Sunday, April 6, 2008

5 - cartilages of the nose ( external nose )

the External Nose (Nasus Externus; Outer Nose)—The external nose is pyramidal in form, and its upper angle or root is connected directly with the forehead; its free angle is termed the apex. Its base is perforated by two elliptical orifices, the nares, separated from each other by an antero-posterior septum, the columna. The margins of the nares are provided with a number of stiff hairs, or vibrissæ, which arrest the passage of foreign substances carried with the current of air intended for respiration. The lateral surfaces of the nose form, by their union in the middle line, the dorsum nasi, the direction of which varies considerably in different individuals; the upper part of the dorsum is supported by the nasal bones, and is named the bridge. The lateral surface ends below in a rounded eminence, the ala nasi. Structure.—The frame-work of the external nose is composed of bones and cartilages; it is covered by the integument, and lined by mucous membrane. The bony frame-work occupies the upper part of the organ; it consists of the nasal bones, and the frontal processes of the maxillæ. The cartilaginous frame-work (cartilagines nasi) consists of five large pieces, viz., the cartilage of the septum, the two lateral and the two greater alar cartilages, and several smaller pieces, the lesser alar cartilages . The various cartilages are connected to each other and to the bones by a tough fibrous membrane. The cartilage of the septum (cartilago septi nasi) is somewhat quadrilateral in form, thicker at its margins than at its center, and completes the separation between the nasal cavities in front. Its anterior margin, thickest above, is connected with the nasal bones, and is continuous with the anterior margins of the lateral cartilages; below, it is connected to the medial crura of the greater alar cartilages by fibrous tissue. Its posterior margin is connected with the perpendicular plate of the ethmoid; its inferior margin with the vomer and the palatine processes of the maxillæ.
It may be prolonged backward (especially in children) as a narrow process, the sphenoidal process, for some distance between the vomer and perpendicular plate of the ethmoid. The septal cartilage does not reach as far as the lowest part of the nasal septum. This is formed by the medial crura of the greater alar cartilages and by the skin; it is freely movable, and hence is termed the septum mobile nasi. The lateral cartilage (cartilago nasi lateralis; upper lateral cartilage) is situated below the inferior margin of the nasal bone, and is flattened, and triangular in shape. Its anterior margin is thicker than the posterior, and is continuous above with the cartilage of the septum, but separated from it below by a narrow fissure; its superior margin is attached to the nasal bone and the frontal process of the maxilla; its inferior margin is connected by fibrous tissue with the greater alar cartilage. The greater alar cartilage (cartilago alaris major; lower lateral cartilage) is a thin, flexible plate, situated immediately below the preceding, and bent upon itself in such a manner as to form the medial and lateral walls of the naris of its own side. The portion which forms the medial wall (crus mediale) is loosely connected with the corresponding portion of the opposite cartilage, the two forming, together with the thickened integument and subjacent tissue, the septum mobile nasi. The part which forms the lateral wall (crus laterale) is curved to correspond with the ala of the nose; it is oval and flattened, narrow behind, where it is connected with the frontal process of the maxilla by a tough fibrous membrane, in which are found three or four small cartilaginous plates, the lesser alar cartilages (cartilagines alares minores; sesamoid cartilages). Above, it is connected by fibrous tissue to the lateral cartilage and front part of the cartilage of the septum; below, it falls short of the margin of the naris, the ala being completed by fatty and fibrous tissue covered by skin. In front, the greater alar cartilages are separated by a notch which corresponds with the apex of the nose.

The muscles acting on the external nose have been described in the section on Myology. The integument of the dorsum and sides of the nose is thin, and loosely connected with the subjacent parts; but over the tip and alæ it is thicker and more firmly adherent, and is furnished with a large number of sebaceous follicles, the orifices of which are usually very distinct. The arteries of the external nose are the alar and septal branches of the external maxillary, which supply the alæ and septum; the dorsum and sides being supplied from the dorsal nasal branch of the ophthalmic and the infraorbital branch of the internal maxillary. The veins end in the anterior facial and ophthalmic veins. The nerves for the muscles of the nose are derived from the facial, while the skin receives branches from the infratrochlear and nasociliary branches of the ophthalmic, and from the infraorbital of the maxillary.

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