THEORY OF THE EARTH. 83 



these constitute the only resources of knowledge 

 to the naturalist in this department. It may al- 

 so be stated, that most observers, deterred by 

 these difficulties, have passed slightly over the 

 fossil bones of quadrupeds ; have classed them in 

 a vague manner, according to superficial resem- 

 blances, or have not even ventured to assign them 

 a name ; so that this part of the history of fossil 

 remains, although the most important and most 

 instructive of all, is, at the same time, that which 

 has been the least cultivated *. 



Principle by which this determination is effected. 



Fortunately, comparative anatomy possesses a 

 principle, which, when properly developed, en- 

 ables us to surmount all the obstacles. This prin- 

 ciple consists in the mutual relation of forms in 

 organised beings, by means of which, each species 

 may be determined, with perfect certainty, by 

 any fragment of any of its parts. 



Every organised being forms a whole, a pe- M 

 culiar system of its own, the parts of which mu- 



* I do not intend by this remark, as I have already ob- 

 served on a former occasion, to detract from the merit of the 

 observations of Camper, Pallas, Blumenbach, Sremmering, 

 Merk, Faugas, Rosenmiiller, Home, &c. ; but their excellent 

 works, which have been very useful to me, and which I quote 

 throughout, are incomplete ; and several of these works have 

 only been published since the first editions of this Essay. 



F 2 



