Sacrum: part of both appendicular and axial skeleton. Narrow caudal portion is sacral apex, broad superior surface base. Sacral promontory: prominent bulge at anterior tip of base. Superior articular processes form synovial joints with last lumbar vertebra, only on. Spinal nerve roots continue into sacrum through this canal. extends length of sacrum ending at sacral hiatus. Median sacral crest: series of elevations formed by fused sacral vertebra. Sacral cornu: laminae of 5th sacral vertebra don"t contact each other at midline. Sacral foramina: on either side of median sacral crest. Auricular surface: articulates with auricular surface of innominate bone. Formed by 3-5(often 4) coccygeal vertebrae fusing together by 26. Coccygeal cornu: prominent laminae of first coccygeal vertebrae, curves to meet cornua of sacrum. Made up of thoracic vertebrae, ribs, and sternum. Protects heart, lungs, thymus, and other structures within thoracic cavity.