ELEPHANT. 639 



frontal region of the skull : viewing the upper and lower molars 

 as one complex whole, subject to the same revolving movement, 

 the section dividing such whole into upper and lower portions 

 runs parallel to the curve described by that movement, the upper 

 being the central portion or that nearest the pivot, the lower the 

 peripheral portion : the grinding surface of the upper molars is 

 consequently convex from behind forwards, and that of the lower 

 molars concave : the upper molars are always broader than the 

 low^er ones. The bony plate (ib. fig. 2, a) forming the sockets ol 

 the growing teeth is more than usually distinct from the body ol 

 the maxillary, and participates in this revolving course, advancing 

 forwards with the teeth. The partition between the tooth in use 

 and its successor is perforated near the middle ; and in its pro- 

 gress forwards that part next the grinding surface is first absorbed ; 

 the rest disappearing with the absorption of the roots of the pre- 

 ceding grinder. 



There are few examples of organs that manifest more strik- 

 ingly the adaptation of a highly complex and beautiful structure to 

 the exigencies of the animal endowed with it, than the grinding 

 teeth of the Elephant. We perceive, for example, that the jaw is 

 not encumbered with the whole weight of the massive tooth at 

 once, but that it is formed by degrees as it is required ; the sub- 

 division of the crown into a number of successive plates, and of 

 these into subcylindrical processes, presenting the conditions most 

 favourable to progressive formation. But a more important advan- 

 tage 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 com- 

 menced, 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 inclos- 

 ing the depressed tracts of the dentine, and separated by the 



