o56 PROCEFDTXOfS OF THE ACADEMY OF [l8iU>. 



the character of the food procurable in extreme nortliern K>oalities, 

 as compared with that ot' tlie more southern, has been a factor in 

 the devehipnient of the sUnider protruding incisors. In northern 

 Greenhuui. phuit-life is not only greatly reduced in size and num- 

 ber of species from that of Labrador, but the ditticulty of procuring 

 it is enhanced by the depth and long continuance of the snow in the 

 former locality. For many months in the year the Greenland 

 Hare must subsist entirely on dwarfed plants, whicli it uncovers 

 auil reaches by scratching away the snow,'* while the Labrador ani- 

 mal is living without exertion on the twigs, leaves and branches of 

 a large variety of bushes and shrubs. The character of the iliet in 

 each instance naturally accounts for the relatively weaker dentition 

 of the northern animal and we may believe that the projecting form 

 of incisor was the outcome of the needs of the animal in rooting 

 among snow and stones for its scant repast. To insure such an ar- 

 mature the arc of the tooth must have a larger radius and hence 

 the tooth itself a greater length, bringing its root farther back upon 

 the maxillary than the sharply curved, perpendicular, massive form 

 of the twig-eating animal. Again we see how the projecting form 

 of incisor tooth, meeting its opposing member at a triturating 

 angle of 45°. must, of necessity, have a greater relative vertical re- 

 sistance than opposing pairs of teeth which meet on the same plane 

 or at an angle scarcely appreciable. As a result, we have the nar- 

 row, deep incisors of granlandicus and the long, slender premaxil- 

 lary and ramus enclosing them. By this means, the incisor sulcus 

 is not only diminished but the weakness resulting from its possession 

 is remedied by a special functional provision which tills it with the 

 cenientum-like scale as the animal approaches maturity. 



It may be stated that the Polar Hares of America, contrary to 

 the rule of specific stability in circumpolar animals have proved no 

 exception to the protean character of the many members of the 

 genus Lepus on this continent. On the other hand, they emphasize 

 that fact, and form a group, apparently more sensitive to the min- 

 ute alterations of a Polar environment than any other of the Arctic 

 vertebrata. 



Contrary to what we should expect, it does not appear that our 

 Arctic Hares decrease in size as we go south. The average meas- 

 urements of ;Xorth Greenland Hares are less than those of 

 the series taken in Newfoundland and it will be noted that the 



^*See Feilden. in Appx. Nares' Voy,. 1S7S. 11. pp. 204, 205. 



