|Derivation||The diagonal (oblique) muscle on the external form of the thorax.|
|Origin||Ribs #5-12. The origins are on the ribs near where they meet the cartilages.|
|Insertion||The medial edge meets the lateral edge of rectus abdominis by a tendon completely covering the latter muscle. The lower edge attaches to the anterior half of the iliac crest and the inguinal (IN-gwin-al, referring to the groin) ligament.|
|Action||Rotates the ribcage. The muscle pulls the same side forward: the right external oblique pulls the ribcage so the right shoulder comes around to the front; likewise for the left oblique. It also bends the lower spine laterally. Both sides together bend the ribcage forward toward the pelvis.|
External oblique is regarded as having distinct upper and lower portions. The lower portion is a large mass that, because of its position, is visible on nearly any view of the trunk. It occupies the space between the ribcage and the pelvis, and can be seen to pour downward from under latissimus dorsi, over the pelvis, and into the groin.
The downward sweep of this muscle from the iliac crest, along the ligament, and into rectus abdominis helps to form the
Greek pleat, a muscular division between the torso and the legs that is prominent in classical Greek sculpture.
External oblique is visible in a fully rear view of the figure, as it emerges out from under latissimus dorsi and turns around the body to the front.
The upper portion is attached to the ribcage by a series of bands. These bands drop off the ribs at a 45-degree angle into the lateral tendinous line of rectus abdominis.