6G 
Dli. C. E. BEEVOR AND MR. V. HORSLEY ON THE EXCITABLE 
separating this zone from the j)utamen are in this section extended backwards almost 
to the end of tlm lenticular nucleus. The angle of the genu is nearly a right 
angle, and the limbs of the capsule are approximately equal in length. (See typical 
photograph, Experiment 69.) 
Group VI.—This group is the same as Group V., from which, as the individual 
capsules show, it can only be separated by the smaller angle of the genu and bv 
the axis of the posterior limb, becoming more transverse to the longitudinal axis of 
th(3 hemisphere. (See typical photograph. Experiment 50.) 
Group VII.—This group is very definite since it shows sections of all three zones 
of the lenticular nucleus, and since the level is below the capsular groove between the 
two nuclei in the corpus striatum, it passes through the basal grey matter of the 
floor of the lateral ventricle. The anterior commissure appears near the middle line ; 
the part seen corresponds to the highest point of the arch it forms. Since this 
section is cut along the line of the Fissure of Sylvius, it necessarily is wholly below 
the frontal lobes. As will be seen, there is a sliglit anterior limb in this section, 
see fig. 1. (See typical photograph, Plate G, Experiment 81.) 
Group VIII. —This section just above the crus closely resembles Group VII., save 
that the anterior limb is no longer represented, and the two innermost zones of 
the lenticular nucleus cannot now be separated. (See typical photograph. Experi¬ 
ment 79.) 
Notes on Groups VII. and VIII .—In these groups the basal ganglia and capsule, 
as divided by these sections, present a very constant figure; thus the posterior 
limb of the internal capsule makes an angle with the middle line of about 60°, its 
posterior border being formed by the optic thalamus, while anteriorly there are 
ranged along its front the respective ends of the three grey zones of the lenticular 
nucleus. If the section pass just above the Fissure of Sylvius the three zones will 
be seen, if lower, the two innermost zones are found to be confused into one grey 
mass and cannot be separated. 
In the highest sections {i.e., those in which the three zones are distinct) of these 
groups, there are the remains of the anterior limb of the capsule lying to the 
inner side of the innermost zone of the lenticular nucleus. This remnant of the 
anterior limb is (in the highest sections), about 3 rnm. long in the antero-posterior 
direction. This bundle of white fibres is not in immediate contact with the 
anterior commissure,. but is separated from it by some of the grey matter of the 
lenticular nucleus. This delimitation of what we consequently call the anterior limb 
can be easily seen, and it is from this point that in this group of sections we have 
commenced, the measurement of the capsule, continuing the same as before along its 
outer margin, i.e., contiguous to the lenticular nucleus, as far as the hinder end of 
the outer zone of that nucleus (see fig. 1). 
The remnant of the anterior limb above described is bounded on its inner aspect. 
