648 TEXT-BOOK OF PHYSIOLOGY 



petrosal and jugular ganglia. The single axon from each of these cells soon 

 divides into two branches, one of which passes centrally, the other peripher- 

 ally. The centrally directed branches collectively form the so-called roots, 

 four or five in number, which enter the medulla between the olivary and 

 restiform bodies. The peripherally directed branches collectively form the 

 two main divisions, from the distribution of which, to the tongue and pharynx, 

 the nerve takes its name. (See Fig. 267.) 



Distribution. The axons of the centrally directed branches after 

 entering the medulla pass toward its dorsal aspect, where they bifurcate, 

 give off collateral branches, and terminate in fine end-tufts in the immediate 

 neighborhood of two groups of nerve-cells, the sensor end-nuclei. The axons 

 of the peripherally directed branches, after emerging from the base of the 

 skull through the jugular foramen, pass forward and inward under cover of 

 the stylo-pharyngeal muscle; winding around this muscle they divide into 

 terminal branches which are distributed to the mucous membrane of the 

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



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 the formatio 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 as well. 



Jacobson's 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. 



