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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 147

calculated to bring out these relations in every detail. Following Broca,
he introduced into the brain at certain points small pegs through apertures
drilled in the cranial wall, and then he removed the brain. The measurements
which he gives, although they are manifestly accurate, are not
sufficient for us to establish, in the case of the Sylvian fissure, a satisfactory
comparison with the corresponding relations in man. The value of Fern's
investigation is greatly increased by the fact that he was able to study
the cranio-cerebral relations in two young orangs.

In the prosecution of this part of my research, I have examined the
heads of two chimpanzees, one orang, two macaques, one cynocephalus,
one hamadryas, and one cebus. In all of these, with the exception of the
hamadryas and one chimpanzee, I have exposed the brain according to the
method described in the Introductory Chapter, and have then modelled the
entire head, with the cerebrum in situ. In the case of the hamadryas and
the second chimpanzee, I removed the parietal bone by chiselling through
the cranial wall, along the sutural lines, and when this was done pins were
introduced into the brain in such a manner that they mapped out on its
surface the parietal field.

The models which I obtained, with one exception (a macaque), are
figured in Plate vm. (figs. 18-22).

The apes which I have examined may be classed in three groups according
to the relations which are exhibited by the Sylvian fissure to the
cranial sutures.

Group I.—This group comprises those in which the Sylvian fissure lies
above the entire extent of the squamous suture, as in the case of the
newly-born human infant. The cebus exhibits this condition.

Group II.—In this group we place those in which the front part of the
squamous suture, for a considerable part of its extent, lies immediately
over a corresponding portion of the Sylvian fissure. The macaques, the
hamadryas, and the orang furnish us witli examples of this arrangement.

Group III.—This group includes the chimpanzee and the baboon. The
Sylvian fissure begins at a point some distance below the squamous suture
and crosses under it as it ascends obliquely to end in the lower part of the
parietal lobe.

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