Part 40

7. The transversus (p. 155, and Fig. 69, _l_). Requires no further dissection.

8. The rectus abdominis (p. 155, and Fig. 73, _k_). Open its sheath by a longitudinal incision near the linea alba.

9. The external intercostals (p. 150, and Fig. 73, _m_; Fig. 69, _i_). To see these, remove the origins of the levator scapulæ and serratus anterior; also the serratus posterior superior.

10. The internal intercostals (p. 151, and Fig. 69, _k_). To uncover these, remove the external intercostals from between two or three pairs of ribs.

11. The transversus thoracis (p. 151). To see this muscle, which lies on the inner surface of the thoracic wall, it is necessary to cut through the ribs on one side one or two inches from the sternum, and open the thorax. The muscle can then be observed directly.

(The levatores costarum will be dissected later.)

VI. MUSCLES ON THE VENTRAL SIDE OF THE VERTEBRAL COLUMN IN THE NECK REGION (Fig. 72).

Clean the surface of these muscles, removing pharynx, larynx, œsophagus, and trachea, if this has not been done.

1. Longus capitis (p. 142, and Fig. 72, _a_).

2. Longus colli (p. 144, and Fig. 72, _g′_, _g″_).

3. Levator scapulæ ventralis (p. 120, and Fig. 72, _c′_, _c″_). Observe its origin.

4. Rectus capitis anterior minor (p. 143, and Fig. 72, _b_). To see this, cut through on one side the longus capitis and one head of the levator scapulæ ventralis, and remove the proximal portions, as in Fig. 72.

5. Obliquus capitis superior (p. 136, and Fig. 72, _e_).

6. Rectus capitis lateralis (p. 143, and Fig. 72, _d_).

VII. MUSCLES OF THE BACK (p. 123).

Remove what remains of the dorsal portion of the latissimus dorsi, serratus posterior superior, and serratus posterior inferior. See that the skin is removed completely to the dorsal middle line, or even for a little distance over onto the other side. There is thus exposed the lumbodorsal fascia (p. 126), covering the muscles of the back.

Cut the superficial layer of the lumbodorsal fascia (that from which the latissimus dorsi and obliquus externus abdominis have origin) by an incision parallel to the dorsal median line, and remove it. The muscles of the back are thus exposed (Fig. 69). Observe in the lumbar region the longissimus dorsi (_f_, _f′_, _f″_); in the thoracic region the longissimus dorsi, the spinalis dorsi (_g_), and the iliocostal (_h_); in the cervical region the splenius (Fig. 73, _b_).

1. The longissimus dorsi (p. 126, and Fig. 69, _f_, _f′_, _f″_). Notice in the lumbar region the strong deep layer of the lumbodorsal fascia, by which this muscle is covered, and from the under side of which many of the fibres of the muscle take origin. Cut this fascia by an incision parallel to the dorsal median line and about two centimeters from it, from the level of the crest of the ilium as far craniad as the fascia can be cut without cutting into the muscle-fibres (usually to about the level of the last rib). Reflect the medial division of the fascia to the middle line. Reflect the lateral division of the fascia until it passes into the muscle and cannot be farther reflected.

Observe then in the lumbar region the medial (Fig. 70, _a_) and lateral (Fig. 70, _b_) divisions of the longissimus dorsi, and the portion (_b′_) of the lateral division taking origin from the lumbodorsal fascia (_c_). Dissect apart some of the muscle-fibres of the longissimus and observe their origin and insertion.

Trace the longissimus dorsi into the thoracic and cervical regions (Fig. 69, _f′_, _f″_) noting the separation off from it on the dorsal side of the spinalis dorsi (Fig. 69, _g_); on the ventral side of the iliocostal (Fig. 69, _h_).

2. The extensor caudæ lateralis (p. 137, and Fig. 70, _f_). Uncover this by cutting the lumbodorsal fascia over the sacral region.

