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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 7

frontal lobe. In all cases the shallow furrow lies at some little distance
above the level of the corpus callosum. In illustration of this, figs. 15 and 16,
PI. i.j and figs. 3, 4, 5 and 6, in PL in., may be examined. In fig. 16,
PI. i., and in fig. 6 in PI. in., the commencing true callosal fissure may be
noted at a lower level than the arcuate fissure. In all the figures the
anterior deep part of the fissure still persists as a very distinct and deep
fold. In the course of time it also disappears.

The calcarine and parieto-occipital fissures would naturally fall to be
considered at this stage, but their origin is so closely connected with the
appearance of the transitory fissures, that it is more convenient to defer
their examination until the latter have been dealt with.

III. The Transitory Fissures.—{Vorubergehenden Einnen, of Schwalbe ;
Temporaren Furchen, of Ecker and His; Verganglichen Furchen, of Mihalkovics).
These are a series of fissures which appear at an early period upon the
cerebral wall in consequence of deep infoldings of its thin wall. They
are further distinguished by their transitory character. After existing for
a period of two months or more on the mesial wall, and for about two-thirds
of that time on the outer wall, they are finally completely obliterated, and
the hemisphere surface becomes smooth. When we come to study the
influences at work which lead to their production, we shall see that they
constitute a most interesting and suggestive chapter in the developmental
history of the brain.

It is to J. F. Meckel that the credit is due of having, in the first instance,
recognised these transitory infoldings. In 1815 he published a Paper in
which he remarks:—"Although I find the brain in the six to the seven
weeks' embryo completely smooth, the very thin walls of the lateral
ventricles appear to shape themselves into extremely numerous and deep
convolutions and furrows from the eighth to the ninth week." He asserts
that the fissures are due to deep infoldings of the hemisphere wall, and is
at considerable pains to prove that the condition is not produced by the
shrinkage brought about by the hardening reagent. He therefore holds
that the convolutions are not accidental, but are " primitive formations and
are essentially a part of the development of the brain." His account of