FOSSIL REPTILES. 307 



unites itself to the maxillary bone, is simply the nut of the 

 tooth, which, instead of remaining pulpy as in quadrupeds, 

 until it is destroyed, ossifies, and makes one body with its 

 alveolus. The tooth has no true root, but it adheres strongly 

 to this nut which has secreted it, and is still retained there by 

 the remainder of the capsule, which furnished the enamel, and 

 which, also ossifying and uniting itself to the maxillary bone 

 and to the nut, become osseous, enchases or sets the tooth 

 with new force. It is easy to conceive that this nut, identified 

 with the maxillary bone, must suffer the same changes as it — 

 that the alveolus of the succeeding tooth must penetrate its 

 solidity — that compression must detach it, either by breaking 

 it, or obliterating the vessels by which it is nourished — and 

 that, in fact, as was said before, it must be exposed to revolu- 

 tions analogous to those of the antlers of the stag. 



The cetacea exhibit nothing of this, neither do the croco- 

 diles. The teeth of the cetacea, it is true, fill with age, and 

 become solid ; but far from adhering to the alveolus by an in- 

 termediate osseous piece, they are only feebly retained there 

 by the fibrous substance of the gum, when they are once filled 

 with the substance of the ivory, and their pulpy nut is ob- 

 literated. 



The only hesitation, then, that can remain respecting the 

 place of this animal is between the osseous fishes, and the 

 iguanas and monitors. An examination of the jaws will put 

 an end to this doubt, and confirm the exclusion of the cetacea 

 and of the crocodiles. 



The lower jaw, from a specimen in the French Museum, 

 exhibits fourteen teeth on each side, all conformed, as we have 

 just described, after the fashion of the monitors. But the 

 monitors have only eleven or twelve. The crocodiles have 

 fifteen, but very unequal ; these are all equal, or nearly so. 

 In the iguanas the number is more considerable. 



There are in this jaw ten or twelve large and tolerably regu- 

 lar foramina. There are five or six in the iguanas, six or 



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