below. The
hippocampal gyrus is bounded above by the dentate or hippocampal
fissure which causes the hippocampus major in the descending cornu and
so is a complete fissure. If its lips are separated the fascia dentata
or gyrus dentatus and the fimbria continued from the posterior pillar
of the fornix are seen. Anteriorly the fissure is arrested by the
recurved process of the upper part of the hippocampal gyrus, called
the _uncus_, and in front of this a slight sulcus, the _incisura
temporalis_, marks off the temporal pole or tip of the temporal lobe
from the region of the uncus. It will be seen that the callosal gyrus,
isthmus, and hippocampal gyrus form nearly a complete ring, and to
this the name of _limbic lobe_ is given.

_Interior of the Cerebrum._

If a horizontal slice be removed from the upper part of each
hemisphere (see fig. 12), the peripheral grey matter of the gyri will
be seen to follow their various windings, whilst the core of each
gyrus consists of white matter continuous with a mass of white matter
in the interior of the hemisphere. If a deeper slice be now made down
to the plane of the corpus callosum, the white matter of that
structure will be seen to be continuous with the white centre of each
hemisphere known as the centrum ovale. The _corpus callosum_ does not
equal the hemispheres in length, but approaches nearer to their
anterior than their posterior ends. It terminates behind in a free
rounded end, named the splenium (see fig. 11), whilst in front it
forms a knee-shaped bend, and passes downwards and backwards as far as
the lamina cinerea. If the dissection be performed on a brain which
has been hardened in spirit, the corpus callosum is seen to consist
almost entirely of bundles of nerve fibres, passing transversely
across the mesial plane between the two hemispheres; these fibres may
be traced into the white cores and grey matter of the gyri, and
connect the gyri, though by no means always corresponding ones, in the
opposite hemispheres. Hence the corpus callosum is a connecting or
commissural structure, which brings the gyri of the two hemispheres
into anatomical and physiological relation with each other. On the
surface of the corpus callosum a few fibres, the _striae
longitudinales_, run in the antero-posterior or longitudinal direction
(see fig. 12, b). Their morphological interest is referred to in the
section