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Mr. Victoe Hoesley—Cranio-Cerebral Topography.

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almost every author, localized on the external surface of the skull, beneath
the pterion. Now, as is well known, the form of the pterion varies
according to the relative share taken in its formation by the component
bones, but for the European races it may be assumed to be always in
the shape of an H. Under these circumstances it becomes a matter of
much importance whether the posterior end or the centre or the anterior
end of the parieto-sphenoidal suture, represented by the horizontal bar of
the H, is to be taken as the pterion. Whether, in short, the ptero-
temporal or the ptero-frontal junction indicates the origin of the fissure
of Sylvius. Accepting the account given in Chap. II. of the configuration
of the fossa, the origin of the posterior limit of the fissure will far
more often be found in the adult beneath the ptero-temporal extremity of
the ptero-parietal suture, and this point should therefore, for the purpose
of localizing the commencement of the fissure of Sylvius, be regarded as
the pterion par excellence. The trunk portion of the fissure, running, as it
does, just along and posterior to the edge of the lesser wing of the sphenoid,
where that divides the anterior and middle fossae of the base of the skull,
is situated in a line drawn about transversely, i. e. at right angles to the
plane in which the pterion lies. It reaches, of course, to the anterior
perforated spot, and which lies just external to the anterior clinoid process.
The general direction and relations of the branches of the fissure are as
follows :—

The anterior limbs run forwards beneath the line of the pterion to
just beyond the coronal suture. The posterior branch or limb, in the
adult, courses backwards along the squamous suture, leaving it just beyond
the highest point of that line, and running towards the lambda.

The topography of these component parts of the fissure will now be
separately considered.

The Topograph// of the Anterior Limbs.—In localizing on the external
surface of the head the position of the anterior limbs of the fissure of
Sylvius, we are unfortunately met with the difficulty that the anterior
limbs are not constant in form. The commonest and, since Broca's time,
most received view is that there is in the adult an ascending limb, rising
from the seat of origin of the posterior limb, cutting the frontal operculum