MECHANISM OP THE FOOT. 



731 



power (P) acting upwards by the pull on the tendon due to the 

 contraction of the muscle; while the fulcrum (F) is the ground 

 at the toe. The relations of power and weight in a state of 

 equilibrium, are: — 



W 



WF : PF. 



Hence the farther away the toe is from a perpendicular drawn 

 through the pastern joint (when the animal is standing at rest), 

 the greater will be the strain thrown on the back tendons, both 

 when standing still and during movement. From this the following 

 practical deductions may be drawn: — 



P W ( F 



Fig. 185. — Mechanism of the horse's foot. 



(1) That the longer the hoof is allowed to grow (supposing the 

 heel and toe to increase equally in length), the severer will be the 

 strain on the back tendons ; for the efiect of this increased growth 

 will be to still further remove the toe beyond the perpendicular 

 which passes through the fetlock joint. 



(2) A similar effect will be produced if the heels be lowered 

 without reducing the toe, or if a shoe with a thick toe and thin 

 heels be used. 



(3) The strain on the tendons will be lessened if the reverse of 

 the operations described in (1) and (2) be performed. 



For the sake of simplicity of explanation, I have considered the 

 action only of the perforans. tendon, which, however, is aided by 

 the other back tendon (the perforatus). 



