Chap, ii.] tfbe Tongue, &c. 149 



When the lower jaw, however, is fixed by the ftronger 

 jnufcles, which have been already defcribed, the effect of 

 the digaftricus is different, for the os> hyoides, then 

 becoming the more moveable part, is drawn upwards, 

 and with it the larynx and pharynx, as in the act of 

 fwallowing. 



The mylo-hyoideus paffes from the infide of the 

 lower jaw to the os hyoides, and has nearly the fame 

 effect as the digaftricus. 



The genio-hyoideus alfo pafles from the os hyoides 

 to the chin, and either raifes the former or pulls down 

 the latter, according as the lower jaw or the os hyoides 

 is rendered more fixed by other mufcles. 



The genio-hyo-gloffus arifes 'from the lower jaw, 

 and is inferred partly into the os hyoides, and partly 

 into the tongue. This mufcle, according to the di- 

 rection of its fibres, acts very differently on different 

 occafiens; from the feparate action of its fibres it either 

 draws the tongue backwards-, extends it out of the 

 mouth, or renders its upper part concave. 



Two mufcles pafs from the os hyoides to the trunk. 

 The fterno-hyoideus proceeds from the- fternum, and 

 pulls the os hyoides downwards. The omo hyoideus 

 arifes from the fuperior cofta of the fcapula, and 

 draws the os hyoides obliquely downwards. It is to 

 be noticed, that when there are two mufcles of equal 

 ftrength and equal obliquity attached to a moveable 

 part, and they both act together, they draw it in a 

 Itrait line, the obliquity of the one counterbalancing 

 that of the other. 



The fubftance of the tongue is mufcular, and is 

 diftinguifhed by anatomifts into fix pair of mufcles, 

 which it cannot be neceffary to enumerate. They 

 alfo defcribe fix pair of mufcles belonging to the 

 pharynx : thefe I mall pafs over in filence, and merely 

 L 3 confider 



