Rectus abdominis muscle

The rectus abdominis is a paired muscle running vertically along the front of the abdomen. It flexes the trunk, stabilizes the pelvis, and helps compress abdominal contents.

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Linea alba: A midline band of connective tissue separating the left and right rectus abdominis muscles. The two muscle bellies meet across this central seam.
External oblique muscle: The most superficial flat muscle of the lateral abdominal wall, with fibers running inferomedially. Its aponeurosis contributes to the rectus sheath.
Diastasis recti: Widening and thinning of the linea alba that separates the rectus abdominis muscle bellies. It changes the spacing and tension between the paired muscles.
Pyramidalis muscle: A small triangular muscle in the lower anterior abdominal wall that tenses the linea alba. It lies in front of the lower rectus sheath but does not produce the same trunk-flexion action.
Tendinous intersections: Transverse bands of connective tissue that divide each rectus abdominis into segmented regions. These intersections create the muscle's characteristic segmented appearance.
Internal oblique muscle: A flat muscle of the lateral abdominal wall with fibers generally running superomedially. Its aponeurosis helps enclose the rectus abdominis.
Rectus abdominis muscle flap: A reconstructive tissue flap that uses the rectus abdominis, often with overlying tissue, to repair defects. The muscle's blood supply and location allow it to be transferred for reconstruction.
Psoas major muscle: A deep hip flexor that links the lumbar spine to the femur. It can flex the trunk when the legs are fixed, but acts primarily across the hip.
Rectus sheath: A layered fascial enclosure formed by the aponeuroses of the abdominal wall muscles. It encloses the rectus abdominis and transmits forces from neighboring muscles.
Transversus abdominis muscle: The deepest flat muscle of the lateral abdominal wall, with mostly horizontal fibers. Its aponeurosis joins the layers forming the rectus sheath.