92 THEORY OF THE EARTH. 



the gradations of their forms preserve an uninter- 

 rupted correspondence, even in those cases in 

 which we cannot account for their relations. 



Now, by thus adopting the method of observa- 

 tion as a supplementary means, when theory is no 

 longer able to direct our views, we arrive at asto- 

 nishing results. The smallest articulating surface 

 of bone, or the smallest apophysis, has a determi- 

 nate character, relative to the class, the order, the 

 genus, and the species to which it belonged; inso- 

 much, that when one possesses merely a well pre- 

 served extremity of a bone, he can, by careful ex- 

 amination, and the aid of a tolerable analogical 

 knowledge, and of accurate comparison, determine 

 all these things with as much certainty as if he had 

 the entire animal before him. I have often made 

 trial of this method upon portions of known ani- 

 mals, before reposing full confidence upon it, 

 in regard to fossil remains; and it has always 

 proved so completely satisfactory, that I have no 

 longer any doubts regarding the certainty of the 

 results which it has afforded me. 



It is true, that I have enjoyed all the advan- 

 tages which were necessary for the undertaking ; 

 and that my favourable situation, in the Museum 

 of Natural History at Paris, and assiduous re- 

 search for nearly thirty years, have procured me 

 skeletons of all the genera and sub-genera of qua- 

 drupeds, and even of many species in some 

 genera, and of several varieties of some species. 



