internal oblique abdominis muscle (anatomy)

Last reviewed 01/2018

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