THE EAR, THE EYE, THE SKIN, AND THE FOOT 135 



and the sole, and extending considerably below these on the 

 ground surface of the foot. Thus the frog receives the greatest 

 amount of concussion, but it is seldom injured, for its horn is of 

 very elastic consistency. The inner surface presents a well- 

 marked median cleft. The superior surface has the "frog stay" 

 which aids to bind the frog to the overlying parts. 



The physiologic movements of the hoof are due to the fact 

 that the foot is never at rest. The constant shifting of the weight, 

 even when standing, changes the shape of the hoof. Adams has 

 grouped these changes of form into (1) An expansion or widening 

 • of the whole back half of the foot from the coronet to the lower 

 edge of the quarters. This varies between yij and ^ inch. (2) 

 A narrowing of the front half of the foot, measured at the coronet. 

 (3) A sinking of the heels and a flattening of the wings of the sole. 

 These changes are more marked in the half of the foot that bears 

 the greater weight. In order to keep the foot healthful these move- 

 ments must be maintained with regularity. When the horse is 

 allowed to stand in the stable for days without exercise the results 

 are bound to show in the feet as pathologic changes. 



