Abdomen

The diaphragm separates the thorax from the abdomen. Structures that pass between the thorax and abdomen either penetrate the diaphragm or pass posteriorly to it : the inferior vena cava pierces the central tendon of the diaphragm to enter the right side of the mediastinum near vertebral level TVIII; the esophagus penetrates the muscular part of the diaphragm to leave the mediastinum and enter the abdomen just to the left of the midline at vertebral level TX; the aorta passes posteriorly to the diaphragm at the midline at vertebral level TXII; numerous other structures that pass between the thorax and abdomen pass through or posterior to the diaphragm.