The Larynx, and the Syrinx

The trachea is commonly kept open by complete, or incomplete, rings of cartilage, and the uppermost of these undergo special modifications, which convert them into a Larynx, an organ which, under certain circumstances, becomes an instrument of voice.

When completely developed, the larynx presents a ringlike cartilage called cricoid, which lies at the summit of the trachea. With the anterior and dorsal edge of this, two arytenoid cartilages are movably articulated, and a thyroid cartilage of a V-shape, open behind, is articulated movably with its sides. Folds of the mucous membrane, containing elastic tissue, termed the vocal cords, stretch from the arytenoid cartilages to the reentering angle of the thyroid cartilage, and between them lies a slit - like passage, the glottis. This is covered by a cartilage, the epiglottis, attached to the reentering angle of the thyroid, and to the base of the tongue. Folds of mucous membrane, extending from the epiglottis to the arytenoid cartilages, are the aryepiglottic ligaments. The inner surfaces of these end below in the false vocal cords, between which and the true chordae vocales lie recesses of the mucous membrane, the ventricles of the larynx.

The chief accessory cartilages are the cartilages of Santorini, attached to the summits of the arytenoid cartilages, and the cartilages of Wrisberg, which lie within the aryepiglottic ligaments.

Birds possess a larynx in the ordinary position; but it is another apparatus, the lower larynx or syrinx, developed either at the end of the trachea, or at the commencement of each bronchus, which is their great vocal organ.