THE HUMAN PLACENTA. 93 



ing into and carrying before it a portion of the decidua vera on its entrance 

 into the uterus. But E. H. Weber * is of opinion that the decidua reflexa 

 is really formed of a layer or reflection of the decidua vera, and he con- 

 siders his opinion to be supported by the fact, that in very small ova, minute 

 openings, apparently of the uterine follicles, are found not merely at the 

 margins next the decidua vera (to which situation they were observed by 

 Dr. Sharpey to be chiefly, though not entirely, confined),! but also extend 

 as far as the middle of the decidua reflexa. He found these openings 

 quite distinct even in an embryo examined at the commencement of the 

 third month of pregnancy. In the formation of this reflected portion of 

 the decidua, he believes that the ovum on its entrance into the uterus, is 

 either received into a fold of the thickened mucous membrane (or decidua 

 vera), which at this part which may be situated at the junction of the 

 Fallopian tube to the uterus, or in the anterior or posterior wall of this 

 organ is more developed than elsewhere, and that as it enlarges it carries 

 along with it a covering of this membrane in the manner suggested by Dr. 

 Sharpey ; J or that it becomes simply invested by a superficial layer of 

 the decidua vera, which at the point where the ovum comes in contact 

 with it, separates from the deeper portion and carries with it apertures 

 corresponding to the orifices of the uterine glands just as cuticle raised 

 by a blister bears with it the openings of the sudoriferous ducts. A view 

 somewhat similar to the first of these appears to be entertained also 

 by M. Coste. 



Formation and Structure of the Human Placenta.^ 



A very complete account of the structure of the human placenta, has 

 been given by Professor GoodsirrH his paper has been already referred 

 to, but it now requires a more detailed notice. In many respects his 

 description agrees with that furnished by Professor Weber, Dr. Reid, and 

 Mr. Dalrymple, as contained in Miiller's Physiology.** The existence of 

 two distinct portions in the placenta, the one belonging to the foetus and 

 the other to the parent, is clearly shewn, and he finds that the commu- 

 nication between these two portions is effected by means of nucleated cells. 



As already stated, Professor Goodsir considers the decidua reflexa 

 to be formed of a number of cells secreted by the enlarged follicles of 

 the mucous membrane of the uterus; that these cells possess the power 

 of further development and of multiplication ; and that eventually they 

 completely surround the chorion, to the absorbing villi of which they 

 supply nutritive material for the embryo. At the earliest period of 



* Op. cit. p. 35. t MUller's Physiology, p. 1580. 



Miiller's Physiology, p. 1580. Comptes Rendus, 24 Mai, 1847, p. 893. 



|| Muller's Physiology, chapter iv. p. 1604. ^| Op. cit. p. 50. 



** P. 1 604, ct seq. 



