nasociliary nerve, usually the first branch of the ophthalmic nerve. It branches into the communicating branch with the ciliary ganglion; the long ciliary nerves, which are sensory to the eyeball but may also contain sympathetic fibers for pupillary dilation; the posterior ethmoidal nerve, which supplies the posterior ethmoidal air cells and the sphenoid sinus; the infratrochlear nerve, which distributes to the medial part of the upper and lower eyelids, the lacrimal sac, and the skin of the upper half of the nose; and the anterior ethmoidal nerve, which supplies the anterior cranial fossa, nasal cavity, and skin of the lower half of the nose.
