566 THE CRANIAL NERVES. 



pharynx and fauces, and the state of dryness or moisture of the mucous 

 membrane lining the passages. 



The actual formation of the voice, or the production of sonorous 

 vibrations, takes place, therefore, exclusively in the larynx; while 

 articulation, or the division of the vocal sound into words and phrases 

 by vowels and consonants, is accomplished by the aid of the lips, 

 tongue, teeth, and palate. Consequently, division of the pneumogas- 

 tric nerve or of its inferior laryngeal branch on both sides, by para- 

 lyzing the muscles of the larynx which serve to approximate and extend 

 the vocal chords, produces among its other effects a loss of voice. Fur- 

 thermore, as the two functions of vocalization and articulation are 

 accomplished by distinct nervous and muscular actions, they may be 

 deranged independently of each other, by injury or disease of different 

 parts of the nervous system. That of articulation is regulated by the 

 action of the facial and hypoglossal nerves ; while vocalization is under 

 the control of the pneumogastric. 



Connection with Deglutition. The reflex act of deglutition, which 

 commences in the fauces and pharynx under the control of the glosso- 

 pharyngeal nerve, is continued and completed by the lower portion of 

 the pharynx and the tube of the oesophagus. These parts receive both 

 their sensitive and motor filaments exclusively from the pneumogastric 

 nerve, and it is under its influence that the food, once started upon its 

 downward passage, is conducted by the peristaltic action of the oesoph- 

 agus into the stomach. 



The inferior constrictor muscle of the pharynx and the cervical por- 

 tion of the oesophagus both receive filaments from the inferior laryngeal 

 nerve ; while the thoracic portion of the oesophagus is supplied entirely 

 from the trunk of the pneumogastric. Some fibres are also sent to the 

 inferior constrictor of the pharynx by the superior laryngeal nerve. 

 Deglutition, therefore, becomes incomplete, as shown by the experiments 

 of Bernard upon dogs, horses, and rabbits, by division of the pneumo- 

 gastric nerves in the middle of the neck. The masticated food is still 

 conveyed, by the action of the pharynx, from the fauces into the 

 oesophagus ; but here it accumulates, distending the inert walls of the 

 paralyzed canal, and finding its way into the stomach only in small 

 quantities and by the imperfect effect of compression from above. In 

 the natural condition, the process of swallowing is a connected series 

 of rapidly succeeding contractions, beginning at the fauces and ending 

 at the cardiac orifice of the stomach. Each portion of the mucous 

 membrane receives in turn a stimulus from the contact of the food, 

 which is followed by excitement of the corresponding muscles ; so that 

 the alimentary mass is carried rapidly from above downward by an 

 action which is reflex in character and independent of voluntary control. 

 Section of the pneumogastric nerves destroys at once sensibility and 

 motive power in the whole of the oesophagus, and thus interferes with 

 complete deglutition. 



There is no doubt that the sensitive nerves of the cesophageal mucous 



