438 THE HORSE. 
and rarely remains confined to the former position. The testicles with 
their appendages, the vesicule 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, lst. The artery which supplies the testicles with blood, and is of 
considerable size and tortuous in its course. 2d. The artery of the cerd, 
small and unimportant. 3d. 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 system. 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 before the canal is reached, for operating 
in castration. 
THE FEMALE ORGANS OF GENERATION are essentially the ovaries, the 
uterus and its appendages forming the bed in which the embryo is nurtured 
to maturity. The ovaries are two small oval bodies, about the size of large 
walnuts, situated behind the kidneys, and having the fimbriated extremi- 
ties 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 0s, 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. 1, page 425). 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 between the 
bladder and rectum, and is about eighteen inches in length ; it is lined 
with mucous membrane, and surrounded with muscular fibres, which form 
the sphincter vagine. 
CHAPTER XXIII. 
THE NERVOUS SYSTEM. 
PHYSIOLOGY OF THE NERVOUS SYSTEM—CHIEF DIVISIONS OF THE NERVOUS SYSTEM— 
THE SPINAL CORD—MEDULLA OBLONGATA—THE ENCEPHALON —THE SYMPATHETIC 
SYSTEM. 
PHYSIOLOGY OF THE NERVOUS SYSTEM. 
Hiruerto we have been engaged in examining into the conformation of 
the framework of the body ; into the structure and action of the muscles, 
which serve to move this framework ; and into the several organs which 
afford nourishment to the whole, and keep it sound and in good order. 
