Part 43

The ventral ramus of the first cervical (p. 385) will be found emerging from beneath the wing of the atlas, a little distance craniad of the second (Fig. 156, _j_). Trace it. To find its short dorsal ramus, the suboccipital nerve (p. 384), it is necessary to dissect apart the muscles on the dorsal side of the atlas till the nerve is found passing from the atlantal foramen.

Dissect the third, fourth, and fifth nerves (p. 385, and Fig. 158).

_Brachial Plexus_ (p. 386, and Figs. 159 and 160).--The brachial plexus has been partly uncovered in dissecting the vagus and sympathetic. (If a new specimen or the opposite side is used, reflect the skin from the ventral surface of the thorax and arm, and cut the pectoral muscles, thus uncovering the vessels and nerves of the axilla.) Reflect the skin from the ventral surface of the upper arm. (Do not use scalpel, but tear the skin from the muscles. In this way the nerves will be seen passing to the skin, while if the scalpel were used the nerves might be cut.)

Tie the axillary vein or its two branches in two places, and cut the vein between the tied regions. Leave the arteries as guides for dissection, but remove the veins. Now clean thoroughly the nerves forming the brachial plexus as they pass from the thorax or neck. Be careful not to injure any of the fine nerves or the interconnections of the nerves in doing this. Find and distinguish clearly the fifth, sixth, seventh, and eighth cervical nerves and the first thoracic, as they emerge from the neck or thorax. (Compare Fig. 159 and Fig. 157, _V_-_VIII_ and _I′_.)

Follow out the branches of the plexus, noting the origin and distribution of each branch, in order to determine its name. To follow the phrenic (p. 388, and Fig. 157, _f_), remove a portion of the thoracic wall. In following the other branches of the plexus, pull back the skin wherever an exposure is to be made, and separate the muscles. The epitrochlearis may be cut near the elbow, and the clavobrachial near the shoulder. In following the interosseous branches of the median nerve the fifth head of the flexor profundus, and the extensor brevis pollicis, may be cut. As a rule it will not be necessary to cut other muscles.

_Thoracic and Lumbar Nerves._--One or two of the thoracic nerves (p. 393) should be dissected from the outside by finding the intercostal nerve along the caudal border of one of the ribs and tracing it in both directions. The nerve may be exposed by removing the external muscles covering the rib, and cutting the external intercostal muscles. The dorsal ramus should be traced after the ventral ramus has been studied.

The first lumbar nerve (p. 395) should be dissected in the same way.

The other lumbar and sacral nerves (pp. 395-400) are best dissected from within.

The alimentary canal and its appendages should be removed from the abdomen, leaving only five or six centimeters of the caudal end of the rectum. The kidneys and urogenital organs may be left, to be removed during dissection. (Compare Fig. 162.)

Turn one of the kidneys to the other side, and find the second lumbar nerve (Fig. 162, _a_) appearing at the lateral border of the iliopsoas muscle. Trace it to its origin; trace it also distad, following both branches. It will be necessary to trace the nerves through the abdominal wall, then find them from the outside, and follow them to their distribution.

The third nerve (Fig. 163, _b_) may be found by dissecting apart the fibre-bundles of the iliopsoas and psoas minor, and following in the same way. The kidneys, ureters, vena cava, and aorta may be removed as occasion arises.

The remainder of the lumbar nerves may be found in order, in a similar manner. Follow the saphenous nerve and its branches (p. 397) by removing the integument from the medial side of the leg (see Fig. 127, p. 310). To dissect the sacral nerves (p. 399) separate the innominate bones at the pubic symphysis and divaricate them. Find the nerves arising from the sacral plexus, by cutting the levator ani muscle. After N. hemorrhoidalis inferior and N. pudendus have been traced, the rectum and urogenital organs may be removed, taking great care not to remove more than is necessary. To dissect the great sciatic nerve (p. 400, and Fig. 163), separate the biceps and caudofemoralis near their proximal ends and find the large nerve-trunk (_a_). Then lift the biceps away from the nerve, cut that muscle near its middle, and reflect it. The nerve may now be followed to its terminal branches; during the process cut the muscles only when absolutely necessary. The inferior gluteal nerve (_i_) will be found on the dorsal surface of the great sciatic; by cutting the caudofemoralis and gluteus maximus muscles near their insertions and turning them back the distribution of the nerve may be followed. The superior gluteal (_j_) will be found at the cranial margin of the pyriformis by reflecting the gluteus medius in the same way; the tensor fasciæ latæ may also be cut.

