>I don't remember seeing any rough breathings in the
> middle of Greek words.)
Rough breathings survive in compounds only if the previous letter can show
it - that means t/tH, k/kH and p/pH. Elsewhere there was no way of spelling
it. It is debatable whether or not it survived in pronunciation - perhaps
when it was an obvious compound, it did.
Two interesting words that show this in English are anode and cathode (the
opposite poles of a battery). Both are compounds of hodos = path, but only
with the prefix cat'- (="down") could the aspirate be shown. With the
prefix an'- (="up") there was no way to spell it - and now in English the
"h" is gone for ever.
Peter