

6 Muscles of Head ana Neck 



upon the sterno-thyroid and thyro-hyoid, being covered by the platysma 

 and fascias. 



The omo-hyoid crosses the carotid sheatli at the level of the fifth 

 cervical vertebra (see p. 23). 



THE ELEVATORS OF THE HYOID BONE 



The digastric arises posteriorly from the deep aspect of 

 mastoid process, and, therefore, under cover of the sterno-mastoid, 

 splenius, and tracheo-mastoid, but upon the outer side of the occipital 

 artery. And. as the parotid gland fills in the hollow in front of the 

 sterno-mastoid, it also lies over the posterior belly of the digastric. 

 This part of the muscle soon ends in a shining tendon, which, piercing 

 the fleshy stylo-hyoid, joins with the tendon of the anterior belly, 

 being bound down to the hyoid bone by the deep fascia. 



Relations. The posterior belly rests upon the stylo-glossus and 

 stylo-pharyngeus, the internal jugular vein, pneumogastric nerve, and 

 internal carotid artery ; the occipital artery and hypoglossal nerve ; 

 the external carotid, and the lingual and facial arteries, and then upon 

 the hyo-glossus (see p. 27). Its course is indicated by a line drawn 

 from the mastoid process to the body of the hyoid bone. 



The anterior belly arises from a depression close against the 

 symphysis, and, passing downwards and backwards to the central 

 tendon, rests upon the mylo-hyoicl, being covered by skin, platysma, 

 and fasciae. 



The posterior belly, with the stylo-hyoid, forms the upper limit of 

 the superior carotid, and the hinder limit of the submaxillary triangle. 



Nerve-supply. The anterior belly helps the mylo-hyoid in raising 

 and drawing forward the hyoid bone, and in depressing the jaw, and 

 receives its supply from the mylo-hyoid nerve. The posterior belly 

 acts with the stylo-hyoid in raising and drawing back the hyoid bone, 

 and, like that muscle, is supplied by the facial nerve. 



The stylo-hyoid arises from the outer side of the styloid process 

 and is inserted into the body of the hyoid bone. It is pierced by the 

 tendon of the posterior belly of the digastric. Its course, actions, and 

 relations resemble those of the posterior belly of the digastric ; and its 

 nerve supply is identical. 



The mylo-hyoid descends from the ridge at the back of the maxilla 

 to the body of the hyoid bone, the posterior border being free, whilst 

 the anterior is blended with its fellow in a median raphe. 



Relations. It is covered by the platysma and fasciae ; the anterior 

 belly of the digastric ; the mylo-hyoid nerve and artery ; the su 

 maxillary gland, and submental arteiy. Its deep surface helps to 

 form the floor of the mouth, and is in contact with the genio-hyoid, 

 genio-hyo-glossus ; the hypoglossal and gustatory nerves ; the deep 

 part of the submaxillary gland and its duct, and the sublingual 



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