158 Vocal Cords in Quiet Respiration in Man, Sj-c. [June 12, 



This arrangement could consist either in a rhythmical opening of 

 the glottis synchronous with each inspiration, or in a tonic dilatation 

 of the glottic space during both phases of respiration. 



It having been shown that, though both these alternatives are 

 actually met with, the latter is much more representative of the 

 participation of the larynx in quiet respiration of man than rhythmic 

 movements, it remained to be investigated, as previously mentioned, 

 whether this tonic widening represents a state of tonic innervation of 

 both the glottis-openers and glottis-closers, with preponderance of the 

 former, or, on the other hand, a tonic innervation of the glottis- 

 openers alone. 



This question is discussed at length, and from anatomical, physio- 

 logical, pathological, and experimental reasons the conclusion is 

 arrived at that the glottis-openers (posterior crico-aryteenoid muscles) 

 alone are, during life, in a state of semi-tonic contraction. 



The only remaining question, viz., whether this tonus is automatic 

 or reflex, is answered, on the basis of experimental evidence, to the 

 effect that in all probability the tonus of the abductor muscles is of a 

 reflex character, and that the impulses acting upon their ganglionic, 

 i.e., bulbar, centres, are mainly, though not exclusively, conducted 

 along the pneumogastric nerves. The experiments upon which thia 

 conclusion is based (division of the pneumogastric nerves below the 

 points from which the recurrent laryngeal nerves are given off), and 

 which were kindly performed for the author by Professor Victor 

 Horsley, are communicated in full in the paper. 



The final conclusions arrived at by the author are as follows : 



1. The glottis in man is wider open during quiet respiration (in- 

 spiration and expiration) than after death or after division of the 

 vagi or recurrent laryngeal nerves. 



2. This wider opening during life is the result of a permanent activity 

 of the abductors of the vocal cords (posterior crico-aryttenoid 

 muscles), which therefore belong cot merely to the class of accessory, 

 but of regular respiratory, muscles. 



3. The activity of these muscles is due to tonic impulses, which 

 their centres receive from the neighbouring respiratory centre in the 

 medulla oblongata. It is very probable that these impulses rhythmi- 

 cally 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, therefore, 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. 



