122 THE MECHANICAL FUNCTIONS OF THE FOOT. 



apparatus in such a way as to permit all parts of the hoof to be- 

 examined. He experimented both on the animal at rest and 

 in motion, and demonstrated movements in all parts of the wall. 

 His researches prove the occurrence of expansion at the 

 coronary and bearing surfaces of the heels, and simultaneous 

 depression of the sole at the moment when the fetlock joint was 

 most extended (or dorsally flexed). Dominik's experiments, on 

 the other hand, which extended to both living and dead hoofs, 

 seem rather to favour Lechner's rotation theory. 



The complicated construction and form of the hoof, its con- 

 nection with the limb, and the continuous variation of the 

 conditions during movement, prevent our attaching the same 

 importance to post-mortevi experiments as to those made on 

 the living animal. Infra-vitam experiments, moreover, have 

 a greater claim to consideration, partly because of the great 

 number which have been performed, and partly because of the 

 agreement in their results. The following principles, based on 

 numerous experiments, agree in great part with the more 

 important experiments both old and new, and only conflict with 

 those of Lechner and a few others. 



The point of rotation is the pedal joint. At the moment 

 when the foot first meets the ground pressure is slight. It 

 increases as the limb approaches the perpendicular, and is 

 greatest when the fetlock is most markedly extended, after 

 which it diminishes until the hoof is raised from the ground. 

 The changes in form are most marked at the moment of 

 greatest extension (dorsal flexion) of the fetlock joint. They 

 consist, firstly, in lateral expansion of the entire heel region ; 

 secondly, in contraction of the coronary border of the anterior 

 half of the hoof ; thirdly, in diminution in the height of the 

 hoof as a whole, with simultaneous descent of the bulbs, and, 

 fourthly, in descent of the sole. These changes occur simul- 

 taneously and bear a direct proportion to the weight imposed 

 on the foot. Leisering accepts Peters' depression theory as 

 explaining these, with, however, the qualification that he 

 regards the moment of greatest change in form as coincident 

 not with the removal of weight but with greatest extension (or 

 dorsal flexion) of the fetlock joint. The extent of displace- 

 ment of the heels and sinking of the sole is slight, and varies 

 from 0'5 to 2 millimetres, seldom more. 



