CHAPTER X.

PLATE XX.- -THE PAROTID GLAND.

FIG. 1. A dissection to exhibit the parotid gland.

FIG. 2. Explains the former; a, a, the integuments turned back; b, the parotid gland; c, its pipe or duct passing over the masseter, then perforating, d, the buccinator muscle, and opening into the mouth opposite the second molar tooth. The flow of saliva into the mouth is incessant, and it is one of the most useful digestive fluids. It is favorable to the maceration and division of the food, it assists it in deglutition and transformation into chyme; it also renders more easy the motions of the tongue in speech and singing.

FIG. 1. The larynx, pharynx, &c. a, the os hyoides, b, the epiglottis pressed down, thus covering the glottis, or opening of the larynx; as it does in the act of deglutition.

FIG. 2. Exhibits the larynx, and trachea; which is a continuation of the former; b, the epiglottis ; g, the arytenoid cartilages; e, the thyroid cartilage, exceedingly strong, for the protection of the upper part of the air tube; d, the cartilaginous ringlets of the trachea or wind-pipe, each forming nearly two-thirds of a circle, and com pleted by f, a soft membrane, which, from its apposition to, e, Fig. 1, the œsophagus, accommodates itself to tne substances passing into the stomach,

FIG. 3. The larynx or upper part of the wind-pipe of a bird. This is called the inferior larynx, where the vocal organ is formed by a compression of the trachea, for it is here contracted into a narrow chink, and divided into two openings by a slender bone, or tense membrane, which, in producing sounds, resembles the mechanism of a musical instrument. In the plate this part of the larynx is a little turned up to show the tendinous band at this extremity stretched across it, which is furnished from the surrounding parts with muscles to modulate the tone.