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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 187

of Rolando forms with the mesial plane is greater in the female and
approaches more nearly to a right angle than in the male; in other words,
the male fissure of Rolando, on an average, courses somewhat more
obliquely from above downwards and outwards than in the female." This
author represents the average male angle to be 60o,9, and the average
female angle as 64°-2. More recently Dr. Josef Victor Rohon,* another
worker in the laboratory of Professor Riidinger, goes so far as to assert that
the same sexual distinction in the angle of Rolando may be detected in the
chimpanzee.

Giacomini gives the angle of the fissure of Rolando as varying from
570,5 to 620,5, whilst Hare,f who measured it in situ, found it to vary from
60° to 73°, the average being 67°. Eberstaller, on the other hand, who
examined no less than 300 hemispheres, states that the Rolandic angle
varies from 70° to 75°, and that he could discover no sexual difference in
this respect. To quote his own words: " Meine Messungen, die sich auf
rund 300 Hemispharen erstreckten, ergaben nun fast constant einen Winkel
von 70°—75°; einen nennenswerthen Geschlechts-unterschied konnte ich
nicht constatiren."

To measure this angle correctly is a matter of very great difficulty, and
therefore we need not be surprised that the various authors I have quoted
should have arrived at such divergent results. A very simple instrument,
which I had constructed for the purpose, enabled me, I believe, to measure
the angle accurately. Two straight, narrow, and flexible bands of brass
were jointed together in the manner described and figured in page 132.
In adjusting the instrument the long strip of brass was bent over the
middle line of the head from the glabella in front to the external occipital
protuberance behind, and in such a position that the joint between the
two bands of metal was placed immediately behind the point at which the
fissure of Rolando overstepped the mesial border of the hemisphere. The
short limb of the instrument was then bent round the surface of the
cerebrum, and moved until its anterior border corresponded to the general
direction of the fissure. The angle was thus secured, and, after tracing it

* Zur Anatomic der Hirnwindiingen bei den Primaten. Miincheri, 1884.

f "The Position of the Fissure of Rolando," Joum. Auat, and Phys., vol. xviii., p. 717.

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