The rib measures 15 centimetres (6 inches) and is "well-preserved"

Forensic expert Philippe Charlier and his team will spend six months testing remains including a rib and some skin.

The relics are said to have been found at the stake in the Normandy town of Rouen where Joan was burned in 1431.

France's national heroine - canonised in 1920 - was convicted of heresy and witchcraft and burned alive aged 19.

Dr Charlier said the tests would not determine with certainty whether the remains are Joan of Arc's - but they would help to work out how likely they are to be genuine.

The rib, currently housed at a museum in Chinon owned by the Archdiocese of Tours, is "remarkably well preserved" according to Dr Charlier.

Researchers at the Raymond-Poincare Hospital in Garches near Paris will use DNA testing and carbon dating to determine whether the bone belonged to a woman, as well as its exact age, Dr Charlier said.

Complex case

He said no DNA comparison with possible descendants will be carried out because Joan of Arc's family tree is probably false.

LEGEND OF ST JOAN 1412: Born in Domremy, Champagne 1425: Saints' voices tell her she will be France's saviour in Hundred Year's War 1429: Helps mount a campaign against the English in Orleans 1430: Captured and ransomed to English, condemned for heresy and witchcraft 1431: Burned at the stake 1455: Trial verdict annulled 1909: Beatified 1920: Made a saint

Dr Charlier said Joan of Arc was burned three times on 30 May in 1431, following her trial in the Normandy town of Rouen. She died of smoke inhalation.

Nothing was said to remain after the third cremation except her ashes - which were reportedly thrown in the River Seine in Paris.

Dr Charlier has a track record in forensic history.

Last year he identified the cause of death of Agnes Sorel, mistress of the 15th Century French king Charles VII, as mercury poisoning, but was unable to determine whether it was murder.