440 THE NERVOUS SYSTEM. 



glottis unaffected, but deprives it of its sensibility. 4. The 

 motions of the oasophagus are dependent on motor fibres of 

 the pneumogastric, and are probably excited by impressions 

 made upon sensitive fibres of the same ; for irritation of its 

 trunk excites motions of the oesophagus, which extend over 

 the cardiac portions of the stomach ; and division of the trunk 

 paralyzes the ossophagus, which then becomes distended with 

 the food. 5. The cardiac branches of the pneumogastric 

 nerve are one, but not the sole channel through which the in- 

 fluence of the central organs and of mental emotions is trans- 

 mitted to the heart. 6. The pulmonary branches form the 

 principal, but not the sole channel by which the impressions 

 on the mucous surface of the lungs that excite respiration, are 

 transmitted to the medulla oblongata. Dr. Keid 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 fila- 

 ments of the superior laryngeal branch of the pneumogastric ; 

 and the impression conveyed to the medulla oblongata, whe- 

 ther it produce sensation or not, is reflected to the filaments of 

 the recurrent or inferior laryngeal branch, and excites con- 

 traction of the muscles that close the glottis. Both these 

 branches of the pneumogastric co-operate also in the produc- 

 tion and regulation of the voice ; the inferior laryngeal deter- 

 mining the contraction 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. 182). 



