231 



botli originated, had also brains of incomparably small volume; side 

 by side with the brain cast of Pheuacodiis, from the Wasatch 

 Formation of Wjoniing, tliar of a pig of similar size of the body 

 appears as gigantic (Fig. J, B). Also other Eocene Hoofed Mammalia, 

 the Amblypoda, had very sinall brains. Tims Coryphodon, from the 

 Wasatcij Formation, in comparison with a Rhinoceros of similar 

 size (Fig. 1, C). 



Fig. 1. Brain cast of: A. Arctocyon and Ganis ; B. Phenacodus 

 and Sus; C. Coryphodon and Rliinoceros. (After Osborn) i). 



In all these cases the most compounded, functionally most intri- 

 cate parts of the encephalon, especially the cerebrum (hatched in 

 Fig. J), have the smallest volume. They in particular have not yet 

 come to a fuller growth. But in the Miocene, partly already in the 

 Eocene Period, the brain in the Mammalia reaches the volume and 

 the proportion of its sub-divisions of most modern types. 



As remarkal)le as this sudden, at all events comparatively rapid 

 increase of the volume of the brain in the classes of Reptiles, Birds, 

 and Mammals is tlie other paleontological fact, that in the Hominides, 

 which geologically do not appear until very late, the brain imme- 

 diately possessed the same volume already in the earliest of the 

 Itnown crania as in modern ones. The expectation that by means of 

 these skulls a gradual increase of the volume of the brain might 

 be shown, up to the exceptional capacity whose possession raises 



1) H. F. OsBORN, The Age of Mammals in Europe, Asia and North America, 

 p. 173. New York 1910. 



15* 



