Page:Structure and functions of the body; a hand-book of anatomy and physiology for nurses and others desiring a practical knowledge of the subject (IA structurefunctio00fiskrich).pdf/95

Fig. 32.—A type of vertebra. (Leidy.) 1, Body; 2, pedicle; 3, lamina; 4, spinal foramen; 5, spinous process; 6, transverse process; 7, articular process.

Although the vertebræ of the different groups differ more or less in size and shape in accordance with the various demands of their positions, they all have certain general characteristics. Each has a body, two laminæ, two pedicles, two transverse processes, and one spinous process. The pedicles extend back from the body on either side and support two broad plates of bone, the laminæ, whose juncture at the back completes the spinal foramen for the passage of the cord. At their juncture is the spinous process, which can be felt beneath the skin, while the transverse processes project from the juncture of the laminæ with the pedicles. All the processes are for the attachment of muscles that move the spine. The body is formed of cancellous bone with a compact layer outside. Transversely it is slightly oval, while its upper and lower surfaces are flat, except in the crevical region, where the upper surface is concave laterally and the under convex laterally and concave from before back. Between the bodies are disks of fibro-cartilage, which increases motion and springiness. The spinous process or spine is short in the cervical region, long and directed downward in the dorsal region, thick and projecting almost straight out in the lumbar region. The pedicles are notched above and below so that when articulated the notches of two verte-