290 STUDIES IN PHYSIOLOGY 



in extent. In the higher mammals, on the other hand, the 

 convolutions increase enormously the gray matter on the 

 surface of the brain, and this accounts in a large measure 

 for the fact that man is the highest type of animal life. 



(2) While the relative size and importance of the cerebral 

 hemispheres of the forebrain increase as one ascends the 

 series from fish to man, one notes a more or less propor- 

 tional decrease in the size of the olfactory lobes. In man 

 the olfactory lobes are very small. Other mammals, like the 

 dog, in which the sense of smell is keen, have somewhat 

 larger olfactory lobes. 



(3) The increase in size and complexity of the midbrain 

 and the hindbrain is not as striking as is that of the fore- 

 brain. Yet when one compares the structure and functions 

 of the optic lobes, the cerebellum, and the medulla of man 

 with these parts of the brain of any of the lower groups of 

 animals, one sees that these parts, too, develop enormously 

 as one follows up the animal series. Doubtless one of the 

 surest ways of determining whether an animal stands high 

 or low in the scale of life is by making a careful study of 

 the degree of complexity of its nervous system. 



