170 VERTEBRATE ZOOLOGY 



The Hepatic Portal System. We have already seen where the 

 hepatic portal vein enters the liver. This vein is very short, al- 

 though one of the largest in the body ; it will be seen to be formed 

 by the union of three large veins, which with their branches are 

 prominent objects in the intestinal mesentery. These are the gas- 

 troduodenal vein, which comes from the gizzard, the duodenum, 

 and the small intestine ; the anterior mesenteric vein, which comes 

 from the small intestine and receives numerous branches ; and the 

 posterior mesenteric vein, which lies immediately dorsal to and 

 parallel with the hinder part of the small intestine and the rectum, 

 receiving small branches from them. 



Without cutting the mesentery find these three veins and their 

 chief branches. The first two are easily studied by turning over 

 the various loops of the small intestine. In order to see the pos- 

 terior mesenteric, press forward the gizzard and the entire small 

 intestine. Note also in this connection the arteries which lie in the 

 mesenteries accompanying the branches of these mesenteric veins. 



The Renal Portal System. Lying against the dorsal body wall 

 will be seen the large red kidneys, one on each side. The posterior 

 mesenteric vein corresponds to the abdominal vein of reptiles and 

 amphibians, although it differs from it somewhat in position, and 

 joins the hepatic with the renal portal system. At its inner (dor- 

 sal) end this vein receives the small caudal vein and immediately 

 divides into two short veins, the right and left renal portals ; each 

 of these goes directly into the hinder end of one of the kidneys, 

 receiving first, however, from behind, the internal iliac vein. 



The dissection of these veins will be completed when the kid- 

 neys are studied. 



Exercise 7. Draw a diagram showing the portal veins so far as 

 observed. 



The Digestive System {Continued) . Straighten out the intestine 

 by cutting its mesentery; leave, however, the duodenal loop un- 

 cut. Separate the liver and gizzard from the air sacs at their 

 left and turn them toward the animal's right. The glandular 

 stomach will be brought into view ; it appears as a forward con- 

 tinuation of the gizzard. Trace it forward to the oesophagus, 



