ABSTRACT
The jejunum begins as a direct continuation of the predominantly retroperitoneal duodenum at the duodenojejunal flexure. Distally, it is continuous with the ileum, with no line of demarcation. The ileum joins the medial wall of the caecum at the ileocaecal valve. The jejunum and ileum have a complete peritoneal covering and lie as free loops in the peritoneal cavity suspended on their mesentery. The mesentery contains, between its two layers, the arteries, veins, lymphatics and nerves of the small intestine. Its root, or line of attachment to the posterior wall, extends obliquely from the duodenojejunal flexure to the caecum.
