GENITAL ORGANS. 177 



the external surface of the fihrous tunic, and determines the rapid ascending 

 movements of the testicle. 



e. The fibrous tunic, which surrounds the serous sac in which the testicle is 

 susjiended. 



f. Finally, the vaginal tunic or sheath, a diverticulum of the peritoneum, 

 covering the inner face of the fibrous tunic and surrounding the testicle as well as 

 its suspensory cord. 



The development of the testicular envelopes varies according to 

 diverse circumstances, such as the degree of descent of the testicles, the 

 .state of health or of disease; rest or exercise, the temperature, the 

 race, etc. 



Contrary to the general opinion, they are always formed at birth, 

 at which time occurs the commencement of the descent of the testicles ; 

 but they soon disappear, to reappear towards the end of the first year, 

 following, consequently, the migration of the organs which they protect. 



These tunics, thin, soft, unctuous, and shiny in fine and well-nour- 

 ished subjects, are thick, coarse, dull-colored, and rough in common 

 horses. The scrotum or skin is, with few exceptions, almost hairless, 

 of a black color, or only covered by some downy hairs. Nevertheless, 

 in light-colored animals it is sometimes deprived of pigment in certain 

 places, and then offers white or red spots of a variable area, to which 

 is given the name leprous spots. 



2d. The Testicles. — Suspended at the extremity of a cord con- 

 stituted by the vas deferens, blood-vessels, and nerves, these glands 

 consist of ovoid masses depressed laterally, and related by their external 

 face and superior border each to an elongated organ, the epididymis, 

 enlarged at its two extremities and formed by an indefinite number of 

 convolutions of its excretory canal. They float freely in their envelopes, 

 but are neither in the same horizontal plane nor in the same transverse 

 line : the left is always more inferior and more posterior than the right. 

 The two testicles are, therefore, so disposed that they can approach the 

 median line without being mutually compressed during the adduction 

 of the thighs, between which they are situated. It is apparent hoAv 

 painful to the animal and dangerous to these organs such friction and 

 compression would be if frequently repeated. 



The examination of the testicidar region requires some precautions, 

 particularly in irritable and sensitive horses. 



Let us suppose that this examination be practised upon the left 

 testicle. 



The head is maintained in an elevated position by an assistant ; in 

 addition, the anterior right foot may be raised. This being done, the 



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