DEVELOPMENT. g05 



ing the course of the blood, which, after being carried out to the pla- 

 centa by the two umbilical arteries, has returned, cleansed and replen- 

 ished, to the foetus by the umbilical vein. 



It is at first conveyed to the under surface of the liver, and there the 

 stream is divided, a part of the blood passing straight on to the m- 



Fig. 500. Diagram of the Foetal Circulation. 



ferior vena cava, through a venous canal called the ductus venosus, while 

 the remainder passes into the portal vein, and reaches the inferior vena 

 cava only after circulating through the liver. Whether, however, by 

 the direct route through the ductus venosus or by the roundabout way 

 through the liver, all the blood which is returned from the placenta by 

 the umbilical vein reaches the inferior vena cava at last, and is carried 

 by it to the right auricle of the heart, into which cavity is also pouring 



