THE FiKTAL HEART <)41 



Tlic Itlood t)f the superior vena cava passes from the riglit aurich- into the rijrht 

 ventricle, and thence through the jiuhnonary artery (a small ])ortion only reaching 

 the lungs) and ductus arteriosus to the descending aorta. Througli tliis trunk it 

 is conducted to the lower lialf of the hody as well as to the jilacenta through the 

 uml)ilical arteries. From thesi> parts it is returned to the right auricle Ity the 

 inferior cava, which also receives the l^lood returning from tlu' i)lacenta as alrcadv 

 descrihed. 



The current which passes through the inferior cava only in a slight degree 

 mingles with that of the superior cava, as it is guided directly through the foramen 

 ovale by means of the Eustachian valve into the left auricle. This cavity also 

 receives a small quantity of blood (which has traversed the lungs) through the 

 pulmonary veins. From the left auricle the blood current passes into the left 

 ventricle, and thence through the aorta to the head and neck and the upper 

 extremities. 



