Rectus Sheath

• Internal Oblique aponeurosis splits into anterior and posterior layers to enclose the Rectus

• External Oblique aponeurosis fuses with the anterior layer to the form the anterior layer of the Rectus Sheath

• Transversus Abdominis aponeurosis fuses with the posterior layer to form the posterior layer of the Rectus Sheath

• Below Arcuate Line, all three aponeuroses pass in front of the muscle

• Posterior Layer of Rectus Sheath:

  • Free lower margin – forms Arcuate Line (Semicircular Line of Douglas)
  • Superior margin – attached to costal margin (7th, 8th and 9th costal cartilages)

• Anterior Layer of Rectus Sheath:

  • Above the costal margin – Consists of only the External Oblique aponeurosis

• Rectus Sheath Contents:

  • Rectus Abdominis
  • Pyramidalis muscle
  • Ends of the lower 6 thoracic nerves and their accompanying Posterior Intercostal vessels
  • Superior Epigastric vessels
  • Inferior Epigastric vessels

A = Above costal margin, B = Above Arcuate Line, C = Below Arcuate Line