Freiburger historische Bestände - digital

18

Cunningham Memoirs.

it was ^not, in every case, continued round the occipital pole into the
precursor of the calcarine fissure on the medial face of the cerebrum
(PL i., fig. 12, e. c).

In PI. i., fig. 1, the left hemisphere of an embryo at about the
eleventh week is represented. Two short fissures—one in front and the
other behind—are alone present on the outer surface of the cerebrum.
Between these, however, the cerebral mantle is faintly streaked by a
series of grooves, which present very much the direction of the transitory
fissures when fully developed. Most likely these markings indicate the
initial stages in the formation of the fissures. When fully formed, a deep
infolding is the result. This figure maybe compared with fig. 1, PI. in.
In this a brain about the same stage is depicted, and yet there are well-
marked fissures present. This shows the variability in the time at which
these infoldings occur.

Figure 2 shows a transverse microscopical section through the middle
of the fissure indicated in the frontal region of the brain depicted in PI. i.,

Fig. 2. Fig. 3. Fig. 4.

Fig. 2.—Transverse section through the middle of the fissure lettered "/" in PI. i., fig. 11.
Fig. 3.—Transverse section through the extremity of the same fissure.
Fig. 4.—Transverse section through the fore-part of the central vesicle figured in PI. r.,
fig. 13. On inner side, note shallow fore-part of the fissura arcuata.

fig. 13 (/.). The lips of the furrow are closely applied to each other at the
surface, and it is this that gives to such fissures their sharply-cut linear
appearance ; but, towards the bottom of the sulcus, the walls of the fold are
separated to a small extent, and a slight recess is formed between them.