3. The iliocostalis (p. 128, and Fig. 69, _h_). Uncover this completely; note its connection with the longissimus dorsi at the caudal end. Dissect apart some of its muscle-bundles, to see origin and insertion.

4. The splenius (p. 131, and Fig. 73, _b_). Transect this by an incision beginning at its lateral border about four centimeters from the cranial end of the muscle and extending obliquely craniodorsad to the craniomedial angle of the muscle. Be careful not to injure the longissimus capitis (Fig. 73, _g_).

5. The longissimus capitis (p. 131, and Fig. 73, _g_). Transect.

6. The spinalis dorsi (p. 129, and Fig. 69, _g_). Separate some of its muscle-fibre bundles and trace to origin and insertion.

7. The biventer cervicis (p. 132, and Fig. 69, _a_). Raise its lateral border, turning it toward the middle line, and transect it near its caudal end.

8. The complexus (p. 133, and Fig. 69, _b_). Raise its medial border, and transect it near its cranial end.

9. The longus atlantis (p. 134, and Fig. 71, _f_).

10. The multifidus spinæ (p. 130, and Fig. 70, _d_). Remove a part of the longissimus dorsi in the lumbar region, and trace the course of the fibres of the multifidus spinæ. (If desired the entire longissimus may be removed and the multifidus spinæ completely uncovered.)

11. The extensor caudæ medialis (p. 136, and Fig. 70, _e_).

12. The semispinalis cervicis (p. 133, and Fig. 71, _c_). Dissect apart some of its fibre-bundles to see origin and insertion.

13. The interspinales and intertransversarii (p. 131) may be seen in the region from which the longissimus dorsi was removed, by removing the bundles of the multifidus spinæ.

14. The rectus capitis posterior major (p. 134, and Fig. 71, _a_). Transect.

15. The obliquus superior (p. 136, and Fig. 71, _e_).

16. The obliquus capitis inferior (p. 136, and Fig. 71, _b_).

17. The rectus capitis posterior medius (p. 135). Transect.

18. The rectus capitis posterior minor (p. 135).

19. The levatores costarum (p. 150). Remove in a part of the thoracic region a portion of the iliocostal and longissimus dorsi, so as to expose the dorsal ends of the ribs. The levatores costarum will be seen as but slightly separated bundles continuous with the external intercostals.

VIII. MUSCLES OF THE HIND LIMBS (p. 186).

Remove the skin and superficial fascia from the lateral surface of the thigh. Examine the _fascia lata_ (p. 186, and Fig. 68, _z_). Dissect:

1. The biceps femoris (p. 194, and Fig. 68, _t_). Work under its cranial and caudal borders. Find the tenuissimus (Fig. 90, _g_) passing obliquely beneath it and reaching its caudal border in its distal half. Transect the biceps without injuring the tenuissimus, and reflect its halves.

2. The tenuissimus (p. 195, and Fig. 90, _g_). Transect.

3. The caudofemoralis (p. 195, and Fig. 68, _s_). Transect.

4. The gluteus maximus (p. 187). Transect.

5. The sartorius (p. 197, and Fig. 68, _q_; Fig. 91, _a_). Transect.

6. The tensor fasciæ latæ (p. 187, and Fig. 68, _r_). Cut the fascia lata along the distal end of the muscle-fibres and reflect the muscle.

7. The gluteus medius (p. 188, and Fig. 90, _b_). Work under it carefully, separating it from underlying muscles; cut it close to its tendon of insertion, and reflect it.

8. The pyriformis (p. 188, and Fig. 163, 7, p. 401). Cut and reflect it.

9. The gemellus superior (p. 189, and Fig. 163, 6). This and the next muscle will sometimes be found to be completely united. Transect.

10. The gluteus minimus (p. 189, and Fig. 163, 5). Transect.

11. The obturator internus (p. 192, and Fig. 90, _e_). Cut it at the dorsal border of the ischium in order to reflect it. The whole origin cannot be seen at this stage.

