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Mr. Victoe Hoksley—Cranio-Cerebral Topography.

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The general direction of the fissure has hitherto always been taken as a
straight line connecting the upper and lower ends of the fissure, and this
will be employed in the present pages; but for accurate delineation of the
fissure on the exterior of the skull, it is very important to notice that the
actual line taken by the fissure is an oblique one downwards and forwards
in the upper third of its course, i. e. to beyond the superior genu; then
chiefly forwards and also somewhat downwards to the inferior genu, and
from thence almost straight* downwards (including forwards) to its termination
in the lower end. From this it follows that whereas the upper part
of the fissure fairly coincides with the line of general direction, the noteworthy
region of the inferior genu is considerably above and in advance of this
latter.

The lower end of the fissure may terminate as usual (Hefftler and all
observers) a few millimetres above the Sylvian fissure, or it may cutf the
operculum, and enter the last-named fissure. For present purposes the latter
variety, which occurs relatively rarely (19 per cent., Cunningham), will be
ignored, and the fissure regarded as being separated from the fissure of
Sylvius by a narrow annectant gyrus. Reference to the point now
omitted will be made in describing the topographical value of the subordinate
sulci.

In proceeding to discuss the means of topographically determining on
the exterior, with accuracy, the position of the fissure and of its component
parts, especially the inferior genu, the factors of age and sex are naturally
of much importance, although of not such influence as in the case of the
fissure of Sylvius. The changes they produce will be touched upon under
each point. The facts may here be arranged according to the principal
features of the fissure, and to which allusion has just been made.

The Upper End.—The determination of the position of the upper end of
the fissure of Rolando has been accomplished in various ways, which may be
grouped thus—

[a) Relative Measurements.

(b) Absolute Measurements.

* Almost perfectly straight in the orang.

f Xot completely as in the sense understood by Giacomini and the majority of anatomists.

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