598 



GENITAL ORGANS OP THE MAEE 



The stroma of the ovary (Stroma ovarii) is a network of connective tissue. In the 

 meshes of the stroma there are (in young subjects) numerous ovisacs or folliculi 

 oophori, containing ova (Ovula) in various stages of development. The immature 

 ovum is surrounded by foUicle cells; those more advanced in development are 

 enclosed by several (5-8) layers of follicle cells, forming the stratum granulosum, and 

 by a condensation of the stroma termed the theca folliculi; within the theca is a 

 quantity of fluid, the liquor foUiculi. At one point the follicle cells are heaped up as 

 a sort of mound (Cumulus oophorus), in which the ovum is enclosed. Such sacs 

 are termed folliculi oophori vesiculosi;i they enlarge as they mature, becoming 

 visible to the naked eye as vesicles with a diameter of a centimeter or more. When 

 fully developed, the follicles are superficially situated, and often project slightly 

 from the surface of the ovary. At intervals follicles rupture and their contents 

 escape. This process, which sets free the ovum, is termed ovulation; it 



takes place in the mare only 

 I at the ovulation fossa, and 



occurs during the periods of 



oestrum. 



The structure of the ovary of 

 the mare is peculiar and differs from 

 that of other animals in the fact 

 that it does not consist of a cortex 

 (zona parenchymatosa), in which 

 the follicles are situated, and a me- 

 dulla (zona vasculosa), which con- 

 tains the vessels and nerves. This 

 arrangement is present in the foetus, 

 but later the follicles become dis- 

 tributed throughout the interior of 

 the gland, and the vascular zone is 

 superficial. 



After rupture of a follicle, its 

 cavity is partly occupied by a blood- 

 clot, constitutiog what may be 

 termed a corpus nibrum. By prolif- 

 eration and enlargement and fatty 

 changes, the follicle cells are trans- 

 formed into lutein cells, forming a 

 yellow mass known as a corpus lu- 

 teum. If impregnation takes place, 

 the accompanying increase in vas- 

 cularity of the ' organs may cause 

 the corpus luteum to reach a large 

 size; if impregnation does not oc- 

 cur, it is much smaller, and is 

 sooner replaced by scar tissue, form- 

 ing the corpus albicans s. fibrosum. 

 In the new-bom foal the ovaries are large and oval m form. The free border is convex and 

 is covered by germinal epithelium, which extends over a large part of the surfaces also. This area 

 is distinguishable by its duU gray appearance from the peritoneal surface, which has the usual 

 smooth glistening character. The Umit of the peritoneal epithelium is a distinct line, termed by 

 Waldeyer the margo limitans peritonasi. As growth proceeds the ovary gradually becomes bent 

 until it assumes its definitive curved shape. The germinal epithelium is then limited to the ovu- 

 lation fossa. The ovary migrates somewhat during development from its primitive position, 

 which is the same as that of the testicle. 



Fig. 532. — Schematic Representation of Changes in Ovary of 

 M-ARE from Fcetal TO Adult State. (After Born.) 

 The changes affect chiefly the free border (upper in figure) and 

 the extent and form of the area covered by germinal epithehum (4). 

 1, Peritoneum (broad ligament); 2, ligament of ovary; 3, fimbria of 

 uterine tube; 4. germinal epithelium; 5, vessels, which reach the 

 ovary at the attached border {6). The latter represents the hilus, 

 while the deep depression at the free border is the ovulation fossa. 

 (EUenberger, in Leisering's Atlas.) 



In old animals the ovaries commonly consist largely of fibrous tissue, in which 

 there are often cysts of various sizes. The ova, present in enormous number at 

 birth, have then been extruded, or destroyed by phagocytic action or degeneration. 



Vessels and Nerves. — The arteries of the ovary are derived from the ovarian 

 artery. The artery is relatively large and is flexuous; it reaches the attached 

 border of the ovary by passing between the layers of the mesovariurri. The veins 

 are large and numerous. They form a plexus somewhat like that of the spermatic 



' Also known as Graafian follicles. 



