78 THE GEOLOGICAL EVIDENCES 



on the dorsal aspect of the brains of modern 

 mammals were also largely absent in the 

 earlier forms, or were disposed longitudinally, 

 instead of transversely, as we find them in 

 the lowest of recent placental mammals the 

 rodents, edentates, and insectivores. The same 

 law of cerebral development which is here indica- 

 ted for the Mammalia is also applicable to reptiles 



5. 6. 



5, Skull of Elotherium crassum, Miocene ; 6, Platygonus compressus 

 (peccary), Pliocene. (After Marsh.) 



