556 



CRANIAL NERVES. 



is of very small size, and involves only the outer side of the trunk of the nerve, 



a small fasciculus passing 



Fig. 284. Course and Distribution of the Eighth Pair of bevond it which is not 



N t) r v tj s 



connected directly with it. 



The inferior or petrous 

 ganglion is situated in a 

 depression in the lower 

 border of the petrous por- 

 tion of the temporal bone; 

 it is larger than the for- 

 mer, and involves the whole 

 of the fibres of the nerve. 

 From this ganglion arise 

 those filaments which con- 

 nect the glosso-pharyngeal 

 with other nerves at the 

 base of the skull. 



Its branches of communi- 

 cation are with the pneu- 

 mogastric, sympathetic, 

 and facial, and the tympanic 

 branch. 



The branches to the 

 pneumogastric are two fila- 

 ments, one to its auricular 

 branch, and one to the up- 

 per ganglion of the pneu- 

 mogastric. 



The branch to the sym- 

 pathetic is connected with 

 the superior cervical gan- 

 glion. 



The branch of commu- 

 nication with the facial 

 perforates the posterior 

 belly of the Digastric. It 

 arises from the trunk of 

 the nerve below the petrous 

 ganglion, and joins the fa- 

 cial just after its exit from 

 the stylo-mastoid foramen. 



The tympanic branch 

 (Jacobson's nerve) arises 

 from the petrous ganglion, 

 and enters a small bony 

 canal on the base of the 

 petrous portion of the tem- 

 poral bone. (This opening 

 is pla.ce'd on the bony ridge 

 which separates the ca- 

 rotid canal from the jugular 

 fossa.) It ascends to the 

 tympanum, enters this cavity by an aperture in its floor close to the inner wall, 

 and divides into three branches, which are contained in grooves upon the surface 

 of the promontory. 



Its branches of distribution are, one to the fenestra rotunda, one to the fenestra 

 ovalis, and one to the lining membrane of the Eustachian tube and tympanum. 



