|Origin||External surfaces of the fifth to twelfth ribs|
|Action||Lateral flexion of the torso
Rotation of the torso
Flexion of the torso
Assists in forced expiration
|Nerve||Intercostal nerves (T8-T11)
Subcostal nerve (T12)
|Artery||Lower posterior intercostal artery
Deep circumflex iliac artery
The superior and inferior epigastric arteries
Location & Overview
The external oblique muscle is located superficially to the internal oblique muscle (closer to the skin’s surface). The external oblique is one of the five abdominal muscles. The other four are: the internal oblique, rectus abdominis, transversus abdominis and the pyramidalis. It is the most superficial of the anterolateral abdominal wall muscles. It is also the largest of the three flat muscles of the abdominal wall (the internal oblique and transversus abdominis are the other two flat muscles). These flat muscles also the three muscles which make the rectus sheath  .
Origin & Insertion
The external oblique originates from the fifth through twelfth ribs. Its fibres travel in an inferior, medial and anterior direction from its origin. When these fibres reach the midline, they form an aponeurosis which merges with the linea alba, which contributes to the anterior rectus sheath. This aponeurosis also inserts onto the iliac crest, pubic crest and pubic tubercle    .
The external and internal oblique muscles can work together to cause rotation and lateral flexion of the trunk. If only one side of the external oblique muscle contracts (unilateral contraction), it can cause lateral flexion of the trunk. Unilateral contraction can also cause a rotation of the trunk in the direction of the other side (e.g if the right extenal oblique contracts, the toso rotates to the left). If both sides of the external oblique contract together (bilateral contraction), this causes a flexion of the trunk. In addition to flexion and rotation, it also provides support to other nearby abdominal structures. It can also assist in forced expiration by depressing the ribs by pulling on the fifth to twelfth rib origins  .
The external abdominal oblique gets its blood supply from: the lower posterior intercostal artery, subcostal artery, deep circumflex iliac artery, and the superior and inferior epigastric arteries  .
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External Oblique Flashcards
|↑1||Flynn W, Vickerton P. Anatomy, Abdomen and Pelvis, Abdominal Wall. [Updated 2021 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK551649/|
|↑2, ↑5, ↑9, ↑11||Varacallo M, Scharbach S, Al-Dhahir MA. Anatomy, Anterolateral Abdominal Wall Muscles. [Updated 2021 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470334/|
|↑3, ↑7||Flynn W, Vickerton P. Anatomy, Abdomen and Pelvis, Abdominal Wall. [Updated 2021 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK551649/|
|↑4, ↑8||Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017|
|↑6, ↑10, ↑12||Seeras K, Qasawa RN, Ju R, et al. Anatomy, Abdomen and Pelvis, Anterolateral Abdominal Wall. [Updated 2021 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK525975/|