20 A MANUAL OF DENTAL ANATOMY. 



with the palatine root, but still more frequently the pos- 

 terior labial and palatine roots are confluent : occasionally, 

 also, four distinct roots may be met with. 



Lower molars. The first lower molar is the most con- 

 stant in form, and is somewhat the largest; its grinding 

 surface presents five cusps. 



Four cusps are placed regularly at the four corners of a 

 square, these being divided from one another by a crucial 

 fissure ; the posterior arm of the crucial fissure bifurcates, 

 and between its diverging arms is the fifth cusp, which is 

 thus to be described as median and posterior. 



FIG. 9 



The transverse fissure passes over the limits of the grind- 

 ing surface, and on the outside or labial surface of the tooth 

 ends in a pit, which is a common site for caries ; although it 

 occasionally passes over the lingual surface, it is here less 

 pronounced. They are implanted by two fangs, placed 

 anteriorly and posteriorly ; the roots are much flattened 

 from before backwards, and they are very usually curved 

 slightly backwards. In the median line of each root there 

 is usually a groove, by the deepening of which four fangs 

 may be produced ; or this may happen with the one root 

 only, so that a three rooted tooth is the result. 



: -( l ) Masticating surface of a first lower molar, right side, tlie five cusps 

 of which are indicated by figures. 



