect of each bronchus the vagus nerve breaks up into the posterior pulmonary plexus. Occupying the angular interval between the bronchi there is a cluster of bronchial lymphatic glands, and a chain of these glands accompanies each tube towards the lung. A small fleshy slip passing from the posterior aspect of the left bronchus to the oesophagus is frequently present. It is called the brotuho-xsophageal muscle. The relations of the bronchi in the roots of the lungs have already been studied (p. 32). 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, THORACIC CAVITY 81 except in its very lowest portion, where the anterior wall is formed by the posterior surface of the diaphragm (Fig. 45). Behind, it is limited by the bodies of the dorsal vertebrae 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. 44 and 45 are taken from tracings of transverse sections 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 structures which it contains : — Pericardium Thoracic Vena cava inferior CEsophagus Thoracic duct Vena azygos major Pleura Fig. 44.- -Tracing of section through the Posterior Mediastinum at the level of the eighth dorsal vertebra. 1. The descending thoracic aorta. 2. The oesophagus. 3. The pneumogastric nerves. 4. The thoracic duct. 5. The vena azygos major 6. Certain of the right aortic inter- costal arteries. 7. The vena azygos minor superior. 8. The vena azygos minor inferior. The great splanchnic nerves. 10. Some lymphatic glands. Dissection. — To open into the posterior mediastinal space it is neces- sary to make a vertical incision through the pericardium, which 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 plenro-cesophageal mitscle. In the majority of cases, however, this muscle is only represented by a few slender muscular fasciculi, which are difficult to isolate from the areolar tissue in which they lie. Pneumogastric Nerves (nervi vagi). — The pneumogastric nerves can now be followed throughout their entire course vol. 11 — 6 82 THORAX within the thorax. They traverse both the superior and posterior mediastinal spaces, but differ so much in their relations on the two sides of the body that it is best to examine each separately. The left pneumogastric nerve enters the thorax in the in- terval between the left common carotid and left subclavian arteries, and behind the left innominate vein (Fig. 40, p. 71). It has already been observed crossing the arch of the aorta behind and to the left side of the -phrenic nerve and the two superficial cardiac nerves (Fig. 38, p. 68). Here also it has been seen to give off its recurrent laryngeal branch. Leaving the aorta, it sinks behind the root of the left lung (Fig. 39, Pericardium Diaph Diaphragm CEsophagus Thoracic aorta f^4 Left pleura pf| s ... Thoracic duct QTifiV;"" Right Pleura . Vena azygos major Fig. 45. — Tracing of a section through the lower part of the Posterior Mediastinum, where its anterior wall is formed by the diaphragm. p. 69), and at once breaks up into a number of branches, which unite in a plexiform manner to form the left posterior pulmon- ary plexus. It issues from this plexus in the form of one or two cords, which pass to the anterior aspect of the oesophagus. Upon the oesophagus another plexus — the plexus gulce — is formed. Both of the pneumogastric nerves take part in the formation of this plexus. From the plexus gulae the left pneumogastric emerges as one trunk, and passes out of the thorax by the oesophageal opening of the diaphragm. Within the abdomen it breaks up into branches upon the anterior surface of the stomach. The right pneumogastric nerve, in the upper part of the superior mediastinum, lies deeper in the thorax than the left nerve. It enters by passing between the subclavian THORACIC CAVITY 83 artery and the right innominate vein, and descends by the side of the trachea (Figs. 40 and 38) to the posterior aspect of the root of the right lung (Fig. 39, p. 69). Here it breaks up into the right posterior pulmonary plexus, and, issuing from this in the form of two nerve cords, it takes part in the formation Left common carotid artery Left vagus nerve Left subclavian artery Left innominate vein Trachea Left pulmonary artery' Left bronchu Left pulmonary veins Right vagus ner\ I diaphragmatic surface of heart Innominate artery (Esophagus Right vagus nerve Superior vena cava Vena azygos major Right posterior pulmonary- plexus 5| Right pulmonary artery Right bronchus Right pulmonary- veins Plexus gulae Portion of peri- cardium Left vagus nerve Inferior vena cava FlG. 46. — Posterior Aspect of the Heart with the Descending Aorta, the Trachea and Bronchi, and the CEsophagus. of the plexus gulce. It leaves this plexus upon the posterior aspect of the oesophagus, and, entering the abdomen through the oesophageal opening of the diaphragm, it breaks up into branches on the posterior aspect of the stomach. The pneumogastric nerves give off the following branches within the thorax : — 11 — 6 a 84 THORAX 1. Recurrent laryngeal (left side). 2. Thoracic cardiac (right side). 3. Pulmonary. 4. Oesophageal. 5. Pericardial. The left recurrent laryngeal nerve (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 in the interval between this and the oesophagus to the larynx. The right re- current laryngeal nerve (nervus laryngeus inferior dexter) arises in the root of the neck, and hooks round the subclavian artery. The thoracic cardiac branches (rami cardiaci inferiores) ot 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 re- current laryngeal nerve as it turns round the aortic arch. The pulmonary branches have already been studied in connexion with the root of the lung (pp. 31, 32). The oesophageal branches (rami cesophagei) are dispensed to the gullet in two sets — (1) 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 gulae 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 gulae 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 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 enters somewhat to the left of the middle line ; but on tracing it downwards, it will be noticed to incline inwards, so as to assume a mesial position opposite the fifth dorsal vertebra. THORACIC CAVITY 85 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 immedi- ately behind the trachea (Figs. 40 and 38); below this, it is crossed by the left bronchus, with which it is sometimes connected by the broncho -oesophageal muscle (Fig. 39). From this point onwards through the posterior mediastinum it is covered in front by the pericardium, which is applied closely to it (Fig. 44). Just before entering the abdomen it lies behind the posterior part of the diaphragm (Fig. 45). From above downwards, therefore, the immediate anterior relations of the oesophagus are : (1) 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 from the spine, while in the posterior mediastinum it is placed in front of the vena azygos major and the thoracic duct. The vena azygos minor inferior and superior and the right intercostal arteries also 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. 44 and 45. Upon the right side, during its course through the posterior mediastinum, the oesophagus is clothed by the mediastinal pleura, whilst on the left 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 (Fig. 45). In the superior mediastinum the thoracic duct is closely applied to the left side of the oesophagus, and the left pleura comes into relation- ship with it (Fig. 40, p. 71). Below this, however, except immediately above the point where it pierces the diaphragm, it is not directly related to the pleura of the left side. The pneumogastric nerves form the plexus guise on the walls of the gullet, as it traverses the posterior mediastinum, and accompany it in the form of two nerve-trunks through the oesophageal opening — the right nerve being placed on its posterior aspect, whilst the left nerve is placed in front of it. 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 n— 6 6 86 THORAX 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 proceeds downwards it inclines inwards, so that at its termination it is mesial in position. It lies upon the bodies of the vertebrae, and therefore it shows a curve corresponding to that of the vertebral column in the dorsal region. In fro?it, 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 inter- vertebral 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 mediastinum ; whilst on its right side will be noticed the thoracic duct and the vena azygos major. The oesophagus presents important relationships 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 and still distinctly in front. The Branches of the Descending Thoracic Aorta may be grouped under the heads of visceral and parietal. Visceral. Bronchial. Pericardial. (^Esophageal. |( V. Posterior mediastinal. p . . j Intercostal (nine on each side). -L arietai. ~i o i_ *. i { Subcostal. 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 right 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. THORACIC CAVITY 87 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 (arteriae oesophageal) 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 anastomosing branches on the wall of the oesophagus. Above, this chain communicates with branches of the inferior thyroid artery, whilst below, it communicates with the ascending oesophageal branches of the coronary artery of the stomach. The posterior jnediastinal branches (rami mediastinales) are very small, and are given to the areolar tissue and glands in the posterior mediastinal space. The i?itercostal branches (arteriae 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. The pair of subcostal arteries lie in series with the intercostal branches, and may be studied along with them. Thoracic Duct (ductus thoracicus). — The thoracic duct, although 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 (in- cluding 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. It will be found by dissecting in the loose areolar tissue which lies between the aorta and the vena azygos major, and it will be recognised from its position, and by the great elasticity which it exhibits when it is pulled by the forceps. Trace it downwards, and it will 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 bodies of the first and second lumbar vertebrae as an elongated dilatation, called the receptaculum chyli. At the level of the fifth dorsal vertebra it passes from the right to the left of the mesial plane by crossing behind the oesophagus (Fig. 39, p. 69). It now ascends into the 11— 6 c 88 THORAX neck between the oesophagus and left pleura, and arching 17 18 Fig, 47. — The Thoracic Duct and \\s Tributaries. 1. Lumbar veins. 2. Left renal vein. 3. Right renal artery. 4. Inferior vena cava. 5. Suprarenal body. 6. Receptaculum chyli. 7. Thoracic duct. S. Descending thoracic lymphatic trunk. 9. Vena azygos major. 0. Mediastinal lymphatic vessel. 1. Superior intercostal vein. 2. Subclavian vein. 3. Subclavian artery. 4. Clavicle. 5. Scalenus anticus muscle. Phrenic nerve. Thyroid axis. Internal jugular vein. Vertebral artery. 20. Common carotid artery. 21. Trachea. 22. Thyroid body. 23. (Esophagus. 24. Common carotid artery. 25. Internal jugular vein. 26. Vertebral artery. 27. Thyroid axis. 28. Common lymphatic trunk from head and upper limb. 29. Scalenus anticus muscle. 30. Subclavian artery. 31. Superior intercostal vein. Bronchial lymphatic vessel. Vena azygos minor superior. Aorta. Vena azygos minor inferior. 36. (Esophagus. 37. Descending thoracic lymphatic trunk. Inferior phrenic artery. Suprarenal body. Cceliac axis. Superior mesenteric artery. Common intestinal lymphatic trunk. Renal artery. Renal vein. Common lumbar lymphatic trunk. THORACIC CAVITY 89 outwards it 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. 44, p. 81; 39, p. 69; 38, p. 68; 40, p. 71). 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 situation, before the parts are disturbed by dissection, it can readily be exposed by raising the right lung and dividing the right mediastinal pleura ; in the latter situation the left lung must 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 frequently 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 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 lymphatic glands. These are of considerable importance, seeing that their enlargement in disease is not infrequently the cause of serious thoracic trouble. The following are the chief groups : — (1) 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 (lympho- glandulae sternales), and are joined by lymphatic vessels from the anterior thoracic wall, the mammary glands, the front part 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 accompany the intercostal vessels between the intercostal muscles. They are therefore called the intercostal glands (lymphoglandulce intercostales), and they receive the lymphatics of the posterior thoracic wall. (3) Anterior mediastinal glands (lymphoglandulse mediastinales anteriores), two or three in number, which receive lymphatics from the diaphragm and upper surface of the liver. They occupy the lower open part of the anterior mediastinum. (4) Posterior mediastinal glands (lymphoglandulx mediastinales posteriores), which follow the course of the thoracic aorta, and are joined by lymphatics from the diaphragm, pericar- dium, and 'esophagus. (5) Superior mediastinal glands (lymphoglandulce mediastinales superiores), an important group, eight to ten in number, and placed in relation to the aortic arch. The lymphatics of the heart, peri- cardium, and thymus body enter these. (6) Bronchial glands (lympho- glanduku 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 pour their contents into them. In the adult, they are generally dark in colour, and sometimes as black as ink. qo THORAX 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 dividing 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 Bronchi and Vessels within the Lungs. — The student has previously observed that the two lungs 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, gives off branches for the different lobes. The right bronchus sends 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 hand, takes origin about twice that distance from the trachea. The 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 second 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 backwards above the level of the first bronchial branch, and therefore holds the highest place in the left pulmonary root. On the right side, then, the first bronchial branch is placed above the pulmonary artery, and it is termed the eparterial bronchus ; all the others lie below it, and are termed hyparterial bronchi. On the left side there is no eparterial tube ; they are all hyparterial. When the main stem of the bronchus is followed into the inferior lobe on either side, it will be observed to travel down- wards towards the back part of the base, and give off, as it proceeds, a series of ventral, and a series of smaller dorsal THORACIC CAVITY 9i 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) may be regarded as the first member of the ventral group (Fig. 48). 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 being disposed around the tube on all its aspects, in the form of -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 ?< on each side indicates the first hyparterial bronchus, or, in other words, the branch to the upper lobe of the left lung and the middle lobe on the right lung. irregular flakes, and imperfect rings. The farther the tubes are 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 we have noted, turn backwards to reach their posterior aspect, and this relation they maintain in the lung substance. 92 THORAX 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 vertebrae and the inner surface of the ribs. Gangliated Cord of the Sympathetic (pars thoracicalis nervi 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 are usually eleven in number. For the most part these lie on the heads of the ribs, but the first is placed over the inner part of the first intercostal space. Towards the diaphragm the cord inclines forward, so that one or two of the lower ganglia come to lie upon the bodies of the dorsal vertebrae. The first ganglion is considerably larger than those which succeed it. They are all linked together by intervening nerve cords. Superiorly, the thoracic part of the sympathetic is continuous with the cervical sympathetic ; whilst inferiorly it becomes continuous with the abdominal portion of the sym- pathetic by passing behind the ligamentum arcuatum internum of the diaphragm. The branches which spring from the ganglia may be divided into two sets : (a) central communicating and (b) peripheral branches of distribution. Central Communicating Branches. — One of the leading characters of the thoracic portion of the sympathetic cord is the intimate manner in which it is brought into connection with the spinal nerves. White rami communicantes pass from each of the intercostal nerves into the sympathetic cord. They become connected either with the ganglia or with the intervening portions of the cord. G?~ey rami conwiunicantes, on the other hand, arise from each ganglion, somewhat irregularly, and convey fibres to the various intercostal nerves. Peripheral Branches of Distribution. — These take origin irregularly, and are (i) pulmonary, (2) aortic, and (3) the three splanchnic nerves. The pulmonary branches spring from the second, third, and fourth ganglia, and join the posterior pulmonary plexus. The aortic branches are fine filaments which arise from the upper five ganglia and proceed to the coats of the thoracic aorta. The splanchnic nerves are three in number, and are dis- tinguished by the terms, great, small, and smallest, and they are destined for the supply of abdominal viscera. THORACIC CAVITY 93 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 nerve than 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 the semilunar ganglion. Upon the last dorsal vertebra, a ganglion called the splanchnic 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 dis- tinct oval bulging on the nerve-trunk. A few slender filaments 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) arises by two roots from the ninth and tenth or from the tenth and eleventh thoracic ganglia. It enters the abdomen by piercing the crus of the diaphragm, and it ends by joining the lower part of the semilunar ganglion. The smallest sftlatichnic 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 plexus. 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 be 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 (p. 4). The internal intercostal ??iuscle, 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 connexions of which can now be ascertained. 94 THORAX The posterior i?itercostal membrane is a strong aponeurotic layer which is continuous internally with the outer margin of the superior costo-transverse ligament, 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 muscles are 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 over one or, in many cases, two intercostal spaces. 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 nine lower intercostal spaces upon both sides of the body. As the aorta lies somewhat to the left of the middle line, the right aortic intercostal arteries are longer 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 bra?ich which passes back- wards in the interval between the transverse 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 intercostal 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 highest level, the nerve the lowest level, whilst the artery is intermediate. The distribution of these vessels in the thoracic parietes has already been studied (p. 6). The position of the intercostal artery in the intercostal THORACIC CAVITY 95 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 artery descends upon the necks of the first two ribs, and external to the gangliated 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. Subcostal Arteries. — These arteries form a pair of vessels in series with the intercostal arteries. They enter the abdomen by passing under the ligamentum arcuatum externum, and run in company with the last dorsal nerves along the lower borders of the last pair of ribs. Intercostal Nerves. — 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 or an anterior branch. The second dorsal or intercostal nerve, 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 96 THORAX 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 right side they terminate in three different ways : — 1. The intercostal vein of the first or highest space joins the right innominate vein (sometimes the vertebral vein). 2. The intercostal veins of the second and third spaces (and sometimes of the fourth space) unite into a common trunk, which joins the upper part of the vena azygos major. The common trunk is termed the superior intercostal vein. 3. The intercostal veins of the eight lower spaces join the vena azygos major. On the left side of the body four modes of termination may be recognised : — 1. The intercostal vein of the first or highest space has the same termina- tion 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 sometimes of the fourth space) converge, and by their union form a single trunk, termed the superior intercostal vein, which crosses the arch of the aorta and joins the left innominate vein independently of the first intercostal vein. 3. The intercostal veins of the fourth, fifth, sixth, seventh, and eighth spaces terminate in the vena 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 the right ascending lumbar veiti (vena lumbalis ascendens), a vessel which links together certain of the lumbar veins, and sometimes presents a direct communica- tion 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 aorta. In the thorax it extends upwards upon the bodies of the dorsal vertebrae 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 by joining the superior vena cava. It is situated in the posterior mediastinum, with the aorta and thoracic duct lying to the left (Fig. 47, p. 38). The tributaries of the vena azygos major are as follows : — (1) the superior intercostal vein of the right side; (2) the intercostal veins of the eight lower spaces of the right side ; THORACIC CAVITY 97 (3) the vena azygos minor superior; (4) the vena azygos minor inferior ; (5) the bronchial veins from the right lung ; (6) certain of the oesophageal veins; (7) some minute pericardiac veins. The vena azygos major communicates below with some 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. Vena Azygos Minor Superior (vena hemiazygos accessoria). — This 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 veins. Vena Azygos Minor Inferior (vena hemiazygos). — This vein takes origin within the abdomen as the left ascending lumbar vein. It enters 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, it 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. 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- vor.. n — 7 98 THORAX sternal, and inter-chondral articulations require examination. Very little dissection is necessary. After the ligaments have been defined, the dissector should remove a thin slice from the anterior aspect of each articulation, in order that the interior of the joint may be displayed. Manubrio-gladiolar Articulation. — This joint, between the manubrium and the gladiolus of the sternum, partakes of the nature of an amphiarthrosis. The opposing surfaces of bone are covered by a layer of hyaline cartilage, and are united by intermediate fibro-cartilage. 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. Sterno- chondral 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 each of the cartilages of the other true ribs 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 sterno-chondral joint of the seventh costal cartilage. With the exception of the first, and very frequently the seventh, the sterno-chondral 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 liga?ne?its (ligamenta sterno-costalia radiata) are strong, flattened bands of fibres which radiate from the extremities of the rib-cartilages, and blend 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. THORACIC JOINTS 99 Inter-chondral Articulations. — These joints are formed between 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 articulates with the bodies of two vertebrae and the intervening inter- vertebral substance (articulatio capituli costae). The costal Anterior common ligament Rib lips \ Three si of stellate-1 ligament I Superior costo-transverse ^ ligament Fig. 49. — Costo-vertebral. Joints as seen from the front ; also Anterior Common Ligament of Vertebral Column. head is wedge-shaped, and the socket formed for its reception presents a corresponding form. From the intervertebral 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 successfully 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, as a rule, takes a considerable share in the formation of its socket. The articulations between the heads of the ribs and the bodies of the vertebrae are termed the capitular joints (articulationes capitulorum). ioo THORAX 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 articulations (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. Capitular Joints. — These joints b.elong to the diarthrodial variety, and are provided with — (i) an anterior capitular ligament ; (2) an interarticular ligament ; and (3) two synovial membranes. In the case of the four ribs, however, which articulate with the body of one vertebra alone (viz., the first, tenth, 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 — (1) the uppermost, which is the largest, passes upwards and inwards to the body of the vertebra, which forms the upper part of the 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 ligament is composed of only two slips. Of these, the lower 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. Dissection. — 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 composed 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 THORACIC JOINTS 101 absent in those cases in which the head of the rib articulates with the body of one vertebra. The synovial membranes are two in number, except in the capitular joints of the first and last three ribs. One is placed above, and the other below the interarticular ligament. Costo-transverse Articulations. — These 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-transverse ligament (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-transverse ligament (ligamentum tuberculi costae) 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, supplemented 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 bodies of the vertebrae are held together by a series of amphiarthrodial joints, supported 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 diarthrodial joints surrounded by capsular ligaments, and lined by synovial membranes. ( Certain ligaments pass between different portions of the neural arches and their processes, viz., the ligamenta subflava between adjacent laminae, the inter-transverse, the inter-spinous, and the supra-spinous ligaments. 102 THORAX Pedicle of vertebra (cut) Posterior common ligament The laminae and the spinous processes of the vertebrae have been removed by the dissector of the head and neck in opening up the spinal canal to display the spinal cord. Consequently, the ligamenta subflava, the inter-spinous and supra-spinous ligaments, cannot be 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 verte- bral bodies and to the intervertebral discs. The most super- ficial 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 ad- jacent vertebrae. The dis- sector cannot fail to notice that the origin of the longus colli muscle is inseparably connected with this liga- ment. The posterior common ligament (ligamentum longi- tudinale posterius) is placed on the back of the vertebral bodies, and therefore within the spinal canal. It is firmly Fig. 50. —Posterior Common Ligament connected to the margins of of the Vertebral Column. The neural .«. , 1 ■, 1 j- „ 1 .„ , , , , f ., the vertebral bodies, and to arches have been removed from the \ vertebrae. 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 intervertebral substance (fibro-cartilago intervertebralis) is disposed between the vertebras 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 Inter- vertebral disc THORACIC JOINTS 103 central portion soft and pulpy (nucleus pulposus). In a transverse section the peripheral portion appears concentrically laminated : in a vertical section the most peripheral laminae are seen to be bent with the convexity 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 arrange- ment increases the elasticity of the spine, and tends to restore it to its natural curvature after it has been deflected by mus- cular action. The intervertebral discs constitute the main bond of union between the bodies of the vertebrae, 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 displayed. The facets of the articular processes are coated by hyaline cartilage. A capsular ligament lined by a synovial membrane 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. io4 HEAD AND NECK 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. 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. — (1) skin; (2) superficial fascia; (3) the small extrinsic muscles of the ear ; (4) the thin lateral part of the epicranial 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 should 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. — (1) from the root of the nose along the middle line of the cranium, to a point a little beyond the external occipital protuberance ; (2) from the tip of the mastoid process on one side, over the summit of the head to a corresponding 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 SCALP 105 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, P§Mi§ Integument £_ Superficial fascia B- Kpicranial aponeurosis Lax connective tissue Pericranium Cranial wall Dura mater Fig. 51. — Section through the Scalp and Cranial Wall. which give this layer a granular appearance. As the fascia is traced forwards towards the forehead, and downwards 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 proceed 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. Occipito-frontalis (epicranius). — This is a (juadricipital muscle which presents two occipital and two frontal bellies. The occipital bellies (musculi occipitales) — Fig. 52 (2) — are quite distinct from each other, and are separated by a marked interval. Each arises from the outer twu-thirds of the superior 106 HEAD AND NECK curved line of the occipital bone, 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. The frontal bellies (musculi frontales) are composed of pale fibres, and are not perfectly distinct from each other. For 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. Epicranial Aponeurosis (galea aponeurotica). — This apo- neurosis connects the occipital and frontal bellies of the occipito-frontalis muscle, and 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 attachment to the external occipital protuberance and the superior curved line of the occipital- bone. Laterally, it presents no sharply defined margin, but, losing its aponeurotic character, it is prolonged downwards as a fine expansion over the temporal fascia. In this locality it gives origin to two of the small auricular muscles. Dissection. — Divide the epicranial aponeurosis by a mesial incision of about an inch and a half in length, and then carry across the middle of this a second short transverse cut. On raising the corners thus marked out, the aponeurosis will be seen to rest upon a layer of loose flocculent areolar tissue, containing no fat — the fourth stratum of the scalp. Owing to the great laxity of this tissue, the occipito-frontalis muscle by its contractions can move the hairy scalp freely over the pericranium which invests the bone. Extrinsic Muscles of the Ear. — In man these muscles are very poorly developed, and the auricle possesses in SCALP 107 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. 52 (1). — -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 on the surface of the temporal fascia from the epicranial apo- neurosis, and it is inserted into the anterior aspect of the helix of'the pinna. The retrahens auriculam (musculus auricularis posterior) — Fig. 52 (3) — consists of two or three short bundles of muscular fibres which spring from the mastoid process of the temporal bone, and are inserted 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 retrahe?is 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 branch of the ophthalmic division of the trigeminal nerve. These are (a) the supra-trochlear, (b) the supra-orbital. The supra-trochlear nerve (nervus supra-trochlearis) leaves the orbit close to its inner angle and then turns upwards io8 HEAD AND NECK Fig. 52. — Superficial Nerves on the Side of the Neck and Back of the Scalp. (Hirschfeld and Leveille\ ) 1. Attollens auriculam. 2. Posterior belly of occipito- frontalis. 3. Retrahens auriculam. 4. Great occipital nerve. 5. Great auricular nerve. 6. Splenius muscle. 7. Sterno-mastoid muscle. 8. Small occipital nerve (pre- sent as two branches). Great auricular nerve. External jugular vein. Superficial cervical nerve. Spinal accessory nerve. Descending branches of cervical plexus. Cervical branches to trapezius 15. Trapezius muscle. 16. Clavicular branches. *3 14 '7 Acromial branches. Auricular twigs of great auricular nerve. 19. Parotid gland. 20. Facial nerve. 21. Masseter muscle. 22. Infra-mandibular nerve. 23. Anterior jugular vein. 24. Sternal branches. 25. Platy.Nma myoides. SCALP 109 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 ?-egion, nerves from three sources are to be found, — (a) from the facial nerve ; (b) from the orbital branch of the superior maxillary division of the trigeminal nerve ; (c) from the auriculo-temporal branch of the inferior maxillary division of the trigeminal nerve. The temporal branches 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 branch of the o?'bital 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 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. no HEAD AND NECK The auriculotemporal 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 as they ascend, and a careful dissector may be able to trace twigs from these as far as the summit of the head. Its 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: (a) the posterior auricular branch of the facial nerve — Fig. 52 (3) I ip) tne mastoid branch of the great auricular nerve ; (c) the small occipital nerve from the anterior primary division of the second cervical nerve — Fig. 52 (8); and (d) the great occipital nerve from the posterior primary division of the second cervical nerve — Fig. 52 (4). The posterior auricular (nervus auricularis posterior) is a small nerve which ascends upon the front of the mastoid process, immediately behind the ear, to supply the superficial muscles in this region. 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 process on a more superficial plane, and is distributed to the skin in this region. 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 integu- ment, 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 SCALP 1 1 1 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 twig to the skin over the cranial aspect of the ear, and communicates 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 associ- ated with the supra-trochlear nerve, and the latter with the supra-orbital nerve. The veins corresponding 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 forehead, and supplies numerous branches to the integument, muscles, and pericranium. Further, it anastomoses with the frontal and supra-orbital arteries, and with the corresponding vessel of the opposite side. The posterior superficial tempoi-al 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 opposite, side, and with the posterior auricular and occipital arteries. The posterior auricular artery (arteria 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 anastomoses with the posterior superficial temporal artery. The mastoid branch in- clines backwards towards the occiput, where it communicates with the occipital artery. The posterior auricular vein is a comparatively large vessel. It joins the posterior division of the temporo-maxillary vein, near the angle of the lower jaw, to form the external jugular vein. ii2 HEAD AND NECK 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 posterior 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. When this is removed the strong temporal fascia which covers the temporal muscle is brought fully into view. Its connections will be studied at a later period. Surgical Anatomy of the Scalp. — The close connexion between the three superficial layers of the scalp (viz., skin, superficial fascia, and epi- cranial aponeurosis), and the loose manner in which these are bound by areolar tissue to the pericranium, are points of great interest from a surgical point of view. When the scalp is wrenched from the head by machinery, or by any other means, the separation is effected in the plane of the areolar layer. The blood vessels, however, lie for the most part in the superficial fascia, and therefore large flaps of detached 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 pro- duce 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 sub- jacent areolar tissue, and the pericranium, from the root of the nose in REMOVAL OF THE BRAIN 113 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, 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 reaching 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 back- wards 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. Vein Sub-arachnoid space and trabeculae -- Dura mater - -Subdural space "-Arachnoid mater N Pia mater Fig. 53. — Diagrammatic section through the Meninges of the Brain. (Schwalbe. ) co. Grey matter of cerebral convolutions. 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 with a piece of string, and then marking the cranium with a pencil along the 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 lambda1 and the external occipital protuberance. The saw should only be used to divide the outer table of the skull. When the diploe 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 off. 1 The term " lambda " signifies the apex of the occipital bone, or the point at which the sagittal and lambdoidal sutures meet. VOL. II — 8 ii4 HEAD AND NECK Dura Mater (dura mater encephali). — The brain is clothed by three distinct membranes, which are termed the meninges. These are from without inwards — (i) the dura mater; (2) the arachnoid mater; and (3) the pia mater. 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 rough- ness would become still more manifest, and be seen to be due to a multitude 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 numerous 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 ruptured. 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 strongly adherent along the lines of the sutures ; and, further, it is much more firmly attached to the base 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 clean 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 must also be looked upon as the nutrient vessels of the inner 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 REMOVAL OF THE BRAIN US are small granular bodies, ranged in clusters on either side of the superior longitudinal sinus, into which many of them protrude (Fig. 54). 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 enlargements 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 Pacchionian body Opening of cerebral vein Bone FiG. 54. — Mesial section through the Frontal Bone and corresponding part of the Longitudinal Blood Sinus. The Pacchionian bodies are seen pro- truding into the sinus. (Enlarged.) spaces or intervals which communicate with the sinus either by a small aperture or a narrow channel. These recesses are termed parasinoidal sinuses or lacnnce laterales, and the independent meningeal veins, and some of the diploic veins, pour their blood into them. Pacchionian 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 the Pacchionian bodies enlarge, they cause absorption of the cranial wall, and small pits are hollowed out on its deep surface for their reception. The superficial walls of the lacunre — 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 rebral 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: (1) it acts as an internal periosteum to the bones forming the cranial cavity ; 11— 8 a u6 HEAD AND NECK 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 endocranial and the supporting layers. Along certain lines these two layers separate from each other. In some cases they separate so as to form channels, termed blood sinuses (sinus durae matris), for the conveyance of venous blood ; in other cases they separate in Parasinoidal sinus Pacchionian ^^^^(j^g^^^^^ 'CA Pacchionian body Parasinoidal sinus Longitudinal sinus Blood vessels-' Grey cortex of a convolution Dura mater Pia mater Subarachnoid space Falx cerebri Fig. 55. — Diagram of a coronal section through the middle portion of the cranial vault and subjacent brain to show the membranes of the brain and the Pacchionian bodies. 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 com- partments communicating freely with each other, and each holding a definite subdivision of the brain (Fig. 57). 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. 56). The dura mater covering the upper aspect of the brain is thus divided into a central strip containing the superior longitudinal sinus and four triangular flaps. The flaps should now be turned downwards over the cut margin of the skull, and in this REMOVAL OF THE BRAIX ii7 position they preserve the brain during its removal from laceration by the sharp bony edge. Subdural Space (cavum subdurale). — This is the term which is applied to the interval between the dura mater and the arachnoid mater- -Figs. 53 and 55. It contains a very small quantity of serous fluid which moistens the opposed surfaces of these membranes. A striking contrast between superior longitudinal sinus Pacchionian bodies Middle meningeal artery Mouth of cerebral vein Cerebral vein Fig. 56. — The Dura 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. the two surfaces of the dura mater will be observed. The superficial surface, as we have noted, is rough and flocculent. The 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 for the most part in the sulci between the convolutions, and run upwards to the middle 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. 56). n n8 HEAD AND NECK Superior Longitudinal Sinus (sinus sagittalis superior). — Open into this venous channel by running the knife through its upper wall from behind forwards (Figs. 56 and 57). It begins in front at the crista galli of the ethmoid bone, where it not unfrequently communicates with the veins in the nasal cavity through the foramen caecum, and it extends backwards, grooving the cranial vault in the middle line, to Falx cerebri Inferior longitudinal sinus Superior longitudinal Cavernous sinus Eustachian tube Nasal septum Vena Galeni magna Tentorium Straight sinus Lateral sinus Falx cerebelli Lateral sinus Inferior petrosal sinus Superior petrosal sinus Fig. 57. — Sagittal section through the Skull a little to the left of the mesial plane to show the processes of Dura Mater. V. Fifth cranial nerve. VII. Facial nerve. VIII. Auditory nerve. IX. Glossopharyngeal nerve. X. Vagus nerve. XL Spinal accessory nerve. XII. Hypoglossal nerve. the internal occipital protuberance, on the right aspect ot which it becomes continuous with the right lateral sinus. Its lumen, which is triangular in cross-section, 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. 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 veins are directed from behind forwards, whilst the blood in the sinus flows from before backwards. Opening into the sinus are also REMOVAL OF THE BRAIN 119 the mouths of the lacuna laterales, whilst bulging into it on either side are as a rule numerous Pacchionian bodies. The channel is crossed at its inferior angle by a number of minute bands. These receive the name of chorda Willisii. Falx Cerebri (Fig. 57). — This is a sickle-shaped redupli- cation 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 outwards. 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. The anterior part of the falx is frequently cribriform, and is some- times perforated by apertures to such an extent that it almost resembles lace-work. Along each border it splits into two layers so as to enclose a blood-sinus. Along its upper convex margin runs the superior longitudinal sinus ; along its concave free border courses the much smaller inferior longi- tudinal sinus ; whilst along its attachment to the tentorium is enclosed the straight sinus. Its inferior concave margin overhangs the corpus callosum, with which, however, it is not in contact, except, perhaps, to a very slight extent, behind. 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 lingers, 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 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 ii— 8 c i2o HEAD AND NECK 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.1 Sever in turn each of these structures. We then come upon the oculo-7)iotor ?ierves (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 trochlear nerve (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 hemisphere with the fingers, it will be observed to rest upon the tentorium cere- belli— a broad horizontal process of dura mater, which inter- venes 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 backwards 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) perforating the dura mater near the apex of the petrous portion of the temporal bone ; the abducent nerve (sixth cranial nerve) piercing the dura mater behind the dorsum sellse of the sphenoid bone ; the portio dura or facial nerve, the pars intermedia, and the portio mollis or auditory nerve disappearing into the internal auditory meatus ; the glossopharyngeal, the vagus, and the spinal accessory nerves leaving the skull through the jugular foramen ; and the two slips of the hypoglossal nerve 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. 1 In dividing the cranial nerves, it 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. REMOVAL OF THE BRAIN 121 In the case of the three nerves 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 backwards, 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 harden- ing reagent. Methylated spirit, with a small amount of formalin (4 per cent) added to it, gives the best results. The dissector must obtain a vessel large enough to hold the brain, and, at the same time, allow the hardening reagent to surround and cover it completely. It must likewise be provided with an accurately fitting lid to prevent evaporation. A small amount of cotton wadding 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 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. 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 like manner from the base of the cranium. It is closely adherent to the crista galli, to the posterior margins of the lesser wings of the sphenoid, to the posterior clinoid processes, to the petrous portions of the temporal bones, to the basilar process of the occipital bone, and around the margin of the foramen magnum. Another cause of its close adhesion in this locality is, that it gives sheaths to the cranial nerves, and 122 HEAD AND NECK passes out of the cranium through the basal foramina to become continuous with the periosteum on the external surface 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, processes which act as partial partitions within the cranial cavity. These are four in number, viz. : — i. The falx cerebri (which has already been studied). 2. The tentorium cerebelli. 3. The falx cerebelli. 