REPRODUCTIVE ORGANS IN THE FEMALE. 327 



PREGNANCY. 



During pregnancy the mucous membrane of the 

 uterus becomes modified into a membrane called the 

 decidua gramditatis. This membrane may be divided 

 into (i) the decidua serotina or basalis, that part of 

 the mucosa to which the ovum is attached and in 

 which the placenta develops; (2) the decidua re- 

 ftexa, that which envelops the ovum, and (3) the 

 decidua uera, the part that lines the rest of the 

 uterus. 



In the early stages of pregnancy the changes in the 

 uterine mucosa resemble those of the decidua men- 

 strualis. At the end of the first half of pregnancy 

 the decidua serotina is i cm. thick. The epithelial 

 lining has disappeared and two layers can be recog- 

 nized: (i) a superficial compact layer, and (2) a deep 

 spongy layer. The compact layer consists of con- 

 nective-tissue elements and some very large pig- 

 mented cells called the decidua cells. These cells 

 usually have one large nucleus, but some of them 

 may be polynucleated. .The cells are thirty to one 

 hundred // in diameter, and oval or elongated, re- 

 sembling epithelial cells, although they are supposed 

 to develop from the interstitial connective-tissue 

 cells of the normal mucosa. They are of diagnostic 

 value in uterine curetments where they become a 

 probable evidence of pregnancy. In post-mortems 

 they have no medico-legal significance, as these cells 

 may be found in the decidua menstrualis. In the 

 spongy layer the connective-tissue cells form septa 

 between the flattened and sacculated as well as tor- 



