The tentorial nerve in monkeys is a branch of the cavernous plexus

The origin and content of the tentorial nerve in cynomolgus and rhesus monkeys were studied using light and electron microscopic inspection of interrupted serial sections of the trigeminal/cavernous sinus region combined with selective nerve degeneration. The nerve was invariably a branch of the cavernous plexus rather than a branch of the trigeminal ganglion or ophthalmic nerve as described in earlier reports. The cavernous plexus branch forming the tentorial nerve joined and passed back in the trochlear nerve while it remained in the lateral wall of the cavernous sinus, then left the trochlear to be distributed in the tentorium cerebelli. It was composed of trigeminal fibres mainly from the ophthalmic division together with sympathetic fibres from the superior cervical ganglion. The source of another group of unmyelinated fibres was unidentified but they are likely to be parasympathetic.