Anatom3DInternal oblique
Musculus obliquus internus abdominis · Vnitřní šikmý sval břišní
Muscles
Looks like
The middle layer of the side wall, its fibres fanning up and forward at right angles to the outer layer.
What it does
Works with the opposite external oblique to twist the trunk and keeps the belly wall firm.
Keeping it well
Strained like the outer layer; a lump in the groin that appears on standing and vanishes lying down is a hernia and needs assessing.