THE ANATOMY OF THE HORSE 
n 
into two small pouches or sacs, called the vesiculae seminales. 
These store up the semen as it is secreted by the testicles, 
and when full present the appearance of a pear. 
5. — Vesiculae Seminales. — These sacs or pouches are situ- 
ated at the upper side, over the neck of the bladder, one on each 
side. They have the vas deferens emptying into them at the front 
end, while at the back end of each is a small opening that leads 
out into another small tube which passes backward and empties 
into the urethra, mentioned before as carrying the water out from 
the bladder. These sacs or pouches store up the semen or 
seed of the horse. During sexual intercourse, these sacs or 
pouches contract and force the semen through the little tubes 
mentioned out into the urethra, leading down through the 
penis. 
6. The Penis. — The penis is the main organ of sexual inter- 
course. Its substance is formed of what is known as erectile 
tissue, which, under certain circumstances, becomes enormously 
distended with blood. Passing up the under side, there is 
what has already been mentioned, the urethra, or the tube, 
which carries the water or urine out of the body, and also in 
the act of intercourse carries the semen. This tube is used 
for two purposes, as we have already mentioned. 
7. The Sheath. — The sheath is a loose process of skin which 
passes downward from the scrotum or bag, generally from about 
four to six inches, according to the size of the animal. It is at- 
tached to each side, leaving a hole or opening in the centre 
through which the penis passes. The outside of the sheath is cov- 
ered by a thin, delicate skin, similar to that of the scrotum. It is 
lined inside by a membrane containing many small glands, 
which secrete a thick dark fluid to lubricate this passage. 
Sometimes this fluid collects in here and has the appearance 
of tar. This is important, for when it collects to a large 
extent the sheath should be washed out. 
8. The Semen. — The semen or seed of the horse is a light 
fluid which when examined under a microscope, is found to con- 
tain small objects called spermatozoa. These move about, and 
when in the womb meet the ovum of the female, which is se- 
creted by a gland called the ovary. When these two small objects 
unite, they form the fcetus, or what may be called the animal 
in its first stage. 
