الفهرس 
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Abstract
The thymus is a major lymphatic organ involved in the maturation and differentiation of T-lymphocytes in the prenatal and postnatal periods. The thymus is a bilobate gland placed in the upper anterior thorax, between the sternum and the heart. Thymic tissue attaches to the pericardium through the eighth week of pregnancy. At the 12th week of pregnancy, the thymus is completely descended to its location ventral to the base of the heart and the aortic arc. Estimation of the thymus ultrasonographically is possible approximately throughout the 12th–14th week of pregnancy.