back of the cricoid cartilage on which the arytenoid cartilages rest and thus produces tension in the vocal cords. The vocal cords are relaxed and shortened by the thyroarytenoid muscles and by the muscles in the vocal cords themselves. The thyro-arytenoid muscles lie parallel to and Epiglottis and its Cushion FIG. 12. THE SUPERIOR APERTURE OF THE LARYNX AND THE RIMA GLOTTIDIS AS SEEN BY THE AID OF THE LARYNGOSCOPE UNDER DIFFERENT CONDITIONS A, ordinary quiet inspiration; B, very deep inspiration; C, vocalization, especially in singing high notes; R.G., rima glottidis. (From Buchanan, A Manual of Anatomy.) continuous with the true vocal cords. They are attached in front to the lower front surface of the arytenoid cartilages, and their action is to bring the arytenoid cartilages nearer to the thyroid cartilage (Figure 11). The larynx as a whole is acted upon by extrinsic muscles connected with the sternum, the hyoid bone, the tongue, and the pharynx, by means of which it may be raised and lowered and tilted forward and backward. Some of these movements are necessary in swallowing and in various types of breathing; others seem to have a direct bearing upon resonance. The Pharynx The pharynx (Figure 1) is a vertical passage lying behind the mouth and extending from the base of the skull above to the larynx and œsophagus below. It is cone-shaped, wide above and narrow below. The back and side walls consist of muscular and fibrous tissue; in front the pharynx opens into three spaces which lie one immediately above the other, the larynx, the mouth, and the nasal cavity (Figure 1). In the production of voice the pharynx serves the double purpose of providing a free passage for the current of air and acting as a resonator to reinforce the tone generated in the larynx. The pharynx is capable of modification in all of its dimensions. It can be shortened from above by lifting the soft palate against its back wall, thus cutting off the upper pharynx. It can be shortened from below by the contraction of the fibres that run lengthwise through its walls from the base of the skull to the larynx and by the raising of the larynx. The horizontal dimension can be modified by the contraction and relaxation of the circular fibres which make up the greater part of its muscular wall and by the moving forward or backward of the tongue and larynx (Figures 13 and 14). Below, the pharynx has two openings which are capable of variation in size but which are not normally open at the same time. In eating, the pharynx is continuous with the œsophagus, the larynx being closed by the epiglottis and the false vocal cords, as has been described. In breathing, the opening into the oesophagus becomes a narrow slit, and the pharynx opens into the larynx (Figure 1). The front opening from the pharynx into the mouth may be wholly or partially closed by the action of the tongue, the FIG. 13. THE POSTERIOR WALL OF THE PHARYNX pillars of the fauces, and the soft palate. Above, the opening into the nasal passages may be partially or entirely closed by the elevation of the soft palate. The Mouth Like the pharynx, the mouth (Figure 15) is a resonator which is capable of many changes, both in capacity and in size of openings. It is nearly oval in shape and consists of two cavities, the back cavity (the mouth proper) and a front cavity having for its outer wall the lips and cheeks, and for its inner, the teeth and gums. The lips, which are of considerable use in eating, are of very particular importance FIG. 14. THE PHARYNX OPENED FROM BEHIND in the production of voice. Through their system of muscles they are capable of changing the size of the mouth aperture, and by projection the size of the cavity itself, thus increasing the adaptability of the mouth as a resonator. The structural base of the mouth is the lower jaw or mandible. It is the largest and strongest bone of the face. Its front part is shaped somewhat like a horseshoe and contains the lower teeth; at each extremity it bends sharply upward at an angle which is little short of a right angle. Each of these perpendicular extremities of the jaw is attached to the skull in front of the middle part of the ear by means of a movable joint, the most mobile in the body. These joints, together with the strong muscles with which the jaw is furnished, make possible the powerful movements necessary for the mastication of food. The movements of the lower jaw also influence the character of the mouth resonator both as to capacity and to size of openings (Figure 1). The mouth cavity proper is bounded in front by the teeth and gums, above by the hard and soft palates (the roof of the mouth), and below by the floor of the mouth, the greater part of which is taken up by the tongue. At the back it |