In vertebrates, cervical spine or cervical vertebrae (singular: vertebra) are those vertebrae immediately inferior to the skull.
In some species, some parts of the skull may be composed of vertebra-like elements, e.g. the occipital bone in humans is composed of four vertebra-like segments.
In many vertebrate species, cervical spine or cervical vertebrae are variable in number; however, almost all mammals have seven (including those with very short necks relative to body size, such as elephants or whales, and those with very long necks, such as giraffes).
The few exceptions include the manatee and the sloths, of which the two-toed sloth has six cervical vertebrae and the three-toed sloth has up to nine cervical vertebrae (Wetzel, 1985).
Thoracic vertebrae in all species are defined as those vertebrae which also carry a pair of ribs, and lie caudal to the cervical vertebrae.
In humans, cervical spine or cervical vertebrae are the smallest of the true vertebrae, and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a foramen (hole) in each transverse process, through which passes the vertebral artery.
The remainder of this article focuses upon human anatomy.