\Pro`to*ver"te*bra\, n.; pl. {Protovertebr[ae]} .
[Proto- + vertebra.] (Anat.)
One of the primitive masses, or segments, into which the
mesoblast of the vertebrate embryo breaks up on either side
of the anterior part of the notochord; a mesoblastic, or
protovertebral, somite. See Illust. of {Ectoderm}.
Note: The protovertebr[ae] were long regarded as rudiments of
      the permanent vertebr[ae], but they are now known to
      give rise to the dorsal muscles and other structures as
      well as the vertebral column. See {Myotome}.