PROFESSORS V. HORSLEY AND E. A. SCHAFER 
Excitation over the lower third {loivcr face-centre) is accompanied by varying 
movements of the jaw and tongue, some of them being very hke those of mastication. 
As a rule excitation of the posterior part of this centre is accompanied by retraction, 
of the anterior part by protrusion, of the tongue* in combination with movements of 
the mouth generally. On the other hand, if the electrodes are applied in the middle 
of the centre, alternate movements of protraction and retraction may be obtained. 
At the lower end of the ascending parietal gyrus, and extending in some instances 
to the lower end of the ascending frontal, is a centre, excitation of which causes the 
mouth to be opened, accompanied by retraction of the tongue and of the lower lip, 
and sometimes a bending of the head to the side. This is due to contraction of the 
platysma myoides. Its action is sometimes produced over a considerable part of the 
face-area, but always most markedly along that part of the area which lies behind 
the lower end of the fissure of Rolando, t 
The head-area or area for visual direction comprises an oblong portion of the 
surface of the frontal lobe, extending from the margin of the hemisphere, round 
which it dips for a short distance, outwards and somewhat backwards to the upper 
and anterior limit of the face-area. Posteriorly, it is bounded by the arm-area, and 
in front by the non-excitable portion of the lobe. It extends, therefore, in front as 
far as the extremity of the precentral sulcus, and it includes the middle part of the 
frontal lobe above the antero-posterior limb of that sulcus, the part included in the 
angle formed by the antero-posterior and vertical limbs of the sulcus, and perhaps a 
small portion of the ascending frontal gyrus, close to the vertical limb of the same 
fissure. The effects produced by excitation of this area are similar to those described 
by Ferrier as resulting from excitation of the rather more limited area marked 12 in 
his diagrams, viz., opening of the eyes, dilatation of the pupils, and turning of the 
head to the opposite side, with conjugate deviation of the eyes to that side. If the 
electrodes are applied near the angle of the precentral sulcus, the ears are frequently 
also strongly retracted. 
Besides these three main areas, which occupy the greater part of the excitable region 
of the external surface, portions of two other areas, one concerned with movements 
of the lower limb, and the other with movements of the trunk, occupy a part of this 
surface close to the great longitudinal fissure, although their main parts are found 
upon the marginal gyrus. The leg-area is partly situated upon the mesial surface of 
the hemisphere, where its limits will be presently pointed out, but it also extends, as 
we have just explained, over the margin, occupying a strip of the external surface 
from the parieto-occipital fissure nearly to the level of the anterior end of the small 
* As mentioned by Feerier for his centres (9) and (10), ' Functions of the Brain,' p. 242. 
t Since our experiments, Dr. Felix Semon, working in conjunction with Professor Horsley, has 
found that the lower end of the ascending frontal gyrus anteriorly is also excitable ; an effect being 
produced upon the glottis by its excitation, viz., to bring about phonatory closure of the vocal cords. 
A similar centre was discovered in the Dog by H. Krause. 
