The Abdominal Muscle 20% of Us Are Missing
The Abdominal Muscle 20% of Us Are Missing
Five paired muscles make up the anterolateral compartment of the abdominal wall, including the rectus abdominis, internal oblique, external oblique, transversus abdominis, and a lesser-known muscle that you might not even have—the pyramidalis.
The pyramidalis is a small, triangular muscle situated anterior to the lower rectus abdominis. Like the rectus abdominis, the pyramidalis contains a mix of type I and II muscle fibers, originating from the pubis and extending vertically and superiorly. However, their similarities largely end there. The pyramidalis averages just 2-3 inches in length and inserts on the linea alba halfway between the pubis and umbilicus. Due to its size and attachment sites, it acts bilaterally to tense the linea alba with merely 2 newtons of force.
I wish I had a more compelling story to tell—something worthy of a title like “The Pyramidalis: Your Abs’ Hidden Edge” or “The Unsung Hero of the Core” (both courtesy of AI). But the truth is, the pyramidalis doesn’t do much. It’s considered vestigial, meaning it no longer serves its original purpose, and it’s absent on one or both sides in 20% of people.
While the pyramidalis may not be your core’s secret weapon, it does play a valuable role as an anatomical landmark for caesarean section incisions, a muscle flap for reconstructive surgeries and a source of stem cells. Long live the pyramidalis!
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Lovering RM, Anderson LD. Architecture and fiber type of the pyramidalis muscle. Anat Sci Int. 2008 Dec;83(4):294-7. doi: 10.1111/j.1447-073X.2007.00226.x. PMID: 19159363; PMCID: PMC3531545.
Sumalatha S, Rao S, Ankolekar VH. Morphometry of pyramidalis muscle and its role in reconstructive surgeries: A cadaveric study in South Indian population. F1000Res. 2024 Jan 8;12:484. doi: 10.12688/f1000research.132477.2. PMID: 37811201; PMCID: PMC10558977.
