Pyramidalis Muscle; Origin, Nerve Supply, Function

Pyramidalis Muscle is a small triangular muscle, anterior to the rectus abdominis muscle, and contained in the rectus sheath. Pyramidalis muscles are small triangular-shaped muscles that lie between the anterior surface of the rectus abdominus and the posterior surface of the rectus sheath. The precise function of pyramidal muscles is unclear, but together the muscles are thought to tense the linea alba. The muscles are not always present, or are often unilateral, and vary greatly in size. Their wider inferior margins attach to the pubic symphyses and pubic crests, whereas their narrow superior margins attach to the linea alba.

Anatomy of Pyramidalis Muscle

• Inferiorly, the pyramidal attaches to the pelvis in two places: 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 pyramidalis 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.
• The pyramidalis muscle is present in 80% of the human population.^[rx] 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 also extend higher than the usual level.

Origin of Pyramidalis

• Pyramidalis originates inferiorly by tendinous fibers from symphysis pubis and pubic crest.

Insertion of Pyramidalis

• 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.

Nerve supply of Pyramidalis Muscle

• The pyramidalis is innervated by the ventral portion of T12. Pyramidalis is innervated by the terminal branches of the subcostal nerve (the anterior ramus of 12^th thoracic nerve).

Blood supply

• The inferior and superior epigastric arteries supply blood to this muscle.
• The major portion of the blood supply of pyramidalis comes from the inferior epigastric artery. Some contribution is made by the deep circumflex iliac artery.

Function of Pyramidalis Muscle

• The pyramidalis, when contracting, tenses the linea alba. Pyramidalis has a function of tensing the linea alba, however, the physiologic significance is doubtful.

References

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