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the bony substance of the primordial tooth itself. These secondary teeth, 

 by continuing to grow, seem to make, by degrees, sufficient cavities in 

 the bony roots of the primary teeth; but what becomes of them at last, 

 and how they are shed, he adds, I am not able to guess *. 



From the existence of a hollow in the primary teeth of the fossil ani- 

 mal, and from the growth of the secondary tooth in this hollow, M. Fau- 

 jas is led to exclaim : " It is difficult to conceive how this illustrious phi- 

 losopher could permit so striking a character to escape him; and, after 

 witnessing this circumstance (the secondary tooth being formed near the 

 centre of the bony support of the primary tooth), how he could conceive 

 these teeth to belong to a cetaceous animal ~f ." The approximation of 

 the secondary towards the centre of the primary tooth appears, however, 

 in this animal, to have been merely an accidental occurrence. Nor does 

 it appeaj that the mode of dentition at all coincided with that which is 

 known to take place in the crocodile. 



On this subject, M. Cuvier observes, that in the crocodile : the tooth is 

 always liollow; -that it is fixed in, but never attached to the bone of the 

 jaw ; and that the secondary tooth forms in the same socket, and fre- 

 quently grows into the hollow of the primary tooth, thus shivering it, 

 and occasioning it to be shed. 



The fossil animal of Maestricht, he remarks, on the contrary, like 

 other animals, appears to have had its teeth hollow only whilst they 

 were growing, they afterwards filling up, and becoming solid and fixed 

 in the jaw by a fibrous and osseous substance, materially differing from 

 the real substance of the teeth, although closely united with it. The se- 

 condary tooth, too, is here formed in a particular socket, which is formed 

 at the same time with this tooth, which passes out, sometimes at the side, 

 arid sometimes through the osseous substance which supports the primary 

 tooth. In the end, it detaches this substance from the jaw, occasioning 

 it to fall off, by a species of necrosis like that by which the horns of stags 



* Philos. Trans, for 1786, p. 178, f Hist. Nat. de la Mont, de St. Pierre, p. 240. 

 VOL. III. P P 



