What is in a tail? Your back is made of a series of small bones stacked together called vertebra (plural is vertebrae). This is the reason why animals with vertebrae, such as fish, amphibians, reptiles, birds, and mammals, are called vertebrates. A typical mammalian back shows five regional variants or types of vertebrae. These are neck (cervical) vertebrae supporting the head, thoracic vertebrae anchoring the ribcage, lumbar vertebrae with the abdomen, sacral vertebrae with the pelvis, and caudal vertebrae with the tail. These five types are readily distinguished from each other, with their structure reflective of their function and position within the spine or vertebral column. A back walks a delicate balance between two seemingly incongruent functions—strength to provide support and flexibility to allow movement. It is the battle between these that in bipeds like us often ends in back pain.