332 



SPLANCHNOLOGY. 



CRICO-THYROIDEUS. 



(Fie. 115. c.) 



This is a small muscle whose fibres run upwards 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 

 drawing the two cartilages together. 



CRICO-ARYTENOIDEUS. POSTICUS. 

 (Fie. 116. &.)' 



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, 

 whence its fibres converge upwards 

 and outwards. 



Insertion. To the posterior tuber- 



cie f the ar y ten id cartiia s e > covered 



by the oesophagus and crico-pharyngeus 



FlG - 115 - 



tbyroideus ; c, Crico-tbyroideus. 



muscle. 



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

 glottis, by separating the vocal cords. 



CRICO-ARYTENOIDEUS LATERALIS. 



(Fie. 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. 



