Nostrils

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Anatomy and function of the main organs of the respiratory system.

The nostrils, also known as the anterior/external nasal apetures or nares, are the two pear-shaped anterior openings to the nasal cavity.

The external anatomy of the nose comprises a pyramidal structure that protrudes from the face and it is mostly composed of cartilage. The apex is considered to be the tip of the nose. The base of this pyramidal structure refers to the inferior surface, commonly recognized as the area containing the nostrils. This base is continuous with the anterior part of the head.

The section between the base and apex is termed the nasal dorsum. Below the apex are the two openings called the nostrils and they serve as entrances to the nasal cavity. These nostrils are separated by the nasal septum. Laterally, they are bordered by the ala of the nose. The supporting skeleton of the nose is composed of both bone and hyaline cartilage.

The bony part consists of nasal bones, the frontal processes of the maxillae, the nasal part of the frontal bone and its nasal spine, and the bony parts of the nasal septum. The cartilaginous part consists of five main cartilages: two lateral cartilages, two alar cartilages, and one septal cartilage. The alar cartilages are U-shaped, flexible and mobile, and regulate the dilation or constriction of the nostrils through the contraction of the nasalis muscle.