601. As long as the operations of mastication and insalivation go on, the mouth forms a closed cavity from which the food cannot escape; for the lips enclose it before, the cheeks at the sides, the tongue below, and the soft palate behind, the inferior edge of which being applied in close and firm contact with the base of the tongue, prevents all communication between the mouth and the pharynx. 602. When, by mastication, the food is sufficiently divided, and by insalivation softened and animalized to fit it for the future changes it is to undergo, it is collected by the tongue, and carried by that organ to the back part of the mouth. The soft palate (fig. CLII. 1), obedient to the stimulus of the duly prepared food, rises the instant it is touched by it, and affords it a free passage to the pharynx (figs. CLIII. 10, and CLIV. 10). 603. The pharynx (fig. CLIII. 10), a muscular bag, immediately continuous with the mouth (fig. CLIII. 1), is a vestibule into which open several highly important organs. Before is the entrance to the windpipe, termed the glottis (fig. CLIV. 9), leading directly to the larynx (fig. CLIV. 8); at the sides are the mouths of two ducts, termed the Eustachian tubes, which lead to the internal part of the organ of hearing; above are two entrances to the nose (fig. CLIV. 1); and below is the passage to the stomach (fig. CLIII. 12). 604. Were the food to enter the Eustachian tubes or the nose, it would occasion great inconvenience; were it to enter the glottis, it would cause death. It is prevented from entering the Eustachian tubes and the nose by the soft palate (fig. CLII. 1 and 2), which by the very act of rising to afford an opening from the mouth to the pharynx, is carried over the other apertures so as completely to close them. By the varied direction of the muscular fibres which enter into the composition of this organ, it is enabled to execute the different and even opposite motions required in the performance of its important office.