expressed. As regards the presence of the superior bridging
convolution, I am inclined to think that it has existed in one
hemisphere, at least, in a majority of the brains of this animal
which have, up to this time, been figured or described. The
superficial position of the second bridging convolution is
evidently less frequent, and has as yet, I believe, only been
seen in the brain (A) recorded in this communication. The
asymmetrical arrangement in the convolutions of the two
hemispheres, which previous observers have referred to in their
descriptions, is also well illustrated in these specimens" (pp.
8, 9).

Even were the presence of the temporo-occipital, or external
perpendicular, sulcus, a mark of distinction between the higher
apes and man, the value of such a distinctive character would be
rendered very doubtful by the structure of the brain in the
Platyrrhine apes. In fact, while the temporo-occipital is one of
the most constant of sulci in the Catarrhine, or Old World, apes,
it is never very strongly developed in the New World apes; it is
absent in the smaller Platyrrhini; rudimentary in Pithecia (73.
Flower, 'On the Anatomy of Pithecia Monachus,' 'Proceedings of
the Zoological Society,' 1862.); and more or less obliterated by
bridging convolutions in Ateles.

A character which is thus variable within the limits of a single
group can have no great taxonomic value.

It is further established, that the degree of asymmetry of the
convolution of the two sides in the human brain is subject to
much individual variation; and that, in those individuals of the