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.