LARYNGEAL MUSCLES. 351 



LARYNGEAL MUSCLES. 



The muscles of the laryax are extrinsic, or those' arising 

 from neighbouring parts, and intrinsic, or those acting between 

 the diflferent cartilages. The extrinsic muscles are three in 

 number : — 



Sterno-thyro-hyoideus. | Hyo-thyroideus. 



Hy o-epigl ottideus. 



STERNO-THYRO-HYOIDEUS. 



(See page 179.) 



HYO-THYROIDEUS. 

 ^FiG. li5. 0.) 



This is a triangular muscle, its fibres running backwards and 

 downwards. 



Origin. — The inferior border of the heel process of the os 

 hyoides. 



Insertion. — To a line on the external side of the wing of the 

 thyroid cartilage. 



Action. — To depress the os hyoides, or elevate the larynx. 



HYO-EPIGLOTTIDEUS. 

 (Fig. 115. a.) 



Single and fusiform, this muscle is usually enveloped in 

 adipose tissue. 



Origin. — The middle of the body of the os hyoides. 



Insertion. — The inferior part of the anterior surface of the 

 epiglottis, covered by the mucous membrane. 



Action. — To draw the epiglottis forward, and thus open the 

 larynx. 



The intrinsic muscles consist of four pairs and one single 

 muscle, as follows : — 



Crico-thyroideus. Crico-arytenoideus lateralis 



Crico-arytenoideus posticus. Thyro-arytenoideus. 



Arytenoideus. 



