THE ARTERIES 



303 



radices aortae (fig. 311), or, again, it may involve the whole of the radices, the 

 aorta in this case extending to the most anterior arch. 



In human anatomy the different parts of the aortic vessels have names 

 different from those adopted here. The persistent portion of the ventral aorta 

 is called the ascending aorta, the persistent fourth arch is the aich of the 

 aorta, and the adjacent part of the dorsal aorta is the descending aorta. The 

 rest of the dorsal aorta is divided into the thoracic and abdominal aortee, accord- 

 ingly as they lie in the regions of the corresponding cavities. These terms are 

 inapplicable in comparative anatomy. 



The arteries arisin g fro m th e dorsal aorta m aybe grouped under 



^_the two categorie5? ^j yisceral a n d somati c (p. 289). To the former 



belong the vessels running through the mesenteries to supply the 



digestive tract. In the primitive condition these are numerous, but 



they do not show a metameric character. In the majority of verte- 



FiG. 322. — Diagram of vertebrate circulation based on a urodele. Arteries cross- 

 lined; veins black except the pulmonary vein, white, av, abdominal vein; c, coeliac 

 artery; ca, cv, caudal artery and vein; d, dorsal aorta; ec, external carotid; g, gonad; h, 

 hepatic vein; ha, hepatic artery; ky, hyjjogastric artery; ic, internal carotid; il, iliac 

 artery and vein; j, jugular; Iv, liver; m, mv, mesenteric artery and vein; pa, pulmonary 

 artery; pcd, post-cardinal; pcv, postcava; pv, hepatic portal vein; r, rectal artery; ra, 

 renal advehent vein; sc, subclavian artery and vein. 



brates they become united into a smaller number of main trunks from 

 which branches go to the various regions of the canal. The principal 

 of these trunks are the following : There is usually present a Qoeliac 

 artery^ arising fr om one radix or from the do rsal aorta near it, and 

 dividing in the mesogaster into gastric, splenic and hepatic arteries, 

 distributed to stomach, spleen and liver. The superior mesenteric 

 artery is connected in development with the omphalomesenteric 

 arteries (p. 291) and goes to the anterior part of the intestine; while 

 frequently an inferior mesenteric artery is distributed to the posterior 

 part of thej3igestivew:act,--^tiie" superior mesenteric may fuse with 

 the coeliac to form a coeliac axis, while not infrequently other mesen- 

 teric arteries may be developed. 



The hypogastric arteries, already mentioned, primitively connect 



