Freiburger historische Bestände - digital

14

Cunningham Memoirs.

majority of the radial transitory fissures on the medial face of the hemisphere
do not reach so far as the border of the hemisphere, but two at
the occipital or postero-superior pole, very constant in position and longer
than the others, almost invariably do so {p. o. and <?.); and occasionally
in the frontal region and at the end of the temporal lobe one or more may
also show a similar extension.

In addition to the radial furrows issuing from the fissura arcuata we
frequently find others parallel to them, but close to the free border of the
hemisphere, and not connected with the arcuate fissure. These may be
independent infoldings, or they may merely represent the upper extremities
of fissures on the outer surface of the cerebrum, turning over the upper
border of the hemisphere.

As we have stated the number of radiating temporary fissures on the
medial aspect of the hemisphere varies very greatly. In one cerebral
hemisphere Bichter counted nine, and in another only five. The number
is usually the same, or approximately so, on the two hemispheres of the
same brain, and the usual number seems to be eight. Eighteen hemispheres
all between the beginning of the third and the end of the fourth months
yielded the following results in this respect:—

In 9 there were 8 fissures.

CO

n 6 »

» 2

„ 11 „

„ 1

„ 4 „

„ 1

„ 5 „

„ 1

„ 7 „

„ 1

„ 9 „

No doubt the difference in the number of fissures on the medial surface
is partly due to the different periods of development at which the brains
were examined, but I do not believe that this is the only factor present in
determining the variations. The influence at work in calling the infoldings
of the cerebral wall into existence appears to be a purely mechanical one,
viz. a restraint placed upon the longitudinal growth of the hemisphere;
and this being the case it is easy to understand how the number and depth