Freiburger historische Bestände - digital

20

Cunningham Memoirs.

From the above list it will be seen that the number of temporary
fissures which appear on the outer surface of the mantle is very variable;
and this variability is, in all probability, due to the different conditions of
growth-restraint to which the growing hemisphere is subjected in different
cases. No doubt, also, it may to a certain extent be accounted for by the
fact that the brains examined belong to different periods of development.

In only one brain were the fissures arranged absolutely symmetrically
on the two hemispheres. This was one of the most instructive specimens
of the series, and several views of it are given in Plate i. (figs. 11, 12, 13).
Although not disposed in other brains in exactly the same way on the two
sides, there was always noticed a general correspondence between the two
hemispheres in the number and character of the fissures.

IV. The Persistence of the Transitory Fissures under certain
conditions. — A very interesting question arises at this point:—Do
circumstances ever arise under which these primitive complete fissures
of the early cerebrum are retained permanently ? There is good reason
to believe that in some cases one or other of those we have named the
precursors of the parieto-occipital and calcarine show an unbroken continuity
of existence with the fissures which bear the same name in the
fully-developed brain. Further, it is possible that the corresponding
fissures on the outer face of the occipital lobe (external perpendicular of
Bischoff and external calcarine), in rare instances, may also be preserved.
Certainly they always enjoy a much more prolonged existence than the
other transitory fissures, although it must also be borne in mind that one
of these at least (external perpendicular) appears at a much later period.
Lastly, there cannot be a doubt that in certain malformations of the brain,
as, for example, absence or defective formation of the corpus callosum, this
primitive and, under normal circumstances, transitory fissural system is in
a measure preserved. Anton* is of opinion that the disappearance of
the transitory furrows is largely due to the development of the corpus

* Zeits. fur Heilkunde, Band vn. 1886. I regret very much to say that I am obliged to
quote Anton's Paper second-hand. I have not been able to obtain a copy of it, and my only
knowledge of the views which he enunciates are obtained from the brief passing reference which is
made to it by Kichter.