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BLOOD-VESSEL SYSTEM OF THE HEAD, ETC. 249

they are in close proximity to the sterno-thyroid muscles. The vein of
the left side empties into the left innominate vein, while that of the right
side varies in its termination. It may empty into the left innominate
vein in common with the vein of the left side or at the junction of the
right and left innominate veins, or into the right innominate vein.
Occasionally there exists a median vein which is independent of the
others, and which passes down along the central portion of the trachea
anteriorly. These veins are all supplied with valves, which are situated
at their terminal extremities.
The Tributaries of the Inferior Thyroid Yeins are the tracheal and
inferior laryngeal.

Veins of the Head and Neck.
The blood of the head and the greater portion of the neck is returned
to the heart through the medium of tMO veins on either side, the exter-
nal and internal jugular (Fig. 112). Close to their termination these
large veins have valves. The other veins of the head and neck are
generally not supplied with valves. They are divided into external
and endocranial veins.
The External Veins are the temporo-maxillary, facial, temporal, inter-
nal maxillary, posterior auricular, occipital, lingual, and pharyngeal.
The Facial or Anterior Facial Vein commences near the inner
angle of the eye at the termination of the angular vein. It passes
downward and outward along the side of the nose, then extends
obliquely to the facial notch in front of the lower border of the
masseter muscle, where it passes inward and backward under the
platysma myoides and deep fascia, and crosses the digastric muscle,
below w^iich it joins the anterior division of the temporo-maxillary
vein. This union forms the common facial vein, which is a short trunk
terminating in the internal jugular vein on a level with the hyoid bone.
The general course of the iacial vein is similar to the facial artery,
though it is more superficially situated and less tortuous. Upon the
face it is imbedded in the subcutaneous fat, and passes above all the
facial muscles excepting the zygomaticus major, beneath Avhich it ex-
tends.
The Tributaries of the Facial Vein are the
Angular, Buccal,
Frontal, Masseter,
Supraorbital, Parotid,
Inferior palpebral (two or three), Submental,
Superior labial. Submaxillary,
Deep facial, or Inferior palatine.
Anterior internal maxillary.
The Angular Vein is formed by the union of the frontal and supra-
orbital veins at a point near the articulation of the nasal and frontal
bones. It is quite superficially situated, and passes obliquely downward
and outward between the side of the nose and the inner margin of the
orbit.
The Tributaries of the Angular Vein are the nasal arch, which, when