External Oblique
Abdomen · Trunk
The external oblique is the largest and most superficial of the three flat muscles of the anterolateral abdominal wall. It arises from the external surfaces of ribs 5 to 12 and its fibres run downward and forward, in the same direction as hands slipping into front pockets, to insert into the linea alba, the pubic tubercle, and the anterior half of the iliac crest. The lower border of its aponeurosis folds back to form the inguinal ligament. Acting on both sides it compresses the abdomen and flexes the trunk, and acting on one side it rotates the trunk to the opposite side, so the right external oblique turns the torso to the left. It is supplied by the thoracoabdominal nerves (T7 to T11) and the subcostal nerve (T12).
Origin, Insertion, Action & Nerve
Origin
External surfaces of ribs 5–12
Insertion
Linea alba, pubic tubercle, and anterior half of iliac crest
Action
Compresses abdomen; flexes trunk; rotates trunk to the opposite side
Nerve
Thoracoabdominal nerves (T7–T11) and subcostal nerve (T12)
Attachments explained
The External Oblique is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
External surfaces of ribs 5–12
Insertion
Linea alba, pubic tubercle, and anterior half of iliac crest
Action & function
When the External Oblique contracts, it produces the following movements: Compresses abdomen; flexes trunk; rotates trunk to the opposite side.
As part of the Abdomen group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The External Oblique receives its nerve supply from the Thoracoabdominal nerves (T7–T11) and subcostal nerve (T12). This nerve carries fibres from spinal segment(s) T7, T11, T12.
Because a muscle can only contract when its nerve is intact, injury to the Thoracoabdominal nerves or to its spinal roots (T7, T11, T12) can weaken or paralyse the External Oblique, impairing the movements it normally produces (compresses abdomen). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the External Oblique (the OIANS method)
Learn the external oblique by its hands-in-pockets fibre direction, down and forward, which is the mirror image of the internal oblique beneath it. This layering, with the two obliques running perpendicular, is what gives the abdominal wall its plywood-like strength when compressing the viscera.
Nail the rotation rule by pairing it across the body: because its fibres pull obliquely, the external oblique on one side works with the internal oblique on the opposite side to rotate the trunk, so contracting the right external oblique turns the torso to the left. Remembering that its aponeurosis rolls under to form the inguinal ligament links this muscle to the anatomy of the groin and hernias.
Frequently asked questions
Where is the External Oblique located?
The External Oblique is a muscle of the Abdomen group, located in the Trunk.
What is the origin of the External Oblique?
External surfaces of ribs 5–12
What is the insertion of the External Oblique?
Linea alba, pubic tubercle, and anterior half of iliac crest
What movements does the External Oblique produce?
Compresses abdomen; flexes trunk; rotates trunk to the opposite side
What nerve supplies the External Oblique?
Thoracoabdominal nerves (T7–T11) and subcostal nerve (T12)
Is the External Oblique free to study in OIANS?
The External Oblique is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
Study the External Oblique
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