linothorax and other white cuirases

[Dan Howard]

The simple fact is that leather and textile armour are not flexible. Any sculpture depicting something that is flexible is 1) not armour or 2) not realistic. Here are two explainations for the apparent sleeves

1) Roman sculptures were painted. Any detail not carved into the stone will be picked out with paint.
2) The sculptor simply didn't see it as important to make the armour photo-realistic.