Part 92

19. The quadratus labii superioris (p. 105).

a. The levator labii superioris proprius (Fig. 64, f).

b. The levator labii superioris alæque nasi (Fig. 64, g).

20. The caninus (p. 106, and Fig. 64, f′).

21. The buccinator (p. 106).

22. The myrtiformis (p. 106, and Fig. 64, h).

23. The “moustachier” (p. 107).

24. The quadratus labii inferioris (p. 107).

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).