324 THE EXTERIOR OF THE HORSE. 



In the wild horse the continual growth, always compensated by a 

 proportional loss from wear, does not induce a deformity of the nail 

 but the case is different in horses which we utilize as motors, on 

 account of the shoe, which restrains the elasticity of the foot and 

 disturbs the normal growth of the hoof. In such cases the wall may 

 acquire an excessive length if the farrier does not take the care to 

 shorten the whole extent of its inferior border to the limits required by 

 the natural wear. As to the sole and the frog, their mode of exfoliation 

 is such that their thickness never becomes excessive ; they become dried, 

 cracked, and peel off spontaneously in more or less voluminous scales. 



The secretion of the horn is exaggerated by certain influences, as 

 the external temperature, the state of health or of disease, the nourish- 

 ment, etc. We know that the process is more active in w T arm than in 

 cold countries, in summer than in winter, in the healthy animal, abun- 

 dantly nourished, than in the diseased animal, suffering from bad 

 hygiene and an insufficient alimentation. This is so true that the hoof 

 itself often testifies, by the unequal zones of which it is the seat, of the 

 physical conditions or suffering which the horse has endured. 



Certain rammy or circled hoofs have in most instances no other 

 origin. 



Elasticity of the Foot. The digital extremity of the equidse, 

 below the pastern, is disposed so as to disperse or break the con- 

 cussions and the pressure which it receives during locomotion at 

 the moment when the body, at great speed, comes in contact with 

 the ground. Not only is the quantity of movement with which the 

 body is animated dispersed and decomposed by the inclined planes of 

 surface and of segment, but it is destroyed also by the intervention of 

 the elasticity of several organs which we will recognize. It is there- 

 fore already considerably lessened when it arrives at the hoof, where 

 it meets several elastic apparatus, whose mode of functional activity 

 we must rapidly review. These apparatus are : the perforans tendon, 

 the lateral cartilages, the plantar cushion, and the diverse parts of the 

 nail (the wall, the sole, and the frog). 



The first effect of the contact of the foot Avith the soil is the dis- 

 placement of the third phalanx from above to below in the interior of 

 the horny covering (Fig. 106). This movement of the bone is coun- 

 teracted by the mechanical action of three very evident causes : ante- 

 riorly and peripherally, by the adherence of the podophyllous and 

 keraphyllous tissues ; above and laterally, by the resistance of the 

 lateral cartilages ; finally, below, by the presence of the plantar apo- 

 neurosis and the plantar cushion. 



