Freiburger historische Bestände - digital

32

Cunningham Memoirs.

expand in size, may have some influence in bringing" about the unfolding
of the temporary fissures, and in smoothing out the surface of the cerebral
hemisphere.

VI.—Parieto-occipital and Calcarine Fissures in the Adult.—

The parieto-occipital and calcarine fissures form upon the mesial aspect
of the posterior part of the adult cerebral hemisphere a -shaped
figure. In this we recognise a "stem" with two diverging branches. The
"stem" is prolonged obliquely downward and forward, and cuts into the
gyrus fornicatus. In its lower half it is placed on the tentorial surface of
the human cerebrum, while its upper half occupies the mesial surface. Of
the two diverging branches the parieto-occipital, on superficial inspection,
appears to run more in a direct line with the " stem" than the calcarine
branch. It ascends to the upper border of the hemisphere, which it incises
deeply, forming on the cranial aspect of the cerebrum the external parietooccipital
fissure. The length of this external fissure corresponds with the
depth of the internal fissure. Frequently the upper extremity of the
parieto-occipital fissure divides, in which case two branches cut the upper
border of the hemisphere. Of these the anterior is usually a shallow
offset.

The calcarine branch proceeds backward in a horizontal direction
toward the occipital pole. On this it ends by dividing into an ascending
and descending branch. These are usually placed at right angles to the
parent trunk. This terminal part of the calcarine fissure lies at the bottom
of the groove, which on the right cerebrum marks the continuation of the
longitudinal sinus into the lateral sinus.

Both the calcarine and parieto-occipital branches of this fissural system
lie in the human brain entirely on the mesial surface of the cerebrum,
altogether above the low-lying border which intervenes between this
surface and the tentorial surface.

The study of the parieto-occipital and calcarine fissures is surrounded
with many difficulties, and it is necessary to enforce, at the very outset,
the distinction which I have drawn between the "stem" and the two
branches. It is one of deep morphological importance, as we shall see