442 GENERATION. 



short time, the sense of want of air becomes sufficiently intense 

 to give rise to an inspiratory effort, and the first inspiration 

 is made. The pulmonary organs are then, for the first time, 

 distended with air, the pulmonary arteries carry the greatest 

 part of the blood from the right ventricle to the lungs, and a 

 new circulation is established. During the later periods of 

 foetal life, the heart is gradually prepared for the new cur- 

 rents of blood. The foramen ovale, which is largest at the 

 sixth month, after that time, is partly occluded by the gradu- 

 al growth of a valve, which extends from below upward and 

 from behind forward, upon the side of the left auricle. The 

 Eustachian valve, which is also largest at the sixth month, 

 gradually atrophies after this time, and, at full term, has nearly 

 disappeared. At birth, then, the Eustachian valve is practi- 

 cally absent ; and, after pulmonary respiration becomes estab- 

 lished, the foramen ovale has nearly closed. The arrange- 

 ment of the valve of the foramen ovale is such, that, at birth, 

 a small quantity of blood may pass from the right to the left 

 auricle, but none can pass in the opposite direction. The sit- 

 uation of the Eustachian valve, on the right side of the inter- 

 auricular septum, is marked by an oval depression, called the 

 fossa ovalis. 



As a congenital malformation, the foramen ovale may re- 

 main open, producing the condition known as cyanosis neo- 

 natorum. This may continue into adult life, and is then at- 

 tended with more or less disturbance of respiration and diffi- 

 culty in maintaining the normal heat of the body. Usually, 

 the foramen ovale is completely closed at about the tenth 

 day after birth. The ductus arteriosus begins to contract at 

 birth, and is occluded, being reduced to the condition of an 

 impervious cord, at from the third to the tenth day. 



When the placental circulation is arrested at birth, the 

 hypogastric arteries, the umbilical vein, and the ductus veno- 

 sus contract, and they become impervious at from the second 

 to the fourth day. The hypogastric arteries remain pervious 

 at their lower portion, and constitute the superior vesical 



