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FIGURE 1. Diagrammatic representation of routes of descent of thymus, parathyroid glands, and "last branchial body" during fetal life. Parathyroid glands originating more cranially in third branchial pouch migrate in close association with thymus to reach final position more caudally with respect to parathyroid glands originating in fourth branchial pouch. Final location of last branchial body is intimately embedded in thyroid gland, to constitute parafollicular C-cells producing calcitonin. Thyroid gland originates at "blind foramen" along midline and migrates down to first tracheal ring (modified from (115)).
