166 THE ELASMOBRANCH FISHES 



and the united trunk of the fifth and sixth efferents. The unpaired dorsal aorta 

 then passes backward ventral to the spinal column, becoming in the tail region 

 the caudal aorta. In its course through the body it gives off arteries to the di- 

 gestive tract and its appendages, to the extremities, and to the body muscula- 

 ure and deeper structures. 



AKTERIAL SUPPLY TO DIGESTIVE TRACT 



The arteries given off from the dorsal aorta to the digestive tract consist of 

 three large trunks, the coeliac axis, the anterior mesenteric, and the posterior 

 mesenteric arteries. 



COELIAC AXIS AND ITS BRANCHES 



In Heptanchus maculatus the coeliac axis (ce., fig. 155) arises as a single trunk 

 from the ventral side of the dorsal aorta, only a short distance posterior to the 

 union of the last efferents. It passes downward and backward as a relatively 

 long artery and at the place where it strikes the portal vein it di^ddes into : 

 (1) a very short gastrohepatic which bifurcates into a small hepatic branch 

 (k., fig. 155) to the liver and a large gastric branch to the stomach, and (2) a 

 large anterior intestinal artery (a.i.a.) which is continued along the valvular 

 intestine as the ventral intestinal artery. 



The gastric artery separates into two main divisions, the anterior gastric 

 (a.g.) and ventral gastric (v.g.) arteries. The anterior gastric sends a branch 

 to the ventral union of oesophagus and stomach and also supplies a branch to 

 the dorsal side of the anterior part of the cardiac stomach. The ventral gastric 

 artery (v.g.), which is the posterior of the gastric divisions, passes down the 

 ventral side of the cardiac stomach and at the angle between the cardiac and 

 the pyloric arms of the stomach breaks up into numerous branches some of 

 which pass along the pylorus and anastomose with a posterior gastrosplenic 

 artery. 



The hepatic artery (h.) passes toward the liver, and after giving branches 

 to the anterior segment of the spleen, bifurcates, giving off a smaller artery to 

 the left lobe of the liver and a larger branch to the right lobe. These two he- 

 patic divisions follow the course of the larger hepatic veins almost to the tip of 

 the liver, giving off numerous branches as they go. 



The anterior intestinal division of the coeliac axis {a.i.a., figs. 155 and 156) 

 runs posteriorly and strikes the anterior part of the duodenum. Before enter- 

 ing the duodenum as the intraintestinal artery (see fig. 156, i.a.) it gives off: 

 (1) a posterior gastro-pancreaticosplenic artery (p.gps.), (2) the ventral in- 

 testinal artery (v.i.a.), and (3) the gastroduodenal artery (gd.). The poste- 

 rior gastro-pancreaticosplenic supplies a short branch to the distal part of the 

 pylorus (py.a.) and a long branch which after supplying branches to the pan- 

 creas (pn.) and spleen passes along the pyloric arm as the posterior gastro- 

 splenic {p.gs., fig. 155) . This branch finally reaches the posterior side of the 

 pylorus where it gives off splenic branches and receives certain anastomosing 



