LARYNGEAL NERVES 537 



and the reflex phenomena of deglutition are influenced by this section. 

 So far as one can judge from the distribution of the filaments to the 

 mucous membrane, it would seem that they combine with the pharyngeal 

 filaments of the fifth, and possibly with sensory filaments from the 

 glosso-pharyngeal, in giving general sensibility to these parts. 



In experiments on the reflex phenomena of deglutition, it has been 

 shown that the action of the pharyngeal muscles can not be excited by 

 stimulation of the mucous membrane of the supralaryngeal region and 

 the pharynx after section of the fifth and of the superior laryngeal 

 branches of the pneumogastrics. This would seem to indicate that the 

 pharyngeal branches of the pneumogastrics are of little importance in 

 these reflex phenomena. 



Properties and Uses of the Superior Laryngeal Nerves. The stimu- 

 lation of these nerves produces intense pain and contraction of the 

 crico-thyroids ; but it has been shown by experiment that the arytenoid 

 muscles, through which the nerves pass, receive no motor filaments. 

 The influence of the nerves on the muscles resolves itself into the action 

 of the crico-thyroids, which has been treated of fully under the head 

 of phonation. When these muscles are paralyzed the voice becomes 

 hoarse. The filaments to the inferior muscles of the pharynx are few 

 and comparatively unimportant. The superior laryngeals do not receive 

 their motor supply from the spinal accessory. 



The sensory filaments of the superior laryngeals have important 

 uses connected with the protection of the air-passages from the entrance 

 of foreign matters, particularly in deglutition ; and they also are con- 

 cerned in the reflex action of the constrictors of the pharynx. When 

 both superior laryngeals have been divided in living animals, liquids 

 often pass in small quantity into the larynx, owing to the absence of the 

 reflex closure of the glottis when foreign matters are brought in con- 

 tact with its superior surface, and the occasional occurrence of inspira- 

 tion during deglutition. 



Aside from the protection of the air-passages, the superior laryngeal 

 is one of the sensory nerves through which the reflex acts in deglutition 

 operate. There are certain parts that depend for their sensibility entirely 

 on this nerve ; namely, the mucous membrane of the epiglottis, of the 

 aryteno-epiglottidean fold and of the larynx as far down as the true 

 vocal chords. W T hen an impression is made on these parts, as when 

 they are touched with a piece of meat, regular and natural movements 

 of deglutition ensue. 



If the superior laryngeal nerves are divided and a stimulus is applied 

 to their central ends, movements of deglutition are observed, and there 

 also is arrest of the action of the diaphragm. From these experiments, 



