2i 4 ANIMAL BIOLOGY. [Parti. 



Thus the placenta and hinder regions receive less arterialised 

 blood. 



14. Note that during foetal life it is the blood that flows 

 along the aorta that will be arterialised. Hence the necessity 

 of keeping open the foramen ovale, and directing by means of 

 the Eustachian valve the blood which falls into the right auricle 

 across into the left. In adult life it is the blood that flows 

 along the pulmonary artery that will be arterialised. Hence 

 the foramen ovale closes, and the Eustachian valve becomes 

 functionless. 



In Fig. 67 the foetal (A.) and adult (li) condition are com- 

 pared. For the sake of diagrammatic convenience the bulbus 

 arteriosus is placed at the lower part of the figure. 



