LOCALISATION OF FUNCTION. 263 



widely separated on the surface of the body tend to be 

 distributed in widely separated portions of the cortex. 

 This relation between the larger areas is repeated in a 

 very remarkable way by the smaller centres composing 

 them. It is there found, as can be seen by consulting 

 the diagram, Fig. 55, that the point of the cortex, the 

 stimulation of which gives rise to movements of the 

 muscles controlling the most proximal joints of a limb, 

 the shoulder, for example, is farthest separated from the 

 portion which controls the most distal joints, those of 

 the fingers, and that the intermediate joints are repre- 

 sented by centres lying between them. In this respect, 

 also, the separation of parts at the periphery of the body 

 is accompanied by a corresponding separation in the 

 cortex. 



The division of the motor areas, according to the 

 segment of the limb in which the movement is initiated, 

 is, however, but one way of dividing them. An ex- 

 tremely suggestive subdivision is that made according to 

 the general character of the movements following" its 

 excitation, these movements being classified as those of 

 extension, confusion, or flexion. In the arm area it is 

 found to be the upper and frontal part which most 

 readily gives rise to movements of extension, while the 

 lower and occipital portion gives rise to those of flexion, 

 an area for confused movements lying between them, and 

 this separation of opposite movements probably holds 

 for those of the leg area also. 



The more carefully the relations of the cortex to the 

 lower centres are studied the plainer it becomes that the 

 impulses which pass down from it act on them as but 

 one of several groups of stimuli, comparable with those 

 arriving directly from the periphery, and subject to modi- 

 fications by them. The cortical centres do not usually 

 control individual muscles, but groups of muscles, the con- 



