248 VERTEBRATES. 



riorly near its origin a large innominate artery, and a 

 little farther out from the heart a smaller left subdavian 

 artery, which goes to the left shoulder, and thence to the 

 fore limb. A branch of the subclavian, which runs along 

 the inner side of the ventral wall of the thorax, is the 

 mammary artery. The innominate artery soon divides 

 off a left carotid artery, and then bifurcates into right 

 carotid and right subclavian arteries. 



That part of the aorta which extends posteriorly beyond 

 the arch is called the dorsal aorta. It gives off in the 

 thorax a series of small intercostal arteries, which extend 

 laterally along the inner walls of the thorax, one behind 

 each rib. Its principal branches in the abdomen are three 

 single arteries, which pass ventrally through the mesentery 

 to the digestive organs, and three paired arteries. 



The foremost of the single arteries (the cceliac artery) 

 arises close behind the diaphragm, and its branches are 

 distributed to the liver, stomach, and spleen ; the second 

 (the anterior mesenteric artery) arises a short distance be- 

 hind the first. Its branches supply the greater part of 

 the intestine. The third (the posterior mesenteric artery) 

 is small. It arises toward the posterior end of the abdomi- 

 nal cavity. Its branches are distributed to the hinder 

 end of the intestine. 



Of the paired arteries, the foremost are the large renal 

 arteries, which go to the kidneys. The second are the 

 very small spermatic (or ovarian) arteries, which go to 

 the reproductive organs. % The hindmost are the very 

 large common iliac arteries, into which the dorsal aorta 

 seems to divide. Posterior to the body cavity, these are 

 called femoral arteries. Between the spermatic and com- 

 mon iliac arteries, several small lumbar arteries arise on 

 the dorsal side of the aorta, to be distributed right and 

 left to the dorsal abdominal wall, and to the thick muscles 

 of the back. 



