552 



VOICE AND SPEECH. 



cles, the most complicated of all the intrinsic muscles in their attachments and the direc- 

 tion of their fibres, give rigidity and increased capacity of vibration to the vocal chords. 



The posterior crico-arytenoid muscles, arising from each lateral half of the posterior 

 surface of the cricoid cartilage and 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 inspiration. 



The muscles mainly concerned in the modifications of the voice, by their action upon 



FIG. ill. Posterior view of the muscles of the larynx. 

 (Sappey.) 



FIG. 172. Lateral view cf the muscles of the larynx. 

 (Sappey.) 



1, posterior crico-arytenoid muscle ; 2. 8, 4, different fas- 1, body of the hyoid bone ; 2, vertical section of the thy- 

 ciculi of the arytenoid muscle; 5, aryteno-epiglot- roid cartilage; 3, horizontal section of the thyroid 



tidean muscle. cartilage turned downward to show the deep attach- 



ment of the crico-thyroid muscle ; 4, facet of articu- 

 lation of the small cornu of the thyroid cartilage with 

 the cricoid cartilage ; 5, facet on the cricoid cartilage ; 



6, superior attachment of the crico-thyroid muscle ; 



7, posterior crico-arytenoid muscle; 8, 10, arytenoid 

 muscle; 9, thyro-arytenoid muscle ; 11, aryteno-epi- 

 glottidean muscle; 12, middle thyro-hyoid ligament; 

 13, lateral thyro-hyoid ligament. 



the vocal chords, are the crico-thyroids, the arytenoid, the lateral crico-arytenoids, 

 and the thyro-arytenoids. The following is a sketch of their attachments and mode of 

 action : 



Crico-thyroid Muscles. These muscles are situated on the 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 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 muscles, noted hoarseness of the voice due to relaxation of the vocal chords; 

 and, by imitating their action mechanically, he approximated the cricoid and thyroid car- 

 tilages in front, carried back the arytenoid cartilages, and rendered the chords tense. 



Arytenoid Muscle. This single muscle fills up the space between the two arytenoid 

 cartilages and is attached to their posterior surface and borders. Its action evidently is to 

 approximate the posterior extremities of the chords and to constrict the glottis, as far as 



