THE MOUTH. 



405 



It is in relation, outwardly, with the mylo-hyoideus, stylo-glossus, the great 

 hypo-glossal nerve, Wharton's duct, and the hngual mucous membrane ; inwardly, 

 with the small hyo-glossus, the small cornu of the os hyoides, the pharyngo- 

 glossus, genio-glossus, lingual artery, the terminal divisions of the glosso-pharyn- 

 geal nerves, and great and small hypo-glossals. 



It retracts the tongue in depressing its base, according as it acts singly or 

 simultaneously with its fellow. 



(In 1850, Briihl described as the middle descending sft/Io-glossus, a long, 

 narrow muscle arising from the lower extremity of the inner face of the styloid 

 bore, or large cornu of the os hyoides, and terminating near the tip of the tongue, 

 where it is covered by the hyo-glossus. It has since been described as the 

 internal or small kerato-glossus. Its action is the same as the stylo-glossus.) 



Genio-glossus (Genio-hyo-glossus) (Fig. 220, 4). 



This is a beautiful muscle, the fibres of which are disposed Uke a fan in the 

 vertical and median plane of the tongue. 



It arises from the inner surface of the lower jaw, near the symphysis, by a 



MUSCLES OF THE TONGUE, SOFT PALATE, AND PHARYNX. 



1, Stylo-glossus ; 2, great hyo-glossus ; 3, the same, covered by the submucous layer formed by the 

 expansion of the small hyo-glossus ; 4, genio-glossus ; 5, pharyngo-glossus ; 6, palato-pharyngeus ; 

 7, hyo-pharyngeus ; 8, thyro-pharyngeus ; 9, crico-pharyngeus ; 10, oesophagus; 11, 12, tensors 

 palati ; 13, stylo-hyoideus ; 14, hyoideus magnus ; 15, genio-hyoideus ; 16, hyo-thyroideus [ 

 17, sterno-thyroideus ; 18, crico-thyroideus. 



tendon parallel to that of the genio-hyoideus. From this tendon are detached 

 a multitude of divergent fibres which pass backwards, upwards, and forwards, to 

 reach the upper surface of the tongue, and become continuous with the vertical 

 fibres of the submucous layer. 



The two genio-glossi lie together on the median plane of the tongue, except 

 towards their origin, where they are constantly kept apart by adipose tissue. 

 Their inferior border responds to the genio-hyoid muscles, and their anterior 

 fibres are partly included between the two mucous layers of the frgenum linguae. 

 They are related, by their external face, to the great hyo-glossus, the stylo-glossus, 



