Part 93

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).