THE GLOSSO-PHARYNGEAL NERVE 951 



The cochlear nerve is separate from the vestibular at the bottom of the internal 

 auditory meatus and at its entrance into the medulla. 



THE GLOSSO-PHARYNGEAL NERVE 



The glosso-pharyngeal or ninth cranial nerves are mixed nerves and each is 

 attached to the medulla by several roots which enter the posterolateral sulcus, 

 dorsal to the anterior end of the olivary body and in direct line with the facial 

 nerve. 



The filaments, when traced lateralward, are seen to blend, in front of the 

 flocculus, into a trunk which lies in front of the vagus nerve, but which passes 

 through a separate opening through the arachnoid and the dura mater and through 

 the jugular foramen. In the foramen this trunk lies in front, and lateral to the 

 vagus nerve in a groove on the petrous portion of the temporal bone; and in this 

 situation two ganglia are interposed in it, a superior or jugular, and an inferior 

 or petrosal. After it emerges from the jugular foramen the glosso-pharyngeal 

 nerve descends at first between the internal carotid artery and the internal jugular 

 vein and to the lateral side of the vagus; then, bending forward and medial ward, 

 it descends medial to the styloid process and the muscles arising from it, and 

 turning around the lower border of the stylo-pharyngeus it passes between the 

 internal and the external carotid arteries, crosses the superficial surface of the 

 stylo-pharyngeus, and runs forward and upward medial to the hyoglossus muscle 

 and across the middle constrictor and the stylo-hyoid ligament, to the base of the 

 tongue (fig. 743). 



Ganglia. — The superior or jugular ganglion (ganglion of Ehrenritter), is a small, 

 ovoid, reddish-grey body which lies on the back part of the nerve-trunk in the 

 upper part of the jugular foramen. No branches arise from it. It is sometimes 

 continuous with the petrosal ganglion or it may be absent. 



The inferior or petrosal ganglion, (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. 



Branches and communications. — (1) The petrosal ganglion is connected with the superior 

 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 inv^ersely in size with the latter branch 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 ganghon the trunk of the nerve is connected by a 

 twig with that branch of the facial nerve which suppUes the posterior belly of the digastric 

 muscle. There is also a small twig (probably sensorjO to the stylo-hyoid. 



(5) From the petrosal ganglion : The tympanic branch (nerve of Jacobson) arises from the 

 petrosal ganghon and passes through a foramen, which lies in the ridge of bone between the car- 

 otid canal and the jugular fossa, into the tympanic canaliculus (Jacobson's canal), where it is 

 surrounded by a small, fusiform mass of vascular tissue, the intumescentia tympanica. After 

 traversing the tympanic canaliculus it enters the tympanum at the junction of its lower and 

 medial walls, and, ascending on the medial wall, breaks up into a number of branches which take 

 part in the formation of the tympanic plexus on the surface of the promontory (fig. 739). The 

 continuation of the nerve emerges from this plexus as the S7nall superficial petrosal nerve, which 

 runs through a small canal in the petrous portion of the temporal bone, beneath the canal for the 

 tensor tympani, and appears in the middle fossa of the cranium through a foramen which lies 

 in front of the hiatus Fallopii. From this foramen it runs forward and passes through the fora- 

 men 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 geniculo-tympanic branch from the geniculate ganghon 

 of the glosso-palatine nerve. 



(6) Branches from the tympanic plexus : — (a) The tubal branch (ramus tubae), a delicate 

 branch, which runs forward to the mucous membrane of the tuba auditiva (Eustachian tube) 

 and sends filaments backward to the region of the fenestra vestibuli (ovalis) and the fenestra 

 cochleae (rotunda). 



(6) The superior and inferior carotico -tympanic (carotid) branches pass median ward to 

 the internal carotid plexus (fig. 741). 



The above communications carry fibres almost entirely concerned with the synipathetic 

 plexuses of the head and they will be again mentioned below with the ganghated cephalic plexus. 



Branches 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 petrosal ganghon. The prin- 

 cipal and most constant of these passes on the lateral 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 ganglion to form the pharyngeal plexus (fig. 743). 



