THE TRIGEMINUS. 537 



and discharges a purulent secretion. This process, after commencing 

 in the cornea, increases in intensity and spreads to the iris, which be- 

 comes covered with an inflammatory exudation. The cornea grows 

 more opaque, until it is at last altogether impermeable to light, and 

 vision is consequently suspended. Sometimes the diseased action goes 

 on until it results in sloughing and perforation of the cornea and dis- 

 charge of the humors of the eye; sometimes, after a few days, the 

 inflammatory appearances subside, and the eye is finally restored to its 

 natural condition. 



According to the observations of Bernard, although these, conse- 

 quences usuall3 r follow division of the fifth nerve when performed at the 

 situation of the Gasserian ganglion, or between it and the eyeball, they 

 are either retarded in their appearance or altogether wanting when the 

 section is made posteriorly to the ganglion, between it and the base of 

 the brain. Thjs indicates that the influence exerted by this nerve upon 

 the nutrition of the eyeball does not reside in its own proper fibres, but 

 in additional filaments derived from the Gasserian ganglion. 



Influence on the Sense of Taste. The lingual branch of the fifth 

 pair communicates to the anterior portion of the tongue at the same 

 time its acute general sensibility and its sensibility of taste ; both of 

 which are, of course, abolished by its division. Whether both kinds of 

 sensibility reside in the same or in different fibres cannot yet be deter- 

 mined ; but cases which have been observed in man, of impairment of 

 the sense of taste, while tactile sensibility remains entire, make it pos- 

 sible that there may be two distinct sets of fibres in the lingual nerve, 

 one devoted to general sensibility, the other to that of taste. How- 

 ever that may be, it is evident that the exercise of the sense of taste is 

 facilitated by the presence of general sensibility in the mucous mem- 

 brane of the tongue, and is influenced by the state of the local circula- 

 tion and the buccal secretions. In a tongue which is dry or coated, as 

 in the febrile condition, taste is practically abolished ; as much so as 

 the sense of sight from opacity of the cornea. The sense of taste, 

 accordingly, depends for its exercise, not only upon the special sensi- 

 bility of the lingual nerve, but also upon all the physiological conditions 

 requisite for the integrity of the mucous membrane. 



Influence upon the Sense of Hearing. The influence of the fifth pair 

 upon the sense of hearing is less certainty known than that exerted 

 upon the other special senses, and is only to be surmised from the simi- 

 larity of its anatomical relations. This nerve provides for the general 

 sensibility of the external ear by twigs from its auriculo-temporal branch, 

 which supply the skin of the anterior border of the concha and that of 

 the anterior wall of the external auditory meatus. Its relation with the 

 deeper parts of the organ is established by means of the otic ganglion 

 of the sympathetic, which receives a few short fibres from the inferior 

 maxillary division of the fifth pair, and which sends a filament back- 

 ward to join the tj'mpanic plexus on the inner surface of the membrane 

 of 'the tympanum. This plexus is also supplied with filaments from 

 35 



