other musical instrument is capable; and, lastly, we have a specific contrivance for dividing the pneumatic part from the mechanical, and for preventing one set of functions from interfering with the other. The mouth, with all these intentions to serve, is a single cavity; is one machine, with its parts neither crowded nor confined, and each unembarrassed by the rest.” It should be added, the mouth is also the immediate seat of one of the senses, and is in intimate communication with a second sense; both these senses are always excited while the principal business performed by the machine is carried on, and are necessarily excited by the very working of the machine, and the sensations induced in the natural and sound state of the apparatus are invariably pleasurable. 611. The food is delivered by the pharynx to the esophagus (fig. CLIII. 12), a tube composed partly of membrane and partly of muscle. Its muscular fibres consist of a double layer, an external and an internal layer; the external has a longitudinal direction; the internal describes portions of a circle around the tube. By the contraction of the longitudinal fibres the length, and by the contraction of the circular fibres, the diameter of the tube is diminished. Cellular membrane envelops these layers of fibres externally, and mucous membrane covers them internally. When the tube is contracted, the mucous membrane is disposed in folds, which disappear when it is dilated, and these folds allow of the expansion of the tube without injury to the delicate tissue that lines it. The food passes slowly along the esophagus urged towards the stomach, not by its own gravity, but by a force exerted upon it by the tube itself, chiefly by the contraction of its circular fibres. Delivered at length to the stomach, the food is incapable of returning into the esophagus in consequence of the oblique direction in which the esophagus enters the stomach, the obliquity of its entrance serving the office of a valve. [Illustration: Fig. CLXVI.—_View of the Stomach with its Muscular Coats displayed._ 1. The esophagus terminating in the stomach. 2. The cardiac orifice. 3. The pylorus. 4. The commencement of the duodenum. 5. The large curvature of the stomach. 6. The small curvature. 7. The large extremity. 8. The small extremity. 9. The longitudinal muscular fibres. 10. The circular muscular fibres.] 612. The stomach is a bag of an irregular oval shape (fig CLXVI.), capable, in the adult, of containing about three pints. It is placed transversely across the upper part of the abdomen (fig. LX. 7). It occupies the whole epigastric (fig. CV. 3), and the greater part of the left hypochondriac regions (fig. CVII. 3). Above, it is in contact with the diaphragm, the arch of which extends over it (fig. LX. 7, b); below with the intestines (fig. LX. 8, 9), on the right side with the liver (fig. LX. 6), and on the left side with the spleen (fig. CLXVIII. 5).