712 



ANATOMY OF VERTEBRATES. 



Ovum, with tunica granulosa, of the Rabbit, in tlie act 

 of escaping from a ruptured Graafian follicle, cix'. 



blood to the ovarium, and especially to the swollen ovisac and its 

 adventitious coverings : a thinning of these takes place at the 

 most prominent part, to which the ovum tends : blood is extravu- 



sated into the ovisac, which, 

 partly by absorption, partly 

 by pressure, yields and gives 



issue to the ovum, fig. 559. 



* ~ 



This happens whether the 

 male have access to the fe- 

 male in heat or not. In the 

 Human kind the ovipont 

 concurs with and probably 

 occasions the menstrual dis- 

 charge. 1 The unimpregnated 

 ovum may escape, as an 

 impregnated one has some- 

 times done, into the abdo- 

 minal cavity : but, save that 

 it probably perishes in its 

 normal progress outward, it 

 might be said that a woman lays an egg every time she men- 

 struates an egg resembling in all essential structures that of 



~~ o 



the bird, but not exceeding T ^?rth of an inch in diameter. 2 Some- 



O 1 o U 



thing like a sanguineous discharge has been observed in Qua- 

 drumana ; but the more constant concomitant of the rut in that 

 order is the swelling and vascularity of the external parts of 

 generation. In the Mare an opaque white secretion is ejected per 

 vulvam at the heat. 



397. Corpus luteum. After the escape of the ovum, with 

 other contents of the ovisac, the w r alls of that cavity become 

 thickened and altered in colour : in most Mammals they are 

 partially everted at the ruptured orifice, fig. 566, b, b. In the 

 Cow and Sheep such altered ' Graafian follicle ' assumes a brick- 

 red colour ; in the Sow a yellowish brown ; and in the Woman 

 the brighter colour led to its being called a ' corpus luteum.' In 

 her the walls of the distended ovisac, compressed by the tunica 

 albtiginea and surrounding stroma, are thrown into delicate folds, 



~ C 1 



fig. 560 : the blood-clot which may have remained after the 

 escape of the ovum is progressively absorbed. The plicated 

 ovisac then contracts upon the cavity, and by the time the suc- 



1 CCLIIl". CCLIV". CCLV". 



2 In cccviu. the diameter of the mature ovarian ovum is given, as "being, in man ^-j, 

 dog T i_., cat --, ralibit T ^, rat ~ r} , mouse ^-, pig ^. cow ^, giiinea-pig ^ 6 , of an inch. 



