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The thoracoabdominal nerves and the subcostal nerve inferiorly and anteriorly between the internal abdominal oblique muscle and the transversus abdominis muscle. Medially these nerves enter the rectus sheath. Replace the internal abdominal oblique muscle and identify again the iliohypogastric nerve . Follow the course of iliohypogastric nerve distally and confirm that it does not enter the rectus sheath.

Links and References:
Grant's: 2.6
Netter: 234
Rohen/Yokochi: 200, 203