FKICTION AND THE HOOF. 31 



was therefore unable to wear away the hoof by 

 friction. As may be seen from the illustration, the 

 hoof had curled round like a ram's horn, forcing the 

 animal to walk on the side of the hoof and not on 

 its face. As to the frog and sole, it is not easy to 

 identify them, so completely are they enveloped by 

 the overgrown horn of the wall. 



The accompanying illustration is drawn from a 

 specimen in the Museum of the College of Surgeons. 

 It may be seen among the series of epidermal 

 appendages, and forms a good reply to those persons 

 who think that the hoof was formed for marsh v ground. 



Should the reader be a keeper of cage birds, 

 especially canaries, he will remember that both the 

 claws and beak are apt to be overgrown for want of 

 the friction to which they would be subjected had 

 the bird lived a natural life. Unless both beak and 

 claws be artificially cut, as a succedaneum for the 

 natural friction, the bird will be greatly incon- 

 venienced, and may probably die from inability to 

 procure food. 



A similar result of overgrowth for lack of friction 

 is often seen in rabbits, mice, rats, and other rodent 

 animals. One of the incisor teeth is accidentally 

 broken, and the corresponding tooth of the opposite 

 jaw not having anything to rub against, continues 

 to grow until the tooth attains an astonishing length. 



