Freiburger historische Bestände - digital

94

Cunningham Memoirs.

scheint aber folgendes Verhaltniss zu bestehen. Unter dem untersten Rande
des M der Stirnwindung besteht eine kurze (dritte) Incision der sylvischen
Spalte als hinterstes Stuck der ausseren Orbitfurche. Dieses Stiick fehlt
oft ganz, oder ist nur durch einen leichten Eindruck angedeutet." He
further states that this fissure may communicate with the external orbital
furrow.

Zuckerkandl* has also noticed these two orbital limbs, and has very
truly observed how easy it would be to mistake the external one for the
true anterior horizontal limb in cases where the latter is weakly developed,
or entirely absent.

But Eberstaller has given the fullest and the best account of these
orbital limbs. He terms them the " third and the fourth anterior limbs of
the Sylvian fissure," and he has found the former (7. e. the external) present in
22 per cent, of the hemispheres he has examined, whilst the internal was only
found in 13 per cent. Further, he has shown that the external orbital limb
is much, more frequently present on the right side (viz. in the proportion
of 15 to 7). The results which I have obtained coincide very closely with
those given by Eberstaller. Thus I found that the external orbital limb
occurs very nearly with equal frequency in the two sexes, although it
shows a slight preference for the male. It was found, however, in 11 per
cent, on the right side, and in only 6 per cent, on the left. It is further
very evident that the development of the external orbital limb is in a
measure correlated with that of the true anterior limbs. Thus, it is found
more commonly in those hemispheres in which the latter are deficient. In
cases where there is only a single anterior limb, it occurs most frequently;
and it is observed oftener in connexion with the Y condition of the anterior
limbs than in cases where the two anterior limbs are completely separate.

I have applied the term " orbital" to these limbs, and have not adopted
the terminology of Eberstaller, because these short fissures when they exist
have no claim to be placed in the same category with the true anterior
limbs of the Sylvian fissure. It is true that they generally cut through the
entire thickness of the orbital operculum, but they fail to come up to our

* "Ueber den Einnuss des ISTahtwachsthunies und der Schadelform auf die Richtung der
Grelrirnwindungen,'' Medizinische Jahrtmcher, 1883, m. und iv. Heft, p. 449.