TELE LARYNX. 



533 



Fig 315. 



muscle is separated from that of the opposite side by the median crest of 

 the cricoid bezel. 



The posterior crico-arytaenoid muscles dilate the entrance to the larynx, as 

 well as the glottis, in causing the arytsenoid cartilages to rotate or swing on the 

 cricoid cartilage, and in separating them from one another by their anterior and 

 inferior borders. They act as a lever of the first order. 



Lateral Crico-arytsenoideus (Figs. 314, 6 ; 315, 5). A triangular muscle, 

 smaller than the preceding, situated between the thyroid and arytasnoid cartilages, 

 and formed of fasciculi longer in front than behind ; these arise on the side of 

 the anterior border of the cricoid cartilage, and are directed upwards, to 

 terminate outside the posterior crico-arytte- 

 noidens, on the tubercle of the arytaenoid 

 cartilage. 



It is a direct antagonist of the last muscle, 

 and, consequently, a constrictor of the larynx. 



Thyro-arytsenoideus (Figs. 314, 8, 9 ; 

 315, 6). — Lodged at the inner face of the thyroid 

 ala, this muscle comprises two fascicuh, sepa- 

 rated by the ventricle of the glottis. 



The anterior fasciculus is a long and pale 

 band, arising from the internal surface of the 

 ala of the thyroid cartilage, near its receding 

 angle, and ascending to the arytasnoid cartilage, 

 bending round its external face to join on the 

 median line, the analogous fasciculus from the 

 opposite side, mixing its fibres with those of the 

 arytgenoideus. By its inner face, it covers the 

 superior vocal cord and the laryngeal mucous 

 membrane. 



The posterior fasdeulus, wider than the 

 anterior, comports itself in a somewhat similar 

 manner. It commences from behind the same 

 point, and terminates on the external crest 

 (processus muscularis) of the arytfenoid carti- 

 lage ; but its most anterior fibres pass over this 

 crest, and join the arj^tenoid muscle. Its in- 

 ternal face is in contact with the vocal cord, and its posterior border is con- 

 founded with the fibres of the lateral crico-aryttenoideus. 



Sometimes it happens that these fasciculi are not distinct from each other, 

 and exist only as a wide muscular band applied against the ventricle of the 

 glottis. 



It is surmised that this muscle is a constrictor of the larynx. Its function 

 is particularly marked in phonation, when it modifies the length, separation, and 

 tension of the vocal cords. 



Arytsenoideus.— Situated beneath the pharyngeal mucous membrane, above 

 the arytenoid cartilages, this, the smallest of the laryngeal muscles, is composed 

 of two lateral portions, the fibres of which arise from a median raphe and, diverg- 

 ing, pass to the superior part of the external face of these cartilages, where they 

 are inserted into the crest dividing that face, and unite with the thyro-arytaenoid 

 muscle. 



POSTERO-LATERAL VIEW OF THE 

 LARYNX. 



1, Epiglottis ; 2, arvtsenoid cartilages ; 

 3, thyroid cartilage ; 4, arytsenoi- 

 deus muscle ; 5, crico-arytsenoideus 

 lateralis ; 6, tliyro-arytaenoideus ; 

 7, crico-arytffinoideus posticus ; 8, 

 crico-thyroideus ; 9, ligament be- 

 tween the cricoid cartilage and first 

 ring of trachea, 10; 11, infero- 

 posterior extremities of crico-thyroid 

 cartilages. 



