This group consists of eight muscles, one of which, the hyoideus
transversus, is unpaired.
1. =Mylo-hyoideus.=—This muscle, together with its fellow, forms a sort
of sling between the two rami of the lower jaw, in which the tongue is
supported.
_Origin._—The inner surface of the alveolar border of the mandible.
_Insertion._—(1) A median fibrous raphé extending from the symphysis to
the hyoid bone; (2) the lingual process and body of the hyoid bone.
_Action._—It raises the floor of the mouth, the tongue, and the hyoid
bone.
_Structure._—Each muscle consists of a thin curved sheet, the fibers
passing downward from their origin and then curving toward the median
raphé. It is chiefly fleshy, and is thickest behind. The anterior
superficial part of the muscle is termed the mylo-glossus.
_Relations._—On the superficial surface of the muscles are the ramus,
the internal pterygoid and digastricus muscles, and the submaxillary
lymph glands. The deep surface is in contact with the mucous membrane of
the mouth, the stylo-glossus, hyo-glossus, and genio-hyoideus muscles,
the sublingual gland and vessels, the submaxillary duct, and the lingual
and hypoglossal nerves.
_Blood-supply._—Sublingual artery.
_Nerve-supply._—Mylo-hyoid branch of the mandibular nerve.
2. =Stylo-hyoideus.=—This is a slender, fusiform muscle, having a
direction nearly parallel to that of the great cornu of the hyoid bone
(Fig. 436).
_Origin._—The heel-like prominence on the proximal extremity of the
great cornu of the hyoid bone.
_Insertion._—The anterior part of the thyroid cornu of the hyoid bone.
_Action._—It draws the base of the tongue and the larynx upward and
backward.
_Structure._—It arises by a thin, short tendon, and has a fusiform
belly. The tendon of insertion is perforated for the passage of the
intermediate tendon of the digastricus, and at this point there is a
small synovial sheath.
_Relations._—Superficially, the internal pterygoid muscle and the
parotid gland; deeply, the guttural pouch, the pharynx, the external
carotid and maxillary arteries, and the hypoglossal nerve.
_Blood-supply._—External carotid artery.
_Nerve-supply._—Facial nerve (stylo-hyoid branch).
3. =Occipito-hyoideus= (M. jugulo-hyoideus; occipito-styloideus).—This
is a small triangular muscle, which lies in the space between the
paramastoid process and the great cornu of the hyoid bone.
_Origin._—The paramastoid (styloid) process of the occipital bone.
_Insertion._—The proximal extremity and ventral edge of the great cornu
of the hyoid bone.
_Action._—It carries the distal extremity of the great cornu backward
and upward. Acting with the genio-hyoideus and digastricus, it raises
the hyoid bone and the larynx.
_Structure._—The muscle is somewhat triangular, its fibers being longer
as the ventral border is approached. It blends with the posterior belly
of the digastricus.
_Relations._—Superficially, the parotid gland; deeply, the guttural
pouch.
_Blood-supply._—Occipital artery.
_Nerve-supply._—Facial nerve.
4. =Genio-hyoideus.=—This is a long, spindle-shaped muscle, which lies
under the tongue in contact with its fellow of the opposite side (Fig.
243).
_Origin._—The angle of union of the rami of the mandible.
_Insertion._—The extremity of the lingual process of the hyoid bone.
_Action._—It draws the hyoid bone and tongue forward.
_Structure._—The muscle arises by a short tendon, which is succeeded by
the belly, composed of long bundles of parallel fibers.
_Relations._—Below, the mylo-hyoideus; above, the hyo-glossus,
stylo-glossus, genio-glossus, the sublingual gland, submaxillary duct,
and the lingual nerve.
_Blood-supply._—Sublingual artery.
_Nerve-supply._—Hypoglossal nerve.
5. =Kerato-hyoideus.=—This small triangular muscle lies in the space
between the thyroid and small cornu, under cover of the hyo-glossus
(Fig. 243).
_Origin._—The posterior edge of the small cornu and the adjacent part of
the ventral border of the great cornu.
_Insertion._—The dorsal edge of the thyroid cornu.
_Action._—It raises the thyroid cornu and the larynx.
_Relations._—The muscle is crossed outwardly by the lingual artery.
_Blood-supply._—Lingual artery.
_Nerve-supply._—Glosso-pharyngeal nerve.
6. =Hyoideus Transversus.=—This is a thin, unpaired muscle, which
extends transversely between the two small cornua of the hyoid bone.
_Attachments._—The small cornua close to the junction with the great
cornua.
_Action._—When relaxed, its upper surface is concave; when it contracts,
it elevates the root of the tongue.
_Structure._—Fleshy, composed of parallel transverse bundles.
_Blood-supply._—Lingual artery.
_Nerve-supply._—Glosso-pharyngeal nerve.