Freiburger historische Bestände - digital

4

Cunningham Memoirs.

the part which more particularly corresponds with the Ammonsfurche of
Mihalkovics. It appears about the same time as the fore-part, but in the
first instance the two portions remain distinct and separate. Ultimately,
however, they meet at the hinder end of the choroid fissure to form the
continuous furrow which we have described.

The arcuate and choroid folds can best be studied by removing the
roof of the hemisphere. The manner in which they project into the
ventricular cavity so as to overlie the corpus striatum can then be
seen.

As we have already mentioned, the term arcus marginalis is applied
to the portion of the mesial face of the hemisphere which lies between the
choroid and arcuate fissures. This is an important strip of mantle surface.
In connexion with it the fornix, corpus callosum, and gyrus dentatus are
formed.

The facts stated above regarding the fissura arcuata are well known,
and have been carefully and faithfully described by several embryologists.
It would appear, however, that the fissure does not always present the
simple condition which we have noted. His,* who maintains that the
inner face of the cerebrum is at no time smooth and devoid of furrows,
figures the fissura arcuata in a ten weeks' foetus; and he represents its
hinder end rising upon the mesial face of the hemisphere until it
ultimately reaches the upper border; turning round this it is continued
downward on the outer surface of the back-part of the cerebral mantle.
Mihalkovics, t commenting upon this, denies that the fissura arcuata ever
extends upward to the free border of the hemisphere. I entirely agree
with the latter observer. In none of the specimens in my possession is the
condition described by His present.

The hind-part of the primitive fissura arcuata, which bounds the arcus
marginalis, is retained in the adult brain as the hippocampal fissure, and
gives rise to the elevation in the floor of the descending horn of the lateral
ventricle which is known as the hippocampus major.

The fore-part of the fissura arcuata is generally believed to form in the

* His, TJnsere Korperform, Leipzig, 1875, p. 113, fig. 112.

f Mihalkovics, Entwicklungsgeschichte des Gehirns, Leipzig, 1877, p. 158.