4. The diaphragma sellse. Tentorium Cerebelli (Fig. 57 and Fig. 58). — This is a large crescentic fold of dura mater which constitutes 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 hori- zontal. It is accurately applied to the upper surface of the cerebellum. Its highest point, therefore, is in front, in the mesial plane, and from this it gradually slopes downwards to its attached border. Except in cases where formalin has been injected into the cranial cavity during the preservation of the subject, only an imperfect idea of the natural appear- ance of the tentorium can be obtained, seeing that its connections have been severed in the removal of the brain. Before it is disturbed it is 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. The posterior border of the tentorium is convex, and is attached to the horizontal ridge which marks the deep surface of the occipital bone. Beyond this, on each side, it is fixed to the posterior inferior angle of the parietal bone, and then forwards along the upper border of the petrous portion of the temporal bone. From the internal occipital protuber- ance to the postero-inferior angle of the parietal bone this border encloses the lateral blood sinus, whilst along the upper border of the petrous bone it encloses the superior petrosal sinus. The anterior border of the tentorium is sharp, free, and concave, and forms, with the dorsum sellae of the sphenoid, an oval opening (incisura tentorii), within which the mesencephalon is placed. Beyond the apex of the petrous portion of the tern- REMOVAL OF THE BRAIN 123 poral bone the two margins of the tentorium cross each other like the limbs of the letter X ; the free margin is carried forwards to be attached to the anterior clinoid process, whilst the attached border is continued inwards to be fixed to the posterior clinoid process (Fig. 59). Falx Cerebelli. — This is a small falciform fold of dura mater placed under the tentorium, which extends forwards in the mesial plane from the internal occipital crest (Fig. 58). It occupies the notch which separates the two lateral hemispheres Cerebral fossa' Superior longitudinal sinus cerebri Tentorium Tentorium cerebelli Fig. 58. — Coronal section through the Cranial Cavity in a plane which passes through the hinder part of the foramen magnum. The posterior part of the cranial cavity, from which the brain has been removed, is depicted. 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. Diaphragma Sellae. — This 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 passage of the infundibulum. An almost complete case of dura mater is thus formed for the pituitary body. Cranial Nerves. — The dissector should now turn his atten- tion to the cranial nerves, and study the manner in which 124 HEAD AND NECK they leave the cranial cavity. Each nerve carries out with it a covering derived from each of the three membranes of the brain. In the case of the optic nerve these remain distinct ; but in all the others the sheath derived from the arachnoid very soon disappears. 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. Optic nerve Olivary process of sphenoid Optic foramen Oculo-motor cranial nerve Trochlear cranial nerve Trigeminal cranial nerve Hypoglossal nerve— - Anterior clinoid process Posterior clinoid process jr- Abducent cranial nerve Anterior free edge of tentorium The aperture in front of the tentorium FlG. 59. — Aperture between the Dorsum Sella; and the anterior concave free margin of the Tentorium. (Hirschfeld and Leveille. ) The second or optic nerve (nervus opticus) — Figs. 59 and 60 — 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. The third or oculo-motor nerve (nervus oculomotorius) — Figs. 59 and 60 — 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 to the clinoid processes. The nerve enters the wall of the cavernous sinus, in which it will be afterwards traced. REMOVAL OF THE1 BRAIN 125 The minute thread-like fourth or trochlear nerve (nervus trochlearis) — Figs. 59 and 60 — 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. Infundibulum .Sixth nerve Fifth nerve Fourth nerve^ JM Auditory and facial nerves Glosso-pharyn- geal nerve"~ jf* Vagus nerve— Jjfii Hypoglossal nerve i Spinal accessory \j^ nerve Section through \ the medulla Lateral Optic nerve Internal carotid artery i\ . Posterior %r^communicating , Vj -Third nerve Jii_Posterior cerebral f^|\_Superior cerebellar Tentorium Basilar artery Vertebral artery Superior petrosal sinus Lateral sinus ;ipital sinus Superior longitudinal sinus Straight sinus divided FlG. 60. — Floor of the Cranium after the removal of the Brain and the Tentorium Cerebelli. 'I lie blood vessels forming the circle of Willis have been left in place. The fifth or trigeminal nerve (nervus trigeminus) — Figs. 59 and 60 — is composed of two parts — viz., a large, soft, sensory portion, consisting of loosely connected funiculi, and a small, firmer, motor portion, which lies upon the inner or deep 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. 126 HEAD AND NECK The sixth or abducent nerve (nervus abducens) — Figs. 59 and 60 — 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 auditory 7ierve (nervus acusticus), the facial nerve (nervus facialis) (Fig. 60), and the small pars intermedia (nervus intermedius), all enter the auditory meatus, where the pars intermedia joins the facial nerve. They are accom- panied by the auditory artery. The glosso- pharyngeal (nervus glossopharyngeus), the pneumo- gastric (nervus vagus), and the spinal accessory (nervus acces- sorius) pierce the dura mater over the internal jugular foramen in the order in which they have been named, from before backwards (Fig. 60). 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 acces- sory 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 foramen. The spinal acces- sory has already been noticed ascending from the spinal canal. The hypoglossal nerve (nervus hypoglossus) pierces the dura mater opposite the anterior condyloid foramen at two separate points, in the form of two distinct slips (Fig. 60). These unite in the foramen. Venous Blood Sinuses (sinus durae matris). — The blood sinuses which traverse the dura mater should next be ex- amined. 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 : — 1. Superior longitudinal. 6. Spheno-parietal. 2. Inferior longitudinal. 7. Circular. 3. Straight. 8. Superior petrosal. 4. Occipital. 9. Inferior petrosal. 5. Cavernous. 10. Basilar. 11. Lateral. 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 reduplica- tions 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. REMOVAL OF THE BRAIN 127 Torcular Herophili (confluens sinuum). — The superior longi- tudinal 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 protuber- ance. Here it is somewhat dilated, and then turns suddenly outwards, to form the lateral sinus of that side. This ex- pansion of the superior longitudinal sinus is termed the torcular Herophili, and it communicates by means of a trans- verse 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. 57. — 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. Straight Sinus (sinus rectus). — This venous channel ex- tends 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 the two layers of the falx on the upper surface of the tentorium. At its anterior extremity it receives the blood from the inferior longitudinal sinus and the vena magna Galeni. 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. 57). 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. 60. — This is a minute blood-channel, which is placed between the layers of the falx cerebelli. Above, it opens into the torcular Herophili, whilst below, at the foramen magnum, it bifurcates, and the two divisions not infrequently run forwards to join the lower i28 HEAD AND NECK end of the lateral sinus upon either side. Sometimes the occipital sinus is double throughout its whole course. Lateral Sinuses (sinus transversi) — Figs. 57 and 58. — These 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 com- mence one upon either side of the internal occipital protuber- ance, 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 longitudinal 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 temporal bone, it is joined by the superior petrosal sinus ; and leaving the tentorium, it suddenly curves downwards and inwards, in the deep furrow upon the mastoid portion of the temporal bone, and the jugular process of the occipital bone. Lastly, it turns forwards and disappears into the posterior compartment 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 with 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 co?idyloid vein (emis- sarium condyloideum), which joins it through the posterior condyloid foramen. Cavernous Sinus (sinus cavemosus) — Fig. 57. — 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, there- REMOVAL OF THE BRAIN 129 fore, at present, that this sinus lies upon the side of the body of the sphenoid bone. Circular Sinus (sinus circularis). — The circular sinus is formed 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 infundi- bulum of the pituitary body. Petrosal Sinuses — Fig. 57. — The petrosal sinuses 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 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. Basilar Sinus (plexus basilaris). — The basilar sinus 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 communicates below with the anterior intraspinal veins. Spheno-Parietal Sinus (sinus alae parvae). — The spheno- parietal sinus is a minute blood channel which runs in- wards on each side under shelter of the lesser wing of the sphenoid bone. Externally it commences in one of the 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. Petro Squamous Sinus. — Very frequently a small blood channel will be noticed running backwards along the petro-squamous fissure, in the angle between the squamous and petrous parts of the temporal bone. It is of importance in connection with the surgery of the middle ear. 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 — VOL. 11 — 9 130 HEAD AND NECK 1. The vertebral arteries. 2. The internal carotid arteries. 3. The meningeal arteries. Vertebral and Internal Carotid Arteries. — These vessels carry blood for the supply of the encephalon and the parts within the orbit. The i?tternal 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 the dura mater immediately below the foramen magnum, through which it enters the cranium. Here it passes between the highest denticulation of the ligamentum denticulatum and the hypoglossal nerve. 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 the middle meningeal, which comes from the internal maxillary artery. The others are small twigs, and, except in a well-injected subject, will not be easily made out. They are: — (1) anterior meningeal from the anterior ethmoidal artery; (2) the small meningeal from the internal maxillary artery; (3) some small branches 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 upon the deep surface of the great wing of that bone 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 branches which proceed from these trunks spread out widely and occupy the arborescent grooves on the deep surface of the cranial vault. Two veins accompany the middle meningeal artery. They pass through the foramen spinosum and unite in a common trunk which joins the pterygoid plexus. REMOVAL OF THE BRAIN T31 The anterior meningeal 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 and bone in the anterior fossa of the cranium. The small meningeal artery (ramus meningeus accessorius) is somewhat inconstant, and not infrequently springs from the middle meningeal. It enters the cranium through 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. The meningeal branches from the ascending pharyngeal artery Fig. 6i. — 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. ro. Optic recess of the third ventricle. o. Optic nerve. a'. Infundibulum with projection from anterior lobe upwards in front of it. 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. The meningeal veins may be regarded as being arranged in two sets : one set consists of small channels which pour their blood into the blood sinuses; the other set is composed of small veins which accompany the meningeal arteries and 132 HEAD AND NECK carry their blood to venous trunks on the exterior of the cranium. Pituitary Body (hypophysis cerebri) — Fig. 61. — The over- hanging margin of the diaphragma sellas should be freely cut in two or three places, and the pituitary body carefully dis- lodged 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 downwards, and with its long axis directed transversely. Further, it may be noticed to consist of a large anterior lobe, and a smaller posterior lobe. The former of these is hollowed out behind so as to form a concavity for the lodgment of the latter. If a vertical section be made through the bod)7, the line of separation between the two lobes is very distinct. The infundibulum which connects the pituitary body with the tuber cinereum of the brain is continued into the posterior lobe, and is in no way structurally continuous with the larger anterior lobe, although a surface inspection of the body is apt to give the dissector that impression (Fig. 61, i). Thus, even* in the adult, we have a clue to the different modes of development of the two lobes. The posterior lobe is derived from the brain, whilst the anterior lobe is an offshoot from the primitive buccal cavity. The dissectors of the head and neck must now prepare for the changing of the position of the subject. Some tow, or a sponge, soaked in a mixture of methylated spirit and carbolic acid (to which a little formalin may be added with advantage), 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 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. 62). During the four days that the body is allowed to lie in this position, the dissectors of the head and neck have DORSAL ASPECT OF THE TRUNK 133 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 fascice 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 supply. The levator anguli scapulae and the omo-hyoid are to be regarded as common property. The dissectors of the upper limbs are allowed two days to complete this work. 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 Fig. 62. 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 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 outwards towards the mastoid process, press deeply into the neck immediately below the occiput, and in the middle line ; here the bifid i34 HEAD AND NECK extremity of the massive spinous process of the axis vertebra can be felt. In the middle line of the neck is the nuchal furrow. Carrying the finger downwards in this, the posterior edge of the ligamentum nuchae can be distinguished, but the short spines of the third, fourth, and fifth cervical vertebrae as a rule can hardly be detected. The spines of the sixth and seventh cervical vertebrae, however, are usually very prominent. Reflection of Skin (Fig. 62). — Three incisions are required — (1) Along the middle line, from the external occipital protuberance to the prominent spine of the seventh cervical vertebra. (2) From the lower end of this mesial incision transversely outwards to the inner border of the acromion process of the scapula. (3) From the upper end of the primary incision transversely outwards over the occiput to the ear. The quadrilateral flap of skin thus marked out must be raised from the subjacent superficial fascia. On reaching the side of the neck, the head must be held well over to the opposite side. Here, unless the dissector keep close to the skin, there is a danger of the knife slipping in under the posterior border of the sterno-mastoid muscle. Superficial Nerves. — The nerves to be looked for in the superficial fascia, 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 : — . ( 1, Great occipital. *rom posterior j 2 Terminal twi s of the internal branches primary divisions. (^ of the ^ fourthj and fifth nerves From anterior f 1. Small occipital, primary divisions. ^ 2- Great auricular. Dissection. — The main trunk of the great occipital nerve may be found piercing the trapezius muscle about an inch below the occipital protuber- ance, and about half an inch external to the m-esial plane. The fascia at this spot is usually very dense, and the readiest method to adopt in ex- posing the nerve is to carefully shave it off in slices until the plane of the muscle is reached. The great occipital (nervus occipitalis magnus) — Fig. 63 — is the internal branch of the posterior primary division of the second cervical nerve, and its branches of distribution have already been noticed, spreading out on the back of the scalp (p. no). As it becomes superficial, it joins the occipital artery, and both are directed upwards to supply the scalp. The terminal twigs of the internal branches of tJie posterior divisions of the third, fourth, and fifth cervical nerves enter the DORSAL ASPECT OF THE TRUNK i35 superficial fascia close to the mesial plane, and then turn transversely outwards to supply the skin of the neck. The third cervical branch sends in addition a large twig upwards to the integument over the occiput. This nerve runs along the inner side of the great occipital, and, as a rule, Epicranial aponeurosis Great occipital nerve Occipital artery Posterior hell}- of occipi to-frontal is Complexus Retrahens aariculani Splenius capitis Posterior auricular nerve — Parotid gland Small occipital nerve Sterno-inastoid Great auricular nerve Levator anguli scapula; Kk;. 63. — Superficial dissection of the Back of the Neck. communicates with it. From its distribution, it is frequently termed the third occipital nerve (nervus occipitalis tertius). Dissection. -The small occipital nerve will be found by dividing the fascia along the posterior border of the sterno-mastoid muscle. The small occipital nerve (nervus occipitalis minor) — Fig. 63 — springs from the anterior primary division of the second cervical nerve, and runs upwards to assist in the supply of the integument over the occiput. Its terminal twigs have already been dissected in the superficial fascia of the scalp (p. 110). 11— 9 a 136 HEAD AND NECK Occasionally the 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-mastoid muscle very obliquely. 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. The great auricular ?ierve (nervus auricularis magnus) — Fig. 63 — is a branch of the cervical plexus, and takes origin from the second and third cervical nerves. Turning round the posterior border of the sterno-mastoid muscle, it proceeds upwards and forwards on the surface of that muscle towards the lobule of the 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 dissection 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 auricle ; 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 mastoid branch extends upwards upon the mastoid process, wrhere 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 very 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 trapezius and sterno-mastoid, two contiguous muscles, taking a somewhat oblique course, will be observed. The higher of these is the splenius capitis, and the lower is the levator anguli scapulae. These, together with the posterior border of the sterno-mastoid, must be cleaned. In carrying out this dissection the dissector must proceed with some degree of caution ; and above all, 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 scapulae 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 spinal accessory nerve, and two or three cervical nerves crossing from the posterior border of the sterno-mastoid to the trapezius, should be dissected out. DORSAL ASPECT OF THE TRUNK 137 Posterior Triangle. — The upper part of the posterior triangle which is thus displayed is bounded in front by the posterior border of the sterno- mastoid, and behind by the anterior border of the trapezius. The apex, which is directed upwards, is formed at the superior curved line of the occipital bone by the apposition of the occipital attachments of these two muscles. The floor 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 — (1) 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. Spinal Accessory Nerve (nervus accessorius). — This im- portant nerve appears in the posterior triangle by emerging from the substance of the sterno-mastoid muscle. It crosses the triangle obliquely, running from above downwards and backwards, and finally disappears under the anterior border of the trapezius. Cervical Branches to the Trapezius. — These are two or three nerves which spring from the third and fourth cervical trunks. They enter the posterior triangle by leaving the shelter of the sterno-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 arc somewhat smaller than the spinal accessory, is sufficient to distinguish them from that nerve. They finally disappear under the anterior border of the trapezius. 138 HEAD AND NECK Dissection. — On the second day after the subject has been placed on its face, the trapezius may be reflected. This must be done in conjunction 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 vertebrae. The muscle can now be raised and thrown outwards 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 scapuhe 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, passing downwards under cover of this muscle, the ne7've to the rhomboids and the posterior scapular artery will be found. Almost invariably the nerve to the rhomboids gives one or two twigs to the levator anguli scapulae. Levator Anguli Scapulae (levator scapulae). — This muscle arises by four slips from the posterior tubercles of the transverse processes of the upper four cervical vertebrae. 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 scapulae comes from the third and fourth cervical nerves, and also from the nerve to the rhomboids. Transversalis Colli Artery. — This vessel 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 suprascapular artery and nerve, can now be displayed by dissecting towards the upper margin of the scapula. This dissection must be carried out 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. Posterior Belly of the Omo-hyoid. — This 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 connexions of the omo-hyoid will be studied in the dissection of the triangles of the neck after the body has been turned. DORSAL ASPECT OF THE TRUNK 139 Suprascapular Artery and Nerve. — The suprascapular artery will be noticed to enter the supraspinous fossa of the scapula, by passing over the suprascapular ligament. The suprascapular ?ien*e, on the other hand, is carried into the fossa under cover of the ligament. The second day's 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 the first day, all the muscles, fascia, 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 fibres, which are placed upon the posterior aspect of the thoracic wall. The serratus posticus superior (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 nuchae ; (2) from the spinous process of the seventh cervical vertebra ; and (3) from the spinous processes of the upper two or three dorsal vertebrae. From this origin it proceeds obliquely downwards and outwards, 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. The serratus posticus inferior (serratus posterior inferior) will be brought 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 vertebrae, 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 serratus posticus inferior is directed upwards and outwards, i4o HEAD AND NECK and is inserted by four digitations into the lower borders of the four lower ribs. Vertebral Aponeurosis. — The connections of the vertebral 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 vertebrae 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 of the apo- neurosis to the spines of the dorsal vertebrae and to the angles of the ribs will be rendered manifest. In the next place, note that when it is followed in an upward and down- ward direction the fascia presents a different relation to the two serrati muscles. Superiorly, it proceeds under cover of the serratus posticus superior and the splemus muscles, and is lost in the deep layers of fascia of the neck ;. 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. 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 lamellae, 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 outwards 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 spinas 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 DORSAL ASPECT OF THE TRUNK 141 the erector spinae, where this lies upon the dorsum of the sacrum. The erector spinas 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 of the transverse processes of the lumbar vertebrae, may be seen. Note, however, that whilst the main attachment of Serratus post. inf. ^- — Erector spinae Quadratus lumborum Trans versalis (---Kg Internal \ f| oblique \ * External \ oblique \ Fascia transversalis""" FlG. 64. — Diagram to show the Connections of the Lumbar Fascia. 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 muscle should be pushed inwards. This brings into view the third or (Ulterior 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. 142 HEAD AND NECK The lumbar fascia, therefore, is formed at the outer borders of the erector spinae and quadratus lumborum muscles by the union of these three lamellae. Superiorly, it is attached to the last rib ; inferiorly, it is fixed to the 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 divided 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 ligamentum nuchas, and from the spines of the seventh cervical and upper six dorsal vertebrae. From this the fibres pass obliquely upwards and outwards in the form of a thick, flat muscle, which soon divides into a cervical 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 spinas 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 cervical nerves which pierce it. When 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 of the occipital bone. The floor of this little space is formed by the superior oblique muscle of the head, and it is traversed by the occipital artery, which in this part of its course gives off its arteria princeps cervicis branch. DORSAL ASPECT OF THE TRUNK 143 Next remove the vertebral aponeurosis and turn the latissimus dorsi, the serratus posticus inferior, and the superficial lamella of the lumbar fascia outwards. Erector Spinae (sacro -spinalis). — Under this name we 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 which may be considered the starting-point. This bulky mass sends a pointed process downwards on the back of the sacrum, and has the following origin: — (1) from the spines of the lower two dorsal, all the lumbar, and all the sacral vertebrae; (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-iliac ligament ; (4) from the posterior fifth of the iliac crest. In great part the superficial 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 spinae 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 longissiinns dorsi ; and the inner column, which only becomes quite distinct as we approach the upper part of the dorsal region, is called the spifialis dorsi. Ilio-costalis (ilio-costalis lumborum). — The intermuscular interval between this muscle and the longissimus 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 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 the1 outer column of the erector spinae upwards. This muscle is called the musculus accessorius. i44 HEAD AND NECK Musculus Accessorius (ilio-costalis dorsi). — The musculus accessorius, therefore, 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 in- serted 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 vertebrae. Longissimus Dorsi. — The longissimus dorsi is the largest of the three divisions into which the erector spinae 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 skull by two muscular continuations termed respectively — (i) the transversalis cervicis, and (2) the trachelo-mastoid. Transversalis Cervicis (longissimus cervicis). — The trans- versalis cervicis muscle takes origin in the upper dorsal region, by four or five slips from the transverse processes of a corresponding number of the upper dorsal vertebrae, and it gains insertion into the posterior tubercles of the transverse processes of all the cervical vertebrae, with the exception of the first and the last. Trachelo-mastoid (longissimus capitis). — The trachelo- mastoid is prolonged upwards in the neck under cover of the splenius. Its origin from the transverse processes of three or four of the upper dorsal vertebrae is intimately associated with that of the transversalis cervicis. In addition to its DORSAL ASPECT OF THE TRUNK 145 dorsal origin, however, it also draws three or four slips from the articular processes of a like number of the lower cervical vertebras. The narrow fleshy band which results is inserted into the back part of the mastoid process, under cover of the splenius capitis and sterno-mastoid muscles. Spinalis Dorsi. — This, the innermost, shortest, and weakest of the three columns, is in some respects the most difficult to define. Below, it is intimately blended with the longissimus dorsi, but it may be regarded as taking origin by four tendons from the spines of the two upper lumbar and two lower dorsal vertebrae. These, by theip union, form a small muscle, which is inserted by a series of slips into a very variable number of the upper dorsal spines. It is closely connected with the subjacent semispinalis dorsi. Dissection. — The occipital artery has already been observed crossing the apex of the posterior triangle (p. 137), and its terminal branches have been dissected as they ramify in the scalp (p. 112). The second part of the vessel, which extends from under shelter of the mastoid process, along the superior curved line of the occipital bone, to the point where it pierces the trapezius to become superficial, can now be fully exposed. To effect this, the trachelo-mastoid must be divided a short distance below its insertion, and along with the splenius capitis thrown upwards as far as possible. Occipital Artery (arteria occipitalis). — The second part 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 (enumer- ating them in order from the vessel outwards) — (1) 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.1 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 insertion of the superior oblique and the complexus. 1 It is not uncommon to find the artery at this point of its course nearer It may pass backwards between the splenius and the trachelo- mastoid. VOL. II — 10 1 46 HEAD AND NECK The following branches may be traced from this portion of the occipital artery : — i. Arteria princeps cervicis. 2. Mastoid. 3. Muscular. The arteria prijiceps cervicis (ramus descendens) is a twig of some size, which passes inwards to the outer border of the complexus. Here it divides into a superficial and a deep branch. The former ramifies on the surface of the com- plexus, whilst the latter pursues a deeper course. It sinks under cover of that muscle, and will be followed to its destina- tion at a later stage in the dissection. The small mastoid artery (ramus mastoideus) enters the posterior cranial fossa through the mastoid foramen, and supplies the dura mater and cranial wail in this region. 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 vertebral and deep cervical veins. The outermost of the occipital veins effects, as a general rule, a communication (emissarium mastoideum) with the lateral sinus through the mastoid foramen. Dissection. — In cleaning the complexus muscle, and in defining its attachments, care must be taken of the 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, runs little risk of injury, but the others are liable to be overlooked. They all emerge from the substance of the muscle close to the mesial plane. Complexus. — The complexus muscle, placed in the cervical and upper dorsal regions, inclines obliquely upwards and inwards to its insertion into the occiput. It arises by tendin- ous slips from the transverse processes of the upper 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, some- what oval impression between the superior and inferior curved lines of the occipital 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, which is to a certain extent distinct from the general mass, and is divided into two DORSAL ASPECT OF THE TRUNK i47 bellies by an intermediate tendon, is frequently designated the biventer cervicis. Dissection. — The com plexus must now be reflected by detaching it from the occiput and throwing it outwards. This dissection requires 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 Posterior occipito- atlantoid ligament Sub-occipital nerve Great occipital nerve — J Vertebral artery Anterior primary division of spinal nerve terior arch of atlas igamentum nucha; Posterior primary divisions of spinal nerves Fig. 65. L— Seventh cervical vertebra -Dissection of the Ligamentum Nucha: and of the Vertebral Artery in the Neck. nerves and the anastomosis between the arteria princeps cervicis and arteria profunda 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 contact with a mesial fibrous partition which separates it from the corre- sponding muscle of the opposite side. This is the ligamentum nuchae. Ligamentum Nuchae (Fig. 65). — This is a strong fibrous partition placed in the mesial plane between the muscles on each side of the back of the neck. It represents a powerful clastic structure in quadrupeds, which helps to sustain the weight of the dependent head. In man, however, there is not much 11 — 10 a 148 HEAD AND NECK elastic tissue developed in connexion 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 somewhat triangular. By its base it is attached to the crest of the occipital bone ; by its anterior border it is fixed by a series of slips to the posterior tubercle of the atlas, and to the bifid spines of the cervical vertebrae in the intervals between their tubercles. Its apex is formed by its attachment 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 deep cervical artery springs from the superior intercostal 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 upon 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 nerves of the back must now be examined. They are the posterior primary divisions of the spinal nerves. With four 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 these nerves successively in the cervical, dorsal, and lumbar regions. It is well, however, to defer the dissection of the sacral and coccygeal nerves until the multifidus spinae muscle has been studied. Cervical Region. — Here the posterior primary divisions of the spinal nerves are eight in number. The posterior division of the first or sub-occipital nerve, which, as we have seen, fails to divide into an external and an internal branch, DORSAL ASPECT OF THE TRUNK 149 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 vertebrae. The posterior primary divisions of the succeeding six cervical nerves arise from the corresponding 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 spinae. The internal branches are not all distributed alike, nor indeed do they present the same relations. Those from the second, third, fourth, and 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 neigh- bouring 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. no). The internal branch of the third nerve likewise sends an offset to the occipital portion of the scalp (p. 135). 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 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 out- wards under cover of the middle column of the erector spinas 150 HEAD AND NECK 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 ex- hausted in the supply of the middle and outer columns of the erector spinae, and the levatores costarum ; the loiver 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 cutaneous distribution of these nerves has already been examined by the dissector of the upper limb. The internal branches are also distributed differently in the upper and lower portions of the dorsal region. The lower five or six are very 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 backwards, and become superficial. In passing towards the surface they pierce the splenius, rhomboideus, and trapezius muscles, and thus gain the superficial fascia, where they have been already dissected. Lumbar Region. — The internal bra?iches of the posterior divisions of the five lumbar nerves 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 branches 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 nerves are of large size, and become cutaneous by piercing the superficial lamella of 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 corresponding 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, however, minute twigs may be discovered, in a well-injected subject, passing DORSAL ASPECT OF THE TRUNK 151 backwards from the vertebral artery in the intervals between the transverse processes, and also in the sub-occipital space. These supply the muscles, and anastomose with the other arteries in this region. In the dorsal regio?i the dorsal branches of the aortic inter- costal 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 ligament. 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 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 oblique course. As the term given to the whole system implies, these slips for the most part stretch from the transverse processes upwards and in- wards to be inserted into the spinous processes of the vertebrae. The superficial slips pass over five or more vertebrae and connect distant points on the column ; the deeper slips are shorter, and the most deeply placed of all merely pass be- tween contiguous vertebrae. The superficial layer is termed the semispinalis muscle; the intermediate layer is called the multifidus spituc ; whilst the deep stratum is composed of a series of short muscles, termed the rotatores spincc. In the dorsal and cervical regions we find the three layers ; in the lumbar and sacral regions the semispinalis is absent. n—10 6 152 HEAD AND NECK Dissection. — The semispinalis muscle is already in great part exposed. To display it fully, however, it is necessary to remove the spinalis dorsi muscle. Semispinalis Muscle. — This muscle may be 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 vertebrae (viz., from the sixth to the tenth). It is inserted into the spines of the upper four dorsal and lower two cervical vertebras. The semispinalis colli lies under cover of the complexus. It springs from the transverse processes of the upper five dorsal vertebrae, and is inserted into the spines of four cervical vertebrae (viz., from the second to the fifth). The slips composing the semispinalis muscle stretch over five or more vertebrae. Dissection. — The multifidus spina? is of great extent. Beginning in the sacral region, it passes upwards as far as the axis vertebra. It is weakly developed in the dorsal region, but is strongly marked in the 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 spinas 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-iliac 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 vertebrae, and in the cervical region from the articular processes of at least four of the lower cervical vertebrae. The bundles which compose the multifidus pass over two, three, or four vertebrae, and are inserted into the whole length of the various spinous processes of the movable vertebrae as high up as the axis. Rotatores Spinae (submultifidus). — These 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 DORSAL ASPECT OF THE TRUNK 00 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). Interspinals and Intertransversales. — The dissector should next examine the minute interspinous and intertrans- verse 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 atlas. In the lumbar region they are also well marked and in pairs ; here they are attached to the whole length of the spinous processes. The ifitertransverse muscles (intertransversarii) 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 fan-shaped muscles, which pass from the transverse processes to the ribs. To bring them thoroughly into view, the longis- simus 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 downwards 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 emerging from 154 HEAD AND NECK the posterior sacral foramina ; the fifth appears at the lower end of the sacral canal. To expose the upper three the multifidus spinae 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 multi- ndus spinae. 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 posterior division of the fourth sacral nerve. Branches proceed from the loops thus formed to the surface of the great sacro-sciatic ligament. Finally they become superficial by piercing the gluteus maxi- mus 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 communi- cating 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. Posterior Division of the Coccygeal Nerve. — This 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 situ- ated upon the superficial aspect of the neural arches of the vertebrae, subjacent to the multindus 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. DORSAL ASPECT OF THE TRUNK *55 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-occipital triangle, and to the display of the spinal cord, its membranes, nerve-roots, and blood-vessels. In the event of the dissector being pushed for time, it is better that he should proceed at once to expose the spinal cord, and defer the dissection of the sub-occipital region until the head and neck has been removed from the body. Arteria princeps cervicis Occipital artery Transverse process of atlas Arteria profunda cervicis Great occipital nerve Lywa>^ Superior oblique fflllJl III fel*r-r^ muscle Rectus capitis posticus minor Sub-occipital nerve Vertebral artery Posterior arch of atlas Rectus capitis posticus major Inferior oblique muscle Spine of axis Semispinalis colli Fig. 66. — Dissection of the Sub-occipital Region. Note that in this specimen the occipital artery is superficial to the trachelo-mastoid muscle. Sub-Occipital Space. — The sub-occipital space is a small triangular area, exposed by the reflection of the complexus muscle. It is boutided by three muscles — viz., (i) the rectus capitis posticus major, which forms its upper and inner boundary; (2) the obliquus 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 i56 HEAD AND NECK 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 dissection in conse- quence is rendered somewhat difficult. Rectus Capitis Posticus Major. — This muscle springs by a pointed origin from the spine of the axis, 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. Rectus Capitis Posticus Minor. — This 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 foramen magnum. Obliquus Capitis Inferior. — This muscle stretches from the bifid spine of the axis, from the extremity of which it takes origin, to the posterior tubercle of the transverse process of the atlas. The great occipital nerve will be seen hooking round its lower border. Obliquus Capitus Superior. — This small muscle springs from the transverse process of the atlas, and is inserted into the occipital bone in the interval between the curved lines. Posterior Division of the Sub -Occipital Nerve. — 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 communicating, and sometimes a cutaneous filament. The communicating branch generally proceeds from the nerve to the obliquus capitis inferior, and joins the great DORSAL ASPECT OF THE TRUNK 157 occipital nerve. The cutaneous bra?ich 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 for- wards 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 laminae and spinous processes upon either side. The multifidus spinae must also be completely removed from the back of the sacrum. At the same time the posterior primary divisions must be retained, so that their continuity with the various spinal nerve- trunks may be afterwards established. The posterior wall of the spinal canal should now be removed in one piece by sawing through the laminae of the vertebrae on either side, and dividing the ligamenta subflava, 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 attend to the following points: — (1) the cut should be directed through the laminae close to the inner side of the articular processes ; (2) the saw must be used in an oblique plane, so that the cut through the lamina.1 slants slightly inwards ; (3) in cutting through the cervical laminae the head and neck should hang over the end of the table, and be pressed as far 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 laminae and spinous processes which are thus removed are connected with each other by the ligamenta subflava and the supraspinous and interspinous ligaments. They should therefore be laid aside for the present. A description of these ligaments will 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 stretching the specimen. Between the dura mater and the walls of the spinal canal, ihe dissector 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- fatty material, great numbers of large veins and minute arteries are found ramifying upon the walls of the canal. 158 HEAD AND NECK 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 each of the three regions. Each spinal artery may be looked upon as giving off three main twigs : of these, one, termed the pre-laminar branch, a very small twig, ramifies upon the deep surface of the neural arches and ligamenta subflava ; another, the neural branch, can be followed to the dura mater, which it pierces immediately above the point of exit of the corresponding spinal nerve; whilst the third, the post-central branch, 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 so as to form a series of cross anastomoses with the corresponding vessels of the opposite side. 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 com- plicated 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 by wide 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. DORSAL ASPECT OF THE TRUNK 159 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 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. 67. — 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 membranes are directly continuous with the corresponding investments 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 necessary, also, to carefully define the numerous lateral prolongations which the membrane gives to the spinal nerves. Dura Mater Spinalis — Fig. 67. — 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 i6o HEAD AND NECK uniform ; in the cervical and 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 terminate, 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 ; below, 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 relations 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, however, 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 foramen 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 periosteum 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 connexion 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 cranial 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 does not lie free within the vertebral canal, although its attachments are of such a nature that they do not in any way interfere with DORSAL ASPECT OF THE TRUNK 161 the free movement of the vertebral column. On either side the spinal nerve -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 connexion of any Dura mater Arachnoid Ligamentum denticulatum Arachnoid Posterior nerve-root Spinal ganglion Anterior division of nerv. Posterior divisiot of nerve — — Dura mater Anterior nerve-root (cut) Posterior nerve-root Anterior nerve-root (cut) Ligamentum denticulatum Pia mater Anterior nerve-root Fig. 67. — Membranes of the Spinal Cord, and the mode of origin of the Spinal Nerves. kind exists between the dura mater and the neural arches ol the vertebrae or ligamenta subflava. Dissection. — The tube of dura mater may now be 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. 67. The deep surface of the dura, which is turned towards this space, is smooth, moist, and polished. Upon either side the dissector will notice the VOL. II — 11 1 62 HEAD AND NECK series of apertures of exit for the roots of the spinal nerves. These are ranged in pairs opposite each intervertebral foramen. The subdural space is prolonged outwards for a short distance upon each of the nerve-roots, and has a free communication with the lymph paths present in these nerves. 