376 THE VERTEBRATE SKELETON. 



They are all fixed in the bone by tapering roots, and none of 

 them grow from persistent pulps. 



They are divisible into four distinct groups, the incisors, 

 canines, premolars and molars. There are three incisors, 

 one canine and four premolars on each side of each jaw. 

 But while there are three molars on each side of the lower 

 jaw, the last is wanting in the upper jaw. The dentition of 

 the dog may then be represented by the formula 



31 42 



i^ c j pm ^ m - x 2 = 42. 



In each jaw there is one large specially modified tooth 

 called the carnassial, the teeth in front of this are more or 

 less pointed and compressed, while those behind it are more or 

 less flattened and tuberculated. 



Teeth of the upper jaw. 



The first and second incisors are small teeth with long 

 conical roots and somewhat chisel-shaped crowns. Surround- 

 ing the base of the crown there is a rather prominent ridge, 

 terminated laterally by a pair of small cusps. This ridge, the 

 cinglllum, serves to protect the edge of the gums from injury 

 by the hard parts of food. The third incisor is a good deal 

 like the others but larger, and has the cingulum well developed 

 though not terminated by lateral cusps. All the incisors 

 are borne by the premaxillae, the remaining teeth by the 

 maxillae. 



The canine is a large pointed tooth, slightly recurved and 

 with a long tapering root. 



The premolars are four in number, and in all the cingu- 

 lum is fairly well seen. The first is a very small tooth with a 

 single tapering root, the second and third are larger and have 

 two roots, while the fourth, the carnassial, is much the largest 

 and has three roots. Each of the second, third and fourth pre- 

 molars has a stout blade, the middle portion of which is drawn 

 out into a prominent cone ; the posterior part of the fourth 



