Pyramidalis muscle
Musculus pyramidalis
Pyramidalis is a small triangular muscle low on the front of the abdomen, lying in front of rectus abdominis inside its sheath.
At a glance
- English
- Pyramidalis muscle
- Latin (TA2)
- Musculus pyramidalis
- System
- Muscle
- Region
- Trunk
- Side
- Paired, left and right
About the pyramidalis muscle
Pyramidalis is one of the smallest muscles of the abdominal wall. It sits in the lowest part of the front wall, just above the pubis, and is enclosed with the bottom of rectus abdominis in the rectus sheath, lying on the front of that muscle. It is not always present: it is missing on one or both sides in a good share of people, and when it is absent the lower end of rectus tends to be a little bulkier.
The muscle takes its name from its triangular shape. Its broad base is fixed below to the front of the pubis, at the pubic crest and the area by the pubic symphysis, and to the ligament that covers the front of the symphysis. From there its fleshy fibres climb upward and medially, narrowing as they go, and end in a pointed tip that attaches to the linea alba. The apex usually lies somewhere between the pubis and the umbilicus, often about halfway, but it may reach higher. The two muscles of a pair are frequently of unequal size, and one side may be doubled.
Its only action is to tense the linea alba, the midline seam into which the abdominal aponeuroses blend. Because it is so small, its contribution is minor, and its absence causes no noticeable loss of function. It may help to steady the lower midline when the abdominal wall is tightened.
The muscle is supplied by the subcostal nerve, the anterior ramus of the twelfth thoracic nerve, sometimes with a branch from the iliohypogastric nerve. Blood comes from the inferior epigastric artery, which runs up behind rectus close by. To surgeons it is a handy guide when opening the lower abdomen through a vertical midline cut: the two pyramidales lie either side of the linea alba and point straight to the midline.
Attachments, action and supply
- Origin
- Front of the pubis at the pubic crest and symphysis, and the anterior pubic ligament.
- Insertion
- Linea alba, usually between the pubis and the umbilicus.
- Action
- Tenses the linea alba.
- Nerve supply
- Subcostal nerve (T12), sometimes with a branch of the iliohypogastric nerve.
- Blood supply
- Inferior epigastric artery.
Anthromica
See the pyramidalis muscle where it really sits, with every layer of the body around it.
- Every layer, one body. Peel from muscle to bone, nerve, vessel and organ, and turn it any way.
- English and Latin. Every structure named the way your exam names it.
- Quiz until it sticks. Short drills on the structures you keep missing.
Free to start. No card.
