CHAP. XL]. MEMBRANA DECIDUA. 577 



mation of a soft pulpy tissue, containing cellular elements in great 

 abundance, over the whole internal surface of the uterus. In this 

 soft spongy substance the ovum becomes imbedded, and with it 

 the chorion becomes intimately connected. This membrane, in 

 consequence of its being thrown off at each parturition, has been 

 termed the " membrana decidua" 



The decidua was formerly looked upon as an exudation from the 

 mucous membrane of the uterus ; but from the observations of 

 Professor E. H. Weber and Dr. Sharpey, it has been shown to con- 

 sist of the much thickened and altered mucous membrane itself. 

 It appears to be composed of glands lined with epithelium, between 

 which ramify vessels surrounded by much soft pulpy tissue, com- 

 posed principally of nucleated cells. At the time of its formation 

 the ordinary ciliated epithelial lining of the unimpregnated uterus 

 entirely disappears, and its cavity soon becomes filled with a fluid 

 secreted by the soft and swollen decidua. The os uteri is plugged 

 up by a soft, viscid, mucous-like mass, com- Fig. 272. 



posed of a secretion from the decidual 

 membrane ; but the cells which are found 

 in it differ materially in character from 

 those immediately surrounding the ovum, 

 in being of an elongated form, while the 

 latter are spherical, and, according to Pro- 

 fessor Goodsir, perform the very important 

 office of elaborating the nutrient material 

 for the ovum. 



Structure of the Membrana Decidua. In 

 the unimpregnated uterus of the bitch, and 

 other animals, and probably also in that of 

 the human subject, but more minute, are 

 situated numerous small glands, which in- 

 crease enormously in size immediately after 

 conception. In the human uterus, soon 

 after impregnation, they are seen as elon- 

 gated wavy tubes, having a tolerably 

 straight course in their more superficial 



part, but much Contorted towards their Section of human uterus at com- 

 mencing pregnancy, snowing tne 



deep aspect, Where theV terminate in two glands in the mucous membrane, and 

 * . . their openings. Twice the natural 



or three coecal extremities. The space size. After weber. 

 between these tubes, contains capillary vessels and numerous cells, 

 to the increased development and multiplication of which, accord- 

 ing to Professor Goodsir, the greatly increased thickness of the mem- 



