Polymelia

Polymelia (from Greek πολυ- = "many" plus μέλος (plural μέλεα) = "limb") is a birth defect involving limbs (a type of dysmelia), in which the affected individual has more than the usual number of limbs. In humans and most land-dwelling animals, this means having five or more limbs. The extra limb is most commonly shrunken and/or deformed.