196 Darwin, and after Darwin. 



evolved into larger and larger proportions in respect of 

 its cerebral hemispheres, or the upper masses of it 

 which constitute the seat of intelligence. Thus, if we 

 look at the above series of wood-cuts, which re- 

 presents the comparative structure of the brain in the 

 existing classes of the Vertebrata, we can immediately 

 understand why the fossil skulls of Mammalia should 

 present a gradual increase in size and furrowing, so 

 as to accommodate the general increase of the brain 

 in both these respects between the level marked 

 " maml " and that marked " man," in the last of the 

 diagrams. (Fig. 87.) 



The tabular statement on the following diagram, 

 which I borrow from Prof. Cope, will serve at a glance 

 to reveal the combined significance of so many lines 

 of evidence, united within the limits of the same group 

 of animals. 



To give only one special illustration of the principle 

 of evolution as regards the skull, here is one of the 

 most recent instances that has occurred of the dis- 

 covery of a missing link, or connecting form (see 

 Fig. 88). The fossil (B), which was found in New 

 Jersey, stands in an intermediate position between the 

 stag and the elk. In the stag (A) the skull is high, 

 showing but little of that anterior attenuation which 

 is such a distinctive feature of the skull of the elk (C). 

 The nasal bones (N) of the former, again, are re- 

 markably long when compared with the similar bones 

 of the latter, and the premaxillaries (PMX), instead 

 of being projected forward along the horizontal plane 

 of the base of the skull, are deflected sharply down- 

 ward. In all these points, it will be seen, the newly 

 discovered form (Cervalces) holds an intermediate 