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 special and distinct sheath. When 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 fact that the two sheaths are closely held together on the outside by inter- vening connective tissue, which can be removed with a little careful dissec- tion. When this is done, the two tubular sheaths will be observed to remain distinct as far as the ganglion on the posterior root of the nerve. At this point they blend with each other. Arachnoidea Spinalis — Fig. 67. — The arachnoid resembles the dura mater in forming a loose, wide investment for the spinal cord. Unlike the dura, however, it is remark- able 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 collection of long nerve-roots which constitute the Cauda 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 blowpipe. Above, the arachnoid mater becomes continuous at the level ot the foramen magnum with the corresponding membrane which clothes the brain, whilst, laterally, it is prolonged outwards upon the various nerve -roots, thus contributing to each a tubular sheath. Sub-arachnoid Space (cavum subarachnoideale) — Fig. 67. — 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 septa partially subdivide the spinal sub-arachnoid space into compartments. One of these septa is a mesial partition called the septuni 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 represented by a number of strands passing between the two membranes ; in the lower part of the cervical region and in the dorsal region DORSAL ASPECT OF THE TRUNK 163 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. It is thicker and denser than the corre- sponding membrane which envelops the brain. This is largely due to the addition of an outer fibrous layer in which the fibres chiefly run in the longitudinal direction. The pia mater is firmly attached to the surface of the spinal cord, and in front it sends a fold into the antero-median fissure of the cord. The septum which occupies the postero-median fissure of the cord is likewise firmly attached to its deep surface. Anteriorly, in the mesial plane, the pia mater is thickened in the form of a longitudinal glistening band, which receives the name of the linea sple?ide?is. Of course, this can only be seen after the cord has been removed from the spinal canal. The blood vessels of the cord lie between the two layers of the pia mater, and the various spinal nerves receive from it closely fitting sheaths which blend with their connective-tissue sheaths. Ligamentum Denticulatum — Figs. 67 and 68. — This 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 be- tween 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 margin is widely serrated or denticulated. From twenty to twenty-two denticulations may be recognised. They occur in the intervals between the spinal nerves, and, pushing the arachnoid before them, they are attached by their pointed extremities to the inner surface of the dura mater. The ligamenta denticulata partially subdivide the sub- arachnoid space into an anterior and a posterior compart- ment. 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. n — ll a 164 HEAD AND NECK By means of the ligamentum denticulatum of either side, the spinal cord is suspended 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 conns medullaris. From the extremity of this, a slender filament, termed the filuni ter- Ligamentum denticulatum ?ninale or central liga- FlG. 68. — Lateral view of the Spinal Cord, Dura Mater, and Ligamentum Denticula- tum. (Hirschfeld and Leveilte. ) ment, is prolonged downwards. In the female the average length of the spinal cord is 43 cm. ; in the male it is 45 cm. Throughout 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 lumbar enlargements. From these expansions proceed the nerves which supply the upper 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 vertebra. The Iwnbar swelling (intumescentia lumbalis) begins at the level of the tenth dorsal vertebra, and attains its maximum transverse diameter (n to 13 mm.) opposite the last dorsal vertebra. Below, it rapidly tapers into the tapering conus medullaris. Filum Terminate. — This delicate thread-like filament lies amidst the numerous long nerve-roots which occupy the lower DORSAL ASPECT OF THE TRUNK 165 L.V.I. Conus medullaris part of the spinal canal, and it can readily be detected from these (1) by its silvery glistening appearance, and (2) by its continuity with the extremity of the conus 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 sub- stance for a like distance, the filum terminale is chiefly composed of pia mater carried down- wards 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 tube of dura mater, and re- ceives an invest- ment from it, and, finally, reaching the lower end of the sacral canal, it ter- minates byblending 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 the filum terminale internum, the portion outside is distinguished as the filum termi?iale externum. Spinal Nerves. — Thirty-one spinal nerves take origin from each side of the spinal cord. These are classified into five S.V.I. Fig. 69. Coccyx -Sagittal section through the lower part of the Vertebral Canal. 1 66 HEAD AND NECK groups, according to the vertebrae with which they are associ- ated. The dorsal, lumbar, and sacral nerves correspond in number with the number of vertebrae 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 corresponds. 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 the sub-occipital fierue. There is only one coccygeal nerve on each side. Spinal Nerve-Roots — Figs. 67 and 70. — 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 distin- guished by possessing an oval ganglion, termed the spinal root-ganglion (ganglion spinale). There is, likewise, a wide physiological difference between the two roots, — the posterior root is composed of afferent fibres, the anterior root consists of efferent fibres. Immediately beyond the ganglion the two roots unite to form the spinal nerve-trunk, which, in con- sequence, contains a mixture of both efferent and afferent nerve-fibres. The mode of attachment of the two nerve-roots to the side of the spinal cord is somewhat different in the two cases. In each instance they are attached by several separate fasci- culi (fila radicularia), which spread out from each other as they approach the cord. 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 portion of the spinal cord which stands in connection with a pair of nerves receives the name of a "segment of the cord." The size of the nerve-roots will be observed to differ greatly. The lower lumbar and upper sacral nerve-roots are 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 DORSAL ASPECT OF THE TRUNK 167 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 differences. 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 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 Fig. 70. — A segment of the spinal cord ; anterior aspect. (Schwalbe, after Allen Thomson. ) 1. Anterior median fissure. 2. Posterior median fissure. 3 and 5. Fasciculi of anterior nerve-root. 4. Postero-lateral groove. 6. Posterior nerve-root. 6'. Spinal ganglion. 7. Anterior primary division. 7'. Posterior primary division. are exceedingly long, and descend vertically from the lower portion of the cord, in the form of a bunch or leash which, from its appearance, 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 foramina ; whilst the two divisions of each of 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, however, follow a different course. The sub-occipital emerges by passing over the neural arch of the atlas, and the 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. 71). i68 HEAD AND NECK Dissection. — The nerve-roots of one or two spinal nerves in each region should be followed into the corresponding intervertebral foramina. 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 spinal nerve-trunk, and the division of the latter into the anterior Filum trrminale Cauda equina Dura mater Filum terminale Fifth sacral nerve Coccygeal nerve Fig. 71. — Sacral Canal opened up from behind to show the Sacral Xerve-roots (lower part of Cauda Equina) and the Membranes in relation to them. (After Testut. ) and posterior primary divisions, can thus be studied. An attempt should also be made at the same time to discover the minute ramus meningeus. This is a fine twig which is formed 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. 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. DORSAL ASPECT OF THE TRUNK 169 They are usually found upon the posterior roots of all the nerves, although occasionally the ganglion may be absent in the case of 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 the first two cervical nerves, on the neural arches of the atlas and axis. The nerve-trunk is exceedingly short ; indeed, it almost immediately divides into its anterior and 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 distinctly 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. 148). 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 preservative fluid. If, on the other hand, it is soft and not fit for proper preservation, 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. Wherever 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- i7o HEAD AND NECK 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 a?iterior and posterior spinal arteries which spring from the vertebral, and a series of lateral spinal or neural arteries which reach the side of the spinal cord and are derived from different sources in each region. In the ?ieck they come from the spinal branches of the vertebral, ascending cervical, and deep cervical arteries ; and in the dorsal and lumbar regions 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 anteromedian artery. The other four are 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 ant ero -median 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 antero-median artery 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 post ero- 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 artery. Lower down their continuity is maintained by twigs which reach them on the posterior roots of the spinal nerves from the lateral spinal arteries. It may be regarded as a rule, that where a lateral spinal artery gives a branch to one of the postero-lateral arterial trunks, it does not furnish another to the antero-median arterial trunk. In this way different lateral spinal DORSAL ASPECT OF THE TRUNK 171 arteries are in connexion with the longitudinal trunks on the anterior and posterior 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 correspond with that of the arteries. They are very tortuous, and form a plexus with elongated meshes. Six more or 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 four are lateral, and are situated two on either side of the cord in relation respectively to the anterior and posterior 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. Linea splendens. Single anterior spinal artery in mesial plane. Anterior nerve - roots smaller than posterior, and springing by fasciculi which emerge from 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. the cord, not in a continuous ; 3. Posterior nerve-roots larger than straight line, but irregularly the anterior, and provided with over an area of some width. 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 methyl- ated spirit, to which a small amount (4 per cent) of formalin has been added. 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. 172 HEAD AND NECK It is partially subdivided into a right and a left half by two median clefts, — one upon the anterior, and the other upon the posterior aspect. These clefts are called the antero- media?i and the posteromedian 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, Postero-mesial column Posterior column /Postero-lateral column Entering posterior nerve-root Formatio reticularis Lateral column Central canal Spinal accessory root Anterior horn of grey matter Posterior horn of grey matter Spinal accessory root — Anterior nerve-root Anterior column Fig. 72. — Transverse section through the upper part of the Cervical Region of the Cord. in addition to its being deeper and narrower, contains only a single septum of neuroglia. 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 between 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 DORSAL ASPECT OF THE TRUNK 173 already observed, these fascicles emerge over a broad area, which corresponds in its width to the thickness of the sub- jacent 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 column (funiculus posterior) is placed between the postero-median fissure and the postero-lateral furrow; the lateral colum?i (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 colmnn (funiculus anterior) includes that district which extends from the antero- median fissure to the emergence 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. Grey 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, the con- cavity 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 inter- vening strip of white matter which is termed the anterior white commissure (commissura anterior alba). In the grey com- missure 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 portion of the grey commissure which lies behind the itral canal is called the posterior grey commissure (commissura posterior); the portion in front receives the name of anterior grey commissure (commissura grisea anterior). 174 HEAD AND NECK 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 transverse grey commissure are termed respectively the posterior and the anterior cornna of grey matter (columnae grisese). These can be distinguished from each other at a glance. The a?iterior cornu is short, thick, and very blunt at its extremity. Further, its extremity falls short of the surface of the cord, and is separated from it by a tolerably thick 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 cornu, 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 cornu ; 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 translucent appearance. It is termed the substantia 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 size of the nerves attached to a particular part of the cord, 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 of grey matter is not the same in all regions. In the dorsal region both horns are narrow, although the distinction between the anterior horn DORSAL ASPECT OF THE TRUNK *75 B and the more at- tenuated posterior horn is still suffici- ently manifest. In the cervical region the contrast be- tween the cornua is most marked ; the anterior horn is very thick in com- parison with the much narrower posterior horn. In the lumbar region, on the other hand, the difference in the thickness of the two horns is not nearly so apparent owing to a broad- ening 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 pro- minent triangular projection juts out from the external aspect of the cres- centic mass of grey matter nearly opposite Postero-median fissure Para-median septum Column of Goll Column of Burdach Substantia Rolandi Lateral column Central canal Anterior horn Grey commissure Antero-median fissure Fascicles of anterior nerve-root Anterior column Postero-median septum Substantia Rolandi Posterior vesicular column Lateral horn Anterior horn Antero-median fissure — Postero-median septum Entering posterior nerve-root _\ Posterior vesicular column Lateral horn Antero-median fissure Postero-median fissure Fig Antero-median fissure 73. — Transverse sections through the Cord in different regions. A. Cervical Region ; B. Mid -dorsal Region ; C. Lower Dorsal Region ; D. Lumbar Region. the grey commissure. This is called 176 HEAD AND NECK the lateral horn (Fig. 73, B and C). It disappears in the region of the cervical and lumbar swellings, but, curiously enough, it again becomes evident both in the upper cervical and in the lower sacral regions of the cord. Below the dorsal region of the cord the postero-median cleft becomes gradually shallower and the antero-median cleft deeper, until in the sacral region they are found to present a very nearly equal depth. The central canal, in correspondence with this change, comes to occupy the centre of the cord in its lower part. White Matter of the Spinal Cord. — The white matter forms a thick coating on the outside of the fluted column of Tract of Goll Postero-median fissure Postero-lateral groove Crossed pyramidal_ tract Direct pyramidal tract IYact of Burdach _ Substantia gelatinosa Rolandi Direct cerebellar tract Fascicle of origin of the spinal accessory nerve \ntero-median furrow FlG. 74. — Transverse section through the upper cervical part of the Cord of a full-time Foetus treated by the Pal-Weigert process. grey matter. It is marked off into three columns (funiculi medullar 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 outer- most fasciculi of the anterior nerve -roots as they pass out from the anterior grey horn. The anterior 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. DORSAL ASPECT OF THE TRUNK 177 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 groove is termed the paramedian furrow ; the smaller and more internal of the two strands is called the postero-median column or the tract of Go//, whilst the outer and larger strand receives the name of the postero-externa/ column or the tract of Burdach. 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 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, possessing different functions and presenting different connexions. In the fcetal 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 dyed black and stand out in marked contrast to the non-medullated tracts which remain pale (Fig. 74). 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 (1) the ascending direct cerebellar tract; (2) the descending crossed pyramidal tract ; (3) the descending direct pyramidal tract. The direct cerebellar tract medullates comparatively early. Conse- quently in Fig. 74 it stands out conspicuously as a narrow area placed on 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. 74. It is placed in the lateral column in front of 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 anteromedian furrow. Like the crossed pyramidal tract it medullates late, and therefore in Fig. 74 it appears pale. It only reaches down to about the middle of the dorsal region of the cord and then disappi VOL. 11—12 178 HEAD AND NECK 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, it will be rendered evident. The region in front of the sterno-mastoid 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 distinctly from the surface. In its upper part the trachea is 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. With 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. SIDE OF THE NECK 179 Next comes the thyroid cartilage with its prominent po?mim Adami. Beyond the thyroid cartilage is an interval occupied 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 placed under the shoulders of the subject, the head is pulled backwards Fig. 75. and the chin dragged over to the opposite side. The parts 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. — (1) 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 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 repre- sentative in the human subject of the panniculus carnosus in the lower animals. In the male, the adipose tissue which [i—12a i So HEAD AND NECK 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 nerve 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 to the front of the chest and upper part of the shoulder, it cannot be fully studied until the dissector of the arm has reflected the skin from these regions. Platysma Myoides. — This 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 proceeds 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, many, however, blending with the depressor anguli oris. The anterior fibres decussate below the chin with the corresponding fibres of the opposite muscle, whilst the posterior fibres proceed upwards over the angle of the jaw 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 super- ficial 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. External Jugular Vein (vena jugularis externa) — Fig. 76 (10). — This is usually a vein of some size. It will be seen SIDE OF THE NECK 1S1 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 posterior auricular vein, and posterior division of the temporo-maxillary vein. From this it descends in a nearly vertical direction upon the deep 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 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 external jugular vein. They vary from four to six in number. Anterior Jugular Vein (vena jugularis anterior) — Fig. 76 (23). — The anterior jugular vein is small in comparison with the preceding. 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 short transverse branch which 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 are two in number, and both have u—126 182 HEAD AND NECK already been examined in the superficial dissection of the back of the neck (p. 135). They are (a) the small occipital — Fig. 76 (8), — springing from the second cervical nerve,- and (b) the great auricular — Fig. 76 (5), — 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. 76. This arises from the second and third cervical nerves, and, winding round the posterior border of the sterno-mastoid about its middle, proceeds transversely forwards upon the deep fascia to reach the area over the anterior triangle of the neck. Here it divides into two branches, of which one in- clines 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. 76). 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, under 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., (1) acromial; (2) clavicular; (3) sternal — (Fig. 76). 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 free communica- tion with the upper branch of the superficial cervical nerve (Fig. 76). Deep Cervical Fascia (fascia colli) — Fig. 77. — The cervical fascia should now be cleaned, and its connexions .„ ■* SIDE OF THE NECK Fig. 76. — Superficial Nerves on the Side of the Neck and Back oi the Scalp. (Hirschfeld and Leveilte.) 1. Attollens auriculam. 2. Posterior belly of occipito- frontal is. 3. Retrahens auriculam. 4. ( ireat occipital nerve. 5. (ireat auricular nerve. 6. Splenius musj lei 7. Sterno-ma toid muscle. B. Sniall occipital nerve (pre- s>ent as two brancbe 1). 9, Great auricular nerve. 10. External jugular vein. 11. Superficial cervical nerve. 12. Spinal accessory nerve. 1 j. Desi ending branches of cervical plexus. 14. Cervical branches to tra- pezius. 1 5. Trapezius musclei j 16. Clavicular branches. 17. Acromial branches. 18. Auricular twigs of great auricular nerve. 19. Parotid gland. 20. Facial nerve. 21. Masseter mu 22. Infrft-matxlibular nerve. 23. Anterior jugular vein. 24. Stomal branches. 25. Platysma myoides. 184 HEAD AND NECK studied. It constitutes a continuous and strong aponeurotic 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 penetrate 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 Depressor muscles of the larynx and hyoid bone\ Prevertebral muscles Carotid artery and its sheath Sterno-mastoid Scalenus amicus . Platysma External jugular vein Trachea Trapezius' Deep muscles on back of neck'' FlG> J7. — 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.) 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 back- wards, it splits at the anterior border of the trapezius into two lamellae to enclose this muscle. The superficial layer is very thin, and both blend posteriorly with the ligamentum nuchae. SIDE OF THE NECK 185 When the investing aponeurosis is followed forwards it is found to split again at the posterior border of the sterno- mastoid into the two lamellae, 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 dis- tinctly 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 toffee other, it obtains a firm attachment to the hyoid bone. | r- — » Its connexions at the upper and lower limits of the neck \J / may now be examined. Above, it is attached along 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 connexion 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. Its connexions 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 somewhat intricate character. As the fascia is traced downwards between the two sterno-mastoid muscles, it will be found to split a short distance above the sternum into two layers. Of these, the superficial layer is weak, and is attached to the anterior border of the manubrium sterni. The deeper layer lies immediately 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 head of origin of the sterno-mastoid ; and the space between them contains — (1) a little fatty 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) sometimes 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 partitions which proceed from the deep surface of the cervical fascia cannot in every case be displayed 186 HEAD AND NECK 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 appreciate their bearings as they are unfolded in the subsequent dissection of the neck. Those requiring special notice are : — 1. The prevertebral fascia. 2. The pretracheal fascia. 3. The carotid sheath. 4. The stylo-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 out- wards 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 upward 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 septum thus subdivides the investing tube of cervical fascia into — (a) a posterior compartment which contains the vertebral column and the muscles which surround it ; and (p) an anterior or visceral compartment, 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 attach- ment 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 outermost part of the visceral compartment on either side of the neck. They are enclosed within a special investment of fascia which re- ceives the name of the carotid sheath. Both the prevertebral SIDE OF THE NECK 187 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 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 triangle placed in front of it, and a posterior triangle behind it. This muscle, therefore, should be 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. Sterno - 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 is 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 line 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 upper limb, should arrange to work at different hours. Again, the lower part of the posterior triangle, 1 88 HEAD AND NECK and the upper part of the axilla, constitute a region of the highest import- ance 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 necessary, however, that the dissector of the head and neck should stop work. After he has displayed the parts in the space as far as he can without dividing the clavicle, he may proceed with the dis- section of the anterior triangle, and on the fourth 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 posterior triangle has already been displayed in the dissection of the posterior aspect of the neck (p. 137), but the space can only be studied in its entirety when the subject is placed upon its back. The trapezius which has been reflected should be restored as far as possible to its natural position and retained by means of a stitch. When the investing cervical fascia which bridges over the lower part of the posterior triangle between the trapezius and the sterno-mastoid muscles is removed, a variable amount of fatty areolar tissue is exposed in the supraclavicular region. Embedded within this will be found the trans- versalis colli and the suprascapular vessels, with the posterior belly of the omo-hyoid muscle and some lymphatic glands. The suprascapular artery emerges from under cover of the sterno-mastoid, and passes 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 disposed around it, and is then prolonged downwards to obtain an attachment to the clavicle. As the muscle disappears under cover of the sterno-mastoid 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 nerve 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 cervical 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 fascia and the posterior part of the carotid sheath. In a downward direction it may be followed into the axilla as the sheath of the axillary vessels and nerves, and here it establishes a connection with the SIDE OF THE NECK 189 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 suprascapular 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 vertically down- wards 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 also in its lower part by the platysma myoides muscle. 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 clavicular descending branches of the cervical plexus, and a very short portion of the external jugular vein. IQO HEAD AND NECK In front, 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 Occipital artery t ireat occipital nei Occipital artery External carotid artery Facial artery Hypoglossal nerve Small occipital nerve Great auricular nerve Superficial cervical nerve Spinal accessory nerve Cervical nerves to trapezius Scalenus amicus Lingual artery Superior thyroid artery Sterno-hyoid ransversalis colli Brachial nerves Suprascapular artery Subclavian artery Phrenic nerve Subclavian vein Interna] mammary Internal jugular vein Sterno-hyoid Vagus Internal jugular vein Vertebral vein Inferior thyroid artery Fig. 78. — Dissection of the Posterior Triangle of the Neck. 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. Occipital Triangle. — The occipital or upper triangle is much the larger subdivision. It is bounded in front by the SIDE OF THE NECK 191 sterno-mastoid ; behind by the trapezius ; whilst its base is formed by the omohyoid. 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 fourth cervical nerves which cross the space to supply the trapezius muscle. 4. The superficial branches of the cervical plexus as they appear at the posterior border of the sterno-mastoid previous to piercing the deep fascia. 5. Branches of supply to the levator anguli scapulae from the third 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 brachial plexus of nerves. The contents of the occipital triangle have already in a great measure been studied (p. 137). Supraclavicular Triangle. — The supraclavicular or sub- clavian 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 connexions of the 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 con- sequence is the triangle. In a few instances these muscles will be observed to meet on the clavicle, and thus obliterate the space altogether. This latter condition, however, is not necessarily associated with a specially high development of the 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 : — i92 HEAD AND NECK ( Subclavian. Arteries -J Transversalis colli. ( Suprascapular. / External jugular. Veins J Suprascapular, veins ^ Transversalis colli. ^ Subclavian. Nerves — The trunks of the brachial plexus and their branches. Lymphatic glands. Subclavian Artery (arteria subclavia). — It is only the third pari of 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 vessel are the coverings of the space in which it lies — viz., superficial fascia, platysma, superficial descending clavicular branches of the cervical plexus, and the deep cervical fascia. Towards its termination, how- ever, 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 embarrass the surgeon, is that established by the external jugular vein and certain of its tributaries. This vein crosses in front of the 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 suprascapular, and the anterior jugular veins. Observe further that the small nerve to the subclavius is carried vertically downwards in front of the artery behind the veins. Below, the third 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. The subclavian vein is placed at a lower level than the artery, and on a plane slightly anterior to it. SIDE OF THE XECK 193 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 relations of the subclavian artery, with the view of determining those which would constitute the most trustworthy guides in cases where it is necessary 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 immediately 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 scapulae) proceeds outwards under shelter of the clavicle and across the third part of the subclavian artery and the brachial nerves. At the outer limit of the supraclavicular triangle it passes under cover of the trapezius to reach the superior border of the scapula where it has already been examined (p. 139). The transversalis 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. 138). Veins. — The arrangement of the veins has been noticed in studying the relations of the subclavian artery. The ex- ternal jugular vein, as a rule, crosses the third part of this artery at the outer border of the scalenus anticus 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 certain 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 vol. 11 — 13 i94 HEAD AND NECK is constituted "from above downwards by — (i) the splenius capitis; (2) the levator anguli scapulae; and (3) by the scalenus medius and posticus. At the apex of the triangle an c.v c.vi C.VII C.VIII D.ll Fig. 79. — Diagram of the Brachial Plexus. S1, S2, S3. — The three subscapular nerves. Cir. — Circumflex nerve. 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 magnus muscle. SIDE OF THE NECK 195 Section of the Clavicle.— In order that a satisfactory view may be obtained of the nerves forming the brachial plexus, it is necessary to re- move the 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 the clavicle at two points — viz., at the posterior margin of the sterno-mastoid, and the anterior margin of the trapezius — and remove the intermediate piece of bone, after having 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 nerve plexus is formed by the anterior primary divisions of the four lower cervical nerves and the greater part of the large anterior primary division of the first dorsal nerve. Above, the plexus is further rein- forced by a very small twig of communication which passes from the fourth to the fifth cervical nerve ; whilst belowT, 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 four lower cervical nerves are brought into connection with the middle and inferior ganglia of the cervical sympathetic by means of fine grey rami communicantes. The great brachial nerves emerge from the interval between the scalenus anticus and scalenus medius, and proceed down- wards 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 plexus, 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 inner- most 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. From the above description it will be seen that the plexus, ir— 13a 196 HEAD AND NECK from changes which are effected in the arrangement of its fibres, may be divided into four stages : — 1st Stage. 2nd Stage. 3rd Stage. 4th Stage. 5 separate nerves (viz., 4 lower cervical and first dorsal). 3 nerve trunks (viz., an upper, middle, and lower). 3 anterior divisions and 3 posterior divisions. 3 nerve cords (viz., an outer, inner, 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 considerable 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 : — 1. Nerve to rhomboids, from the 5th cervical nerve. 2. Nerve to subclavius, 1 r t, „., ■, <■.* • , „ c , ' - irom the Sth and 6th cervical nerves. 3. Suprascapular, J J ^" r d 1 1 r from the 5th, 6th, and 7th cervical nerves, nerve of Bell, J J ' ' * 5. Twigs to scalene I r , , , r . , , J ° . 1 , irom the lower four cervical nerves close to muscles and longus Y ., . , . , , r ,,• fa the intervertebral foramina. Communicating: twig; \ c ., . , . , • ° fe } from 5th cervical, to phrenic nerve, J J 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 back of the fifth cervical nerve as it lies upon the scalenus medius. Draw the fifth cervical nerve forwards, and the branch in question will be seen passing backwards through the fibres of that muscle to reach the deep surface of the levator anguli scapulae. 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 scapulae, and is finally exhausted in the rhomboids. SIDE OF THE NECK i97 The nerve to the subdavius (nervus subclavius) is a minute twig which springs from the front of 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 communication 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 com- municating 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 back of the upper trunk of the plexus, and runs down- wards, outwards,, 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 posterior 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 which arise from the back of the fifth, sixth, and seventh cervical nerves close to the intervertebral foramina. The roots from the fifth and sixth cervical nerves pass back- wards 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 downwards 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 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 must 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. Ik-gin 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 H—13 6 198 HEAD AND NECK sterno-mastoid. The anterior triangle is subdivided into 4jir.ee 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. The anterior belly of the omo-hyoid appears by emerging from under cover of the anterior border of the sterno-mastoid, a short distance above the sternal origin of the latter. 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 its 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, care must be taken not to injure the twigs from the descendens hypoglossi nerve, which enter its upper or outer 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 differs from the posterior triangle in having its base above and its apex below. It is bounded behind by the anterior margin of the sterno-mastoid, and in front by the middle line of the neck. Its base is formed by the inferior margin of the lower jaw, and a line 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 posterior 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 subdivision is termed the SIDE OF THE NECK 199 lower or muscular triangle; the intermediate space receives the name of carotid triangle ; whilst the highest subdivision is called the submaxillary or digastric triangle (Fig. 80). 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 Occipital triangle Subclavian triangle Digastric triangle Carotid triangle Muscular triangle Fig. 80. — Diagram to show the Boundaries of the Triangles of the Neck. 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 below and behind by the posterior belly of the digastric and the stylo-hyoid muscle, and below and in front 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 the angle of the mandible to the sterno-mastoid muscle ; its apex points down- wards, and is formed by the intermediate tendon of the digastric muscle. 200 HEAD AND NECK Dissection. — The numerous and diverse structures contained within the anterior triangle must now be displayed. This is a dissection which requires some preliminary knowledge of the parts to be exposed. The student is therefore advised to read the general account which is given of the parts which are brought into view, as each subdivision of the space is opened up (p. 200 to p. 204), before undertaking the work. The dissec- tion 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 open 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 carefully in an oblique direction and along a line connecting the cricoid cartilage 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. Muscular 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. 3. The external laryngeal nerve. 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 this reason that the term muscular is applied to the space. As the dissection is proceeded with, however, the large nerve of supply for these muscles, which comes from the ansa hypo- glossi, will be found lying near the outer border of the sterno- thyroid and breaking up into numerous twrigs. 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 SIDE OF THE NECK 20I muscle. Under cover of the sterno-hyoid and sterno-thyroid muscles will be observed the larynx, the isthmus and a con- siderable 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 : — , Common carotid dividing into external and internal carotid arteries. Arteries Veins 2. Superior thyroid. 3. Lingual. 4. Facial. 5. Occipital. ^6. Ascending pharyngeal. fi. Internal jugular. 2. Facial. I 3. Anterior temporo-maxillan , Lingual. Superior thyroid. Middle thyroid. Branches of the external carotid. Tributaries of the internal jugular. Nerves Hypoglossal. f Crossing the space in a ^ transverse direction. 2. Descendens hypoglossi. 3. Nerve to thyro-hyoid. Crossing 4. Internal laryngeal. !•• the space 5. External laryngeal. obliquely. 6. Spinal accessory. J 7. Vagus. ) Descending ^8. Sympathetic. J vertically. Carotid body. Portion of the larynx and pharynx. ( Greater cornu 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 202 HEAD AND NECK carotid sheath should be slit open, care being taken of the descendens hypoglossi nerve, which also descends obliquely within it. The intimate connexion which this sheath pre- sents with the prevertebral layer of fascia can now be made out. The common carotid usually bifurcates opposite the upper border of the thyroid cartilage. Observe that the internal carotid artery at first lies behind, and to the outer side of the external carotid. Upon the coats of these vessels numerous sympathetic twigs ramify, and, at the point of bifurcation of the common carotid, a small oval body, termed the carotid body, will be found closely applied to the deep surface of the vessel. 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 thyroid artery, which, after having given off its hyoid, superior laryngeal, and sterno-mastoid branches, disappears under cover of the omo-hyoid muscle, and enters the mus- cular triangle; (2) the lingual artery, which forms a small loop or arch above the great cornu of the hyoid bone and leaves the space by passing under cover of the digastric and stylo-hyoid muscles ; and (3) the facial artery, which ascends under the same muscles to gain the digastric triangle. The occipital artery commonly springs from the posterior aspect of the external carotid close to the lower border of the digastric, and soon quits the space by running upwards and backwards under cover of the sterno-mastoid muscle. The sterno-mastoid branch of the occipital artery comes off as the latter leaves the triangle, and accompanies the spinal accessory nerve. The ascending pharyngeal 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, which from a surgical point of view is the most important structure in the anterior triangle of the neck, 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 the carotid triangle. The most conspicuous of these is the common facial SIDE OF THE NECK 203 vein, which is formed by the union of the facial vein and the anterior division of the temporo- maxillary vein. The common facial vein enters the internal jugular at the level of the hyoid bone, and certain lymphatic glands which over- lie the veins at this point are of especial importance, seeing that they are frequently the seat of tubercular disease (Stiles). 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 below the lower margin of the digastric muscle. Two descend vertically — viz., the vagus and the gangliated cord of the sympathetic. The vagus lies in the posterior part of the carotid sheath between the common carotid artery and the internal jugular vein. The syt7ipathetic cord is embedded in the posterior wall of the carotid sheath. The remaining five nerves traverse the triangle obliquely. Four run from above downwards and forwards, viz., the 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 the hypoglossal nerve as it hooks round the occipital artery, and descends within the carotid sheath. It is joined at the upper border 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 laryngeal 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 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 ?ierve 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 about one and a half inches below the lip of the mastoid process. 2o4 HEAD AND NECK Digastric Triangle. — The digastric space may be divided very conveniently into an anterior and posterior part by the stylo-maxillary 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. Hypoglossal nerve. 4. Mylohyoid nerve. 5. Mylo-hyoid artery. 6. Lymphatic glands. 1. Portion of the parotid gland. 2. External carotid artery. 3. Posterior auricular artery. The most conspicuous object in the fore-part of the digastric triangle is the submaxillary gland. The facial artery passes first upwards and then forwards in the midst of this gland, whilst the facial vein lies superficial to it. But whilst the facial artery runs through the gland, 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 branches arise within the gland. The submental artery runs forwards 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 hypo- glossal nerve is seen in this space. It lies upon the hyoglossus muscle immediately above the hyoid bone, and disappears under cover of the posterior border of the mylo-hyoid muscle. Numerous small ly?nphatic glands lie under shelter of the base SIDE OF THE NECK 205 of the lower jaw. They receive their afferent vessels from the tongue, teeth, and face. 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 especi- ally 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 upper supra-hyoid and a lower infra-hyoid portion. In the supra-hyoid part are found structures which are con- cerned 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 bellies 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 slighlty from each other so as to leave a narrow triangular space, termed the submental triangle, be- tween them (Fig. 81). The floor of this space is formed by the anterior portions of the two mylohyoid muscles, whilst bisecting the triangle in the mesial plane is the fibrous raphe, into which these muscles are inserted. Not infrequently the inner margins of the digastric muscles send decussating fibres across the interval between them. Within the sub- mental triangle are the supra-hyoid glands, which lie above the body of the hyoid bone and are not infrequently the seat of abscess following impetigo of the lower lip. 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 pomum Adami. 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 2o6 HEAD AND NECK by two muscular strata, viz., a superficial layer formed by the sterno-hyoid and omo-hyoid which lie on the same plane, and a deeper layer formed by the sterno-thyroid and its continua- tion upwards, the thyro-hyoid. In addition to these an elongated process of the thyroid gland not infrequently Anterior belly of digastric Mvlo-hvoid Submaxillary gland Thyro-hyoid membrane Thyroid cartilage Superior thyroid artery Crico-thyroid membrane Cricoid cartila_ Lateral lobe of thyroid Common carotid Phrenic nerve Inferior thyroid Transversalis colli Vertebral artery_- Anterior belly of digastric Mylo-hyoid Submaxillary gland Omo-hyoid Sterno-hyoid Internal jugular vein Superior thyroid vein Common carotid artery Sterno-mastoid Crico-thyroid muscle Lateral lobe 01 thyroid body Isthmus of thyroid Scalenus anticus Scalenus medius Subclavian artery First rib Subclavian artery Suprascapular artery Common carotid artery Internal mammary arte Innominate artery Inferior thyroid vein Fig. 8 i.— Dissection of the Front of the Neck sterno-mastoid muscles have been removed, and the lower part of the right common carotid artery cut away to show the deeper parts. The lower portions of the 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 glandule thyroidea. The divergent inner margins of the two small crico-thyroid muscles, as they extend upwards and outwards upon the cricoid cartilage towards the lower margin of the thyroid SIDE OF THE NECK 207 cartilage, will also be seen. Upon the crico-thyroid membrane, as it 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 margin of the sternum it lies very deeply. 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 attitude, the length of the cervical part of the trachea is diminished by fully three-quarters of an inch or even more. 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: (1) the isthmus of the thyroid 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 isth?nus 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. 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 isthmus and the lateral lobes, and proceed downwards upon the front of the trachea, one upon either side of the mesial plane. As they descend they frequently anastomose, and the branches which pass between them may assume a plexiform arrangement. Sometimes the two inferior thyroid veins unite at a variable point in front of 2oS HEAD .AND NECK the trachea into one large trunk. 