Internal Abdominal Oblique Muscle: The internal abdominal oblique is also a broad thin muscular sheet that lies deep to the external oblique. It arises from the thoraco-lumbar fascia, the lateral two-thirds of the inguinal ligament and the anterior two-thirds of the iliac crest. The muscle fibers transmit superomedially and insert into the inferior borders of the lower three ribs and their costal cartilages, the xiphoid process, the linea alba, and the symphysis pubis.
Beside their insertion, the lowest tendinous fibers are connected with similar fibers from the transversus abdominis to form the conjoint tendon.
Nerve Supply of the Internal Abdominal Oblique
The lower six thoracic nerves and the iliohypogastric and ilioinguinal nerves.
Function of the Internal Abdominal Oblique
Working unilaterally, contraction of the internal oblique muscle results in ipsilateral side flexion and rotation of the trunk. It acts as the external oblique muscle of the opposite side to complete this torsional movement of the trunk.
It also acts to press the abdominal viscera, forcing them up into the diaphragm, producing in forced expiration.