THE TEETH OF MAMMALS 129 



which there is provided a peculiar dentition. The 

 teeth are adapted to the crushing of the chitinous 

 covering of insects, and for this purpose are 

 armed with many long, sharp cusps. The best 

 known members of the order are the Hedgehogs, 

 Moles, and Shrews. The teeth are variable, but 

 always bristle with cusps. The molars have a 

 "W" pattern of the arrangement of the occluding 

 ridges which is present in most of the order. The 

 common English Hedgehog has the formula, — 



i. H «."£$ p.m. t* m . H = 36< 



2-2 0-0 F 3-3 3-3 



In the upper jaw there is a wide interval between 

 the first pair of incisors, which are very large and 

 caniniform in shape. The second pair of incisors 

 above are quite small and resemble premolars in 

 form, the inner cingule being raised to a level 

 with the edge. The third incisor has two roots, 

 and is like a cusped premolar also. The canines 

 are absent. In the lower jaw the first pair of in- 

 cisors are large, but not separated widely. The 

 second pair are smaller, and the third pair larger 

 and caniniform in shape. The canine is absent, 

 but the first premolar has an oblique crown with 

 five sharp cusps, one at each corner and a fifth 

 on the inner side. The molars are reduced from 

 this size, the last below having but one cusp. The 

 upper premolars are square with four cusps, and 

 the molars gradually decrease to the back, but 



