Freiburger historische Bestände - digital

280

Cunningham Memoirs.

upwards to the conditions present in the cerebrum of the anthropoids and
man.

Let us begin with Cebus (fig. 64). The outer aspect of the frontal
lobe exhibits an exceedingly simple surface pattern. There are only two
fissures. Of these one presents a T-shaped figure, and is composed of a lower
vertical (p. c. i.) and an upper horizontal limb (L). The latter has the
appearance of a terminal bifurcation of the former, and therefore it consists
of an anterior and a posterior branch. In the early human foetal
brain the inferior praecentral sulcus sometimes presents a figure precisely

Fio. 64.—The outer surface of the cerebrum of Cebus albifrons. Drawn by the American instrument
for tracing orthogonal projections of the skull, r., fissure of Rolando ; p. c. i., sulcus
prsecentralis inferior; h., ramus horizontalis ; f.2, inferior frontal sulcus.

similar to this (vide fig. 12, p. c. i., PI. n.). The second furrow is a straight
clean cut fissure (/2), which begins behind in the angle between the anterior
branch of the horizontal limb and the vertical limb of the T-shaped fissure,
but it never in the lower apes communicates with either. It is important
to note particularly its position below the level of the horizontal limb of
the T-shaped fissure. From this it extends forwards to the pointed frontal
pole. It is called by Eberstaller the sulcus rectus ;* and this name we shall
apply to it until we establish its proper homology.

The next form which we shall examine is Callithrix (fig. 65). In
this the arrangement is slightly different. The posterior branch of the
horizontal limb of the T-shaped sulcus of Cebus is wanting. The furrow
consequently presents an F-shaped figure. This form of the fissure

* Das Stirnhirn, p. 112. Leipzig, 1890.