118 FORM AND ACTION. 



shewing whereabouts the power for fast and efficient galloping 

 should be lodged. 



Although we are unable to account for the production of muscu- 

 lar motion, the principles directing its agency on the framework of 

 the skeleton are clearly those of mechanics ; the lever being the 

 power according to the laws of which locomotion may be said to 

 be effected. The bones constitute " a series of levers," on which 

 the muscles operate with more or less advantage and effect, de- 

 pending upon their length, their position, their prominences or pro- 

 cesses, &c. Of levers we know there are three kinds; and of each 

 of them examples may be found in the animal economy. 



For instance, the extension of the fore-limb is effected on the 

 principle of that description of lever in which the fulcrum, or axis, 

 or centre of motion, is situated between the moving power and the 

 resistance or part to be moved ; whereas, in the flexion of the limbs, 

 both fore and hind, in general, the power holds the intermediate 

 place. When the arm is extended, the elbow-joint becomes the 

 fulcrum ; the point of the elbow, to which the muscles are attached, 

 the power ; and the limb itself the weight or resistance. When 

 the arm is flexed, the elbow-joint is still the fulcrum, but the power 

 is now transferred to the radius, the resistance being the same : 

 thus furnishing us with an example of a lever of another kind, one 

 in which the power is intermediately placed. A third kind of lever 

 is exemplified in the extension of the hock, the foot being upon the 

 ground : the foot now becoming the fulcrum, the point of the hock 

 the seat of the power, and the resistance or weight to be moved 

 forward, falling down the shaft of the tibia, operating upon the hock- 

 joint. The same lever appears in the extension of the fetlock 

 after it has been flexed in action for the purpose of pointing and 

 fixing the toe in the ground, which then becomes the fulcrum, 

 the power being exerted at the summit of the sesamoids, and the 

 resistance bearing upon the large pastern. These laborious duties 

 in the work of progression which the hind fetlocks, in concert with 

 the hocks, have to perform, acccount for their failure in horses 

 doing much heavy draught, or that have hunted or raced much in 

 heavy grounds. 



It being a law in mechanics, that any deviation of the direction 

 of the power from a perpendicular line to the arm of the lever is 



