Thin bone projections that subdivide each nasal cavity into a series of groovelike passageways and curve from the outer part of the nose in toward the septum (cartilage wall between the nostrils). The turbinates are covered by thick mucous membranes. Under the membrane, sensitive, spongy, erectile tissue causes the tissues in the area to fill with blood and swell when exposed to cold, dry, or contaminated air. This swelling narrows the nasal passages and slows the air coming in so that it can be warmed and humidified by mucus as the air is breathed in. The mucus also serves to trap dust particles. When the tissues lining the turbinates are exposed to cold air, mucus production increases, which results in a runny nose in cold weather.