914 



THE LARYNX. 



its laryngeal side and upper end is a thin lajer of muscular fibres (com- 

 pressor sacculi laryngis, arytaeno-epiglottideus inferior, Hilton) connected 

 above with those found in the aryteno-epiglottidean folds. The upper fibres 

 of the thyro-arytenoid muscles pass over the outer side of the pouch, a 

 few being attached to its lower part. The laryugeal pouch is supplied 

 abundantly with nerves, derived from the superior laryngeaL 



Muscles of the Larynx. 



Besides certain extrinsic muscles already described viz., the sterno-hyoid, 

 omo-hyoid, stern o- thyroid, and thyro-hyoid muscles, together with the 

 muscles of the suprahyoid region, and the middle and inferior constrictors 

 of the pharynx, all of which act more or less upon the entire larynx there 

 are certain intrinsic muscles which move the different cartilages upon one 

 another, and modify the size of the apertures and the state of tension of 

 the soft parts of the larynx. These intrinsic muscles are the crico-thyroid, 

 the posterior and lateral crico-arytenoid, the thyro-arytenoid, the arytenoid, 

 and the aryteno-epiglottidean, together with certain other slender muscular 

 fasciculi. All these muscles, except the arytenoid, which crosses the middle 

 line, are in pairs. 



The crico-thyroid muscle is a short thick triangular muscle, seen on the 

 front of the larynx, situated on the fore part and side of the cricoid cartilage. 

 It arises by a broad origin from the cricoid cartilage, reaching from the 



Fig. 639. 



Fig. 639. LATERAL VIEW OP THE CARTILAGES 

 OP THE LARYNX WITH THE CRICO-THYROID 

 MUSCLE (after Willis). 



8, thyroid cartilage; 9, cricoid; 10, crico- 

 thyroid muscle ; 11, crico-thyroid ligament or 

 membrane ; 12, upper rings of the trachea. 



median line backwards upon the lateral 

 surface, and its fibres, passing obliquely 

 upwards and outwards and diverging 

 slightly, are inserted into the lower bor- 

 der of the thyroid cartilage, and into the 

 anterior border of its inferior cornu. 

 The lower portion of the muscle, the 

 fibres of which are nearly horizontal, and 

 are inserted into the inferior cornu, is 

 usually distinct from the rest. Some 

 of the superficial fibres are almost 

 always continuous with the inferior con- 

 strictor of the pharynx. The inner 

 borders of the muscles of the two sides 

 are separated in the middle line by a triangular interval, broader above 

 than below, and occupied by the crico-thyroid membrane. 



The posterior crico-arytenoid muscle, situated behind the larynx, beneath 

 the mucous membrane of the pharynx, arises from the broad depression on 

 the corresponding half of the posterior surface of the cricoid cartilage. From 

 this broad origin its fibres converge upwards and outwards to be inserted 

 into the outer angle of the base of the arytenoid cartilage, behind the 

 attachment of the lateral crico-arytenoid muscle. The upper fibres are short 



