THE LEGS. 39 



alternate ; and though two or three, or even all four feet may be 

 in the air at the same instant of time, they never leave the ground 

 nor alight upon it again simultaneously : by such a mode of action 

 the purposes of progression are excellently served on the one hand, 

 while on the other, the machine experiences no such concussion as 

 it would have done had there existed but three legs, or had two of 

 them come to the ground simultaneously, as is the case sometimes 

 in gallopping and leaping. 



One advantage more accruing from the gift of four over a less 

 number of legs is, that, having two before and two behind, the 

 quadruped is enabled to use either pair as weapons of defence : the 

 horse can rear or kick against his enemy; indeed, the hind legs 

 may be said to be the horse's especial armaments against his foes. 

 Some animals use their fore-legs in the way we do our arms, 

 having claws instead of hoofs, which serve them after the manner 

 of fingers : this they could not do were they not provided with 

 two hind-legs, upon which they have the power of sitting or sup- 

 porting themselves while their fore-limbs are otherwise employed. 



The Position, as well as the number of the limbs of the 

 quadruped, evinces excellent contrivance of design. Not only 

 have the limbs to support the body, but they have to carry it 

 from place to place, and at the same time to move themselves 

 under their burthen with more or less velocity. In a three-legged 

 stool, or in a four-legged form or table, the legs are placed at the 

 circumferent parts or projecting angles, as far apart as possible 

 from each other, the objects being to extend the base or standing, 

 and at the same time avoid the risk of the legs coming at any 

 time, from weight imposed too near the edge, within the centre of 

 gravity, and thereby proving incapable of saving the stool or table 

 from upsetting. In these cases stability and strength is all that is 

 required ; but in the instance of the vital machine, not only are 

 strength and stability needed, but facility of motion likewise; 

 and extension of the sphere of the base or standing, which would 

 have better insured the one, would have added difficulties or im- 

 pediments in the way of the other. 



Nature has placed her props of support at the extreme points 

 or salient angles of the animal machine, and longitudinally has 



