1636 



A MANUAL OF ANATOMY 



At its circumference the placenta is connected with the chorion 

 leve, decidua capsularis or reflexa, and decidua vera. 



The usual site of the placenta is the posterior wall of the cavity of 

 the body of the uterus near the fundus. It may, however, be attached 

 to any part of the internal surface of the body of the uterus. When 

 it is implanted over the os uteri internum, it forms the lowest of the 

 contents of the gravid uterus, and under these circumstances it 

 gives rise to the condition called placenta prcevia, or placental presen- 

 tation. In some of these cases the placenta is attached round the 

 entire circumference of the os uteri internum, this condition being 

 known as complete placenta prcevia, or placenta centralis. In other 

 cases the attachment of the placenta in this region is incomplete, 

 and such a condition is spoken of as partial placenta prcevia or 

 placenta lateralis. 



The placenta consists of two parts — namely, foetal and maternal 

 or uterine, which cannot be separated from each other. 



Fig. 675. —Placenta : Fcetal and Maternal Surfaces. 



Fcetal Part of the Placenta. — ^The foetal or chorionic part consti- 

 tutes the largest portion of the placenta. It is formed by the 

 chorion frondosum, which is joined by the chorionic end of the 

 allantoic stalk. The chorion leve takes no part in its formation, 

 the villi of the chorion leve, at first few and scattered, becoming 

 atrophied. The villi of the chorion frondosum are of large size, and 

 they undergo ramifications, forming, as stated, arborescent tufts or 

 cotyledons. Some of these villi are attached to the maternal part of 

 the placenta, with which they become continuous. Hence the 

 foetal and maternal parts cannot be separated from each other. 

 These attached villi are, as previously stated, called fixation- or root- 

 villi. Other villi project into, and lie free within, the maternal 

 blood-lacunae, where they are bathed by the maternal blood. 



Each villus, as stated in connection with the chorion, consists of 

 the following elements: (i) An external covering of ectoderm, the 

 superficial lamina of which is formed by syncitium, and (2) a core of 



