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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 273

20, p. c.&.), is very instructive. Either the horizontal or the vertical portion
may appear first. In figure 17 a deep pit marks the spot where the two
parts of the fissure would ultimately unite, and from this three exceedingly
shallow depressions radiate. In figure 16 the posterior part of the horizontal
ramus is alone evident, whilst in figures 19 and 20 the vertical
stem is the only part which can be detected. Figure 18 presents an
interesting condition of the early inferior prsecentral sulcus. There is a
tolerably distinct vertical stem, and immediately above this there may be
detected a very slight depression which represents the fore-part of the
horizontal limb.

Fig. 61.—Lateral vie-w of the left cerebral hemisphere of a female fcetus in the early part of the eighth

r.

c. i.
p. c. s.
s.
c.

month of development,
projections of the skull,
gyri-

Fissure of Rolando.
Sulcus prsecentralis inferior.
Sulcus prsecentralis superior.
Single anterior limb of Sylvius.
Sulcus prsecentralis medialis.

Drawn by the American apparatus for tracing orthogonal
The dotted lines indicate the position of the deep annectant

/-1 . . Sulcus frontalis primus.
/. m. . Sulcus frontalis medius.
/.2 . . Sulcus frontalis secundus.
h. . . Horizontal limb of the inferior prascentral
sulcus.

It is apparent, therefore, that although in certain cases the sulcus
prsecentralis inferior may be developed continuously by three furrows
radiating in a downward, backward, and forward direction from a central
point which corresponds in the adult to the place of union between its
vertical and horizontal limbs (PL n., fig. 17), it may also be formed by the
fusion of separate pieces which have an independent origin. The vertical

ROYAL IRISH ACADEMY.-CtTXNINGHAU MEMOIRS, NO. VII.

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