The ethmoidal air cells are small, interconnected cavities located within the ethmoid bone, which is situated between the eyes and forms part of the nasal cavity. These air-filled spaces help to lighten the weight of the skull and contribute to the overall structure of the nasal passages. These cells are lined with mucous membranes that produce mucus, aiding in the humidification and filtration of inhaled air. They also play a role in the sense of smell by allowing air to flow through the nasal cavity, where olfactory receptors are located.