OVUM. 



57 



Fig. 41. 



Relation of the ova and ovaries in Mammalia. 



A. (From Coste, as reduced by Longet.) Human ovary, enlarged four diameters, partially dissected at 

 ooo, to show the Graafian follicles in the ovarian stroma: one of these, more advanced", has had its 

 double tunic, o v, cut into and reflected ; the granular membrane, m g, has also been partially opened, 

 showing the thickened portion or granular disc, dg, in which the ovum is imbedded near the most 

 projecting part. At o V, another Graafian follicle has been burst, and the ovum in its granular disc 

 is seen expelled from it. 



u. Transverse section of human ovary, to show the general arrangement of the developed Graafian 

 follicles towards the surface ; twice the natural size. 



c. Diagrammatic representation, in section, of two^Graafian follicles, in different stages of advance- 

 ment in the ovary of a mammifer, enlarged about ten diameters, p. Peritoneal covering of the ovary, 

 st, ovarian stroma; ov, the two layers of the ovisac; mg, membrana granulosa, near which is the 

 discus granulosus, with the ovum imbedded. 



stroma ; and it has been observed, that these 

 are present from a very early period in the 

 ovaries, as first noticed by Carus, and since 

 by myself and others in the child at birth. 



The more developed of these ovi-capsules 

 are enclosed by a strong theca or membrane, 

 consisting of two layers ; the external thinner 

 and firmer, of a fibrous and vascular struc- 

 ture, the internal thicker and softer, of a 

 fibro-cellular structure and also of consider- 

 able vascularity. The capsules are filled with 

 a fluid nearly transparent, which coagulates 

 under the action of heat ; and inside the 

 theca, or lining it and covering the fluid, there 

 is a layer of nucleated cells united together in 

 the form of a soft, easily-lacerated membrane, 

 somewhat like an epithelial lining of the cap- 

 sule. It is in this cellular layer (tunica gra- 

 nu/osa of Von Baer) that the ovum is placed, 

 being situated in the thicker portion of it 



(cumulus proligerits), directed towards the 

 surface of the ovary. 



When one of the ovicapsules and its con- 

 tained ovule has reached maturity, which 

 takes place in one or more of them at regu- 

 larly recurrent periods, besides the swelling 

 of the ovicapsule itself from the increase of 

 its fluid and other causes, the stroma of the 

 ovary between the capsule and the surface 

 undergoes considerable thinning, and the ovi- 

 capsule comes thus to project more imme- 

 diately from the surface of the ovary. An 

 increased vascularity is also apparent in the 

 same situation ; and finally a small circum- 

 scribed fissure near the middle of the most 

 projecting part occurs, allowing the escape of 

 the ovule and the granular layer and fluid 

 from the ovicapsule. 



The ovule, surrounded by a portion of the 

 cellular layer in which it was embedded, is 



