Linea semilunaris

The linea semilunaris (also semilunar line or Spigelian line) is a curved tendinous intersection found on either side of the rectus abdominis muscle.

Each corresponds with the lateral border of the rectus abdominis, extends from the cartilage of the ninth rib to the pubic tubercle, and is formed by the aponeurosis of the internal oblique at its line of division to enclose the rectus, reinforced anteriorly by the external oblique and posteriorly by the transversus abdominis above the arcuate line (also known as linea semicircularis or Douglas' line).

A hernia through the linea semilunaris is called a Spigelian hernia, which is also referred to as a spontaneous lateral ventral hernia.