THE TEETH OF MAMMALS 131 



ing mammals, — the Bats. The modification of 

 structure for flying — the long fingers with the 

 membrane stretched between, the hooks for sus- 

 pending, etc. — distinguishes these remarkable 

 mammals from all others. They are closely re- 

 lated to the Insectivora in their dentition, as most 

 of them subsist on insects. The formula of the 

 common red bat is, — 



. 2-2 1-1 3-3 3-3 Qa 



k 2=2 C - 1=1 P ' m - 3=3 m ' 3=3 = 36 * 



The canines are round and sharp, and the molars 

 have sharp cusps with the insectivorous "W" 

 pattern. This dentition is of great constancy. 

 The frugivorous bats vary from the insectivorous 

 in having the incisors larger, the canines reduced, 

 and the molar cusps rounded. The Vampire bat 

 is a remarkable form that sucks the blood of 

 larger mammals. For this purpose the two upper 

 centrals are wide and scoop-shaped, with sharp 

 edges for puncturing the skin to draw blood. 

 There are no other incisors above, but the canines 

 are of about the same shape and size as the cen- 

 trals. The other teeth are much reduced in size 

 and shape, as the diet requires no dental manipu- 

 lation. 



The Rodentia are a very numerous order, and 

 include such animals as the Beavers, Squirrels, 

 Eabbits, Rats, and Mice. It is so named on ac- 

 count of their principal peculiarity, — i.e., the two 



