874 THE GENERATIVE APPARATUS. 



veins are of large calibre, and form a very rich network around the gland 



the bulb of the ovary ; they terminate in the vena cava, near the renal veins. 



The lymphatics pass to the sublumbar glands. The nerves emanate from 

 the small mesenteric plexus. 



DEVELOPMENT. The ovary of Solipeds is of great size in the foetus, 

 being often nearly as large as in the adult animal. It becomes wasted in 

 aged animals. 



FUNCTIONS. The productive organs of the germ or ovum, the ovaries 

 are the testicles of the female. They form the ovulum, and then at a cer- 

 tain period set it at liberty. As the ovulaB are contained in the ovisacs, 

 it is necessary to study : I, The development of these ovisacs ; 2, Their 

 rupture or dehisence ; 3, The phenomena occuring in them after this 

 rupture. 



Development of the Ovisacs. The ovisacs already exist in the ovary of 

 the foetus and the young animal, but only assume their greatest activity at 

 the age of puberty. They are not all formed at birth, but are incessantly 

 re-developed, this development taking place beneath the tunica albuginea. 

 (At puberty, the stroma of the ovary is crowded with ovisacs so minute, 

 that in the Cow it has been computed that a cubic inch would contain two 

 hundred millions of them.) 



At first the ovisac consists of a small cell, which 

 presents all the constituent parts of the ovulum. As 

 it becomes developed it sinks into the cortical layer, 

 being pushed deeper into it by the cells that grow 

 outside it ; and it is also surrounded by a granular 

 membrane, formed at the expense of the nuclear 

 elements of the adjacent connective tissue. This 

 membrane soon separates at a given point into two 

 layers, to form a cavity that gradually extends and 

 becomes filled with fluid : this is the cavity of the 

 ovulum. As the separation is not complete, the 

 ovulum, enveloped by the internal granular membrane, 

 remains beside the external granular membrane, and 

 while the cavity is increasing, the tissue of the ovary, 

 pressed around it, is condensed, constituting the 

 fibrous wall of the ovisac, which afterwards receives 

 a network of vessels. 



Rupture of the Ovisacs. Until puberty, the ovisacs 

 do not exhibit any very marked phenomena ; at this 

 period, however, the ovary becomes vascularised, and 

 a certain number of Graafian vesicles increase in 

 OVARIUM OF THE RABBIT volume. At the period of oestrum, one or more of 

 ^STRUM, SHOWING ^ ese ' according to the species, participate in the 

 VARIOUS STAGES OF change in the ovary, become vascular and distended, 

 THE EXTRUSION OF and finish by rupturing and evacuating the discus 

 OVA> proligerus and ovulum. The latter is received into 



the Fallopian tube and conveyed towards the uterus. 

 Corpus Luteum. After the rupture of a Graafian vesicle, its cavity is 

 filled by a clot of blood which gradually contracts and loses its colour ; at 

 the same time the fibrous membrane becomes hy'pertrophied, and the granular 

 layer is wrinkled and transformed into cylindrical epithelium. To 

 this period of progression succeeds one of regression, during which the 

 cylindrical cells become infiltrated with fat and are gradually absorbed. 



