The rectus sheath is the fibrous condensation of the aponeurotic layers on the anterior aspect of the abdominal wall investing the rectus abdominis muscle. Also, it encloses the epigastric vessels, the inferior five intercostal and subcostal vessels and nerves, and occasionally pyramidalis. It is incomplete posteriorly at a level inferior to the arcuate line and superiorly above the costal margin.
The anterior wall is formed from the external oblique aponeurosis and a superficial layer of the internal oblique aponeurosis where it divides at the lateral edge of the rectus abdominis muscle. The posterior wall is formed from the aponeurosis of the transversus abdominis muscle where it joins the deeper layer of the internal oblique aponeurosis. Together, both walls form the linea alba.