After I learned the bass part for "The Raven" (part of it, anyway), I discovered a phrase in it that sounded familiar. And eventually I realized that the same figure starts (and frequently recurs in) "Breakdown." There are some parts in my recording that aren't very accurate, but most of it is pretty close. Really, I just wanted to record a version to point out that phrase:
(I'm still not very good at reading music, but I think that's the right notation.)
What's interesting is that the bass parts for "The Raven" and "Breakdown" were played by different musicians. Joe Puerta played bass on "The Raven," and David Paton played bass on "Breakdown."