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Dk. Cunningham—Surface Anatomy of the Primate Cerebrum. 263

furrow placed close to the superciliary margin of the frontal lobe, and
usually in front of the anterior horizontal limb of the Sylvian fissure. It
is only present in exceptional cases, and in certain of these it is joined
superficially to the transverse furrow which lies behind it (*. e. to the
sulcus radiatus of Eberstaller).

It must be apparent from what has been said that the sulcus frontalis
secundus may appear in one, two, three, four, or even five pieces. In the
fifty-seven hemispheres in which I have examined this sulcus I have seen
no less than fourteen different varieties resulting from different combinations
of its parts, according as the annectant gyri are absent, hidden within
the furrow, or on the surface.

When Sernoff* speaks of the sulcus frontalis inferior as being occasionally
completely absent, he, no doubt, refers to those cases in which it
is broken up into its several parts.

The sulcus diagonalis of Eberstaller very frequently opens into the
sulcus frontalis secundus (fig. 59, p. 262). This union may be complete, or
interrupted by a deep gyrus. In cases where the junction is effected with
a second frontal sulcus which is distinct and separate from the inferior
prsecentral sulcus an F-shaped furrow is produced, which bends round the
ascending limb of the fissure of Sylvius (fig. 54, p. 250). At first sight
the condition might readily be mistaken for a doubling of the inferior
prsecentral furrow.

VI. Sulcus Frontalis Primus.— We have noted the intimate relationship
which exists between this furrow and the sulcus prascentralis superior.
Continuous with the latter behind, it runs forwards with a slight inclination
inwards, and, as Eberstaller has pointed out, ends close to the mesial
border, about one inch, or rather more, from the superciliary margin
(fig. 53, p. 248). In a large number of cases, however, a small furrow
presenting the same direction intervenes between its anterior extremity
and the frontal pole, and must, in consequence, be regarded as a separate
portion of the furrow (fig. 53, p. 248). I have noted the presence of this

* " Individualniye tipy mozgovykh izvilin u tcheloveka." (Individual types of the convolutions
of the brain in man). Moskovv, 1877.