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. (Tig. 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 (sce 
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 
