452 THE MUSCLES 



imiscles will he described later; the former or extrinsic muscles constitute a grou}> 

 which is nearly related to those which have been just described. It consists of 

 four muscles — viz. the genio-hyo-glossus, the hyo-glossus, the stylo-glossus, and 

 the palato-glossus. 



1. GENIO-HYO-GLOSSUS 



The genio-hyo-glossus — named from its attachment to the chin (ji^s'.ov), hyoid 

 bone, and tongue (yXdxTffa), is a flat sheet forming the quadrant or, more correctly, 

 the sector of a circle, and separated from its fellow by a thin stratum of connective 

 tissue, the septum of the tongue. 



Origin. — The upper genial tubercle. 



Insertion. — (1 ) The whole length of the tongue in the submucous tissue just 

 external to the median plane, from the tip along the dorsum to the root; (2) the 

 upper part of the anterior surface of the body of the hyoid bone; (3) by a few 

 fibres into the side of the pharynx. 



Structure. — Its origin is by a short tendon, froai which its fleshy fi):)res diverge 

 in a fan-shaped sheet to their extensive insertion. 



Nerve-supply. — The hypoglossal, by filaments which enter its outer surface. 



Action. — (1) To draw downwards and forwards the mesial portion of the 

 tongue so as to make its dorsum concave upwards in a transverse direction; (2) by 

 its anterior fibres to drawback the tip of the protruded tongue; (3) by fibres which 

 pass to the back part of the dorsum of the tongue to draw it forwards, and protrude 

 the tongue; (4) by its lowest fibres to draw upwards and forwards the hyoid bone, 

 and so help the genio-hyoid and anterior belly of the digastric in raising the 

 tongue; (5) acting from below, its hyoid portion will help in depressing the lower 



Relations. — Externally, the inferior lingualis, hyo-glossus, and stylo-glossus 

 muscles, the ranine artery, the terminal branches of the hypoglossal and lingual 

 gustatory nerves, the mucous membrane of the floor of the mouth, the sublingual 

 gland, and Wharton's duct; internally, the fellow muscle and septum linguae; 

 along its lower border, the genio-hyoid muscle. 



2. HYO-GLOSSUS 



The hyo-glossus — named from its attachments to the hyoid bone and tongue 

 (y/.uxrtja) — is a thin square sheet. 



Origin. — (1) From the front of the hyoid bone near the upper border of the 

 outer third of its body; (2) from the upper border of all its great cornu; (3) by a 

 small slip from the lesser cornu. 



Insertion. — The submucous tissue and adjacent muscular mass of the posterior 

 half of the tongue external to the preceding muscle. 



Structure. — The fleshy fibres arise directly from the bone in a thin sheet, and 

 ascend nearly parallel to one another. The anterior fibres, however, diverge 

 slightly forwards, and they all, having reached the upper surface of the sides of the 

 tongue, course inwards, interlacing with the fibres of the palato-glossus and super- 

 ficial lingualis to form a submucous cover to the tongue. 



Those which arise from the lesser cornu are often described as a distinct muscle, 

 the cJwn(Jro-filofif<iif<, which is separated from the rest of the muscle by some bundles 

 whicVi ])ass from the lower part of the genio-hyo-glossus to the superior constrictor. 



Nerve-supply. — The hypoglossal nerve, which sends filaments into its outer 

 surface. 



Action. — (1) To draw downwards the sides of the tongue, increasing its trans- 

 verse convexity; (2) to draw backwards the protruded tongue. 



Relations. — Externally, the mylo-hyoid, digastric, stylo-hyoid, and stylo- 

 glossus muscles, the lingual vein, lingual gustatory and hypoglossal nerves, the 

 submaxillary gland and Wharton's duct; deeply, the inferior lingualis, genio-hyo- 

 glossus, middle constrictor, and part of the origin of the superior constrictor, the 

 lingual artery, and glosso-pharyngeal nerve. 



