Freiburger historische Bestände - digital

266

Cunningham Memoirs.

and a union of the two is by no means uncommon (fig. 59, /. m., p. 262).
These small furrows, undoubtedly, belong to the same system as the portion
of the sulcus described by Eberstaller. They prolong it backwards, and
bring it into close association with the horizontal part of the inferior
prsecentral sulcus. They are intermediate links, as it were, and the truth
of this is to be seen in those rare cases where they are not only joined to
each other, but also to the portion of the middle frontal furrow which lies
in front of them, and to the horizontal part of the inferior prgecentral sulcus
which lies behind them. Eberstaller has therefore little reason for comparing
the small transverse sulcus, in which he says the middle frontal
furrows begins, to the prsecentral sulci in their relations to the first and
second frontal furrows. In many cases these small transverse sulci establish
a superficial connexion with the first and second frontal furrows.

Eberstaller lays considerable stress upon the depth of the sagittal stem
of the sulcus. He asserts that it has " meist eine grossere Tiefe, als irgend
eine der sagittalen Stirnf urchen, eine Tiefe, wie wir sie, abgesehen, von der
Centralspalte, am Stirnhirne nur in der Prsecentralis inferior wieder-
finden." This is not my experience. As a general rule I have found it
shallower than either the second or the first frontal furrows. In a large
proportion of cases it is interrupted by one or two deep annectant gyri.
These may appear at different places, but, as a rule, one is situated midway
between its two extremities, whilst the other is placed at its junction
with its anterior terminal cross-piece. It is not very uncommon to find one
or both of these annectant gyri on the surface, thus breaking up the furrow
into separate pieces. When this occurs the isolated portions of the sulcus
tend to assume a more or less transverse direction. Taking into consideration
, then, the two pieces of the furrow which lie in front of the horizontal
part of the inferior praecentral furrow, it is possible to imagine a hemisphere
in which the sulcus frontalis medius is represented by five completely
separate portions. I have not met with such a condition, because it would
appear that, in cases where there is a tendency for the anterior usually
continuous part of the furrow to break up, there is also a concurrent
tendency for the hinder usually separate pieces to run into each other. In
eight hemispheres, however, I have observed the sulcus in four pieces.