One of the grand divisions of the animal kingdom,
   comprising all animals that have a backbone composed of bony or
   cartilaginous vertebrae, together with Amphioxus in which the backbone
   is represented by a simple undivided notochord. The Vertebrata always
   have a dorsal, or neural, cavity above the notochord or backbone, and a
   ventral, or visceral, cavity below it. The subdivisions or classes of
   Vertebrata are Mammalia, Aves, Reptilia, Amphibia, Pisces,
   Marsipobranchia, and Leptocardia.