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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 189

fixity of the fissure of Rolando, once its preliminary development is
fairly established. In the first two months of its existence the Eolandic
fissure presents a more open angle with the mesial plane. It traverses
the surface of the hemisphere in a more transverse direction (73°*6).
Mingazzini* has noticed this point. He says: " In the human foetus of
the sixth month the fissure of Rolando is nearly perpendicular, and with
its development it gradually becomes more oblique." In several of the
foetal brains which I examined, the angle reached 79° and 80°. Hamy,
in a Paper already referred to, contends that in the young subject the
Rolandic angle is only 52°, whilst in the adult it is 70°, and he seeks to
associate this with the development of the third frontal convolution. It is
needless to say that there is no foundation whatever for this statement.

As might be expected from what we have seen in regard to the position
of the upper and lower ends of the fissure of Rolando in the anthropoid
cerebrum the Rolandic angle is more acute in the orang and the chimpanzee
than in man. In the lower apes it is as a rule more obtuse ; but it may be
(as for example in Hamadryas) very similar to the angle in the human brain.

Hamy f considers that striking differences in the inclination of the
fissure of Rolando may be noted in the brains of young and old apes
belonging to the same species. I strongly suspect that these differences
are merely individual and do not bespeak growth changes. In a young
chimpanzee he remarks that the angle was 64°, whilst in one considerably
older it was 68°. Again, in the macaque he states that it increases from
62° to 70°.

Nor is there anything in the angle of the fissure of Rolando by which
we can establish sexual distinctions. I quite agree with Eberstaller in
this. The above Table shows differences, it is true, but the increase or
diminution of the angle is as often found on the one side as the other.
How can we account for these differences ? Riidinger was not far from the
truth when he hinted that the form of the head might have some influence

* " Intorno ai solcbi e le cireonvoluzioni cerebrali dei Primati e del feto umano." Estratto
dagli Atti della E. Accad. Med. Ponia, Anno, xv., vol. iv., serie n., p. 15.

f "Contribution a l'etude du developpement des lobes cerebranx cbez les Primates,"
Arcbiv. de Zool. exper. et gen. 1872, pp. 430 and 431.