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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 91

Single Anterior Limb.—We have already stated the manner in which this
limb is developed, and insisted upon its being regarded as quite distinct
from the anterior horizontal limb with which it lias been frequently confounded
. It is invariably placed on the outer face of the hemisphere. I
have never seen it on the orbital face of the frontal lobe. As a rule it lies
somewhat above the lower margin of the cerebrum, and it presents a very
variable inclination—sometimes more or less horizontal, at other times it is
distinctly ascending.

In eighty hemispheres it was found twenty-four times, or, in other
words, in 30 per cent. This is a somewhat higher percentage for this condition
than that which was obtained by Eberstaller.

Two Anterior Entirely Separated Limbs.—The anterior ascending, and
the anterior horizontal limbs when distinct, as Broca and Eberstaller
have pointed out, may issue from the stem of the Sylvian fissure, so
close together, that together they form a V-shaped figure, or they may be
slightly separated at their origin, and then they give rise to a U-shaped
figure. They diverge with very varying degrees of obliquity. The
ascending limb, in rare cases, is vertical, but much more frequently it
takes an oblique upward and forward course. The usual direction of the
horizontal limb is one straight forwards immediately above the margin
which separates the outer from the orbital face of the frontal lobe. In this
case both limbs appear on the outer surface of the hemisphere. But very
frequently the anterior horizontal limb is distinctly on the orbital face of
the frontal lobe, and cannot be seen when the cerebrum is viewed in profile.
In such cases it must be borne in mind that no fissure on the under aspect
of the hemisphere can be considered the anterior horizontal limb of the
fissure of Sylvius unless it lies to the outer side of the external orbital sulcus.
The so-called fourth anterior limb of the Sylvian fissure which, when it
exists, is placed on the inner side of the external orbital sulcus, is very apt
to be mistaken for the anterior horizontal limb.

In thirty hemispheres out of the eighty, in which the two anterior limbs
of Sylvius were quite distinct and separate from each other (*. e. in 37*5
per cent,), the anterior horizontal limb was placed on the orbital face of
the frontal lobe in twelve (*. c. 40 per cent,), and on the external face in

[12*]