Final answer:
The coccyx, or tailbone, is made up of four fused coccygeal vertebrae and supports some body weight when sitting. It articulates with the sacrum, which itself is formed by the fusion of five sacral vertebrae. Together, they contribute to the sacrococcygeal curve of the spinal column.
Step-by-step explanation:
The coccyx, often referred to as the tailbone, is a small bone located at the inferior end of the adult vertebral column. It is comprised of four coccygeal vertebrae that are fused together. This fusion creates a triangular shape that tapers down and articulates with the sacrum. The coccyx is not involved in weight-bearing when a person is standing but may support some body weight while sitting, particularly in a leaning back position.
The sacrum is a larger triangular-shaped bone situated above the coccyx, formed by the fusion of five sacral vertebrae. This process of fusion begins after the age of 20 and the places of fusion are indicated by the presence of transverse ridges. The merged spinous processes along the posterior side form what is known as the median sacral crest, while the lateral sacral crest is derived from the fused transverse processes of the sacral vertebrae.
Together, the sacrum and coccyx form a curvature in the vertebral column known as the sacrococcygeal curve, which is anteriorly concave and considered a primary curve of the spine.