THE CRANIAL NERVES. 551 



tute the upper portion of a collection of cells known as the nucleus 

 ambiguus. 



Distribution. From this origin the efferent fibers pass dorsally 

 to near the 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-pharyn- 

 geal and to the middle constrictor muscles of the pharynx. In addi- 

 tion to the foregoing efferent fibers the glosso-pharyngeal nerve 

 contains at its emergence from the medulla both vaso-motor and 

 secretor fibers. 



Jacobsorfs Nerve. This is a_small hmnrfy ffh^ r ^ !***" 

 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 con- 

 nected with the general motor area of the cortex through fibers de- 

 scending 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 cortical connections of the afferent 

 tract are unknown. 



Properties. Electric stimulation of the glosso-pharyngeal trunk 

 calls forth evidence of pain and contraction of the stylo-pharyngeal 

 and middle constrictor muscles. 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. 



Functions. The afferent fibers of the glosso-pharyngeal trans- 

 mit 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 efferent fibers trans- 

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

 ganglion, which in turn dilates blood-vessels and excites secretion. 



