Freiburger historische Bestände - digital

44

Cunningham Memoirs.

fact, that in each case the gyrus eunei is on the surface, and, further, that
the " stem" of the calcarine fissure is prolonged up into the cuneus in a
very ape-like manner.

To put the matter briefly, then, we may say : (1) that the calcarine
fissure of the ape's brain corresponds with the "stem" of the -^-shapedfissure
in the adult human brain, and with the entire length of the precursor of
the calcarine fissure in the human foetal brain; (2) in the human brain
the posterior part of the precursor of the calcarine fissure of the foetus is
obliterated, and in its place a secondary sulcus is laid down at a later date
(the posterior calcarine sulcus). In the brain of the ape there is no
representative of the latter sulcus.

The position of the calcarine fissure in the ape is very different
from that of the corresponding fissure in man. Almost the entire
shaped fissure in the human brain lies upon the mesial surface of the
hemisphere. The lower half of the "stem" is the only part which
occupies a place on the tentorial surface. In the ape, however (both in
the higher and lower forms), the entire length of the calcarine fissure, with
the exception of its hinder end, is situated on the tentorial face of the
cerebral hemisphere.

We have referred to the variability of the parieto-occipital fissure in the
ape. In the anthropoid it is deep and strongly developed, but in the
lower apes it is often extremely feeble; so much so, indeed, that it is not
always an easy matter to distinguish it from neighbouring sulci. Often it
fails to reach the mesial border of the hemisphere, and it is not an
uncommon thing to see it doubled. This latter condition we have also
observed occasionally occurring in the human brain.

In the chimpanzee the calcarine fissure cuts only to a very slight
extent into the gyrus fornicatus. It is separated, therefore, from the
hippocampal fissure by a superficial convolution. In the orang the
calcarine fissure cuts the gyrus fornicatus more deeply than in man, but
still a very manifest " isthmus" separates it from the hippocampal fissure.
In many of the low apes the connexion between the two fissures at first
sight appears to be complete. Indeed, Gratiolet described the calcarine
and hippocampal fissures under one name, and regarded them in these