48 SCIENTIFIC HORSESHOEING. 



external branches by a median cleft, each branch forming a 

 rounded elastic eminence at the heels where they cover the 

 angles of inflection of the wall. The internal face of the frog 

 is indented with pores like the sole, and is molded to conform 

 to the body of the sensitive frog, having a triangular fissure 

 divided into two channels by a spine or ridge-like spur, called 

 the frog-stay, into and over which the sensitive frog is bedded. 

 The frog, like the sole, exfoliates or scales off by usage and 

 growth, and is the natural buffer of a healthy foot when al- 

 lowed to come in contact with the srround. 



iD' 



Development of the Hoof. — The horny substance consti- 

 tuting the hoof of a horse is of a fibrous nature, formed of mi- 

 nute hair-like tubes, cemented together by a tenacious opaque 

 matter, taking its general color from the skin of the limb to 

 Avhich it adjoins ; the inner face of the wall, however, is al- 

 ways of a light tint. The horny tissue of the hoof, being a de- 

 pendency of the skin, is developed like it; that is, by cells in 

 rows and layers. The perioplic ring forms the beriople; the 

 coronary cushion, the wall, and the velvety tissue, the sole and 

 frog. The consistence of the horn in the wall is dense, solid 

 and compact, while that of the sole and frog is of a scaly, 

 spongy nature. The growth of the wall of the hoof is constant 

 or indeflnite, but the sole and frog, after attaining a certain 

 thickness, exfoliate and fall off, unless prevented by shoes from 

 maintaining their natural flexibility. See colored plates. 



It may here be noted that the angle of wall of the hoof in 

 front varies from forty-five to fifty-six degrees. The inner face 

 of the wall at the middle of the toe is in line with the frog-stay, 

 and in mules frequently shows a more or less prominence of base 

 toward the lower margin of wall, which corresponds to a ver- 

 tical depression in the coffin-bone, and it is not improbable that 

 it serves the same purpose as the frog-stay — to maintain the posi- 

 tion of the coffin-bone, and prevent its rotation within the hoof. 



