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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 211

This arrangement of the different parts of the intraparietal sulcus was,
therefore, present in 6*3 per cent, of the adult Irish hemispheres examined.
In the full-time and eighth-month foetus the percentage is greater, which
would seem to show that in certain cases the union of the different elements
of the sulcus is delayed until after birth. It is interesting to note the high
percentage for the negro brain. This indicates a foetal condition; but seeing
that it also bespeaks a greater number of superficial bridging gyri on the
surface of the parietal lobe we cannot say that it is a degradation. Indeed,
had it been present in the European brain probably the opposite conclusion
would have been drawn.

Fig. 39.—Posterior part of the left hemisphere of a young man twenty-five years old. The
four factors of the intraparietal sulcus are all separate and distinct.

Senior?,* who has also studied the disposition of the different parts of
the sulcus in the adult, has found this arrangement rather more frequently
in the Russian brain than I have observed it in the Irish brain.

Variety II.—Ramus horizontalis confluent with the sulcus postcentrals
inferior ; sulcus postcentral superior separate (fig. 40).—This is the condition
of the intraparietal sulcus, which was originally described by Sir William
Turner ; and in the last edition of Quain's Anatomy it is given as the
normal arrangement. The development of the fissure and the condition in

* Individualniye tipy mozgovykh izvilin u tcheloveka —(Individual types of the convolutions
of the brain in man). Moscovr, 1877, p. 34.

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