822 SPECIAL MUSCULAR MECHANISMS. 



in pairs. They are the essential muscles concerned in the movements of the 

 arytenoid cartilages and chordae vocales. The extrinsic muscles connect the 

 larynx with adjacent parts, and are for the most part concerned in the 

 elevation and depression of the organ. 



The larynx is lined with a mucous membrane which is continuous above 

 with that lining the pharynx and mouth, and below with that lining the 

 trachea. Above the chorda vocales it is lined with pavement epithelium, 

 excepting at the lower anterior portion, where it is ciliated ; below the 

 chordae vocales the epithelium is of a ciliated columnar variety. The mu- 

 cous membrane contains many mucous glands, which are pretty uniformly 

 distributed ; they are, however, very abundant in the part of the membrane 

 lining the sacculus laryngis.] 



756. A blast of air, driven by a more or less prolonged expiratory 

 movement, throws into vibrations two elastic membranes the chordce 

 vocales. These impart their vibrations to the column of air above them, 

 and so give rise to the sound which we call the voice. Since the sound is 

 generated in the vocal cords, we may speak of them and of those parts of 

 the larynx which decidedly affect their condition as constituting the essential 

 vocal apparatus ; while the chamber above the vocal cords, comprising the 

 ventricles of the larynx with the false vocal cords, the pharynx and the 

 cavity of the mouth, the latter varying much in form, constitutes a sub- 

 sidiary apparatus of the nature of a resonance tube, modifying the sound 

 originating in the vocal cords. In the voice, as in other sounds, we distin- 

 guish : 1, Loudness. This depends on the strength of the expiratory blast. 

 2, Pitch. This depends on the length and tension of the vocal cords. 

 Their length may be regarded as constant, or varying only with age. It 

 consequently determines the range only of the voice, and not the particular 

 note given out at any one time. The shrill voice of the child is deter- 

 mined by the shortness of the cords in infancy, and the voices of a soprano, 

 tenor, and baritone are all dependent on the respective length of their 

 vocal cords. Their tension is, on the contrary, variable ; and the chief 

 problems connected with the voice refer to variations in the tension of the 

 vocal cords. 3, Quality. This depends on the number and character of 

 the overtones accompanying any fundamental note sounded, and is deter- 

 mined by a variety of circumstances, chief among which is the physical 

 quality of the cords. 



757. The vocal cords, attached in front to the thyroid cartilage, end 

 behind in the processus vocales of the arytenoid cartilages. Hence a dis- 

 tinction has been drawn between the rirna vocalis, i. e., the opening bounded 

 laterally by the vocal cords, and the rima respiratoria, or space between the 

 arytenoid cartilages behind the processus vocales ; these names, however, 

 are not free from objections. In quiet breathing (Fig. 208, B) the two 

 form together a V sna P e( i space, which, as we have seen (p. 343), in deep 

 inspiration is widened into a rhomboidal opening by the divergence of the 

 processus vocales (Fig. 208, C ). When a note is about to be uttered, the 

 vocal cords are by the approximation of the processus vocales brought into 

 a position parallel to each other, and the whole rima is narrowed (Fig. 

 208, A). By their parallelism and by the narrowness of the interval be- 

 tween them the cords are rendered more susceptible of being thrown into 

 vibration by a moderate blast of air. The problems we have to consider 

 are, first, by what means are the cords brought near to each other or drawn 

 asunder as occasion demands ; and, secondly, by what means is the tension 

 of the cords made to vary. We may speak of these two actions as narrow- 

 ing or widening of the glottis, and tightening or relaxation of the vocal 

 cords. 



