910 



GENERATION. 



of the placenta. In corroboration of this, in 1864, we examined the uterus, with the 

 placenta attached, of a woman who died in the latter months of pregnancy, in the pres- 

 ence of the late Prof. G. T. Elliot and Prof. J. P. White, and forced air from the uterine 

 sinuses throughout the entire thickness of the placenta, between the foetal tufts. In 

 view of these facts, concerning which there can be no doubt, it seems unnecessary to 

 discuss the more or less theoretical views of writers who have not made injections of the 

 uterus with the placenta attached. The observations of Dalton have since been con- 

 firmed by numerous anatomists, so that we must consider the fact of an intra-placental 

 circulation of maternal blood as definitively established. 



Structure of the Fully -developed Placenta. The placenta of the human subject pre- 

 sents certain differences in its structure at various periods of utero-gestation, most of 

 which have been indicated in treating of its development. At about the end of the third 

 month, the limits of the placenta become distinct, and the organ rapidly assumes the ana- 

 tomical characters observed after it may be said to be fully developed. It then occupies 



FIG. 293. Diagrammatic figure, showing the placenta and deciduce. (Li6geois.) 



c, embryon ; i, intestine ; p, pedicle of the umbilical vesicle ; o, umbilical vesicle ; m, m, m, amnion ; a', chorion ; 

 a, lower end of the umbilical cord ; g, 5, vascular tufts of the chorion, constituting the foetal portion of the pla- 

 centa ; M', w, maternal portion of the placenta ; ?i, n, decidua vera ; , decidua reflexa. 



about one-third of the uterine mucous membrane, and it is generally rounded or ovoid in 

 form, with a distinct border connected with the decidua and the chorion. It is from 

 seven to nine inches in diameter, a little more than an inch in thickness at the point of 

 penetration of the umbilical cord, slightly attenuated toward the border, and weighs 

 from fifteen to thirty ounces. Its foetal surface is covered with the smooth amniotic 

 membrane, and its uterine surface, when detached, is rough, and divided into numerous 

 irregular lobes or cotyledons, from half an inch to an inch and a half in diameter. Be- 

 tween these lobes, are membranes, called dissepiments, which penetrate into the sub- 

 stance of the organ, frequently as far as the foetal surface. 



