192 Professor Marsh's Monograph of the Dinocerata. 
“The nerves passing off from the brain were large, and can 
be made out with reasonable certainty. The olfactory lobes 
were separated in front by an osseous septum, the position of 
ich is shown distinctly in figure 22. 
“In the genus Zinoceras, the brain was similar in its general 
characters to that of Dinoceras, but appears to have been some- 
what more highly developed. The hemispheres were more 
elongate, and the olfactory lobes relatively smaller. 
FIGURE 26,—Skull of Mastodon Americanus, Cuvier. Pliocene. 
Brain GrowrTu. 
“The Dinocerata are, by far, the largest of all known Eocené 
animals, and that they have, also, a very diminutive brain 18 4 
noteworthy fact, which attracted the author’s attention 800? 
after their discovery. 
‘The comparison of the brain in this group with that of other 
mammals from the same formation soon showed that the 
cerata although most remarkable in this respect, were not 
alone in diminutive capacity of brain power. A more &© 
tended comparison led to vf fact that all the early Tertiary 
mammals had very small brains. 
