DEVELOPMENT OF ELEPHANT'S GRINDERS. 291 



than the grinding teeth of the elephant. We perceive, for 

 example, that the jaw is not incumbered with the whole 

 weight of the massive tooth at once, but that it is formed 

 by degrees as it is required ; the division of the crown 

 into a number of successive plates, and the subdivision of 

 these into cylindrical processes, presenting the conditions 

 most favorable to progressive formation. But a more 

 important advantage is gained by this subdivision of the 

 tooth ; each part is formed like a perfect simple tooth, 

 having a body of dentine, a coat of enamel, and an outer 

 investment of cement. A single digital process may be 

 compared to the simple canine of a carnivore ; a transverse 

 row of these, therefore, when the work of mastication has 

 commenced, presents by virtue of the different densities 

 of their constituent substances, a series of cylindrical 

 ridges of enamel, with as many depressions of dentine, and 

 deeper external valleys of cement ; the more advanced 

 and more abraded part of the crown is traversed by the 

 transverse ridges of the enamel inclosing the depressed 

 surface of the dentine, and separated by the deeper chan- 

 nels of cement ; the forepart of the tooth exhibits its least 

 efficient condition for mastication, the inequalities of the 

 grinding surface being reduced, in proportion as the 

 enamel and cement have been worn away. This part of 

 the tooth is, however, still fitted for the first coarse crush- 

 ing of the branches of a tree; the transverse enamel 

 ridges of the succeeding part of the tooth divide it into 

 smaller fragments, and the posterior islands and tubercles 

 of enamel pound it to the pulp fit for deglutition. 



The structure and progressive development of the 

 tooth not only give to the elephant's grinder the advantage 

 of the uneven surface which adapts the millstone for its 

 office, but, at the same time, secure the constant presence 



