The skeletal system is a living, dynamic, bony framework of the
body, with networks of infiltrating blood vessels. Inside every
person is a skeleton, a sturdy framework of about 206 bones that
protects the body's organs, supports the body, provides
attachment points for muscles to enable body movement, functions
as a storage site for minerals such as calcium and phosphorus,
and produces blood cells. Living mature bone is about 60%
calcium compounds and about 40% collagen. Hence, bone is strong,
hard, and slightly elastic. Humans are born with over 300 bones
but some bones, such as those in the skull and lower spine, fuse
during growth, thereby reducing the number. Although mature
bones consist largely of calcium0% calcium salts and about 30%
organic matrix, mostly collagen fibersost bones in the skeleton
of vertebrates, including humans, began as cartilage. Cartilage
is a type of connective tissue, and contains collagen and
elastin fibers. The hard outer part of bones are comprised
mostly of a proteins such a