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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 257

sulcus. In certain cases the upper portion of the superior prsecentral sulcus
is completely cut off from the lower piece by the presence of this annectant
gyrus on the surface.

2. In the second variety the deep annectant gyrus is placed below the
junction of the first frontal sulcus, which is therefore brought into direct
and uninterrupted continuity with the upper part of the superior prsecentral
sulcus, whilst the lower portion is partially separated from both (fig. 55,
p. 251, p. c. s.). This variety is not so common as the first.

3. In the third variety we have the cruciform arrangement mentioned by
Eberstaller. The sulcus frontalis primus is carried backwards beyond the
line of the superior prsecentral furrow. In this case the upper and lower
portions of the upper prsecentral sulcus are separated from the frontal
furrow by deep annectant gyri. In this variety one or both of these
bridging gyri may reach the surface, and produce a complete separation
of the fissural system into two or three parts (fig. 59, p. 262).

The close association of the first frontal sulcus with the superior
prsecentral furrow is one of the most constant features of this fissural
system; and this is still further emphasized when we study the development
of the two furrows, and note their rudimentary condition in the
lower members of the primate group. Eberstaller considers the connexion
to be an absolutely constant one. Speaking of the sulcus frontalis primus
he remarks: "Ihr hinteres Ende geht fast immer Beziehungen zur oberen
Pracentralfurche ein und selbst, wenn aus der Wurzel der mittleren Stirn-
windung ein Zuzug zur oberen Stirnwindung erfolgt, welcher Zuzug sich
dann als ' laterale Wurzel' der letzeren prasentirt, bleibt noch immer ein
hinteres Sttick unserer Furche mit der Prsecentralis superior inVerbindung."*
That this is true in the vast majority of cases there cannot be the least
doubt, but it is right to mention that, in rare instances, I have seen the
posterior end of the sulcus frontalis primus cut off from the sulcus prsecentralis
superior by a deep, or even by a superficial annectant gyrus.

In addition to the main portions of the prsecentral furrow (viz. the
sulcus prsecentralis inferior and the sulcus prsecentralis superior), two other

* Das Stimlrirn, p. 69. Leipzig, 1890.

ROTAL IEISH ACADEMY.-CUNNINGHAM. MEMOIRS, NO. 711.

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