THE ELASMOBRANCH FISHES 211 



the valve. At the anterior end of the valvular intestine it receives branches 

 from the lobes of the pancreas and the posterior gastro-pancreaticosplenic 

 vein (p.gs.v., fig. 173b) . 



The posterior gastro-pancreaticosplenic is continued in the mesentery 

 (omentum) between the spleen and the stomach as the gastrosplenic vein 

 {p.gs.v., figs. 173-175). While in Heptanchus it is relatively small, although 

 a long vessel, in most of the other sharks it is well developed, and in the ray 

 (Dasyatis, fig. 175) is of relatively immense size. Here, in the absence of a 

 spleen on the greater curvature of the stomach, it drains only the stomach 

 and pancreas. 



The anterior intestinal then passes forward to join the posterior intestinal. 

 The segment of the anterior intestinal vein as it passes forward to join the pos- 

 terior intestinal varies greatly in length. In ScylUuDi it is exceedingly short, 

 but in Acanthias and Miistelus (fig. 173b) it is a relatively long segment. 



The posterior intestinal vein is the direct continuation of the dorsal intes- 

 tinal vein (d.i.v., fig. 173) which arises within the tissue of the rectal gland, 

 from the tip of the gland (leopard shark, fig. 173a) , or from a sinus which runs 

 longitudinally along the lumen of the gland to its base (Acanthias, Mustelns, 

 fig. 173b). The dorsal intestinal passes along the dorsal side of the valvular 

 intestine, receiving annular branches. In some forms the posterior intestinal 

 vein leaves the intestine at the place where the posterior intestinal artery 

 strikes it, that is, at about the middle of the intestine {Acanthias, Dasyatis, 

 fig. 175), or it may leave it farther forward {Heterodontus, fig. 174; Triakis, 

 fig. 173) . It extends forward by the spleen, from which it receives the anterior 

 gastrosplenic vein {Squalus sucklii; Heterodontus, fig. 174, a.gs.v.). The pos- 

 terior intestinal vein then proceeds forward to join the anterior intestinal 

 vein to form the portal. 



The anterior gastro-pancreaticosplenic vein, which is an important vessel 

 in Heptanchus, is much simpler in Mustelus (fig. 173b) and in ScylUum. In 

 all types it is divided into gastric and splenic parts, and as in Triakis (fig. 

 173a) it usually receives a branch from the dorsal lobe of the pancreas. 



The portal or hepatic portal is formed by the union of the posterior intes- 

 tinal vein, anterior intestinal trunk, and one or more gastrics. It passes to the 

 liver usually as a vessel of large size, receiving on its w^ay the large ventral 

 gastric {v.g.v., figs. 174 and 175), two or more branches of which drain the 

 ventral surfaces of the cardiac and pyloric stomach. Upon reaching the liver 

 the portal divides into two branches, one to each of the lobes. These branches 

 extend to the tips of the lobes, giving off in their course numerous other 

 branches which break up into a net. 



The blood thus distributed to the liver by the hepatic portal vein and by the 

 hepatic arteries is re-collected by the hepatic veins and taken to the heart. The 

 hepatic veins may empty near the median line by a right and left vein, as in 

 Acanthias; or these veins may break up into a more or less complex net before 

 entering the sinus venosus {Lamna) . In other forms the two hepatic vessels 

 join and enlarge in the anterior part of the liver, forming immense hepatic 



