734 THE POPULAR SCIENCE MONTHLY. 



the brain if spread out would be much greater in man than in the 

 lower animals, and far too great to be laid out fiat within the 

 head. There are many interesting facts which make one believe 

 that the greater the extent of brain surface in a man, or, to put it 

 a little differently, the more the folds and deeper the creases be- 

 tween them, the greater are the man's mental powers ; and just 

 here it becomes apparent that to judge of the extent of the entire 

 brain surface by the size of the head, or by the extent of the super- 

 ficial irregular surface which is covered by the skull without any 

 regard to the number of folds or their depth, is to fall into an 

 absurd error, and here we begin to see how baseless the old phre- 

 nology really is. 



For a little brain with many deep folds may really when spread 

 out have a larger surface than a large brain with few shallow 

 folds, and a so-called bump or elevation on the apparent surface 

 of the organ, even if it produces a corresponding elevation on the 

 head, which it frequently fails to do, will indicate nothing regard- 

 ing the number of the folds or the depth of the creases which lie 

 about it, so that it may be stated without hesitation that from the 

 size or shape of the head no conclusion whatever can be made as 

 to the extent of surface of the brain, and consequently no conclu- 

 sion can be reached regarding the mental capacity. 



But what lies underneath the brain surface ? The inner struct- 

 ure of the brain is interesting. Everywhere coming off from the 

 under surface are white threads which gather into bands and pass 

 downward and inward, and finally come out below in the form of 

 nerves. These are the lines of communication by which messages 

 from various parts of the body reach the brain, and along which 

 the impulses are sent out from the brain to the body which result 

 in speech and action. Imagine for a moment that from every 

 part of your hand little threads pass up the arm and find their 

 way to the brain, and there go to a special part of its surface and 

 end. It can be seen at once that you would have a little map of 

 the hand laid out on the brain surface, projected there, to use the 

 terms of the geographer; and in fact such a map of the entire 

 body could really be drawn on the brain surface if we could fol- 

 low all the little threads to their ends. A sensation which has 

 been sent in from your little finger has always gone to a definite 

 place in your brain, and whenever a message passes along that 

 thread and goes to the brain you feel a sensation in the little 

 finger. The thread goes along your funny-bone at the elbow, and 

 if you happen to strike it there you send a message along it to 

 the brain ; but as all such messages have usually come from the 

 little finger, the brain supposes that this one has also come from 

 there, and that is the reason that, although you strike your funny- 

 bone, you feel it in the finger. That also is the reason why peo- 



