Nerve to piriformis
Nerve to the piriformis muscle also known as piriformis nerve arises from the S1 and S2 nerve roots of the sacral plexus. The nerve supplies the piriformis muscle.
The nerve to the piriformis muscle arises from the sacral plexus. The nerve branches from the posterior division of the ventral rami of the first and second sacral nerves. The piriformis occasionally receives a branch from the fifth lumbar nerve.
Unlike the majority of nerves that originate from the sacral plexus the nerve to piriformis remains within the pelvic cavity and pierces the anterior surface of the piriformis muscle.
The sciatic nerve is the largest branch of the sacral plexus and at its origin is closely related to the piriformis muscle. The nerve which receives contributions from L4-S3 forms on the anterior surface of the piriformis muscle and leaves the pelvic cavity through the greater sciatic foramen inferior to piriformis.
Additionally, a number of small nerves that branch from the sacral plexus remain within the pelvic cavity, for example nerves that supply levator ani and coccygeus muscles.
Bifid piriformis muscles have been noted previously on cadaveric examination.