ACTION OP THE FEMALE. 



977 



latter; and the foetal portion of each tuft will thus be inclosed in a layer of 

 maternal cells and basement-membrane (Fig. 255, a, b, c; and Fig. 256, a, I, e). 

 In this manner, the whole interior of the placental cavity is intersected by 

 numerous tufts of foetal vessels, disposed in fringes, and bound down by reflec- 

 tions of the delicate membrane that forms its proper wall ; just as the intestines 

 are held in their places by the reflections of the peritoneum that covers them. 

 This view was suggested to Dr. R. by the very interesting fact that the tufts 

 of foetal vessels not unfrequently extend beyond the uterine surface of the pla- 

 centa, and dip down into the uterine sinuses (Fig. 258); where they are still 

 covered and held in their places, by reflections of the same membrane. All the 

 bands which connect and tie down the tufts (Fig. 257, g) are formed of the 

 same elements as the envelops of the tufts themselves ; namely, a fold of the 

 lining membrane of the decidual sinuses, and a layer of the cellular decidua. 



982. The blood is conveyed into the Placental cavity by the " curling arteries" 

 of the uterus (Fig. 259, a); and is returned from it by the large veins, that are 

 commonly designated as sinuses (Fig. 259, 6). The foetal vessels, being bathed 

 in this blood, as the branchiae of aquatic animals are in the water that surrounds 

 them, not only enable the foetal blood to exchange its venous character for the 

 arterial, by parting with its carbonic acid to the maternal blood, and receiving 

 oxygen from it; but they also serve as rootlets, by which certain nutritious ele- 



Fig. 258. 



Fig. 259. 



Diagram of the structure of the Placenta; showing a, the substance of the uterus; 6, the cavity of a sinus; 

 c, c, the foetal tufts dipping down into this; d, d, the decidual lining of the uterus; e, curling arteries. 



ments of the maternal blood (probably those composing the liquor sanguinis) 

 are taken into the system of the foetus. In this, they closely correspond with 

 the villi of the intestinal canal ; and there is this further very striking analogy 

 that the nutrient material is selected and prepared by two sets of cells, one of 

 which (the maternal) transmits it to the other (the foetal), in the same manner 

 as the epithelial cells of the intestinal villi seem to take up and prepare the 

 nutrient matter, which is destined to be still further assimilated by the cells 

 that float in the circulating current ( 461). It is pro- 

 bable, too, that the placenta is to be regarded as an ex- 

 creting organ; serving for the removal, through the ma- 

 ternal blood, of excrementitious matter whose continued 

 circulation through the blood of the foetus would be pre- 

 judicial to the latter. And it will be in this mode that 

 the blood of the mother may become impregnated with 

 substances, or impressed with attributes, originally be- 

 longing to the male parent, so as to impart these to the 

 products of subsequent conceptions by a different father 

 ( 975). There is no more direct communication between 

 the mother and foetus than that which is afforded by this 

 immersion of the foetal tufts in the maternal blood ; all 

 the observations which have been supposed to prove the 

 existence of real vascular continuity, having been falsi- 

 62 



Diagram of the Placental 

 cavity, according to Dr. Reid : 

 a, curling artery of the ute- 

 rus; fo, uterine sinus; c, cavity 

 of the placenta; d, fuetal tuft 

 imbedded in it, and held in 

 place by reflections of its 

 walls. 



