A nose is a sensory organ and respiratory structure in vertebrates. It consists of a nasal cavity inside the head, and an external nose on the face. The external nose houses the nostrils, or nares, a pair of tubes providing airflow through the nose for respiration. Where the nostrils pass through the nasal cavity they widen, are known as nasal fossae, and contain turbinates and olfactory mucosa. The nasal cavity also connects to the paranasal sinuses (dead-end air cavities for pressure buffering and humidification). From the nasal cavity, the nostrils continue into the pharynx, a switch track valve connecting the respiratory and digestive systems.
In humans, the nose is located centrally on the face and serves as an alternative respiratory passage especially during suckling for infants. The protruding nose that is completely separate from the mouth part is a characteristic found only in therian mammals. It has been theorized that this unique mammalian nose evolved from the anterior part of the upper jaw of the reptilian-like ancestors (synapsids).