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Structure

Muscles of the abdominal wall

Not medically reviewed · Content last updated · 2 min read ·

This is the date the draft was written, not a medical review date.

The anterolateral abdominal wall consists of three flat muscles (external oblique, internal oblique, transversus abdominis) and the paired rectus abdominis, enclosed by aponeuroses and fascia. Together they contain the viscera, move the trunk and raise intra-abdominal pressure.

Terminologia Anatomica (Latin): Musculi abdominis · Open in the 3D atlas

Location

The wall extends from the costal margin and xiphoid process above to the iliac crest, inguinal ligament and pubis below. Posteriorly the quadratus lumborum and psoas contribute to the posterior wall.

Structure

The aponeuroses of the three flat muscles form the rectus sheath and meet in the midline at the linea alba. Above the arcuate line (about midway between umbilicus and pubis) the internal oblique aponeurosis splits to enclose the rectus; below it all three aponeuroses pass anterior to the rectus. The inguinal canal, about 4 cm long, runs above the inguinal ligament with the deep ring (in transversalis fascia) and the superficial ring (in the external oblique aponeurosis).

Blood supply

Superior epigastric (from the internal thoracic) and inferior epigastric (from the external iliac) arteries anastomose within the rectus sheath; musculophrenic, deep circumflex iliac, lower posterior intercostal, subcostal and lumbar arteries supply the lateral muscles.

Innervation

Anterior rami of T7-T12 (thoracoabdominal and subcostal nerves) supply all the wall muscles; L1 (iliohypogastric and ilioinguinal nerves) supplies the lower fibres of the internal oblique and transversus. Dermatome landmarks: T10 at the umbilicus, L1 at the inguinal region.

Function

They support and compress the abdominal contents (Valsalva, defaecation, micturition, parturition, forced expiration, cough), flex the trunk (rectus), rotate and laterally flex it (obliques) and, with the back muscles, stabilise the trunk and pelvis.

Clinical correlations

Inguinal hernias pass through the inguinal canal: indirect hernias enter at the deep ring lateral to the inferior epigastric vessels and may reach the scrotum; direct hernias bulge through Hesselbach triangle medially. Other sites are femoral, umbilical, incisional and epigastric hernias. Rectus diastasis, rectus sheath haematoma and abdominal wall incisions (midline, paramedian, transverse) are relevant surgically.

Common exam points

  • Layers (superficial to deep): external oblique, internal oblique, transversus abdominis, transversalis fascia, extraperitoneal fat, peritoneum.
  • Rectus sheath: arcuate line (about midway between umbilicus and pubis); below it all aponeuroses pass anterior to the rectus.
  • Indirect inguinal hernia: lateral to inferior epigastric vessels, through the deep ring; direct: medial, through Hesselbach triangle.
  • Linea alba: avascular midline raphe, preferred for midline incisions.
  • Dermatomes: T7 xiphoid, T10 umbilicus, L1 inguinal region.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Netter FH. Atlas of Human Anatomy. Elsevier — Tier 3 (textbook)

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