THE SKELETON IN MAMMALIA. THE TEETH. 441 



The milk teeth are very slender and have sharp recurved cusps; 

 they are quite unlike the permanent teeth. The permanent 

 teeth are of two types. In the Insectivorous forms the molar 

 teeth are cusped, and resemble those of Insectivora. In the 

 blood-sucking Vampire bat Desmodus, the teeth are peculiarly 

 modified ; the canines and the single pair of upper incisors are 

 much enlarged and exceedingly sharp, while all the other 

 teeth are much reduced in size. 



In the Frugivorous bats the molar teeth have nearly always 

 smooth crowns. The dental formula in the chief genus Pteropus 



9 1 32 



is i - c pm - m - , total 34. 

 2 1 o 5 



The PRIMATES have a diphyodont and heterodont dentition, 

 generally of an omnivorous type, with cheek teeth adapted for 

 grinding. The incisors are generally -|, and the molars, except 

 in the Hapalidae, are . In the Lemurs the upper canines 

 are large, and the lower incisors slender and directed almost 

 horizontally forwards. The Aye Aye, Chiromys, has the follow- 

 ing singular dentition : i - c ^ pm - m ~ , total 18. The in- 



1 U U o 



cisors much resemble those of rodents having persistent pulps, 

 and enamel only on the anterior face. 



In Man and in the Anthropoid and Old World Apes 



21 23 

 the dental formula is always i - c - pm - m ^ , total 32. 



In the Cebidae there is an extra premolar in each jaw 

 bringing the number up to 36. In the Hapalidae, as in the 

 Cebidae, there is a third premolar, but the molars are reduced 

 to f . Man is the only Primate that has the teeth arranged 

 in a continuous series. In all the others there is a gap or 

 diastema of larger or smaller size between the incisors and 

 canines. In all except man also the canines are enlarged, 

 especially in the males. 



