In most teleost fish, such as the bluegill sunfish (Lepomismacrochirus), the shape of the tail is described as homocercal,meaning that the upper and lower lobes of the tail fin are roughlyequal in size. The vertebral column extends in a straight line poste-riorly until the penultimate vertebra; the last vertebra is modifiedand more posterior axial elements form a fan composed of theuroneurals, epurals, parahypural, and hypural plates (Fig. 5A) dur-ing embryonic development. Without support by the vertebralcolumn, the tail fin is composed of a thin membrane only, reinforcedby fin rays, or lepidotrichia. The hypural plates are the origin for thelarge intrinsic caudal muscles that insert onto the tail fin. While theintrinsic caudal muscles are thought to be derived from the axialmyomeres of the trunk