THE HYOID MUSCLES 265 



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. 559). 



Origin. — The muscular angle of the dorsal 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 medial 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). 



In rare cases an anomalous arrangement is present in which the stylo-hyoideus is not at- 

 tached to the thyroid cornu but is continuous with the intermediate tendon of the digastricus, 

 and no iibrous ring is formed. The posterior bellj' of the digastricus is inserted chiefiy on the 

 thyroid cornu, but also sends a deUcate tendinous slip to the intermediate tendon. 



3. Occipito-hyoideus (M. jugulo-hyoideus). — 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 process of the occipital bone. 



Insertion. — The dorsal extremity and ventral edge of the great cornu of the 

 hyoid bone. 



Action. — It carries the ventral extremity of the great cornu backward. 



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.— '^wpGAcidWj, 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. 330). 



Origin. — A small depression on the medial surface of the ramus of the mandible, 

 close to the symphysis. 



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. 



i^eZafo'ows.— Ventrally, the mylo-hyoideus ; dorsally, the hyo-glossus, stylo- 

 glossus, genio-glossus, the sublingual gland, mandibular 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. 331). 



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 laterally by the lingual artery. 



Blood-supply. — Lingual artery. 



Nerve-supply. — Glosso-pharyngeal nerve. 



6. Hyoideus transversus. — This is a small, unpaired muscle, which extends 

 transversely between the two small cornua of the hyoid bone. 



