Secondary cartilaginous joints.
Articular surfaces of the vertebral bodies are covered by a layer of hyaline cartilage called end plates.
A concentric, peripheral ring of fibrous tissue, the annulus fibrosus, connects the two cartilaginous layers. The annulus fibrosus contains multiple layers stacked together like laminae.
Alternate layers lie at right angles to one another and as a result, the annulus can resist strain from multiple directions.
Within the annulus, there is a remnant of the embryonic notocord called the nucleus pulposus. This gelatinous structure generally lies in the centre of the disc, but lies more posteriorly further down the vertebrae.
This is one of the reasons central disc herniations are more common in the lower lumbar spine.