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150

Cunningham Memoirs.

with a differently formed cranium and a difference in the extent of the
surface areas of the brain, we should find a correspondence in the craniocerebral
topography of the orang and of man. It would almost seem to
indicate that there is some obscure relationship between the different bony
factors which go to form the cranial capsule and the areas into which the
surface of the cerebrum is subdivided.

It is very evident, from the facts stated above, that we cannot be too
careful in instituting a comparison between the cranio-cerebral relationships
of man and those of the apes; and further, that many features which,
at first sight, appear to be similar in both, are found, on closer examination
, to be more or less of a spurious character.

XVI. The relation presented by the anterior limbs of the Sylvian
Fissure to the Cranial Wall at different periods of growth.—The
relations of the anterior limbs of the Sylvian fissure to the cranial wall are
subject, even in the adult, to a considerable amount of variation. This is
due chiefly to the many different forms in which these limbs may appear,
and also, but to a less degree, to a variability in the line pursued by the
lower part of the coronal suture. We have noted that the two anterior
limbs may be completely distinct and separate from each other. In this
case, the size and degree of development of the pars triangularis of the
.inferior frontal convolution influences the cranial relations of both. Again,
only one limb—a combination of both, and presenting very different
degrees of inclination—maybe present. In such cases it would be difficult
to find two heads in which the anterior limb presents precisely the same
cranial relations. Still further, the two limbs may be arranged in the
form of a Y. In these cases the cranial relations alter with the lengthening
out, or shortening of, the common stem, and also with the different degrees
of divergence of the two limbs.

Such being the case, it is difficult to pick out those differences in the
cranial relations of the anterior limbs of the Sylvian fissure which are due
to general growth-changes. That such do exist there cannot be a doubt,
and to establish this point I shall have to give in detail the observations
which I have made on the cranial topography of the fissures in question.