THE HYOID MUSCLES 223 



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 in- 

 ternal 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 hypo-glossal nerves. 



Blood-supply. — Sublingual artery. 



A^ervc-supplij. — 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 ])one. 



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 i)one. 



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 up- 

 ward. 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. 



