32 COMPAKATIVE DENTAL ANATOMY 



which is compressed to form the wide cutting 

 edge. The canine is a single cone, the base of 

 which is compressed into a trihedral, pointed 

 prism. The bicuspids are formed of two cones 

 fused together, — the base rounded to make the 

 cusps, — and two cones are distinct the entire 

 length of the tooth. The typical upper molar is 

 formed by the coalescence of three cones, which 

 are plainly marked, and the lower molar of four 

 cones. Thus the teeth of all animals, even the 

 highly complex and specialized tooth of the higher 

 mammals, are evolved. As Cope says, "The 

 transition from single to complex teeth is ac- 

 complished by repetition of the simple cone in va- 

 rious directions. First, there are cylindrical in- 

 cisors, then flat ones, then divided roots; then 

 internal repetition of a root and cusp; then pos- 

 terior repetition. Very complex teeth, as multi- 

 tubercular molars, are formed by both posterior 

 and lateral repetition.'' Thus the primitive form 

 of tooth is that of a simple cone, from which all 

 subsequent forms, however complex, have been 

 derived by repetition, duplication, and modifica- 

 tion of cones and cusps. 



