132 COMPARATIVE DENTAL ANATOMY 



central incisors, one on each side of the median 

 line, which are large, long, curved, in a circle, and 

 grow out of the deep parts of each jaw from per- 

 sistent pulps, so that they are of continuous 

 growth. The tissues are so arranged that the 

 enamel is thicker on the front than on the back 

 of the tooth, so that a sharp edge is preserved on 

 the front by the wearing away of the rear portion, 

 producing a chisel-shaped crown; hence the name 

 given to these teeth, — scalpriform. Continuous 

 growth preserves the length of the tooth and the 

 apposition of the edges. Wear and use are neces- 

 sary to compensate for their growth, for if by 

 accident an incisor becomes broken the opposite 

 incisor continues to grow and curves around in a 

 circle, piercing the soft parts of the head and pro- 

 ducing death by starvation. Such accidents are 

 not infrequent with rodents. The enamel of these 

 teeth is usually of a light orange or reddish-brown 

 color. Sometimes there are two longitudinal 

 grooves on the anterior surface. There are usu- 

 ally no deciduous predecessors to those teeth in 

 rodents, except in the Hares, so that their 

 monophyodontism is nearly constant. There is 

 an entire absence of lateral incisors, canines, and 

 in some species of the premolars, in the order. 

 The Hares have supplementary incisors behind 

 the upper centrals. The molar teeth are few in 

 number, obliquely implanted, and present many 



