Arcuate line of rectus sheath

The arcuate line of the abdomen, linea semicircularis or Douglas' line is a horizontal line that demarcates the lower limit of the posterior layer of the rectus sheath. It is also where the inferior epigastric vessels perforate the rectus abdominis.

Superior to the arcuate line, the internal oblique aponeurosis splits to envelop the rectus abdominis muscle. Inferior to the arcuate line, the internal oblique and transversus abdominis aponeuroses merge and pass superficial (i.e. anteriorly) to the rectus muscle.