CRANIAL NERVES. 97 



Hearing. At times the hearing is impaired, from disorders of nutrition 

 in the middle ear and external auditory meatus. 



Alteration in the nutrition of the special senses is not marked if the sec- 

 tion is made posterior to the ganglion of Gasser, and to the anastomosing 

 filaments of the sympathetic which join the nerve at this point ; but if the 

 ganglion be divided, these effects are very noticeable, due to the section of 

 the sympathetic filaments. 



Function. Gives sensibility to all parts of the head and face to which 

 it is distributed ; through the small root endows the masticatory muscles 

 with motion ; through fibres from the sympathetic governs the nutrition of 

 the special senses. 



7th Pair. Portio Dura. Facial Nerve. 



Apparent Origin. From the groove between the olivary and restiform 

 bodies at the lateral portion of the medulla oblongata, and below the mar- 

 gin of the pons Varolii. 



Deep Origin. From a nucleus of large cells in the floor of the 4th ventri- 

 cle, below the nucleus of origin of the 6th pair, with which it is connected. 

 Some filaments are traceable to the lenticular nucleus of the opposite side. 

 Some of the fibres cross the median line and decussate. It is intimately 

 associated with the nerve of Wrisberg at its origin. 



Distribution. From its origin the facial nerve passes into the internal 

 auditory meatus, and then, in company with the nerve of Wrisberg, enters 

 the aqueduct of Fallopius. The filaments of the nerve of Wrisberg are 

 supplied with a ganglion, of a reddish color, having nerve cells. These 

 filaments unite with those of the root of the facial, to form a common 

 trunk, which emerges at the stylo-mastoid foramen. 



In the aqueduct the facial gives off the following branches, viz.: 



1. Large petrosal nerve, which passes forward to the spheno-palatine, or 

 Meckel's ganglion, and through this to the levator palati and azygos uvulae 

 muscles, which receive motor influence from this source. 



2. Small petrosal nerve, passing to the otic ganglion and thence to the 

 tensor-tympani muscle, endowing it with motion. 



3. Tympanic branch, giving motion to the stapedius muscle. 



4. Chorda tympani nerve, which after entering the posterior part of the 

 tympanic cavity, passes forward between the malleus and incus bones, 

 through the Glasserian fissure, and joins the lingual branch of the 5th 

 nerve. It is then distributed to the mucous membrane of the anterior 

 two-thirds of the tongue and the sub-maxillary glands. 



