THE MUSCLES OF THE HYOID BONE. 



461 



( gejiio- hyoid muscles; and also two muscles, the genioglossus and hyoglossus, 

 which will be described along with the extrinsic muscles of the tongue. 



M. Digastricus. The ' digastric muscle, as its name implies, possesses two 

 bellies anterior and posterior. 



The posterior ~belly arises, under cover of the sterno-mastoid muscle, from the 

 mastoid notch medial to the mastoid process. It is directed forwards and down- 

 wards, in company with the stylo-hyoid muscle, to end in an intermediate tendon, 

 which is connected by a pulley-like band of cervical fascia to the body of the hyoid 

 bone. 



The anterior belly of the muscle is directed forwards and upwards, over the 

 rnylo-hyoid muscle, to the chin, and is inserted into the oval digastric fossa on the 

 inferior border of the mandible close to the symphysis (Fig. 410). 



The muscle forms the inferior boundary of the submaxillary division of the 

 anterior triangle, containing the submaxillary gland. The posterior belly in 

 company with the stylo-hyoid crosses the carotid arteries and internal jugular vein. 

 The occipital artery ex- 

 tends posteriorly along 

 its inferior margin, and 

 the parotid gland covers 

 its superior border. 

 Thp- hypoglossal nerve 

 emerges from under 

 cover of the muscle. 

 The anterior belly, as it 

 passes to its insertion, 

 lies upon the mylo- 

 hyoid muscle.- 



Nerve - Supply. The 



rterior belly is supplied 

 the facial nerve ; the 

 anterior belly by the nerve 

 to the mylo-hyoid, a branch 

 of the inferior alveolar 

 nerve. 



External ptery- 

 goid (insertion) 



Genio- 

 glossus 

 (origin) 



Genio-hyoid 

 (origin) 



FIG. 410. MUSCLE-ATTACHMENTS ON THE MEDIAL SIDE OF THE 

 MANDIBLE. 



M. Stylohyoideus. 

 -The stylo-hyoid 

 muscle arises from the 

 posterior border of the styloid process of the temporal bone. 



Crossing the anterior triangle obliquely, along with the posterior belly of the 

 digastric muscle, it is inserted into the body of the hyoid bone, by two slips which 

 enclose the tendon of the digastric muscle. 

 Nerve-Supply. Facial nerve. 



M. Mylohyoideus. The mylo-hyoid muscle forms with its fellow a 

 diaphragm in the floor of the mouth. It arises from the inferior three-fourths of 

 the mylo-hyoid ridge of the mandible (Fig. 410). 



t is directed downwards and medially, to be inserted into (1) the superior border 

 the body of the hyoid bone, and more anteriorly (along with the opposite muscle) 

 into (2) a median raphe extending from the hyoid bone nearly to the chin. 



The muscle is in contact, on its superficial or lateral surface, with the digastric 



muscle and the submaxillary gland. Its deep or medial surface is partially 



ered by the mucous membrane of the floor of the' mouth, and is separated from 



B muscles of the tongue by the deep part of the submaxillary gland, the sub- 



;ual gland, the submaxillary duct, and the lingual and hypoglossal nerves. 



Nerve-Supply. The muscle is supplied by the nerve to the mylo-hyoid, a branch of the 

 inferior alveolar nerve. 



M. G-eniohyoideus. The genio-hyoid muscle arises from the inferior of the 

 ) mental spines on the posterior surface of the symphysis of the mandible 

 (Fig. 410). 



