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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 195

it lias become broken up into three more or less distinct parts, whilst a new
factor has been superadded. The term " intraparietal," therefore, as
applied to the human brain, includes not one sulcus but a system of sulci.
Of the different factors which go to form the intraparietal sulcus in man,
we recognize : 1, a vertical part which separates the supramarginal convolution
from the ascending parietal convolution, and stands parallel to the
lower portion of the fissure of Rolando ; 2, a horizontal portion which
stretches backwards in a more or less horizontal direction between the
superior and inferior parietal lobules ; and 3, a continuation of this into
the occipital region which bounds externally the first annectant gyrus.
The fourth element which has been superadded, and which has not resulted
from the disruption of the originally single sulcus, consists of a short
vertical limb which intervenes between the superior parietal lobule and the
upper part of the ascending parietal convolution.

The description which was given by Sir William Turner of the intraparietal
sulcus in the human brain has been in all its essential features
adopted by the anatomists of this country. The three disrupted parts of
the originally single fissure are represented as being in the adult, superficially
at least, continuous, whilst the fourth superadded element is represented
as remaining separate. Leaving out of count for the present the
relations which the intraparietal sulcus establishes in the occipital lobe,
the description is all that could be desired from a morphological point of
view. The triple constitution of the parietal part of the sulcus is clearly
indicated, whilst occipital connexions are hinted at which are of the highest
interest and importance. It fails, however, in so far that the arrangement
of the three parietal limbs which is detailed is not the usual one. There
are several varieties of the intraparietal sulcus. The one which is referred
to in the above description only occurs in 19 T per cent, of adult cerebral
hemispheres. All the different varieties of the sulcus can be explained and
understood by a reference to its mode of appearance in the foetal brain and
to its condition in the brain of the apes.

For convenience in description it is necessary that we should apply
special terms to the different factors which go to form the intraparietal
system of sulci. The two vertical limbs which together bound posterioriv

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