ENDOCRANIAL ANATOMY OF FOSSIL MAMMALS 369 
SUMMARY 
The brain of the ancient rodents, as indicated in the single 
cast studied, shows no more primitive characters than many 
modern rodents. There has been no cerebral development in 
this group since Oligocene times. 
The Insectivora, as indicated by Ictops, have retrograded in 
cerebral structure, as they have in other ways. This is shown 
by the fact that the Oligocene forms had a much more expansive 
neopallium than modern forms, as in the European hedgehog. 
There has been no advance in cerebral complexity in the group 
since Oligocene times. 
The aeluroid carnivores studied show a clear case of cerebral 
evolution. The three machairodonts, Dinictis, Hoplophoneus 
(?), and Smilodon, show progressive stages in the development of 
cerebral complexity. The neopallium, in this group of cats, was 
almost as extensive in Oligocene times as now. The rhinal 
fissure occupies nearly the same position in all forms studied. 
The acme of cerebral complexity of the fossil cats studied was 
reached in Smilodon from the Pleistocene, though a somewhat 
greater complexity is indicated in some modern cats. Modern 
cats, however, are not descended from these machairodonts. 
The two cynoid carnivores, Daphaenus and Aenocyon, indi- 
cate another clear instance of cerebral development since Oligo- 
cene times. This development is shown in the developing 
complexity of cerebral pattern and in the greater overhang of 
the cerebrum over the cerebellum. A close study of the menin- 
geal arteries in the Pleistocene wolf reveals important endocranial 
characters. 
The three types of oreodonts shown represent only a slight 
amount of diversity among these pig-like ruminants. 
