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116

Cunningham Memoirs.

lateral length of the hemisphere as being equal to 100, the following Table
gives the percentage of this, which is formed by the insula, as well as of
the portions of cerebrum in front and behind. The measurements were
made in precisely the same manner as that adopted for the human brain :—

Relative Length of the Submerged part of the Insula in Man and the

Anthropoid Apes.

Lateral length of the Hemisphere = 100.



Number of
Hemispheres
Examined.

Fronto-Central
Index.

Central Index.

Occipito-
Central Index.

European, .....

28

26-3

29-6

44-1

Orang, .....

2

32-2

21-5

46-3

Chimpanzee, ....

4

34-1

18-2

47-7

No one who handles the brain of an anthropoid ape can fail to see that
the submerged part of the insula is relatively smaller than the insula in
the brain of man, but I was certainly not prepared to find the marked
difference which is brought out by the above Table. It is in the forepart
that it chiefly fails. In the chimpanzee, the distance at which the
so-called anterior limiting sulcus is situated from the fore-end of the cerebrum
is expressed by the index 34*1, and in the orang by the index of 32\2.
In the European the corresponding index is only 26*3. Our examination
of the gyri on the surface of the anthropoid insula, as we have already
noted, afforded results which are altogether in keeping with these measurements
. At the same time it will be observed that in neither the chimpanzee
nor in the orang does the island of Eeil extend so far backwards.
The difference in this respect, however, is not great.

The size of the island of Reil, which may be regarded as the surface
expression of the magnitude of the subjacent lenticular nucleus, &c,
exercises a marked influence on the configuration of the fore-part of the
cerebral hemisphere. Indeed I believe that the difference in the dimensions
of the insula and the lenticular nucleus in man and the ape is in some