26 THE AMERICAN BEAVER. 



the main direction of the enameled eminences of the 

 molar teeth, and then limited its horizontal move- 

 ment to a single direction, which was forward and 

 back. The American beaver is an exception to the 

 general rule.^ The powerful muscles, before referred 

 to, give to this animal the "horrid bite" [horrendus 

 morsus), to use the language of Pliny, for which his 

 tree-cuttings, if not his combative propensities, show 

 him to be distinguished. Each condyle is movable 

 upon its fulcrum, which is a plain surface, and must 

 be held with immense strength to sustain the grasp 

 of the incisors while in the act of cutting down trees. 

 In swimming, the propelling power is furnished by 

 the hind legs. To adapt their feet for this purpose 

 they are completely webbed to the roots of the claws, 

 and are capable of a lateral spread of eight or nine 

 inches on the exterior line of the membrane. The 

 legs are thrown out behind, in the act of swimming, 

 like those of a duck, and nearly in a horizontal line. 

 While swimming, the fore feet are not used, but are 

 pressed back against the abdomen,^ their smallness 

 rendering them nearly useless for this purpose. Dr. 

 Ely, however, discovered a rudimentary membrane 

 between the fore fingers of these paws which is par- 

 , ticularly conspicuous between the second and third. 

 The paws are very small relatively to the size of the 

 animal, and very much smaller than the hind feet; 

 but as they are capable of a very considerable rotary 

 movement, he is able to hold sticks and limbs of trees, 



^ The squirrel, the rabbit, and the rat also appear to be excep- 

 tions. 



^ The otter is a more rapid swimmer than the beaver, but does 

 not use his fore feet, which are placed in the same position. 



