Internal Oblique Muscle Anatomy

Overview
Origin Thoracolumbar fascia
Iliac crest
Inguinal ligament
Insertion Inferior margins of tenth to twelfth ribs and adjacent costal cartilages
Linea alba
Pectineal line
Action Lateral flexion of the torso (unilateral contraction)
Rotation of the torso (unilateral contraction)
Flexion of the torso (bilateral contraction)
Can assist in increasing intraabdominal pressure
Nerve Anterior rami of intercostal nerves (T7-T11)
Subcostal nerve (T12)
Iliohypogastric nerve (L1)
Ilioinguinal nerve (L1)
Artery Lower posterior intercostal arteries and subcostal arteries
Superior and inferior epigastric arteries
Superficial and deep circumflex arteries
Posterior lumbar arteries

Location & Overview

The internal oblique muscle is located deep to the external oblique muscle and superficial to the transversus abdominis muscle (i.e located between these two muscle). Its fibers are obliquely oriented hence the name. The internal oblique is much thinner and smaller than the external oblique and much like the external oblique it is a flat and sheet like shape which wraps around the abdomen. The internal oblique is one if the five abdominal muscles. The other four are: the external oblique, rectus abdominis, transversus abdominis and the pyramidalis [1] [2] [3].

internal oblique muscle without its aponeurosis

Pictured here we can the internal oblique muscle without its aponeurosis.

internal oblique muscle with its aponeurosis

Pictured here we can the internal oblique muscle with its aponeurosis connecting into the linea alba at the midline.

Origin & Insertion

The internal oblique originates from the thoracolumbar fascia, iliac crest, and the lateral two thirds of the inguinal ligament. Its fibers run in a superomedial direction and as they near the midline, they form an aponeurosis. This aponeurosis then inserts at the linea alba. The superior aspect of the internal oblique inserts onto the inferior borders of the tenth to twelfth ribs. Inferiorly the internal oblique inserts at the pectineal line (also known as the pectin pubis) [4] [5] [6].

origin of the internal oblique muscle on the inguinal ligament

Pictured here we can see an origin of the internal oblique muscle on the lateral two thirds of the inguinal ligament (highlighted in red).

origin of the internal oblique muscle on the iliac crest

Pictured here we can see an origin of the internal oblique muscle on the iliac crest (highlighted in red).

origin of the internal oblique muscle on the thoracolumbar fascia

Pictured here we can see an origin of the internal oblique muscle on the thoracolumbar fascia (highlighted in green).

internal oblique insertion on the inferior margins of tenth to twelfth rib

Pictured here we can see an insertion of the internal oblique muscle on the inferior margins of tenth to twelfth rib (highlighted in blue). This is from a posterior view, from an anterior view we will be able to see it connecting onto the adjacent costal cartilages also.

insertion of the internal oblique muscle on the tenth rib and the adjacent costal cartilages

Pictured here we can see the continuation of the insertion on the tenth rib and you can now also see the insertion connecting to the adjacent costal cartilages (highlighted in blue).

insertion of the internal oblique muscle on the linea alba

Pictured here we can see an insertion of the internal oblique muscle on the linea alba highlighted in blue. The linea alba is a tendinous, fibrous line that runs vertically down the middle of the abdomen.

Pictured here we can see an insertion of the internal oblique muscle (highlighted in blue) on the pectineal line.

Actions

When acting with the external oblique, the internal oblique is able to cause flexion, rotation and lateral flexion of the vertebral column. These movements are dependant on if just one side contracts (unilateral contraction) or if both sides contract together (bilateral contraction). Unilateral contraction will result in lateral flexion and rotation of the torso. Bilateral contraction will result in flexion of the torso in an anterior direction. The internal oblique can also work together with other abdominal muscles to increase intrabdominal pressure [7] [8].

Innervation

The internal oblique muscle is innervated by the anterior rami of intercostal nerves (T7-T1), subcostal nerve (T12), iliohypogastric nerve (L1) and the ilioinguinal nerve (L1) [9] [10].

Blood Supply

Blood is supplied to the internal oblique muscle via the lower posterior intercostal arteries and subcostal arteries, superior and inferior epigastric arteries, superficial and deep circumflex arteries, and the posterior lumbar arteries [11] [12].

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

References

References
1, 4, 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/
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, 6, 8 Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017
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/