The vertebral column extends in a straight line posteriorly
until the penultimate vertebra; the last vertebra is modified
and more posterior axial elements form a fan composed of the
uroneurals, epurals, parahypural, and hypural plates ) during
embryonic development. Without support by the vertebral
column,the tail finis composed of a thin membrane only, reinforced
by fin rays, or lepidotrichia. The hypural plates are the origin for the
large intrinsic caudal muscles that insert onto the tail fin. While the
intrinsic caudal muscles are thought to be derived from the axial
myomeres of the trunk