DEVELOPMENT OF THE CIRCULATORY SYSTEM 849 



closed. The arrangement of the valve of the foramen ovale is such that 

 at birth a small quantity of blood may pass from the right to the left 

 auricle, but none can pass in the opposite direction. The situation of 

 the Eustachian valve on the right side of the interauricular septum is 

 marked by an oval depression, called the fossa ovalis. 



When the placental circulation is arrested at birth, the hypogastric 

 arteries, the umbilical vein and the ductus venosus contract, and they 

 become impervious between the second and the fourth days. The hypo- 

 gastric arteries remain pervious at their lower portion and constitute the 

 superior vesical arteries. A rounded cord, which is the remnant of the 

 umbilical vein, forms the round ligament of the liver. A slender cord, 

 the remnant of the ductus venosus, is lodged in a fissure of the liver, 

 called the fissure of the ductus venosus. 



