BATS. 



427 



with an internal and posterior talon ; the second premolar is 

 larger than the first, with a triedral crown, and an anterior 

 and posterior talon at the base of the long, sharp middle cusp. 

 The first and second true molars have sub-compressed quin- 

 que-cuspid crowns ; the third molar is compressed from before 

 backwards, and has a tri-cuspid crown. The first and second 

 premolars below are simple and larger than those above, especially 

 the first ; the first and second true molars have two large external 

 and three small internal cusps, and the last molar differs only by 

 a slight inferiority of size. 



The dentition of the true blood-sucking Vampire Bats, which 

 form the genus Desmodus (PI. 112, fig. 9) deviates, as might be 

 anticipated, in a remarkable degree from that of the Insectivorous 

 Bats : the crushing instruments required for the food of those species 

 are not needed ; and the true molars, with their bristled crowns, are 

 entirely absent in the Desmodus. The teeth at the fore-part of the 

 mouth are especially developed and fashioned for the infliction of 

 a deep and clean triangular puncture, like that made by a leech. The 

 incisors {i) are two in number above, closely approximated, one 

 in each intermaxillary bone, with a very large, compressed, curved, 

 and sharp-pointed crown, implanted by a strong fang which extends 

 into the maxillary bone. The upper canines have similar large, 

 lancet-shaped crowns, and their bases touch those of the incisors. 

 In the lower jaw the incisors are two in number on each side, much 

 smaller than the upper pair, and with bilobed crowns. The lower 

 canines are nearly equal in size to those above. The molar series 

 is reduced above to two very small teeth, each with a simple com- 

 pressed conical crown, implanted by a single fang. The first two 

 molars below resemble those above ; but they are followed by a 

 third which has a larger compressed and bilobed crown, implanted 

 by two fangs ; this tooth corresponds with the last premolar in the 

 more normal genera of Insectivorous Bats. The dental formula 

 of the true Vampire-bat (Desmodus) is thus reduced to : — 



1-1 1-1 2-2 „„ 



m. — : c. — ; pm. — : = -<iO.(l) 



2—2 ' 1— 1 ' -'^ 3—3 ^ ^ 



The opposite extreme which the aberrant varieties of the 



(1) The intestinal canal, like the dentition, is modified in conformity with the easily 

 assimilated food, viz. the blood of living animals, on which the true Vampires habitually 



