ART OF SHOEING. 527 



The frog is a triangle of very elastic horn, filling up a 

 space of corresponding figure in the sole ; it extends nearly 

 two- thirds through the centre and bottom surface of the 

 foot. At its anterior part or apex, it consists of one ridge ; 

 about one-third of its length from the point, the organ 

 divides into two equal parts, leaving an interspace termed 

 the cleft. By this arrangement, provision is made for motion 

 in the posterior parts of the hoof. 



The frog is composed of horn of a fine tough texture, 

 more elastic and pliable than the sole ; besides, it covers an 

 exquisitely elastic organized structure of its own shape. 



Some notice of the bones of the foot may now be taken ; 

 on their form, relative position, and connection depends its 

 motion, which in the horse, physiologically considered, begins 

 where the radius terminates in the fore, and the tibia in the 

 hind limbs, that is, the knee and hock and all below enter 

 into the pedal function. 



The bones which enter into the construction of the foot 

 should be understood with reference to their particular func- 

 tions; to the required action of these solid parts, all other 

 structures concerned in the locomotive functions are made 

 subservient. 



The bones of the limbs belong to two distinct orders as 

 regards function, one of which, sustaining the weight, are 

 acted on, and are the levers which give velocity, and all 

 motion; the others are formed into projecting pulleys, but- 

 tresses, and also become levers in connection with the 

 shafts alluded to in the first order, of which the cannon, 

 pastern, coronary, and pedal bones, constitute those of the 

 foot extremity in both fore and hind limb, and of the latter, 

 there are two pairs, and two single bones in each extremity, 

 viz., the navicular, the two sessamoids, and the two splint 

 bones, with the pisiform in the fore, and the os calcis in the 



