AIA 171 Å image of an active region on the limb (left panel) and a schematic drawing of some features that we wish to draw the reader's attention to (right panel). Note how the thickness of the loops changes at the apex and at the horizontally elongated brightness enhancements at the loop tops. These features are also present in the synthetic images. These features account for the realistic cross sections of the flux tubes (Figures 16 and  17), which support the hypothesis that the cross sections of coronal loops iare in general not circular.