16 Histology of the Island of Reil. By Herbert C. Major, M.D. 
it will be my endeavour to supply in the present article, resolve 
themselves into the following : 
I. Can any structural peculiarity be detected in the arrange- 
ment of the cortical layers of the human Insula, or in the nervous or 
other elements composing them ? 
II. Do the gyri which collectively form the Insula, agree with 
each other in minute structure ? 
III. Does any structural difference exist, under ordinary con- 
ditions, between the right and left Insula ? 
IV. Does the white matter of the Insula maintain the same 
plan of union with the cortex, as regards the course of the fibres, 
as in other convolutions generally ? 
I. It is not strange that at the time when Fr. Gennari, Vic 
d’Azyr, Meckel, Cazauveilh, and even Baillarger wrote, considerable 
differences of opinion should have existed with regard to the layers 
of the cortex of the brain, and that, consequently, the descriptions 
given by these authors should have varied. For them, the chief 
method of investigation consisted in pressing a small portion of 
brain substance between two pieces of glass, and examining it with 
the unaided eye, or, at most, very imperfectly magnified. But it is 
strange that more recent investigators, with all the means for 
accurate observation at their disposal, should, on a simple matter of 
observation, fail generally to arrive at a common conclusion. And 
yet such is the case. Kolliker * distinguishes four cortical layers 
as constituting the general plan of arrangement. L. Clarke f gives 
the number as eight ; Th. Meynert,i five ; Charcot, § five. Doubt- 
less there are many sources of difficulty and fallacy. Frequently it 
happens that at one spot the cortical layers appear so mingled and 
thrown into confusion as to render a candid and truthful enumera- 
tion of them almost a matter of impossibility ; while in another 
section, taken only a line from the first, the layers of celLs manifest 
themselves with unmistakable accuracy and precision. But then, 
such accidental sources of fallacy should disappear before systematic 
and extended observation, and should not long occasion doubt. 
And in truth, much of the uncertainty and confusion on the subject, 
and which are only now beginning to pass away, thanks to the 
labours of Bets and others, would have been avoided if authors had 
more frequently delineated the objects which they desired to de- 
scribe. In so complex a study as that of the structure of the brain, 
long descriptions, unaided by actual demonstration or by plates, are 
in reality of little value. 
Since, then, there exists this diversity of opinion with regard to 
the elementary points of cortical structure as usually presented 
to us, it is necessary that I should in the first place state what, in 
* ‘ Histologie Humaine.’ f ‘Proceed. Roy. Soe.,’ September 1863. 
J ‘ Strieker’s Handbook,’ vol. ii. § ‘ Progres Medecal,’ 1875. 
