598 TEXT-BOOK OF PHYSIOLOGY. 



posterior one-third of the tongue, pharynx, soft palate, uvula, and tonsils 

 (Fig. 281). 



Origin of the Efferent Fibers. The efferent fibers serve to bring the 

 nerve-cells from which they arise into connection with a portion of the mus- 

 culature of the fauces and pharynx. These nerve-cells are located in the 

 lateral portion of iheformatio reticularis at some distance below the floor of 

 the fourth ventricle. They constitute the upper portion of a collection of 

 the cells known as the nucleus ambiguus. 



Distribution. From this origin the efferent fibers pass dorsally to near 

 sensor end-nuclei, then turn outward and forward and finally emerge from 

 the medulla in intimate association with the afferent fibers. They are 

 ultimately distributed to the stylo-pharyngeus, and to the middle constrictor 

 muscle of the pharynx. In addition to the foregoing efferent fibers the 

 glossopharyngeal nerve contains at its emergence from the medulla both 

 vaso-motor and secretor fibers. 



Jacobsorfs Nerve. This is a small branch which leaves the glosso- 

 pharyngeal at the petrous ganglion. After passing through a small canal in 

 the base of the skull it enters the tympanic cavity, within which it gives off 

 branches to the great and lesser petrosal nerves, to the mucous membrane of 

 the foramen ovale, the foramen rotundum, and to the Eustachian tube. 



Cortical Connections. The motor nucleus is doubtless connected with 

 the general motor area of the cortex through fibers descending in the 

 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. Divison 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 



