406 BUllEAU OF ANIMAL INDUSTRY. 



extensor tendon, caries of the coffinbono, or the growth of u horny 

 tumor known as a keraphyllocele. 



Causes. — Relative drjaiess of the horn is the principal predisposing 

 cause of sand-cracks. Excessive dryness is perhaps not a more pro- 

 lific cause of cracks in the horn than alternate changes from damp to 

 dry. It is even claimed that these injuries are more common in ani- 

 mals working on wet roads than in those working on roads that are 

 rough and dry; at least these injuries are not common in mountainous 

 countries. Animals used to running at pasture when transferred to 

 stables with hard, dr}- floors are more liable to quarter-cracks than 

 those accustomed to stables. Small feet, with thick, hard hoofs, and 

 feet Avhich are excessively large, are more susceptible to sand-cracks 

 than those of better proportion. A predisposition to quarter-cracks 

 exists in contracted feet, and in those where the toe turns out or the 

 inside quarter turns under. 



Heavy shoes, large nails, and nails set too far back toward the 

 heels, together with such diseases as canker, quittor, grease and sup- 

 purative corns, must be included as occasional predisposing causes of 

 sand-cracks. 



Fast work on hard roads, jumping, and blows on the coronet, 

 together with calk wounds of tlie feet, are accidental causes of quar- 

 ter-cracks in particular. Toe-cracks are more likeh^ to l)e caused by 

 heavy pulling on slipper}' roads and pavements or on steep hills. 



Symptoms. — The fissure in the horn is ofttimes the only evidence 

 of the disease; and even this may be accidentally or purposely hidden 

 from casual view by mud, ointments, tar, wax, putty, gutta-percha, 

 or by the long hairs of the coronet. 



Sand-cracks sometimes commence on the internal face of the wjill, 

 involving its whole thickness excepting a thin laj^er on the outer 

 surface. In these cases the existence of the injury may be suspected 

 from a slight depression, which begins near the coronary band and 

 follows the direction of the horny fibers; but tlie trouble can onl}' be 

 positively diagnosed b}' paring awa}' the outside layers of horn until 

 the fissure is exposed. In toe-cracks the walls of the fissure are in 

 close apposition when the foot receives the weight of the bod}-, but 

 when the foot is raised from the ground the fissure opens. In quarter- 

 crack the opposite is true; the fissure closes when the weight is 

 removed from the foot. As a rule, sand-cracks begin at the coronary 

 band, and as they become older they not only extend downward, but 

 they also grow deeper. In old cases, particularly in toe-crack, the 

 horn on the borders of the fissure loses its vitality and scales off, 

 sometimes through the greater part of its thickness, leaving behind 

 a rough and irreg-ular channel extending from the coronet to the end 

 of the toe. 



