Freiburger historische Bestände - digital

Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 69

This is a most important point, because it not only shows that the
fissura perpendicularis externa and the " Affenspalte" are similar in
their mode of origin, and therefore in all probability homologous, but
also that, if this fissure in man be transitory, as it undoubtedly is, the
sulcus transversus occipitalis of Ecker cannot be regarded as the
equivalent in the adult human brain of the " Affenspalte" in the ape's
brain.

It is only in the brains of the low apes that I have proved the presence
of an elevation on the outer wall of the ventricle corresponding to the
bottom of the " Affenspalte." I cannot tell whether or not it exists in the
anthropoid brain. Specimens of these are so valuable that I am unwilling
to destroy those I have got, even in the determination of a point of this
importance.*

For a time I considered the fissure which I have named the external
calcarine as the same as the fissura perpendicularis externa, but its
position and direction are such that I am now inclined (provisionally
at least) to look upon it as a distinct fissure. It is placed very obliquely
along the lower border of the occipital part of the cerebrum (PL I., fig. 14,
&c, e. c), and corresponds on the outer surface of the hemisphere with
the calcarine fissure on the mesial face. When transverse sections are made
through the occipital part of the cerebral hemisphere, the external calcarine
fissure is seen to be a deep infolding of the hemisphere wall, and the
bulging which it forms into the ventricular cavity lies exactly opposite,
and may bo actually in contact with the calcar avis (PL I., figs. 18
and 19).

The external calcarine fissure appears very early. It can be distinguished
in a large number of cases amongst the primitive transitory
furrows (PL i.} figs. 3, 10, &c), and at this period, as we have already
noticed, it is sometimes continuous around the occipital pole of the
hemisphere with the precursor of the true calcarine fissure. This connexion
, where it exists, is always obliterated about the fourth month. In
the human brain the external fissure is transitory. It is effaced towards

* The apes which I have specially examined "with reference to this point are the Sooty
Man gaby and the Cehus.