Pyramidalis muscle

Pyramidalis muscle
	Muscles at the front of the abdomen, showing the pyramidalis at the bottom centre.
Details
Origin	pubic symphysis and pubic crest
Insertion	linea alba
Artery	Inferior and superior epigastric arteries
Nerve	Subcostal nerve (T12)
Actions	tensing the linea alba
Identifiers
Latin	musculus pyramidalis
TA	A04.5.01.007
FMA	15568
	Anatomical terms of muscle

The pyramidalis muscle is a small triangular muscle, anterior to the rectus abdominis muscle, and contained in the rectus sheath.

Structure

Inferiorly, the pyramidalis attaches to the pelvis in two places: the pubic symphysis and pubic crest, arising by tendinous fibers from the anterior part of the pubis and the anterior pubic ligament.

Superiorly, the fleshy portion of the pyramidalis passes upward, diminishing in size as it ascends, and ends by a pointed extremity which is inserted into the linea alba, midway between the umbilicus and pubis.

Nerve supply

The pyramidalis is innervated by the ventral portion of T12.

Blood supply

The inferior and superior epigastric arteries supply blood to this muscle.

Variation

The pyramidalis muscle is present in 80% of human population.[1] This muscle may be absent on one or both sides; the lower end of the rectus then becomes proportionately increased in size.

Occasionally it is double on one side, and the muscles of the two sides are sometimes of unequal size. It may also extend higher than the usual level.

Function

The pyramidalis, when contracting, tenses the linea alba.

Clinical significance

While making the longitudinal incision for a classical caesarean section, the pyramidalis is used to determine midline and location of the linea alba.

Additional images

Right hip bone viewed from outside, showing a small line where the pyramidalis attaches

References

"7 Vestigial Features of the Human Body". Encyclopedia Britannica. Retrieved 2017-11-09.

External links

Anatomy photo:35:11-0100 at the SUNY Downstate Medical Center - "Anterior Abdominal Wall: The Pyramidalis Muscle"
Anatomy image:7283 at the SUNY Downstate Medical Center
Cross section image: pelvis/pelvis-female-17—Plastination Laboratory at the Medical University of Vienna

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[1] "7 Vestigial Features of the Human Body". Encyclopedia Britannica. Retrieved 2017-11-09.