SENSE-ORGANS.

I. THE EYE (p. 410).

Use any specimen on which one side of the head has been left intact. Remove the head from the body by cutting through the neck a little craniad of the first rib.

Study the eye externally. Observe the eyelids, the conjunctiva, nictitating membrane with its cartilage, and the Harderian gland (Fig. 165); the two openings of the lachrymal duct, the Meibomian glands if possible.

Remove the zygomatic arch and expose the orbit and the structures which it contains. Study the periorbita (p. 409), and find the lachrymal gland (p. 410).

Study the muscles of the eyeball (p. 411, and Fig. 166). The lateral rectus on the lateral surface will perhaps be first found, and its tendon traced beneath the inferior oblique. Use great care not to injure the levator palpebræ superioris.

After studying the muscles, find the optic nerve. Cut it and the muscles, and remove the eyeball for farther study.

_The Eyeball_ (p. 412, and Fig. 167).--For an examination of the eye it is well to have a fresh specimen and one hardened in formalin or alcohol. The hardened specimen is more essential, however. An eye from one of the specimens used in dissection is usually satisfactory. All accessory portions should be trimmed from the eyeball, leaving only the spherical ball with a short stalk formed by the optic nerve.

Observe such features of the eye as can be seen externally: the optic nerves, sclerotic, cornea, iris, and pupil. This should be done on a fresh specimen, if one is at hand. The changes in size and form of the pupil can be observed in the living cat by changing it from a light to a dark place and _vice versa_.

_Dissection._--Examine the internal structures on a preparation. Then with fine scissors and forceps remove from the eye about one-fourth of the wall, in the form of a quadrant having one point at the optic nerve, the other at the centre of the cornea. The coats of the eye can then be studied on the piece removed, while the other structures will be visible within the eyeball. No special directions are necessary for observation of the structures described, unless it be the capsule of the lens and the zonula ciliaris. The capsule of the lens may be demonstrated by tearing a bit of it off with fine forceps. The zonula ciliaris is easily seen by divaricating the edges of the cut made in removing the quadrant, so as to stretch the fine fibres of which the zonula is formed.

II. THE EAR (p. 415).

(The muscles of the external ear are of little practical importance, and will doubtless usually be omitted.)

(1) The External Ear. Read the description of the external ear (p. 415), verifying it by examination and comparison of an ear still covered with integument, in the natural condition, and of a preparation of the isolated cartilages of the ear (Fig. 168). The latter may be obtained by dissecting the skin and muscles from a fresh ear.

(2) The scutiform cartilage (p. 418) should be observed in the natural position, and as isolated.

(3) The muscles of the external ear (p. 418, and Fig. 169). Those connecting the external ear with other parts of the head have been studied in connection with the facial muscles. The remainder will be studied on an external ear removed according to the directions given on page 435.

Remove the integument from the convex surface of the auricle, sufficiently to expose the entire extent of the muscles.

1. The rotator auris. Transect.

2. The adductor auris superior (Fig. 169, 1).

3. The adductor auris medius (2).

4. The transversus auriculæ (Fig. 63, _i_, p. 97).

5. The auricularis externus (Fig. 169, 10).

6. The helicis (Fig. 169, 3). To expose this it will be necessary to remove the integument from along the cranial border of the inner surface of the auricle.

7. The antitragicus (Fig. 169, 6). Remove the integument farther if necessary.

8. The tragicus medialis (Fig. 169, 5, 5′).

9. The conchæus externus (Fig. 169, 9).

(4) Remove the tympanic bulla and petrous bone from the rest of the skull, by the use of bone-forceps and scalpel. Trim away all soft tissue (including the cartilaginous auditory meatus), and all other bony parts from these, but leave them uninjured.

