External Obliques

The external obliques are a pair of abdominal muscles that lie superficial to the internal obliques. Where the fibers of the internal obliques run in an inverted V position from the bottom of the ribs to the front of the pelvis, the external obliques run in a V. The line is similar to the direction of putting your hands in your pockets.

Anatomy of the External Obliques

The external oblique is situated on the lateral and anterior parts of the abdomen. It is broad, thin, and irregularly quadrilateral, its muscular portion occupying the side, its aponeurosis the anterior wall of the abdomen.

In most humans (especially males), the oblique is not visible, due to subcutaneous fat deposits and the small size of the muscle.

It arises from eight fleshy digitations, each from the external surfaces and inferior borders of the fifth to twelfth ribs. These digitations are arranged in an oblique line which runs downward and backward, with the upper digitations being attached close to the cartilages of the corresponding ribs, the lowest to the apex of the cartilage of the last rib, the intermediate ones to the ribs at some distance from their cartilages.

Functions of the External Obliques

The external obliques function to pull the chest downwards and compress the abdominal cavity, which increases the intra-abdominal pressure. They also affect the spine, ribs and pelvis.

They do several other functions:

• Flex the trunk forward,
• Support and contain the abdominal contents,
• Function during breathing, particularly exhaling,
• Rotate the ribs and pelvis in opposite directions from one another,
• Tilt the pelvis, and
• Laterally flex the spine.

For some of these actions, the external obliques work with other abdominal muscles. This is especially true of the rotation and lateral flexion motions.

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