Vertebrate Zoology is the study of animals with backbones such as fish, amphibians, reptiles, birds and mammals. Vertebrates are all characterized by a segmented spinal column and a distinct differentiated head. These animals possess internal skeletons which include the vertebral column which at least partially encloses the spinal cord and a skull which houses the brain. Though we tend to think of vertebrates having limbs, most do not have external limbs.