872 THE CENTRAL NERVOUS SYSTEM 



of artificial nystagmus, the reaction deviation in that segment will fail to 

 be obtained. The exact site of the cerebellar lesion is diagnosed partly 

 from the nature and direction of the deviation which is produced and 

 partly from the segment of the limb in which it occurs, the explanation 

 for the disturbances being that interference with the cerebellar control of 

 one muscle group causes the antagonistic muscular groups to perform their 

 movements in an exaggerated manner, so that the segment moves too much 

 in their direction. 



Barany's conclusions so far may be summarized as follows: 



(1) The centers for the extremities are located on the cortex of the 

 hemispheres in the semilunar (superior and inferior) and digastric lobules 

 (see Fig. 225). The representation is uncrossed or homolateral, thus con- 

 trasting with cerebral localization, in which it is crossed or heterolateral. 



(2) Within each of these chief centers there is a further localization, 

 which however does not refer to anatomic groups of muscles but rather to 

 the functional performances of the different segments of the limb. Thus, 

 within the arm centers there are subsidiary centers concerned in the 

 movements of the limb in the various planes in rotation, in pronation 

 and in supination. It is a functional rather than an anatomic localization. 



(3) When a center concerned in the movements of the limb in a certain 

 direction, e. g., to the right, is suddenly destroyed, a spontaneous devia- 

 tion is produced in the opposite direction (to the left). 



