236 



HAND-BOOK OF PHYSIOLOGY. 



Graafian Vesicles. If the human ovary be examined at any period 

 between early infancy and advanced age, but especially during that period 

 of life in which the *power of conception exists, it will be found to con- 

 tain a number of small vesicles or membranous sacs of various sizes; these 

 have been already alluded to as the follicles or vesicles of De Graaf, the 

 anatomist who first accurately described them; they are sometimes called 

 ovisacs. 



At their first formation, the Graafian vesicles are near the surface of 

 the stroma of the ovary, but subsequently become more deeply placed; 

 and, again, as they increase in size, make their way toward the surface 

 (Fig. 394). 



When mature, they form little prominences on the exterior of the ovary, 

 covered only by a thin layer of condensed fibrous tissue and epithelium. 



A 



\V^.^-.?=S5SS5^?X- 





FIG. 394. Section of the ovary of a cat. A, germinal epithelium; B, immature Graafian follicle; 

 C, stroma of ovary ; D, vitelline membrane containing the ovum ; E, Graafian follicle showing lining 

 cells; F, follicle from which the ovum has fallen out. (V. D. Harris.) 



Each follicle has an external membranous envelope, comprised of fine 

 fibrous tissue, and connected with the surrounding stroma of the ovary by 

 networks of blood-vessels. This envelope or tunic is lined with a layer of 

 nucleated cells, forming a kind of epithelium or internal tunic, and 

 named membrana granulosa. The cavity of the follicle is filled with an 

 albuminous fluid in which microscopic granules float; and it contains also 

 the ovum. 



Ovum. The ovum is a minute spherical body situated, in immature 

 follicles, near the centre; but in those nearer maturity, in contact with 

 the membrana granulosa at that part of the follicle which forms a promi- 

 nence on the surface of the ovary. The cells of the membrana-granuloso 

 are at that point more numerous than elsewhere, and are heaped around the 

 ovum, forming a kind of granular zone, the discus proligerus (Fig. 395). 



