MUSCLES OF THE LARYNX. 495 



The posterior crico-arytenoid muscles, arising from each 

 lateral half of the posterior surface of the cricoid cartilage, 

 passing upward and outward to be inserted into the outer 

 angle of the inferior portion of the arytenoid cartilages, 

 rotate these cartilages outward, separate them, and act as 

 dilators of the chink of the glottis. These muscles are 

 chiefly concerned in the respiratory movements during in- 

 spiration. 



The muscles mainly concerned in the modifications of 

 the voice by their action upon the vocal chords are the crico- 

 thyroids, the arytenoid, the lateral crico-arytenoids, and the 

 thyro-arytenoids. The following is a sketch of their attach- 

 ments and mode of action : 



Crico-thyroid Muscles. These muscles are situated on 

 the outside of the larynx at the anterior and lateral por- 

 tions of the cricoid cartilage. Each muscle is of a triangular 

 form, the base of the triangle looking posteriorly. It arises 

 from the anterior and lateral portions of the cricoid cartilage, 

 and its fibres diverge to be inserted into the inferior border 

 of the thyroid cartilage, extending from the middle of this 

 border posteriorly, as far back as the inferior cornua. Longet, 

 after dividing the nervous filaments distributed to these mus- 

 cles, noted hoarseness of the voice, depending upon relaxation 

 of the vocal chords ; and by imitating its action mechanically, 

 he approximated the cricoid and thyroid cartilages in front, 

 carried back the arytenoid cartilages, and rendered the chords 

 tense. 1 



Arytenoid Muscle. This single muscle fills up the space 

 between the two arytenoid cartilages and is attached to 

 their posterior surface and borders. Its evident action is 

 to approximate the posterior extremities of the chords and 

 constrict the glottis, as far as the articulations of the 

 arytenoid cartilages with the cricoid will permit. In any 

 event, this muscle is important in phonation, as it serves 

 to fix the posterior attachments of the vocal chords and 



1 LONGET, loc. dt. 



