134 PHILOSOPHY 01' ZOOLOGY. 



time, the latter bends in order to its being moved forward. 

 While they are off the ground, the right hind-foot begins 

 to extend itself, and the moment they touch the ground, 

 the left lure-foot moves forward to support the impulse of 

 the right foot, which likewise moves forward. The body 

 is thus supported alternately by two legs placed in a dia- 

 gonal manner. When the right fore-foot moves, in order to 

 sustain the body, pushed forward by the right hind-foot, 

 the motion is then called an amble. The body, being al- 

 ternately supported by two legs on the same side, is obli- 

 ged to balance itself to the right and left, in order to avoid 

 falling ; and it is this balancing movement which renders 

 the gait so soft and agreeable to women and persons in a 

 weak state of body *. 



In walking with two feet, as takes place in man and birds, 

 the whole weight of the body rests on each leg alternately ; 

 so that the movement is in a zig-zag direction. These un- 

 dulations are rendered more conspicuous in some birds, by 

 the form of their feet and toes, by which they are prevented 

 from moving them in the direction of the mesial line ; but 

 are, at each step, compelled to move the leg outwards, in a 

 semicircular manner. In some quadrupeds, as the seal, 

 and in many reptiles, the limbs are placed perpendicular to 

 the mesial line ; and, in the progressive motion, the body is 

 dragged along the ground, as the flexion and extension of 

 the limbs are unable to elevate it above the surface. Such 

 animals are said to crawl. 



But, besides these modes of walking, which we have now 

 stated, there are others, in which the progressive motion is 

 similar, but the means employed to accomplish it are diffe- 

 rent. The principal of these may be termed the Serpen- 

 tine Motion. It consists in bringing up the tail towards 



* CUVIER'S Cpmp, Anat. Lcct. vii. 



