Skeleton supports the body, gives rigidity to body, provides surface for attachment of muscles, and protects soft internal organs like the brain, heart, lungs, etc.
In the vertebrates, skeleton is made of bone and cartilage. It is located inside the body and hence termed endoskeleton. Another rigid skeleton is the exoskeleton in the form of hard, calcareous shells in molluscs and the covering of chitin (a carbohydrate) in insects and other arthropods.
Many invertebrates, such as the earthworm use their muscles, which are not attached to any rigid skeletal elements, by contracting against fluid in their body cavity. Coelomic (Coelom means body cavity) fluid within limited space acts as skeleton for muscle movement and is hence termed hydrostatic skeleton.
The human skeleton is divided into following parts: