COMPARATIVE ANATOMY OF THE CIRCULATORY SYSTEM 233 



vein, the hepatic portal vein. It runs completely across the liver imbedded in 

 its wall, and at the right, at the point where the bile duct enters the duodenum, 

 turns abruptly posteriorly, penetrating the mesentery. On the left note the 

 numerous gastric veins entering the hepatic portal vein from the stomach. 

 Just to the right of the bridge connecting the two lobes of the liver, two or three 

 anterior pancreatic veins pass from the pancreas into the hepatic portal vein. 

 Near the bile duct it receives cystic veins from the bile duct, posterior pancreatic 

 veins from the right end of the pancreas, and a long duodenal branch from the 

 first part of the small intestine. The hepatic portal vein should be followed 

 posteriorly; it is imbedded in the pancreas and at the bend of the duodenum 

 penetrates the mesentery and emerges to the left of the duodenum. Liver and 

 duodenum must be pressed forward to follow it. The vein next passes to the 

 posterior side of the adjacent loop of the small intestine which should also be 

 pressed forward. The vein will then be found to pass on the left side of the 

 spleen in contact with that organ and to receive numerous splenic tributaries 

 from it. Shortly posterior to the spleen the hepatic portal vein reaches the 

 central point of the mesentery where the mesentery is thrown into a coil. At 

 this place the numerous mesenteric veins, accompanied by arteries, will be seen 

 passing in the mesentery from all parts of the intestine into the hepatic portal 

 vein. 



Draw the hepatic portal vein and its branches. 



Now by dissecting away the liver substance trace the anterior portions of 

 the ventral abdominal veins into the liver and find their union with the hepatic 

 portal vein. Note how the hepatic portal vein breaks up into many branches 

 in the liver substance. As in other vertebrates the direction of flow in the 

 hepatic portal vein is from the digestive tract into the liver. 



Add to the drawing the connections of the ventral abdominal vein in the liver. 



4. The systemic veins. — Four large systemic veins enter the sinus venosus. 

 Turn the ventricle forward so as to obtain a clear view of the sinus. As already 

 noted, it is not symmetrically placed but is displaced slightly to the right, con- 

 necting with the right auricle. A large vein enters the left wall of the sinus, 

 passing around the border of the left auricle. This is the left precaval vein 

 (also called anterior vena cava and descending vena cava). Another vein, the 

 left hepatic vein, emerges from the bridge of the liver and enters the left angle of 

 the posterior wall of the sinus. The very large vein which passes into the right 

 angle of the posterior wall of the sinus is the postcaval vein (also named posterior 

 vena cava and ascending vena cava) ; it emerges from the right lobe of the liver. 

 Just in front of the entrance of the postcaval vein and best seen by pressing the 

 heart to the left, the right precaval vein passes into the right anterior angle of 

 the sinus venosus. 



a) The branches of the precavals: Each precaval enters the pericardial cavity 

 by passing through the anterior wall of the pericardial sac. From this point 



