On the bottom of each lesser toe joint (excludes the big toe), there is a ligament between the base of the toe and the metatarsal (foot bone). This ligament is called the plantar plate. The ligament keeps the toe in the joint and prevents it from over extending or drifting out of normal range.
In the gait cycle the toes bend at the base of the toe joint, just before the foot pushes off the ground. The plantar plate holds the toe in place and brings the toe back straight. There is no muscle associated with this ligament.