12. The gemellus inferior (p. 190).

13. The gracilis (p. 198, and Fig. 91, _b_). Transect.

14. The semitendinosus (p. 196, and Figs. 90 and 91, _j_; Fig. 92, _i_). Transect.

15. The semimembranosus (p. 196, and Figs. 90 and 91, _i_; Fig. 92, _h_, _h′_). Transect.

16. The adductor femoris (p. 198, and Figs. 90 and 91, _h_; Fig. 92, _g_). Transect.

17. The quadratus femoris (p. 191, and Fig. 90, _f_). Transect.

18. The obturator externus (p. 191).

19. The adductor longus (p. 199, and Fig. 92, _f_). This and the following will sometimes be found to be almost completely united. Transect.

20. The pectineus (p. 200, and Fig. 92, _e_). Transect.

21. The iliopsoas (p. 193, and Fig. 91, _c_; Fig. 92, _d_). Only its distal part, near the insertion, can be seen at present.

22. The capsularis (p. 190). Transect.

23. The quadriceps femoris (p. 201). Isolate the rectus femoris (Fig. 92, _b_) as far as its junction with the vastus lateralis; cut it at this point and reflect its proximal portion. Turn aside the distal end and find beneath it the transverse aponeurosis between the vastus medialis and the vastus lateralis, and covering the vastus intermedius. The vastus lateralis (Fig. 90, _d_) may be cut near the middle and dissected up from its origin in both directions; the vastus intermedius is thus exposed. The vastus medialis (Fig. 92, _c_) and the vastus intermedius need not be cut.

24. The gastrocnemius (p. 203, and Fig. 90, _m_; Fig. 91, _k_). It may be raised cautiously near its middle and divided. Care should be taken not to divide the underlying plantaris (Fig. 90, _l_). After noting the connection of the outer head with the plantaris, the latter may be divided and reflected, together with the outer head.

25. The plantaris (p. 205, and Figs. 90 and 91, _l_).

26. The flexor brevis digitorum (p. 212). In tracing its tendon note the three branches of the common plantar ligament which emerges from between the second and third tendons. The outer branch is inserted into the fascia covering the base of the fifth digit, while the other two spread out into the bilobed pad of the sole.

27. The soleus (p. 205, and Fig. 90, _o_). Cut and reflect.

28. The popliteus (p. 206, and Fig. 92, _k_). Cut very near the origin and reflect.

The three following deep muscles on the ventral surface of the shank are covered by the deep crural fascia (p. 206) which separates them from the overlying muscles. It should be removed.

29. The flexor longus hallucis (p. 207, and Fig. 91, _m_). Divide the muscle at its junction with the tendon. Open the canals on the astragalus and calcaneus and reflect the tendon, cutting the tendon of the flexor longus digitorum near its insertion and dividing at the middle the quadratus plantæ (p. 213) which may be found inserted into its ventral surface.

