sacral vertebra

…the fifth lumbar and first sacral vertebrae). Treatment, depending on the severity of the condition, may include bed rest, analgesic medication (e.g., aspirin), traction, orthopedic support, and physical therapy or surgical removal of the protruded portion of the disk and fusion of the spinal vertebrae at the point affected.

…than the other vertebrae, (4) sacral, often fused to form a sacrum, which articulates with the pelvic girdle, (5) caudal, in the tail. The atlas and axis vertebrae, the top two cervicals, form a freely movable joint with the skull.