Freiburger historische Bestände - digital

128

Cunningham Memoirs.

naturally arises: Is this difference in the size of the two insulse not the
cause of the difference in the length of the two posterior horizontal limbs
of the Sylvian fissures ? My own belief is that it is not, because, as we
shall see later on, a similar difference in the size of the insula in the two
sexes is not followed by a corresponding difference in the length of the
fissure in the male and female ; and, further, the fissure in the ape is relatively
much longer than in man, and yet the insula is shorter. The cause
is to be looked for in the condition of the transverse temporal convolutions
of Heschl, and also of the arching convolutions which connect the supra-
marginal and angular gyri with the upper two convolution-tiers of the
temporal lobe. We shall require to return to this question when we have
fully studied all the facts in connexion with the varying length of the
fissure.

But the Table which I have given of the length-indices of the Sylvian
fissure show that the posterior horizontal ramus does not possess the same
relative length at all periods of growth. In the full-time foetus, and in the
immature foetus of from seven and a-half to eight and a-half months the
fissure is relatively longer than in the adult. In the intermediate stages it
would appear to be relatively shorter.

As we have mentioned, Eberstaller also maintains that the fissure of
Sylvius is on an average longer in the female than in the male. " Die
Differenz, 2*5 mm.," he remarks, " ist an sich nicht grossund wiircle kaum
beachtenswerth sein, gewanne sie an Bedeutung nicht durch die bekannte
Thatsache, dass das Weiberhirn als Clanzes genommen kleiner ist, als das
Mannerhirn, daher viel eher das Gregentheil zu erwarten war."

The results which I have obtained from measurements of the Sylvian
fissure do not give support to this statement by Eberstaller. In fact what
difference there is I have found in favour of the male. Taking the lateral
length of the hemisphere as 100, 31 male hemispheres yielded an average
length-index of the Sylvian fissure of 26-8; whilst 22 female hemispheres
gave an index of 25. It must be noted, however, that although Eberstaller
only gives the average absolute length of the fissure in the two sexes, he
measured a much larger number of hemispheres, viz. 81 female and 272
male. The question certainly requires further investigation, and it should