56 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
Repeated observations on excitation of the cortex of the precentral convolution, 
confirm an opinion we had formed at the time of our former communication, and 
indicated in the diagram then furnished, but that we did not verbally express. This 
is to the effect that the anterior limit of the ' motor ' field is not of sharp, abrupt 
character, but fades off forward somewhat gradually. This edge extends further 
forward under ' Bahnung? Under general conditions producing lowered excitability 
of the cortex it retires backward in the direction of the central fissure. 
In a similar manner the boundary of the area for any particular movement 
may by £ Bahnung' be extended beyond its average limit. The special form of move- 
ment provoked from a given spot of cortex is thus influenced by the particular forms 
of movement excited from neighbouring points just antecedently. 
Among movements elicited from the cortex of the 'facial' region, we have in 
two instances seen protrusion of the tongue, succeeded by forcible closure of the jaws 
following rapidly before retraction had withdrawn the tongue behind the arcades of 
the teeth ; so that in these instances the tongue was caught by the closure of the 
teeth. This sequence of movements presents interest, as evidencing that a sequence 
of movements evoked by excitation of the cortex may exhibit in some respects faulty 
co-ordination. The movement is also of interest as a result of direct cortical 
excitation, which harmonizes with the biting of the tongue in epileptic seizures. 
Ablation of the facial area of the ' motor ' region was performed in one 
individual. A crossed hemiparesis ensued in the lips, cheek, tongue, nasal fold, 
and lower eyelid (very slight), but not in the upper lid, eyebrow, or frontal 
region. 
As to the recovery of movement that occurs in a limb rendered paretic by 
ablation of its cortical area in the ' motor ' region, we find the following points : If 
all the area, which when faradized evokes movements of fingers, thumb, and wrist 
primarily, and not as a later sequel to movements starting elsewhere, be excised, the 
paretic condition of the hand which ensues is severe, but rapidly diminishes. In a 
few weeks the hand is again very fairly and freely used. If, then, the whole of the 
corresponding area in the opposite hemisphere is removed, a similar paresis similarly 
ensues in the other hand, and runs a similar course ; but this second lesion does not 
produce, so far as we have been able to discover, the slightest recrudescence of the 
paresis already recovered from in the first hand. On the contrary, the first hand is 
almost at once employed more freely and successfully than prior to the second 
operation, presumably because of greater inducement to use it during the disability 
existing in the second hand. If, then, later, after the second hand has regained its 
use, the remaining part of the arm area first operated upon be ablated, this causes no 
obvious recrudescence of paresis either in the first hand or in the second hand. It 
causes severe paresis at shoulder, and to some extent at elbow, on the side crossed to the 
lesion, but this, again, is in great part of temporary character, and is largely recovered 
