Freiburger historische Bestände - digital

86

Cunningham Memoirs.

pars triangularis, but also of two anterior limbs of the Sylvian fissure. As
we have seen, however, in those cases where the primitive anterior angle of
the fossa is retained and becomes acute, there is no pars triangularis formed,
and only one anterior limb of the fissure is developed. This limb is distinct
from both the anterior ascending and the anterior horizontal limbs. It is
homologous with neither, but in its lower part corresponds with the stem
of the Y when the parieto-frontal and the orbital opercula meet below the
pars triangularis. Every gradation is met with between this Y condition

o., . . . frontoparietal operculum.
m., . . . frontal operculum.
i., . . . temporal operculum.
e., . . . orbital operculum.
b., . . . posterior horizontal limb of Sylvian
fissure.

e., . . . anterior ascending limb.
Fig. 26.—Broca's diagram of the development of the Sylvian opercula.

of the anterior limbs of the Sylvian fissure and the single anterior limb.
The latter may be considered to represent a fusion of the two others; but
as we have said, it is not strictly homologous with either, although,
according to the inclination which it assumes, it is frequently, and in the
most arbitrary manner designated, " ascending," or " horizontal," as the
case may be. The inclination of the single anterior limb, as well as of the
two anterior limbs, when they are present, is determined by the relative
development of the opercula between which they intervene.

II. Anterior Limbs of the Sylvian Fissure in the Adult Brain.—It

is very necessary that we should establish clearly the conditions by which
we can recognize " an anterior limb " of the Sylvian fissure. Some confusion
has arisen from the fact that different authors have had different
ideas as to the characters by which an " anterior limb" should be judged.
Very few have condescended to give a sufficiently precise definition.