Complex sentence: It is an anatomical variant that, when present, supplies blood to the thyroid gland primarily, or the trachea, the parathyroid gland and the thymus gland (as "thymica accessoria") in rare cases.
Split into simpler sentences: It is an anatomical variant that, when present, supplies blood to the thyroid gland. The artery also supplies the trachea, the parathyroid gland and the thymus gland (as "thymica accessoria") in rare cases.