(5) Find the Eustachian tube and study it (p. 423).

(6) Study specimens of the bones of the middle ear (p. 423, and Figs. 171 and 172).

(7) The middle ear should be studied on a demonstration preparation, then dissected as follows:

Remove with bone-forceps the medial side of the tympanic bulla (the entotympanic). Note the two cavities within the bulla, with the shelf separating them. Observe the fenestra cochleæ. Now remove with the forceps the shelf, first breaking through the middle part, then removing the rest with care. Remove part also of the membranous lining of the cavity, till the inner surface of the tympanic membrane, with the malleus crossing it, is visible. Observe the tensor tympani muscle (p. 424) attached to the malleus by its small tendon. Next, with bone-forceps, fracture the thick, bony portion uniting the caudal end of the petrous with the caudal part of the ring of bone surrounding the external auditory meatus. These two parts may then be separated with the fingers, leaving the petrous bone on one side, the meatus, tympanum, and malleus on the other (Fig. 170). The head of the malleus may then be observed, with the incus attached to it. Note also the stapes, in the fenestra vestibuli, with the stapedius muscle (p. 424) attached to it.

(8) The internal ear (p. 424). Note the fenestra vestibuli and fenestra cochleæ and the promontory (p. 34). Study the cochlea and vestibule on a demonstration preparation and compare with Fig. 173. Then remove the wall of the promontory and find the cochlea. Open the vestibule and find as many of the openings of the semicircular canals as possible. Study the semicircular canals on demonstration preparations, consulting Fig. 173. The semicircular canals may, if desired, be exposed on your own specimen, by cutting away the surface of the bone in places indicated in the description (p. 426), and inserting fine bristles (those from the sensory hairs on the face of the cat are excellent for this purpose).

The membranous labyrinth (Fig. 173) may be isolated by decalcifying the petrous bone with ten per cent. nitric acid, then dissecting out the labyrinth. This is an operation of considerable delicacy, but at least one or two specimens for demonstration should, if possible, be prepared thus and kept in the laboratory.

INDEX.

