This article is an EXCELLENT list of rib shapes in a discussion about how it affects bra shapes.

Rib Cages and Bra Fitting - a Masterpost

I've realised that while there are titbits (pun intended) of information about how rib Cages can affect bra fit floating around, it's never been collated into one easy to access article. So I've tried to do that: most of the information in this post is credited to other hardworking bloggers, please check out the credits at the end to support their work!