e _gyrus_ of the _parietal
eminence_. Above and behind the gyrus of the parietal eminence is the
_angular gyrus_, which bends round the posterior extremity of the
parallel fissure, while arching over the hinder end of the inferior
temporo-sphenoidal sulcus is the post-parietal gyrus. Lying in the
parietal lobe is the _intra-parietal_ fissure (fig. 9, p^3 and p^4),
which separates the gyrus of the parietal eminence from the
supra-parietal lobule.

The _Central Lobe_ of the hemisphere, more usually called the _insula_
or _island of Reil_, does not come to the surface of the hemisphere,
but lies deeply within the Sylvian fissure, the opercula forming the
margin of which, conceal it. It consists of four or five short gyri,
which radiate from the _locus perforatus anticus_, situated at the
inner end of the fissure. This lobe is almost entirely surrounded by a
deep sulcus called the limiting sulcus of Reil, which insulates it
from the adjacent gyri. It lies opposite the upper part of the
ali-sphenoid, where it articulates with the parietal and
squamous-temporal.

[Illustration: FIG. 10.--Orbital surface of the left frontal lobe and
the island of Reil; the tip of the temporo-sphenoidal lobe has been
removed to display the latter.

17. Convolution of the margin of the longitudinal fissure.
O. Olfactory fissure, over which the olfactory peduncle and lobe are
situated.
TR. Orbital sulcus.
1" 1"'. Convolutions on the orbital suface.
1,1,1,1. Under surface of infero-frontal convolution.
4. Under surface of ascending frontal; and 5, of ascending parietal
convolutions.
C. Central lobe or insula.]

In front of the central lobe, on the base of the brain, are the
_orbital gyri_, which are separated from one another by the _orbital
sulcus_. This is usually H-shaped, and the gyri are therefore
anterior, posterior, external and internal. Bisecting the internal
orbital gyrus is an antero-posteripr sulcus (_s. rectus_), beneath
which lies the olfactory lobe, bulbous in front, for the olfactory
nerves to arise from.

On the mesial surface of the hemisphere, as seen when the brain is
longitudinally bisected and the cerebellum and medulla removed by
cutting through the crus cerebri (see fig. 11), the divided corpus
callosum is the most central object, while below it are seen the
fornix, septum lucidum and third ventricle, the descr