30. Flexor longus digitorum (p. 208, and Fig. 91, _n_). This may be divided very near its origin.

31. Tibialis posterior (p. 208, and Fig. 91, _o_). This may be divided near its tendon.

32. Peroneus longus (p. 209, and Fig. 90, _q_). The overlying tendons may be cut in tracing its insertion.

33. Peroneus brevis (p. 210, and Fig. 90, _s_).

34. Peroneus tertius (p. 210, and Fig. 90, _r_).

35. Extensor longus digitorum (p. 210, and Fig. 90, _p_).

36. Tibialis anterior (p. 211, and Fig. 90, _n_).

37. The extensor brevis digitorum (p. 212, and Fig. 90, _u_).

38. The quadratus plantæ (p. 213). It was cut in dissecting the flexor longus hallucis.

39. The lumbricales (p. 213).

40. The interossei (with the muscles of the fifth digit) (p. 214).

41. The tarsal muscles (p. 215). The overlying ligaments must be removed in order to expose the scaphocuneiform.

IX. THE DIAPHRAGM AND THE MUSCLES ON THE VENTRAL SIDE OF THE VERTEBRAL COLUMN IN THE LUMBAR AND PELVIC REGIONS.

Remove the ventral and lateral walls of the thorax completely, as far back as the diaphragm,--leaving only a ring attached to the margin of the diaphragm. Remove the abdominal walls in the same way, as far back as the pubis, leaving the diaphragm in position. Remove the thoracic viscera (the heart and lungs may be preserved for future study). Remove also the abdominal viscera as far back as the beginning of the pelvis, cutting the large intestine where it passes into the pelvis. The dorsal wall of the abdominal cavity should be cleared of fat, blood-vessels, etc., without injury to the crura of the diaphragm.

1. The diaphragm (p. 151, and Fig. 74). Study by transmitted light, to see the tendons, etc.

2. The psoas minor (p. 139, and Fig. 162, 9, p. 398). Find its tendon and separate it from the iliopsoas (Fig. 162, 8) as far craniad as this can be done without tearing the fibres.

3. The iliopsoas (p. 193, and Fig. 162, 8). Find both portions; isolate them as far as it can be done.

4. The quadratus lumborum (p. 139). Free the lateral edge of the iliopsoas from the abdominal wall and turn the whole muscle mediad as far as possible. The bundles of the quadratus lumborum will be found beneath it, against the transverse processes of the lumbar vertebræ.

With a heavy cartilage-knife separate the two innominate bones along the pelvic symphysis. This is easily done if the knife is inserted exactly into the line of junction of the two bones. Divaricate the edges some distance, so as to make a ventral opening into the pelvic cavity. If necessary, part of the innominate bone of one side may be removed to make the opening larger.

Find the thin sheet of fibres forming the levator ani muscle (Fig. 162, 11) at the side of the rectum, attached to the edge of the symphysis. Carefully free the rectum and urogenital organs from this and remove them as far as the anus, leaving the levator ani intact.

5. The iliocaudalis (p. 137, and Fig. 162, 11′).

6. The levator ani (p. 269, and Fig. 162, 11).

Remove with great care the levator ani and iliocaudalis of one side, by cutting first the attachment to the symphysis and the ilium, turning the muscle mediad, then cutting the attachment to the tail. There are thus exposed on the lateral wall of the thorax the medial surface of the obturator internus, craniad of it the pyriformis, caudad of it the quadratus femoris. Dorsad of these is the abductor caudæ internus.

7. The abductor caudæ internus (p. 137).

On the ventral surface of the tail are exposed the following:

8. The flexor caudæ longus (p. 138, and Fig. 162, 12).

9. The flexor caudæ brevis (p. 138, and Fig. 162, 13).

X. MUSCLES OF THE TAIL (p. 136).

By removing the skin of the tail, all the muscles of the tail are now easily seen.

1, 2, 3, 4, 5--see 5, 6, 7, 8, 9, above (IX).

6. The abductor caudæ externus (p. 137, and Fig. 113, _b_; Fig. 70, _g_).

7. The extensor caudæ lateralis (p. 137, and Fig. 70, _f_).

8. The extensor caudæ medialis (p. 136, and Fig. 70, _e_).

THE VISCERA.

Kill the specimen with chloroform and inject with the five per cent. formalin, or the mixture of formalin and glycerine, as for the muscles. (It is an advantage if the preliminary examination of the viscera can be done in a perfectly fresh, uninjected specimen; such a specimen can be kept but a day or two, however. After one day’s examination the skin may be removed and the specimen placed in two per cent. formalin; it will usually be fairly well preserved by this, though the formalin is too strong to make the later dissection pleasant. The specimen cannot be preserved in this manner unless the skin is removed, and a sufficient quantity of formalin used.)

PRELIMINARY EXAMINATION OF THE VISCERA.

