1264 HUMAN ANATOMY. 



The petrous ganglion (g. petrosum) is larger than the jugular and involves 

 the entire nerve. It is oval or fusiform in shape, measures from 4-5 mm. in length, 

 and is lodged within a slight depression in the lower part of the groove for the 

 nerve in the jugular foramen. 



The communications of the petrous ganglion include filaments (a) from 

 the superior cervical ganglion of the sympathetic, {b) to the auricular branch of the 

 vagus and sometimes (<r) to the ganglion of the root of the vagus. 



Branches. — The branches of the glosso-pharyngeal nerve are: (i) the Hj/m- 

 panic, (2) \\\Q pharyngeal, (3) the muscular, (4) ^\e tonsillar -dxidi (5) the lingual. 



1. The tympanic nerve (n. tympanicus) or Jacob son' s nerve., arises from 

 the petrous ganglion as its most important branch and traverses a tiny canal in the 

 osseous bridge between the jugular fossa and the carotid canal. Entering the tym- 

 panic cavity and receiving fibres from the carotid plexus of the sympathetic by way 

 of the small deep petrosal (n. caroticotympanicus), the tympanic nerve passes 

 upward and forward in a groove on the promontory and breaks up in this situation 

 to form the tympanic plexus (plexus tympanicus [Jacobsoni] ). After distributing 

 filaments to the mucous membrane lining the tympanic cavity and the associated 

 air-spaces (mastoid cells and Eustachian tube), its fibres reassemble and join with a 

 filament from the geniculate ganglion to continue as the small superficial petrosal 

 nerve to the otic ganglion (Fig. 1075). 



Branches. — These are : («) tho. small superficial petrosal nerve, {b) the branch 

 to the fenestra avails, (c) the branch to the fenestra rot^mda, (d) the branch to the 

 Eustachian tube, (^) the branch to the mastoid cells and (_/") the branch to the great 

 superficial petrosal nerve. 



a. The small superficial petrosal nerve (n. petrosus superficialis minor) (Fig. 1075) is the 

 continuation of the tympanic nerve, formed by a reassembling of the fibres of the plexus, sup- 

 plemented by a filament from the geniculate ganglion of the facial. It traverses a canal which 

 begins at the anterior superior portion of the tympanic cavity, passes beneath the upper end of 

 the canal for the tensor tympani and appears on the superior surface of the petrous portion of 

 the temporal bone, to the outer side of the cranial opening of the hiatus Fallopii. While in the 

 canal it sometimes receives a communicating branch from the great superficial petrosal nerve. 

 It leaves the cranium through a canal in the greater wing of the sphenoid, or through the fissure 

 between the greater wing and the petrous portion of the temporal bone, and on reaching the 

 base of the skull, joins the otic ganglion as its sensory root ( Fig. 1075). 



b. The branch to the fenestra ovalis supplies the mucous membrane in the neighborhood 

 of the oval window. 



c. The branch to the fenestra rotunda is distributed to the mucous membrane over and 

 around the fenestra. 



d. The branch to the Eustachian tube supplies the mucous membrane linmg the osseous 

 portion of that canal. 



e. The branch to the mastoid cells supplies the mucous lining of these cells. 



f. The branch to the great superficial petrosal nerve joins the latter in the hiatus Fallopii. 



2. The pharyngeal branches (rr. pharyngei) number two or more, of which 

 the largest descends along the course of the internal carotid artery and joins the 

 pharyngeal branches of the vagus and sympathetic to form the pharyngeal plexus, 

 w^hich supplies the mucous membrane and muscles of the pharynx. The smaller 

 pharyngeal branches pierce the superior constrictor and are distributed to the 

 mucous membrane lining the upper portion of the pharynx. 



3. The muscular branch (r. stylopharyngeus) enters the stylo-pharynegus, 

 and, after giving off fibres for the supply of that muscle, passes through it to be 

 distributed to the mucous membrane of the pharynx. 



4. The tonsillar branches (rr. tonsillares) are given of? near the base of 

 the tongue. They are slender filaments which form a plexiform ramification, the 

 circulus tonsillaris, around the tonsil. From this plexus filaments are distributed to 

 the tonsil, the soft palate and the faucial pillars. 



5. The lingual branches (rr. linguales) are the two terminal filaments of the 

 nerve. The larger posterior branch passes upward and separates into a number of 

 filaments which supply the circumvallate papillae and the mucous membrane covering 



