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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 271

figure 3, PI. iv.), although he gives it no name. Thus, he says:
'' A more feeble furrow divides the middle frontal convolution into two
branches, of which one is united to the first, and the other to the third
frontal convolution."

In my study of the developing sulci on the outer surface of the frontal
lobe, I have been greatly puzzled to account for the presence of a long
deep furrow which is occasionally observed in the fifth-month cerebrum
immediately in front of, and parallel to, the coronal sutural line. Its extremities
are placed at an equal distance from the mesial border of the hemisphere
above, and the open insula below, and, with the exception of the
external perpendicular fissure, it is the only sulcus on the outer surface of
the hemisphere at this period (PL i., fig. 14, also PI. n., figs. 8 and 9, p. c).
In certain cases its hinder lip is raised above the level of the anterior lip—a
character which renders it still more conspicuous (PI. n., fig. 9). At first sight
it is apt to be mistaken for the fissure of Polando, but its position and direction
are sufficient to show that it cannot be regarded as an early condition
of that furrow. It is not so oblique, and, as we have noted, it lies in front
of the coronal line. Further, by measurement we can ascertain that its
upper end is placed very much further forward on the cerebral surface.
Taking the mesial length of the hemisphere as equal to one hundred, the
distance of the upper end of this furrow from the frontal point is 39-7,
whereas the relative distance of the upper end of the early fissure of
Rolando from the frontal point is 52"7 (vide p. 176). It holds a position,
therefore, and presents a direction which brings it more into association
with the inferior prsecentral sulcus. At the same time I am not prepared
to insist strenuously that it is an early condition of this furrow, because
there are many points in connexion with its further history which render
it very difficult to come to a decided conclusion on the question.

If the furrow under consideration really is the sulcus praecentralis
inferior, it undergoes a retrograde development in the further stages of
the growth of the cerebrum. As exhibited in the fifth-month hemispheres
alluded to the furrow presents a relative length very much greater than
the vertical stem of the inferior prsecentral sulcus at any subsequent
period in the development of the brain. Such being the case, we must