CIRCULATORY SYSTEM 791 



VISCERAL ARTERIES (Fig. 444) 



Coeliac Artery: 



Origin, Radix or adjacent dorsal aorta. 

 Branches, Gastric, splenic, hepatic. 



Superior Mesenteric Artery (running to cephalic portion of intestines). 



Develops with the omphalomesenteric. 

 Inferior Mesenteric Artery (to caudal portion of intestine). 



(Not always present, while other mesenteric arteries appear.) 



Coeliac Axis is the name applied if the superior mesenteric fuses with 

 the coeliac artery. 



Hypogastric Arteries: 



Originally connect dorsal aorta with subintestinal vein near anus, 

 later supplying rectum. 



In animals higher than vertebrates a urinary bladder grows from 

 the rectal region and this is supplied by hypogastric branches called 

 vesical arteries. 



In amniotes, where the distal end of the bladder becomes the allan- 

 tois, parts of the vesical arteries become allantoic arteries or umbilical 

 arteries, because they pass through the umbilicus. With the disappear- 

 ance of the allantois these arteries degenerate, leaving only the rectal 

 and vesical branches of the hypogastric trunk. 



Caudal Aorta: 



That portion of the dorsal aorta caudad to the hypogastric arteries. 



SOMATIC ARTERIES 



Distributed to body wall and its derivatives. (Contrary to the 

 visceral arteries, the somatic arteries are arranged metamerically.) 

 Intercostal Arteries (Fig. 444) : 



One pair develop between each pair of myotomes, beginning at the 

 radices and the -dorsal aorta. As the aortic arches disappear and change, 

 the intercostals become connected close to their origin by a pair of ver- 

 tebral arteries, running through the openings in the transverse processes 

 of the vertebrae. The intercostals have different names, depending on 

 their location, as thoracic, lumbar, sacal, etc. 



Vertebral Arteries: 



In both man and other vertebrates the vertebral arteries pass in a 

 cephalad direction toward the ventral side of the medulla oblongata 

 where the right and left arteries unite to form one trunk called the 

 basilar artery. This runs straight forward underneath the brain. Two 

 branches of the vertebrals extend caudad from points just before where 

 the two vertebrals unite. 



