A VIEW IN PERSPECTIVE. 145 



the small animals, such as armadillos and sloths 

 succeeded in perpetuating themselves. The gigantic 

 Dinotherium and the Mastodon were exterminated, 

 and only two species of elephants remain to repre- 

 sent this once abundant type. In general, among 

 mammals, it was the smaller animals, those which 

 developed speed, as in the ungulates, or immense 

 activity and strength in capturing prey, as in the 

 Carnivora, that gradually became the most abundant, 

 and thus eventually the predominant types. The 

 development of bulk had been superseded by a new 

 phase of progression. Increased activity, as shown 

 by the power of flight, and the development of claws 

 and teeth for defence, took the place of size as the 

 most potent factor in the struggle for existence. 



The Mental Factor. 



But this phase of nature was soon to yield to 

 another higher force. From the earliest record we 

 have of animals we can see an indication of the final 

 era in the history, i. e., the era of mental activity. 

 The brain of the lower vertebrates was small and 

 indicated the possession of little intelligence. The 

 same was true of the brain of early mammals. In 

 some of them the brain was so small that it could 

 be passed through the neural canal of the lumbar 

 vertebrae, and was thus only a little larger than the 

 spinal cord. From the early Tertiary (9) period, 

 however, the size of the brain has been increasing. 

 At the same time with its increase in size, the brain 

 has been increasing also in complexity, the cerebral 

 lobes becoming larger and showing more of a ten- 



10 



