THE GLOSSO-PHARYNGEAL NERVE. 



1263 



amongst its fibres and contains numerous nerve-cells of small size which constitute the reception- 

 station for the greater number of the afferent fibres of the ninth nerve. Since these fibres are 

 continually ending at different levels in their descent, it follows that both the fasciculus and 

 its nucleus gradually diminish in size, until, at about the level of the sensory decussation, they 

 are no longer distinguishable. Considering the fact that the afferent fibres of the facial nerve, 

 which constitute the pars intermedia of Wrisberg are distributed peripherally chiefly by the 

 chorda tympani, are also concerned in conveying taste-impulses and end, in part at least, in 

 the same nucleus as does the ninth, the sensory portion of the seventh nerve may be regarded, 

 at least functionally, if not from a morphological standpoint, as an aberrant strand of the 

 glosso-ph ary ngeal . 



Course and Distribution. — Leaving the superficial origin along the groove 

 separating the olivary eminence from the inferior cerebellar peduncle, the isolated 

 root-fasciculi, about half a dozen in number and in series with those of the vagus, 

 assemble to form a single trunk, which passes outward in front of the flocculus of the 

 cerebellum to the jugular foramen. As it traverses this foramen, the glosso-pharyn- 



FiG. 1075. 



a oi^^ 



3VMP. 



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Diagram showing tympanic plexus and connections of glosso-pharyngeal nerve. 



geal lies external and anterior to the tenth and eleventh nerves and in its own 

 separate dural sheath. It occupies a groove, or sometimes a bony canal, in the fora- 

 men and in this situation presents two thickenings, the j'ugu/ar zn^ petrous ganglia. 

 Emerging from the foramen, the nerve passes between the internal carotid artery 

 and the internal jugular vein and, dipping beneath the styloid process, follows a 

 downward course along the posterior border of the stylo-pharyngeus muscle, with 

 which it passes between the internal and external carotid arteries. Turning gradually 

 forward, it reaches the outer side of the stylo-pharyngeus muscle and stylo-hyoid 

 ligament and disappears beneath the hyo-glossus muscle to break up into its terminal 

 branches to the tongue (Fig. 1079). 



Ganglia of the Glosso-Pharyngeal Nerve. — In the course of the nerve 

 two ganglia are found, the jiigjtlar and the petrous. They contain aggregations of 

 neurones whose dendrites constitute the peripheral sensory fibres and whose centrally 

 directed axones-form the sensory root-fibres of the nerve. 



The jugular ganglion (g. superius) which may be regarded as a detached 

 portion of the petrous ganglion, hes in the upper part of the groove occupied 

 by the glosso-pharyngeal nerve in its transit through the jugular foramen. It is 

 variable in size and not always present and measures only from 1-2 mm. in length. 

 The ganglion does not include the entire thickness of the nerve but only the 

 inferior portion, the fibres of the superior portion passing uninterruptedly over it. 



