Thanks Bud - they were done on a machine
I think i'd go insane if I tried to do it all by hand!
For this little experiment, I designed one rib (not based on any particular pattern), then copied and pasted three more. Once the design was done, it took around 5 minutes to cut the parts, another 5-10 minutes or so to separate each rib and do a cursory clean up, and then assembly. The problem that I am trying to overcome now is that the ribs were cut from 0.10" plastic and are flimsy, so it's hard to keep them straight. I think rib caps may help here.
If I can get it to work, this should give me the ability to create skeletal structures relatively quickly and (hopefully) consistently.
Cheers,
BC