DISEASES. 619 



tlie wall has been thinned down or partly removed. In other 

 cases it is adherent to the two borders of the crack, and this forms 

 a natural cicatrix. This horny column, of varying length and 

 strength, according to its age, presses upon the tissues beneath, 

 and gives rise to severe lameness. With time there is correspond- 

 ing atrophy of the podophyllous tissue, or even of the os pedis. 

 This is often followed by a marked deformity of the hoof, and 

 especially a deep fissure, parallel to the direction of the crack. 

 The soft tissues under the keraphyllocele often in time become 

 harder, in consequence of the disappearance of the papillae ; the 

 hoof then is no longer adherent to the tissues beneath, and so 

 incurable cracks are the result. A double wall or false quittor 

 have often also been observed. Thus deformed, the foot is always 

 subject to lameness, even if the crack is cured. Contraction or 

 atrophy of the frog have been observed with quarter-crack. 



IV. Progress, duration, termination. — Ordinarily, cracks once 

 existing become worse. From being superficial and imperfect 

 they become deep and complete as a natural result of the ordinary 

 motions of the foot. If rest and some hygienic attention can be 

 given, they may recover spontaneously, and disappear by the nat- 

 ural downward growth of the hoof. This fortunate termination, 

 however, is principally obtained when the crack is due to acci- 

 dental causes, without deformity of the foot. 



V. Prognosis. — Simple cracks, superficial and incomplete, 

 especially arising from the plantar border, almost always recover 

 under rational treatment, which has for its principal aim the pre- 

 vention of increase in the size of the fissure. Cracks starting from 

 the coronary band are always of a more serious nature, with a ten- 

 dency to increase easily. Still they are no longer to be consid- 

 ered incurable. Cracks in which the borders are much separated 

 by the motion of walking ; those which are oblique ; those whose 

 edges are incurvated inward ; those where a poi-tion of the wall, 

 is loose ; those which bleed, and those where there is a continued 

 irritation of the sub-horny tissues, are the most serious ; and so 

 much so, that they may require quite serious surgical interference, 

 and after all baffle the best skill of the operator. 



VI. Etiology. — The causes of cracks vary greatly, and are 

 often multiple in a single case. Seldom the result of accident, 

 they are most commonly the combined effect of both a predispos- 

 ing and an extraneous cause. A frequent one among others is 



