Embryonic thymic development in fetuses of domestic cats (Felis domesticus)

During fetal life, and during the neonatal period, the thymus is a very important immune organ, and is the largest lymphatic organ, which exhibits high lymphopoietic activity as a precursor of lymphopoiesis. Morphological studies on the development of the thymus are rare and only include general information. Given the above, this study aimed to characterize the morphological development of the thymus of embryos and fetuses of domestic cats (Felis domesticus), from natural pregnancy, using macroscopic dissection techniques and light microscopy. The thymus of the cats was pale pink and was resting in the region of the cranial mediastinum, medially to the lungs and dorsally to the base of the heart. Histologically, two distinct regions were observed (cortical and medullar). The medullary region had reticular epithelial cells with large nuclei and dendritic extensions. The fetuses had exponential growth and were more pronounced starting on the 35th day of gestation.