916 



THE LA11YNX. 



and the interior of the larynx, being lined within by the mucous membrane 

 of the larynx. Its anterior part is covered by the upper part of the crico- 

 thyroid muscle. The upper part is in close contact and indeed is sometimes 

 blended with the thyro-arytenoid muscle. 



The thyro-arytenoid is a broad flat muscle situated above the lateral crico- 

 aryteuoid. It is thick below and in front, and becomes thinner above and 

 behind. It consists of several muscular fasciculi, which arise in front from 

 the internal surface of the thyroid cartilage, adjacent to the lower two-thirds 

 of the angle formed by the junction of the two alee. They extend almost 

 horizontally backwards and outwards to reach the base of the arytenoid 

 cartilage. The lower portion of the muscle, which forms a thick fasciculus, 

 receives a few additioual fibres from the posterior surface of the crico- 

 thyroid membrane, and is inserted into the anterior projection on the base 

 of the aryteuoid cartilage and to the adjacent part of the surface close to the 

 insertion of the lateral crico-arytenoid muscle. The thinner portion of the 

 thyro-arytenoid muscle is inserted higher up on the anterior surface and 



Fig. 642. Fig. 642. VIEW OP THE INTERIOR 



OF THK LEFT HALF OF THE LA- 

 RYNX (after Hilton). 



a, left arytenoid cartilage ; c, c, 

 divided surfaces of the cricoid car- 

 tilage ; t, thyroid cartilage ; e, 

 epiglottis; v, left ventricle of the 

 larynx ; ?, left inferior or true 

 vocal cord ; s, placed on the inner 

 wall of the laryngeal pouch ; 6, 

 aryteno-epiglottidean muscle ; /, 

 interior of the trachea. 



outer border of the arytenoid 

 cartilage. The lower portion 

 of the muscle assists in the 

 formation, or at least contri- 

 butes to the support, of the 

 true vocal cord, lying parallel 

 with the rim a glottidis, im- 

 mediately on the outer side 

 of the inferior thyro-arytenoid 

 ligament, with which it is in- 

 timately connected, and into 

 the outer surface of which 

 some of its fibres are inserted. 

 The upper thin portion, ex- 

 ternal to the lower, lies upon 



the laryngeal pouch and ventricle, close beneath the mucous membrane. 

 The entire muscle may be dissected indeed from the interior of the larynx, 

 by raising the mucous membrane of the sinus and vocal cord. Fibres from 

 this muscle pass round the border of the arytenoid cartilage, and become 

 continuous with some of the oblique fibres of the arytenoid muscle, to be 

 presently described. 



Santorini described three thyro-arytenoid muscles, an inferior and a middle, which 

 are constant, and a superior, which is sometimes present. The fibres of the superior 

 fasciculus, when present, arise nearest to the notch of the thyroid cartilage, and are 



