Freiburger historische Bestände - digital

16

Cunningham Memoirs.

expression of a fissure on the outer surface of the hemisphere, but the
process is virtually the same with all the transitory furrows, whether on the
mesial or the lateral surface of the cerebrum.

But as we have already mentioned, the fisura arcuata itself breaks up
(PI. i., fig. 12). In all cases the posterior hippocampal portion is preserved
in situ, and, in connexion with it, the precursors of the calcarine and
parieto-occipital fissures may remain attached. The obliteration of the forepart
of the fissura arcuata with the radial fissures in connexion with it, as
we have already observed, may be effected in different ways. The manner
in which the stellate furrows free themselves from the arcuate fissure
previous to their complete disappearance is well seen in figs. 3, 4, 5, and 6,
PI. in. The persistence of the foremost part of the arcuate fissure on the
inner face of the frontal lobe is very remarkable. In figs. 15 and 16, PL i.,
which represent two hemispheres from an embryo in the early part of the
fifth month of development, it is still apparent, although all the radial
furrows have become completely obliterated.

Transitory Fissures on the Outer Surface of the Hemisphere.—The transitory
fissures are not, as a rule, disposed so uniformly on the outer face of the
hemisphere as they are upon the medial face. (PI. i., figs. 1 to 4, and
6 to 11 ; also PI. n., figs. 1 to 7.) Starting from the free border of the hemisphere
, they run in a convergent manner towards the Sylvian region, or,
in other words, towards the hilum of the bean-shaped cerebrum; but as a
general rule they fall short of this. In well-marked cases they are present
all the way round the mantle border from the frontal pole in front to the
temporo-sphenoidal pole below. At some particular part of the circumference
it is usual to see them more concentrated or more closely placed
and more numerous than elsewhere. In certain cases this may occur in the
frontal region (PI. i., figs. 4, 7, and 9); in other instances it is in the parietal
region that the crowding together takes place (PI. I., figs. 2 and 3).

But the fissures have not always the simple and uniform arrangement
described above. With these, others are usually associated. Thus, it is by
no means uncommon to see a fissure occupying a position and possessing a
direction similar to that of the adult Sylvian fissure (PI. i., figs. 6, 7, 8,
and 9 b). This was present in eight instances, and it was no mere super-