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818 THE NERVOUS SYSTEM. 



involves the whole of the fibres of the nerve. From this ganglion arise those 

 filaments which connect the glosso-pharyngeal with the pneumogastric and sym- 

 pathetic nerves. 



The branches of communication are with the pneumogastric, sympathetic, and 

 facial. 



The branches to the pneumogastric are two filaments, arising from the petrous 

 ganglion, one to its auricular branch, and one to the upper ganglion of the 

 pneumogastric. 



The branch to the sympathetic, also arising from the petrous ganglion, is con- 

 nected with the superior cervical ganglion. 



The branch of communication 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 digastric branch of the facial (see page 813). 



The branches of distribution are the tympanic, carotid, pharyngeal, muscular, 

 tonsillar, and lingual. 



The tympanic branch (Jacobsons nerve) arises from the petrous ganglion, and 

 enters a small bony canal in the lower surface of the petrous portion of the tem- 

 poral bone, the lower opening of which is situated on the bony ridge which sep- 

 arates the carotid canal from the jugular fossa. It ascends to the tympanum, 

 enters that cavity by an aperture in its floor close to the inner wall, and divides 

 into branches which are contained in grooves upon the surface of the promontory, 

 forming the tympanic plexus. 



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

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



Its branches of communication are three, and occupy separate grooves on the 

 surface of the promontory. One, the small deep petrosal, arches forward and 

 downward to the carotid canal (piercing the bone) to join the carotid plexus. A 

 second, the long petrosal nerve, runs forward through a canal in the processus 

 cochleariformis and enters the foramen lacerum medium, where it joins the 

 carotid plexus of the sympathetic, and generally the large superficial petrosal 

 nerve. The third branch runs upward through the substance of the petrous por- 

 tion of the temporal bone. In its course it passes by the gangliform enlargement 

 of the facial nerve, and, receiving a connecting filament from it, becomes the 

 small superficial petrosal nerve. This nerve enters the skull through a small 

 aperture situated external to the hiatus Fallopii on the anterior surface of the 

 petrous bone, courses forward across the base of the skull, and emerges through 

 the petro-sphenoidal fissure or a foramen in the great wing of the sphenoid, and 

 joins the otic ganglion. 



The carotid branches descend along the trunk of the internal carotid artery 

 as far as its commencement, communicating with the pharyngeal branch of the 

 pneumogastric and with branches of the sympathetic. 



The pharyngeal branches are three or four filaments which unite opposite the 

 Middle constrictor of the pharynx with the pharyngeal branches of the pneumo- 

 gastric, the external laryngeal, and sympathetic nerves to form the pharyngeal 

 plexus, branches from which perforate the muscular cdat of the pharynx to sup- 

 ply the muscles and mucous membrane. 



The muscular branch is distributed to the Stylo-pharyngeus. 



The tonsillar branches supply the tonsil, forming a plexus (circulus tonsillaris) 

 around this body, from which branches are distributed to the soft palate and 

 fauces, where they communicate with the palatine nerves. 



The lingual branches (terminal] are two: one supplies the circumvallate papillae, 

 the mucous membrane covering the base of the tongue, and the anterior surface 

 of the epiglottis ; the other supplies the mucous membrane of the side of the 

 tongue for about one-half its length. 



