Till''. OLOSSO-PHARYNOEAL NERVE (isi 



upper part of tin- jnirular foramen. \o branches arise lioni it. Jt is .sometimes con- 

 tinuous with t lie pet runs ganglion or it may he absent. 



The inferior or petrous ganglion, or ganglion of Andersch, is an ovoid grey body 

 which lies in the lower part of the jugular foramen, and appears to include all the 

 fibres of the nerve. 



Communications. (1) The petrou- i:anglioii is connected with the su]>erior 

 cervical ganglion of the sympathetic by a fine filament . 



(2) It also has a filament of communication with the auricular branch of the vagus 

 which varies inversely in si/e with the latter nerve and sometimes entirely replaces 

 it. .This filament may be absent. 



(3) An inconstant communication with the ganglion of the root of the vagus. 



(4) A short distance below the petrous ganglion t he trunk of the nerve is connected 

 by a twig with that branch of the seventh nerve which supplies the posterior belly 

 Oi the digastric muscle. 



Branches. (n) From the petrous ganglion : The tympanic branch, or nerve 

 of Jacobson, arises from the petrous ganglion and passes t hrougli a foramen, which lies 

 in the ridge of bone between the carotid canal and the jugular fossa, into t he tympanic 

 canalicnliis i.lacobson's canal), where it is surrounded by a small, fusiform mass 

 of vascular tissue, the intumescentia li/mpanica. After traversing the tympanic 

 canaliculus it enters the tympanum at the junction of its lower and inner walls, and, 

 ascending on the inner wall, breaks up into a number of branches which take part 

 in the formation of the tympanic plexus on the surface of the promontory. The 

 continuation of the nerve emerges from this plexus as the xiniill XII/H rficial petmxnl 

 in rve, \\ Inch runs t hrough a small canal in the petrous portion of the temporal bone, 

 beneath the canal for the tensor tympani. aud appears in the middle fossa of the cra- 

 nium through a foramen which lies in front of the hiatus Fallopii. From this foramen 

 it runs forwards and passes through the foramen ovale, the canaliculus innominatus, 

 or the spheno-petrosal suture, and enters the zygomatic fossa, where it joins the otic 

 ganglion. While it is in the canal in the temporal bone the small superficial petrosal 

 nerve is joined by a branch from the geniculate ganglion of the facial nerve. 



(6) Branches from the plexus : (1) The tubal branch, a delicate branch, which 

 runs forwards to the mucous membrane of the tuba auditiva (Eustachian tube) and 



Is filaments backwards to the region of the fenestra vestibuli (ovalis) and the 

 fenestra cochlea 1 (rotunda). 



(2) The superior and inferior carotico-tympanic (carotid) branches pass 

 medianwards to the internal carotid plexus. 



(c) From the trunk of the nerve : (1) Pharyngeal branches, which may be 

 two or three in number, arise from the nerve a short distance below the petrous 

 ganglion. The principal and most constant of these passes on the outer side of 

 the internal carotid artery, and after a very short independent course joins with 

 the pharyngeal branch of the vagus and with branches of the superior cervical gan- 

 glii >n to form the pharyngeal plexus (fig. 707). 



(2) A muscular branch is distributed to the stylc-pharyngeus muscle. This 

 branch receives a communication from the facial nerve (fig. 707). 



(3) The tonsillar branches arc a number of small twigs which arise under cover 

 of the hyo-gloseus muscle; they proceed to the tonsil, around which t hey form a plexus, 

 the circulus tonsillaris. From this plexus fine twigs proceed to the pillars of the 

 fauces and to the soft palate. 



(4) The lingual branches arise from the termination of the nerve and supply the 

 mucous membrane of the posterior half of the dorsum of the tongue, where, chiefly 

 as taste-fibres, they are distributed to the vallate papilla-. Some small twigs pass 

 backwards to the follicular glands of the tongue, and to the anterior surface of 

 the epiglottis. Other twigs are distributed around the foramen ca'cum, where they 

 communicate with the corresponding twigs of the opposite side. 



The Sensory Fibres. The sensory fibres of the ninth nerve spring from the 

 superior and petrous ganglia and pass peripherally and centrally. The peripheral 

 fibres of the ganglion cells are those which are distributed to the mucous membrane 

 of the tongue and pharynx, and the central fibres pass inwards to the medulla. In 

 the medulla they pass dorsal wards and mec lian wards, t hrough the ret icular formation 

 and. bifurcating into ascend ing and descending branches, they end in the nucleus of 

 termination of i he ninth nerve, that is. in the upper part of the nucleus alae cinerea: 

 and in the nucleus of the tract us solitarius. 



