THE MOTOR AREAS 645 



removed without destroying the animal's ability to close the fist on the opposite 

 side or to use the hand in grasping objects. Sherrington has made similar obser- 

 vations on the anthropoid apes. 



Goltz had the opportunity of observing for more than ten years a monkey in 

 which the greater part of the frontal and parietal lobes on the left side had been 

 destroyed. Thus the motor region of the left hemisphere was entirely or almost 

 entirely thrown out of function. Nevertheless, by practice the monkey succeeded 

 in recovering his ability to use the right arm and right hand for definite pur- 

 poses. He learned to grasp fruits with the right hand and to offer it in greet- 

 ing, etc. He could move all of the muscles directly under control of the will, but 

 the movements of the right limbs remained incomplete, cumbrous and awkward. 



After these observations it scarcely ought to be longer assumed that the 

 motor region in the monkey is of much greater importance than it is in 

 the dog. It is indeed very probable that there is a difference in degree be- 

 tween the two, but certainly not a difference in kind. 



Horsley and Schafer's observations point to the interesting fact that in 

 the monkey the motor cortical areas on the upper medial surface of the hemi- 

 spheres are concerned mainly with what we may call the coarser movements, 

 those by which the body is kept in its natural position and moves itself from 

 place to place. The cortical areas on the convex surfaces of the hemisphere 

 are of decidedly greater importance for the more refined movements, e. g., 

 those which are executed by the muscles of the head, face and arms. 



In order to establish the location and influence of the motor cortical areas 

 in the human brain, we have recourse either to excitation experiments or to 

 clinical and pathological observations. The former evidently can never be 

 very numerous, and our knowledge of the functions of the human motor cortex 

 rests mainly on clinical observations of the effects of lesions in the cerebrum. 



It not infrequently happens that in post-mortem examinations very ex- 

 tensive lesions of the cerebral cortex are found, which were not accompanied 

 in life by any observable disorder. Compilations of such cases, which we 

 owe to Charcot and Pitres, Exner, Nothnagel and others show that these 

 cortical fields which have no direct significance for the bodily movements 

 embrace all parts of the cortex with the exception of the anterior central 

 convolution inclusive of the operculum, the paracentral lobule, and the pos- 

 terior part of the frontal convolutions. But if the lesions are found within 

 the portions just named, a more or less extensive disturbance in the move- 

 ments of the opposite half of the body is sure to have been observed. Hence 

 we can say that the motor cortical field in man has on the whole the same 

 extent as the cortical zone in the anthropoid apes, and that this covers the 

 anterior central convolution inclusive of the paracentral lobule, and the foot 

 of the frontal convolutions. 



For working out the cerebral localization in detail the very small cortical 

 lesions are of course the important ones. The more restricted the lesion, the 

 more limited will be the disturbance of function, and of course the more 

 definitely can the location of a particular field be decided upon. Such lesions 

 have yielded results which agree essentially with the corresponding observa- 

 tions on the brain of the anthropoid apes, and with the excitation experi- 

 ments on the human brain itself. 



