=The Stomach.=—The stomach is the principal organ of digestion. It is the most dilated part of the alimentary canal, and is situated between the termination of the esophagus and the commencement of the small intestines. It is placed in part immediately behind the anterior wall of the abdomen and beneath the diaphragm.
_The lesser curvature_ of the stomach extends between the cardiac and the pyloric orifices along the right border of the organ.
_The greater curvature_ of the stomach is directed to the left, and is four or five times as long as the lesser curvature.
_The cardia_ is the point at which the esophagus enters the stomach wall.
[Illustration: FIG. 23—The coeliac axis and its branches. (Gray)]
_The cardiac orifice_ is the opening by which the esophagus communicates with the stomach. It is sometimes called the esophageal opening. It is situated on a level with the body of the tenth and eleventh dorsal vertebrae. It is to the left of and in front of the aorta. On the anterior surface of the body the cardiac orifice corresponds to the articulation of the seventh left costal cartilage to the sternum.
_The pylorus_ is the point at which the stomach passes into the duodenum.
_The pyloric orifice_ is the opening by means of which the stomach communicates with the duodenum.
This orifice is guarded by the _pyloric valve_. When the stomach is empty the pylorus is situated just to the right of the median line of the body on a level with the upper border of the first lumbar vertebra. On the anterior surface of the body its position would be indicated by a point one inch below the tip of the ensiform process and a little to the right.
The size of the stomach varies considerable in different subjects. The distance between the two orifices is from three to six inches. The weight of the stomach is about four and one-half ounces.
The capacity of the adult male stomach is from five to eight pints. The stomach of a new born child holds about one ounce.
The stomach is held in place by the attachment of the esophagus to the diaphragm and the fixation of the duodenum to the front of the vertebral column.
The wall of the stomach consists of four coats: serous, muscular, areolar, and mucous.