362 A MANUAL OF DENTAL ANATOMY. 



its last or larger molar, although in it the ridges are in- 

 dividually wide and strongly pronounced. 



In the Indian elephant the ridges or plates are still more 

 numerous, the roots very inconspicuous and the whole 

 formed into a solid block by cementum. 



The gradual increase in complexity in the " ridge formula" 

 (or number of ridges in each tooth), of the molars, is well 

 seen in the following table, from Prof. Flower's Hunterian 

 lecture ("Nature," March 2, 1876); it is a corrected table 

 taken from Dr. Falconer's " Pakcontological Memoirs." 



Milk Molars. ^rueMolars. Total. 

 I. II. III. I. II. III. 



Dinotlierium giganteum . . . .123 



Mastodon (Trilophodon) americanus ..123 



(Tetralophodon) arvernensis .234 



,, (Pentalophodon) sivalensis ..345 



Elephas (Stegodon) insignis . . .257 



322 

 334 

 445 

 556 



7 8 10 



(Loxodon) africanus . ..367 7 8 10 



meridionalis . . 3 6 8 j 8 9 12 



(Euelephas) antiquus . .. 3 6 10 j 10 12 16 



13 



16 

 22 

 28 

 39 

 41 

 46 

 57 



primigenius . . . 4 8 12 ! 12 16 24 i 76 

 indicus . . . 4 8 12 12 16 24 j 76 



Some variability exists in the number of ridges, especially 

 when they are very numerous, but the above may be taken 

 as averages ; and some species intermediate in the " ridge 

 formula " have been since discovered, thus M. pentelici and 

 M. andium bridge the distinction between Trilophodon and 

 Tetralophodon, and Elephas melitensis comes between 

 Loxodon and Euelephas (Flower). 



It remains to describe, somewhat more in detail, the 

 structure of an elephant's tooth, and this has been deferred 

 till the last, because it can be the more easily understood 

 when the manner of its origin has been mastered. In the 

 Mastodon the molar consists of a crown with strong cusps, 

 standing apart, and with marked roots ; in the African 

 elephant that part which consists of cusps has become the 



