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Cunningham Memoirs.

of the middle gyrus rest on the floor of the middle fossa, i. e. on the anterior
portion of the petrous bone, the inferior portion of the squamous, and the
posterior margin of the great wing of the sphenoid.

The inner and posterior limiting border of the inferior surface of the
temporal lobe is coincident with the margin and attachment of the tentorium,
against the anterior extremity of which the uncus lies.

The aspect of the inferior surface of the temporal lobe is directed
downwards and backwards.

The inferior surface of the occipital lobe is continuous with that just
described, but rests wholly on the tentorium. Owing to the very marked
median elevation of the vermiform process of the cerebellum, the line which
marks the separation of the median aspect of the lobe from the inferior,
rises from the tip of the occipital lobe to the splenium of the corpus callosum,
thus taking a line which is almost at right angles to the parieto-occipital
fissure. The result of this is, that although the calcarine fissure is situated
on the mesial aspect of the lobe, it lies close to the margin of the inferior
surface. The inner half of the inferior surface of the occipital lobe is
occupied by the lingual lobe, the remainder by the adjoining occipitotemporal
gyri.

In consequence of the outward slope of the tentorium, the general
aspect of the inferior surface is directed downwards, forwards, and inwards,
the reverse of that of the temporal lobe ; the region where these opposed
planes meet is above the "vertical" plane of the pulvinar, i.e. just below
the splenium of the corpus callosum.

The remaining surfaces need no special description beyond the details
furnished later respecting the topography of their individual parts.

III. Topography of Fissures.—Class I. Those separating Lobes :—

(A) Sylvius.

(B) Rolando.

(C) External Parieto-Occtpital.

(A) Fissure of Sylvius.—In the adult, the commencement of the
fissure of Sylvius at the anterior extremity of the Sylvian fossa is, by