A framework of bones and cartilage that performs several functions. Provides a place of attachment for muscles. Bone is a living tissue, consisting of cells surrounded by a non-living solid matrix. Its hardness is due to calcium and phosphorus salts. Its resiliency is due to strands of the elastic protein collagen. The human body has 206 bones that vary in size and shape. Most bones contain both compact and spongy bone in proportions that depend on the bone"s size and shape. Dense outer layer with little internal spaces. Forms most of the shaft (diaphysis) of long bones (arms, legs). Covered by the periosteum that nourishes the bones. Injury to the periosteum (bruise, fracture) generates pain. Found at the ends (epiphysis) of the shafts of long bones. Found in small, flat bones like the skull bones of the head. The spaces of spongy bones are filled with red marrow where red blood cells form.