Nasal lining. Transmission electron micrograph (TEM) of a transverse section through cilia (purple) covering the epithelial lining of the nasal cavity. Cilia are microscopic hair-like structures that are covered with a sticky mucus and trap dust and other inhaled particles. Co- ordinated wave-like beating of the cilia propels the mucus to the back of the nose (pharynx), where it is swallowed.