Pyramidalis is a paired triangular muscle of the anterior abdominal wall found on each side of the linea alba. According to the narrowest anatomical classification, pyramidalis belongs to the anterior abdominal muscles, together with the rectus abdominis muscle. However, in a broader picture that takes the functional anatomy into account, these two muscles comprise the anterolateral abdominal wall along with the lateral abdominal muscles; external oblique, internal oblique and transversus abdominis muscles.
Pyramidalis muscle tenses the linea alba, which is an action that doesn't have a significant function when occurring on its own. However, acting together with the rest of the abdominal muscles, pyramidalis muscle contributes to a variety of abdominal wall functions, such as increasing the intra abdominal pressure when necessary (e.g. labor, forced expiration, defecation).
|Origin||Pubic crest, pubic symphysis|
|Action||Tenses linea alba|
|Innervation||Subcostal nerve (T12)|
|Blood supply||Inferior epigastric artery|
This article will discuss the anatomy and function of 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.
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.
Pyramidalis is innervated by the subcostal nerve, which is the anterior ramus of spinal nerve T12.
Blood supply to the pyramidalis muscle comes from branches of the inferior epigastric artery.
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.