Abdominal aorta, 301 arteries, 301 cavity, 217, 218 muscles, 153 dissection, 441 veins, 326 Abducens nerve, 347, 375 Abductor auris brevis, M., 100, 435; longus, M., 100, 435 brevis pollicis, M., 184, 439 caudæ (coccygis) externus, M., 137, 447; internus, M., 137, 446 cruris, M., 195 digiti quinti, M., 185, 439; secundi, M., 185 medius digiti quinti, M., 215 Accelerator urinæ, M., 271 Accessory nerve, 346, 382 process, 6, 8 Acetabular bone, 76, 78 notch, 79 Acetabulum, 76, 78, 87 Achilles, tendon of, 204, 206 Acromiodeltoid muscle, 157, 438 Acromion process, 62, 64 Acromiotrapezius, M., 116, 436 Adductor auris inferior, M., 104, 435; medius, M., 419, 470; superior, M., 419, 470 digiti secundi, M., 185 femoris, M., 198, 444 longus, M., 199, 444 medius digiti quinti, M., 215 pollicis, M., 185, 439 Aditus laryngis, 246 Adrenolumbar arteries, 304 veins, 326 Alæ magnæ, 26, 27 parvæ, 29 Albuginea, 260 Alcohol as preservative, 431 Alcohol-formalin for brains, 463 Alimentary canal, 221; dissection of, 449 Alisphenoids, 25, 27 Alveolar border, 39, 47 nerve, inferior, 374, 375 process, 39 Alveoli, 48 Ampulla (ear), 426 of Vater, 236 Anal glands or sacs, 239; constrictors of, 269 Anapophysis, 6 Anastomotica magna, A., 297 Anconeus, M., 170, 438 Anconeus internus, M., 170 lateralis, M., 167 longus, M., 168 posterior, M., 168 Angle of rib, 18 Angular process, 19, 48 vein, 321 Ankle, bones of, 82 ligaments of, 91 Annularis, 72 Annular ligaments, 75, 173, 213 Ansæ, 386 Anterior cerebral artery, 289 circumflex artery, 296 commissure, 357, 365 facial vein, 321 fossa, 59 perforated substance, 362 spinal artery, 291 superior process, 78 Sylvian gyrus, 359 sulcus, 359 thoracic artery, 294; nerves, 387 tibial artery, 313 transverse processes, 11 Antibrachial fascia, 172 Antibrachium, muscles of, 172 Anticlinal vertebra, 6 Antihelix, 416 Antitragicus, M., 421, 470 Antitragus, 417 Anus, 239 muscles of, 268 Aorta, 275, 279, 281, 301 abdominalis, 301 Aortic plexus, 408 semilunar valves, 279 sinus, 279 Apparatus digestorius, 221 respiratorius, 243 urogenitalis, 255 Appendicular fossa, 35, 58 lobe, 348 Appendix, 429 Aqueduct of Sylvius, 342, 343, 350, 351, 352 Aqueductus cerebri, 342, 343, 350, 351, 352; Fallopii, 35 Aqueous humor, 414 Arachnoid, 337, 369 Arbor vitæ, 349 Arch, bicipital, 166 supraorbital, 37, 51 zygomatic, 47, 49, 52 Area elliptica, 345 ovalis, 345 perforata posterior, 352 Arm, arteries of, 294 articulations of, 73 bones of, 64 muscles of, 156 dissection of, 436 nerves of, 388 veins of, 318 Arteria adrenolumbalis, 304 alveolaris inferior, 288 anastomotica magna, 297 anonyma, 282 articularis genu suprema, 311 auricularis anterior, 287; posterior, 287 axillaris, 294 basilaris, 291, 292 brachialis, 296 bronchiales, 283 carotis communis, 282, 283; externa, 285; interna, 285 cerebelli anterior, 292; inferior posterior, 292 cerebri anterior, 289; media, 289; posterior, 292 cervicalis ascendens, 293; profunda, 293 circumflexa femoris lateralis, 311; humeri anterior, 296; humeri posterior, 296; scapulæ, 294 cœliaca, 301 colica dextra, 304; media, 303; sinistra, 306 collateralis radialis superior, 297; ulnaris, 297 coronariæ, 275, 279, 281 digitales dorsales, 297; plantares, 314 dorsalis penis, 308 epigastrica inferior, 309 femoralis, 307, 310 gastrica sinistra, 303 gastroduodenalis, 302 gastroepiploica dextra, 303 genu posteriores, 313 glutea inferior, 308; superior, 308 hemorrhoidalis media, 308; superior, 306 hepatica, 302 hypogastrica, 307 ileocolica, 304 iliaca externa, 307, 309; interna, 307 iliolumbalis, 306 infraorbitalis, 290 intercostales, 283 intercostalis suprema, 293 interosseæ, 298, 300 lienalis, 303 lingualis, 285, 286 lumbales, 283, 306 lumboabdominalis, 304 mammaria interna, 292 maxillaris externa, 285, 286; interna, 287 mesenterica inferior, 306; superior, 303 meningea media, 289 metatarsea, 315 occipitalis, 285 œsophageæ, 283 ophthalmica, 289 palatina descendens, 290; minor, 290 pancreaticoduodenalis inferior, 303; superior, 303 phrenica, 304 poplitea, 311, 312 princeps pollicis et indicis, 300 profunda brachii, 296; femoris, 309 pulmonalis, 275, 278, 280 pylorica, 302 radialis, 297; recurrens, 298 renalis, 304 sacralis lateralis, 309; media, 301, 309 saphena, 311 spermatica externa, 309; interna, 304 sphenopalatina, 290 spinalis anterior, 291 subclavia, 282, 283, 290 subscapularis, 294 superior profunda, 296 suprascapularis, 293 suralis, 313 tarsea medialis, 315 temporalis superficialis, 287 thoracica anterior, 294; longa, 294 thoracicodorsalis, 296 thyreoidea ima, 283, 284; superior, 284 tibialis anterior, 313; posterior, 313; recurrens, 314 transversa colli, 293; scapulæ, 293 ulnaris, 300; recurrens, 298 umbilicalis, 307 uterina, 308 ventriculi dorsalis, 303 vertebralis, 291 Arteries (see Arteria), 280 abdomen, 301 arm, 294 bladder, 307 brain, 289, 291 foot, 312, 314 hand, 300 kidneys, 304 intestine, 304 limbs, 294, 309 liver, 302 stomach, 303 Artery (see Arteria) cystic, 302 labial, 286 mediastinal, 282 ovarian, 306 submental, 286 superior laryngeal, 285 Articular artery, superior, 311 circumference, 67 facet, 4 processes, 6, 8 Articulation, atlanto-occipital, 17 intervertebral, 16 Articulations of arm, 73 hind limb, 86 mandible, 61 Arytenoid cartilages, 248 Arytenoideus transversus, M., 250 Astragalus, 82 Atlantal foramen, 14 Atlanto-occipital articulation, 17 Atlas, 14 Atrium dextrum, 275 sinistrum, 279 Attollens auris. M., 100 Auditory bulla, 32 meatus, external, 32, 33, 52, 55, 415, 416; internal, 35, 58 nerve, 347, 377 organ, 415 Auricle (ear), 415 Auricles of heart, 274, 275, 279 Auricula, 415 Auricular appendage, 275, 279 arteries, 287 cartilage, 415, 416 facet, 10 impression, 77 Auricularis anterior, M., 104, 419 externus, M., 420, 470 posterior, M., 99 superior, M., 100, 435 Auricular nerve, 379; great, 385; posterior, 377 vein, anterior, 324; posterior, 324 Auriculotemporal nerve, 373 Auriculoventricular septum, 274 Axillary artery, 294 border, 63 nerve, 388 vein, 318 Axis, 15 Azygos vein, 316

