4 INTRODUCTION TO CLASSIFICATION. 



skull with which it articulated, a knowledge of this law may 

 enable the palaeontologist to affirm, with great confidence, that 

 the animal of which it formed a part suckled its young and had 

 non-nucleated red blood- corpuscles ; and to predict that, should 

 the back part of that skull be discovered, it will exhibit two 

 occipital condyles and a well-ossified basi-occipital bone. 



Deductions of this kind, such as that made by Cuvier in the 

 Samous case of the fossil opossum of Montmartre, have often 

 been verified, and are well calculated to impress the vulgar 

 imagination ; so that they have taken rank as the triumphs of 

 the anatomist. But it should carefully be borne in mind, that, 

 like all merely empirical laws, which rest upon a comparatively 

 narrow observational basis, the reasoning from them may at any 

 time break down. If Cuvier, for example, had had to do with a 

 fossil Thylacinus instead of a fossil Opossum, he would not have 

 found the marsupial bones, though the inflected angle of the jaw 

 would have been obvious enough. And so, though, practically, 

 any one who met with a characteristically mammalian jaw 

 would be justified in expecting to find the characteristically 

 mammalian occiput associated with it; yet, he would be a bold 

 man indeed, who should strictly assert the belief which is implied 

 in this expectation, viz., that at no period of the world's history 

 did animals exist which combined a mammalian occiput with a 

 reptilian jaw, or vice versa. 



Not that it is to be supposed that the correlations of struc- 

 ture expressed by these empirical laws are in any sense acci- 

 dental, or other than links in the general chain of causes and 

 effects. Doubtless there is some very good reason why the 

 characteristic occiput of a Mammal should be found in association 

 with mammae and non-nucleated blood-corpuscles ; but it is one 

 thing to admit the causal connection of these phenomena with 

 one another, or with some third ; and another thing to affirm 

 that we have any knowledge of that causal connexion, or that 

 physiological science, in its present state, furnishes us with any 

 means of reasoning from the one to the other. 



Cuvier, the more servile of whose imitators are fond of 

 citing his mistaken doctrines as to the nature of the methods of 

 palaeontology against the conclusions of logic and of common 



