CorpusHuman Anatomy
MuscularMembrane

Rectus sheath

Vagina musculi recti abdominis

Also known as: arcuate line, semicircular line of Douglas

The strong aponeurotic compartment enclosing rectus abdominis, formed by the aponeuroses of the three flat abdominal muscles. Its structure changes at the arcuate line.

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Overview

Above the arcuate line (upper ≈ two-thirds): the anterior layer is formed by the external oblique aponeurosis plus the anterior lamina of the internal oblique aponeurosis. The posterior layer is formed by the posterior lamina of the internal oblique aponeurosis plus the transversus abdominis aponeurosis. Above the costal margin, the posterior wall is absent and the muscle lies directly on the costal cartilages.

Below the arcuate line (≈ one-third of the way from the umbilicus to the pubic crest): all three aponeuroses pass in front of rectus. The posterior surface of the muscle is then covered only by transversalis fascia, extraperitoneal fat and peritoneum. The inferior epigastric vessels enter the sheath at the arcuate line.

Contents: rectus abdominis, pyramidalis, the superior and inferior epigastric vessels, and the terminal parts of the T7–T12 nerves.

Parts & subdivisions

  1. Anterior layer
    External oblique aponeurosis + internal oblique aponeurosis (anterior lamina). Below the arcuate line it also includes the transversus aponeurosis.
  2. Posterior layer
    Internal oblique aponeurosis (posterior lamina) + transversus aponeurosis. Absent below the arcuate line.
  3. Arcuate line
    The crescent-shaped lower edge of the posterior layer, about a third of the way from the umbilicus to the pubic crest.

Function

  • Contains and supports rectus abdominis
  • Transmits the forces of the lateral muscles to the linea alba
  • Carries the epigastric vessels and segmental nerves

Clinical significance

Spigelian hernia

A hernia through the spigelian aponeurosis at the linea semilunaris, usually near the arcuate line where the posterior sheath is deficient.

Surgical incisions

Paramedian and transverse incisions open the sheath and are closed by suturing its layers. The posterior sheath is used in mesh repairs placed behind the rectus muscle.

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.