172 HORSE AND MAN. 



This variation is a provision of Nature to enable the 

 hoof to adapt itself to the altered condition it has to 

 meet hard horn to hard ground, soft horn to soft 

 ground. 



4 In this way we can account for the influence of 

 locality upon the shape of the foot. On hard dry 

 ground the hoof is dense, tenacious, and somewhat 

 small, with a concave sole, and a little but firm frog ; 

 while in marshy regions it is large and spreading, the 

 horn is soft and easily destroyed by wear, the sole is 

 thin and flat, and the frog is only an immense spongy 

 mass, which is badly fitted to receive pressure from 

 even hardened soil. 



4 In a dry climate we have an animal small, com- 

 pact, wiry, and vigorous, travelling on a surface which 

 demands a tenacious hoof, and not one to prevent 

 sinking. In the marshy region, we have a large, 

 heavy, lymphatic creature, one of whose primary 

 requirements is a wide, flat foot to enable it to travel 

 on a soft, yielding surface. 



' Change the respective situations of these two 

 horses, and Nature immediately begins to transform 

 them and their feet. At first the light, excitable, 

 vigorous horse, with its small vertical hoofs and con- 

 cave soles, so admirably disposed to traverse rocky 

 and slippery surfaces, is physically incompetent to 

 exist in low-lying swamps. The unwieldy animal, 



