Freiburger historische Bestände - digital

114

Cunningham Memoirs.

destitute of a frontal and an orbital operculum, there are many of the
lower apes, as, for example, the baboon, the macaque, hamadiyas,
cercopithecus, &c. which show a faint trace of an operculum in this
locality, although it cannot in any respect be regarded as being equivalent
to the same structure in man. When the temporal lobe is pulled well
downwards the outer portion of the orbital part of the frontal lobe is seen
to be undermined to a slight extent. A structure resembling a feeble
orbital operculum is thus formed, which is directly continuous with the
fore-part of the fronto-parietal operculum. These meet at an angle, and
on examining them from below it will be observed that the deep surface
of the operculum at this angle is deeply scored by a furrow which rarely
reaches the surface (PI. iv., fig. 10). The question, of course, arises: can
this be the representative, in the lower apes, of an anterior limb of the
Sylvian fissure ? I am satisfied that it is not. It lies immediately below,
and in the same line as the prsecentral sulcus, and is to be regarded rather,
I believe, as the outer branch of a bifurcation of the anterior limiting furrow
of the island of Reil.

In the lower apes the sulci on the surface of the elliptical and very
projecting island of Reil are, as a rule, feeble and variable. Sometimes
the surface is perfectly smooth (PI. iv., fig. 8) ; at other times, as in
the chimpanzee, there may be two furrows, or perhaps only one. In the
hamadryas, and occasionally in the baboon, I have observed the three
radial sulci, as they exist in the orang. In almost all my specimens there
is a well-marked gyrus transversus connecting the pole of the insula with
the orbital surface of the frontal lobe. The following was the condition
found in the different brains of the low apes which I examined :—

I. The Macaque.—Five cerebral hemispheres examined.

In one, . . Insula quite smooth.

In two, . . Sulcus centralis Reillii alone present.

In one, . . Sulcus centralis and sulcus postcentralis present.

In one, . . A faint Y"snaPe(l furrow. The two limbs joining a stem, which

was continued downward and forward toward the insular

pole.