338 



THE DIGESTIVE APPARATUS IN MAMMALIA. 



becoming detached from this point of insertion, are insinuated beneath the 

 preceding muscle, spread out under the mucous membrane covering the 

 lateral aspect of the tongue, and for the most part are reflected inwards, nearly 

 'io the superior face, to constitute the transverse fibres of the organ. 



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

 great hypo-glossal nerve, Wharton's duct, and the lingual mucous membrane ; 

 inwardly, with the small hyo-glossus, the small branch of the os hyoides, the 

 pharyngo-glossus, genio-glossus, lingual artery, the terminal divisions of the 

 glosso-pharyngeal nerves, and great and small hypo-glossals. (Fig. 149, 2. ) 



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 stylo-glossus, a long, 

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

 styloid bone, or large branch 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.) 



CENIO-GLOSSUS. 



(Synonym. Genio-hyo-glossus PercivaU.) 



This is a beautiful muscle, whose fibres are disposed like a fan in 

 the vertical and median plane of the tongue. 



It originates from the inner surface of the lower jaw, near the symphysis, 

 by a tendon parallel to that of the genio-hyoidous. 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. 



Fig. 149. 



MUSCLES OP 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, Pterygo-pharyngeus ; 7, Hyo-pharyngeus ; 8, Thyro-pha- 

 ryngeus; 9, Crico-pharyngeus ; 10, (Esophagus; 11, 12, Tensors palati ; 13, 

 Stylo-hyoideus ; 14, Hyoideus magnus ; 15, Genio-hyoideus ; 16, Hyo-thyroideus ; 

 17, Sterno-thyroideus ; 18, Crico-thyroideus. 



