External Oblique Muscle Anatomy

Overview
Origin External surfaces of the fifth to twelfth ribs
Insertion Iliac crest
Pubic crest
Pubic tubercle
Linea alba
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
Subcostal 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 [1] [2].

external oblique muscle

Pictured here we can see the external oblique muscle in isolation without its aponeurosis.

external oblique and its aponeurosis

Pictured here we can see the external oblique and its aponeurosis which is connecting into the linea alba.

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 [3] [4] [5] [6].

origin of the external oblique highlighted in red

Pictured here we can see the origin of the external oblique highlighted in red on the external surfaces of the fifth to twelfth ribs.

insertion of the external oblique on the iliac crest

Highlighted in blue we can see one of the insertions of the external oblique on the iliac crest.

insertion of the external oblique on the pubic crest and pubic tubercle

Highlighted in blue we can see one of the insertions of the external oblique on the pubic crest and pubic tubercle.

linea alba highlighted in blue

Highlighted in blue we can see the final insertion of the external oblique on the linea alba.

Actions

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 [7] [8].

Innervation

The external abdominal oblique is innervated by the intercostal nerves (T8-T11) and the subcostal nerve (T12) [9] [10].

Blood Supply

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 [11] [12].

Want some flashcards to help you remember this information? Then click the link below:
External Oblique Flashcards

References

References
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/