Operculum (fish) Operculum (fish) The operculum is a series of bones found in bony fish that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding. The opercular series contains four bone segments known as the preoperculum, suboperculum, interoperculum and operculum. The preoperculum is a crescent-shaped structure that has a series of ridges directed posterodorsally to the organisms canal pores. The preoperculum can be located through an exposed condyle that is present immediately under its ventral margin; it also borders the operculum, suboperculum, and interoperculum posteriorly. The suboperculum is rectangular in
Caudal cell mass Caudal cell mass In humans and other mammals, the caudal cell mass (sometimes tail bud in humans) is the aggregate of undifferentiated cells at the caudal end on the spine.The caudal end of the spinal cord first begins to form after primary neuralation has taken place, indicating that it develops after the cranial portion of the spinal cord has developed. Following neuralation, the caudal tail begins to form a neurocele as it develops a hollow core. After this, secondary neuralation occurs in which the medullary cord begins to form and is filled with many cavities that ultimatelly form the lumen.