MOTION OF THE HEART AND BLOOD 



In the fetus a lateral anastomosis joins the vena 

 cava to the pulmonary vein. This is located before 

 the vena cava opens into the right ventricle of the 

 heart, or gives off the coronary vein, just above its 

 exit from the liver. This is a good-sized oval-shaped 

 hole opening a passage from the vena cava to the 

 pulmonary vein, so that blood may freely flow from 

 the one to the other, then into the left auricle of the 

 heart, and then to the left ventricle. In t\\\s foramen 

 ovaky there is a thin tough membrane, larger than 

 the opening, hanging like a cover from the pulmonary 

 vein side. In the adult this blocks the foramen, and 

 adhering on all sides, finally closes and obliterates it. 

 In the fetus, however, this membrane hangs loosely, 

 opening an easy way to the lungs and heart for the 

 blood flowing from the vena cava, but at the same 

 time blocking any passage back into that vein. In 

 the embryo, one may conclude then that blood con- 

 tinually passes through this foramen from the vena 

 cava to the pulmonary vein, and then into the left 

 ventricle of the heart. After making this passage, 

 it can not regurgitate. 



Another junction is by the pulmonary artery where 

 it divides into two branches after leaving the right 

 ventricle. It is like a third trunk added to these two, 

 a sort of arterial canal passing obliquely toward 

 and perforating the aorta. Thus in dissecting a 

 human embryo it appears as though there were two 

 aortae or roots of the great artery rising from the 

 heart. 



[55] 



