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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 15

of the fissures will vary with the degree and kind of restraint which is
applied.

Primitive Cuneate Subdivisions of the Medial Hemisphere Wall.—By the
presence of the stellate fissures, when they are developed in a marked
form, the medial surface of the hemisphere outside the fissura arcuata
is subdivided into a number of wedge-shaped or cuneate portions. That
portion which intervenes between the two long fissures, which we have
mentioned as being always present on the occipital part of the hemisphere,
is retained as the cuneus of the adult brain. The other portions in front
of this region, and also those below it, again run into each other when their
bounding fissures are obliterated, and they then form the smooth tracts out
of which the gryus fornicatus, calloso-marginal convolution, prsecuneus,
and the convolutions on the under surface of the occipital and temporal
lobes are ultimately formed. The primitive fissures which bound the
cuneus are the precursors of the calcarine and parieto-occipital fissures.

Obliteration of the Transitory Fissures.—To study in all its details the
manner in which the transitory fissures disappear and vanish from the
mesial face of the hemisphere, so as not to leave a single trace of their
former existence either on the inside or the outside of the cerebral wall,
would require a very large number of specimens, and these very varied
as to their term of development, because it is clear that the process differs
considerably in different cases. Still in the material at my disposal a
number of interesting points can be determined, and the general details
can be ascertained. As the wall of the cerebral vesicle thickens, and the
hemisphere elongates, one or more of the stellate fissures become detached
from the fissura arcuta. They then appear as short isolated fissures
(PL i., fig. 12 ; PI. in., figs. 3, 4, 5, and 6). These continue to decrease
in length until they appear as little more than mere points or shallow
dimples, corresponding with which small rounded elevations on the inner
aspect of the wall of the ventricular cavity are seen. Finally these disappear
also, and both surfaces of the wall become smooth and even. In
fig. 18, PI. i. (e. <?.), the rounded intra-ventricular elevation corresponding
to a reduced and rapidly vanishing transitory fissure, the remains of
an inward fold, is seen on each side. It is true that this is the internal