Page:Popular Science Monthly Volume 35.djvu/759

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animals certain regions of the brain can be mapped out and can be assigned to the different senses. It has thus been proved that in their action as well as in their structure the brains of man and of animals are alike.

If in structure and in function all brains are somewhat similar, it may be interesting to obtain a little notion of what a brain is really like. The figure will demonstrate this very well.

PSM V35 D759 Diagram of the left cerebral hemisphere.jpg
Fig. 1.—Diagram of the External Surface of the Left Cerebral Hemisphere (modified from Ecker).

It shows that the brain is an egg-shaped organ with an irregular surface of a yellowish-gray color. The irregularities are formed by a folding of the surface layer so as to accommodate itself to the small space in the head. To illustrate this, when a handkerchief is spread out over the hands it takes up a great space, and a box in order to hold it would have to be of large size; but by gathering the handkerchief up in the hands it is thrown into folds, and, although its actual surface is not decreased, the space it occupies is much diminished, and it could now be put in a very small box and yet all be there, but then its surface would be irregular and show many creases. Now, what was done to the handkerchief Nature has done to the brain as it has developed. In the lower animals and in an early stage of life the folds are few and simple, but in man when full grown they are many and complex. This only means that the actual surface of