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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 235

course of the postcentral sulcus three deep gyri may be present. The
highest of these marks the point of junction between the sulcus postcentrals
superior and the sulcus postcentralis inferior. In many cases the union
between these two elements of the fissure is so complete that not a trace
of this deep annectant gyrus can be detected. The second deep gyrus
within the postcentral sulcus marks the point of union between the inferior
transverse sulcus of Eberstaller and the main stem in those cases in which
these are found confluent. The third deep annectant gyrus is only present
in very exceptional cases. It intercepts the continuity of the sulcus postcentralis
inferior, and shows, even in the adult brain, that this portion of
the fissure may be developed out of two pieces [vide fig. 51, p. 232). As we
have seen, in our study of the adult condition of this fissure, the superior
annectant gyrus remains on the surface in about every fourth hemisphere
(25'4c per cent.). The inferior annectant gyrus is in the great majority of
cases on the surface. The presence of the middle annectant as a superficial
gyrus is an exceedingly rare occurrence.

In those instances in which the ramus horizontalis is confluent with the
postcentral sulcus, the presence of a deep gyrus, partially interrupting the
union, is a very common occurrence. It is termed, by Eberstaller, "the
anterior deep annectant gyrus "; further, when the ramus occipitalis runs
into the ramus horizontalis, the point of union is almost invariably indicated
by a deep gyrus, viz. the "posterior deep annectant gyrus" of
Eberstaller. These are the deep gyri which are present in the sagittal
part of the furrow in t}^pical cases, but additional deep bridging convolutions
are occasionally met with: viz. (1) in the course of the ramus horizontalis
; (2) in the course of the ramus occipitalis; (3) at the junction of
the ramus occipitalis and the sulcus transversus occipitalis of Ecker; and
(4) at the point where the superior limb of the sulcus transversus of Ecker
joins the inferior limb. Of these occasional deep annectant gyri, the two
latter have already been referred to, and their presence explained (pp. 230
and 232). The deep interrupting gyri in the course of the ramus horizontalis
and ramus occipitalis simply indicate that these segments of the sulcus may
each be developed out of two pieces which, in the course of time, run into
each other.

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