PLACENTA L CIRCULATION 



357 



they enter the heart. The Eustachian valve, together with the 

 direction of the entering current, causes the blood from the 



FIG. no. Diagram illustrating the circulation through the heart and the 

 principal vessels of a fetus. (From Yeo after Cleland.) 



a, umbilical vein; b, ductus venosus; /, portal vein; e, vessels to the viscera; d, 

 hypogastric arteries; c, ductus arteriosus. 



ascending vena cava to pass through the foramen ovale into the 

 left auricle. 



Blood from the upper extremities (impure) enters the right 



