G8 
DR. C. B. RBEVOR ART) MR. V. HORSLEY OR THE EXCITABLE 
Genu .—Hitherto we have only indirectly spoken of the genu and its relation to the 
snrrounding parts. To determine its position exactly at the different levels of the 
capsule, we first, by means of successive horizontal sections parallel to the longest 
antero-posterior diameter of the hemisphere, exposed the level of our Group I. We 
then inserted (vertically) a long needle at right angles to the plane of the section just 
at the genu immediately in front of the most anterior extremity of the optic 
thalamus. Each successive horizontal (parallel) section of the hemisphere contained, 
consequently, the position of the genu as in the highest section (the upper level, 
Grou]) I.). 
From these data we found that the position of the genu in its antero-posterior 
relations varied extraordinarily little, but that the position of the entering angle of 
the inner border was gradually transferred to that of the outer border, and, finally, 
in the last three groups, the puncture revealed the fact that the position of the genu, 
as seen in the highest section and now projected upon the lowest, had moved about 
2 mm. in front of, and outside the angle of the outer border of the capsule, or 4 mm. 
from its original site. In other words, the genu had moved backwards and inwards, 
and this change of position was more rapidly developed in the lower than the upper 
sections. 
Of coiu’se, the inward and backward direction of the efferent tracts is also seen 
(especially the former) in frontal sections of the capsule. 
Lariiince Medullares .—The white fibres, which in horizontal sections of the hemi¬ 
sphere, appear as lamellfe to separate the zones of the lenticular nucleus, but which, 
in vertical frontal sections, appear to run into and connect the zones, we have 
repeatedly excited without any result. We, therefore, are led to conclude that 
these fibres, whatever be their function, do not belong to the great excitable cortico- 
efferent system. 
Obeesteineii" gives a schematic diagram, in which he figures fibres passing down 
from the cortex through the laminae medullares to end in the subthalamic region. 
Weenicket suggests that these interzonular, or lamellary fibres, are in part 
derived from the nucleus caudatus, and are passing down to the crus. 
MeynertI believes that such fibres are derived from the cortex rather than from 
the nucleus caudatus. 
Method of Investigation in the Present Pesearch. 
Animal Einployed .—The Bonnet Monkey [Macacus svnicus), i.e., the smaller 
variety of that species of Monkey, was the animal which we have invariably used. 
In all we have performed 45 experiments, and in every case the animal was com- 
* Lnc. cit., p. 334 
f Loc. cit. 
X Tmc. cit. 
