232 Relations of the Frontal Lobe in the Monkey 
passing from the anterior segment around the genu to the posterior seg- 
ment of the internal capsule, leave the capsule after a short downward 
course with the capsular fibers and pass into the external nucleus of the 
thalamus. Here they probably break up into collaterals or fine terminals, 
some of which end in terminal arborizations around the cells of the ex- 
ternal nucleus, while others pass on as fine filaments which can be fol- 
lowed into the sub-thalamic region, where their course becomes confused 
with that of numerous fine fibers coming more directly from the anterior 
segment through the genu and anterior portion of the thalamus. 
A few fibers from the frontal lobe, probably belonging to short associa- 
tion tracts, pass to the lower portions of both central convolutions. There 
was also some degeneration in the striations of the lenticular nucleus, 
especially in the upper portion. There was not a trace of degeneration in 
the caudate nucleus. 
The great mass of degenerated fibers passing backward from the lesion 
is composed of fine fibers in the anterior segment of the internal capsule 
from the level of the foramen of Monro downward. In the upper levels 
a good deal of this degeneration appears to end in the anterior nucleus 
of the thalamus, but in lower levels it passes inward and backward through 
the thalamus, dividing at the fasciculus of Meynert into two tracts, the 
larger of which passes, mesial to that fasciculus, downward and backward 
into the gray matter surrounding the aqueduct of Sylvius (Figs. 6, 7, 
and 8). The smaller tract mingling with those fibers from the posterior 
segment of the internal capsule passes backward external to the fasciculus 
of Meynert and ends partly in the superior and partly in the inferior 
colliculus of the same side. Some of these fibers, also, find their way into 
the central gray matter surrounding the aqueduct. <A few fibers pass 
around the aqueduct and cross the middle line as if to reach the superior 
colliculus of the opposite side (Figs. 9 and 10). No degenerated fibers 
appear to cross in the posterior commissure, although occasional fibers 
pass through it, at right angles to the transversely running fibers, to reach 
the superior colliculus. In the sub-thalamic region some of the degen- 
erated fibers leaving the posterior segment of the internal capsule enter 
the capsule of the body of Luys, but it is impossible to say whether or 
not they end there. 
EXPERIMENT C. 
The lesion in this case was meant to be similar to that in the experi- 
ment just described, but the button of bone removed was a little posterior 
to the other and the external wound was nearly in the center of the pre- 
