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.
. [1913 Webster
" The protovertebræ were long regarded as rudiments of the permanent vertebræ, but they are now known to give rise to the dorsal muscles and other structures as well as the vertebral column. See Myotome."