In addition to emptying the stomach into the small intestine, these muscles also aid in emptying the organ upward and through the esophagus and mouth, should occasion require. Vomiting in case of poisoning, or if the food for some reason fails to digest, is a necessary though unpleasant operation. It is accomplished by the contraction of all the muscles of the stomach, together with the contraction of the walls of the abdomen. During these contractions the pyloric valve is closed, and the muscles of the esophagus and pharynx are in a relaxed condition.(59) [Fig. 70] Fig. 70—*Passage from stomach* into small intestine. Illustration also shows arrangement of mucous membrane in the two organs. _D._ Bile duct. *The Small Intestine.*—This division of the alimentary canal consists of a coiled tube, about twenty-two feet in length, which occupies the central, lower portion of the abdominal cavity (Fig. 71). At its upper extremity it connects with the pyloric end of the stomach (Fig. 70), and at its lower end it joins the large intestine. It averages a little over an inch in diameter, and gradually diminishes in size from the stomach to the large intestine. The first eight or ten inches form a short curve, known as the _duodenum_. The upper two fifths of the remainder is called the _jejunum_, and the lower three fifths is known as the _ileum_. The ileum joins that part of the large intestine known as the cæcum, and at their place of union is a marked constriction which prevents material from passing from the large into the small intestine (Fig. 73). This is known as the _ileo-cæcal valve_. _The mucous membrane_ of the small intestine is richly supplied with blood vessels and contains glands that secrete a digestive fluid known as the _intestinal juice_. The membrane is thrown into many transverse, or circular, folds which increase its surface and also prevent materials from passing too rapidly through the intestine. One important respect in which the small intestine differs from all other portions of the food canal is that its surface is covered with great numbers of minute elevations known as the villi. The purpose of these is to aid in the absorption of the nutrients as they become dissolved (Chapter XI). _The muscular coat_ of the small intestine is made up of two distinct layers—the inner layer consisting of circular fibers and the outer of longitudinal fibers. These muscles keep the food materials mixed with the juices of the small intestine, but their main purpose is to force the materials undergoing digestion through this long and much-coiled tube.