consider the mechanism of swallowing, we shall study the arrangements which prevent food, passed through the fauces, from entering either the nasal chambers above or the windpipe below and in front. At the level of the lower border of the thyroid cartilage the pharynx becomes the relatively narrow œsophagus. This tube, which lies behind the trachea, and slightly to its left side, passes with a straight course to the abdomen. It traverses the chest, lying behind the heart, pierces the diaphragm, and just beneath it joins the stomach. Its length is about 9 inches. The stomach is a sickle-shaped bag. It has two apertures—the cardiac orifice, or junction with the œsophagus; and the pyloric orifice, or junction with the small intestine. It is so folded on itself that these two apertures are not more than 4 inches apart. Its outline may be drawn on the body-wall with a piece of charcoal from a point an inch below and an inch to the left side of the lower end of the breast-bone, the position of the cardiac orifice, to a point about 4 inches below the end of the breast-bone, and an inch or two to the right side of the mid-line of the body, the position of the pyloric orifice, with a slight curvature to represent the upper border; to represent the lower border the same two points are joined by a bold curve, bulging upwards to the nipple, outwards to the side of the body, and downwards some distance on the abdomen (_cf._ Fig. 2). [Illustration: FIG. 6. The stomach has been cut across a short distance from the pyloric valve, and removed, to show the viscera which lie behind it. The descending aorta and the vena cava rest upon the vertebral column. They are crossed by the pancreas and the transverse portion of the duodenum. The head of the pancreas is enclosed by the curvatures of the duodenum. The ducts of the liver and pancreas are seen entering the descending duodenum side by side.]