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Even the most advanced human anatomy is peppered with parts that appear redundant—male nipples, the tiny muscles that let some people wiggle their ears, and more. Yet biologists find that many of these vestigial structures still serve hidden roles, even if their original purpose faded over millennia.

The pyramidalis muscle is a prime example. This small, triangular muscle lies within the abdominal wall and is often described as vestigial. Some researchers trace its lineage back to marsupial pouches, while others suggest it evolved alongside the upright posture that defines us. A 2020 study of 30 cadavers reported that 13.33% of individuals lack a pyramidalis muscle entirely.

So how can a muscle absent in a significant minority still be functional? While its precise contribution remains debated, several functions have been proposed.

What exactly does the pyramidalis muscle do?

The muscle is believed to reinforce the abdominal wall and tighten the linea alba—a fibrous band that runs along the midline of the abdomen. Its contraction synchronizes with other abdominal muscles, aiding in the overall tension of the core. This action helps protect internal organs and supports activities that require forced respiration, singing, and even defecation.

Interestingly, the 2020 study found that individuals without a pyramidalis muscle did not exhibit any noticeable loss of function, underscoring the mystery surrounding its role. Nevertheless, surgeons use it as a landmark for abdominal incisions, and it can serve as a source for grafts or stem cells.

A 2017 investigation in the Journal of Clinical and Diagnostic Research highlighted additional clinical uses: treatment of severe dysuria and microsurgical transfer for small foot and ankle wounds. The authors concluded that the pyramidalis muscle’s significance should not be underestimated.

In sum, while the pyramidalis may seem like a relic of our evolutionary past—and it is indeed absent in some—its potential benefits in medicine and physiology make it a muscle worth recognizing.

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