FUNCTIONAL PARTS OF THE NERVOUS SYSTEM 71 



the contractions become more and more spasmodic and radiate to sur- 

 rounding muscles, until, finally, general convulsions, such as one sees in 

 epilepsy (" grand mal"), occur and put an end to this demonstration of 

 the motor centers. When these overlapping areas are destroyed in any 

 natural or artificial way, the corresponding muscles are paralyzed, and 

 most often permanently. Just what occurs in this cortical region when 

 the normal animal wills to make a muscular movement is not definitely 

 known. It is likely that incoming messages from the muscles, joints, and 

 skin direct in someway the continued innervation of the particular 

 outward motor paths to be employed in the movement, but just how we 

 cannot say. Morat supposes that there is a continual circulation of ner- 

 vous energy in the sensorimotor paths which store up stimuli for the 

 voluntary movements. Of the original stimulus to deliberate movements 

 we know nothing. In this sense these centers are not wholly motor, but, 

 as often called, sensorimotor. We have thus already taken a step here 

 toward considering the cortex essentially a network that is actuated as 

 a unit, at least in performing its motor functions. 



There is one aspect of the relations of the motor cortex, so called, to 

 muscular function which is attaining increased prominence namely, the 

 relations of the flexor movements to the extensor movements. There 

 is evidently a basal contrast between these sorts of movements related not 

 only to the method of balance in voluntary control, but at the foundation 

 also of emotional expression. Flexion is more characteristic of the 

 unpleasant emotions, while extensor movements are common in pleasant 

 emotions. This contrast appears to be far-reaching, involving perhaps 

 the whole matter of inhibition. Thus, Wedensky, in 1897, saw in stimu- 

 lation experiments on the motor cortex that excitation, for example, of 

 the motor center for extension on one side of the brain, augmented the 

 excitability of the flexor center of the other hemisphere and diminished 

 the excitability of the flexor center of the same side of the brain and 

 vice versa. Such a suggestion introduces interesting possibilities as to the 

 complexity of the arrangement of the nuclei controlling the coordination 

 of the various muscle-groups. This reciprocal mode of action is not 

 unknown in other parts of the organism and in widely differing functions. 

 Like many other problems, this one awaits more exact knowledge as to 

 the relation of the brain-paths and centers. 



THE SENSORY AREAS. The sensory areas of the cortex are more 

 numerous and more extensive than are the motor areas. The kinesthetic 

 sensations, concerned with the control of the muscles, as already noted, 

 are situated in the posterior central convolution just behind the fissure 

 of Rolando, in the region posterior to this, and in the anterior central 

 convolution. These are co-extensive with the centers of voluntary 

 movement. In addition, the mesial cortex seems to represent, in some 

 regions, these important afferent impulses, part of the frontal lobe and the 

 upper and posterior part of the gyrus fornicatus being also concerned. 

 On the lateral surface of the hemisphere still farther back is probably 

 the center which controls the stereognostic sense, by which the limbs, 



