42 SEATS AND SADDLES. 



peculiar shape and position, a different function from 

 that of the other vertebrae, all of which evidently ad- 

 mit of movement towards it, within certain limits, 

 whilst this one, not being adapted for this purpose, may 

 so far be considered to be intended for the centre of 

 motion. But the construction of the horse's legs, and 

 the relative position of the various bones composing 

 them, furnish us with very clear proof of this same 

 vertebra being the real centre of motion when the 

 horse is in action. For there is one bone in each of 

 the hind and fore legs through which the remainder of 

 the limb acts as a lever on the whole frame, either for 

 the purpose of propelling it (hind legs), or supporting 

 and lifting it (fore legs). These are the thigh-bone t, 

 and the arm-bone v (fig. 4), whose upper ends have 

 their fulcrums or points of support in the hip-bones A 

 and shoulder-blades D (Plate I.) respectively, the power 

 being applied through the medium of the remaining 

 portions of the legs at their lower ends. Now the 

 greatest result of lever action is exercised at a right 

 angle to the lever, and drawing the lines P Q and R S 

 through the lower ends of these two bones at right 

 angles to them, we find that they intersect (or cross) 

 each other precisely at this same fourteenth vertebra. 

 The figure shows us, indeed, the horse in a state of rest, 

 and not in action; but it is necessary to remember that 

 the propelling action of the hind leg commences, and is 

 precisely most powerful, when the thigh-bone is in this 

 position, diminishing in intensity as the leg is stretched 

 out towards R, and the angles become flatter; whereas, 

 on the contrary, the supporting and lifting action of 

 the fore leg ends, the arm-bone being as shown in the 

 figure, and is also most intense, diminishing as the fore 



