When an animal swallows, the larynx is raised to press against the epiglottis and root of the tongue, preventing food from entering the air passages. Just below the epiglottis is the angular thyroid cartilage, composed of two vertical plates that join in the front of the neck. The rear portions of the thyroid cartilage grip the circular cricoid cartilage, which keeps the laryngeal passageway open at all times. On each side of the rear upper border of the cricoid cartilage is a small, movable arytenoid cartilage. In frogs and toads the voice box leads directly from the pharynx into the lungs.
Frogs have auxiliary vocal sacs that, when inflated, serve to make the voice more resonant.
Analogues of such resonating chambers are found among mammals in the hollow hyoid bone of the howling monkey and in the sac leading from the larynx of a gorilla virtually to its armpit. In birds, the voice is produced in an organ known as the syrinx. In the human larynx, two pairs of vocal cords are present. They are made of elastic connective tissue covered by folds of mucous membrane. Below the false cords are the true vocal cords, extending from the arytenoid cartilages to the angle of the thyroid cartilage.