Chapter III: Muscles of the Fore Limb

A. _Muscles connecting the Arm with the Body._--If the skin-muscles have been dissected, as above, cut the cutaneus maximus near its insertion, and reflect it toward the median dorsal line; in this way remove it completely. Remove the platysma in the same way. The first layer of body-muscles is thus exposed.

If the skin-muscles are not to be dissected, these may be removed with the skin. If the skin has not yet been removed, proceed as follows:

Beginning at the cranial end of the manubrium make two incisions in the skin, one passing to the lambdoidal ridge and the other to the spinous process of the thirteenth thoracic vertebra. Raise the triangular flap thus formed, taking up the skin-muscles with it.

1. The trapezius group of muscles (pp. 115-117, and Fig. 68, _d_, _h_, and _j_) is now exposed and may be dissected. Begin with the spinotrapezius (Fig. 68, _j_). Read the description of the muscle, then raise its caudal border and work under it until its cranial border is reached and the middle of its inner surface is free. Then transect it, and reflect the two halves of the muscle toward the origin and insertion, clearing the fat, etc., from the inner surface of the muscle and the parts covered by it. Determine origin and insertion.

2. The acromiotrapezius (Fig. 68, _h_). Dissect in the same manner, being careful not to injure the broad thin tendon which connects the two muscles across the middle line.

3. The clavotrapezius (Fig. 68, _d_). Separate it carefully, from the cleidomastoid (p. 120). Transect and reflect, as before.

4. The occipitoscapularis (Fig. 73, _a_, p. 149). Note the strong fascia which separates it from the deeper muscles of the neck. Be careful not to injure adjacent muscles in tracing this toward origin and insertion. Transect.

5. The rhomboideus. Transect.

Recognize the levator scapulæ ventralis (Fig. 68, _f_), the sternomastoid (Fig. 68, _c_; Fig. 65, _g_), and the cleidomastoid (Fig. 65, _h_). Then dissect--

6. The levator scapulæ ventralis (Fig. 68, _f_). Its origin (Fig. 72, _c_, _c′_) cannot be seen at this stage and should be left until the cervical muscles are dissected. Be careful in transecting this muscle to separate it well from the cleidomastoid. Transect.

7. The cleidomastoid (Fig. 65, _h_). Its origin cannot be fully seen at this stage. Transect.

Make a midventral incision of the skin from the cranial end of the manubrium to a point opposite the crest of the ilium. From the caudal end of this incision make an incision to the root of the tail. From the cranial end of the incision in the ventral middle line make a cut around the base of the fore limb on its caudal side, thus connecting the ventral incision with the incision which passes between the manubrium and the thirteenth thoracic vertebra.

Make another incision from the convexity of the knee at the joint along the fold of the skin which connects the hind limb and body, to the incision which leads to the root of the tail.

Reflect the flaps thus formed so as to expose the body and flank, removing the skin-muscle with the skin.

8. The latissimus dorsi (p. 121, and Fig. 68, _m_). Dissect it up and transect it. Work carefully toward its insertion and note the origin from its outer surface in the axilla of a part of the cutaneus maximus, and at about the same place of a thin muscle, the epitrochlearis (p. 164, and Fig. 65, _r_), _without_ determining the insertion of the latissimus.

9. Dissect the pectoralis group of muscles (Fig. 65, and p. 144), i.e., the pectoantibrachialis (Fig. 65, _m_), the pectoralis major (_l_), pectoralis minor (_o_), and xiphihumeralis (_p_).

Determine the border of each muscle before lifting it, then work it up at its middle, transect it, and work toward its ends, determining origin and insertion.

Refer constantly to the skeleton.

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).