364 THE ANATOMY OF THE HOESE. 



suspension in that cavity has already been noticed. Their more com- 

 plete examination can now be undertaken along with the dissection 

 of the purely pelvic parts of the same apparatus, and at the same time 

 it is convenient to examine the female urethra. 



The OvABiES, as already seen, are situated in the lumbar region of the 

 abdominal cavity {see page 312). In an adult mare of ordinary size each 

 ovary has a volume about equal to that of a hen's egg, and in form 

 it somewhat resembles a short haricot-bean. For descriptive purposes 

 one may recognise in it two surfaces, two edges, and two extremities. 

 The surfaces — right and left, or outer and inner — are convex, smooth, 

 and covered by peritoneum. The upper edge is convex and attached to 

 the broad ligament of the uterus. By this edge the vessels and nerves 

 of the organ enter it. The lower edge is shorter than the upper, and 

 concave ; towards its centre it shows the opening of a cavity or depres- 

 sion — the ovulation fossa (Born). It is here that the mature Graafian 

 follicles burst, and discharge their contents. In front of this opening, 

 the lower edge has the fimbriated extremity of the Fallopian tube 

 attached to it. Both extremities of the ovary are blunt and rounded ; 

 but, while the anterior is free, the posterior has the ligament of the ovary 

 attached to it. The ligament is a cord of non-striped muscular tissue, 

 and, between the layers of a fold of peritoneum forming part of the 

 broad ligament of the uterus, it passes backwards and is lost on the 

 concave edge of the uterine horn. 



If one of the ovaries be divided by a longitudinal mesial incision it 

 will be seen to be composed of a rather firm greyish tissue, embedded in 

 which are the so-called Graafian follicles. These are rounded cyst-like 

 cavities, of which the largest may have the volume of a hazel-nut or 

 more.^ 



Structure of the Ovary. This comprises (1) the germinal epithe- 

 lium, (2) a fibrous framework or stroma, and (3) the Graafian follicles. 



1. The Germinal Epithelium. This is so-named because the ova, or 

 germ-cells, are separated from it in the foetal ovary. It forms a single 

 stratum of columnar cells, and, as explained below {see foot note), 

 it gradually shrinks after birth, and disappears before the period of 

 adult life is reached. 



I The ovary of the adult mare, as was fir.st pointed out by Born, departs in a remarkable 

 way from the common mammalian type. In the new-born foal the organ is almost ovoid 

 in shape, both its edges being thus convex and rounded from side to side. At this time 

 also the exterior of the organ is only partially covered by peritoneum, the upper edge 

 and a small part of the lateral surfaces contiguous to it carrying a single layer of short 

 columnar epithelium — the so-called germinal epithelium. During the first year of extra- 

 uterine life the ovary undergoes an important change of shape, the two extremities curv- 

 ing towards each other, so as to produce the ovulation fossa and give the lower edge a 

 concave outline. While this change is being effected the germinal epithelium shrinks 

 into the ovulation fossa and ultimately disappears, the whole of the exterior of the organ 

 acquiring an endothelial covering. 



