356 PULMONARY MUCOUS TISSUE. 



the vocal cord, and what we have said of its structure suffi- 

 ciently proves that it is admirably adapted to this end. 1 



The different degrees of contraction of the glottis have also 

 the effect of increasing or diminishing the production of 

 sounds : as the glottis becomes more contracted the sound 

 becomes sharper, and when it reaches the highest possible 

 pitch, the glottis can contract no more without being entirely 

 obliterated (we are speaking of the ordinary voice; there 

 appears to be a special arrangement in regard to what is 

 called the head-voice, or falsetto). 



The anatomical arrangement of the parts obliges the vocal 

 (anatomical) cords to relax as the glottis closes. Yet if 

 these cords formed the vibrating organ, the sounds produced 

 would be lower in proportion to the amount of closure of the 

 lips of the glottis; the narrowness of the aperture, it is true, 

 increases the intensity of the current of air, and may thus 

 help to render the sounds higher ; but the whole process is 

 much more simple if we admit that it is the muscle which 

 vibrates : as in contracting, it contributes to the obliteration 

 of the glottis, and even serves to close it entirely; so 

 when it becomes more contracted, or stretched, it can vibrate 

 more readily. 



The elastic cords, which are called vocal, perform only an 

 accessory part in phonation, that of serving as an intermedium 

 between the mucous membrane and the muscle ; they no more 

 prevent the muscle from vibrating than the soft parts surround- 

 ing the orbicularis of the lips prevent this muscle from vibrat- 

 ing, as, for instance, when playing on the horn. 



The vibrations of the thyro-arytenoid muscle are also 

 assisted by the ventricles of the larynx, whose only office is 

 to give this muscle greater freedom in working (Fig. 92). 



Parts connected with the Organs of the Voice. The sound 

 produced by the glottis is increased by the vibrations of those 

 portions of the air-tube which are above and below the 

 larynx. Special movements, also, take place in these parts, 

 during the production of sounds. Thus, during the emission of 



1 See Henle, " Handbuch der Systematischen Anatomie des 

 Menschen." 1866, Vol. II. p. 259. "The muscular fibres so 

 encroach upon the vocal cords, and are so closely united to the 

 elastic tissue, that we cannot suppose that the elastic fibres vibrate 

 alone, and that the muscular fibres withdraw from the folds of the 

 mucous. . . . The chief utility of the elastic tissue consists in its 

 power of contracting without forming folds and wavy lines, as is 

 the case with some ligaments of the vertebral column. " 



