TEETH OF THE MEGATHERIUM. 293 



its food and many of its peculiar habits ; and also to bring 

 to light a system of dentition, designed, like that of the 

 elephants, for the service of crushing and masticating a 

 coarse vegetable diet throughout a long-protracted indi- 

 vidual existence ; and yet, by a modification of the forma- 

 tive processes and economy of the teeth, quite different 

 from those that have been adopted for the same ends in 

 the elephant tribe. 



In these, as has been shown, the supply of a masticat- 

 ing apparatus, to serve the requirements of a gigantic 

 animal during one or perhaps two centuries of existence, 

 was provided by a succession of different molar teeth pre- 

 senting the due complexity of structure. In the mega- 

 therium, the same end was obtained by a perpetual growth 

 of the same complex molar teeth — the different dental 

 substances being formed at and added to the base of the 

 tooth, in proportion as they were ground down at the 

 exposed summit. 



The true number of teeth was determined by a removal 

 of the mineral substances adhering to the surface of a 

 portion of a fossil skull of a megatherium, brought by 

 Mr. Charles Darwin, from South America (Fossil Mam- 

 malia of the "Voyage of the Beagle," 4to. 1840, p. 102). 

 The animal has not, as in the elephant, any tusks ; its 

 teeth are molars or grinders exclusively ; they are five in 

 number on each side of the upper jaw, and four on each 

 side of the lower jaw — eighteen in all. All these teeth 

 are remarkable for their great length in proportion to 

 their breadth or thickness, being from eight to ten inches 

 in length, and between two and three inches only in 

 breadth. They are very deeply implanted in the jaw, 

 and the lower jaw has a quite peculiar form, in order to 



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