The linea semilunaris (also semilunar line or Spigelian line) is a curved line found on either side of the

rectus abdominis muscle The rectus abdominis muscle, () also known as the "abdominal muscle" or simply better known as the "abs", is a pair of segmented skeletal muscle on the ventral aspect of a person's abdomen. The paired muscle is separated at the midline by a ba ...

History

The linea semilunaris was first described by

Adriaan van den Spiegel Adriaan van den Spiegel (or Spieghel), name sometimes written as Adrianus Spigelius (1578 – 7 April 1625), was a Flemish anatomist born in Brussels. For much of his career he practiced medicine in Padua, and is considered one of the great physi ...

Structure

There are two commonly used definitions identifying the linea semilunaris. The first is defined as corresponding with the lateral border of the

rectus sheath The rectus sheath (also called the rectus fascia.) is a tough fibrous compartment formed by the aponeuroses of the transverse abdominal, transverse abdominal muscle, and the internal oblique, internal and external oblique muscles. It contains the ...

. In this definition, it is formed by the

aponeurosis An aponeurosis (; : aponeuroses) is a flattened tendon by which muscle attaches to bone or fascia. Aponeuroses exhibit an ordered arrangement of collagen fibres, thus attaining high tensile strength in a particular direction while being vulnerable ...

of the internal oblique at its line of division to enclose the rectus. This is reinforced anteriorly by the external oblique, and posteriorly by the transversus abdominis above the arcuate line. The second definition identifies it as the line forming and marking the transition from muscle to aponeurosis in the transversus abdominis muscle, known as the spigelian aponeurosis. In both definitions, it extends from the

cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

of the ninth

rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...

to the

pubic tubercle The pubic tubercle is a prominent tubercle on the superior ramus of the pubis bone of the pelvis. Structure The pubic tubercle is a prominent forward-projecting tubercle on the upper border of the medial portion of the superior ramus of th ...

. The terms ''spigelian fascia'' and ''spigelian aponeurosis'' have also been used to define the linea semulunaris. In this definition it refers to the aponeuroses of the lateral abdominal muscles lateral to the rectus muscle. In other definitions the spigelian aponeurosis/spigelian fascia is the aponeurosis of the transverse abdominal muscle medial to the linea semilunaris and lateral to the rectus muscle.

Clinical significance

A hernia through the linea semilunaris is called a Spigelian hernia. This usually occurs at the meeting point of the linea semilunaris with the arcuate line and the lateral border of the

References

{{DEFAULTSORT:Linea Semilunaris Abdomen