Part I is two verses, then part II starts at letter C. This is where the bass gets interesting. It's swing 16th notes, so two 16th notes feel like three where the first and second are tied. Part II starts with an 8 bar vamp on G7, then goes into a 12 bar blues in F where the last four measures are an A7 chord. Lots of 16th note triplets. Then 6 bars of the G7 vamp, and ends with an Eb7 F7 G7 pattern. I had never heard this before. Thanks to JimK for alerting me to it. Peter Cetera was a great bass player.