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346

Cunningham Memoirs.

chief fissure sub-dividing it is only brought towards completion by the
present work of Professor Cunningham. Under these circumstances no
indices of real value being forthcoming, only the following generalizations
are possible.

The boundary fissures—i.e. Rolando, parieto-occipital, and Sylvius—
having been determined and plotted out on the surface by the methods
already described, the further sub-division may be proceeded with.

Sulcus Postcentralis Superior.—This sulcus, which may properly
(Cunningham) be looked upon as a separate item from the rest of the intra-
parietal furrow, is relatively easy to fix topographically, since it runs
remarkably parallel with the upper half of the fissure of Rolando. The
chief point, therefore, to be determined is its upper extremity. This is to be
localized by its distance from the bregmatic point in the coronal suture.
The upper end of the fissure of Rolando, having been determined beforehand
, and the mesial plane position of the superior prsecentral sulcus, the
distance between these is on the average almost equal (rather greater)
to the distance between the Rolandic fissure and the superior postcentral
sulcus. As the postcentral sulcus is certainly a posterior limit of representation
in the Macacque, and apparently so also in the anthropoid (Beevor and
myself), the fixation of the above point is of value.

From its upper end the direction of the sulcus will be accurately marked
by drawing a line parallel to the fissure of Rolando for the upper half of
the latter furrow.

Sulcus Intraparietalis—(a) Ramus Postcentralis Inferior.—As a matter of
accuracy the lower and anterior part of the intraparietal sulcus, constituted
as it is usually understood to be, is better spoken of as the ramus postcentralis
inferior. Under these circumstances it becomes essential for topography
to determine what part corresponds to the ends of the intraparietal sulcus in
the lower apes, as that has been shown (Ferrier, Schafer and myself, Beevor
and myself) to be a very definite limit of representation. For information
on this point we must naturally depend upon Professor Cunningham's
observations in Chapter IV. Taking the lower end first, consideration of
the facts shows that the inferior postcentral sulcus, as such, does not
exist in the Macacque monkey, unless the view of some anatomists is