THE TEETH OF MAN. 19 



of enamel, the remaining two cusps having no such con 

 nection. 



This oblique ridge on the upper molars is met with in 

 man, the anthropoid apes, and certain New World monkeys. 



The grooves which separate the cusps pass down on to 

 the labial and lingual surfaces of the crown, but are lost 

 before reaching the gum ; where they terminate, however, 

 there is often a pit, which is a very favourite situation for 



FIG. 



caries, especially on the labial aspect of the teeth. It is 

 very rare to see the grooves passing down upon the mesial 

 or distal surfaces of the crown, a raised border of enamel 

 generally cutting them short in this direction. 



The roots are three in number, two external or labial, and 

 one internal or palatal. The latter is the largest, and runs 

 in a direction more strongly divergent from the axis of the 

 crown than the other roots. It is directed obliquely in- 

 wards towards the roof of the palate, is subcylindrical, and 

 often curved. 



The external roots are less cylindrical, being mutually 

 compressed, so that their largest diameter is transverse to 

 the dental arch ; the anterior is rather the larger of the two, 

 and is more strongly pronounced on the side of the neck of 

 the tooth. The anterior labial root is occasionally confluent 



(*) Masticating surface of a first upper molar of the left side ; the 

 oblique ridge connects the anterior internal with the posterior external 

 cusp. 



c 2 



