A, hyoid bone;
  B, thyro-hyoid membrane;
  C, thyroid cartilage;
  D, erico-thyroid membrane;
  E, cricoid cartilage, lateral ligaments seen on each side;
  F, upper ring of the trachea. 
  ("Adam’s apple” is in the V-shaped groove on a line with B and C.)
]

The larynx has for a framework two cartilages, the thyroid and the cricoid, one above the other.  The larger of these, called the thyroid, from a supposed resemblance to a shield, consists of two extended wings which join in front, but are separated by a wide interval behind.  The united edges in front project and form the “Adam’s apple” plainly seen and easily felt on most people, especially on very lean men.

Above and from the sides rise two horns connected by bands to the hyoid bone from which the larynx is suspended.  This bone is attached by muscles and ligaments to the skull.  It lies at the base of the tongue, and can be readily felt by the finger behind the chin at the angle of the jaw and the neck (sec. 41 and Fig. 46).  From the under side of the thyroid two horns project downwards to become jointed to the cricoid.  The thyroid thus rests upon, and is movable on, the cricoid cartilage.

The cricoid cartilage, so called from its fancied resemblance to a signet-ring, is smaller but thicker and stronger than the thyroid, and forms the lower and back part of the cavity of the larynx.  This cartilage is quite sensitive to pressure from the fingers, and is the cause of the sharp pain felt when we try to swallow a large and hard piece of food not properly chewed.

[Illustration:  Fig. 149.—­Diagram of a Sectional of Nasal and Throat Passages.

  C, nasal cavities;
  T, tongue;
  L, lower jaw;
  M, mouth;
  U, uvula;
  E, epiglottis;
  G, larynx;
  O, oesophagus.
]

On the upper edge of the cricoid cartilage are perched a pair of very singular cartilages, pyramidal in shape, called the arytenoid, which are of great importance in the production of the voice.  These cartilages are capped with little horn-like projections, and give attachment at their anterior angles to the true vocal cords, and at their posterior angles to the muscles which open and close the glottis, or upper opening of the windpipe.  When in their natural position the arytenoid cartilages resemble somewhat the mouth of a pitcher, hence their name.

351.  The Vocal Cords.  The mucous membrane which lines the various cartilages of the larynx is thrown into several folds.  Thus, one fold, the free edge of which is formed of a band of elastic fibers, passes horizontally outwards from each side towards the middle line, at the level of the base of the arytenoid cartilages.  These folds are called the true vocal cords, by the movements of which the voice is produced.

Above them are other folds of mucous membrane called the false vocal cords, which take no part in the production of the voice.  The arrangement of the true vocal cords, projecting as they do towards the middle line, reduces to a mere chink the space between the part of the larynx above them and the part below them.  This constriction of the larynx is called the glottis.