732 DEVELOPMENT 



the blood passing straight on to the inferior 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. It is 

 carried by the vena cava to the right auricle of the heart, into which cavity 

 the blood is also pouring that has circulated in the head and neck and arms, 



FIG. 504. Diagram of the Fetal Circulation. 



and has been brought to the auricle by the superior vena cava. It might be 

 naturally expected that the two streams of blood would be mingled in the 

 right auricle, but such is the case only to a slight extent. The blood from the 

 superior vena cava the less pure fluid of the two passes almost exclusively 

 into the right ventricle, through the auriculo- ventricular opening, just as it 

 does in the adult. The blood of the inferior vena cava is directed by a fold 



