2 o VERTEBRATE ZOOLOGY 



The Vascular System. This system consists of the following 

 organs: (i) the heart, the muscular pump which sends venous 

 blood to the gills to be purified; (2) the arterial system, which 

 carries (a) venous blood from the heart to the gills, and (b) 

 arterial blood from the gills to the tissues ; (3) the venous system, 

 which includes (a) the systemic veins, which carry blood directly 

 to the heart, and (b) the portal veins, which carry blood directly 

 to the liver and the kidneys, from which organs it passes to the 

 heart; (4) the capillaries, the minute vessels by which the blood 

 is distributed in the tissues. 



We shall first study the portal veins. Two systems of these 

 veins are present: (1) the hepatic portal system, which carries 

 blood from the digestive tract and spleen to the liver ; and (2) the 

 renal portal system, which carries blood from the hinder portions 

 of the body to the kidneys. 



The Hepatic Portal System. Place the animal on its back, 

 with its head away from you, and open the abdominal cavity in 

 the manner already described (see page 4). A large vein will be 

 seen passing from the anterior end of the intestine to the liver 

 and entering it near the median plane ; this is the hepatic portal 

 vein. Trace it forward into the liver, on the dorsal surface of 

 which it will be seen to break up into several branches, which 

 go to the different lobes of that organ. 



Trace the vein backward; it will be seen to be formed by 

 the union of several large veins from the intestine, stomach, 

 pancreas, and spleen. 1 Cut the mesentery, where necessary, and 

 determine the course of these veins and their branches. 



Exercise 21. Draw a diagram representing the hepatic portal system, 

 including outlines of the liver, stomach, intestine, pancreas, and 

 spleen. 



The Renal Portal System. This system consists of the caudal 

 vein and two renal portal veins. The former lies in the median line 

 in the tail, immediately below the spinal column ; it and the dorsal 



1 If the hepatic portal vein is injected, these veins will be made more promi- 

 nent. They are, however, usually easy to study without injection, because they 

 usually contain blood, which colors them. 



