THE ANATOMY OF THE HORSE 71 



into two small pouches or sacs, called the vesiculse 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 foetus, or what may be called the animal 

 in its first stage. 



