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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 201

" peripherischen Primarfurchen." It may remain distinct and separate,
but more frequently it extends downwards, and joins the sulcus postcentralis
inferior.

There are many variations to be noted in the mode in which the intra-
parietal sulcus developes. For example, there appears to be a tendency
towards the still further break-up of its several elements. Thus, the sulcus
postcentralis inferior, the ramus horizontalis, or the ramus occipitalis, may
each appear in the first instance in the form of two depressions which
ultimately run into each other. The bifurcation of the upper end of the
parieto-occipital fissure, and the appearance of the two resulting branches
on the mesial border of the hemisphere seems to be usually, or at least very
frequently, associated with a duplication of the developing ramus occipitalis.

From what has been said, it will be seen that Eberstaller,* in his
admirable account of the intraparietal sulcus, is justified in applying to it
the term, " Furchenconglomerat." Further, this author has rightly called
attention to the fact that a third element may be added to the postcentral
part of the fissure. This he terms the sulcus retrocentralis transversus. It
is a small furrow which cuts the margin of the fronto-parietal operculum, and
stands in the same relation to the postcentral sulcus as the sulcus centralis
transversus to the fissure of Rolando (p. 164). To quote his own words :
" Dieser Sulcus retrocentralis transversus bedingt durch seine Richtung die
dreieckige Verbreiterung des unteren Endes der hinteren Centralwindung,
bricht aber in seltenen Fallen mit seinem oberen Ende sogar in die
Rolands-spalte durch und iiberschreitet mit seinem unteren Ende haufig
die Opercularkante, so dass der Ursprung des Gyrus supramarginalis aus
der hinteren Centralwindung mehr weniger tief eingedriickt wird . . .
Fliessen alle drei beschriebenen Einzelbestandtheile der Retrocentral-
furche zusammen, so gibt das eine der Centralspalte parallele, von der
Mantelkante bis zur Sylvischen Spalte schrag nach unten und vorne
ziehende Furche."

This lower piece of the postcentral sulcus, the sulcus postcentralis transversus
of Eberstaller, does not appear until the middle of the eighth month

* Zur Oberflachen-Anatoniie der Grosshirn-Henrispharen. Wiener Mediziiiisclie Blatter,
No. 20, 1884, p. 612.

KOYAL IRISH ACADEMY.-CUNNINGHAM MKMOIES. NO. VII. [2Q~]