306 FOSSIL REPTILES. 



planted in the palatine bones. Accordingly, it was with the 

 echidna that M. de Lacepede compared his hyperoodon. 



Contrary to the opinion of M. St. Fond, this animal has 

 nothing in its dentition which is peculiar to the crocodile. 

 All that it has in common with it in this respect, it has in com- 

 mon with an infinitude of fishes and reptiles. On the con- 

 trary, it has many characters which the crocodile has not, and 

 which, of themselves, would be sufficient to distinguish it, were 

 there not a crowd of others. 



We have already, in treating of the osteology of the croco- 

 dile, observed that, in this animal, the tooth in place always 

 remains hollow — that it is never fixed to the bone of the jaw, 

 but always remains merely emboxed there — that the succeeding 

 tooth springs in the same alveolus, and that it often penetrates 

 into the hollow of the tooth in place, and causes it to start and 

 fall out. 



The animal of Maestricht, on the contrary, had the teeth 

 hollow only while growing, like all other animals. They were 

 filled at last, for the most of them have been found entirely 

 solid. They ended by being fixed to the jaw by means of a 

 truly osseous and fibrous body, quite different from their pro- 

 per substance, though intimately united to it. The tooth of 

 succession grew in a peculiar alveolus, formed at the same 

 time as itself It pierced sometimes at the side, sometimes 

 through the osseous body, which supported the tooth in place. 

 As it increased in size, it finally detached this body from the 

 jaw, with which it was intimately connected by vessels and by 

 nerves. That body then fell by a sort of necrosis, like the 

 antlers of a stag, and brought with it the tooth which it car- 

 ried. By little and little the tooth of succession, and its body, 

 improperly called its osseous root, occupied the place which 

 the old tooth had quitted. 



The dentition of osseous fishes, that of monitors and many 

 other Saurian and OphMian reptiles, is exactly of the same 

 character as this. In fact, this cellulous and osseous part, which 



