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Cunningham Memoirs.

exactly what one might expect, seeing that amongst the lower apes the
inferior genu alone is, as a rule, developed. In one specimen this genu is
quite distinct upon the inferior portion of the fissure before it has joined the
upper portion (PI. n., fig. 18, r}). As a rule, however, the fissure remains
straight until the union of its two elements is complete. The superior
genu is developed at the point of junction, and it is not until a later
period that it assumes any degree of prominence.

The upper end of the fissure of Rolando does not overstep the upper
border of the hemisphere until the beginning of the last month of intrauterine
development. In the eighth month it just reaches the margin, and
I have several specimens which show it in the process of turning over and
in the process of developing the backward bend of its upper extremity.

From the seventh month onwards the growth of the two bounding
banks of the fissure does not proceed at an equal pace. There appears to
be a greater growth-energy in the posterior central convolution, and this
leads in the first instance to a greater prominence of that gyrus, and
ultimately to a partial overlapping of the ascending frontal convolution
by the ascending parietal convolution. Heschl and Eberstaller have
called attention to this. It is more obvious in the lower two-thirds of the
fissure, or, in other words, opposite that portion of it which is formed
by the lower element. It is owing to this that the adult fissure cuts into
the cerebral surface in an oblique direction from before backwards. In
certain cases this overlapping of the ascending frontal convolution by the
ascending parietal may be almost imperceptible ; whilst in others it is
strongly marked along the whole length of the fissure.

IV. The Topography of the Fissure of Rolando in Man.—The points
in the topography of the fissure of Rolando which I have chiefly endeavoured
to arrive at are the following :—

1. The relative distance of the upper extremity (a) from the anterior

end of the cerebrum, (b) from the coronal suture.

2. The relative distance of the lower extremity (a) from the anterior

end of the cerebrum, (h) from the coronal suture.