'Middle' in the Bible

As for this image, its head was made of the best gold, its breast and its arms were of silver, its middle and its sides were of brass,

He made answer and said, Look! I see four men loose, walking in the middle of the fire, and they are not damaged; and the form of the fourth is like a son of the gods.

On my bed I saw a vision: there was a tree in the middle of the earth, and it was very high.