These diagrams show the general structure of the abdominal wall. It shows the 3 main muscles in brown. These muscles fuse and form a large aponeurotic tendon sheet (termed the rectus sheath) and this encloses a single strap-like muscle – the rectus abdominis muscle – the rectus sheath fuses in the mid-line to form the linea alba (white). Because this is a single layer here this is a potential weakness and thus a common site where hernias develop – termed ‘epigastric’ hernias.