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 in immediate relation to its anterior aspect, 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, the two layers of the deep cervical fascia close to the upper margin of the sternum, and in the interval between these the cross-branch connecting 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 ; below, however, 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. Behind the muscles is the pretracheal layer of fascia. Surgical Anatomy. — The principal operations which are performed in the middle line of the neck are those of laryngotomy and tracheotomy. In laryngotomy, an opening is made into the larynx. This can most readily be done in the interval 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 transversely close to the upper margin of the cricoid cartilage. Only the middle portion of the crico-thyroid membrane should be divided, so as to avoid injury to the crico-thyroid muscles. Tracheotomy is a more serious operation. The opening into the trachea may be made above or below the isthmus of the thyroid body. The high operation is preferred by the surgeon. Its advantages are very apparent : here the trachea lies near the surface, and no veins of any importance are met with. The only drawback consists in the small portion of trachea which intervenes between the isthmus and the cricoid SIDE OF THE NECK 209 cartilage. Still, by dividing the pretracheal fascia transversely below its attachment to the cricoid cartilage, the isthmus can be pushed downwards and the interval between it and the cricoid considerably increased. In certain cases it may be necessary to divide the isthmus, and even to open into the lower part of the larynx by extending the incision through the cricoid cartilage. The loic 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 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 Muscles. — These are a series of fiat, 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-hyoid (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 into the lower border of the body of the hyoid bone, close to the outer side of the sterno- hyoid. In the anterior triangle of the neck, the anterior belly of the omo-hyoid forms the boundary between the carotid and the muscular subdivisions of this area. Both bellies are supplied by branches from the ansa hypo^Iossi. The sterno-hyoid (musculus sternohyoideus) arises from the posterior aspect of the inner end of the clavicle and the posterior sternoclavicular ligament. Its origin, however, is VOL. II — 14 2io HEAD AND NECK very variable ; thus, it may be shifted either inwards or out- wards. 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 the 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 intersection frequently divides it into two portions. The sterno-hyoid is supplied by branches from the ansa hypoglossi. The sterno-thyroid (musculus sternothyreoideus) lies under cover of the preceding muscle, and is both broader and shorter. It springs from the posterior aspect of the manubrium 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 of the thyroid cartilage. An incomplete tendinous intersection may sometimes be noticed interrupting its muscular fibres. The nerve supply of the sterno-thyroid is derived from the ansa hypoglossi. The thyro-hyoid (musculus thyreohyoideus) lies on the same plane as the sterno-thyroid ; 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. The thyro-hyoid muscle is supplied by a delicate branch from the hypoglossal nerve. Digastric Muscle (musculus digastricus). — This muscle limits the submaxillary triangle inferiorly, and intervenes between it and the carotid triangle. The a?iterior belly of the digastric springs from an impres- sion 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 intennediate tendon. 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 the hyoid bone by a strong aponeurotic band. The anterior belly of the digastric SIDE OF THE NECK 211 is supplied by the ?nylo-kyoid nerve ; the posterior belly by a twig from the facial nerve. 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 intermediate tendon of the digastric passes forwards between the two slips of insertion of the stylo-hyoid. This muscle receives its nerve of supply from the facial nerve. Hypoglossal Nerve (nervus hypoglossus). — The portion of the hypoglossal 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 digastric, and im- mediately curves forwards by hooking round the occipital artery. Near the upper border of the hyoid bone it dis- appears from the present dissection by passing under cover of the mylo-hyoid muscle. It forms a loop on the side of the neck which lies upon the external carotid and lingual arteries, and finally, above the hyoid 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 branches will be seen to arise from this portion of the hypoglossal nerve, viz. : — 1. The ramus descendens. 2. The thyro-hyoid. The ramus descendens hypoglossi, as a rule, leaves the hypo- glossal nerve at the point where it turns round the occipital artery. It proceeds downwards and inwards so as 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 ramies cervicalis descendens, and by its union with the ramus descendens hypoglossi a nerve loop is formed in front of the common carotid artery, which is called the ansa hypoglossi. From the convexity of this loop branches are given off which supply both bellies of the omo-hyoid, the sterno-hyoid, and sterno-thyroid muscles. 21 2 HEAD AND NECK 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 laminae of the fascial sheath which retains 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 Joint capsu Joint cavity-. Interarticular ligament Joint cavity Rhomboid ligament Anterior sterno- clavicular ligament Anterior chondro- sternal ligament Fig. 82. — Sternoclavicular and Costo-sternal Toints. may sometimes be traced into the thorax, where it communi- cates with the phrenic and cardiac nerves. The 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. Sternoclavicular Articulation (articulatio sterno-clavicu- laris). — The dissector must now examine the sterno-clavicular joint, as the next step consists in the disarticulation of the clavicle and the reflection of the clavicular origin of the sterno-mastoid muscle. SIDE OF THE NECK 213 The structures which hold the two bones in position at this joint are the following : — Anterior sternoclavicular. Posterior sterno-clavicular. Ligaments proper. -! A ,. . f Interclavicular. Accessory ligaments. 4 ^ , , . , , 1 • ■, 3 & ( Costo-clavicular 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 ligament springs from the front of the inner end of the clavicle, and proceeds obliquely downwards and inwards to gain attachment to the anterior aspect of the manubrium sterni. The posterior sterno-clavicular ligament has a corre- sponding position, and presents similar attachments on the posterior aspect of the joint. These ligaments limit the backward and forward move- ments of the inner end of the clavicle, upon the sternal facet. Interclavicular Ligament (ligamentum interclaviculare). — This is a strong band which connects 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. Rhomboid Ligament (ligamentum costoclaviculare). — The costoclavicular or rhomboid ligament 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 lower border to the cartilage of the first rib. From this it is carried obliquely upwards, backwards, and out- wards, 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 n—14 a 2i4 HEAD AND NECK 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 movement of the clavicle. Dissection. — The interarticular 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 sur- face, and its fibres divided. The clavicle should now be forcibly pulled outwards, when the interarticular fibro-cartilage will become apparent. Interarticular Fibro-Cartilage (discus articularis). — This is a nearly circular meniscus or plate interposed between the inner end of the clavicle and the sternal facet. 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. By its circumference it is closely attached to the capsule of the joint 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 in the mechanism of the joint 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 pro- vided 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 the latter 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 SIDE OF THE NECK 215 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. Occipital artery Great occipital nerve Occipital artery External carotid artery Facial artery .Hypoglossal nerve ; Mi Small occipital nerve Great auricular nerve Superficial cervical nerve Spinal accessory nerve ervical nerves to trapezius ^ Scalenus amicus Lrngual artery Superior thyroid artery Sterno-hyoid ansversalis colli Brachial nerves Suprascapular artery / Subclavian artery Phrenic nerve Subclavian vein Internal mammary Internal jugular vein Sterno-hyoid Vagus Internal jugular vein Vertebral vein Inferior thyroid artery Fig. 83. — Dissection of the Posterior Triangle of the Neck. The clavicular portion of the sterno-mastoid has been detached from the clavicle and thrown forwards. 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 duel on the right side. 6. The lower part of the internal jugular vein. 7. The vagus nerve. 8. The lower part of the common carotid artery. 9. The lower part of the cervical sympathetic. 216 HEAD AND NECK 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 subclavian 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 anticus 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 the scalenus anticus, the cervical pleura bulges upwards for a short distance into the neck, and 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 artery, 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 vertebrae to the upper two costal arches. They are three in number, and are named, from their relative positions, anticus^ medius, and posticus. The scalenus anticus (musculus scalenus anterior) is a well- defined muscle which is separated from the scalenus medius by the brachial nerves and the subclavian artery. It arises from the anterior tubercles of the transverse processes of four cervical vertebras — viz., the third, fourth, 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 medius (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. SIDE OF THE NECK 217 The scalenus posticus (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 corresponding number of the lower cervical vertebrae in common with the scalenus Serratus posticus superior (insertion) Scalenus posticus (insertion) Scalenus medius (insertion) Serratus magnus (origin) Serratus magnus (origin) lenus anticus (insertion) Subclavius (origin) Pectoralis minor (occasional origin) Fig. 84. — Muscle-Attachments to the Upper Surface of the First Rib, and the Outer Surface of the Second Rib. A, First rib ; B, Second rib. medius. It is inserted into the upper border of the second rib, immediately in front of the insertion of the levator costse. The scalene muscles are supplied by twigs from the lower four cervical nerves. 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 2l8 HEAD AND NECK behind the sternoclavicular 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 in front of the cervical dome of pleura, a short distance below its summit. 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, Fig. 85. — Diagram of the Subclavian Artery and its Branches. (Turner. ) I. Innominate arteiy. 11. Deep cervical. 2. Common carotid artery. 12. Internal mammary. 3* Vertebral artery. i3- Posterior scapular. 4- Thyroid axis. 14. Ascending cervical. 5- Inferior thyroid artery. a. First rib. 6. Transversalis colli. b. Scalenus anticus. 7- Superficial cervical. c. Thyroid body. 8. Posterior scapular. d. Phrenic nerve. 9- Suprascapular. c. Vagus nerve. 0. Superior intercostal. /■ Recurrent laryngec and so varied in 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 ; the second portion lies behind this muscle ; whilst the third part extends from the outer border of the scalenus anticus to the outer border of the first rib. First part. — Owing to the difference of origin, the relations SIDE OF THE NECK 219 presented by the first portion of the subclavian artery are not the same on the two sides of the body. Let us examine, in the first instance, the vessel of the right side, and then compare it with that of the left side. The first 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. In front, it is covered by the skin, superficial fascia, platysma, deep fascia, and three muscular strata — viz., the clavicular origin of the sterno-mastoid, the sterno-hyoid, and the sterno-thyroid. Three veins and some nerves are also placed in front of it. Thus, close to the inner margin of the scalenus anticus, it is crossed by the internal jugular and vertebral veins, as these proceed from above downwards, whilst the anterior jugular vein, as it passes out- wards 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 the cardiac branches of the vagus and sympathetic as they run towards the thorax, and a loop from the sympathetic (annulus Vieusseni). As the vagus nerve leaves the artery it gives off its recurrent branch. The first part of the subclavian artery presents 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 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, it curves 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., (1) the 220 HEAD AND NECK 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 or right side, and then arches over it to reach the angle of junction between the subclavian and internal jugular veins. 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, indeed, it may reach the level of the lower part of the lateral lobe of the thyroid body. In this part of its course the vessel is not so deeply placed. In front, it is covered by — (1) skin; (2) superficial fascia and platysma ; (3) deep fascia; (4) clavicular head of the sterno-mastoid ; (5) scalenus anticus. The phrenic nerve 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. Behi?id 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 part of the subclavian artery has already been examined (p. 192). Branches of the Subclavian Artery. — Four branches spring from the subclavian trunk (Figs. 83 and 85). 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 — fi. Vertebral. ■p , ( Inferior thyroid. f \2' Thyroid axis. - Transversalis colli. jirs par . [Suprascapular. V3- Internal mammary. y , ( ( Superior intercostal seconTpal j Superior intercostal, .proper. r { l^Ueep 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, SIDE OF THE NECK 221 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. Vertebral 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 anterior 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 between the phrenic and pneumogastric nerves, and almost immediately breaks up into its three terminal branches — viz., the inferior thyroid, the suprascapular, and the transversalis colli. Inferior Thyroid Artery (arteria thyreoidea inferior). — This vessel 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, at the level of the cricoid cartilage, it turns suddenly down- wards and inwards, and passes behind the sympathetic, vagus, and the common carotid artery ; lastly, it bends upwards, and ends in branches at the base of the lateral lobe of the thyroid body. 222 HEAD AND NECK The following branches will be noticed arising from the inferior thyroid artery : — i. Ascending cervical. 2. Inferior laryngeal. 3. Tracheal. 4. (Esophageal. 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 major, and dispenses branches to the muscles in front of the vertebral column. Other twigs from the ascend- ing cervical, termed spinal bra?iches, 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 (p. 158). 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 (Esophageal (rami cesophagei) branches in like manner supply the trachea and gullet. They are of small size, and anasto- 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. They 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, and frequently unite to form a short common stem, which opens into the innominate trunk. In other 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 as it issues SIDE OF THE NECK 223 from the foramen transversarium of the sixth cervical vertebra. Suprascapular and Transversalis Colli Arteries. — Both of these arteries have already been examined in the greater part of their course (p. 193). 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-mastoid. 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 subclavian or the external jugular vein. Internal Mammary Artery (arteria mammaria interna). — The internal mammary springs from the lower aspect of the sub- clavian 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 thoracic cavity. In the cervical part of its course it will be observed to pass behind the' subclavian vein, and to be crossed from without inwards by the phrenic nerve. In the neck, the internal mammary 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 upwards and backwards over the pleura to the neck of the first rib, where it divides into the deep cervical artery and the superior intercostal artery proper. The deep cervical artery (arteria cervicalis profunda) passes backwards, and disappears from view between the transverse process of the seventh cervical vertebra and the neck of the first rib. It has been already noticed in the dissection of the back of the neck (p. 148). The stiperior intercostal artery (arteria intercostalis suprema) turns downwards in front of the neck of the first rib, between the last dorsal nerve and the first thoracic ganglion of the 224 HEAD AND NECK sympathetic, and ends in the thorax by giving branches to the upper two intercostal spaces. The deep cervical vein is a large vessel. It joins the vertebral vein. Subclavian Vein (vena subclavia). — The subclavian vein 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, and behind the inner end of the clavicle, it joins the internal jugular to form the innominate vein. In connexion with the subclavian vein, note: (i) that the arch which it forms is not so pronounced as in the case of the corresponding artery ; (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. The sheath of the subclavian vein is attached to the posterior surface of the costocoracoid membrane. This is a relation of some practical import- ance. A forward movement of the clavicle drags upon the vein, and in cases where the vessel is wounded there is always a danger of air being sucked into the vein by such a movement. A fatal result ensues upon the entrance of air into the heart. The tributaries of the subclavian vein are (1) the external jugular vein, and (2) in some cases the anterior jugular vein. These join it at the outer margin of the scalenus anticus muscle. 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, are poured into the venous system on the left side (see p. 87). Its terminal or cervical portion is displayed in the present dissection. It is 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 be sought. When it reaches 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 the internal jugular vein at its angle of union with the subclavian, and into this it opens. As the thoracic duct courses outwards, it is placed at a higher level than the subclavian artery, and SIDE OF THE NECK 225 passes behind the internal jugular vein. Further, as it ap- proaches the point at which it ends, it crosses the first part of the subclavian artery. Stern Sym Inferior constrictor Thyro dragged Inferior thyroid artery 1 Recurrent laryngea nerve < Esophagus Common carotid artery Internal jugular vein nferior thyroid vein Innominate artery ternal x carotid artery Internal jugular vein Scalenus medius ^|^ Rectus capitis anticus major ^ Vagus nerve Phrenic nerve ertebrai vessels Scalenus anticus Dome of pleura Brachial nerves ^Subclavian vessels Suprascapular and trans- versalis colli arteries Thoracic duct Pleura Internal mammary artery and phrenic nerve Left innominate vein FlG. 86. — Deep Dissection of the Root of the Neck on the Left Side to show the Dome of the Pleura and the relations of the Terminal Part of the Thoracic Duct. The sterno-mastoid and the depressors of the hyoid and larynx have been removed. 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. vol. 11 — 15 226 HEAD AND NECK The right lymphatic duct (ductus lymphaticus dexter) is the corresponding vessel upon the right side. It is a very insignifi- cant duct, and draws its supply of lymph from a much more restricted field. It is formed by the union of the lymphatic vessels from the right upper limb with the right common jugular lymphatic trunk. It likewise receives the efferent lymphatic vessels from the intercostal glands which lie in the upper interspaces of the right side and from the thoracic visceral glands of the right side. It constitutes, therefore, the main lymphatic drain for the following districts : (i) right upper limb; (2) right side of the head and neck; (3) upper part of right thoracic wall ; (4) right side of diaphragm and upper surface of liver; (5) thoracic viscera on right side of mesial plane, viz., right side of heart and pericardium and the right lung and pleura. In length the right lymphatic duct rarely measures more than half an inch. It will be found at the inner margin of the scalenus anticus opening 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 the root of the neck, and the dissector should now examine the height to which it rises, and the connections which it estab- lishes. Its height with reference to the first pair of costal arches 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. These differences depend on the degree of obliquity of the thoracic inlet. Posteriorly, and in all cases, the apex of the pleura will be found to cor- respond in level with the neck of the first rib. It forms a dome-like roof for each side of the thoracic cavity, and is strengthened by a fascial expansion (frequently termed Sibson's fascia), which covers it completely, and 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 ascends into the neck, and that the subclavian artery arches outwards upon its anterior surface near its apex. Cervical Plexus (plexus cervicalis) — Fig. 87. — This plexus SIDE OF THE NECK 227 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 plexus, and they have only a short course to run as independent trunks. With the exception of the first, each divides into an ascending and a descending branch ; and these joining with each other, constitute the plexus, which, therefore, consists of three loops. Small occipital I " R Great auricular, Hypoglossal Transverse cervical Thyro-hyoid nerve Descendens hypoglossi Branch to levator, anguli scapulae Branch to levator anguli scapula; Descending trunk FIG. 87.- /'Ansa hypoglossi Phrenic -Diagram of the Cervical Plexus and the Ansa Hypoglossi. I, II, III, IV. — Anterior primary divisions of the upper four cervical nerves. R. Branches to recti muscles. S.M. Branches to the sterno-mastoid. C.C. Rami communicantes hypoglossi. C.H. Communicating branch to hypo- glossal. 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 communicating twigs it receives from the first cervical nerve. The descending branch of the fourth nerve, which is very small, proceeds downwards to unite with the fifth nerve, and thus establishes a connexion with the brachial plexus. The cervical plexus thus formed has very definite relations. It lies under cover of the upper part of the sterno-mastoid and upon the scalenus medius and the levator anguli scapulae muscles. 11 — 15 a 228 HEAD AND NECK Its branches are very numerous, and may be classified in the following manner Superficial or ' Cutaneous. [Ascending. - Transverse. .Descending. Deep. Muscular. Communicating. From 2nd. From 2nd & 3rd. From 3rd & 4th. From 1st & 2nd. From 2nd. f Small occipital. \ Great auricular. Superficial cervical. f Clavicular. J Sternal. I Acromial. r I. To rectus capitis anticus major. To rectus capitis anticus minor. To rectus capitis lateralis. To sterno-mastoid. Ramus cervicalis A X descendens (rami I „ „ , c „ , > • \ VProm 2nd & 3rd. commumcantes J hypoglossi). J 6. To levator angulH scapulae. 7. To scalenus medius VFrom 3rd & 4th. and posticus. 8. To trapezius. J 9. Phrenic to dia- \ From 3rd, 4th, ^ phragm. J & 5th. f 1. To hypoglossal. j 2. To vagus. J 3. From sympathetic. ! « .2 ' ^ 4. To spinal acces-/From 2nd, 3rd, sory. \ & 4th. 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 anterior recti muscles and the rectus lateralis 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 filaments to the muscle. The levator anguli scapula always receives two or three branches from the third and fourth nerves, whilst the scalenus medius and scalenus posticus obtain their nerve-supply from the same nerve trunks before these have entered the SIDE OF THE NECK 229 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 twTo roots of the descen- dens cervicalis remain 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 difficulty 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 mammary artery from without inwards. As it proceeds downwards on the scalenus anticus, it passes behind the omo-hyoid, the trans- versalis 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. — (1) At the base of the skull, the first loop of the cervical plexus is brought into close connexion, by means of connecting twigs, with the vagus and hypoglossal nerves. These cannot be displayed at present, but will be examined in a subsequent dissection. The fibres which enter the hypoglossal nerve from the first cervical nerve proceed downwards in its trunk and conic off as the descendens hypoglossi The ansa hypoglossi is thus in all probability composed entirely of fibres derived from the 1st, 2nd, and 3rd cervical nerves. It is 230 HEAD AND NECK also believed that the branches which the hypoglossal nerve gives to the thyro-hyoid muscle and the genio-hyoid muscle likewise come from the 1st cervical nerve. (2) Each of the four cervical nerves which form the plexus is connected by means of one or more grey rami communicantes with the superior cervical ganglion of the sympathetic. (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 common 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 side, it arises within the thorax, from the aortic arch. In both cases the common carotid ends opposite the lower border of the third cervical 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 subdivision takes place is subject to a considerable amount of variation within certain limits, and it has been noticed that 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 twro 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 angle of 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 pneumogastric nerve, and the descendens hypoglossi nerve, the vessel is enveloped by a strongly marked sheath derived from the SIDE OF THE NECK 231 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. 186, 201, 202). 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 Thyrohyoid membrane True vocal cord Processus vocalis Arytenoid cartilage Platysma Posterior wall of pharyn Retropharyn- geal space^ Carotid sheath Sterno-hycid jfc^. Thyro-hyoid N^ Thyroid cartilage Omo-hyoid ^%.^C .Sinus pyriformis - - Superior thyroid Descendens iV' hypoglossi ^ ^Common carotid Scalenus anticu Lonarus colli \ 9- ^ \ Internal jugular Kv%VVagus Sympathetic cord Vertebral artery Fig. 88. — Transverse section through the Neck at the level of upper part of Thyroid Cartilage. 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 : — 4. Sterno-mastoid artery. 5. Descendens hypoglossi nerve and the ansa hypoglossi. 1. Superior thyroid vein. 2. Middle thyroid vein. 3. Anterior jugular vein. The three veins cross the common carotid from within out- wards, and at different levels, viz., the superior thyroid near its bifurcation, the middle thyroid below the level of the cricoid cartilage, and the anterior jugular at the root of the neck ; whilst, however, the thyroid veins are in immediate relation to the vessel, the anterior jugular vein is separated from it by the sterno-hyoid and sterno-thyroid muscles. The sterno- n—15 6 2^2 HEAD AND NECK mastoid artery, a branch of the superior thyroid, crosses the vessel obliquely as it lies within the carotid triangle. The 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 below, and with the rectus capitis anticus major higher up. These intervene between it and the transverse processes of the cervical vertebrae. The gangliated cord of the sympathetic, the recurrent laryngeal Anterior jugular vein Superior thyroid arter- V Pharyny Descender! hypogloss Common carotic' v Internal jugulai N Vagus*- Sympathetic--, Sterno-hyoid Cric0.thyroid ^Superior thyroid artery .Sterno-thyroid ens hypoglossi hyoid ommon carotid Vagus nternal jugular ^Sympathetic cord ^Cervical nerves Longus colli Retro-pharyngeal space Vertebral artery Fig. 89. — Transverse section through the Neck at the level of the Cricoid Cartilage. nerve, and the inferior thyroid artery are also related to it posteriorly. The syjnpathetic cord descends vertically in the substance of the carotid sheath, behind the artery, and is interposed between the vessel and the prevertebral muscles ; the recurrent lar)>ngeal nerve is carried upwards and inwards behind the lower part of the vessel ; the itiferior 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,1 whilst 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 233 internally, it is in contact with a succession of structures as it proceeds upwards, viz., (1) the trachea and cesophagus, 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. 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. Carotid Body. — 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 in structure it is similar in its nature to the minute coccygeal body which rests upon the anterior aspect of the tip of the coccyx. It is included, therefore, in the group of ductless glands. Entering it are numerous minute arterial twigs, which take origin from the termination of the common carotid and the commence- ment of the external carotid. The function of this remark- able little body is quite unknown. Most likely it is a vestigial structure. External Carotid Artery (arteria carotis externa). — The external carotid artery 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 dis- tributed 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 carotid, 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 first stage is contained within the carotid triangle. It is therefore, com- 234 HEAD AND NECK paratively 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 digastric and Superficial temporal artery Internal maxil- lary artery Posterior auricu- lar artery ^j^^S&L. •' ^> ^ External carotid — Occipital artery Sterno-mastoid artery Hypoglossal nerve Ascending pharyngeal artery Submental artery Facial artery Internal carotid artery Descendens hypoglossi Superior thyroid artery Sterno-mastoid art Lingual artery Inferior hyoid artery Internal laryngeal artery Pomum Adami Stemo-hyoid Common carotid artery Omo-hyoid Fig. 90. — Diagram of the External Carotid Artery and its Branches. 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 termination by the facial nerve, whilst the temporo-maxillary vein passes downwards superficial to it. SIDE OF THE NECK 235 These relations cannot be seen at present, but they will afterwards be exposed when the face is dissected. It should be noted that while the artery is in the gland it lies much nearer its deep than its superficial surface. At its commencement, the external carotid artery lies in relation to the pharynx. Higher up it rests upon the stylo- pharyngeus muscle, the styloid process, and the glosso- pharyngeal nerve — three structures which intervene between it and the internal carotid artery. 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 thyroid, . Lingual, Facial, . Internal maxillary, Occipital, Posterior auricular, Ascending pharyngeal, Superficial temporal, Directed forwards and inwards. \ Directed backwards and J outwards. Directed almost vertically upwards. But these are not the only branches which come off from the external carotid. Small twigs are also given to the parotid gland, and to the masseter and internal pterygoid muscles. Superior Thyroid Artery (arteria thyreoidea superior). — This vessel 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 forwards, under cover of the omo-hyoid, sterno-hyoid, and sterno-thyroid muscles, and ends by breaking up into twigs, which enter the substance of the thyroid body. The following branches proceed from it : — 1. Hyoid. 2. Superior laryngeal. 3. Sterno-mastoid. 4. Crico-thyroid. 5. Thyroid. The infra-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. 236 HEAD AND NECK 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, along the upper border of the anterior belly of the omo-hyoid muscle, and 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. The crico -thyroid artery (ramus cricothyreoideus) runs in- wards 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. 207). The thyroid or terminal branches (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 distri- buted 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. 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 ultimate distribution in the dissection of the sub- maxillary region. Note in the meantime, however, that the part under observation lies in the carotid triangle, and that SIDE OF THE NECK 237 the loop which it forms is crossed by the hypoglossal nerve. One small branch, termed the supra-hyoid artery, springs from this part of the vessel. The supra-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. Facial Artery (arteria maxillaris externa). — The facial artery 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 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 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: (1) that the vessel can be disengaged from the submaxillary gland by dissection without 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 downwards superficial to the sub- maxillary gland. Four named branches spring from the facial artery in the cervical part of its course : — 1. The inferior palatine. 2. The tonsillitic. 3. The submaxillary. 4. 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 nnd Eustachian tube. It ascends between the stylopharyngeus and styloglossus muscles. The 238 HEAD AND NECK 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 submaxillaiy 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 glands, and anastomoses with the sublingual artery by branches which pierce the mylo-hyoid muscle. In the face it anastomoses with the inferior labial branch of the facial and the mental branch of the inferior dental. Facial Vein (vena facialis anterior). — The cervical portion of the facial vein will be noticed passing backwards and downwards, superficial to the submaxillary gland and facial artery. After picking up 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. Internal Maxillary Artery (arteria maxillaris interna). — This vessel 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, under cover of the sterno- mastoid muscle, to reach the interval between the mastoid portion of the base of the skull 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. 112 and 145). The first part of the vessel crosses the internal carotid artery, the vagus nerve, the spinal accessory nerve, and the internal jugular vein. The hypoglossal nerve hooks round SIDE OF THE NECK 239 it, and it is overlapped by the lower border of the posterior belly of the digastric muscle. The only branches which spring from this portion of the occipital are: — (1) muscular twigs; and (2) a meningeal branch. The 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 meningeal branch (ramus meningeus) associates itself with the internal jugular vein, and can be followed upwards upon it to the jugular foramen, through which it passes into the cranium. Posterior Auricular Artery (arteria auricularis posterior). — The posterior auricular artery 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. in). 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 — (1) muscular twigs ; (2) a few branches to the parotid gland ; and (3) the stylo-mastoid artery. The stylomastoid artery (arteria stylomastoidea) is a slender vessel which enters 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. Ascending Pharyngeal Artery (arteria pharyngeaascendens). — The ascending pharyngeal artery 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 24o HEAD AND NECK carotid artery and the pharynx. It will be subsequently traced in the deep dissection of the neck. Superficial Temporal Artery (arteria temporalis super- ficialis). — This vessel cannot be displayed at present. In the dissection of the face the student will have an opportunity of studying it. Thyroid Body (glandula thyreoidea). — The thyroid body may now be examined. It is a highly vascular solid body, which clasps the upper part of the trachea, and extends upwards for some distance upon each side of the larynx. In size it varies greatly in different 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 pretracheal layer of cervical fascia, from which it derives a sheath, and also by the sterno-thyroid, sterno-hyoid, and omo-hyoid muscles. It is further overlapped by the sterno- mastoid muscle (Fig. 89, p. 232). Its 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 posterior 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 generally present in connexion 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 glandulce thyreoidea. In some cases this little muscle has an attachment to the thyroid body independently of the pyramidal process. The thyroid body is firmly connected to SIDE OF THE NECK 24 1 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 great vascularity of the thyroid body. Four large arteries, and occasionally a fifth smaller vessel, convey blood to its substance. The two superior thyroid branches of the Anterior belly cf digastric Mylohyoid Submaxillary gland Thyro-hyoid membrane Thyroid cartilage Superior thyroid artery Crico-thyroid membrane Cricoid cartilage Lateral lobe of thyroid Common carotid Phrenic nerve Inferior thyroid- Transversalis colli Vertebral artery -L Subclavian artery Suprascapular artery ^ v Common carotid artery Internal mammary artery Innominate artery Inferior thyroid vein Fig. r;r. — Dissection of the Front of the Neck Anterior belly of digastric Mylo-hvoid > Submaxillary gland Omo-hyoid Sterno-hyroid Internal jugular vein Superior thyroid vein Common carotid artery Sterno -mastoid Crico-thyroid muscle Lateral lobe of thyroid body Isthmus of thyroid Scalenus anticus Scalenus medius Subclavian artery y ——First rib Trachea The lower portions of the ste;rno-mastoid muscles have been removed, and the lower part cf the right common carotid artery cut away to show the deeper parts. external carotid arteries divide at the apex of each lateral lobe into three branches for its supply ; the two inferior thyroid branches from the thyroid axis trunks 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 ima, 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 VOL. II — 16 242 HEAD AND NECK 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 thyroid 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. Trachea and the (Esophagus. — The windpipe and the gullet 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 Thyroid body Trachea ommon carotid artery % ^0^^^f%l'lr^ • Inferior thyroid artery -Jw) - > Recurrent laryngeal nerve Gullet Fig. 92. — Transverse section through the Thyroid Body, Trachea, and Gullet, at the level of the first Dorsal Vertebra. extend downwards in front of the vertebral column to the thoracic cavity. The trachea, or windpipe, 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. 207). 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 oesophagus. SIDE OF THE NECK 243 The (esophagus or gullet is a narrow tube with thick muscular walls, which extends from the pharynx to the 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 body 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 face. 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 placed over the orbital arch of the frontal bone, so as to inter- vene between the forehead above and the ocular regions below. The short stiff hairs which spring from these have an outward inclination. The eyelids (palpebrse) are two semilunar curtains provided 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 outline. This interval is termed the palpebral fissure (rima palpebrarum). When the eye is closed and the margins of 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 con- dition is placed below the level of the cornea or clear part of the eyeball, ir— 16a 244 HEAD AND NECK 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 lacus lachry mails. 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 Margin of the upper eye- !id with openings of Meibomian ducts Papilla lachrymalis with ounctum lachrymale on the summit Plica semilunaris Caruncula lachrymalis Papilla lachrymalis Meibomian openings Meibomian glands shining through the conjunctiva Fig. 93. — Eyelid slightly everted to show the Conjunctiva (enlarged). 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 lachrymalis 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 lachry- DISSECTION OF THE FACE 245 ma/is, whilst the perforation, called the punctum lachrymale^ 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 lachry- malia and the lachrymal canals it becomes continuous with the lining membrane of the lachrymal sac. The line of re- flection of the conjunctiva from the lids on to the eyeball is termed the fornix conjunctiva. 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 connexion with the lower lid. The connexion 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 membrane becomes thinned down to a mere epithelial covering, which is closely adherent. In connexion with the conjunctiva the plica semilunaris and the caruncula lachrytnalis 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 it slightly overlaps the eyeball at this point. Dissection. — The dissection of the face is both difficult and tedious. The ramifications of the nerves are so intricate, and the fibres of the facial muscles are so pale, and so closely surrounded by the soft subcutaneous fat of the region, that great care and patience are required on the part of the Student to obtain a propel 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 tin- one side, and to the vessels and muscles on I lie opposite side. At the same time it must be clearly understood that a good dissector should be able to make a com- plete 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. 246 HEAD AND NECK The margins of the lips may then be stitched together. In doing this it is necessary to employ a fine needle. Only one incisionals 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. Carefully 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. 180). The little risorius muscle as it passes forwards from the masseteric region to the angle of the mouth is apt to be injured, and must therefore be remembered. In the case of the eyelids the skin is thin and is separated from 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 success- fully. 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 connexion 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. Facial Branch of the Great Auricular Nerve. — The branch which the great auricular nerve gives to the face should 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 vessels 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. Parotid Gland (glandula parotis). — The parotid is the largest of the salivary glands. It is lodged in the niche or recess between the lower jaw and the ear, and being adapted to this recess, it presents an irregular figure. Above, it is limited by the zygoma. Below, its lower border overlaps the DISSECTION OF THE FACE 247 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 fronts it rests against the posterior border of the masseter, the posterior margin of the ramus of the lower jaw, Parotid duct Lower jaw Wharton's 1 Mucous me Sublingual Internal pterygoid Lingual nerve Lower jaw Mylo-hyoid Surface of submaxil- lary gland covered by mandible Surface covered by intesfument and fascia; Mylo-hyoid' Anterior belly of digastric' Fig 94. — Dissection of the Parotid, Submaxillary, and Sublingual Glands. and the posterior border of the internal pterygoid muscle. From this aspect of the gland a thin and somewhat triangular portion of the gland termed the facial process is prolonged forwards for some distance upon the surface of the masseter muscle. It is from the anterior margin of the facial process towards its upper part that the duct of the gland emerges, and frequently a small detached lobule of gland substance will be observed lying upon the masseter in relation to the upper aspect of the' duct (Fig. 94). This is termed the soda n— 1Gb 248 HEAD AND NECK parotidis. The supe7'ficial or external surface of the parotid is slightly convex, and is covered by the dense parotid fascia which the dissector has already observed to be a prolongation upwards into the face of a portion of the deep cervical fascia (p. 185). In relation to this surface, and under cover of the fascia, there are usually one or two small lymphatic glands. Levator labii superioris Antrum of Highmore Zygomaticus major Buccinator muscle Temporal muscle Tonsil Mandibular vessels and nerve Pharynx Stylo-pharyngeus Stylo-glossus ternal carotid Sympathetic 12 34567 Fig. 95. — Transverse section through the Head at the level of the Hard Palate. It shows 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. 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 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. DISSECTION OF THE FACE 249 The fascial connexions of the parotid gland deserve some attention. The recess in which it lies is lined by a well- marked fascia, which separates it from subjacent structures, and 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 sub- stance, and accentuates its lobular appearance. The parotid fascia presents very important connexions. Above, it is attached to the zygoma ; behind, it 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. The front wall of this sheath in its lower part is thickened so as to form the stylo-maxillary ligament. This fascial band intervenes between the parotid gland on the one hand and the internal pterygoid muscle and a small part of the submaxillary gland on the other. Parotid Duct (ductus parotideus). — This is also called Stensoiis 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 are some branches of the facial nerve. At the anterior border of the masseter, it turns abruptly inwards through the soft fat of the. cheek, and, pierc- ing the buccinator muscle, 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. Dissection. — The parotid gland should now be removed piecemeal by following the various nerves anrl vessels which traverse it through its substance. 25° HEAD AND NECK Vessels and Nerves which traverse the Parotid. — By the removal of the gland, the vessels and nerves which traverse the gland are brought into view. These are : — Superficial temporal arteries Temporal branch of orbital nerve Auriculotemporal nerve Parotid Internal carotid — External carotid External jugular vein Superficial cervical nerve Descendens cervicalis Sterno-mastoid Parotid duct ansverse facial Masseter Facial artery and vein Submaxillary gland Hypoglossal nerve Lingual artery Superior thyroid artery Thyro-hyoid muscle Ansa hypoglossi , Fig. 96. — Dissection of the Parotid Region and the upper part of the Anterior Triansfle of the Neck. External carotid artery, f Superficial temporal. dividing into . . ^ Internal maxillary. Transverse facial artery. Temporo-maxillary vein. Facial nerve, or the seventh cranial nerve. Communicating twigs from the great auricular and auriculo-temporal nerves to the facial nerve. DISSECTION OF THE FACE 251 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 stage the artery is not placed within the gland, but merely in a groove on its deep surface, and 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 internal maxillaty 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 temporo-maxillary 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 the 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. Superficial Temporal Artery (arteria temporalis super- ficialis). — The superficial temporal artery 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 superficial temporal (ramus parietalis) arteries. These are described on p. in. The superficial temporal artery is closely accompanied by the auriculo-temporal nerve and the superficial temporal vein. In addition to its terminal branches it gives off — 1. Parotid twigs. 