412 



Dr. C. S. Sherrington. Note on the [May 4, 



7. By contraction of the left internal and right external rectus 

 associated with inhibition of the tonus of their antagonistic muscles 

 (left external rectus and right internal rectus) ? 



The plan of experiment adopted has been as follows : — The appro- 

 priate portion of the left cortex having been ascertained by excitation, 

 and having assured myself that the desired conjugate deviation is 

 regularly obtained, I at once sever the 3rd and 4th cranial nerves 

 of the left side between their origin and the point of their entrance 

 into the cavernous sinus. The position of the left eyeball in rest is, 

 immediately after performance of that section, scarcely perceptibly 

 different from what it has been before, nor is usually the pupil 

 dilated immediately, although it soon becomes so. Excitation of the 

 cortex as before is at once proceeded with. The movement obtained 

 is still conjugate deviation of both eyeballs to the right. The right 

 globus appears to move exactly as before ; the left globus, on close 

 examination, although it moves, clearly does not move as it did before. 

 Its movement starts usually just perceptibly later than the movement 

 of the right eyeball ; the movement, when started, is somewhat 

 slower than that of the right eye, and it travels only some two- 

 thirds as far ; on discontinuing the excitation both eye-balls return 

 together. Sometimes the movement of the left eye, instead of starting 

 later than that of the right, starts simultaneously with it ; sometimes 

 it starts distinctly earlier, and this especially when the external 

 squint that soon appears has become well developed. But the move- 

 ment is never seen quite so rapid or so ample as that of the right 

 eye. On excitation of the corresponding part of the right cortex the 

 movement of the left eye outwards may be very slight, especially if 

 there be marked outward strabismus ; in two experiments there fre- 

 quently occurred on excitation of the right cortex together with the 

 usual movement of the right eye to the left a movement of the left 

 eye to the right and sometimes, apparently, to beyond the primary 

 position. A few times a double movement occurred, the left globus 

 at first moving to the left conjugately with the right, and then 

 suddenly reversing its movement and turning inwards to the right. 

 At each discontinuance of the excitation of the right cortex when the 

 eyeballs have reacted by conjugate movement to the left, the left does 

 not return so quickly as the right ; indeed it may be many seconds in 

 returning. 



These experiments succeed uniformly, so far as I have seen, with 

 both Macacus rhesus and with sinicus, even when very young speci- 

 mens are used. Ferrier and Munk have shown that conjugate move- 

 ments of the eyes are obtainable from the cortical surface posterior 

 to the " motor " region, and Schafer, by demonstrating inter alia the 

 great difference in the reaction time for the movements in the two 

 •cases, has provided an index for the profound distinction that must be 



