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258 ANAT03TY.

ToRCULAR Herophili.—Before passing to a description of the
sinuses it will be well to describe what is known as the torcular Hero-
phili. This is a dilatation formed by the confluence of the superior
longitudinal, the straight, the occipital, and the two lateral sinuses, and
is situated on the internal surface of the occipital bone at the internal
protuberance, where the superior longitudinal sinus terminates and the
lateral sinuses commence.
The Siqjerlor Lo)t(/ifu(Jinal tSi)U(s commences at the foramen cfficum
in the frontal bone, just anterior to the crista galli. In infancy, and
occasionally in adult life, this foramen is not a blind one, but opens
into the nasal chambers. AVhen this is the case the sinus commences
within the nose. It passes upward, backward, and downward on the
under surface and in the median line of the dome of the brain-case, its
lower wall being formed by the upper border of the falx cerebri. It
terminates in the torcular Herophili. In shape it is triangular, and it
is crossed by numerous chords or trabeculiTe (chordae Willisii). At its
commencement it is quite small, but increases gradually in size to its
termination. In its course it occasionally deviates from the median
line, especially as it passes along the occipital bone. It receives tribu-
taries from the veins of the brain, Avhich enter the sinus in a forward
direction or opposite to the flow of blood along the sinus. Occasion-
ally a few of these veins which enter the sinus at its anterior portion
do so in the direction of the blood-current. The tributary from the
external surface of the parietal bones which communicates with the
veins of the scalp ]5asses through the parietal foramen to empty into
the sinus. It is small in calibre, and inconstant in existence on one or
both sides.
The Infei-ior Longitudinal Sinus is shorter and much smaller than
the superior. It is nearly cylindrical in form, and is often called the
inferior longitudinal vein. It commences at the anterior portion of the
free or inferior extremity of the falx cerebri, passes backward along its
inferior border to the tentorium cerebelli, and terminates in the straight
sinus. As it passes l)ackward it receives several branches from the
falx.
The Straight Sinus (sinus tentorii) commences at the termination of
the inferior longitudinal sinus, which is situated at the anterior junction
of the falx cerebri and the tentorium cerebelli. It passes backward and
slightly downward in a straight line along the union of the falx cerebri
and tentorium cerel)elli, increasing in size as it extends, and terminates
in the confluence of the sinuses. Its transverse section is triangular, a
few crossing cords being found in it. Besides the inferior longitudinal
sinus, its tributaries are the vense Galeni magnse, the inferior median
cerebri, the superior cerebellar, and small branches from the tentorium
cerebelli.
The Posterior Occipital Sinus is small and single, though occasionally
it is represented Iw two sinuses. It commences by l)ranches situated
around the posterior border of the foramen magnum which conuiiuni-
cate with the posterior spinal ])lexus ; it passes backward along the
inferior border of the falx cerebelli, and terminates in the confluence
of the sinuses. It receives small branches from the cerebellum.