The passive stay apparatus of the frontlimb enables a horse to rest while standing and use a minimal amount of muscular energy to do so. Instead of using muscles to stabilise joints, this function is performed by tendons and ligaments which do not fatigue to the same extent. The shoulder joint is prevented from flexing through the M. biceps, the elbow is fixed in extension by the M. triceps. A tendon (Lacertus fibrosus) which effectively extends out of the biceps tendon and the forearm fascia inserts below the carpal joint and locks this in extension. The carpal, fetlock and pastern joints are prevented from overextension by the tension of the flexor tendons and the suspensory ligament.