Palontology. 195 
construction of teeth, which has already been depicted 
as regards the particular case of the Horse-family (Fig. 
83), is no less apparent in the pedigree of all the 
other mammalia, wherever the palaontological history 
is sufficiently intact to serve as a record at all. 
(weve 
Fic. 87.—Ideal section through all the above stages. (After Le Conte.) 
Lastly, as regards the skull, casts of the interior 
show that all the earlier mammals had small brains 
with comparatively smooth or unconvoluted surfaces ; 
and that as time went on the mammalian brain 
gradually advanced in size and complexity. Indced 
so small were the cerebral hemispheres of the primitive 
mammals that they did not overlap the cerebellum, 
while their smoothness must have been such as in this 
respect to have resembled the brain of a bird or reptile. 
This, of course, is just as it ought to be, if the brain, 
whichthe skull has to accommodate, has been gradually 
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