From The Collaborative International Dictionary of English v.0.48 [gcide]:
Vertebra \Ver"te*bra\ (v[~e]r"t[-e]*br[.a]), n.; pl.
{Vertebrae}. [L. vertebra, fr. vertere to turn, change. See
{Verse}.]
[1913 Webster]
1. (Anat.) One of the serial segments of the spinal column.
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Note: In many fishes the vertebrae are simple cartilaginous
disks or short cylinders, but in the higher vertebrates
they are composed of many parts, and the vertebrae in
different portions of the same column vary very
greatly. A well-developed vertebra usually consists of
a more or less cylindrical and solid body, or centrum,
which is surmounted dorsally by an arch, leaving an
opening which forms a part of the canal containing the
spinal cord. From this dorsal, or neural, arch spring
various processes, or apophyses, which have received
special names: a dorsal, or neural, spine, spinous
process, or neurapophysis, on the middle of the arch;
two anterior and two posterior articular processes, or
zygapophyses; and one or two transverse processes on
each side. In those vertebrae which bear well-developed
ribs, a tubercle near the end of the rib articulates at
a tubercular facet on the transverse process
(diapophysis), while the end, or head, of the rib
articulates at a more ventral capitular facet which is
sometimes developed into a second, or ventral,
transverse process (parapophysis). In vertebrates with
well-developed hind limbs, the spinal column is divided
into five regions in each of which the vertebrae are
specially designated: those vertebrae in front of, or
anterior to, the first vertebra which bears ribs
connected with the sternum are cervical; all those
which bear ribs and are back of the cervicals are
dorsal; the one or more directly supporting the pelvis
are sacral and form the sacrum; those between the
sacral and dorsal are lumbar; and all those back of the
sacral are caudal, or coccygeal. In man there are seven
cervical vertebrae, twelve dorsal, five lumbar, five
sacral, and usually four, but sometimes five and rarely
three, coccygeal.
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2. (Zool.) One of the central ossicles in each joint of the
arms of an ophiuran.
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