Part 38

10. Then recognize the teres major (p. 163, and Fig. 75, _d_; Fig. 77, _c_) and the common insertion of the teres major and latissimus (Fig. 79, _d′_); find the bicipital arch (Fig. 65, _t′_) and determine its composition (p. 166).

11 and 12. The serratus anterior and levator scapulæ (Fig. 73, _h_ and _i_, and p. 122). In order to expose the origin of these muscles, the external oblique muscle (Fig. 68, _p_) must be recognized, and that part of it which has its origin from the fourth to the ninth rib should be transected about an inch and a half from its origin and reflected.

The thoracic portion of the rectus abdominis (Fig. 73, _k_) and of the scalenus (Fig. 73, _f_-_f‴_) should also be recognized and then raised at their outer borders and displaced toward the median line. _No part_ of any of these muscles should be removed or cut except as directed.

The serratus anterior and levator scapulæ should be transected and reflected to get at their origin and insertion.

B. _Muscles of the Arm_ (p. 156).--The arm is thus removed from the body and the dissection may be continued on the separated arm.

13. The clavobrachial (Fig. 65, _k_, and p. 157). Its origin is best seen later. Dissect it up, but do not transect it.

Search now with great care for the coracobrachialis. Consult the figures (Fig. 79, _c_) and descriptions (p. 164), and be especially careful not to injure the long head of the muscle and its tendon.

14. Dissect the coracobrachialis (Fig. 77, _f_). Cut and reflect it.

15. The subscapularis (Fig. 77, _a_, and p. 161). Near its glenoid end, its glenoid and coracoid borders are separated by triangular intervals from the adjacent muscles. Transect the muscle by a line connecting the apices of these triangles. Carry an incision from the middle of this one to the middle of the vertebral border of the scapula, and reflect the muscle on both sides of this incision,--thus determining its area of origin. Reflect the humeral end without injuring the capsule of the joint.

16. Dissect the supraspinatus (Fig. 75, _a_, and p. 159). Cut the strong fascia free from the border of the scapula and its spine. Then transect the muscle and reflect it, being careful not to injure the capsule of the joint.

17. The spinodeltoideus (Fig. 75, _e_, and p. 156). Find its two borders, beginning with the caudal one. In freeing the very short cranial border do not injure the acromiodeltoideus (Fig. 75, _f_). Transect and reflect the spinodeltoid.

18. The acromiodeltoideus (p. 157, and Fig. 75, _f_). Transect and reflect.

19. The infraspinatus (p. 160, and Fig. 75, _c_). Locate the borders in the region of the great scapular notch. It is difficult to separate the glenoid border from the adjacent teres minor (Fig. 80, _c_). The separation should be begun at the humerus. Transect the muscle at the great scapular notch and reflect. Be careful not to injure the teres minor (Fig. 80, _c_).

20. The teres major (p. 163, and Fig. 75, _d_; Fig. 77, _c_) should be cut near its junction with the latissimus dorsi (Fig. 77, _e_).

21. The teres minor (Fig. 80, _c_, and p. 161) need not be cut.

22. The epitrochlearis (p. 164, and Fig. 65, _r_).

23. The triceps (p. 166). (_a_) The long head of the triceps (Fig. 77, _i_; Fig. 75, _g_). Find first its medial border and separate it from the medial head. Note the union of its lateral surface with the dorsal border of the lateral head by strong fascia, and then cut the fascia.

(_b_) The lateral head (Fig. 75, _h_).

(_c_) The medial head (Fig. 79, _g_, _h_, and _j_).

24. The anconeus (p. 170, and Fig. 80, _l_).

25. The brachioradialis (p. 173, and Fig. 75, _k_). Reflect it carefully to its origin and insertion.

26. The biceps (Fig. 77, _g_, and p. 165). The capsule of the shoulder-joint may be opened in order to expose its origin. Its insertion cannot be seen at this stage.

27. The brachialis (Figs. 75 and 79, _i_, and p. 166). Work under it near its union with the clavobrachial; cut it at that point and reflect it.

