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CHAPTER I.

THE COMPLETE FISSURES OF THE HUMAN CEREBRUM.

PAGE

I. General Statement, .... 1
II. The Choroid and Arcuate Fissures, . 2

III. Transitory Fissures, .... 7

IV. The Persistence op the Transitory

Fissures under certain conditions, . 20
V. Relation of the Transitory Fissures to
the Growth of the Cerebral Hemispheres
and the Mapping-out of an

Occipital Lobe,.....26

VI. Parieto-occipital and Calcarine Fissures
in the Adult, . . . .32

PAGE

VII. Parieto-occipital and Calcarine Fissures
in the Ape, . . . .40

VIII. Development of the Parieto-occipital

and Calcarine Fissures, . . .44
IX. Topography of the Parieto-occipital

Fissure, ...... 53

X. External Perpendicular and External

Calcarine Fissures, . . . .65

XI. The Collateral Fissure, . . .70
XII. Summary,......72

I. General Statement.—The complete fissures of the cerebral mantle
(the " Totalfalten " of His) appear at an early period in the development
of the hemispheres. They are distinguished by the fact that they are the
result of a series of deep infoldings of the thin cerebral wall. On the
surface of the fore-brain they present a sharply-cut linear appearance.
The walls of the different folds are, as a rule, closely applied to each
other; and they constitute shelf-like projections into the cavity of the
primitive lateral ventricle.

The study of these infoldings is a matter of extreme difficulty, because
by far the greater number of them have only a temporary existence. As
cerebral growth advances they are obliterated, and the hemisphere surface
again becomes smooth. Several, however, occupy positions which later on
are occupied by permanent furrows. It is not surprising, then, that very
different opinions should be expressed regarding the fate of these primitive
infoldings which present this relation to the permanent furrows. More
especially do we find the calcarine and parieto-occipital fissures the subject
of contending views.

ROYAL IRISH ACADEMY.-CUNNINGHAM MEMOIRS, NO. YII. [l]