ON THE FUNCTIONS OF THE CEREBRAL CORTEX. 
15 
by recovery ; and it is not impossible that in those instances in which recovery seems 
to occur the permanent injury has been less complete than was at first supposed 
from the effects exhibited, but has been temporarily extended by the disturbance 
produced in the neighbouring grey matter by the operation. 
We have performed the operation of removing the grey matter of the gyrus 
marginalis of one side of the brain, at least of its posterior two-thirds or more, in 
eight cases, and in some of these, after a lapse of time, varying from a few days to 
several weeks, it was followed by a second operation for the removal of some other 
portion of the motor cortex. 
Conclusions and remm'ks. — The results of ablation in the motor regions of the cortex 
afford very direct corroborative evidence regarding the functions of those regions 
which are deducible from the effects of excitation. This is already perfectly well 
known so far as regards the roreas of Ferrier upon the external surface, and our 
experiments on the ablation of these areas are so far only confirmatory of those of 
previous observers. They show, however, in addition, that in order that the hemi- 
plegia or paraplegia which is produced by cortical ablation shall be complete it is 
necessary to include the part of the marginal gyrus corresponding in longitudinal 
extent to the excitable areas of the external surface, and indeed that the amount of 
paralysis produced by ablation of the marginal gyri alone is as great as, or even greater 
than, that caused by removal of the much more extensive external areas. But, on the 
other hand, the complexity of the muscular movements which are governed from 
these areas, including as they do most of the movements of the arm and fingers, and 
of the face and head, is evidently much greater than in those which are governed from 
the marginal gyrus. 
Effects of ahlation of the excitable areas of the cortex upon sensibility. — It is much 
more difficult than would at first sight appear to determine in animals whether a part 
in which motor paralysis has been produced by a lesion of the cerebral cortex is 
deficient in sensibility. For, on the one hand, the subject of the experiment no longer 
possesses the power of voluntarily withdrawing the irritated part, and thus the most 
obvious indication of perception of sensation is necessarily absent, while, on the other 
hand, there is the possibility of an involuntary or reflex response which might without 
due care be taken to indicate the continued existence of sensibility. It is, however, 
undoubtedly the fact that in our cases of cerebral lesion producing paralysis of 
-voluntary motion reflex movements of the paralysed part are produced with great 
difficulty and require a powerful stimulus ; from which it would appear that the 
inhibitory action exercised by the brain over reflex movements is not only not removed 
by a lesion of the cortex which is accompanied by loss of power voluntarily to produce 
contraction of the muscles, but is on the contrary markedly increased by such 
lesion. 
We have seen sufficient, however, to convince ourselves that a lesion of the cortex 
which produces paralysis of voluntary motion in a part is not necessarily accompanied 
