THE CRANIAL, NERVES. 479 



Ninth Pair. The GlossopharyngeaL 



The fibres of the glossopharyngeal nerve originate from a nucleus 

 situated a little behind and below that of the auditory, and near the 

 outer border of the fasciculus teres, by which it is separated from the 

 median line. The root-fibres, after leaving the nucleus, pass downward 

 and outward through the medulla, and emerge from its lateral surface, 

 next behind the auditory nerve, in a series of five or six filaments, which 

 soon unite into a single cord. The nerve then passes into and through 

 the jugular foramen, in company with its associated nerves, the pneumo- 

 gastric and spinal accessory. In this situation it presents a ganglionic 

 enlargement, known as the petrosal ganglion, from its occupying a 

 shallow depression in the petrous portion of the temporal bone. It 

 here gives off a small branch, the " nerve of Jacobson," which is dis- 

 tributed to the lining membrane of the tympanum and Eustachian 

 tube, and sends a filament of communication to the otic gang-lion of 

 the sympathetic. The trunk of the glossopharyngeal nerve then passes 

 downward and forward, receiving branches of communication from both 

 the facial and the pneumogastric nerves, after which it separates into 

 two main divisions, one of which is destined for the tongue, the other 

 for the pharynx ; a double distribution, to which the nerve owes its 

 name. The portion passing to the tongue is distributed to the mucous 

 membrane of the posterior third of this organ, namely, to that portion 

 situated behind the V-^haped row of circumvallate papillae, and to these 

 papillae ; it also supplies filaments to the tonsils and to the mucous 

 membrane of the pillars of the fauces and the soft palate. The re- 

 maining portion of the nerve is distributed to the mucous membrane 

 of the pharynx and to the digastric and stylopharyngeal muscles, by 

 junction with a branch of the facial to the styloglossal muscle, and by 

 junction with branches of the pneumogastric to the superior and middle 

 constrictor muscles of the pharynx. The muscles, accordingly, to which 

 this nerve is directly or indirectly distributed are those by which the 

 tongue is drawn backward (styloglossal), the larynx and pharynx ele- 

 vated (digastric and stylopharyngeal), and the upper part of the pharynx 

 contracted (superior and middle constrictors) ; that is, those concerned 

 in the act of deglutition. 



Physiological Properties of the Glossopharyngeal. The glossopha- 

 ryngeal is for the most part a nerve of sensibility. Its origin from 

 the gray substance in the medulla oblongata corresponding to the pos- 

 terior horns of the spinal cord, the ganglion located upon its trunk 

 in the jugular foramen, and its principal distribution to the mucous 

 membranes of the tongue and pharynx, all indicate its anatomical re- 

 semblance to other sensitive nerves or nerve roots. The result of 

 direct experiment corroborates this view. Longet, in irritating the 

 glossopharyngeal nerve within the cranium, was never able to pro- 

 duce muscular contraction ; and although Chauveau, in experimenting 

 upon this nerve in the same situation in recently killed animals, saw 



