Each vertebra consists of two essential parts - an anterior solid segment or body, and a posterior segment arch. The arch is formed of two pedicles and two laminas, supporting seven processes-viz. four articular, two transverse, and one spinous.

The bodies of the vertebras are piled one upon the other, forming a strong pillar for the support of the cranium and trunk; the arches forming a hollow cylinder behind the bodies for the protection of the spinal cord. The different vertebras are connected together by means of the articular processes and the intervertebral fibro-cartilages; while the transverse and spinous processes serve as levers for the attachment of muscles, which move the different parts of the spine. Lastly, between each pair of vertebrae apertures exist through which the spinal nerves pass from the cord. Each of these constituent parts must now be separately examined.

The Body or Centrum is the largest part of a vertebra. Above and below, it is flattened; its upper and lower surfaces are rough for the attachment of the intervertebral fibro-cartilages, and present a rim around their circumference. In front, it is convex from side to side, concave from above downward. Behind, it is flat from above downward and slightly concave from side to side. A few small apertures, for the passage of nutrient vessels, perforate its anterior surface; whilst on the posterior surface is a single large, irregular aperture, or occasionally more than one, for the exit of veins from the body of the vertebra - the venae basis vertebrae.

The Pedicles are two short, thick pieces of bone, which project backward, one on each side, from the upper part of the body of the vertebra, at the line of junction of its posterior and lateral surfaces. The concavities above and below the pedicles are the intervertebral notches; they are four in number, two on each side, the inferior ones being generally the deeper. When the vertebrae are articulated the notches of each contiguous pair of bones form the intervertebral foramina, which communicate with the spinal canal and transmit the spinal nerves and blood vessels.

The Laminae are two broad plates of bone, which complete the neural arch by fusing together in the middle line behind. They enclose a foramen, the spinal foramen, which serves for the protection of the spinal cord; they are connected to the body by means of the pedicles. Their upper and lower borders are rough, for the attachment of the ligamenta subflava.

The Spinous Process projects backward from the junction of the two laminae, and serves for the attachment of muscles and ligaments.

The Articular Processes, four in number, two on each side, spring from the junction of the pedicles with the laminae. The two superior project upward, their articular surfaces being directed more or less backward; the two inferior project downward, their articular surfaces looking more or less forward.

The Transverse Processes, two in number, project one at each side from the point where the lamina joins the pedicle, between the superior and inferior articular processes. They also serve for the attachment of muscles and ligaments.