STRUCTURE OF PLACENTA. 



463 



layer of the cellular structure of the latter (Fig. 148, and Fig. 149, e) ; 

 and this will also form a part of all the bands that connect and tie 



Fig. 147. 



Fig. 148. 



Extremity of a Placental villus : a, external mem- 

 brane of the villus, continuous with the lining mem- 

 brane of the vascular system of the mother ; b, external 

 cells of the villus, belonging to the placental decidua ; 

 c, c, germinal centres of the external cells ; d, the space 

 between the maternal and foetal portions of the villus; 

 c, the internal membrane of the villus, continuous with 

 the external membrane of the chorion ; /, the internal 

 cells of the villus, belonging to the chorion; g, the loop 

 of umbilical vessels. 



Portion of the external mem- 

 brane, with the external cells, 

 of a Placental villus; a, cells 

 seen through the membrane; &, 

 cells seen from within the vil- 

 lus; e, cells seen in profile along 

 the edge of the villus. 



down the tufts (Fig. 149, g). The blood is conveyed into the cavity of 

 the placenta by the "curling arteries," so named from their peculiar 

 course (Fig. 149, (?), which proceed from the arteries of the uterus ; and 



Fig. 149. 



Diagram illustrating 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; d, 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 foetal 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 foetal tufts, showing the internal 

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

 tufts. 



it is returned by large, short, straight trunks, which pass obliquely 

 through the decidua (Fig. 149, 6), and discharge their contents into the 

 great uterine sinuses. 



820. There is no more direct communication between the Mother 

 and Foetus than this ; all the observations which have been supposed to 

 prove a direct vascular continuity, being certainly fallacious. The 

 function of the Placenta is manifestly double. The foetal tufts draw, 

 from the maternal blood, the materials which are required for the 

 nutrition of the embryo, these materials having been first selected 



