Abdominal internal oblique muscle

The internal abdominal oblique muscle, also internal oblique muscle or interior oblique or musculus obliquus abdominis internus, is an abdominal muscle in the abdominal wall that lies below the external abdominal oblique muscle and just above the transversus abdominis muscle. == Structure == Its fibers run perpendicular to the external oblique muscle, beginning in the thoracolumbar fascia of the lower back, the anterior 2/3 of the iliac crest (upper part of hip bone) and the lateral half of the inguinal ligament.

Source: Wikipedia — Abdominal internal oblique muscle (CC BY-SA 4.0)