Vertebrates are animals in the chordate subphylum Vertebrata. Their best-known traits include a backbone (vertebral column) of cartilage or bone that partly encloses the spinal cord, a skull that protects the brain, and an internal skeleton that usually supports two pairs of limbs.
Encyclopaedia Britannica also notes bilaterally paired muscle masses, a central nervous system partly enclosed within the backbone, and a distinct head with a differentiated brain and paired sense organs (nasal, optic, and otic). The body is divided into trunk and tail regions. Living vertebrates include fishes, amphibians, reptiles, birds, and mammals.