566 , THE TISSUES. 



There are from 30 to 100 in each ovary, and often even 200 ; while 

 in old women only 2 to 10, or even none at all, are to be found. 



Each mature ovisac consists of a membrane and contents. The 

 former resembles a mucous membrane, consisting of (1,) a highly 

 vascular fibrous layer (tunica fibrosa), and (2,) an epithelium. Baer 

 distinguished the outer portion of the fibrous layer, which is united 

 to the stroma by a loose connective tissue, from the internal thicker, 

 softer, and reddish portion. The epithelium (membrana granulosa), 

 lies upon a basement-membrane, is riVo to ToVo OI> an i n h thick, 

 lines the whole sac, and on the side of it towards the surface of the 

 ovary, presents a wart-like thickening, the germinal eminence (cumu- 

 lus proligerus). This is g 1 ^ of an inch broad, and envelops the 

 ovum to be described further on. (Fig. 392.) 



"Pis 1 ^?Q2 



Its cells are polygonal, with large nuclei and 

 frequently yellowish fatty granules disposed 

 in several layers. (Fig. 145.) The contents of 

 the ovisac within the membrana granulosa are 

 (1,) a clear light yellowish fluid of the density 

 of the serum of the blood (liquor folliculi)', al- 

 most always containing (2,) isolated granules, 

 nuclei, and cells detached from the mem- 

 foiiicie of the sow. brana granulosa. 



a External, 5, internal layer TQ return ^ fa Q Q Qr Thig lieg 



of the fibrous membrane of the 



foiiicie. c. Membrana granulosa. close upon the fibrous membrane of the ovi- 



sac > on tte side of the latter looking to the 



ranulosa. /. Ovum surface of the ovary, and imbedded' in the 

 iCt cells of the germinal eminence before de- 

 fled about 10 diameters. (Km- scribed. When the ovisac bursts, the ovum 

 escapes, completely inclosed by the cells of 



the eminence and the contiguous portion of the epithelium, consti- 

 tuting the germinal disk (discus proligerus). The ovum itself is a 

 spherical vesicle, ^ to T ^ of an inch in diameter, possessing the 

 nature and constitution of a simple cell, though in some respects 

 peculiar. The cell wall (vitelline membrane), is a simple mem- 

 brane, is usually 3^ to ^Vo .of an i n k thick, very elastic and 

 firm, and, surrounding the contents as a clear transparent ring, is 

 "called zona pellucida. (Fig. 393.) The cell is completely filled by 

 the light-yellowish yolk. This is a viscid fluid having many minute 

 pale granules dispersed in it, and fatty granules; besides in the fully 



