9 C.F.R. § 310.15
Disposition of thyroid glands and laryngeal muscle tissue
(a) Livestock thyroid glands and laryngeal muscle tissue shall not be used for human food.
(b) Livestock thyroid glands and laryngeal muscle tissue may be distributed to pharmaceutical manufacturers for pharmaceutical use in accordance with § 314.9 or § 325.19(c) of this subchapter, if they are labeled in accordance with § 316.13(f) of this subchapter. Otherwise, they shall be disposed of at the official establishment in accordance with § 314.1 or § 314.3 of this subchapter.