The mesentery proper (mesenterium) is the broad, fan-shaped fold of peritoneum which connects the convolutions of the jejunum and ileum with the posterior wall of the abdomen. Its root—the part connected with the structures in front of the vertebral column—is narrow, about 15 cm. long, and is directed obliquely from the duodenojejunal flexure at the left side of the second lumbar vertebra to the right sacroiliac articulation. Its intestinal border is about 6 metres long; and here the two layers separate to enclose the intestine, and form its peritoneal coat. It is narrow above, but widens rapidly to about 20 cm., and is thrown into numerous plaits or folds. It suspends the small intestine, and contains between its layers the intestinal branches of the superior mesenteric artery, with their accompanying veins and plexuses of nerves, the lacteal vessels, and mesenteric lymph glands. The mesentery is the double layer of peritoneum that suspends the jejunum and ileum from the posterior wall of the abdomen. Its meaning, however, is frequently extended to include double layers of peritoneum connecting various components of the abdominal cavity.