332 



SPLANCHNOLOGY. 



CRICO-THYEOIDEUS. 



(Fig. 115. c.) 



This is a small muscle whose fibres run up^Yards and backwards. 

 Origin. — The external surface of the cricoid cartilage. 



Insertion. — To the posterior border 

 of the thyroid cartilage. 



Action. — To shorten the larynx by 

 drawinof the two cartilases tosfether. 



CRICO-ARYTENOIDEUS POSTICUS. 



(Fig. 116. b.) 



The most powerful of the intrinsic 

 muscles, this is situated on the infero- 

 posterior aspect. 



Origin. — The cavity on the poste- 

 rior surface of the cricoid cartilage, 

 AV'hence its fibres converge upwards 

 and outwards. 



Insertion. — To the posterior tuber- 

 cle of the arytenoid cartilage, covered 

 by the oesophagus and crico-pharyngeus 

 muscle. 



Action. — To dilate the entrance of the larynx, and also the 

 glottis, by separating the vocal cords. 



Muscles of the larynx— left Literal 

 view, a, Hyo-epiglottideus ; l>, llyo- 

 thyroideus 



L", Crico-tbyrouleus. 



CRICO-ARYTENOIDEUS LATERALIS. 

 ^FiG. 116. c.) 



This muscle is triangular in shape, and lies between the wing 

 of the thyroid and the arytenoid cartilage. 



Origin. — The side of the anterior border of the cricoid carti- 

 lage, passing upwards. 



Insertion. — To the outer tubercle at the base of the arytenoid 

 cartilage outside the posticus. 



Action. — To contract the opening of the larynx, and thus 

 antagonise the posticus. 



