Freiburger historische Bestände - digital

Mr. Victor Horsley—Cranio-Cerebral Topography.

319

junction, but, as it were, arrested and opposite the middle of the pterion
line, i.e. the upper border of the great wing of the sphenoid.

The Topography of the Posterior Limb.—The first point to be determined
in the topography of the posterior limb is the all-important relationship
which the body of this deep fissure bears to the squamo-parietal suture.
Since, as is well known, this relationship varies greatly with the age of the
individual, it is necessary, in determining topographically the situation of
the posterior limb of the Sylvian fissure, to first discuss the conditions that
prevail in the child, and later the relations of the fissure in the adult.
Fortunately this has been exhaustively treated by Prof. Cunningham
(see page 140 of this Memoir). On page 142 Prof. Cunningham sums
up his conclusions, viz. that at the time of meeting of the opercular lips,
i.e. shortly after birth, the fissure and suture are furthest apart, that up
to the fifth year they approach each other rapidly, that after the fifth
year this occurs more slowly, and that it is not until the ninth year
that the adult relationship of the two structures is attained.

In the Child.—Under these circumstances the accurate position of the
posterior limb of the Sylvian fissure in the infant and young child can only
be arrived at in the following manner:—The origin of the limb being
already determined (yid. sup.), and the highest point in the squamo-parietal
suture noted, a u vertical" is drawn through this at right angles to the
mesial plane, and carried down to below the zygoma. The next step is to
determine the whole temporo-parietal depth of the surface of the hemisphere
. This is unfortunately not easy. The upper limit of the hemisphere
is readily marked, of course, but the lower border can only be
roughly estimated, according to the data given on p. 141, to lie just below
the level of the lower border of the zygoma. The temporo-parietal length
obtained in this manner is obviously open to the damaging criticism that it
is estimated by tape measurement over the soft parts and zygomatic arch,
which carry the line so far outwards as to cause error by lengthening it.
As a matter of fact the error produced is balanced by the fact that any
lengthening of the more or less vertical outer line is only equal to the
marked curve of the surface of the hemisphere itself; and we have only to
regard the thickness of the enveloping cranium and scalp at the upper