Polymelia
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. In the paired ventral part of the fin line, normally only the pectoral and pelvic fins survive (but the Devonian acanthodian fish Mesacanthus developed a third pair of paired fins); but along the non-paired parts of the fin line, other fins develop. In tetrapods, only the four paired fins normally persisted, and became the four legs. Notomelia and cephalomelia are atavistic reappearances of dorsal fins. Some other cases of polymelia are extra development along the paired part of the fin lines, or along the ventral posterior non-paired part of the fin line. Notable cases Humans 1995: Somali baby girl born with three left arms. In March 2006, a baby boy identified only as Jie-jie was born in Shanghai with a fully formed third arm: he had two full-sized left arms, one ventral to the other. This is the only documented case of a child born with a fully formed supernumerary arm. It is an example of an extra limb on a normal body axis. On November 6, 2007, doctors at Bangalore's Sparsh Hospital in Bangalore, India successfully completed surgery on a two-year-old girl named Lakshmi Tatma who was born with four arms and four legs; this was not true polymelia but a case of ischiopagus Siamese twinning where one twin's head had disappeared during development. Frank Lentini had a third leg, as well as a fourth foot and two sets of genitals. Other animals A four-legged chicken was born at Brendle Farms in Somerset, Pennsylvania, in 2005. The story was carried on the major TV network news programs and USA Today. The bird was found living normally among the rest of the chickens