Page:Popular Science Monthly Volume 42.djvu/780

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THE POPULAR SCIENCE MONTHLY.

muscle rotates the body outward on the fixed thigh and thus brings the center of gravity of the person over the resting foot. If it were not for these muscles we should run a risk of falling down as we lifted one leg instead of balancing ourselves with comfort upon that one which is resting upon the ground.

But we may now pass away from the muscles and nerves to the nervous centers from which they receive their stimulus to action, and whatever doubt may exist in regard to the adaptation of the muscles to the peripheral nerves and the action of pluckingPSM V42 D780 Dog brain diagram.jpgFig. 11.—Diagram of Brain of Dog. (After Ferrier.) C. S., Crucial sulcus. 1. Movements of eyes, as if to see freely. 2 and 3. Movements of fore leg, and 4, of hind leg, as in running. 5. Movements of tail requisite in turning quickly, as when a greyhound is following a hare when it doubles, x x x Movements of mouth and jaws. and eating the apple, I think there can be no doubt at all that such an arrangement exists in the motor centers of the brain. These centers were localized in the monkey by Ferrier, and it is the difficulty I have had in remembering their position that has led me to arrange them in accordance with some definite movements in a series of actions to which I have found they corresponded. If we start from the posterior part of the second frontal convolution, pass upward along it and then across to the ascending frontal convolution, follow this downward parallel to the fissure of Rolando, and then turning the end of this fissure ascend again upward along the parietal convolution which lies behind the fissure, we find (Fig. 9) that the centers are arranged in the very order required for looking at the apple, stretching out the hand to take it, bringing it to the mouth, separating the seeds and throwing them away. The aim and object of the whole series of actions is to eat the apple, and we find that the centers for doing this are situated exactly where we should expect them—at the very end of the fissure of Rolando. In Ferrier's description we know that the movement which brings the hand to the mouth appears to be repeated on both sides of the fissure of Rolando, but it appears that the part anterior to the former would bring the hand to the mouth with the apple, while the part situated behind the fissure of Rolando would throw the remnants of it away. And here comes in a very interesting point: In order to complete the series of actions necessary for Eve to go and get another apple for Adam, you require movements of the leg (Fig. 10), and these are not fully represented on the surface of the brain. But