DEVELOPMENT OF THE CIRCULATORY SYSTEM 



847 



which joins the portal vein and enters the liver; and the smaller, which 

 is the ductus venosus, passes to the vena cava ascendens, at the point 

 where it receives the left hepatic vein. Thus the greater part of the 

 blood returned to the foetus from the placenta passes through the liver, 

 a relatively small quantity being emptied into the vena cava, by the 

 ductus venosus. 



The vena cava ascendens containing the placental blood which has 

 passed through the liver, the blood conveyed directly from the umbilical 



Superior vena cava 



Ductus venosus 



Hepatic vein 



*~ Ductus arteriosus 



r ~~ Pulmonary artery 

 Pulmonary vein 



Inferior vena cava 



Aorta 



inferior vena cava 



Umbilical artery 



Umbilical vein 



Fig. 246. Diagram of the feet al circulation (Kollmann). 



vein by the ductus venosus and the blood from the lower extremities 

 passes to the right auricle. As the blood enters the right auricle it is 

 directed by the Eustachian valve, passing behind the valve, through the 

 foramen ovale, into the left auricle. At the same time the blood from 

 the head and the superior extremities passes down, by the vena cava 

 descendens, in front of the Eustachian valve, through the right auricle, 

 into the right ventricle. The arrangement of the Eustachian valve is 

 such that the right auricle simply affords a passage for the two currents 



