FUNCTIONS OF THE CEREBRUM. 701 



Comparative Development of the Cerebrum in the Lower Animals. It is only neces- 

 sary to refer very briefly to the development of the cerebrum in the lower animals as 

 compared with the human subject, to show the connection of the hemispheres with intel- 

 ligence. In man, the cerebrum presents an immense preponderance in weight over other 

 portions of the encephalon ; and, in some of the lower animals, the cerebrum is even less 

 in weight than the cerebellum. In man, also, not only the relative but the absolute 

 weight of the brain is greater than in lower animals, with but two exceptions. Todd 

 cites a number of observations made upon the brains of elephants, in which the weights 

 ranged from nine to ten pounds. Rudolphi gives the weight of the encephalon of a whale, 

 seventy-five feet long, as considerably over five pounds. With the exception of these 

 animals, man possesses the largest brain in the zoological scale. 



Another interesting point in this connection is the development of cerebral convolu- 

 tions in certain animals, by which the relative amount of gray matter is increased. In 

 fishes, reptiles, and birds, the surface of the hemispheres is smooth ; but, in many mam- 

 malia, especially in those remarkable for intelligence, the cerebrum presents a greater or 

 less number of convolutions, as it does in the human subject. 



Comparing the relative size of the brain, its complexity of organization, and the 

 increase of its gray substance by convolutions, with the development of intelligence in the 

 animal scale, it is so evident that the cerebrum is the organ presiding over the intellectual 

 faculties, that this point in our argument seems to need no farther discussion. 



Development of the Cerebrum in Different Races of Men and in Different Individuals. 

 It may be stated as a general proposition, that, in the different races of men, the cere- 

 brum is developed in proportion to their intellectual power ; and, in different individuals 

 of the same race, the same general rule obtains. Still, this law presents marked excep- 

 tions. Certain brains in an inferior race may be larger than the average in the superior 

 race ; and it is frequently observed that unusual intellectual vigor is coexistent with a 

 small brain, and the reverse. These exceptions, however, do not take away from the force 

 of the original proposition. As regards races, the rule is found to be invariable, when a 

 sufficient number of observations are analyzed, and the same holds true in comparing a 

 large number of individuals of the same race. Average men have an advantage over 

 average women of about six ounces of cerebral substance ; and, while many women are 

 far superior in intellect to many men, such instances are not sufficiently numerous to 

 invalidate the general law, that the greatest amount of intellectual capacity and mental 

 vigor is coincident with the greatest quantity of cerebral substance. If we accept the 

 view, which is in every way reasonable, that the gray substance of the cerebral hemi- 

 spheres is the generator of the mind, it would be necessary, in comparing different indi- 

 viduals with the view of establishing a definite relation between brain-substance and 

 intelligence, to estimate the amount of gray matter; but it is not easy to see how this can 

 be done with any degree of accuracy. 



It is undoubtedly true that proper training and exercise develop and increase the vigor 

 of the intellectual faculties, and that thereby the brain is increased in power, as are the 

 muscles under analogous conditions. This will perhaps explain some of the exceptions 

 above indicated ; but an additional explanation may be found in differences in the quality 

 of brain-substance in different individuals, independently of the size of the cerebral hem- 

 ispheres. One evidence that these differences in the quality of intellectual working 

 matter exist is, that some small brains actually accomplish more and better work than 

 some large brains. This fact may be due to differences in training, to the extraordinary 

 development in some individuals of certain qualities, to intensity and pertinacity of pur 

 pose, capacity for persistent labor in certain directions, a fortunate direction of the men- 

 tal efforts, opportunity and circumstances, etc. ; but, aside from these considerations, it 

 is exceedingly probable that there are important individual differences in the quality of 

 generating nervous matter. 



