THE LARYNX 



1081 



Posteriorly it is limited by the mucous membrane passing between the arytenoid 

 cartilages. The rima glottidis is the .narrowest part of the cavity of the larynx, 

 and its level corresponds with the bases of the arytenoid cartilages. Its length, 

 in the male, is about 23 mm.; in the female from 17 to 18 mm. The width 

 and shape of the rima glottidis vary with the movements of the vocal folds 

 and arytenoid cartilages during respiration and phonation. In the condition 

 of rest, i. e., when these structures are uninfluenced by muscular action, as in 

 quiet respiration, the intramembranous part is triangular, with its apex in front 

 and its base behind the latter being represented by a line, about 8 mm. long, 

 connecting the anterior ends of the vocal processes, while the medial surfaces of 

 the arytenoids are parallel to each other, and hence the intercartilaginous part 

 is rectangular. During extreme adduction of the vocal folds, as in the emission 

 of a high note, the intramembranous part is reduced to a linear slit by the ap- 

 position of the vocal folds, while the intercartilaginous part is triangular, its apex 

 corresponding to the anterior ends of the vocal processes of the arytenoids, which 

 are approximated by the medial rotation of the cartilages. Conversely in extreme 

 abduction of the vocal folds, as in forced inspiration, the arytenoids and their 



Median glosso-epiglottic fold 

 Vallecvla I Epiglottis 



\ / /Tubercle of epiglottis 



/ -/"^ 



. Vocal fold 



Ventricular fold. 



Aryepiglottic fold 

 Cuneiform cartilage 



Corniculate cartilage 



Trachea 

 Fia. 956. Laryngoscopic view of interior of larynx. 



vocal processes are rotated lateralward, and the intercartilaginous part is trian- 

 gular in shape but with its apex directed backward. In this condition the entire 

 glottis is somewhat lozenge-shaped, the sides of the intramembranous part 

 diverging from before backward, those of the intercartilaginous part diverging 

 from behind forward the widest part of the aperture corresponding with the 

 attachments of the vocal folds to the vocal processes. 



Muscles. The muscles of the larynx are extrinsic, passing between the larynx 

 and parts around these have been described in the section on Myology; and 

 intrinsic, confined entirely to the larynx. 



The intrinsic muscles are: 



Cricothyreoideus. 

 Cricoaryta?noideus posterior. 



Cricoarytsenoideus lateralis. 

 Aryteenoideus. 



Thyroarytsenoideus. 



The Cricothyreoideus (Cricothyroid) (Fig. 957), triangular in form, arises from the 

 front and lateral part of the cricoid cartilage ; its fibers diverge, and are arranged 

 in two groups. The lower fibers constitute a pars obliqua and slant backward 

 and lateralward to the anterior border of the inferior cornu; the anterior fibers, 

 forming a pars recta, run upward, backward, and lateralward to the posterior part 

 of the lower border of the lamina of the thyroid cartilage. 