(In this preliminary examination the descriptions in the text need not be read, except when this is specially directed.)

Wet the hair along a line from the symphysis of the jaw to the pubis. Part it and make a longitudinal incision through the skin along the line. Make a transverse incision of the skin five centimeters caudad of the xiphoid process and reflect the flaps. Incise the body wall from the last rib to the pelvis along the same line as above and also transversely. Reflect the flaps without injuring the ligaments of the bladder. Make an incision through the pectoral muscles between the first rib and the ventral attachment of the diaphragm and about one centimeter from the median line. Make a second incision of the muscles from the cranial end of the first incision along the angles of the ribs to near the dorsolateral attachment of the diaphragm. Cut the ribs and thoracic wall along these incisions with strong scissors; connect the two incisions at their caudal ends, and remove the lateral thoracic wall thus circumscribed. Note the thoracic and abdominal cavities, separated by the diaphragm.

Note the following viscera in their fresh condition:

A. In the abdominal cavity (without injuring anything)

1. The liver, dark red and lobed, in the cranial part of the cavity, lying against the diaphragm.

2. The gall-bladder partly imbedded in the right median lobe.

3. Displacing the liver craniad, the stomach is seen dorsad of its left lobe. It may extend dorsad of the right lobe, its size depending on the degree of distension.

4. The duodenum or first part of the small intestine leaves the stomach at its right side craniad and makes a U bend, the head of which is directed caudad; it then turns toward the middle line dorsad of the remaining part of the small intestine.

5. The great omentum is a thin fold of peritoneum with many bands of fat. It passes like a curtain from the great curvature of the stomach ventrad of the coils of the small intestine (ileum). It is tucked beneath the mass of coils at the sides and caudally, and folds of it extend between the individual coils. Turn it craniad and note--

6. The numerous coils of the third part of the small intestine or ileum. Turn these to one side and note--

7. The connection of the ileum with the duodenum across the middle line. An indefinite part of the intestine between the ileum and duodenum is called the jejunum, because in man it is found empty after death.

8. The passage of the ileum into the side of the large intestine which begins on the right side just caudad of the loops of the duodenum. The first part of the large intestine is the colon. It may be traced first toward the head (ascending colon), then sinistro-caudad (transverse colon) and then caudad (descending colon). The descending colon returns to the middle line and the large intestine then continues to the anus as the rectum.

The blind pouch of the colon which lies caudad of the opening of the ileum is the cæcum.

9. Turn the duodenum toward the left and note the pancreas, a light red, elongated organ which stretches along the greater curvature of the stomach and thence between the two lines of the duodenal U to its bottom.

10. The spleen, parallel to the gastric portion of the pancreas. It is deep red (darker than the pancreas and not so brown as the liver) and is held against the great curvature of the stomach by a part of the great omentum.

11. The kidneys, close against the dorsal body wall and in contact with the caudal part of the liver.

12. The bladder, in the median line at the caudal end of the cavity, held in place by the suspensory ligament, which passes to the midventral line, and by the lateral ligaments.

13. The mesenteric glands, large grayish-red glands one to four centimeters long, more numerous in the mesocolon.

14. In the female, lying against the ventral surface of the rectum, the uterus. It divides into two horns which diverge. Near the end of each horn the ovary.

15. The peritoneum. Study and understand the description of it (p. 218). Dissect some of it free from the body wall. (Trace the folds by aid of a diagram and model.)

B. In the thoracic cavity:

1. The lungs. Each is divided into lobes, three on the left, four on the right. The caudal right lobe pushes the mediastium toward the left and thus lies in a pocket dorsocaudad of the heart and dorsad of the vena cava inferior.

2. The pleuræ. Each pleura is a membrane like the peritoneum. It covers the diaphragm and the thoracic walls and is reflected onto the lungs. Hence it is divided into costal and pulmonary portions. Read the description (p. 217) and trace their connection. Each pleura forms a closed sac.

