652 t)ouhts respecting 



iguanas for example ; and then the root of the tooth is "e- 

 chancree en ogive au cote interne de la base" 



A fourth, is that of the venomous serpents, among which 

 the teeth being neither implanted, nor furnished with roots, 

 terminate by uniting themselves with the maxillary bone by a 

 kind of ossification of the "membrane gyngivale" 



The class Amphibia, presents very nearly the same modi- 

 fications of the dental system, with which, however, these 

 animals are often altogether unprovided, and which is seldom 

 largely developed ; and their teeth present a constant simpli- 

 city in the two portions, of which one, namely the root, is 

 almost always wanting, an almost complete similitude in 

 the dental series of each species, and finally, a solid implan- 

 tation as in the Ccecilia, or a simple application, as in the 

 frogs. 



The class of fishes presents still less uniformity with regard 

 to its dental system than that -of reptiles, even if we turn our 

 attention only to that part of it which occupies the jaws ; 

 being all that we require for our present purpose. In fact, 

 without speaking of the merely "dents gyngivales" which do 

 not actually penetrate into the bone, nor of those which being 

 in numerous rows, one within another, applied to the surface 

 of the bone or sunk into it, cannot serve here for purposes of 

 comparison, — there exist species in which the teeth being 

 provided with a root as long as the crown, are fixed deeply 

 in the jaw, in a definite order and proportion ; but I know 

 of none at present, which ever have either in whole or in part, 

 the crown, and still less the root, complex in its structure. 



After this exposition of the essential characters presented 

 by the dental system in the four classes of vertebrated animals 

 which are provided with it, it seems we have reason to con- 

 clude, that the class of Mammalia being the only one in 

 w r hich, up to this time, posterior teeth having complex roots 

 and crowns, combined with anterior teeth that are simple in 

 both parts, and all these teeth firmly fixed into the jaw, have 

 been found ; — among which also there is an articulating con- 

 dyle, and a perfectly formed coronoid process, — the analogy 

 of one at least of the Stonefield jaws with this class, to have 

 been clearly demonstrated ; and that therefore the animal to 

 which it originally belonged must necessarily have been a 

 mammal. As to the other jaw, from which we acquired our 

 knowledge of the roots of the teeth, which are double and of 

 great length, and which jaw we have compared with the pre- 

 ceding, the resemblance we observe in the very remarkable 

 structure of the crowns hardly allows us to admit that where 

 the first is placed the second must not follow. We should 



