Birds: spinal column and sacrum

I recently mentioned, in another thread, a drawing of several modern-day animal skeletons (specifically referring to a giraffe’s pelvis). What I’d like to know has to do with another critter.
In the same drawing, which shows 14 animals’ skeletons postioned in natural standing poses, is a penguin’s skeleton. Unlike the mammal skeletons, the penguin’s spinal column, halfway down from the shoulders, becomes a solid bone which takes on a swallowtail shape at the bottom and a jagged coccyx-like shape in the tail, also apparently solid. Is this common to all birds?
Also, the sternum is not continuous, but at the top of the rib cage there is a gap in it, between the top of the rib cage and a crescent-shaped descending bone apparently attached to the clavicle. Is this, too, a feature common to birds?