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110

Cunningham Memoirs.

The difference in extent of the insula on the two sides of the brain is very
slight, but it is seen in every stage indicated above, with the exception of
the six and a-half to seven and a-half months' foetal period, and the four to
five years' child. In both of these cases, however, it will be observed that
the number of hemispheres examined was very small.

VII. The Sylvian Eegion in the Ape.—One of the most remarkable
characters of the cerebrum in the chimpanzee and the orang is the total
absence of the frontal and orbital opercula. The temporal and parietofrontal
opercula are alone present. Pansch incidentally alludes to this. He
says: 11 Wichtiger noch ist das Resultat, dass an der ganzen sogenannten
Orbitalflache keine Ueberwucherung des Mantels stattgefunden hat, so dass
hier also Insel und Mantel in demselben Niveau liegen. Der hier vorhan-
dene Ramus ascendens fossae Sylvii ist also nicht wie beim Menschen eine
zwischen zwei wuchernden Lappen gebildete Furche, sondern nur der freie
Rand des gewucherten obern Lappens."*

There is a so-called anterior limb of the Sylvian fissure, but it does
not come within the description which we have given of such a limb. As
Pansch has observed, it bounds the parieto-frontal operculum in front,
and the fore-border of this operculum forms its superficial wall. It cuts
obliquely backwards and inwards into the hemisphere, and the surface of
its. deep wall is carried, in some cases (in the chimpanzee) almost continuously
on to the surface of the island of Reil. Pansch, however, is hardly
correct in saying that the insula and the mantle lie in the same plane.

But it may be asked why we have so decidedly stated that the frontal
operculum (pars triangularis) is absent in the anthropoid, seeing that we
might very well suppose that it was merely fused with the fore-part of the
parieto-frontal operculum. This is, no doubt, the view of those who hold
that the so-called " anterior limb " of the Sylvian fissure is homologous with
the anterior horizontal limb in man. Broca f has given expression to this
view, and Herve^: has repeated, with emphasis, the same opinion. Both of

* "Ueber die typische Anordnung der Furchen und Windungen," &c, Archiv f. Anthrop.,
Dritter Band, p. 245.

f Morphologie du cervean de l'homme et des primates.—Berne d'Anthropologic, 1878, 2e
Serie, t. ler.

| La Circonvolution de Broca, Paris, 1888.