CHAP. XX.] THE GLOSSO-PHARYNGEAL NERVE. 117 



membrane of that cavity and of the Eustachian tube. But its 

 principal branches are those on the pharynx and tongue, which latter 

 region, however, it must not be forgotten, has another nerve distri- 

 buted to its mucous membrane. Its digastric branch seems to be 

 anastomotic with a similar one from the facial. 



The mode of origin of this nerve affords but a feeble clue to the dis- 

 covery of its physiological import. Miiller and others attach some 

 value to the existence of the ganglion, involving only some of its fibres 

 shortly after their origin, and from the analogy with spinal nerves 

 and with the fifth, they infer that the glosso-pharyngeal must be a 

 compound nerve of double origin, containing both motor and sensi- 

 tive fibres. There is not, however, sufficiently certain evidence of 

 the existence of two roots to this nerve to justify us in founding 

 upon it an argument respecting its function. 



The most extensive series of experiments on this subject are those 

 of Dr. John Reid, and they have very satisfactorily developed the 

 proper functions of the nerve. 



Section of the nerve, or irritation of it, always caused pain, and 

 hence it may be said to contain fibres of common sensation. 



When the trunk of the nerve was irritated before giving off its 

 pharyngeal branches, extensive muscular movements of the throat 

 and lower part of the face were produced. It was found that 

 these movements were equally produced, and to as great an ex- 

 tent, if the nerve had been cut a short way below its exit 

 from the cranium, and the cranial end of it irritated. Hence 

 it was evident that the movements were caused, not by the 

 direct influence of the branches of the glosso-pharyngeal upon the 

 muscles, but by that of the cranial end of tne nerve upon the me- 

 dulla oblongata, whence the change was propagated to the muscles 

 through the fibres of the vagus nerve and through those of the 

 facial, which emanate from the same part of the nervous centre. 



This view of the mode in which the glosso-pharyngeal causes mus- 

 cular action is confirmed by the result of experiments on it in ani- 

 mals just dead. When the nerve was irritated under those circum- 

 stances, no movements could be excited, provided it was sufficiently 

 insulated from the pharyngeal branches of the vagus. Now, were the 

 fibres of the glosso-pharyngeal motor, there is no doubt that mechan- 

 ical irritation of them would have caused muscular contraction. 



Hence, the glosso-pharyngeal is one of those sensitive nerves which 

 is capable of exciting motion through its influence upon motor 

 fibres implanted immediately contiguous to it in the nervous centre. 



It appeared, however, that other fibres were capable of exciting the 



