352 THE ANATOMY OF THE HORSE. 



abdominal cavity (see page 303). Each ovary is about half the size of 

 the testicle — the corresponding organ of the male. In form it is ovoid, 

 with a distinct depression on its upper surfixce — the hilus. At the hilus 

 the nerves and vessels of the organ enter from the broad ligament of the 

 uterus, and in its neighbourhood the expanded end of the Fallopian tube 

 is attached by one of its fimbrice to the surftxce of the ovary. From the 

 posterior extremity of the ovary a cord of non-striped muscular tissue — 

 the ligament of the ovary — passes to the uterine coniiu The lateral 

 surfaces, the inferior border, and the anterior end of the ovary are 

 rounded and free. 



Structure of the Ovarv. This comprises (1) an epithelial covering 

 on the surface of the organ, (2) a fibrous framework, or stroma, and 

 (3) Graafian follicles. 



1. The Germinal Epithelium. — This is a single layer of short columnar 

 cells with granular contents. In veterinary text-books the surface of 

 the ovary is desci'ibed as having a serous covering derived from the 

 broad ligaments. The cells of this surface covering, however, are in 

 marked contrast to the cells of the broad ligament, which have the 

 ordinary flattened and transparent endothelial characters. The term 

 germinal is applied to this layer because the ova, or gei-m-cells, are 

 separated from it in the fojtal ovary. 



2. T\\e Stroma is composed of fibrous connective-tissue with some bundles 

 of non-striped muscular tissue. The blood vessels of the ovary ramify 

 in it, and it surrounds the Graafian follicles. Around the hilus it is 

 most vascular and open in texture, and this portion of the stroma is 

 sometimes termed the zona vasculosa or the medullary substance, in contra- 

 distinction to the peripheral cortical substance. A layer of condensed 

 stroma without any Graafian follicles lies beneath the surface epithelium, 

 and is sometimes termed the tunica albuginea of the ovary. 



3. The Graafian Follicles, or Ovisacs. — These are vesicular bodies for 

 the matui'ation and extrusion of the ova. A large-sized follicle possesses 

 the following parts : — 



a. The wall of the follicle, composed of an inner delicate tunica 

 propria, and an outer layer — the tunica fibrosa — derived from the 

 surrounding stroma. 



6. The Menibrana Gramdosa. — This forms an epithelial lining to the 

 wall of the follicle, and consists of several layers of cells. At one point 

 these epithelial cells are heaped up to form the cumulus or discus 

 ptroligerus, the cells of which surround the ovum. 



c. The Liquor Folliculi. — This is a fluid which fills up the remainder of 

 the cavity of the follicle. 



The Ovum is a typical animal cell. It consists of an outer envelope — the 

 zonaj)ellucida; protoplasmic cell-contents — the vitellus or yelk; a nucleus — 

 the germinalvesicle; and, within the nucleus, a nucleolus — i\\Q germinal spot. 



