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8 THE VIBRATORY APPARATUS.
to pass out into the throat, and when it is lowered and shut prevents the food from going into the larynx during swallowing.
12. The Cricoid.—The lower piece of cartilage, shaped like a ring and consequently named the cricoid or ring-shaped cartilage, forms the foundation of the larynx (Fig. 3). It has a fancied resemblance to a signet ring; it is horizontal below, but above it gradually slopes upwards from the narrow ring part in front to the expanded signet part behind (Fig. 4).
On the top of the signet part on each side is a little hollow into which the arytenoid cartilages fit. Lower down on each side is another hollow where the thyroid cartilage forms a joint with the cricoid (Fig. 4).
13. The Arytenoids.—The two arytenoid cartilages (so called because of their shape, which is supposed to be that of a pitcher) are jointed on to each side of the top of the signet part of the cricoid in such a way that they can be rotated around an axis passing straight through them from top to bottom (Fig. 9). Their lower surfaces are triangular in shape and are prolonged into two processes, a front process called the vocal process and an external process called the muscular process (Fig. 8). To the vocal process are attached the posterior ends of the vocal cords, and to the external process are attached the muscles that make the arytenoids rotate on the cricoid, and so regulate the distance between the two vocal cords (Figs. 8 and 9).
14. The Thyroid.—The thyroid cartilage protects the vocal cords. It consists of two wings, which meet together in front forming a definite angle surmounted by a notch (Fig. 2) ; this can be easily felt in the middle of the neck, |
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