The spine contains dozens of vertebrae and can a real pain to animate. To simplify the animation process, most animators don't create a bone for every vertebra in the spine; you can use as little as three to more than a dozen. The more spinal joints you use, the more accurate the deformations are, but the more complex the setup is.
One of the key tricks to setting up a biologically correct spine is to keep the pivot points of the spine as close to the back of the character as possible. The joints in the spinal column run along the arch of the back. Figure 13 shows an incorrect setup, while Figure 14 shows a more natural solution.
Figure 13 This spine is biologically incorrect as it runs through the center of the torso.
Figure 14 This is much better, and the resulting character will look more natural.
Because there are so many joints in the spine, it is usually a good idea to create sliders to control its bend. Simply tying the rotations of the joints to one controlling object can do this quite simply and make it easy for the animator.
Create an object to control the spine (see Figure 15).
Select the first joint of the spine. Connect the X rotation of the spine to the X rotation of the object, as shown in Figure 16. Do the same for the Y and Z rotation.
Rotating the object should rotate this joint (see Figure 17). Repeat this for the rest of the joints of the spine. Manipulating the control object then should manipulate the spine, as shown in Figure 18.
Figure 15 Create an object to control the spine.
Figure 16 Connect the rotation of the object to that of the spine.
Figure 17 Rotating the object rotates the spine.
Figure 18 Repeating this for the rest of the joints will manipulate the entire spine.