560 THE NERVOUS SYSTEM. 



are transmitted to the medulla oblongata. Dr. Reid was 

 unable to determine whether they contain motor fibres. 



From these results, and by referring to what has been 

 said in former chapters, the share which the pneumogastric 

 nerve takes in the functions of the several parts to which 

 it sends branches, may be understood : 



1 . In deglutition, the motions of the pharynx are of the 

 reflex kind. The stimulus of the food or other substance 

 to be swallowed, acting on the filaments of the glosso- 

 pharyngeal nerve as well as the filaments of the superior 

 laryngeal given to the pharynx, and of some other nerves, 

 perhaps, with which these communicate, is conducted to the 

 medulla oblongata, whence it is reflected, chiefly through 

 the pneumogastric, to the muscles of the pharynx. 



2. In the functions of the larynx, the sensitive filaments 

 of the pneumogastric supply that acute sensibility by 

 which the glottis is guarded against the ingress of foreign 

 bodies, or of irrespirable gases. The contact of these 

 stimulates the filaments of the superior laryngeal branch 

 of the pneumogastric ; and the impression conveyed to the 

 medulla oblongata, whether it produce sensation or not, 

 is reflected to the filaments of the recurrent or inferior 

 laryngeal branch, and excites contraction of the muscles 

 that close the glottis. Both these branches of the pneumo- 

 gastric co-operate also in the production and regulation 

 of the voice ; the inferior laryngeal determining the con- 

 traction of the muscles that vary the tension of the vocal 

 cords, and the superior laryngeal conveying to the mind 

 the sensations of the state of these muscles necessary 

 for their continuous guidance. And both the branches 

 co-operate in the actions of the larynx in the ordinary 

 slight dilatation and contraction of the glottis in the acts 

 of expiration and inspiration, and more evidently in those 

 of coughing and other forcible respiratory movements 

 (p. 222). 



3. It is partly through their influence on the sensibility 



