122 INNERVATION. [CHAP. xx. 



been made the subject, accord in a striking manner with the con- 

 clusions deducible from anatomy. Thus mechanical and galvanic 

 irritation of the pharyngeal branches has always produced contrac- 

 tions of the pharynx : irritation of the superior laryngeal nerve 

 causes contraction of the crico- thyroid muscle only, whilst that of 

 the inferior laryngeal causes forcible contraction of the laryngeal 

 muscles as well as of the inferior constrictor of the pharynx. In a 

 living animal the slightest touch to the mucous membrane of the 

 glottis will cause the instant closure of that fissure, if the superior 

 laryngeal nerve be uninjured, but if that nerve be divided on both 

 sides, the glottis may be irritated with impunity. It is plain then 

 that the inferior laryngeal is the principal motor nerve of the larynx, 

 and that the superior laryngeal is at once its sensitive nerve, and 

 the excitor of the motor action of the inferior laryngeal through the 

 medulla oblongata. 



It is scarcely necessary to remark how untenable is the opinion 

 advocated by Majendie, that an antagonism exists between the su- 

 perior and inferior laryngeal nerves, the one acting upon the con- 

 strictors, the other upon the dilators of the larynx. The superior 

 laryngeal nerve supplies, as we have seen, only one muscle, and the 

 inferior, to which he assigns the office of opening the glottis, sup- 

 plies those muscles which are the principal agents in closing it. 



Impairment or destruction of vocal power is a constant accom- 

 paniment to injury or complete section of the recurrent nerve. 



An interesting experiment of Dr. J. Reid illustrates the power of 

 each laryngeal nerve respectively. When the inferior laryngeals 

 were cut, the superior remaining intact, a probe introduced into the 

 glottis occasioned signs of pain and efforts to cough, without any 

 contraction of the glottis. But when the superior laryngeal nerves 

 were cut, the recurrents being unimpaired, the probe could be 

 introduced without exciting any irritation or effort whatever. 



This experiment demonstrates unequivocally, that the spasmodic 

 action induced in the larynx by the application of a stimulus to its 

 mucous membrane must be referred to the class of physical nervous 

 actions, and results from the influence of the superior laryngeal upon 

 the inferior, through the connexion of their respective points of im- 

 plantation in the nervous centre. 



There can be no doubt that the motions of the oesophagus are re- 

 gulated by the various oesophageal fibres given off from this nerve, in 

 its course through the thorax. Irritation of its trunk has always pro- 

 duced contractions of the oesophagus, as testified by many experi- 

 menters. These contractions, Dr. Reid states, extended throughout 



