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Other Terms: Mesentery of transverse colon, Mesocolon transversum, Mésocôlon transverse
The transverse mesocolon is the broad fold of peritoneum connecting the transverse colon to the posterior wall of the abdominal cavity. In the adult, it is formed by the ascending layer of the greater omentum. In the fetus, the ascending layers of the greater omentum pass over the transverse colon to the posterior wall of the abdominal cavity, where they separate at the lower border of the pancreas. One layer passes in front of the pancreas, as in the adult. The posterior layer turns downward, reaches the transverse colon, which it surrounds, and then passes backward to the abdominal wall. It then descends to form the mesentery, in the adult. In the fetus, both descending and both ascending layers of the greater omentum lie in front of the transverse colon. In the adult, both descending layers and only one ascending layer lie in front of the transverse colon. In the adult the ascending layers of the greater omentum have merged with the upper layer of the transverse mesocolon, making it practically one layer. The transverse mesocolon is continuous, through its under layer, upon each side with the ascending and the descending mesocolon. Between its layers pass the blood vessels, lymphatics, and nerves supplying the transverse colon. It divides the abdominal cavity proper into two incomplete compartments: the upper compartment contains the liver, the stomach, and the spleen, and the lower contains the intestines.