6 3 4 TEXT-BOOK OF PHYSIOLOGY 



pyramidal tract. The exact location of the cortical area for the pharynx 

 is not well determined, but is most likely to be found in the lower part of the 

 general motor area near the termination of the Rolandic fissure. The exact 

 cortical connections of the afferent tract are unknown, but are most likely to 

 be found in the general sensor area. 



Properties. Stimulation of the glosso-pharyngeal trunk with induced el- 

 ectric currents calls forth evidence of pain and contraction of the stylo-pharyn- 

 geus and middle constrictor muscles. Peripheral stimulation of the termi- 

 nals of the nerve-fibers in the mucous membrane of the posterior third of the 

 tongue with different kinds of organic matter in solution, develops^ nerve 

 impulses which transmitted to the cortex evoke sensations of taste. Division 

 of the nerve abolishes sensibility in the mucous membrane to which it is 

 distributed, impairs the sense of taste in the posterior third of the tongue, 

 and gives rise to paralysis of the above-mentioned muscles. 



Stimulation of Jacobson's nerve is followed by dilatation of the blood- 

 vessels of, and secretion from, the mucous membrane of the lower lip, cheek, 

 and gums, and from the parotid gland. Division of the nerve is followed by 

 the opposite results. The course of the fibers which give rise to these results 

 is by way of the lesser petrosal to the otic ganglion, around the cells of which 

 the fibers arborize. From the cells of this ganglion non-medullated fibers 

 pass to the blood-vessels and gland cells. These nerve-fibers are thus 

 members of the autonomic system of nerves. 



Functions. The afferent fibers of the glosso-pharyngeal transmit 

 nerve impulses from the parts to which they are distributed to the cerebral 

 cortex, where they evoke sensations of pain and sensations of taste; they 

 also assist in all probability in the performance of certain reflexes connected 

 with deglutition. The afferent fibers are therefore divisable into nerves of 

 general sensibility and nerves of special sense. The efferent fibers transmit 

 impulses to muscles, exciting them to activity, and to the otic ganglion, 

 which in turn dilates blood-vessels and excites secretion. The fibers excit- 

 ing secretion have their origin in the nucleus salivatorius , from which the 

 efferent autonomic fibers in the chorda tympani nerve arise. 



THE TENTH NERVE. THE PNEUMOGASTRIC OR VAGUS 



The tenth cranial nerve, the pneumogastric or vagus, consists, as shown 

 by histologic methods of research, of both afferent and efferent fibers, in- 

 dependent of those derived in its course from adjoining motor or efferent 

 nerves. Near the exit of the nerve from the cavity of the cranium it presents 

 two ganglionic enlargements known respectively as the ganglion of the root 

 (the jugular) and the ganglion of the trunk (the plexiform). 



Origin of the Afferent Fibers. The afferent fibers take their origin 

 in the monaxonic cells of the ganglia on the root and trunk. The single 

 axon from each of these cells soon divides into two branches, one of which 

 passes centrally, the other peripherally. The centrally directed branches 

 collectively form the so-called roots, ten to fifteen in number, which enter the 

 medulla between the restiform body and the lateral column. The periph- 

 erally directed branches collectively form a portion of the common trunk 

 of the nerve. 



Distribution. The axon of the centrally directed branches after entering 

 the medulla pass toward its dorsal aspect, where they bifurcate, give collat- 



