probably should have used a smaller needle, stuffing showed through a bit too much.

Back spine:
Mark center of back for a line to follow

1. Starting either at top of head or tip of tail, pick up and knit two stitches
2. K2, p/u and K1
3. K3
4. K3, p/u and K1
5. K4
6. bind off 3 stitches, p/u and K1 then cast off 4th stitch, p/u and K1 more

repeat from row 2

as pictured - spines on the neck picked up every stitch, spines on the back and tail picked up every other stitch.
You can pick up more stitches for bigger spines, or less for smaller.