Freiburger historische Bestände - digital

Mr. Victor Horsley—Cranio-Cerebral Topography.

353

separate subordinate sulcus crossing the lower and posterior angle of the
parietal bone (in the adult).

V. Topography of the Island of Reil.—The topography of the
island of Reil is necessarily easy to fix roughly, after that the position of
the Sylvian fissure is determined as stated on page 317. The exact position,
however, of the sulcus circularis Reillii varies with the development of the
vallecula. To project the limiting outline of the insula on the exterior of
the cranium, therefore, it is necessary to define the average covering of the
vallecula space by the various opercula, and this is best studied by transverse
sections. The temporal operculum has such a broad basis in the
temporal lobe as to make the level of the temporal limiting sulcus difficult
of accurate determination. In the vertical plane through the lower end of
the fissure of Rolando, it corresponds externally with the level of the
parallel sulcus and upper border of the middle temporal gyrus. Since
from this point anteriorly the line of limitation trends downwards, it
gradually crosses posteriorly the superior temporal gyrus to reach the
fissure of Sylvius at the point indicated by the Table of Indices elaborated
by Professor Cunningham (see page 107), and that in the adult corresponds
in the antero-posterior direction with the anterior extremity of the ramus
sagittalis sulci intraparietalis. This, it will be seen, is just in front of
the vertical plane of the posterior surface of the pulvinar.

The upper limit of the fronto-parietal opercular depth is similarly found
to lie in the vertical plane through the lower end of Rolando, short of the
upper ends of the transverse sulci (Eberstaller). Certain it is that this
upper portion is notably narrower than the lower, and that the parietal
operculum is relatively shallow. Anteriorly the frontal operculum is
similarly shallow—in fact more so than the parietal, and a fortiori than
the temporal operculum. The covering gyrus is the lowermost portion
of the promontory of the third frontal gyrus ("cap" of Broca), and
the hindmost edge of the continuation of this into the external orbital
gyrus.

That this is the correct view of the external projection of the insula is
confirmed by putting together outlines of Plates 15 and 21, in Professor

ROYAL IRISH ACADEMY.-CUNNINGHAM MEMOIRS, NO. VII. [45]