THE KEBVOUS SYSTEM. 



bral cortex responded to electric irritation. They employed a weak con- 

 stant current in their experiments, applying a pair of fine electrodes not 

 more than y 1 ^ in. apart to different parts of the cerebral cortex. The 

 results tl;us obtained have been confirmed and extended by Ferrier and 

 many others, chiefly with induction currents. 



The fundamental phenomena observed in all these cases may be thus 

 epitomized: 



(1). Excitation of the same spot is always followed by the same 

 movement in the same animal. (2). The area of excitability for any 

 given movement is extremely small, and admits of very accurate defini- 

 tion. (3). In different animals excitations of anatomically corresponding 

 spots produce similar or corresponding results. 



The various definite movements resulting from the electric stimulation 

 of circumscribed areas of the cerebral cortex, are enumerated in the de- 

 scription of the accompanying figures of the dog and monkey's brain. 



In the case of the dog, the results obtained are summed up as fol- 

 lows, by Hitzig: 



(a.) One portion (anterior) of the convexity of the cerebrum is 

 motor; another portion (posterior) is non-motor, (b.) Electric stimu- 

 lation of the motor portion produces co-ordinated muscular contraction 

 on the opposite side of the body. (c. ) 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, (d. ) The portions of the 

 brain intervening between these motor centres are inexcitable by similar 

 means. 



Motorial area of the Monkey^ s Brain. 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 

 figs. 380, 381, produces movements of definite muscles, thus: 



Stimulation of the district marked 1, 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; #, 

 , , 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 eleva- 

 tion of upper lip and depression of lower ; of 9, opening of mouth and 

 protrusion of tongue; of 10, retraction of tongue; of 11, 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 oppo- 

 site ear, head turns to the opposite side, the eyes widely opened, and 

 pupils dilated; of 15, stimulation of this region, which corresponds to 



