The aortic hiatus is a midline[1]: 185  opening in the posterior part of the diaphragm giving passage to the descending aorta as well as the thoracic duct, and variably the azygos and hemiazygos veins.

[citation needed] It is located at the level of the inferior border of the twelfth thoracic vertebra (T12),[2] posterior to the median arcuate ligament[2][1]: 185  between the two crura of the diaphragm.

[citation needed] The hiatus is situated slightly to the left of the midline, and is bound anteriorly by the crura, and posteriorly by the body of the first lumbar vertebra.

[citation needed] Occasionally some tendinous fibers prolonged across the bodies of the vertebræ from the medial parts of the inferior ends of the crura pass posterior to the aorta, and thus convert the hiatus into a fibrous ring.

[citation needed] The aorta is situated on the left, the thoracic duct in the middle, and the azygos vein on the right.