28. Extensor carpi radialis longus (p. 173, and Fig. 75, _l_). Note the oblique tendon on the radial side of the wrist near the insertion of the brachioradialis. A second tendon passes beneath its distal border. This tendon may be separated into a deep and superficial portion. The latter may be traced proximad to its muscle, the extensor carpi radialis longus.

29. Extensor carpi radialis brevis (p. 174). Its tendon is the deeper of the two tendons seen when isolating the tendon of the extensor longus.

30. Extensor communis digitorum (p. 174, and Fig. 75, _m_).

31. Extensor lateralis digitorum (p. 175, and Fig. 75, _n_).

32. Extensor carpi ulnaris (p. 176, and Fig. 75, _o_).

33. Extensor indicis (p. 176, and Fig. 85, _c_).

34. Pronator teres (p. 179, and Fig. 77, _q_).

35. Flexor carpi radialis (p. 179, and Fig. 77, _r_). The tendon of the flexor carpi radialis should not be traced to its insertion until the deep muscles of the palm of the hand have been dissected.

36. Abductor brevis pollicis (p. 184, and Fig. 77, _w_).

37. Flexor carpi ulnaris (p. 180, and Fig. 77, _t_).

38. Palmaris longus (p. 179, and Fig. 77, _s_). In dissecting this muscle be careful not to injure the part of the flexor sublimis (Fig. 77, _x_) that rises from its surface (see flexor sublimis, p. 181). Cut the palmaris proximad of the origin of the flexor sublimis and reflect it.

39. Flexor sublimis digitorum (p. 181 and Fig. 77, _x_). Trace one or two of the tendons through the sheaths on the ventral surfaces of the first phalanges. Cut and reflect the radial portion.

40. Flexor profundus digitorum (p. 181, and Fig. 77, _u_). After recognizing the parts cut through the tendons of the first and fifth parts and reflect them to determine their origin. Then cut through the common tendon so as to reflect the other three parts together. Trace one or two of the tendons to the distal end of the digit.

41. The supinator (p. 177, and Fig. 85, _b_).

42. The extensor brevis pollicis (p. 178, and Fig. 85, _a_).

43. Pronator quadratus (p. 183, and Fig. 87, _a_).

The insertion of the brachialis and clavobrachial (Fig. 87, _c_) and of the biceps (Fig. 87, _b_) should now be examined.

There remain to be dissected the small muscles of the palm of the hand. If these have been injured on the side dissected, the hand of the other side may be used.

44. The lumbricals (p. 184, and Fig. 88, _f_).

45. The flexor brevis pollicis (p. 184, and Fig. 89, _a_).

46. The adductor pollicis (p. 185, and Fig. 89, _b_).

47. The abductor digiti quinti (p. 185, and Fig. 89, _i_).

48. The flexor brevis digiti quinti (p. 186, and Fig. 89, _h_). Cut and reflect it.

49. The opponens digiti quinti (p. 186, and Fig. 89, _g_). Cut and reflect it.

50. The interossei (p. 185, and Fig. 89).

IV. MUSCLES OF THE NECK AND THE DEEP MUSCLES OF THE HEAD.

If the superficial muscles of the head have been dissected according to the directions above given (p. 434), the skin of the head and neck, and the external ear, will have been removed, and the specimen is ready for further study. The parotid and submaxillary glands (Fig. 65, 1 and 2) should be removed if this has not been done; also the lymphatic glands (Fig. 65, 3).

If the superficial muscles of the head have not been dissected and are not to be, remove the skin from the side of the neck, head, and face to the median dorsal line, removing the thin superficial muscles with the skin. Remove also the parotid, submaxillary, and lymphatic glands (Fig. 65, 1, 2, and 3), and cut through the ear-muscles and the cartilaginous auditory meatus (under direction) and remove the external ear. Clean fat, connective tissue, etc., from the surface of the muscles of the thorax, neck, and head; then dissect as follows:

1. The sternomastoid (p. 139, and Fig. 65, _g_). Transect and reflect it.

2. The cleidomastoid (p. 120, and Fig. 65, _h_). This has already been transected; examine now its origin.

Remove the large lymphatic gland beneath the sternomastoid and close to the tympanic bulla, and clean the surface of the muscles in this region.

