The nasociliary nerve is intermediate in size between the frontal and lacrimal nerves and is more deeply placed in the orbit. It passes across the optic nerve and runs a slanting course across to the wall of the orbital cavity. It passes through the anterior ethmoidal opening as the anterior ethmoidal nerve and enters the cranial cavity just above the cribriform plate of the ethmoid bone. It suppliesmycontentbreak branches to the mucous membrane of the nasal cavity and finally emerges between the inferior border of the nasal bone and the side nasal cartilages as the external nasal branch.