Cape Chef,
I think your finger slipped back there. Sweetbread is not thyroid gland but the thymus glands of calves or sometimes lambs. The thymus is located just beneath the upper portion of the sternum in almost all vertebrates. The thyroid is located in front of and on each side of the thyroid cartilage of the larynx.
Who knows maybe thyroid glands are delicious. You should try it sometime maybe you'll invent a new dish.