At the lower end of the rectus abdominis, the pyramidalis tenses the linea alba.

http://en.wikipedia.org/wiki/Pelvis

At the lower end of the rectus abdominis, the pyramidalis tenses the linea alba. The lateral superficial muscles, the transversus and external and internal oblique muscles, originate on the rib cage and on the pelvis (iliac crest and inguinal ligament) and are attached to the anterior and posterior layers of the sheath of the rectus.