42 MANUAL FOR ARMY HORSESHOERS. 



of the frog. These ridges terminate behind in the bulbs of the hoof. 

 Between the sides of the frog and the bars are two cavities called the 

 commissures. 



The upper surface of the frog is the exact reverse of the lower. It 

 has in the middle a ridge of horn called the frog stay, which assists 

 in forming a firm union between the frog and the frog corium. 



The function of the frog is to assist the digital cushion in breaking 

 the jar or concussion, to prevent slipping and to produce expansion 

 and contraction upon which normal blood circulation in the foot 

 depends. (See pars. 33 and 34.) 



STRUCTURE OF HORN". 



32. The horn of the hoof consists of fine fibers, similar to the hair in 

 structure, held together by a cementing substance. The horn fibers 



» run downward and forward and are straight in the wall and sole and 

 wa^^ in the' frog. The fibers of the frog are finer, softer, and more 

 elastic than those of the wall and sole. 



The wall wears away at the lower border, or, if the animal is shod, 

 the growth is removed in preparation for shoeing. The sole and frog 

 scale off when the fibers have reached the proper length; they should 

 not be cut except when necessary in the treatment of a diseased 

 condition. 



MOISTURE. 



33. The wall of the healthy hoof is, by weight, about one-fourth 

 water, the sole more than one-third, and the frog almost one-half. 

 This water is supplied by the blood and preserves the horn in a 

 tough and elastic condition. The periople, which covers the wall, 

 prevents the evaporation of water, and therefore should never be 

 rasped. As there is no similar covering for the sole and the frog, 



' the layers of horn on their exposed surfaces dry out and die. The 

 dead layers are hard and brittle, and gradually fall or flake off; but, 

 as they preserve the moisture in the layers of live horn beneath, as 

 little as possible should be removed in preparing the hoof for 

 shoeing. 



EXPANSION AND CONTRACTION. 



34. ^Vhen the foot is placed on the ground the frog comes in 

 contact with the ground and is forced upward, compressing the 

 digital cushion against the deep flexor tendon and the bony frame- 



