What is the wedge-shaped bone consisting of five fused vertebrae connecting the two pelvic bones?

• A. Sacrum
• B. Lumbar
• C. Coccyx
• D. Thoracic

Answer: (A)

The sacrum is the wedge-shaped bone formed by the fusion of five sacral vertebrae and sits between the two pelvic bones, forming the base of the spine and the posterior part of the pelvis. Because the five vertebrae fuse into a single bone, the sacrum efficiently transmits the body's weight from the spine into the pelvis and connects with the ilia at the sacroiliac joints on each side. This fusion and location distinguish it from other regions: the coccyx is the tailbone below the sacrum and consists of coccygeal vertebrae, the lumbar vertebrae are the five large lower-back bones that remain separate in adulthood, and the thoracic vertebrae are in the mid-back and articulate with the ribs. Hence, the wedge-shaped bone between the pelvic bones is the sacrum.