The =veins of the brain= (Venæ cerebri) do not in general accompany the
cerebral arteries. They have very thin walls, no muscular coat, and no
valves. They are arranged in two sets, superficial or cortical and deep
or central. The superficial veins are more numerous and larger than the
arteries. They lie on the surface of the brain in the pia mater and the
subarachnoid space.
The =superior cerebral veins= drain the upper and outer part of the
cerebral cortex. They receive veins from the medial surfaces of the
hemispheres and open into the superior sagittal sinus. Their terminal
parts are bulbous and their openings are directed obliquely forward, _i.
e._, contrary to the direction of the bloodstream in the sinus.
The =inferior cerebral veins= lie on the inferior and external aspect of
the hemispheres. They open into the inferior system of sinuses. The
=middle cerebral vein= runs in the lateral fissure (of Sylvius) and
opens into the cavernous sinus.
The =deep cerebral veins= issue from the central or ganglionic parts of
the brain at the transverse fissure. They converge to form the =great
cerebral vein= (of Galen) (V. magna cerebri). This passes upward and
backward behind the splenium of the corpus callosum and is continued as
the straight sinus to join the sagittal sinus.
The =superior cerebellar veins= ramify on the upper surface of the
cerebellum. They open into the superior system of sinuses and the great
cerebral vein. The =inferior cerebellar veins= are larger and go chiefly
to the basilar plexus. The veins of the medulla and pons end in the
inferior system of sinuses.
The =meningeal veins= (Venæ meningeæ) arise in capillary plexuses in the
superficial and deep faces of the dura mater. Some end in the sinuses of
the dura, others accompany the meningeal arteries.
The =diploic veins= (Venæ diploicæ) are anastomosing channels in the
spongy substance of the cranial bones. Their walls are thin, consisting
in many places only of the endothelium, and they have no valves. Some
open inward into venous sinuses, others into extracranial veins.