An endoskeleton grows along with the organism. The vertebrate skeleton supports, protects, and attaches to muscles and stores minerals. The axial skeleton consists of the skull, vertebral column, breastbone, and ribs. Bones in different vertebrate species can differ in width and density. Cartilage and bone make up skeletons.
Cartilage entraps a great deal of water, which makes it an excellent shock absorber.
In compact bone, osteocytes form osteons. The central channel for blood supply is an osteonic canal. Canaliculi connect lacunaes that house bone cells and the osteonic canal. Bone cells extend through canaliculi and pass materials from cell to cell. Bone continually degenerates and builds up.