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Dk. Cunningham—Surface Anatomy of the Primate Cerebrum. 231

offshoot. This is seen in the left hemisphere of the foetal brain figured in
page 232 (fig. 51).

I have already alluded to the fact that in cases where the upper end of
the parieto-occipital fissure on the inner face of the hemisphere bifurcates,
and its two terminal branches appear on the outer surface of the hemisphere
, there is a tendency for the ramus occipitalis to develope in the form
of two sulci—one in relation to the upper end of each branch of the divided
parieto-occipital fissure. Usually these two pieces of the ramus occipitalis
run rapidly into each other, but in one specimen in my possession (a hemisphere
taken from a foetus well on in the eighth month), they are still
quite distinct, and further the posterior extremity in each ends in a terminal
bifurcation or sulcus transversus.

All these facts in connexion with the development of the sulcus transversus
occipitalis of Ecker are directly opposed to the view that it is an
independent fissural element, distinct from the intraparietal sulcus, and the
representative in man of the u Affenspalte." Still, it must be admitted
that in rare cases it is developed in the form of a continuous transverse
furrow which is, in the first instance, separate from the ramus occipitalis.
Ecker figures the brain of an eighth-month foetus in which this is the case,
and, no doubt, this specimen greatly influenced him in the views he has
expressed in regard to its nature. In my collection of foetal brains I have
a very beautiful specimen of the same kind, and I consider it so important
that I have had it figured (fig. 51, p. 232). The condition is only present
in the right hemisphere. The ramus occipitalis is seen to consist of three
parts, viz. an anterior vertical portion, an intermediate sagittal piece, and
a hinder vertical part. It is the last of these which is the representative of
the sulcus transversus. This specimen, no doubt, introduces an element of
difficulty into the question, but it does not shake me in my belief that the
sulcus transversus has nothing to do with the " Affenspalte," because we
see in front of the ramus occipitalis in this specimen an independent transverse
element of a precisely similar character, and it appears to me that
we are merely dealing wTith a case in which the usual U-shaped furrow has
become broken up into three segments.

This aberrant mode of development of the ramus occipitalis explains