Spongy bone is composed of long, needle-like pieces of bone and lots of open space. Compact bone is dense and looks smooth and homogeneous. The adult skeleton is composed of 206 bones and there are two basic types of osseous, or bone, tissue: compact bone and spongy bone, and are classified into four groups according to shape: long, short, flat, and irregular. The skeleton is subdivided into two divisions: the axial skeleton, the bones that form the longitudinal axis of the body, and the appendicular skeleton, the bones of the limbs and girdles.

Blood cell formation, or hematopoiesis, occurs within the marrow cavities of certain bones. Fat is stored in the internal cavities of bones bone itself serves as a storehouse for minerals, the most important of which are calcium and phosphorus because most of the body’s calcium is deposited in the bones as calcium salts, the bones are a convenient place to get more calcium ions for the blood as they are used up. Skeletal muscles, attached to bones by tendons, use the bones as levers to move the body and its parts. Bones protect soft body organs for example, the fused bones of the skull provide a snug enclosure for the brain, the vertebrae surround the spinal cord, and the rib cage helps protect the vital organs of the thorax. Bones, the “steel girders” and “reinforced concrete” of the body, form the internal framework that supports the body and cradle its soft organs the bones of the legs act as pillars to support the body trunk when we stand, and the rib cage supports the thoracic wall.

Functions of the Skeletal Systemīesides contributing to body shape and form, our bones perform several important body functions. Although the word skeleton comes from the Greek word meaning “dried-up body”, our internal framework is so beautifully designed and engineered that it puts any modern skyscraper to shame.

An example of a flat bone would be the