Rogers, P.I. (page 25)

In which a horrifying lesson in puppet anatomy is given.

This is why puppets have vestigial bodies: Their organs, nervous system, and most of their skeletal system have migrated up into their smaller “primary” bodies. The larger “secondary” body is used only for locomotion and support. And of course they have also diverged into several different phenotypes: humanoid, amphibian, feline, bovine, avian, and so on.