Autonomic pathways in the orbit of the human fetus and the rhesus monkey.

In order to study the three-dimensional topography of the intra-orbital autonomic nerve plexuses and the input for these systems, human fetuses and adult rhesus monkeys were investigated. Specimens of the orbits were processed according to the histochemical acetylcholinesterase methods for staining of peripheral nerves. The nerve fibers enter the orbit along the following pathways: 1. bundles of nerve fibers from the pterygopalatine ganglion (mainly parasympathetic) by penetrating the orbital muscle (Müller); 2. perivascularly along the ophthalmic artery (sympathetic). In the orbit the nerve fibers intermingle. The pathways of the nerve fibers from this interwoven nerve plexus towards the target organs are: 1. perivascularly along branches of the ophthalmic artery; 2. perineurally along and in the branches of the ophthalmic and maxillary nerves; 3. independently of blood vessels and cranial nerve branches in Tenon's capsule. Moreover, bundles of nerve fibers from the ciliary ganglion contribute to the innervation of extraocular structures, e.g. the eyelids. It can be concluded that, as far as the autonomic innervation of the orbit is concerned, the monkey is a good animal model for neuroanatomical studies.