DEVELOPMENT AND STRUCTURE OF THE PLACENTA. 909 



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 descrip- 

 tion. It is certain that the portion of the chorion which eventually becomes attached to 

 the uterus undergoes a much greater degree of development than the rest of the mem- 

 brane. 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 corresponding to this portion of the chorion also becomes thickened ; the tubes 

 in which the villi have penetrated are correspondingly enlarged and branched, and the 

 vessels which surround them are increased in size ; and, finally, the union between 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 maternal 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 communicate freely with the uterine sinuses. In these great 

 cavities, we find the vascular foetal tufts ; and it is easy to understand 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 this is '& point concerning which there has been a great deal of discussion. 



In injected specimens of the placenta, when an attempt has been made to fill the 

 maternal as well as the foetal vessels, the material injected into the uterine vessels has 

 sometimes passed through the entire thickness of the placenta and appeared just beneath 

 the transparent chorion at the foetal surface of the organ. This appearance, however, 

 has been thought by some writers to be due to extravasation ; and many physiologists 

 are of the opinion that the placenta has no maternal portion, that it is entirely a foetal 

 organ, and that the maternal vessels do not pass beyond the surface by which it is 

 attached to the walls of the uterus. This opinion, however, we believe to be erroneous. 



The important point in the determination of the connection of what may be termed 

 the placental maternal sinuses with the vessels of the uterus can be settled by injection 

 of the uterine vessels in cases in which the observation can be made while the placenta 

 is still attached to the uterine walls. Dalton, since 1853, has examined the parts in situ 

 in four cases of women who died undelivered at or near the full term of pregnancy, and 

 he adopted the ingenious expedient of filling the uterine vessels with air, by which the 

 course of the injection could be directly observed. This operation is performed in the 

 following manner : The uterus, with its contents, is removed from the body, is carefully 

 opened, and the foetus is taken out, after dividing the umbilical cord. The parts are 

 then placed under water, the end of a blow-pipe is introduced into one of the divided 

 vessels of the uterine walls, and air is forced in by gentle insufflation. By this process, 

 the venous sinuses of the uterus itself are first filled, next, the deeper portions of the 

 placenta, and finally, " the bubbles of air insinuate themselves everywhere between the 

 foetal tufts, and appear in the most superficial portions of the placenta, immediately 

 underneath the transparent chorion. If the chorion be now divided at any point by an 

 incision, passing merely through its own thickness, the air, which was confined beneath 

 it in the placental sinuses, will escape, and rise in bubbles to the surface of the water. 

 Such an experiment shows conclusively that the placental sinuses communicate freely 

 with the uterine vessels, occupy the entire thickness of the placenta, and are equally 

 extensive with the tufts of the foetal chorion." Dalton farther states that the uterine 

 vessels, as they penetrate the placenta, have an exceedingly oblique direction, and that 

 their orifices may be easily overlooked, but can be seen by careful inspection. 



We have no doubt with regard to the accuracy of the observations of Dalton, and we 

 conceive that they have settled the question of the existence of a true maternal portion 



