SPLANCHNOLOGY. 



CRICO-THYROIDEUS. 



(Fig. 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. 



(Fig. 116. 6.) 



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- 

 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. 



Fig. 115. 

 Muscles of the larynx— left lateral 

 view, a, Hyo-epiglottldeus ; b, Hyo- 

 thyroideus ; c, Crico-thyroideus. 



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 cartil- 

 age, 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. 



