CARTILAGES OF THE FOOT 229 



pying the whole of the space, and answering several 

 important purposes, it being an elastic bed on which 

 the navicular bone and the tendon can play with 

 security, and without concussion. This will be under- 

 stood by referring to Plate vi, fig. lo, /. Thus all 

 concussion to the cartilages of the foot is prevented, 

 and these cartilages kept asunder, and the expan- 

 sion of the upper part of the foot preserved. This 

 mechanism is both beautiful and important. The 

 yielding and elastic substance of the frog is pressed 

 upon by the navicular bone as well as the tendon and 

 the pastern, and being incapable of condensing into 

 less compass, is forced out on each side of them, and 

 expands the lateral cartilages ; and these again, by 

 their inherent elasticity, revert to their former situation, 

 when they are no longer pressed outward by the frog. 

 It thus appears that by a different mechanism, but 

 both equally admirable and referable to the same 

 principle, namely, that of elasticity, the expansion of 

 the upper and lower portions of the hoof are effected, 

 the one by the descent of the sole, and the other by 

 the compression and rising of the frog. The pre- 

 servation and usefulness of the limbs of the horse are 

 chiefly maintained by this upward expansion, when 

 the destructive methods which are adopted in shoeing 

 are calculated to destroy the expansion beneath. 

 From the long-continued and violent pressure on 

 the frog in draught-horses, and conveyed from the 

 frog to the cartilage, inflammation is frequently pro- 

 duced, and too often terminates in the cartilages 

 being turned into bony matter. 



