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256 ANAT031Y. :

the interfascial space just above the sternum. This vein is not supplied
with valves.
The Ixterxal Jugular Vein is the largest and most import-
ant of the veins which descend the neck, and returns the blood from
the greater portion of the brain-case and superficial structures of the
face and neck. It commences at the termination of the lateral and
inferior petrosal sinuses in the enlarged and rounded portion of the
posterior lacerated (jugular) foramen, from which it passes downward
almost along a vertical line, and then slightly forward, and becomes
superficial at the lower portion of the neck. Its j)osition is indicated
by a line drawn from the anterior portion of the mastoid process of the
temporal bone to the sterno-clavicular articulation, beneath which it ter-
minates by joining the subclavian vein to form the innominate vein.
This vein is not of uniform calibre throughout its course. At its com-
mencement is the dilatation known as its bulb or si)ius. Opposite the
hvoid bone it increases in size through its confluence with the common
facial and several deep veins. Near its termination it is slightly dimin-
ished in calibre, and furnished with a single or double valve which is
situated on its outer wall. This vein may be entirely absent on the
left side (Grul)er).
Relatione.—At its commencement the internal jugular vein is situ-
ated posterior to the internal carotid artery, the ninth, tenth, eleventh,
and twelfth nerves, and rests upon the rectus capitis lateralis muscle.
It then passes to the lateral side of the internal carotid artery, the
ninth (glosso-pharyngeal), and the twelfth (hypoglossal) nerves, pass-
ing between the vessels, while the tenth (pneumogastric) nerve passes
downward posteriorly between the vein and the artery, within the com-
mon sheath, the eleventh, (spinal accessory) nerve passing backward to
the inner side of the vein. After reaching the common carotid artery
the vein extends downward, somewhat overlapping this vessel. The
right internal jugular vein as it approaches its termination generally
diverges slightly from the artery, while the vein of the left side crosses
toward the median line.
Tributaries.—In addition to the lateral and inferior petrosal sinuses,
the veins that empty into the internal jugular ai"e as follows
The pharyngeal, Superior thyroid,
Lingual, Middle thyroid.
Common facial, Occipital (occasionally).
The pharyngeal, lingual, and common facial veins have already been
described.
The Superior Thyroid Vein commences on the superficial surface
of the thyroid body by numerous small branches W'hich extend from
its surface and the muscles in this region. It receives communicating
l)ranchcs from the superior laryngeal and crico-thyroid veins, and passes
upward and backward to terminate in the internal jugular vein. Occa-
sionally it empties into the common facial vein.
The. Middle Thyroid Vein commences by branches situated in the
lateral portion of the thyroid body, receiving tributaries from the
larvnx and the trachea. It passes outward over the common carotid