AIIMEN'TARY CANAL, in mammalia, is that portion of the digestive apparatus through which the food passes after mastication. It is lined by a mucous membrane, which extends from the lips to the anus, being modified in each region. See Mucous MumBRAxE. The A. C. really begins at the back of the mouth, in the lower part of the bag called the pharynx, which communicates with the nostrils above, and the gullet or oesophagus below, and also with the mouth and the larynx. The pharynx is sur rounded by three muscles, the constrictors, which grasp the food, and force it into the next portion of the A. C., the msophagus. This is a tube composed of an outer layer, of longitudinal muscular fibers, and an inner of circular, which extend down to, and out upon the stomach. These fibers, by a series of peristaltic contractions, carry the morsel of food along into the stomach. In vomiting, there is a reversal of these .
actions, which ruminating animals can accomplish at The cesophagus passes through an opening in the diaphragm, and joins the stomach, which is a pouch curved with the concavity upwards, expanded into a cul de sac on the left side (the cardiac extremity), and gradually narrowed to the right or pyloric end. It consists of muscular fibers continuous with those of the esophagus, which become thicker towards the pylorus. Its external surfaces are covered and it is lined by a thick soft
mucous membrane, which, when the stomach is empty, lies in folds. Between the mus cular and mucous layers is a fibrous layer, in which the blood-vessels lie before they pass into the mucous layer. See STOMACH. At his pyloric or left extremity the stomach communicates with the small intestine, which is about 20 ft. in length, becoming gradu ally narrow towards its lower end, and arranged in numerous convolutions, which occupy the middle of the abdominal cavity, and are kept in position by the peritoneum, which attaches them to the back of the abdomen.
The small intestine is subdivided into three parts. The first 10. in from the stomach is the duodenum, into which open the duct of the pancreas and the common bile duct ; of the remainder, the jejunum includes about two fifths, and the ileum, three fifths. The differences between these last two are not visible externally, but consist in modifications of their internal structure. The tube consists of peritoneum, longitudinal and circular muscular fibers, a fibrous layer, and a mucous membrane. See INTESTINES,