14 
PROFESSORS V. HORSLEY AND E. A. SCHAFER 
almost entirely by the arms, the Monkey dragging itself along with tiie aid of these, 
assisted by the flexion which occurs at the hips ; the legs are quite limp and draggled, 
the dorsal surface of the toes being drawn over the ground. 
This ablation, although involving a more limited removal of the skull-cap, and a 
smaller cerebral injury than almost any other operations that we have undertaken, 
and although it can be performed with very little hiemorrhage and disturbance of the 
cerebral circulation (for the veins which are passing from the external surface to the 
longitudinal sinus can generally be avoided without the necessity of cutting or tying 
them), is nevertheless followed by much, more considerable shock than any other lesion, 
even of much greater extent. Indeed it is difficult to keep an animal, on which the 
bilateral operation has been performed, alive for more than a few days, even although 
it may be got to feed fairly well, for diarrhoea is apt to supervene, and the animal 
soon gets emaciated and dies. Out of four cases in which we have performed the 
bilateral operation at one sitting, two died, in spite of every care, on the eighth day, 
and the other two survived only three or four weeks. But even in these last cases 
there was no recovery from the paralysis, although the animals learned to get about 
and even to climb the wires of the cage quite readily with the use of their arms, the 
legs being always used merely passively as props. 
The results which follow unilateral removal of the gyrus marginalis are perfectly 
well marked, but far less striking. This arises from the fact that the animal is able 
to assume and maintain a nearly normal attitude ; a result due, no doubt, to the action 
of the muscles upon the one side of the spine being sufficient for this purpose. 
Rotation of the trunk to the side opposite to the cerebral lesion appears, however, 
to be deficient, and paralysis of the opposite leg is always very distinct ; the 
foot and leg hanging down when the animal is seated upon a perch, and remaining 
passive when the animal is taken up by the shoulders and somewhat rapidly lowered 
to the ground. Under these circumstances a normal Monkey will always extend 
the hip and put down the foot to meet the ground, but in cases with a unilateral 
lesion of this description it is only the foot which is upon the same side as the 
cerebral lesion which is thus lowered. The hip can, however, be freely flexed, and 
the paralysis of the leg-muscles does not appear to be nearly so well marked when 
only one side is involved as it is after the performance of the double operation. 
Indeed, while the animal has been running and climbing, it is difficult to dis- 
tinguish the paralysed side. It is certain that such constantly recurring actions as 
walking and running, to which, in the case of the Monkey, we may add climbing, 
may by habit almost cease to lose their distinctively voluntary character, and it 
is conceivable that they may be often carried on by the action of the lower 
nerve-centres in the cord and medulla oblongata after having been started by that of 
the higher centres in the cerebral cortex. But it must be admitted that when the 
paralysis of any true voluntary movement which has been produced by ablation of a 
pa,rt of the cerebral cortex is complete and extensive it is in most cases not followed 
