Charles Ellicott Commentary Daniel 2:32

"As for this image, its head was of fine gold, its breast and its arms of silver, its belly and its thighs of brass," — Daniel 2:32 (ASV)

Breast ...—It should be noted that though many different parts of the body of the image are mentioned, Daniel regards the whole thing as made up of only four parts, each corresponding to one of the four metals. Similarly, he shows that the history of the world in its relation to God’s people, complicated though it may be and varied in its aspect, consists of no more than four principal parts. It will be noted that by the additional details mentioned in Daniel 2:41-42, certain minor complications of history are intended, which, however, do not interfere with the fourfold division of which the outline is given here.