The _thyroid cartilage_ consists of two V-shaped pieces, one on either side of the larynx, meeting at their points in front, and each terminating at the back in an upward and a downward projection. Between the back portions of the thyroid is a space equal to about one third of the circumference of the larynx. This is occupied by the greater portion of the _cricoid cartilage_. This cartilage has the general shape of a signet ring and is so placed that the part corresponding to the signet fits into the thyroid space, while the ring portion encircles the larynx just below the thyroid. Muscles and connective tissue pass from the thyroid to the cricoid cartilage at all places, save one on each side, where the downward projections of the thyroid form hinge joints with the cricoid. These joints permit of motion of either cartilage upon the other. At the summit of the cricoid cartilage, on each side, is a small piece of triangular shape, called the _arytenoid cartilage_. Each arytenoid is movable on the cricoid and is connected with one end of a vocal cord. [Fig. 150] Fig. 150—*Vocal cords* as seen from above. _A._ In producing sound, _B._ During quiet breathing. *The Vocal Cords* are formed by two narrow strips of tissue which, connecting with the thyroid cartilage in front and the arytenoid cartilages behind, lie in folds of the mucous membrane. They have the general appearance of ridge-like projections from the sides of the larynx, but at their edges they are sharp and smooth. The open space between the cords is called the _glottis_. When sound is not being produced, the glottis is open and has a triangular form, due to the spreading apart of the arytenoid cartilages and the attached cords. But when sound is being produced, the glottis is almost completely closed by the cords. Above the vocal cords, and resembling them in appearance, are two other folds of membrane, called the _false vocal cords_ (B, Fig. 149). The false cords do not produce sound, but they aid in the closing of the glottis. *How the Voice is Produced.*—The voice is produced through the vibrations of the vocal cords. A special set of muscles draws the arytenoid cartilages toward each other, thereby bringing their edges very near and parallel to each other in the passage. At the same time other muscles act on the thyroid and cricoid cartilages to separate them at the top and give the cords the necessary tension. With the glottis now almost closed, blasts of air from the lungs strike the sharp edges of the cords and set them in vibration (Fig. 150). The vocal cords do not vibrate as strings, like the strings of a violin, but somewhat as reeds, similar to the reeds of a French harp or reed organ.