The middle flat abdominal muscle with fibres perpendicular to the external oblique. Its lowest fibres arch over the inguinal canal to form the conjoint tendon providing the posterior inguinal canal wall.
| Origin | Thoracolumbar fascia, anterior iliac crest, lateral inguinal ligament |
|---|---|
| Insertion | Lower 3-4 costal cartilages, linea alba, pubic crest via conjoint tendon |
| Nerve Supply | Ventral rami of T7-T12, iliohypogastric and ilioinguinal nerves (L1) |
| Blood Supply | Lower posterior intercostal arteries |
| Actions | Bilateral: trunk flexion; Unilateral: same-side lateral flexion and same-side rotation (opposite to external oblique); Lowest fibres form the cremaster in males |
|---|
The conjoint tendon weakness contributes to direct inguinal hernia. The ilioinguinal nerve runs between internal oblique and transversus and must be preserved in inguinal surgery. The TAP block targets the internal oblique-transversus plane.
The middle abdominal layer — palpable during resisted ipsilateral trunk rotation.
Conjoint tendon weakness allowing peritoneal protrusion through Hesselbach's triangle, repaired by mesh or suture reinforcement.
