Polymelia is a birth defect in which an affected individual has more than the usual number of limbs. It is a type of dysmelia. In humans and most land-dwelling vertebrates, this means having five or more limbs. The extra limb is most commonly shrunken and/or deformed. The term is from Greek πολυ- "many", μέλεα "limbs". Sometimes an embryo started as conjoined twins, but one twin degenerated completely except for one or more limbs, which end up attached to the other twin. Sometimes small extra legs between the normal legs are caused by the body axis forking in the dipygus condition. Notomelia (from Greek for "back-limb-condition") is polymelia where the extra limb is rooted along or near the midline of the back. Notomelia has been reported in Angus cattle often enough to be of concern to farmers.Cephalomelia (from Greek for "head-limb-condition") is polymelia where the extra limb is rooted on the head. Origin
Tetrapod legs evolved in the Devonian or Carboniferous geological period from the pectoral fins and pelvic fins of their crossopterygian fish ancestors. Fish fins develop along a "fin line", which runs from the back of the head along the midline of the back, round the end of the tail, and forwards along the underside of the tail, and at the cloaca splits into left and right fin lines which run forwards to the gills.
She was initially set to be sold to a freak show, but was instead bought by a dog lover who had the extra leg removed. An eight-legged lamb has been reported on at least two occasions including in 1898 and 2018. In mythology
Many mythological creatures like dragons, winged horses, and griffins have six limbs: four legs and two wings. The dragons science is discussed in Dragons: A Fantasy Made Real. In Greek Mythology:

The Hekatonkheires were said to each have one hundred hands. The Gegenees were a race of giants with six arms. The centaurs had six limbs: four horse legs and two human arms.Sleipnir, Odins horse in Norse mythology, has eight normal horse legs, and is usually depicted with limbs twinned at the shoulder or hip. Several Hindu deities are depicted with multiple arms and sometimes also multiple legs. In popular culture
Edward Albees stage play The Man Who Had Three Arms tells the story of a fictional individual who was normal at birth but eventually sprouted a third functional arm, protruding from between his shoulder blades. After several years of living with three arms, the extra limb was reabsorbed into his body and the man became physically normal again. In Albees play, the title character is extremely angry that we (the audience) seem to be much more interested in the period of his life when he had three arms, rather than his normal life before and after that interval. Monty Pythons Flying Circus performed a skit about a man with three buttocks.