The body of a vertebra is a cylindrical, or somewhat dorso-
ventrally compressed, mass of bone, which bears at either end an
articular surface for attachment to the adjacent vertebra. The
articular surfaces are borne on thin plate-like epiphyses, the epiphy-
sial lines being evident even in older animals, especially in the
lumbar region. The dorsal portion of the body bears on either side
the pedicle, or root of the vertebral arch (radix arcus vertebrae),
the dorsal surface of the body forming in this way the floor of the
vertebral foramen. The dorsal portion of the arch, borne on the
pedicle, is distinguished as the lamina. The anterior and posterior
margins of the pedicle are notched, each notch or incisure being
converted, through its association with that of the adjacent verte-
bra, into a rounded aperture, the intervertebral foramen (fora-
men intervertebrale), for the passage outward of a spinal nerve.
The arch of the vertebra is noteworthy for its projections or
processes. On either side is a horizontal plate of bone, the
transverse process (processus transversus), and, dorsally, a
median projection, the spinous process (processus spinosus), all
three serving for the attachment of the vertebrae to one another
by ligaments, and for the attachment of the spinal musculature.
Special articular surfaces, borne on low articular processes
(processus articulares), are found on the anterior and posterior
margins of the arch. The anterior, or Superior articular surfaces
are directed for the most part toward the dorsal surface, and are
overlapped in the natural condition by the inferior articular
surfaces, which are directed toward the ventral surface. A
certain amount of movement is permitted by one surface slipping
across the other, the mechanism illustrating the arthrodia, or
gliding-joint.
