224 VERTEBRATE ZOOLOGY 



just behind the diaphragm, bringing blood from the liver ; and the 

 phrenic veins, which meet the postcaval as it is passing through 

 the diaphragm, bringing blood from that organ. 



Observe the course of these veins ; follow the postcaval through 

 the liver and find the hepatic veins. 



Study the common iliac vein and its branches, but do not injure 

 the arteries which accompany them. About an inch from its 

 anterior end it is formed by the union of two veins, the smaller 

 being the internal iliac, or hypogastric, and the larger the external 

 iliac. Note the small caudal, or sacralis media vein, which joins 

 one of the common iliacs near its base. The internal iliac vein 

 receives branches from the bladder, the genital organs, the rectum, 

 and the muscles of the back and thigh. The external iliac is the 

 principal vein of the hind leg. A short distance from its union 

 with the internal iliac it receives the deep femoral vein from the 

 muscles of the thigh. A branch of this vein, the epigastric vein, 

 anastomoses with the internal mammary vein, which is a tributary 

 of the precaval vein in the forward part of the body. The external 

 iliac becomes in the leg the femoral vein. Follow it and its 

 branches. Trace the epigastric and note its relation to the in- 

 ternal mammary. 



Exercise 15. Draw a diagram showing the postcaval vein and its 

 branches so far as observed. 



The Arteries. Two groups of arteries may be distinguished: 

 (i) the pulmonary arteries, which carry venous blood to the 

 lungs; and (2) the aorta and its branches, which carry arterial 

 blood to the tissues. 



The aorta is the great artery which lies in the mid-dorsal line 

 of the body cavity and sends branches to all the various organs of 

 the body. It is divided into two parts, the thoracic aorta and the 

 abdominal aorta. 



The abdominal aorta lies just beneath the spinal column in the 

 abdominal cavity and extends from the diaphragm to the hinder 

 end of the trunk. It has been seen while dissecting the postcaval 

 vein. Observe carefully its relation to this vein ; remove the vein. 

 Study the following branches of the aorta. 



