The internal skeleton; bony and cartilaginous structure (especially of vertebrates).
The internal supporting structure of vertebrates, made up of cartilage or bone. It provides support, and acts as a system of levers to which muscles are attached to provide movement. Certain parts of the skeleton (the skull and ribs) give protection to vital body organs.
Sponges are supported by a network of rigid, or semirigid, spiky structures called spicules; a bath sponge is the proteinaceous skeleton of a sponge.