432 DISEASES OF THE HOESE. 



When thrush is present as a complication, its cure must be sought 

 by measures directed under that heading. If sidebones, ringbones, 

 navicular disease, contracted tendons, or other diseases have been the 

 cause of contracted heels, treatment vi^ill be useless until the cause is 

 removed. 



SAND CRACKS, 



A sand crank is a fissure in the horn of the v?all of the foot. These 

 fissures are quite narrow, and, as a general rule, they follow the di- 

 rection of the horny fibers. They may occur on any part of the wall, 

 but ordinarily are only seen directly in front, when they are called 

 toe cracks ; or on the lateral parts of the walls, when they are known 

 as quarter cracks. (Plate XXXVI.) 



Toe cracks are most common in the hind feet, while quarter cracks 

 nearly always affect the fore feet. The inside quarter is more liable 

 to the injury than the outside, for the reason that this quarter is not 

 only the thinner, but during locomotion receives a greater part of the 

 weight of the body. A sand crack may be superficial, involving only 

 the outer parts of the wall, or it may be deep, involving the whole 

 thickness of the wall and the soft tissues beneath. 



The toe crack is most likely to be complete — ^that is, extending from 

 the coronary band to the sole — while the quarter crack is nearly al- 

 ways incomplete, at least when of comparatively recent origin. Sand 

 cracks are most serious when they involve the coronary band in the 

 injury. They may be complicated at any time by hemorrhage, in- 

 flammation of the laminse, suppuration, gangrene of the lateral car- 

 tilage and of the extensor tendon, caries of the coffin bone, or the 

 growth of a homy tumor known as a keraphyllocele. 



Causes. — Eelative dryness of the horn is the principal predispos- 

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

 prolific cause of cracks in the horn than alternate changes from 

 damp to dry. It is even claimed that these injuries are more common 

 in animals working on wet roads than those working on roads that 

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

 tainous countries. Animals used to running at pasture when trans- 

 ferred to stables with hard, dry floors are more liable to quarter 

 cracks than those accustomed to stables. Small feet, with thick, hard 

 hoofs, and feet which 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. 



