58 DTNOOERATA. 



'^riie comparison of the brain in this group with that of other mammals 

 from the same formation soon showed that the Dinocerata, although most 

 remarkable in this respect, were not alone in diminutive capacity of brain 

 power. A more extended comparison led to the fact that all of the 

 early Tertiary mammals had very small brains, and in many of them 

 the brain was of a low, almost reptilian, t\-})e. As the comparison 

 was extended to include tlie mammals from the higher divisions of the 

 Eocene, and from the Miocene, the same fact became more apparent, but a 

 gradual increase In size and quality of the brain soon became evident in 

 extending" the Investlo-ation to the animals of more recent "eoloolcal aye. 

 In bringing Into the Investigation the mammals from tlio Pliocene and 

 Quaternary, tlie improvement in brain ])ower became still more apparent, 

 and the outline of a general law of brain growth was soon determined. 



In tracing thus the different groups of mannnals, each from the early 

 Tertiary to tlie ])resent time, it Avas found tliat in every series where the 

 material was sufficient to make a fair comjjarison, the brain-growth had 

 been constant, and followed the same law. 



The results of this investigation Avere embodied b}' the author In a 

 general law of brain-growth in the extinct mammals throughout Tertiary 

 time. This law, briefly stated, was as follows : 



1. All Tertiarv mammals had small brains. 



2. There was a gradual Inci-ease in the size of the brain diu'ing this 

 period. 



o. This increase was confined mainly to tlie cerebral hemispheres, or 

 higher portion of the brain. 



4. In some groups, the convobitlons of the brain have gradually 

 become more complex. 



f). In some, the cerebellum and the olfactory lobes have even 

 diminished in size. 



6. There is some evidence that the same general hiw of brain 

 growth holds good for lilrds and Keptlles from the C^retaceous to the 

 present time.' 



^American Journal of Science and Ar/s, Vol. VIIT, p. GO, July, 18'74; and Vol. XII, 

 p. 61, July, 1876; see also the author's Monograph on tlie Odontornithes, p. 10, 4to, 

 Washington, 1880. 



