GENITAL ORGANS. 183 



particular sound. Its intensity appears to depend upon the flaecidity and the 

 disproportion of voUime of the parts concerned in the mechanism of its produc- 

 tion ; its absence is due, on the contrary, to a more complete coajjtation of these 

 same parts, which exists in those animals in which this sound is not produced. 



2d. The Penis. — The penis is the male organ of copulation. 

 It represents an erectile shaft, constituted principally by the corpus 

 cavernosuni, and supports along its entire length the urethral canal. 

 In the study of the exterior of the horse, however, we shall occupy 

 ourselves only with the free 'portion of this organ, which in a state of 

 relaxation is contained within the sheath, and appears externally only at 

 the moment of erection, when the blood distends and elongates it. 



It then appears covered by a fine, unctuous, glistening skin, sometimes rosy 

 and marbled in the places deprived of pigment. Limited at its base by a sort of 

 circular cul-de-sac, it has an almost cylindrical form, excepting at its free 

 extremity, where it suddenly enlai-ges. The latter, known under the name head 

 of the penis, and notched below and behind {sub-urefhml notch), is hollowed in its 

 middle by a shallow excavation which surmounts a round eminence formed by the 

 extremity of the corpus cavernosum, and in the centre of which opens the 

 urethral tube, projecting about one or two centimetres. Above the latter is the 

 urethral sinus, a spacious bilocular cavity, often filled with hardened sebaceous 

 matter {the bean), which may compress the urethra and interfere with micturition. 



It is the erectile tissue of the urethra, altogether independent of that of the 

 corpus cavernosum, which composes the head of the penis. At the beginning of 

 erection the latter alone is dilated so as to give the necessary rigidity to the 

 organ to penetrate the genital passages of the female. As soon as the penis is 

 inserted, the urethra dilates and gives to the free extremity of the organ the 

 aspect of a mushroom or the nose of a watering-can, as is seen in the stallion 

 immediately after the ejaculation of the semen. 



Under ordinary conditions the head of the penis is not visible at 

 the entrance of the sheath : it is concealed bv the folds of the skin. It 

 is incorrect for painters and sculptors to represent this part almost with 

 the same disposition as that which it affects in man. 



The penis of the entire horse is more voluminous and more firm 

 than that of the gelding ; but in this respect it differs much in different 

 animals. These variations have not, as is generally believed, any 

 influence upon the qualities of horses which are destined for reproduc- 

 tion ; it is the same with those variations which concern the head of 

 the penis, which is often very different in different stallions of the same 

 race, the same form, and equal ardor. 



It is more important to assure ourselves that the penis moves with 

 ease in the interior of its protecting envelope. The stallion has quite 

 frequent erections ; it is common even to see him masturbate, either in 

 the stable or at rest when he is harnessed. When these erections occur, 



