MOTOR FUNCTION OF THE CEREBRAL CORTEX 579 



movement is extremely small, and admits of very accurate definition. 3. In 

 different animals excitations of anatomically corresponding spots produce 

 contractions in similar or corresponding muscles. 



The various definite movements resulting from the electric stimulation 

 of circumscribed areas of the cerebral cortex are enumerated in the description 

 of the accompanying figures of the dog's and monkey's brains. 



In the case of the dog the results obtamed are summed up as follows by 

 Hitzig: i, One portion, anterior, of the convexity of the cerebrum is motor; 

 another portion, posterior, is non-motor. 2, Electric stimulation of the motor 

 portion produces coordinated muscular contraction on the opposite side of the 

 body. 3, With very weak currents, the contractions produced are distinctly 

 limited to particular groups of muscles; with stronger currents the stimulus 

 is communicated to other muscles of the same or neighboring parts. 4, The 

 portions of the brain intervening between these motor centers are inexcitable. 



Following strong stimulation of cortical motor centers other groups of 

 muscles than those innervated by the centers stimulated may also take part in 

 the contractions. 



According to the observations of Ferrier, confirmed and extended by later 

 experimenters, stimulation of various parts of the monkey's brain, as indicated 

 by the numbers in figures 409, 410, produces movements of definite muscles, 

 thus: Stimulation of the district marked i causes movement of hind foot; 

 of 2, chiefly adduction of the foot; of 3, movements of hind foot and tail; 

 of 4, of latissimus dorsi ; of 5, extension forward of arm; a, b, c, d, movements of 

 hand and wrist; of 6, supination and flexion of forearm; of 7, elevation of the 

 upper lip; of 8, conjoint action of elevation of upper lip and depression of 

 lower; of 9, opening of mouth and protrusion of tongue; of 10, retraction of 

 tongue; of n, action of platysma; of 12, elevation of eyebrows and eyelids, 

 dilatation of pupils, and turning head to opposite side; of 13, eyes directed to 

 opposite side and upward, with usually contraction of the pupils; of 13', similar 

 action, but eyes usually directed downward; of 14, retraction of opposite ear, 

 head turns to the opposite side, the eyes widely opened and pupils dilated; of 

 15, stimulation of this region, which corresponds to the tip of the uncinate 

 convolution, causes torsion of the lip and nostril of the same side. 



It is thus seen that the motor areas chiefly correspond with the ascending 

 frontal and ascending parietal convolutions, and that the movements of the leg 

 are represented at the upper part of these convolutions, then follow from above 

 downward the centers for the arms, the face, the lips, and the tongue. 



According to the further researches of Schafer and Horsley, electrical stim- 

 ulation of the marginal convolution internally at the parts corresponding with 

 the ascending frontal and parietal convolutions, from the front backward, 

 produces movements of the arm, of the trunk, and of the leg. 



A good deal of doubt was thrown upon the experiments of Ferrier by Goltz 

 and other observers, from the results of excising the so-called motor areas of 



