668 



THE BRAIN. 



the portion of Figs. 149, 150 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 latter or on the 

 mesial surface, or of the gyrus fornicatus (Fig. 150) 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 stim- 

 ulated, but these are not only feeble and experimentally uncertain, but 

 appear to be of a different nature from those resulting from stimulation of 



FIG. 150. 



Po.F 



Mesial Aspect of the Left Half of the Brain of Macacus, displayed by Section in the Median 

 Sagittal Plane and Removal of the Cerebellum. (Sherrington, after Horsley and Beevor.) Natural 

 size. The hatched and stippled parts of the surface show the regions of the cortex connected 

 with movements of the/oo<, knee, hip, tail, trunk, and neck respectively. The several positions of 

 the areas of cortex connected with vision and smell and with cutaneous sensation are indicated by 

 the appropriate words. The plane of section has passed through the corpus callosum, cc., cc., cc., 

 and through the anterior commissure, c., sparing the left pillar of the lornix, F.; behind it has 

 bisected the anterior part of the pons, laying open the aqueduct, Aq. (iter a tertio ad quartum 

 ventrieulum) ; Pons, the left half of the pons in frontal section ; Op., the optic commissure cut 

 across ; in, the root of the third cranial nerve ; FR., the frontal pole ; Oc., the occipital pole ; 

 On., the cuneus ; Pen , the precuneus ; Gfn, Gfn, Gfn, the gyrus fornicatus ; the unlettered fissure 

 seen to form the upper boundary of this gyrus in its supra-callosal part is the calloso-marginal ; 

 Pof, the parieto-occipital fissure. 



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. 

 569. 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 

 (Macac-us 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 move- 

 ments of the wrist, but also of the shoulder or of the digits, or of the neck ; 

 and so with the other areas. 



