Vertebrae

The vertebrae, thirty-three in number, articulating together, form the spinal column. They are named according to the region in which they are placed :

Cervical: 7 - neck region.

Dorsal: 12 - thoracic region.

Lumbar: 5 - abdominal region.

Sacral: 5 - pelvic region.

Coccygeal: 4 - caudal region.

Fig. 25. A Typical Vertebra

The vertebrae are all constructed on the same plan, but differ slightly from one another in the various regions according to their necessities.

A typical vertebra consists of a body more or less cylindrical in shape; the sides and upper and lower surfaces are slightly concave. Posteriorly, two short, stout processes-the pedicles-are formed; these support flattened laminae, which fuse in the middle line; thus, the posterior surface of the body, the pedicles, and the laminae form a bony canal through which the spinal cord runs. The pedicles are not as deep vertically as the bodies, so that between the pedicles of two adjacent vertebrae there are spaces left-the intervertebral foramina-through which the spinal nerves emerge. Immediately in front of the pedicles are other processes-the transverse, to which the muscles of the back are attached, and on the upper and lower surfaces of the pedicles are articular processes (four in all) for the articulation of the vertebrae one with another. At the junction of the laminae a third process is developed, called the spine, for the attachment of muscles.

Fig. 30. - Spinal Column.

Principal Variations In Vertebrae Of Different Regions