438 THE NERVOUS SYSTEM. 



tongue from which the clearest sensations of taste are derived, 

 are the base, as far as the foramen caecum and lines diverging 

 forwards on each side from it ; the posterior palatine arches 

 down to the epiglottis; the tonsils and upper part of the 

 pharynx over the root of the tongue. These are the seats of 

 the distribution of the glosso-pharyngeal nerve. The anterior 

 dorsal surface, and a portion of the anterior and inferior sur- 

 face of the tongue, in which the lingual branch of the fifth is 

 alone distributed, conveyed no sense of taste in the majority 

 of the subjects of Valentin's experiments ; but even if this were 

 generally the case, it would not invalidate the conclusion that, 

 in those who have the sense of taste in the anterior and upper 

 part of the tongue, the lingual branch of the fifth is the nerve 

 by which it is exercised. 



Physiology of the Pneumogastric Nerve. 



The pneumogastrie nerve, nervus vagus, or par vagwn (Fig. 

 151), has, of all the cranial and spinal nerves, the most various 

 distribution, and influences the most various functions, either 

 through its own filaments, or those which, derived from other 

 nerves, are mingled in its branches. 



The parts supplied by the branches of the pneumogastrie 

 nerve are as follows : By its pharyngeal branches, which enter 

 the pharyngeal plexus, a large portion of the mucous mem- 

 brane, and, probably, all the muscles of the pharynx ; by the 

 superior laryugeal nerve, the mucous membrane of the under 

 surface of the epiglottis, the glottis, and the greater part of 

 the larynx, and the crico-thyroid muscle ; by the inferior 

 laryngeal nerve, the mucous membrane and muscular fibres 

 of the trachea, the lower part of the pharynx and larynx, and 

 all the muscles of the larynx, except the crico-thyroid ; by 

 cesophageal branches, the mucous membrane and muscular 

 coats of the oesophagus. Moreover, the branches of the pneu- 

 mogastrie nerve form a large portion of the supply of nerves 

 to the heart and the great arteries through the cardiac nerves, 

 derived from both the trunk and the recurrent nerve ; to the 

 lungs, through both the anterior and the posterior pulmonary 

 plexuses ; and to the stomach, by its terminal branches pass- 

 ing over the walls of that organ ; while branches are also dis- 

 tributed to the liver and to the spleen. 



From the parts thus enumerated as receiving nerves from 

 the pneumogastrie, it might be assumed that this latter is a 

 nerve of mixed function, both sensitive and motor. Experi- 

 ments prove that it is so from its origin, for the irritation of 

 its roots, even within the cranial cavity, produces both pain 



