Q: 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.
Hyperplasia in this organ is associated with myasthenia gravis, while aplasia of it results from failure of the third and fourth pharyngeal pouches to develop and is known as DiGeorge syndrome. Keratinized cells called Hassalls corpuscles are found in its medulla, and dendritic cells at its corticomedullary junction recognize self-reactive cells. Epithelial cells in its cortex express MHC molecules that allow for positive selection. Found posterior to the manubrium of the sternum, this pyramid-shaped organ reaches its maximum size at puberty. For 10 points, identify this lymphoid organ, the site of T cell development.
A:
Science