Measure Fifteen!

Moving along in the continuing saga of my attempt to learn The Black Page, we come now to measure fifteen. I will admit right out that this one is really stumping me. I actually thought that I must have written the figure wrong because it doesn't make sense to me. However, comparison to the melody score taken from Guitar Player magazine shows that this is indeed the way Zappa wanted it to be played. Two things are confusing to me. First, I count five independent quarter note length groups in this measure: one quarter note on beat one, two eighths on beat two, a septuplet on beat three, four sixteenths on beat four, and a quintuplet on beat five. Shouldn't five quarter notes played in one measure of 4/4 time be called a quintuplet? How is this to be played as a triplet? I honestly do not know. The second confusing thing is the septuplet on beat three which is rendered 7:2. This is seven against two. The septuplet is occuring as seven sixteenth notes in the space of a quarter note, so the 2 in 7:2 must be referring to two eighth notes (= 1 quarter note), If this is correct, then why isn't the quintuplet on beat five rendered 5:2? What makes the septuplet different such that it needs additional information other than just a seven over the figure? Am I interpreting 7:2 incorrectly? Is it this 7:2 that somehow makes what appear to be five quarter notes a triplet rather than a quintuplet? What's the meaning of all of this? Who did kidnap the Lindberg baby? Where can I go to get my poodle clipped in Burbank? Where can I go to get organic Vaseline?

Questions, questions, questions flooding the mind of the concerned youth. Ahhh, but it is a great time to be alive... (pointless, esoteric Frank Zappa song quote digression).

Anyway, this is what I'm trying to work out. I admit it, I'm completely baffled at this point. I'm sure that someday, after I've worked this whole thing out, I will be a better person for the effort. Who knows, you may be a better person too! Probably not better than me though.