Lacrimal nerve

The lacrimal nerve is the smallest of the three branches of the ophthalmic.

It sometimes receives a filament from the trochlear nerve, but this is possibly derived from the branch which goes from the ophthalmic to the trochlear nerve.

It passes forward in a separate tube of dura mater, and enters the orbit through the narrowest part of the superior orbital fissure.

In the orbit it runs along the upper border of the lateral rectus, with the lacrimal artery, and communicates with the zygomatic branch of the maxillary nerve.

It enters the lacrimal gland and gives off several filaments, which supply the gland and the conjunctiva.

Finally it pierces the orbital septum, and ends in the skin of the upper eyelid, joining with filaments of the facial nerve.

The lacrimal nerve is occasionally absent, and its place is then taken by the zygomaticotemporal branch of the maxillary nerve. Sometimes the latter branch is absent, and a continuation of the lacrimal nerve is substituted for it.

Functions
It provides innervations for the lacrimal gland, conjunctiva, and the lateral upper eyelids.

The zygomatic nerve carries sensory fibers from the skin. It also carries post-synaptic parasympathetic fibers (originating in the pterygopalatine ganglion) to the lacrimal nerve via a communication. These fibers will eventually provide innervation to the lacrimal gland.