Freiburger historische Bestände - digital

252

Cunningham Memoirs.

The ramus horizontalis, into which the upper end of the vertical part of
the inferior praecentral furrow opens, presents a great variety of conditions
in the adult brain, and, as a consequence it has, as a rule, escaped recognition
. It is placed, in relation to the upper end of the ramus verticalis, somewhat
after the manner of the horizontal limb of the letter T or F (fig. 53, h.,
p. 248). As a rule, it is not horizontal in its direction, but is directed from
behind obliquely upwards and forwards into the posterior part of the
middle frontal convolution. This obliquity is, in a measure, due to the
backward curve of the vertical limb of the fissure, and is not so marked in
the foetal as in the adult brain (figs. 54 and 55, A., pp. 250 and 251).

Both Eberstaller and Herve" have taken notice of the ramus horizontalis
of the inferior praecentral sulcus. The former observer says: " Aus der
unteren Pracentralfurche geht haufig ausser der unteren Stirnfurche
ungefahr von derselben Stelle aus noch eine zweite Furche nach vorne ab.
Wahrend aber die untere Stirnfurche unter rechtem Winkel sie verlasst,
zieht das Furchenstiick, von dem ich jetzt reden will, schrag nach vorne
und oben in die mittlere Stirnwindung hinein."* He terms it the "ramus
anterior."

Herve^s remarks upon the horizontal portion of the inferior praecentral
sulcus are somewhat ambiguous. In page 70 of his work upon the " Convolution
of Broca," he states, that "it is not very rare" to find the " bent
branch " of this furrow; whilst in page 48, in a footnote, he mentions that
" in man it appears that the branch in question is entirely effaced, at least
in many cases."

I have very rarely seen the horizontal portion of the inferior prsecentral
furrow absent, although an increase in the degree of its obliquity frequently
gives rise to a difficulty in its recognition. As a rule, it has the appearance
of a terminal bifurcation of the upper end of the vertical portion of the
furrow, the diverging limbs of which are widely spread out from each
other. In most cases the hinder limb is the shorter of the two, and often
it lies more in a line with the vertical portion of the sulcus than the longer
more horizontally directed anterior limb. This is the condition which is

* Das Stirnhirn, p. 61. Leipzig, 1890.