The small intestine is a convoluted tube, extending from the pylorus to the colic valve, where it ends in the large intestine.
It is about 7 meters long, and gradually diminishes in size from its commencement to its termination.
It is contained in the central and lower part of the abdominal cavity, and is surrounded above and at the sides by the large intestine; a portion of it extends below the superior aperture of the pelvis and lies in front of the rectum.
It is in relation, in front, with the greater omentum and abdominal parietes, and is connected to the vertebral column by a fold of peritoneum, the mesentery.
The small intestine is divisible into three portions: the duodenum, the jejunum, and the ileum.