2. Anterior auricular branches. 3. The transverse facial. 4. The middle temporal. 5. The orbital. The anterior auricular branches (rami auriculares anteriores) supply the anterior aspect of the external auricle and anasto- mose with the posterior auricular artery. The transverse facial (arteria transversa faciei) is given off in the substance of the parotid. It runs transversely forwards, 25 2 HEAD AND NECK and, emerging from under cover of the anterior border of the gland, proceeds onwards across the masseter between the zygoma and Stenson's duct to end in twigs which anastomose with branches of the facial, buccal, and infra-orbital arteries. 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 in- constant branch which runs forwards above the zygoma between the two layers of the temporal fascia 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 groip around the mouth ; and a ?iasal group in connexion with the nose. Each of these groups may be examined in turn. It is convenient to begin wTith the palpebral and superciliary muscles. These are three in number : — 1. Orbicularis palpebrarum. 2. Tensor tarsi (Horner's muscle). 3. Corrugator supercilii. The upper eyelid has a special elevator, termed the levator palpebrce superior is, but this muscle is contained within the orbital cavity, and does not come under the notice of the dissector 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 out- wards, a prominent cord-like ligament becomes apparent on the inner side of the inner canthus. This extends outwards 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 palpebrarum. Orbicularis Palpebrarum (orbicularis oculi). — This k- the sphincter muscle of the palpebral fissure. It is a thin sheet of muscular fibres, which occupies a very considerable area of the face. It is customary to regard it as being composed of two parts, a palpebral and an orbital. The palpebral portion DISSECTION OF THE FACE 253 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, down- wards on the cheek, and outwards so as to encroach upon the temporal region. The fasciculi 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. They take origin (1) from the inner part of the internal tarsal ligament, (2) from the internal angular process of the frontal bone, and from the ascending process of the superior maxillary bone immediately in front of the lachrymal groove. Above and to the inner side, the fasciculi of the orbicularis muscle are closely connected, and to a certain extent interlaced with the fasciculi of the frontal part of the occipito-frontalis, the corrugator supercilii and the pyramidalis nasi, whilst from its lower margin a few delicate fleshy bands are carried down- wards 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 exposed 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 proportion 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. Oral Group of Muscles. — The muscles of the lips and mouth which are included in this group are the following : — 254 HEAD AND NECK I. Orbicularis oris. 5- Levator labii superioris. 2. v .. f major. Zygomaticus-! ■J Jb y minor. 6. 7- Levator anguli oris. Depressor anguli oris. 3- Risorius. 8. Depressor labii inferioris 4- Levator labii superioris 9- Levator menti. alceque nasi. IO. Buccinator. Orbicularis Oris. — The orbicularis oris is a sphincter muscle which surrounds 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 alseque 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 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 orbicu- laris. The levator menti has little connexion 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 in 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 are 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 DISSECTION OF THE FACE 255 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 Frontalis Orbicularis palpebrarum Levator labii superioris, aljeque na Compressor naris Levator labii superioris Zygomaticus major Levator anguli oris Risorius PyramidalU -Orbicularis oris Orbicularis oris Depressor labii inferioris Depressor anguli oris Fig. 97. — The Facial Muscles. 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 256 HEAD AND NECK of the cheek to the angle of the mouth, where they are inserted into the skin. The depressor anguli 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 Up in the orbi- cularis oris. The mental branch of the mandibular nerve and its ac- companying artery appear on the face under cover of this muscle. Levator Labii Superioris Alaeque Nasi. — This is a thin fleshy band which lies along the side of the nose. It is narrow above where it arises from the nasal process of the superior maxillary bone, but it expands somewhat as it proceeds downwards, and finally 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 labial slip is prolonged into the upper lip, where some of its fibres blend with the orbicularis oris, and others obtain a direct attach- ment to the skin. Levator Labii Superioris. — This band-like muscle 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 iftfra-orbital nerve emerges on the face, and joins with branches of the facial nerve in the infra-orbital plexus. Zygomaticus Minor. — 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 downwards 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 outer margin of the levator labii superioris. Levator Anguli Oris (musculus caninus). — The origin of this muscle is hidden by the levator labii superioris. It DISSECTION OF THE FACE 257 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. 99). Depressor Labii Inferioris (quadratus labii inferioris). — The depressor labii inferioris is a quadrate muscle partially hidden by the depressor anguli oris, which overlaps it Fig. 98. — Arrangement of the Fibres of the Buccinator Muscle at the Angles of the Mouth. (Fig. 97). 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, it joins the corresponding muscle of the 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 facial nerve and the long buccal nerve form a plexus upon its surface, and great numbers of nerves enter it, both for the purpose of supplying it, and also for the purpose of reaching the mucous membrane of the mouth which lines its deep surface. Buccinator Muscle. — This important muscle occupies the interval between the upper and lower jaws, and forms the chief muscular layer of the cheek. Above and below, its fibres take origin from the outer surface of the alveolar vol. 11 — 17 258 HEAD AND NECK 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 bond 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 Levator labii superioris alaeque nasi Levator labii superioris Levator anguli oris Depressor anguli oris Depressor labii inferioris Fig. 99. — Diagram of the Orbicularis Oris Muscle. The fibres which enter it from the buccinator are not represented. 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 lip (Fig. 98). 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 DISSECTION OF THE FACE 259 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 is 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. The fasciculi of the buccinator muscle 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 corresponding fasciculi of the opposite side. These fibres form the marginal part of the orbicularis, and also the deeper peripheral part. The labial portions of the levator anguli oris and the depressor anguli oris are arranged quite 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 peripheral part of the orbicularis. In 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., (1) the naso-labial band (m. naso-labialis), and (2) the superior incisive band (m. incisivus superior) ; and one, the inferior incisive band (m. incisivus inferior), 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 incisive 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 connexions in the lower lip. The incisive slips can be easily exposed by everting the lips, and re- moving the mucous membrane from the neighbourhood of these fossae. By this dissection two other small muscles will be displayed : (1) the depressor ake 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 arrange- ment 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 dis- played by the same proceeding. Levator Menti. — To expose this small muscle the lower lip must be everted, and the mucous membrane removed at 26o HEAD AND NECK the side of the frenum of the lower lip. It is a short, well- marked fleshy band, which springs from the incisor fossa of the lower jaw, and proceeds downwards and slightly forward, to be inserted into the skin of the chin between the two depressor muscles of the lower lip. Nasal Group of Muscles. — Under this head are com- prised : — 1. Compressor naris. 2. Levator labii superioris akeque nasi (already 3. Pyramidalis nasi. 4. Depressor alae nasi. 5. Dilatator naris posterior. examined). 6. Dilatator naris anterior. Compressor Naris. — -This 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 corre- sponding aponeurosis of the opposite side. Pyramidalis Nasi. — This narrow slip of muscular fibres springs from the aponeurosis of the compressor 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. Depressor Alse Nasi. — This is a minute muscle, the origin of which has already been displayed by the removal of the mucous membrane at the side of the frenum of the upper lip. It springs from the incisor fossa of the superior maxilla above and to the inner side of the superior incisive slip of the orbicularis oris muscle. Its outer 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. Dilatator Muscles. — These can rarely be satisfactorily displayed. 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 alse nasi anterior) is placed on the lower part of the side of the nose towards the fore-part of the nostril, and a posterior slip (levator proprius alee 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 nervus facialis. The sensory nerves come from various sources, and DISSECTION OF THE FACE 261 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. Facial nerve. I. Motor. 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. : — f Supra-orbital. x? n. i4. 1 • Supra-trochlear. °mdWision miC ! Infra-trochlear. Palpebral branch of the lachrymal. \ Nasal. t, ,, ( Infra-orbital, from the superior c , . , .„ j- • • -[ Subcutaneus malae. maxillary division. ~ , , , r ., ... , 3 I Temporal branch of the orbital. ^ . • c • i Auriculo-temporal. rrom the inferior T , , r ... ,. . . - Lone buccal, maxillary division. I Mei£al> {b) Reaching the face indirectly. 1. Communicating branches from the great auricular nerve to the facial nerve. 2. Communicating branches from the auriculo-temporal 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. Dissection. — The facial nerve is already, in a great measure, displayed. 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 obtained of the origin of the posterior belly of the digastric, of the stylo-mastoid branch of the posterior auricular artery as it enters the foramen 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 nerve emerges 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 temporo-farial and the cervicofacial divisio?is. From this part 11 17" 262 HEAD AND NECK s. 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, attollens auriculam, and posterior belly of the occipito-frontalis (p. no). Its origin is now exposed, and it will be seen to arise Supra-orbital Temporal branch of orbital Supra-trochlear Lachrymal Infra-trochlear Mental Malar branch of orbital Auriculo- temporal Posterior auricular Trunk of facial Branch to posterior belly of digastric and stylo-hyoid Long buccal Fig. 100. — Nerves of the Face. The facial nerve is depicted in yellow, the sensory branches of the trigeminal in black. 1, 2, 3. The three branches of the temporo-facial division of the facial nerve. 4, 5, 6. The three branches of the cervico-facial division of the facial nerve. 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 auditory meatus ; and after sending a branch to join the posterior auricular nerve, it ends in filaments for the integument on the posterior aspect of the ear. The nerve to the posterior belly of the digastric (ramus digastricus) is a stout, short branch which inclines downwards DISSECTION OF THE FACE 263 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 communication with the glosso-pharyngeal. The nerve to the stylo-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. Temporo-facial Division. — The temporo-facial division of the facial nerve is prolonged 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 be three, stout branches of com- munication 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 anserifius or plexus parotideus. The branches into which this portion of the facial trunk divides are classified, according to the direction which they take, into— 1. Temporal. 2. Malar. 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 bra?iches are small, 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 n—176 264 HEAD AND NECK 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 infra-orbital plexus), under cover of the levator labii superioris. Cervicofacial Division. — The cervico-facial division of the facial trunk is smaller than the temporo-facial division. It proceeds forwards, with a slight inclination downwards, and breaks up in the substance of the parotid into three main branches, which are termed from the course which they take — i. Buccal. 2. Mandibular. 3. Cervical. In the parotid gland the cervico-facial division crosses the external carotid artery and receives several communicating twigs from the great auricular nerve. The buccal branches run forwards upon the buccinator muscle to the angle of the mouth, where they end in fila- ments for the orbicularis oris. They supply the buccinator muscle, and form, with the long buccal branch of the 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 connexion with the lower lip. Under cover of the depressor anguli oris it communicates with the mental branch of the inferior dental nerve. The cervical or infra-mandibular branch has already been examined in the dissection of the neck (p. 182). Sensory Branches to the Face from the Trigeminal Nerve. — The branches which come from the ophthalmic division of the trigeminal nerve may first be studied. Of these, two go to the skin of the forehead and scalp — viz., the supra-orbital and the supra-trochlear ; two to the eyelids — viz., the palpebral branch of the lachrymal and the infra-trochlear ; and one, the nasal, to the skin of the nose. DISSECTION OF THE FACE 265 The supra- orbital and the supra-trochlear have already been dissected in the scalp (pp. 107, 109). 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 occipito-frontalis and the orbicularis palpebrarum, under cover of which they pass upwards. The supra-orbital quits the orbit by the 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 appears in the upper eyelid above the outer canthus, where it pierces the superior palpebral ligament, and gives filaments to the skin and conjunctiva. The infra-trochlear nerve 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 nasal nerve (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 superior maxillary 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. 109); the malar branch of the orbital nerve ; and the infra-orbital. The malar nerve (ramus zygomatico-facialis) is an exceedingly minute twig which emerges 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 nerve (nervus infra-orbitalis) is the terminal 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 266 HEAD AND NECK facial nerve, a plexus, and distributes palpebral, nasal, and labial branches. The palpebral twigs turn upwards to supply the skin and conjunctiva of the lower eyelid ; the nasal bra?iches 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 auriculotemporal, which has been described on p. no; the long buccal nerve ; and the mental nerve. The long 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. Those which go to the mucous membrane pierce the buccinator muscle. The mental nerve (nervus mentalis) is a large branch of the mandibular or inferior dental 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. 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. Arteries of the Face. — There are two main channels concerned in conveying blood to the face — viz., (i) the transverse facial artery, a branch of the superficial temporal, already examined (p. 251) ; (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 is not infrequently small in size. In such cases its DISSECTION OF THE FACE 267 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 Superficial temporal |\ Frontal branch of jm^-' ophthalmic artery Ntf Supra-orbital branch of the MSst"" ophthalmic artery ransverse facial Angular Lateral nasal fra-orbital Superior coronary '^iS^cs* Inferior coronary Inferior labial Buccal branch of internal maxillary Facial FlG. ioi. — Arteries ol the I been noted (p. 237). It enters the face by passing on to the mandible immediately in front of the masseter muscle. It then takes a very tortuous course forwards and upwards to a point 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 268 HEAD AND NECK terminates by anastomosing with the nasal branch of the ophthalmic artery. Throughout its whole length it is comparatively superficial. It is true that it is placed some- what deeply in the fat of the cheek, but the only muscles which cover it are, from below upwards : the platysma, the risorius, the zygomaticus major, and the levator labii superi- oris. Its terminal part is usually embedded in the midst of the fibres of the levator labii superioris alaeque nasi. The parts upon which it rests as it extends through the face will be seen to be — (i) the lower jaw ; (2) the buccinator ; (3) the levator anguli oris. The facial vein does not accompany it closely in the face, but, above the level of the lower jaw, lies 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 forwards, and, being of larger size, they receive special designations. They are : — 1. Inferior labial. 2. Inferior coronary. 3. Superior coronary. 4. Lateral nasal. 5. Angular. The inferior labial arises immediately above the base of the lower jaw, and is carried forwards under cover of the depressor anguli oris to supply the parts in connexion 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 the mouth, and runs inwards in the lower lip 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 zygomaticus 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 DISSECTION OF THE FACE 269 Crus antiheliois Darwin's tubercle Fossa scaphoidia Helix 4 Antitragus Fossa triangularis Crus antihelicis Concha Crus helicis Tragus Incisura intertragica 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 the union of the supraorbital and frontal veins (p. 111). 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 pro- ceeds in a nearly vertical direction along the anterior border of the mas- seter muscle, and at the base of the lower jaw the two vessels come together. Numerous tributaries 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. Auriele 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 anti/ielix is the curved prominence which bounds this posteriorly ; the helix is the folded or incurved margin of the pinna ; and the lobule is its soft dependent part. The concha is partially subdivided into an upper and a lower part by the commencement of the helix, which curves upwards and for- wards on its floor to become continuous with the anterior border of the pinna. This portion of the helix is called the crus helicis. A small prominence in front of the meatus, and projecting backwards so as to overshadow it, is termed the Lobulus Fig. 102. — The Pinna. 270 HEAD AND NECK tragus, whilst a similar eminence behind and below the meatus receives the name of the antitragus. The notch between these two prominences is termed the incisura intertragica. But it will be noted that the upper end of the ahtihelix 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 thin plate of yellow fibro-cartilage, covered by integument. It is fixed in position by certain ligaments, and possesses two sets of feeble muscles — viz., one group termed the extrinsic muscles, passing to the cartilage from the aponeurosis of the occipito-frontalis and the mastoid process, and a second group in connexion with the cartilage alone, and therefore called the intrinsic micscles. T . f Anterior. Ligaments, . . . • r> <. • fa ' ^ rostenor. fAttrahens. \ Extrinsic muscles, -J Attollens. /-Already examined, p. 107. [Retrahens. J f Musculus helicis major. ~\ Museums helicis minor. I Upon the outer face of the T . • • , f Musculus tragdeus. | cartilage. Intrinsic muscles, J ,, , p. b ' Musculus antitragicus. J Musculus transversus. ) Upon the cranial face of ^Musculus obliquus. / the 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 corresponds 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, but it does not form a complete tube. It is deficient above and in front, and here the tube of the meatus is completed by tough fibrous membrane, which stretches between the tragus and the commencement 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 caudatus, 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 DISSECTION OF THE FACE 271 aurictdar ligament stretches from the spine of the helix to the root of the zygomatic process. The posterior aurictdar ligament will be found under cover of the retrahens auriculam. It is stronger than the preceding, 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 antitragicus, are placed upon the outer face of the cartilage. The transversus and the obliquus lie upon the cranial surface of the pinna. The musculus antitragicus is the best-marked member of the outer group. It lies upon the outer surface of the antitragus, and its fibres pass obliquely upwards and backwards. Some fasciculi can be traced to the processus helicis caudatus. The mnsculus tragicus is a minute bundle of short vertical fibres situated upon the outer surface of the tragus. When well developed a slender fasciculus may sometimes be observed to pass upwards from it to the fore-part of the helix, where it gains insertion into the spine of the helix. The mnsculus helicis 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 musculus helicis minor is a minute bundle of fleshy fibres which is placed upon the crus helicis as it crosses the bottom of the concha. The musculus transversus auriculce is found upon the cranial aspect of the pinna. It is generally the most strongly developed muscle of the series, and it consists of fibres bridging across the hollow which, on this aspect of the auricle, corresponds to the antihelix. The musculus obliqtius auriculce is composed of some vertical fasciculi bridging across the depression which corresponds 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. Lower Lid. 1. Integument. 2. Palpebral part of the orbicularis palpebrarum. 3. The tarsus, the palpebral liga- ment, and the expanded ten- don of the levator palpebral 1. Integument. 2. Palpebral part of the orbicularis palpebrarum. 3. The tarsus and the palpebral ligament. supenons. 4. Conjunctiva. 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 time. 272 HEAD AND NECK Integument and Orbicularis. — These strata have already been examined, and the skin has been reflected. The palpebral part of the orbicularis muscle in each lid forms a thin layer of arching muscular fibres loosely connected with the integument by some lax areolar tissue. A fasciculus, somewhat thicker than the others (ciliary bundle or muscle of Riolan) 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. 253). 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. 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 writh the subjacent conjunctiva, whilst its superficial surface is clothed by the orbicularis muscle, and is in relation to the roots of the eyelashes. Its superior border is thin, convex, and continuous writh the tendinous expansion of the levator palpebral 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 (glandular tarsales). — At this stage the attention of the student cannot fail to be attracted by the Meibo77iian follicles, which are placed on the deep surfaces of the tarsal plates. 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 eyelashes, and by the DISSECTION OF THE FACE 273 aid of a magnify ing-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. Margin of the upper eye- lid with openings of Meibomian ducts Papilla lachrymalis with punctum lachrymale on the summit Plica semilunaris Caruncula lachrymalis Papilla lachrymalis Meibomian openings Meibomian glands shining through the conjunctiva Fig. 103. — Eyelid slightly everted to show the Conjunctiva (enlarged). In front of the bases of the eyelashes, between them and the ciliary muscle, are two or three rows of modified sweat-glands. These are called the glands of Moll, and when their ducts become occluded the condition familiarly known as stye results. Palpebral Ligaments. — These 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 the circumferential part of the orbital opening, termed the sephcm orbitale. The superior ligament blends along the orbital arch with the pericranium clothing the frontal bone, VOL. II —18 274 HEAD AND NECK 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 tarsal ligament, the palpebral ligaments become thin and delicate, and receive attachment to the lachrymal bone behind the lachrymal sac. Tarsal Ligaments. — The palpebral ligaments fix the tarsi Frontal bone Orbicularis palpebrarum Superior palpebral ligament — Superior conjunctival fornix Superior tarsal plate Conjunctival recess — Inferior conjunctival fornix Inferior palpebral ligament^ Fig. 104. — Diagram of the Structure of the Eyelids. 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. 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. The internal tarsal ligame?it is a much more important DISSECTION OF THE FACE 275 structure. It has a double function to perform, viz., (1) 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 spring from its upper and lower margins must be completely removed. The internal tarsal ligament is a strong fibrous band which springs from the nasal process of the superior maxil- Tendon of levator palpebrae superioris Superior palpebral ligament ""■■* Palpebral branch of lachrymal nerve" Superior tarsus - _ External tarsal ligament / Inferior palpebral ligament Infra-orbital nerve Supra-orbital nerve m£& \ Supra-trochlear nerve Superciliary ridge m Infra-trochlear nerve Lachrymal sac Internal tarsal ligament Inferior tarsus Fig. 105. — Dissection of the Right Eyelid. The orbicularis palpebrarum has been completely removed. 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- 276 HEAD AND NECK 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 palpebrae 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 connexions of this tendon. It 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 superior (Fig. 104). Vessels and 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 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- sory twigs for the upper lid come from the lachry77ial, supra- orbital, supra-trochlear, and infra-trochlear nerves, whilst the lower lid is supplied by branches from the infra-orbital nerve. Lachrymal Apparatus. — The following structures are in- cluded 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 DISSECTION OF THE FACE 277 Lachrymal canal Lachrymal sac Op 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 reflection of this membrane upon the anterior surface of the globe of the eye. The tears secreted by the lachrymal gland thus reach the under i»ferior surface of the upper lid, and by the involuntary closure of the lids 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 lachrymalis they are drained away by the lachrymal canals. The Lachrymal Canals (ductus lacrimales) have in a measure been already examined. The dissector has noted the punda 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 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 margins of the 11— 18 a FlG. 106. — Diagram of the Lachrymal Ducts and Sac, and of the Nasal Duct. (Gegenbaur. ) 278 ' HEAD AND NECK 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 hori- zontal in direction. 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 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 inferior meatus of the nose. In length it measures about half an inch. Dissection. — In cases where the dissector is dealing with undissected 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 muscular slip which can now be seen arising from the crest of the lachrymal bone behind the lachrymal sac. It is simply a deep portion of the orbicularis palpebrarum, with which it blends on the outer side of the lachrymal sac. The lachrymal canaliculi and lachrymal sac are thus enclosed in muscular fibres. Dissection. — The cartilaginous part of the nose should now be examined by stripping off the compressor naris muscle and the remains of the integument. 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 upper lateral cartilage 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 DISSECTION OF THE FACE 279 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 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 back- wards as far as the nasal notch of the superior maxilla. 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 sesamoideae) appear. In front, the bent part of cartilage comes into con- tact 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. Nasal nerve Lateral cartilage Sesamoid cartilages Cartilage of the aperture Fig. 107. — Cartilages of the Nose. THE TEMPORAL AND PTERYGO-MAXILLARY REGIONS. Under this heading are grouped the parts which are dis- sected in the temporal and zygomatic fossae of the skull. Dissection. — The structures which cover and lie superficial to the tem- poral fascia have already been examined in the dissection of the scalp (pp. 109, no). n—186 28o HEAD AND NECK Throw the temporal part of the orbicularis palpebrarum forwards ; pre- serve 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 part of the epicranial aponeurosis and of the two upper ear muscles. The temporal fascia is in this manner laid bare. Temporal Fascia (fascia temporalis). — The temporal fascia 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 curved 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 laminae, 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 com- paratively 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 laminae it becomes perfectly opaque. Dissection. — The masseter rfiuscle must now be thoroughly cleaned. To do this effectually, it will be necessary to divide the trunk of the facial nerve 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 buccal region. The transverse facial artery must be also turned backwards. 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. Masseter. — 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 superficial 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 TEMPORAL AND PTERYGOID REGIONS 281 only 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 inserted into the outer surface of the ascend- ing 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 to injure its nerve and artery of supply. These pass outwards through the sigmoid notch, between the neck of the lower jaw and the posterior margin of the temporal muscle. When they are exposed and cleaned, they must be divided in order that the muscle may be fully re- flected. On no account detach the masseter from the angle of the jaw. The temporal muscle may now be cleaned. Temporal Muscle (musculus temporalis). — The temporal muscle 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 infra-temporal crest on 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 intermediate 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 and 282 HEAD AND NECK 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 prominence by an inser- tion 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 body of the mandible. First use the saw, and then complete the division with the bone pliers. The long buccal nei"ve and its companion artery are in a position of danger during this dissection, and must be care- fully guarded. They proceed downwards and forwards under cover of the lower part of the temporal muscle, and not infrequently 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 temporal fossa. This will bring into view the deep temporal nerves and arteries as they 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 im- mediately above the level of the inferior dental foramen. To find the level of the latter, the handle of the forceps should be thrust forwards 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, embracing 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 same 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 internal maxillary artery — pro- TEMPORAL AND PTERYGOID REGIONS 283 ceeds forwards upon (frequently under cover of) 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 infratemporal crest are the masseteric and the two deep temporal nerves ; appearing from under cover of Internal maxillary Posterior superior dental Long buccal nerve and artery Temporal muscle Deep temporal artery Deep temporal nerve Deep temporal artery /Deep temporal nerve Masseteric nerve i Superficial temporal artery Auriculo-temporal nerve External pterygoid Middle meningeal artery Mastoid process — External carotid Small meningeal artery r.i \ srnau meningeal a \ Inferior dental artery Huccinator Fig. 108. Mylo-hyoid artery and nerve Inferior dental nerve Lingual nerve Internal pterygoid muscle -Dissection of the Pterygo-maxillary Space. its lower border are the mandibular or inferior dental and the lingual nerves ; whilst the auriculo-temporal nerve 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-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. 284 HEAD AND NECK External Pterygoid Muscle (musculus pterygoideus ex- ternus). — The external pterygoid arises in the zygomatic fossa by two heads, an upper and a lower. The upper head springs from the infratemporal ridge and the zygomatic surface of the great wing of the sphenoid ; the loiver head takes origin from the outer surface of the external pterygoid plate. As the muscle passes backwards it diminishes some- what in width, and is inserted into the fore-part of the neck of the mandible, and also into the anterior margin of the inter-articular fibro- cartilage of the temporo -maxillary articulation. Internal Pterygoid Muscle (musculus pterygoideus in- ternus). — The internal pterygoid is also bicipital at its origin. Its two heads embrace 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 down- wards with an inclination backwards and outwards. They gain insertion 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. Internal Maxillary Artery (arteria maxillaris interna). — This vessel 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 zygomatic 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 customary to divide it into three parts for convenience in description. The first part runs horizontally forwards under cover of the neck of the mandible, 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 TEMPORAL AND PTERYGOID REGIONS 285 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. 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 internal and external 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 ty?npanic 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 either side of it, and it is placed behind the inferior dental nerve. Just before entering the canal, the inferior dental artery gives off the slender mylo- 286 HEAD AND NECK hyoid branchy which is carried downwards and forwards with the corresponding nerve, upon the deep aspect of the mandible, to the digastric triangle of the neck. The branches from the second part are given off for 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. The pterygoid branches (rami pterygoidei) are a few irregular twigs, which are given to the pterygoid muscles. The deep temporal arteries (arteriae temporales profundae) are two in 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 buccal nerve, and is distributed to the buccinator muscle and the mucous membrane of the cheek. It anastomoses with the facial artery. The posterior superior dental bratich (arteria alveolaris superior posterior), from the third part of the internal maxillary artery, descends upon the posterior aspect of the superior maxilla, and sends branches through the posterior dental foramina for the supply of the upper molar and bicuspid teeth (Fig. 108). 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 plexus, around the external pterygoid muscle. Tributaries corre- sponding to the branches of the internal maxillary artery open into this network, whilst the blood is led away from its back part by a short wide trunk, called the internal maxillary vein. This vessel accompanies the first part of the internal maxillary artery into the parotid gland, and joins the super- ficial temporal vein behind the neck of the jaw, to form the temporo-77iaxillary trunk. The pterygoid venous plexus also establishes, by various TEMPORAL AND PTERYGOID REGIONS 287 offsets, certain highly important connexions. 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 ophthalmic vein through the spheno-maxillary fissure. Temporo-Maxillary Articulation (articulatio mandibularis) — This joint must next be studied, in order that the external pterygoid muscle may be thrown forwards. In connexion with it we find : — Ligaments Proper. 1. The external lateral. 2. The capsular. Accessory Ligaments. An interarticular fihro-cartilage. 1. Internal lateral. 2. Stylo-maxillary. 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 pro- ceed 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 springs from the spinous process of the sphenoid bone, and is attached below to the lingula and to the sharp inner margin of the mandibular foramen of the lower jaw. It is not in direct relationship with the joint. Above, it lies under cover of 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-maxillary ligament has already been noticed. It is an aponeurotic band, derived from the deep cervical fascia as it forms a part of the capsule of the parotid gland. It is HEAD AND NECK 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 liga- ments as upon the strong muscles of mastication, which keep the head of the mandible in its place. The interarticular fibro-cartilage is an oval plate, with its long axis directed transversely. It is interposed between the condyle of the mandible and the glenoid cavity, and divides the joint cavity into an upper and lower portion, each of Eminentia articularis Upper joint cavity Meniscus Lower joint cavity Capsule / Mastoid process Styloid MANDIBl Fig. 109. — Section through Temporo-maxillary Joint. which is provided with a separate synovial membrane. To expose the cartilage, the external lateral ligament must be removed. It will then be seen to be adapted to the two bony surfaces between which it lies. Above, it is concavo- convex in correspondence with the eminentia 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 liga- ment, and that anteriorly the external pterygoid muscle is partly inserted into it. The synovial membrane which lines the upper cavity of the TEMPORAL AND PTERYGOID REGIONS 289 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. Movements. — The movements which the mandible can perform at the temporo- maxillary joint are the following: — (1) depression; (2) elevation ; (3) protraction ; (4) retraction ; (5) lateral or chewing move- ments. When the lower jaw is depressed the interarticular fibro-cartilage 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 compart- ment 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 trans- verse axis which traverses the bone in the neighbourhood of the mandi- bular foramen. This is the point, therefore, of least movement, and consequently in opening and shut- ting 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: — (1) depressors — the platysma, the mylo- hyoid, and the anterior belly of the digastric ; (2) elevators — the masseter, internal pterygoid, temporal; (3) protractors — the external pterygoid, and to some extent the internal pterygoid and the superficial 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. Fig. no. — Diagram of the different positions occupied by the head of the mandible and the interarticular carti- lage as the mouth is opened and closed. Reflection of External Pterygoid. — The hea/1 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 ex- amined. Care must be taken not to injure the auriculotemporal 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 VOL. II — 19 29o HEAD AND NECK 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 trigeminal nerve, emerging from the foramen ovale, and breaking up into its branches of distribution. The slender chorda tympani will likewise be found proceeding downwards and forwards to join the lingual nerve, and the middle menin- geal, 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 already 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. 130). It will generally be observed to be embraced by the two heads of origin of the auriculo-temporal nerve. The small meningeal (ramus meningeus accessorius) and ty77ipa?iic (arteria tympanica) arteries arise more frequently from the preceding vessel than from the trunk of the internal maxillary. The small meningeal inclines forwards and up- wards, and enters the cranial cavity by passing through the foramen ovale ; the tympanic runs upwards and slightly back- wards, and reaches the tympanum by passing through the Glaserian fissure. In the tympanic cavity it anastomoses with the stylo-mastoid branch of the posterior auricular artery. Inferior Maxillary Division of the Trigeminal Nerve (nervus mandibularis). — The inferior maxillary nerve arises within the cranium from the Gasserian ganglion, and enters the pterygo-maxillary region through the foramen ovale. It is composed of sensory fibres, but it is accompanied through the foramen by the small motor root of the trigeminal nerve, and, a junction being effected between the two immediately after they gain the exterior of the cranium, a mixed nerve-trunk is the result. This nerve-trunk lies under cover of the ex- ternal pterygoid muscle, and after a very short course (not exceeding two or three lines) it ends by dividing into two parts, named the anterior and posterior divisions of the inferior maxillary nerve (Fig. in). Before it divides, the trunk of the inferior maxillary nerve gives off two branches, viz., (1) the recurrent nerve (nervus spinosus), and (2) the nerve to the internal pterygoid muscle. The recurrent nerve is a very slender twig which enters TEMPORAL AND PTERYGOID REGIONS 291 the cranium by accompanying the middle meningeal artery through the foramen spinosum to supply the dura mater. The internal pterygoid nerve will be found passing under 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. GASSERIAN GANGLION. ophthau: DIV; FlG. i 11. — Diagram of the Gassenan Ganglion and the Inferior Maxillary Division of the Fifth or Trigeminal Nerve. The motor root of the fifth nerve is tinted yellow. From the two terminal divisions of the inferior maxillary trunk the chief branches of distribution arise. The 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 chose which form the long buccal nerve. It gives off the following branches: — 1. Masseteric. 2. Two deep temporal. External pterygoid. Long buccal. The large posterior division is chiefly sensory. It contains 11 — 19 « 292 HEAD AND NECK only a very few fibres from the motor root, and these are prolonged into its inferior dental branch, and afterwards come off in the form of the mylo-hyoid nerve. The branches of the posterior division are : — i. Auriculotemporal. 2. Inferior dental. 3. Lingual (or gustatory). The masseteric ?ierve (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 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 and 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. Long Buccal Nerve (nervus buccinatorius). — The long buccal is the largest of the branches proceeding from the anterior division of the inferior maxillary nerve. It proceeds outwards 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 the buccal plexus, and to be distributed to the mucous membrane and skin of the cheek (p. 266). 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., (1) in the nerve to the external pterygoid, TEMPORAL AND PTERYGOID REGIONS 293 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. 108). In some cases the long buccal nerve may be observed to pierce the temporal muscle instead of passing under cover of it. Auriculo-Temporal Nerve (nervus auriculo-temporalis). — The auriculotemporal, composed of sensory fibres, springs from the posterior division of the inferior maxillary by two roots. These 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 between the neck of the lower jaw and the internal lateral ligament. 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. no). The following branches proceed from it: — (1) one or two strong branches of communication to the temporo-facial nerve; (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. no); (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. Inferior Dental Nerve (nervus alveolaris inferior). — This 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 u—196 294 HEAD AND NECK downwards within its sheath as far as the mandibular foramen. At this point they come off as the slender mylo-hyoid 7ierve. The mylo-hyoid nerve, accompanied by the artery of the same name, pierces the internal lateral ligament and pro- 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 mylo-hyoid nerve has already been dissected. It appears upon the surface of the mylo- hyoid muscle, and, issuing from under cover of the super- ficial 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 tympani branch of the facial nerve. Not infrequently, also, a communicating twig passes between it and the inferior dental nerve. Chorda Tympani. — This 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 connexion with the root of this branch. Its connexions, however, can only be made out by TEMPORAL AND PTERYGOID REGIONS 295 dissecting from the inside, and it is well to defer its examina- tion 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 nerve. These give off twigs which enter the fangs of the molar and bicuspid teeth, and each terminates by dividing into a mental and incisor branch. The mental artery and nerve 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 corresponding 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. 204). It is now necessary to carry the dissection to a deeper plane, in order to expose a number of parts in connexion 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. f Hyoglossus. 5. Muscles. J Styloglossus. 3 J Geniohyoid. V. Genio-hyoglossus. ( Hypoglossal. 6. Nerves. -J Lingual. ^ Glosso- pharyngeal. 7. Submaxillary ganglion. 8. Lingual artery and veins. 9. Stylo-hyoid ligament. Dissection. — 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 296 HEAD AND NECK then the tip 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 are encountered, viz., the mylohyoid, the hyoglossus, the genio-hyoglossus. In the intervals between these, certain important structures will be exposed. Begin with the first muscular stratum. The mylo-hyoid muscle 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 super- ficial surface of the mylo-hyoid is in this way completely exposed, and its fibres may be cleaned and its attachments made out. Mylo-hyoid (musculus mylohyoideus). — This 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. The 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 diaphragma oris. The mylo-hyoid muscle is supplied by the mylo-hyoid branch of the inferior dental nerve. 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 small piece may be left attached to the mandible to serve as a landmark in the future dissection. This must be done 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 SUBMAXILLARY REGION 297 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 care must be taken to preserve 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. 