232 THE TEETH. 



minating in cusps. On the posterior surface "undulating 

 ridges," running transversely, are seen, but more distinct 

 in the upper than in the lower canines. The summits of 

 the canines are tubercular and oblique, and their cusps 

 disappear in the adult. 



Ei-Cusplds (Bi-Cuspidati Fig. 59.) The bi-cuspids are 

 upon either side of the canines, and are four in each jaw ; 

 they are intermediate in size between the canines and mo- 

 lars, and derive their name from having two tubercles on 

 their grinding surfaces. A groove running in the direction 

 of the alveolar arch separates these tubercles; the outer is 

 larger than the inner, and those of the upper larger than 

 those of the lower jaw. The body is thicker, and the sides 

 are flatter, than either the incisors or cuspidati. Their 

 roots are single, though the groove is much deeper than 

 the canine, and often divides it into two. 



The necks of the bi-cuspids are smaller, in proportion to 

 their crowns, than those of any other teeth ; hence the 

 necessity of using more caution in their extraction, as they 

 are more liable to fracture. 



Professor Harris gives a bi-cuspis five surfaces, two ap- 

 proximalj one buccal, one palatine or lingual, and a grinding 

 surface; also four angles, one anterior, and one posterior 

 palato-approximal, and one anterior, and one posterior 

 bucco-approximal. 



MolareSj or Multi-Cuspidati. The posterior teeth in the 

 alveolar arch of each jaw constitute the true molars or 

 grinders, and with the bicuspids form what is called the 

 buccal range. There are six to each jaw, three upon either 

 side behind the bicuspids. Their greater size distinguishes 

 them. The crown of each presents a square form, and 

 has on the grinding surface four and five tubercles, with 

 as many depressions, which are so arranged that the tuber- 

 cles of either jaw are adapted to corresponding depressions 

 in the other. 



There are three roots, and sometimes four, to the upper 

 molars; two of these roots are external, nearly parallel and 

 vertical. The third is internal, directed to the roof of the 



