The olfactory nerve comprises (a) the olfactory filaments; (b) olfactory bulb; (c) olfactory tract; and (d) olfactory roots.

Olfactory Filaments

These non-medullated fibres, twenty in number, are the axons of the bipolar nerve cells situated in the olfactory mucous membrane. Three groups are described (a) medial, from the nasal septum; (b) central, from the roof of the nose, and (c) lateral, from the lateral wall. The filaments pass through the cribriform plate (lamina cribrosa) of the ethmoid, to enter the under surface of the olfactory bulb.

Olfactory Bulb

A small oval-shaped mass of grey matter resting upon the upper surface of the cribriform plate.

Olfactory Tract

This elongated band of white matter arises from the posterior extremity of the olfactory bulb, and occupies a groove, the olfactory sulcus, on the inferior aspect of the frontal lobe. It is connected to the cerebrum by the olfactory roots (striae).

Olfactory Roots

There are two olfactory roots, the lateral of which can be traced to the piriform area of the temporal lobe, while the medial root passes to the gyrus fornicatus.