Ultimobranchial Bodies

(postbranchial bodies), epithelial structures in vertebrate animals and man that correspond to a pair of rudimentary gill pouches; they consist of aggregates of closed vesicles containing colloid. Ultimobranchial bodies are derived from the epithelium of the pharynx, as are the branchioge-nous glands—the thyroid, thymus, and parathyroid. They are found in higher amphibians (in the region of the glottis), in reptiles, and in birds (in the pigeon they are adjacent to the thyroid gland). In mammals, with the exception of anteaters, the ultimo-branchial bodies are unformed: during embryonic development, sections of the corresponding tissue are incorporated into the tissue of the thyroid gland. Ultimobranchial bodies consist of what are known as C cells, which produce the hormone thyrocalcitonin (calcitonin).