It can be seen here as the thin, slightly curved horizontal bone between the two massive shoulder bones. One of the distinguishing characteristics of birds is their wishbone. The two small long bones running side by side across the middle of this picture are the wishbone of this bird. Fusion of the vertebral bones in the sacral area provide a massive bar of bone that helped support the enormous weight that had to be carried across this joint. Dinosaurs, like modern birds, have hollow long bones that make them lighter while still retaining strength.
Birds have a similar leg and sacral structure.
As in T. rex, fusion of the back bones in the sacral area provide strength to support the weight at this joint. One major difference between modern birds and dinosaurs is that birds lack the long tail. We will probably never know for sure, but a sculptor's rendition is probably pretty accurate. Note that Sue's eyes faced forward, giving her good depth perception. Sue's brain had very large olfactory lobes.