THE GLOSSOPHARYNGEAL. 553 



tions of Dean, in the medulla of the sheep, the transition between the 

 pneumogastric and glossopharyngeal roots or nuclei is so gradual that 

 it is impossible to point out any exact line of demarcation. Each of 

 these nerves has upon its trunk a distinct ganglion, situated within its 

 point of emergence from the cranium. The motor portion of the group, 

 or the spinal accessory, originates from a special nucleus of its own, 

 and sends branches of communication to both the other nerves. While 

 the three nerves of this group, therefore, can hardly be regarded as a 

 single pair, they have nevertheless a close mutual relation both in ana- 

 tomical arrangement and in their physiological properties. 



Ninth Pair. The Glossopharyngeal, 



The fibres of the glossopharyngeal nerve originate from a nucleus 

 situated a little behind and below that of the auditory, and near the 

 outer border of the fasciculus teres, by which it is separated from the 

 median line. This nucleus is continuous posteriorly with that of the 

 pneumogastric nerve, which projects above it on the floor of the fourth 

 ventricle (Fig. 168, Ngl, Nv). The nerve fibres, after leaving the nu- 

 cleus, pass downward and outward through the substance of the medulla, 

 and emerge from its lateral surface, next behind the auditory nerve, in 

 a series of five or six filaments which soon afterward unite into a single 

 cord. The nerve then passes into and through the jugular foramen, in 

 company with its associated nerves, the pneumogastric and spinal 

 accessor}*. While passing through this opening in the skull, it presents 

 a ganglionic enlargement, similar to those of the posterior spinal nerve 

 roots, and known as the petrosal ganglion, from its occupying a shallow 

 depression in the petrous portion of the temporal bone. At the situa- 

 tion of the petrosal ganglion it gives off a small branch, the " nerve of 

 Jacobson," which is distributed to the mucous membrane of the tym- 

 panum and Eustachian tube, and sends a filament of communication to 

 the otic ganglion of the sympathetic system. The trunk of the glosso- 

 pharyngeal nerve then passes downward and forward, receiving branches 

 of communication from both the facial and the pneumogastric nerves, 

 after which it separates into two main divisions, one of which is des- 

 tined for the tongue, the other for the pharynx; a double distribution, 

 to which the nerve owes its name. The portion passing to the tongue 

 is distributed to the mucous membrane of the posterior third of this 

 organ, namely, to that portion situated behind the V-shaped row of cir- 

 cumvallate papillae, and to these papillae ; it also supplies filaments to 

 the tonsils and to the mucous membrane of the pillars of the fauces and 

 of the soft palate. The remaining portion of the nerve is distributed 

 to the mucous. membrane of the pharynx and certain of the adjacent 

 muscles, namely, the digastric and stylopharyngeal muscles, by union 

 with a branch of the facial to the styloglossal muscle, and by union 



1 Gray Substance of the Medulla Oblongata and Trapezium. Washington. 

 1864, p. 30. 

 36 



