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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 121

that during this process, the frontal bone, to all intents and purposes,
remains passive. In other words, the overlapping is not brought about
by a backward growth of the posterior edge of the frontal bone: indeed
the measurements which I have made would rather seem to indicate
that in its lower part the area of the frontal bone is, if anything,
more extensive in the child than in the adult.

The extent of the overlapping squamous portion of the parietal bone
varies very greatly in different skulls, and thus it arises that the relation of

Fig. 30.—Lateral view of the skull of a child about six years old. The cranial wall has been drilled
from the interior along the internal sutural lines. These can therefore be compared with
the external sutural lines.

the external coronal line to the insula is by no means the same in all adult
heads. Probably the figures which are given convey a tolerably accurate
estimate of the average condition, but I have seen one head in which the
coronal suture very nearly coincided with the anterior end of the insula,
and another in which 24*6 per cent, of the length of the insula lay in front
of the suture.

It is interesting to observe that the external coronal line corresponds

KOi'AL IRISH ACADEMY.—CUNNINGHAM MEMOIRS, No. VII. [16]