Pyramidalis muscle

Origin and insertion

Pyramidalis muscle originates from the pubic symphysis and pubic crest. The part of the muscle originating from the symphysis arises by ligamentous fibers, while the bony attachment arises by tendinous fibers. The muscle belly narrows down as it courses superiorly and inserts to the linea alba, halfway between the umbilicus and pubis.

Relations

Pyramidalis muscle lies within the rectus sheath, a multilayered fascial compartment composed of the aponeuroses of the external abdominal oblique, internal abdominal oblique and transversus abdominis muscles. Within the sheath, pyramidalis lies superficially to the inferior part of rectus abdominis muscle.

Innervation

Pyramidalis is innervated by the subcostal nerve, which is the anterior ramus of spinal nerve T12.

Blood supply

Blood supply to the pyramidalis muscle comes from branches of the inferior epigastric artery.

Function

Pyramidalis muscle tenses the linea alba. The muscle usually contracts together with the other abdominal muscles, contributing to contracting the abdominal wall and increasing the positive abdominal pressure. 

These actions play a dual role. The first is as an important defense mechanism, whereby contraction of the abdominal muscles physically protects the abdominal organs. The second is to support certain physiological processes such as forced respiration, singing, micturition and defecation.