938 GENERATION. 



month, after that time, is partly occluded by the gradual 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, it has nearly disappeared. At birth, then, the Eustachian valve is 

 practically absent; and, after pulmonary respiration becomes established, the foramen 

 ovale has nearly closed. The arrangement 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 

 oan pass in the opposite direction. The situation 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 remain open, producing the 

 condition known as cyanosis neonatorum. This may continue into adult life,. and it is then 

 attended with more or less disturbance of respiration and difficulty 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 it 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 um- 

 bilical vein, and the ductus venosus contract, and they become impervious at from the 

 second to the fourth day. The hypogastric arteries remain pervious at their lower por- 

 tion and constitute the superior vesical arteries. A rounded cord, which is the remnant 

 of the umbilical vein, forms the round ligament of the liver. A slender cord, the rem- 

 nant of the ductus venosus, is lodged in a fissure of the liver, called the fissure of the 

 ductus venosus. 



A history of the development of the various tissues of the body belongs really to gen- 

 eral anatomy and is usually given in works specially devoted to that subject. We have 

 only treated of it incidentally, in our account of the development of the various organs 

 .and systems. 



CHAPTER XXVIII. 



F(ETAL LIFE DEVELOPMENT AFTER BIRTH-DEATH. 



Enlargement of the uterus in pregnancy Duration of pregnancy Size, weight, and position of the foetus The foetus 

 at different stages of intra-uterine life Multiple pregnancy Cause of the first contractions of the uterus in nor- 

 mal parturition Involution of the uterus Meconium -Dextral preeminence Development after birth Ages- 

 Death Cadaveric rigidity Putrefaction. 



As the development of the ovum advances, the uterus is enlarged and its walls are 

 thickened. The form of the organ, also, gradually changes, as well as its position. Im- 

 mediately after birth, its weight is about a pound and a half, while the virgin uterus 

 weighs less than two ounces. It is a remarkable fact, demonstrated upon the living sub- 

 ject, by Prof. I. E. Taylor, of New York, that the neck of the uterus, while it becomes 

 softer and more patulous during pregnancy, does not change its length, even in the very 

 latest stages of utero-gestation. This fact is in opposition to the statements of most 

 obstetricians, who believe that the os internum dilates, and that the neck is gradually 

 absorbed, as it were, by the body of the uterus, during the later months of pregnancy. 



We have already studied the remarkable changes which take place in the mucous 

 membrane of the uterus during pregnancy and the mode of formation of the decidua, 

 and we have seen that the mucous membrane of the neck does not participate in these 

 changes and is not thrown off in parturition. The only change, indeed, which we note 

 in the neck, aside from the softening of its texture, is the secretion of the plug of mucus 

 which closes the os. 



