Freiburger historische Bestände - digital

106

Cunningham Memoirs.

we meet with cerebral hemispheres belonging to the same period of development
and to the same sex, which present very different degrees of complexity.
In the case of the insula the law certainly does appear to hold good.

The following is a brief account of the condition of the insula in those
foetal brains which I have specially examined with the view of determining
the development of the gyri and sulci :—

I. 5 to 5J months—6 hemispheres examined.

In three, . . Insula perfectly smooth (viz. 1 right and 2 left).

In two, . . Insula with sulcus centralis only (1 right and 1 left).

In one, . . Insula with sulcus prsecentralis and sulcus centralis (right).

II. 5J to 6 months.—10 hemispheres examined.

In two, . . Insula perfectly smooth (both left).
In four, . . Insula with sulcus centralis only (2 right and 2 left).
In four, . . Insula with sulcus centralis and sulcus prsecentralis (3 right

and 1 left).

III. 6 to Q~ months.—8 hemispheres examined.

In one, . . Insula perfectly smooth (right).

In one, . . Insula with sulcus centralis alone (left).

In three, . . Insula with sulcus centralis and sulcus prsecentralis (2 right

and 1 left).

In three, . . Insula with three sulci (2 right and 1 left).

IV. 6~ to 7 months.—3 hemispheres examined.

In each of these the insula showed all the three sulci.

In the latter weeks of intra-uterine life the development of the gyri and
sulci on the surface of the insula takes place very rapidly. Consequently,
at birth the insula presents very nearly the same convolution-pattern that
it does in later life. All the details are filled in, and, as we have noticed,
the prsecentral furrow, instead of having fallen back, as Guldberg supposed,
to form the sulcus centralis, has in reality moved very slightly forwards,
so that it does not lie so accurately in line with the corresponding furrow
on the mantle as it did on its first appearance. This is brought about by
the formation of that triangular depression which marks off the gyrus brevis
secundus from the gyrus centralis anterior (gyrus brevis tertius).