190 MAMMALIAN" DENTITION 



coated only in front and laterally, uncompressed, broad and 

 powerful, beveled upon their posterior aspect and strongly 

 curved so that the persistently growing roots are not subject 

 to injury. This method of protecting tooth roots from pressure 

 insults is also seen to some extent in the molars but the curva- 

 ture is much more strongly marked in the cheek teeth of the 

 Wombat (page 90). The premolars and their milk predeces- 

 sors have already been mentioned. Although the first milk 

 <-ooth in the upper jaw is very small it is replaced by a much 



Fig. 67. — Dentition of Woodchuck (Arctomys monax, 9.3213-1). This is the skull 

 of a young animal. The first and second upper and the first lower cheek teeth belong 

 to the deciduous dentition. Observe the characteristic Rodent incisors and glenoid 

 fossae and also the relatively slight divergence from the primitive mammalian molar 

 pattern. 



larger and molariform premolar. At first sight the molar 

 crowns do not appear to resemble at all closely the typical 

 mammalian pattern. If however the first and second upper 

 molars be examined with care it will be seen that they exhibit 

 a well-marked protocone from which ridges pass laterally to 

 the paracone and the metacone and that about midway along 

 the hinder ridge there is a clearly marked metaconule. Al- 

 ready in the Marmot the croAvn is complicated by the occur- 



