662 



REPRODUCTIVE ORGANS. 



From this time until birth the fetus depends upon the piacental or 

 fetal circulation for its nourishment and maintenance. 



The blood of the fetus is freed from much of its impurities in 

 the placenta, and there likewise it receives oxygen and nutritive 

 materials. It returns to the fetus through the umbilical vein, 

 passing to the liver. In this organ the current is divided : the 



UmbiUcut 



FIG. 444. Diagram of the fetal circulation. 



greater part joins with the venous blood of the portal vein ; a 

 second portion goes directly into the hepatic circulation ; while a 

 third part goes through the ductus venosus into the ascending 

 vena cava without passing through the liver. The currents all 

 meet again in the ascending vena cava, here mixing with the blood 

 returning from the lower extremities. The ascending vena cava 



