5i6 NERVOUS SYSTEM 



After many unsuccessful trials, he succeeded in overcoming all difficul- 

 ties 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 usually is most successful in cats, although Bernard fre- 

 quently succeeded 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 dis- 

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

 and trapezius muscles, the voice becomes extinct. Animals operated on 

 in this way move the jaws and make evident efforts 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 (Flint), show that the in- 

 ternal branch of the spinal accessory is the nerve of phonation. The 

 filaments that preside over the vocal movements of the larynx pass in 

 greatest part through the recurrent laryngeal branches of the pneumo- 

 gastrics ; but the recurrent laryngeals also contain filaments from other 

 motor nerves, which latter are concerned in the respiratory movements 

 of the glottis. 



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

 tion. There are two ways in which deglutition is affected through this 

 nerve : i. 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 passage 

 of foreign particles into the larynx. 



Influence of tJie Spinal Accessory on tJie Heart. The spinal accessory 

 furnishes to the pneumogastric the inhibitory fibres that influence the 

 action of the heart. A sufficiently powerful faradic current passed 

 through one pneumogastric will in some animals arrest the cardiac 

 movements ; and it has been noted that the influence of the right nerve 

 on the heart is greater than that of the left. Waller found that if he 

 extirpated the spinal accessory on one side, after four or five days the 

 action of the heart could not be arrested by stimulating the pneumogas- 

 tric of the same side ; but inhibition followed stimulation of the pneumo- 



