ACTS OF WALKING AND KUNNING. 495 



(fig. 240), the wing of a Bat (fig. 251), and the fore-paw of a 

 Squirrel or a Mole, we find the same bones as in the arm of 

 Man (fig. 223). And even in the fore-legs of the Ruminant 

 Quadrupeds, and in those of the Solidungula, or single-toed 

 animals (such as the Horse), we can usually perceive traces of 

 the existence of three or four toes, whose bones are more or 

 less completely united. 



659. From what has already been stated as to the influence 

 of the length of the levers on the quickness of the movement 

 of the extremities (. 614), it is easy to see that animals 

 which have the most rapid progression must necessarily have 

 long members ; since, the quickness with which the extensor 

 muscles act remaining the same, the change of place in the 

 free extremity of the lever will be greater, in proportion as 

 that extremity is more distant from the point of insertion of 

 the muscles that move it, and from the fulcrum on which the 

 tever works. But in proportion to the elongation of this arm 

 of the lever, must be the increase in the power of the muscles 

 that move it, in order to overcome the same resistance ; 

 according to the general principle that what is gained in 

 velocity is lost in power. Hence, in order to endow an animal 

 with great agility, it is only necessary to lengthen its limbs, 

 and to render its muscles capable of exerting a proportional 

 power. 



660. We have seen that in walking, the body is sustained 

 upon one limb (in quadrupeds, upon one pair of limbs), 

 whilst it is pushed onwards by the other ; so that it never 

 ceases to bear upon the ground. In running r , however, the 

 body of Man momentarily quits its support at intervals ; the 

 foot in advance not being planted on the ground by the time 

 that the hinder one quits it. In this action, the Ostrich and 

 its allies probably surpass all other animals ; as they can out- 

 strip the fleetest horse at full gallop, or the swiftest greyhound 

 at its greatest speed. The amble of Quadrupeds is a pace 

 which resembles the walk or run of bipeds, the two legs on 

 one side being moved together, whilst the body rests upon the 

 other. This pace is peculiar to the Giraffe, and to horses 

 which have been trained to execute it. The trot, however, is 

 a step of a different and much more secure nature. The fore- 

 foot of one side is raised and advanced with the hind foot on 

 the other side ; and when these are set down, the other fore 



