Irregular bones are all others that do not fall into the previous categories. They have varied shapes, sizes, and surfaces features and include the bones of the vertebrae and a few in the skull. Bone Composition Bones are composed of tissue that may take one of two forms. Compact, or dense bone, and spongy, or cancellous, bone. Most bones contain both types.
Compact bone is dense, hard, and forms the protective exterior portion of all bones.
Spongy bone occurs in most bones. W.B. Saunders Company. Van De Graaff, Kent M. Human Anatomy 5th Edition.