DEVELOPMENT. 695 



and has been brought to the auricle by the superior vena cava. It 

 might be naturally expected that the two streams of blood would be 

 mingled in the right auricle, but such is not the case, or only to a slight 

 extent. The blood from the superior vena cava, the less pure fluid of the 

 two passes almost exclusively into the right ventricle, through the au- 

 riculo-ventricular opening, just as it does in the adult; while the blood of 



FIG. 481. Diagram of the Foetal Circulation. 



the inferior vena cava is directed by a fold of the lining membrane of 

 the heart, called the Eustachian valve, through the foramen ovale into 

 the left auricle, whence it passes into the left ventricle, and out of this 

 into the aorta, and thence to all the body, but chiefly to the head and 

 neck. The blood of the superior vena cava, which, as before said, 

 passes into the right ventricle, is sent out thence in small amount 



