COMPARATIVE ANATOMY OF THE CIRCULATORY SYSTEM 249 



are four chambers and the reptilian heart where the number of different chambers 

 is reduced to three. 



2. The hepatic portal system. Turn to the peritoneal cavity. Press the 

 lobes of the liver forward and the other viscera to the left. Put the hepatoduo- 

 denal ligament on a stretch by widely separating the stomach and liver, without, 

 however, tearing the ligament. In the ligament lying dorsal to the common bile 

 duct is the large hepatic portal vein (commonly called simply the portal vein in 

 mammals, since mammals have but one portal system). Free it by carefully 

 cleaning connective tissue from its surface. Follow it anteriorly and note how 

 it branches into the liver substance. Follow it posteriorly, ripping away fat 

 and connective tissue from its surface with the dull point of a probe. Note the 

 large branch it sends into the right lateral lobe of the liver. The branches 

 received by the portal vein from the digestive tract are slightly different in the 

 rabbit and cat. In preserved specimens the branches are not always easy to 

 follow, and the student should identify as many as possible. The arteries 

 accompanying the veins must not be injured. 



Rabbit: Immediately posterior to the branch into the right lateral lobe ot 

 the liver, the portal vein receives on the right side the gastroduodenal vein. This 

 vein is soon seen to be formed by the union of two veins, a larger anterior 

 pancreatico-duodenal vein, which appears as a continuation of the main vein and 

 the smaller right gastro-epiploic vein. The first-named vessel runs in the tissue 

 of the pancreas alongside the first part of the duodenal loop, collecting tribu- 

 taries from both pancreas and duodenum. The right gastro-epiploic vein comes 

 from the pyloric region of the stomach and receives also branches from the great 

 omentum. Shortly posterior to the entrance of the gastroduodenal vein into 

 the portal, the portal receives on the left side the larger gastrosplenic vein. This 

 vein is seen to be formed a short distance from the portal by the union of the 

 splenic and coronary veins. The latter comes from the lesser curvature of the 

 stomach where it is seen to be formed by numerous branches collecting from both 

 surfaces of the stomach. The splenic vein is a large vessel running in the great 

 omentum past the spleen and extending as far as the left end of the stomach. 

 In its course it collects numerous splenic branches from the spleen and the left 

 gastro-epiploic veins from the stomach and omentum. Some distance posterior 

 to the entrance of the gastrosplenic vein, the portal receives the posterior 

 pancreatico-duodenal vein, which runs in the mesentery of the duodenal loop, 

 collecting from pancreas, and duodenum, and anastomosing with the anterior 

 pancreatico-duodenal vein. At the same level as the entrance of this vein, the 

 portal receives on the opposite side the inferior mesenteric vein. This may be 

 traced alongside the descending colon and rectum, from which it receives many 

 branches as well as some from part of the transverse colon. The main trunk 

 of the hepatic portal posterior to this point is now named the superior mesenteric 

 vein. It collects from all parts of the intestine not already mentioned. In 



