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De. Cunningham—Surface Anatomy of the Primate Cerebrum.

xi

cranium a ridge indicating the position and direction of the posterior
horizontal limb of the Sylvian fissure could usually be detected. The
point of the knife was drawn along this line so as to incise the dura
mater and make a distinct mark.

The falx cerebri was now stitched tightly back in its place so as to
render the tentorium tense and a cast of the interior of the cranium taken.
The pegs which had been introduced opposite the upper ends of the
fissure of Rolando, and parieto-occipital fissures projected slightly into the
interior of the cranium, and marked on the cast the position of each of
these fissures. Before drawing the cast the sutural lines were mapped
out on its surface by driving an awl through the skull at short intervals.

On such a cast accurate information was obtained—(1) upon the
position of the upper ends of the parieto-occipital and Rolandic fissures
with reference to each other, to the fore and hinder ends of the cerebrum,
and to the coronal and lambdoid sutures; (2) upon the position and
direction of the Sylvian fissure and its relation to the squamous suture.

But it was impossible to note the sutural relations of the fissures in
every instance. Time would not allow of this. A large number of measurements
have therefore been made upon brains removed from the cranial
cavity. In every case, however, they have in the first instance either been
carefully hardened in situ or plunged at once into a chloride of zinc bath,
and thus fixed in their natural shape.

Measurements.—In determining the length of the cerebrum, either
along its upper border or its lateral surface, it is absolutely essential that
the points between which the measurements are taken should be rigidly
adhered to throughout., and it is by no means an easy matter to select
points which are in every respect satisfactory. Eberstaller measures from
the inner angle of the trigonum olfactorium to the point where the occipital
lobe first touches the tentorium. There cannot be a doubt that this is a
good method, and one which is calculated to give accurate results ; but
both of his points are on the under surface of the brain, and consequently
it is impossible to adopt his plan when the brain is being measured in situ.
I have been forced therefore to select different points from which to make
my measurements. In front I fixed upon a point on the upper or mesial