There are 5 sacral vertebrae, which are fused as one bone and known as the sacrum, in the sacral region. There are 3 to 5 coccygeal vertebrae, which are fused as one bone and known as the coccyx ...

The hierarchical structure of the intervertebral disc (approximately 45–55 mm diameter in the human lumbar spine and 2.5–5 mm in the rat coccygeal spine) is composed of the outer fiber ...