iMECHANISM OF THE FOOT. 721 



(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). 



THE FOOT AS A SPRING.— Besides the action of the foot as 

 a lever, it also serves as a spring; the mechanical advantages of 

 the one being directly opposed to those of the other. Thus, the 

 better the leverage, the worse the spring; and vice versa. It is 

 evident from the considerations already discussed, that the lower 

 the heels with relation to the toe and the less upright the 

 pastern, the greater freedom does the leg enjoy from concussion; 

 although the power which it derives from the back tendons will 

 work at a greater mechanical disadvantage. 



Fig. i8i.— Slope of 50^. Fig. 182.— Slope of 55^. 



COMPARATIVE LEVERAGE AND SPRING OF THE FORE 

 AND HIND FEET. — Were there no such thing as injury to the 

 limbs from concussion, we would naturally get the hoof as upright 

 as practicable, so as to allow the back tendons to work at the 

 greatest possible mechanical advantage. The bad effects of con- 

 cussion have, however, to be provided for, especially as regards 

 the fore-feet, which are much more liable to suffer from them 

 than are the hind feet. It is impossible to determine with exact- 

 ness the proper respective slopes of the fore and hind hoofs; but 

 from an examination of a large number of feet which have never 

 worn iron, I conclude that the former should be about 50° and the 

 latter not less than 55° (Figs. 181 and 182). It is instructive 

 to note that a considerable amount of power of propulsion is 

 lost by the angle of inclination of the hind feet being too small ; 

 which condition is also a predisposing cause of spavin (p. 254). 

 This is a practical point which is very important to owners, and 

 especially to those who keep race-horses. 



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