STRUCTURE OF THE HORSE'S HOOF. 63s 



tinually growing downwards from this coronary cushion 

 to meet the demands of attrition ; and if hindered from 

 coming into contact with the earth, would increase to an 

 indefinite length. The fibres of the horny sole follow 

 exactly the same direction as those of the wall, and are 

 destined, like them, to come more or less in contact with 

 the ground, and support the weight of the body. They 

 vary in length, being shortest towards the middle of the 

 sole, and longest at their junction with those of the wall. 

 At this part the sole is equal to the wall in thickness. 

 Unlike the wall fibres, however, those of the sole only 

 attain a certain length, when the horny matter of which 

 they are composed dries and fractures like the human 

 hair. By this means the sole seldom, if ever, becomes 

 abnormally thick in a state of nature, and the loose fiakes 

 that are continually forming are not only active agents in 

 retaining the moisture necessary for maintaining the elas- 

 ticity and proper development of horn, but also play the 

 part of so many pliant defences to guard the plantar surface 

 of the hoof from injury by extraneous substances, with 

 which it is always coming in contact. 



The frog is a most important organ. It is ana- 

 logous to the elastic pads on the foot of the dog, cat, 

 camel, elephant, and other creatures. It is designed, like 

 these pads, to meet the ground, diminish the jar to which 

 the limb would otherwise be subjected, especially 

 during violent exertion, and, by its india-rubber-like pro- 

 perties, prevent slipping. In conjunction with the ad- 

 mirably constructed vascular cushion, or ' sensitive frog,' 

 lying above it, and contained between the wings of the 

 pedal bone, it acts as a protection and support to the large 



