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Mr. Victor Horsley— Cranio- Cerebral Topography:

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acceded to, viz. that the subordinate sulcus which divides the foot of the
ascending parietal gyrus is the precursor of the sulcus postcentralis inferior
in man.

The Sulcus retrocentralis transversus of the Macacque is, I believe, the
human sulcus retrocentralis transversus of Eberstaller. It is present in
the anthropoids ; and when in man the inferior postcentral sulcus terminates
in the fissure of Sylvius, it is, as Professor Cunningham points out,
by fusion with the post- (or retro-) central sulcus.

The transverse retrocentral sulcus lies in advance of the line of the
inferior postcentral sulcus, and practically bisects the lower end of the
ascending parietal gyrus. In the Macacque it never cuts the margin
of the Sylvian fissure, but in man it does so in the very large majority
of cases. The topographical position of this sulcus is intermediate between
the line of the postcentral sulci and the fissure of Rolando, the fissure of
Sylvius having been previously determined.

To return to the inferior postcentral sulcus, it follows from what has
been said that the lower end of this furrow in man is not determinable with
certainty. The upper end, which coincides with the anterior extremity
of the sagittal portion is, however, the more important, and its topography
may now be considered. The reasons of its influence (from the functional
point of view) is that in the Macacque monkey and in the orang this point
lies behind and below the inferior genu of the fissure of Rolando, and
divides (in the ascending parietal gyrus) the representation of the upper
limb from that of the face.

If in man the inferior postcentral sulcus is a separated element, it will
then be found that the sagittal intraparietal sulcus terminates as in the apes,
and consequently its topographical position coincides (posteriorly to the
breadth of the ascending parietal gyrus) almost with the level of the genu
in question. As a matter of fact, it will be below (as well as behind) the
genu, in proportion as the latter is well marked, i.e. approaches a right
angle. Allowance must therefore be made for this.

(b) Ramus Sagittalis.—The localization of this, the main part of the intraparietal
sulcus, depends on the proportionate development of the superior
and inferior parietal lobules. Unfortunately a decision on this subject is

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