has part has part has_part characteristic of part of has modifier abnormal pharyngeal pouch morphology abnormal fourth pharyngeal pouch morphology abnormal 4th pharyngeal pouch morphology abnormal 4th branchial pouch morphology any structural anomaly of the fourth endodermal branchial pouch located between the fourth and sixth branchial arches (a fifth arch never establishes itself in amniotes); in most mammals, excluding rodents, the dorsal part of each fourth pouch develops into a superior parathyroid gland (parathyroid IV), which lies on the dorsal surface of the thyroid gland (the parathyroid glands derived from the third pouches descend with the thymus and are carried to a more inferior position than the parathyroid glands that are derived from the fourth pouches); the elongated ventral part of each fourth pouch develops into the ultimopharyngeal body, which fuses with the thyroid gland, giving rise to the calcitonin-producing parafollicular or C-cells of the thyroid gland MP:0013265 abnormal fourth branchial pouch morphology morphology abnormal pharyngeal pouch 4