Stabilize the intercostal spaces during ventilation; elevates rib below. Stabilize the intercostal spaces during ventilation; depresses rib above. Xiphoid process and costal cartilages of ribs 57. Fibers from the right external oblique and left. Action internal oblique work together to produce trunk rotation to the left. Fibers from the right external oblique and left internal oblique work together to produce trunk rotation to the left. Inside the rib cage above the costal arch. Thoracoabdominal nn. (t711), subcostal n. (t12), and l1. Flexes & rotates trunk; compresses & supports abdominal viscera. Costal part: internal surfaces of lower 6 ribs at costal margin. Lumbar part: lumbar vertebrae as low as l3 on the right and l2 on the left. Draws the central tendon down & forward during inspiration. Upper part of iliac fossa & iliac crest. Lesser trochanter by tendon shared with psoas major m. Tp of upper lumbar vertebrae & 12th rib.