604 



ARRANGEMENT OF THE LARYNX. 



that the glottis between them appears as a space having the form of 

 a myrtle leaf, must be fully stretched, so that the glottis assumes the 

 shape of a linear slit (Fig. 214). This compensation likewise is brought 

 about by the internal thyro-arytenoid muscle. It is this muscle, 

 moreover, that effects those delicate gradations of tension in the vocal 

 band itself that are necessary for the production of tones of slightly 

 different pitch. It is especially adapted for this purpose, as it comes 

 close to the edge of the vocal band and is firmly inserted into the elastic 

 tissue of the latter. The contracting muscle in addition gives to the 

 vibrating vocal band the resistance necessary for its vibrations. As 

 some of the fibers of the vocal muscle terminate in the elastic tissue of 

 the vocal band itself, they may impart increased tension to individual 

 segments of the vocal band, as a result of which modifications in tone- 

 formation are possible. It must, therefore, be assumed that the coarser 

 variations in tension are caused by separation of the thyroid cartilage 

 from the arytenoid cartilages, while the finer gradations of tension are 



induced by the vocal muscle. 

 The usefulness of the elastic 

 tissue in the vocal bands does 

 not consist so much in its ex- 

 tensibility, as in its property 

 of shortening without forming 

 folds or creases. 



Pathological. When these 

 muscles are paralyzed the voice 

 can be produced only by powerful 

 blasts, as much air escapes through 

 the glottis. At the same time the 

 tones are deep and impure. Uni- 

 lateral paralysis results in napping 

 of the corresponding vocal band. 



Relaxation of the vocal 

 bands occurs spontaneously 

 when the stretching forces 

 cease to act, the thyroid car- 

 tilage drawn forward and the 

 arytenoid cartilages fixed pos- 

 teriorly returning to the posi- 

 tion of rest in consequence of the elasticity that is peculiar to their 

 arrangement. Relaxation of the vocal bands may result also from the 

 action of the thyro-arytenoid and lateral crico-arytenoid muscles. 



From the foregoing it follows that tension of the vocal bands and 

 narrowing of the glottis are necessary for phonation. 



The epiglottis, which becomes more erect with high tones and falls 

 with low ones, has an influence on the timbre (clear or muffled) of the 

 voice, but has no effect on the pitch. 



The mucous membrane of the larynx, as well as the submucosa, is rich in 

 delicate, elastic networks of fibers. The submucosa is loose and yielding in the 

 region of the entrance to the larynx and the ventricles of Morgagni, a fact that 

 explains the enormous swelling that often occurs in connection with so-called 

 edema of the glottis. A clear, even, limiting layer lies beneath the epithelium. 

 The epithelium is stratified, cylindrical, and ciliated, interspersed with goblet-cells, 

 except on the true vocal bands and the upper surface of the epiglottis, where a 

 stratified, squamous epithelium covers the mucous membrane, which in this situa- 



FIG. 210. Diagrammatic Horizontal Section through the 

 Larynx, to Illustrate the Action of the Internal Thyro- 

 arytenoid Muscles in Narrowing the Glottis: //, //, Po- 

 sition of the arytenoid cartilages during quiet respiration. 

 The arrows indicate the direction of traction of the mus- 

 cles. /, /, Position of the arytenoid cartilages brought 

 about by action of these muscles. 



