[pl. vertebrae]. One of the 33 bones of the spinal column. The spinal column is made up of 7 cervical (neck), 12 thoracic (chest), 5 lumbar (lower back), five sacral (base of the vertebral column), and 4 coccygeal (or vestigial caudal) vertebrae. The five sacral vertebrae are fused to form the sacrum, and the four coccygeal vertebrae are fused to form the coccyx, or tail bone.