THE MOTOR AREAS 641 



this does not teach us anything definite as to the part of the central nervous 

 system in which the stimulus branches off from Lae main path to reach muscles 

 of the same side. It is probable that this place is to be sought among the gray 

 masses of the brain-stem. As Gotch and Horsley suggest, the cerebellum might 

 have a large share in this distribution of impulses from the cerebrum. 



D. THE COMMISSURES BETWEEN THE CORTICAL AREAS OF THE TWO 



HEMISPHERES 



One would suppose a priori that the corpus callosum, the great commissure 

 binding together the two hemispheres, must be of very great physiological 

 importance; and, in fact, the most far-reaching hypotheses have been erected 

 on this supposition. But the results of actual experiments designed to throw 

 light on the purpose of this part are very meager. Several authors (Longet, 

 Magendie, Flourens, Franck, Ferrier, Koranyi and others) have found that 

 separation of the two hemispheres by a complete sagittal section through the 

 corpus callosum produces no effect on the behavior of the animal (rabbit, 

 dog) provided the hemispheres be left entirely uninjured. Lesions of the 

 corpus callosum also produce no permanent effect (Wernicke). The neces- 

 sary cooperation between the two hemispheres in the functions of the brain 

 is therefore not brought about by the corpus callosum. 



The fibers running in the corpus callosum from one motor zone to the 

 other when stimulated from the upper surface of that body (except rostrum 

 and the splenium) produce bilateral muscular movements. Applying the 

 stimulus just behind the anterior genu gives movement of the head and eyes ; 

 applying it farther posteriorly we get in serial order: movements of the two 

 arms at the shoulder joints, and of the upper half of the trunk ; movements 

 of the forearm, hands and fingers; movements of the posterior half of the 

 trunk and of the tail; movements of the posterior extremities. No move- 

 ments of the face muscles have been obtained. It was only very rarely that 

 the movements were so isolated and so sharply localized as with stimulation 

 of the cortex. 



After extirpation of the motor zone on one side, the movements are uni- 

 lateral; they are induced therefore with the help of the motor zone. When 

 the corpus callosum is stimulated after sagittal section and after extirpation 

 of one hemisphere, unilateral movements are obtained on the side from which 

 the hemisphere has been removed. The excitation aroused by stimulating 

 the fibers of the corpus callosum passes therefore to both motor regions and 

 thence is propagated in the usual way to the nuclei of the motor nerves 

 (Mott and Schafer). 



For the effects of sectioning the corpus callosum in cases of lesion of the 

 cerebral cortex, see page 660. 



E. CORTICAL EPILEPSY 



It was observed by Fritsch and Hitzig in their early work on this sub- 

 ject that by continuous stimulation of the cerebral cortex of mammals, cramp- 

 like contractions can be produced which do not remain confined to the set 

 of muscles associated with the area stimulated, but may extend to all the 



