Trigeminal nerve pathways to the cerebral arteries in monkeys.

Two or three or sometimes more fine intracavernous branches were traced from the ophthalmic nerve using serial section reconstruction and induced nerve degeneration. They joined the cavernous plexus and were distributed forward with autonomic nerves to the adventitia of the internal carotid artery, emerging from the sinus with the artery. A strong recurrent branch from the plexus joined the abducent nerve, passed back and left the nerve at pontine level to innervate the basilar artery and the caudal circle of Willis. The recurrent nerve was absent from one side of two animals and showed asymmetry in others. No branch issued intracranially to the plexus from the maxillary nerve, but in the pterygopalatine fossa the orbitociliary branch of the maxillary nerve gave off one or two filaments that re-entered the cranial cavity through the medial infraorbital fissure and joined the cavernous plexus. Their content augmented the ophthalmic afferent distribution. All plexus branches with trigeminal fibres also contained autonomic fibres. The results show, firstly, that the cavernous plexus consists of a mixture of sensory and autonomic nerves (sympathetic and parasympathetic) and, secondly, that afferents of the internal carotid artery and rostral circle of Willis and those to the basilar artery and caudal circle of Willis are distributed separately.