Here is a shot the Smithsonian staff took from the inside of the saucer, when they placed a camera into the hole ordinarily covered by the bridge dome.
The book on the building of the TOS Entrerprise miniatures, by Richard Datin, Jr. and N. Datin McDonald, is an interesting read….unfortunately, there are no behind the scenes photos documenting the building of the Enterprise miniatures.
I'd heard recently that the Okudas had a memo from Gene that he wanted the inboard nacelle grilles to light up when they did the upgrades for lighting, but he didn't have the budget so he had to leave it out. Is this true? Does anyone have a photo of the memo?
I think he didn’t just want it lit, but be a continuation of the pattern laid down on the forward nacelle cap.
So the inside facing trench would be lines across the length rising or falling—and the aft nacelle “ball” a mirror image of the pattern on the front nacelle dome—
—as if the nacelle had an egg-beater spinning like mad inside.