CHAP. IL] THE BRAIN. 1043 



not come out so clearly by this method, as by that of taking for 

 our guide distinctive movements of the several parts of the body. 



It will be observed that all these areas taken together, repre- 

 sented by the portion of Figs. 126, 127 shaded in one way or 

 another, occupy chiefly the parietal region of the cerebral surface 

 though they also reach into the frontal region. Stimulation of the 

 frontal region in front of this motor area or of the occipital region 

 behind, whether on the lateral or on the mesial surface, or of 

 the temporal region, whether also on the lateral or on the mesial 

 surface, or of the gyrus fornicatus (Fig. 127) connecting the frontal 

 and occipital regions on the mesial surface, and running ventral 

 to the marginal gyrus, does not give rise to movements ; or to be 

 more exact, does not give rise to movements comparable to those 

 just described as resulting from stimulation of various parts of the 

 motor region. Movements do take place when certain parts of the 

 occipital or of the temporal region are stimulated, but these are 

 not only feeble and experimentally uncertain, but appear to be of 

 a different nature from those resulting from stimulation of the 

 motor region ; it will be convenient to speak of the nature and 

 meaning of this kind of movement when we come to discuss the 

 development of sensations. 



656. It is obvious from the foregoing that the mechanism 

 for the development of these movements of cerebral origin are far 

 more highly differentiated in the monkey than in the dog. But 

 even in the monkey (Macacus and allied forms) the differentiation 

 is still very incomplete. If we explore for instance the area for the 

 wrist we find that its limits are ill-defined. In some parts of the 

 area we obtain movements of the wrist only, but in other parts of 

 the area stimulation produces not only movements of the wrist, 

 but also of the shoulder or of the digits, or of the neck ; and so 

 with the other areas. 



If, however, not a Macacus or other ordinary monkey, but the 

 more highly developed ourang otang be taken as the subject of 

 experiments, the differentiation is found to be distinctly advanced ; 

 the several areas are more sharply defined, and what is important 

 to note, the respective areas tend to be separated from each by 

 portions of cortex, stimulation of which gives rise to no movement 

 at all. 



The opportunities of stimulating the cortex of man himself have 

 been few and far between, and have for the most part been con- 

 ducted under unfavourable circumstances ; but as far as the results 

 so obtained go, they shew that the topographical distribution of 

 areas for the several movements is carried out on the same plan as 

 in the monkey (we are purposely confining ourselves now to the 

 results of artificial stimulation) ; and moreover, justify the con- 

 clusion, which a priori reasons would lead us to adopt, that in man 

 the differentiation is advanced still farther than in the monkey. 



Thus when we survey a series of brains in succession, from the 



