NEKVOUS SYSTEM. 



ments tliat have demonstrated the influence of the spinal 

 accessory nerve over these muscles have pointed out the des- 

 tination of the fibres that join the pneumogastric, which could 

 never have been done so satisfactorily by dissection. They 

 have shown further that the movements involved in phona- 

 tion are more or less independent of the respiratory move- 

 ments of the larnyx. 



If the larnyx be exposed in a living animal, with all its 

 nervous connections intact, it w r ill be seen to open widely 

 during inspiration, being passive in expiration. The wide 

 opening of the glottis at this time is due to the fact that, 

 after the operation, respiration is usually more or less la- 

 bored ; but if we carefully observe the parts when the respira- 

 tory acts are perfectly tranquil, the movements of the glottis 

 seem to be very slight. The larynx is then permanently 

 opened to a moderate degree, but the chink of the glottis is 

 slightly dilated with each expiration. If the recurrent laryn- 

 geal nerves, which are distributed to all of the muscles of 

 the larynx except the crico-thyroid, be now divided upon 

 both sides, the larynx is entirely paralyzed, and in cats and 

 young animals, in which the cartilages are soft and flexible, 

 the parts are occluded by the effort of inspiration, and death 

 takes place from suffocation. Of course the division of the 

 recurrent laryngeal nerves abolishes the voice, but it arrests 

 the other movements of the larynx as well. The distinction 

 thus established between the action of the spinal accessory 

 and the recurrent laryngeal nerves was fully illustrated by 

 Bernard, in the following experiments : 



In a cat, in which the voice had been completely de- 

 stroyed by extirpation of both spinal accessory nerves, the 

 larynx was exposed. The glottis was seen dilated so as to 

 permit the free passage of air in respiration. The mucous 

 membrane retained its sensibility, and when the interior of 

 the larynx was irritated, a very slight but ineffectual effort 

 was made to close the glottis. It was impossible for the 

 animal to approximate the posterior points of attachment of 



