What qualities of the bone ensure its lightness and strength?

Bones are elements of the musculoskeletal system, they are composed of two types of substances, organic (collagen) and inorganic (salts and minerals). Elasticity, as well as flexibility, the bone is provided by organic substances, and inorganic strength, in addition, the bones are hollow inside, and the edges (heads of bones) consist of a spongy substance, which in turn consists of many septa, and are located along the line of compression or expansion, all these qualities provide bones with lightness and strength.