The Musculus obliquus internus abdominis (lat.: internal diagonal belly muscle) is one muscles of the abdomens. Its fibers are arranged from kaudal lateral (with humans down outside, with the animal in the back outside) after kranial medial (with humans above inside, with the animal in front inside). They cross with those of the Musculus obliquus externus abdominis in the angle of 90"°. Its Aponeurose (chord in the center spreads) forms the Linea together with those of the Musculus obliquus externus abdominis and the Musculus transversus abdominis alba.