748 MOVEMENTS OF CORTICAL ORIGIN. [BOOK in. 



mesial portion ; that the upper thoracic with the lower cervical 

 nerves belong to a region lying lateral to, and the upper cervical 

 nerves to one lying in front of the preceding area ; and lastly 

 that the remaining lateral and ventral portions of the whole 

 motor region appertain to the cranial nerves. But the topo- 

 graphical differentiation does not come out so clearly by this 

 method, as by that of taking for our guide distinctive move- 

 ments of the several parts of the body. 



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

 sented by the portion of Figs. 123, 124 shaded in one way or an- 

 other, 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. 124) connecting 

 the frontal and occipital regions on the mesial surface, and run- 

 ning ventral to the marginal gyrus, does not give rise to move- 

 ments ; 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 less striking and experiment- 

 ally less certain than, 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. 



485. It is obvious from the foregoing that the mechanisms 

 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 differ- 

 entiation 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 ad- 

 vanced ; 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 

 conducted under unfavourable circumstances ; but so far as the 

 results obtained go, they shew that the topographical distribu- 



