Freiburger historische Bestände - digital

28

Cunningham Memoirs.

His whole description shows that he regards the appearance of the occipital
lobe as being due to a general, and not to a local growth.

It is also right to mention that BischofT took up a somewhat similar position
with regard to the occipital lobe. He says : aIch sehe mich auf diese Weise
im Widerspruch mit Arnold und Reichert, welche, wie ich oben angegeben,
den Hinterlappen nur als einen spateren Auswuchs oder Verlangerung des
hinteren Theiles der embryonalen Hemispharenbetrachten. Ich behaupte
im Gegentheil, dass derselbe wie alle librigen Theile dieser Hemispharen
sich allmahlig aus dem anfangs noch nicht in einzelne Lappen unterscheid-
baren Keime da entwickelt, wo er spater bemerkt wird. Ja, die Selbststandig-
keit dieses Hinterlappens wird durch das friihe Auftreten der inneren
senkrechten Occipital- und der Hippocampus (calcarine) Spalte, sowie der
transitorischen ausseren senkrechten Occipital-Furche ganz besonders
bewiesen."*

There are many points which indicate in the clearest manner that the
occipital lobe is not a local secondary outgrowth which has sprouted out
from the hinder end of the cerebral hemisphere in a bud-like fashion.
From the end of the second to about the beginning of the fourth month the
young embryonic human cerebrum presents the characteristic bean-shaped
outline which has led German authors to apply to it the term ''ringformigen
Lappen." At this stage the primate cerebral hemisphere resembles in
outline the adult condition of the hemisphere in most quadrupeds. A
further similarity may be noted in the fact that the Sylvian fissure in the
quadruped brain stands upright and nearly vertical, and thus corresponds
with the vertical direction of the Sylvian fossa in the foetal primate
cerebrum. But as the occipital lobe in the latter takes form, the Sylvian
fossa becomes more and more oblique, which clearly shows that the growth
is not restricted to the hinder end of the hemisphere, but affects it from
one end to the other—in other words, that it is interstitial and general.

The shape of the occipital part of the cerebrum depends upon the
restricted space it is called upon to occupy above the cerebellum. As it is
pushed backward by the general cerebral growth it is moulded into shape

* Die Grosshirnwindungen des Menschen. Abh. d. 11. CI. d. bay. k. Ak. d. Wiss., x., Ed. 11.
Abtb., p. 416.