168 Ley ton and Sherrington 



the long list of motor items assembled in the large precentralis motor field. 

 Although that, as a broad statement, is true, it requires some modification, 

 inasmuch as occasionally, and, in our experience, very rarely with weak and 

 moderate stimuli, eye-opening is evoked from precentralis. It is not then 

 a primary movement, in our experience, but is secondary to, or developed 

 from, the turning of neck and head elicitable from a restricted area between 

 hand and face regions ; and with it sometimes occurs movement of eyeballs 

 to opposite side, also not a primary movement from precentralis. More 

 usually this neck movement, which is a movement carrying the face away 

 from the side stimulated, is associated with movement of eye-closure, as 

 mentioned above. From the evidence of our experiments in anthropoids, we 

 infer that the eye-opening sometimes elicited from this part of precentralis 

 region is not to be taken as evidence of the existence in precentralis of 

 motor foci there situate and directly executive of eye-opening, but rather 

 of secondary connections of the precentralis neck focus with foci for eye- 

 opening situate extrinsic to precentralis motor region proper. 



In addition to the instances of eye-opening coming under one or other 

 of the three groups in the above category, there are instances of its occur- 

 rence under faradic stimulation of still other regions of cortex. Such 

 instances as these latter are those we had especially in mind in the opening 

 paragraph as desultory, unexpected, and unreliable of repetition even at one 

 and the same period of an experiment. When they have occurred they 

 have been noted by us, and the places of their occurrence have variously 

 included points in the first temporalis, calloso-marginalis, and post-centralis, 

 as well as various parts of precentralis. In regard to the whole of this 

 group of " desultory " eye-opening responses, it is to be borne in mind that 

 the movement of eyes-opening is one commonly accompanying an awaken- 

 ing from sleep, and that the grade of narcosis under which the faradic 

 examination of the cortex has to be carried out is one which in its depth 

 somewhat resembles natural sleep. Any stimulus which arouses the animal 

 is likely to evoke an opening of the eyes. For instance, the application of 

 the faradic stimulus to the dura mater instead of to the cortex commonly 

 does so. The eyes-opening has therefore to be accepted with much caution 

 as evidence that the stimulus which evokes it is one really playing in a 

 direct manner upon a " motor " eye-opening centre in the cortex. 



Movement of Eyeballs. — This, as obtained from cortex cerebri in the 

 anthropoids, is, as in the small monkeys, almost always lateral conjugate 

 deviation to the side away from the stimulus. It is obtainable from (1) 

 the calcarine region and occipital pole in the same area as that already 

 mentioned under eye-opening ; (2) a frontal area embracing a considerable 

 part of the surface of the 2nd and 3rd frontal gyri, corresponding fairly 

 well with the frontal area above mentioned under eye-opening. The con- 

 jugate deviation of the eyeballs to the opposite side seems usually purely 

 lateral, but sometimes the deviation is partly downward or partly upward 

 as well as lateral ; a partly downward deviation has, in our experience. 



