COMPARATIVE ANATOMY OF THE CIRCULATORY SYSTEM 213 



posterior margin of the pancreas it is found to be formed by the union of two 

 veins, a left-hand lienogaslric vein and a right-hand posterior mesenteric vein. 

 The lienogastric vein has a posterior dorsal gastric vein from the stomach and the 

 posterior splenic vein from the posterior end of the spleen, and adjacent walls of 

 the stomach. The posterior mesenteric vein runs along the left side of the small 

 intestine, where it receives branches on both sides along the lines of insertion of 

 the turns of the spiral valve. The pancreatico-mesenteric vein passes dorsal 

 to the pylorus, receiving pancreatic veins from both lobes of the pancreas and 

 the anterior splenic vein from the anterior part of the spleen and adjacent stomach 

 wall. At about the region of the pylorus the vein is formed by the union of two 

 large branches from the intestinal wall. One of these, the intraintestinal vein, 

 is a short branch from the anterior part of the spiral valve. The other branch, 

 the anterior mesenteric, lies along the right side of the intestine corresponding in 

 position and branches to the posterior mesenteric. 



Skate: The hepatic portal vein is soon seen to be formed by the union of 

 three tributaries: a gastric vein from the left, a lienomesenteric vein from the 

 middle, and a pancreatico-mesenteric from the right. Follow each of these. The 

 gastric vein passes to the right margin of the stomach and there receives 

 the dorsal and ventral gastric veins from the dorsal and ventral surfaces of the 

 stomach. The dorsal gastric vein receives tributaries from the spleen. The 

 lienomesenteric vein receives a splenic branch from the spleen. Its main 

 tributary, the posterior mesenteric vein, runs along the left side of the intes- 

 tine beginning in the tip of the rectal gland; in its course along the intestine 

 it receives branches along the lines of attachment of the spiral valve. It also 

 collects from the pancreas. The pancreatico-mesenteric vein collects from the 

 pancreas and, as the anterior mesenteric vein, from the duodenal region. It also 

 receives a posterior gastric vein from the narrow portion of the stomach between 

 the pylorus and the bend. 



Trace the hepatic portal vein anteriorly in all three forms. It reaches the 

 dorsal surface of the liver and here divides into branches which penetrate the 

 substance of the liver. In the liver the branches fork into smaller and smaller 

 veins and finally pass into capillaries. From these capillaries originate other 

 veins which empty into the hepatic sinuses which as already seen open in the 

 sinus venosus (dogfish) or common cardinal vein (skate). As already explained 

 (see Fig. 55, p. 205) the hepatic sinuses are the persistent proximal portions of the 

 vitelline veins of the embryo, while the hepatic portal vein and its branches 

 develop from one of the vitelline veins and the subintestinal vein of the embryo. 



Draw an outline of the digestive tract and place on this outline the hepatic 

 portal vein and its tributaries from the various parts of the digestive tract. 



4. The renal portal system.— In the renal portal system the venous blood 

 passes into a network of capillaries in the kidneys. Cut across the tail just 

 posterior to the anal opening. In the cross-section locate the caudal blood 



