PHYSIOLOGICAL TOPOGRAPHY OF SURFACE OF CEREBRUM. 



795 



In accordance with their seat these convulsive movements are designated 

 facial, brachial, crural monospasm, and the like. Such movements naturally 

 may also involve several centers at the same time. In men with the surface of 

 the hemisphere freely exposed, the region of the motor centers has been success- 

 fully stimulated by electricity by Bartholow, Sciamanna, and others. 



If intense irritation be applied upon one side bilateral convulsive 

 movements with suspension of consciousness may occur (properly desig- 

 nated Jacksonian or cerebral epilepsy). 



The following observations have been made bearing upon the center for 

 voluntary combined movements of the eyes in the cortex in man : Both eyeballs 

 are controlled from each hemisphere. In the presence of paralyzing lesions of 

 the cortex or of the tracts that pass off from it both eyeballs are occasionally 

 found in a state of lateral deviation. If the paralyzing lesion be situated 

 in a cerebral hemisphere con- 

 jugate deviation of the eye- 

 balls takes place toward the 

 unaffected side. If, how- 

 ever, it be seated in the 

 conducting tracts, where de- 

 cussation has already taken 

 place, namely in the pons, the 

 deviation of the eyes takes 

 place toward the paralyzed 

 side. If the seat of the lesion 

 is in a state of irritation caus- 

 ing contractions on one side 

 of the body, the deviation of 

 the eyes is naturally in a direc- 

 tion opposite to that in which 

 it would be in association with 

 paralysis. In cases of cere- 

 bral paralysis there is occa- 

 sionally, instead of the marked 

 lateral deviation of the eye- 

 balls, only a paresis of the 

 lateral rotators of the eyeballs, 

 so that though during rest the 

 eyes are not rotated toward 

 the unaffected side, they can- 

 not be adequately rotated to- 

 ward the affected side. Also 

 the elevator of the upper eye- 

 lid appears to have its center in the angular gyrus; but according to some 

 observers this is situated in the posterior limb of the second frontal convolution, 

 extending into the first frontal convolution. 



The motor speech-center, which controls the voluntary movements 

 of the tongue (hypoglossal nerve) and the mouth (facial nerve), including 

 the lower jaw (third division of the fifth nerve), is situated in most per- 

 sons in the left third frontal convolution (Fig. 260, F 3 ). The fact 

 that most persons are right-handed also indicates a more refined develop- 

 ment of the motor apparatus for the upper extremity in the left hemi- 

 sphere. Human beings with well-developed right-handedness are ob- 

 viously left -brained. Perhaps this arrangement is dependent upon an 

 embryological basis. By far the majority of persons are thus left- 

 brained speakers, although there are exceptions. As a matter of fact, 

 left-handed persons have been observed to lose the faculty of speech 

 after lesions of the right hemisphere. 



Studies of the brains from distinguished men have shown that in 

 them the third frontal convolution attains a greater size and a less simple 



FIG. 261. Secondary Degeneration of the Motor Tracts in the 

 Cerebral Peduncle, the Pons and the Pyramid. The shaded 

 areas (*) are degenerated (after Charcot). 