112). — The side of the tongue is now brought into view, with a number of structures in connexion with it. First note the mucous membrane stretching from the tongue to the gum of the lower jaw ; then identify the various muscles. Styloglossus Stylo-pharyngeus Glossopharyngeal nerve Stylo-hyoid ligament (Lingual nerve Deep part of submaxillary gland Submaxillary ganglion Whai ton's duct Cut edge of mucous membrane Sublingual gland ai)^ Sublingual artery Genio- hyoglossus nio-hyoid Lingual artery Middle constrictor Lingual artery Hypoglossal nerve ■a-hyoid artery Fig. 112. — Dissection of Submaxillary Region. The hyoglossus, a portion of which was previously visible behind the mylo-hyoid, is fully exposed. It is a quadrangular 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 relation- ship to it. Thus, behind, and to some extent superficial to its upper part, will be recognised the stylo-glossus muscle, whilst in front of it are the genio- hyoglossus and the genio -hyoid. The genio-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 hyoglossus. Upon the surface of 298 HEAD AND NECK 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. The lingual ?ierve occupies the highest level, and passes forward upon the muscle near its insertion into the tongue. The hypoglossal ?ierve, accompanied by the ranine veiti, crosses it close to the hyoid bone, whilst the deep part of the submaxillary gland and Wharton's duct occupy an intermediate place. Although Internal pterygoid External pterygoid Inferior turbinated bone Soft palate Temporal muscle Stylo-glossus Inferior dental vessels and nerve Lingual nerve Facial artery- Superficial part of x submaxillary- gland "^XWJW^ Wharton's duct^V^^^* Deep part of>>^3 submaxillary gland \x^ Hypoglossal nerve Lingual artery Hyoglossus Mylo-hyoid Digastric tendon Genio-hy Tongue Inferior dental vessels and nerve in the mandib- ular canal Facial artery Mylo-hyoid Lingual nerve 'Deep part of submaxillary gland 'Wharton's duct Hypoglossal nerve Lingual artery \ 'Digastric Hyoglossus ^Genio-hyoid Fig. 113. — Coronal section through the Tongue and Submaxillary Region in a plane behind the molar teeth. the submaxillary ganglion 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- hyoglossus, 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 : — SUBMAXILLARY REGION 299 (1) the glossopharyngeal nerve immediately below the stylo- glossus muscle; (2) the stylo-hyoid ligament, a little lower down ; and (3) the lingual artery, close to the hyoid bone. Hyoglossus. — This 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 Parotid duct Lower jaw Wharton's d Mucous membrane Sublingual Internal pterygoid Lingual nerve Lower jaw Mylo-hyoid Surface of submaxil- lary gland covered by mandible urface covered by tegument and fasciae Mylo-hyoid' Anterior belly of digastric' FlG. i 14. —Dissection of the Parotid, Submaxillary, and Sublingual Glands. under cover of the stylo-glossus. The hyoglossus is supplied by the hypoglossal nerve. Styloglossus. — The stylo-glossus muscle 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 down- wards 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 hyoglossus muscle. The nerve of supply to the stylo-glossus comes from the hypoglossal. 3°° HEAD AND NECK Genio-hyoid (musculus geniohyoideus). — The genio-hyoid muscle is placed 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 down- wards 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. Inferior meatus of nose Tongue Vestibule of mouth Sublingual gland Wharton's duct- Lingual nerve Genio-hyoglossu \ntrum of Highmore Great posterior .palatine artery and nerve Vestibule of mouth Buccinator Ranine artery Sublingual gland Inferior dental artery and nerve in the mandibular canal ~Mylo-hyoid Platysma Genio-hyoid Anterior belly of digastric Fig. 115. — Coronal section through the Closed Mouth in the plane of the second molar teeth. Submaxillary Gland (glandula submaxillaris). — The sub- maxillary gland consists of a superficial and a deep portion ; the superficial or itiain 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 is contained within a capsule derived from the deep cervical fascia. Its superficial surface presents two areas, an upper and a lower. Of these the upper lies under shelter of the body of the lower jaw and looks upwards and outwards ; the lower, which looks downwards and outwards, is covered by the skin, superficial fascia, platysma, deep fascia, and is crossed by the facial vein. The deep surface of the gland rests upon the mylo-hyoid, SUBMAXILLARY REGION 301 and behind this upon the hyoglossus and the posterior belly of the digastric with the stylo-hyoid. From this surface the deep part of the gland is prolonged forwards under cover of the mylo-hyoid muscle along with the duct. Lodged in a deep groove upon the posterior and upper aspects of the gland is the facial artery (Fig. 113). Wharton's Duct (ductus submaxillaris). — The duct of the submaxillary gland is termed IVharton's duct. It emerges from the deep surface of 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 which lies above it and the hypoglossal nerve which is placed below it. Reaching the surface of the genio-hyoglossus muscle, it inclines slightly upwards and is crossed by the lingual nerve. Here it passes under cover of the sublingual gland, and gains the floor of the mouth, where it opens by a small orifice placed on the summit of a papilla which lies close to the side of the frenum 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 dissector will experience little difficulty in passing a fine probe or bristle along it into the mouth. Sublingual Gland (glandula sublingualis). — The sublingual gland lies on the floor of the mouth, and 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 definite. Its prominent upper border can be seen within the mouth, beneath the fore-part of the tongue, where it is covered by a fold of mucous membrane termed the plica sublingualis (Fig. 115). 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 symphysis, and above the mylo-hyoid ridge. 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 lingual nerve are prolonged forwards under cover of the sublingual gland. Numerous small ducts (the number varying from eight to twenty; proceed from the sublingual gland. These are called the duds of Rivinus, and they all, as a rule, open 302 HEAD AND NECK into the mouth on the summit of the plica sublingualis (Birmingham). Lingual Nerve (nervus lingualis). — In the dissection of the pterygo-maxillary region, the lingual nerve has been seen passing downwards between the ramus of the mandible and the 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 im- mediately 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. C 1. Two or more to the submaxillary ganglion. Twigs of I 2. One or two which descend along the anterior Communication.! border of the hyoglossus muscle to unite with t the hypoglossal nerve. ■r, , f 1. Slender filaments to the mucous membrane of the Branches ,, , c I mouth and gums. tv .-••.. ] 2. A few twigs to the sublingual gland. Distribution. t, , ? ., . & ^ V. 3. Branches 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 papillae over the anterior two- thirds of this organ. Submaxillary Ganglion. — This is a minute ganglion which will be found lying upon the upper part of the hyoglossus 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 SUBMAXILLARY REGION 303 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 connexion with the branches of the fifth cranial nerve, this ganglion has three roots — viz., (1) a sensory root from the lingual nerve ; (2) a 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 — (1) to the submaxillary gland; (2) to Wharton's duct ; (3) from the branch which it gives to the lingual nerve to the sublingual gland ; and (4) to the mucous membrane of the mouth. Hypoglossal Nerve (nervus hypoglossus). — This nerve has been traced in the dissection of the anterior triangle to the point where it disappears under cover of the mylo-hyoid muscle (p. 211). It is now seen passing forwards upon the hyoglossus 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 muscular substance of the tongue. Upon the hyoglossus muscle it is accompanied by one of the lingual veins, frequently termed the ranine vein. The branches which spring from the hypoglossal nerve in this region are very numerous, and are entirely distributed to muscles. It supplies— (1) the stylo-glossus; (2) the hyoglossus; (3) the genio-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 connexions 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. Reflection of the Hyoglossus. —The hyoglossus should now be carefully detached 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 stages of the lingual artery, with its dorsalis linguae branch and the veins which accompany it; (2) the posterior part of the genio-hyoglossus; (3) the 304 HEAD AND NECK origin of the middle constrictor of the pharynx ; and (4) the attachment of the stylo-hyoid ligament. Genio-hyoglossus (musculus genio-glossus). — This 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 ; 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., (1) 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 hyoid bone ; (3) a portion ascending 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. 112). The first 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. SUBMAXILLARY REGION 305 The bra?iches of the lingual artery are : — 1. Suprahyoid from the first part (p. 237). 2. Dorsalis linguae from the second part. 3. Sublingual from the third part. 4. The ranine or terminal branch. The dorsalis lingiice 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 supplied 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 sublingual gland which it supplies. It also gives branches to the surround- ing muscles, and anastomoses with its fellow of the opposite side and with the submental branch of the facial artery. The ranine artery (arteria profunda linguae) runs forwards upon 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 frenum of the tongue, and to be con- tinued forwards in the interval between the genio-hyoglossus 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. — -The lingual artery is accompanied by two small venae comites which lie with it under cover of the hyoglossus ; but the main vein of the tongue, termed the ranine, accompanies the hypoglossal nerve upon the superficial 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. Stylo-hyoid Ligament. — This 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. vol.. 11 — 20 306 HEAD AND NECK DEEP DISSECTION OF THE NECK. In the deep dissection of the neck the following structures are displayed : — i. The styloid process, with the three muscles which take origin from it. 2. The internal carotid artery. 3. The ascending pharyngeal artery. 4. The tonsillitic and ascending palatine branches of the facial artery. 5. The internal jugular vein. 6. Glosso-pharyngeal nerve. 7. Vagus nerve. 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 posterior auricular arteries, it can be turned forwards out of the way. Of the parts in connexion 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. Stylo-pharyngeus. — This 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 downwards 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 DEEP DISSECTION OF THE NECK 307 muscle is supplied by a branch from the glossopharyngeal 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 glossopharyngeal, vagus, spinal accessory, and hypoglossal nerves, and the sicperior cervical ganglion, with their various connexions and branches, must at the same time be dissected. This is an exceedingly difficult dissection. A dense and tough fascia envelops these structures, and a great amount of patience is required to trace the branches of the nerves through it. One nerve— the pharyngeal branch of the vagus — which proceeds downwards and forwards upon the superficial or outer aspect of the internal carotid, is especially liable to injury, and must therefore be borne in mind from the very outset of the dissection. The internal laryngeal and the external laryngeal jierves have been previously displayed in the anterior triangle of the neck. These, if traced upwards, will lead to the superior laryngeal branch 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 be 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 the first loop of the cervical plexus will be seen. Internal Carotid Artery (arteria carotis interna). — The internal carotid artery 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., (1) 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. Three nerves and two arteries will also be noticed to cross the vessel superficially, viz. : — 11 — 20" 3o8 HEAD AND NECK 1. The occipital artery. 2. The posterior auricular artery. 1. The hypoglossal nerve. 2. The glosso-pharyngeal nerve. 3. The pharyngeal branch of the vagus nerve. The relationship of the external carotid artery to the Spinal accessory- L| jj|iy — Vagus -Ganglion of root —Glosso-pharyngeal Superficial temporal Ganglion of trunk Pharyngeal branch Superior laryngeal Hypoglossal Descendens hypoglossi Ascending pharyngeal Internal carotid Internal maxillary External carotid Posterior auricular ^-Occipital Facial Lingual Branch to thyro-hyoid Internal laryngeal External laryngeal Common carotid Fig. 116. — Diagram of Carotid System of Vessels in the Neck with the Glosso-pharyngeal, Vagus, Spinal Accessory, and Hypoglossal Nerves. 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 DEEP DISSECTION OF THE NECK 309 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 ascending pharyngeal artery. 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. 239). 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. The pharyngeal branches (rami pharyngei) supply the pharynx, and the lower members of the series anastomose with the superior thyroid artery. Higher up, a larger palatine branch distributes twigs to the Eustachian tube, the soft palate, and the tonsil. The prevertebral branches are small twigs which are given to the prevertebral muscles, and anastomose with the ascending cervical artery. The meningeal twigs 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 11— 205 3io HEAD AND NECK branches which are given off by the facial artery. They have already been described (p. 237), but their relations as they ascend in the neck can now be more satisfactorily studied. The size of the inferior or ascending palatine is very variable, and depends very much upon that of the palatine branch of the ascending pharyngeal. Internal 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 proceeds downwards, until it reaches the posterior aspect of the inner end of the clavicle, where it joins the subclavian vein to form the innominate or brachio-cephalic vein. Its commencement in the jugular foramen shows a slight dilatation, termed the bulb, the lumen of which remains at all times patent owing to the connexion of its walls to the margins 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 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, DEEP DISSECTION OF THE NECK 311 and it is bisected by the vagus nerve. It should also be remembered that on the left side the terminal part of the thoracic duct passes behind the internal jugular vein. The tributaries which join the internal jugular vein have for the most part been previously studied. They are : — 1. Inferior petrosal sinus (p. 129). 2. Pharyngeal veins. 3. Lingual veins (p. 305). 4. Common facial vein (p. 238). 5. Superior thyroid vein (p. 236). 6. Middle thyroid vein (p. 242). 7. Thoracic duct on the left side and the right lymphatic duct on the right side (p. 224). The inferior petrosal sinus leaves the cranial cavity by the anterior compartment of the jugular foramen, and joins the Sheath of dura mater around vagus and spinal accessory nerves Ganglion of trunk Internal jugular vein Superior laryngeal nerve Spinal accessory nerve r^ft Vagus nerve Sheath of dura mater around glosso-pharyngeal nerve Inferior petrosal sinus Internal carotid artery Glosso-pharyngeal nerve Pharyngeal branch of vagus. Internal laryngeal nerve External laryngeal nerve FlG.117. — Diagram of the relation of parts in the Jugular Foramen. 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 connexion 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, and presents free communications above with the pterygoid plexus. Dissection.— The internal jugular vein should now be slit open. 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, ir— 20 c 312 HEAD AND NECK Glossopharyngeal, Vagus or Pneumogastric, and Spinal Accessory Nerves. — These nerves have, on 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. 126, and Fig. 60, p. 125). It is well that the dissector should again examine the interior of the cranial cavity and refresh his Oculo-motor nerve Trochlear nerve Sensory root of the trigeminal nerve Motor root of the trigeminal -^ nerve \bducent nerve Facial nerve 1 Cut edge of the tentorium -.Pars inter- media Auditory nerve Right lateral sinus Glosso-pharyngeal nerve Vagus nerve Spinal accessory nerve S8#' Jf^ Vertebral artery > jff^ Hypoglossal nerve First spinal nerve ^Spinal accessory nerve FiG. 118. — Section through the Head a little to the right of the Mesial Plane. It shows the posterior cranial fossa and the upper part of spinal canal after the removal of the brain and the cord. memory as to the manner in which they enter the foramen. The glossopharyngeal 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, 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 hypo- glossal nerve, in the interval between the internal jugular vein and the internal carotid artery, but soon they choose different DEEP DISSECTION OF THE NECK 313 routes. The spitial accessory inclines backwards over 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. 117). 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 dissection 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 superficially. It passes under cover of the styloid process and 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. The conwiunicating branch from the facial 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. The stylopharyngeal nerve is a small twig which enters the muscle of the same name. The greater part of its fibres, however, arc continued through the muscle to the mucous membrane of the pharynx. 'I he pharyngeal branches consist — (1) of one or two small twigs which perforate the superior constrictor to reach the mucous membrane of the pharynx; and (2) a larger nerve 3i4 HEAD AND NECK 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-pharyngeal near the base of the tongue. They form a plexus over 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 brandies will be followed in the dissection of the tongue. There are still other points in connexion with the glosso-pharyngeal nerve which require mention. At the lower part of the jugular foramen two small 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. The 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. No branches arise from it. The petrous ganglion is a larger swelling, which involves the entire nerve-trunk, and lies at the opening of the jugular foramen between the inferior petrosal sinus (which intervenes between it and the anterior border of the foramen) and 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 communication enter or proceed from it. These connect it with — (i) the superior cervical sympathetic ganglion; (2) the auricular branch of the vagus ; and (3) the root-ganglion of the vagus. In addition to these twigs the tympanic nerve or the nerve of Jacob son 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 small foramen on the ridge which separates the jugular fossa from the carotid foramen on the under 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 promon- tory. 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 supeificial petrosal nerve is lodged opens into the cranial cavity upon the anterior face of the petrous bone, immediately external to the hiatus Fallopii. Through this the nerve emerges, and soon leaves the interior of the cranium by passing down- 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 tympanic nerve gives branches of supply — (1) to the mucous membrane of the tympanum; (2) to the lining membrane of the mastoid cells ; and (3) to the mucous membrane of the Eustachian tube. It also gives off a fine branch termed the small deep eptrosal ne>i>e (n. petrosus profundus minor). This enters a canal in the DEEP DISSECTION OF THE NECK 315 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 nervus carotico-tympcuiicus. 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 dowrnwards between the common carotid and left subclavian arteries, and passes under cover of the left innominate vein. As in the case of the glossopharyngeal, the vagus shows two ganglia in connexion with its upper part. These are the ganglion of the root (ganglion jugulare) and the ganglion of the trunk (ganglion nodosum). The Ganglion of the Root is situated within the jugular foramen. It is a rounded swelling which is connected by communicating twigs with several of the nerves in the neighbourhood, and which gives off two branches of distribution. 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 recurrent 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 nerve (Arnold's nerve) obtains a filament of communica- tion 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 3i6 HEAD AND NECK 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 connected with it by an ascending and a descending branch of communication. Penally, 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. 262. Ganglion of the Trunk. — After emerging from the jugular foramen, the vagus nerve is joined by the accessory porlio?i of the spinal accessory nerve, and swells out into the ganglion of the trunk. The gang/ion 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 com- munication pass between this ganglion, the first loop of the cervical plexus, and the superior cervical ganglion of the sympathetic. Further, the hypoglossal nerve is generally closely bound to it by fibrous attachment, in the midst of which some interchange of nerve filaments takes place. Branches of Distribution of the Cervical Part of the Vagus. — The branches which spring from the vagus as it traverses the neck are the following : — 1. Pharyngeal. 2. Superior laryngeal. 3. Inferior or recurrent laryngeal. 4. Cardiac. Pharyngeal Branch (ramus pharyngeus). — This 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 pharyngeal plexus. Very frequently it is replaced by two branches, of which the upper is the larger. Superior Laryngeal Nerve (nervus laryngeus superior). — This 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 tinder 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 (p. 203). Before it divides, the superior laryngeal effects communications by means of fine twigs with the superior cervical ganglion of DEEP DISSECTION OF THE NECK 317 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 filaments 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. Recurrent Laryngeal Nerve (nervus laryngeus inferior).— The recurrent laryngeal arises differently on the two sides. On the right side, it springs from the vagus as it crosses the first part 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 ob- literated ductus arteriosus). In the neck each nerve ascends in the groove between the trachea and oesophagus, and passing behind 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., (1) 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. Cardiac Branches. — Two cardiac branches arise from the vagus in the neck. On the right side, both of these enter the thorax by passing behind the subclavian artery and end in the deep cardiac plexus. On the left side, the upper nerve joins the deep cardiac plexus, whilst the lower nerve enters into the formation of the superficial cardiac plexus. Spinal Accessory Nerve (nervus accessorius). — This nerve consists of two parts — an accessory and a spinal. In the foramen jugulare the accessory portio?i is connected 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. 0 1 8 HEAD AND NECK 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-ganglion, 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 spinal 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 of the sterno-mastoid muscle. Its further course has been already studied (pp. 137 and 203). It is distributed to two muscles — viz., the sterno-mastoid and the trapezius. Pharyngeal Plexus (plexus pharyngeus). — This is a mesh- work of fine 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 sympathetic enter into its construction, and one or more minute ganglia are developed in connexion with it. Its terminal twigs are given to the muscles and mucous membrane of the pharynx, and one branch (the ra??ius lingualis vagi) connects the plexus with the hypoglossal nerve. Hypoglossal Nerve (nervus hypoglossus). — The hypoglossal nerve makes its exit from the cranium, through the anterior condyloid foramen. It pierces the dura mater in tw7o 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 immediately inclines out- wards, 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 connexion 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 hypo- glossal 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. Brandies of communication. — Near the base of the skull the hypoglossal is brought into connexion with (1) the superior cervical ganglion ; (2) the vagus j and (3) the first cervical DEEP DISSECTION OF THE NECK 319 nerve. Further, as it turns round the occipital artery it receives the ramus lingualis vagi from the pharyngeal plexus. The importance of the connexion between the hypoglossal and the first cervical nerve has already been referred to (p. 227, Fig. 87). Branches of distribution. — With the exception of the minute recurrent and vascular twigs, which come off within the con- dyloid foramen, the branches of distribution which proceed from the hypoglossal nerve have been described (pp. 211 and 303). The recurrent branch arises in the upper part of the anterior condyloid foramen, and, regaining the interior of the cranium, it is distributed to the dura mater around the foramen magnum. The vascular 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 down- wards 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, and no white rami com?mtnica?ites enter either the cord or the ganglia from the cervical spinal nerves. 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 the posterior wall of the carotid sheath. Above, it is prolonged upwards in the form of a stout, ascending nerve-trunk, which accompanies the internal carotid artery into the carotid canal ; be/ozv, it 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. Superior Cervical Ganglion (ganglion cervicale superius). — 32o HEAD AND NECK This is the largest of the three ganglia. It is an elon- gated 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 vertebrae, and behind the internal carotid artery. From its upper end the stout branch proceeds which enters the carotid canal, whilst its lower end tapers into the downward continuation of the cord. Numerous branches issue from it ; of these some connect it with neigh- bouring nerves, whilst others are distributed in various ways. The connecting branches are: — (i) slender grey rami cotmnunicantes which connect it with the upper four cervical nerves ; (2) twigs to both ganglia of the vagus ; (3) to the petrous ganglion 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. Pharyngeal. 3. Superior cardiac. The rami vasculares (nervi carotici externi) are soft delicate filaments which run towards the external carotid artery, and form a loose interlacement around it and its branches. From this plexus a branch is given to the carotid body ; further, the part continued upon the facial artery supplies, as we have already noted, the sympathetic root to the submaxillary ganglion, whilst the subdivision upon the middle meningeal artery furnishes the corresponding root to the otic ganglion, 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 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. DEEP DISSECTION OF THE NECK 321 Middle Cervical Ganglion (ganglion cervicale medium). — This ganglion 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 infrequently rests. It presents the following branches : — 1. Grey rami communicantes which connect it with the fifth and sixth spinal nerves, and which pass between the contiguous margins of the scalenus anticus and longus colli muscles. 2. Thyroid branches which run to the thyroid body along the inferior thyroid artery, and which form connexions 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. 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. Inferior Cervical Ganglion (ganglion cervicale inferius). — This ganglion is lodged in the interval between the transverse process of the seventh cervical vertebra and the neck of the first rib. 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 connexion 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. Grey rami communicantes to the seventh and eighth cervical nerves. 2. Rami vasculares. 3. Inferior cardiac nerve. The rami vasculares are fine branches which form a plexus around the subclavian artery and its branches. Others, remarkable for their large size, join the vertebral artery. The lower cardiac nerve (nervus cardiacus inferior) on both sides enters the deep cardiac plexus. Dissection. — The little 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. VOL. II — 21 322 HEAD AND NECK Eectus Capitis Lateralis. — The rectus lateralis arises from the fore-part of the upper 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 transverse process of the atlas, and, joining the ascending branch 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 con- nexion by means of communicating 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 ; further, 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 through the vertebral column at the level of the intervertebral disc between the third and fourth dorsal vertebrae. By this proceeding the three upper dorsal vertebrae, 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 preserved intact. LATERAL PART OF MIDDLE CRANIAL FOSSA 323 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 of the cranial cavity looks upwards. The following are 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-motor nerve (3rd cranial). 7. Trochlear nerve (4th cranial). 8. Abducent nerve (6th cranial). • 9. Cavernous plexus of the sympathetic. 10. Great superficial petrosal nerve. 11. Small superficial petrosal nerve. Dissection. — To expose these structures, the dura mater must be stripped from the 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 taken 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 attached to the ophthalmic division of the trigeminal nerve, whilst over the petrous bone it is united to the surface of the Gasserian ganglion. 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). — 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 apex of the petrous 324 HEAD AND NECK portion of the temporal bone. In front, blood is conducted into it 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 connexions ; 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. 129). Lastly, one or more emissary veins leave its under aspect, and, passing out of the cranium by the foramen ovale, or it may be through the foramen Vesalii when such exists in the sphenoid bone, connect it with the pterygoid venous plexus. The cavernous sinus is formed in the same manner as INT. CAROTID INFU_Nb|BULU ocuLO-r TROC H OPHTHAL SUPRAM AXILLARY INFRAMAXILLARY N Fig. 119. — Section through the Cavernous Sinus. (After Merkel, somewhat modified.) 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 trabecular 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 a special importance, on account of its being traversed by the internal carotid artery, the cavernous plexus, and the oculo-motor, trochlear, and abducent nerves, with the ophthalmic 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 nerve, lie more distinctly within the interval between the two layers of the dura mater than the others. They are shut out from the LATERAL PART OF MIDDLE CRANIAL FOSSA 325 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 closely applied to the outer wall of the sinus. 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 Third nerve Fourth nerve Ophthalmic nerve Sixth nerve Superior maxillary nerve Internal carotid artery Inferior maxillary nerve Sphenoidal Infundibulum Pituitary body Optic nerve Internal carotid artery Third nerve Fourth nerve Ophthalmic nerve Int. carotid artery Sixth nerve Superior maxillary nerve rygoid fossa Posterior nare> Vomer FlG. 120. — Coronal section through the Cavernous Sinus to show the position of the Nerves in its wall. Note the branch given to the pituitary body by the internal carotid artery. nerve-roots within the cranium may be studied. It will be noticed that the loosely connected and parallel funiculi of the large sensory 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 somewhat crescentic in form, and lies upon the sutural junction between the apex of the petrous bone and the L.rreat wing of the n—21 a HEAD AND NECK 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 cavum Meckelii. 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, Levator palpebral superioris Superior rectus' Superior oblique Lachrymal gland External rectus Sixth nerve Lenticular ganglion Xasal nerve Ophthalmic division / *^« of fifth nerve / ■- / Superior maxillary P division of fifth nerve /j Motor root of fifth nerve Trochlea Superior oblique ferior rectus Internal rectus Fourth nerve Sixth nerve Optic nerve Gasserian ganglion Third nerve Sixth nerve Fourth nerve Inferior maxillary division of fifth nerve FlG. 121. — Dissection of the Orbit and the Middle Cranial Fossa. Both roots of the fifth nerve with Gasserian sransflion are turned outwards. and from it emerge the three main divisions of the trigeminal nerve. These are, from before 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. LATERAL PART OF MIDDLE CRANIAL FOSSA 327 The motor 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 connexion 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 (p. 290). The three principal divisions of the trigeminal nerve may next be examined. Begin with the inferior maxillary division, 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 of sensory fibres, is prolonged forwards in relation to the lower part of the cavernous sinus, 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 of the middle fossa of the cranium. 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, n—21 b 328 HEAD AND NECK the ophthalmic nerve gives off a recurrent branch to the dura mater. 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 the frontal These three nerves enter the orbit through the sphenoidal fissure. Third or Oculomotor Fourth or Trochlear, and Sixth or Abducent Nerves. — The oculo-motor and trochlear nerves, 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 trochlear nerve, and im- mediately 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 sellae, 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 (Fig. 120). 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, however, 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 until it reaches the root of the posterior clinoid process ; here it makes a bend and is prolonged forwards to the lower root of the anterior clinoid process, where it abruptly LATERAL PART OF MIDDLE CRANIAL FOSSA 329 turns upwards and pierces the dura mater immediately behind the entrance of the optic nerve into the optic foramen and on the inner side of the anterior clinoid process. At this point it has been severed in the removal of the brain, but it will be afterwards seen to end at the commencement of the Sylvian fissure on the basal aspect 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 : — 1. Branches to the pituitary body, j These are minute twigs 2. Branches to the Gasserian ganglion, I which arise in the 3. Branches to the dura mater, cavernous sinus. 4. Ophthalmic, ^ 5. Posterior communicating, \ These will be studied at a later 6. Anterior cerebral, ) terminal j stage. 7. Middle cerebral, / branches. J Cavernous Plexus (plexus cavernosus). — The sympathetic 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 bend upwards. It supplies filaments 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 superficial 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 large deep petrosal nerve from the carotid plexus. The trunk 330 HEAD AND NECK formed by the union of these two filaments is the Vidian nerve. The Small Superficial Petrosal Nerve appears upon the anterior face of the petrous bone through an aperture which is placed immediately external to the hiatus Fallopii. It leaves the cranial cavity by passing downwards between the great wing of the sphenoid, and the petrous part of the temporal bone, to reach the otic ganglion. This minute nerve, as has already been mentioned (p. 314), is formed by the union of the tympanic branch of the glosso-pharyngeal 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 fourth petrosal nerve — the external superficial petrosal. It takes origin from the sympathetic plexus, which accompanies 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 middle meningeal artery through the foramen spinosum should now be examined. It gives minute twigs to the Gasserian ganglion, and one — the petrosal artery — which accompanies the great superficial petrosal nerve into the hiatus Fallopii. The further course of the middle meningeal artery has already been described (pp. 130 and 290). The small recurrent branch of the inferior maxillary division of the fifth nerve also enters the cranium through the foramen spinosum (p. 290). The small meningeal artery enters the cranium through the foramen ovale, and is chiefly distributed to the Gasserian ganglion. DISSECTION OF THE ORBIT. Within the orbital cavity we find grouped around the eyeball and the optic nerve the following structures : — 'Rectus superior. Rectus inferior. Rectus externus. Rectus internus. Obliquus superior. Obliquus inferior. ^Levator palpebrce superior. Muscles, T Ophthalmic artery and its branches. . \ Ophthalmic veins (superior and inferic Vessels, . . < Ophthalmic veins (superior and inferior) with their tribu- [ taries. DISSECTION OF THE ORBIT 331 'Oculo-motor (3rd cranial). Trochlear (4th cranial). Abducent (6th cranial). Nerves, . .-' |ro^ta1' | from ophthalmic division of the trigeminal Lachrymal, - or fifth cranial nerve- ISasal, J Orbital branch of the superior maxillary division of the trigeminal or fifth cranial nerve. Lenticular ganglion. Lachrymal gland. The capsule of Tenon. Dissection. — 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 preserve 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 successfully carried out, the periosteum clothing the under surface of the orbital roof will be exposed uninjured. The periosteum 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 be observed to be directly continuous through the sphenoidal fissure with the dura mater. Expand- ing with the cavity, it becomes continuous in front around the orbital opening with the periosteum, which clothes the exterior of the skull. Here also it presents important con- nexions with the palpebral ligaments (p. 273). Reflection of the Periosteum and the subsequent Dissection. — The periosteum should be divided along the middle line of the orbit, and then transversely close to the orbital opening. It can now be thrown inwards and outwards. When this is done, the lachrymal gland will be exposed in the fore and outer part of the cavity resting upon the upper 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 approaches the fore-part <>l 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 tills up the interstices between the different orbital contents. On carefully separating this, along the inner wall of the orbit, the superior HEAD AND NECK oblique muscle will be more fully displayed, and lying upon and entering the hinder part of this muscle the small trochlear 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 Lachrymal gland Frontal nerve Short ciliary nerves Lachrymal nerve' Infra-trochlear nerve -Supra-trochlear nerve Supra-orbital nerve j Nasal nerve proper Long ciliary nerves Nasal nerve Ophthalmic ganglion \ --VOptie nerve Ophthalmic nerve- Superior maxillary nerve -- Motor root of trigeminal •Inferior maxillary nerve *xGasserian ganglion (thrown outwards) Fig. 122. — The Ophthalmic Nerve of the Left Side. a ringdike 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 palpebral 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 palpebral 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, however, take care that the needle does not penetrate the cornea, because this might render the subsequent inflation of the eyeball impossible. DISSECTION OF THE ORBIT 333 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 lachry- mal and nasal branches. It enters through the sphenoidal fissure above the muscles, and proceeds forwards upon the upper surface of the levator palpebral 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 pulley of the superior oblique muscle, above which it leaves the orbit, by turning round the orbital arch to reach the forehead. Its further course has already been described (pp. 107 and 265). In the orbit it gives off one small twig close to the pulley of the superior oblique muscle. This passes downwards 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. 109 and 265). In the dissection of the scalp this nerve has been seen to divide into an outer and inner division. Sometimes this division takes place within the orbit, and in that case the outer larger part occupies the supra-orbital notch. Lachrymal Nerve (nervus lacrimalis). — This 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. 265). Within the orbital cavity it gives 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 334 HEAD AND NECK 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 obliquely 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 separated 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 rests upon the levator palpebral superioris and external rectus, which intervene between it and 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 palpebral 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. 276) ; 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. 277). Levator Palpebral Superioris. — This muscle rests upon the upper surface of the rectus superior. Behind, it is narrow and pointed, but it expands as it passes forwards above the eyeball to reach the upper 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- nexions of which have already been described (p. 276). The outer and inner margins of this expansion are fixed to the rim of the orbital opening, in close proximity to the external and internal tarsal ligaments. By these attachments excessive action of the muscle upon the upper eyelid is in a measure checked. Dissection. — The frontal nerve should be divided, and the ends thrown forwards and backwards. The levator palpebne superioris may also be DISSECTION OF THE ORBIT cut midway between its origin and insertion. On raising the posterior portion a minute nerve 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 forcibly forwards into the interior of the eyeball. The pipe should be provided with a stylette so as to keep the aperture free. When 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 sclero-corneal junc- tion, with the point of a sharp narrow -bladed knife. Through this the blow-pipe may be intro- duced, 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 pair 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 gauged, and perhaps even the prolongations or sheaths which it gives to the tendons of the ocular muscles made out. The description of the capsule of Tenon is given on p. 345. Rectus Superior. — The rectus superior, which lies under cover of the levator palpebrae superioris, is now fully exposed. 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. Superior Oblique Muscle (musculus obliquus superior). — This muscle arises from the roof of the orbit immediately in front of the upper and inner part of the optic foramen, and Fig. 123. Oblique Meyer. ) - Diagram of the Superior Muscle. (From Hermann a. Pulley and synovial sheath. 336 HEAD AND NECK 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 and at once changes its direction. It now proceeds outwards and slightly back- wards upon 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. Dissection. — The superior rectus muscle should now be divided midway between its origin and its insertion, and the cut ends thrown backwards and forwards. On raising the posterior part of the muscle the superior division of the third nerve is brought into view, and will be seen to sink into its deep or ocular surface, and at the same time send a twig to the levator palpebrae superioris. The removal of some fat will bring the optic nerve more fully into view. At the back 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 superior ophthalmic vein. These should be carefully cleaned and their branches followed out. From the nasal nerve, one or two delicate thread-like branches — the long 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 ophthahnic ganglion. 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 plexus may be found. Optic Nerve (nervus 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 invest- ment 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 DISSECTION OF THE ORBIT 337 already observed, its 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 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 — viz., the infra-trochlear and the nasal proper. In ad- dition to these it gives off in the orbit the following branches: — 1. Long root to the lenticular ganglion. 2. Long ciliary nerves. The long ganglionic 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 long 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 ?ierve runs forwards along the inner wall of the orbit under cover of the superior oblique muscle. Passing under the trochlea of that muscle, it emerges from the orbit and appears upon the face, where it has already been dissected (p. 265). Near the pulley it receives a communicating twig from the supra-trochlear nerve. The nasal proper is the larger of the two terminal branches of the nasal nerve. It leaves the orbit by the anterior internal 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 VOL. II — 22 33% HEAD ANT) NECK 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 disappears through a slit-like aperture at the side of the crista galli, to reach the 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. 265). The nasal nerve proper, therefore, takes a most circuitous route, being found — (1) in the orbit ; (2) in the cranium : (3) in the nasal fossa ; and (4) in the face. Lenticular Ganglion (ganglion ciliare) — (Fig. 122). — The lenticular ganglion is a minute quadrangular 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 short ciliary nerves are given off. 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 oblique 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. DISSECTION OF THE ORBIT 339 Ophthalmic Artery (arteria ophthalmica). — The ophthalmic artery 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. 125). The branches of the ophthalmic artery are very numerous, -Cc Canal of Schlemm Anterior ciliary — artery Sclerotic coat Vena vorticosa Long posterior ciliary artery Anterior ciliary artery Ciliary muscle Long posterior ciliary artery Vena vorticosa Fig. 124. Long posterior ciliary artery -Dissection of the Eyeball showing the Distribution of the Ciliary Nerves and Vessels. and they can seldom be satisfactorily displayed, unless a special injection has been made, or a cold injection used. They are : — 7- Ciliary. Supra-orbital. Ethmoidal. Palpebral. 8. Nasal. 9. Frontal. 1. The lachrymal. 2. Muscular. 3. Arteria retina.