Pyramidalis
Abdomen · Trunk
The pyramidalis is a small, triangular muscle that lies in front of the lower part of the rectus abdominis, within the rectus sheath, and is absent in a notable minority of people. It arises from the pubic crest and pubic symphysis and inserts a short way up into the linea alba, tapering to a point below the umbilicus. Its modest action is to tense the linea alba, the fibrous midline raphe of the abdominal wall. It is supplied by the subcostal nerve (T12), the only muscle in this batch driven by that single anterior ramus. Though functionally minor, it is a reliable surgical landmark for locating the midline.
Origin, Insertion, Action & Nerve
Origin
Pubic crest and pubic symphysis, anterior to rectus abdominis
Insertion
Linea alba, midway to the umbilicus
Action
Tenses the linea alba
Nerve
Subcostal nerve (T12)
Attachments explained
The Pyramidalis is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Pubic crest and pubic symphysis, anterior to rectus abdominis
Insertion
Linea alba, midway to the umbilicus
Action & function
When the Pyramidalis contracts, it produces the following movement: Tenses the linea alba.
As part of the Abdomen group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Pyramidalis receives its nerve supply from the Subcostal nerve (T12). This nerve carries fibres from spinal segment(s) T12.
Because a muscle can only contract when its nerve is intact, injury to the Subcostal nerve or to its spinal roots (T12) can weaken or paralyse the Pyramidalis, impairing the movements it normally produces (tenses the linea alba). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Pyramidalis (the OIANS method)
Study pyramidalis as a tiny triangle riding on the front of the lower rectus abdominis, pointing up toward the umbilicus. Its only job is to tense the linea alba, so rather than moving anything it simply steadies the midline, which is easy to remember from its pointed shape converging on that fibrous line.
Fix its nerve by exception: unlike the rectus abdominis and obliques with their spread of thoracoabdominal nerves, pyramidalis is supplied by the subcostal nerve (T12) alone. Remembering that it is frequently absent, yet valued by surgeons as a marker of the midline, gives the muscle a memorable clinical identity despite its small size.
Frequently asked questions
Where is the Pyramidalis located?
The Pyramidalis is a muscle of the Abdomen group, located in the Trunk.
What is the origin of the Pyramidalis?
Pubic crest and pubic symphysis, anterior to rectus abdominis
What is the insertion of the Pyramidalis?
Linea alba, midway to the umbilicus
What movements does the Pyramidalis produce?
Tenses the linea alba
What nerve supplies the Pyramidalis?
Subcostal nerve (T12)
Is the Pyramidalis free to study in OIANS?
The Pyramidalis is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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