344 DEFOEMITIES AND DISEASES OF THE HOOF. 



toes and low heels, and in which the anterior and posterior 

 margins, viewed from the sides, form an angle of less than 

 45° with the earth. The more oblique the hoof, the more 

 rapidly does contraction proceed, whatever the previous condi- 

 tion of the heels. Despite every care in shoeing, contraction 

 may still occur in consequence of the altered direction of the 

 walls at the heel and of the greatly increased load they are 

 called on to bear. It is the excessive pressure on oblique and 

 inw^ardly-directed heels, in the absence of counter-pressure on 

 the sole and frog, which so rapidly produces the change in form. 

 At the same time, instead of the coronary and bearing margins 

 of the heels being equally exposed to the expanding strain when 

 weight is thrown on the foot, dilatation occurs only at the 

 coronary margin, which is, therefore, continually in tension, 

 while the bearing margin is fixed or even thrust from all sides 

 towards the centre of the sole. A well-developed frog and 

 strong bars, especially when exposed to the counter-pressure 

 of the ground, prevent contraction. If, however, the parts 

 are weak or diseased and the horny frog no longer bears 

 weight there is nothing to oppose its progress. It has even 

 been suggested that a small or diseased frog and weakened bars 

 form the sole cause of contraction, a view in a measure sup- 

 ported by the following examples. 



In severe thrush in flat feet the portion of the frog 

 marked &, in fig. 35, may be lost. Under such circum- 

 stances the hoof contracts precisely to the extent left vacant 

 by tlie portion lost. In upright hoofs, on the other hand, even 

 when this part of the frog is lost, contraction does not occur. 

 The cause of contraction is, therefore, not thrush, but the pres- 

 sure of the body-weight, which forces the w^alls of the heel 

 downwards, forwards, and inwards. On the same day two 

 young carriage horses were shod for the first time. In one 

 horse the front hoofs formed an anole of 40 and in the other 

 of 55 with the ground. All four hoofs were sound. These 

 animals were shod in precisely the same way for a year, but^ 

 despite similar treatment, the fiat hoof was visibly contracted 

 as compared with the other. In this case the greater weight 

 thrown on the posterior half of the hoof was not the only cause. 



A pair of trotting horses, of similar age, size, weight, and 

 breed, had each weak fore-heels. In one case, however, th& 



