THE GENERATIVE ORGANS 480 



are contained within the abdomen above the peritoneum, but being attached 

 to the scrotum by a thin muscle (the cremaster), they are gradually dragged 

 downwards through the inguinal canal ; and each brings a double layer of 

 peritoneum, which continues its connection through life, so that fluid injected 

 into the cavity of the tunica vaginalis will flow into the peritoneum. Hence 

 inguinal hernia in the horse becomes scrotal in a very short space of time, 

 and rarely remains confined to the former position. The testicles with their 

 appendages, the vesicular seminales, form the semen by the usual process of 

 secretion. They are of about the size of a duck's egg, and besides their 

 attachment by the reflexions of the tunica vaginalis to the scrotum, they 

 have also the spermatic cord which suspends them to the inguinal canal 

 through which it passes. This cord it is which is divided in castration, and 

 it is well to ascertain its component parts. They are, 1st. The artery 

 which supplies the testicles with blood, and is of considerable size and 

 tortuous in its course. 2nd. The artery of the cord, small and unimport- 

 ant. 3rd. The veins which accompany these arteries. 4th. The nerves 

 and absorbents, the division of the former giving great pain and causing a 

 slight shock to the sj'stem. 5th. The vas deferens or duct carrying the 

 semen to the urethra, and possessing walls of such thickness that it feels 

 like whipcord under the finger. These several parts are connected together 

 by cellular membrane and covered by the two layers of reflected peritoneum, 

 namely, the tunica vaginalis and tunica vaginalis reflexa, by the thin layer 

 of cremaster muscle, as well as by a fourth investment, a continuation of 

 the superficial fascia of the abdomen. All these parts must be divided be- 

 fore the canal is reached, for operating in castration. 



The female organs op generation are essentially the ovaries, the uterus 

 and its appendages forming the bed in which the embyro is nurtured to 

 maturity. The ovaiies are two small oval bodies, about the size of large 

 Avalnuts, situated behind the kidneys, and having the fimbriated extremities 

 of the fallopian tubes hanging loosely adjacent to them. These tubes, one 

 on each side, terminate in the uterus, which is of a remarkable shape in the 

 mare. It consists of a body and two horns. The body has a mouth, or os, 

 which opens into the end of the vagina, while, in itself, it is oblong, and in 

 the unimpregnated state it is entirely contained within the pelvis. Anteriorly 

 it divides into two horns (cornua), which diverge towards the loins, turning 

 upwards, and lying under the wings of the ossa ilii (see Fig. 75, page 475). 

 They terminate in rounded extremities. Each cornu receives the fallopian 

 tube of its own side, the opening being so small as scarcely to admit a silver 

 probe. The vagina lies loetween the bladder and rectum, and is about 

 eighteen inches in length ; it is lined with mucous membrane, and suxTounded 

 with muscular fibres, which form the sphincter vaginie. 



