Blood and Bones and Feathers

It's a line from One Flew Over the Cuckoo's Nest, selected completely without reference to its original context.

I did some more thinking and research—it ought to be possible to block all business links automatically on Google searches, since searching "ribs" brings up 8 vigintillion sodding restaurants—and I decided my felinoids' ribs are going to be roughly the same as earthly ones. Except their sternum's segments (sternebrae, yes they have a name) aren't fused, but jointed, like a cat's or possum's, and their manubrium only joins to the first rib and the clavicles, rather than the first two ribs and the clavicles, and I don't think they have a xyphoid process (I assume their solar plexus takes a different route). Each of their sternebrae (including the manubrium) joins to one rib, enhancing flexibility. And their ribcages are lined with highly elastic connective tissue, and the segments of the sternum separated by elastic pads, similar to in the spine.

I don't think I've mentioned it, but their homeworld has no bird-analogues, only mammal-analogues and archosaur-analogues (for warm-blooded critters, I mean). The "archosaur" flyers are more like bat-snakes than birds, but they do have a feathered flyer. Well, technically they're modified quills, like on a porcupine...because it's a "mammal". 'Course, their keratin[-analogue]s is β-sheets, like reptiles', not α-helices like mammals (all their hair might be considered feathers), but anyway, their fliers are basically...sea-lions. With wings. I'm not sure about their tails, if any; I think they might have feather flight-quill crests on the side of their hind legs that they can spread to act as a horizontal stabilizer. And I'm not sure about their feet, either—maybe something like a possum's. And they're probably not monophyletic, though they do all have sea-lion (and probably also fur-seal) type faces; they have a lot of herbivorous species, and carnivore-descended herbivores (like pandas) tend to use adaptations that are incompatible with flight, like large bodies and sedentary habits. So some of them are more like earless rabbits, or kangaroos, or something.

I think I'll use the heartcase, geodesic frame, and tensegrity-rib ideas on other aliens. And as for the longeron thing, well, like I mentioned, there are already animals on earth with those, they're called the "uncinate processes" and the only birds that don't have them are screamers and Archaeopteryx.