POSTERIOR EXTREMITY. 175 



tumors soon soften, ulcerate, and acquire a repulsive aspect and an unpleasant 

 odor, and they lead to fatal results whenever sufficient inflammation is excited. 



Anal fistulas were quite common at the time when the operation of docking 

 the tail was more usually practised, of which they constituted one of. the compli- 

 cations. It was not less frequent to find here other fistulae which were voluntarily 

 made, under the name of whistle, or nightingale, with the object of relieving horses 

 affected with emphysema, in which the expulsion of gas through the anus is 

 almost constant. As we have shown on a previous page, this practice_has long 

 since fallen into disrepute, and is now only the appendage of a gross empiricism. 



In certain horses a particular larva is sometimes found, attached strongly to 

 the margin of the anus by the hooks of its cephalic appendix ; it is that of the 

 CEstrus hcemorrhoidalis, which comes from the stomach and is expelled from the 

 digestive tube to perform its metamorphosis. 



There is another larva, that of the Hippobosca equina, or horse-tick, better 

 known under the name of flat fly, or spider-fly, because of its special form. These 

 larvae are seen under the tail, on the sides of the anus, and on the genital organs, 

 particularly in Oriental horses. They are flat, resistant to pressure, and very 

 adherent to the above-mentioned parts. These flies sometimes emigrate to animals 

 which are not accustomed to them, and excite the horses to such a state of agita- 

 tion that they are suddenly seized with fright, run away, and demolish everything 

 in their way. It is only necessary to remove the cause of this agitation as soon 

 as it manifests itself, in order to avoid with certainty such formidable dangers. 



C. The Perineum and the Median Raphe'. 



The perineum is a single region comprised between the anus and 

 the external genital organs. 



In the male it extends from the posterior part of the scrotum to 

 just below the anus. Situated at first between the thighs, then between 

 the buttocks, it is in relation anatomically to the corresponding part of 

 the urethra and to the perineal aponeurosis which covers the latter. Its 

 skin is black, or sometimes marbled, from the presence of leprous spots, 

 which peculiarity should not be omitted in the description of the horse. 



It offers neither beauties nor defects for consideration ; it should be 

 perfectly distinct and exempt from cicatrices, which might be the result 

 of a dangerous operation, urethrotomy , practised in the treatment of 

 calculus of the bladder, or the consequence of blow^s received by the 

 animal. 



In the mare this region is much smaller ; it corresponds only to 

 the narrow space situated between the vulva and the anus. 



Some authors have regarded it as extending to the mammae, whose 

 situation is quite similar to that of the testicles. But even if we should 

 observe this analogy, the study of the perineum, with regard to the 

 exterior, would not gain in importance. 



As to the raphe, as its name indicates, it is a kind of cutaneous 



