826 THE REPRODUCTIVE ORGANS [cH. LVltL 



epithelium becomes stratified; stratified epithelium also lines the 

 vagina. 



At each menstrual period the uterus becomes congested, and 

 some of the blood-vessels of the mucous membrane are ruptured ; 

 the blood, together with the secretion of the glands and some 

 epithelial debris from the surface, constitutes the menstrual flow, 

 which usually lasts two or three days. The amount of destruction 

 of the surface epithelium is not, however, a marked phenomenon ; 

 still less is there any disintegration of the deeper parts of the 

 mucous membrane. 



For Parturition (see p. 677), and for a description of the 

 mammary glands (see p. 464). 



