Page:Popular Science Monthly Volume 42.djvu/23

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tary movement, and we know approximately, but with less accuracy, the sensory area—i. e., the region essential to sensory processes. It will be seen from the accompanying diagrams that all the posterior half of the brain surface is, we may say roughly, sensory; and that it has been provisionally subdivided into regions for vision, hearing, tasting, etc.[1] If the surface at these points were crushed, pressed upon, replaced by a foreign growth, or removed by accident, there would be a corresponding mental loss—blindness, deafness, etc.

It is important to notice what a large part of the cortex is concerned with sensory processes, for it suggests in the strongest way that sensation must play some very great part in our mental life, and this modern psychology now most clearly recognizes. In fact, the extent of our sensory activity determines in great

PSM V42 D023 Median surface of the monkey brain.jpg

Fig. 3.—Median Surface of Brain of Monkey (after Horsley and Schäfer). Figs. 2 and 3 may be said to embody the views of Horsley and Schäfer more especially in regard to motor localization.

measure the degree of our consciousness, for there are all degrees of consciousness, from a maximum down to such a condition as we find in sleep, which has its degrees also.

The case of the boy that had but one seeing eye and one hearing ear, and who could at any time be put to sleep—i. e., rendered unconscious—by closing up the avenues of sense, is very instructive.

It will further be noticed that localization of function conse-

  1. The figures in this article are taken from Mills's Comparative Physiology, D. Appleton & Co., New York, 1890.