Ah, the cover art! D'you know, that never even occurred to me? But
Tolkien's design is indeed very clear. That answers that.
(Incidentally, the cover art for
The Two Towers also
answers once and for all what the 'two towers' were - it's Orthanc and Minas Morgul. And is that a very bird-like Fell Beast flying between them...? But that's probably a question for another thread.)
hS