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BLOOD-VESSEL SYSTEM OF THE HEAD, ETC. 261

temporal bone. It receives tributaries from the cerebrum, cerebellum,
aud tympanum, the last-named vessels passing through the petro-squa-
mous fissure.
The Inferior Petrosal Sinus is much shorter and wider than the
superior. It commences at the posterior extremity of the cavernous
sinus, passes downward and outward along a groove over the articula-
tion of the petrous portion of the temporal bone with the basilar process
of the occipital bone, extends through the anterior compartment of the
posterior lacerated foramen, aud terminates by emptying into the ante-
rior portion of the bulb of the internal jugular vein.
The Anterior Occipital, or Transverse JSinus (basilar plexus of Vir-
chow) is a communicating canal or plexus of vessels situated between
the right and left inferior petrosal sinuses in front of the foramen mag-
num. It receives branches from the anterior spinal veins.

Veins of the Orbit.
Tlie veins of the orbit are two in number, superior and inferior
ophthalmic.
The Supeeior Ophthalmic Vein is considerably larger than the
inferior, and is by far the more important of the two. It commences
by the confluence of the frontal vein and a large communicating branch
from the angular vein, a tributary of the facial. It extends back-
ward through the orbit, in company with the ophthalmic artery, to a
point near the optic foramen, Avhere it turns a little outward to enter the
proximal extremity of the anterior lacerated foramen. Here it j)asses
into the brain-case, and terminates by emptying into the cavernous
sinus.
Its tributaries are the veins which return the blood from the region
supplied by the ophthalmic artery as from the nasal chamber, the
anterior and posterior ethmoidal cells, the muscles of the eyeball, the
lachrymal gland, the eyeball, etc. These veins receive names corre-
sponding precisely to the arteries of the same region, and anastomose
freely with each other.
The Inferior Ophthaoiic Vein is an accessory to the superior.
It commences at the terminations of the posterior ciliary and interior
muscular veins, passes backward close to the floor of the orbit between
the inferior and external recti muscles, and usually leaves the orbit by
the spheno-maxillary fissure to terminate in the pterygoid plexus. It
occasionally terminates by emptying into the superior ophthalmic vein,
or it may pass through the anterior lacerated foramen to terminate inde-
pendently in the cavernous sinus. It receives tributaries from the
facial vein, from the temporal vein through the malar bone, and a
communicating branch from the superior ophthalmic vein.
The Diploic Veins (Fig. 115) are those situated in the diploe of
the cranial bones. They can be seen to best advantage by stripping off
the pericranium, and then with a dental or surgical engine removing the
outer plate of bone. They will then be seen in great numbers, running
in various and tortuous directions, but with a general inclination down-
ward, and joining larger main branches in thpir course. They are