228 HUMAN PHYSIOLOGY. 



branches to the base of the tongue ; palatal branches to the soft 

 palate, uvula, and tonsils ; pharyngeal branches to the mucous mem- 

 brane of the pharynx. 



Properties. Irritation of the roots at their origin calls forth 

 evidences of pain ; it is, therefore, a sensor nerve, but its sensibility 

 is not so acute as that of the trigeminal. Irritation of the trunk after 

 its exit from the cranium produces contraction of the muscles of the 

 palate and pharynx, owing to the presence of motor fibers. 



Division of the nerve abolishes sensibility in the structures to 

 which it is distributed and impairs the sense of taste in the posterior 

 third of the tongue (see Sense of Taste). 



Function. Governs the sensibility of the pharynx, presides partly 

 over the sense of taste, and controls reflex movements of deglutition 

 and vomiting. 



Tenth Pair. Pneumogastric. Vagus. 



Origin. From nerve-cells situated along the trunk of the nerve 

 near the medulla oblongata viz. : the jugular and the plexiform 

 ganglia. From the nerve-cells in these ganglia a short process 

 emerges which soon divides into two branches one of which passes 

 centrally, the other peripherally. The central branches enter the 

 medulla oblongata, where they terminate around nerve-cells ; the 

 peripheral branches collectively form the main portion of the trunk 

 of the nerve. 



The pneumogastric also contains efferent fibers which have their 

 origin in nerve-cells beneath the floor of the medulla oblongata. It 

 also receives motor fibers from the spinal accessory, the facial, the 

 hypoglossal and the anterior branches of the two upper cervical 

 nerves. 



Distribution. As the nerve passes down the neck it sends off the 

 following main branches : 



1. Pharyngeal nerves, which assist in forming the pharyngeal plexus, 

 which is distributed to the mucous membrane and to the muscles of 

 the pharynx. 



2. Superior laryngeal nerve, which enters the larynx through the 

 thyrohyoid membrane, and is distributed to the mucous membrane 

 lining the interior of the larynx, and to the cricothyroid muscle and 

 the inferior constrictor of the pharynx. The ' depressor nerve," 



