476 THE NERVOUS SYSTEM. 



the tympanum, known as the "tympanic plexus," which supplies the 

 lining membrane of the tympanic cavity, while the otic ganglion sends 

 a motor filament to the tensor tympani muscle. 



From the concave border of the facial nerve, as it bends downward, 

 a fine motor filament, the stapedius branch ( n ), passes forward to the 

 stapedius muscle. The facial, therefore, in this part of its course, has 

 an influence on the mechanism of hearing, through the muscles which 

 regulate the tension of the membrana tympani. This influence is 

 exerted directly by its stapedius branch, and indirectly, through the 

 otic ganglion, by the filament supplied to the tensor tympani. Facial 

 paralysis is sometimes accompanied by partial deafness, and sometimes 

 by abnormal sensibility to sonorous impressions ; but it has not been 

 determined how far these symptoms are due to paralysis of the muscles 

 of the middle ear, or to the implication of other parts. 



From its descending portion, the facial nerve gives off two small 

 branches of communication (12,13)1 one to the pneumogastric and one to 

 the glossopharyngeal nerve, both of which are usually considered as 

 motor filaments. This seems nearly certain in regard to the glosso- 

 pharyngeal branch ; since Cruveilhier describes a separate filament of 

 the facial sometimes passing to the styloglossal and palatoglossal mus- 

 cles, and Longet cites an instance in which a branch of the facial, on 

 one side, without making connection with the glossopharyngeal nerve, 

 was distributed directly to the palatoglossal and glossopharyngeal mus- 

 cles; that is, to the constrictors of the isthmus of the fauces. 



Finally the facial nerve, shortly before its exit from the stylomastoid 

 foramen, gives off from its concave border the chorda tympani ( M ). 

 It first passes in a recurrent direction, traverses the cavity of the tym- 

 panum near the inner surface of the membrana tympani, curves down- 

 ward and forward, and at last joins the descending portion of the 

 lingual nerve. Some of its fibres afterward diverge, passing to the 

 submaxillary ganglion and the submaxillary gland ; while others con- 

 tinue onward with the lingual nerve and accompany its distribution in 

 the tongue. 



The most positive knowledge in our possession as to the physiologi- 

 cal character of the chorda tympani relates to its influence on the phe- 

 nomena of circulation and secretion in the tongue and the submax- 

 illary gland. The experiments of Bernard, corroborated by subsequent 

 observers and especially by Vulpian,* show that galvanization of the 

 chorda tympani increases both the circulation of the blood and the 

 secretion of saliva in the submaxillary gland. But if the chorda tym- 

 pani be divided both these actions suffer diminution, and the gland 

 remains inexcitable when a sapid substance is introduced into the mouth. 

 If the peripheral extremity of the divided nerve be galvanized, circula- 

 tion and secretion are excited as before ; and the same effect is pro- 

 duced by stimulating, either the lingual nerve, or the filament which 



* Le9ons sur 1'Appareil Vaso-moteur. Paris, 1875, tome i., p. 150. 



