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108 ANAT03IY.
attached just below the superior border of the bone, sometimes extend-
ing well up on this border—a fact which, in such jaws, interferes^ in
a measure with the wearing of artificial teeth. The endeavor to bring
the jaws together after the "teeth and alveolar process are lost causes the
angle between the ramus and body of the bone to assume almost the
same obtuse form as at birth (Fig. 56). The employment of artificial
teeth immediately after the loss of the natural ones delays to a certain
extent this change of form.

The Hyoid Bone.
The hyoid bone (Fig. 57), or os linguae, is symmetrical in outline. It
Fig. 57.
Greater Cornu.
Middle Constrictor of Pharynx.,

Thyrohyoid,
tylo-hyoid.
Onio-hyoid.
^Mylo-hyoid.
Gcnio-hyoid. Sterno-hyoid.
Hyoid Bone, anterior surface (enlarged).
is situated in the median line of the upper part of the neck, at the
base of the tongue, and above the larynx. It is so superficially
placed that ordinarily the outlines of the bone can be traced beneath
the skin below the chin. It is a floating bone, having no osseous
articulation. In form it is U-shaped, the convexity of the U being
directed forward and its concavity backward. It is divided into a
body and four processes called horns or cornua, two on each side.
The Body or Central Portion (basihyal) of the bone is quadrilateral
in form. It is compres.sed from before backward, the anterior surface
being convex and marked in the median line by a vertical ridge. On
each side of this ridge are eminences and depressions for tlie attachment
of the genio-hyoid nuisclcs. Below these the two mylo-hyoid, the two
stylo-hyoid, and the aponeuroses of the digastric muscles are inserted.
Between the surfaces for the attachment of these muscles are inserted
portions of the two hyo-glossus muscles.
The Poslenor Surface is smooth and deeply concave. It is directed
backward and downward toward tlie epiglottis. The space between
this surface and the epiglottis is filled by loose areolar tissue.
The Superior Border is thin, rounding, and continuous with the
inner margin of the great cornua. It gives attachment to the thyro-
hyoid membrane.