The first pair of cranial nerves is the olfactory, a number of fine filaments whose superficial origin is the olfactory bulbs. These bulbous bodies are lodged in the ethmoidal fosste of the ethmoid bone, two depressions in front of the cranium, in which a number of minute openings appear and allow of their passage out of the cranium into the superior parts of the nostrils, where they are distributed over the schneiderian membrane.

The olfactory nerves are the first pair of special nerves, whose function is that of receiving the impressions of odours, which they carry to the 1 train.