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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 281

is also met with in the human foetus (vide PI. 11., fig. 15, p. c). Seeing,
therefore, that the furrow under consideration may exhibit a different
appearance in different forms, we may distinguish it by the provisional
name of sulcus arcuatus (first applied to it by Mingazzini*) until we are
in a position to give to it a name which will indicate its homology.

The sulcus rectus (f.2) presents the same appearance and relations as
the corresponding furrow in Cebus. In Callithrix, however, we have two
additional sulci. These are exceedingly shallow and short furrows. The
one is placed in front of the lower part of the vertical limb of the sulcus
arcuatus an d immediately above the superciliary margin of the frontal lobe.

Fig. 65.—Outer surface of the cerebrum, Callithrix. Drawn by the American apparatus for tracing
orthogonal projections of the skull, r., fissure of Rolando; p. c. i., sulcus prsecentralis
inferior ; f.2, sulcus frontalis inferior; p. c. s., sulcus prsecentralis superior (?) ; e. o.,
a sligbt trace of the sulcus fronto-orbitalis.

It is a feeble representative of the sulcus fronto-orbitalis of Waldeyert or
the sulcus orbito-frontalis of Broca. The second little furrow is situated
above the level of the sulcus arcuatus and is in all probability a feeble
representative of the sulcus prsecentralis superior or of the basal part of the
first frontal sulcus.

The cerebrum of the baboon (fig. 66) brings us a step nearer to the
condition which is found in the brain of the anthropoid apes. The sulcus
arcuatus (j>. c. i.) is easily recognized. It exhibits the T-shaped form, but

* Intorno ai solchi e le circonvoluzioni cerebral! dei primati et del feto umano. Estratto
dagli Atti della R. Accademia Med. di Roma. 1888. Vol. iv., serie n.

f Das Gibbon-Hirn. Internationale Beitriige zur Wissenscbaftlicben Medicin. Festscbrift,
Rudolf Yirchow gewidmet zur Yollendung seines 70. Lebensjabres. Band 1, p. 26.

KOYAL IRISH ACADEMY.-CUNNINGHAM MEMOIRS. NO. VII. [361