The author describes a rare variation of the popliteus muscle. The medial portion of the popliteus muscle originated on the lateral condyle of the femur and not on the articular capsule in the region of the posterior horn of the lateral meniscus. This variation found bilaterally is similar to other variations of the tendon of the popliteus muscle, of the posterior horn of lateral meniscus and of meniscofemoral ligaments, which is a manifestation of a complicated phylogenetic development of the femoro-tibial joint.