FIBRES OF THE INTERNAL CAPSULE OF THE BONNET MONKEY. 
75 
We there showed that the deviation of the eyes was a combined movement of 
opposed muscles {internal rectus with external rectus) of both sides of the body to 
produce one effect, and that the ojiposite hemisphere, when excited, produced exactly 
the opposite effect. 
Further, considering that the visual field is hemiopic, and that the two eyes always 
have their axes parallel (when not accommodated for near objects), we may look upon 
the two eyes as acting’ like one, and we may also regard their movements to be of the 
same kind as those of the head. 
Stimulation of the left cortex produces movement of the head and also of tlie eyes 
to the right, and, conversely, when the right cortex is irritated these parts move to 
the left. Movement to the same side is never observed, hence these movements we 
regard as distinctly unilateral. 
Class II.—Imperfectly Bilatercd Movements. 
(a.) Opening of Eyelids. —In ‘Phil. Trans.,’ B., 1888, p. 241, we describe how we 
observed in one Monkey that there were two millimetre-squares on the cortex, exci¬ 
tation of which caused opening of the opposite eyelids to occur before those of the 
same side. In the present research we have obtained the same result from the 
internal capsule in one case (Monkey No. 69), at points 50-55 (whole capsule, 100), 
the movement being also stronger. 
The extreme rarity of this phenomenon—occurring, as it does, only twice in about 
seventy different experiments in the same variety of Macacus—makes it clear that the 
movement of opening the eyelids is practically bilaterally represented. However, the 
phenomenon is not without interest in discussing the evolution of function in the 
“motor” cortex, 
(b.) Closure of Eyelids. — In contradistinction to what we find witli regard to 
opening of one eye before the other, we have obtained closure of the opposite eyelids, 
not only taking place before those of the same side, but even independently of the 
eyelids of the same side. 
We drew attention for the first time to this differentiation of cortical representa¬ 
tion of the eyelids in our second paper just referred to, where we described the 
opening of one eye before the other. Since writing that paper, we have been engaged 
in investigating the cortical representation of closure of the eyes, and we have found 
that there is a nearly horizontal zonular strip of the cortex just below and slightly 
overlapping the lower border of the upper limb area of representation, in which the 
single movement of closure of the opposite eyelids is represented. 
In some cases this is imperfect, be., the eyelids of the side stimulated closed 
as well as those of the opposite side. It is clear, therefore, that this movement is 
only imperfectly bilateral, a fact of the greatest importance, as is evidenced by the 
fact that we have been able with this observation to correctly diagnose that the 
homologous portion of the cortex in man was the seat of an irritative lesion. 
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