218 NERVOUS SYSTEM. 







The stimulation 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. 1 



The action of the nerves upon the muscles is very sim- 

 ple, and resolves itself into the function of the crico-thyroids, 

 which has been treated of fully under the head of phona- 

 tion. 3 When these muscles are paralyzed, the voice be- 

 comes hoarse. The filaments to the inferior muscles of the 

 pharynx are few and comparatively unimportant. It is im- 

 portant in this connection to note that the superior laryn- 

 geals do not receive their motor filaments from the spinal 

 accessory. 



The sensory filaments of the superior laryngeals have 

 Important functions connected with the protection of the 

 air-passages from the entrance of foreign matters, particu- 

 larly in deglutition, and are further concerned, as we shall 

 see, in the reflex action of the constrictors of the pharynx. 

 In treating of deglutition, in another volume, we have fully 

 discussed the importance of the exquisite sensibility of the 

 top of the larynx in the protection of the air-passages. 

 When both superior laryngeals have been divided in living 

 animals, liquids often pass into the larynx in small quantity, 

 owing to the absence of the reflex closure of the glottis 

 when foreign matters are brought in contact with its supe- 

 rior surface, and the occasional occurrence of inspiration 

 during deglutition. 3 



Aside from the protection of the air-passages, the supe- 

 rior laryngeal is one of the sensory nerves through which 

 the reflex acts in deglutition operate. There are certain parts 

 which depend for their sensibility entirely upon this nerve ; 

 viz., the mucous membrane of the epiglottis, the aryteno-epi- 

 glottidean fold, and the larynx, as far down as the true vocal 

 cords. When an impression is made upon these parts, as 



1 LONGET, Traite de physiologic, Paris, 1869, tome Hi., p. 525. 



2 See vol. iii., Voice and Speech, p. 495. z See vol. ii., Digestion, p. 19V. 



