This is the Abdominal External Oblique Muscle!
AKA External Oblique Muscle (of abdomen)
The external oblique is situated on the lateral (outer) and anterior (front) parts of the abdomen.
- the external surfaces and inferior borders of the fifth to twelfth ribs (lower eight ribs)
- lowest ribs pass nearly vertically downward, and are inserted into the anterior half of the outer lip of the iliac crest
- the middle and upper fibers, directed downward and forward, become aponeurotic (fibrous tissue similar to a tendon, but broader) at approximately the mid-clavicular line (a theoretical line running vertically down the surface of the body passing through the midpoint of the clavicle) and forms the anterior layer of the rectus sheath.
- Pull the chest downwards and compress the abdominal cavity
- Ipsilateral (same side) side-bending
- Contralateral (opposite side) rotation.
- So the right external oblique would side bend to the right and rotate to the left.