A FROG 183 



along the mid-dorsal wall of the abdominal cavity, just beneath 

 the doFsal aorta, to the liver, through which it goes to the heart. 

 Press the intestine to one side, but without cutting anything, and 

 observe it and its branches. 



The postcaval vein receives the following branches : the renal 

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

 matic 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 ; the hepatic veins, three 

 in number, from the liver. 



Exercise 15, 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 either to 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 will have been cut in opening the abdominal cavity. 

 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. 



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, 

 and the third joins the hepatic portal vein. 



Study the hepatic portal and its branches. It is a short, wide 

 vein which lies in the mesentery and enters the left lobe of the 

 liver. Near the point where it enters the liver it is joined by the 



