1220 THE RESPIRATORY SYSTEM 



It draws forward the arytsenoid cartilage (and also tilts the cricoid), and rotates it so that 

 the vocal process passes medialward and downward, relaxing the vocal ligament. It is the 

 antagonist of the crico-thyreoid (fig. 984). Its nerve-supply is the anterior branch of the in- 

 ferior laryngeal. 



The vocal muscle [m. vocalis], (fig. 988), prismatic in form, is the inner con- 

 stant part of the thyreo-arytaenoideus. It lies in the vocal lip lateral to the vocal 

 ligament. Its fibres run from their origin in the angle of the thyreoid laminae to 

 their insertion in the vocal process and oblong fovea of the arytsenoid cartilage. 



It draws forward the vocal process, relaxing the vocal ligament. Its nerve comes from the 

 anterior branch of the inferior laryngeal. 



The insertion of certain fibres of this muscle into the elastic vocal ligament has been observed 

 (ary- vocalis muscle of Ludwig). D. Lewis has shown that some of the elastic fibres in the vocal 

 ligament are derived from the perimysium of the vocal muscle. 



The ventricular muscle [m. ventricularis] consists of a few fibres derived from the thyreo- 

 arytaenoideus which reach the back of the laryngeal saccule and enter the ventricular fold. 

 The small thyreo-arytcenoideus superior extends from the angle of the thyreoid to the muscular 

 process of the arytsenoid upon the lateral surface of the main muscle. 



The oblique arytaenoid muscle [m. arytaenoideus obliquus] is a slender band 

 lying at the back of the larynx and under the pharyngeal submucosa. It arises 

 from the muscular process of the arytsenoid posteriorly, and, ascending obliquely, 

 crosses its fellow in the median line. Some fibres are inserted into the apex of 

 the opposite arytsenoid cartilage; other fibres sweep around the apex and accom- 

 pany the thyreo-arytsenoid to an insertion in the angle of the thyreoid cartilage, 

 constituting the thyreo-arytcenoideus obliquus. 



This muscle contracts the laryngeal aperture and vestibule of the larynx. Its nerve is 

 derived from the anterior branch of the inferior laryngeal. 



Closely connected with the thyreo-arytaenoideus is a bundle of fibres of fairly 

 regular occurrence, called the thyreo -epiglottic muscle [m. thyreoepiglotticus] 

 (fig. 981). It originates from the inner surface of the thyreoid lamina and pro- 

 ceeds upward and backward to end in the quadrangular membrane and to become 

 attached to the lateral border of the epiglottis. 



The ary-mcmhranosus and ary-epiglolHc muscles are inconstant fascicles of the constrictor 

 group which run in the ary-epiglottic fold and become fixed into the quadrangular membrane 

 and margin of the epiglottic cartilage. 



Summary of the Actions of the Laryngeal Muscles 



According to their actions, the laryngeal muscles may be divided into — (a) those which 

 effect the tension of the vocal folds; (b) those which control the rima glottidis; (c) those which 

 effect the closure of the laryngeal aperture and vestibule. 



(a) The vocal ligaments are made tense by the action of the crico-thyreoid, the lateral and 

 posterior cricoarytsenoid and the transverse arytenoid muscles. The vocal ligaments are re- 

 laxed as the result of the action of the external thyreo-aryta^noid and vocal muscles. 



(b) The rima glottidis is widened by the crico-arytamoidous posterior and made narrow 

 by the contraction of the aryta^noids. The crico-arytajnoideus lateralis also assists in closing 

 the rima glottidis by rotating the vocal processes medialward, and if the crico-arytajnoideus 

 posterior contracts sinmltaneously, it aids in the closure. The vocal ligaments are approxi- 

 mated also by the thyreo-arytajnoideus [externus]. 



(c) The laryngeal aperture and vestibule are closed mainly by the arytienoideus transversus 

 and thyreo-aryta;noideus (externus), by which the arytu'noid cartilages are brought into apposi- 

 tion and drawn toward the epiglottis. Other muscles derived from the constrictor group, 

 arytajnoideus obliquus and ary-epiglotticus assist in closing the laryngeal aperture. 



CAVrrY OF Till] LARYNX AND LARYNGEAL MUCOSA 



The cavity of the larynx [cavum laryngis] is relatively narrow and does not 

 correspond in sliapc^ with tli(! outer sui'faec^ of the organ. Its form is shown in 

 fig. 9S() taken from a cast of the laryngeal cavity and tlie s])a('('s continuous with 

 it. Its walls are covered throughout by the mucous membrane of the larynx 

 (figs. 987,988). 



"^rhc mucosa of the larynx is continuous above with the mucous membrane 

 of the i)harynx, bellow with that of the trachea (figs. 970, 971). At the root of 

 the tongue the pharyngeal mucosa is refiected l^ackward to the anterior surface 

 of the epiglottis, presenting tiie median and- lateral glosso-epiglottic folds [plica 



