PROGRESSIVE MOTION IN QUADRUPEDS. 497 



siderable power of leaping. This is exemplified 

 in the Jerboa and the Kanguroo, animals, which, 

 from the disproportionate shortness of their 

 fore legs, are totally incapacitated from walk- 

 ing ; and for the same reason, they cannot run 

 with any degree of swiftness. It is only in 

 climbing up a steep acclivity that the jerboa is 

 enabled to employ all its limbs : in a descent, 

 on the contrary, it uses only its fore legs, the 

 hinder being dragged after them. But, when 

 pursued, these animals are capable, for a long 

 continuance, of taking leaps of nine feet dis- 

 tance, and of repeating these leaps so quickly, 

 that the Cossacks, though mounted on the 

 swiftest horses, are unable to overtake them. 



The Kanguroo, in almost all his movements, 

 brings into action his powerful tail, which is fur- 

 nished with very strong muscles, and may be 

 considered as constituting a fifth limb. It is of 

 great assistance to the animal in taking leaps, 

 and during its repose, contributes, together with 

 the hind feet, to support the weight of the body, 

 as on a tripod, and to leave at liberty the fore 

 legs, which may then be employed as arms. 



The Hare and the Rabbit furnish other in- 

 stances of an extraordinary length of the hinder 

 legs depriving the animal of the power of walk- 

 ing, and obliging it to move forwards only by 

 a succession of leaps. The hare may be said, 

 indeed, to walk with its fore legs only, while it 



VOL. I. K K 