- centralis. The lachry?nal artery (arteria lacrimalis) accompanies the lachrymal nerve, and supplies the gland of that name and the conjunctiva. Two branches, named external palpebral (aiterizc palpebrales laterales), form an arch (arcus tarseus) in each eye- lid, near the free margin, with the internal palpebral arteries. The muscular twigs (rami musculares) come off at variable points, not only from the main artery, but also from certain of its branches. They supply the muscles contained in the orbital cavity. [l — 22 a 34° HEAD AND NECK The arteria retince centralis is a minute but important artery. It pierces the inner and under aspect of 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. The posterior ciliary arteries run with the ciliary nerves. They arise by Internal palpebt Nasal Frontal — Infra-orbital nerve Anterior ethmoidal and nasal nerve Ciliary Posterior ethmoidal — Ophthalmic External palpebral Supra-orbital Arteria retina; centralis Ciliary Muscular Lachrymal Ophthalmic "Nasal nerve -Internal carotid Fig. 125. — Diagram of the Ophthalmic Artery and its Branches. (After Quain and Meyer, modified. ) 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 arteries (arterise ciliares posteriores longae) (Fig. 124). The anterior 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 DISSECTION OF THE ORBIT 341 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 supra-orbital artery (arteria supraorbitalis) accom- panies the supra -orbital nerve, and thus gains the forehead, where it has been dissected at a previous stage (p. in ). The ethmoidal arteries are two in number — anterior and posterior — and they run to the anterior and posterior internal orbital foramina on the inner wall of the orbit. The posterior ethmoidal artery (arteria ethmoidalis posterior) supplies 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. 130); 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 palpebrals medi- ates) come off near the orbital opening, and are two in number — one for the upper and the other for the lower eye- lid (p. 276). The nasal branch (arteria dcrsalis nasi) is distributed at the root of the nose, and anastomoses with the angular branch of the facial artery. The frontal artery (arteria frontalis) accompanies the supra-trochlear nerve to the forehead, where it has already been dissected (p. in). 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 communica- tion with the pterygoid venous plexus by an offset which passes through the spheno - maxillary fissure. The two ophthalmic veins receive numerous tributaries during their n—22 6 342 HEAD AND NECK 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. 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 en- closed 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 Frontal nerve Lachrymal nerve Fourth nerve Nasal nerve External rectus Superior rectus Levator palpebrae superioris Superior division of third nerve Fourth nerve Superior oblique Optic foramen Internal rectus Inferior rectus Inferior division of third nerve Sixth nerve Spheno-maxillary fissure Fig. 126. — Diagram of the Orbital Cavity, and of the origin of the ocular muscles in relation to the optic foramen and the sphenoidal fissure, and the nerves that traverse the latter. inner side of the optic foramen, and the rectus inferior takes origin from a fibrous band which bounds the inner ex- tremity of the sphenoidal fissure. 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 lower 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 DISSECTION OF THE ORBIT 343 divisions of the oculo-motor nerve, the nasal nerve, the abducent nerve, and the ophthalmic veins (Fig. 126). 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 coat, about a quarter of an inch behind the sclero-corneal junction. Third Nerve (nervus oculomotorius). — The two divisions of this nerve enter the orbit through the sphenoidal fissure, between the two heads of the external rectus. The superior division has been traced to the rectus superior and the levator palpebrae 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 rectus inferior and rectus externus, and enters the hinder border of the inferior oblique muscle. Soon after its origin this branch gives the short motor root to the lenticular ganglion, and likewise supplies two or three ad- ditional filaments to the inferior rectus muscle. Sixth Nerve (nervus abducens). — The sixth nerve 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 supply 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 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. 126). 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. 11— 22 c 344 HEAD AND NECK J)issection. — 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. Levator palpebrte super Superior rect Superior oblique Lachrymal gland — External rectus Sixth nerve Lenticular ganglion Nasal nerve Ophthalmic division of fifth nerve Superior maxillary division of fifth nerve Motor root of fifth nerve trochlea I l'|HJ\l 3*7 — Superior oblique Inferior rectus Internal rectus — Fourth nerve i==- Sixth nerve Optic nerve Gasserian ganglion Inferior maxillary division of fifth nerve Third nerve Sixth nerve Fourth nerve Fig. 127. — Dissection of the Orbit and the Middle Cranial Fossa. Both roots of the fifth nerve with Gasserian ganglion are turned outwards. Inferior Oblique (musculus obliquus inferior). — This muscle arises from a small depression on the orbital plate of 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 DISSECTION OF THE ORBIT 345 of the inferior division of the third nerve has been traced to the posterior margin of the inferior oblique muscle. Capsule of Tenon (fascia bulbi). — This is a firm, loose membrane in relation to the globe of the eye. Its con- nexions are somewhat complicated, and they cannot in every detail be satisfactorily displayed in an ordinary dissection. It may be studied from a threefold point of view — (1) in its connexion with the eyeball; (2) in its connexions with the muscles inserted into the globe of the eye ; and (3) in its connexions with the walls of the orbit. The relation which the capsule of Tenon exhibits to the eyeball is very simple. The 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 nerve, 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 ad- herent, while farther forwards, as we have noted, this surface is firmly attached to the ocular conjunctiva. 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. 128). 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 mpre 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 becoming attached to its margin. The sheath of the inferior oblique may be traced upon the muscle as far as the floor of the orbit. The inner ,46 HEAD AND NECK or ocular edge of each of the four apertures through which the recti muscles pass is strengthened by a slip of fibrous tissue (Lockwood). The importance of these slips will be understood when 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, and protect the globe of the eye from pressure during contraction of the muscles. The aperture 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 ___- 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 rectus Fig. 128. — Dissection of the Capsule of Tenon from the front. Capsule of Tenon thrown back from eyeball 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 eyelids widely apart, so as to expose as much as possible of the 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 care- fully 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. 128. 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 connexions of the capsule of Tenon to the walls of the orbital cavity are somewhat complicated. The suspe?isory ligament (Lockwood) plays an important part in this respect. It stretches across DISSECTION OF THE ORBIT 347 the fore-part of the orbit, after the fashion of a hammock, and gives support to the eyeball. Its two extremities are narrow, and are attached respectively to the malar and lachrymal bones. Below the eyeball it widens out and forms a part of the capsule of Tenon. The external and internal check ligaments also constitute bonds of union between the capsule of Tenon and the orbital wall. They are 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 contraction 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 provision by means of which the action of the superior and inferior recti muscles is limited. The action of the former muscle is checked through its intimate connexion with the levator palpebral superioris in the fore-part of the orbit ; the action of the inferior rectus is checked through its connexion with the suspensory ligament. Dissection. — In order that the temporo-malar, or orbital branch of the superior maxillary 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. Temporo-malar Nerve (nervus zygomaticus). — This small nerve arises in the spheno-maxillary fossa, from the superior maxillary division of the trigeminal nerve, and it enters the orbit by passing through the spheno-maxillary fissure. It almost immediately divides into two terminal branches — viz., the temporal and the malar. The temporal branch (ramus zygomaticotemporal) runs forwards and upwards upon the outer wall of the orbit, under cover of the periosteum, and, after receiving a communicating 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. 109 and 265). The ?nalar 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 348 HEAD AND NECK which perforates the malar bone. Here it has been displayed in the dissection of the face (p. 265). 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-vertebral articulations. Dissection. — In order that we may obtain a proper view of the pharynx and the prevertebral muscles, it is necessary to make a somewhat 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 the level of the neck of the first rib, draw the trachea and cesophagus, 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 occipital bone between the pharynx and the vertebral muscles, so as to divide the thick investing periosteum. The basilar process must now be divided by means of a chisel. Still retaining 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 aspect 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 pharynx 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 PREVERTEBRAL REGION 349 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 with the trunk ganglion of the vagus, it retains its position. The pharynx 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 prevertebral region and the ligaments of the cervical vertebrae and the occiput have been studied. Returning to the posterior part of the skull and the cervical portion of the spine, the dissector should proceed to define the attachments of the muscles which lie in front of the transverse processes and the bodies of the vertebrae. These are three in number on each side, viz. : — 1. The longus colli. 2. The rectus capitis anticus major. 3. The rectus capitis anticus minor. Longus Colli. — This is the most powerful of the prevertebral muscles, and it lies nearest to the mesial plane. Its con- nexions are somewhat intricate, but when it has been 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 division of the longus colli arises from the lateral aspect of the bodies of the upper two or three dorsal vertebrae. 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 colli and the scalenus anticus, the vertebral artery will be observed. The upper oblique part of the longus colli arises by three tendinous slips from the anterior tubercles of the transverse processes of the third, fourth, and fifth cervical vertebrae, and tapers somewhat as it proceeds upwards and inwards, to obtain a pointed and tendinous insertion into the anterior tubercle of the atlas. The vertical part of the muscle 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 oblique part by two or three slips from the sides of the bodies of the upper two or three dorsal vertebrae ; above this it derives additional slips of origin from 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 vertebrae. It stretches vertically upwards and is inserted upon the inner side of the 35° HEAD AND NECK upper oblique part of the muscle, by three tendinous processes, which obtain attachment to the bodies of the second, third, and fourth cervical vertebrae. Rectus Capitis Anticus Major. — The rectus capitis anticus Rectus lateralis Rectus capitis anticus minor Rectus capitis anticus major L0112US i.ulli Fig. i 29. —Prevertebral Muscles of the Neck. On the right side the rectus capitis anticus major has been removed. (Paterson. ) major 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 PREVERTEBRAL REGION 351 it ascends upon the front of the vertebral column. It is supplied by twigs from the first loop of the cervical plexus. Rectus Capitis Anticus Minor. — This is a small muscle. It is in great part concealed by the upper part of the preceding muscle, which should be detached from its insertion, and turned downwards so as to bring it fully into view. It arises from the anterior aspect of the root of the transverse process of the atlas, and proceeding upwards and inwards 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. 216). 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, which connect the bifid extremities of the cervical transverse processes. 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 the atlas and the axis ; the lowest pair connects the transverse process of the seventh cervical vertebra with the transverse process of the first dorsal vertebra. Cervical Nerves. — The cervical spinal 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 behind the posterior muscular slips. The upper two cervical nerves emerge from the spinal canal differently from the others. They pass backwards over the neural arches of the atlas and axis respectively. The first or suboccipital nerve has been sufficiently examined at a previous stage of the dissection (p. 322); but the dissector is now in a position to observe that the anterior primary division of ""the second cervical nerve turns forwards under cover of the posterior slip of the first intertransverse 352 HEAD AND NECK muscle, and winds round the outer side of the vertebral artery, to appear in front of the anterior slip of the same muscle. Dissection. — The vertebral artery as it traverses the succession of foramina in the transverse processes of the cervical vertebrae 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? should then be snipped off by the bone pliers. Posterior arch of atlas Posterior primary divisions of spinal nerves Fig. 130. — Dissection of the Ligamentum Nuchae and of the Vertebral Artery in the Neck. Vertebral Artery (arteria vertebralis). — This vessel 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 upper surface of the atlas it again changes its direction and proceeds backwards, behind the lateral mass, in a groove on the upper surface of the posterior arch of that bone. Finally, PREVERTEBRAL REGION 353 it turns forwards under the posterior occipito-atlantal liga- ment, 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 back- wards 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 twigs go to the muscles in the neighbourhood. The lateral spinal branches enter the spinal canal upon the cervical nerves, and have been described on p. 158. Vertebral Vein. — 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. 221). Dissection. — The muscles must now be completely removed, in order that the vertebral and cranio-vertebral joints, and the ligaments in con- nexion with the cervical portion of the spine, may be examined. The Joints of the Neck. The axis, atlas, and occipital bone present a scries of articulations in which the uniting apparatus is very different from that of the vertebrae below. Articulations of the Lower Five Cervical Vertebrae. — The lower five cervical vertebrae are united together very much vol. 11- 23 ;54 HEAD AND NECK 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 vertebrae — viz., a central amphiarthrodial joint and two small lateral diarthrodial joints. The amphiarthrodial joint occupies by far the 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 '^W ""'."■"''*' ' His ';Ki Joint between articular processes Synovial part of joint between bodies of vertebrae Capsule around joint between two articular processes Intervertebral disc FlG. 131. — Coronal section through bodies of certain of the Cervical Vertebrae. 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 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. The ligaments which bind the bodies of the five lower cervical vertebrae together are the direct continuation upwards of the anterior and the posterior common ligaments of the JOINTS OF THE NECK 355 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 connexions of both of these ligaments. The anterior co??imon ligament is a strong band placed in front of the vertebral bodies. It is more firmly fixed to the intervening 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 (a) the articulations between the articular processes; (b) ligamenta subflava; (c) by interspinous liga- ments ; and (d) intertransverse ligaments. The joints 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 laminae which were removed for the display of the spinal cord, and which the dissector 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 laminae of the vertebrae, and can be best seen when the fore aspect of the specimen is viewed. The ligamenta sub/lava (ligamenta flava) are 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 laminae 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 connective tissue, and it allows the egress from the spinal canal of some small veins. The width of the ligaments 356 HEAD AND NECK 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 subflava, 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 interspi?ious ligaments are most strongly developed in the lumbar regions, where they fill up the intervals between the adjacent margins of contiguous spinous processes. In Pedicle of divided Fig. 132. — The Ligamenta Subflava in the Lumbar Region of Spine. 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. 147). The intertra?isverse 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 anterior face of JOINTS OF THE NECK 35 7 the odontoid process and the posterior face of the anterior arch of the atlas. Between the atlas and occipital bone there is a pair of joints — viz., between the occipital condyles 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 : — Ligaments connecting atlas with axis, . . . ' Anterior atlanto-axial. Posterior atlanto-axial. Capsular. I Transverse portion of the cruciform liga- ment. Accessory ligaments of the atlanto-axial joints. T . .. . | Anterior occipito-atlantal. Ligaments connecting oca- J Posterior occipito-atlantal. pital bone with atlas, . • [ Capsular. f Posterior occipito-axial. T . . . Appendices superior and inferior of the Ligaments connecting occi-J Fcruciform H^nt. pital bone with axis, . . ^ odontoid 0* 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. Anterior Atlanto-axial Ligament (Fig. 133). — This 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. Posterior Atlanto-axial Ligament. — This 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 repre- sentative, as its attachments show, of the ligamenta subflava. It is pierced on each side by the second cervical nerve as this passes backwards over the neural arch of the axis. Atlanto-axial Capsular Ligaments. — These are somewhat lax, and on removing the outer part of each, the joint cavities will be opened into. Anterior Atlanto- Occipital Ligament dig. 133). — This 358 HEAD AND NECK ligament 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 plane it is thin and membranous, and stretches outwards so as to abut against the atlanto-occipital capsular ligament. In the middle line there is an exceedingly strong cord-like band, which stands out in strong relief from the rest of the ligament, and is carried downwards to the Basilar process of occipital bone Dura mater Vertebral artery and first cervical nerve Posterior occipito- axial ligament Anterior atlanto- occipital ligament Two parts of tbe suspensory odontoid ligament Appendix superior Anterior arch of atlas -Transverse ligament Anterior atlanto- axial ligament Appendix inferior Lenticular disc ot cartilage between the body of the axis and the odontoid process Fig. 133. — Mesial section through the Basilar Process of Occipital Bone, the Atlas, and the Axis. (From Luschka, slightly modified.) Between the posterior occipito-axial ligament and the transverse ligament a small synovial bursa may be seen. anterior tubercle of the atlas. Part of its fibres are attached to this, but a certain proportion become continuous with the central thickening of the anterior atlanto-axial ligament, and through this with the anterior common ligament of the spine. Posterior Atlanto-Occipital Ligament. — This is a thin and weak membrane which occupies the 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 JOINTS OF THE NECK 359 connected with the dura mater, and on each side it reaches the atlanto-occipital 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. Atlanto- Occipital Capsular Ligaments. — These connect the occipital condyles with the lateral masses of the atlas. They completely surround the joints, and are connected 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 connexion 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 occipital 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 or membrana tectoria. Posterior Occipito-axial Ligament or the Membrana Tectoria. — This is a broad ligamentous sheet which is attached below to the posterior aspect of the body of the axis vertebra, where it is continuous with the posterior common ligament of the spine. It extends upwards, covering completely the odontoid process and the anterior margin of the foramen magnum, and 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 upwards upon the basilar process of the occipital bone. By this proceeding the accessory ligaments of the atlanto-axial joints and the cruciform ligament are brought into view, and very little further dissection is required to define them. Accessory Atlanto-axial Ligaments (Fig. 134). — These 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- :6o HEAD AND NECK 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 movements of the atlas upon the axis. Cruciform Ligament (ligamentum cruciatum) (Fig. 134). — The cruciform ligament is composed of a transverse and a vertical part. The transverse ligament (ligamentum trans- versum atlantis) is by far the most important constituent of this apparatus. It is a strong band which stretches from Membrana tectoria rus superius Occipital bone Suspensory ligament Check ligament Crus superius Transverse ligament vT- Lateral mass of atlas Atlanto axial joint Body of axis 2g=5=xA. Accessory atlanto- " axial ligament Crus inferius Membrana tectoria Fig. 134. — Dissection from behind of Ligaments connecting the Occipital Bone, the Atlas, and the Axis with each other. 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 process — 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 connexion with the mesial joint between the odontoid process and the anterior arch of the atlas. Indeed, in some cases a communication exists between the two synovial cavities. The vertical part of the cruciform ligament consists of an JOINTS OF THE NECK 361 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 cms 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 posterior aspect of the basilar process immediately beyond the anterior margin of the foramen magnum. The cms in/erius, much shorter, extends downwards, and is fixed to the posterior aspect of the body of the axis vertebra. Dissection. — Detach the appendix superior from the basilar process, and throw it downwards. The suspensory ligament is thus displayed, and a better view of the alar or check ligaments obtained. Suspensory Ligament (ligamentum apicis dentis). — The suspensory ligament 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, is a structure of considerable morphological interest. The anterior part of the suspensory ligament is a fiat 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. Check or Alar Ligaments (ligamenta alaria) (Fig. 134). — These 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 occipitoatlantal articulations. Rotatory movements <>f 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 ligani' 362 HEAD AND NECK 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 being carried on. The mouth and pharynx should, in the first instance, engage his attention. Mouth. — The mouth is the expanded upper part of the alimentary canal. It is placed in the lower part of the face, below the nasal chambers, 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, termed the vestibule, which is bounded in front by the lips and cheeks, and behind by the teeth and gums, and a large part, the 771011th 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. The vestibule of the mouth which passes round the teeth and gums is a mere fissure- like space except when the cheeks are inflated with air. It is into this subdivision of the mouth- that the parotid duct opens (p. 249). Above and below, it is bounded by the reflection of the mucous membrane 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 variable aperture with the cavity of the mouth proper. When all the teeth are in place the existence 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. In paralysis of the facial muscles the lips and cheeks fall away from the dental arcades and food is apt to lodge in the vestibule. 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 communicates by means of the isthmus faucium with the pharynx. The floor is formed by the tongue and the mucous membrane which stretches to this from the inner aspect of the mandible ; the MOUTH 363 roof is vaulted, and is composed of the hard and the soft palate. Into this part of the buccal cavity the ducts of the submaxillary glands (Wharton's ducts) and the ducts of the sublingual glands (ducts of Rivinus) open (pp. 301 and 302). When the mouth is closed the dorsum of the tongue is usually applied more or less closely 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 (labia oris). — The structure of the lips has in a great measure been already examined in the dissection of the face (p. 258). Each lip may be regarded as being composed of four layers. From before backwards these are — (1) cuta- neous; (2) muscular; (3) glandular; and (4) mucous. The skin and ??iucous ??iembrane become continuous with each other at the free margin of the lip. From the deep aspect 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 the frenida ; in the dissection of the face they have been more or less destroyed. The muscular layer constitutes the chief bulk of the lips. It is formed by the orbicularis oris and the various muscles which converge upon the mouth, many of the fibres of which are attached to the skin. The labial glands are very numerous, and lie in the submucous tissue which intervenes between the mucous membrane and the muscular fibres. The ducts of these glands pierce the mucous membrane, and open into the vestibule. In each lip there is an arterial arch formed by the corresponding coronary arteries (p. 268). The lymphatic vessels of both lips join the submaxillary lymphatic glands. This has an important bearing in con- nexion with epithelioma of the lip. Cheeks (buccae). — The cheeks have five layers entering into their construction, all of which have been examined in the dissection of the face. They are — (1) skin; (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 mucous membrane. Numerous buccal glands, similar in character to the labial glands, lie in the submucous tissue between the mucous membrane and the buccinator muscle. Four or five mucous glands of larger size, termed the molar 364 HEAD AND NECK glands, occupy a more superficial position. They lie upon the buccal aponeurosis, close to the point where this is pierced by the parotid duct, and their ducts also open into the vesti- bule of the mouth. 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 mandi- bular 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 Tip of tongue turned up Ranine vein Orifice of Wharton's duct Frenum linguae Plica fimbriata 'Plica sublingualis Fig. 135. — The Sublingual Region in the Interior of the Mouth. the posterior fibres of the platysma. The parotid duct pierces the three inner layers of the cheek, and opens into the vesti- bule of the mouth opposite the second molar tooth of the upper jaw. Gums and Teeth. — The mucous membrane of the gums is smooth, vascular, and firmly bound down to the subjacent periosteum 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. MOUTH 365 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 the inner aspect of the lower jaw, on to the side of the tongue, but in the fore-part of the mouth the tongue lies more or less 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 Uvula Posterior pillar Tonsil Anterior pillar — Posterior wall of _JM]ttl oral pharynx t^H^<|j5 Tongue Fig. 136. — Isthmus of the Fauces as seen through the widely opened Mouth. The tonsils in the individual from which this drawing was taken were somewhat enlarged. by the sublingual gland can be distinguished. Further, if the tongue be pulled upwards, a mesial fold of mucous membrane will be seen to connect its under surface to the floor. This is the frenum linguce. 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 frenum. Farther back, between the side of the tongue and the jaw, and on the summit of the plica sublingualis, are the openings of the ducts of Rivinus. Roof of the Mouth. — The hard and the soft palate form the continuous concave and vaulted roof of the mouth (Fig. 366 HEAD AND NECK 138). Projecting from the middle of the posterior free margin of the soft palate, and resting upon the dorsum of the tongue, will be seen the uvula (Fig. 136). 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 termed the incisive pad ox palatine papilla. In the anterior part of the hard palate the mucous membrane on each side of the raphe is thrown into three or four trans- verse hard corrugations or ridges ; behind this it is compara- tively smooth. Isthmus Faucium. — This name is given to the communi- cation between the buccal cavity and the pharynx (Fig. 136). To obtain a good view of it from the front, the mouth must be well opened and the tongue depressed. The isthmus faucium and the parts which bound it can best be examined in the living subject (Fig. 136). 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 re- spectively 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 inclines forwards, and ends upon the side of the posterior part of the tongue ; the posterior pillar (arcus pharyngopalatinus), more strongly marked, inclines 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 divergence of these two folds will be observed the tonsil. Strictly speaking, the term isthmus fauciwn should be con- fined to the interval between the two anterior palatine arches, as the tonsil and the posterior palatine arches belong to the lateral wall of the pharynx. Pharynx. — The pharynx is a wide musculo-aponeurotic canal about 5 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. PHARYNX 367 To obtain a proper idea of the connexions of the pharynx, the dissector 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 vertebrae, 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 deglutition. 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 is from the structures which lie in proximity to these apertures that it derives its principal attachments. Thus from above downwrards it is fixed — (a) to the internal pterygoid plate ; (b) to the 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 ; Qf) to the cricoid cartilage. Above, 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 an altogether 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 transverse slit. Pharyngeal Wall. — The wall of the pharynx may be said to consist of three well-marked strata — viz., an external mus- 368 HEAD AND NECK cular, an intermediate aponeurotic, and an internal mucous. The muscular layer, which is composed of the three con- strictor 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 muscles should now be carefully cleaned in the direction of the muscular fibres, by removing the bucco- pharyngeal fascia which covers them. Bucco- pharyngeal Fascia. — This coating is sometimes spoken of under the name of the tunica pharyngis externa ; more frequently, however, it is called the bucco-pharyngeal fascia, seeing that it is continuous in front with the buccal aponeurosis. This fascial investment must not be con- founded with the prevertebral layer of cervical fascia which forms a distinct lamina behind it. The bucco-pharyngeal 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. 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. 137, /) is narrow in front at its origin, but it PHARYNX 369 spreads out as it passes backwards towards its insertion. It arises by two heads ; of these the lower 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 upper border of the g> h. k. I. Buccinator. Tensor palati. Levator palati. Superior constrictor. Middle constrictor. Inferior constrictor. Thyro-hyoid. Hyoglossus. Stylo-hyoid. Mylo-hyoid. Crico-thyroid. Stylo-pharyngeus. Stylo-glossus. Stylo-hyoid ligament. Pterygo-maxillary ligament. Glosso-pharyngeal nerve. Superior laryngeal artery. Superior laryngeal nerve. External laryngeal nerve. Inferior laryngeal nerve and artery. FlG. 137. — Profile view of the Pharynx to show the Constrictor Muscles. (From Turner.) 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 margin of the inferior constrictor overlaps the commencement of the (esophagus, and passing upwards under cover of it, so as to vol. 11 — 24 37° HEAD AND NECK reach the larynx, will be seen the recurrent laryngeal nerve and the laryngeal branch of the inferior thyroid artery. The middle constrictor (musculus constrictor pharyngis medius) is a fan-shaped muscle (Fig. 137, e). Narrow, and pointed in front, it arises from the great and small cornua of the hyoid bone as well as from the stylo-hyoid ligament. 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. Dissection. — The superior constrictor possesses a somewhat complicated origin, and to bring this fully 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. 137, 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, and the hamular process ; (b) the pterygo-maxillary ligament which is common to it, and the buccinator muscle; (c) the posterior end of the mylo-hyoid ridge on the inner aspect of the mandible ; (d) the mucous membrane of the mouth, and side of the tongue. From this somewhat extensive origin, the fibres curve backwards to reach the median 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. 137, n). In the same interval will be seen the glossopharyngeal nerve. The upper border of the muscle is free and crescentic, and it falls short of the basis cranii. Pterygo-maxillary Ligament (Fig. 137, g). — This is a strong, narrow, tendinous band, which extends from the hamular process of the internal pterygoid plate, to the PHARYNX 37i posterior part of the mylo-hyoid ridge of the mandible. It acts as a tendinous bond of union between the buccinator and superior constrictor muscles, and its connexions can be best appreciated by introducing the finger into the mouth and pressing outwards along its course. Sinus of Morgagni. — This name is applied to the semi- lunar space which intervenes between the upper crescentic margin of the 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 palati (Fig. 137, c and 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 turning 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. Pharyngeal 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. It is also united to the Eustachian tubes and the bony margins of the posterior nares. Dissection. — The pharynx should now be opened by a vertical and mesial incision through the entire length of the posterior wall. At the upper extremity of this cut, the knife should be carried transversely out- wards, 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. — The mucous membrane, or inner- most stratum which enters into the construction of the pharyngeal wall, is now exposed, and it should be observed that it is continuous, through the various apertures which open into the pharynx, with the mucous membrane of the 372 HEAD AND NECK nasal chambers, of the Eustachian tubes and tympanic cavities, of the buccal cavity, of the larynx, and of the (esophagus. Race??wse glands, which lie immediately subjacent to the mucous membrane and which secrete mucus, are present in Middle turbinated bone Middle meatus Atrium Inferior turbinated bone Inferior meatus Vestibule of nasal cavity Soft palate Anterior pillar of fauces Superior meatus Recessus spheno-ethmoidalis Sphenoidal sinus Pituitary body Pharyngeal recess Pharyngeal tonsil Eustachian orifice Upper surface of soft palate Salpingopharyngeal fold Posterior pillar of fauces Tonsil Pharyngeal part of tongue Genio-glossus Genio-hyoid Cartilage of epiglottis Thyroid cartilage Epiglottis Cuneiform tubercle Tubercle of Santorini Laryngeal sinus Cricoid cartilage Fig. 138.— Sagittalsection through the Nasal Chamber, the Mouth, Larynx, and Pharynx, a little to the right of the mesial plane. great numbers. There are also numerous lymphoid follicles, and in certain localities these are aggregated together into large masses (the tonsils and the pharyngeal tonsil), which will require to be studied with the section of the pharynx in relation to which they are placed. PHARYNX 373 The soft palate, which projects backwards into the pharynx behind the isthmus faucium like a curtain, divides the cavity of the pharynx into an upper and a lower part. The upper part, called the naso-pharynx, is brought into communication with the nasal chambers and the tympanic cavities by four apertures, viz., the two choanal or posterior nares and the mouths of the two Eustachian tubes. The lower portion of the pharynx may be regarded as consisting of an oral part, which lies behind the mouth and tongue, and a laryngeal part, which is placed behind the larynx. Below the soft palate there are three mesial open- ings into the pharynx, viz., the opening of the 7?iotcth or isthmus faucium, the ope?iing of the larynx, and the opening of the oesophagus. Naso-Pharynx (pars nasalis). — The naso-pharynx is situated immediately behind the nasal chambers and below the body of the sphenoid and the basilar part of the occipital bone. It is the widest part of the pharynx. Its walls are not capable of movement, and consequently its cavity always remains patent, and presents under all conditions very much the same form. The front wall of the naso-pharynx is deficient. Here the posterior nares or choance open directly into the naso-pharynx. These are two large oval apertures which constitute the com- munication between the nasal fossae and the pharynx. They 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 its widest part is about half an inch. By looking through the posterior nares a partial view of the two lower meatuses of the nose and of the posterior ends of the middle and inferior turbinated bones may be obtained. On the lateral wall of the naso-pharynx, on each side, is seen the orifice of the Eustachian tube, and behind this the pharyngeal recess. The Eustachian orifice (ostium pharyngeum) is placed behind the lower part of the choana at a level which corresponds closely with the posterior end of the inferior turbinated bone. It is bounded above and behind by a high prominent and rounded margin termed the Eustachian cushion (torus tuberius), which is altogether deficient below and in front. A fold of mucous membrane, termed the salpingo- pharyngeal fold, descends upon the lateral wall of the pharynx from the posterior part of the Eustachian cushion. As this is 374 HEAD AND NECK traced downwards it gradually disappears. The prominent posterior part of the Eustachian cushion favours very materi- ally the passage of the Eustachian catheter.1 In the natural condition of parts there is a deep slit-like recess on the lateral wall of the naso-pharynx immediately behind the prominent posterior lip of the Eustachian orifice. This is termed the lateral recess of the pharynx, or the fossa of Rosenmilller, and it possesses considerable interest from a developmental point of view. The roof and posterior wall of the naso-pharynx are not marked off from each other. They together form a continuous curved surface. The upper portion of this surface looks downwards and may be regarded as the roof; the lower portion which looks forwards constitutes the posterior wall. The roof is formed by the basilar part of the occipital bone, and also by a small part of the under surface of the basi-sphenoid covered by a dense periosteum and a thick coating of mucous membrane. The posterior wall is supported behind by the anterior arch of the atlas and the odontoid process of the axis vertebra. In that part of the roof which stretches across between the two lateral recesses of the naso-pharynx there is a marked collection of lymphoid tissue, and over its surface the mucous membrane is thickened and wrinkled. This is the pharyngeal tonsil, and in its lower part there will usually be found a small median pit termed the pharyngeal bursa, just large enough to admit the point of a fine probe. The floor of the naso-pharynx is formed by the curved, sloping upper surface of the soft palate. Between the lower border of the soft palate and the posterior wall of the pharynx there is an interval termed the pharyngeal isthmus, through which the naso-pharynx communicates with the oral pharynx. It is important to note that the posterior wall and roof of the naso- pharynx can be explored by the finger, introduced through the mouth and the pharyngeal isthmus. 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 choanoe, and the inferior meatus of the nose is altogether out of sight. The middle and superior meatuses of 1 A Eustachian catheter can be very readily improvised by bending the extremity of an ordinary blow-pipe. The dissector is recommended to practise the passage of this instrument into the Eustachian tube through the nose. PHARYNX 375 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. Oral Pharynx (pars oralis). — The oral pharynx lies behind the tongue and mouth. The pharyngeal part of the tongue which looks more or less directly backwards forms its anterior wall in its lower part. Above this is the isthmus of the fauces, or the opening into the mouth, limited on either side Tongue Hyoid True vocal cord Kima gIottidi> j I I Pynform sinus_/_M Superior cornu /*; of thyroid"^ Pharyngeal wall (cut) Middle glosso- epiglottidean ligament ' Vallecula Pharyngc- epiglottic fold Epiglottis Cushion of epiglottis Aryteno- id epiglottidean fold Laryngeal sinus False vocal cord Cuneiform cartilage Tubercle of Santorini Posterior aspect of cricoid cartilage FlG. 139. -—.Superior Aperture of Larynx exposed by laying open the pharynx from behind. by the anterior pillar of the fauces. These pillars may be regarded, therefore, as giving the lateral boundary lines between the mouth and the pharynx. On the lateral wall of the oral pharynx the posterior pillar of the fauces forms a prominent fold which is gradually lost as it is traced downwards. Within this fold is the palato-pharyngeus muscle. This is an im- portant relation when it is remembered that the posterior pillars of the fauces form the lateral boundaries of the pharyn- geal isthmus. By the contraction of the palatopharyngeal 11 24 a 376 HEAD AND NEC* v muscles the two posterior pillars can be approximated so as to greatly reduce the width of the pharyngeal isthmus. The anterior and posterior pillars of the fauces form on each lateral wall of the oral pharynx the limits of a triangular interval in which is lodged the tonsil. The upper part of this area, above the level of the tonsil, presents a small depression termed the supra-tonsillar fossa. Laryngeal part of the Pharynx (pars laryngea). — The portion of the pharyngeal cavity which lies behind the larynx diminishes rapidly in width in its lower part so as to bring its lumen into conformity with that of the oesophagus, with which it is continuous. In its front wall from above down- Thyro-hyoid membrane True vocal cord Processus vocal i Arytenoid cartilage ^sd^jk Platysma w~*&A Posterior wall of pharynx Retropharyn-^ £ geal space" Carotid sheat Sterno-hyoid Thyro-hyoid Scalenus anticu Longus colli cartilage hyoid us pyriformis Superior thyroid Descendens hypoglossi Common carotid AInternal jugular Vagus Sympathetic cord Vertebral artery Fig. 140.— Transverse section through the Neck at the level of upper part of Thyroid Cartilage. wards may be seen: (1) the epiglottis; (2) the superior aperture of the larynx with the pyriform fossa or sinus on either side ; and (3) the posterior surfaces of the arytenoid and cricoid cartilages, covered by muscles and mucous membrane. The superior aperture of the larynx, situated below the pharyngeal part of the tongue, is a large obliquely placed opening which slopes rapidly from above downwards and backwards. Somewhat triangular in outline, the basal part of the opening, placed above and in front, is formed by the free border of the epiglottis. Behind, the opening rapidly narrows, and finally ends in the interval between the two arytenoid cartilages. The sides of the aperture are formed by two sharp and prominent folds of mucous membrane, termed the aryteno-epiglottidean folds, which stretch between the lateral PHARYNX 377 margins of the epiglottis in front and the arytenoid cartilages behind. Two small nodules of cartilage in the hinder part of the aryteno-epiglottidean fold give rise to two rounded emi- nences, called respectively the cuneiform tubercle in front and the tubercle of Santorini behind. On either side of the lower part of the laryngeal opening there is a small three-sided or pyramidal recess or depression, called the sinus pyriformis. On the outer side it is bounded by the posterior part of the ala of the thyroid cartilage ; on the inner side by the arytenoid cartilage ; whilst its hinder wall is formed by the posterior wall of the pharynx when this is in place. The sinus pyriformis presents a wide entrance which looks upwards, but it rapidly narrows towards the bottom (Figs. 139 and 140), and it is important to the surgeon because it is in this little pocket that foreign bodies introduced into the pharynx are most 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 projects downwards and backwards into the pharynx. During deglutition, it is raised so as to shut off the 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 ; on each side it is connected with the lateral wall of the pharynx j whilst posteriorly it presents a free border. From the centre of this free margin the conical elevation termed the uvula projects, whilst the sharp concave part of the border on either side of the uvula becomes con- tinuous with the posterior palatine arch which descends on the side wall of the pharynx. The upper surface of the soft palate is convex and continuous with the floor of the nasal fossae ; the inferior surface is concave and continuous with the vaulted roof of the mouth. The anterior palatine arch curves outwards from this surface of the soft palate a short distance in front of its posterior free border. Upon the inferior surface may be seen a slightly marked mesial ridge or raphe. The soft palate is composed of a fold of mucous membrane, between the two layers of which are interposed muscular, 378 HEAD AND NECK aponeurotic, and glandular structures, together with blood- vessels and nerves. r The two levatores palati. The two tensores palati. Palatal muscles, . < The two palato-glossi. The two palato-pharyngei. I The azygos uvulae. Palatal aponeurosis. Palatal glands. i Ascending palatine from facial. . , • ! Palatine branch from ascending pharyngeal. I Twigs from the descending palatine branch of the internal I. maxillary. Nerves ' Small posterior palatine, . f from the spheno- palatine ( External posterior palatine, . I ganglion. The racemose mucous glands in the soft palate form a very thick and continuous layer immediately subjacent to the mucous membrane which clothes its inferior surface. Close to the posterior border of the hard palate the soft palate con- tains very few muscular fibres, and here it is chiefly composed of the two layers of mucous membrane enclosing the glands, and above these the palatal aponeurosis. Dissection. — The dissection of the soft palate is difficult, and it is only in a fresh part that the precise relations of the different 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. Palato-glossus (musculus glosso-palatinus). — The palato- glossus is a delicate muscular slip, which arises from the side of the posterior part of the tongue, and curves upwards and inwards to reach the under surface of the soft palate above the glandular layer. 