6OO THE NERVOUS SYSTEM 



The fundamental phenomena observed in all these cases may be thus 

 epitomized: 



i. Excitation of the same spot on the cortex 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 definition. 

 3. In different animals excitations of anatomically corresponding spots pro- 

 duce 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 descrip- 

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



In the case of the dog the results obtained 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 co-ordinated 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 further researches of Schafer and Horsley, electrical 

 stimulation of the marginal convolution internally at the parts corresponding 

 with the ascending frontal and parietal convolutions, from the front back- 

 ward, 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 the dog's brain. It was found that the part might be sliced away or 

 washed away with a stream of water, but that no permanent paralysis ensued. 



More extensive observations, however, have, in the main, confirmed 

 Ferrier' s original statement, at any rate \vith regard to the monkey's brain. 

 Destruction of the motor areas for the arm produces some permanent paraly- 

 sis of the arm of the opposite side, and similarly of that for the leg, paralysis 

 of the opposite leg. If both areas are destroyed, permanent hemiplegia 

 ensues. Paralysis of so extensive and permanent a character does not, how- 

 ever, appear the rule when the brain of a dog is used instead of that of the 

 monkey. It is suggested that in the animal lower in the scale the functions 

 which in the monkey are discharged by the cortical centers may be subserved 

 to a greater extent by the basal ganglia. 



Motor Areas of the Human Brain. It is naturally of great impor- 

 tance to discover how far the results of experiments upon the dog and monkey 

 hold good with regard to the human brain. Evidence furnished by diseased 



