EXTERNAL BRANCH, OF THE SPINAL ACCESSORY. 177 



bility of the filaments that join the pneumogastric to become 

 extinct ; but the experiment is sufficient to show the direct 

 inhibitory influence of the spinal accessory on the heart. 

 The subject will be more fully considered, however, in con- 

 nection with the functions of the pneumogastrics. 



Functions of the External, or Muscular Branch of the 

 Spinal Accessory. The most interesting feature ' in the 

 recent researches into the functions of the spinal accessory 

 is, that experimentalists have been able to separate physio- 

 logically the internal from the external branch. Observa- 

 tions have conclusively demonstrated that the internal 

 branch, and the internal branch only, is directly concerned 

 in the vocal movements of the larynx, and, to a great ex- 

 tent, in the closure of the glottis during deglutition. It has 

 been noted, in addition, that animals in which both branches 

 have been extirpated present irregularity of the movements 

 of the anterior extremities and suffer from shortness of 

 breath after violent muscular exertion. The use of the cor- 

 responding extremities in the human subject is so different, 

 that it is not easy to make a direct application of these ex- 

 periments ; still, we can draw from them certain inferences 

 with regard to the functions of the external branch in man. 



In prolonged vocal efforts, the vocal cords are put upon 

 the stretch, and the act of expiration is very different from 

 that in tranquil breathing. In singing, for example, the 

 shoulders are frequently fixed ; and this is done to some ex- 

 tent by the action of the sterno-cleido-mastoid and the trape- 

 zius. "We may suppose, then, that the action of the branch 

 of the spinal accessory which goes to these muscles has a cer- 

 tain synchronism with the action of the branch going to the 

 larynx and the pharynx ; the one fixing the upper part of 

 the chest so that the expulsion of the air through the glottis 

 may be more nicely regulated by the expiratory muscles, 

 and the other acting upon the vocal cords. 1 



1 It is unnecessary to make any further reference in detail to the admirable 



