140 NERVOUS SYSTEM. 



Why is not the ocular paralysis of the seventh nerve as serious as 

 that of the fifth? 



The eyelids remain open in facial paralysis, and the conjunctiva 

 is subject to injury by drying and by foreign bodies ; but the injury 

 is not so great as in paralysis of the fifth nerve, because the seventh 

 has no trophic influence. 



What is the origin of the glosso-pharyngeal or ninth nerve ? 



It arises in the medulla from centres near those for the vagus 

 and spinal accessory nerves. Its fibres pass through the substance 

 of the medulla and emerge in company with those of the vagus and 

 spinal acessory to pass with them from the skull through the jug- 

 ular foramen. It gives off a small branch which passes to the 

 tympanum and Eustachian tube (Jacobson's nerve) while in the 

 jugular foramen, and presents a small ganglion, the petrosal ; and 

 it has communicating branches to the seventh and tenth nerves 

 and to ihe otic ganglion. It divides as it passes down, one branch 

 passin/!; forward to the tongue, and one going to the pharynx 

 (when: 3 its name). 



How s the glosso-pharyngeal distributed ? 



The portion which passes to the tongue is distributed to the pos- 

 terior portion of the organ, to the circumvallate papillae, and the 

 mucous membrane behind them, some fibres going to the lining of 

 the soft palate, pillars of the fauces, and tonsils. The other branch 

 is distributed to the mucous membrane of the pharynx, and by 

 direct branches and communications with other nerves to all the 

 muscles involved in swallowing. 



What is the function of the glosso-pharyngeal nerve ? 



(1) It is the nerve of taste; and (2) it is essentially a nerve of 

 deglutition. 



Explain the action of the glosso-pharyngeal as a nerve of taste. 

 It is only in the latter part of the stay of food in the mouth that 

 it reaches the region supplied by this nerve. When the food is to 

 be swallowed, it is pressed by the base of the tongue against the 

 palate arch and pushed into the pharynx. It is then that the sense 

 of taste is exercised here. The reflex stimuli then excited start up 

 the motor chain which pushes the bolus on to the stomach. As 

 already said, there is considerable question as to whether the tri- 

 geminal or glosso-pharyngeal is really the conductor of this sense, 

 but it is quite likely that both are essential. 



