Freiburger historische Bestände - digital

90

Cunningham Memoirs.

Zuckerkandl, therefore, concludes that the anterior horizontal limb is
more inconstant than the ascending limb. In this respect his views are in
accordance with those of Giacomini.* For my own part the only inference
which I can draw from these figures of Zuckerkandl is that the combination
of the two limbs appears to be a more common condition than the
presence of a single limb.

Eberstallerf entertains a very just conception of the relationships which
exist between the anterior limbs of the Sylvian fissure. He points out that
we may find all possible gradations between the single anterior limb, which
he indicates by the letter I ; to the Y, to the V, and to the U conditions.
Under such circumstances he very properly considers it superfluous to
argue which is the more constant of the two limbs. The two branches are
merely the product of the differentiation of the single branch, and are
brought into existence by the growing downwards, into the single limb, of
the pars triangularis—a part of the strongly-developed inferior frontal
convolution. He further states that in 45 per cent, of the hemispheres
he examined he found the two anterior limbs completely separated from
each other; whilst in 24 per cent, he found the single anterior limb alone
present.

Three different conditions, then, of the anterior limbs of the Sylvian
fissure may be recognized:—

1. A single anterior limb.

2. Two entirely separate limbs, viz. an ascending and a horizontal.

3. Two limbs (ascending and horizontal) opening into the Sylvian

fissure by a common stem. This may be distinguished as the
Y-shaped condition.

observed in the brain of the eighth-month foetus, in cases where the true ascending limb was
absent, a superficial furrow developing in its place. The same sulcus can frequently be seen in
the adult brain ; but in so far as it does not represent a primitive deficiency in the operculum it
cannot be considered as a true ascending limb. It is the sulcus diagonals of Eberstaller.

* Varieta della circonvoluzioni cerebrali dell' uomo. Torino, 1882.

f Das Stirnhirn. Wieu und Leipzig, 1890, p. 19.