Thymus (thymus) as an important body in lymphoid organs,a ductless glandular organ at the base of the neck that produces lymphocytes and aids in producing immunity; atrophies with age which is closely associated with immune function. which locat in the chest before the mediastinum. during the late embryonic stage and birth, the human thymus weighing about 10 to 15 grams. With age, the thymus continues to develop, to the adolescent about 30 ~ 40 grams. After puberty, the thymus shrinks to only 15 grams aged thymus.