External Oblique Muscle Anatomy

Overview
OriginExternal surfaces of the fifth to twelfth ribs
InsertionIliac crest
Pubic crest
Pubic tubercle
Linea alba
ActionLateral flexion of the trunk
Rotation of the trunk
Flexion of the trunk
Assists in forced expiration
NerveIntercostal nerves (T8-T11)
Subcostal nerve (T12)
ArteryLower posterior intercostal artery
Subcostal artery
Deep circumflex iliac artery
The superior and inferior epigastric arteries

Location & Overview

The external oblique muscle, located superficially to the internal oblique muscle (closer to the skin’s surface), is one of the five abdominal muscles. The other four include the internal oblique, rectus abdominis, transversus abdominis, and the pyramidalis. The external oblique is the most superficial and largest of the anterolateral abdominal wall muscles. Along with the internal oblique and transversus abdominis, it is one of the three flat muscles that compose the abdominal wall. These flat muscles also contribute to the formation of the rectus sheath [1] [2].

external oblique anterior view

Here we can see the external oblique from an anterior view.

external oblique anterolateral view

Here we can see the external oblique from an anterolateral view.

external oblique lateral view

Here we can see the external oblique from a lateral view.

external oblique posterior view

Here we can see the external oblique from a posterior view.

external oblique highlighted in red

Here we can see the external oblique highlighted in red amongst the other muscles of the body. The muscle we can see in the middle is the rectus abdominis muscle.

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 work together to enable trunk rotation and lateral flexion. When only one side of the external oblique muscle contracts (unilateral contraction), it results in lateral flexion of the trunk. Unilateral contraction also causes trunk rotation in the opposite direction (e.g., if the right external oblique contracts, the trunk rotates to the left). When both sides of the external oblique contract simultaneously (bilateral contraction), it leads to trunk flexion. In addition to flexion and rotation, the external oblique muscle also provides support to nearby abdominal structures and assists in forced expiration by depressing the ribs, pulling on the fifth to twelfth rib origins [7] [8].

Image of a person demonstrating the movement of trunk lateral flexion.

This image demonstrates trunk lateral flexion, which involves bending the torso to the side. Unilateral contraction of the external oblique can cause lateral flexion of the trunk.

Image of a person demonstrating the movement of trunk rotation.

This image demonstrates trunk rotation, which involves twisting the waist/torso to the side. Unilateral contraction of the external oblique can cause rotation of the trunk.

Image of a person demonstrating the movement of trunk flexion.

This image shows an example of trunk flexion, which involves bending the torso forwards. The opposite of trunk flexion is trunk extension. Bilateral contraction of the external oblique can cause flexion of the trunk.
The external oblique muscle also provides support to nearby abdominal structures and assists in forced expiration

Innervation

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

intercostal nerves

Here we can see the intercostal nerves highlighted in red. These nerves are an innervation of the external oblique muscle.

subcostal nerve

Here we can see the subcostal nerve highlighted in red. The subcostal nerve innervates the external oblique muscle.

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

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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/