The phrase "right spine" is a way of saying that someone has a strong, confident, and assertive demeanor. It means they stand up straight and carry themselves with self-assurance. Full definition
The volume rocker is on the right spine, and so is a dedicated camera key. (cnet.com)
Other than the home key, Nook's only other physical attribute is the covered microSD card slot on the right spine. (ubergizmo.com)
On the right spine are the volume rocker and the camera shutter / convenience key (a function key that you can program to open any app of your choice). (infoworld.com)