PRACTICAL DIRECTIONS. 457 



tudinal incision through the skin from the symphysis of the jaw to 

 the caudal end of the xiphoid process. About three or four centi- 

 meters caudad of the cranial end of the sternum make an incision at 

 nearly right angles to this, passing from the first incision on the 

 ventral side of the left arm about to the elbow. Reflect the flaps of 

 skin, so as to uncover the left side of the thorax and the under sur- 

 face of the arm, exposing the pectoral muscles. Isolate and transect 

 the pectoral muscles one at a time, cutting each near its thoracic 

 attachment. (The muscles (p. 145) should be reviewed at the same 

 time.) In this way the nerves and blood-vessels of the axilla are 

 exposed (Fig. 122, p. 295). 



Find the axillary artery and vein (Fig. 122, /"and Demerging 

 from the thorax just craniad of the first rib, along with the nerves of 

 the brachial plexus. Remove connective tissue, etc., so that the 

 vessels and nerves are well isolated as they pass out of the thorax. 

 Take great pains not to puncture the vessels, particularly the veins. 



Then remove the left side of the thorax by cutting through the 

 first rib near its sternal end and then near its dorsal end, without 

 injury to the vessels and nerves, cut the other ribs in the same way, 

 and take out the thoracic wall. 



Now find with tracer and forceps the great blood-vessels leaving 

 the cranial end of the heart (see Fig. 1 18). 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 oesophageal 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 : 



