and of the Determination of Fossils. 291 



servers. T shall here endeavour to shew what are the me- 

 thods that ought to be followed ; at the same time warning 

 those who engage in the science for the first time, that the 

 theoretical considerations which follow can guide them only 

 in a general manner, and that nature alone can furnish the 

 knowledge necessary for ready and accurate determinations. 



Two of the principal laws of comparative anatomy ought 

 to be regarded as regulating the determination of fossil bones, 

 namely, the law of unity of organic composition, and the law 

 of agreement of characters. 



The law of unity of organic composition, by establishing 

 that all animals are composed of the same parts, similarly 

 disposed, renders the palaeontologist certain that the bone he 

 has to determine, even though belonging to a species of forms 

 altogether extinct, may be referred to one of the known bones 

 of the skeleton. It is, in some measure, this law which renders 

 the determination possible, and which regulates the first pro- 

 ceedings, as I shall afterwards shew. It must be here re- 

 marked that the opinion which may be entertained respect- 

 ing the generality of the law of the unity of organic compo- 

 sition, has but little influence on its applications. Whether 

 we consider it, as is done by some modern schools, as neces- 

 sary, and a priori to be proclaimed universal ; or whether we 

 confine ourselves to establish, a posteriori, a unity of plan in 

 vertebrate animals, the result is the same as regards palae- 

 ontology. AU naturalists are now agreed in recognising the 

 same important pieces of the skeleton in vertebrate animals, 

 or, at least, in each of the classes which compose this depart- 

 ment. 



The law of concordance of characters rests on the principle 

 that all the organs of an animal being arranged for a cer- 

 tain object, to secure for it a kind of special life, we may. 

 from the form of one of them, conjecture the principal cha- 

 racters of the rest. It consequently enables us, by the in- 

 spection of some fragments, to reconstruct the entire ani- 

 mal, and admits of more numerous and varied applications 

 in palaeontology than the preceding. It is by this law, for 

 example, that we can infer, from the form of some of the 

 bones of the feet, whether the animal was herbivorous or 



