THE REPRODUCTIVE ORGANS. 215 



cellular tissue between the uterine glands becomes more hyper- 

 plastic than during the intervals separating the menstrual periods, 

 and at the same time the cells composing it become hypertrophied, 

 until they closely resemble large epithelial cells. These cells have 

 been called "decidual cells." The ovum, when it reaches the 

 cavity of the uterus, becomes embedded in this tissue, which grows 

 around and encloses it, after which it is differentiated into three 

 portions. The part beneath the ovum is called the decidua sero- 

 tinti ; that which invests the ovum, the decidua reflexa ; and that 

 lining the rest of the uterine cavity, the decidua vera. While the 

 decidual tissue is developing and its cells enlarging the uterine 

 glands suffer changes. Their mouths become widened, and their 

 lower portions down to the muscularis mucosae dilated, after which 

 the epithelial lining atrophies and seems to disappear, so that the 

 lamina of the glands appear as spaces in the decidual tissue. As 

 the ovum enlarges, the decidua reflexa comes in contact with the 

 decidua vera, and the two layers exert a mutual pressure upon each 

 other, which flattens the spaces they contain and may obliterate 

 many of them. The decidual tissue now consists of a number of 

 flattened spaces which are separated from each other by thin walls 

 of fibrous tissue produced by the further development of the de- 

 cidual tissue. The decidua reflexa and the decidua vera blend 

 with each other to form a part of the membranes that are expelled 

 from the uterus, along with the placenta, after the birth of the child, 

 the rest of the membranes and most of the placenta being derived 

 from the foetus. After the birth of the child and the expulsion of 

 the membranes the mucous membrane is regenerated from the tis- 

 sues remaining in the superficial layers of the muscularis mucosse. 



The mucous membrane of the cervical portion of the uterus does 

 not participate in these changes incident to menstruation and preg- 

 nancy, and the connective tissue underlying its epithelial lining is 

 more fibrous in character than that in the corresponding part of the 

 uterine body. About the middle of the cervical canal the ciliated 

 epithelium, which is continuous with that of the body, passes into 

 a stratified epithelium, which extends over the cervix uteri, the 

 portio vaginalis, and the inner surface of the vagina to join that of 

 the epidermis upon the labia minora. The fibrous tissue beneath 

 this stratified epithelium possesses papillae similar to those upon the 

 skin, and contains mucigenous glands, which secrete a tenacious 

 mucus serving to close the cervical canal during pregnancy. The 



