THE VEINS. 353 



iii. The right internal mammary vein runs for 

 wards on the inner surface of the ventral 

 thoracic wall, near the middle line, and opens 

 into the vena cava opposite the first rib. 



iv. The right subclavian vein returns blood from the 

 fore-limb and shoulder. 

 In dissecting the next two veins, take great care to avoid 

 injury to the muscles, vessels, and nerves of the neck. 



v. The right external jugular vein is a large vein 

 running along the side of the neck. It is 

 formed in front by the union, just behind the 

 angle of the jaw, of the anterior and posterior 

 facial veins, returning blood from the face 

 and ear. 



vi. The right internal jugular vein is a small vein 

 returning blood from the brain, and running 

 down the neck alongside the trachea, to open 

 into the right external jugular vein close to 

 its union with the subclavian. 



b. The left anterior vena cava resembles the right, 



except that it receives no azygos vein, and that 

 its course in the thorax is somewhat different, as 

 already described (p. 350). 



c. The posterior vena cava is a large median vein, 



commencing at the hinder end of the abdomen, 

 and running forwards close to the vertebral 

 column and to the right (or left) of the aorta. 

 In front it leaves the abdominal wall and be- 

 comes imbedded in the dorsal surface of the 

 liver, beyond which it enters the thorax through 

 an aperture in the central tendon of the dia- 

 phragm, and runs forwards, as already described 

 (p. 350), to open into the right auricle. 



The following are the principal veins opening 

 into the posterior vena cava : 

 In dissecting these veins, take care not to damage the 

 arteries, which accompany and roughly correspond to them, 