Backbone, 1 Back, fascia of, 126 muscles of, 115, 123; dissection of, 442 Basilar artery, 291, 292 Basioccipital bone, 22 Basisphenoid bone, 25 Biceps brachii, M., 165, 438, 439 femoris, M., 194, 444 Bicipital arch, 166 groove, 66 tubercle, 64 tuberosity, 67 Bicuspid valve, 279 Bile duct, 241 Biventer cervicis, M., 132, 443 Bladder, 256 arteries of, 307 ligaments of, 219, 257 Blind spot, 414 Blood vessels, 280 dissection of, 456 injection of, 456 Body cavity, 217 Body muscles, 115 Bones, 1 ear, 423 head, 21 pelvic extremities, 76 preparation of, 430 sesamoid, 73, 80, 86 study of, 431 thoracic extremities, 62 Bony labyrinth, 425 Brachial artery, 296 Brachialis, M., 166, 438, 439 Brachial plexus, 386; dissection of, 467; vein, 318 Brachioradialis, M., 173, 438 Brachium conjunctivum, 348, 349 Brachium, muscles of, 164 pontis, 347, 348, 349 quadrigeminum inferius, 351, 354; superius, 351, 354 Brain, 339 arteries of, 289, 291 diagrams of, 343 dissection of, 464 preparation of, 462 preservation of, 462 removal of, 462 study of, 464 veins of, 324 Breast, muscles of, 144; dissection of, 437; nerves of, 387 Broad ligament, 264, 266 Bronchi, 252 Bronchial arteries, 283 veins, 318 Buccæ, 222 Buccal cavity, 221 nerves, 377 Buccinator, M., 106, 435 nerve, 374 Bulbocavernosus, M., 271, 454 Bulbourethral glands, 261 Bulbus olfactorius, 362 urethræ, 261 Bulla, auditory, 32, 55 tympanic, 32, 55 Burdach, column of, 337, 345