Rectus Abdominis

The Rectus Abdominis muscles originate at the pubic bone, run up the center of the abdomen, and insert into the cartilage of the fifth, sixth, and seventh ribs. The muscle is crossed by three tendinous sections called the linae transversae, which when not covered by dermal fat, creates a washboard appearance. The rectus abdominus is enclosed in a thick sheath formed by the intersecting fibers from each of the three other muscles of the lateral abdominal wall.