224 



UROGENITAL SYSTEM 



located and the follicle cells directly surrounding it constitute the cumulus 

 oophorus (egg-bearing hillock). About the stratum granulosum formed by the 

 original follicle cells there is differentiated from the stroma of the ovary the theca 

 folliculi. This is composed of an inner vascular tunica interna and of an outer 

 fibrous tunica externa. 



Fully formed Graafian follicles are found in the ovaries during the second 

 year and they may even be present before birth. Ovulation may occur at this 

 time but usually these precociously formed follicles degenerate with their con- 







FIG. 223. Graafian follicle and ovum from the ovary of a fifteen-year-old girl. X 30. 



tained ova. Thus, although thousands of ova are produced in the ovary, only a 

 comparatively few are set free ready for fertilization during the sexually active 

 life of the female, from puberty to the climacteric period or menopause. The 

 relation of ovulation to menstruation has been discussed on p. 96. 



The Corpus Luteum. After ovulation a blood clot, the corpus hemorrhagicum, forms 

 within the empty follicle. The follicle cells of the stratum granulosum proliferate, enlarge and 

 produce a yellow pigment. The whole structure, composed of lutein cells and connective tissue 

 strands, is termed the corpus luteum or yellow body. The blood clot is resorbed and replaced 

 by fibrous scar tissue white in color and known as the corpus albicans. If pregnancy does 

 not intervene the corpus luteum spurium reaches its greatest development within two weeks 

 and then degenerates. In cases of pregnancy the true corpus luteum continues its growth until 



