COMPARATIVE LOCOMOTION 259 



have already been enunciated, and we have no doubt 

 that others will soon receive an accurate formulation. 



But to determine these laws the character of an 

 animal's locomotion must be as precisely defined as 

 its anatomical structure. Chronophotography, and 

 more particularly the diagrams which it enables us to 

 construct, leave nothing to be desired in point of 

 truthful expression of certain types of locomotion. A 

 few examples will show the value of this method. 



Comparative Locomotion among Different Terrestrial 

 Mammals. — A striking feature among terrestrial mam- 

 mals is the variety of morphological form, and this is 

 equally the case as regards their mode of locomotion. 

 But beneath this apparent diversity, zoologists have 

 discovered profound analogies; only to instance the 

 most obvious of these, the lower limbs of a man 

 evidently correspond to the hind legs of a quadruped, 

 and all through the mammalian series some similarity 

 may be recognized, either as regards limb or bone or 

 muscle. Differences, indeed, exist among different 

 species, but they are chiefly referable to inequality of 

 development, fusion of some parts, atrophy or mal- 

 formation of others, or to anatomical disproportion. The 

 important point to establish is the connection between 

 anatomical and functional variation. 



Xow, by means of chronophotography, it is easy to 

 trace among different species the respective movements 

 of the different segments of the limb in walking or 

 running. One animal supports itself on the ground 

 by its digital extremities, another by the entire plantar 

 surfaces of the feet. One animal will progress by 

 means of alternate oscillations of its limbs, another by 

 sudden extension ending in a jump. But the unaided 

 eye cannot determine with certainty the respective 

 parts played in these actions by the various bony 

 segments. Chronophotography, however, shows every 



