326 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



gins and usually lasts for four days. This results 

 in a complete or partial exfoliation of the superficial 

 part of the mucous membrane of the uterine fundus 

 and body, but does not involve the cervix. The 

 exfoliation begins at the internal os and advances 

 progressively toward the fundus. The restoration 

 of the mucosa proceeds in the same order, from be- 

 low upward, and in the course of five or six days the 

 mucous membrane is restored. The epithelial lining 

 regenerates from the free ends of the mucous glands 

 that did not partake in the exfoliation. 



The uterus is thus a seat of great physiological 

 activity. During at least one-half the menstrual 

 period of twenty-eight days there are marked struc- 

 tural changes manifest in the uterine mucosa. In 

 such an active organ pathological disturbances are 

 naturally of frequent occurrence. 



Menstruation and ovulation are related phenom- 

 ena, and yet there is evidence that neither one de- 

 pends on the other. Pregnancies may occur before 

 the menstrual period is inaugurated. Even at the 

 early age of nine years pregnancy has been reported ; 

 also in mature women after confinement, but before 

 menstruation has reappeared, pregnancy may occur. 

 A woman who does not menstruate does not become 

 pregnant, as a rule, but there are exceptions. Ovu- 

 lation, therefore, may go on without menstruation, 

 and there is evidence that menstruation may prevail 

 without ovulation. For a further discussion of this 

 subject, see Raymond's "Human Physiology." 



