(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.)
1. The coronary arteries and the veins of the heart (p[p. 281] and 316).