3. The levator scapulæ ventralis (p. 120, and Fig. 72, _c_, _c′_, _c″_). This has already been cut; study now its origin.

4. The sternohyoid (p. 140, and Fig. 65, _e_). In raising it begin at the cranial end and take care not to injure the subjacent sternothyroid (Fig. 65, _g′_). Transect.

5. The sternothyroid (p. 141, and Fig. 65, _g′_). Transect.

6. The stylohyoid (p. 112, and Fig. 65, _d_). Transect.

7. The digastric (p. 107, and Fig. 65, _b_). Transect, and reflect completely, to the origin and insertion.

8. The mylohyoid (p. 114, and Fig. 65, _c_). Transect and reflect.

9. The geniohyoid (p. 113, and Fig. 67, _g_).

10. The jugulohyoid (p. 113, and Fig. 67, _b_).

(The extrinsic muscles of the tongue (p. 228, and Figs. 67 and 96) may be dissected at this point, if desired. (_a_) The styloglossus; (_b_) the genioglossus; (_c_) the hyoglossus. They need not be cut.)

11. The masseter (p. 108, and Fig. 65, _a_). Cut the superficial and middle layers near their insertions by incisions parallel to the border of the jaw. Cut the deep layer near its origin. Look for the origin of fibres of the temporal muscle from the inner surface of the middle layer.

12. The temporal (p. 110, and Fig. 63, _n_). Clear its outer surface completely. Cut the temporal fascia transversely and reflect it toward the insertion of the muscle, with the superficial portion of the muscle. Cut through the zygomatic arch at its two ends and remove it, dissecting the fibres of the temporal free from their origin on its inner surface. Then examine the insertion of the temporal.

(The muscles of the pharynx (p. 232) may be dissected at this point; for directions, see page 451.)

13. The ceratohyoid (p. 115). To uncover this, the middle constrictor of the pharynx (Fig. 67, _j_) must be cut and reflected.

Cut the mylohyoid, geniohyoid, genioglossus, and the mucosa of the floor of the mouth free from the mandible on both sides, so that the tongue and the floor of the mouth may be drawn ventrad and turned out of the way, exposing the roof of the mouth (as in Fig. 66, p. 112). Cut through one side of the pharynx near the ventral surface and turn the tongue toward the uncut side.

The roof of the mouth is thus exposed. Dissect next--

14. The pterygoid muscles (Fig. 66). Remove the mucosa of the roof of the mouth, especially at the sides of the soft palate, and the two pterygoid muscles (p. 111) are exposed. The lower jaw may be removed on one side to get at their origin.

(The muscles of the soft palate (p. 230, and Fig. 66, _d_ and _e_), and the superior constrictor of the pharynx (p. 233, and Fig. 66, _f_) may be observed at this point, if desired.)

V. MUSCLES OF THE WALL OF THE THORAX AND OF THE ABDOMEN.

1. The scalenus (p. 141, and Fig. 73, _f_-_f‴_). To trace its cervical portion, cut the trachea and œsophagus just craniad of the first rib, cut the pharynx and hyoid free from the ventral side of the head and neck, and remove the pharynx, larynx, œsophagus, and trachea (these should be preserved for future study of the larynx).

2. The transversus costarum (p. 150, and Fig. 73, _j_).

3. The serratus posterior superior (p. 148, and Fig. 73, _l_). Transect this at about the middle of the muscle-bundles, and reflect it in both directions.

4. The serratus posterior inferior (p. 148, and Fig. 73, _n_). Transect and reflect as in the last.

5. The external oblique (p. 153, and Fig. 68, _p_). Transect it by an incision parallel to its tendon of origin and about an inch from it, and reflect in both directions.

6. The internal oblique (p. 154, and Fig. 73, _o_). Transect and reflect as above.

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).