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108

Cunningham Memoirs.

exhibited in the course of the first twelve months, but from the fourth
year up to adult life the average percentage distance of the hinder end of
the island of Reil from the posterior extremity of the occipital lobe was the
same for each period examined, viz. 44*1. The same constancy of position,
however, does not exist for the anterior limit of the insula. In the full-
time brain the island of Reil attains its maximum length (32), and
approaches most nearly to the anterior end of the hemisphere (24-3).
From this period on to adult life it falls back slightly, and finally attains
an index of 29'6. It is extremely interesting, therefore, to note, that
whilst during intra-uterine life the anterior limit of the insula maintains a
nearly fixed relation to the anterior end of the cerebrum, and the posterior
end an extremely varying relation to the posterior extremity of the
occipital lobe, towards which, indeed, it steadily and rapidly grows, in
extra-uterine life the reverse condition is observed. The posterior end of
the region is fixed, whilst the anterior limit oscillates—at first approaching
more closely to the anterior end of the cerebrum, and then falling back
to the position which it occupied during intra-uterine life.

In the foregoing Table I have included the results which I obtained
from the measurement of five negro brains. The island of Reil in these
appear to be smaller than in the European brain. Further, its anterior
limit is at a relatively greater distance from the fore end of the cerebrum,
whilst its hinder end approaches more closely to the occipital extremity of
the hemisphere. The number of specimens examined is certainly too small
to justify us in drawing any final deductions from these points of comparison
between the European and negro brains. I excluded from this
inquiry six negro hemispheres which were distorted; the five which I
selected for measurement were not hardened with the necessary precautions
for the thorough preservation of external configuration.

But the question of sex and side must also be studied in connexion with
the area occupied by the insula. In so far as sex is concerned, no decided
difference was apparent in the early stages of the island of Reil in the male
and female. But in adults there seems to be good reason to believe that
in the male brain the antero-posterior length of the island of Reil is relatively
greater than in the female, The following are the indices;—