The duodenum is the first or proximal (nearest) portion of the small intestine, extending from the pylorus (opening in a vertebrate from the stomach into the intestine) to the jejunum (the portion of the small intestine that extends from the duodenum to the ileum), so called because it is about twelve finger widths in length.

The ileum is the last portion of the small intestine that communicates with the large intestine.