358 DEFORMITIES AND DISEASES OF THE HOOF. 



lameness, though even hoofs with very strong walls do not 

 always escape it. 



The comparative frequence after the first shoeing of this 

 form of contraction in horses which work on hard dry ground 

 leaves little doubt that desiccation of the hoof and want of 

 counter-pressure are its principal causes, though these again 

 depend upon the artificial conditions set up by shoeing. All 

 who have carefully studied the question agree that the change 

 in the normal direction of the heel wall is produced by inter- 

 ference with the expansion of the hoof. Dominik, who first 

 described the condition, refers it to interference with expan- 

 sion at the coronet. The tendency to contraction is, therefore, 

 greatest at the coronary margin. Fambach regards it as due 

 partly to excessive obliquity of the heel wall, and to removal 

 of support from the frog. In this connection it may be pointed 

 out that almost all hoofs that show local contraction of the heel 

 wall are otherwise sound. The contraction at the coronary 

 margin probably results as follows : — By lifting the frog clear 

 of the ground, the shoe more or less prevents expansion of the 

 bearing margin of the heel. The coronary margin, being the 

 most yielding part, spreads outwards under the continuous strain 

 of the body-weight. The direction of the coronary papillae is 

 changed, the horn they secrete takes a more perpendicular 

 course, and the wall, previously quite straight, shows, after 

 eight to ten days, an apparent slight contraction opposite the 

 lower third of the coronary groove. By grov*^th from the 

 coronet the contracted part is thrust downwards ; finally it 

 reaches the centre of the heel wall, where it produces an 

 appearance resembling an hour-glass. Arrived at the bearing 

 margin it gradually disappears just as it had appeared above. 

 The effects, however, continue, for on close observation it will 

 be seen that the entire portion of wall involved has become 

 more upright, so that instead of pointing outwards and back- 

 wards it now points forwards and inwards. In other words, 

 the heel walls previously diverged ; now they converge. The 

 hoof has become narrower at the bearing margin of the heels. 

 When the weight is greater on one side and the hoof very 

 flat, well-marked furrows may appear on one or other heel wall, 

 as can be proved by comparative measurements of the hoof 

 immediately before the first shoeing and a few weeks or months 



