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In biology, the skeleton or skeletal system is the biological system providing support in living organisms. (By extension, non-biological outline structures such as gantries[?] or buildings may also acquire skeletons.)
External skeletal systems are restricted in their maximum size so larger animals, such as the order chordata, have internal skeletal systems. Examples of this are found in arthropods and shellfish: the skeleton forms a hard shell-like covering protecting the internal organs.
An internal skeletal system consists of rigid structures within the body, moved by the muscular system. If the structures are mineralized or ossified[?], as they are in humans and other mammals, they are referred to as bones. Cartilage is another common component of skeletal systems, supporting and supplementing the skeleton. The human ear and nose are shaped by cartilage. Some organisms have a skeleton consisting entirely of cartilage and without any calcified bones at all, for example sharks. The bones or other rigid structures are connected by ligaments[?] and connected to the muscular system via tendons[?].
The fully-developed human skeleton consists of 206 bones.