Bones (or osseous material) serve a number of diverse purposes in the human anatomy. In addition to providing structure, protection, and support for the organs of the body, bones also house |marrow|, which produces |blood cells|. Within the bones are also stored the calcium deposits which the body may access, via resorption, when needed. Additionally, bones detoxify the system, by removing heavy metals, such as lead and arsenic, as well as other toxins, from the bloodstream. Osseous tissue itself is made of water (about 1/4 of the bone weight), organic material (about 1/3 of the bone weight, most of which is the |protein|, ossein) and inorganic |minerals| (calcium, phosphorus, and magnesium predominate, though iron, sodium, potassium, chlorine, and fluorine are also present in small amounts). Most bones (with the exception of those of the cranium) are initially pre-formed in ~cartilage~ and are then ossified as the newborn develops.
Two basic classification methods exist to categorize the bones of the body. These two classification systems are based upon anatomical location (axial or appendicular), and shape (long, short, flat, and irregular). Axial bones are the eighty bones which lie along the central, vertical |axis| of the body and support and protect the head and torso and include the |skull| and the spinal (vertebral) column. Appendicular bones include the one hundred twenty-six bones which comprise the appendages, including the shoulders and hips, arms and legs, hands and feet, and fingers and toes. The shape classifications include long bones (such as the |radius|, |humerus|, and |femur|), the short bones (such as the |carpals|, |tarsals|, and manual and |pedal phalanges|), flat bones (such as the |sternum|, |skull| bones, and scapulae), and irregular bones (such as the |vertebrae|).
