abnormal fourth pharyngeal pouch morphology absent fourth pharynegal pouch MP:0013266 MPheno.ontology absence of the fourth endodermal branchial pouch, normally 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 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 absent 4th branchial pouch absent 4th pharyngeal pouch absent fourth branchial pouch