636 PHYSIOLOGY OF THE CEREBRUM 



thus the lower part of the two central convolutions is related to the muscula- 

 ture of the face, the middle part to that of the anterior extremity, and the 

 upper part to the muscles of the posterior extremity. On the very edge of the 

 hemisphere is an area for the movements of the trunk. That portion of the 

 motor zone lying immediately in front of the anterior central convolution is 

 adapted for movements of the head and eyes. 1 



In the gyrus marginalis on the medial surface of the hemisphere we find 

 in serial order from anterior to posterior areas for the head, the anterior 

 extremity, the trunk 2 and the posterior extremity. 



On closer investigation of the subject we find that within each of the 

 cortical areas for the greater divisions of the musculature, a specialization 

 like that shown diagrammatically in Fig. 287 3 can be demonstrated. 



The movements obtained by cortical stimulation are in many respects 

 similar to voluntary movements. As a rule they represent the combined 

 action of several groups of muscles; they are seldom performed by a single 

 group and never by a single muscle. 



In stimulating the cerebral cortex of the monkey Sherrington observed 

 that simultaneously with the contraction of certain eye muscles, the tonus 

 of the antagonistic muscles decreased (cf. page 6-10). This is by no means 

 an isolated phenomenon, for according to further observations by Hering, Jr., 

 and Sherrington, it appears to be a general rule that on stimulation of a 

 definite point in the cortex, contraction of the appropriate muscle is accom- 

 panied by relaxation of its antagonist. For example, on stimulation of the 

 point in the cortex for extension of the elbow, one gets contraction of the 

 triceps group and at the same time relaxation of the biceps, or on stimulation 

 of the point for extension of the fingers, one gets contraction of the extensores 

 and relaxation of the flexores digitorum, etc. These authors declare that in 

 the monkey they never observed simultaneous contraction of true antagonists, 

 such as the extensor and flexor of the elbow. The simultaneous contractions 

 of antagonistic muscles described by other authors might have been due among 

 other things to diffusion of the stimulus from one cortical field to another 

 lying near it. 



When a stimulus applied to a given field in the cortex produces movements 

 in other muscles than those corresponding strictly to that field, it is observed 

 that the movement always spreads first to other muscles of the same member 

 e. g., contractions of the shoulder muscle are accompanied by movements in 

 all the muscles of the anterior extremity even down to the fingers. If the 

 initial contraction be in the muscles of the thumb, the movements spread 

 farther and farther up the arm to the wrist, elbow and shoulder. 



The contributions of Beevor and Horsley on the motor zone of the orang- 



1 According to Bechterew, contractions of the brow, closure of the lids, and movements 

 of the ear are also obtained from this part of the cortex. 



2 According to H. Munk, the cortical area for the musculature of the trunk lies in the 

 frontal lobe. 



3 For the sake of simplicity, the different fields in this figure have been represented as 

 if they were sharply distinct from one another, whereas in reality there are no sharp 

 boundaries demonstrable, either between the smaller areas or the larger areas. One field 

 always passes gradually into the other. 



