48o THE POPULAR SCIENCE MONTHLY. 



To the nature of the convolutions our especial attention must be 

 directed. The brain-substance consists of gray and white nervous 

 matter. The gray matter forms the outermost layer of the brain- 

 substance, and incloses the white ; the opposite arrangement being 

 seen, curiously enough, in the spinal cord. Now, one evident purpose 

 of the convolutions of the brain is to largely increase the amount of its 

 gray matter relatively to the space in which the organ of mind is con- 

 tained ; while the perfect nutrition of the brain is also thus provided 

 for through its convoluted structure permitting a fuller distribution of 

 the minute blood-vessels which supply the brain with the vital fluid. It 

 is a very noteworthy fact that the structure of the gray matter differs 

 materially from that of the white. In the gray matter nerve-cells are 

 found in addition to nervous fibers, the former originating nervous 

 force, while the latter are simply capable of conveying this subtile force. 

 Thus it may be said that it is in the gray matter that thought is chiefly 

 evolved, and from this layer that purposive actions spring. The white 

 matter, on the other hand, merely conveys nerve-force and nervous im- 

 pressions, and is thus physiologically inferior in its nature to the gray 

 substance. The observations of Gratiolet, Marshall, and Wagner seem 

 to leave no room for doubt that the convolutions of the brain increase 

 with culture, and are therefore more numerous and deeper in civilized 

 than in savage races of men. It is curious, however, to observe that 

 certain groups of quadrupeds are normally " smooth-brained," and pos- 

 sess few or no convolutions. Such are rats, mice, and the rodents or 

 "gnawing" animals at large, and it can hardly be maintained that 

 in those animals intelligence is normally low or instinct primitive — 

 although, indeed, the just comparison of human with lower instincts 

 must be founded on a broader basis than is presented by this single 

 anatomical fact. 



A final observation concerning the anatomy of the brain relates to 

 its size and weight as connected with the intelligence. The phre- 

 nological doctrine of the disposition of the faculties must be held to 

 include the idea that the larger the brain, the better specialized should 

 be the mental quahties of the individual ; the greater the amount of 

 brain-substance forming the good and bad qualities and regions of the 

 phrenologist, the more active should be the mental organization. Now, 

 it is a patent fact that this rule tells strongly against the phrenologist's 

 assumption. True, various great men have had large brains ; but cases 

 of great men possessing small brains are equally common, as also are 

 instances where insanity and idiocy were associated with brains of large 

 size. The normal average human male brain weighs from 49 to 50 

 ounces ; man's brain being ten per cent, heavier than that of woman. 

 Cuvier's brain weighed 64|^ ounces ; that of Dr. Abercrombie 63 ounces ; 

 that of Spurzheim, of phrenological fame, 55 ounces ; Professor Good- 

 sir's brain attained a weight of 57|^ ounces ; Sir J, Y, Simpson's 

 weighed 54 ounces ; that of Agassiz 63'4 ounces ; and that of Dr. 



