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 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. In many species, though not in mammals, the cervical vertebrae bear ribs. In many other groups, such as lizards and saurischian dinosaurs, the cervical ribs are large; in birds they are small and completely fused to the vertebrae. The transverse processes of mammals are homologous to the cervical ribs of other amniotes. 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 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.

http://upload.wikimedia.org/wikipedia/commons/f/f8/Illu_vertebral_column.jpg

vertebrae cervicales

uberon

UBERON:0002413

Cervical vertebra

• scalenus medius
• scalene muscle

• cervical rib

• erector spinae muscle group
• semispinalis cervicis

• levator scapulae muscle
• nuchal ligament

• cervical vertebra cartilage element

• anterior tubercle of transverse process of cervical vertebra
• posterior tubercle of transverse process of cervical vertebra
• postzygapophysis of cervical vertebra
• prezygapophysis of cervical vertebra
• cervical vertebral arch
• transverse process of cervical vertebra
• cervical vertebral foramen
• transverse foramen