RESPIRA TION 149 



peripheral ends stimulated, adduction of the larynx is obtained ; 

 but if the ether narcosis be pushed to a dangerous extent and 

 the nerves then stimulated the glottis dilates, that is, abduction 

 follows. These and other observations have furnished a law 

 which is of clinical significance — viz., that in functional disturb- 

 ance of the larynx the adductor muscles are first affected, but 

 that in changes accompanied by organic lesions the abductor 

 muscles are the first to suffer. 



When one recurrent laryngeal nerve is divided, the vocal 

 cord on that side remains immovable and therefore cannot 

 approach its fellow ; the healthy cord endeavours to com- 

 pensate for the weakness of its companion by passing beyond 

 the middle line of the larynx in its attempt to come into contact 

 with it. 



The inspiratory distress occasioned in ' roaring ' is not brought 

 about, as has been described, by a paralysed vocal cord flapping 

 about, for the elastic nature of the cord, and the fact that the 

 only muscle never affected with paralysis is the one which helps 

 to keep the vocal cord tense, negative this. The sound is pro- 

 duced by the paralysed left arytenoid cartilage being drawn 

 into the glottis at each inspiration, and this is the explanation 

 why the noise which accompanies the disease is always inspiratory 

 and never expiratory. 



Phonation. — Voice is produced by the approximation and 

 vibration of the vocal cords, the pitch of the voice being produced 

 by the tension of the cords, whilst the quality is due to the shape 

 of the cords — viz., their thickness or thinness. The position of 

 the resonant chambers such as the mouth, pharynx, posterior 

 nares, and even nasal chambers also importantly affects the 

 quality of the voice. It is obvious that the chief alterations in 

 the larynx during phonation refer to the vocal cords ; these are 

 approximated by the adductor muscles, and separated by the 

 abductor muscles, whilst they are relaxed by the thyro- 

 arytenoideus and tightened by the crico-thyroid. The latter 

 muscle has a peculiar action ; it lowers the thyroid cartilage on 

 the cricoid and swings the wing of the thyroid outwards, thus 

 rendering the cords tense. These changes in the vocal cord 

 produce changes in the shape of the V-shaped glottal opening ; 

 in a high note the glottis is reduced to a mere slit, in deeper notes 

 the cords are separated. If air be forced through the larynx 

 of a dead horse and the tension of the cords altered, a sound 

 remarkably like a neigh may be produced. The ventricles of 

 the larynx and cavities of the mouth, nose, pharynx, etc., act 

 as resonators. Being filled with air, they effect the needful 

 alterations in the quality of the voice, and assist in giving it its 

 distinctive character ; thus the false nostrils furnish the ' snort ' 



