Muscles of the Abdomen

The wall around the abdominal cavity can be divided into anterolateral and posterior regions.

The walls of the anterolateral region comprise five paired muscles. They are classified into the lateral and anterior groups.

Starting from the surface and going inwards, the lateral group has three flat muscles: the external oblique, the internal oblique, and the transversus abdominis.

The internal oblique muscles run perpendicular beneath the superficial external oblique muscles, while the transversus abdominis muscle mainly runs transversely around the abdominal wall.

The aponeuroses of these muscles interlace, forming the linea alba, a vertical band of fibrous connective tissue running from the sternum to the pubic symphysis.

The anterior muscles — the rectus abdominis and the pyramidalis — are positioned bilaterally to the linea alba.

The posterior abdominal wall lies between the last thoracic and lumbar vertebrae. Its paired muscles include the quadratus lumborum, psoas major, and iliacus.

While the psoas major and iliacus muscles extend until the lower limbs, the quadratus lumborum muscle spans from the iliac crest to the last rib.