ACTS OF WALKING AND RUNNING. 495 
Ge 240), the wing of a Bat (fig. 251), and the fore-paw of a 
guirrel or a Mole, we find the same bones as in the arm of 
n (fig. 223). And even in the fore-legs of the Ruminant 
Quad rupeds, and in those of the Solidungula, or single-toed 
s (such as the Horse), we can usually perceive traces of 
Raeietsince of three or four toes, whose. bones are more or 
less ss completely united. 
_ 659. From what has already been stated as to the influence 
f the length of the levers on the quickness of the movement 
the extremities (§. 614), it is easy to see that animals 
which have the most rapid progression must necessarily have 
lo ng members ; since, the quickness with which the extensor 
muscles act remaining the same, the change of place in the 
ee extremity of the lever will be greater, in proportion as 
nat extremity is more distant from the point of insertion of 
the muscles that move it, and from the fulcrum on which the 
leyer works. But in proportion to the elongation of this arm 
of the lever, must be the increase in the power of the muscles 
t move it, in order to overcome the same resistance ; 
according to the general principle that what is gained in 
velocity is lost in power. Hencé, in order to endow an animal 
vith great agility, it is only necessary to lengthen its limbs, 
md to render its muscles capable of exerting a proportional 
ower. 
_ 660. We have seen that in walking, the body is sustained 
upon one limb (in guadrupeds, upon one pair of limbs), 
ilst it is pushed onwards by the other ; so that it never 
zases to bear upon the ground. In running, however, the 
body of Man momentarily quits its support at intervals ; the 
dot in advance not being planted on the ground by the time 
hat the hinder one quits it. In this action, the Ostrich and 
is allies probably surpass all other animals ; as they can out- 
rip the fleetest horse at full gallop, or the swiftest greyhound 
t its greatest speed. The amble of Quadrupeds is a pace 
which resembles the walk or run of bipeds, the two legs on 
e side being moved together, whilst the body rests upon the 
er, This pace is peculiar to the Giraffe, and to horses 
rhich have been trained to execute it. The trot, however, is 
| step of a different and much more secure nature. The fore- 
ot of one side is raised and advanced with the hind foot on 
ve other side ; and when these are set down, the other fore 
