740 
MR. W. BE VAR LEWIS ON THE COMPARATIVE 
coarse fasciculi of the outer lenticular nucleus are usually one-third or one-fourth the 
diameter of the latter. Each coarse fasciculus is formed by the union of two or three, 
and occasionally a large number of such bundles, and during their passage through 
the outer grey segment frequently divide into two, and appear in their further course 
through the inner segment subject to still further subdivision. At the upper pole of the 
lenticular body fasciculi are observed passing from the first segment directly into the 
internal capsule without previously traversing the inner segment, whilst coronal 
fasciculi are here also distinctly seen to pass down the internal capsule without 
establishing any connexion with the ganglia. Upon a plane passing through the 
anterior or olfactory commissure in horizontal sections of the brain, other fasciculi of 
medium size, are directed directly backwards into the inner segment of the striate 
body from the frontal aspect of the caudate nucleus, and obliquely backwards and 
inwards from its marginal aspects, each fasciculus frequently subdividing on its way 
but occasionally passing uninterruptedly through the outer segment. In this course 
they are directed over, beneath, and through the posterior olfactory fasciculus 
(Plate 49, fig. 9, D), Within the inner segments we meet with two systems of 
fibres : the coarse fasciculi already dealt with, and a large proportion of minute 
medullated fibres running separately, and not in fascicles. These ultimate nerve fibres 
are peculiarly liable to varicosity—they take curved and spiral directions—-cross each 
other frequently, are often much contorted, but are chiefly distributed longitudinally 
along the course of the large bundles, or in arches across the inner segments of the 
lenticular nucleus concentric to its base. 
They attain a diameter of ‘004 to ’005 mm. At a little lower level we find them still 
more abundantly, but here the orifices of large divided vessels and the peculiar oval 
nuclei betwixt the coarser bundles indicate that we are examining the anterior- 
perforated space or olfactory area, and now we immediately identify these minute 
twisted fibres with those already described as peculiar to this region, and can readily 
trace their connexion with those surrounding the granule layers of the olfactory 
bulb. At higher levels passing through the anterior end of callosal commissure, 
coronal radiations pass betwixt cortex of the tip and inner margin of the frontal 
lobe to the head of the caudate nucleus—the fibres of the corpus callosum crossing 
their course in their radiations outwards. 
To recapitulate— 
1. The anterior end of the frontal lobe is connected chiefly with the head of the 
caudate nucleus. 
2. The cortex of the marginal angle at the vertex in front of the thalamus and of 
a limited surface outside is connected with the centric pole of the lenticular nucleus. 
3. The cortex of the outer aspect of the hemisphere behind the latter, and that of 
the outer aspect of the occipital lobe is connected with that portion of the wedge- 
shaped nucleus which bends backwards and downwards towards the base. 
