DEVELOPMENT OF THE CIRCULATORY SYSTEM. 



937 



intense to give rise to an inspiratory effort, and the first inspiration is made. The pul- 

 monary organs are then, for the first time, distended with air, the pulmonary arteries 



Pulmonary Art. 



Foramen Ovale. / 



Eustachian Valve.- 

 Right Auric. -Vent. Opening. 



ry Art. 

 Left Auricle. 

 r Left Auric. - Vent 



Bladder 



Hepatic Vein.*. 



Branches of the 

 Umbilical 'Vein-*., 

 to the Liver. 



Internal Mac Arteries. 

 FIG. 311. Diagram of the foetal circulation. 



carry the greatest part of the hlood from the right ventricle to the lungs, and a new cir- 

 culation is established. During the later periods of foetal life, the heart is gradually pre- 

 pared for the new currents of blood. The foramen ovale, which is largest at the sixth 



