768 THE NERVOUS SYSTEM 



The term aweiuliiiji as applied to the fibres of the glosso-pharyi)geal nei-ve which he in the 

 funiculus solitarius is unjustifiable. In reality the funiculus consists of fibres of the glosso- 

 pharyngeal and vagus nerves, derived from the ganglicjii cells of these nerves, which are i)assing 

 downwards to lower levels of the medulla, and which correspond, therefure, tn a certain extent, 

 with the fibres of the descending comma-shaped tract of the spinal cord. 



From its superficial origin the glosso-pharyngeal nerve proceeds outwards and 

 sliglitly forwards, below and in front of the flocculus, to reach the middle compart- 

 ment of the jugular foramen, which it traverses in common witli the vagus and 

 spinal accessory nerves. As it passes through the foramen it is jilaced in front of. 

 and a little internal to, the vagus and spinal accessory nerves, but occupies a sepa- 

 rate compartment in the dura mater, and is lodged in a groove on the lower l)order 

 of the petrous portion of the temporal bone. Having emerged at the base of the 

 skull, it lies at first in contact with the vagus, but leaves the latter almost immedi- 

 ately and passes forwards and inwards between the internal jugular vein and the 

 internal carotid artery and curves round the outer side of the latter vessel between 

 it and the external carotid. In this part of its course it is placed under cover of the 

 stylo-pharyngeus muscle. It then winds round the lower border of that muscle, 

 and finally passes upwards in front of it and gains the deep surface of the hyo- 

 glossus, where it breaks up into its terminal or lingual branches. In the course 

 above described, the glosso-pharyngeal descril)es a curve with the convexity directed 

 downwards and backwards. 



In its course through the jugular foramen, two ganglia are formed upon the 

 trunk. of the nerve, the lower of these bodies (petrous ganglion) is the more con- 

 stant, the upper or jugular ganglion being generally regarded as a segmentation 

 from the petrous ganglion. The two ganglia taken together are generally assumed 

 to l)e equivalent to the ganglion on the posterior root of a spinal nerve. 



The jugular ganglion (ganglion of Ehrenritter) is a small greyish body which 

 involves only tlie back part of tlie nerve. It is lodged in the U]^])er part of the 

 groove in the temporal bone through which the nerve passes. This ganglion does 

 not give off any branches. 



The petrous ganglion (ganglion of Andersch) is an ovoid greyish body which 

 prolmbly involves all the fibres of the nerve. Its long axis" coincides with the axis 

 of the nerve, and measures two or three millimetres. It is placed in the lower part 

 of the jugular fossa. The nerve of Jacobson and some communicating 1)ranches 

 arise from it. 



Branches. — The following branches are given off by the glosso-pharyngeal 

 nerve: — (1) meniingeal; (2) tympanic; (8) communicating; (4) muscular; (5) 

 pharyngeal; (G) tonsillar; and (7) lingual. 



(1) The meningeal branches are slender twigs Avhieh are given off within 

 the cranium, and are distributed to the pia mater and arachnoid. (Boch- 

 dalek. ) 



(2) The tympanic branch, or nerve of Jacobson, is a small twig which arises 

 from the petrous ganglion. It enters a minute canal (the tympanic canaliculus), 

 which commences below on the ridge between the jugular fossa and the inferior 

 opening of the carotid canal, and ends above, in the tympanic cavity, immediately 

 below the promontory. The nerve, having traversed this canal, ramifies on the 

 promontory, grooving the bone, and forming the tym])anic plexus. The following 

 i)ranches arise from the nerve within the tympanum: (a) a communicating twig 

 to the great superficial petrosal; (b) a twig to the lesser superficial petrosal, whieii 

 is considered by some anatomists to be the main root of the nerve; (c) a twig to 

 the mucous membrane surrounding the fenestra ovalis; (cZ) a twig to the fenestra 

 rotunda; (e) a twig to the lining membrane of the Eustachian tube; (/) a twig 

 which passes through the carotico-tympanic canal to join the carotid plexus of the 

 sympathetic. 



(3) The communicating branches arise from the petrous ganglion. One joins 

 the superior cervical ganglion of the sym])at}ietic; another forms a loop Avith the 

 auricular branch of the vagus; while a third, l(>ss constant than the other two, joins 

 the ganglion of the root of the vagus. Immediately below the })etrous ganglion 

 a twig is given off which joins the lingual branch of the facial as above 

 described (i)age 764). 



