Now find with tracer and forceps the great blood-vessels leaving the cranial end of the heart (see [Fig. 118]). Take the greatest pains not to injure them. Find the aorta and aortic arch ([p. 281]); the left subclavian artery ([p. 283]) (continuous with the axillary); the innominate artery ([p. 282]), and the beginnings of its three branches (see [Fig. 115]). Find also the superior vena cava, the innominate veins, and the subclavian vein, continuous with the axillary vein.
I. Study the smaller branches of the thoracic aorta ([p. 283], and [Fig. 118])—the intercostals, the bronchial and œsophageal arteries, and the first pair of lumbar arteries. (The coronary arteries will be examined later.)
II. Dissect the subclavian and its branches ([p. 290]) as follows:
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.