THE FROG 113 



The postcaval is a large median vein which enters the pos- 

 terior end of the sinus venosus. It arises between the kidneys 

 and runs along the mid-dorsal wall of the abdominal cavity, just 

 beneath the dorsal aorta, to the liver, through which it goes to the 

 heart. Press the intestine to one side, but without cutting any- 

 thing, and observe this vein and its branches. 



The postcaval vein receives the following branches: the renal 

 veins, five or six pairs in number, from the kidneys ; the spermatic 

 veins (in the male) or ovarian veins (in the female), from two to 

 four pairs in number, which join the postcaval between the renal 

 veins, bringing blood from the genital organs ; the adipose veins, 

 a pair of veins from the fat bodies ; and the hepatic veins, three 

 in number, from the liver. 



Exercise 18. Draw a diagrammatic sketch showing the postcaval vein 

 and its branches, so far as observed. 



The Portal System of Veins. A portal vein is one which does 

 not go directly to the heart but to either the liver or the kidneys, 

 where it divides up into capillaries and distributes the venous 

 blood throughout these organs. In the frog two portal systems are 

 present,— the hepatic portal, by which blood is taken to the liver, 

 and the renal portal, by which it is taken to the kidneys. 



The Hepatic Portal System. This system is made up of two 

 large veins and their branches,— the abdominal vein, which brings 

 blood from the hind legs, and the hepatic portal vein, which brings 

 it from the digestive tract and the spleen. 



The abdominal vein is a median ventral vein which has already 

 been seen. It is formed by the union of the right and left pelvic 

 veins, which come from the hind legs. Trace the abdominal vein 

 back and find them. Note the branches the abdominal vein receives 

 from the gall bladder, the heart, the urinary bladder, and the body 

 wall. Cut the abdominal vein in the middle ; turn the liver forward 

 and expose its dorsal surface; fasten it with pins in this position. 



Trace the abdominal vein forward to the liver. Just to the 

 left of the gall bladder it divides into three branches, two of which 

 go to the right and left lobes of the liver, while the third joins the 

 hepatic portal vein. 



