The larynx extends from the top of the epiglottis to the lower edge of the cricoid cartilage. It is composed of the three large cartilages - epiglottis, thyroid, and cricoid - and three pairs of small ones - the arytenoids, the corniculae laryngis or cartilages of Santorini, and the cuneiform or cartilages of Wrisberg.

The position of the larynx in relation to the spine varies according to age. In the infant it lies opposite the second, third, and fourth cervical vertebrae; in the adult it lies opposite the fourth, fifth, and sixth. The larynx being loosely attached varies in relation to the vertebrae according to the position of the head, so that the anterior portion of the cricoid cartilage may be opposite the seventh cervical vertebra in some positions.

Fig. 157.   Anterior view of hyoid bone and larynx.

Fig. 157. - Anterior view of hyoid bone and larynx.

Epiglottis

Usually the tip of the epiglottis lies lower than the dorsum of the tongue, so that looking into the mouth it is not seen; it may, however, be brought into view by depressing the base of the tongue and drawing it forward with a long tongue depressor. As the epiglottis rises above the level of the hyoid bone, a cutthroat wound passing above that bone may cut its tip entirely off. In viewing the epiglottis from above downward it is seen to project somewhat backward in its middle. This is visible in the laryngoscopic mirror and is called the cushion of the epiglottis.

Running forward from the epiglottis to the base and the sides of the tongue are three folds of mucous membrane, one median and two lateral, called the glosso-epiglottic folds. These form four fossae; those on each side of the median line are called the vallecula. In these fossae foreign bodies, such as fish-bones, etc., may become lodged. They are readily seen by the laryngoscopic mirror.

The thyrohyoid membrane passes between the hyoid bone above and the thyroid cartilage below; crossing it is the hyoid branch of the superior thyroid artery. It is a quite small vessel, of little clinical importance, and ordinarily does not reach the median line.

The posterior edge of this membrane, running from the superior cornu of the thyroid cartilage to the hyoid bone, is called the thyrohyoid ligament. This ligament has a small cartilaginous nodule in it, the cartilago triticea. Piercing the membrane on its side are the internal branches of the superior larvngeal nerve and the superior laryngeal vessels. The external branch of the superior laryngeal nerve supplies the cricothyroid muscle, while the internal is the nerve of sensation of the larynx.

Pharyngotomy

Sometimes, in order to remove foreign bodies in the larynx or oesophagus, an opening is made through the membrane between the hyoid bone and thyroid cartilage.

Thyroid Cartilage

This is the largest cartilage of the larynx and contains the vocal cords. They lie immediately behind or just below the most prominent portion of its anterior edge, commonly called "Adam's apple." Since the cartilage is large and strong and as age advances tends to calcify, cut-throat wounds, while opening the cavity within, do not often pass entirely through the cartilage. This cartilage may be fractured by violence. This is often fatal on account of the blood flowing into the trachea and lungs below or on account of oedema of the lining mucous membrane causing obstruction of the breathing. Thyrotomy or division of the thyroid cartilage in the median line is sometimes done to remove foreign bodies or new growths. In these cases the voice will be likely to be impaired by the interference with the vocal cords.

Fig. 158.   Side view of hyoid bone and larynx.

Fig. 158. - Side view of hyoid bone and larynx.