378 GENERATION. 



Beginning with the first development of the placenta, the 

 observation which we have quoted from Reichert, in which, 

 it will be remembered, the tufts of the foetal chorion were 

 actually drawn out of the tubules of the uterine mucous 

 membrane, seems to demonstrate beyond question the fact of 

 penetration of the villi of the chorion into the maternal 

 tubes. This is a capital point in our view of the mode of 

 development of the placenta ; and this cannot be questioned, 

 if we admit the accuracy of Reichert' s description. It is 

 certain that the portion of the chorion which eventually be- 

 comes attached to the uterus undergoes a much greater de- 

 gree of development than the rest of the membrane. The 

 villi in this situation become branched and arborescent ; they 

 are filled with blood-vessels, while the vascularity in other 

 parts of the chorion disappears ; the mucous membrane cor- 

 responding to this portion of the chorion also becomes thick- 

 ened ; the tubes in which the villi have penetrated are cor- 

 respondingly enlarged and branched, and the vessels which 

 surround them are increased in size ; finally, the union be- 

 tween the villi and the tubes becomes so close that they 

 cannot be separated from each other. It is evident that, if 

 this be the mode of development of the placenta, the mater- 

 nal portion is formed from a restricted and an hypertrophied 

 part of the mucous membrane of the uterus, and the foetal 

 portion is simply an exceedingly vascular and villous part of 

 the chorion. 



As development advances, the vessels of the maternal 

 portion of the placenta coalesce into great lakes, which com- 

 municate freely with the uterine sinuses. In these great 

 cavities, we find the vascular foetal tufts ; and it is easy to un- 

 derstand how transudation of nutritive material and gases 

 can take place from the blood of the mother to the vascular 

 system of the foetus. 



If the above description be correct, we should be able to 

 pass an injection from the uterine sinuses into the maternal 

 portion of the placenta, even as far as its foetal surface ; but 



