409. Two inquiries concerning these bones have excited the curiosity of naturalists; first, to discover among the living tribes at present inhabiting the earth, those to which the fossil remains may with the greatest probability be referred; and, secondly, to find out the cause why these remains exist in such quantities, in countries where the animals to which they belong, whatever they be, are at present unknown. The solution of the first of these questions, is much more within our reach than the second, and at any rate must be first sought for. On the authority of so eminent a naturalist as Pallas, the bones from Siberia may safely be referred to the elephant, the rhinoceros, and buffalo, as mentioned above, though perhaps to varieties of them with which we are not now acquainted. With respect to the bones of North America, the question is more doubtful, for they have this particular circumstance attending them, viz. that along with the thighbones, tusks, &c. which might be supposed to belong to the elephant, grinders are always found of a structure and form entirely different from the grinders of that animal.[216] Some naturalists, particularly M. DAUBENTON, referred these grinders to the hippopotamus; but Dr W. HUNTER appears to have proved, in a very satisfactory manner, that they cannot have belonged to either of the animals just mentioned, but to a _carnivorous_ animal of enormous size, the race of which, fortunately for the present inhabitants of the earth, seems now to be entirely extinct.[217] The foundation of Dr Hunter's opinion is, that in these grinders the enamel is merely an external covering; whereas, in the elephant, and other animals destined to live on vegetable food, the enamel is intermixed with the substance of the tooth.[218] [Footnote 216: See Mr Collinson's papers, above referred to. Phil. Trans. vol. lvii.] [Footnote 217: Phil. Trans. vol. lviii. p. 3, &c.] [Footnote 218: A fossil grinder in the collection of JOHN MACGOWAN, Esq. of Edinburgh, answers nearly to Mr Collinson's description, and is very well represented by the figure which accompanies it. This grinder weighs four pounds one-fourth avoirdupois; the circumference of the _corona_ is eighteen inches; the coat of enamel is one-fourth of an inch thick; there are five double teeth; in Mr Collinson's specimen there are only four.]