hemispheres of the cerebrum. A smaller sickle-shaped
vertical mesial band, the _falx cerebelli_, attached to the internal
occipital crest, passes between the two hemispheres of the cerebellum.
A large band arches forward in the horizontal plane of the cavity,
from the transverse groove in the occipital bone to the clinoid
processes of the sphenoid, and is attached laterally to the upper
border of the petrous part of each temporal bone. It separates the
cerebrum from the cerebellum, and, as it forms a tent-like covering
for the latter, is named _tentorium cerebelli_. Along certain lines
the cranial dura mater splits into two layers to form tubular passages
for the transmission of venous blood. These passages are named the
_venous blood sinuses_ of the dura mater, and they are lodged in the
grooves on the inner surface of the skull referred to in the
description of the cranial bones. Opening into these sinuses are
numerous veins which convey from the brain the blood that has been
circulating through it; and two of these sinuses, called _cavernous_,
which lie at the sides of the body of the sphenoid bone, receive the
ophthalmic veins from the eyeballs situated in the orbital cavities.
These blood sinuses pass usually from before backwards: a _superior
longitudinal_ along the upper border of the falx cerebri as far as the
internal occipital protuberance; an _inferior longitudinal_ along its
lower border as far as the tentorium, where it joins the _straight
sinus_, which passes back as far as the same protuberance. One or two
small _occipital sinuses_, which lie in the falx cerebelli, also pass
to join the straight and longitudinal sinuses opposite this
protuberance; several currents of blood meet, therefore, at this spot,
and as Herophilus supposed that a sort of whirlpool was formed in the
blood, the name _torcular Herophili_ has been used to express the
meeting of these sinuses. From the torcular the blood is drained away
by two large sinuses, named _lateral_, which curve forward and
downward to the jugular foramina to terminate in the internal jugular
veins. In its course each lateral sinus receives two _petrosal_
sinuses, which pass from the cavernous sinus backwards along the upper
and lower borders of the petrous part of the temporal bone. The dura
mater consists of a tough, fibrous membrane, somewhat flocculent
externally, but smooth, glistening, and