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.