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Mr. Victor Horsley—Cranio-Cerebral Topography.

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latter furrow, the squamo-parietal suture, and then coursing upwards and
backwards under the parietal bone. The line it takes from the suture
divides very nearly the lower border of the parietal bone at the junction
of the middle and posterior thirds, and this may be at present taken as
sufficiently exact in the absence of more accurate details.

From this point it courses upwards towards the lambda, so as to cut off
a surface of cortex corresponding to a triangular piece of the parietal bone,
including the postero-inferior angle of the same. This statement applies
only in the case of adults. In the child the posterior third of the parietal
bone more correctly corresponds with the portion of the occipitotemporal
region below the parallel sulcus.

In considering the topography of the posterior end of this very
important sulcus, the first feature is its relation to the parieto-occipital
fissure. The two extremities of these furrows tend to approach one
another. That of the parallel is right in advance of the parieto-occipital,
which is lying at or more often just in front of the lambda. Consequently
if they near each other, it is by the parieto-occipital coursing outwards
parallel to the lambdoid suture, and separating this line from the hinder
end of the parallel sulcus.

The next feature to be described is very vaguely obtained, viz. the
second part of the so-called u pli courbe." The first part is known as the
supra-marginal gyrus, the topography of which has already been mentioned,
and the second the angular gyrus.

The angular gyrus, which is so marked a feature in the lower apes as a
simple gyrus of angular outline, is much sub-divided in man. Its commencement
, commonly spoken of as the anterior limb, corresponds in site
with the posterior portion of the supra-marginal gyrus, i.e. just behind the
centre of the parietal eminence. Since the parallel sulcus almost invariably
runs towards the margin of the hemisphere, and either directly or by the
introduction of a subordinate sulcus, delimits externally the second annec-
tant gyrus, the " anterior limb" of the angular gyrus in man may be said
to commence above and just behind the centre of the parietal eminence.
It now remains to determine the point round which the gyrus changes
direction and forms the posterior limb. This point the upper and posterior