The Collaborative International Dictionary of English v.0.48:

Sartorius \Sar*to"ri*us\, n. [NL., fr. L. sartor a patcher,
   tailor, fr. sarcire, sartum, to patch, mend.] (Anat.)
   A muscle of the thigh, called the tailor's muscle, which
   arises from the hip bone and is inserted just below the knee.
   So named because its contraction was supposed to produce the
   position of the legs assumed by the tailor in sitting.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sartorius
    n 1: a muscle in the thigh that helps to rotate the leg into the
         sitting position assumed by a tailor; the longest muscle in
         the human body [syn: sartorius, sartorius muscle,
         musculus sartorius]