3(34 A Manual of Veterinary Physiology. 



be seen that it is on the wall of the foot where the horse's 

 weight is supported. On examining the horny wall, we 

 find that it is thickest at the toe, thinner at the quarter, 

 and thinnest at the heels. It is thickest at the toe owing 

 to the wear and tear of the foot at this part. As the frog 

 is the first to come to the ground, so is the toe of the wall 

 the last to leave it ; and when, as we have seen in studying 

 locomotion, the propulsion is given to the body by the toe 

 of the foot, we can understand how necessary it is to thicken 

 the part here. The toe of the wall appears to grow faster 

 than either the quarter or the heels, but this is more 

 imaginary than real. It is the tendency of the foot to grow 

 forward as well as downward which produces the illusion. 

 That the foot does grow forward may readily be determined 

 by experiment, for if we cut or saw a groove in the wall at 

 the coronet, say an inch or so from the heels, that groove 

 will in course of time be carried some considerable distance 

 forward. The exact amount can be determined b} T observ- 

 ing the obliquity of the horn fibres. The object of the wall 

 becoming thin towards the posterior part of the foot is to 

 allow of the elastic movement which we have described as 

 expansion and contraction. 



Two physical conditions have to be provided for in the 

 wall, viz., elasticity of the posterior part, and toughness of 

 the anterior portion. Some of the methods by which the 

 needful provision is made we have spoken of, but here is a 

 general summary of the subject : 



The posterior portion of the foot first receives the weight 

 of the body (certainly in all fast paces) : the expansion of 

 this part saves it from destruction, and the various pro- 

 visions which exist are considerably assisted by the fact 

 that the wall is thinner at the heels than elsewhere, and so 

 yields outwards ; but besides being thinner the wall of the 

 heel contains more moisture than the wall of the tot.', and 

 this moisture ensures its elasticity. The younger the horn, 

 viz., the nearer to the coronet at which the horn is taken, 

 the more moisture it contains, the further away from the 

 coronet the less moisture it contains, and the tougher and 

 more resisting the horn. 



