VAGUS NERVE. 705 



form plexus, nbers of unknown function from the hypoglossal, the 

 superior cervical ganglion of the sympathetic and the cervical plexus 

 unite with the vagus. 



According to Grossmann the fibers for the cricothyroid arise in rabbits from 

 the glossopharyngeal, as do also the Hering-Breuer pulmonary fibers. According 

 to Grabower, the fibers for the muscles of the larynx come from the vagus itself. 

 According to Kreidl, the fibers for the esophagus are situated in the glossopharyn- 

 geal in the rabbit, but enter the trunk of the vagus. 



To the pharyngeal plexus the vagus (2) sends from the upper 

 portion of the gangliforrn plexus one or two branches that at the level 

 of the middle constrictor of the pharynx, together with the pharyngeal 

 branches of the ninth nerve and the superior cervical ganglion of the 

 sympathetic, form the pharyngeal plexus at the side of the ascending 

 pharyngeal artery. The posterior portion of the trunk of the vagus 

 itself supplies through this plexus the three constrictors of the pharynx, 

 as well as the palatoglossus and palatopharyngeus muscles (according 

 to observations on the ape) .with motor fibers. Filaments from the 

 middle of the anterior accessory root innervate the elevator of the veil 

 of the palate. Sensory fibers from the vagus to the pharyngeal plexus 

 supply the pharynx from a point below the level of the veil of the palate 

 downward. These fibers stimulate reflexly the constrictors of the 

 pharynx in the act of deglutition. In case of considerable abnormal 

 irritation they are also capable of inducing vomiting. The sympathetic 

 fibers of the pharyngeal plexus give vasomotor fibers to the vessels of 

 the pharynx. The pharyngeal branches of the ninth nerve are described 

 on p. 703. 



The vagus sends two branches to the larynx: (a) The superior 

 laryngeal nerve (3), which after receiving a vasomotor filament from the 

 superior cervical ganglion of the sympathetic divides into an external 

 and an internal branch, (i) The external branch receives from the same 

 source vasomotor fibers (which later on accompany the superior thyroid 

 artery) and it supplies the cricothyroid muscle with motor fibers (which 

 in the ape are derived from the posterior fibers of the trunk of the 

 vagus) and the inferior lateral portion of the laryngeal mucous mem- 

 brane with sensory fibers. (2) The internal branch gives off only sensory 

 fibers: to the glottoepiglottic fold and the adjacent lateral portion of 

 the root of the tongue, to the aryepiglottic fold and to the entire interior 

 of the larynx (in so far as it is not supplied by the external branch). 

 Irritation of these sensory branches causes reflex cough, although irrita- 

 tion of the vocal bands does not, but only that in the vicinity of the 

 respiratory glottis. The same effect is brought about through the sen- 

 sory branches of the vagus to the trachea, particularly at the point of 

 bifurcation, also through those of the bronchial mucous membrane, as 

 well as those of the pulmonary tissue and of the pleura when altered 

 by disease (inflammation). The cough-center is supposed to be situ- 

 ated on either side of the raphe in the neighborhood of the ala cinerea. 

 Severe attacks of coughing may be attended with vomiting in conse- 

 quence of irritation of the pharynx or as an associated movement. 

 Hedon found in the superior laryngeal nerve vasodilator and secretory 

 fibers for the mucous membrane of the larynx and Kokin in both laryn- 

 geal nerves secretory fibers for the mucous glands of the larynx and the 

 trachea. 

 45 



