The course of postganglionic sympathetic fibres distributed with the facial nerve in the cat.

Electrophysiological techniques have been used to determine whether sympathetic fibres are present in branches of the facial nerve. Compound action potentials could be recorded from all branches of the facial nerve during stimulation of the cervical sympathetic trunk. The course taken by the sympathetic fibres was determined by observing whether nerve sections at different sites blocked these responses. Two pathways were found: one group of fibres leaves the superior cervical ganglion in the internal carotid nerve, joins the auricular branch of the vagus nerve at the jugular foramen and passes via this nerve to the facial nerve, which it joins in the facial canal just central to the stylomastoid foramen. A second, apparently smaller group of fibres travels in the internal carotid nerve, crosses the roof of the tympanic bulla in the tympanic plexus, enters the middle cranial cavity through the foramen lacerum and passes with the greater superficial petrosal nerve to join the facial nerve at the geniculate ganglion.