976 



OF GENERATION. 



formed the maternal portion of the placenta, which may be regarded in its adult 

 state (as was well pointed out by Dr. J. Reid 1 ) in the light of a large sac (Fig. 



Fig. 255. 



Fig. 256. 



Extremity of a Plaoental Yillus : a, external 

 membrane of the villus, continuous with the 

 lining membrane of the vascular system of the 

 mother ; b, external cells of the villus, belong- 

 ing to the placentaljdecidua: c, c, germinal 

 centres of the external cells ; d, the space be- 

 tween the maternal and foetal portions of the 

 villus; e, the internal membrane of the villus, 

 continuous with the external membrane of the 

 chorion ; /, the internal cells of the rillus, be- 

 longing to the chorion ; g, the loop of umbilical 



Portion of the external membrane, with 

 the external cells of a placental villus ; a, 

 cells seen through the membrane ; b, cells 

 seen from within the villus; e, cells seen 

 in profile along the edge of the villus. 



259, c) formed by a prolongation of the inner coat of the uterine vessels ; against 

 the foetal surface of which sac, the tufts just described may be said to push 

 themselves, so as to dip down into it, carrying before them a portion of its thin 

 wall, which constitutes a sheath to each tuft. Now, as every extension of the 



Fig. 257. 



Diagram illustrating the arrangement of the Placental Decidua : a, decidua in contact with the interior of 

 the uterus; b, 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, separated foetal tufts, showing the internal membrane and cells, 

 which, with the loops of umbilical vessels, constitute the true foetal portion of the tufts. 



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 structure of the 



1 "Edinb. Med. and Surg. Journ.," Jan. 1841 ; and 

 searches," chap. vm. 



Anat., Phys., and Pathol. Re- 



