Vocal Cords in Quiet Respiration in Man, Sfc. 433 



First, the glottis in man is wider open during qniet respiration 

 (inspiration and expiration) than after death or after division of the 

 vagi or recurrent laryngeal nerves. 



Second, this wider opening during life is the result of a permanent 

 activity (tonus) of the abductors of the vocal cords (posterior crico- 

 arytenoid muscles) which, therefore, belong not merely to the class 

 of accessory, but of regular, respiratory muscles. 



Thirdly, the activity of these muscles is due to tonic impulses 

 which their ganglionic centres receive from the neighbouring respira- 

 tory centre in the medulla oblongata. It is very probable that these 

 impulses rhythmically proceed to the respiratory centre from the 

 stimulation of certain afferent fibres contained mainly, but not 

 exclusively, in the trunks of the pneumogastric nerves, and that they 

 are in the respiratory centre changed into tonic impulses. The 

 regular activity of the abductors of the vocal cords during life, there- 

 fore, belongs to the class of reflex processes. The permanent half- 

 contraction of these muscles, in which form their tonic innervation is 

 manifested, can be further increased, in concord with the general 

 laws of the mechanism of respiration, by either volition or other reflex 

 influences. 



Fourthly, in spite of their extra innervation, the abductors of the 

 vocal cords are physiologically weaker than their antagonists. 



Fifthly, these antagonists, the adductors of the vocal cords, have 

 primarily nothing at all to do with respiration and ordinarily serve 

 the function of phonation only. Their respiratory functions are 

 limited to 



(a.) Assistance in the protection of the lower air passages against 



the entry of foreign bodies ; 

 (6.) Assistance in the modified and casual forms of expiration 



known as cough and laughing. 



VOL. XLVIII. 2 H 



