Freiburger historische Bestände - digital

256

Cunningham Memoirs.

(c) Complete union to anterior branch of the ramus horizontalis of the
inferior prsecentral sulcus. This connexion usually takes place near the
base of the anterior branch of the ramus horizontalis.

Adults, . . . . . . . 6-5 per cent.

Pull-time foetuses, . . . . . 8-3 ,,

Eighth-month foetuses, . . . . . 0-0 ,,

(d) Incomplete union to the anterior branch of the ramus horizontalis
—a deep annectant gyrus intervening between the two.

Adults, ....... 10-9 per cent

Eull-time foetuses, . . . . . 8-3 ,,

Eighth-month foetuses, ..... 16-6

I may further mention, that in six negro hemispheres which were
examined, the union between these two furrows was only observed in two.

In some cases a connexion is also established between the ramus horizontalis
of the inferior prsecentral furrow and the sulcus frontalis medius
of Eberstaller. This arrangement we shall discuss when we come to study
the latter sulcus.

III. Sulcus Preecentralis Superior.—In its simplest form this sulcus
is present in the shape of a continuous vertical furrow which lies in front
of the anterior central convolution in its upper half. Its upper end falls
short of the mesial border of the hemisphere, whilst its lower end may be
placed above and between the two branches of the ramus horizontalis of the
sulcus prsecentralis inferior (fig. 53, p. c. s., p. 248), or it may reach a lower
level and lie behind both (fig. 57, p. c. s., p. 259). The sulcus frontalis
primus joins it about its middle, and usually passes uninterruptedly into it.

But whilst this may be considered the typical condition of the sulcus
prsecentralis superior the arrangement is subject to much modification.
Three principal varieties may be recognized.

1. In the first variety the furrow is broken up into two pieces—a
superior and an inferior—by the presence of a deep annectant gyrus.
This interruption takes place immediately above the junction of the sulcus
frontalis primus, which passes continuously into the inferior portion of the