324 THE HOESE AND HIS STRUCTUBE. 



hard external horn of the crust, formed of flat laminae set 

 side by side, and admirably suited for clinging to pro- 

 jecting stones when the animal is picking its way over 

 steep or rocky ground. So sure-footed indeed is the 

 animal, that in most places where a man can climb on 

 his hands and knees an unshod horse can follow him. 

 The sure-footedness of the mule is proverbial, and yet 

 there is no appreciable difference in the form and struc- 

 ture of the two creatures. Indeed, the hoof of the ass is 

 formed exactly like that of the horse, and only differs 

 from it in being rather longer and narrower in proportion 

 to its size. Its horny crust is meant to be worn away by 

 constant friction against the hard ground, just as the 

 incisive teeth of the rodents are kept in order by perpetu- 

 ally gnawing hard substances. 



The paAving and scraping of the foot, which people are 

 apt to admire as a proof of " blood " or spirit, is owing 

 to the rapid growth of the front portion of the crust. 

 Being protected from friction by the shoe, it grows with- 

 out hindrance, and so disturbs the balance of the animal, 

 tilting it backwards just as we should be if we removed 

 the thick leather of the boot-heel to the toe. Not know- 

 ing that the iron shoe is in the way, the horse tries to 

 scrape down the front of the hoof, so as to bring him to 

 his proper bearings, and is actuated, not by exuberance 

 of spirits, but by uneasiness of foot. 



Then comes the sole, serving to protect the sensitive 

 interior of the hoof from the loose and sharp stones, and 

 falling off in successive flakes as it is worn out. Lastly 



