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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 103

But in the later stages of development the very evident relation which
the inferior limiting sulcus of the insula bears to the incisura temporalis
and the collateral fissure becomes obscured. Towards the end of foetal
life the deep surface of the temporal pole becomes scored with two or three
transverse sulci. These have been figured and described in the adult brain
with great care and exactness by Eberstaller; * and the same author has
very correctly pointed out that in the adult the lower limiting sulcus of
the insula usually ends in front by running forwards upon the deep surface
of the temporal pole and taking up a position parallel to and behind these
transverse sulci (fig. 27, p. 97). This, however, is a purely adventitious
arrangement which is brought about through one of the transverse sulci,
about the ninth month of foetal life, running into the limiting sulcus of Reil,
and thus becoming continuous with it. In the adult brain, therefore, the
true relations of the inferior limiting sulcus of the insula are somewhat
misleading.

In the ape the transverse sulci on the deep surface of the temporal pole
are not developed, and the incisura temporalis is generally well-marked.
The relation which exists between the posterior part of the insula and the
uncus can thus be seen to great advantage, and also the continuity between
the inferior limiting sulcus of the insula and the incisura temporalis
confirmed.

The examination of the foetal brain renders the relationship which
exists between the sulci and convolutions of the insula and the fissures and
gyri on the surface of the mantle still more obvious. Three radial " Primar-
furchen " appear in each region, not only at the same stage in the development
of the brain, but also as a rule in very much the same order. In the
latter half of the fifth month the central sulcus becomes evident as a faint
line or furrow which runs upwards and backwards from the lower part of
the Sylvian fossa (PI. il, figs. 12 to 15, 2). From the very first it lies
accurately in the line of the fissure of Rolando, and it appears at the same
date. At this period the sulcus centralis is situated much nearer to the
hinder end of the insula than in the later stages, because the Sylvian fossa

* Anatomischer Anzeiger, Xo. 24, Nov., 1887, p. 745.