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