External oblique muscle

Last revised by Dr Henry Knipe on 15 Sep 2021

The external oblique muscle (EOM) is one of the muscles that forms the anterior abdominal wall. Its free inferior border forms the inguinal ligament, and its aponeurotic part contributes to the anterior wall of the inguinal canal

  • origin: outer surface of the shaft of the lower 8 ribs
  • insertion: upper aponeurotic fibers to the whole length of the linea alba and extends to the pubic crest and the pectineal line; lower fleshy fibers to the outer lip of the anterior end of the iliac crest
  • innervation: segmental supply by lower 6 thoracic nerves
  • action: contributes in forming the anterior abdominal wall and the action is along with the other abdominal wall muscles

The external oblique muscle arises from the outer surface of the middle of the shaft of the lower six ribs as fleshy fibers. At its origin upper four slips and lower four slips interdigitate with the serratus anterior and the latissimus dorsi muscles respectively. The muscle gradually becomes aponeurotic, which inserts into the whole length of the linea alba with extension onto the pubic crest and the pectineal line. Lower fleshy fibers attach to the outer lip of the anterior two thirds of the iliac crest. Muscle fibers are directed obliquely downwards and medially. 

The muscle has some important features:

The upper part of the muscle is supplied by the lower intercostal arteries, and the lower part is by the deep circumflex iliac artery branches.

Venous drainage follows the arterial supply.

Along with other abdominal wall muscles, the external oblique muscle flexes the trunk, assists expiration by depressing the ribs, and assists to maintain intra-abdominal pressure in evacuation of luminal contents and supports intra-abdominal viscera.

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Cases and figures

  • Figure 1: external oblique (Gray's illustrations)
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  • Figure 2
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  • Figure 3: rectus sheath (diagram)
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