3. The mediastinal septum or median vertical portion formed by the apposition of the medial walls of the two pleural sacs. It divides the thorax into halves.

4. In the mediastinum or space between the halves of the mediastinal septum are seen--

_a._ Ventrally (i.e., in the anterior mediastinum), blood-vessels and fat, and craniad the pink thymus gland. Read the description of the thymus (p. 254, and Fig. 107).

_b._ Dorsally (i.e., in the posterior mediastinum) the trachea (best seen craniad), the œsophagus (best seen caudad), and the aorta.

_c._ In the middle (reckoning in a dorsoventral line) (i.e., in the middle mediastinum) the heart, with the inferior vena cava approaching it from the rear. Prick into the mediastinum and inflate it. Remove the thoracic wall opposite the one already removed, so as to stretch the mediastinum and show it more clearly. Expose the trachea beneath the caudal end of the sternomastoidei. Note the thyroid gland (Fig. 96, 6, p. 229). Insert a blowpipe without injury to the thyroid, and inflate the lungs. Cut the sternum at its caudal end and turn it craniad, cutting the mediastinal septum and noting its double character.

Dissect the mediastinal septum from the thymus so as to expose this organ.

_d._ The pericardium, a relatively thick-walled sac, within which the heart lies. The pericardium is covered by the mediastinal septum on each side, but not dorsally and ventrally. Dissect the mediastinal septum from the pericardium. Prick and inflate the pericardium. Open it and expose the heart.

DISSECTION OF THE ALIMENTARY CANAL.

Study and verify the descriptions of the organs as they are dissected.

I. Salivary glands (p. 223).

1. Keep the mouth open by a cork between the teeth. Find the papillæ upon which open the sublingual and submaxillary ducts (pp. 223 and 224); remove the mucosa and enlarge the opening and insert a black bristle into either duct. Trace the duct by the bristle as far as possible on the floor of the mouth.

2. Find the white ridge formed on the cheek by the parotid duct (p. 223). It is opposite the molar tooth, and at its cranial end the opening of the duct is seen. Enlarge the opening and insert a black bristle as far as possible.

3. Remove the skin and the skin-muscles from the side of the face, beginning at the caudal end and working craniad. At the cranial border of the carotid on the ventral side look carefully for the parotid duct with the bristle in it. The duct is then easily traced by the removal of the skin and muscles. Study the parotid gland (Fig. 131, 10, p. 322).

4. Remove the facial vein (Fig. 131, _b_ and _c_) and lymphatic gland (Fig. 131, 12) covering the submaxillary gland (Fig. 131, 11) and clean its outer surface. Raise it and find the submaxillary duct leaving its inner surface. Reflect the digastric and mylohyoid muscles and trace the duct to the oral mucosa. The remainder of its course is shown by the bristle on the inside of the mouth.

5. The sublingual gland is uncovered in dissecting the submaxillary. Its duct is seen by the side of the submaxillary. It may be pricked near the gland and a bristle passed to its opening.

6. The infraorbital gland. Expose it by removal of the zygomatic arch and masseter muscle. Find its duct by dissecting apart the lobules at its ventral end. Prick the duct and insert a bristle to find its inner opening.

7. The molar gland. Find it by raising the orbicularis oris of the lower lip. By raising its ventral border and dissecting between it and the mucosa the ducts may be found and perhaps pricked and bristles inserted.

II. The mouth-cavity. Study the general description (p. 221); the lips and the cheek. Then remove the masseter muscle and the caudal part of the zygoma. Cut through the mandible between the first premolar and the canine tooth. Then disarticulate the mandible, cut the cheek and also the mylohyoid muscle and oral mucosa parallel to the medial border of the mandible, and remove the mandible with the parts thus left attached to it. The organs in the mouth-cavity are thus left exposed and should be studied. To demonstrate the incisive ducts (p. 222) pass a bristle into them.