[TA] flat muscle of anterolateral abdominal wall; origin, iliac fascia deep to lateral part of inguinal ligament, anterior half of crest of ilium, and lumbar fascia; insertion, tenth to twelfth ribs, with aponeurosis contributing to the sheath of rectus; some of the fibers from inguinal ligament terminate in the conjoint tendon; action, diminishes capacity of abdomen, flexes lumbar vertebral column (bends thorax forward); nerve supply, lower thoracic. SYN: musculus obliquus internus abdominis [TA], abdominal internal oblique muscle.