560 NERVOUS SYSTEM. 



results were more satisfactory. After division of the nerve upon one side, 

 the voice became hoarse. As the filaments were divided upon the opposite 

 side, the voice was enfeebled, until finally it became extinct. The sound 

 emitted afterward was one which could in nowise be called voice (" qui neuti- 

 quam vox appellari potuit"). This experiment was made in the presence of 

 Tiedemann and Seubertus and was not repeated. 



Bernard, who determined exactly the influence of the spinal accessory 

 over the vocal movements of the larynx, first repeated the experiments of 

 Bischoff ; but the animals operated upon died so soon, from haemorrhage or 

 other causes, that his observations were not satisfactory. After many unsuc- 

 cessful trials, he succeeded in overcoming all difficulties, by following the 

 trunk of the nerve back to the jugular foramen, seizing it here with a strong 

 forceps and drawing it out by the roots. The operation is generally most 

 successful in cats, although Bernard succeeded frequently in other animals. 



When one spinal accessory is extirpated, the vocal sounds are hoarse and 

 unnatural. When both nerves are torn out, in addition to the disturbance 

 of deglutition and the partial paralysis of the sterno-mastoid and trapezius 

 muscles, the voice becomes extinct. Animals operated upon in this way 

 move the jaws and make evident eiforts to cry, but no vocal sound is emitted. 

 Bernard kept animals, with both nerves extirpated, for several months and 

 did not observe any return of the voice. His observations, which have been 

 fully confirmed, show that the internal branch of the spinal accessory is the 

 nerve of phonation. The filaments which preside over the vocal movements 

 of the larynx pass in greatest part through the recurrent laryngeal branches 

 of the pneumogastrics ; but the recurrent laryngeals also contain motor fila- 

 ments from other sources, which latter are concerned in the respiratory move- 

 ments of the glottis. 



Influence of the Internal Branch of the Spinal Accessory upon Degluti- 

 tion. 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 can not be completely closed to prevent the entrance 

 of foreign bodies into the air-passages. In rabbits particularly, it has been 

 noted that particles of food penetrate the trachea and find their way into the 

 lungs. 2. The spinal accessory furnishes filaments to the pharyngeal branch 

 of the pneumogastric, and through this nerve, it directly affects the muscles 

 of deglutition ; but the muscles animated in this way by the spinal accessory 

 have a tendency to draw the lips of the glottis together, while they assist in 

 passing the alimentary bolus into the oesophagus. When these important 

 acts are wanting, there is some difficulty in the process of deglutition itself, 

 as well as danger of the passage of foreign particles into the larynx. 



Influence of the Spinal Accessory upon the Heart. The spinal accessory 

 furnishes to the pneumogastric the inhibitory fibres which influence the 

 action of the heart. A sufficiently powerful Faradic current, passed through 

 one pneumogastric only, will in some animals arrest the cardiac movements. 

 Waller found that if he extirpated the spinal accessory upon one side, after 

 four or five days the action of the heart could not be arrested by stimulating 



