CorpusHuman Anatomy
MuscularMuscle

External oblique

Musculus obliquus externus abdominis

Also known as: external abdominal oblique, inguinal ligament, superficial inguinal ring

The largest and most superficial flat abdominal muscle. Its fibres run inferomedially ("hands in pockets"), and its aponeurosis forms the inguinal ligament and the superficial inguinal ring.

Show on body map Muscles — Posterior View

Overview

External oblique arises by fleshy digitations from the external surfaces of ribs 5–12, interdigitating with serratus anterior and latissimus dorsi. Its fibres run inferomedially. The posterior fibres descend almost vertically to the anterior half of the iliac crest. The rest end in a broad aponeurosis that passes in front of rectus abdominis to the linea alba and to the pubic tubercle. The free posterior border between the 12th rib and the iliac crest bounds the lumbar triangle.

The lower border of the aponeurosis, folded back on itself between the anterior superior iliac spine and the pubic tubercle, forms the inguinal ligament. Medially, this gives off the lacunar and pectineal ligaments. Just above and lateral to the pubic tubercle, a triangular gap in the aponeurosis forms the superficial inguinal ring. The aponeurosis forms the anterior wall of the inguinal canal and contributes the external spermatic fascia around the spermatic cord.

Acting on both sides, it compresses the abdomen and flexes the trunk. Acting on one side, it laterally flexes the trunk and rotates it to the opposite side, working with the internal oblique of the opposite side.

Location

Anterolateral abdominal wall, the most superficial of the three flat muscles.

Parts & subdivisions

  1. Aponeurosis
    Forms the anterior layer of the rectus sheath and the linea alba.
  2. Inguinal ligament
    From the ASIS to the pubic tubercle. It is the lower in-rolled edge of the aponeurosis and forms the floor of the inguinal canal.
  3. Superficial inguinal ring
    A triangular opening above the pubic tubercle, with medial and lateral crura. The spermatic cord or round ligament exits here.

Anatomy

Origin

External surfaces of ribs 5–12.

Insertion

Linea alba, pubic tubercle and the anterior half of the iliac crest (via the aponeurosis and inguinal ligament).

Action

Compresses the abdomen; flexes the trunk; laterally flexes it to the same side and rotates it to the opposite side.

Innervation

Thoraco-abdominal nerves (anterior rami of T7–T11) and the subcostal nerve (T12).

Nerve roots

T7–T12

Arterial supply

Lower posterior intercostal and subcostal arteries; superior and inferior epigastric arteries; superficial and deep circumflex iliac arteries.

Relations

Superficial to the internal oblique. Covered by superficial fascia (Camper and Scarpa layers). Its lower fibres interdigitate with serratus anterior.

Function

  • Compresses and supports the abdominal viscera
  • Flexes the trunk (bilaterally); rotates it to the opposite side (unilaterally)
  • Assists forced expiration, coughing, defecation and parturition

Clinical significance

Inguinal hernia

The superficial ring in the external oblique aponeurosis is where indirect inguinal hernias and the cord emerge toward the scrotum. In open repair the aponeurosis is incised to open the inguinal canal, and the ilioinguinal nerve beneath it must be preserved.

Test yourself

The inguinal ligament is formed by the thickened, in-rolled lower border of which muscle's aponeurosis?
  1. Transversus abdominis
  2. Internal oblique
  3. External oblique
  4. Rectus abdominis

Answer: External oblique

The inguinal ligament is the folded-back inferior edge of the external oblique aponeurosis, running from the ASIS to the pubic tubercle. All the anterolateral abdominal muscles assist forced (not quiet) expiration.

More muscular system questions

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.