Anterior ethmoidal nerve

The anterior ethmoidal nerve is an extraconal branch of the nasociliary nerve, a branch of the ophthalmic division of the trigeminal nerve. Some authors describe it as either the terminal branch or a direct continuation of the nasociliary nerve.  It branches off distal to the infratrochlear nerve and courses through the medial aspect of the extraconal space of the orbit.

It exits the orbit through the anterior ethmoidal foramen and runs in the roof of the anterior and middle ethmoidal sinuses supplying the mucosa of these sinuses before ascending into the anterior cranial fossa briefly through the cribriform plate, supplying the dura of the anterior cranial fossa as it does so.

It then enters the superior nasal cavity by descending through the cribriform plate by passing through the nasal slit immediately lateral to the crista galli to supply the mucosa of the anterosuperior half of the nasal septum and lateral nasal wall. It grooves the internal surface of the nasal bone and terminates by piercing nasal cartilage to become the external nasal nerve, supplying the skin of the dorsal nose and the nasal apex.