The external oblique muscle is a flat and broad muscle that lies on the anterolateral surface of the abdominal wall. It arises from the lateral surface of the lower eight ribs by eight slips. Then it extends down vertically, covering the internal oblique, to be inserted into the anterior half of the outer lip of iliac crest through its aponeurosis.
Although the external oblique muscle, as a whole, stretches vertically downwards, its fibers run obliquely down and forwards, towards the middle line of abdomen, ending up in the aponeurosis (a sheet of fibrous tissue). The upper part of this aponeurosis extends to the midline, contributing to the formation of the anterior wall of the rectus abdominis muscle sheath of connective tissue.
There is an oval opening in the lower portion of the aponeurosis of the external oblique, near the inguinal ligament. It lets the spermatic cord (in males) and the round ligament of the uterus (in females) run through and out.
Action/function
Along with the rectus abdominis, the external oblique muscle contributes to pull the trunk downwards (from a standing position), and upwards (from a supine position). It also rotates the trunk to the opposite side.
Blood Supply
It receives oxygenated blood from the intercostal, lateral thoracic, and the superficial circumflex iliac artery.
Innervation
The external oblique muscle is supplied by the intercostal nerves (5th to 12th) and the lumbar nerve (T5 to T12 and L1)
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| Above, a schematic picture of the abdominal muscles, showing the external oblique (cut away) and the internal oblique muscle. |
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