THE TEETH OF MAMMALS. '295 



from HCICTTOS, a nipple). The three transverse ridges coalesce 

 at their bases, and the crown is supported upon a number 

 of roots corresponding to the ridges. 



If we take the next tooth, or the third true molar, the 

 general character remains the same, save that there are five 

 ridges, and indications of as many roots ; still the general 

 correspondence of the ridges with the cusps of less aberrant 

 teeth is obvious. 



The crown is coated by enamel, over which there is a 

 thin layer of cement, which does not fill up the whole 

 interval between the ridges. 



Thus the tooth is not a very aberrant one it is obviously 

 nothing more than a tooth in which the somewhat numerous 

 cusps are connected by transverse ridges, and are very long 

 and strongly pronounced. 



To convert the tooth of a mastodon into that of an 



FIG. 124 



elephant, we should have to multiply the number of ridges, 

 to further increase their depth, to fill up solidly the inter- 

 spaces between them with cementum, and to stunt the 

 roots. The completed tooth of an elephant is a squarish 

 or rather oblong mass, from the base of which spring con- 

 tracted and stunted roots. It consists of a common pulp 

 cavity, small in proportion to the bulk of the tooth, and 



( ] ) Molar tooth of an Asiatic Elephant, showing the transverse plates of 

 dentine bordered by enamel. 



