Research Note: Avian Thyroid Isthmus

Abstract An avian equivalent of the mammalian thyroid isthmus appeared in thiouracil-treated (.1% in feed from hatching to 6 and 8 weeks of age) chickens. In two experiments in which chickens were fed a diet containing thiouracil, thyroid tissue was found connecting the thyroid glands. Histological examination of the connecting tissue revealed that it was of the same cellular composition as the thyroid glands.