116 THE MECHANICAL FUNCTIONS OF THE FOOT. 



is no exceptioD. The character and extent of these changes of 

 form, and how and at what times they occur, are points which 

 have been studied both in living and dead hoofs, though results 

 vary greatly, and in some instances even contradict one another. 

 This is explained partly by the different interpretations of 

 different observers, partly by the difference of the objects 

 examined, and partly by variations in methods of examination, 

 though it is also probable that contradictory results have, in 

 certain cases, been caused by unappreciated or doubtful 

 anatomical conditions in the hoof. 



Historical. — The elasticity of the hoof was recognised even 

 in the last century by Lafosse, jun., and J. Clark, although 

 they attributed it to the elasticity of the horn alone. In 

 1810 Bracy Clark went a step further. He referred the 

 elasticity of the hoof to the formation of the horny capsule, 

 which he divided into three chief paits — wall, sole, and frog. 

 He also laid great stress on the flattening of the concavity of 

 the sole, and the driving apart of tlie heels by the frog at the 

 moment when weight was placed on the foot. He concluded 

 that any interference wdth this lateral movement of the heels 

 by the shoe might be injurious, and his observations were, 

 therefore, of great practical importance, for they form part of 

 the foundation of our present system of shoeing. The shoe he 

 recommended had no heels, possessed a perfectly horizontal 

 bearing surface, and had nail holes distributed through its 

 anterior half only. A Frenchman, Perier, attacked these 

 views to some extent in 1835, for while he allowed that the 

 sides of the bearing surface of the hoof might move slightly, 

 he denied that the heels as a whole did so. An English 

 experimenter, Gloag, of the Army Veterinary Department, 

 working on both livino' and dead hoofs, initiated new ideas in 

 1849. He found no lateral movement, no sinking of the sole, 

 but only a slight sinking of the bulbs of the heel. Next 

 year, however, Gloag's results were contradicted by Eeeve. 

 In order to demonstrate the descent of the sole in the living 

 horse, he used a shoe which carried between the quarters 

 a cross bar provided on the upper side with small upright 

 spikes. After the horse had been walked a few steps, the 

 hoof w^as examined, but showed nothing to indicate that the 

 sole descended. The horse was then trotted and galloped ; 



