INTERNAL BRANCH OF THE SPINAL ACCESSORY. 175 



the vocal cords, or to put the cords on the stretch. If such 

 irritation be applied to the larynx of an animal wi'th the 

 spinal accessory nerves intact, the glottis is instantly and 

 firmly closed. 1 



In a cat about five weeks old, both spinal accessory 

 nerves were extirpated, and the voice was thus destroyed. 

 Two days after, both recurrent laryngeal nerves were di- 

 vided, and the animal died almost immediately of suffo- 

 cation. 2 



These experiments show conclusively that the internal, 

 or communicating branch of the spinal accessory is the 

 nerve which presides over the movements of the larynx in 

 phonation. The filaments undoubtedly pass to the larynx 

 in greatest part through the recurrent laryngeal branches of 

 the pneumogastric ; but the recurrent laryngeals also con- 

 tain motor filaments from other sources, which are chiefly 

 concerned in the respiratory movements of the glottis. 



Influence of the Internal Branch of the Spinal Accessory 

 upon Deglutition. We must refer again to the experiments 

 of Bernard for an account of the influence of the spinal 

 accessory upon deglutition. There are two ways in which 

 deglutition is affected through this nerve: 1. When the 

 larynx is paralyzed as a consequence of extirpation of both 

 nerves, the glottis cannot be completely closed to pre- 

 vent the entrance of foreign bodies into the air-passages. 

 In rabbits particularly, it was rioted that particles of food 

 penetrated the trachea and found their way into the lungs. 3 

 2. The spinal accessory furnishes numerous filaments to the 

 pharyngeal branch of the pneumogastric, and, through this 

 nerve, directly affects the muscles of deglutition ; but the 

 muscles animated in this way by the spinal accessory have a 



1 BERNARD, op. 7., p. 745. 

 8 Loc. tit., p. 749. 



3 BERNARD, Lemons sur la physiologic et la pathologie d*. systbne nervevx, 

 Paris, 1858, tome ii., p. 323. 

 112 



