OVULATION AND MENSTRUATION 



777 



Ovulation and Menstruation. In the process of development in the 

 ovary, the individual vesicular ovarian follicle increases in size and gradually 

 approaches the surface of the ovary. When fully ripe or mature, it forms a 

 little projection on the exterior. Coincident with the increase in size, which 

 is caused by the augmentation of its liquid contents, the external envelope 

 of the distended vesicle becomes very thin and eventually bursts. The ovum 

 and fluid contents of the vesicle escape on the exterior of the ovary, whence 

 they pass into the uterine tube. 



FIG. 496. 



FIG. 497. 



FIG. 498. 



FIG. 496. Diagram of Uterus just Before Menstruation. The shaded portion 



represents the thickened mucous membrane. 

 FIG. 497. Diagram of Uterus when Menstruation has just Ceased, Showing the 



Cavity of the Uterus Deprived of Mucous Membrane. 



FIG. 498. Diagram of Uterus a Week After the Menstrual Flux has Ceased. The 

 shaded portion represents renewed mucous membrane. (J. Williams.) 



In man and mammals ovulation apparently occurs only at certain periods. 

 These periods are closely connected with the changes in the woman that con- 

 stitute the phenomenon of menstruation, or, in the lower mammals, of oestrus, 

 or heat. 



That ovulation and discharge occur periodically, and only during the 

 phenomenon of heat, in the lower mammalia, is indicated by the facts 

 that, in all instances in which ovarian vesicles have been found presenting 

 the appearance of recent rupture, the animals were at the time or had recently 

 been in heat. There are few authentic and detailed accounts of ovarian 

 vesicles being found ruptured or of ova being fertilized in the intervals 



