Page:Popular Science Monthly Volume 35.djvu/760

734 the train if spread out would be much greater in man than in the lower animals, and far too great to be laid out flat 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 between 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 superficial 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 phrenology 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 regarding 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 conclusion can be reached regarding the mental capacity.

But what lies underneath the brain surface? The inner structure 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 follow 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