In vertebrates, cervical vertebrae (singular: vertebra) are those vertebrae immediately inferior to the skull. Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further they caudally follow the lumbar vertebrae, which also belong to the trunk, but they do not carry ribs. In reptiles, all trunk vertebrae carry ribs and are called dorsal vertebrae. In humans, 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. By convention, the cervical vertebrae are numbered, with the first one (C1) located closest to the skull and higher numbered vertebrae (C2-C7) proceeding away from the skull and down the spine.