Bones are structures made out of calcium carbonate that form the general structure of the body, known as the skeleton. Despite being very hard and inflexible, they too are living tissue. They can support large loads in compression, but lesser loads in tension and shear. As such, most broken bones are the result of striking the bone at an angle perpendicular to the way the bone runs, or by stressing it in two different directions at once.
Despite their strength, bones are also very light as they are made up out of a honeycomb structure where most of the interior of the bone is made up of fine mineral structures. The inside of most bones contains bone marrow, which produces the cells in blood.
Some diseases, such as osteoporosis, are the result of the loss of bone mass, making bones very thin, brittle and susceptible to breaking.
All the bones in the body have a name, and medical students are required to memorize these as part of their education. Many doctors resort to mnemonics in order to remember the bones in certain fine structures.
Adults have fewer bones than children as many bones, particularly those in the skull, fuse together into a single structure as a person becomes older.