Lesser diaphragmatic apertures
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The lesser diaphragmatic apertures allow the passage of smaller structures from the thoracic cavity to abdominal cavity across the diaphragm. They are very much smaller than the other diaphragmatic apertures:
two in the right crus of the diaphragm: transmit greater and lesser right splanchnic nerves
three in the left crus of the diaphragm: transmit greater and lesser left splanchnic nerves as well as the hemiazygos vein
under the medial arcuate ligament: usually transmit the sympathetic trunks
left phrenic nerve pierces the dome of the left hemidiaphragm
A small interval exists between the sternal and costal parts of the diaphragm where the muscular fibers of the diaphragm are deficient and are replaced by areolar tissue and through which the superior epigastric branch of the internal mammary artery and some lymphatics from the abdominal wall and convex surface of the liver pass through.