200 Leyton and Sherrington 



Ablation-Experiment 5. Removal of Area yielding Closure 

 of Eyelids from both Hemispheres (tig. 12). 



December 2. — Gorilla savagei, young, ^. Under deep chloro- 

 form narcosis trephined over the left hemisphere, lower centralis region. 

 With strict aseptic precautions the centralis from superior genu downward 

 and the frontal region anterior to it exposed and explored. Closure of 

 eyelids extremely readily and regularly elicited as a primary movement 

 from a small area which was made up of a seemingly continuous field of 

 points, each of which evoked closure of eyelids, especially of contralateral 

 eye, usually accompanied or followed immediately by some other secondary 

 movement. In this area on some occasions, from a small part of it the 

 eyelids-closure was not primary, but followed upon a briefly precedent 

 movement of mouth (retraction of angle of mouth contralateral to stimulus). 

 The map (fig. 12, A) illustrates with simplification of details the condition 

 and area found. The area's general position in the functional topography 

 of centralis anterior was determined carefully by test stimulations of points 

 above and below it. The centralis anterior was found to yield a seemingly 

 continuous field of motor points from genu superius above to the very tip 

 of the centralis fissure below. Characteristic localising points, as found in 

 it, are entered on the map (fig. 12, A). Centralis posterior was nowhere 

 found excitable. 



Forward of the centralis anterior, in the region exposed, two fields were 

 found, giving eyelid movements in addition to the area yielding closure of 

 lids in the precentral gyrus itself. Both these frontal fields yielded open- 

 ing of eyes, and were functionally characterised by other distinctions, also 

 from the eyelid region in precentralis. These distinctions were that (1) 

 the responsive movement could be evoked only by stronger faradisation 

 than that sufficing to evoke motor response, including eyelid-closure re- 

 sponse from precentralis; e.g. precentralis, eye-closure at 125 cm. of 

 second coil ; eye-opening from frontal regions at 105 cm. of second coil ; 

 (2) neither of the frontal fields yielding eye-opening offered a seemingly 

 continuous field of excitable points, but consisted of scattered points which 

 were excitable, yet even these were not excitable so regularly as were the 

 eye-closure points in the precentralis ; (3) the eye-opening movement was 

 usually to all appearance fully symmetrically bilateral, sometimes it seemed 

 slightly quicker or stronger contralateral to stimulation, but on the whole 

 its bilateral equality was in marked contrast to the decided asymmetry of 

 the eyelid-closure movement evoked for precentralis ; this latter was never 

 observed to be fully equal in both eyes, there being always a detectible 

 preponderance of the movement on the contralateral side. Not rarely the 

 eyelid -closure from precentralis was confined to the contralateral eye, and, 

 when weak, was observed on one occasion to be confined to the contralateral 

 eye's lower lid only, and on more than one occasion seemed to be confined 

 to the upper lid of crossed eye only. 



