RECURRENT LARYXGEAL NERVES. 221 



the pharynx. The function of these filaments is sufficiently 

 evident. 



The inferior laryngeals contain chiefly motor filaments, 

 judging from their distribution as well as from the effects 

 of direct irritation. All who have experimented upon these 

 nerves have noted little or no evidence of pain when they 

 are stimulated or divided. 



One of the most important functions of the recu'rrents is 

 connected with the production of vocal sounds. In another 

 volume, we have fully treated of th'e mechanism of the voice 

 and the action of the intrinsic muscles of the larynx ; 1 and 

 in our account of the physiology of the internal, or com- 

 municating branch from the spinal accessory to the pneu- 

 mogastric, it has been shown that this is the true nerve of 

 phonation. 8 In the older works upon physiology, before the 

 functions of the spinal accessory were fully understood, the 

 experiments on the inferior laryngeals led to the opinion 

 that these were the nerves ol phonation, as they showed loss 

 of voice following their division in living animals. It is 

 true that these nerves contain the filaments which preside 

 over the vocal movements of the larynx ; but it is also the 

 fact that these vocal filaments are derived exclusively from 

 the spinal accessory, and that the recurrents contain as well 

 motor filaments which preside over movements of the larynx 

 not concerned in the production of vocal sounds. 



The muscles of the larynx concerned in phonation are, 

 the crico-thyroids, animated by the superior laryngeals, and 

 the arytencid, the lateral crico-arytenoids, and the thyro- 

 arytenoids, animated by the inferior laryngeals. The poste- 

 rior crico-arytenoids are respiratory muscles ; and it is curi- 

 ous that these are not affected by extirpation of the spinal 

 accessories, but that the glottis is still capable of dilatation, 

 so that inspiration is not -impeded. If, however, the spinal 

 accessories be extirpated, and the larynx be then exposed 

 in a living animal, the glottis still remains dilated, but will 



1 See vol. ill, Voice and Speech, p. 490, et seq. 8 See page 170, et sey. 



