Strictly speaking, it is not an aperture in the diaphragm but an osseoaponeurotic opening between it and the vertebral column, and therefore behind the diaphragm; occasionally some tendinous fibers prolonged across the bodies of the vertebræ from the medial parts of the lower ends of the crura pass behind the aorta, and thus convert the hiatus into a fibrous ring.
The hiatus is situated slightly to the left of the middle line, and is bounded in front by the crura, and behind by the body of the first lumbar vertebra.
Other sources state that the Aorta does not pass through the aortic hiatus, rather, it passes posterior to it. According to this definition, only the azygos vein and thoracic duct pass through this opening.
