748 THE NERVOUS SYSTEM. 



(Fig. 329). In its passage through the jugular foramen it grooves the lower 

 border of the petrous portion of the temporal bone, and at its exit from the skull 

 passes forward between the jugular vein and internal carotid artery, and descends 

 in front of the latter vessel, and beneath the styloid process and the muscles con- 

 nected with it, to the lower border of the Stylo-pharyngeus. The nerve now 

 curves inward, forming an arch on the side of the neck, and lying upon the Stylo- 

 pharyngeus and Middle constrictor of the pharynx. It then passes beneath the 

 Hyoglossus, and is finally distributed to the mucous membrane of the fauces and 

 base of the tongue, and the mucous glands of the mouth and tonsil. 



In passing through the jugular foramen the nerve presents, in succession, two 

 gangliform enlargements. The superior, the smaller, is called the jugular gan- 

 glion ; the inferior and larger, the petrous ganglion, or the ganglion of Andcrsch. 



The superior or jugular ganglion is situated in the upper part of the groove in 

 which the nerve is lodged during its passage through the jugular foramen. It is 

 of very small size, and involves only the lower part of the trunk of the nerve. 

 It is usually regarded as a segmentation from the lower ganglion. 



The inferior, or petrous, ganglion is situated in a depression in the lower bor- 

 der of the petrous portion of the temporal bone ; it is larger than the former and 

 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 facial just after its exit from the stylo-mastoid foramen. 



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. This plexus gives off (1) the greater part of the 

 small superficial petrosal nerve ; (2) a branch to join the great superficial petrosal 

 nerve; and (3) branches to the tympanic cavity, all of which will be described in 

 connection with the anatomy of the ear. 



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

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

 mogastric and with branches of the sympathetic. 



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

 dle constrictor of the pharynx with the pharyngeal branches of the pneumogastric 

 and sympathetic nerves to form the pharyngeal plexus, branches from which perforate 

 the muscular coat of the pharynx to supply the muscles and mucous membrane. 



The muscular branch is distributed to the Stylo-pharyngeus. 



The tonsillar branches supply the tonsil, forming a plexus (circuluB 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 are two in number : one supplies the circumvallate papillae 

 and the mucous membrane covering the surface of the base of the tongue ; the other 

 perforates its substance, and supplies the mucous membrane and follicular glands of 

 the posterior half of the tongue and communicates with the lingual nerve. 



