Page:Popular Science Monthly Volume 27.djvu/82

70 that end in closing the fist; in connection with these centers we may note Nos. 4 and 5; they produce movements of the opposite arm and hand. It is plain that 4 and 5, and a, b, c, d, are closely related to one another.

According to the theory of localization of functions, we should expect the centers, a, b, c, d, to be extensive in the monkey's brain, and to be wanting in the brains of lower animals. As matter of fact, they are absent in cat, dog, and jackal, except that a is found in the brain of the cat. This animal uses the front-paw for seizing and holding. Upon stimulating center No. 6, the fore-arm bends, and the hand lifts to the mouth. This movement is constant with the monkey. There is no corresponding center in the brain of the dog or cat. The centers marked 7, 8, 9, 10, 11, are all concerned with movements of the mouth—such as elevating the angle of the mouth, depressing the lower lip, thrusting out and withdrawing the tongue. No. 12 lies quite to the front of the brain; when it is stimulated, the eyes open widely, the pupils dilate, head and eyes turn toward the opposite side.

These are the centers in the brain which, by some authorities, are thought to have a purely motor significance. The centers marked 13, 13', 14, and 15, give movements—the former of the eyes, the latter of the nostrils but they are believed to be primarily connected with sensations.

Aside from the centers enumerated, no other parts of the brain respond to stimulation.

I have purposely stated the results of Ferrier's earlier experiments on the so-called motor zone. These experiments have been, in general, confirmed by other investigators. That is to say, the movements above described have been found by many to follow stimulation. It is, however, a part of the present confusion and contradiction which prevails respecting cerebral localization that the interpretation of these movements is disputed.

Munk appears ("Transactions of the Physiological Society of Berlin," 1876-1878) with a series of experiments which, as he thinks, prove that the motor zone is primarily a zone of feeling. He therefore divides this portion of the brain into spheres of feeling—one for the forward limbs, one for the head, one for the eyes, one for the ears, etc. Munk believes that the animal's movements are affected by destruction of these centers, because four distinct kinds of feeling are destroyed. For example, loss of the center concerned with movements of the fore-limb would, according to Munk, cause a loss—1. Of the consciousness of pressure on the limb; 2. Of the consciousness of the position of the limb; 3. Of the consciousness of the motions belonging to the limb; and, 4. Of the consciousness of touch in the limb. Whereas Ferrier and others find sensibility, both general and special, intact after destruction of these motor regions, Munk finds a loss of