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Mr. Victoe Horsley—Cranio-Cerebral Topography.

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may be at present regarded as relatively constant or of morphological
significance and functional importance. These are the superior and
inferior genu respectively. In the human brain these are almost invariably
marked, and possess, as far as my observations go, a constant relation to
the neighbouring sulci, of the following general character:—

The inferior genu.—The more important inferior genu lies midway
between the horizontal level of the superior (or first) frontal sulcus and
the upper end of the prsecentral sulcus, while it is exactly opposite, i.e. on
the same level as the centre of the sulcus prsecentralis medius when that is
present, free or joined, as most commonly it is, to the posterior or superior
branch of the inferior prsecentral sulcus.

Under these circumstances, and having regard to the position of the
sulcus prsecentralis superior and its direction, it is obvious that the lower
extremity of this sulcus bears an important relation to the genu, and assists
in defining its position on the exterior of the head. On page 300 are given
the indices whereby this point is fixed. Between it and the fissure of
Rolando lies the principal area of representation of the upper limb.

Messrs. Anderson and Makins have stated that, on obtaining tracings of
the whole length of the fissure of Rolando, comparison of the drawings
failed to show a constancy in the sinuosities, and that from the curvatures
of the fissure alone it was not possible to fix the position of the genu.
Exception ought to be taken to the methods employed, inasmuch as the brains
from which the tracings were made were not previously hardened ; but there
is no doubt that, in certain exceptional cases (probably brachycephalic) in
which from the shallowness of the sinuosities and the want of antero-posterior
direction, it is difficult to fix the position of the genu from only the aspect
of the fissure. Under these circumstances additional assistance may be
obtained by determining first the lower end of the superior prsecentral sulcus
and the position of the middle prsecentral sulcus.

Finally, as regards the grouping of points of localization of function
about the inferior genu and which render close attention to it necessary,
reference may be made to Papers by Dr. Beevor and myself in the Philosophical
Transactions since 1887.

The superior genu lies near the separation of the respective limb areas,