102 THE GKOWTH OF THE HOOF. 



horse which has been employed in field work, and has not been 

 much on hard roads, will show that they are of the same size and 

 length. If the hoof be marked with a rasp or file, it will be 

 found, after some time, that the mark is receding from the 

 coronary border and approaching the ground ; in a word, it is 

 " growing " downwards. If, however, the horse is not working 

 (or is shod) its hoofs will become longer. 



Both appearances — the recession of the mark and the elonga- 

 tion of the hoofs — show tliat the latter grow from above down- 

 ward, just as do our nails and hair. The explanation, however, 

 why the unshod hoof of a horse working on the land remains 

 the same length and the shod hoof increases, is to be found in 

 the fact that in the first instance as much horn is worn away 

 from the bearing surface as is produced above, whilst in the 

 other, wear is prevented by the protection afforded by shoes or 

 by the absence of movement. 



Growth seems to be regular, at least in the wall. Hartmann, 

 who made numerous experiments to discover w^hether the toe 

 grew faster than the (quarters or heel, always found that the 

 fine transverse incisions, which he made at similar distances 

 from the coronary border (though at different points of the 

 circumference of the foot), preserved an equal distance from the 

 coronary border during their passage downwards, so that he 

 concluded growth was equal at all points in the wall. It 

 being so difficult to study the growth of horn in the sole and 

 frog, it is at present not possible to say whether it takes 

 place there more rapidly than in the wall. Hartmann says 

 the frog grows most rapidly when the animals are kept hard 

 at work, though only then if the part comes in contact with 

 the ground. 



Grohn ascertained negatively the influence exerted by nerve 

 supply upon the growth of the hoof, and found that when the 

 digital nerves of one leg were divided, the wall of the corre- 

 sponding foot grew more rapidly than that of its fellow. The 

 time required for the horn to grow from the coronary border 

 to the ground edge of the wall varies greatly, being from 

 eight to sixteen months at the toe, six to ten months at 

 the quarters, and four to six months at the heel. The length 

 (or height) of the wall and the angle it makes with the 

 ground must, of course, be taken into consideration. If we 



