154 VERTEBRATE ZOOLOGY 



Study the hepatic portal system. Cut the two abdominal veins. 

 Raise the right lobe of the liver and examine its dorsal surface. 

 Observe the gall bladder near its posterior border and follow the 

 bile duct which joins it with the intestine. If the animal has been 

 freshly killed, the green bile may be squeezed into this duct from 

 the gall bladder. Lift up the left lobe of the liver; note the 

 mesentery which joins it with the stomach, and the numerous 

 gastric veins which run from the wall of the stomach to the 

 liver. Observe again the pyloric end of the stomach and the 

 whitish pancreas which extends from it along the intestine to 

 the bile duct. 



With a sharp scalpel or scissors cut the mesentery just men- 

 tioned, freeing the liver from the stomach and the anterior end of 

 the intestine as far back as the bile duct, taking care, however, 

 not to cut the large blood vessels near it. Turn the entire liver 

 forward and pin it there, thus exposing its dorsal surface. 



Observe the large and conspicuous branches of the portal vein 

 which run across the dorsal surface of the liver, partly buried in 

 its substance. Find the point where the branches which traverse 

 the two main liver lobes meet ; the single large vein thus formed 

 is the portal. Trace it backward; it will be found to receive a 

 number of veins, of which the largest are the pancreatic vein from 

 the pancreas, and the mesenteric vein from the mesentery. The 

 latter vein is formed of a number of veins which lie in the mesen- 

 tery and bring blood from the wall of the intestine. Lift up the 

 intestine and trace the mesenteric vein and its branches, without, 

 however, cutting the mesentery. Note that the mesenteric veins 

 are accompanied by smaller vessels, the mesenteric arteries. Note 

 the gastric veins, which enter the left branch of the portal vein 

 from the wall of the stomach. 



During this examination the spleen will be seen— a dark-red 

 organ the size of a pea— lying in the mesentery alongside the in- 

 testine and near the point where the mesenteric vein is formed by 

 the union of its intestinal branches. The postcaval, the largest 

 vein in the body, will also be seen near this place, and must not 

 be confused with the veins of the portal system. It comes from 

 between the kidneys, in the hinder part of the body cavity, passes 



