DECIDUAL MEMBRANES. 



303 



its umbilical cord extending through the vagina to the placenta. In the 

 course of half an hour the placenta and membranes are expelled, the sac 

 which they form being inverted in the process. Thus the smooth or 

 amniotic surface of the placenta is exposed. The very thin membranes 

 attached to its margin consist of amnion, chorion and fragments of decidua 

 vera. The denuded uterine mucosa is gradually restored to its normal 

 condition, as after menstruation. Epithelium spreads over its surface 

 from the bases of the glands. In the following account the histology of 

 the decidua vera and adjacent membranes will be considered first, then 

 the placenta and finally the cord. 



y.s 



FIG. 346. THE UTERCS AND DECIDUAL MEMBRANES IN EARLY PREGNANCY. A, AND IN LATE PREG- 

 NANCY, B. THE CORD HAS BEEN CUT AND THE EMBRYO REMOVED FROM B. 



am., Amnion: am. c., amniotic cavity; c., cervix; ch., chorion; c. u., cavity of the uterus; d. b., decidua 

 basalis; d. c., decidua capsularis; d. v., decidua vera; m., amnion and chorion laeve drawn as one 

 line; pi., placenta; u. c., umbilical cord; y. s., yolk sac. 



DECIDUA VERA, AMXIOX, AND CIIORIOX LAEVE. 



On the upper surface of the section Fig. 347, is seen the amnion, 

 having its simple cuboidal or flat epithelium toward the embryo, and its 

 mesodermic connective tissue toward the chorion. Adhesions in the 

 form of slender strands bind it to the connective tissue of the chorion. 

 The chorionic epithelium forms, a layer over the surface of the vera; it 

 presents slight irregularities but is without villi. The superficial uterine 

 epithelium has degenerated; it disappeared in an earlier stage. The modi- 

 fied mucosa or decidua vera is divisible into a superficial compact layer 

 and a deep cavernous layer. After the epithelium of the glands in the 

 compact layer degenerated and was resorbed, the connective tissue came 

 together obliterating the gland cavities. The compact layer is therefore 



