Freiburger historische Bestände – digital

142

Cunningham Memoirs.

region. From this period on to the end of the fifth year the fissure
and the suture rapidly approach each other. After this date the process
appears to go on more slowly, and as Symington has pointed out the
permanent condition is in all probability gained about the eighth to
the ninth year. The process, however, may be retarded or accelerated.
Symington has instanced a case of retardation ; whilst the head of the girl
of four years old, figured in Plate vi. (fig. 6), is a remarkable example of
acceleration. On the right side of this head the Sylvio-squamous index
was 2-8, and on the left side 3-8. These indices would not be considered
remarkable were they met with in the adult. Indeed in the head of the
young man aged twenty-five years, figured in Plate vn. (fig. 12), the
right Sylvio-squamous index was 4-6, and the left Sylvio-squamous index
was 3"6.

To account for the great difference which is exhibited in the cranial
relations of the Sylvian fissure at different periods of growth it has been
supposed that, in addition to the marked changes which occur in the
position of the suture, there is also a gradual depression of the Sylvian
fissure itself. Further, that the depression of the fissure is brought about
by a portion of the outer surface of the temporal lobe slipping round so as to
take up a position on the floor of the cranium. In other words, the infero-
lateral margin of the hemisphere is not fixed, but is altered so as to transfer
a portion of the external surface of the hemisphere to the inferior surface.
This highly ingenious theory was first propounded by Symington, and
when we consider the mode of growth of the infantile cranium the hypothesis
appears extremely plausible. If there is one feature more prominent
than another in the infantile cranium it is the narrowness of the floor in
comparison with the width of the vault. As the base gradually expands one
might very naturally expect a displacement of a portion of the outer surface
of the cerebrum to the under surface. At first I was inclined to accept this
theory, but as the investigation advanced, I saw that it was untenable, and
for this reason, that throughout all periods of growth the same sulci and the
same convolutions of the temporal lobe lie between the Sylvian fissure
above and the infero-lateral border of the hemisphere below. In support
of this assertion I would call attention to the series of figures which are