Freiburger historische Bestände - digital

72

Cunningham Memoirs.

praecentral, the intraparietal, and the parallel sulci. It is well on in the
sixth month before it appears, and it usually first shows in the form of
two or more shallow depressions, which ultimately run into each other.
In some cases one of these pieces assumes a more or less transverse course,
and is placed immediately below the end of the "stem" part of the parieto-
calcarine fissure. This is an important part of the fissure, because it may
produce on the floor of the ventricle an infolding, or elevation, which is
the earliest form of the eminentia collateralis. It is only this central or
middle part of the fissure which has any claim to the term "complete."
The front and back portions of the sulcus, which ultimately join this part,
present no corresponding ventricular elevations. (PI. iv., fig. 4.) It is
by no means uncommon for the lower end of the calcarine "stem" to
be joined by a shallow intervening furrow with this transverse central
part of the early collateral fissure. In several of the figures in PI. in. a
more or less intimate connexion of this kind is seen (figs. 19, 25, 26, 27,
and 28). Further, in the left hemisphere of the male Fuegian figured and
described by Seitz, a persistence of this early connexion between these two
fissures was observed.*

In PL iv., figs. 3, c.e., the elevation corresponding to the mid-collateral
fissure in the floor of the ventricle is very evident, and it is seen to present
a distinctly fold-like character.

At the same time it must be understood that in many brains no part of
the early collateral fissure produces an elevation in the floor of the ventricle,
and if the eminentia collateralis is formed at a later period, it is developed
quite independently of the fissure. It appears to me that the connexion
between the fissure and the ventricular elevation depends a good
deal on the time at which the former appears. If the mid-part of the
fissure developes early an infolding is produced; if late, there is no such
result.

It is interesting to note that in all the specimens of the low apes
which I have examined I have never seen the slightest trace of an
eminentia collateralis. As is well-known, it is not an absolutely constant
feature of the human brain.

* Zwei Feuerlander-Gehime. Zeitschrift fur Ethnologie, 1886.