48 



OBSTETRICAL ANATOMY. 



it is lined by an epithelial or granular membrane {tunica gra?iulosa), com- 

 posed of round or polygonal granular cells. At the bottom of the vesicle 

 this epithelium forms an aggregation (the cumulus, or discus proliger), in 

 the centre of which exists the ovum or ovulum of mammalia. The con- 



Fig. 20. 



Ovary Opened Vertically. 



b b, Graafian Vesicles at different 

 stages of development. 



Fig. 21. 



Portion of the Ovary of a Pig. 



a. Point at which a ripe Vesicle is about to 

 escape ; b, Fissure by which an Ovule has 

 escaped. 



tents of the vesicle is a yellowish, transparent, albuminous mass, that 

 becomes reddened by an admixture of blood when the vesicle ruptures. 

 The ovulum, ovule, or ovum, is a small cell imbedded in the cumulus, 



Fig. 22. 



Graafian Vesicle in Mare's Ovary. 



a, Membrana Propria of the Graafian Fol- 

 licle ; b, Membrana Granulosa ; bi, Dis- 

 cus Proligerus ; c, Ovum. Magnified 

 5 Diameters. 



Fig. 23- 



Ovulum of the Mare. 



, Zona Pellucida ; b, Vitellus, containing 

 the Vesicula Germinativa ; c, Cells of the 

 Discus Proligerus. 



and surrounded by an amorphous, thick, white membrane, which has been 

 designated the zona pellucida ; within this membrane is a granular layer, 

 the vitellus or yolk, the larger granules of which are superficial and com- 

 pact, while internally it is a transparent albuminous fluid, in which are 

 but few granules. Enclosed in this vitellus, though nearer its circumfer- 



