Parafollicular cells (also called C cells) are neuroendocrine cells in the thyroid which primary function is to secrete calcitonin. They are located adjacent to the thyroid follicles and reside in the connective tissue. These cells are large and have a pale stain compared with the follicular cells or colloid. In teleost and avian species these cells occupy a structure outside the thyroid gland named the ultimobranchial body.