THE FROG 27 
the arm, and the musculo-cutaneous vein, a large vein running 
in the skin along the side of the body and returning blood from 
the skin and muscles of the dorsal and lateral regions of the trunk 
and head. 
2. Vessels which enter the posterior vena cava. 
(a) The hepatic veins from the liver enter the posterior vena 
cava not far from the sinus venosus. 
(b) The renal veins from the kidneys pass straight toward the 
middle line and form by their union the beginning of the posterior 
vena Cava. 
(c) The genital (ovarian or spermatic) veins from the ovaries 
or testes, according to the sex, lead into the posterior vena cava, 
either directly or by uniting with renal veins. 
3. The portal systems. A portal system may be defined as a 
system of veins which carries blood from one network of 
capillaries to another in an entirely different organ. There are 
two portal systems in the frog: the renal portal system carrying 
blood from the hind legs to the kidneys, and the hepatic portal 
system conveying blood from several sources to the liver. 
(a) The renal portal system. ‘The renal portal vein enters 
the kidney from behind, coursing along its entire lateral edge. It 
receives the following branches: 
The dorso-lumbar vein from the dorsal wall of the abdomen 
(in the female also from the oviduct) enters the renal portal 
vein near the middle of the kidney. 
The iliac vein. This is the dorsal branch of the great femoral 
vein of the thigh and leg. The latter runs forward near the 
dorsal surface of the thigh past the hip-joint, then turns toward 
the ventral surface, dividing into two branches: the pelvic vein 
which unites with its fellow of the opposite side to form the 
anterior abdominal vein, and the iliac vein which passes dorsally 
and anteriorly to unite with 
The sciatic vein. This, like the iliac vein, conveys blood from 
the thigh to the renal portal vein. 
(b) The hepatic portal system. The liver receives venous 
blood from two sources: first, from the posterior limbs and 
bladder by means of the anterior abdominal vein; second, from 
the digestive system by means of the hepatic portal vein. 
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