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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 45

apes as forming one fissure. This is not the case, however. The connexion
is only a superficial one, as the gyrus fornicatus is carried on in the
form of a high, deep, annectant gyrus between them, and prevents their
free communication. The whole question is one of degree. No communication
of any kind occurs in the chimpanzee; a superficial connexion is
established in the low apes, whereas in man and the orang an intermediate
condition is seen.

VIII. Development of the Parietooccipital and Calcarine Fissures.

—The views which have been advanced by different authors regarding the
origin of the parieto-occipital and calcarine fissures are very conflicting;
and no doubt there are many points in connexion with their first appearance
and history which are extremely puzzling.

v. Kolliker* maintains that they appear synchronous with the temporary
fissures on the mesial aspect of the hemisphere, and constitute members of
the same series, differing from them only in so far that they are permanent,
and not evanescent. He says :—" As early as the separation of the frontal
lobe from the temporal lobe by the Sylvian fossa there arises a boundary
for the occipital lobe by the appearance of the parietooccipital fissure.
This is distinct in the third month. Schmidt even figures it in the eighth
week."

Richter,"!' who gives a good account of the transitory furrows in a series
of early embryos, appears to entertain the same view. Referring to a brain
with hemispheres 3*3 cm. long, he remarks :—" An der medialen Seite der
Hemispharen gingen einige radiare Falten mehr von der Bogenfurche aus
als bei Fotus 3. Bei letzerem zahlte man im Verlauf der ganzen Bogenfurche
fiinf, bei Fotus 4 neun. Die Fiss. parieto-occ. und calc. standen bei
Fotus 4 zur Bogenfurche ungefahr noch in demselben Verhaltniss wie bei
Fotus 3. Ausser der parieto-occ. und calc. verschwinden diese iibrigen
radiaren Furchen der medialen Hemispharenwande dieser Entwicklungs-
epoche sammt und sonders wieder und theilen so das Geschick der schon

* EntTvicklungsgeschicMe des Menschen und der hoheren Thiere, 1879.

f "TJeber die Entstehung der Grosshirnwindimgen,'' Yirchow's Archiv, 1887, p. 398.