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Internal oblique abdominis muscle (anatomy)

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Internal oblique is one of the muscles of the abdominal wall. It originates from the:

  • thoracolumbar fascia
  • anterior two thirds of the iliac crest
  • lateral two thirds of the inguinal ligament

Its fibres radiate widely from these origins around the abdominal wall. Its fibres insert into the:

  • inferior borders of the most inferior three ribs
  • aponeurosis of rectus sheath:
    • both sides join in the midline with the aponeuroses of the other abdominal wall muscles to form the linea alba
    • laterally, the superior fibres of internal oblique split at the border of the rectus abdominis muscle to contribute to both the anterior and posterior walls of the rectus sheath
    • inferior to the arcuate line, all fibres pass anterior to rectus abdominis
  • pubic crest and pectineal line as the conjoint tendon:
    • inferior fibres of internal oblique pass over the spermatic cord within the inguinal canal
    • constitues part of the posterior wall of the canal at its medial end

Internal oblique acts to:

  • support the abdominal wall
  • raise intra-abdominal pressure eg for defaecation
  • flex and rotate the trunk
  • support the posterior wall of the inguinal canal

Internal oblique is innervated by:

  • anterior primary rami of the most inferior five intercostal nerves (T7-T12)
  • ilioinguinal nerve (L1) for the conjoint tendon

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