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External oblique abdominal muscle
Last reviewed: 07.07.2025
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The external oblique muscle of the abdomen (m. obliquus extemus abdominis) is the most superficial and extensive of the abdominal muscles. It begins with large teeth on the outer surface of the eight lower ribs. The upper five teeth of the muscle enter between the teeth of the anterior serratus muscle, and the lower three - between the teeth of the latissimus dorsi. The upper bundles of the external oblique muscle of the abdomen begin on the ribs near their cartilages and pass almost horizontally. The lower bundles go obliquely from top to bottom and medially. The bundles of the lowest part of the muscle follow almost vertically downwards. The muscle bundles of the external oblique muscle of the abdomen, not reaching the edge of the rectus abdominis muscle in front and the wing of the ilium below, pass into a wide aponeurosis.
The lowest part of the aponeurosis of the external oblique muscle of the abdomen is directed to the outer lip of the iliac crest (laterally, posteriorly) and to the pubic tubercle (anteriorly, medially). The lower thickened edge of the aponeurosis of the external oblique muscle of the abdomen is stretched between the superior anterior iliac spine and the pubic tubercle and forms the inguinal ligament (ligamentum inguinale). At the point of attachment to the pubic bone, the aponeurosis of the muscle divides into two crura - medial and lateral. The medial crus (crus mediate) is attached to the anterior surface of the pubic symphysis, and the lateral crus (crus laterale) - to the pubic tubercle.
Function: with a strengthened pelvic girdle and bilateral contraction, the external oblique abdominal muscle lowers the ribs, facilitating the act of exhalation, and also flexes the spine. With a unilateral contraction, this muscle turns the torso in the opposite direction. With free, unsupported lower limbs (in the supine position), the muscles lift the pelvis. The muscles are part of the abdominal press structures.
Innervation: intercostal nerves (ThV-ThXII), iliohypogastric nerve (ThXII-LI) and ilioinguinal nerve (LI).
Blood supply: posterior intercostal arteries, lateral thoracic artery, superficial circumiliac artery.
Above the iliac crest, between the posterior edge of the external oblique muscle of the abdomen and the lower anterior edge of the latissimus dorsi muscle, there remains a triangular-shaped space - the lumbar triangle (Petitov). The base (lower side) of this triangle is formed by the iliac crest. The lumbar triangle can serve as a site for the formation of hernias.
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