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Mr. Victor Horsley—Cranio-Cerebral Topography.

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the vertical limb of trie latter furrow. As moreover the representation of
motor function is more closely connected with the prsecentral sulcus itself,
the projection of the inferior frontal furrow is readily made with sufficient
accuracy.

Sulcus Frontalis Medius.—This sulcus which lies intermediately parallel
to the two chief frontal furrows just described, divides longitudinally, when
present, the middle frontal gyrus. As such it comes frequently into
relation with the frontal eminence.

Sulcus Frontalis Mesialis.—The secondary and very subordinate furrows
which subdivide the superior gyrus are so close to the border of the hemisphere
as to practically coincide with it. Moreover, they are not known to
have any topographical significance.

Sulcus Frontalis Diagonalis of Eberstaller.—This value of this small
furrow as a landmark, which has only quite recently received attention
from anatomists, is in the Macacque [Macacus sinicus) a sulcus of remarkable
constancy, and an index of limitation of representation.

In 1887 it was so described by Beevor and myself, we provisionally
regarding it then as being from its position possibly homologous with the
anterior ascending limb of the fissure of Sylvius. But from an examination
of 63 human hemispheres (of which 15 were of children below 15 years, the
rest adults), I am convinced that this sulcus is homologous with the sulcus
diagonalis of Eberstaller, and this latter therefore, is worthy of some
detailed attention. Prof. Cunningham, however, thinks that the small
sulcus in the lower apes is the homologue of the sulcus termed fronto-orbi-
talis in the anthropoid, and this he identifies with the anterior limiting
furrow of the island of Reil in man. In the same way he regards the
anterior limb of the fissure of Sylvius in the anthropoid to be only the termination
of the fronto-parietal operculum.* In the anthropoid the results of
excitation by Beevor and myself would seem to suggest that this view of
the homologies of these sulci will have to be tested by further research. In
the meantime it is sufficient for our present purpose to note that the sulcus
diagonalis is necessarily dependent for its topographical position upon the

* It must be observed that this would not dispose of the idea, that at least tbe upper border
of this sulcus is truly homologous with the upper border of the human anterior Sylvian limb.