THE CRANIAL NERVES. 487 



while articulation, or division of the sound into vowels and consonants, 

 words and phrases, is accomplished by the lips, tongue, teeth, and pal- 

 ate. Consequently, division of the pneumogastric nerve or of its inferior 

 laryngeal branch on both sides, produces loss of voice. Furthermore, 

 as vocalization and articulation are distinct nervous actions, they may 

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

 parts of the nervous system. The movements of articulation are regu- 

 lated by the facial and hypoglossal nerves ; while vocalization is under 

 the control of the pneumogastric. 



Connection icith Deglutition. The act of deglutition, which com- 

 mences in the fauces and pharynx, is continued and completed by the 

 lower portion of the pharynx and by the oesophagus. These parts 

 receive both their sensitive and motor filaments from the pneumogastric 

 nerve, and under its influence the food, once started on its downward 

 passage, is conducted by the peristaltic action of the oesophagus into 

 the stomach. 



The inferior constrictor of the pharynx and the cervical portion of 

 the oesophagus both receive filaments from the inferior laryngeal nerve ; 

 while the thoracic portion of the oesophagus is supplied from the trunk 

 of the pneumogastric. Deglutition, therefore, becomes incomplete, as 

 shown by Bernard in dogs, horses, and rabbits, by division of the 

 pneumogastric nerves in the neck. The masticated food is still con- 

 veyed by the pharynx from the fauces to the oesophagus ; but here it 

 accumulates, distending the walls of the paralyzed canal, and finding 

 its way into the stomach only in small quantities under the pressure 

 from above. The normal process of swallowing is accomplished by 

 a series of contractions, beginning at the fauces and ending at the 

 stomach. Each portion of the mucous membrane receives in turn a 

 stimulus from the contact of the food, followed by excitement of the 

 corresponding muscle ; so that the alimentary mass is carried rapidly 

 downward by reflex action, independent of voluntary control. Section 

 of the pneumogastric nerves destroys sensibility and motive power 

 in the oesophagus, and consequently interferes with deglutition. 



Protection of the Glottis in Deglutition. As the laryngeal orifice 

 communicates directly with the cavity of the pharynx, and as all solids 

 and liquids, in swallowing, pass over its surface, portions of the food 

 would find their way into the larynx unless there were some means for 

 its protection. The epiglottis, which stands in front of the glottis, and 

 shuts over it like a cover when the tongue is drawn back in degluti- 

 tion, might seem to be a safeguard in this respect. 



But experience shows that this organ is not essential to protect the 

 glottis in deglutition. It may be completely excised, in dogs, without 

 any subsequent difficulty in swallowing either liquid or solid food. 

 The epiglottis, furthermore, exists only in mammalians, being absent 

 in all other vertebrate animals. Finally, the epiglottis does not pre- 

 vent foreign substances passing into the larynx when the other con- 

 ditions of normal deglutition are disturbed. The protection of the 



