THE COURSE AND PHYSICS OF THE CIRCULATION 243 



the portal vein and partly to the inferior vena cava of 

 the embryo. 



FIG. 51. A conventional diagram of the circulation before birth 

 (compare with Fig. 45). Spatial relations are ignored. It will be 

 seen that both ventricles pump into the arteries, that a diversion of 

 blood takes place to the placenta (at the right of the diagram) and that 

 the returning blood may enter the portal vein or the general venous 

 system. What is less clear is the filling of the left auricle from the right, 

 indicated by a dotted arrow. 



The usual distinctions of arterial and venous blood 

 cannot be made in this case. The blood is nowhere up 

 to the arterial standard of the mother. The best of it 



