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Mr. Victor Horsley—Cranio-Cerebral Topography.

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at the present day, the various divisions and questions are arranged in the
order :—

I. Topography of the cerebrum as a whole—its borders.

II. Topography of the cerebrum as a whole—its surfaces.

III. Topography of the fissures separating lobes.

IV. Topography of the furrows subdividing lobes.
V. Topography of the island of Eeil.

The conclusions arrived at on these questions by previous observers will
be found referred to under each of the above headings.

I. Topography of the Cerebrum viewed as a whole—its Borders.—

The margins and surfaces of the cerebral hemisphere are moulded upon
the folds of the dura mater and the bony prominences of the interior of
the skull. When these are well understood it only remains to point out
certain minute details which frequently escape notice. The whole
hemisphere, viewed in its uppermost margin and in a sagittal plane, is
bordered by nearly a semicircle, the frontal lobes in their lower third
alone presenting a flattened surface, the edge of which does not continue
the general arc-like curve, but is directed backwards as well as downwards.

On tracing round the lateral margin which separates the lateral from
the inferior surfaces, and on starting from the extreme tip (nasion)
of the frontal lobe, the margin of the hemisphere rises forthwith as the
roof of the orbit slopes upwards as well as outwards, and finally arrives
above the outer angle of the orbit which is formed, of course, by the
union of the frontal orbital plate with that of the great wing of the
sphenoid. As the outline of the hemisphere follows round this outer
border of the orbit, it gradually comes to bulge outwards on the alisphe-
noid just where the ptero-frontal suture commences, i. e. at the anterior
extremity of the pterion. This bulging edge of the frontal lobe is more
marked often in children, and thereby forms a promontory or cape, as
Broca called the more posteriorly lying folds of the third frontal gyrus,
viz. the pars triangularis. The lateral margin is then lost in the Sylvian
fissure, but reappears immediately by crossing it on to the temporal sphenoidal
lobe just above the anterior extremity of the parallel sulcus; from