1888.] On Electrical Excitation of the Monkey s Brain. 409 



ward inclination when the anterior limb ivas stimulated, and a down- 

 ward inclination when the electrodes were applied to the posterior 

 limb. Luciani and Tamburini obtained only a conjugate deviation to 

 the opposite side, without any constant upward or downward inclina- 

 tion, and they got a similar but less marked movement by stimulating 

 the whole of the external surface of the occipital lobe. 



The following are the results of my own observations : — Electrical 

 excitation of the posterior limb of the angular gyrus, of the upper 

 end of the middle temporal gyrus* (which is continuous with it) of 

 the whole cortex of the occipital lobe (inclusive of its mesial and 

 under aspects) and of the quadrate lobule, causes conjugate deviation 

 of the eyes to the opposite side. The movement is not, however, in 

 all cases a simple lateral deviation, .but the lateral movement may be 

 combined with an upward or downward inclination according to the 

 part stimulated. Thus (1) excitation of a superior zone which com- 

 prises on the external surface the posterior limb of the angular gyrus, 

 the upper (posterior) end of the middle temporal gyrus, and the part 

 of the occipital lobe immediately behind the external parieto-occipital 

 fissure, and on the mesial surface the quadrate lobule immediately in 

 front of the upper end of the internal parieto-occipital fissure, and 

 the occipital lobe for a short distance behind the upper end of that 

 tissure, produces, besides the lateral deviation, a downward inclination 

 of the visual axes which is sometimes — especially when the stimula- 

 tion is applied at or near the mesial surface — so marked as greatly to 

 obscure the lateral deviation. 



(2.) Excitation of an inferior zone comprising the whole of the 

 inferior surface of the lobe, the lower part .of the mesial surface, 

 and the posterior or lo wermost part of the convex or external surface, 

 produces, besides the lateral deviation, an upward inclination of the 

 visual axes which, like the downward movement resulting from stimu- 

 lation of the superior zone, may be so marked as partly to obscure the 

 lateral deviation. 



(3.) Excitation of an intermediate zone which comprises the greater 

 part of the external surface (where it gradually broadens out laterally) 

 and extends over the margin of the great longitudinal fissure to in- 

 clude a narrow portion of the mesial surface, produces neither upward 

 nor downward inclination of the visual axes, but a simple lateral 

 movement. 



These zones are not sharply marked off from one another but merge 

 gradually into one another, so that if the electrodes be applied near to 

 the upper or lower limit of the intermediate zone there is produced a 



* Excitation of the upper end of the superior temporal gyrus gives a similar 

 result. Since this is commonly accompanied by a movement of the opposite ear, it 

 is usually considered that subjective auditory sensations have been called up by the 

 excitation. 



