364 THE ANATOMY OF THE HORSE. 



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 Ovaries, 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. 1 



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 footnote), it 

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

 life is reached. 



1 The ovary of the adult mare, as was first pointed out by Born, departs in a remark- 

 able 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 curving 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. 



