Quiz 7

There were 3 men standing in a single row.
The shortest was in front.
The tallest was the last.

The shortest can see no one.
The middle can see the back of the shortest head only.
The tallest can see the back of the shortest as well as the middle's head.

Then, All 3 were blind folded.
They were told that there are 4 hats.
2 black and 2 white.

'Someone' placed a hat on each of the men's head while they are STILL BLIND-FOLDED.
The fourth (extra) hat was thrown out of the room.

Here comes the question:
The blind-fold was removed.
None of them were allowed to move ANY PARTS OF THEIR BODY.
The man who could tell what's the colour of the hat which is on HIS OWN HEAD, may leave the room.

The man in the middle was the ONLY one who said the colour of his own hat correctly and left the room.
Why was it him?