o/>9 



712 ANATOMY OF VERTEBRATES. 



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 whicli the ovum tends : blood is extrava- 



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- 

 x minal cavity : but, save that 



Ovum, with tunica granulosa, of the Rabbit, in the act J* nvr»l~kaV»l-i7- TAOv'aVina in i+a 

 of leaping from a ruptured Graafian follicle, cix'. ll V l0 ^ m J periSUeS 111 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 

 the bird, but not exceeding y^th of an inch in diameter. 2 Some- 

 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 walls 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 

 albuginea and surrounding stroma, are thrown into delicate folds, 

 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 ccevm. the diameter of the mature ovarian ovum is given, as being, in man T ~, 

 dog T £o, cat t!o> rabbit lfo> rat 2oo> mouse ^ 5 , pig jfo, cow ^ guinea-pig jfo of an inch . 



