EMBRYOLOGY. 



263 



Menstruation is a periodic discharge of blood from the mucous 

 membrane of the uterus, due to a fatty degeneration of the small 

 blood-vessels. Under the pressure of an increased amount of blood 

 in the reproductive organs, attending the process of ovulation, the 

 blood-vessels rupture, and a hemorrhage takes place into the uterine 

 cavity ; thence it passes into the vagina. Menstruation lasts from 

 five to six days, and the amount of blood discharged averages about 

 five ounces. 



Corpus Luteum. For some time previous to the rupture of a 

 Graafian vesicle it increases in size and becomes vascular ; its walls 

 become thickened from the deposition of a reddish-yellow, glutinous 

 substance, a product of cell growth from the proper coat of the 

 follicle and the membrana granulosa. After the ovum escapes there 

 is usually a small effusion of blood into the cavity of the follicle, 

 which soon coagulates, loses its coloring-matter, and acquires the 

 characteristics of fibrin, but it takes no part in the formation of the 

 corpus luteum. The walls of the follicle become convoluted and 

 vascular, and undergo hypertrophy, until they occupy the whole of 

 the follicular cavity. At its period of fullest development the corpus 

 luteum measures 54 of an inch in length and ^ of an inch in depth. 

 In a few weeks the mass loses its red color and becomes yellow, con- 

 stituting the corpus luteum, or yellow body. It then begins to retract 

 and becomes pale ; and at the end of two months nothing remains but 

 a small cicatrix upon the surface of the ovary. Such are the 

 changes in the follicle if the ovum has not been impregnated. 



The corpus luteum, after impregnation has taken place, undergoes 

 a much slower development, becomes larger, and continues during 

 the entire period of gestation. The difference between the corpus 

 luteum of the unimpregnated and pregnant condition is expressed 

 in the following table by Dalton : 



Corpus Luteum of Menstruation. Corpus Luteum of Pregnancy. 



At the end of 

 three weeks. 

 One month. 



Two months. 



Three quarters of an inch in diameter ; central clot 

 reddish ; convoluted wall pale. 



Smaller ; convoluted 

 wall bright yellow ; 

 clot still reddish. 



Reduced to the con- 

 dition -of an insignifi- 

 cant cicatrix. 



Larger ; convoluted wall 

 bright yello w ; clot still reddish. 



Seven eighths of an inch in 

 diameter ; convoluted wall 

 bright yellow; clot perfectly 

 decolorized. 



