The skeletal system is the system of bones in an organism's body that gives it structural rigidity. Also often included in the skeletal system are the cartilage, ligaments, and tendons that connect all of the bones together as well. The human skeletal system is composed of 206 bones. Human babies are actually born with many more bones (closer to 300) but over time some of them fuse together to make a total of 206. It is divided into two major parts. The axial skeleton is composed of 80 bones and comprises the backbone, rib cage, and skull. The appendicular skeleton is composed of 126 bones and is comprised of everything else (pelvis, pectorals, and extremities).
As a side note, most animals do not have internal skeletal systems (in other words are invertebrates instead of vertebrates). Only about 2% of animals are classified as vertebrates.
A skeleton is any part of an animal which provides support for the rest of the body. Nearly every species of multicellular animal has a skeleton. Most are made of hard material. Examples: bone, cartilage, chitin or chalk. They are either exoskeletons on the outside of the body (example: insect skeletons) or endoskeletons inside the body (example: vertebrate skeletons). The skeleton helps give body its shape, and provides a frame from which organs are suspended. The skeleton surrounds and protects soft parts of the body. Example: in vertebrates, the skull protects the brain.
All vertebrate skeletons are built on the same general plan which includes the following:
(1) An axial skeleton, made up of the skull and vertebral column
(2) An appendicular skeleton, made up of the limb girdles and limbs or paired fins in fish.
Singh, Pramod.(2013). Life Sciences