706 



OF REPRODUCTION. 



of the uterine vessels carries the decidua before it, every one of the vascular 

 tufts that dips down into it will be covered with a layer of the cellular struc- 

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

 layer of maternal cells and basement-membrane (Fig. 280, , 6, c ; and Fig. 



281, a, b, e). In this manner, the whole interior of the placental cavity is in- 

 tersected by numerous tufts of foetal vessels, disposed in fringes, and bound 

 down by reflections of the delicate membrane that forms its proper wall ; just 

 as the intestines are held in their places by 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 sur- 

 face of the Placenta, and dip down into the uterine sinuses ; Avhere they are 

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

 (Plate I., Fig. 24). All the bands which connect and tie down the tufts (Fig. 



282, g), are formed of the same elements as the envelopes of the tufts them- 

 selves ; namely, a fold of the lining membrane of the decidual sinuses, and a 

 layer of the cellular decidua. 



Fig. 282. 



Diagram illustrating 1 the arrangement of the placental decidua : a, decidua in contact with the interior 

 of the uterus; ft, venous sinus passing obliquely through it by a valvular opening; c, a curling artery 

 passing in the same direction ; cl, the lining membrane of the maternal vascular system, passing in from 

 the artery and vein, lining the bag of the placenta, and covering e, e, the fcctal tufts, passing on to them 

 from their stems from the foetal side of the cavity, also by the terminal decidual bars/./, from the uterine 

 side, and from one tuft to the other by the lateral bar, g ; h, h, separated fcetal tufts, showing the internal 

 membrane and cells, which, with the loops of umbilical vessels, constitute the true foetal portion of the 



tufts. 







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

 arteries" of the Uterus ; and is returned from it by the large veins, that are 

 commonly designated as sinuses. 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 arte- 

 rial, 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 

 elements 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 fcctal), in the same man- 

 ner 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 

 special absorbing cells of their interior ( 672). There is no more direct 

 communication between the Mother and Foetus than this; all the observations 

 which have been supposed to prove the existence of real vascular continuity, 



