FORM AND ACTION OF THE FOOT. 19 



•dry and brittle, when the movements of the horse cause 

 it to break np and fall off. 



The frog, when it takes a bearing on the ground, 

 wears off in shreds. A frog which takes no bearing 

 ■dries up, and sometimes a large, superficial layer is cast 

 -off. Though the softest of the horny divisions of the 

 hoof, the frog is able to withstand wear and tear as well 

 as any of the others. Being elastic and resting upon soft 

 tissues, it is able to yield to any undue pressure and 

 leave the firmer horn of the wall and bars to sustain the 

 greater strain. The growth of the frog depends a great 

 deal upon the form of the back parts of the wall. If the 

 heels become overgrown, the frog is removed from bear- 

 ing and consequently wastes. High heels have always 

 between them a small frog. On the other hand, low, 

 weak heels have always a large frog, and the explanation 

 is that the increased bearing thrown on the frog causes 

 greater development. 



Properties of Horn. — Horn is light, hard, tough, 

 and elastic, properties most essential to its usefulness as 

 a i:)rotector of the foot. Horn is porous, and absorbs 

 moisture. Too much moisture in horn weakens it, and 

 therefore it must be remembered that the natural pro- 

 tection against this is the hard outer layer of the hoof. 

 "When this layer is rasped off, moisture is more easily 

 absorbed until the dry, hard surface is restored by 

 ■exposure and friction. 



Horn is a bad conductor of heat, and thus an equally 

 .good protective against the effects of snow in some coun- 

 tries, and of hot, dry sands in others. With a sound, 

 thick hoof, the application of a red-hot shoe produces 

 very little effect on the internal structures, provided, of 

 course, it remain in contact only a reasonable time. 

 With a foot protected by a thin layer of horn, fitting a 

 red-hot shoe must be done quickly, or it may damage the 

 soft tissues. 



Dissection of the Foot. 



So far we have only described the outer covering of 

 the foot and the structure from which it grows and by 



