188 THE ELASMOBRANCH FISHES 



The anterior intestinal arterj^ (a.i.a., figs. 173 and 174) is a relatively large 

 vessel in the sharks, while in the rays it is usually less important. In both it is 

 continued as the intraintestinal (i.a.) along the free edge of the spiral valve. 

 In sharks before it enters the intestine as the intraintestinal it gives off the 

 ventral intestinal artery which runs along the ventral side of the vahoilar in- 

 testine to which it gives numerous annular branches. In the rays a ventral 

 intestinal artery is characteristically absent. 



In Dasyatis the anterior intestinal gives off an anterior gastro-pancreatico- 

 splenic artery (a.gps., fig. 175), which in sharks is given off from the dorsal 

 aorta. In Rhinohatis and Raja this artery is a branch from the superior mesen- 

 teric arter3^ This artery sends a strong branch to the dorsal lobe of the pan- 

 creas (fig. 175), and then, as the anterior gastrosplenic (a.gs., fig. 173b) 

 divides, supplying the spleen and the dorsal side of the cardiac stomach. Just 

 before the anterior intestinal disappears as the intraintestinal it gives off a 

 posterior gastro-pancreaticosplenic (p.gps., fig. 176), which artery after sup- 

 plying pancreatic branches to the ventral lobe of the pancreas passes in the 

 gastrosplenic omentum around the outer margin of the pyloric stomach as the 

 posterior gastrosplenic artery (p.gs., fig. 175). In the rays, where there is no 

 spleen on the angle of the stomach, all the branches of this artery go to the 

 stomach. A second branch, the gastroduodenal artery (gd.), is given off at 

 about the same place or farther posteriorly (Raja) from the anterior intes- 

 tinal artery. This supplies the duodenum and may also supply the dorsal side 

 of the pyloric arm of the stomach as did a similar artery in Heptanchus. 



There is usually considerable anastomosing of the branches on the pyloric 

 angle of the stomach. Branches of the anterior gastrosplenic join with those 

 from the posterior gastrosplenic as also do branches from the ventral gastric 

 artery. 



SUPERIOE MESENTERIC ARTERY 



The superior or anterior mesenteric artery is variable as to its place of origin. 

 It may arise in the midbody far removed from the coeliac axis, as in Hetero- 

 dontus (s.m., fig. 174), or it may more nearly approach the coeliac as in Scyl- 

 lium, Galeus, Triakis (fig. 173a). In the rays the superior mesenteric and the 

 coeliac are often in close proximity (Raja clavata; Dasyatis, fig. 177b). The 

 office of the superior mesenteric in the sharks is to supply blood to two general 

 areas. The main arterj' to one of these areas is the anterior gastro-pancreatico- 

 splenic (fig. 173b), which supplies the distal part of the cardiac stomach 

 (a.gs.), the pancreas, and the spleen. The other is the posterior intestinal 

 (p.i.a.), which is continued along the dorsal wall of the vah^lar intestine as 

 the dorsal intestinal artery (d.i.a.) . 



A superior mesenteric, as just described, is present in Heterodontus {sm., 

 fig. 174) and may occasionally be found also as a short trunk in Acanthias (out 

 of 500 specimens examined in Squalus sucMii seven had short superior niesen- 

 teric trunks) . In this form, then, while a short trunk is occasionally present, in 

 the majority of occurrences the branches of the superior mesenteric arise sepa- 



