Trunk (thorax, abdomen, back)

Internal Oblique

Musculus obliquus internus abdominis

Origin

Iliac crest, inguinal ligament and the thoracolumbar fascia

Insertion

10th through 12th ribs and, via the aponeurosis, the linea alba

Function

Flexion and rotation of the trunk (to the same side), compression of the abdominal contents

Innervation

Thoracoabdominal nerves (T7-T12), iliohypogastric/ilioinguinal nerve (L1)

Movement & chain

Works unilaterally together with the contralateral external oblique in rotation; bilaterally active in abdominal straining, coughing and forced expiration.

Palpation

Located deep to the external oblique, with fibers running perpendicular to it (craniomedially); harder to distinguish directly on palpation.

Clinical

Together with transversus abdominis, important for the 'corset' function of the abdominal wall; weakening contributes to low back complaints and inguinal hernias.

Segmental innervation

Thoracoabdominal nerves, myotomes T7-T12; iliohypogastric/ilioinguinal nerve, L1.

In clinical practice

Wound management post-laparotomy/chest drain and abdominal wall monitoring; support incision site during coughing to prevent wound dehiscence.

Region in the model

Trunk (thorax, abdomen, back)