146 PRINCIPLES OF VETERINARY SCIENCE 



tunica vaginalis propria, closely envelops the testicle. The testi- 

 cles secrete the spermatic fluid or semen. 



The scrotum is the sac in which the testicles are normally en- 

 closed. It has an outer layer of soft, oily skin, beneath which is 

 a strong fibrous layer. The tunica vaginalis communis lines the 

 scrotum. It is a serous membrane, and directly continues the 

 peritoneum, of which it is a pouch-like diverticulum. Between 

 the two vaginal tunics is normally found a potential cavity con- 

 taining a serous fluid to prevent friction as the testicle changes 

 position. 



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Fig. 49. — Section of prepuce and part of penis of horse: P, Internal part of 

 prepuce or prepuce proper; P', external part of prepuce or sheath; C.p. pre- 

 putial cavity ;Fg., fossa of glands ;Z>. diverticulum; P.u., end or urethra. (Sisson, 

 Anatomy of Domestic Animals.) 



The ductus deferens is a thick-walled duct, about % inch in 

 diameter, which carries away the secretion of the testicle. There 

 is one for each of these glands. It passes upward through the 

 inguinal canal to the abdominal and pelvic cavities. It ends 

 by entering the urethra. 



The spermatic cord is that mass of tissue which is severed 

 when the animal is castrated. It is composed of the ductus 

 deferens, the blood-vessels, the nerves, and the tunica vaginalis. 



The seminal vesicles are in contact with the dorsal surface of 

 the bladder. In some animals they serve as reservoirs for the 

 semen. In the bull they are distinctly glandular. 



The prostate and Cowper's glands lie at the beginning of the 



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