MUSCLES OF THE LARYNX 



437 



have shown that such an effect is produced by the contraction of the 

 crico-thyroid muscles. 



The articulations of the different parts of the larynx are such that 

 the arytenoid cartilages can be approximated to each other posteriorly, 

 thus diminishing the interval between the posterior attachments of the 

 vocal chords. This action can be effected by contraction of the single 

 muscle of the larynx (the arytenoid) and also by the lateral crico-aryte- 

 noids. The thyro-arytenoid muscles, the most complex of all the in- 

 trinsic muscles in their attachments and the direction of their fibres, are 

 important in regulating the tension and 

 capacity of vibration of the vocal chords. 



The posterior crico-arytenoid mus- 

 cles, arising from each lateral half of 

 the posterior surface of the cricoid 

 cartilage and passing upward and out- 

 ward to be inserted into the outer angle 

 of the inferior portion of the arytenoid 

 cartilages, rotate these cartilages out- 

 ward, separate them and act as dilators 

 of the chink of the glottis. These mus- 

 cles are concerned chiefly in the respir- 

 atory movements of the glottis during 

 inspiration. 



The muscles mainly concerned in the 

 modifications of the voice by their action 

 on the vocal chords are the crico- 

 thyroids, the arytenoid, the lateral crico- Flg ' 

 arytenoids and the thyro-arytenoids. x> posterior cr i co .arytenoid muscle ; 2, 3 , 



The following is a Sketch Of their attach- 4, different fasciculi of the arytenoid muscle; 

 . 5, aryteno-epiglottidean muscle. 



ments and mode ot action : 



Crico-thyroid Muscles. These muscles are situated outside of the 

 larynx, at the anterior and lateral portions of the cricoid cartilage. 

 Each muscle is of a triangular form, the base of the triangle presenting 

 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. After dividing the ner- 

 vous filaments distributed to these muscles, a certain degree of hoarse- 

 ness of the voice is observed, due to relaxation of the vocal chords ; and 

 by imitating their action mechanically the cricoid and thyroid cartilages 

 may be approximated in front, carrying back the arytenoid cartilages and 

 rendering the chords tense. 



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