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lower extremities, but a portion of it is directed, by the hypogastric 

 arteries, to the placenta, to be again oxygenated. 



At birth, the placental circulation gives way to the circulation of 

 the adult. As soon as the child begins to breathe, the lungs expand, 

 blood flows freely through the pulmonary capillaries, and the ductus 

 arteriosus begins to contract. The foramen ovale closes about the 

 tenth day. The umbilical vein, the ductus venosus, and the hypo- 

 gastric arteries become impervious in several days, and ultimately 

 form rounded cords. 



