250 UROGENITAL SYSTEM 



of the ruptured placental vessels and prevent extensive hemorrhage. From the 

 persisting portions of the spongy layer and from the epithelium of the glands the 

 tunica propria, glands, and epithelium of the uterine mucosa are regenerated. 



The decidual membranes and the structures attached to them when expelled 

 constitute the "after-birth." The placenta usually is everted so that its amniotic 

 surface is convex, its maternal surface concave. It is composed of the amnion, 

 chorion frondosum, villi with intervillous spaces incompletely divided by the septa 

 into cotyledons, and bounded on the maternal side by the basal plate and a por- 

 tion of the spongy layer of the decidua basalis. The amnion is usually attached 

 to the chorion but may be free and, failing to rupture, surround the child at 

 birth as the "caul." Near the center of the placenta is attached the umbilical 

 cord, and at its margins the placenta is continuous with the decidua vera and 

 the remains of the chorion lseve and decidua capsularis. 



The Position of the Placenta in Utero and its Variations. — The position of 

 the placenta is determined by the point at which embryo is implanted. In 

 most cases it is situated on either the dorsal or ventral wall of the uterus. Oc- 

 casionally it is lateral in position and very rarely (1 in 1600 cases) it is located 

 near the cervix and covers the internal os uteri, constituting a placenta prcevia. 

 A partially or wholly duplicated placenta may be formed by the development of 

 two groups of villi. Cases have been observed in which from three to seven sub- 

 divisions of the placenta occurred. 



