THE ENCEPHALIC OR CRANIAL NERVES 633 



reflexly to certain adaptive and protective movements by which the equi- 

 librium of the body -in both dynamic and static conditions is maintained. 



THE NINTH NERVE. THE GLOSSO-PHARYNGEAL 



The ninth cranial nerve, the glosso-pharyngeal, consists, as shown by 

 both histologic and experimental methods of research, of both afferent and 

 efferent nerve-fibers, of which the former, however, are by far the more 

 abundant. Near its exit from the cavity of the skull the nerve presents two 

 ganglionic enlargements known as the petrosal and jugular ganglia. 



^ Origin of the Afferent Fibers. The afferent fibers serve to bring cer- 

 tain end-nuclei in the medulla oblongata into anatomic and physiologic 

 relation with portions of the mucous membrane of the tongue, pharynx, and 

 middle ear. The afferent fibers are axons of the monaxonic cells of the 

 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. 



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^iuclei. 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 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. 



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 



