The Sartorius muscle – the longest muscle in the human body – is a long thin muscle that runs down the length of the thigh. Its upper portion forms the lateral border of the femoral triangle.

The sartorius muscle arises by tendinous fibres from the anterior superior iliac spine, running obliquely across the upper and anterior part of the thigh in an inferomedial direction.

It descends as far as the medial side of the knee, passing behind the medial condyle of the femur to end in a tendon.

This tendon curves anteriorly to join the tendons of the gracilis and semitendinous muscles which together form the pes anserinus, finally inserting into the proximal part of the tibia on the medial surface of its body.

Sartorius comes from the Latin word sartor, meaning tailor, and it is sometimes called the tailor's muscle.

There are four hypotheses as to the genesis of the name: One is that this name was chosen in reference to the cross-legged position in which tailors once sat. Another is that it refers to the location of the inferior portion of the muscle being the "inseam" or area of the inner thigh tailors commonly measure when fitting a pant. A third is that the muscle closely resembles a tailor's ribbon. Additionally, antique sewing machines required continuous cross body pedalling. This combination of lateral rotation and flexion of the hip and flexion of the knee gave tailors particularly enlarged sartorius muscles.