THE HEAD AND NECK it33 



related to the inferior lingualis muscle, the ranine artery, the hyo- 

 glossus and stylo-glossus muscles, and the sublingual gland. The 

 upper or anterior border is covered by the buccal mucous membrane, 

 and the lower or posterior border by the genio-hyoid muscle. 



Hyo-glossus — Origin. — (i) The great comu of the hyoid bone 

 over its entire length ; (2) the anterior surface of the body of the 

 bone over about its outer half ; and (3) the small comu (inconstant). 

 The innermost fibres of origin from the hyoid bone pass inwards 

 between the two laminae of the genio-hyoid muscle. 



Insertion. — ^The posterior half of the imder surface of the tongue 

 close to its lateral border, the fibres being situated internal to those 

 of the stylo-glossus, and both sets of fibres being intimately inter- 

 mixed with each other and with the intrinsic lingual muscles. 



Nerve-supply. — ^The hypoglossal nerve, the branches of which 

 enter the superficial surface. 



The muscle is for the most part directed upwards, but its anterior 

 fibres have a slight inclination forwards. 



Action. — (i) To depress the side of the tongue, and, along with 

 its fellow, to render the dorsum of the organ convex ; and (2) to 

 assist in retracting the protruded tongue. 



The hyo-glossus is a flat, four-sided muscle. 



Relations — Superficial. — ^The mylo-hyoid muscle ; the intervening 

 tendon of the digastric, and stylo-hyoid muscle ; the lingual nerve, 

 with the submaxillary ganglion lying a little below it ; the deep part 

 of the submaxillary gland, and Wharton's duct ; the hypoglossal 

 nerve ; and the ranine vein. Posterior Border. — ^The following struc- 

 tures pass beneath this border, in order from above downwards : 

 (i) the glosso-pharyngeal nerve ; (2) the stylo-hyoid ligament ; 

 and (3) the lingual artery. Deep. — ^The posterior part of the genio- 

 hyo-glossus ; a portion of the middle constrictor muscle of the 

 pharynx ; the lingual artery ; the lower end of the stylo-hyoid liga- 

 ment ; and the glosso-pharyngeal nerve. 



The fibres of the hyo-glossus which arise from the small comu of 

 the hyoid bone are separated from the rest of the muscle by those 

 fibres of the genio-hyo-glossus which take insertion into the side 

 of the pharynx, and they are regarded by some as a separate 

 muscle, called the chondro-glossus. These fibres, however, are 

 inconstant. 



Stylo-glossus — Origin. — (i) The front of the styloid process of the 

 temporal bone neai its tip ; and (2) the upper extremity of the 

 stylo -mandibular ligament. 



Insertion. — ^The under surface of the tongue close to its lateral 

 border. The fibres extend as far forwards as the tip, and are 

 situated external to the fibres of the hyo-glossus, both sets of fibres 

 being intimately intermixed with each other, and with the intrinsic 

 lingual muscles. 



Nerve-supply. — ^The hypoglossal nerve. 



The muscle is directed downwards, forwards, and inwards. 



Action. — (i) To draw the tongue backwards ; and (2) to elevate the 

 root of the tongue. 



