CRANIAL NERVES. 44? 



was the only result. If the nerve on one side is cut the 

 subject gets hoarse, though not aphonic. 



It is remarkable in connection with the control exercised 

 by this nerve over the muscles of the larynx, that when the 

 former is paralysed or divided, the loss of motor power in 

 the latter is associated with inability to close the glottis ; 

 whereas, after division of the pneumogastric or recurrent 

 nerves, the absence of motor power in the larynx is asso- 

 ciated with a closed condition of the glottis, which the 

 animal cannot obviate. In the former case, respiration is 

 free, but pellets of food fall through the glottis during de- 

 glutition, and irritate the air-passages. In the latter, food 

 does not readily enter the air-passages during swallowing, 

 but inspiration is rendered difficult, as is well exemplified 

 in the case of the roarer. According to Bernard, therefore, 

 the fibres of the spinal accessory convey to the larynx the 

 influence necessary to the production of vocal sound, which 

 is to some extent incompatible with respiration, while the 

 proper fibres of the pneumogastric, rendered to the laryngeal 

 muscles through the recurrent nerve, preside, on the other 

 hand, over respiration. In this we meet with a substantia- 

 tion of Sir Charles Bell's opinion, that when an organ re- 

 ceives nerves from different sources, it is not for the purpose 

 of increasing the nervous force, but to convey to it nervous 

 influences of different kinds. 



It seems probable that the external branch of the spinal 

 accessory, which is supplied to the levator humeri and 

 trapezius muscles of the neck, has likewise a purpose to 

 perform, for which the cervical motor nerves furnished to 

 the same muscles are not fitted ; and Bernard is of opinion 

 that it is in movements incompatible with respiration, as 

 severe straining and the like, that they are had into re- 

 quisition. 



