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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 255

examined fifty adult hemispheres, twelve full-time foetal hemispheres, and
eighteen eighth-month foetal hemispheres, with the following results —

1. The sulcus frontalis secundus stood completely apart from the inferior
prsecentral sulcus, and was separated from it by a superficial gyrus in—

32-6 per cent, of the adult hemispheres,

41*7 ,, of the full-time foetal hemispheres,

50-2 ,, of the eighth-month foetal hemispheres.

From this we may infer that the union is frequently deferred until after
birth. Eberstaller states that this condition is only present in 24 per cent.,
or in about one-fourth of the cases examined. The percentage which I
have obtained is considerably higher. A good example of the complete
separation of the two sulci is seen in figure 53, f2, p. 248.

2. The sulcus frontalis secundus may either be joined to the vertical
stem, or to the anterior branch of the ramus horizontalis of the sulcus
prsecentralis inferior. The former arrangement is seen in Plate IV.,
figure 1, the latter in Plate i., figure 33. The following are the conditions
under which the union may take place:—

(a) Complete union to the vertical stem of the sulcus prsecentralis
inferior.

Adults,........ 28-3 per cent.

Full-time foetuses, . . . . . . 41-7,,

Eighth-month foetuses, . . . . . 16-6 ,,

(b) Incomplete union to the vertical stem of the sulcus prsecentralis
inferior.

Adults,.......21-7 per cent.

Full-time foetuses, ..... 0-0 ,,

Eighth-month foetuses, ..... 16-6 ,,

In these a deep annectant gyrus intervened between the two sulci under
consideration.