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external oblique abdominis (anatomy)
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The external oblique muscle is the most superficial of the flat muscles of the abdomen. It arises from the anterior angles of ribs 5 to 12. The superior slips of muscle merge and fuse with the slips of serratus anterior. The inferior slips interdigitate with latissimus dorsi.

External oblique inserts into the:

  • anterolateral half of the iliac crest
  • inguinal ligament; the reflection posteroinferiorly of the external oblique forms the inguinal ligament
  • pubic tubercle
  • pubic crest
  • aponeurosis of anterior rectus sheath; in the midline, the aponeuroses from both side fuse to form the linea alba

There is a triangular deficiency in the aponeurosis of external oblique immediately superolateral to the pubic tubercle. This is the superficial inguinal ring.

The action of external oblique is dependent on the action of other muscles:

  • supports anterolateral abdominal wall
  • raises intra-abdominal pressure
  • abduct trunk
  • rotates trunk

External oblique is innervated by:

  • anterior primary rami of T7-T12
  • subcostal nerve
  • iliohypogastric nerve