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Cunningham Memoirs.

it were kept moist, would retain its full size, and not undergo the least
shrinkage for at least twenty-four hours. A sixth of this time, and indeed
latterly very much less, was quite sufficient for obtaining a satisfactory
mould.

At first I took the mould entirely in plaster of Paris, but this was a
lengthy process, and necessitated no less than thirteen or fifteen separate
pieces. Before I had gone far (after my sixth model had been completed)
I hit upon a much more satisfactory and expeditious plan. I made a combination
mould of plaster of Paris and gelatine. The surface impression of
the brain I took in four or five plaster pieces, and the remainder of the
head I took in gelatine. This method yielded excellent results.

Twenty-two models of the human head, one of the orang, one of the
chimpanzee, one of the baboon, two of the Macacque, and one of Cebus
were prepared. The majority of these are figured in Plates V. to VIII.

But this was a very laborious undertaking, and could only be carried
out on a comparatively small number of individuals. It was therefore
found necessary to supplement the facts obtained in this way by others
acquired by a less tedious process.

The following method afforded excellent results. One-half of the
cranial vault was removed by a sagittal cut a little to the one side of the
mesial plane, and a horizontal cut a short distance below the highest
point of the squamous suture. The cerebral hemisphere of that side was
then removed, and the head placed so that it rested upon the opposite side.
The falx cerebri was next detached, and the mesial surface of the hemisphere
still in position exposed. Upon this it was easy to recognize the
parieto-occipital fissure, and the upper end of the fissure of Rolando. The
latter could be determined from its position in relation to the upturned
extremity of the calloso-marginal sulcus. The point at which the fissure
of Rolando turns over the upper margin of the hemisphere being
determined, a peg was here driven through the cranial wall from within
outwards. Another peg was driven in a similar manner into the skull,
opposite the point where the parieto-occipital fissure reached the upper
border of the hemisphere. The cerebral hemisphere was then extracted
without injury to the tentorium or the cerebellum. On looking closely at
the dura mater as it clothed the deep surface of the lateral wall of the