 During walking it not only lifts the heel, but also flexes the knee, assisted by the plantaris.In the "deep layer" of posterior muscles tibialis posterior arises proximally on the back of the interosseous membrane and adjoining bones and divides into two parts in the sole of the foot to attach to the tarsus.In the non-weight-bearing leg, it produces plantar flexion and supination, and, in the weight-bearing leg, it proximates the heel to the calf.