Aug 31, 2018
(source 1, 2, 3)
Pictured: A Klingon scientist, Antaak, before and after being injected with the Augment Virus. Left: Antaak with ridges. Right: Antaak with out.
[caption: Enterprise’s “Divergence” and “Affliction” episodes gave us an in canon explanation for the missing ridges. That reason was, those Klingons were infected with an Augment Virus, to make them super warriors, that had a side effect of taking away the ridges. While this is an in canon explanation, the real reason was that TOS simply did not have the budget for the ridge prosthetics.]