20 Histology of the Island of Beil. By Herbert C. Major, M.D. 
layer stands out from all the others, in the Insula it is much less 
conspicuous. 
The above, then, I apprehend to be the chief feature of dis- 
tinction ; and while at present I would not venture to suggest an 
inference, there can, I think, he no doubt that the point is an 
important one. For it must be remembered that it is in the cells 
of the third layer that degenerative changes described by myself 
and others are most frequently apparent. 
II. The next point for consideration is as to whether any 
structural differences can be detected between the several gyri 
which collectively form the Insula. To ascertain this, sections 
were made through the entire Insula at different levels, so that in 
each section the gyri were viewed side by side, and structure could 
be compared under exactly similar conditions. The result, how- 
ever, has been negative ; no structural variation being discoverable 
in the various gyri, even under the severe comparison above in- 
dicated. This result is probably in accordance with what would 
have been anticipated, but nevertheless it is, I consider, important. 
III. In like manner I have failed to establish, after a careful 
and prolonged search, any structural difference between the right 
and the left Insula. Doubtless the point is a difficult one to 
determine with absolute certainty, but at present I am decidedly of 
opinion that the structure on both sides is identical ; and if the 
opinion is expressed with some confidence, it is only because I know 
that peculiarity of structure does not readily escape detection when 
the eye (to put it so) has become perfectly familiar with the intimate 
structure of the cerebral tissue. 
IV. The course of the fibres issuing from the Island of Beil has 
been studied and described more especially by Clarke, Meynert, 
Gratiolet, and Broadbent, who have dealt very fully with the 
subject. The only point I desire to refer to has reference to the 
course of the fibres as they pass into the cortex of the Insula. It 
was shown by Baillarger,* and again by Broadbent, f that all parts 
of the cortex do not receive fibres coming directly from the central 
stem of white matter, and the portions which do not so receive 
fibres are those at the bottom of the sulci between the convolutions. 
Baillarger states, with perfect accuracy, that long and numerous 
fibrils run from the central white stem to the summits of the con- 
volutions ; that such fibrils become rarer and shorter as the sulcus 
is approached, and become transverse at the sulcus, where the white 
matter is almost, as it were, applied to the cortex, instead of being 
fused with it as it is at the summit of the gyrus. Hence it is that, 
as also remarked by Baillarger, a section of brain (in some of the 
lower animals more especially) will often show the cortex, owing to 
a little pressure, actually separating from the white matter at the 
* Loc, cit, t Loc, cit. 
