From the dorsal nucleus, nucleus ambiguus and tractus solitarius in the floor of the fourth ventricle, at the back of the medulla. The greater number of the fibres, however, arise from ganglia on the nerve trunk.
The nerve emerges from the medulla as a series of five or six filaments between the olivary and restiform bodies. The fibres are below the facial, and above the vagus.
The rootlets unite as a single trunk which leaves the skull through the middle compartment of the jugular foramen, along with the vagus and spinal accessory. The glosso-pharyngeal is enclosed in a separate sheath of dura mater. In the foramen it presents two ganglia, the jugular and the petrous. The former is of small size, and only involves a few of the fibres of the nerve; it occupies the upper part of the foramen; no branches arise from it. The petrous ganglion lies in the lower part of the foramen and gives off three or four branches.
In the neck the nerve appears between the internal carotid artery and the internal jugular vein. It then passes between the internal and external carotid arteries, winds round the stylo-pharyngeus muscle, and finally reaches the under surface of the base of the tongue by going beneath the hyoglossus.
To superior cervical ganglion of sympathetic.
To Arnold's nerve (auricular branch of vagus). To vagus (occasionally).
f Tympanic nerve to stylo-pharyngeus. Pharyngeal.
Lingual to mucous membrane of posterior third of dorsum of tongue.
The tympanic or Jacobson's nerve enters Jacobson's canal (on the bony ridge between the carotid canal and the jugular foramen) to form along with twigs from the carotid sympathetic plexus, the tympanic plexus. It then joins a small branch from the geniculate ganglion of the facial to produce the lesser superficial petrosal, the latter going to the otic ganglion.