Cervical vertebrae

In vertebrates, cervical vertebrae (singular: vertebra) are those vertebrae immediately behind (posterior to) the skull.

Variation among species

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, 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 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.

General characteristics (C3-C6)

These are the general characteristics of the third through sixth cervical vertebrae. (The first, second, and seventh vertebrae are extraordinary, and detailed later.)

• The body of these four vertebrae is small, and broader from side to side than from front to back.
  • The anterior and posterior surfaces are flattened and of equal depth; the former is placed on a lower level than the latter, and its inferior border is prolonged downward, so as to overlap the upper and forepart of the vertebra below.
  • The upper surface is concave transversely, and presents a projecting lip on either side;
  • the lower surface is concave from front to back, convex from side to side, and presents laterally shallow concavities which receive the corresponding projecting lips of the underlying vertebra.

• The pedicles are directed laterally and backward, and are attached to the body midway between its upper and lower borders, so that the superior vertebral notch is as deep as the inferior, but it is, at the same time, narrower.

• The laminae are narrow, and thinner above than below; the vertebral foramen is large, and of a triangular form.

• The spinous process is short and bifid, the two divisions being often of unequal size.

• The superior and inferior articular processes of neighboring vertebrae often fuse on either or both sides to form an articular pillar, a column of bone which projects laterally from the junction of the pedicle and lamina.

• The articular facets are flat and of an oval form:
  • the superior face backward, upward, and slightly medially.
  • the inferior face forward, downward, and slightly laterally.

• The transverse processes are each pierced by the foramen transversarium, which, in the upper six vertebrae, gives passage to the vertebral artery and vein, as well as a plexus of sympathetic nerves. Each process consists of an anterior and a posterior part. These two parts are joined, outside the foramen, by a bar of bone which exhibits a deep sulcus on its upper surface for the passage of the corresponding spinal nerve.
  • The anterior portion is the homologue of the rib in the thoracic region, and is therefore named the costal process or costal element. It arises from the side of the body, is directed laterally in front of the foramen, and ends in a tubercle, the anterior tubercle.
  • The posterior part, the true transverse process, springs from the vertebral arch behind the foramen, and is directed forward and laterally; it ends in a flattened vertical tubercle, the posterior tubercle.

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