27. Rectus Sheath
The rectus sheath is a durable, multi-layered fibrous compartment (aponeurosis) that surrounds the rectus abdominis and pyramidalis muscles in the anterior abdomen. It acts as a protective sleeve, providing structural integrity, abdominal wall strength, and preventing muscle bowing during contraction. It is formed by the fused aponeuroses of the external oblique, internal oblique, and transversus abdominis muscles.