MUSCLES OF THE NECK. 315 



Inserted, by its anterior belly, into a rough sinuosity at the 

 inferior and anterior edge of that part of the lower jaw called 

 the chin. 



Use. To open the mouth by pulling the lower jaw down- 

 wards, and backwards ; and when the jaws are shut, to raise 

 the os hyoides, and, consequently, the pharynx, upwards, as in 

 deglutition. 



2. Mylo'Hyoideus,(Seefig'lS,) 



Arises, fleshy, from all the inside of the lower jaw, between, 

 the last dens molaris and the middle of the chin, where it joins 

 with its fellow. 



Inserted into the lower edge of the basis of the os hyoides, 

 and joins with its fellow. 



Use. To pull the os hyoides forwards, upwards, and to one 

 side. 



3. Genio-Hyoideus, 



Arises, tendinous, from a rough protuberance in the middle of 

 the lower jaw internally, or on the inside of the chin. 

 Inserted into the basis of the os hyoides. 

 Use. To draw- this bone forwards to the chin. 



4. Genio-Hyo-Glossus. 



Arises, tendinous, from a rough protuberance in the inside of 

 the middle of the lower jaw ; its fibres run like a fan, forwards, 

 upwards, and backwards ; and are 



Inserted into the whole length of the tongue, and base of the 

 os hyoides, near its cornu. 



Use. According to the direction of its fibres, to draw the tip 

 of the tongue backwards into the mouth, the middle down- 

 wards, and to render its dorsum concave ; to draw its root and 

 os hyoides forwards, and to thrust the tongue out of the mouth. 



The two muscles at the side are, 



1. Hyo-Glossus, 



Arises, broad and fleshy, from the base, cornu, and appendix, 

 of the os hyoides ; the fibres run upwards and outwards ; to be 



