The piriformis is a muscle in the buttock.

piriformis muscle
The piriformis muscle is triangular and reaches from the sacrum ("buttock bone") to the greater trochanter of the femur. The sciatic nerve runs emerges between it and the muscle group below it, where it can become irritated if the piriformis is tight.
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Dr Sheila StroverĀ (Editor)
BSc (Hons), MB BCh, MBA

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