CEREBRAL LOCALIZATION 



847 



very small part of the superficial gray matter. They extend also into 

 the fissure of Rolando and the other fissures, and the extent of the ex- 

 citable area which is thus buried away in the fissures may exceed that 

 on the free surface of the hemispheres. 



It will be noted that there are two centers for the movements of the 

 eyes, one in the frontal lobe isolated from the motor area, and the 

 other at the tip of the occipital lobe. The former is the motor- center 

 for the conjugated movements of the two eyeballs, whereas the latter 

 functionates in association with the so-called visual center, which re- 

 ceives the visual impressions and transmits them to other parts of the 



Anus & fagina 

 Toes,? 

 Ankle > 

 Knee. 



,Sulcus centralis 



,-Abdomen 

 Chest 



Fingers 



sthum 



VES 



far 

 Eyelid- 

 Nose 



Closure 

 of jaw 



Vocal cords 



Sulcus central is 



Fig 219. Outer aspect of the brain of the chimpanzee, showing the position of the centers. 

 Electric stimulation at the parts indicated causes coordinate movements of the corresponding mus- 

 cle groups. (After Sherrington.) 



brain to be interpreted and correlated. Excitation of the center for 

 eye movements in the frontal lobe, say, of the right side, causes con- 

 jugate deviation of both eyes to the opposite side, that is, to the left; 

 and it can readily be shown that this movement of the eyeballs is the 

 result of reciprocal innervation of the extraocular muscles (page 814). 

 Even at the risk of repetition we w T ill again describe the fundamental 

 experiment that demonstrates this. When the eyes, as in the above 

 experiment, move to the left, it means that the internal rectus of the 

 right eye and the external rectus of the left are contracting, w r hereas 

 the external rectus of the former and the internal rectus of the latter 



