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28

Cunningham Memoirs.

upper surface of which it was closely adapted. It was spread out, so as
to cross the mesial plane, and its posterior border showed an angular
deficiency which gave it a forked appearance (fig. 10 a). The under-
wall of this outgrowth or lappet was formed of an epithelial layer only.
Its precise attachment to the cerebrum could not be made out without
destroying the specimen, but it appeared to be attached by a stalk to the
under and back part of the cerebrum. The posterior part of the temporo-
sphenoidal lobe, which was completely separated from the remainder of
the cerebrum by a deep temporary fissure, overlapped this stalk, and hid
its connexions.

It is difficult to imagine what the further history of such an embryo
would have been had it survived. The deformity cannot be very rare, as
Richter has figured a specimen which shows a very similar condition

(fig. 11 a).

V. Relation of the Appearance and Obliteration of the Transitory
Fissures to the Growth of the Cerebral Hemispheres and the Mapping-
out of an Occipital Lobe.—The transitory infoldings of the early hemisphere
wall play an important part in the general growth of the cerebrum
and in the appearance of an occipital lobe. When we read the accounts
which are given of the formation of the occipital lobe, an impression is
conveyed to the mind that this part of the cerebrum is a local outgrowth
or bud which grows backward from the hinder and upper part of the
hemisphere about the beginning of the fourth month ; in other words, that
it is a secondary formation.

Such is the view which is advanced by Schwalbe; and he may be
regarded as giving expression to the opinion which is held by many
anatomists on this question. He says:—" We have to separate on
developmental grounds the annular lobes (ringformigen Lappen) from the
occipital lobes, which have a secondary origin, and which are onty present,
characteristically developed, in Man and the Apes."*

Reichertf considers that the occipital lobe must be regarded upon an

* Lehrbuch der Neurologie. Erlangen, 1881, p. 534.

+ Der Ban des menschlichen Gehirns. Leipzig, 1861, p. 80.