External Obliques
The external obliques are the largest and most superficial of the lateral abdominal muscles. Their fibers run diagonally downward and forward, like hands in pockets, and they play a crucial role in trunk rotation and flexion.
Origin, Insertion, Action, Innervation
OOrigin
External surfaces of ribs 5-12
IInsertion
Linea alba, pubic tubercle, iliac crest (anterior half)
AAction
- • Flexion of the trunk (bilateral contraction)
- • Rotation of the trunk to opposite side (unilateral contraction)
- • Lateral flexion of the trunk (unilateral contraction)
- • Compression of abdominal contents
NInnervation
Intercostal nerves (T7-T11) and subcostal nerve (T12)
Blood Supply
Lower intercostal and subcostal arteries
Clinical Relevance
The external oblique aponeurosis forms the inguinal ligament and contributes to the inguinal canal. Oblique muscle strains are common in sports involving rotation. The muscles protect abdominal organs and assist with breathing.
Palpation
Palpate on the lateral abdominal wall. Have the patient rotate the trunk against resistance to feel the muscle contract.
Study Tips
- ✓Fibers run like 'hands in pockets' (down and medially)
- ✓External oblique = rotate to OPPOSITE side
- ✓Forms inguinal ligament (from ASIS to pubic tubercle)
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Common questions about the external obliques
The external oblique fibers run diagonally downward and medially, like the direction of putting hands in front pockets. This is opposite to the internal oblique fibers, which run upward and medially.
Unilateral external oblique contraction rotates the trunk to the opposite side. For example, the right external oblique rotates the trunk to the left.
The inguinal ligament is formed by the inferior edge of the external oblique aponeurosis, running from the anterior superior iliac spine (ASIS) to the pubic tubercle. It forms the floor of the inguinal canal.
During trunk rotation, the external oblique on one side works with the internal oblique on the opposite side. For rotating left, the right external oblique and left internal oblique contract together.