The llise of the Mammals 



situated on tlie back of tlie head, the largest 

 of the series. These may have supported horns, 

 or they may merely have been covered with 

 callosities like those on the cheeks of the wart- 

 hog. From the smooth, rounded nature of the 

 bone this last sup2)osition seems the more prob- 

 able, but still short homs, something after the 

 fashion of those of a rhinoceros, may have been 

 present. Although herbivorous, the upper jaw 

 was armed with long, dagger-like canines, and 

 these, when the mouth was closed, w^ere guarded 

 by curious projecting flanges on the lower jaw. 

 Compared with the great Jurassic dinosaurs 

 and the mosasaurs and pterodactyls of the Cre- 

 taceous, this Eocene life was tame and common- 

 place, but none the less was it important, for 

 it marked the ascendency of animals with the 

 best developed brains. Not that our Eocene 

 friends had anything to boast of in the way of 

 cerebral development, although they were a 

 great improvement over Brontosaurus with his 

 2 pounds of brain to 20 tons of flesh. In all 

 of them the olfactory lobes, the organ of smell, 

 formed a much larger portion of the brain 



229 



