226 



NORMAL HISTOLOGY. 



as cylindrical masses which penetrate the stroma and undergo prolif- 

 eration. With the increase in size which accompanies their devel- 

 opment the Graafian 



, follicles pass towards the 



P a . .. *\ . , 



inner limits of the cortex 



bordering on the me- 

 dulla, where they un- 

 dergo further enlarge- 

 ment ; after a time their 

 diameter includes al- 

 most the entire cortex, 

 and extends from the 

 medulla to the surface 

 of the ovary. Subse- 

 quently the position of 

 the follicle becomes evi- 

 dent as a distinct pro- 

 jection on the free 

 surface, marking the 

 point at which the final 

 rupture of the sac and 

 the escape of the ovum 

 take place. Such dis- 

 charge usually coincides 

 with the phenomena at- 

 tending menstruation. 



The mature Graaf- 

 ian follicles appear as 

 clear vesicles, 4-8 mm. 

 in diameter, and, on 

 section, exhibit a char- 

 acteristic arrangement. The follicle is defined from the surrounding 

 tissue by a condensed layer of stroma, which forms a sheath, the 

 theca folliculi ; this envelope is composed of two layers, an outer 

 tunica fibrosa, containing fibrous connective tissue and coarser 

 blood-vessels, and an inner tunica propria, rich in cells, small 

 blood-vessels, and capillaries. Within the theca follows the mem- 

 brana granulosa, consisting of many layers of small polyhedral 

 epithelial cells, the descendants of the single row of original cells 

 contained within the young follicle ; at one point the membrana 

 granulosa presents a thickening, which is continued as a zone of 

 cells immediately surrounding the ovum ; this constitutes the discus 

 proligerus, which remains in contact with the ovum after its escape. 

 The cells of the discus which lie next the ovum are placed vertically 



Section of cortex of cat's ovary, exhibiting large Graafian folli- 

 cle : a, peripheral zone of condensed stroma ; b, groups of im- 

 mature follicles ; c, theca of follicle ; d, membrani granulosa ; 

 e, discus proiigerus ; _/", zona pellucida : g, vitellus ; h, germinal 

 vesicle ; i, germinal spot ; k, cavity of liquor folliculi. 



