Pyramidalis muscle

The pyramidalis is a muscle that is considered insignificant in humans. It is small and triangular, anterior to the Rectus abdominis, and contained in the rectus sheath.

Attachments and actions
Inferiorly, it attaches to the pubic symphysis and pubic crest, arising by tendinous fibers from the anterior part of the pubis and the anterior pubic ligament.

Superiorly, the fleshy portion of the muscle passes upward, diminishing in size as it ascends, and ends by a pointed extremity which is inserted into the linea alba, midway between the umbilicus and pubis.

Therefore, when contracting, it has the function of tensing the linea alba.

Variations
It is absent in 20% of normal humans.

This muscle may be absent on one or both sides; the lower end of the rectus then becomes proportionately increased in size.

Occasionally it is double on one side, and the muscles of the two sides are sometimes of unequal size.

It may extend higher than the usual level.

Innervation
The muscle is innervated by the ventral portion of T12.