CHAPTER XVL 



THE EVOLUTION OF MIND. 



That the amc ant of intelligence manifested by any V(;rtel)rate 

 animal depends to a certain extent upon the amount of nerve- 

 tissue integrated in its cephalic ganglia, and especially in the 

 cerebrum, is a truth familiar to everyone, though often crudely 

 stated and incorrectly interpreted. In the lowest vertebrate, 

 the amphioxus, there is no brain at all. In fishes, the cere- 

 brum and cerebellum are much smaller tb.an the optic lobes ; 

 the cerebrum being in many large ftshes about the size of a 

 pea, though in the shark it reaches the size of a plum. Con- 

 tinuing to grow by the addition of concentric layers at the 

 surface, the cerebrum becomes somewliat larger in birds and 

 in the lower m.ammals. It gradually covers up the optic 

 lobes, and extends backwards as we pass to higher mamma- 

 lian forms, until in the anthropoid apes and in man it covers 

 the whole upper surface of the cerebellum. In these highest 

 animals it begins also to extend forwards. In the chimpanzee 

 and gorilla the anterior portion of the cerebrum is larger than 

 in inferior mammals ; but in these animals, as in the lowest 

 races of men, the frontal extension is but slight, and the fore- 

 head is both low and narrow. In civilized man, the anterior 

 portion of the cerebrum is greatly extended both vertically 

 and laterally. As already observed, the most prominent 

 physiological feature of human progress has been the growth 

 of the cerebrum. The cranial capacity of an averag Euro- 



