\Ver"te*bra\, n.; pl. {Vertebr[ae]}. [L. vertebra, fr.
vertere to turn, change. See {Verse}.]
1. (Anat.) One of the serial segments of the spinal column.
Note: In many fishes the vertebr[ae] are simple cartilaginous
      disks or short cylinders, but in the higher vertebrates
      they are composed of many parts, and the vertebr[ae] 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 vertebr[ae] 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 vertebr[ae] are
      specially designated: those vertebr[ae] 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 vertebr[ae], twelve dorsal, five lumbar, five
      sacral, and usually four, but sometimes five and rarely
      three, coccygeal.
2. (Zo["o]l.) One of the central ossicles in each joint of
   the arms of an ophiuran.