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. Palato-pharyngeus (musculus pharyngo-palatinus). — The palato-pharyngeus forms two muscular strata in the soft palate which enclose between them the azygos uvulae 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 PHARYNX 379 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 fauces, and spreads out into a thin sheet of fibres in the wall of the pharynx. Blending to some extent with the stylo-pharyngeus, it is inserted into the superior and posterior borders of the thyroid cartilage. Some of its fibres, however, incline backwards, and are inserted into the pharyngeal aponeurosis. 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 dissector will observe the ascending palatine artery in relation to this muscle. Levator Palati (musculus levator veli palatini). — The levator palati 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 aponeu- rosis 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 380 HEAD AND NECK 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 the Eustachian tube. It descends perpendicularly and ends in a tendon which turns horizontally inwards under the hamular 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 trans- verse 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 it very soon becomes lost as it is traced back into the soft palate. The small portion of the soft palate which it supports contains few muscular fibres, and remains always more or less horizontal in position. The much more extensive hinder muscular part of the soft palate constitutes the movable sloping portion. The tensor palati operates upon the anterior aponeurotic portion of the soft palate. Vessels and Nerves of the Soft Palate. — The inferior or ascending 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. 237 and 309). 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 pharyngeal 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. 310). The descending balati?ie 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 small posterior palatine and the accessory posterior palatine nei-ve. It would appear, however, that they do not supply the muscles, but are distributed to the mucous membrane. The levator palati, the azygos uvulae, the palato-glossus, and the palato-pharyngeus are supplied by twigs from the pharyngeal branches of the vagus, which convey to them fibres which are originally derived from the accessory part of the spinal accessory {v. p. 318) PHARYNX 381 (W. Aldren Turner). The tensor palati is probably supplied by the branch which it receives from the otic ganglion, and which probably leads to it fibres which originally come from the motor part of the trigeminal nerve. Tonsils (tonsillar palatini). — The tonsils are two prominent masses of lymphoid tissue placed one on each lateral wall of the pharynx in the triangular interval between the two palatine arches and immediately above the pharyngeal part of the tongue. The phary?igeal or internal surface of the tonsil is perforated by a number of orifices which lead into crypts or recesses in its substance. The deep or external surface is embedded in the pharyngeal wall and is supported by the superior constrictor muscle of the pharynx. It is covered by a layer of fibrous tissue which forms an incomplete capsule for the organ. It is important to note that between the tonsil and the superior constrictor there is some lax connective tissue, so that the organ can be pulled forwards by the volsellum without dragging the wall of the pharynx with it. 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 linguae. 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 wall. Thus, in the outer part of its course as it nears the tympanum, its wall is 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 wall. 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 inclina- tion upwards. At the same time it will be noticed to pass between the origin of the levator palati, which lies upon its inner side, and the origin of the tensor palati, which is placed 382 HEAD AND NECK upon its outer side. This relationship 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 externally, its place being taken by dense fibrous tissue, which connects the margins of the cartilage and completes the wall of the canal. The projecting free margin of the cartilage gives rise to the Eustachian cushion already ex- amined on the lateral wall of the naso-pharynx (p. 373). 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 tuba (Rudinger). It joins the tensor palati. The interior of the tube is lined by mucous membrane continuous with that of the pharynx, and its calibre is very different in different parts of its course. It is narrowest at a point termed the isthmus, situated at the junction of the osseous and cartilaginous parts. As the tube is traced from this to the pharynx it gradually increases in calibre, and attains its greatest width at its opening into the nasal pharynx. CAROTID CANAL. The carotid canal, which traverses the fore -part of the petrous bone, contains the internal carotid artery and the upward continuation of the cervical sympathetic. Dissection. — The carotid canal may be opened up by removing its inferior wall 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. Internal Carotid Artery. — 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, and enters the cranial cavity by piercing the external layer of the dura mater. From this point onwards the internal carotid artery has been CAROTID CANAL 3§3 already examined (p. 328). Whilst within the carotid canal it lies in front of and below the cochlea and the tympanum. The Gasserian ganglion is placed above it, and separated from it by a thin plate of bone, which is sometimes absent. Ascending Part of the Cervical Sympathetic. — The dissector 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. This almost immediately 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 some difficulty, and can only be satisfactorily effected under specially favourable circumstances. The external branch breaks up into the carotid plexus ; the internal branch is con- tinued into the cavernous plexus. From these primary off- shoots 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— (1) one or two filaments to the abducent or sixth nerve as it turns round the internal carotid artery ; (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 nerve runs to the posterior aspect of the body of the sphenoid, and at the entrance to the Vidian canal it joins the great supe)-Jicial petrosal nerve and forms the Vidian nerve (p. 329). The carotico-tym panic branch of the carotid plexus joins the tympanic branch of the glosso-pharyngeal as it traverses the tympanum (p. 315). The carotid plexus also receives the small deep petrosal nei-ve from the tympanic branch of the glosso-pharyngeal. The cavernous plexus has already been sufficiently described on p. 329. SUPERIOR MAXILLARY NERVE. As the superior maxillary nerve proceeds forwards from the Gasserian ganglion 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. Dissection. — 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 hour mid the great wing of the sphenoid towards the inner end of the sphenoidal fissure. This saw-cut should enter the sphenoidal fissure 3^4 HEAD AND NECK 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, immedi- ately above the anterior margin of the great wing of the sphenoid bone, downwards into the sphenoidal fissure to meet the first saw-cut. The wedge-shaped 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 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 upper 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 deeply under the lower part of the rim of the orbital opening, and here the chisel must be em- ployed. 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. Sphenopalatine ganglion Fig. 141. — Diagram of the Superior Maxillary Nerve. Superior Maxillary Nerve (nervus maxillaris). — The superior maxillary nerve springs from the Gasserian ganglion within the cranial cavity (p. 326). It is composed entirely of sensory fibres, and proceeds forwards under the dura mater and in relation to the lower part of the cavernous sinus 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 The infra -orbital canal traverses the floor of the orbit, which also, it should be remembered, forms the roof of the antrum of Highmore. Finally the nerve 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 SUPERIOR MAXILLARY NERVE 385 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. 327). [ Orbital or temporo - malar (already de- 2. In the spheno-maxil-J scribed, p. 347). lary fossa, . . | Spheno-palatine. I Posterior superior dental. 3. In the infra-orbital /Middle superior dental. canal,. . . ( Anterior superior dental. ( Palpebral, \ 4. In the face, . . -J Nasal, V- already described, p. 266. (_ Labial, ) The temporo-malar nerve, which has already been dissected in the orbit, can now be traced back to its origin from the superior maxillary nerve in the spheno-maxillary fossa. The sphe?io-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 constitute 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 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 ?niddle superior dental nerve supplies the two bicuspid 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 floor of the canal. It descends in a minute canal which traverses the outer wall of the antrum of Highmore. The anterior superior dental nerve, much the largest of the vol.. n-25 386 HEAD AND NECK 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 endeavour 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. Infra-orbital Artery (arteria infra-orbitalis). — The infra- orbital artery 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 buccal 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 accompanies 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. OTIC GANGLION— NASAL FOSS^. 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 OTIC GANGLION 387 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 connexions. 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. Otic Ganglion (ganglion oticum). — This is a minute oval body about 4 mm. in length. It is placed immediately below the foramen ovale, between the deep surface of the inferior maxillary nerve and the tensor palati which separates it from the cartilaginous part of the Eustachian tube. The middle meningeal artery lies behind it, and it lies in the most intimate relationship to the origin of the nerve to the internal pterygoid muscle. The otic ganglion is usually described as receiving motor, sensory, and sympathetic roots. The motor root is supplied by the nerve to the internal pterygoid muscle ; the sympathetic root comes from the plexus around the middle meningeal artery. In addition to these, the small superficial petrosal newe enters the posterior border of the ganglion, and conveys to it sensory fibres from the glossopharyngeal nerve (p. 314). The following are the branches which proceed from the otic ganglion : — C A twig which passes downwards and forwards to the Branches of tensor palati. distribution. | A twig which proceeds upwards and backwards to V. supply the tensor tympani. ( One or more fine filaments to one or both of the roots Connecting of the auriculo-temporal nerve, branches. 1 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 fossae. It is not placed accurately in the mesial plane, but almost invariably shows a bulging or deviation to one or other side (more frequently to the right side), so as to reduce the width of one fossa, and increase the capacity of 388 HEAD AND NFXK the other. Immediately above the orifice of the nostril, or 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 nasal chamber. The vestibular part of the partition is clothed by skin, continuous with the external integument ; from this a number of stiff hairs, termed vibrissa, project. Over the rest of its extent the septum nasi is covered Frontal sinus Nasal bone Vestibule of^ nasal chamber Opening of Jacobson's organ Sublingual gland Mandible Septal cartilage Mes-ethmoid Vomer Sphenoidal air sinus % IKM Eustachian cushion \^»*'i ?,'L. Eustachian opening VAi'r Pharyngeal recess Pharyngeal tonsil _l Atlas -V^/l Soft palate iv^Z— Transverse ligament WM— Axis vertebra «"$ — Epiglottis Hyoid bone Fig. 142. — Antero-posterior section through the Nose, Mouth, and Pharynx, a little to the left of the mesial plane. with mucous membrane, and presents two districts, viz., a lower or respiratory area, and a much smaller upper or olfactory area, comprising not more 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 thick. In the fresh state it presents a yellowish colour, and the glands are smaller. NASAL FOSSAE 389 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 cartilage. This aperture varies in diameter from \ mm. to \\ mm. (Schwalbe). It leads into a narrow canal, which passes backwards for a short distance, and then ends blindly. It is of interest because it represents in the human subject the rudiment of the organ of Jacobson, a tubular structure which is highly developed in some of the lower animals. Construction of the Nasal Septum. — Strip the mucous membrane from the exposed surface of the septum nasi. By this proceeding the intimate connexion which exists between the mucous membrane and the subjacent periosteum 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 other bones take a minor part in its con- struction. 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 bones of opposite sides. The septal cartilage (cartilago septi nasi) fills up the wide angular gap which intervenes between 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 ap- position with the fore border of the mes-ethmoid ; its lower 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 aperture Its connexion with the lateral cartilage of each side is a very intimate one; indeed, below the nasal bones the three cartilages are directly continuous, but lower down they are separated by a fissure which runs upwards for 39° HEAD AND NECK 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 anterior 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. 279). 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. Dissection. — The septal cartilage and thin bony lamina? 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 this 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. ( 1. Naso-palatine. Nerves of Common | 2. Septal branch of the nasal nerve proper. Sensation, . . 13. Nasal branches from Meckel's ganglion V. and from 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 down- wards in grooves on the surface of the perpendicular 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 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, it changes its direction 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 open into the common anterior palatine canal, the nerves of opposite sides unite in a plexus NASAL FOSS^ 391 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 branches from 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 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 vestibule. The arteries which convey blood to the septum nasi are : (1) the naso-palatine, which accompanies the nerve of the same name; (2) a branch of the anterior ethmoidal accom- panying the septal branch of the nasal nerve ; (3) some minute twigs to the upper part of the septum from the posterior eth- moidal artery ; (4) the septal branch of the superior coronary artery, which is distributed upon the columna nasi. Dissection. — The mucous membrane of the septum may now be divided by the scissors along the roof of the nasal cavity. Before doing this, disengage from its surface the naso-palatine nerve and 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 detached from the roof of the nose is thrown inwards the nasal fossa is exposed. Nasal Fossse (cavum nasi). — These are two chambers placed one on each side of the septum nasi. They are extremely narrow, but the vertical depth and antero-posterior 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 nasal fossae or nostrils are two oval orifices which open upon the face and look down- wards. The posterior apertures or choanal open into the naso- pharynx and look directly backwards. 192 HEAD AND NECK The narrow roof of the nasal fossa consists of an inter- mediate 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 nasal spine of the frontal bone, the nasal bone, and the angle Anterior ethmoidal cell Infundibulum Posterior angle of septal cartilage between vomer. and perpendicular plate of ethmoid ■Middle meatus Middle turbin- ated bone Antrum of Highmore Inferior meatus Inferior turbinated bone Fig. 143. — Coronal section through the Nasal Cavities opposite the Crista Galli of the Ethmoid Bone ; viewed from behind. The upper arrow passes through the opening of the anterior ethmoidal cell into the hiatus semilunaris. The lozver arrow passes from the antrum of Highmore into the hiatus semilunaris. between the lateral cartilage and the septal cartilage. The posterior part of the roof, which slopes downwards and back- wards, 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 floor of the nasal fossa is of considerable width. It is NASAL FOSS.E 393 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, being 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. Outer Wall of the Nasal Fossa. — The outer wall of the nasal cavity is rendered uneven and complicated by the pro- jection of the three turbinated bones. The part which the different bones take in the formation of the outer wall of the cavity 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 cavity 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 lachrymal, the ethmoid, and the inferior turbinated bones, with a small portion of the body of the superior maxillary bone, enter into its construction ; whilst still farther back are the vertical plate of the palate bone and the internal pterygoid plate of the sphenoid. Placed in relation to the outer aspect of this wall are the ethmoidal air-cells, which intervene between the upper part of the nasal cavity and the orbit, whilst, at a lower level, the great air sinus of the superior maxillary bone, termed the antrum of Ilighmore, is situated immediately to the outer side of the nasal fossa (Fig. 143). 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 — (1) the vestibule, (2) the atrium meatus medii, (3) the region of the turbinated bones and intervening meatuses. Vestibulum Nasi. — The vestibular part (Pig. 144, 6, 6') of the outer wall is a depression of a somewhat oval form placed immediately above the aperture of the nostril. It is partially divided into an upper and lower portion by a short ridge which projects forwards from its posterior boundary, and it is clothed throughout by integument continuous with the skin. From this a number of stout, stiff hairs, termed vibrissa', project (Fig. 144, 5). The vibrissas 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 394 HEAD AND NECK 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 ampullated entrance to the nasal fossa. The capacity and shape of this Fig. 144. — Outer Wall of the Left Nasal Fossa. (From Schwalbe. ) 1. Frontal air sinus. 2. Free border of the nasal bone. 3. Cribriform plate of ethmoid. 4. Sphenoidal air sinus. 5. Vibrissas. 6', 6. Two parts of the vestibular area. 7. Elevation intervening between the vestibular district and the atrium. 8. Atrium meatus medii. 9. Agger nasi, or rudiment of an anterior turbinal. 10. Upper part of the superior turbinated bone (concha suprema) 11. Recessus spheno-ethmoidalis. 12. Superior turbinated bone. 13. Superior meatus. 14. Middle turbinated bone. 15. Inferior turbinated bone. 16. Plica naso-pharyngea. 17. District intermediate between nose and pharynx, and termed the region of the ductus naso-pharyngeus. 18. Orifice of Eustachian tube. 19. Prominent posterior lip of this orifice. 20. Wall of pharynx. 21. Anterior palatine canal. a, b, c. Free border of the middle turbin- ated bone. section of the cavity is influenced to a certain extent by the contraction of the nasal muscles. Atrium Meatus Medii. — This part of the outer wall of the nasal fossa (Fig. 144) is placed above, and slightly behind the vestibular district, and it receives its name from the fact that it leads directly backwards into the middle meatus of NASAL FOSSAE 395 the nose. It is slightly hollowed out and concave, and on its upper part, near the nasal bone, a feeble elevation termed the agger nasi may be noticed ; this begins close to the fore- part of the attached margin of the middle turbinated bone, and proceeds obliquely downwards and forwards. It has been termed by Schwalbe the " rudiment of the 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 olfac- tory district of the outer wall of the nasal fossa, and receives the name of sulcus ol f actor ius. Turbinated Bones. — Behind the vestibule and the atrium are the turbinated bones with the intervening meatuses. The superior turbinated bone (concha superior) (Fig. 144), which projects from the lateral mass of the ethmoid bone, is very short, and is placed on the upper and back part of the outer wall of the fossa. Its free border 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 middle turbinated bofie (concha media) (Fig. 144) is also a part of 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 ; then, bending suddenly, it proceeds backwards, and ends midway between the body of the sphenoid and the posterior border of the hard palate. The inferior turbinated bone (concha inferior) (Fig. 144) 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. 144) 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 entire length, and forcing it upwards. Care should be taken not to injure the mucous membrane more than is absolutely necessary. The middle meatus is a much more roomy passage which 396 -*- HEAD AND NECK lies between the middle and inferior turbinated bones, and is continued directly forwards into the atrium. The middle spongy bone should be forcibly tilted upwards and back- wards. The upper and fore part of the middle meatus leads into a funnel-shaped passage which passes upwards into the corre- sponding frontal sinus. This passage is called the infundi- bulum, and constitutes the channel of communication between the frontal sinus and the nasal chamber. Frontal air-sinus Bulla ethmoidalis Orifice of middle ethmoidal cells Orifices of posterior ethmoidal cells Recessus spheno-ethmoidalis enoidal sinus Orifice of anterior ethmoidal cells Hiatus semilunaris Atrium Orifice of antrum of Highmore Vestibule Orifice of nasal duct Cut edge of middle turbinated bone —Middle meatus Pharyngeal T recess ^ Eustachian :tt — orifice Salpingo- i \ pharyngeal fold >^ttt— Soft palate Inferior meatus Cut edge of inferior turbinated bone Fig. 145. — Outer wall of Nasal Chamber and Naso-pharynx. The three turbinated bones have been removed. Upon the lateral wall of the middle meatus 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 semilunaris (Fig. 145), are the openings of the anterior ethmoidal cells, and the antrum of Highmore. The upper boundary of the hiatus semilunaris is prominent and bulging. 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. 145). The slit -like opening of the antrum of Highmore will be noticed in the hinder part of the hiatus semilunaris. NASAL FOSSAE 397 The dissector should now proceed to open up the antrum of Highmore by removing its outer wall. This may be 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 immediately above the middle point of the attached margin of the inferior turbinated bone. 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 downwards in front so as to limit it anteriorly (Fig. 144). This condition, together with the back- ward slope of the floor, renders the inferior meatus more accessible to the current of expired air than to the current of inspired air. 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. 145). 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. 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 splieno-ethmoidalis (Meyer), and 398 HEAD AND NECK into its back-part opens the aperture of the sphenoidal air sinus (Fig. 145). This orifice may be circular or slit-like, according to the manner in which the mucous membrane is disposed around it.1 The upper portion of the superior turbinated bone which is placed above this additional meatus is called the concha suprema (Fig. 144). Mucous Membrane of the Outer Wall of the Nose. — The vestibule, as we have noted, is lined by integument. The remainder of the outer wall, as well as the roof and floor of the nasal fossa, is lined by mucous membrane, which is con- tinuous through the nasal duct with the ocular conjunctiva, 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 without any sharp line of demarcation into the other. The olfactory region (regio olfactoria) comprises merely the upper turbinated bone ; the respiratory region (regio respiratoria) includes the middle and inferior turbinated bones, 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 venous 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 than 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 1 When the recessus spheno-ethmoidalis is absent, the sphenoidal air sinus opens into the interval between the roof of the nasal fossa and the superior turbinated bone. NASAL FOSSAE 399 are visible to the naked eye. In the olfactory region the lining membrane 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. '1. External branch of nasal proper. 2. Nasal branch of anterior superior dental. 3. Superior nasal branches from Meckel's ganglion and from the Vidian nerve. 4. Two inferior nasal branches from the great posterior palatine nerve. Nerves of Common Sensation, . The olfactory nerves are from twelve to twenty in number. They are fine filaments which spring 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 inner or septal nerves have been already described (P- 39°)- 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 upper turbinated bone and the region immediately below. The dissection of these nerves is exceedingly difficult even in the fresh subject, but in a well-preserved part they can gener- ally 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 distribution 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 to 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 care- fully dissecting the mucous membrane in its neighbourhood the superior nasal nerves may be detected entering the nasal fossa. 400 HEAD AND NECK They are distributed to the mucous membrane over the upper and middle turbinated bones ; and some filaments are prolonged to the septum. The inferior nasal nerves are two in number, and they both arise from the great posterior 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 process, and turn it cautiously over from behind forwards. The upper of the two inferior nasal nerves will be found 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. 338). It gives, as we have noted, a branch inwards to the septum ; 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 splwio-palatine, 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 — accom- panies the latter nerve, whilst others are distributed upon the outer wall of the cavity. Several twigs are also given by the descending or posterior palatine branch of the internal maxillary and the two ethmoidal arteries, but these are small and will only be seen in cases where the injection of the subject has been unusually successful. SPHENOPALATINE GANGLION 401 SPHENO-PALATINE GANGLION AND INTERNAL MAXILLARY ARTERY. The spheno-palatine ganglion or the ganglion of Meckel is situated in the spheno-maxillary fossa on the outer side of the spheno-palatine foramen, and can best be exposed at this stage by dissecting from the inner or nasal side. Dissection. — 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 lamina of bone which forms the inner wall of the posterior palatine canal is so thin that the nerve can be 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 maxillary artery, from which numerous branches are given off. Spheno-palatine Ganglion (ganglion sphenopalatinum). — This is a small triangular flattened body, which is lodged in the spheno-maxillary fossa. It is embedded in soft fat, and sur- rounded by the terminal branches of the internal maxillary artery. The two stout spheno - palatine branches which descend from the superior maxillary nerve join it from above, but only a certain proportion 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 constituting 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 connexions with the facial nerve and carotid plexus, as well as to supply the mucous membrane of the pharynx ; and upwards to the orbit. T . , , . f Superior nasal. Internal branches, . WT 1 r~„ ' \ Naso-palatine. [Large posterior palatine. Descending branches, -| Small posterior palatine. I Accessory posterior palatine. VOL. II — 26 4o2 HEAD AND NECK Posterior branches, . \ ™ ' , ^ Pharyngeal. Ascending branches, . Orbital. From the internal maxillary artery twigs are given off which accompany these nerves. The superior nasal and the naso-palatine nerves have been already described (pp. 399 and 390). They arise from the inner aspect of the ganglion, but in some cases the naso- palatine may be seen to take origin from the commencement of a common palatine trunk, or even from one of the spheno- palatine branches of the superior maxillary nerve. The posterior palatine nerves (nervi palatini) are three in number, and are distinguished as large, small, and accessory. 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 small and the accessory posterior 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 process, 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 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.1 This must be divided, in order that the posterior palatine nerve may be followed to its distribution. The accessory posterior palatine ne)"ve 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 large posterior 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 large posterior palatine nerve, as it emerges from the posterior palatine foramen, turns forwards, and divides into branches, which lie in grooves on the under aspect of the hard palate. It supplies the gum, the mucous membrane, 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. SPHENO-PALATINE GANGLION 403 and giands of the vault of the mouth, and in the neighbour- hood of the anterior palatine foramen it effects a communi- cation with the naso- palatine nerve. During its passage through the posterior palatine canal this nerve has already been observed to supply two mferior nasal branches (p. 400). In tracing the large 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.1 Dissection. — Considerable difficulty will be experienced in exposing the pharyngeal and Vidian nerves. They proceed backwards from the posterior part of the ganglion in canals which are very 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 pre- viously 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 carotid plexus (p. 329). It traverses the Vidian canal, and joins 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 accompanying artery. It has already been observed to give some fine filaments to the mucous mem- brane of the nose. The orbital bra?iches (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 An equally good method of tracing the large 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. 4o4 HEAD AND NECK i. The posterior dental (arteria alveolaris superior posterior) (p. 286). 2. The infra-orbital (p. 386). 3. The descending palatine. 4. The Vidian. 5. The pterygo-palatine. 6. The spheno-palatine. The descending palatine (arteria palatina descendens) accompanies the large posterior palati?ie nerve. During its passage through the posterior palatine canal, it gives off twigs which accompany the small and accessory posterior 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 Vidia?i artery (arteria canalis pterygoidei) runs back- wards 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 spheno-palatine (arteria sphenopalatina) enters the nasal fossa through the spheno-palatine foramen, and has already been followed to its distribution (p. 400). INTRAPETROUS PART OF THE FACIAL NERVE AND THE AUDITORY NERVE. The facial and auditory nerves, together with the pars intermedia, have already been traced into the internal auditory meatus (p. 126). The dissector should now open up this meatus and follow the facial nerve in its course through the petrous portion of the temporal bone. The canal which it occupies is termed the aqueduct of Fallopius. This begins at the bottom 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. INTRAPETROUS PART OF FACIAL NERVE 405 Dissection. — Perhaps 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 understood that, with a little care, there is nothing to hinder the dissector carrying out the dissection on the hard bone by means of the saw and the chisel. Separate 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 back- wards. 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 dis- section, 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 exposed. 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 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 meatus to the geniculate ganglion. 3. A part which occupies that portion of tin- aqueduct <>f 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 406 HEAD AND NECK nerve runs almost directly outwards in company with the auditory nerve and the pars intermedia. In this stage of its course it lies in relation to the upper 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 ,-Portio intermedia , -''.-Geniculate ganglion Facial- Stapedius Large superficial petrosal ,- Small superficial petrosal -Small deep petrosal ,-Large deep petrosal .Vidian \J^~ ^l'c SanS'i°n Lingual j» Superior maxillary Spheno-palatine KIP ganglion Digastric. Stylo-hyoid From great -- auricular From auriculotemporal ---Temporo-facial Cervico-facial Fig. 146. — Diagram of the Facial Nerve. (Thane, Quairi s Anatomy.) C/i. Ty. Chorda tympani ; its middle part is removed. Ty. Tympanic branch of the glosso- pharyngeal. Sy. Sympathetic on the internal carotid artery. Car, Ty. Caroticotympanic nerve. 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, immedi- ately above the fenestra ovalis. 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. INTRAPETROUS PART OF FACIAL NERVE 407 The fourth 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, "| 2. Communicating twig to tympanic branch of the | from geniculate glosso-pharyngeal, J ganglion. 3. External superficial petrosal nerve, J 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. 329). 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. 314). The external superficial petrosal nerve is not always present. It joins the sympathetic plexus which accompanies the middle meningeal artery. The nerve 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 communicating twigs to the auricular branch of the vagus arise a short distance above the stylo-mastoid foramen. Chorda Tympani. — The chorda tympani, which represents 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 4o8 HEAD AND NECK 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. 294). 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, termed the cochlear and vestibular divisions. These trunks again sub- divide and supply the different parts of the labyrinth of the ear through the foramina of the lamina cribrosa. 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 larynx com- menced. General Construction and Position. — The larynx 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 con- nexions of the nine laryngeal cartilages in a permanent speci- men (v. p. 425). 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 front it is covered by the integument and deep cervical fascia, and on either side of the mesial plane by two thin strata of muscles, viz., 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 lode, is also continued upwards 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 • THE LARYNX 409 by this it is separated from the prevertebral muscles. If we consider the tip of the epiglottis to represent its upper limit, the larynx in the adult may be regarded as being placed in front of that portion of the vertebral column which extends from the lower border of the third to the lower border of the sixth cervical vertebra ; 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 folds of mucous membrane which extend from before back- wards, 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 true vocal cords. The latter are the chief agents in the production of the voice, and the larynx is so constructed that changes in their relative position and in their degree of tension are brought about by the action of the muscles and the recoil of the elastic ligaments. The Upper Subdivision of the laryngeal cavity (Fig. 147) extends from the superior aperture of the larynx down to the upper or false vocal cords. It is called the vestibule (vestibulum laryngis). In its lower part it exhibits a marked lateral compres- sion. Its width therefore diminishes from above downwards, whilst owing to the obliquity of the upper opening of the larynx its depth becomes rapidly reduced from before backwards. In front it is bounded by the posterior surface of the epiglottis and the thyro-epiglottidean ligament, both covered by mucous membrane. This wall descends obliquely from above down- wards and forwards, and becomes narrower as it approaches the anterior ends of the false vocal cords. The lateral wall of the vestibule is formed by the inner surface of the aryteno- epiglottidean fold. For the most part it is smooth and slightly concave, but in its posterior part the mucous mem- brane bulges out in the form of two elongated vertical eleva- tions placed one behind the other. The anterior elevation is formed by the cuneiform cartilage and a mass of glands associated with it enclosed within the aryteno-epiglottidean fold ; the hinder elevation is produced by the anterior margin of the arytenoid cartilage and the cartilage of Santorini. A shallow groove descends between these rounded elevations 4io HEAD AND NECK Epiglottis and terminates below by running into the interval between the false and the true vocal cords. The posterior wall of the vestibule is narrow, and corresponds to the interval between the upper parts of the two arytenoid cartilages. The superior aperture of the larynx has already been ex- amined in the dissection of the pharynx (p. 376). The parts which bound it should again be carefully studied. The epiglottis projects upwards behind the root of the tongue. Its lingual or anterior surface is only free in the upper part of its extent, and is at- tached to the back part of the tongue by a prominent mesial fold of mucous membrane, termed the glosso- epiglottidean fold or frenum of the epi- glottis. Two lateral folds are also present which con- nect its margins with the lateral walls of the phar- ynx • these are called the phar- Hyoid bone Aryteno- epiglottidean fold Cushion of epiglottis Thyroid cartilage False vocal cord Laryngeal sinus True vocal cord Thyro-arytenoid muscle Cricoid cartilajre Fig. 147. — Coronal section through Larynx to show Compartments. yngo folds. two epiglotiidean Between the layers of mucous membrane which constitute each of these three folds, there is a small amount of elastic tissue. The depression on each side between the tongue and the epiglottis which is bounded by the glosso-epiglottidean and the pharyngo-epiglottidean folds is termed the vallecula (Fig. 148). The posterior free surface of the epiglottis forms, as we have noted, the greater part of the anterior boundary of the vestibule of the larynx. The upper part of this surface is convex, owing to the manner in which the upper margin is curved forwards THE LARYNX 411 towards the tongue ; below this there is a slight concavity and still lower a marked bulging or convexity over the upper part of the thyro-epiglottidean ligament. This swelling is called the tubercle or cushion of the epiglottis, and it forms a conspicuous object in laryngoscopic examinations of the larynx. The aryteno-epiglottidean folds of mucous membrane enclose 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. As already mentioned, these small nodules of cartilage raise the hinder part of the aryteno-epiglottidean fold in the form Of tWO rOUnded Base of tongue eminences or tubercles well seen when the larynx is ex- amined by means of the laryngoscope. The Middle Subdivision of the laryngeal cavity (Fig. 147) is the smallest of the three. Frenum epiglottidis Epiglottis Cushion True vocal cord Cuneiform Cornicula laryngis Fig. 148. — The Larynx as seen in the living person by means of the laryngoscope. 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 compartment of the larynx on the other. The false vocal cords (plica? ventriculares) are two pro- minent 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. Within the fold of mucous membrane which forms this cord are contained — ( 1 ) the feeble superior thyro-arytenoid ligament; (2) numerous glands which are chiefly aggregated in its middle part; and (3) a few muscle fibres. The interval between the false vocal cords is sometimes termed the false glottis, and is con- siderably wider than that between the true vocal cords. 412 HEAD AND NECK 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 (plicae vocales), placed below the false cords, extend from the angle between the alse of the thyroid cartilage in front to the vocal processes of the arytenoid i tt cartilages behind /Hyoid bone piglottidean ligament Cartilage of epiglottis Fatty pad Thyro-hyoid membrane Thyroid cartilage Elevation produced by cuneiform cartilage _, False vocal cord Philtrum ventriculi Elevation produced byarytenoid cartilag Laryngeal sinus True vocal cord Arytenoid muscle Processus vocalis Cricoid cartilage Cricoid cartilage FlG. 149. — Mesial section through Larynx to show the Outer Wall of the Right Half. The true vocal cord is sharp and pro- minent, and the mucous membrane which is stretched over it is thin and firmly bound down to the subjacent liga- ment. In colour it is pale, almost pearly white, whilst pos- teriorly the point of the processus vocalis of the arytenoid cartilage, which stands out in relief, presents a yellowish tinge. In section each true vocal cord is somewhat pris- matic in form, and the free border looks upwards and in- wards. 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 appreci- able difference in the voice result. The ritna glottidis or glottis vera is the elongated fissure by means of which the middle compartment of the larynx com- municates with the lower subdivision. It is placed somewhat below the middle of the laryngeal cavity, of which it con- stitutes the narrowest part. In front it corresponds to the THE LARYNX 413 interval between the true vocal cords ; behind it corresponds to the interval between the bases and vocal processes of the arytenoid cartilages (Fig. 150). It is composed, therefore, of two very distinct parts — (1) a narrow anterior portion, between the true vocal cords, involving less than two -thirds of its length, and called the glottis vocalis (pars intermem- branacea); (2) a broader, shorter portion between the arytenoid cartilages, and termed the glottis respiratoria (pars inter- cartilaginea). The form of the rima glottidis undergoes Thyroid cartilage Inferior thyro- arytenoid ligament Rima Vocal process of arytenoid cartilage Arytenoid cartilage Fig. 150. — Diagram of Rima Glottidis. A. During ordinary easy hreathing. B. Widely open. frequent alterations during life, but during ordinary quiet respiration it is lanceolate in outline. The glottis vocalis presents, under these conditions, the form of an elongated triangle with the base directed backwards. When the glottis is widely opened the broadest part of the fissure is at the extremities of the vocal processes of the arytenoid cartilages, and here the side of the rima presents a marked angle. The two vocal cords, on the other hand, may be approximated so closely to each other, as in singing a high note, that the glottis vocalis is reduced to a linear chink. The length of the entire fissure differs considerably in the 4i4 HEAD AND NECK two sexes. In the male its average length is 23 mm.; in the female, 17 mm. The side wall of the larynx in the interval between the true and the false vocal cords shows a pocket-like depression or recess, termed the laryngeal sinus (ventriculus laryngis). 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, a slit- like aperture will be detected. This leads into the laryngeal saccule (appendix ventriculi), 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 saccule, with cotton wadding. This will greatly facilitate the subsequent dissection. The Lower Subdivision of the Laryngeal Cavity (Fig. 147) 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 sloping inner surfaces of the crico-thyroid membrane, and by the inner aspect of the cricoid cartilage. It is through the anterior wall of this compartment that the opening is made in the operation of laryngotomy. Mucous Membrane of the Larynx. — This is continuous above with that lining the pharynx, and below with the mucous lining of the trachea. Over the laryngeal or hinder surface of the epiglottis it is closely adherent, but elsewhere above the level of the true vocal cords it is loosely attached by submucous tissue. As it passes over the true vocal cords it is very thin and tightly bound down. In inflammatory conditions of the larynx attended by oedema this prevents the infiltration of the submucous tissue extending downwards below the rima glottidis. The mucous membrane of the larynx has a plentiful supply of racemose glands which secrete mucus. Over the surface of the true vocal cords these are completely absent. Dissection. — Place the larynx upon a block so that its anterior surface looks upwards, and fix it in this position with pins. The branches which THE LARYNX 415 the external laryngeal nerve gives to the cricothyroid muscle should in the first place be followed out, and carefully preserving the superior and inferior laryngeal vessels and the internal and recurrent laryngeal nerves, the dis- sector 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 and cricoid cartilages. The broad thyro- hyoid membrane, the central portion of the crico-thyroid membrane, and the crico-thyroid muscles are now exposed, and their attachments may be defined. Thyrohyoid Membrane. — This is a broad membranous sheet, which occupies the interval between the hyoid bone and the thyroid cartilage. It is not equally strong throughout, 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 {ligamentum thyreo- hyoideum medium) is largely composed of elastic fibres. 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 deep 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 {ligamentum thyreo-hyoideum /atera/e), and is chiefly composed 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 t?-iticea. Crico-thyroid Muscle. — 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 416 HEAD AND NECK Cricothyroid membrane 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 com- posed of those fibres which are attached to the ala of the thyroid cartilage ; the posterior or horizo?ital part is formed of those fibres which are inserted into the inferior cornu of the thyroid cartilage. It is closely associated with the inferioi constrictor muscle. The crico-thyroid muscle is supplied by the external laryngeal branch of the superior laryngeal nerve. Middle Portion of the Crico-thyroid Membrane. — This can be studied in the in- terval between the two crico-thyroid 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 carti- lage, and above to the lower margin of the middle portion of the thyroid cartilage. It is pierced by minute aper- tures, 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 connexions. 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 larynx 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 Oblique part Horizontal part Fig. 151. 1 :^