510 



GENITAL ORGANS OF THE MARE 



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the vessels and nerves enter; this area is termed the hilus. The ovulation fossa 

 is covered by a layer of columnar cells, a remnant of the primitive germinal epithe- 

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

 and unstriped muscular fibers. In the deeper or medullary portion of the stroma 

 (Zona vasculosa) the meshes are largely occupied by the numerous Ijlood-vessels. 

 In the peripheral or cortical portion (Zona parenchymatosa) are numerous ova 

 (Ovula) in various stages of development. The immature ova are surrounded by 

 follicle cells; those more advanced in development are inclosed also by a condensa- 

 tion of the stroma termed the theca f olliculi ; within tlio theca is a ciuantity of 

 fluid, the liquor folliculi. These constitute the Graafian follicles (Folliculi oophori), 

 which 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 super- 

 ficially 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 at the ovulation fossa, 

 and occurs during the periods 

 of oestrum. 



After rupture of a follicle its 

 cavity is partly occupied by a 

 blood-clot, constituting what may 

 be termed a corpus rubrum. By 

 proliferation and enlargement and 

 fatty changes, the follicle cells are 

 transformed into lutein cells, form- 

 ing a yellow mass known as a cor- 

 pus luteurti. If impregnation takes 

 place, the accompanying increase in 

 vascularity of tlie organs may cause 

 the corpus luteum to reach a large 

 size; if impregnation does not occur, 

 it is much smaller, and is sooner 

 replaced by scar tissue, the corpus 

 albicans. 



In the young foal the ovaries 

 are large and oval in form. The 

 free border is convex and is covered 

 by germinal epithelium, which ex- 

 tends over part of the surfaces also. 

 This area is distinguishable by its 

 dull gray appearance from the peritoneal surface, which has the usual smooth glistening 

 character. As growth proceeds the ovary gradually becomes bent until it assumes its 

 definitive curved shape. The germinal epithelium is then limited to the ovulation fossa. 

 The ovary migrates somewhat during development from its primitive position, which is the 

 same as that of the testicle. 



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 mun- 

 ber at birth, have then l)een extrudetl, or destroyed by phagocytic action or de- 

 generation. 



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 bortler 

 of the ovary by passing between the layers of the mesovarium. The veins are 

 large and numcn-ous. They form a plexus somewhat like that of the s]:)ermatic 

 cord. The lymph vessels pass to the lumbar glands. The nerves are derived from 

 the sympathetic system through the renal and aortic plexuses. They accompany 

 the arterial branches. 



Fig. 409. — Schematic Representation op Changes in Ovary of 

 Mare prom 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; S, fimbria of 

 Fallopian 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. 

 (Ellenberger, in Leisering's Atlas.) 



