1. The internal mammary (p. 292). Follow it onto the ventral wall of
the abdomen. Follow the vein at the same time (p. 318).
2. The vertebral artery (p. 291). Find its beginning, but do not trace
it at present.
3. The costocervical axis (p. 292). Find its beginning, and trace the
superior intercostal branch some distance The other branches are not to
be followed at present.
4. The thyrocervical axis (p. 293). Find its beginning, but do not
trace it at present.
5. The axillary artery (continuation of the subclavian) (p. 294).
Follow its branches, tracing at the same time the axillary vein (p.
318). (Consult Fig. 122.) In tracing the blood-vessels, separate the
muscles, but do not cut them except where absolutely necessary. (The
muscles should be reviewed as the vessels are traced.)
The following notes may be of assistance in following the different
branches:
(_a_) The anterior thoracic was probably cut in dissecting the pectoral
muscles; it may be found, but its distal end is probably cut off.
(_b_) The long thoracic is easily followed.
(_c_) The subscapular. Follow the main artery before dissecting its
branches. Where the subscapular disappears between the long head of the
triceps, the latissimus dorsi, and the scapula, it may be traced and
found again as follows: Remove the skin from the outer side of the
shoulder,--taking great pains to remove _only_ the skin and not to
injure the vena cephalica (p. 319), a large vein that lies just beneath
the skin on the lateral surface of the shoulder, coming from the elbow.
The branches of the subscapular will be found appearing on the lateral
surface of the arm in the angle between the spinotrapezius, the long
head of the triceps, and the infraspinatus. The distal branches may then
be followed.
(_d_) The posterior circumflex (p. 296) may be traced distad in a
similar manner, by seeking it beneath the caudal border of the
spinotrapezius. (Do not injure the vena cephalica.)
(_e_) The other branches of the brachial artery and vein present no
difficulty till we come to the collateralis radialis superior (Fig. 122,
_x_). This must be traced with great care, along with the vena mediana
cubiti (p. 319, and Fig. 122, _y_). Remove the skin from the extensor
side of the forearm, taking great pains not to remove anything more than
the skin. The artery and vein lie beneath the skin and should be traced
to the hand (see Fig. 130).
Along with the collateral radial artery trace the vena cephalica (p.
319, and Fig. 130, _a_ and _c_). Follow it across the shoulder, noting
the branch to the posterior circumflex vein.
The remainder of the blood-vessels of the arm present no special
difficulty (see Figs. 123 and 124).
Make a diagram of the subclavian artery, as far as dissected.
III. Remove the skin from the sides of the neck, exposing the
sternomastoid muscles and the external jugular veins crossing them (see
Fig. 131). Clean the surface of the sternomastoid muscles, without
injuring the vein; separate the two muscles caudad, and cut each close
to the attachment to the sternum. Find the sternohyoid and sternothyroid
muscles, and cut them close to their attachment to the first rib.
Uncover the right side of the thorax in the same way as the left, cut
the ribs without injury to the nerves and vessels of the right axilla,
cut the internal mammary artery and vein (after tying the latter), and
thus remove the sternum with nearly the entire thoracic wall.
The blood-vessels of the thorax may now be more completely exposed. (If
the nerves are to be dissected on the same specimen, find the phrenic,
vagus, and sympathetic nerves (Fig. 157), and take the greatest pains
not to injure them.)