Click here to see the place of the fragment relative to nearby surviving sections of the frieze.
Welcoming the Vatican's action, Greek culture minister Mikhalis Liapis said: "This gesture provides an example for others to follow, to achieve the final unification of the Parthenon sculptures."
About half of what survives of the temple decoration is in the British museum in London, including 247 ft of the original 524 ft frieze. Most of the other surviving sculptures are in Athens.
The Greek authorities wish to reunite all the surviving sculptures from the Parthenon in the new Acropolis museum, which they say will open next year.
But the British Museum has refused to return its Parthenon sculptures, almost all of which were brought back from Athens in the early 19th century by the British diplomat, Lord Elgin.
Unchanged
The Vatican had not previously acceded to Greek appeals to return the Parthenon carvings in its collection.
At the handover of the head on Wednesday Giandomenico Spinola, the head of the Vatican museums' classical antiquities department, could not say for certain whether the loan of the sculpture would be extended, or whether the Vatican might lend the Greeks the other two Parthenon fragments it owns.
The pieces were the property of the Pope, and the decision would be his, Mr Spinola said.
Last month a piece of the frieze formerly held at a museum in Sicily was returned to the Greeks by the Italian president.
The British Museum said in response to the Italian move that its trustees' position on the sculptures remained unchanged.
"Here in London the sculptures are an important part of a world collection which is free to all and which allows six million visitors a year to explore the complex network of interconnected world cultures," it said in a statement.
The head handed over by the Vatican is thought to be of one of the tray- bearers on the lost fifth slab of the Parthenon north frieze.
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