Final answer:
The coccyx, or tailbone, is the bone that is not made of fused bones.
Step-by-step explanation:
The bone that is not made of fused bones is the coccyx or tailbone, which is derived from the fusion of four very small coccygeal vertebrae. It articulates with the inferior tip of the sacrum. The coccyx is not weight bearing in the standing position, but may receive some body weight when sitting.