FIBRES OF THE INTERNAL CAPSULE OF THE BONNET MONKEY. 
57 
and part of the amygdaloid nucleus had to be cut away to reveal the anterior 
commissure (a.c.) running under the corpus striatum. 
The convergence of the fibres of the capsule is seen in fig. 6, in which the whole of 
the corona radiata, outer capsule and claustrum, have been removed. It shows the 
caudate nucleus terminating posteriorly in the surcingle, wliich ends in the grey matter 
under the lenticular nucleus. 
It is clear that these fibres, when they approach the basal ganglia, either end in 
these ganglia or pass between them to and from the mesencephalon. 
(1) Do any of the fibres descending from the cortex end in the basal ganglia ? 
This is a question which will recur, and as its elucidation does not immediately 
concern us in considering the present point, it may be postponed, see pp. 68, 72. 
(2) Do the fibres pass between the basal ganglia to the mesencephalon, and if so 
which of the classes above enumerated ? 
The answer to this cpiestion is easier. In the first place the important fibres 
known as the pyramidal tract pass downwards from the cortex, through the internal 
capsule into the crus and to the pyramidal region of the mesencephalon. These 
fibres are universally recognised to be the efferent or motor fibres of the cortex 
system, and it is the result of the excitation of these fibres which forms the subject 
of the present communication. In order to make the arrangement of these fibres— 
as we believe them to exist—more intelligible, we must first refer to the prse- 
frontal class. 
I. Prwfrontal .—The fibres coming from the prmfrontal region unquestionably 
appear in the anterior limb of the internal capsule as horizontal bundles, and compose 
its antero-inferior border. 
Excitation of the prsefrontal region of the cortex, as is well-known, has produced 
no muscular movement except in the hands of Munk.'“ Ablation of the same region 
has been stated by Professor FERRiERt to have been followed by descending degene¬ 
ration in the fibres of the anterior limb of the internal capsule. His results, however, 
judging from the figures he gives of the brains thus operated upon, seem to have 
included portions of the excitable area for the representation of the movements of the 
head and eyes. 
Anatomical investigation goes to show that the fibres of the anterior limb of the 
capsule pass to the mesial side of the crus and also to the subthalamic region. Of 
such fibres our method gave only negative evidence, since in Groups III., VI., VII. 
(see fig. 1) the anterior limb was practically inexcitable, it is therefore clear that 
these prsefrontal fibres at any rate do not possess efferent motor function. 
* Munk, “ Ueber die Stimlappen des Grossbirns‘ Sitzungsbericlite der k. Preussiscben Akademie,’ 
1882. 
t ‘ Functions of the Brain,’ 2nd edition, pp. 898, 399. 
MDCCCXC.-B. 
I 
