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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 11

With one or two exceptions where it was necessary to prepare the
hemispheres for microscopic examination, all my specimens have been
preserved by the same method. A mesial incision having been carefully
made through the cranial capsule, and the dura mater cut on each side,
the whole embryo was immersed in a saturated solution of chloride of zinc.
In this it was allowed to float for a period of thirty-six hours, and then
it was transferred to methylated spirit. The brain was thus hardened in
situ. When dealing with fresh embryos in which the head had not been
previously subjected to pressure or otherwise damaged, I have never found
this method to result in the production of artificial infoldings of the
cerebral wall. When the brain substance had attained a proper consistence,
the cerebrum was exposed by cutting through the cranial capsule and dura
mater along the sutural lines with a pair of scissors. In the few cases in
which it was desirable to prepare the brain for microscopic examination, I
employed Midler's fluid.

But in addition to the specimens which have come into my own
possession, I have been allowed, in the most generous manner, to handle,
describe, and photograph four very characteristic embryonic brains which
are preserved in the museum of University College of London. These
range from the beginning of the third month up to the first week of the
fourth month or thereabouts. Further, Professor Victor Horsley has been
so kind as to furnish me with a beautiful series of photographs of the foetal
brain preparations which are displayed in the museum of the University of
Oxford. One of these, figured in Plate i. (figs. 9 and 10), which has
probably reached the fourth month of development, is especially interesting
. The figures which are given by Schmidt, v. Kolliker, and Pichter
I have also found useful, although those which we commonly see in our
text books, and which have been taken from Ecker and Mihalkovics,
cannot be regarded as giving a proper idea of the transitory furrows as
they exist during the period of maximum development.

Duration of the Transitory Fissures.—The mesial wall of the hemisphere
is considerably thinner than the outer wall; and it is partly in
consequence of this that the transitory fissural infoldings first make their
appearance upon it. But we have the most conflicting statements regarding

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