Given the task definition and input, reply with output. In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

Aplasia of this organ may occur in Digeorge syndrome, while tumors originating in this organ often occur in patients with myasthenia gravis. Capillaries in this organ have a barrier which is impervious to macromolecules, and it is the only other organ other than the brain, testes, and placenta to have one. A pyramidal organ with two fused lobes, it is derived most of the time from the third pharyngeal pouch and is often the site of ectopic parathyroid tissue. Located above the heart, deep to the sternum, and in front of the trachea, FTP name this ductless gland in which T cells migrating from the bone marrow mature, which notably atrophies after puberty and which makes a yummy treat as "sweetbread. "
Science