22 
PROFESSORS V. HORSLEY AND E. A. SCHAFER 
in a number of* Monkeys, and, although we have never succeeded in effecting a 
complete removal of the grey matter of the convolution — indeed, from the depth at 
which it is situated this is scarcely possible without injuring neighbouring parts or 
producing fatal licemorrhage — we have in several instances removed or destroyed 
considerable portions without lesion to other parts, or with but a small injury to the 
marginal gyrus, the effect of which, from our previous experiments upon this region, 
could be readily discounted. As the result of these experiments, we have found that 
any extensive lesion of the gyrus fornicatus is followed by hemianaesthesia more or 
less marked and persistent. In some cases the anaesthetic condition has involved 
almost the whole of the opposite side of the body, in others it has been localised 
to either the upper or the lower limb and to particular parts of the trunk, but 
we have not yet succeeded in establishing the relationship between special regions 
of the body and the parts of the convolution which have been destroyed. More- 
over, the anaesthesia was frequently very pronounced and general during the 
first three or four days after the operation (and indeed in several instances took the 
form of complete insensibility to both tactile and painful impressions, so that even a 
sharp prick or the contact of a hot iron would produce no indication of sensation), 
but after that time this general condition would become gradually in great part 
recovered from, or more localised in definite regions. In all cases, however, in which 
the diminution of sensibility was well marked during the first few days, it has 
persisted, although with lessened intensity, for many weeks in those instances in 
which the animals have been preserved for so long. In other cases, in which 
apparently the lesion was slight, the diminution of sensibihty, although at first 
well marked, subsequently disappeared entirely. In some instances the hemi- 
ansesthesia took the form of inability (or a diminution of ability) to localise the seat 
of irritation, whilst in one case, in which diminution of sensibility was exhibited in a 
very striking manner, the irritation, when rendered sufiiciently intense for the Monkey 
to become conscious of it, was responded to by the animal scratching a different part 
of its body from that to which the stimulus was applied. 
These experiments were frequently, but by no means in every case, complicated 
by the presence of a certain amount of motor paralysis, chiefly, if not entirely, 
affecting the muscles of the leg. We have no doubt that this condition was always 
due to a lesion (accidentally produced during the operation, or subsequently, as the 
result of interference with the circulation) in the leg-area of the marginal convolution. 
Now in one or two of these cases the anaesthesia affected chiefly the paresed limb, and 
it might therefore be argued by those who, like Schiff and Munk, hold that the 
excitable areas of the cortex are concerned with the perception of sensory impressions 
from the corresponding regions of the body that the loss of sensibility was due to 
the lesion of the motor area. But against this argument we may not only put 
orward those experiments in which there has been no accompanying paralysis, but 
also others in which the hemianaesthesia has been well marked in the upper limb and 
