The mesenteric organ comprises the small intestinal mesentery (distal to the duodenojejunal flexure), the right mesocolon, the transverse mesocolon, the left mesocolon, the mesosigmoid and mesorectum. The gastrointestinal margin of the mesentery is that edge to which the gastrointestinal tract is attached. The region of gastrointestinal tract attached permits the naming of respective regions of the mesenteric organ. The transverse mesocolon is that region of the mesentery for which the transverse colon is attached to its gastointestinal margin. The mesosigmoid is that region of the mesenteric organ to which the sigmoid colon is attached at the gastrointestinal mesenteric margin.